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The pyrolysis of mixtures of acetylene with other hydrocarbons
246
Letters to the Editors
hypothesis that the correlation of the d a t a was due to chance. The p r o b a b i l i t y of this was found to be less t h a n 0.1 p e r cent.
7 3 G
'/
0
0"2
0"4
k c a l / g . Thus, the combustion of the charcoal residue would account for 29 or 30 per cent of the heat released b y the combustion of u n d e c o m p o s e d wood. The course of the decomposition reactions in wood a n d the yield of charcoal are affected b y a m b i e n t pressure, rate of h e a t i n g a n d sample size, amongst other things 4. The above analysis therefore only applies strictly to wood samples p r e p a r e d as stated, b u t it serves as a guide to other situations until more d a t a are available. The determinations of the calorific values of the sa:mples were made by Mr D. Brookes. The text and illustrations of this paper are Crown Copyright reproduced with the permission o 1 the Controller oI H . M . Stationery O]fice.
1
0"8 1-0 Y Figure, I. Calorific value data plotted as yc versus y
0"6
I t was therefore concluded that the calorific v a l u e of the evolved volatile m a t t e r was sensibly constant t h r o u g h o u t the decomposition process, a n d equal to 3.96 k c a l / g . The calorific value of the u n h e a t e d wood was found, from equation 3, to be 4-66 k c a l / g - - a value five p e r cent higher t h a n that quoted b y H. M. SI'IERS'~. The calorific v a l u e derived for the charcoal residue depends on the assumed yield of charcoal. E q u a t i o n 3 was used to calculate values of c for values of y in the range 0.16 to 0.20; these values are given in Table 2. Table 2.
Vol. 8
Derived calorific values Jot the charcoal residue
% yield o/ charcoal
Calorific values (hcal/g)
16 17 18 19 20
8"33 8'06 7"83 7"63 7"45
Spiers 3 quotes an a p p r o x i m a t e charcoal yield of 20 p e r cent from wood, a calorific value foi charcoal of 8.30 k c a l / g , a n d a calorific v a l u e for p u r e a m o r p h o u s c a r b o n of 8..08 k c a l / g . T h e e x p e r i m e n t a l d a t a a n d Spiers's d a t a are consistent with a charcoal yield of 16 to 17 per cent a n d a charcoal calorific value of 8.2+_0,-1
A. F . ROBERTS Salely in Mines Research Establishment, B u x t o n , Derbyshire (Received May 1964) .
.
.
.
J
References l B.S. 1016. 'Methods for the analysis and testing of coal and coke.' Part 5: 'Gross calorific value of coal and coke.' British Standards Institution: London, 1987 ,2 ROm~RTS, A. F. and CLouc~I~, G. Ninth Symposium (International) on Combustion. Academic Press: New York 1963 a SPI~RS, H'. M. (Ed.). Technical Data on Fuel. World Power Conference, London -~ BROWNE, F. L. Rep. No. 2136, Forest Pr6ducts Laboratory, U.S. Dept of Agriculture
The Pyrolysis of Mixtures of Acetylene with Other H y d r o c a r b o n s IT HAS been suggested 1 that the p y r o l y s i s of acetylene (A) involves as the initial step conversion to the triplet state ( A * ) . Reaction m a y then proceed either b y a series of addition reactions 2 : A* + A = A . * Aa* + A = A a *
} etc.
....
[1]
resulting in the formation of higher molecular weight species also in the triplet state (as d e m a n d e d b y the W i g n e r - W i t m e r spin conservation rules) or b y the regeneration of the
Table I.
Decomposition products o/ binary mixtures o[ acetylene with ethane, ethylene and methylacetylene. Temperature 725°C: pressure 760 m m o[ mercury
Composition o/ reactants (a) C o n t a c t t i m e : 30 sec
H2
CH 4
C2H 4
100% CzH 2
2"0
10"0
4"2
0"5
100% C t I 6
2"2
4"0
C4H 4
C6H 6
1'0
8.3
14'6
6"9
15"8
47"3
--
--
--
3'6
95% C2H ~ ] +
calc.
2"7
9"8
4-7
2"8
2"1
4"0
1.0
8'0
5% C2H 6
expt. calc.
2"4
9"8
4-7
2'9
2-1
4"1
0"9
8"2
90% C , H2 .
