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KINETICS OP PRODUCTION
OP
ACETYLENE PROM METHANE
H.J. LEON
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
IN CHEMICAL ENGINEERING
We accept t h i s t h e s i s as conforming to the
standard required from candidates f o r the
degree of MASTER OF APPLIED SCIENCE.
Members of the Department of
THE UNIVERSITY OF BRITISH COLUMBIA
March 1 9 5 8
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ABSTRACT
The p y r o l y s i s of methane d i l u t e d with nit rog en at
1200°C and 1.00 atm t o t a l pressure was i n v e s t i g a t e d in a flow
reactor made of alundum. The r e a c t i o n i s unaffected by a
carbon surface but s l i g h t l y catalyzed by an alundum su rface.
The i n i t i a l rate of decomposition of methane i s
governed by
3P0H4 _ 5. 7 P 0 C H 4 (atm/sec)dt
f o r p a r t i a l pressures ranging from 0.100 to O.672 atm.
The experimental pressure-time curves for methane
up to 0.70 atm, acetylene up to 0.010 atm, hydrogen up to
0 .30 atm, and time up to 0 . 05 sec were reproduced by the
f o l l o w i n g equations:
PCH 4 = P 0 C R 4 e" 4.80 (1 + P 0 C H 4 ) t ± 5 f o
PC 2H 2 = 0.00586 (e32 . 3 t _].) p o C H 4 e-4.80(l+p oCH 4) t ± 15$
PH2 - 2 P o C H 4
f i - e-3-50(l+2PoCH 4) t l ±- 7%
~ 1 f P 0 C H 4 L ;
11
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An autocatalyti c effect of acety lene, represented
by the empirical equation
dPC2Hp f *i, d t = (0.00586)(32.3) PCH 4 + [32.3 - 4.80(l+PoCH4)|PC 2H2
was observed i n the i n i t i a l stages of the reaction.
I l l
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I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f
the requirements for an advanced degree a t t he U n i v e r s i t y
o f B r i t i s h Columbia, I agree t h a t th e L i b r a r y s h a l l make
i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r
agree t h a t permission f o r extensive copying o f t h i s t h e s i s
f o r s c h o l a r l y purposes may be granted by the Head o f my
Department o r by h i s r e p r e s e n t a t i v e . I t i s understood
t h a t copying o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l
g a i n s h a l l not be allowed without my w r i t t e n permission.
Humberto Leon
Department o f Chemical Engineering
The U n i v e r s i t y o f B r i t i s h Columbia, Vancouver $, Canada.
Date J u l y 2 9 , 1958
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ACKNOWLEDGEMENT
I am indebted to Dr. D.S. Scott
f o r h i s guidance i n t h i s research, and
to the Shell Caribbean Petroleum Company
f o r f i n a n c i a l assistance.
I
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March 17, 1958
Dean of the Faculty of Applied Science
U n i v e r s i t y of B r i t i s h Columbia
Vancouver, B. C , Canada
Dear S i r :
I submit herewith my t h e s i s , K i n e t i c s of
Production of Acetylene from Methane, i n quadruplicate,
i n p a r t i a l f u l f i l m e n t of the requirements fo r the
degree of Master of A p p l i e d Science in Chemical
Engineering, at the U n i v e r s i t y of B r i t i s h Columbia.
R e s p e c t f u l l y yours,
Humberto Leon
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CONTENTS
Acknowledgement I
Abstract II
Diagrams V
Introduction 1
Apparatus 7
Procedure 11
A n a l y t i c a l Methods 13
Homogeneity of the Reaction 15
E f f e c t of barbon Deposition 19
E f f e c t of the P a r t i a l Pressures of
Methane and Acetylene 23
Limitations 37
Cone lus ions 40
Bibliography 41
Appendix 42
IV
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DIAGRAMS
1. Schematic flow diagram of system 8
2. The percentage conversion of methane versus
the surface-to-volume-ratio 18
3» Percentage conversion of methane versus
reaction time c o r r e c t e d fo r carbon
d e p o s i t i o n at various on-stream-times..... 22
4» The p a r t i a l pressure of methane versus
r e a c t i o n time at various i n i t i a l p a r t i a l
pressures of methane 27
5« The p a r t i a l pressure of acetylene versus
reaction time at various I n i t i a l methane
p a r t i a l pressures 28
6. The p a r t i a l pressure of acetylene versus
the p a r t i a l pressure of methane at
constant reaction time 33
7« The p a r t i a l pressure of hydrogen versus
reaction time at various i n i t i a l methane
p a r t i a l pressures 3 8
V
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KINETICS OF PRODUCTION
OF ACETYLENE FROM METHANE
Introduction
The object of this i n v e s t i g a t i o n was to study the
thermal.decomposition of methane d i l u t e d with nitrogen, at
1200°C and a t o t a l pressure of 1.00 atm with the Idea of
determining the dependence of the r e a c t i o n rate on-the reactor
surface and on the p a r t i a l pressures of methane, acetylene,
and hydrogen.
The f i r s t k i n e t i c work of any importance done on
t h i s subject was reported i n 1932 by L.S. K a s s e l 1 . Using a
s t a t i c system made of quartz, sometimes coated with carbon,
Kassel a r r i v e d at the conclus ion that the i n i t i a l part of the
r e a c t i o n was f i r s t order and homogeneous, apart from an induc
t i o n period of obscure nature. From t h e . r e s u l t s of his exper
iments made at temperatures between 976 and 1113°C, Kassel
determined an energy of a c t i v a t i o n of 79 k-cal/mole and a
1
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f i r s t order reaction rate constant
(1) k » 1.0 x 1 0 1 2 e -79585/RI
The rate equation.was determined from the i n i t i a l reaction
rates at various i n i t i a l r e a c t i o n pressu res.
p
Also i n 1932, H.H. Storch repor ted the r e s u l t s of
his experiments on the decomposition of methane by a carbon
filament i n a bulb immersed i n l i q u i d nitrogen or oxygen.
He found the early products of the r e a c t i o n to be ethane and
unsaturates corresponding to the ethylene formula. Although
he found an average energy of a c t i v a t i o n of 77 k-cal/mole, i n
agreement with the value obtained by Kassel, h i s indiv idua l
values ranged from 40 to 120 k-cal/mole, and h is temperatures
may have been i n er ror .
Based on Storch's analysis of the products o f the
r e a c t i o n , on the r e s u l t s of h i s own experiments, and on
t h e o r e t i c a l considerations, Kassel suggested the fol lowing
mechanism f o r the homogeneous decomposition of methane:
(2) CH 4 CH 2 + H2 ( k l f r x )
(3) CH 4 + CH 2 C 2H 6 ( k 2, r 2 )
(4) C 2 H 6 ^ = T C 2 H 4 + H 2 ( k 3 , r 3 )
(5) Cg ^, C 2H 2 + H 2 ( k 4, r 4 )
(6) C 2 H 2 ^ = ^ 2C + H 2 ( k 5 , r 5 )
from which the followin g rate equation may be deduced
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(7)-— d fc*Q- 2 [k,kak,k A k, fc H . f - r, i\r,, r+r* CHJ4")
d t r t r x r\ r« fa J 3-+ r, r x k ,60+ r, ( t y kj k4k ,( H J+ k J ^ k / c H J
where k and r stand f or the forward and reverse re ac ti on r ate
constants re sp ect iv ely . This rate equation accounted f o r the
i n i t i a l f i r s t order reaction rate f o r the methane decomposi
t i o n and, although not q u a n t i t a t i v e l y , f o r the r e t a r d a t i o n of
the reaction due to the increase i n hydrogen concentration.
