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Ind. Eng. Chem. Prod. Res. Dev. 1986, 25,262-267
Two-Stage Reaction System for Synthesis Gas Conversion to Gasoline Kaoru FuJlmoto, Kenjl Asaml, Hltoshi Salma, Tsutomu Shlkada, and Hlro-o Tomlnaga Department of Synthetic Chemistry, Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan
An advanced two-stage reaction system has been developed that produces gasoline in excellent yield from syngas. The system consists of two reactors; in the first reactor syngas is converted to a mixture of methanol and dimethyl ether (DME), which is successively converted to hydrocarbons in the second one. DME synthesis has thermodynamic advantage, over methanol synthesis, of higher equilibrium yield. Since DME is converted to hydrocarbons with ZSM-5 alone, the product profile is substantially the same as that of the methanol-to-gasoline process. By use of this reaction system, 91 % of CO conversion and 57% of hydrocarbon yield were obtained for the first and second reactors, respectively, at 5.1 MPa, W/F 40 and 5 (g of catalyst.h)/mol, and H,/CO = 2.
Introduction The Mobil methanol-to-gasoline (MTG) process (Meisel et al., 1976; Chang and Silvestri, 1977; Chang et al., 1979) is an excellent process that produces gasoline-range hydrocarbons rich in aromatics from methanol. The process is now on the way to commercialization in New Zealand to produce gasoline from natural gas. In the process, methanol should be produced from syngas in a separate plant. Although methanol synthesis from syngas has been technically established, the reaction requires high operating pressure, about 10 MPa, because the thermodynamics is not in favor of methanol formation. The Fischer-Tropsch synthesis, which produces hydrocarbons directly from syngas, on the other hand, gives far higher conversion under pressures as low as 1.0 MPa, because the reaction is practically free from the thermodynamic limitation. The product quality, however, is too low for marketing as gasoline. Recently, several investigations have been made on the syngas-to-gasoline (STG) process (Chang et al., 1979; Fujimoto et al., 1984) utilizing hybrid catalysts composed of a methanol synthesis catalyst and ZSM-5 or other zeolites to obtain high-quality gasoline directly from syngas. The method takes advantage of the possibility to produce hydrocarbons beyond the thermodynamic limit of methanol yield from syngas because of successive conversion of methanol to hydrocarbons. However, the product is largely different from that of the MTG reaction and is composed mostly of C1-CI paraffins and poly(methy1benzenes). This is attributed to the proximity of the two catalyst components. That is, lower olefins, which are the essential intermediates from methanol to aromatics, diffuse from the zeolite to the methanol synthesis catalyst, where they are easily hydrogenated to lower paraffins. Poly(methy1benzenes) are assumed to be formed by the successive methylation of toluene or xylenes with methanol on the zeolite. Another difficulty of the hybrid catalyst system lies in the optimization of working temperatures for the respective catalysts, which are considerably different. Topsoe (1982) has demonstrated that syngas could be converted to high-quality gasoline by combining a methanol synthesis reactor and an MTG reactor in series. Although the above-mentioned difficulties could be solved in this way, the problem of low conversion of syngas to methanol still remains, particularly under low pressure, to be solved. In the present work, an advanced two-stage reactor system has been proposed, where syngas is converted first
to a mixture of methanol and dimethyl ether (DME) and then it is converted to hydrocarbons in the presence of synthesis gas unchanged in the first stage.
