A STUDY OF THE METHAMATTON OF A FLOWING *
H2- 00 GAS MIXTURE TN A PLASMA CATALYZED
REACTOR

PART T- THE METHAT “AARON OF A FLOWTNG H2- CO
GAS MIXTURE TN A PLASMA CATALYZED REACTOR

PART A - THE MICROWAVE PLASMA AS CATALYST
TR THE METHANATION STEP

Thesis for the Degree of M. S.
MICHIGAR STATE UNIVERSITY
RICHARD L. HOLLOWAY
1973

ABSTRACT

THE METHANATION OF A FLOWING H2 - CO GAS MIXTURE
IN A PLASMA CATALYZED REACTOR

By

Richard L. Holloway

MixTures of H2 - CO were conTinuously pasTed Through a microwave
plasma in a quarTz Tubular reacTor. Conversions up To 25% were obTained
for residence Times of 0.07 To 1.5 seconds and pressures of 2 To 50 mmHg.
CH4 conversions increased wiTh increasing H2 concenTraTion, wiTh a 4:1
volumeTric raTio giving The highesT yield under The experimenTal operaT-
ing condiTions. The power ThaT gave The highesT yield To CH4 was 250
To 600 waTTs, wiTh Thermal decomposiTion of hydrocarbons occurring aT
higher power levels. ApproximaTely I50 waTTs were required To mainTain
The microwave plasma. CHECH was idenTified as The major biproducT, and
a mechanism lncorporaTing a (CH-) inTermediaTe is posTulaTed To accounT

for The Two hydrocarbon producTs.

A STUDY OF THE METHANATION OF A FLOWING H2 — CO GAS
MIXTURE IN A PLASMA CATALYZED REACTOR

PART I - THE METHANATION OF A FLOWING H2 — co GAS MIXTURE IN A
PLASMA CATALYZED REACTOR
PART II - THE MICROWAVE PLASMA AS CATALYST IN THE METHANATION STEP
By

a.

Richard L: Holloway

A THESIS

SubmiTTed To
Michigan STaTe UniversiTy
in parTial fulfillmenT of The requiremenTs
for The degree of

MASTER OF SCIENCE

DeparTmenT of Chemical Engineering

1973

(A

ACKNOWLEDGMENTS

The auThor graTefulIy acknowledges The DeTroiT Edison Company
and The Division of Engineering Research aT Michigan STaTe UniversiTy
for Their financial supporT of This work.

AppreciaTion is exTended To Dr. M. C. Hawley, Dr. B. W. Wilkinson,
and Dr. J. Asmussen for Their Technical assisTance and guidance during

The course of The projecT.

TABLE OF CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ACKNOWLEDGMENTS . .

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . .
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . .
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . .
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . .

PARTII - THE METHANATION OF A FLOWING H2 - CO GAS MIXTURE IN A
PLASMA CATALYZED REACTOR . . . . . . . . . . . . . . .

MaTerials and EquipmenT . . . . . . . . . . . . . . . . .
ExperimenTal Procedure . . . . . . . . . . . . . . . . .
Model of SysTem and DefiniTions . . . . . . . . . . . . .
ResulTs and Discussion . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . .

References 0 O O O O O O I I O O O O O O I O O O Q

PART H - THE MICROWAVE PLASMA AS CATALYST IN THE METHANATION STEP
DescripTion of Plasma CharacTerisTics and ParameTers . .
Microwave Plasma ChemisTry and Proposed ReacTion Mechanism

Microwave Plasma ReacTor and RF SysTem . . . . . . . . .

References 0 O O O O O O O O O O O O O O O O O O O O O O 0

APPENDIX A - Infrared SpecTra DaTa

APPENDIX B - Residence Time CompuTer Program

11
12
I4
28

29

30

31

4O

51

ll.

12.

LIST OF FIGURES

Process Flow Diagram for The Plasma CaTaIyzed MeThanaTion .

Chemical Processing EquipmenT .

RF Plasma ReacTor .

Equilibrium ConsTanTs for H2 - CO - CH4 .
MeThane Yield Versus Residence Time .

MeThane Yield Versus Power InpuT

ElecTron DensiTy as a FuncTion of LengTh and Radius for

The TE*||2 Mode . . . . .
DissociaTion RaTe ConsTanT K1 Versus E/P
Cylindrical Plasma ReacTor

The RF SysTem .

Behavior of The Plasma CaviTy When The ExciTaTion Frequency

is ConsTanT . . . . . . . . . . . . . .

The TE*||| Mode used in ExperimenTal Work .

iv

21
24

26

33
39
41

42

44

50

LIST OF TABLES

Page

I. Summary of ExperimenTal Runs . 15

INTRODUCTION

Many chemical reacTions in elecTric discharge or plasma have been

sTudied over The pasT TwenTy years,1’2’3'4’8

The majoriTy of These
being in baTch sysTems. However, never has The need been greaTer To
pursue The possibiliTy of producTion of synTheTic naTural gas from coal
in a conTinuous flowing plasma reacTor. In view of The criTical supply
and demand siTuaTion for energy in This counTry and The increasing
concern on environmenTaI quaIiTy iT is essenTial ThaT new coal process-
ing Techniques be invesTigaTed Through engineering research and develop-
menT. This sTudy is a reporT and analysis of The firsT resulTs of The
research efforT aT Michigan STaTe UniversiTy To produce meThane from CO
and H2 via microwave caTalysis. The sysTem for meThanaTion experimenTs
consisTed of a flowing H2 - CO gas mixTure Through a microwave field To
produce The caTalysis effecT. IT should be emphasize ThaT The projecT
alThough speculaTive in naTure enTails a unique, unexplored area in boTh
plasma opTimizaTion and chemical process developmenT.

The overall research projecT is broken down inTo separaTe sTudies
of The meThanaTion in a plasma reacTor, gasificaTion in a plasma, hydro-
_ genaTion of coal in a plasma, and finally The uITimaTe goal of a combined
meThanaTion and gaslficaTion process. Preliminary economics for a plasma
sysTem have been developed by Asmussen, Hawley, and Wilkinson in The
original Michigan STaTe UniversiTy research proposal.14 Their speculaTive

economics indicaTed a poTenTial l5% savings in capiTal lnvesTmenT and a

IO% decrease in operaTing cosT. FurTher experimenTal work will esTablish
a firmer base case for preliminary design and comparison wiTh oTher
schemes in coal processing.

