Group Title: gas phase and surface radiation chemistry of hydrogen-carbon monoxide mixtures
Title: The gas phase and surface radiation chemistry of hydrogen-carbon monoxide mixtures
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Title: The gas phase and surface radiation chemistry of hydrogen-carbon monoxide mixtures
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Language: English
Creator: St. Charles, Frank Kelly, 1951-
Copyright Date: 1984
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THE GAS PHASE AND SURFACE RADIATION CHEMISTRY
OF HYDROGEN-CARBON MONOXIDE MIXTURES











By

FRANK KELLEY ST.CHARLES


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1984


































In Memory

Frank St.Charles
1923-1971

Knowing him was knowing life
and warmth and joy and love.
The joy is gone,
but the warmth remains.
And the love echos forever.














ACKNOWLEDGMENTS


The author wishes to express his sincere thanks and appreciation

to his research director, Dr. Robert J. Hanrahan, and to

Dr. M. Luis Muga for sharing their experience, time, and energy, and

for encouragement, advice, and friendship throughout this work.

Thanks are also extended to Dr. Phillip M. Achey for his interest in

this work and for the many "hall-talks."

Special thanks are given to the participants in Dr. Muga's

extended course on The Kinetics of a Prolate Spheroid; Avinash Gupta,

Jorge Ramirez, Dawit Techlemariam, Tom Buckley, Bob Doyle,

Ron Daubach, John Eyler, and Lee Morgenthaler; for their friendship

and assistance.

Special appreciation is also expressed to Vicki Rittenhouse for

her valuable help in preparing this manuscript.

Finally, the author expresses his deepest love and gratitude to

his family, especially his wife, Janet, for the love, encouragement,

and assistance that made this work possible.













TABLE OF CONTENTS


Page


ACKNOWLEDGEMENTS . . . . . . . . . .


LIST OF TABLES. . . . . . . . .


LIST OF FIGURES . .. . . . . . . .


ABSTRACT . . . . . . . . . . .


I. INTRODUCTION AND REVIEW OF THE LITERATURE . .
A. Foreword . . . . . . . . .
B. UV Photolysis . . . . . . . .
C. Alpha Particles . . . . . . . .
D. Beta Particles. . . . . . . . .
E. Fission Fragments . . . . . . .
F. Electron Beams. . . . . . . . .
Static System . . . . . . .
Flow System . . . . . . . .
G. Catalytic Irradiations. . . . . . .
Carbon Monoxide . . . . . . .
Hydrogen. . . . . . . . .
Hydrogen-Carbon Monoxide Mixtures . .


II. EXPERIMENTAL. . . . . . . . . .
A. Sample Preparation. . . . . . . .
Reagents and Their Purification . . .
Vacuum System . . . . . . .
Preparation of Hydrogen-Carbon Monoxide M


Catalyst Preparation and Characterization .
B. Sample Irradiation. . . . . . . .
Cobalt-60 Gamma Ray Source. . . . .
Radiolysis Vessels. . . . . . .
Sample Holder . . . . . . . .
Dosimetry . . . . . . . . .
C. Sample Analysis . . . . . . . .
Spark Discharge . . . . . . .
Gas Chromatography Sample Loops . . .
Product Transfer. . . . . . . .
Gas Chromatography. . . . . . .
Gas Chromatography Infrared Spectroscopy.
Gas Chromatography Mass Spectrometry. .
D. Product Identification and Measurement. . .
Hydrocarbons. . . . . . . . .
Alcohols. . . . . . . . .
Aldehydes . . . . . . . . .
Ketones . . . . . . . . .
Carboxylic Acids. . . . . . . .
Ethers. . . . . . . . . .
Esters. . . . . . . . . .


. . ix


2
2
3
5
6
7
. . 1
. . 1
. . 2


. . 3
. . 5
* 6
. . 7


. . 11
. . 11
. . 11
. . 11


fixtures


. . 22
. . 25
. . 25
. . 28
. . 31
. . 32
. . 33
. . 33
. . 37
. . 39
* . 40
S. 50
. . 52
. . 54
* . 54
* . 54
* . 55
* . 55
. . 56
. . 56
. . 56


. . . . vi










III. RADIOLYSIS WITHOUT CATALYSTS. . . . .
A. Experimental Results. . . . . .
Product Yield versus Irradiation Time
Hydrocarbon Yield versus Pressure .
Hydrocarbon Yield versus Temperature.
Mass Balance. . . . . . .
B. Discussion. . . . . . . . .


IV. RADIOLYSIS WITH THE ALUMINA CATALYST . . . . ... 80
A. Experimental Results . . . . . . . .. 80
Product Yield versus Irradiation Time . . .. 80
Hydrocarbon Yield versus Temperature. . . . 85
Mass Balance . . . . . . . . .. 92
Effect of Transfer Temperature on Product
Desorption. . . . . . . . . ... 94
B. Discussion . . . . . . . ... . .. 97

V. RADIOLYSIS WITH THE NICKEL-ALUMINA CATALYST . . .. 106
A. Experimental Results . . . . . . . .. 106
B. Discussion. . . . . . . . . . . 110
Nickel Surface . . . . . . . .. 110
Carbon Reactions . . . . . . . .. 113
Hydrocarbon Formation . . . . . . .. 114

VI. COMPARISON OF PACKED AND UNPACKED VESSELS . . . .. 117
A. Experimental Results. . . . . . . . . 117
B. Discussion . . . . . . . . . .. 121

APPENDIX--DOSIMETRY CALCULATIONS . . . . . . ... 123

BIBLIOGRAPHY . . . . . . . . . . . .. 128

BIOGRAPHICAL SKETCH . . . . . . . . ... . .. 134
















LIST OF TABLES


Table Page

2-1 Catalyst Specifications . . . . . . .. 23

2-2 Summary of Dosimetry Calculations. . . . . . 35

3-1 Yield of products versus time. Unpacked metal
vessels . . . . . . . . .. . . . 59

3-2 Mean hydrocarbon yields for all pressures . . . 65

3-3 Hydrocarbon yields from unpacked vessels at
differing reactant pressures for 48 hr. irradiations
at 270C. Normal vessel preparation methods . . .. 66

3-4 Hydrocarbon yields from unpacked vessels at
differing reactant pressures for 48 hour irradiations
at 27C. Vessels heated red hot during preparation . 68

3-5 Mass balance of products for a 48 hr., 250 torr,
27C irradiation. No catalyst. . . . . . ... 73

4-1 G-values for oxygenated products and total hydrocarbons.
Alumina Catalyst. . . . . . . . . ... .84

4-2 G-values for hydrocarbon products and carbon dioxide.
Alumina catalyst. . . . . . . . . ... .87

4-3 Mass balance of products for a 48 hr., 250 torr, 27C
irradiation. Alumina catalyst. . . . . . ... 93

4-4 Measured product yields for differing product transfer
procedures. Alumina catalyst . . . . . ... 95

4-5 Irradiation product desorption rate and energy of
desorption from alumina . . . . . . ... .98

5-1 Hydrocarbon and carbon dioxide yield with the
nickel-alumina catalyst . . . . . . ... 108

5-2 G-value of hydrocarbon products. Nickel-alumina catalyst. 111

6-1 G-values for major products with and without added
catalysts. . . . . . . . .. .. .... 118
















LIST OF FIGURES


Figure Page

1 Vacuum system used for sample preparation and
transfer. . . . . . . . ... ..... .16

2 Vacuum quick-couple, glass to metal seal. . . ... 18

3 Surface area data . . . . . . . .. 26

4 Cross section of irradiation through center, left
side view . . . . . . . .... .. . 27

5 All nickel vacuum tight radiolysis vessel . . . 29

6 Stainless steel vacuum tight radiolysis vessel with
removable top . . . . . . . . .. 30

7 Ethylene dosimetry. Energy deposited in ethylene vs.
irradiation time. . . . . . . . . ... 34

8 Spark discharge vessel. . . . . . . .. .36

9 Gas chromatography sample loops used for the analysis
of products condensible and non-condensible in liquid
nitrogen . . . . . . . . . . 38

10 Gas chromatograms of hydrocarbon products (48 hr.
irradiation time) . . . . . . . . . 42
(a) No catalyst, 250 torr H2-CO . . . . .. 43
(b) Alumina catalyst, 250 torr Hz-CO. . . . ... 44
(c) Nickel-alumina catalyst, 1.59 nmol HzCO .... 45

11 Gas chromatograms of oxygenated products. . . .. 46
(a) No catalyst, 48 hr. irradiation of 250 torr
Hz-CO . . . . . . . . ... . . 47
(b) Alumina catalyst, 49 hr. irradiation of 250 torr
H2-CO . . . . . . . .... ..... 48

12 Stainless steel gas cell used for infrared spectroscopy. 51

13 Infrared spectra using the gas cell . . . ... .53

14 Yield of methanol, ethanol, and acetaldehyde vs.
irradiation time. No catalyst. . . . . ... 60










15 Yield of acetone, 20-butanone, and hydrocarbons vs.
irradiation time. No catalyst. . . . . ... 61

16 Arrhenius plots of ethane, propane, ethylene.
No catalyst . . . . . . . . . . 70

17 Arrhenius plots of propylene, butanes, pentanes
No catalyst. . . . . . . . . . 71

18 Yield of methanol, ethanol, and n-propanol/n-propyl
propionate vs. irradiation time. Alumina catalyst. 81

19 Yield of hydrocarbons, acetaldehyde, acetone,
acrolein, and propionaldehyde vs. irradiation time.
Alumina catalyst. . . . . . . . . ... 82

20 Arrhenius plots of Cz-C4 alkenes. Alumina catalyst 89

21 Arrhenius plots of Cz-C4 alkanes. Alumina catalyst 90

22 Arrhenius plots of pentanes, pentenes, and carbon
dioxide. Alumina catalyst . . . . . ... 91

23 Gamma-alumina surface coverage with hydroxide vs.
evacuation temperature. . . . . . . ... 101

24 Effect of reactant gas adsorption on vessel pressure.
Nickel-alumina catalyst . . . . . . .. 107


viii
















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


THE GAS PHASE AND SURFACE RADIATION CHEMISTRY OF
HYDROGEN-CARBON MONOXIDE MIXTURES

By

Frank Kelley St.Charles

August, 1984

Chairman: Dr. Robert J. Hanrahan
Major Department: Chemistry

The gamma radiolysis of a 3:1 mol, hydrogen-carbon monoxide

mixture was investigated with and without added alumina and nickel-

alumina catalysts. Product yields were measured while varying

temperature, pressure, and irradiation time. The added substrates

exhibited selective catalytic behavior. Both the product yields and

distributions differed considerably with each added substrate and with

the homogeneous radiolysis. Negligible results from unirradiated

control experiments for all three systems indicate the reactions to be

initiated by ionizing radiation alone.

For the homogeneous radiolysis, the major products and their

G-values (molecules formed/100 eV deposited) were water + carbon

dioxide, -1: methane, 0.27; methanol, 0.12; ethanol, 0.13;

formaldehyde, >0.1; acetaldehyde, 0.07; acetone, 0.075; and Cz to

Cs hydrocarbons, 0.02. The hydrocarbon yield decreased with

increasing carbon number with alkane production being preferred over









the corresponding alkene. Primary product formation was believed to

occur from reactions of CHO, OH, and CH3 radicals and the H3'

ion. In addition, evidence points to surface reactions on the metal

vessel walls contributing to hydrocarbon formation.

With the alumina catalyst, the production of carbon dioxide and

strongly adsorbed alkenes was particularly enhanced. The major

products and their G-values were carbon dioxide, 59; ethylene, 11;

propylene, 3.8; C4 to Cs alkenes, 5; methanol, 1.0; ethanol, 0.85;

acetaldehyde, 0.7; acetone, 0.31; diethyl ether, 0.22; ethane, 0.36;

and propane, 0.11. The mechanism was believed to involve the initial

formation of a surface format species with subsequent desorption to

form CO2 or hydrogenation to form hydrocarbons. Over the

temperature range studied (-77* to 1000C), hydrocarbon yields

increased with increasing temperature while COz yields decreased.

The G-value of CO incorporated into products remained relatively

constant at -100.

With the nickel-alumina catalyst, essentially all of the CO

reacted to form COz in the first few irradiations with COz yield

decreasing below detection limits by the tenth irradiation. As CO2

yield decreased, alkane yields increased to give a G-value of -300

for methane and 0.4 for ethane. The mechanism appears to involve

initial formation of COz and surface carbide followed by

hydrogenation of the carbide.
















I. INTRODUCTION AND REVIEW OF THE LITERATURE


A. Foreword



The purpose of this study was to investigate the effect of Co-60

y-rays on hydrogen-carbon monoxide gas mixtures with and without

added catalytic substrates. Gamma-alumina and nickel impregnated

gamma-alumina were used as catalytic substrates. The ratio of the two

gases was held constant throughout the study at three moles of

hydrogen to one mole of carbon monoxide. Product yields were measured

while varying the temperature, pressure, and irradiation time as well

as the catalytic substrates. No extensive work on the gamma

radiolysis of these systems has been reported in the literature.

The effects of ionizing radiation on hydrogen and carbon monoxide

mixtures have been studied using ultraviolet (UV) light (1),

a-particles (2,3), tritium B's (4,5), fission fragments (6), and

electron beams (7-14).

The product distributions from these studies vary considerably

and similar or duplicate studies have yielded dissimilar results.