The role of f r e e r a d i c a l s i n the decomposition of
methane and other hydrocarbons has been i n v e s t i g a t e d by
Belchetz and R i d e a l ^ , and Rice^, using te ll ur iu m mirr ors.
They a r r i v e d at the conclusio n that, when the r e a c t i o n takes
place on a carbon filament (heterogeneous r e a c t i o n ) , methylene
r a d i c a l s are present instead of the methyl r a d i c a l s i n the
mechanism proposed by Kassel f o r the homogeneous r e a c t i o n .
4
Rice and coworkers had found methyl r a d i c a l s , but these were
probably the r e s u l t of the secondary reaction
(8) CH 4 ~ CH 5 + H
or of the homogeneous reactions
(9) CH 4 Z=t CH 2 + H 2
(10) CH 2 • CH 4 2 CH
g
A.S. Gordon i n 1948, working at temperatures bet
ween 1000 and 1100°C with a reactor made of p o r c e l a i n ,
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i n v e s t i g a t e d the decomposition of methane i n the presence of
steam and i n the presence of n i t r o g e n . He found that steam
reacted with carbonaceous m a t e r i a l formed i n the decomposition
of methane and not -with methane d i r e c t l y . Consequently, the
decomposition of methane was unaffected by d i l u t i o n with steam
or n i t r o g e n . Gordon used a mass spectrograph to analyze the
product, gases, among which he found hydrogen, ethane, ethylene
acetylene, and, In small q u a n t i t i e s , propylene, p r o p y l i n e , and
benzene. In the carbonaceous m a t e r i a l produced i n the react i o n were i d e n t i f i e d : naphthalene, anthracene, phenanthrene,
and pyrene. A c a t a l y t i c e f f e c t of acetylene on the decomposi
t i o n of methane and a large i n i t i a l e f f e c t caused by the
p o r c e l a i n surface on the r e a c t i o n are report ed.
The r o l e of free r a d i c a l s on the methane decomposi-7
t i o n was studied again by A.J.B. Robertson i n 1949, using an
incandescent platinum filament and pressures of the order of
10""-' mm Hg. The mass spectrometer used for the analysis
showed methyl but no methylene r a d i c a l s at 1000°C. In the
dehydrogenation of ethane to ethylene at 950°C, he found no
methyl or e t h y l r a d i c a l s and the r e a c t i o n proceeded at the
same rate In the presence of methyl r a d i c a l s from methane.
He concluded that the decomposition of methane on a platinum
filament took place by molecular dehydrogenation. On the
other hand, Rice and H e r z f e l d have proposed, on the b a s i s of
experimental r e s u l t s , a sound mechanism f or the homogeneous
decomposition of ethane, with the p a r t i c i p a t i o n of free
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5
r a d i c a l s •
Apart from i t s importance i n the f i e l d of Chemical
K i n e t i c s , the decomposition of methane has importance i n indus
try, In the manufacture of hydrogen and carbon black from nat
u r a l gas. The i n c r e a s i n g demand f or acetylene, both as wel ding
f u e l and as a s t a r t i n g m a t e r i a l f o r organic synthesis, has led
to i n v e s t i g a t i o n s into the p o s s i b i l i t y of manufacturing acet
ylene, i n commercial scale, from methane and other l i g h t hydro
carbons contained i n n a t u r a l gas. The acetylene produced by
decomposition of l i g h t hydrocarbons and subsequent p u r i f i c a t i o n
i s cheaper but s l i g h t l y more impure than the acetylene produced
by the carbide process, which accounts fo r most of the a c e t y l
ene p r e s e n t l y i n use.
Three general methods are in use at present f or
decomposing the hydrocarbons: e l e c t r i c a l discharge, p a r t i a l
o x i d a t i o n , and thermal cracking. The e l e c t r i c a l disch arge
method developed by Schoch^ at the U n i v e r s i t y of Texas, uses
a r a p i d l y r o t a t i n g blower to stream a sheet of gas between the
e l e c t r o d e s . Y i e l d s of 21% using a methane feed, and acetylene
concentrations i n the e f f l u e n t gas of n e a r l y 1 0 $ , are reported.
In the p a r t i a l o x i d a t i o n or Sa ch ss e^ process, the
heat required fo r the decomposition r e a c t i o n i s s u p p l i e d by
the combustion of part of the hydrocarbons w it h pure oxygen.
The gases are preheated separately, and then fed to a burner,
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6
where the reaction takes place at 1§00°C. The gases are
quenched by a water spray a f t e r a residence time of 0 .1 sec.
Yields of acetylene may be as high as 30$.
" 11In the thermal cracking or Wulff x process, the
hydrocarbons, d i l u t e d with steam or i n e r t gases, are quickly
heated to the cracking temperature of more than 1000°C,
allowed to react fo r about 0.05 sec, and cooled immediately.
T h i s operation i s
best c a r r i e d out i n a
regenerative furnace,i n which the re fr ac to ry material"absorbs heat of combustion
during a heat c y c l e , and surrenders i t to the reactants during
a make cycle.
These methods of producing acetylene from hydro
carbons are based on the fact that acetylene i s formed i n the
i n i t i a l stages of the reaction, so that by.arres ting the
decomposition a f t e r a short contact time, reasonably high
y i e l d s of acetylene may be obtained.
Although many f a c t s are known about the decomposi
tion of methane, the mechanism of the reaction i s not yet
f u l l y understood. In the present study, an e f f o r t was made
to obtain information which, added to that already existing,
might help c l a r i f y the chemical k i n e t i c s of the rea cti on, with
a s p e c i a l regard to the production of acetylene.
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Apparatus
A diagram of the apparatus used i n t h i s study-
appears i n Figure 1. The gases were i n commercial cyli nders
of 9 9 $ methane from the Matheson Company and 9 9 • 5 $ nitrogen
from the Canadian Liquid Ai r Company. The flows could be
adjusted by a combination of pressure reducers and needle
valves. The p u r i f i c a t i o n chain consis ted of bubblers contain
ing alkaline py ro ga ll ol sol uti on fo r the removal of oxygen
and carbon dioxide, and drying tubes containing s i l i c a gel
f or the nitrogen and " D r i e r i t e " f o r the methane.
The c a p i l l a r y flow meters were made from pieces of
glass tubing 1.0 mm i n diameter and 7*6 cm long, and were
immersed i n a water bath kept at 20°C. The pressure drop
across the c a p i l l a r i e s , ind ica ted by water manometers, and
the downstream pressure of the c a p i l l a r i e s , measured at the
mixing f l a s k and in di ca te d by a mercury manometer, were
c a l i b r a t e d against a Pre ci sio n Wet Test Meter, and correlated
as F vs. (P m .Ap), vtfiere F Is the flow rate i n gram moles per
hour, P m i s the mean absolute pressure i n i n . Hg, and Ap i s
the pressure drop across the c a p i l l a r y i n i n . Hg. The gases
were allowed to mix i n a f l a s k whose outlet tube contained
" A s c a r i t e " for f i n a l drying.