The Two rouTes for producing SNG (high BTu gas) which are being
developed and commercialized are I) SNG from naphTha and 2) SNG from coal.
BoTh schemes are similar in ChemisTry; i.e., boTh require gasificaTion,
shifT, and meThanaTion. The chemical reacTions for These sTeps are
wriTTen for SNG from coal as follows:

(a) GasificaTion

2C + 2H O + 2C0 + 2H

2 2
(b) ShifT
C0 + H20 + 002 + H2
(c) MeThanaTion
nickel
3H2 + CD + CH4 + H20
caTalysT

The neT process can be summarized as

2C + ZHZO + CH4 + CO2

A unique feaTure of The projecT is ThaT The microwave source pro-
vides only The energy To mainTain The plasma for caTalysis of The meThan-
aTion reacTion. This will also be The case in fuTure work on a plasma
reacTor which will carry ouT boTh The gasificaTion and meThanaTion reacTions
in a single uniT, Thus eliminaTing a porTion of The cosle process equip-
menT of The currenT SNG rouTes.

Many invesTigaTors have sTudied The producTion of hydrocarbons in
elecTric discharges and There have been several H2 - CO - C02 sTudies
in microwave,5’6 megaherTz,7 and corona discharges.8’9 One of parTicular

inTeresT is by Epple and ApT7 who have shown if possible To converT

mixTures of H2 and 002 To meThane in elecTrical discharges ranging in
frequency from 2-llO megacycles. Their work was performed in a sTaTic
sysTem wiTh residence Times of 2—3 minuTes and reporTed conversions as

high as 55% of The ToTal inpuT of carbon To CH4.

PART I - THE METHANATION OF A FLOWING H2 - CO GAS
MIXTURE IN A PLASMA CATALYZED REACTOR

MATERIAL AND EQUIPMENT

The process flow diagram is shown in Figure 1. A 5 TT3 cylinder
was used for The premix Tank, wiTh a gas regulaTor ThaT gave a consTanT
discharge pressure of 5 psig. The premix Tank was evacuaTed and Then
flushed several Times wiTh H2 To remove any oxygen ThaT mighT have been
in Tank afTer use. Oxygen being a free radical accepTor musT be com-
pleTely eliminaTed in order To achieve The meThanaTion sTep.. The feed
gases are Then passed over a CaSO4 packed bed To insure The removal of
any H20 since This drives The meThanaTion reacTion in The reverse direc-
Tion. Flow raTes are Then measured using a roTameTer wiTh a selecTion
of roTameTer Tubes ThaT allowed a flow range of 5-l0,000 cc/min aT S.T.P.
The gases were preheaTed in some experimenTs using a high volTage-low
amp elecTrical source which conducTed a currenT Through a 30' secTion
of 1/32" OD pipe.

The reacTor sysTem consisTs of a I2" diameTer caviTy wiTh cooling
coils around The ouTer perimeTer and l/64" holes for elecTric field
sTrengTh probes (Figure 3). As The hoT gases leave The preheaTer They
enTer The I" OD quarTz Tube where The plasma is generaTed and The reacTion
Takes place. ReacTor discharge gases are Then passed Through a Two sTage
cooling sysTem, The firsT a dry ice-eTherne gycol soluTion (-30°F) and
Then a waTer baTh. This cooling secTion may be bypassed if sufficienT
naTural convecTion occurs from The reacTor ouTIeT To The cooling sysTem

from The pipe. A final drying bed of CaSO4 is uTilized To remove any Traces

5

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Figure 2 . Chemical processing equipment

Figure 3 . rf plasma reactor

 

of waTer produced from The reacTion. WaTer absorbs in The same region

as CH4 in The IR so musT be removed. The IR analysis was done wiTh a
Perkin-Elmer specTrophoTomeTer uTilizing a l meTer gas cell. A reference
cell was also used. AfTer The gases were analyzed They were drawn Through
The vacuum pump and discharge To an exhausT fan.

InsTrumenTaTion consisTed of TemperaTure and pressure gages locaTed
abouT The reacTor and cooling sysTem, along wiTh sample poinTs for mass
SpecTra. Piping up To The preheaTer was 1/4" OD copper Tubing while
1/2" OD sTainless sTeel was used afTer The preheaTer. Due To The exTremely
Toxic naTure of The CD, a MSA carbon monoxide deTecTor was used during all
work. A safeTy shield enclosed The reacTor as an explosion proTecTion
device.

During The course of The experimenTal work The following mechanical
or process problems were encounTered.

Problem: The enTire sysTem had To be vacuum TighT wiTh a leakage

raTe of less Than 2 cc/min of air.

AcTion: All connecTions were sealed wiTh gypToI or high vacuum

grease.

Problem: High power inpuTs caused The deposiTion of carbon on

The walls and The quarTz reacTor Tube To melT.

AcTion: Provided an air cooling sysTem in The reacTor caviTy and

changed The power divider To reduce power inpuT.

Problem: PreheaTer was fabricaTed wiTh sTainless sTeel Tubes

conTaining nickel which aT higher pressures could produce
CH4 due To The caTalysis effecT.
AcTion: Nickel in Tubes was poisoned using sulfur dioxide.

Problem: TemperaTure measuremenT of gases under high vacuum.

iO

AcTion: An infrared pyromeTer was TesTed.
Problem: Excessive dusT from drying Tube collecTed on I.R. cell
mirrors.

AcTion: Glass wool filTer was insTalled afTer drying Tube.

EXPERIMENTAL PROCEDURE

The compleTe sysTem is firsT evacuaTed To less Than I mm Hg. The
H2 - CO feed valve is opened To esTablish a flowing sysTem under high
vacuum and purge ouT any remaining air. As an iniTial sTarT-up sTep,
The roTameTer flow is seT To IOO cc/min of H2 - CO mixTure and a pres-
sure of 2 mm Hg. The microwave rf source is Turned on and The sliding
shorT adjusTed To produce enough power To creaTe The necessary ioniza-
Tion required To esTablish a plasma. The caviTy (plasma) lengTh is
Then adjusTed in order To opTimize or reTune The plasma. Once The
plasma is generaTed The pressure is increased sTep wise, each Time
adjusTing The sliding shorT and caviTy lengTh (see Part II. Microwave
Plasma ReacTor Design for mechanical deTails). When The sysTem has
reached sTeady sTaTe, The reacTor discharge is analyzed on The
Infrared SpecTrophoTomeTer by scanning The 4000-1300 cm.1 region.
The appropriaTe variables are recorded and The sysTem changed To a new

seT of parameTers.