This is not surprising since even though the reactants are simple

molecules, they contain the basic building blocks for the field of

organic chemistry.









B. UV Photolysis

Noyes and Leighton have reviewed the UV photolysis of H2-CO

mixtures (1). The main products were formaldehyde and glyoxal with

the maximum yield obtained with a 1:1 mixture. The following

reactions were suggested.

H + CO (+M) = HCO (+M) 1

HCO + HCO = (HCO)2 2

HCO + HCO = HzCO + CO 3

HCO + Hz = HzCO + H 4

HCO + H = HzCO 5

With traces of oxygen present, hydrogen peroxide was formed (1).

This was believed to be due to Oz reacting with HCO to form CO and

HOz with the HOz reacting further to form HzOz.

Quantum yields for aldehyde formation were found to be 0.5

aldehyde group per quantum absorbed (1).



C. Alpha Particles

The first published work on the radiolysis of hydrogen-carbon

monoxide mixtures was performed by Scheur (2). He irradiated a gas

mixture containing 43.71% Hz and 56.29% CO at an initial pressure of

1471 torr with a particles (96.05 millicuries) from radon ("1'

emanation du radium") decay for 19 days. After irradiating for two

days, formaldehyde was detected and an extremely faint white solid was

observed which disappeared after four days. At the end of the

experiment, the gas composition was 34.19% Hz, 60.38% CO, 5.31%

CH4, and 0.12% CzHs. Water formation was also observed. No









formaldehyde nor methanol was detected. He concluded that CO was

reduced by H2 to HCHO which was subsequently reduced to CH4 as the

primary final product.

In an attempt to repeat Scheur's work, Lind and Bardwell found no

CH4 nor HzO, but did observe CO2 and an abundant white solid

(3). This solid reacted neither as an aldehyde nor a sugar and was

insoluble in water. Carbon monoxide and hydrogen disappeared in a 1:1

ratio at a rate of three molecules (CO + Hz) per ion pair. The

solid was tentatively identified as a formaldehyde polymer.



D. Beta Particles

Douglas self-irradiated tritium-carbon monoxide mixtures and

observed a white solid as the principal reaction product (4).

Analysis of condensable products from the gas phase by mass

spectrometry showed formaldehyde as the principal product with water,

carbon dioxide, acetaldehyde, ethylene glycol, and glyoxal also formed.

The tritium-carbon monoxide radiolysis was studied in much more

detail by Beattie in the range of 3 to 33% CO (5). The major products

formed were a white solid believed to be polyformaldehyde, CH4 and

HzO. Small quantities of COz, CzH4, HCHO, and possibly

HzOz and C2H2 were found. A low concentration of 02 was

always detected which increased to a value of about 0.1% during the

first ten hours. The following reaction scheme was proposed.










H2- -\ H H2 + e 6

Hz-vAA Hz* 7

CO-"CAr CO+ + e- 8

H2* + Hz 2Hz 9

H2* + CO 4 CH + OH 10

H2* + CO C + OH + H 11

CH + H2 CH3 12

CH3 + H2 CH4 + H 13

H2* + H2z + H3++ H 14

Hz++ CO CO+ + Hz 15

H3+ + CO CHO+ + H2 16

CO+ + H2 4 CHO+ + H 17

CHO+ + e -+ CHO* 18

CHO* + Hz CH20 + H 19

CHO+ + e- CO + H 20

CH3 + CH3 4 C2Hs CzH4 + H2 21

OH + Hz HzO + H 22

OH + CO C02 + H 23

H + H + M H2 + M 24

The rate of formation of CH4 was found to be independent of CO

partial pressure down to 4 torr. In double isotopic labeling

experiments with C0O and 1CO2, it was found that CH4 was

not formed directly from CO2. Rates of formation of CH4 were not

affected by added HzO or COz. It was found that the initial rate

of formation of CH4 was directly related to the formation of H2+.

This indicates that the rate controlling step for CH4 formation was

a reaction between CO and a species derived from energy absorbed in









H2. From kinetic and thermodynamic arguments, it was concluded that

the major reaction pathway for the initial formation of CH4 were

reactions [10], [12], and [13].

The kinetics of formation for COz were found to be analogous to

those of CH4; the rate controlling step being a reaction between CO

and a species derived from the energy absorbed in Hz. Unlike CH4,

water vapor increased the rate of formation of COz. The primary

oxidant for CO was concluded to be OH with reaction [23] being the

major reaction pathway.

The formation of polymer was found to occur on the walls of the

vessel with water added, but without added water a turbidity formed in

the gas mixture before condensation on the wall. It was concluded

that for polymer formation, sufficient water must be present in order

to catalyze the polymerization. At higher temperatures, the rate of

polymerization of HCHO decreased.

G-values ranges for COz, CH4, and HzO were 0.1 1.1,

0.2 0.4, and 0.6 2.9, respectively.



E. Fission Fragments


Moseley, Truswell, and Edwards irradiated Hz-CO gas mixtures

with fission fragments from thin films of 23SU308 (6). Carbon

dioxide was the major product with small yields of formaldehyde and

methane detected.

G-values for COz increased with the partial pressure of CO to a

value of 1.4 at a CO pressure of 1 atmosphere. The yield of COz was

found to be very slightly enhanced with the addition of water vapor.










For CH4 and HCHO, the yields of each increased with dose and the

highest G-value for either was 0.3. No white polymer was found. When

fission fragments were blocked with a platinum shield, no measurable

reaction induced by reactor n, y radiation, or 3, y emissions

from the fission fragments was observed.



F. Electron Beams

Early work on reactions of Hz-CO gas mixtures in electrical

discharges has been reviewed by Glocker and Lind (7). Various

products reported were formaldehyde, formaldehyde polymer, an oily

yellow liquid with empirical formula C12H18011, water, carbon

dioxide, formic acid, "CzOH.CHO" (sic), acetylene, methane, ethane,

and higher hydrocarbons.

Mikhailov, Kiselev, and Bogdanov irradiated Hz-CO gas mixtures

with 115 KeV electrons at integral doses of 0.4-3.3 x 1023 eV at

room temperature (8). In equimolar mixtures, COz, carboxylic acids,

glyoxal, and small amounts of HCHO were found. No methanol,

peroxides, nor gaseous hydrocarbons were detected. Yields of COz

and acids increased with increasing amounts of CO while those of the

other products decreased. With an increase in pressure from 0.2-5

atmospheres, COz yield decreased while yields of all other products

increased. Maximum G-values were 1.4 for COz, 1.0 for carboxylic

acids, 0.7 for glyoxal, 0.2 for formic acid, and 0.1 for formaldehyde.

Considerable work has been performed at the Osaka Laboratory for

Radiation Chemistry, JAERI, on the electron beam radiolysis of Hz-CO

gas mixtures using both Van de Graff (VDG) and high dose rate electron

accelerators (HDRA) (9-14). Experiments were performed with both










static and flow systems, with and without cold-traps (11-13), while

studying the effects of pressure (10, 12), temperature (10, 13), CO

content (9, 12), electron beam energy and dose rate (10), and chemical

additives (11, 13). The rest of this review on the non-catalytic

radiolysis will cover work from this laboratory.



Static System

In the static system at 600 torr (9), the products and their

G-values were formaldehyde (1.5), methanol (0.42), acetaldehyde

(0.32), formic acid (0.12), glyoxal (0.14), acetic acid (0.11), and

trioxane (0.13). After 5 x 103 seconds, the vessel wall was coated

with an involatile sticky substance which showed -CH2-, aliphatic

-OH, ester or aldehyde C=0, and -C-O-C- bondings with infrared

spectroscopy.

Pressure. Upon varying CO content at 600 torr total pressure,

acetic acid and carbon dioxide were the main products at high CO

content. Methanol yield increased with Hz content, and acetic acid

yield maximized with a 50% mixture, while formaldehyde and trioxane

yields maximized at 14.7% CO. At 5000 torr total pressure, the maxima

occurred at approximately the same CO content (13).

When pressure was increased over a range of 200-400 torr in the

static system using 15% CO, the G-values for methanol, acetic acid +

methyl format, and minor products were constant, G-values for

acetaldehyde increased, and formaldehyde and trioxane G-values

decreased (10).

Electron Energy. As electron energy was increased, yields for

formaldehyde, methanol, acetic acid, and methyl format were










unchanged, while yields for trioxane and glyoxal decreased. Trioxane

yields decreased with increasing dose rate although those of the other

products were constant (10). An increase in temperature caused

trioxane and tetroxane yields to decrease while those of the other

products increased slightly. It was concluded that trioxane and

tetroxane were not formed by successive reactions of primary stable

products, and cluster ions of the form CO+(CO)n(Hz)m were

proposed as precursors (10).


Flow System

Cold Traps. The flow system was set up in such a manner as to

recirculate gases through the reaction region either through a series

of cold traps or bypassing them (11-13). The effect of the cold traps

was studied in order to gain insight into whether certain products

were further reacted in the radiolysis (indicated by an increase in

yield when using the traps) or whether they were formed as secondary

products (indicated by a decrease in yield with traps present).

G-values for the products formed from a 15% CO mixture at 1000 torr

without and with traps, respectively, were CH4 (0.5-0.6), C2H6

(0.035-0.035), C3H8 (0.007-0.007), C4Hio (0.001-0.001),

CH30H (0.06-0.06), HCHO (0.3-0.45), trioxane (0.09-0.34), tetroxane

(0.008-0.04), CH3CHO (0.07-0.03), HCOOCH3 (0.11-0.04), and

CH3COOH (0.11-0.04) (11). Also, yields for water decreased with

traps in place, while CO2 yields remained constant (12). This

implies that formaldehyde, trioxane, and tetroxane react to form

secondary products, and that acetaldehyde, methyl format, acetic

acid, and water are formed as secondary products.









Carbon Monoxide Content. The effect of CO content was also

studied using the flow system (12). Carbon monoxide content was

varied from 8-77% at 1000 torr total pressure and constant dose.

Methane and ethane had maximum yields at 25% CO with G-values of 0.65

and 0.6, respectively. Propane had a maximum G-value of 0.01 at 15%

CO, acetylene and ethylene had a maximum G-value of 0.01 at 45% CO,

and propylene yield maximized at 0.002 at 30% CO. Tetroxane yields

increased slightly to a G-value of 0.025 at 25% CO, while trioxane,

formaldehyde, and methyl format yields maximized at 15% CO with

G-values of 0.13, 2.5, and 0.15, respectively. Carbon dioxide, carbon

suboxide, and acetaldehyde yields all increased with increasing CO

content to 77% CO with G-values at 60% CO (highest value listed) of

0.35, 0.03, and 0.06, respectively. Methanol yields maximized at

<5% CO with a maximum G-value of 0.2.

Pressure. When pressure of the gas mixture was varied from

450-1500 torr in the flow system, most G-values decreased with

increasing pressure except those for acetaldehyde, trioxane, and

hydrocarbons, which remained constant, and those for tetroxane which

increased (12). The G-value for consumption of products increased

with pressure. These results suggest that conversion of products to

unidentified products of higher molecular weight decreases the

G-values of the products (12).

In a pressure range of 1000-9500 torr, methane and ethylene yields

were constant while ethane and propane yields decreased rapidly with

increasing pressure to about 2000 torr, then leveled off (13).

Formaldehyde yield increased asymptotically; trioxane, tetroxane, and

acetic acid yields increase slightly; and methyl format yield









decreased with an increase in pressure. Acetaldehyde yield increased

sharply as pressure was increased.

Temperature. The effect of varying temperature from -20*C to 50C

was also studied in a flow system (13). Methane yield decreased with

increasing temperature, formaldehyde, trioxane and tetroxane yields

all decreased sharply as temperature was increased to 150C then

leveled off, while yields of the other products were constant.

Scavengers. Chemical additives were added to the gas mixture in

order to gain insight about reaction intermediates (11). Added

ammonia (a cation scavenger) decreased the yields of formaldehyde,

trioxane, and tetroxane implying ionic intermediates in their

formation. An increase in the yield of water was also observed but

labeling experiments showed this to be due to extra hydrogen atoms

from the ammonia. Methanol, acetaldehyde, methyl format, and acetic

acid yields increased with added ammonia although no definite

conclusion could be drawn since irradiation time was also varied.

Methane and ethane yields did not change when ammonia was added.

When methane or carbon dioxide was added to the gas mixture,

trioxane and water yields were enhanced (11). Formaldehyde yield

increased with added COz but decreased with added CH4. The

addition of NzO caused methanol, methyl format, acetic acid, and

tetroxane yields to decrease while water yield was enhanced.

Nagai, Matsuda, Arai, and Hatada also of the Osaka Laboratory for

Radiation Chemistry, irradiated Hz-CO gas mixture using the HDRA

(14). These experiments were performed using their catalytic bed flow

system without catalyst added. The effect of reactant gas composition

was similar to results obtained by their colleagues (12). However, in









a study of the effect of varying temperature, it was found that

methane yield increased with increasing temperature as opposed to the

decrease in yield observed in (12). Formaldehyde yields changed

similarly with temperature as observed in (13); however, COz and

methanol yields decreased with a temperature increase as opposed to

remaining constant as observed in (13).



G. Catalytic Irradiations

Carbon Monoxide

In the gamma-irradiation of CO in the presence of alumina, CO was

chemisorbed on alumina with a G-1.3 forming the format ion as a

surface species (15). Carbon dioxide was also produced from surface

impurities or gaseous oxygen reacting with CO, although

disproportionation of CO into C and COz did not occur (15).