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Precision Wet Test Meter Acetylene Abaorption Continuous Sampler Exhaust
figure I. Schematic Flow Diagram of System.
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9
The reactor was made of an alundum tube of 7 /16 i n .
inside diameter, 11/16 i n . o u ts i d e diameter and 30 i n . l o n g .
Two s e c t i o n s of alundum thermocouple tubing of 3/8 i n . outside
diameter, l / l 6 i n . double bore, and 18 In. long were f i t t e d
inside the alundum tube l e a v i n g i n the center a space f o r the
r e a c t i o n chamber, whose length could be adjusted by the s l i d i n g
i n and out of the thermocouple t u b i n g . A rubber s e a l at the
i n l e t end and an asbestos se al at the ou tl et side held the
thermocouple tubing i n p l a c e . The r e a c t o r was packed with
alundum p e l l e t s of various sizes, but i t s f r e e volume was kept
constant at 5 .0 cm .̂ The two l / l 6 - i n c h holes i n the thermo
couple tubing at one side c a r r i e d the thermocouple wires and
also served as gas i n l e t to the r e a c t i o n chamber, whereas the
holes at the other sid e served as r e a c t o r o u t l e t .
The reactor was place d Inside a t u b u l a r carborundum
heater of 1-1/8 i n . i n s i d e diameter, 2-1/8 i n . o u t si d e diameter
and 28 i n . long, ins ula ted with 6 i n . "Superex" and 2 i n .
of 9 5 $ magnesia.
The re ac ti on products passed through a settling
f l a s k f i l l e d with glass wool, where carbon and ta r were c o l l e c
t e d . No e f f o r t was made to determine the nature of the t a r ,
and since the amount was s m a l l , i t was not considered i n the
m a t e r i a l balances. The volume of gases produced was measured
by a P r e c i s i o n Wet Test Meter. The volume reading from the
meter, the temperature, and the average pressure of the gases
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combined w i t h the time o f the run, gave the o u t l e t flow r a t e
o f the gases. A f t e r being measured, the gases flo wed ,th rou gh
a tube f i l l e d w i t h " A s c a r i t e " f o r the removal o f carbon d i o x i d e
which i n t e r f e r e s w i t h the a c e t y l e n e d e t e r m i n a t i o n . The a c e t
ylene was absorbed i n a f r i t t e d g l a s s b u b b l e r c o n t a i n i n g 10 $
s i l v e r n i t r a t e s o l u t i o n . A l t e r n a t i v e l y , w h i l e the a djustments
were being made, the gases were detoured through a dummy tube
c o n t a i n i n g s i l i c a g e l i n s t e a d o f " A s c a r i t e " and a dummy bubbler
c o n t a i n i n g water i n s t e a d o f s i l v e r n i t r a t e s o l u t i o n . The
o b j e c t o f the dummy system was t o produce as l i t t l e a l t e r a t i o n
as p o s s i b l e t o the r e a c t i o n c o n d i t i o n s a t the moment o f s t a r t
i n g the ru n p r o p e r . The gases were then exhausted through a
water e j e c t o r . A sample o f the r e a c t i o n products a f t e r a c e t
ylene a b s o r p t i o n c o u l d be drawn by a contino us sampling dev ic e
made w i t h two t w o - l i t e r f l a s k s . T h i s sample was analyzed f o r
oxygen, hydrogen, carbon monoxide, methane, and n i t r o g e n In a
Burrel-type gas a n a l y s i s s et .
The c u r r e n t f o r the carborundum h e a t e r was s u p p l i e d
by a D.G. generator o f adjustable volta ge. The thermocouple
was made o f platinum-pla tinum 1 3 $ rhodium and th e tempera ture
was recorded by a "Speedomax" r e c o r d e r and c o n t r o l l e r , with
on-off controlL.on the h e a t i n g c u r r e n t , a c t i n g through a r e l a y .
The temperature o s c i l l a t e d w i t h an amplitude o f 4°C and a
p e r i o d o f l e s s than one minu te. Sin ce each r u n l a s t e d about
t e n minutes, the e f f e c t o f the o s c i l l a t i o n s was averaged out
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by the continous sampling device and the determination of
t o t a l acetylene.
The pressure i n the r e a c t i o n zone was measured
through a tap i n the i n l e t rubber s e a l of the reactor by a
mercury manometer which had on-off c o n t r o l on a bleeder of
the suction l i n e operating through a r e l a y . The a c t i o n of
the c o n t r o l l e r could be adjusted by the stopcock i n the bleeder
l i n e . The maximum amplitude of the pressure o s c i l l a t i o n was
2 mm Hg.
Procedure
With the system open to the atmosphere at the ca
p i l l a r y downstream pressure manometer, the reactor was slowly
brought up to temperature. While the reactor was being
heated the c a p i l l a r y water bath temperature was regulated
at 20°C, the s i l v e r n i t r a t e bubbler was f i l l e d with 100 ml of
s o l u t i o n of known concentration (about 0.7 N) and the gas
sample f l a s k was i n s t a l l e d and freed of ai r .
Once the reactor was up to temperature, the suction
was turned on with the dummy system i n operation and thus,
a i r c i r c u l a t e d through the reactor to burn any carbon dep
osits present. The pressure c o n t r o l l e r was set at 760mm Hg,
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i . e . , a height of mercury equal to the difference between one
atmosphere and the actual atmospheric pressure; the ni trogen
was turned on and the a i r i n l e t was slowly clo sed . The me
thane was then turned on and the flows were adjusted to the
d e s i r e d rates according tbo the c a l i b r a t i o n curves. After
steady conditions were reached, s u f f i c i e n t time was allowed
for the product gases to displace the gases between the re
a c t o r and the acetylene absorption system, and to approach
e q u i l i b r i u m between the product gases and the water i n the
Wet Test Meter, and then the gases were switched from the
dummy system to the acetylene absorption system, the i n i t i a l
time and volume recorded, and the gas sampling device opened.
The rate o f sampling could be regulated by a pinch cock i n
the water l i n e between the two f l a s k s . The pressure of the
gas at the Wet Test Meter was recorded about four times during
each run and averaged for the c a l c u l a t i o n of the gas volume.
To complete the run, the gas sample was isolated
and the pressure of the gas made s l i g h t l y p o s i t i v e to avoid
contamination with a i r ; the rea cti on products were switched
back to the dummy system and the f i n a l volume and time re
corded. The methane was turned o f f, the stop cock i n the
bleeder of the suction l i n e was shut and when the c a p i l l a r y
downstream pressure decreased to atmospheric pressure the
system was opened to the atmosphere. This method avoided
sudden changes i n flows. The nitrogen was then turned of f .
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A f t e r the carbon was burned, the s u c t i o n and the heat c ould
be turned o f f . ,
The s i l v e r n i t r a t e bubbl er was di sc onn ect ed from
the l i n e (upstream side f i r s t to av oi d l o s i n g the s o l u t i o n ) ,
and the s i l v e r a c e t y l i d e was f i l t e r e d out. F i n a l l y the s i l v e r
n i t r a t e s o l u t i o n was d i l u t e d and t i t r a t e d , and the o u t l e t
gas sample was an al yz ed .