11

MODEL OF SYSTEM AND DEFINITIONS

Consider a H2 - CO gas mixTure flowing Through a Tubular reacTor
wiTh a microwave plasma being generaTed inside The Tube producing a
chemical reacTion. This is illusTraTed below along wiTh The associaTed
variables. The objecTive of The plasma caTalyzed reacTor is To maxi-
mlze conversion To meThane by The following reacTion, while

(1) 3H2 + CO —-—-—--+-CH4 + H20

minimizing power requiremenTs and biproducT formaTion.

 

 

 

 

 

 

uf
P . ‘ %Gv
Tin , V, Ne, Te .27 Tb
R
[PW
Tin - inleT TemperaTure
P - sysTem pressure
uf - volumeTric flow raTe of H2 - CO mixTure which is a funcTion
of The sysTem pressure, P, and inleT TemperaTure, Iin'
- raTio of HZ/CO
V - reacTor volume dependenT on The caviTy lengTh
PW - power absorbed in caviTy
Ne - elecTron densiTy which is a funcTion of pressure, P, and power
absorbed, EW_
Te - elecTron TemperaTure in reacTor which is dependenT on elecTron
densiTy, Ne, and power, EW_
Tb - bulk TemperaTure of gas leaving plasma reacTor

%GV - percenT by volume of hydrocarbon producT in reacTor discharge
which is a funcTion of The following,

12

1)
2)
3)
4)
5)

13

TemperaTure, IQ! and Te

Pressure, E_ -_-

ElecTron densiTy, N_e_

VolumeTric flow raTe, 2i! and raTio of H2/CO, 3

Power absorbed in caviTy, EW_

If we assume no volume change occurs in The reacTor The design

equaTion for The sysTem is shown in equaTion (2).

(2)

where (CH4)
r

3;.-

_J d(CH4)
r(Tb,Te,P,Ne,R)

meThane concenTraTion
raTe of reacTion of reacTanTs

RESULTS AND DISCUSSION

The firsT meThanaTion experimenTs shown in Table 1 (runs l300l-
20lO4) had flow raTes of lOOO-3000 cc/min producing very small resi-

dence Times in The plasma reacTor. All previous works’7

in This area

had been on sTaTic sysTems using very high residence Times of 2-3

minuTes, however in The iniTial work on The economics of The projecT

residence Times of less Than 2 seconds were necessary To esTablish

saTisfacTory power savings. The power levels were above 1500 waTTs

which creaTed a plasma wiTh a reddish glow ThaT compleTely filled The

quarTz Tube in The caviTy. There was no basis for sTarTing aT These

power levels, excepT providing enough power To produce The plasma in

The flowing H2 - CO sysTem. The firsT H2 - CO feed Tried was a l0:l

mixTure (by volume) of hydrogen rich gas. Since previous experimenTal

work on hydrogen in a microwave plasma had been conducTed by Asmussen, O’l'

one of The principal invesTigaTors, The iniTial generaTion of The plasma

was done in a hydrogen rich feed. The TEOII mode was The resonanT

frequency used in These runs corresponding To a caviTy lengTh of 9.8 cm.
The flowing gases were analyzed on The IR specTrophoTomeTer in

These runs, however, They showed no meThane bands. Also mass specTra

samples gave negafive resulTs. However, a very significanT finding of

These runs (lBOOI-20l04) was The observaTion of a carbon deposiTlon on

The quarTz Tube wall. This cerTainly indicaTed The presence of a chemi-

cal reacTion occurring in The flowing gas mixTure. Figure 4, for The

14

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.mo0> 0cm 0.ma 0 +0 mco.+.vcoo co+0sm+oL +0 30.. 000 ..

 

 

 

 

 

"m0+oz
0N 00.. >0. 000 = = N 00 .\v N.0.0
0N 0 >0. 0Nv : = N 00 .\v ..0.0
0N 0 >0. 0>N : = N 00 .\v 0.0.0
0N 00.. >0. 000 N..*0> 0.0. N 00 .\v 000.0
mxcmsmm Looszc 0:0 oom.0s.+ m++mz 000s so mzss c.s\oo 00\NI Eonssc
0>cao os:.o> Nmocov 0L0300 v .c+0c0. .moca .zo.+ o.+mc csc

m. a I.moc >+.>mo mm0 000+

.00::.+coo. m+mo _m+cos.coaxm .. 0.nm>

Equilibrium Constants , X

10000

1000

100

10

 

  

21

 

C"
l—
__ 3H2 + C0 w-r‘CHu + H20
C:
F'-
I:
r-
I J
700 800 900 1000

Temperature . °K

Figure‘I. Equilibrium constants for
Hz-CO-Cflu system

22

H2 - C0 sysTem was used To explain This phenomena. IT can be seen ThaT
above 850°K any meThane formed would be Thermally decomposed To carbon.
During These runs hoT spoTs were observed in The plasma aT The walls,
and once The quarTz Tube sTarTed To melT which would indicafe Tempera-
Tures above 1500°K, iT was The general conclusion ThaT The reddish
elecTric discharge was Too hoT a plasma To produce meThane.

AfTer These firsT runs The elecTrical sysTem was modified by
varying The sliding shorT posiTion on The power divider which reduced
The power absorbed in The caviTy. Also in order To provide addiTional
cooling a forced air circulaTion sysTem was insTalled in The caviTy.

IT was felT ThaT longer residence Times would be required in The colder
plasma so new roTameTers were insTalled. Coupled wiTh These modifica-
Tions was The need To change The caviTy lengTh To keep The resonanT
frequency consTanT. The caviTy lengTh was increased To 13.8 cm and
This corresponded To The TE*l12 hybrid mode (discussed fully in ParT ll).
Since during our iniTial runs (l300l-20l04) no Trouble was experienced
in The generaTion of The plasma The feed mixTure was changed To 4:1
hydrogen To carbon monoxide (by volume). This beTTer reflecTed The
sToichomeTry of The meThanaTion reacTion. AfTer These mechanical mod—
ificaTions The power could be varied from IOO-800 waTTs and The flow
beTween 5-l|0 cc/min aT The roTameTer pressure and TemperaTure.

The nexT experimenTs (runs 3OIOI-30ll3) were successful in ThaT
meThane was produced and idenTified by The IR bands aT 2980 cm" and
l300 cm"l as shown in IR specTra number 2 and 5. Comparison wiTh lR
specTra 3 and 4 also confirms The presence of meThane when The plasma
was generaTed. This is The firsT reporTed producTion of meThane in a

microwave plasma using a conTinuous flowing H2 - C0 feed. No aTTemst

23

were made To maximize The amounT of meThane in These runs, however
meThane was observed wiTh flow raTes from 75-l00 cc/min, residence Times
of .25 - I.I sec, and power levels of 200-300 waTTs. The plasma con~
sisTed 0T Two blueish spherical shaped glows in The quarTz Tube.