3'3
9"7
5"3
5"2
2"0
3"6
0"9
7"8
10% C2H c J
expt.
3.5
9-7
5'4
5.1
2'1
3"5
0.8
7-5
I'0
6"1
56'0
calc.
2'0
9"8
6.7
0"5
2"1
3'8
1"0
7"9
expt. ealc.
2-0 1.9
9.5 9-6
6.8 9.3
0.5 0.5
2.0 1"9
3.8 3.6
1.0 0.9
7.9 7.6
expt.
1"8
9'6
9-0
0-5
1'6
3.4
1'0
7"4
100% C2]~ 4 95°/oaC2H2 ~ Y
.
.
.
.
1"5
~
5% CzH 4 j 90°/o C~H2 ] 7-
~
10% C2H 4 )
0.3
4.1
1.3
trace
11"4
--
trace
2'8
calc.
1-9
9-7
4.0
0.5
2"7
3.8
1.0
8"0
expt. cal¢.
2.1
10.1
4.3
0'5
2.8
3.5
0.9
8.0
1.8
9.4
3.9
0.5
3.1
3.6
0'9
7"7
expt.
2.1
9.6
4.1
0-5
3' 1
3'4
0.8
7.9
2-6
20"0
3"7
0"7
0"1
0"2
0-4
5"9
100% C a l l 4 95% C2H 2 ] + 5% C a l l 4 ] 90% C H ] + 10 % C a l l 4 (b)
O//oexit gases found as." C2H ~ Call 4 Call 2
C o n t a c t t i m e : 60 sec 100% C 2 H , 100% C H
34.2
10.9
30'1
37"4
--
--
--
0'8
95% C t-I 2 ] +
calc.
4"2
19"6
5"0
2"5
0'1
0"2
0"4
5"6
5% C2H 6 )
expt. calc.
4"2
19"3
4"7
2'8
0"1
0"2
0"4
5"7
5-8
19.1
6"5
4-4
0"1
0"2
0"4
5-4
expt.
5"7
18'6
6"6
4"6
0.1
0"2
0"3
5"3
3"3
20'2
38'7
.
95% C2H 2 ] +
calc.
2"7
20"0
5"5
0'7
0.1
0"2
0'4
5"7
5% Coil 4 )
expt. ealc.
2"7
20"6
5'8
0'7
0"2
0'2
0"2
5"6
2'9
20"0
7'2
0"6
0"1
0"2
0'4
5"4
expt.
3"2
21'0
6"8
0-7
0.1
0-2
0"3
5"2
0"8
4-8
1"9
0"7
7-4
--
--
2'4
calc.
2"5
19.2
3'6
0-7
0"5
0"2
0"4
5"7
expt. calc.
2.4 2.4
20.2 18.5
3"5
0-6
0'5
0-2
0'4
5"8
3'5
0-7
0"8
0"2
0-4
5"6
expt.
2.7
19.2
3'5
0'9
0'9
0"2
0"4
5'6
90% C2H 2 ] + 10% C 2 H ] 100% C2H 4
90% C2H: ] + 10% C2H a I 100% C a l l a 95°/o,C2H ~ T
.
.
.
1'0
~
5% C a l l 4 ] 90% C 2 H ~ + 10% C a l l 4 )
248
Letters to the E d i t o r s
corresponding singlet species by reaction at the walls of the containing vesseP : A ~ * -- A 2
/
A~* - - A 3 etc.
~
where R is a monoradical. Furthermore the results with methylacetylene (M) suggest that interactions of the type:
[2]
A* + M = A + M *
The more or less exclusive operation of such a biradical chain mechanism in the pyrolysis of acetylene is strongly supported by the apparent absence of 'crossing' of chains during the thermal decompositon of binary mixtures of acetylene with other hydrocarbons. Thus, acetylene containing 1, 5 or 10 per cent of a second component was allowed to flow through a heated silica tube (55 cm long, 1 cm diameter) and the gaseous products were analysed b y gas chromatography. Partition columns containing respectively MS 550 silicone oil and polyethylene glycol (mol. wt=400) were used for the determination of methylacetylene, vinylacetylene and diacetylene and of benzene, and a silica gel column was used for the estimation of light hydrocarbons and hydrogen ~. Some typical results for the analysis of the pyrolysis products of binary mixtures of acetylene with ethane, ethylene and methylacetylene are shown in Table I, a n d it is clear that, if allowance is made for the breakdown products of the second components, the composition of the products is virtually the same as would be expected if both compounds decomposed independently. Similar results were obtained at other contact times and with other hydrocarbons as the second component. This striking and rather surprising finding suggests that, although m a n y o5 the monoradicals which are involved in the decomposition of ethane and ethylene, e.g. H atoms and CH 3 radicals, are known to react quite rapidly with acetylene ~,6, reactions of type 1 are much faster than processes such as
M* + A = M + A *
or
R" + C~H~ = R C H : CH" R" + C2H 2 : R H + C 2 H "
. ...