Hydrogen

Hydrogen which was gamma-irradiated in the presence of alumina

dissociated into H* atoms which could either be strongly absorbed as

OH or exist as mobile surface H atoms (15).



Hydrogen-Carbon Monoxide Mixtures

The irradiation of Hz-CO gas mixtures in the presence of

catalytic surfaces has been studied mainly from the point of view of

irradiating an ongoing thermal reaction and noting the combined

effects of both thermal and radiation induced reactions. Examples of

these types of studies can be found in Refs. (15-18). Radiolytic

studies of H2-CO mixtures in the presence of catalytic surfaces at









temperatures where little or no thermal reaction takes place are

comparatively few.

The most notable work to date has been performed by the group at

the Osaka Laboratory for Radiation Chemistry using high dose rate

electron beams (14, 19-24). Studies were made on an extensive number

of catalysts. These include silica gel and alumina (14, 19, 20),

diatomaceous earth (KG as kieselguhr), Fe-KG, Co-KG, MnO2-KG, and

Ru-A1203 (23), Fe-Cu-KG (14, 19, 21-24), MgO (19, 22), Ag and

ZnO-CrzO3 (14, 19), SiC, graphite and TiOz (19). These can be

grouped as having low or high activity.

Low Activity Catalysts. With the Fe-Cu-KG, Fe-KG, TiOz, and

Zn-CrzO3 catalysts, it was found that the radiation chemical

reaction of H2-CO mixtures was not sensitized although secondary

effects were noted, and results with Ag, SiC, and graphite were

analogous to those for TiOz (19, 23). Co-KG gave higher yields of

products than the Fe-KG although the products distribution was

similar. Diatomaceous earth (KG) gave fewer products than the thermal

reaction (23). Ru-A1203 selectively enhanced methane production,

but this could have been due to the temperature increase of the

catalyst surface under irradiation (23). The MnOz-KG catalyst

increased the COz yield over that of the thermal reaction, but the

hydrocarbon yields (especially olefins) were lower (23).

High Activity Catalysts. Silica gel, alumina, and MgO all

demonstrated catalytic activity under electron beam irradiation (19).

The MgO catalyst increased the yields of COz, CH4, CzHs, and

C3HA compared to the thermal reaction, with the yield of CH4

increasing by a factor of 15.5 (22). Small amounts of olefins were









produced and no oxygenated hydrocarbons were detected. The absence of

oxygenated products was ascribed to their absorption and decomposition

on the MgO catalyst (22).

Results using alumina and silica gel catalysts were similar, with

the silica gel catalyst forming twice the amount of total hydrocarbons

as alumina and about 20 times that of the homogeneous reaction when

irradiated at about 300*C (20). The olefin to paraffin ratio was

about 0.1 and 0.2 with silica gel and alumina, respectively. Yields

of oxygenated products over silica gel were decreased over that of the

homogeneous gas phase irradiation.

When the irradiation of 1:6 CO-H2 mixture with silica gel was

carried out at 1400C, products were desorbed by argon flow for more

than 150 minutes, while at 2950C less than 10% of the products

remained on the surface following irradiation (20). In addition, much

higher yields were obtained at the higher temperature.

Carbon monoxide irradiated over silica gel produced COz and the

silica gel color changed to dark brown, indicating a

disproportionation reaction (20). Yields of carbon dioxide were

higher at 2350C than at 3000C. When hydrogen was passed over the

irradiated catalyst at 3000C, Cl to C5 hydrocarbons were produced.

A mechanism was proposed for the formation of hydrocarbons by

irradiation of H2-CO mixtures over silica gel in which carbon

produced from CO reacts with Hz to form hydrocarbons.


















II. EXPERIMENTAL


A. Sample Preparation



Reagents and Their Purification

Hydrogen. Matheson Company 99.9995% research grade hydrogen was

used. When filling the 3 liter storage vessels S (Figure 1), the

hydrogen was slowly passed through a liquid nitrogen cooled stainless

steel U-tube filled with 13X molecular sieve (Ul) followed by a liquid

nitrogen cooled Pyrex U-tube packed with Pyrex helices (U2).

Carbon Monoxide. Matheson Company 99.99% research grade carbon

monoxide was further purified using the same procedure as used for

hydrogen.

Ethylene. Matheson Company c.p. grade ethylene used in the

dosimetry experiments was first passed through a barium oxide drying

tube, then further purified by several freeze-pump-thaw cycles and

vacuum distilled to a Pyrex storage vessel, taking the middle half of

the sample.

Nitrogen. Airco Products grade 4.5 nitrogen used for surface area

measurements was further purified by passing through an uncooled tube

containing 13X molecular sieve and a liquid nitrogen cooled Pyrex

U-tube packed with Pyrex rings.










Helium. Airco Products grade 4.5 helium used as a blank for

surface area measurements was further purified in the same manner as

nitrogen.

Nickel Nitrate Hexahydrate. Mallinckrodt analytical reagent grade

nickel nitrate hexahydrate used for preparation of the nickel-alumina

catalyst was further purified by recrystallization from distilled water.

Alumina. Alfa Products 99% gamma alumina, 3.2 mm pellets were heated

to 290 150C under vacuum over night before each use.

The pellets used for preparation of the nickel on alumina catalyst

were used as received.

Gas Chromatograph Calibration Standards. Reagents were used as

received.



Vacuum System

The vacuum system used for sample preparation, sample transfer, and

reagent storage is shown in Figure 1. The low pressure Pyrex manifold is

shown to the left and the high pressure stainless steel manifold is shown

to the right. The manifolds were pumped by a two-stage mercury diffusion

pump backed by a Welch Duo-Seal vacuum pump. A liquid nitrogen cold trap

was used between the two pumps and between the diffusion pump and the

manifold.

High Pressure Manifold. The high pressure manifold (MS) was

constructed of 1/4 inch stainless steel tubing inside box H and 3/8 inch

stainless steel tubing between the box and the Pyrex manifold (MG). All

connections in this manifold were either silver soldered or made with

stainless steel SWAGELOK couplings.











To
Pumps


X_
Si Pumps
MG GM MSSM
4rT


TT


0-.- L U2
M SM


B Stainless Steel Bellows
C Calibrated Volume
E High Pressure Gas Exhaust
G Pressure Gauge, Absolute
GM Glass to Metal Coupling
H High Pressure H2 and CO
Storage. Vented to Fume Hood.
L Copper Strain Relief Loop
M Mercury Manometer
MG Glass Submanifold
MS Stainless Steel Submanifold


0 #15 O-Ring Joint
S 3 liter Storage Vessels
SF Female SWAGELOK Coupling
SM Male SWAGELOK Coupling
T Teflon Stopcocks
TC Thermocouple Gauge
Ul Liquid Nitrogen Trap Packed
with Pyrex Rings
U2 Liquid Nitrogen Trap Packed
with 13X Molecular Sieve
V Glass Vacuum Stopcocks


Figure 1. Vacuum system used for sample preparation and transfer.


SF









The compressed gas cylinders of hydrogen and carbon monoxide were

completely enclosed in a box (H) made of 1/2 inch plywood. This box

was directly connected to the fume hood ducts with 1.5 inch PVC

tubing. The exhaust from the Welch Duo-Seal vacuum pump was also

plumbed into the PVC tubing. This was done to prevent a hazardous

buildup of hydrogen or carbon monoxide in the laboratory.

In order to speed pumping, the high pressure gas exhaust (E) was

used to reduce the pressure inside this manifold to atmospheric

pressure before evacuating it and it was also used as a connection for

compressed gases other than hydrogen or carbon monoxide as needed.

When used for exhausting the manifold, the exhaust tube extended well

inside the PVC tubing.

Liquid nitrogen trap U2 was packed with 13X molecular sieve to

further purify gases admitted to the vacuum line. The #15 "0" ring

joint (0) and the 1/4 inch female SWAGELOK coupling (SF) on the

stainless steel manifold were used to attach radiolysis vessels when

they were to be filled to pressures greater than one atmosphere.

Viton-A "0" rings and 1/4 inch Vespel ferrules were used on the

respective connections.

The vacuum quick couple glass to metal seal (GM) between the

stainless steel manifold and the Pyrex manifold is shown in Figure 2

(25). The brass portion (A) was silver soldered to the stainless

steel manifold. All other glass to metal joints were made with 1/4

inch SWAGELOK couplings using a reversed back ferrule and two #9 or

#10 Viton-A "0" rings in place of the front ferrule.

Low Pressure Manifold. In the Pyrex submanifold (MG), liquid

nitrogen trap U2 was packed with Pyrex rings and was used for further





















I/- //8

.415 .380 .257

--- 1.050

1/2"x 13
f


15/16 1
-I 3/16


3/4 1
.L


Knurl
Knurl


Material:

Use #2-010


Nut Aluminum
Others Brass
"O"-ring


Bore 27/64 dia. x 3/4 deep
and tap for I/2"x 13 threads


Figure 2. Vacuum quick-couple, glass to metal seal.


1 1/2


.375 .257
Ir^I


.257









purification of gases admitted to the vacuum system. This portion of

the manifold was usually pumped in parallel with the main sample

preparation manifold pictured to the left in Figure 1. The copper

strain relief loop was used for filling the stainless steel radiolysis

vessels and was also used for sample transfers from the radiolysis

vessels to the gas chromatography sample loops. The copper line was

constructed of 1/4 inch copper tubing which had been "soft" annealed

for flexibility by heating the looped section until it glowed red and

then quenching in water. It was then cleaned with dilute nitric acid

solution and rinsed with deionized water before attaching to the

vacuum line.

The stainless steel bellows (B) with a #15 "0" ring joint was used

for connecting the nickel radiolysis vessels or the spark discharge

vessel to the vacuum line for filling.

Two 3-liter storage vessels (S) were used for storing mixtures of

hydrogen and carbon monoxide. These vessels were taped and then

wrapped with black plastic and aluminum foil to reduce implosion

hazard and to exclude light. The connecting line between the storage

vessels and the Teflon stopcocks was constructed of small (5 mm i.d.)

tubing to minimize back diffusion of gases while filling.

The mercury manometer (M) and the thermocouple gauge (TC) were

used to monitor pressure inside the manifold.

Volume Calibration. All volumes were calibrated relative to the

calibrated volume (C). The volume of this vessel was determined by

filling it with water from a buret read to 0.05 ml and by weighing the

full and empty vessel. The volume was 132.0 ml at 270C.










All subsequent volume calibrations were made by assuming ideal gas

behavior and using the "volume sharing" technique. This was done by

opening the calibrated volume to the manifold and recording the

mercury heights in manometer M. The calibrated volume was isolated

from the manifold and the manifold was evacuated. This process was

repeated until the final pressure was less than 10 torr.

Using the Ideal Gas Law

Vcv[(Pi/Pf)-l] = Vmanifold + Ahmanometer

where Pi and Pf are the initial and final pressure, Vcv and

Vmanifold are the volumes of the calibrated volume and manifold, A

is the cross sectional area of the manometer tubing, and h is the

difference in mercury height in the left arm of the manometer relative

to the height at vacuum.

A plot of Vcv[(Pi/Pf)-1] versus h gives the volume of the

manifold as the intercept and the cross sectional area of the

manometer tubing as the slope. The manifold was recalibrated after

any glassblowing. The cross-sectional area of the manometer tubing

was 0.31 cm2



Preparation of Hydrogen Carbon Monoxide Mixtures

Hydrogen carbon monoxide mixtures with the ratio of 3 moles of

hydrogen to 1 mole of carbon monoxide were used throughout the study.

Before filling the storage vessels, they were first evacuated, then

covered with a plastic bag which had a small hole in the top, and hot

air was blown into the bag from the bottom for about four hours while

pumping on the vessels. The vessels were then pumped on for at least

one day before filling.










The vessels were usually filled to approximately 800 torr. When

filling the vessels, carbon monoxide was slowly added to 1/4 the final

pressure desired. The pressure was then read from the mercury

manometer (M) and the storage vessel was isolated from the vacuum

system by closing the Teflon stopcock. The glass and metal manifolds

(MG and MS) were then evacuated and filled with hydrogen to a pressure

approximately twice that inside the storage vessel. The stopcock to

the storage vessel was then opened and hydrogen was admitted until the

desired pressure was obtained.

The small tubing between the Teflon stopcock and the storage

vessel helped to prevent back diffusion of carbon monoxide during

filling since the initial rush of hydrogen into the vessel should have

flushed the carbon monoxide into the storage. The flow of hydrogen

was regulated by the Teflon stopcock between liquid nitrogen trap Ul

and the preparation manifold. After this stopcock was closed, the

stopcock isolating the storage vessel was closed and the pressure

recorded. The stopcock isolating the storage vessel was then opened

and shut quickly in order to assure equal pressures on both sides, and

the pressure was again recorded. This was repeated until two

subsequent identical readings were obtained. Usually the first two

readings were identical. Using this method, the mixture was within

0.35% of the desired 3 to 1 ratio. The storage vessel was not opened

for at least one day in order to assure thorough mixing. Samples were

periodically analyzed by gas chromatography in order to check purity

of the mixture or to insure the proper 3 to 1 ratio of hydrogen to

carbon monoxide.









Catalyst Preparation and Characterization

The alumina catalyst was used as received except for treatment

described earlier. The nickel-alumina catalyst was prepared by

impregnation of the alumina with nickel nitrate hexahydrate. The

nitrate was converted to oxide by heating under helium. The nickel

oxide was then reduced to nickel by heating under hydrogen (26).