Experimental Section Catalysts. Three types of methanol synthesis catalysts were used: a homemade Cu-Zn-A1 mixed oxide catalyst (Cu-Zn(H)), a commercially available Cu-Zn-based catalyst (BASF S3-85) (Cu-Zn(C)), and a homemade Pd/Si02 catalyst. The Cu-Zn(H) catalyst was prepared according to the method reported by Shimomura et al. (1978). A mixed aqueous solution of C U ( N O ~ ) ~ . ~(94.5 H~O g), Zn(N03)2-6H20(68.25 g), and A1(N03)3.H20(139.04 g) (Cu/ Zn/Al=40/23/37 (atom %, total 0.70 M) was precipitated with an aqueous solution of Na2C03(124.96 g, 1.0 M). The precipitates were washed repeatedly with hot water and then dried for 24 h at 110 "C and 1 2 h at 300 "C. The Pd/Si02 catalyst was prepared by the impregnation method, which has been already reported. The silica gel used was Fuji Davison ID gel (specific surface area 270 m2/g, pore volume 1.1cm3/g mean pore diameter 14 nm). The palladium loading was 4 wt %. A 7-AlZ03catalyst (JRC ALO-4 Catalysis Society of Japan, specific surface area 177 m2/g, pore volume 0.66 cm3/g) and a homemade ZSM-5 catalyst, which was prepared following the method described in the patent (Argauer and Landolt, 1972; (Si02/A1,03 = 59.4 in molar ratio), were used as methanol conversion catalysts. The ZSM-5 was activated by exchanging sodium ions to ammonium ions with an NHICl aqueous solution followed by calcining in air a t 500 "C for 3 h. Hybrid catalysts were prepared as described below: (1) The DME synthesis catalyst was prepared by mixing physically granules (20-40 mesh) of methanol synthesis catalyst and r-Al,O, (1:l weight ratio). (2) The hydrocarbon synthesis catalysts were prepared in two different ways. A powdery mixed-type hybrid catalyst (P) was prepared by mixing powders (100 mesh and under) of the Pd/Si02 catalyst and ZSM-5 (1:l weight ratio) and then pressing the mixture into granules (20-40 mesh). A granular mixed-type hybrid catalyst (G) was prepared by mixing granules (20-40 mesh) of the two catalysts (1:l weight ratio). The Cu-Zn(H) and the hybrid catalysts containing Cu-Zn(H) were activated by heating in N2for 0.5 h at 300 "C and then reducing in flowing syngas at 300 "C until no C 0 2 formation was detected. The Cu-Zn(C) and the hybrid catalysts containing Cu-Zn(C) were activated by re-
0196-4321/86/1225-Q262$01.5Q/O0 1986 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
A
-
I,
M
263
Equ i 1 i br i urn
Pd/Si02
200
250
300
350
Temperature ( " C )
Figure 1. Effect of temperature on methanol synthesis reaction: pressure 2.1 MPa; W/F 5 (Pd/SiO,), 1 (Cu-Zn(C)) (g of catalyst. h)/mol; H2/C0 = 2 (Cu-Zn(C) 5% COJ.
cot,
Pd/Si02
feed
H2/C0
P
G
hybrid catolyst H2/C0
ZSPI-5 1OZ CH30H i n CO/H2
Figure 3. Product yield and distribution: temperature 350 "C; pressure 2.1 MPa; W/F 5 (Pd/SiO,, ZSM-5), 10 (hybrid catalysts) (g of catalyst.h)/mol. C O
-
5'
/
t
H 2 e C H 3 P H & C H 3 0 C H 3
/
W/F ( g a t hr/mol) I
Figure 2. Effect of W/F on methanol synthesis reaction: catalyst Cu-Zn(C); temperature; 280 OC; pressure 2.1 MPa; H2/CO/COz 63/32/5.
ducing in flowing Hz a t 150,200,250, and 300 "C for 1h, respectively. The Pd/Si02 and the hybrid catalysts containing Pd/Si02 were activated by reducing in hydrogen flow a t 450 "C for 2 h. Apparatus and Procedures of Syngas Conversion. The syngas conversions were conducted by using a flowtype reaction apparatus with a fixed catalyst bed under pressurized conditions. In one-step reaction, the reactor was a stainless steel tube with a 6-mm i.d. In two-step reaction, the above reactor was used for the second reactor, but the first one was a stainless steel tube with a 14-mm i.d. Reaction conditions were as follows: temperature, 230-350 "C; pressure, 1.1-5.1 MPa; H2/C0 in the feed, 2 (about 5% of C 0 2 was added in the case of methanol formation on Cu-Zn(C)); W/F = 1-40 (g of catalystah)/ mol. All products were analyzed by gas chromatographs.