IT was necessary To deTermine qualiTaTiver The amounT of meThane
produced in The plasma for each seT of condiTions. A gas mixTure in
a raTio of 37:9:I of H2 — CO - CH4 (represenTing IOS conversion of CD
To CH4 if no oTher hydrocarbons are formed) by volume was prepared and
analyzed on The IR aT a varieTy of pressures commonly used during
experimenTal runs. These are shown in IR curves l6 and I7. The percenT
by volume of meThane in each run was Then deTermined based on The area
under The meThane IR peak aT 2980 cm”l compared To The sTandard aT The
corresponding pressure. The percenT by volume in runs 3010I-30113
varied from 0.1 - l.5%.

Once meThane had been produced wiTh plasma caTalysis iT was neces-
sary To deTermine opTimum condiTions which would maximize The hydro-
carbon yield. One imporTanT parameTer explored was The residence Time,
which is a funcTion of boTh roTameTer flow raTe, and reacTor TemperaTure
and pressure. By holding The power and pressure consTanT, and varying
The flow iT was found The percenT meThane in The plasma reacTor gas
discharge wenT Through a maximum. This is shown in Figure 5. A possible
explanaTion To This experimenTal observaTion may be ThaT aT longer resi-
dence Times The bulk gas TemperaTure (or elecTron TemperaTure) are high
enough To Thermodynamically favor The reverse reacTion or oTher side
reacTions such as formaTion of carbon or aceTylene. Figure 4 shows
The equilibrium consTanTs for The meThanaTion reacTion as a funcTion of

TemperaTure.

ms.» 00:00.00H msmH0> 0.0.» 000290: . 0 0ns0Hm

0E.» 00:00.09.

 

.303 0.0 H H039.
SEE 0.» 0.30002.

0.. 0.. 0... N... 0.. 0. .u. N.

_ . . — _ _ _ . .
0303 00m H039”.
00.88 0. u 05000.2.

24

 

0..

N..

0..

928 ionpoxd UT {7H3 ewnTOA Aq 010

25

AnoTher variable was The amounT of power puT inTo The plasma
caviTy. As discussed before The plasma CharacTerisTics were un-
favorable for any hydrocarbon producTion above 1000 waTTs. Several
runs showed similar resulTs when The pressure and flow were held
consTanT and The power varied. This is shown in Figure 6. Since in
order To mainTain The plasma iT Took abouT 125-I75 waTTs, The opTimum
power range for meThanaTion lies beTween 250-650 waTTs depending on The
pressure and flow raTe.

The volumeTric raTio of hydrogen To carbon monoxide in The feed
gas is an imporTanT parameTer in deTermining opTimum operaTing condi-
Tions. The iniTial runs (13001—13004) were aT a |0:l raTio and showed
no meThane, however The power levels were‘kxahigh and a differenT
caviTy lengTh was used which boTh produced unfavorable condiTions. The
majoriTy of runs were wiTh a 4:l H2 — CO raTio. A special case TesTed
was a l:l Hz/CO feed. These experimenTs resulTed in a greale reduced
amounT of meThane in The producT gas sTream and required subsTanTially
.‘higher power leyels To mainTain The plasma. IR specTra 20 wiTh runs
3l30l-3l4ll shows These experimenTs. This is consisTenT wiTh our
proposed mechanism in which generaTion of The hydrogen radical would
be The raTe conTroIling sTep (discussed in ParT ll). Higher power
levels were required since The ionizaTion poTenTial of The CO molecule
ls much greaTer Than ThaT of hydrogen, and consequenle This feed
raTio will favor a hoTTer plasma which is unsuiTable for The meThana-
Tion sTep.

The effecT of pressure on The yield of meThane is a very signifi-
canT facTor In esTablishing The operabiliTy and feasibiliTy of The

meThanaTion reacTion. From The experimenTal daTa, The highesT yield

26

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0.065 0. fl5000nf

H0300 0=0H0> 0.0.0 ocmnpmz . 0 0H50Hm

000 000 00>

5800 0: so:
0358 0.4 R 0.3000me

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27

of meThane was 5.4% by volume aT 2 mm Hg. This corresponds To approx-
imaTer 25% conversion of The C0 in The flowing feed gas. Bell'slz’l3
work showed ThaT aTlower pressures The value of Kl, The raTe consTanT
for generaTion of The hydrogen radical, is higher and hence greaTer
chemical reacTiviTy (Figure 8). Our resulTs would seem To indicaTe
This also, however due To differenT Types of elecTrical discharges and
resonanT frequencies used This has yeT To be fully subsTanTiaTed.
Since The main problem encounTered in subsTaining higher pressures was
The plasma beoomintho hoT above 50 mm Hg, furTher modificaTions in
The cooling sysTem or esTablishmenT of a colder Type plasma aT higher
pressure will be of high prioriTy.

One oTher hydrocarbon idenTified in The producT gas by mass specTro-
phoTomeTry was aceTylene. Epple and ApT7 reporTed This same biproducT
in Their sTaTic sysTem. Because of The very poor sensiTiviTy and broad
band aceTylene has in The infrared region, if was noT possible To deTer-
mine qualiTaTively The amounT In each run. IR specTra 24, of a l:l
mixTure of meThane-aceTylene shows This very broad band aT 3200-3300 cm-l.
Comparing This wiTh The experimenTal runs recorded on The IR, The amounT

of aceTylene in The producT gas would in all cases by much less Than The

amounT of meThane.

FurTher research conducTed during The wriTing of This paper has
shown aceTylene produced exclusively wiTh a 4:1 H2 - C0 feed using The
TE011 mode. The conversion of CO To CHECH based on a meThane free

producT was 15% aT 15 mmHg and 0.4 sec. residence Time.