After transferring the catalyst to a stainless steel radiolysis

vessel, the vessel was evacuated and slowly heated to 2250C until the

catalyst no longer outgassed.

Measured specifications for the catalysts are listed in Table

2-1. Details of the preparation, analysis, and characterization

follow.

Preparation. The alumina pellets (112.4 g) were added to 96.9 g

of nickel nitrate hexahydrate melted in its water of hydration at

900C. After two hours the excess solution was decanted and the

pellets were drained on heated filter paper. These were heated over

night at 150*C. The pellets were then recoated and heated as before.

At this point, the pellets were a yellow-green lime color and nitrogen

oxide fumes could be smelled.

The pellets were then added to a stainless steel cylinder with

stainless steel tubing silver soldered to each end. This was heated

in an oven to 325*C while passing a small flow of helium through the

vessel. The helium was bubbled through NaOH solution to trap nitrogen

oxides. The pellets were heated until the carrier did not make water

more acidic indicating that the conversion was essentially complete.

The helium carrier was then replaced with hydrogen and the vessel

was heated to 3250C for five days. The temperature was kept as low as




























Alumina Weight

Nickel Weight

Volume (measured)a

Volume (calculated)b

BET Surface Area

Pore Volume

Vessel Volume (empty)


Table 2-1

Catalyst Specifications

Y-Alumina

90.0 g



22.5 ml

22.6 ml

142 m2/g

0.43 ml/g

109.1 ml


Nickel-Alumina

90.1 g

25.6 g

25.7 ml

25.0 ml

91.3 m2/g

C

109.1 ml


(a) Measured using helium pycnometry.

(b) Calculated using the density of A1203 (3.98 g/cc) and Ni
(8.90 g/cc) (43).

(c) Not measured.










possible to reduce sintering while assuring complete reduction (27).

Both hydrogen and helium exhaust were vented into a fume hood.

The pellets were cooled under helium and transferred to a

stainless steel radiolysis vessel inside a helium filled glove bag.

At this point the pellets were a grayish, flat black resembling

artists charcoal.

Analysis. The amount of nickel deposited on the alumina was

determined gravimetrically by precipitation with dimethylglyoxime

(28). About 1 g of the sample was crushed and then calcined in a

crucible to constant weight. This was done to convert the partially

hydrated, gamma form of alumina (29) to the dehydrated alpha form.

This also converted the nickel to nickel oxide.

The nickel oxide was then dissolved in 20 ml of 1:1 (vol.)

sulfuric acid solution while heating and stirring. This left a pale

blue powder of alumina and blue nickel aluminate (27). The mixture

was heated daily until the powder was white. The solution was diluted

to 50 ml and 10 ml aliquots were precipitated. Reproducibility was

excellent giving 19.34% nickel on dehydrated alumina.

The procedure was then repeated using an uncalcined sample. The

sample weight for calculations was adjusted in proportion to the

weight loss from the first analysis. The sample dissolved much

quicker since no nickel aluminate was formed. This method gave 19.32%

nickel assuring that all nickel was dissolved in the first analysis.

Characterization. Surface area measurements were made on the

catalysts at 77K using the nitrogen BET method (30-34). The amount of

nitrogen physically adsorbed on the surface was measured as a function

of equilibrium pressure. Prior to the measurement a blank run using










helium was made under identical conditions to determine the dead

volume of the vessels (33). A linear regression of the helium data

was used as a baseline for the nitrogen measurements since it was a

measure of the gas admitted to the vessel but not adsorbed. This was

subtracted from the nitrogen admitted to the vessel to give the amount

of nitrogen adsorbed. The mean deviation from the calculated volume

was 0.3%.

A plot of the data is shown in Figure 3a. The linear portion at

higher pressures indicates that more than a monolayer had been

adsorbed (34). The data are linearized in the BET method by the

equation

P/n(Po-P) = l/nmC + (C-1)(P/Po)/nmC

where P is pressure, Po is the vapor pressure of the gas at the

temperature of measurement, n is the moles of gas adsorbed, nm is

the amount adsorbed in a monolayer, and C is a constant (30). This is

plotted in Figure 3b. The mean deviation from the calculated slope

was 0.8%. The surface area was calculated assuming a cross-sectional

area of 16.2 x 10-20 m2/molecule (33).

The pore volume of the alumina catalyst was measured using water

as described in reference (35).



B. Sample Irradiation



Cobalt-60 Gamma Ray Source

The cobalt-60 source used for this investigation has been

described elsewhere (36). Figure 4 shows a cut away side view of the

irradiator. The source was loaded with 600 curies of cobalt-60 in May

of 1974.































250


50 100 150 200
P (torr)


0



Figure 3.


P/Po


Surface area data.
(a) Nitrogen adsorbed on surface vs. equilibrium pressure.
(b) BET plot of data.












































Legend = (A) counterweight; (B) upper support; (C) control

rod handle; (D) extra top shielding; (E) storage turret;

(F) 400 curie Co60 source; (G) shutter shown open; (H) rear

wall; (I) door; (J) downward shielding; (K) door carriage;

(L) door crank; (M) door frame.


Figure 4. Cross section of irradiation through center, left side view.
From Ref. (36).










Radiolysis Vessels

Two types of radiolysis vessels were used. One type was made of

nickel and the other was made of stainless steel. The nickel

radiolysis vessels (Figure 5) were used only for the radiolysis of the

Hz-CO mixtures with no catalyst added. The internal volume of these

vessels was 103.1 0.1 cc. The stainless steel vessels (Figure 6)

were used for the radiolysis of Hz-CO mixtures with and without

added catalyst. The volume of these vessels was 109.1 0.1 cc.

The use of a copper gasket between knife edge seals proved to be

excellent for vacuum use. The vessels were tested for leaks by

removing from the vacuum line for one week, then after reconnecting to

the vacuum line and isolating the glass manifold from the pumps, the

vessel being tested was opened while monitoring the pressure rise in

the manifold on the thermocouple gauge. The pressure rise for these

vessels was approximately 20 microns for a one week period.

Prior to filling, the vessels were cleaned by heating with a

luminous flame while pumping in order to decompose and outgas any

residue inside the vessel. When the stainless steel vessels contained

a catalyst, a heating jacket was used to heat the vessels to a

controlled temperature. This jacket consisted of insulated nichrome

resistance wire wound around a cylinder made of brass shim metal and

covered with a layer of insulation. The temperature was controlled by

connecting the jacket to a variable transformer and monitoring the

temperature with an iron-constantan thermocouple inserted between the

jacket and the vessel. The vessels were heated to 270 10*C while

pumping overnight.
















4 1/4 1-


11/4" 0.37 1/2" --


HOKE MONEL VALVE
0 RING SEAL


-'* 1/31

HEUARC WELD



DETAL
DETAIL A


Figure 5. All nickel vacuum tight radiolysis vessel. From Ref. (37).













4621N4M HOKE MONEL VALVE


COPPER GASKET


5
I -T
BO16
BOLT


'ILL 6 HOLES
EQUISPACED


SS-400-R-4
SWAGELOK ADAPTOR


All dimensions in inches
Scale 1:1


Figure 6. Stainless steel vacuum tight radiolysis vessel with removable top.


HELIARC
WELD
3


DETAIL A










When filling the vessels, the glass manifold was isolated from the

pumps and the gas mixture was added to the manifold and vessels from

the storage vessel until the desired pressure was reached. The

storage vessel was then isolated and the HOKE valves on the vessels

were closed. The manifold was pumped out and the vessels were removed.

Since the gas mixture adsorbed quickly on the nickel-alumina

catalyst, the "volume sharing" technique was used for filling the

vessels containing this catalyst. Once the volume of the manifold was

determined, the required pressure drop from this volume at room

temperature corresponding to the desired quantity of gas to be

delivered was calculated using the ideal gas law. The manifold was

then filled to a pressure greater than the calculated value and this

value was recorded. The HOKE valve on the vessel was then opened

slightly and the pressure in the manifold was allowed to decrease

until the desired final pressure was reached. The valve was then

closed and the final pressure was recorded.



Sample Holder

An aluminum sample holder was used to assure a reproducible

geometry between the cobalt-60 source and the radiolysis vessels.

This consisted of an aluminum block 5 x 5 x 1.75 inches deep

(12.7 x 12.7 4.45 cm) with a center hole 11/16 inch (1.75 cm) in

diameter and 3/4 inch (1.9 cm) deep for positioning the source. The

center hole was surrounded by four holes 1.625 inches (4.13 cm) in

diameter and 1.5 inches (3.81 cm) deep centered on a circle of radius

1 3/16 inches (3.02 cm) from the center. The radiolysis vessels fit

snugly into these holes. With this geometry, the source was

positioned about midway up on the vessels.










When irradiations were carried out at temperatures greater than

room temperature, a heated enclosure which has been described

previously (38) was used. This was modified by the addition of

fiberglass insulation on the outside of the box and by exchanging the

sample holder for the one described above.

For irradiations carried out below room temperature, a polystyrene

packing container, used for shipping articles packed in dry ice, was

used. This was modified by the addition of a small motor and fan on

the top, cutting a hole for the cobalt source, and installing the

sample holder. When this container was packed with dry ice, the

temperature equilibrated at -77*C as measured with a copper-constantan

thermocouple placed inside a "dummy" radiolysis vessel inside the

box. The temperature remained constant within 2*C for at least 15

hours.



Dosimetry

Ethylene dosimetry was used to determine the absorbed dose rate in

the H2-CO mixture. The ethylene was irradiated in the same vessels

and using the same sample holder as the Hz-CO irradiations. The

ethylene was irradiated from 5 to 33 hours between the pressures of

248.5 and 251.0 0.5 torr at 270C. This pressure range falls in

the region where the G-value for hydrogen production has been reported

to be independent of pressure (39). A G-value of 1.3 molecules of

hydrogen per 100 eV deposited was used in all calculations (40).

After irradiation, the vessel was attached to a Toeppler pump -

McLeod gauge apparatus and cooled in liquid nitrogen. The pressure

and volume of the non-condensable gases were measured and the total

molar yield was calculated using the ideal gas law.










The non-condensable gases were then analyzed by gas chromatography

for methane, ethane, and ethylene. The molar yield of hydrogen was

determined from the difference between the total yield and the yield

of these compounds. For two of the experiments (25 and 30 hrs.

irradiation), the hydrogen yield was measured directly by gas

chromatography utilizing a thermal conductivity detector. No

significant difference in the two methods was indicated.

From the slope of the plot in Figure 7, the energy absorbed in

ethylene, to a 95% confidence level, was 2.37 0.14 x 1019

eV-g-'-hr-' on April 15, 1980. This value was used to calculate

the dose rates summarized in Table 2-2. Details of the calculations

are given in the Appendix. The dose rates were corrected for Co-60

decay assuming a half-life of 5.26 yrs. (41).



C. Sample Analysis



Spark Discharge

The spark discharge technique was used to facilitate the

qualitative analysis of radiolysis products. This technique has been

shown by previous work in this laboratory to give a qualitative

approximation of the products obtained from gamma radiolysis (42).

The vessel used for this technique is shown in Figure 8. The

technique consists of applying a high voltage, high frequency current

from a Tesla coil plugged in to a variable transformer to one of the

metal electrodes and connecting the other electrode to earth ground.

The bulb was filled with the H2-CO mixture and the tip of a Tesla

coil was touched to one of the electrodes for about 5 minutes. The






























6









4




3




2-




1Figure 7.











Figure 7.


TIME OF IRRADIATION (HRS)


Ethylene dosimetry. Energy deposited in ethylene vs.
irradiation time.





























Table 2-2

Summary of Dosimetry Calculations
(All Dose Rates for April 1980)


H2-CO
(eV/mol-hr)

2.07 x 1020

2.17 x 1020

2.15 x 1020


Dose Rate

Catalyst
(eV/hr)


1.75 x 1021

0.37/1.73 x 1021


Vessel Walls
(eV/hr)

2.46 x 1021

2.18 x 1021

2.15 x 1021


Catalyst
Used

None

A1203

Ni/A1203


--

































































Figure 8. Spark discharge vessel.










variable transformer was adjusted to a setting just above that at

which a spark bridged the electrodes.

In this experiment a blue glow covered the tips of the

electrodes. Product yield for a 5 minute spark discharge was

approximately 8 times greater than that of a 48 hour gamma radiolysis

of the gas mixture.

The products were then transferred to a gas chromatography sample

loop for analysis using the same procedure as that used for a gamma

radiolysis sample.



Gas Chromatography Sample Loops

The sample loops used for gas chromatographic analysis are shown

in Figure 9.

Sample loop Ll was used for the analysis of products condensible

in liquid nitrogen. The procedure for the transfer of products to

this loop is given in the next section. The tubing (H) was packed

with Pyrex helices to increase the surface area and to decrease the

dead volume of the loop. The capillary tubing (C) was also used to

decrease the dead volume. The uppermost stopcock (N) was a

Fischer-Porter 3 mm needle valve and the lower one (T) was an Ace

Glass 3 mm stopcock.

The loop was connected by the 1/4 inch glass tubing (Q) using a

SWAGELOK coupling with a reversed back ferrule and 2- #9 or #10 "0"

rings in place of the front ferrule. The two-way stopcock (S) was

used to flush air from the loop before analysis.