Results and Discussion Methanol Synthesis Reaction. Figure 1 shows the methanol yield from syngas on the Cu-Zn(C) and the Pd/SiOz catalysts as a function of reaction temperature under the conditions of 2.1 MPa and H2/C0 = 2. The broken line indicates the equilibrium yield of methanol. From the consideration of the time factors (W/F) for Cu-Zn(C) and Pd/SiOz a t 1 and 5 (g of catalyst.h)/mol, respectively, it is clear that the Cu-Zn(C) is more active than the Pd/SiOz catalyst. However, a t temperatures above 300 "C the methanol yields on both of the catalysts decreased and are close to equilibrium. In Figure 2, methanol yields on the Cu-Zn(C) catalyst were plotted against time, suggesting the equilibrium conversion, ca. 10% a t 280 "C, is attained a t W/F = 1.5.
Figure 4. Reaction scheme on the hybrid catalysts.
One-Step STG Reaction. The product yield and distribution of syngas reaction with the hybrid catalysts composed of the Pd/Si02 catalyst and ZSM-5 are shown in Figure 3. Although methanol yield is very low (1.7%) over the Pd/SiOz alone, hydrocarbons were formed with higher than 10% yield on both the P-hybrid and the Ghybrid catalysts. The marked increase in the conversion with hybrid catalysts is attributed to the immediate conversion of methanol, which is the primary product from syngas, to hydrocarbons by zeolite. It is apparent in Figure 3 that the hydrocarbon distribution with the hybrid catalyst is widely different from that of the methanol conversion on the ZSM-5. The methanol conversion on ZSM-5 gives Cz-C7 aliphatic hydrocarbons and C& , methylbenzenes. On the other hand, in the syngas conversion on the P-hybrid catalyst C1-C4 gaseous hydrocarbons were produced with a selectivity as high as 90% and that of aromatic hydrocarbons was less than 5%. With the G-hybrid catalyst the selectivity of gaseous products was slightly lower and the selectivity of aromatics was about three times higher than that for the P-hybrid catalyst. However, the selectivity of light paraffins is still about 80%, and the aromatics were mostly tetra- or pentamethylbenzenes. The large differences in
264
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Table I. Equilibrium CO Conversion and CHJOH temp, "C 250
pressure, MPa
280
2.1
330
2.1
280
1.1
280
5.1
2.1
+ DME Yield
reaction CO conversion CH30H + DME CO conversion CH30H + DME CO conversion CH30H + DME CO conversion CH30H + DME CO conversion CHBOH+ DME
yield yield yield yield yield
the product distribution from that of the MTG reaction are explained by the reaction scheme shown in Figure 4. Syngas is first converted to methanol on the methanol synthesis catalyst. The methanol then transfers to the zeolite where it is converted to lower olefins and successively to aromatics or higher hydrocarbons. In this process, however, a large part of lower olefins formed diffuse out of zeolite to bulk gas phase, and then they are hydrogenated to lower paraffins on the methanol synthesis catalyst. Therefore, selectivity of light paraffins is increased. The P-hybrid catalyst gave lower paraffins with a selectivity higher than G-hybrid catalyst, probably due to the closer proximity of the acid site on zeolite and the hydrogenation site on methanol synthesis catalyst. The high yield of tetra- and pentamethylbenzenes in the aromatic hydrocarbons over hybrid catalysts could be attributed to the successive methylation of toluene and xylenes. In the MTG process methanol is nearly completely consumed in the upper part of the catalyst bed, and thus little methanol exists in the lower part of the bed where aromatic hydrocarbons are formed. On the contrary, methanol is produced