A n a l y t i c a l Methods
The acetylene produced i n the r e a c t i o n was d et er
mined as s i l v e r a c e t y l i d e , by bu bb lin g the gas thr oug h a
known amount of warm 0 . 7 N s i l v e r n i t r a t e s o l u t i o n and t i
t r a t i n g the unreacted s i l v e r aga ins t potassiu m thy oci ana te
s o l u t i o n (about 0.16 N), ac co rd in g to the Vo lh ar d method. In
order to determine the e f f i c i e n c y of the absorption of
acetylene, t e s t s were c a r r i e d out using commercial acetylene
d i l u t e d with a i r . In every t e s t 2 0 0 ml of ac et yl en e sa tu ra te d
with water at 2 5°C and 1 atm t o t a l pres sure (approximatel y 7 . 9
mg-mole) were used.
The r e s u l t s of the acet ylen e ab so rp tio n t e s t s
appear below.
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Table 1 . Acetylene Absorption Tests
Run Plow Rate Bubbler Solution Acetylene
(mole/hr) Element (mg-mole)
a 1 p l a t e cold 7.17
b 10 p l a t e cold 3.83
c i o plate-* cold*
4.03
d 1 • cylinder hot 7.50
e 5 cylinder hot 7.20f 6 cylinder hot 7.10
•^Bubbler packed with glass beads
Table 1 . shows that the most e f f i c i e n t acetylene
absorption would be obtained using a c y l i n d r i c a l bubbler and
a hot s i l v e r n i t r a t e s o l u t i o n . Under these conditions 96$ of
the acetylene was absorbed at 5 mole/hr and 95$ at 6 mole/hr,
assuming the absorption at 1 mole/hr (run d) to be quantita
t i v e . C y l i n d r i c a l bubblers and hot s i l v e r n i t r a t e solution
were, therefore, used i n the experiments.
The s o l u b i l i t y of acetylene in water con stitute s
a source of error, since the outlet gases were measured
before the acetylene determination. This error could be
estimated at 15$ on the assumptions that at the beginning
of the run the water In the Wet Test Meter is acetylene
f r e e , and at the end of the run is saturated with acetylene
for i t s p a r t i a l pressure In the gas. However, because of
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the r e l a t i v e poor mixing of water and gas i n th d Wet Te st Meter
and the time allowed f o r the gases to flow under steady co ndi
tions before s t a r t i n g the run prop er, the e rr o r was con sid ere d
sma ll and consequentl y di sr eg ar de d.
The o ut l et gas sample c o l l e c t e d a f t e r acetylene
abs orp tio n was analyzed i n a Bu re ll -t yp e gas an al ys is set
where carbon dioxide was determined by absorpt ion i n potassium
hydroxide solution, oxygen by absor pti on In alkaline, p y r o g a l l o ls o l u t i o n , carbon monoxide by oxi da ti on wit h hot cup ric ,ox ide ,
methane by oxi dati on over a hot c a t a l y s t , and nitrogen by
difference.
D e t a i l s about the det erm ina tio n of the a cet yle ne
y i e l d of the re a c t i o n and the gas an al ys is can be found under
"Sample Run" i n the Appendix.
Homogeneity of the Re ac tio n
In order to in ve st ig at e the homogeneity of the
r e a c t i o n on an alundum surface, the surf£ce-to-volume ratio
of the re ac to r was va ri e d from 3 .6 to 24.6 cm"1, maintaining
constant the free volume of the reactor, the feed rates of
methane and nit roge n, the re ac ti on temperature and the reac
t i o n pres sure . This means that the i n i t i a l p a r t i a l pressure
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of methane was constant and that except for minor changes i n
the outlet flow r a t e , the r e a c t i o n time was also kept constant
The v a r i a t i o n i n surface-to-volume r a t i o was accom
p l i s h e d by introducing alundum p e l l e t s i n the r e a c t o r and
i n c r e a s i n g i t s length to obt ain the same free r e a c t o r volume.
Results
The data used i n the determination of the surface
to-volume r a t i o of the r e a c t o r for the i n v e s t i g a t i o n of the
homogeneity of the r e a c t i o n appear under "Reactor Data for
Surface-to-Volume Ratio Runs" of the Appendix.
The r e s u l t s of the surface-to-volume r a t i o runs,
c a r r i e d out at a r e a c t i o n temperature of 1200°C and a reactor
pressure of 1.00 atm, appear below.
Table 2. E f f e c t of Surface-to-Volume Ratio
Run s/v P0 CH 4 Time Conversion
(cm-1) (atm) (sec) of C H 4 { )
1 3.6 0 .322 0.0249 11.1
7 13.1 0.328 0.0248 11.7
3 20.6 0.328 0.0251 13.2
5 24.6 0.326 0.0246 14.5
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Discussion of Results
The r e s u l t s recorded i n Table 2 show the effect
of the surface-to-volume r a t i o on the t o t a l con ver sio n of
methane to ace tyl ene and t o carbon, for an i n i t i a l methane
p a r t i a l pressure of approximately 0.326 atm and a r e a c t i o n
time of approximately 0.0248 sec . The p l o t of t o t a l methane
conversion vs. surface-to-volume r a t i o which appears onFigure 2, shows th at an inc re as e of ne ar ly 700% i n the
surface-to-volume r a t i o increased the rate of reaction by
only 30%, t h e r e f o r e , i t i s concluded tha t the r e a c t i o n was
l a r g e l y homogeneous. The in cre ase i n ra te observed may be
due to one or more of the four p o s s i b i l i t i es given below.
There i s evidence i n suppo rt of the f i r s t or second sup
p o s i t i o n .
a) The r ea ct io n i s ca ta ly ze d by the alundum
surface to a ve ry .s li gh t extent.
b) The r e a c t i o n i s ca ta l yz ed by the alundum
surface to a larger extent than in a) above, but the amount
of free alundum surface is decreased by carbon d e p o s i t i o n
i n the re ac to r. This would mean that the average r a t i o of
alundum surface to reactor volume would be lower than the
i n i t i a l and, t he re fo re , the e f f e c t of the alundum su rf ac e on
the reaction would be l ar ge r than that shown i n Fi gu re 2.
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c) Heat tr a ns f er to the gas i s c o n t r o l l i n g , i . e .
i n the packed r e a c t o r , assumed to be at a uniform tempera
ture, the Reynolds number and the surface area av a il ab le
f o r heat tr an sf er are increased, thus making the gas temp
erature higher (c lo se r to the rea ct or temperature) than
when the re ac tor is unpacked. The s l i g h t l y increased temp
erature would account fo r the high er conv ersi on.
d) Heat t ra ns fe r to the p e l l e t s i s controlling,
i . e . , there i s a temperature gradient between the rea ct or
w a l l and the center of the r e a c t o r where the thermocouple
i s lo ca te d and, conseque ntly, i n the packed reactor the
conversion would corr espon d to an average temperature highe
than the one measured.