Sample loop L2 was used for the analysis of products

non-condensible in liquid nitrogen. The 10/30 standard taper joint















































All Pyrex


specified


Q- 1/4" tubing
S- 2-way stopcock
V- 3-way vacuum stopcock
N- 3 mm Teflon needle valve


Figure 9.


3 mm Teflon stopcock
7 10/30 joint
1 mm i.d. tubing
8 mm tubing packed
with 5 mm helices


Gas chromatography sample loops used for the analysis of
products condensible (LI) and non-condensible (L2) in
liquid nitrogen.


Legend
unless










(J) attached to the three-way vacuum stopcock (V) was used for

connection to the Toeppler-McLeod apparatus. The 1/4 inch glass

tubing (Q) and two-way stopcock (S) served the same purpose as with

sample loop L2.



Product Transfer

Since hydrogen is non-condensable in liquid nitrogen and carbon

monoxide has a vapor pressure of about 400 torr at 77K (43), reaction

products had to be transferred to sample loop L1 dynamically rather

than simply allowing them to condense in the sample loops without

pumping away non-condensable gasses. The samples were transferred as

follows.

The uppermost tube on the sample loop was attached to the vacuum

line at the copper loop, and the vessel containing reaction products

was attached to the lower tube. The entire system was evacuated up to

the valve on the vessel and the loop was heated from 1 to 3 hours to

degas the loop.

After cooling, the bottom portion of the loop was immersed in

liquid nitrogen. After about 15 minutes, the upper Teflon stopcock

was closed, isolating the loop from the vacuum system, and the valve

on the vessel was opened, admitting gases to the loop. The gases

acted as a heat transfer agent to further cool the Pyrex rings.

After a few minutes, the upper Teflon stopcock was slowly opened

until a pressure rise was noted on the thermocouple gauge TC in the

vacuum manifold. The non-condensable gases were leaked into the

vacuum system slowly to maximize the residence time of the gas in the

loop. As the manifold pressure, as indicated on the thermocouple










gauge, reached normal system vacuum, the stopcock was opened gradually

until the manifold pressure increased. This was continued until no

increase in pressure was noted on the gauge. This usually took from 1

to 2 hours. The stopcock was closed again and the procedure was

repeated while heating the vessel to 1500C. By pumping away the

hydrogen and carbon monoxide before heating, the possibilities for a

thermal reaction were minimized.

When the products from a vessel containing alumina were being

transferred, the vessels were heated further to 2400C for 2 1/2 hours

more. This procedure was developed after many attempts to achieve a

reproducible, quantitative transfer while minimizing the temperature

needed for transfer. Only a small portion of the olefinic products

would transfer at a temperature of 150*C or less.

Because of the activity of the nickel-alumina catalyst, vessels

containing this catalyst were only heated to 50-600C during transfer.



Gas Chromatography

A Microtek model 2000-R gas chromatograph (GC) was used for

qualitative and quantitative analysis. The inlet system had been

modified by Ron Marcotte to accept the sample loops in Figure 9 (38).

Although the inlet system allowed a vacuum transfer to be made

directly on the GC, all samples were transferred as described earlier.

The instrument was equipped with a multifunctional temperature

programmer and four detector systems. A GOW-MAC model 10-285 thermal

conductivity detector (TCD) was used in series with a hydrogen flame

ionization detector (FID) for this work.










The FID electrometer output was attenuated by powers of 2 and the

input by powers of 100. In actuality the 102 setting only

attenuated by a factor of 74. Other settings for both the FID and TCD

electrometer were within 2% of their measured attenuations.

Electrometer outputs for the two detectors were recorded by a

Westronics dual pen strip chart recorder, lmV full scale.

Three different packed GC columns were used for product

identification; silica gel for hydrocarbons, Carbowax 20M for

oxygenated hydrocarbons, and Porapak Q for both types of compounds.

Typical chromatograms are shown in Figures 10 and 11.

Silica Gel. Hydrocarbon products were identified and measured

quantitatively using a 3M x 6.4 mm O.D., stainless steel column packed

with 60-200 mesh silica gel. This column was used at 500C with a

helium flow of 40 cc/min., with temperature programming at 5C/min.

after 5 min.

Hydrocarbons were separated by boiling point within a homologous

series. Alkenes were held up longer than alkanes of the same carbon

number with an offset of ~1 carbon number. Water and oxygenated

hydrocarbons were held until high temperatures then bled off. Alkanes

(>C4) and alkenes (>C3) were fit to separate linear

regressions of boiling point vs. the elution temperature of injected

standards. The fits gave calculated elution temperatures which were

within the resolution of the temperature gauge. The marked range for

the elution of isomers on the chromatograms in Figure 10 was based on

both calculated and measured elution temperatures.

Carbowax 20M. Oxygenated hydrocarbons were identified and

measured quantitatively using a 6.25 m x 6.4 mm O.D. stainless steel













Figure 10. Gas chromatograms of hydrocarbon products (48 hr. irradiation time).


(a) Products
(b) Products
(c) Products


from the 48 hr.
from the 48 hr.
from the 48 hr.


irradiation of 250 torr Hz-CO mixture.
irradiation of 250 torr Hz-CO mixture.
irradiation of 1.59 mmol H2-CO mixture.


No catalyst.
Alumina catalyst.
Nickel-alumina catalyst.


Column: 3 m x 6.4 mm stainless steel column packed with 60 200 mesh silica gel.
Carrier: Helium at 50 cc/min.
Temperature programming: 5C/min from 50*C beginning at 5 min.





Peak Identification


Methane
Ethane
Ethylene
Propane
i-Butane
n-Butane
Propylene
neo-Pentane
i-Pentane
n-Pentane
1-Butenes


12. Branched hexanes/
2-Butenes
13. Methyl pentanes
14. n-Hexane
15. Pentenes
16. Hexenes
17. Heptenes
18. Octenes
19. Methyl hexanes
20. n-Heptanes
21. Octanes






















5 6


1920


'32x 8 x 16x 4x 8x 4x

500 750 1000 1250 1500 2000 C

Retention Time (in)
Retention Time (min)


Figure 10(a).


































8x 8z 256x 4x
100 100 100


500
I


5












32x 64x
100


750
I


Ix 8x 16x
100 100 100


1000
I


1250
I


Retention Time (min)


Figure 10(b).


4x
100


2x
100


150o


1750C
I


S[IgI





















1 2


2x 16x Ix 64x
100 100 100


500


8x 4x


750


1vo


14 120




8x


1250
i


1500
I


detention Time (min)


Figure 10(c).


175C
I


r 1 1












Figure 11. Gas chromatograms of oxygenated products.

(a) Products from the 48 hr. irradiation of 250 torr H2-CO.
(b) Products from the 49 hr. irradiation of 250 torr H2-CO.


No catalyst.
Alumina catalyst.


Column: 6.25 m x 6.4 mm stainless steel column packed with
20% Carbowax 20M on 30-60 mesh Chromasorb W.
Carrier: Nitrogen at 45 cc/min.
Temperature programming: 5*C/min from 60C beginning at 20 min.





Peak Identification


1. Hydrocarbons
2. Diethyl ether
3. Acetaldehyde
4. i-Propyl ether
5. Propylene oxide
6. Propionaldehyde
7. Acetone
8. Acrolein
9. n-Butyraldehyde
10. Methanol
11. 2-Pentanone/
Ethyl acetate
12. i-Propanol


13. Ethanol
14. s-Butanol
15. n-Propyl propionate/
Glyoxal
16. n-Propanol
17. i/n-Butanols/
n-Butyl acetate
18. Primary isoamyl alcohol
19. n-amyl alcohol
20. ?
21. i-Hexyl alcohol
22. n-Hexyl alcohol
23. Acetic acid













1
16 7

10


13 11
3
12
2


15 14 4


9 65


16 x 32 x 64 x 32 x 8 x


1200 1000 800 600C
I i I I 1
30 20 10
Retention Time (min)


Figure 11(a).









column packed with 20% Carbowax 20M on 30-60 mesh Chromasorb W. This

column was used at 600C with a nitrogen carrier flow of -45 cc/min.,

with temperature programming at 5C/min. at 20 min. Compounds

separated by boiling point and chain branching within a homologous

series. Branched chain compounds eluted before their straight chain

isomers.

Hydrocarbons eluted from this column as a large injection peak

(Peak 1, Figure 11). To aid identification of the oxygenated

compounds, the column was also used to preseparate hydrocarbons from

the other compounds. After most of the hydrocarbon peak had eluted,

the column effluent was switched to pass through a liquid nitrogen

cooled sample loop. The trapped compounds were then injected onto a

Porapak Q column.

Porapak Q. Both hydrocarbons and oxygenated compounds were

identified and semiquantitatively measured using a 3 m x 3.2 mm O.D.,

stainless steel column packed with Porapak Q. The helium carrier flow

was 35 cc/min. Initial temperatures were either 30 or 50*C, with

temperature programming after 3-5 min. at 3-5*C/min.

Methanol, acetaldehyde, and formaldehyde and the Ci to C3

hydrocarbons were resolved while higher carbon number species

overlapped. When formaldehyde, water, and methanol were injected

together as standards, an unusual broadening of the formaldehyde peak

occurred. This was not seen when these compounds were injected

separately. The radiolysis products also gave a similar peak

broadening allowing only for an estimation of formaldehyde yield.













2 1



3



17 15 7




13 10 5 4
23 22 18 9 8 6
21
2019 12



4 x 100 16 x 100 8 x 100 4 x 100

180 160 1400 1200 100 80 60 C
I I I I I1

40 30 20 10
Retention Time (min)


Figure (b).
Figure 11(b).










column packed with 20% Carbowax 20M on 30-60 mesh Chromasorb W. This

column was used at 60C with a nitrogen carrier flow of -45 cc/min.,

with temperature programming at 5*C/min. at 20 min. Compounds

separated by boiling point and chain branching within a homologous

series. Branched chain compounds eluted before their straight chain

isomers.

Hydrocarbons eluted from this column as a large injection peak

(Peak 1, Figure 11). To aid identification of the oxygenated

compounds, the column was also used to preseparate hydrocarbons from

the other compounds. After most of the hydrocarbon peak had eluted,

the column effluent was switched to pass through a liquid nitrogen

cooled sample loop. The trapped compounds were then injected onto a

Porapak Q column.

Porapak Q. Both hydrocarbons and oxygenated compounds were

identified and semiquantitatively measured using a 3 m x 3.2 mm O.D.,

stainless steel column packed with Porapak Q. The helium carrier flow

was 35 cc/min. Initial temperatures were either 30 or 50*C, with

temperature programming after 3-5 min. at 3-50C/min.

Methanol, acetaldehyde, and formaldehyde and the Ci to C3

hydrocarbons were resolved while higher carbon number species

overlapped. When formaldehyde, water, and methanol were injected

together as standards, an unusual broadening of the formaldehyde peak

occurred. This was not seen when these compounds were injected

separately. The radiolysis products also gave a similar peak

broadening allowing only for an estimation of formaldehyde yield.










Gas Chromatography Infrared Spectroscopy

A stainless steel gas cell was constructed to obtain infrared (IR)

spectra of GC peaks from spark discharge experiments. This is shown

in Figure 12. A Perkin-Elmer model 337 Grating Infrared Spectrometer

was used to record the spectra. The cell was tapered to match the

beam path of the spectrometer so that the total sample was exposed to

the beam. The volume of the cell (10 cc) held about 15 seconds of the

GC effluent.

The cell fit a Connecticut Instrument CH-1A holder. A #2-16 Viton

"0" ring, a 4 mm x 25 mm dia. NaC1 disk, and a posterboard spacer fit

between the cell and the holder with the "0" ring next to the cell. A

3 mm x 32 mm dia. NaCl disk was attached to the front of the cell with

Torr-Seal epoxy.

The GC peak was trapped in a 1/8 inch o.d., stainless steel U-tube

immersed in liquid nitrogen. The U-tube was attached to the larger

SWAGELOK fitting on the gas cell.

The other end of the U-tube was connected to the gas chromatograph

through a small three-way valve temporarily attached between the

column and detectors.

The smaller, 1/16 inch SWAGELOK fitting shown attached to the gas

cell was capped at all times. This cap was loosened slightly when gas

was flowing through the cell. The cell was flushed with carrier gas

and the cap tightened prior to sample injection into the GC.

Just before the peak of interest eluted, the cap was loosened and

the three-way valve was turned to direct gas flow into the cell. The

sensitivity of the flame ionization detector was such that the peak

was observed from minute leaks through the valve. On the downward






51


















SIDE



















TOP


Figure 12. Stainless steel gas cell used for infrared spectroscopy.


FRONT









slope of the peak, the cap was tightened and the valve was turned

back. The U-tube was then disconnected from the GC and quickly

capped. The U-tube was then warmed and the infrared spectra was taken.

Figure 13 shows the infrared spectra of 0.6 pI (15 pmol) of

methanol (upper tracing) and a GC peak obtained from a 2 hr. spark

discharge of the H2-CO mixture (lower tracing). The peak eluted

from the Porapak Q column at 14.5 min., 100*C, temperature programmed

at 4C/min. from 450C at 3 min. Helium carrier flow was 40 cc/min.

The spectra indicates the peak to be that of methanol.



Gas Chromatography Mass Spectrometry

A Bendix model 14-107 time of flight mass spectrometer interfaced

with a gas chromatograph was used to aid product identification.

Details of the system (44) and interface (45) are given elsewhere.

Mass spectral data acquisition was under the semiautomatic control of

a General Automation SPC-12 minicomputer.