SUMMARY

This research efforT, of The DeparTmenT of Chemical Engineering
and The DeparTmenT of ElecTrical Engineering and SysTems Sciences,
reporTs The firsT producTion of meThane in a microwave plasma using a
flowing hydrogen—carbon monoxide sysTem. The highesT yield found was
5.4% by volume meThane in The producT gas (corresponding To 25%
conversion of C0). Residence Times below 2 seconds were found To be
mosT saTisfacTory and enhance The overall economics of The projecT.
Power levels beTween 250—650 waTTs were found To give The highesT
yields of meThane. Pressures were TesTed beTween 2-50 mm Hg wiTh The
highesT conversions obTained aT The lower pressures. AceTylene was
idenTified as a biproducT, and a proposed mechanism for The meThana-
Tion reacTion including This side reacTion was developed. SignificanT
advancemenTs in The area of high pressure - cold plasma Technology

allowed hydrocarbon producTion for The flowing gas mixTure.

28

REFERENCES

Venugopalon, M., ReacTions Under Plamsa CondiTions, Vol. I
(Wiley I968).

 

McTaggarT, F. K., Plasma ChemisTry in ElecTrical Discharges,
Elsevier, New York (I967).

 

Baddour, R. F., and Timmins, R. S., The ApplicaTion of Plasma
To Chemical Processing, MIT Press, Cambridge (1967).

 

 

BlausTein, B. 0., Advances in ChemisTry Series No. 80, A.C.S,
WashingTon, D.C. (I969).

BlausTein, B. D. and Fu, V.C., Chemical ReacTions in EIecTrical
Discharges, Adv. Chem. Ser. 80, A.C.S, WashingTon, D.C. (I969).

 

McTaggarT, F. K., AusTraIian J. Chem. l7, Il82 (I964).

Epple, R. P. and ApT, C. M., The FormaTion of MeThane from
SynThesis Gas by High Frequency RadiaTion, Gas OperaTions
Research ProjecT PF-27, Am. Gas. Assoc. Inc. (July 1962).

WendT, G., and Evans, G. M., J.A.C.S. 50, 2610 (I928).
LunT, R. W., Proc. Roy. Soc. (London) l08A, I72 (I925).

Asmussen, J. and Fredericks, R. M., Appl. Phys. LeTTers, I9, 508
(I971).

Asmussen, J., Fredericks, R. M. and HaTch, A. J., Behavior of
a Bounded Plasma Inside a Microwave CaviTy aT High and Low
submiTTed To J. Applied Physics in SepTember I972.

Pressures,
Bell, A. T., Ind. Eng. Chem. Fund., Vol. II (I972).
Bell, A. T., Chem. Eng. Pro. Symp., Ser. No. I12, Vol. 67, (1972).
Asmussen, J., Hawley, M. C., and Wilkinson, 8. W., SynTheTic

NaTural Gas from Plasma CaTalysTed Chemical ReacTions,
Michigan STaTe Research Proposal (I972).

29

PART II - THE MICROWAVE PLASMA AS CATALYST
FOR THE METHANATION REACTION

3O

DESCRIPTION OF.PLASMA CHARACTERISTICS AND PARAMETERS

In The convenTionaI meThanaTion reacTion of H2 - CO a nickel caTa-
lysT is employed. IT is The purpose of This research To uTilize a
plasma (or elecTric discharge) as an economically feasible subsTiTuTe
for The solid caTalysT. IT is imporTanT To emphasize ThaT only The
energy for mainTaining The plasma for caTalysis will be puT inTo The
sysTem wiTh The microwave source. The minimum energy required To
mainTain a microwave plasma has been esTimaTed To be 150 waTTs. JusT as The
reacTion raTe is a funcTion of such parameTers as porosiTy and pore
size of The solid caTalysT pelleT, The plasma parameTers such as elec-
Tron densiTy, elecTron TemperaTure, and elecTric field sTrengTh deTer-
mine The overall kineTics and reacTion raTe. ElecTric dischargesare
classified inTo Two Types, an "E—discharge" and "H—discharge." The
meThanaTion wiThin The plasma reacTor is of The E—Type discharge which
is characTerized by low bulk gas TemperaTures and high elecTron Temper-
aTures (2000 - I0,000°K). A H-Type discharge in a gaseous sysTem pos-
sesses equal elecTron, ion, and neuTraI parTicIe TemperaTures of up To
10,000°K.

An imporTanT parameTer in The plasma sysTem is The elecTron densiTy
which is nonuniform boTh axially and radially in The quarTz'Tube plasma
reacTor. This nonuniformiTy of The elecTric discharge resulTs in a
plasma reacTor wiTh only zones of high reacTion efficiency. In our work

usually Two or Three zones were visible for The meThanaTion using H2 and

31

32

C0. Also radial zones, or rings, leave open The possibiliTy of bypass-
ing Thus causing low chemical and elecTrical conversion efficiencies
(Figure 7). MaThemaTically The elecTron densiTy, or concenTraTion can

be expressed as

3N 32(r2N ) 32N
e D e e
Uf 32_'+ —2'-_—__'-—'+ D __—§-= RionizaTion = NevionizaTion
r 3r2 32

where D is The ambipolar diffusion coefficienT which can be expressed

as a funcTion of The elecTron energy, kTe, and a mobiliTy Term “e- The
raTe of ionizaTion, R, is proporTional To The elecTron densiTy and is
convenTlonally defined as Nevion’ where Vion is The ionizaTlon frequency.

In characTerizing a plasma The concepT of TemperaTure is difficulT
To define. This is because The kineTic Theory relaTes TemperaTure To
The kineTic energy of The gas molecules. However, The elecTrons will
have very high kineTic energies due To Their relaTively low masses and
very high velociTies which gives an "elecTron TemperaTure" ThaT is much
larger Than The "kineTic TemperaTure." Thus defining raTe consTanTs
can be made possible by use of an "equivalenT TemperaTure" defined by
Epple and ApT8 as The equilibrium TemperaTure To which The sysTem would
have To be broughT in order To aTTain The composiTion observed on chemi-
cal analysis of The consTiTuenTs.

In an elecTric discharge or plasma iT has been found ThaT The
suiTable parameTer To describe The sysTem is E/p, where E is The elecTric
field sTrengTh and p The ToTal pressure. Previous workB’5 has shown ThaT
aT higher values of E/p, The average elecTron energy is larger, Thus The
chemical reacTiviTy of The sysTem is greaTer (Figure 8). This occurs
since elecTrons have a larger acceleraTion aT higher values of E and aT

lower pressures. The smaller number of collisions occurring aT low

33

 

 

I? 178 max
(D
C.‘
0
'U
l G
h o
H
44
o
1 °’
H
0
0
s:
0 6.9
cavity length, cm

 

 

 

AA)

ne electron density

 

 

 

 

diameter, cm

Figure 7 . Electron density as a function of
length and radius for the TE* 112 mode

13.8

34

pressure permiT an elecTron To gain large amounTs of energy. IT should
be noTed ThaT all work on This area has been on sysTems wiTh low elec-
Tron densiTies using baTch Type reacTors. The meThanaTion reacTion is in a
flowing sysTem wiTh elecTron densiTies suSpecTed To be much higher Than

Those previously explored.