Vol. 8
do not readily occur. This conclusion is perhaps consistent witl~ the fact that certain well-defined differences in the mercury-photosensitized decomposition of acetylene and methylacetylene * are attributable to the different behaviour of excited molecules of the two compounds.
The authors thank the British Oxygen Company ]or the award of a Fellowship (to N.H.F.) and ]or valuable financial assistance in the purchase of apparatus. C. F. CULLIS N. H. FRANKLIN
Department of Chemical Engineering and Chemical Technology, Imperial College of Science and Technology, London, S.W.7 (Received June 1964)
References L E . g . \¥ESTBROOK, E. A., I-IELLWIG, K. C. and ANDERSON, R. C. Fifth Symposium (International) on Combustion, p 631. R e i n h o l d : N e w York, 1955 2 BRADLEY, J. ~xl. and KISTIAKOWSKY, G. B. J. chem. Phys. 1961, 35, 264 :~ MINKOFF, G. J. Canad. ]. Chem. 1958, 36, 131 4 CULLIS, C. F. and FRANKLIN, N. H, Proc. Roy. Soc. ,4, 1964, 280, 139 :' DINGLE, J. R. and LE RoY, D. J. J. chem. Phys. 1950, 18, 1632 6 MANDELCORN, L. and STEACIE, E. x~W. R. Canad. J. Chem. 1954, 32, 474 7 KEP,ARLE, P. J. chem. Phys. 1963, 39, 2218
Letters to the Editors
hypothesis that the correlation of the d a t a was due to chance. The p r o b a b i l i t y of this was found to be less t h a n 0.1 p e r cent.
7 3 G
'/
0
0"2
0"4
k c a l / g . Thus, the combustion of the charcoal residue would account for 29 or 30 per cent of the heat released b y the combustion of u n d e c o m p o s e d wood. The course of the decomposition reactions in wood a n d the yield of charcoal are affected b y a m b i e n t pressure, rate of h e a t i n g a n d sample size, amongst other things 4. The above analysis therefore only applies strictly to wood samples p r e p a r e d as stated, b u t it serves as a guide to other situations until more d a t a are available. The determinations of the calorific values of the sa:mples were made by Mr D. Brookes. The text and illustrations of this paper are Crown Copyright reproduced with the permission o 1 the Controller oI H . M . Stationery O]fice.
1
0"8 1-0 Y Figure, I. Calorific value data plotted as yc versus y
0"6
I t was therefore concluded that the calorific v a l u e of the evolved volatile m a t t e r was sensibly constant t h r o u g h o u t the decomposition process, a n d equal to 3.96 k c a l / g . The calorific value of the u n h e a t e d wood was found, from equation 3, to be 4-66 k c a l / g - - a value five p e r cent higher t h a n that quoted b y H. M. SI'IERS'~. The calorific v a l u e derived for the charcoal residue depends on the assumed yield of charcoal. E q u a t i o n 3 was used to calculate values of c for values of y in the range 0.16 to 0.20; these values are given in Table 2. Table 2.
Vol. 8
Derived calorific values Jot the charcoal residue
% yield o/ charcoal
Calorific values (hcal/g)
16 17 18 19 20
8"33 8'06 7"83 7"63 7"45
Spiers 3 quotes an a p p r o x i m a t e charcoal yield of 20 p e r cent from wood, a calorific value foi charcoal of 8.30 k c a l / g , a n d a calorific v a l u e for p u r e a m o r p h o u s c a r b o n of 8..08 k c a l / g . T h e e x p e r i m e n t a l d a t a a n d Spiers's d a t a are consistent with a charcoal yield of 16 to 17 per cent a n d a charcoal calorific value of 8.2+_0,-1
A. F . ROBERTS Salely in Mines Research Establishment, B u x t o n , Derbyshire (Received May 1964) .
.