Problems with adjustment of the stream splitter between the flame

ionization detector and the mass spectrometer (45) were eliminated by

using the total ion current of the mass spectrometer as the GC

detector. This also allowed more of the GC peak into the mass

spectrometer for increased sensitivity. This was an advantage since a

spark discharge of up to two hours was needed to produce enough sample

for analysis. The sensitivity of the mass spectrometry appeared to be

about midway between the flame ionization detector and thermal

conductivity detector.

























0










































(a)
(
.0





















































Figure 13.
(a)
(b)


Frequency (m-1)


Infrared spectra using the gas cell.
0.6 1p methanol.
A trapped gas chromatography peak from a 2 hr. spark discharge.










D. Product Identification and Measurement



Products from the gamma radiolysis and spark discharge of H2-CO

mixtures were identified primarily by matching gas chromatographic

retention times with standards. Gas chromatography (GC) combined with

mass spectrometry (MS) or infrared spectroscopy (IR) was used to

confirm a few of the products from multiple spark discharge samples.



Hydrocarbons

Methane, ethane, propane, ethylene, and propylene all had unique

retention times on both the silica gel and Porapak columns. Ethane

was also confirmed by GC-MS. A peak corresponding to acetylene was

not seen except for a very small peak from the spark discharge

experiment. Isobutane and n-butane eluted as a doublet from silica

gel followed closely by propylene. The propylene peak from the

radiolysis with alumina catalyst was so large that the n-butane peak

was usually obscured. Isopentane, n-pentane, and the 1-butenes eluted

similarly. Following these peaks, the isomeric distribution of the

hydrocarbons led to considerable overlap between alkanes and alkenes.



Alcohols

Methanol was identified with both the Carbowax and Porapak columns

as well as by GC-IR. Ethanol was identified with both columns and

GC-MS. Isopropanol eluted with 2-pentanone from the Carbowax column

and with ethyl format from the Porapak column. Since no peak

corresponding to ethyl format was seen using the Carbowax column, the

presence of isopropanol was confirmed. Normal-propanol eluted with










isopentane from Porapak, but when the hydrocarbons were preseparated

on Carbowax, a peak corresponding to n-propanol was identified on

Porapak. Normal and s-butanol were seen on both columns. Other

alcohols were identified by retention time/temperature on the Carbowax

column only.



Aldehydes

Formaldehyde was identified using the Porapak column only since it

eluted with the hydrocarbon peak from the Carbowax column.

Acetaldehyde was identified with both columns and by GC-MS.

Propionaldehyde matched the retention times of standards from the

Carbowax column consistently but was obscured by C4 hydrocarbons on

Porapak.

Butyraldehyde, methylal, and acrolein were identified using the

Carbowax column only. No peak corresponding to valeraldehyde was

detected.



Ketones

Peaks corresponding to acetone were seen on both columns. Acetone

was also injected as a standard following each Carbowax run. The

retention times matched consistently to an isolated peak seen with the

Carbowax column. Peaks corresponding to 2-pentanone were seen on both

columns. Isopropanol eluted with 2-pentanone from the Carbowax column

making quantitative measurements difficult. No peaks were seen which

corresponded to higher ketones standards injected on the Carbowax

column.










Carboxylic Acids

Only a very small peak corresponding to acetic acid was seen.

Flame ionization detector response to formic acid is poor.



Ethers

Diethyl ether eluted on the tail of the hydrocarbon injection peak

from Carbowax. This made quantitative measurement difficult,

especially with the very large hydrocarbon peak from alumina catalyst

radiolyses. This compound eluted with methyl acetate from the Porapak

column, but a peak corresponding to methyl acetate was not seen with

the Carbowax column confirming identification.

A small peak corresponding to di-isopropyl ether eluted from the

Carbowax column after acetaldehyde and was usually obscured by the

tail of the acetaldehyde peak. No peak corresponding to di-butyl

ether was seen. A peak corresponding to propylene oxide was

consistently matched with injected standards on the Carbowax column.



Esters

No peaks were seen eluting from the Carbowax column which

corresponded to methyl acetate, ethyl format, ethyl acetate, ethyl

propionate, or n-propyl acetate. Methyl propionate, isopropyl

format, or n-propyl format cannot be ruled out. These compounds

elute in the same range as 2-pentanol, isopropanol, and ethanol.

n-propanol and n-butyl acetate elutes with i-butanol. Since some of

the esters were definitely excluded and the alcohols were confirmed on

Porapak, the flame ionization detector response for the alcohols was

used to calculate molar yields.

















III. RADIOLYSIS WITHOUT CATALYSTS


A. Experimental Results



Product Yield versus Irradiation Time

The yields of oxygenated compounds and total hydrocarbons were

measured from irradiations of 250 torr (1.38 mmol) of the H2-CO gas

mixture, at 27*C, in the nickel vessels. The dose deposited in the

reactants was 0.54, 1.09, and 1.63 x 10'9eV corresponding to

irradiation times of 24, 48, and 72 hours, respectively.

The products were identified primarily from their retention times

on a Carbowax 20M G.L.C. column. A Porapak Q column was used for

product confirmation. On one run, the effluent following the

hydrocarbon peak from the Carbowax column was passed through a liquid

nitrogen cooled sample loop. The trapped portion was then injected

onto a Porapak Q column to aid identification.

The major products identified (>1 nmol) and their relative

yields were formaldehyde, methanol, ethanol > acetaldehyde, acetone

> 2-butanone, i-propanol, and total hydrocarbons. The minor

products were propionaldehyde, butyraldehyde, n-propanol, i-butanol,

propylene oxide, diethyl ether, and s-butanol. Only very small,

unmeasurable peaks were seen for carboxylic acids although flame

ionization detector response for formic acid is poor.









The total hydrocarbon peak was made up of C2 to Cs

hydrocarbons. For 48 hours irradiation time, the peak consisted

primarily of ethane (60%), propane (20%), and ethylene (9%).

The G-values and molar yields for the products are listed in

Table 3-1. The G-values were obtained from the linear regression

slope of the yield vs. dose. The molar yields are plotted for the

major products in Figures 14 and 15.

The coefficient of determination for the linear regression (r2)

is also listed in Table 3-1. The r compares the error between two

models used to fit the data (46). They are the model where y is a

linear function of x, and the model where y exhibits no dependence on

x (mean value of y). The r2 is the reduction in error achieved by

using the linear model instead of the mean value as a predictor for

y. This is expressed as

E(yi yi)2 = (1-r2) E(yi-y)2,

where yi is the measured value of y, yi is the calculated value of

y using the linear regression model, and y is the mean value of y.

A value of one indicates that the linear model fits the measured data

exactly and a value of zero indicates no linear dependence of the

y value on x.

Aldehydes. Formaldehyde was not quantified since it eluted with

the hydrocarbon peak from the Carbowax column. Formaldehyde was

identified using a Porapak Q column with a peak area greater than that

of methanol. This column was not used for quantitative analysis since

hydrocarbons eluted along with the oxygenated species, complicating

yield measurements.















Table 3-1

Yield of products versus time.
Unpacked metal vessels.


H2-CO (mmol) 1.38 1.38 1.38 1.38
Pressure (torr) 250 250 250 250
Dose (x10-'9 eV) 0.54 1.09 1.63 0-1.63
Irrad. Time (hrs) 24 48 72 0-72


Products Yield (nmol) G-Value (b> r2

Methanol 10.4 25.1 29.2 0.12 0.96
Ethanol 0.4 8.9 23.4 0.13 0.97
n-Propanol/i-Butanol 0.05 0.2 0.3 0.002 0.99
s-Butanol 0.08 0.25 0.2 0.0006 0.96

Acetaldehyde 6.5 9.5 11.8 0.07(c) 0.99
Propionaldehyde 0.3 0.6 0.5 0.0033 1.00
Butyraldehyde 0.3 0.5 1.2 0.004 0.93

Acetone 12.6 12.7 22.2 0.075 0.89
2-Butanone/i-Butanol 3.1 4.1 6.3 0.022 0.96

Propylene Oxide 0.2 0.2 0.3 0.002 0.94
Diethyl Ether 0.05 0.2 0.3 0.001 0.96
Total Hydrocarbons 3.1 4.5 6.4 0.023 0.97



(a) Calculated using the detector response for ethylene.

(b) The G-value and the coefficient of determination (rZ) were
calculated from the linear regression of yield vs. dose.


(c) Calculated from the initial slope.










Dose (eV x 10-19)

0.0 0.5 1.0 1.5
40. i I I


Methanol =

30. Ethanol = O

SAcetaldehyde = U



20.



O0

10.





0.
0 24 48 72
Irradiation Time (hrs)





Figure 14. Yield of methanol, ethanol, and acetaldehyde vs. irradiation time. No catalyst. o











Dose (eV x 10-19)
1.0


0 24 48 72
Irradiation Time (hrs)


Figure 15. Yield of acetone, 2-butanone, and hydrocarbons vs. irradiation time. No catalyst.


30.
-4
0




24
" 20.



4
P-










Acetaldehyde yield is plotted in Figure 14. The yield increased

linearly with dose from 24-72 hrs. giving a G-value of 0.03. It

appears as if the initial slope was somewhat steeper, leveling off at

some time <24 hrs. If this were the case, the initial G would be

>0.07.

Propionaldehyde yield increases linearly from 0 to 48 hrs. then

levels off between 48 and 72 hours while that for butyraldehyde

increases with dose from 0-72 hrs. However, with the small peak size

for these minor compounds detailed behavior with dose becomes obscured

by small measurement errors.

Alcohols. Methanol and ethanol yields are plotted in Figure 14.

It appears as if methanol yield was beginning to level off between 48

and 72 hrs. irradiation time. The yield increased from 10 to 25 nmol

between 24 and 48 hrs. and increased from 25 to 29 nmol between 48 and

72 hrs. irradiation time. Over the same interval, ethanol yield

appears to have a concave upward slope with an apparent induction time

of -24 hrs. The G-value for methanol was calculated from a linear

regression of all points including zero. The G-value for ethanol was

calculated without zero. The G-values for the other alcohols

decreased with increasing carbon number.

Ketones. Acetone and 2-butanone/i-propanol yields are plotted in

Figure 15. Both 2-butanone and i-propanol were identified using

the Porapak Q column and eluted with similar retention times on the

Carbowax column. Molar yield was calculated using the relative

detector response for 2-butanone.

The yield vs. dose plot shows somewhat unusual behavior for

acetone with the same yield for 24 and 48 hr. irradiations then









increasing for 72 hr. irradiation time. Had this been caused from

error in product transfer and handling techniques, this behavior

should be exhibited for all compounds. One explanation could be that

the electrometer attenuation was recorded wrong, but examination of

the gas chromatograph indicated that the attenuation recorded was

probably correct. Unless the recorder pen was exactly on zero, an

attenuation change caused the pen to jump. Comparing the attenuations

recorded for peaks before and after acetone revealed that the correct

attenuation was probably recorded. Even had the attenuation been

recorded erroneously, the G-value for acetone would be within a factor

of 2 of the G-value reported.

The 2-butanone/i-propanol yield showed some slight deviation

similar to acetone, but the yield increased with dose for all data

points. The G-values for both ketones were calculated from a linear

regression of all data points including zero.

Ethers. The G-values for both propylene oxide and diethyl ether

were very small with the G for propylene oxide being approximately

twice that of diethyl ether.

Hydrocarbons. The hydrocarbon yield, as ethylene, increased

linearly with irradiation time in a manner very similar to that of

2-butanone. The G-value was calculated from a linear regression of

all data points including zero.



Hydrocarbon Yield versus Pressure

Hydrocarbon yields were measured from the 48 hour radiolysis of

the H2-CO gas mixture, at 270C, over a pressure range of 100-3242

torr (13.3 432 kPa). At first glance, this series of experiments










may appear to provide no more information than the relative yields of

hydrocarbon products to augment the previous study, since the energy

absorbed by the reactant gases varied linearly with reactant pressure

as well as with irradiation time. However, there was one important

difference. In this series of experiments, the energy deposited in

the vessel walls was constant (neglecting Co-60 decay) since the

irradiation time and source to vessel geometry was kept constant. The

yield values were scaled to a constant dose to the vessel walls of

1.0 x 1023 eV to remove the influence of Co-60 decay. This is valid

since it was shown that hydrocarbon yield was linear with irradiation

time (Figure 15) and therefore linear with dose to the vessel walls.

The major hydrocarbon products were methane, ethane, propane,

ethylene, butanes, and pentanes. Minor products which were identified

but could not be reliably quantified include hexanes, heptanes,

octanes, butenes, pentenes, and hexenes.

The mean hydrocarbon yields over all reactant pressures are shown

in Table 3-2. For the alkanes there is little difference in the mean

for the two types of vessels. The standard deviation from the mean

yield for both vessels was about 30% for ethane and 40% for the other

alkanes. The standard deviation for the alkenes was about equal to

the mean yield.

Table 3-3 contains the molar yields vs. pressure obtained using

the nickel and stainless steel vessels. The yields reported for 100,

250, and 500 torr were the mean of two replicates. The others were

for single experiments only. With but a few exceptions, the molar

product yield from both types of vessel show no particular trends over

the pressure range studied. The results were essentially constant

within 35% of mean values for this set of experiments.




















Table 3-2

Mean hydrocarbon yield (nmol) for all pressures.