MICROWAVE PLASMA CHEMISTRY AND PROPOSED REACTION MECHANISM

The microwave plasma source will produce a nonequilibrium plasma
wiTh a large number of free radicals aT low bulk gas TemperaTures.6’7
This is made possible Through use of The cold E—Type discharge.6 Besides
free radicals ionic species can be generaTed from inTeracTions beTween
The aTomic and molecular hydrogen species, however Their effecT on
The overall reacTion raTe and kineTics are neglecTible. In a sTeady
sTaTe discharge The concenTraTion of H2+ is governed by The raTe of iTs
formaTion Through ionizaTion of molecular hydrogen. Since The plasma

is approximaTely neuTraI The concenTraTion of H + is considerably below

2
ThaT of The free elecTrons. Yamonel reporTed raTe consTanTs for genera-
Tion of H2+ Two orders of magniTude smaller Than The corresponding
free radical raTe.

For The H2 - CO - CH4 - H20 sysTem in a plasma reacTor a mulTiTude

of reacTions could possibly occur as IisTed below (eqn 1-11).

lniTiaTion

 

(1) H20 + O- + OH-

(2) C0 + H- + CO H-

(3) CH° + H2 + CHZ- + H°

(4) CH2- + H2 + CH3- + H-

PropagaTion

 

(5) C0 + OH- + C0 + H°

2
(6) CH3- + H2 + CH4 + H-
(7) OH: + H2 + H20 + H°

35

36

TerminaTion
(8) CH- + CH- + CH 5 CH
(9) CH2- + CHZ- + C2H4

(10) CH3° + CH3: + C2H6

(11) H- + H- + H2
The reacTion mechanism proposed for The meThanaTion sTep is shown
in equaTions 12-16. Included in This is a heferogenous recombinaTion
Term due To hydrogen radicals diffusing To The wall and recombining.
This mechanism is purely speculaTive for The meThanaTion in a plasma,

however does incorporaTe The basic [CH-] inTermediaTe which would be

required To produce CH4 and CH E CH found in our experimenTal work.

k1
(12) e + H2 -+ 2H-
k2
(13) CO + H2 + H- —+ CH- + H20
k3
(14) CH- + 2H2 —+ CH4 + H-
k

4
(15) ZCH- -+ CH 5 CH

k

w
(16) 2H- —+ H2

AT equilibrium The raTe of formaTion of CH- and H- can be assumed
To be equal To zero (d(CH-)/dT = 0). AddiTionally The wall recombina-
Tion raTe consTanT can be assumed To be small compared To k3 and k4.
Based on These assumpTions~HmaraTe of formaTion of meThane and aceTylene

are shown in equaTions I7 and 18.

_ , 2 _ 5/2 1/2 l/2
(17) rCH4 — k3[CH ][H2] — 1.41 k3 [H2] [Ne]

(kl/k4)

_ , 2 _
(18) rCH 5 CH - k4 [CH ] — 2 k1 [Ne][H2]

37

IT should be noTed ThaT for This proposed mechanism boTh The raTes are
independenT of The carbon monoxide concenTraTion. This is due To The
facT ThaT The raTe conTroIling sTep is The formaTion of The hydrogen

radical governed by k ExperimenTal evidence has shown The raTio of

1.
The raTe of formaTion of meThane To aceTylene is on The order of .01 - I
and using an elecTron densiTy of 1010 cm—3 The values of k3 and k4 can
be esTimaTed To be beTween 100 - |000 (cm3)2/mole2 sec. This compares
favorably wiTh experimenTally deTermined raTe consTanTs for oTher free
radical reacTions.8
GeneraTion of The CH- and H- radical in The plasma reacTor will
be The raTe conTroIling sTeps since boTh of These are highly reacTive

inTermediaTes. The dissociaTion raTe consTanT k1 is convenTionaIly

defined in an elecTric discharge (EquaTion 19) from The

(19) k = (8/nMe)1/2(kT )3/2 IO 6 0 exp (—e/kTE)dc

l E
Me = mass of elecTron
kTE = elecTron energy
\ ‘- - .
‘. .\\ r’ .
e‘\ = dIsso:IaTIon energy
0 = dissociaTion cross secTion

Maxwell-BoIszan disTribuTion of elecTron energies. Khare and
MoiseiwiTsch2 TheoreTically deTermined values for The dissociaTion cross
secTion for The exciTaTion of ground sTaTe molecular hydrogen To The
replusive sTaTe. In Their work They considered This The only process
conTribuTing To The dissociaTion and Their calculaTed values were In

4 3,5

’good agreemenT wiTh previous experimenfal findings by Poole. Bell

has deTermined k1 for The exciTaTion of hydrogen as a funcTion of elecTron

38

TemperaTure (or E/p The raTio of elecTric field sTrengTh To gas pressure).
This is shown in Figure 8.

The formaTion of The CH- radical can be visualized as a bimolecular
inserTion of H- To The C0 molecule, forming a pseudo inTermediaTe CO H-
which combines wiTh a hydrogen molecule To give The CH- inTermediaTe

and a wafer molecule.

Dissociation Rate Constant . x1 (cn3/sec)

10’8

10'9

~10

10‘11

 

39

 

..
I.—
Bell, A. T. . Ind.
Eng. Chem. Vol. 11(1972)
i I I I I i I
10 20 30
E/P (Volt/Cm Torr)
FigureB . Dissociation rate constant K1

versus electric field strength
divided by pressure .

MICROWAVE PLASMA REACTOR AND RF SYSTEM

The microwave plasma caviTy is shown in Figures 2,9,I0. The
reacTanT gases pass Through The plasma creaTed in The quarTz Tube
while pressures in The sysTem can be varied from 2-100 mm Hg. Cool-
ing is provided by waTer coils on The caviTy and forced air circulaTion
Through The caviTy. A probe coupling allows The rf energy To be inTro-
duced inTo The caviTy and produce The plasma. This probe lengTh can
be adjusTed which changes The effecTive elecTrical field sTrengTh pro-
ducing variaTions in reacTion raTes and elecTron densiTy. Radial and
axial measuremenTs of The elecTrical field sTrengTh is accomplished
Through small porTs in The caviTy. The adjusTable caviTy lengTh serves
To reTune The plasma as power, pressure, and probe lengTh are varied.
AdjusTmenT of The caviTy lengTh keeps The plasma resonance equal To
The exciTaTion frequency.

