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Catalytic reactions of C1 and C3 hydrocarbons in the presence of oxygen and oxygen-containing compounds
685
catulysis Today, 13 (1992) 685-688 Elsevier Science Publishers B.V., Amsterdam
CATALYTIC REACTIONS OF C, ANDC, HYDROCARBONS IN TREPRESENCE OF OXYGENAND OXYGEN-CONTAINING COMPOUNDS S.V.Adelson,
T.A. Vorontsova,
O.V. Masloboyshchikova
The State Academy of Oil and Gas named after Moscow,USSR
Y.M.Gubkin
Abstract The reaction rates and selectivity of lower olefines formasuch as catalytic methane tion in high temperature reactions, dehydrodimerization and catalytic pyrolysis of C, hydrocarbons are substantialy enhanced by oxygen and oxygen-containing compounds. 1. EXPERIMENTAL Dehydrodimerization of methane and catalytic pyrolysis of pro ane and pro ylene were studied in a quartz flow reactor wit R a fixed caPalyst bed. The catalysts used were modified vanadium oxides and a mixture of transfer metal oxides u on a su port for catalytic pyrolysis of propane or propylene sn!i dehy&odimerization of methane, respectively. 2. RESULTS ANDDISCUSSION Catalytic dehydrodimerization of methane without oxygen added proceeds only via the catalyst lattice oxygen exhaustion due to thermodynamic restrictions ill. The initiati effect of oxygen-containing compounds - nitric acid and ace? one which enhance catalytic pyrolysis of hydrocarbon feed is very small in the case of catalytic dehydrodimerization of methane 111. This is usually observed at high temperatures (850°C) I23, but may also be due to the peculiarities of methane decomposition. In the presence of oxygen thermodynamic restrictions are withdrawn and the conversion rate of methane and the C, selectivity increase up to 12-14 and 60-80% mass. respectively (Figure 1). This can be ascribed to additional reactions with the paticipation of oxygen: CH, R t CH, CH, t 0, CIjz t Hi, CH, t H& CH, t H,O, 2 CH, = C,H, C,H, f R C,H, t H, t&H, C,H, t R &H, + 0, oxydation products 1992 - Elsevier Science Publishers B.V.
(1 1 (2) (3) (4) (6) (6) (7)
686
Oxygen-contain compounds (excluding eroxides) \ such as acetic 9a dehyde, ethanol only sPightly enhance the acetone, thermal yrolysis of propane at ‘?OO-720° C and are completely ineffect 9ve at higher temperatures. In catalytic yrolysis of ropane an;fpro;yle;Ez;i;action rate and selec Pivity of Power significantly enhanced by very small am.ounts of an initiate? acetone (Figure 2a) [21. The rate of initiation of pro ane decomposition decreases with increasing tern eratures ang conversion rates.Pure ropylene decomposes in t Re presence of acetone yrolysis in the absence of under the condit s ons when catalytic acetone does not yet start (Figure 2g ). The influence of oxygen upon catalytic pyrolysis of propane was investigated in a pulse reactor. The results are presented in Figure 3. The propane conversion increases up to a certain limit, the ethylene yield decreases and the ro ylene yield rises linearly versus increase of oxygen concenPra 9 ion. The sum of ethylene and ro ylene selectivities decreases sli tly due to an increase os C8 and CO yields. The decrease of t Bh e C,H,/ C,H, ratio can be ascribed 10 the reaction of oxydative dehydrogenation of the propyl radical: CH,-CH,-CH, to, -
CH,-CH=CH,+HC,
taking place on the catalyst surface, decomposition of the C,H, radical: n-&H, -
CH, t C,H,
0 0.0s a* a11 RATIO Oa/CHh, moC/moC
(8) simultaneously
with the (9)
02
FIGURE1 .Yethane conversion(1) and ethylene (2)) ropylene (3), CO (4), EO,(5), H2(6) yields VS. oxygen/methane ratio.
FIGURE3.Propylene conversion (1) and ethylene(2), carbon pro ylene ( 3 1, oxi ii es ( 4 ) yields VS. oxygen concentration.
60
a
ACEi+NE C&CENTti~lONj!
ACEfONE iONCEhQATiON,,P
FIGURE2.Propane conversion (2a), propylene conversion (2b) VS. acetone concentration. Reaction (8) can compete with reaction (9) in the voids between the catalyst pellets W, /W, = K,IO,l/K,
= 6.8
l
IO'.
O.l5.lO-2
/1.5.