.
.
J
References l B.S. 1016. 'Methods for the analysis and testing of coal and coke.' Part 5: 'Gross calorific value of coal and coke.' British Standards Institution: London, 1987 ,2 ROm~RTS, A. F. and CLouc~I~, G. Ninth Symposium (International) on Combustion. Academic Press: New York 1963 a SPI~RS, H'. M. (Ed.). Technical Data on Fuel. World Power Conference, London -~ BROWNE, F. L. Rep. No. 2136, Forest Pr6ducts Laboratory, U.S. Dept of Agriculture
The Pyrolysis of Mixtures of Acetylene with Other H y d r o c a r b o n s IT HAS been suggested 1 that the p y r o l y s i s of acetylene (A) involves as the initial step conversion to the triplet state ( A * ) . Reaction m a y then proceed either b y a series of addition reactions 2 : A* + A = A . * Aa* + A = A a *
} etc.
....
[1]
resulting in the formation of higher molecular weight species also in the triplet state (as d e m a n d e d b y the W i g n e r - W i t m e r spin conservation rules) or b y the regeneration of the
Table I.
Decomposition products o/ binary mixtures o[ acetylene with ethane, ethylene and methylacetylene. Temperature 725°C: pressure 760 m m o[ mercury
Composition o/ reactants (a) C o n t a c t t i m e : 30 sec
H2
CH 4
C2H 4
100% CzH 2
2"0
10"0
4"2
0"5
100% C t I 6
2"2
4"0
C4H 4
C6H 6
1'0
8.3
14'6
6"9
15"8
47"3
--
--
--
3'6
95% C2H ~ ] +
calc.
2"7
9"8
4-7
2"8
2"1
4"0
1.0
8'0
5% C2H 6
expt. calc.
2"4
9"8
4-7
2'9
2-1
4"1
0"9
8"2
90% C , H2 .
3'3
9"7
5"3
5"2
2"0
3"6
0"9
7"8
10% C2H c J
expt.
3.5
9-7
5'4
5.1
2'1
3"5
0.8
7-5
I'0
6"1
56'0
calc.
2'0
9"8
6.7
0"5
2"1
3'8
1"0
7"9
expt. ealc.
2-0 1.9
9.5 9-6
6.8 9.3
0.5 0.5
2.0 1"9
3.8 3.6
1.0 0.9
7.9 7.6
expt.
1"8
9'6
9-0
0-5
1'6
3.4
1'0
7"4
100% C2]~ 4 95°/oaC2H2 ~ Y
.
.
.
.
1"5
~
5% CzH 4 j 90°/o C~H2 ] 7-
~
10% C2H 4 )
0.3
4.1
1.3
trace
11"4
--
trace
2'8
calc.
1-9
9-7
4.0
0.5
2"7
3.8
1.0
8"0
expt. cal¢.
2.1
10.1
4.3
0'5
2.8
3.5
0.9
8.0
1.8
9.4
3.9
0.5
3.1
3.6
0'9
7"7
expt.
2.1
9.6
4.1
0-5
3' 1
3'4
0.8
7.9
2-6
20"0
3"7
0"7
0"1
0"2
0-4
5"9
100% C a l l 4 95% C2H 2 ] + 5% C a l l 4 ] 90% C H ] + 10 % C a l l 4 (b)
O//oexit gases found as." C2H ~ Call 4 Call 2
C o n t a c t t i m e : 60 sec 100% C 2 H , 100% C H
34.2
10.9
30'1
37"4
--
--
--
0'8
95% C t-I 2 ] +
calc.
4"2
19"6
5"0
2"5
0'1
0"2
0"4
5"6
5% C2H 6 )
expt. calc.
4"2
19"3
4"7
2'8
0"1
0"2
0"4
5"7
5-8
19.1
6"5
4-4
0"1
0"2
0"4
5-4
expt.
5"7
18'6
6"6
4"6
0.1
0"2
0"3
5"3
3"3
20'2
38'7
.
95% C2H 2 ] +
calc.