at a constant rate throughout the catalyst bed in the present case, so the product aromatics are successivelymethylated on the ZSM-5. It is concluded therefore that gasoline yield from syngas cannot be high when these hybrid catalysts are employed. Two-Stage Syngas Conversion System. A two-stage reaction system, where methanol synthesis catalyst and methanol conversion catalyst are loaded in separate reactors and combined in series, can avoid the difficulty due to mass transfer between the two catalysts. In addition, it ensures the adoption of optimum temperatures for the respective catalysts. The Pd/Si02 was used for the first stage and the ZSM-5 for the second stage. As the maximum yield of methanol was obtained a t about 280 OC (Figure l),this temperature was slected for the first-stage reactor. The temperature of 350 "C was selected for the second-stage reactor on the basis of the preliminary experiments. Figure 5 demonstrates that the product distributions of the MTG reaction on the ZSM-5 and the two-stage syngas reaction are very similar, except for the formation of methane on the Pd/SiOz. This fact indicates that the coexistence of syngas has little effect on the methanol conversion on the ZSM-5. However, the yield of hydrocarbons under 2.1 MPa was as low as 7.4%,entirely due to the small methanol yield in the first reactor. The high conversion of syngas is apparently attained only when the first reactor is operated under higher pressure or a t lower temperature where much more catalyst for a given feed rate is required. Advanced Two-StageReaction System. Dimethyl Ether (DME) Synthesis from Syngas. In the MTG process a two-stage reactor is employed. Methanol is converted to DME in the first reactor and then the mixture of DME, methanol, and water is fed to the second reactor
1
2
25.5 25.5 10.4 10.4 2.0 2.0 3.2 3.2 34.7 34.7
59.7 59.7 33.8 33.8 7.8 7.8 16.9 16.9 65.3 65.3
using eq 1+3 61.6 61.6 39.5 39.5 11.2 11.2 18.7 18.7 65.8 65.8
1+3+4 91.3 64.3 77.2 53.9 34.8 24.4 56.0 38.5 92.1 66.6
A
B
C
React 1 on Reactan:
A Reaction 10% CH30H in H2/CO MT6
Catalyst
B
C
Two Step Reaction
H2/C0
ZCM-5
W/F
(e-catmhr PO!I
T e T e ra ture
(1' 280°C
350°C
(1) 280°C ( 2 ) 350°C
___ ___
4 6
7 q
03
08
( 2 ) 350°C
Y!eld C-mol':)
hvdrccnrSon
C,*
Figure 5. Hydrocarbon distributions and yields of the MTG and two-step reactions: hatched, aromatics.
containing ZSM-5 in order to reduce the heat evolved there. Needless to say, almost the same product as that of the MTG process could be obtained by using DME as a feed material. As will be described later, DME synthesis from syngas is more favorable than methanol synthesis reaction in terms of thermodynamics, thus higher per-pass conversion of CO is expected. Equilibrium Consideration. Equilibrium conversion of syngas to produce methanol (eq 1) or DME (eq 2 ) is CO 2CO
+ 2H2
CH,OH
+ 4H2 s DME + H 2 0
(1) (2)
calculated by thermodynamics as summarized in Table I. Thermodynamics is in favor of DME formation from syngas. For instance, under the conditions of 280 "C, 2.1 MPa, and H2/C0 = 2, equilibrium CO conversion to DME is 33.8%, which is three times higher than that of methanol (10.7%). If DME is formed through dehydrocondensation of methanol (eq 3), 2CH30H F* DME + H,O (3) for example, over a yA120,catalyst, the conversion reaches 39.5% under the same conditions.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
t
265
1-12
bQ
72 3
DME rCH30H
300
250
TEmGerOtJrE
350
250
I['(
1.1 ?PO
300
350
250
300
Ternperatdre ( ' C 1
iemoeroture ( ' C 1
2 1 MPO
5 . 1 MPt
I
al .->
350
Figure 6. Equilibrium composition of reactions 1,3, and 4. Initial condition: H2/C0 = 2.