E f f e c t of Carbon De pos iti on
In order to inv es ti ga te the effect which the
carbon deposited i ns id e the rea ct or could have on the reac
t i o n , the products were determined at i n t e r v a l s of about 20
minutes, without removing the carbon depo site d i ns id e the
r e a c t o r . The fe ed ra te s of methane and hydrogen, the reac
t i o n temperature and the re ac to r press ure were kept cons
tant.
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Results
Table 3 shows the r e s u l t s o f the t e s t s c a r r i e d
out to determine the e f f e c t o f carbon d e p o s i t i o n at 1200°G
and 1.00 atm i n a r e a c t o r o f 13.1 c m - 1 surface-to-volume
r a t i o . Included i n Table 3 ar e the r e s u l t s o f r u n 6 which
was c a r r i e d out under c o n d i t i o n s s i m i l a r t o those of ru n 3,
but f o r a 24.6 c m - 1
surface-to-volume r a t i o .
Table 3 . E f f e c t o f Carbon Depo siti on
Run Averageon-streamtime (se c)
s/v
cm" 1
P C H 4
(atm)
PH 2
(atm)
PC 2H2
(atm)
% conversionRun Averageon-streamtime (se c)
s/v
cm" 1
P C H 4
(atm)
PH 2
(atm)
PC 2H2
(atm) CH 4 C 2 H 2
7 386 13.1 0.278 0.071 0.00240 11 . 7 1.53
8 1576 13.1 0.284 0.062 0.00217 10.2 1.37
9 2654 13.1 0 .290 0 .057 0.00185 9.4 1.16
10 3654 13.1 0 .292 0 .051 - 8.8 -
6 2600 24.6 0.292 0 .059 0.00182 9.3 1.13
D i s c u s s i o n o f Resu lts
The f i g u r e s shown i n Table 3 i n d i c a t e t h a t the
percentage conversion o f methane t o acetylene and the t o t a l
percentage conv ersion of methane decrease with the on-stream
time and consequently, with th e amount of carbon deposited
i n the r e a c t o r . I t was thought t h a t t h i s decrease i n con
v e r s i o n c o u l d be e x p l a i n e d by the decrease i n r e a c t i o n
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time which accompanied the volume r e d u c t i o n by carbon depo
s i t i o n i n the r e a c t o r . An attempt was made to v e r i f y t h i s
p o s s i b i l i t y by estimating the volume o f the carbon de pos it ed
i n the r e a c t o r at any on-str eam-ti me, from the pe rcentage
conversion of methane to carbon and hydrogen. Fo r the meth
ane flow r a t e of 2 . 0 0 mole/hr and an assumed carbon d e n s i t y
o f 2 . 0 g/cm 5
1 / t s
( I D V C • 3 0 , 0 0 0 j o X ° ^
where (cm^) i s th e volume o f carbon dep os ite d i n the
r e a c t o r , X ^ , {%) i s the conversion of methane t o carbon, and
t •''",(sec) i s the on-stream ti me. The volumes o f carbon dep
o s i t e d i n the r e a c t o r were determined by g r a p h i c a l i n t e g r a
t i o n on a p l o t o f XQ v s . t g , and appear on Table 4 together
with the r e a c t o r volumes c o r r e c t e d f o r carbon d e p o s i t i o n V 'r »
and the c o r r e c t e d r e a c t i o n times t * . Figu re 3 shows the
v a r i a t i o n of the percentage con ver sio n of methane w i t h th e
r e a c t i o n time c o r r e c t e d f o r carbon d e p o s i t i o n .
Table 4« C o r r e c t i o n s to Reactor Volume and
Reaction Time f o r Carbon De po si ti on
Run V C V t ' X C H 4(cm5) (cm3) (sec) {%)
7 0.14 4.86 0.0242 11.7
8 0.53 4.47 0.0224 10.2
9 0.80 4.200.0210
9.4
10 • ^ 1.07 3.93 0.0197; 8.8
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22
Figure J . Percentage conversion of methane versus reaction
time corrected for carbon deposition at various
on-stream times
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I t i s apparent t h a t a r a p i d decrease i n conv ersio n
which cannot be accounted f o r by a change i n r e a c t o r volume
accompanies the disappearance of the alundum s u r f a c e . As
the surface becomes covered wi th carbon the r e a c t i o n becomes
e n t i r e l y homogeneous and the p o i n t s l i e on a smooth l i n e
through the o r i g i n .
The homogeneity o f the r e a c t i o n i n a carbon coated
v e s s e l was r e p o r t e d by Kasse l1
and can be supported by a
comparison of the r e s u l t s of runs 6 and 9 (Table 3 ) , which
were c a r r i e d out at surface-to-volume r a t i o s of 24.6 and
13*1 cm" 1 r e s p e c t i v e l y , and at on-str eam time such t h a t
v i r t u a l l y a l l the alundum surface was cove red w i t h carbon.
The r e s u l t s are p r a c t i c a l l y the same i n s p i t e o f the d i f -
ference i n surface-to-volume r a t i o .
E f f e c t o f the P a r t i a l Pressures
o f Methane and Acetylene
In order to i n v e s t i g a t e the e f f e c t of the p a r t i a l
pressures of methane and acetylene on the r a t e of decomposi
t i o n of methane and th e r a t e o f formation o f a c e t y l e n e , the
p a r t i a l pressures of a c e t y l e n e , methane, and hydrogen were
determined at v a r i o u s r e a c t i o n times f o r f i v e i n i t i a l p a r t i a l
pressures o f methane.
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The r e a c t i o n temperature, the r e a c t o r t o t a l pres
sure, and the surface-to-volume r a t i o were kept cons tant f o r
a l l these runs, while the i n i t i a l methane p a r t i a l pressure
was v a r i e d by changing the p r o p o r t i o n of methane t o nitrogen
i n the feed. The v a r i a t i o n i n rea ct io n time was obtained
by changing the t o t a l molal feed rate and keeping the reac
t o r volume constant.
Results
The t e s t s f o r the determination of the e f f e c t o f
the p a r t i a l pressures of methane and acetylene on the rate
o f decomposition o f methane and the rate o f formation o f
acetylene were c a r r i e d out at a r e a c t i o n temperature of
1200°C, a rea cto r pressure of 1.00 atm, and a s u r f a c e - t o -
volume r a t i o of 13.1 cm" 1. The r e s u l t s obtained f o r the var
ious re ac ti on times and i n i t i a l methane p a r t i a l pressures
appear on Table 5.
D i s c u s s i o n o f Results
Considerable d i f f i c u l t y was encountered i n the
t e s t s c a r r i e d out at the higher methane p a r t i a l pressures
because of the large amount of carbon de pos ite d i n the
r e a c t o r and i n the r e a c t o r o u t l e t . Thus, f o r an i n i t i a l
methane p a r t i a l pressure o f 0.672 atm the flow ra te r e q u i r
ed f o r a r ea ct io n time of 0.03 se c could not be maintained
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Table 5 . E f f e c t of I n i t i a l Methane P a r t i a l Pressure
Run P 0 C H 4 Time PCH4 PC2H2 PR "2
(atm) (sec) (atm) (atm) (atm)
21 0.100 0.0322< 0.089 0.0.0089 0.019
22 0.100 0.0536 0.081 0.00159 0.034
16 0.221 0.0260 0.187 0.00148 0.050
18 0.221 0 . 0 3 2 1y 0.186 0.00192 0.054
17 0.221 0.0465 r 0.172 0.00280 0.077
7 0.336 0.0248 0.278 0.00240 0.071
19 0.336 0 . 0 31 4 / 0.280 0.00312 0.081
11 0.336 0.0452 * 0.250 0.00502 0.107
12 0.485 0.0241 0.405 0.00294 0.118
20 0.485 0 . 0 3 2 l / 0.385 0.00410 0.124
13 0.485 0.0470 * 0.346 0.00707 0.177
- 15 0.672 0.0490 * 0.435 0.00957 0.271
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26
for a s u f f i c i e n t length of time to c o l l e c t a r e l i a b l e sample.