2"7
20"0
5"5
0'7
0.1
0"2
0'4
5"7
5% Coil 4 )
expt. ealc.
2"7
20"6
5'8
0'7
0"2
0'2
0"2
5"6
2'9
20"0
7'2
0"6
0"1
0"2
0'4
5"4
expt.
3"2
21'0
6"8
0-7
0.1
0-2
0"3
5"2
0"8
4-8
1"9
0"7
7-4
--
--
2'4
calc.
2"5
19.2
3'6
0-7
0"5
0"2
0"4
5"7
expt. calc.
2.4 2.4
20.2 18.5
3"5
0-6
0'5
0-2
0'4
5"8
3'5
0-7
0"8
0"2
0-4
5"6
expt.
2.7
19.2
3'5
0'9
0'9
0"2
0"4
5'6
90% C2H 2 ] + 10% C 2 H ] 100% C2H 4
90% C2H: ] + 10% C2H a I 100% C a l l a 95°/o,C2H ~ T
.
.
.
1'0
~
5% C a l l 4 ] 90% C 2 H ~ + 10% C a l l 4 )
248
Letters to the E d i t o r s
corresponding singlet species by reaction at the walls of the containing vesseP : A ~ * -- A 2
/
A~* - - A 3 etc.
~
where R is a monoradical. Furthermore the results with methylacetylene (M) suggest that interactions of the type:
[2]
A* + M = A + M *
The more or less exclusive operation of such a biradical chain mechanism in the pyrolysis of acetylene is strongly supported by the apparent absence of 'crossing' of chains during the thermal decompositon of binary mixtures of acetylene with other hydrocarbons. Thus, acetylene containing 1, 5 or 10 per cent of a second component was allowed to flow through a heated silica tube (55 cm long, 1 cm diameter) and the gaseous products were analysed b y gas chromatography. Partition columns containing respectively MS 550 silicone oil and polyethylene glycol (mol. wt=400) were used for the determination of methylacetylene, vinylacetylene and diacetylene and of benzene, and a silica gel column was used for the estimation of light hydrocarbons and hydrogen ~. Some typical results for the analysis of the pyrolysis products of binary mixtures of acetylene with ethane, ethylene and methylacetylene are shown in Table I, a n d it is clear that, if allowance is made for the breakdown products of the second components, the composition of the products is virtually the same as would be expected if both compounds decomposed independently. Similar results were obtained at other contact times and with other hydrocarbons as the second component. This striking and rather surprising finding suggests that, although m a n y o5 the monoradicals which are involved in the decomposition of ethane and ethylene, e.g. H atoms and CH 3 radicals, are known to react quite rapidly with acetylene ~,6, reactions of type 1 are much faster than processes such as
M* + A = M + A *
or
R" + C~H~ = R C H : CH" R" + C2H 2 : R H + C 2 H "
. ...
Vol. 8
do not readily occur. This conclusion is perhaps consistent witl~ the fact that certain well-defined differences in the mercury-photosensitized decomposition of acetylene and methylacetylene * are attributable to the different behaviour of excited molecules of the two compounds.
The authors thank the British Oxygen Company ]or the award of a Fellowship (to N.H.F.) and ]or valuable financial assistance in the purchase of apparatus. C. F. CULLIS N. H. FRANKLIN
Department of Chemical Engineering and Chemical Technology, Imperial College of Science and Technology, London, S.W.7 (Received June 1964)
References L E . g . \¥ESTBROOK, E. A., I-IELLWIG, K. C. and ANDERSON, R. C. Fifth Symposium (International) on Combustion, p 631. R e i n h o l d : N e w York, 1955 2 BRADLEY, J. ~xl. and KISTIAKOWSKY, G. B. J. chem. Phys. 1961, 35, 264 :~ MINKOFF, G. J. Canad. ]. Chem. 1958, 36, 131 4 CULLIS, C. F. and FRANKLIN, N. H, Proc. Roy. Soc. ,4, 1964, 280, 139 :' DINGLE, J. R. and LE RoY, D. J. J. chem. Phys. 1950, 18, 1632 6 MANDELCORN, L. and STEACIE, E. x~W. R. Canad. J. Chem. 1954, 32, 474 7 KEP,ARLE, P. J. chem. Phys. 1963, 39, 2218