353
30
Tewerature ("C) Figure 8. Effect of temperature on DME synthesis reaction on Pd/Si02 + y-A1203hybrid catalyst: pressure 2.1 MPa; W/F 10 (g of catalyst.h)/mol; H2/C0 = 2.
20
15
250
200
'
40
,
n
G .-
E
I
- ' Y AI 250
300
350
Temperature ('C) Figure 7. DME synthesis reaction on Pd/yAlz03: pressure 2.1 MPa; W/F 5 (g of catalyst.h)/mol; H 2 / C 0 = 2.
In the present work, hybrid catalysts composed of a methanol synthesis catalyst and a 7-A1203catalyst have been adopted. Since the methanol synthesis catalyst is also effective for water-gas-shift reaction (eq 4), the water CO + HzO e COZ + H2 (4) produced in (3) would react with CO to form C02 and Hz. The conversion of syngas (Hz/CO = 2) for reactions 1, 3, and 4, and the composition of each component a t equilibrium were calculated. They are computer-simulated based on the available thermodynamic data under several pressure conditions and demonstrated in Figure 6 as a function of temperature. Some of the data are also given in Table I. In summary: (1)The equilibrium conversion of synthesis gas is favored at lower temperature and higher pressure. (2) When methanol synthesis and its dehydrocondensation to DME are combined, the product yields (methanol + DME) can be increased by 4 times or more. (3) The combination of methanol synthesis, methanol dehydrocondensation, and water-gas-shift reaction gives much higher CO conversion, which reaches as high as 77% a t 280 "C and 2.1 MPa. (4) The main products of the combined reaction system are DME and C02, and the selectivities of methanol and water are quite small under every condition examined. Synthesis of DME. Figure 7 shows the results of the synthesis gas conversion on a Pd/r-Al,O, catalyst. It is known that a silica-supported palladium is an effective catalyst for methanol synthesis from syngas and also that 7-A1203 is an execellent catalyst for DME formation from methanol. I t is obvious from the figure that DME (and methanol) is produced with higher yield than on the Pd/Si02 catalyst (Figure 1). However, the coproduction of methane is predominant, especially at high temperature.
0
2
1
3
4
5
(g-catahr/mol) Figure 9. Effect of W/F on DME synthesis reaction on Cu-Zn(C) + y-Al,O, hybrid catalyst: temperature; 280 "C; pressure 2.1 MPa; Hz/CO = 2. W/F
The methane formation is probably due to the direct methanation of CO on the palladium catalyst because of the acidic character of the 7-A1203,while the drastic decrease in DME and the increase in methane a t 330 "C might be attributed to the hydrogenolysis of methanol and DME to methane. On the contrary, the syngas conversion on the hybrid catalyst containing the Pd/SiOz and the 7-Alz03gives DME and methanol selectively, with a trace amount of methane (Figure 8), indicating the superiority of the hybrid catalyst Pd/SiOz-yAl2O3 In either case the yield of DME is higher than that of methanol, and the total yield (DME methanol) increased with the increase in temperature up to 300 "C. It should be also noted that COzis formed with fairly high selectivities in both catalyst systems. Since palladium exhibits little catalytic activity for the Boudouard reaction, the formation of COz should be attributed to water-gas-shift reaction between the feed CO and the product water. Thus it could be concluded that reactions 1 , 3 , and 4 proceed on the hybrid catalyst composed of Pd/SiOz and 7-A1203. Similar phenomena are observed with the hybrid catalyst containing the Cu-Zn(C) catalyst and 7-Alz03as demonstrated in Figure 9. The high product yield at short time factor is responsible for the high catalytic activity for methanol synthesis of the Cu-Zn(C) catalyst. The mole ratio of DME/COz/methanol (1.00/1.00/0.13) is close to that of the equilibrium value (1.00/0.91/0.09). Moreover, the formation of DME and methanol on the hybrid catalyst containing Cu-Zn(C) is far less than the
+
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
266
100
I
!