On the other hand, at the lower methane p a r t i a l pressures, the
hydrogen and methane concentrations were so low that the anal
y s i s gave inaccurate r e s u l t s . For these reasons, the res ults
obtained fo r the intermediate methane p a r t i a l pressures (0.221,
0.336, 0.485 atm) w i l l be given more weight than those obtained
f or the high and low methane p a r t i a l pressures (O .672, 0.100
atm).
The p a r t i a l pressures of methane recorded i n Table 5
are shown i n gra phica l form i n Figure 4 . The i n i t i a l rate of
decomposition of methane was determined f or the various i n i t i a l
p a r t i a l pressures of methane by extrapolating to zero time.
The f i r s t order re acti on rate constants (k Q) c a l c u l a t e d f or
the'various curves are as fo llows :
Table 6 . I n i t i a l Reaction Rates
P0CH4 -d(P0H 4)/dt *o Relative
(atm) (atm sec-1) , (sec" 1) Weight
0.100 O.35 3.5 1
0.221 1.12 5-1 2
0 .336 2.00 5-9 2
0.485 3-08 6 . 4 2
0.672 4.87 7.2 1
The values calculated for the re ac ti on rate constant
are s u f f i c i e n t l y s i m i l a r to indicate an i n i t i a l reaction of
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27
0.0/ 0.02 O.OJ 0.04 O.OS
Reactfon Time (szc)
Figure 4. The partial pressure of methane versus reaction time at
various initial methane partial pressures
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Figure 5. The partial pressure of acetylene versos reaction time
ot various initial methane partial pressures
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2-9
the f i r s t order. Assigning a r b i t r a r y weights to the constants
as indicated i n Table 6, the average value of k Q would be
5.7 see--1 which compares well with the value of 1.66 sec"!
calculated from Kassel's equation ( 1 ) . '
The experimental data on methane p a r t i a l pressures
p l ot t e d as log (PCH^) v s * * y i e l d e d , for each value of the
i n i t i a l p a r t i a l pressure of methane, a straight l i n e whose
slope k^ increased with the value of the i n i t i a l methane par
t i a l pressure, and could be represented approximately by the
equation
(12) k x = 4.80 ( 1 + P 0 C H 4 ) seer1
which means that the methane p a r t i a l pressure could be c o r r e l -
ated as a func tio n of r e a c t i o n time and i n i t i a l methane p a r t i a l
pressure by
(13) P0H4 = PoCH 4 . - • • « > *
Figure 4 shows a comparison of experimental values
of the methane p a r t i a l pressure and values calculated from the
above formula.
On the plot of acetylene p a r t i a l preasure vs. time
(Figure 5) the rate of change of the acetylene p a r t i a l pressure
was determined for various constant acetylene p a r t i a l pressures.
Table 7 shows the calculated rates in atm/sec with the corres
ponding methane and acetylene p a r t i a l pressures.
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31
A plot of the rate of change of the acetylene par
t i a l pressure vs. the methane p a r t i a l pressure shows straight
l i n e s of s i m i l a r slope for the various constant p a r t i a l pres
sures of acetylene. S i m i l a r l y , a p l o t of the rate of change
of the acetylene p a r t i a l pressure vs. the acetylene p a r t i a l
pressure presents s t r a i g h t l i n e s of s i m i l a r slope for constant
methane p a r t i a l pressure, i n d i c a t i n g a rate equation of the
form
/ xD
P C 2 H 2
( 1 4 ) — r k 2 P C H4
+
k 3 P C 2 H 2
where the constants were found to have the f o l l o w i n g average
values:
(15) k 2 = 0.23 sec" 1
(16) k 5 = 21 sec"1
Replacing the p a r t i a l pressure of methane by i t s
equivalent i n terms of time, defined by Eq. (13), the acetylene
rate equation (14) can be integrated to obtain the expression
f o r the acetylene p a r t i a l pressure
(17) PC 2
H
2
= Po C H4
( 6*3* - a**!*)k]_ + k^
S u b s t i t u t i o n i n t h i s equation of the values determined for k^,
k 2, and k^, however, did not reproduce the experimental data
s a t i s f a c t o r i l y .
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Searching f o r a b e t t e r c o r r e l a t i o n , the acetylene
p a r t i a l pressure was p l o t t e d against the methane p a r t i a l pres
sure a t constant r e a c t i o n times. The p l o t , which appears i n
F i g u r e 6, y i e l d e d s t r a i g h t l i n e s through the o r i g i n , suggest
i n g a r e l a t i o n s h i p o f the form
(18) P C 2 H 2 = nt) PCH 4
i n which F ( t ) , the r a t i o o f acetylene p a r t i a l pressure to
methane p a r t i a l
pressure, could be represented by
(19) F ( t ) = 0.00586 ( e 5 2 - 3 * - i )
A comparison o f the values o f F ( t ) determin ed from Fi gu re 6
and those c a l c u l a t e d from Eq. (19) ca n be seen i n Table 8.
Table 8. Acetylene t o Methane Ratio
Reaction Time
(sec)
Experimental
F ( t )
C a l c u l a t e d
F ( t )
0.00 0.0000 0.0000
0.01 0.0025 0.0022
0.02 0.0057 0.0053
0.03 ,0 .0096 0.0096
0.04 0.0154 0.0151
0.05 0.0236 0.0236
S u b s t i t u t i o n o f Eq. (19) i n Eq . (18) gives f o r the
acetylene p a r t i a l pressure
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33
T r
0.10 0.20 OJO 0.40 0.S0 0.60
Methane Partial Pressure (otm)
Figure 6. The partial pressure of acetylene versus the partial
pressure of methane ot constant reotion time
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(20) PC 2H2 = 0.00586 ( e ^2 ' 3 t _ x ) P0CH4
or, rearranging,
(21) PC
= 0.00586 Po C H 4 ,(32.3 - k i ) t _ - k i t
Eq. (21) i s of the same form as Eq. (17) with
0.00586 taking the place of k 2 / ( k T _ + k^), and 32.3 - k-̂ tak ing
the place of k^, but i t represents the r e s u l t s quite wel l, as
can be observed i n Figure 5»
The rate of change of the acetylene p a r t i a l pres
sure derived from Eq. (21)
dpQ^j j j j
(22) — — — = (0.00586)(32.3) PCH4 + (32.3 - kx) PC 2H 2
d i f f e r s i n form from Eq. (14) i n that k 2 i s a constant, whereas
32.3 - k^ depends on the value of the i n i t i a l methane p a r t i a l
pressure.