IO" =
6.8
In several publications, including [41, it was reported that the homogeneous reaction (8) is quite sensitive to S/V ch es and proceeds partly heterogeneously. We assume, that react a? on (8) can proceed on the catalyst surface, hence the increase in conversion rate. We do not consider the reaction C,HB t 0, responsible w,/w,,
k,H, t H& for the increase
(IO) of the conversion rate since
= K,~H0,3/K,,~0,3=6.8~10i~10-6/l
.64.103~0.5~10-2
= 10.9
Besides, reaction(l0) may terminate heterogeneously [41. The increase of the propane conversion can be ascribed the following reactions of the HO, radical: C,H, t Hti, c3H7 t H,O, H,O, t M = 2tlH t M C,H, t 6H k3H7 t H,O At oxygen concentrations above 15% the concentration propane remains constant due to the increase of the velocity recombination of the Ho, radicals 2H& -
H,O t 0,
to (11) (12) (13) of of (14)
The data resented show that in the presence of oxygen the conversion ra Pe of both methane and ropane increases. However, for propane the increase is small an$ an accelaration limit is observed, while in methane dehydrodimerization the influence of oxygen consists in self-acceleration of the reaction.
688
According to N.N.Senlyonov et al initiation by oxygen usually roceeds slowly and the reaction of oxygenation is accelerated gy intermediate oxidation products. This favours our view, that the reactions of methane proceed with the participation of intermediates,such as HO, and probably OH . The lower olefines selectivity decreases for ropane and has a maxima in the case of methane which seems to Ee a result of deep oxydation. Thus,we come to a conclusion that in catalytic pyrolysis of ro ane oxy en takes part mainly in the chain ro agation stage Pea# ing to $he undesirable decrease of the e$hyPene: ropylene ratio, while in methane dehydrodimerization addition os oxy en leads to the reoxidation of the catalyst and activation of Qhe methane molecule by intermediates. Oxygen also takes part in some stages of chain propagation. corn ounds In conclusion we surmiee that oxygen-containing take part in the initiation stage, while oxygen both 9n the initiation and chain propagation stages. 3. RKPKRKNCKS 1
S.V. Adelson, T.A. Vorontsova, V.M. Nikitin, G.V.Dorokhin, Chemical Synthesis on the base of C, molecules. Abstracts, USSR, Moscow, 1987.
2
S.V.Adelson,T.A.Vorontsova,Ya.~e~al,O.V.Masloboyshchikova, osium of Socialist Countries. The IV Petrochemical S Abstracts. Kozubnik, PRP,? 1 88.
3
S.V.Adelson, M.Zh.Zhanshin, N.A. Kutyreva Abstracts, Prague, ChSSR, 1981.
4
S.V. Adelson, V.Y. Nikonov, Ye.Y. Borzenko, Neftekhimia, 14(1974)843.
et al, Khisa- 81, A.A. Lebedieva.
catulysis Today, 13 (1992) 685-688 Elsevier Science Publishers B.V., Amsterdam
CATALYTIC REACTIONS OF C, ANDC, HYDROCARBONS IN TREPRESENCE OF OXYGENAND OXYGEN-CONTAINING COMPOUNDS S.V.Adelson,
T.A. Vorontsova,
O.V. Masloboyshchikova
The State Academy of Oil and Gas named after Moscow,USSR
Y.M.Gubkin
Abstract The reaction rates and selectivity of lower olefines formasuch as catalytic methane tion in high temperature reactions, dehydrodimerization and catalytic pyrolysis of C, hydrocarbons are substantialy enhanced by oxygen and oxygen-containing compounds. 1. EXPERIMENTAL Dehydrodimerization of methane and catalytic pyrolysis of pro ane and pro ylene were studied in a quartz flow reactor wit R a fixed caPalyst bed. The catalysts used were modified vanadium oxides and a mixture of transfer metal oxides u on a su port for catalytic pyrolysis of propane or propylene sn!i dehy&odimerization of methane, respectively. 2. RESULTS ANDDISCUSSION Catalytic dehydrodimerization of methane without oxygen added proceeds only via the catalyst lattice oxygen exhaustion due to thermodynamic restrictions ill. The initiati effect of oxygen-containing compounds - nitric acid and ace? one which enhance catalytic pyrolysis of hydrocarbon feed is very small in the case of catalytic dehydrodimerization of methane 111. This is usually observed at high temperatures (850°C) I23, but may also be due to the peculiarities of methane decomposition. In the presence of oxygen thermodynamic restrictions are withdrawn and the conversion rate of methane and the C, selectivity increase up to 12-14 and 60-80% mass. respectively (Figure 1). This can be ascribed to additional reactions with the paticipation of oxygen: CH, R t CH, CH, t 0, CIjz t Hi, CH, t H& CH, t H,O, 2 CH, = C,H, C,H, f R C,H, t H, t&H, C,H, t R &H, + 0, oxydation products 1992 - Elsevier Science Publishers B.V.