Nickel
Vessel


Stainless Steel
Vessel


Ethane 2.5 1.8
Ethylene 0.95 0.5
Propane 0.70 0.64
i-Butane 0.06 0.07
n-Butane 0.14 0.12
Propylene 0.13 0.22
i-Pentane 0.05 0.06
n-Pentane 0.04 0.04












Table 3-3

Hydrocarbon yields (nmol) from unpacked vessels at
differing reactant pressures for 48 hr. irradiations at 27*C.
Normal vessel preparation methods. (Yield values are scaled
to a constant dose to the vessel walls of 1.0 x 1023 eV.)


(a) Nickel Vessels



Pressure (torr) 149 250 500 874 1370 3242
Gas Phase Dose 7.4 12.5 25.0 43.7 68.5 162.0
(eVxlO-18)


Ethane 5.1 2.2 2.1 2.1 2.3 1.1
Ethylene 0.11 1.6 0.72 0.89 1.8 1.2
Propane 0.8 0.92 0.64 1.3 1.2 0.27
i-Butane 0.05 0.09 0.09 0.11 0.09 0.01
n-Butane 0.2 0.18 0.05 0.18 0.29 0.18
Propylene 0.02 0.04 0.04 0.20 0.35 0.27
i-Pentane 0.03 0.07 0.04 0.09 0.08 0.04
n-Pentane 0.04 0.04 0.01 0.04 0.09 0.07





(b) Stainless Steel Vessels



Pressure (torr) 100 149 250 500 874 1370
Gas Phase Dose 5.0 7.4 12.5 25.0 43.7 68.5
(eVxlO-8)


Ethane 1.6 1.4 1.3 2.0 1.8 1.8
Ethylene tr 0.07 0.07 0.19 0.23 0.40
Propane 0.38 0.25 0.61 0.97 0.77 1.1
i-Butane 0.06 0.02 0.12 0.09 0.04 0.14
n-Butane 0.06 0.04 0.11 0.15 0.22 0.23
Propylene tr tr 0.04 0.04 0.06 0.11
i-Pentane tr 0.02 0.11 0.07 0.05 0.06
n-Pentane tr 0.01 0.07 0.03 0.08 0.06










For the nickel vessels, the exceptions were ethane yield at 149

and 3242 torr and ethylene yield at 149 torr. The molar yield of

propylene also appears to increase slightly with reactant pressure.

The yield of ethane at 149 torr was twice the mean value of 2.5 nmol.

At 3242 torr, the ethane yield was 1/2 the mean value. Ethylene yield

at 149 torr was 10 times lower than the mean value of 1.4 nmol for the

pressure range of 250-3242 torr.

For the stainless steel vessels, the molar yields of all products

but ethane were 3-5 times lower at 149 torr than the mean yield for

the other experiments. The alkene molar yields also appear to

increase slightly as reactant pressure was increased.

The data in Table 3-3 were for experiments conducted using the

normal vessel preparation methods described in Chapter II. The

vessels were cleaned by evacuating and then heating with the heating

jacket or by heating briefly with a luminous flame. Both methods gave

similar results. Another set of experiments were conducted in which

the vessels were heated with a flame until a faint red glow was

observed and then cooled prior to filling. The results are shown in

Table 3-4.

The treatment apparently affected the surface, causing the

hydrocarbon yield at 250 torr to decrease approximately 1/2. At

pressures of 400 torr and above, the different vessel preparation

methods gave similar results.

Neither preparation method appears to be preferred over the

other. Instead, the comparison of each method under comparable

reaction conditions serves to provide even more evidence of the effect

of the surface and the surface treatment on hydrocarbon production.












Table 3-4

Hydrocarbon yield (nmol) from unpacked vessels at
different reactant pressures for 48 hr. irradiations, at 27*C.
Vessels heated red hot during preparation. (Yield values are
scaled to a constant dose to the vessel walls of 1.0 x 1023 eV.)


(a) Nickel Vessels



Pressure (torr) 250 250 500
Gas Phase Dose 12.5 12.5 25.0
(eVxlO- 8)


Ethane 1.0 1.3 3.5
Ethylene 0.10 0.43 1.7
Propane 0.12 0.19 0.63
i-Butane 0.01 0.01 0.04
n-Butane 0.01 0.02 0.13
Propylene 0.05 0.01 0.15
i-Pentane tr tr 0.02
n-Pentane tr tr 0.01







(b) Stainless Steel Vessels



Pressure (torr) 200.5 400 500
Gas Phase Dose 10.0 20.0 25.0
(eVxlO-18)


Ethane 1.4 3.0 2.4
Ethylene 0.08 0.53 2.4
Propane 0.28 0.64 1.1
i-Butane 0.03 0.07 0.12
n-Butane 0.05 0.12 0.21
Propylene 0.28 0.12 0.90
i-Pentane 0.02 0.05 0.10
n-Pentane 0.01 0.02 0.03










Hydrocarbon Yield versus Temperature

Hydrogen-carbon monoxide mixtures were irradiated in unpacked

nickel and stainless steel vessels over a temperature range of

27-150"C. The irradiation time and reactant pressure were held

constant at 48 hrs. and 250 torr except for one irradiation each using

the nickel and stainless steel vessel at 27*C. The pressure for these

experiments was 200 torr. Unirradiated control experiments were also

carried out at 270 and 1500C to check for thermal reactions during

irradiation or product transfer. The results from the control

experiments were negligible at both temperatures.

The effects of temperature on hydrocarbon yields are shown in

Figures 16 and 17. These are Arrhenius type plots of log G versus

1/T. Note that these plots only give information for the overall

series of reactions forming the products and are not meant to supply

information on the elementary reaction steps.

Figure 16 shows ethylene yield to be independent of temperature

over the range studied. This plot also shows that ethylene yields

from the nickel vessel were consistently larger than those from the

stainless steel vessel.

The scatter in the data for propane makes it difficult to tell

whether temperature influenced the yield or not. It is possible that

there was a slight effect at higher temperatures. Propane yields were

comparable with both vessels.

Ethane yield decreased with temperature at the higher temperatures

than leveled off at the lower temperature range. The decrease was

slight compared to the data scatter, but the effect can be seen.

Ethane yields were comparable with both vessels.









Temperature (oC)
150 100 87 75 54 27
I I 1 1 I I

Ethane


0

6

*8 o


2.5
1/T


3.5


3.0
x 103 (K-1)


Figure 16. Arrhenius plots of ethane, propane, ethylene. No catalyst.
(Open symbols = nickel and filled symbols = stainless steel
vessels.)


10-2
10


10-4

10-2


O Propane


oD
03 0


A A A A
1 A A
A Ethylene A



I I I I
______________ I ___ I __ I __


2.0


10-3


10-4









Temperature (oC)


100 87 75


10-2


2.5


3.0


3.5


1/T x 103 (K-1)


Figure 17.


Arrhenius plots of propylene, butanes, pentanes. No catalyst.
(Open symbols = nickel and filled symbols = stainless steel
vessels.)


150


I I I I I I

O Propylene

* 0
0

O 0
0
o o 6
0




- Butanes

3 0
D D
nO []


0




SPentanes
A
A A





I I I I


10-2




10-3


10-2




10-3


2.0










Results for propylene, butanes, and pentanes are plotted in

Figure 17. These compounds exhibited a greater temperature dependence

than those plotted in Figure 16. The slopes at higher temperatures

appear to be similar for these three compounds. However, propylene

yield decreased over the entire temperature range while the alkane

yields leveled off at the lower temperatures. With the butanes, it

was difficult to tell detailed behavior at the lower temperatures

because of scatter in the data; however, five of the seven total

replicates at 270C indicated a relatively constant yield over the

lower temperature range. There appears to be little difference in

yields from the nickel or stainless steel vessels for these three

compounds.



Mass Balance

An estimate of the G-value for C02 and H20 can be made by

considering the mass balance of the system. Since all carbon and

oxygen incorporated into the products originated from CO, the

difference in carbon and oxygen balance for the products detected

gives an order of magnitude estimate of the amounts of COz and H20

formed. This assumes, of course, that all products other than COz

and Hz0 were detected and quantified. The fact that formaldehyde

was not quantified will not affect the calculation since carbon and

oxygen were incorporated equally.

The mass balance was performed by taking the G(-CO) and G(-O) as

the sum of the G-value times carbon or oxygen number, respectively,

for all products. The results of the calculation are summarized in

Table 3-5. The G(-H2) is also shown and was calculated in the same





















Table 3-5

Mass balance of products for a 48 hr., 250 torr, 270C irradiation.
No catalyst.


Product G(Product) G(-CO) G(-H2) G(-0)


Methane 0.27 0.27 0.55 0.0
Methanol 0.12 0.12 0.24 0.12
Alcohols(a) 0.05 0.12 0.16 0.05
Aldehydes(b) 0.06 0.13 0.15 0.06
Ketones 0.10 0.31 0.31 0.10
Ethers 0.003 0.01 0.01 0.003
Hydrocarbons"c) 0.016 0.03 0.05 0.0

Total 0.62 0.99 1.47 0.33


(a) Excluding methanol

(b) Excluding formaldehyde

(c) Excluding methane










manner as the G(-CO) and G(-0). The best estimates of the product

G-values for a 48 hr., 250 torr irradiation at room temperature were

used for the calculation. For oxygenated products, the yields from

the least square fit were used. For hydrocarbon products, the mean

yields for all experiments at these conditions were used.

These calculations gave values of G(-CO) = 1.0 and G(-0) = 0.33.

The difference gave a G-value of 0.7 for COz and H20 combined.

Even had COz alone been formed, this amount (0.12 pmol) would have

barely been detectable using the thermal conductivity detector. This

also indicates that COz and/or HzO were formed as major products.

By assuming a midrange yield for COz and HzO, the relative

conversion of Hz and CO can be calculated. The summation gives a

G(-H2) of 1.9 and G(-CO) of 2.0, indicating that the reactants were

utilized in roughly equimolar amounts. For a dose of l.lx10lOeV

(1.75J), this means that 0.05 mol % of the reactant gas mixture was

converted to products.



B. Discussion



Beattie has presented a series of reactions leading to the primary

species formed in the autoradiolysis of 3H2-CO mixtures (5).

These reactions were shown on page 4 (reactions 6-24). The reactions

were selected by considering all known reactions between the species

and eliminating as many as possible based on thermodynamic, kinetic,

or experimental evidence. These arguments also apply to the gamma

radiolysis since energetic electrons provide energy with both beta and

gamma radiolysis. The difference was that the initial electron energy










is much higher for the Co-60 gamma radiolysis, 0.587 MeV (47) compared

to 0.0186 MeV (maximum) (41) for the tritium radiolysis.

Also to be considered are the reactions

CO + H + M -- CHO + M 25

and the hydrogenation of formaldehyde and polymers to methanol.

The reported rate constants for reaction [25] would give a

psuedo-first order rate constant of -10-9 cc/s for concentrations

used in this experiment (48, 49). This is approximately the same as

the rate constant of 1-2 x 10-9 cc/s for the ion-molecule reaction (50)

H3*+ CO -) CHO+ + Hz. 16

which was considered a major reaction pathway by Beattie.

The reaction pathways initiated by energy deposited in H2 lead

to the formation of the excited and ionized hydrogen species Hz* and

H3+. The primary form of ionized hydrogen has been shown to be

H3+ rather than H2* by mass spectrometry experiments (5). The

primary radical species from the reaction of H3' and CO is CHO. The

ion H3+ can also be neutralized to form H atom, which leads to CHO

formation. The CHO radical is a primary precursor to oxygenated

species.

On the other hand, Hz* leads primarily to hydrocarbon species

via the radical CH3. The OH radical is also formed from Hz*. The

ratio of Hz*/H3+ from tritium radiolysis has been calculated to be

0.6 triplet H2* for every H3+ (5). This ratio is expected to be

smaller for the Co-60 gamma radiolysis since the electron energies

were higher. Thus, the proportion of electrons with an energy low

enough to cause excitation rather than ionization would be lower,










since many more ion producing collisions would have to occur before

the electron energy was reduced to levels where excitation would occur

(51).

Another pathway for CHO formation is from CO' via the reaction

CO+ + Hz CHO+ + H 17

which has a rate constant of 1.2 x 10-9 cc/s (50).

For the 3:1 H2-CO mixture used in these experiments, the

electron stopping power for CO was calculated to be twice that of

Hz. Carbon monoxide has only a slightly lower W value than H2

(32 vs. 36 ion pairs/eV) (52, 53). So the rate of CO+ formation

should be approximately twice that of Hz+. Reaction 17 is also

consistent with Beattie's observation that CH4 formation did not

depend on CO+ formation. Reaction [17] in parallel with the

reaction of CO with H3+ (Reaction [16]) would enhance the formation

of oxygenated species via CHO.

This mechanism is also consistent with the electron beam

radiolysis of H2-CO mixtures with NH3 added as a cation scavenger

(11). The yield of hydrocarbons was unchanged while oxygenated

species decreased. This indicates that hydrocarbon formation did not

follow an ionic mechanism even with the much greater electron energy

of the electron beam experiment. Thus, it follows that this

mechanistic step should also hold for the higher electron energy of

the gamma radiolysis.

The relative yields of the major species with increasing dose may

be indicative of the chemistry involved in forming compounds with a

carbon number greater than one. Consider, for example, the relative

yields of methanol and ethanol (Figure 14). Ethanol was formed with










an apparent induction time of 24 hours and exhibited a concave upward

slope on the yield versus irradiation time curve. This indicates that

ethanol was formed from secondary reactions. Methanol yield, on the

other hand, increased much more between 24 hours and 48 hours

irradiation time than between 48 hours and 72 hours irradiation time,

exhibiting a concave downward slope. This indicates that methanol was

reacting further. The curve for methanol also exhibits an induction

time of approximately 12 hours. Methanol could be formed by the

hydrogenation of formaldehyde.