80
I
c
; K
401
40 .-GI
t.
u
20
O
1
1
20
10
lo
40
30
0
W/F i s - c a t ~ h r / m o l )
Figure 10. Effect of W/F on CO conversion on Cu-Zn(H)
+ y-AlzO,
hybrid catalyst: pressure 2.1 MPa; H2/C0 = 2.
1
2 3 Pressure
4 (MPo)
5
6
0
Figure 12. Effect of pressure on CO conversion and product yield catalyst Cu-Zn(H) + y-A1203; temperature (1) 280 "C, (2) 350 O C ; W / F (1) 40, (2) 5 (g of catalyst.h)/mol; H2/C0 = 2.
100
c
40
" D
e
u
C
20 ,"
1 2
3
4
5
6
7
8 910
0 NTG
A
Reaction
MTG Reaction
Reactant
10%CH30H i n H2/C0
Catalyst
ZSM-5
W/F (9-ca t h r
5
/mol)
Temperature Yield(C-mol%) Hydrocarbon c02
350 'C
___ --_
B
C
5.1 (MPa)
aromatics.
(1) Pd/Si02 + v-AI2O3
i 2 ) ZSM-5
5
3.1
Figure 13. Effect of pressure on hydrocarbon distribution: hatched,
H2/C0
(2)
2,l
Pressure
Two Step R e a c t i o n
(1) 10
1.1
(1) 40
(2)
5
(1) 300°C
(1) 300°C
( 2 ) 350'C
( 2 ) 350°C
9,7
25.8
3.2
10.0
Figure 11. Hydrocarbon distribution and yield of advanced twostage reaction system: hatched, aromatics. equilibrium a t W/F = 4 (Figure 9) under the conditions shown in the figure. The equilibrium conversion level can be attained with a prolonged time factor under 2.1 MPa a t either 280 or 300 "C, as apparently demonstrated in Figure 10. Even when the reaction was conducted with prolonged time factors, little change in the product selectivity was observed, suggesting that the products are sufficiently stable under these conditions. Advanced Two-step Syngas to Gasoline Reaction. The synthesis gas conversions were conducted by using an advanced two-stage reaction system. Figure 11shows the product yields and the distribution of hydrocarbons. A hybrid catalyst composed of equal weights of Pd/Si02 and the 7-A1203was employed for the first reactor, and the ZSM-5 was used for the second reactor. Reaction temperatures of the first and second reactors were 300 and 350 "C, respectively. It is evident that hydrocarbon yields, which correspond to the DME plus methanol yields, are
much higher than those for the two-step method shown in Figure 5 where only a methanol synthesis catalyst is loaded in the first reactor. When the time factor of the first reactor was increased from 10 to 40 (g of catalyst. h)/mol, product distribution shifts slightly to the higher side, which should be caused by the higher partial pressure of DME as reported by Chang et al. (1979). Nevertheless, the product distribution is substantially the same as that of the MTG reaction, indicating excellent quality as gasoline. Figures 12 and 13 demonstrate how the operation pressure affects the conversion level and the product selectivity. In the present cases the hybrid catalyst in the first reactor is composed of the Cu-Zn(H) catalyst and y-A1203. Temperatures of the first and second reactors are selected as the optimum points, respectively. The time factor, 40 (g of catalyst-h)/mol, is believed to be large enough to attain the equilibrium, as demonstrated in Figure 9. As the reaction pressure is raised, CO conversion and product yields are increased to reach 90.8% and 57.3% a t 5.1 MPa, respectively, which are sufficiently high to minimize the recycle of the unchanged syngas. Figure 13 shows the hydrocarbon distribution as a function of reaction pressure. It is also apparent that the distributions are substantially the same as that of the MTG reaction and independent of pressure. Conclusion An advanced two-stage reaction system has been developed in which a mixture of methanol and DME is produced from syngas in the first reactor and is then
Ind. Eng. Chem. Prod. Res. Dev. 1988, 25, 267-272
converted to gasoline in the second reactor containing ZSM-5 in the presence of unchanged syngas. This system has several advantages as follows: (1)DME synthesis reaction is much more favored than methanol synthesis reaction in terms of thermodynamics, and high CO conversion (77.2%) can be attained a t low pressure (2.1 MPa). (2) The high conversion level was proved to be attainable experimentally by utilizing a hybrid catalyst composed of methanol synthesis catalysts and yA1203. (3) By the separate use of methanol synthesis catalyst and ZSM-5, unfavoriible side reactions in the one-step process, such as the hydrogenation of lower olefins or the secondary methylation of methylbenzenes to poly(me-
287
thylbenzenes), could be entirely avoided, and thus substantially the same product profile as that of the MTG process was obtained.