In spite of the good c o r r e l a t i o n obtained for the
acetyl ene pressure-time curves, only k 2 (or the c o e f f i c i e n t of
the methane p a r t i a l pressure i n the rat e equation) has a clear
t h e o r e t i c a l s i g n i f i c a n c e , since i t expresses the dependence of
the rate of formation of acetylene on the p a r t i a l pressure of
methane when the p a r t i a l pressures of acetylene and hydrogen
are zero. The increase i n the rate of acety lene forma tion with
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the p a r t i a l pressure of acetylene may hold true only over the
l i m i t e d range i n i/ihich these experiments were c a r r i e d out,
since, according to the rate equation, the acetylene p a r t i a l
pressure would increase i n d e f i n i t e l y , whereas equ ilibri um
c a l c u l a t i o n s show that the f i n a l acetylene p a r t i a l pressure
would be of the order of 0.003 atm for the conditions of the
present experiments. Obviously the rate equation would not
h o l d true at zero methane p a r t i a l pressure since, at 1200°C
acetylene decomposes almost q u a n t i t a t i v e l y to carbon and hydr
ogen, therefore, k^ (or the c o e f f i c i e n t of the acetylene par
t i a l pressure i n the rate equation) describes only the auto-
catalytic effect of acetylene on the reaction ra te.
In the reaction mechanism proposed by Kassel,
(Eq . 2 3 ) , the rate of formation of acetylene
d ( C 2 H 2 )
(23) — ^ = V C 2 H .4> -r 4(C 2H 2)(H 2) + r 5 ( H 2 ) -k 5(C 2H 2)
contains the term -k^(C 2H 2) which accounts f or the decrease i n
acetylene p a r t i a l pressure i n the l a t t e r stages of the reaction
12as has been shown by Watt . The p o s i t i v e term ( 3 2 . 3-k 1)PC 2H 2
of Eq . ( 2 2 ) Is therefore, empiri cal and v a l i d only i n the range
o f p a r t i a l pressures and rea ctio n times of these experiments,
for which the reaction appears to be i n i t s e a r l y stages and
the rate of decomposition of acetylene i s n e g l i g i b l e with
respect to i t s rate of formation.
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In the d e r i v a t i o n of the formula for the rate of
decomposition of methane from h is proposed mechanism, Kas sel
has assumed under the steady state treatment, that the concen
t r a t i o n of acetylene i s small compared to those of methane and
hydrogen, and then, the rate of change of acetylene concen
t r a t i o n can be set equal to zero. Although the r e s u l t s of
these experiments i n v a l i d a t e the assumption of the n e g l i g i b l e
rate of formation o f acetylene, they do not n e c e s s a r i l y contra
d i c t the proposed mechanism, which cannot be tested f o r repre
sentation of the acetylene rate of formation without knowing
the reaction rate constants k^, k^, and k^ of Eq. (4), (5),
and (6) r e s p e c t i v e l y .
13
L a i d l e r ./has. pointed out that i n the s t a t i c method
used by Kassel, the pressure increase* i n the r e a c t i o n vessel
corresponds not to the rate of decomposition of„methane, but
to the rate of formation of ethylene, on the assumption that
ethane, acetylene, and hydrogen are the main products of the
r e a c t i o n . However, the present experiments show that the
main o v e r a l l reactions are:
(24) 2 GH 4 ^ — ^ G 2H 2 + 3 H 2
(25) CH 4 ^ C + 2H 2
and then the pressure increase corresponds very c l o s e l y to
the rate of decomposition of methane, since
dp d(CH 4) d(C 2H 6) d(C 2H 4)(26) — — - 2 — - — —
dt dt dt dt
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If the main products of the r e a c t i o n arecarbon,
hydrogen, and acetylene, the p a r t i a l pressure of hydrogen may
be expressed as :
P
O C H A - P C HA
1 2 7 P H 2 = 2 1 ? P O C H - P ° 2 H 2
where the f i r s t term represents the p a r t i a l pressure of hydro
gen i f methane reacted only according to E q . ( 2 5 ) . Substitution
i n Eq.(27) of the expressions previo usly obtained f or the
p a r t i a l pressures of methane and acetylere from Eq.(13) and (20)
gives an. equation for the p a r t i a l pressure of hydrogen which
approximately reproduces the pressure-time curves. However,
the p a r t i a l pressure of hydrogen was best c o r r e l a t e d as:
(2S) P H2
= \ ! . e - 5 ' 5 0 ( 1 * 2 P 0 C H 4 » *]
* 1 + POCH^ [ )
Figure 7 shows a comparison of the experimental values for the
hydrogen p a r t i a l pressure, and those c a l c u l a t e d from Eq.(28).
Limitations
The experiments which form the basi s fo r this
study, were carried out under conditions which might affect
the v e r a c i t y of the arguments presented above or the v a l i d i t y
of the conclusions to be drawn from these arguments. These
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38
T
0.01 0,02 0.0 J 0.04 0.05
Reaction Time (sec)
Figure 7. The partial pressure of hydrogen versus reaction time
at various initio/ methane partial pressures
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conditions were the f o l l o w i n g :
1) As evidenced by the traces of carbon monoxide
found i n the o u t l e t gases, the feed to the r e a c t o r was con
taminated with f o r e i g n m a t e r i a l such as oxygen, water, or
carbon dioxide, whose e f f e c t on the r e a c t i o n i s unknown.
2) Although i t was found that the decomposition
of methane was unaffected by a carbon surface and s l i g h t l y
catalyzed by an alundum surface, no e f f o r t was made to com
pensate for the v a r i a t i o n i n the nature of the surf ace d uri ng
a run.
3) Except i n the runs s p e c i f i c a l l y made to inves
t i g a t e the e f f e c t of carbon d e p o s i t i o n , the r e a c t i o n times
were c a l c u l a t e d f or the r e a c t o r volume at the beginning of the
run and, therefore, not corrected f o r the carbon deposition.
4) The small quantities of tar deposited i n the
f l a s k at the o u t l e t of the reactor were disregarded i n the
calculations.
5) E r r o r s in the acetylene determination due to
absorption i n the water of the Wet Test Meter or i n s u f f i c i e n t
absorption i n the s i l v e r n i t r a t e s o l u t i o n were not taken
into account.
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6) The gases i n the re ac to r, i n the Wet Test Meter,
and i n the gas a na ly si s set were assumed to behave i d e a l l y at
a l l times.
Conclusions
Should the aforementioned l i m i t a t i o n s prove to be
immaterial to the results of the experiments, the fo ll ow in g
con clu sio ns can be drawn about the decomposition of methane
at 1 200°C:
1) The re ac ti on proceeds homogeneously on a carbon
surface.
2) The re ac ti on i s s l i g h t l y catalyzed by an alun
dum surface.
3) The i n i t i a l reac tion i s of f i r s t order with
an. average reaction rate constant of 5 . 7 s e c " 1 f o r p a r t i a l
pressures of methane from 0 . 1 0 0 to O .672 atm.
4) Acetylene has an apparent a u t o c a t a l y t i c e f f e c t
on the reaction.