The data for the aldehydes (Table 3-1) also display interesting

yield versus dose behavior. The yield of acetaldehyde appears to have

leveled off even before 24 hours irradiation time indicating that

acetaldehyde was reacting to form secondary species, possibly

hydrogenation to ethanol. Propionaldehyde yield increased with

irradiation time to 48 hours before leveling off, and butyraldehyde

yield increased linearly up to 72 hours irradiation time.

These trends tend to point to higher molecular weight compounds

formed from secondary reactions of the lower molecular weight

compounds. This is in agreement with data from electron beam

irradiation of H2-CO mixtures in a flow system (c.f. Chapter I),

which indicated that formaldehyde reacted to form secondary species

and that acetaldehyde was formed as a secondary species (11).

Although hydrocarbon yield could be explained by the mechanism

presented, the data indicate that surface reactions are a definite

possibility. Consider, for example, the difference in the yield

versus irradiation time (Figure 15) and the yield versus reactant

pressure (Table 3-3). An increase in irradiation time increased the










dose to both the surface and the reactant gas and the hydrocarbon

yield increased linearly. On increasing the reactant pressure at

constant irradiation time, the dose to the gas phase increased, but

the dose to the surface was relatively constant, neglecting Co-60

decay. The hydrocarbon yield was relatively constant for these

experiments. These results indicate that surface reactions play a

major part in hydrocarbon formation.

Also consider the difference in yield at 250 torr reactant

pressure when the vessels were strongly heated prior to filling. The

types of products detected would desorb from the vessel wall with both

methods of heating, so the carry-through of products from one

experiment to another would not be expected. Indeed, unirradiated

control experiments indicated that this was the case, and also that

the products did not originate from impurities in the reactant gas.

This leaves a modification of the surface structure as a possible

explanation.

For thermal reactions of Hz-CO mixtures on nickel, carbide

formation on the surface has been shown to be necessary prior to

methane formation (54). Had this been the case for the radiolysis,

then heating under vacuum would not remove the carbide. However,

heating the metal strongly allows the carbide to be dissolved in the

bulk of the metal, effectively decreasing the amount on the surface

(55). This could explain the trends observed. The carbide would form

more rapidly at higher pressures since the surface would be covered

more completely. Once the carbide were formed, the dose to the

surface would influence the reaction rate.










Since the experiments with the nickel-alumina catalyst provide

more insight into the nature of these surface reactions, these data

for these experiments will be presented before discussing the surface

mechanism further.

Very few trends were noted when the temperature was varied.

Within experimental error, the yields were relatively constant between

27" and 1000C. Product yields at 1500C were generally larger with the

difference being more pronounced with the higher carbon number

compounds. It has been shown that temperatures greater than 50*C are

necessary for the formation of species which initiate the reaction

between Hz and CO on nickel or iron (56) and this was verified by

the negative results from unirradiated control experiments.

Therefore, it must be concluded that thermal reactions during

irradiation and product transfer were negligible and that the products

were formed from radiation induced reactions above.

















IV. RADIOLYSIS WITH THE ALUMINA CATALYST


A. Experimental Results



Product Yield versus Irradiation Time

The yields of oxygenated compounds and total hydrocarbons (as

ethylene) were measured from irradiations of 250 torr (1.16 mmol) of

the H2-CO gas mixture at 270C using the stainless steel vessels

containing the y-alumina catalyst. The irradiations were carried

out in the order 49, 72, 24, and 36 hrs. The dose rate to the gas

mixture was 1.9 x 1017 eV/hr. The actual dose rate allowing for

O6Co decay was within 1% of this value. The dose rate to the

alumina was 1.3 x 1021 eV/hr.

The effect of irradiation time on the yields of the major products

is shown in Figures 18 and 19. Note that there are two distinct types

of behavior. The yields of acetaldehyde, acetone, acrolein,

propionaldehyde, and total hydrocarbons all increase linearly with an

increase in irradiation time. The yields of methanol, ethanol, and

n-propyl propionate/n-propanol increase linearly with irradiation time

initially, then level off at longer irradiation times. Also, note the

apparent induction times for many of the compounds. When the curves

are extrapolated to zero yield, the apparent induction times were 17

hrs. for methanol and acrolein, 15 hrs. for acetaldehyde and

n-propanol/n-propyl propionate, and 9 hrs. for acetone.

80












150. 6

0
= Methanol
O = Ethanol
120. 0 = n-Propanol (or n-propyl O
propionate x 2) l-



90.

~3 90.



0
I60 -0




30.





0.
0 24 48 72

Irradiation Time (hrs)

Figure 18. Yield of methanol, ethanol, and n-propanol/ n-propyl
propionate vs. irradiation time. Alumina catalyst.













































24 48 72


Irradiation Time (hrs)


Figure 19. Yield of hydrocarbons, acetaldehyde,
Alumina catalyst.


acetone, acrolein, and propionaldehyde vs. irradiation time.


150.





120.


;-4
o

90.











30.
o0

3 60.
0





30.





0.










The G values (molecules/100 eV) for the products are listed in

Table 4-1. These were calculated from the initial slopes of the yield

vs. time plots which in turn were calculated from a linear regression

of the initial straight line portions of the curves. The relative

G-values for the products were total hydrocarbons >> n-propanol >

methanol > ethanol > acetaldehyde = n-propyl propionate >

acetone > n/i-butanol = diethyl ether = acrolein >

diisopropyl ether = propionaldehyde > propylene oxide 1"

isoamyl alcohol > n-amyl alcohol > i-hexanol > n-hexanol.

Hydrocarbons. The total hydrocarbon yield was calculated from the

area of the hydrocarbon "injection peak" from the Carbowax 20M column

using the detector response for ethylene. The main point to notice is

that the total hydrocarbon yield was linear with irradiation time.

For a 48 hr. irradiation of 250 torr of the H2-CO gas mixture,

ethylene makes up 72% and propylene makes up 20% of the total

Cz-Cs hydrocarbon yield. Since the flame ionization detector

response was linear with carbon number within 5%, the G value for

total hydrocarbons as ethylene is a measure of the C2 units formed.

The G(-CO) reacting to form hydrocarbons would be twice this value.

A more detailed analysis of the hydrocarbon products follows.

Alcohols and Esters. Methanol exhibits an apparent induction time

of 17 hrs. while ethanol does not appear to have an induction time.

The yields of the two compounds were very close for 48 and 72 hrs.

irradiation time. The G values for n-propanol and n-propyl propionate

are both reported although these were calculated from the same peak.

The two compounds eluted from the Carbowax 20M column at distinct, but

close, retention times and temperatures. The peak matched the















Table 4-1

G-Values for oxygenated products and total hydrocarbons.
Alumina catalyst.




Methanol 1.02
Ethanol 0.85
n-Propanol(a> 1.2
n-Propyl propionateca) 0.6
n/i-Butanol 0.2
i-Amyl alcohol 0.06
n-Amyl alcohol 0.035
i-Hexanol 0.02
n-Hexanol 0.002

Acetone 0.31

Diethyl ether 0.22
Diisopropyl ether(b) 0.14
Propylene oxide 0.08

Acetaldehyde(b) 0.69
Propionaldehyde 0.12
Acrolein 0.23

Total Hydrocarbons 17.4
(as ethylene)


(a) Calculated from the same peak

(b) Calculated from the same peak










retention time/temperature for n-propyl propionate closely and no peak

was detected at the retention time/temperature for n-propanol. The

G-value for n-propanol was reported since no lower molecular weight

esters were detected and lower molecular weight alcohols were.

Aldehydes and Ethers. There is also some question whether the

peak corresponding to acetaldehyde was actually diisopropyl ether or

even a combination of the two. The two peaks were resolved with

smaller yields from irradiations with no catalyst, but they were not

with the greater hydrocarbon yields from these irradiations. Because

of differences in the relative detector response, the G value for

diisopropyl ether would be 1/5 that reported for acetaldehyde. Both

values were reported.

The yield of diethyl ether could only be measured at an

irradiation time of 72 hrs.; therefore, the G value was calculated

from this one measurement only. At other irradiation times, the total

hydrocarbon peak interfered with this measurement.

Ketones. Acetone yield increased linearly with irradiation time

with an apparent induction time of 9 hrs. As with the gas phase

irradiation, 2-pentanone eluted on the tail of the methanol peak.

However, in this case the peak was obscured by the methanol peak

indicating that 2-pentanone yield was much less than methanol yield.



Hydrocarbon Yield versus Temperature

Hydrogen-carbon monoxide mixtures were irradiated in a stainless

steel vessel packed with 90.0 g of y-alumina over a temperature

range of -77* to 1000C. The irradiation time and reactant pressure

were held constant at 48 hrs. and 250 torr. The dose deposited to the










gas phase was within 2.5% of 9.3x101'eV allowing for Co-60 decay.

The dose to the alumina catalyst was 6.5xl022eV.

Unirradiated control experiments were carried out at 270C, 100*C,

and 1500C to check for a thermal reaction on the catalyst, as well as

a possible reaction occurring during the transfer procedure. Results

were negative at 270C; however, a thermal reaction onset was noted to

occur between 1000 and 150*C. An upper temperature limit of 900C was

chosen for the radiolyses to ascertain that reactions were initiated

by ionizing radiation only.

The G-values (molecules of product/l0eV deposited) at the various

temperatures for the major alkanes, alkenes, and carbon dioxide are

listed in Table 4-2. Included for comparison purposes were the mean

G-values for the radiolyses of 250 torr of the Hz-CO mixture at 270C

without added alumina. For temperatures of -77, 27*, and 900C, the

G-values are the mean of 3 or more runs, while the G-values at -20 and

60C are for single runs only.

The yields for n-butane could not be measured accurately because

propylene, which eluted immediately after n-butane on the silica gel

column used, was present in much greater amounts and obscured the

peak. However, with low temperature irradiations, the apex of the

peak could be seen and was of comparable height as that of i-butane.

Also, iso- and normal-l-butene eluted simultaneously, as well as cis-

and trans-2-butene, due to their almost identical boiling points.

These were reported simply an 1-butene and 2-butene, respectively.

The yields reported for 1-pentenes include 3-methyl-l-butene,

1-pentene, and 2-methyl-l-butene with the yield of 2-methyl-l-butene

> 1-pentene > 3-methyl-l-butene at low temperatures and 1-pentene
















Table 4-2

G-values for hydrocarbons and carbon dioxide. Alumina catalyst.
(48 hr. radiolysis of 250 torr of Hz-CO)



Gas
Phase With Alumina Added
Temp. (*C) 270 -770 -20 270 50 900


COz -- 69. 70. 59. 42. 39.

CzHg 0.009 0.24 0.28 0.36 0.55 0.64

C2H4 0.001 7.9 16. 11. 12. 16.

C3HS 0.003 0.064 0.18 0.11 0.16 0.21

C3Hs 0.0003 1.6 3.8 3.8 6.4 6.4

i-C4H10 0.0006 0.007 0.016 0.013 0.041 0.027

1-C4H8 0.00004 0.052 0.14 0.15 0.42 0.63

2-C4Hg -- 0.29 0.70 0.62 1.9 2.3

i-CsH12 0.0006 0.002 0.006 0.005 0.013 0.021

n-CsHiz 0.0004 0.002 0.006 0.006 0.010 0.020

1-CsHio -- 0.009 0.038 0.025 0.092 0.20









> 3-methyl-l-butene > 2-methyl-l-butene at higher temperatures;

the difference in yields never differing by more than a factor of 2.

The yields for 2-pentenes include both 2-methyl-2-butene and

2-pentene with the yield of 2-pentene consistently greater by a factor

of about 3.

Although a peak corresponding to that of methane was seen on every

chromatograph, the yield was not reported. Since the vapor pressure

of methane is 10 torr (1.33 kPa) at liquid nitrogen temperature (13),

the method used for transfer of products to a sample loop also pumped

away part of the methane. This resulted in an unreliable yield.

As can be seen in Table 4-2, there was a substantial increase in

the yields of all products when the gas mixture was irradiated in the

presence of alumina as opposed to the homogeneous reaction. The

yields of the alkanes increased about 1 order of magnitude, while

those of the alkenes increased 3-4 orders of magnitude. With the

homogeneous reaction, the paraffin yields were about 10 times those of

the corresponding olefin. With the alumina added, the alkene yields

were roughly 100 times those of the corresponding alkane product.

The temperatures at which the radiolyses were carried out also

influenced the yield. With all hydrocarbon products, the yields

increased with a temperature increase. The yield of carbon dioxide

decreased with increasing temperature. Also note that the yields of

the hydrocarbon products decreased with increasing carbon number.

Arrhenius type plots of the data are shown in Figures 20, 21, and

22. In all plots except that for COz, the slope decreases

approximately linearly between 2.76 and 3.63 x 10-3 K-' (90*C to

-2C) with the slope becoming steeper as carbon number increases.











I w I I I I I


9 -


C3HA 4


n


2-C4H8


1-C4H8


4 -


2.0 3.0


4.0
1/T x 10-3 (K 1)


Figure 20. Arrhenius plots of Cz-C4 alkenes. Alumina catalyst.


5.0


O C2HH


7




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