The IefT—hand group of curves in Figure 11 demonsTraTes The
behavior of The plasma caviTy when The exciTaTion frequency and The
caviTy size are fixed. The sTabIe operaTing poinTs, a,b, show ThaT as
The incidenT power is increased The plasma densiTy increases relaTively
liTTle. The plasma caviTy sysTem adjusTs iTself To a sTable operaTing
poinT, a, which is deTermined primarily by The plasma caviTy resonanT
frequency, (i.e., caviTy dimensions and exciTaTion frequency). When
The incidenT power is greale increased The operaTing poinT moves To

poinT b and The caviTy becomes more deTunned. ThaT is, only a small

40

41

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43

fracTion of The addiTional incidenT power is absorbed inTo The plasma
and The excess power is reflecTed from The caviTy. Thus The deTunning
of The sysTem by The presence of The plasma does noT allow a significanT
fracTion of The addiTional incidenT power info The caviTy. Even The
addiTion of impedance maTching devices beTween The caviTy and The inpuT
Transmission line only sligthy improves The caviTy sysTem performanceg.
This small change in densiTy for a large change in incidenT power is a
fundamenTal problem when aTTempTing To produce a variable, high densiTy
plasma inside a microwave caviTy.

One proposed soluTion To This problem is To conTinuously vary The
exciTaTion frequency while The rf plasma is susTained. Halverson and
HaTch9 have shown ThaT by increasing The exciTaTion frequency while
holding The incidenT power consTanT The densiTy of a rf plasma inside
The caviTy can be increased seven Times. However, This frequency Tun-
ning generally requires an expensive rf source and is a Tedious process.

An alTernaTive soluTion is To conTinuously vary The caviTy dimen-
sions. Fredericks and Asmussen10 have shown ThaT cylindrical, variable
lengTh caviTies can be Tuned To allow The variaTion of The plasma den-
siTy from less Than one criTical densiTy To over 10 criTical densiTies
aT low pressures. The performance of These caviTies can be qualiTaTively
undersTood by examining The graphical model as a funcTion of caviTy
lengTh L. By holding in incidenT power consTanT aT Pin} and increasing
The caviTy lengTh from L1 To L2 To L3 The power absorbed curve shifTs
To higher densiTies as shown in Figure 11. For lengTh L1 The empTy
caviTy resonanT frequency equals The exciTaTion frequency. When The
incidenT power is increased To Pin3 breakdown occurs inside The caviTy

and a microwave plasma is susTained aT The sTable operaTing poinT b.

44

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45

By conTinuously increasing The caviTy lengTh The caviTy becomes progres~
sively beTTer Tuned and The absorbed power and hence densiTy increase
Tracing ouT The power loss curve bcd. Finally, a caviTy lengTh, L3,
is reached aT poinT d where The inTersecTion beTween The power absorbed
curve and The loss line is only marginally sTable. For any lengTh
larger Than L3 The plasma is abruple exTinguished and The plasma
caviTy sysTem drops ouT of resonance. In order To reigniTo The plasma
The caviTy lengTh musT be reduced To approximaTely L1.
The curves of Figure ll have been ploTTed for a consTanT pressure
and fixed caviTy inpuT coupling. AlTering The pressure will change boTh
The power loss and power absorbed curves, while alTering The inpuT coup-
ling will modify The power absorbed curves. IT is imporTanT To remember
ThaT There can exisT pressures when The slope of The power loss curve
is always greaTer Than The power absorbed curves. Then all inTersecTions
beTween These Two curves will be sTable operaTing poinTs. NoTe also
ThaT increasing The plasma densiTy decreases The coupling of energy To

The plasma“, i.e., given The incidenT power Pi The heighT of The

n3’
power absorbed curves decreases as The densiTy increases.

The Transfer of energy from The microwave rf source of The gas
molecules is broughT abouT by elecTrons undergoing collisions wiTh The
gas molecules. ElecTrons gain and accumulaTe Thermal energy unTil a
sizeable fracTion of The ToTal collisions They undergo wiTh The gas
molecules change from elasTic To inelasTic. When The elecTron undergoes
an inelasTic collision iT imparTs a large fracTion of iTs ToTal energy
which resulTs in The exciTaTion or ionizaTion of The gas.

In order To describe The microwave plasma maThemaTically Maxwell's

equaTions are solved for The differenT fields. Maxwell's equaTion in

46

The elecTromagneTic Theory (EM) relaTes The elecTric (E) and magneTic
(§) fields To The currenT densiTy (j) and charge densiTy (p) which pro-
duce These fields. ExcepT in The case of a sTaTic sysTem, E, E, p,

and j are Time varying quanTiTies. In The maThemaTical developmenT IT

is more convenienT To define 5 and E in Terms of E and E.

(20) E = soar? where 80 = permiTTiviTy of free space

(21) g = “o“rfi ”o = permeabiliTy of free space
Er = relaTive dielecTric consTanT
ur = relaTive permeabiliTy

For a plasma medium wiTh Time harmonic fields (varying as e‘wT)

we can wriTe Maxwell's equaTions 22-25.

(22)v-‘E’=o,p=o
(23) v-iizo

(24) V x E = - jwuofi
<25) in-i= jweOE+il

lf equaTion (25) is expanded for The case of a weakly ionized
plasma, Then The conTribuTion 3 is mainly from The moTion of The elec-

Trons (26).