(1 1 (2) (3) (4) (6) (6) (7)
686
Oxygen-contain compounds (excluding eroxides) \ such as acetic 9a dehyde, ethanol only sPightly enhance the acetone, thermal yrolysis of propane at ‘?OO-720° C and are completely ineffect 9ve at higher temperatures. In catalytic yrolysis of ropane an;fpro;yle;Ez;i;action rate and selec Pivity of Power significantly enhanced by very small am.ounts of an initiate? acetone (Figure 2a) [21. The rate of initiation of pro ane decomposition decreases with increasing tern eratures ang conversion rates.Pure ropylene decomposes in t Re presence of acetone yrolysis in the absence of under the condit s ons when catalytic acetone does not yet start (Figure 2g ). The influence of oxygen upon catalytic pyrolysis of propane was investigated in a pulse reactor. The results are presented in Figure 3. The propane conversion increases up to a certain limit, the ethylene yield decreases and the ro ylene yield rises linearly versus increase of oxygen concenPra 9 ion. The sum of ethylene and ro ylene selectivities decreases sli tly due to an increase os C8 and CO yields. The decrease of t Bh e C,H,/ C,H, ratio can be ascribed 10 the reaction of oxydative dehydrogenation of the propyl radical: CH,-CH,-CH, to, -
CH,-CH=CH,+HC,
taking place on the catalyst surface, decomposition of the C,H, radical: n-&H, -
CH, t C,H,
0 0.0s a* a11 RATIO Oa/CHh, moC/moC
(8) simultaneously
with the (9)
02
FIGURE1 .Yethane conversion(1) and ethylene (2)) ropylene (3), CO (4), EO,(5), H2(6) yields VS. oxygen/methane ratio.
FIGURE3.Propylene conversion (1) and ethylene(2), carbon pro ylene ( 3 1, oxi ii es ( 4 ) yields VS. oxygen concentration.
60
a
ACEi+NE C&CENTti~lONj!
ACEfONE iONCEhQATiON,,P
FIGURE2.Propane conversion (2a), propylene conversion (2b) VS. acetone concentration. Reaction (8) can compete with reaction (9) in the voids between the catalyst pellets W, /W, = K,IO,l/K,
= 6.8
l
IO'.
O.l5.lO-2
/1.5.
IO" =
6.8
In several publications, including [41, it was reported that the homogeneous reaction (8) is quite sensitive to S/V ch es and proceeds partly heterogeneously. We assume, that react a? on (8) can proceed on the catalyst surface, hence the increase in conversion rate. We do not consider the reaction C,HB t 0, responsible w,/w,,
k,H, t H& for the increase
(IO) of the conversion rate since
= K,~H0,3/K,,~0,3=6.8~10i~10-6/l
.64.103~0.5~10-2
= 10.9
Besides, reaction(l0) may terminate heterogeneously [41. The increase of the propane conversion can be ascribed the following reactions of the HO, radical: C,H, t Hti, c3H7 t H,O, H,O, t M = 2tlH t M C,H, t 6H k3H7 t H,O At oxygen concentrations above 15% the concentration propane remains constant due to the increase of the velocity recombination of the Ho, radicals 2H& -
H,O t 0,
to (11) (12) (13) of of (14)
The data resented show that in the presence of oxygen the conversion ra Pe of both methane and ropane increases. However, for propane the increase is small an$ an accelaration limit is observed, while in methane dehydrodimerization the influence of oxygen consists in self-acceleration of the reaction.
688
According to N.N.Senlyonov et al initiation by oxygen usually roceeds slowly and the reaction of oxygenation is accelerated gy intermediate oxidation products. This favours our view, that the reactions of methane proceed with the participation of intermediates,such as HO, and probably OH . The lower olefines selectivity decreases for ropane and has a maxima in the case of methane which seems to Ee a result of deep oxydation. Thus,we come to a conclusion that in catalytic pyrolysis of ro ane oxy en takes part mainly in the chain ro agation stage Pea# ing to $he undesirable decrease of the e$hyPene: ropylene ratio, while in methane dehydrodimerization addition os oxy en leads to the reoxidation of the catalyst and activation of Qhe methane molecule by intermediates. Oxygen also takes part in some stages of chain propagation. corn ounds In conclusion we surmiee that oxygen-containing take part in the initiation stage, while oxygen both 9n the initiation and chain propagation stages. 3. RKPKRKNCKS 1
S.V. Adelson, T.A. Vorontsova, V.M. Nikitin, G.V.Dorokhin, Chemical Synthesis on the base of C, molecules. Abstracts, USSR, Moscow, 1987.
2
S.V.Adelson,T.A.Vorontsova,Ya.~e~al,O.V.Masloboyshchikova, osium of Socialist Countries. The IV Petrochemical S Abstracts. Kozubnik, PRP,? 1 88.
3
S.V.Adelson, M.Zh.Zhanshin, N.A. Kutyreva Abstracts, Prague, ChSSR, 1981.
4
S.V. Adelson, V.Y. Nikonov, Ye.Y. Borzenko, Neftekhimia, 14(1974)843.
et al, Khisa- 81, A.A. Lebedieva.