Literature Cited Argauer, R. J.; Landoh, G. R. US. Patent 3702886, 1972. Chang, C. D.; Sihrestri, A. J. J. Catal. 1977, 4 7 , 249. Chang, C. D.; Lang, W. H.; Smith, R. L. J . Cafe/. 1979, 56, 169. Chang. C. D.; Lang, W. H.; Silvestri, A. J. J. Catal. 1979, 56, 268. Fujimoto, K.; Kudo, Y.; Tominaga, H. J. Catal. 1084, 6 7 , 136. Meisel, S. L.; McCullough, J. P.; Lechthaier, C. H.; Weisz, P. E. CHEMECH 1976, 6, 86. Shimomura, K.; Ogawa, K.; Oba, M.; Kotera. Y. J . Cafal. 1978, 52, 191. Topsoe Top. 1982 (December).
Received for review October 28, 1985 Accepted January 19, 1986
GENERAL ARTICLES Continuous Wave Carbon Dioxide Laser-Induced Chemistry of the Allyl Halides Joseph K. McDonald' and James A. Merrltt Research Directorate, Research, Development 8 Engineerlng Center, U.S. Army Missile Command, Redstone Arsenal, Alabama 35898
James R. Durlgt Department of Chemlstry, Unlverslty of South Carollna, Columbia, South Carollna 29208
Vlctor F. Kalaslnskyt Department of Chemlstry, Mlsslsslppl State Unlverslty, Mlsslsslppi State, Mlssisslppl 39762
Samuel P. McManust Department of Chemlstry, The Unlverslty of Alabama in Huntsville, Huntsville, Alabama 35899
The gas-phase CW C02 laser-induced reactions (LIRs) of allyl chloride, allyl bromide, and allyl fluoride have been studied. I n the case of the chloride, where several other studies have appeared, the results of the LIR have been compared with pyrolytic studies, the SF,-sensitized CW-C02 LIR, and a gas-phase temperature photolysis study at 200 nm. Allyl chloride and allyl bromide appear to follow essentially the same mechanistic pathway for their LIR. There are, however, differences that can be attributed to the weaker C-Br bond and the relative reactivity difference of the halogen radicals. The principal products that both give are benzene, ethylene, propene, acetylene, methane, and the respective hydrogen halide. Allene and propyne were formed In modest yields from the chloride but were trace products from the bromide. Along with HF, allyl fluoride gives principally allene and propyne.
Introduction The development of new chemical processes that are highly selective, efficient, and inexpensive are permanent
* To whom inquiries should be addressed (ATTN: AMSMIRD-RE-QP). 'Research supported by U.S.Army Contract DAAG29-81-D0100 through the Battelle Research Triangle Park office. O196-4321/86/ 1225-0267.$O1.5O/O
goals in our profession. Thus the use of lasers to drive chemical reactions has attracted considerable attention in recent years (Moore, 1975-79; Grunwald et al., 1978; Bloembergen and Yablonovitch, 1978; Zewail, 1980; Letokhov, 1980; h e and Shen, 1980; Zare and Bernstein, 1980; Steinfeld, 1981). The widespread availability of tunable lasers has enhanced the interest in photochemical processes. However, because the output of a carbon di0 1986 American Chemical Society