(26) j = - ne e? where he = elecTron densiTy cm—3
e = charge on elecTron
+ c 0
V = macroscopic velocuTy of elecTrons

.+
From Boszmann's equaTion in plasma Theory V can be relaTed To The

elecTric field sTrengTh (equaTion 27) and rewriTing equaTion (25) in

(27) V-= —e E/m(jw + v) where m _ mass of elecTron

w operaTing frequency

v collison frequency of elecTrons

Terms of This gives The following (equaTion 28)

 

- T] _
(28) vxfi=jweog+ e (v 1;) E
m(v2 + )

w 2 2

VXH=jw€E |—__P_____J_\)_ p
O v2+w2 UL)(\)2.}.002)

_ 2 1/2_
where mp — (ne e /m€O) — plasma elecTron frequency.

lnsTead of defining a complex conducTiviTy for The plasma we can

esTablish an equivalenT relaTive dielecTric consTanT, er, which

2 2
w w
: —' : _.__L___’2._2.___—_
(29) er (er 'JEi) l 2 2 J m 2 2
v + w (v + w )
2
we v (.082
where er — l - —§—E—-§- and 81 — ;--§—E——§

v + w v T w

is characTerized by specifying The densiTy, i.e., (wp/w)2, and v/w.
The deTailed derivaTion of The general characTerisTic equaTion for

l2,|3

The eigenfrequencies has been carried ouT by oThers. A com-

puTer soluTion for The general characTerisTic equaTion for The TE*111
is displayed in Figure 12. For direcT comparison wiTh experimenTal
resulTs resonanT caviTy lengThs are calculaTed lnsTead of The usual
resonanT frequencies. ThaT is, given a consTanT resonanT frequency equal
To The exciTaTion frequency of 2.450 GHz The resonanT lengTh of The
caviTy is ploTTed as a funcTion of plasma frequency and v/w. Due To

The presence of The plasma free space boundary aT r = a boTh Transverse
elecTric and magneTic modes are required To saTisfy The boundary condi-

l2,l4

Tions . Thus resonanT modes of This sTrucTure cannoT, in general,

be separaTed inTo purely Transverse elecTric (TE) and Transverse mag-
neTic (TM) modes, buT mosT modes have boTh TE and TM parTs and are

called hybrid modes.l2 Because of The hybrid naTure of The caviTy

48

resonances and The inTroducTion of new modes by The plasma The usual
caviTy mode idenTificaTion scheme is noT applicable. IT is convenienT
To classify The resonanT frequencies as such.

1. "PerTurbed" cylindrical caviTy resonances.

The resonances are The empTy caviTy elecTromagneTic resonances
which are "perTurbed" by The presence of The plasma. Thus The forward
and backward Traveling waveguide modes associaTed wiTh These resonances
always have a phase velociTy greaTer Than The Speed of lighT, i.e.,
They are fasT wave elecTromognecTic modes. This group of resonances
can be furTher divided inTo Two subclasses of modes:

a. TEOmp or TMOmp; m > 0.

These resonances are pure TE and TM resonances since They are ¢
independenT and Thus They are labeled wiTh respecT To The TE and TM
modes on a circular waveguide. AT high plasma densiTies and for high
losses These modes approach The coaxial mode ThaT has The same index
as The empTy caviTy.

b. TEnmp or TMnmp; n > O, m > 0.

These modes are hybrid resonances. They are labeled wiTh respecT
To The TE or TM modes in an empTy circular waveguide inTo which They
degeneraTe when The plasma densiTy equals zero. As has been used by
oThers12 The asTerisk denoTes The hybrid modes. IT is useful To noTe

ThaT for high plasma densiTies and zero losses (i.e., v/m = O) The

TE* resonance (or TM* resonance) approaches The TM resonance
nmp nmp nmp

' ' ' 'Th eTal i cenTe
(or TEn, m+1,p resonance) in a coaXIaI wavegUIde wn a m I c r

conducTor. The TE*111 mode shown in Figure 12 belongs To This family

of modes. However, for large values of collision frequency (i.e., for

a lossy plasma) The resonanT frequency increases, decreases, and Then

49

increases again reTurning To The TE111 coaxial caviTy resonanT frequency.
This is shown in Figure 12 for v/w = 0.6 or larger.

The plasma-caviTy could be operaTed in many differenT caviTy
resonances simply by adjusTing The caviTy lengTh and inpuT coupling.
For example, The following empTy caviTy modes have eigenfrequencies
equal To 2.450 GHz when The caviTy is varied from 6 cm To 20 cm.

TElll’ TMOll’ TEZII’ T5011' TMlli’ TE112’ TM012' TE212’ TE012, TM112,
TE113, eTc. WiTh The proper caviTy lengTh and rf coaxial coupling

(i.e., loop or probe) The plasma caviTy sysTem will susTain a plasma

on any of These modes. However, only The TMOlp’ TE011p modes, where

p = 1,2, or 3, were sTudied exTensively.

Figure 10 shows The diagram of The exTernal rf sysTem. The rf
source used for The plasma generaTion was a 2.45 GHz magneTron oscillaTor
which delivers llkw of conTinuous wave power. The rf power passes
Through a circulaTor and power divider where The sliding shorT is used
To vary power. The power passes Through The incidenT and reflecTed

couplers where The ToTal power incidenT on The caviTy can be calculaTed

(equaTion 30). The power incidenT on The caviTy is fed info a coaxial

ToTal power
incidenT on caviTy = 2.72 (incidenT power) - 1.53 (reflecTed
power)

(30)

sysTem, and The probe lengTh couples The power inTo The differenT

resonanT modes of The plasma.

SO

 

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14.

REFERENCES

Yamane, M. J., Chem. Phys. 49, 4624 (1968).

Khare, S. P., Proc. Phys. Soc. 88, 607 (1966).

Bell, A. T., Ind. Eng. Chem. Fund. Vol. II (1972).

Poole, H. G., Proc. Roy. Soc. Ser. No. l, 415, 424 (1937).
Bell, A. T., Chem. Eng. Pro. Symp Ser. No. 112 Vol. 67, (1972).
BabaT, G. 1., J. lnsT. ElecT. Engrs. 24, 27 (I947).

Asmussen, J., Hawley, M. C., and Wilkinson, B. W., Michigan STaTe
Research Proposal (1972).

Epple, R. P., and ApT, C. M., The FormaTion of MeThane from SynThesis
Gas by High Frequency RadiaTion, Gas OperaTions Research ProjecT
PF-27, Am. Gas Assoc. (July 1962).

 

Halverson, S. L., and HaTch, A. J., Appl. Phys. LeTTers, Vol. 14,
pp. 79-81, (1969).

Fredericks, R. M., and Asmussen, J., J. Appl. Phys., Vol. 42,
pp. 3647-9 (1971).

Boyen, H. L., Messiaen, A. M., and Vandeplas, P. E., J. Appl.
Phys., Vol. 40, pp. 2296-2305 (1969).

Agdur, 8., and Eneander, B., J. Appl. Phys., Vol. 33, pp. 575-581
(1962).

ShoheT, J. L., and MoskowiTz, C., J. Appl. Phys., Vol. 36,
pp. 1756-1759 (1965).

HarringTon, R. F., Time Harmonic ElecTromagneTic Fields, New York,
McGraw-Hill, pp. 219 (1961).

 

51

APPENDIX A

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APPENDIX 8

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PROGRAM PLASMA (OUTPUT)
PRINT 40

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