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BIBLIOGRAPHY
1. Kassel,L.S., J.Am. Chem. S o c , 54, 3949 (1932).
2. Storch, H.H., J. Am. Chem. S o c , 54, 4188 (1932).
3. Belchetz, L. and
R i d e a l , E.K.,
Trans. Faraday S oc ,
30, 170 (1934).
4. Rice, F.O. and Dooley, M.D., J. Am. Chem. S o c ,
56, 2747 (1934).
5. Rice, F.O., J. Am. Chem. S o c , 6 l , 213 (1939).
6. Gordon, A.S., J. Am. Chem. S o c , 70, 395 (1948).
7. Robertson, A.J.B., Proc. Roy. S o c , A 199, 394 (1949).
8. Rice, F.O. and H e r t z f e l d , K.F., J. Am. Chem. S o c ,
56, 284 (1934).
9 . Schoch-, P., Univ. Texas Publ., 5011 (1950).
10. Sachsse, H., Physik. Chem., B 31, 87 (1935).
11. Wulff Process Co., Fr. 241 (1939).
12. Watt, L.J., The Production of Acetylene from Methane by
P a r t i a l Oxidation,• Univ. B r i t . Col.- (1951).
13. L a i d l e r , K.J., Chemical K i n e t i c s , McGraw-Hill Book
Company, Inc., New York, (1950).
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APPENDIX
Sample Run
. . . . - July 16, 1952
Run,, , #7 •
Barometric Pressure 29.7 i n . Hg
Room Temperature , 2 2 . 5°C
Reaction Temperature . 1200°C
Reactor Pressure . . 2 9 . 9 i n . Hg ( 0 . 2 i n . Hg. ,gauge)
Surface-to-Volume Ratio 13.1,cm~1„
Inlet flow rates from flow meter .calibrations:
Pressure Drop Downstream Pressure Plow Rate
• (in. H20). ( i n . Hg) . (g-mole/hr)
. CH 4 6.00 32.0 . . 1.9 6
. N 2 7.90 . 3 2 . 0 . 3.92
Outlet flow rate
Volume
Temperature
Pressure
Moles
Time
from volume-time measurements:
1.000 f t 5 .
76°P = 535°R (PH 2 0 . = 0 . 9 i n . Hg)
28.1 - 0 .9 = 27.2 i n . Hg
(27.2)(1.000) _ " o n 9 , 9( 2 1 . 8 5 X 5 3 5 ) " ° - 0 0 2 3 2 - l b - n o l e
621 sec =
L 0 5 6 g-mole
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43
Rate ( 1 - 0 ^ 6 0 0 > = 6.12 g-Mole/hr
Acetylene y i e l d :
Start with 100 ml of 0 . 7 0 4 N s i l v e r nit rat e soluti on.
Af ter removal of the s i l v e r a c e t y l i d e p r e c i p i t a t e , the solution
was d i l u t e d to 500 ml and 50 ml of It required 38 . 3 ml of
O . I 6 4 N of potassium thyocyanate solution.
I n i t i a l A g N 0 5 ( 1 0 0 ) ( 0 . 7 0 4 ) = 70.4 mg-mole
P i n a l A g N 0 3 ( 1 0 ) ( 3 8 . 3 )
(O. I 6 4 ) = 62 . 8 mg-mole
Acetylene absorbed (70 . 4 - 62 . 8 ) / 3 = 2 .53 mg-mole
Acetylene concentration (2 . 5 3 ) / ( 1 . 0 5 6 ) ( 1 0 0 0 ) = 0.240 mole %
Orsat Gas Anal ysis
Operation Burette Reading
I n i t i a l (1) 100.0
KOH (2) 100.0
Pyrogallol (3) 99.8
CuO tube (4) 92.8
KOH. (5) 92.5
Reduce to ( 5 r ) 50.2,
Add 0 2 (6'j 96.9 (6) 178 . 5
Catalyst tube (7') 67-7 (7) 124.7
KOH (8») 52.9 (8) 97.3
Pyrogallol (9') 38.0 (9) 70.0
Figures ( 6 ) , ( 7 ) , (8), (9) are r e s p e c t i v e l y ( 6 ' ) ,
( 7 ' ) , ( 8 » ) , (9') m u l t i p l i e d by ( 9 2 . 5 / 5 0 . 2 ) .
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Component CalculationSample Outlet Gas
Component Calculation mole % mole % g-mole/hr
co2 ( l ) - ( 2 ) 0.0
°2(2)-(3) 0.2
H 2 (3)-(4) 7.0 7.1 0.43
CO (4)-(5) 0.3 0.3 0.02
CH 4(6)-(8)
3#27.7-' 27-8 1.70
N 2 (5)-(CH4) #64.8 64.6 3-96
0.240 0.0147
Total 100.0 100.0 6.12
Correction f o r methane i n CuO tube
(2.0)(27.1) Q m 6 '(92.5)
Inlet flow rate c a l c u l a t e d from the outlet flow rate and the
outlet gas a n a l y s i s j on the basis of the reactions:
2 CH 4 C 2H 2 t 3 ^ 2
CH 4 C + 2 H 2
Methane converted to acetylene
2 (0.0147) = 0.0294 g-mole/hr
Methane converted to carbon and hydrogen
0.43 - 3 (0.0147) = 0.195 • g-mole/hr2
Inlet flow rate of methane
1.70 + 0.0294 + 0.195 = 1.924 g-mole/hr
which compares we ll with I . 9 6 from the flow meter c a l i b r a t i o n .
Conversion of methane to acetylene
(0.0294)(100)/(i.924) = 1.53 %
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Conversion of methane to carbon and hydrogen
(0.195)(100)/(1.924) = 10.2 %
T o t a l conversion of methane
1.53 - 10.2 = 11.7 %
The outlet flow rate of nitrogen 3.96 g-mole/hr
compares w el l with the i n l e t flow rate of 3*92 g-mole/hr from
the flow meter c a l i b r a t i o n .
T o t a l Inlet flow rate
3 . 9 6 - 1.924 = 5.88 g-mole/ hr
Average flow rate
( 6.12 - 5.88)/2 = 6.00 g-mole/hr
Reaction time for the reactor volume of 5*0 ml and the molal
volume of 121,000 ml/g-mole:
(5.0)(3600)/(6.00)(121,000) = 0.0248 sec
I n i t i a l p a r t i a l pressure of methane:
1.924/5.88 = 0.328 atm
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Reactor Data for Surface-to-Volume Ratio Runs
Run No. 1 7 3 5
Reactor diameter (cm) 1.11 1.11 1.11 1.11
Reactor length (cm) 5.2 7-5 9.4 9.4
T o t a l r e a c t o r volume (cm3) 5.0 7.3 9.1 9.1
Pellet diameter (cm) - 0.353 0.353 •K-
No. of p e l l e t s 0 100 :.180 250
Volume of p e l l e t s (cm3) 0.0 2.3 4.1 4.1
Free r e a c t o r volume (cm^) 5-0 5.0 5.0 5.0
I n t e r n a l reactor area (cm 2) 18.1 26.2 32.7 32.7
Area of p e l l e t s (cm 2) 0.0 39-1 70.5 90.3
Reactor surface (cm ) 18.1 65.3 103.2 123.0
S/V Ratio (cm"1) 3.6 13.1 20.6 24.6
# Not spherical