I n d . Eng. C h e m . Res. 1989, 28, 1285-1289
1285
Highly Selective Decomposition of Methanol to Syngas on Nickel-Based Composite Catalysts Using an Artificial Intelligence Control Reactor System Yoshiaki Nakazakit and Tomoyuki Inui* Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Sakyo-ku, Kyoto 606, Japan
A flow reactor system controlled by a personal computer was designed and constructed for the purpose of life testing a catalyst containing a deactivation-regeneration process. This system was applied to MeOH decomposition on the Ni-CeOz-Pt/Si02 composite catalysts. Methane was formed as a byproduct a t the initial several hours on stream, but it was gradually decreased with an increase of time on stream. After ca. 60 h, H2and CO were qualitatively produced at a stoichiometric ratio. T h e catalytic activity decreased with an increase of time on stream owing to hydrogen absorption but was, however, almost completely recovered by treatment with N2 flow. T h e deactivation-regeneration processes were automatically controlled by the computer system at least five times during the 42-h reaction. The space-time yield of H2 (H, STY) in the initial stage for each cycle was always as high as 700 mol.L-'.h-'. Recently, significant applications of the catalytic decomposition of MeOH to Hz and CO have been expected. One of the most intriguing objectives would be the use for on-board reforming. Since MeOH decomposition is an endothermic reaction, a large amount of exhaust heat from internal combustion engines of motor vehicles can be absorbed by this catalytic reaction, and the products should be fed back to the engine. Clean combustion is also expected by this system (Inui et al., 1982; Nissan Motors, 1983). Instead of MeOH decomposition, an attempt of MeOH partial combustion was made to supply the reaction heat (Kikuchi et al., 1980). The H2and CO mixed gas is also expected as a source for pure organic synthesis (Sherwin, 1981; Aquil6 et al., 1983). There have been fundamental studies of MeOH decomposition so far on an alkali-earth-metal oxide, MgO (Foyt and White, 1977), and on transition-metal oxides, ZnO (Cheng et al., 1983;Tawarah and Hansen, 1984) and Cr203 (Perrard et al., 1984). However, the purpose of these studies was to study the mechanism or the kinetics under very low pressures or with the technique of temperatureprogrammed decomposition spectroscopy, and the emphasis was not on developing catalysts for practical use. More recently, some studies, aimed at development for practical use, have been made on principally single-metal component catalysts of platinum group metals using a flow reactor (Kasaoka and Shiraga, 1980; Niiyama et al., 1981). However, the space-time yields (STYs) were considerably small, 240 mo1.L-l.h-l H2 STY on Pd/A1203(Kasaoka and Shiraga, 1980) and 55 mo1-L-l.h-l CO STY on Pt/A1203 (Niiyama et al., 1981). The relationship between catalysts' properties and their catalytic performance for MeOH decomposition has not yet been studied extensively. On the other hand, Inui and Suehiro (1982) have found that a Ni-based composite catalyst combined with a small amount of Laz03and a very small amount of Ru exhibited a high activity for MeOH decomposition to H2 and CO with small amounts of formaldehyde and a trace of dimethyl ether and C1-CQhydrocarbons. In the present study, the extremely high activity of the Ni-CeOz-Pt composite catalyst for Hz combustion at room temperature (Inui et al., 1983) was applied to this reaction.
* To whom
all correspondence should be addressed. Present address: Department of Applied Chemistry, Osaka Prefectural College of Technology, Neyagawa, Osaka 571, Japan.
The initial activity of this catalyst at a medium reaction temperature was very high; however, a gradual deactivation was observed. Therefore, the cause of the deactivation and the practical method of regeneration investigated and the continuous reaction cycles involving deactivation-regeneration were conducted with an artificial intelligence (AI) flow reactor system equipped with a personal computer. Experimental Section Catalysts. Fiberfrax, produced by Carborundum Co. Ltd., was used as the base material for catalyst support. It is made of fine ceramic fibers in a plate form of 1-mm thickness. It was impregnated with colloidal silica and then dried. The silica content was 15.870,and the voidness was 88%. This support was impregnated with Pt(NH3)&l2 solution. It was dried and heated to 450 "C and then reduced by heating to 400 "C for 2 h in a N2 stream containing 10% Ha. This was then impregnated with a solution of mixed nitrate salts of Ni and Ce. The reduction procedure was then repeated. The composition of the catalyst was 7.8% Ni-4.4% CeO2-0.44% Pt/15.8% SiOZ/fiberfrax(Inui et al., 1983). The catalyst was shaped in a disk form of 8-mm diameter for the reaction. The silica support was Merck 60-80 mesh (BET surface area, 465 m2.g-l; porosity, 62%; bulk density, 0.49 g ~ m - ~ ) previously washed with aqua regia and calcined at 500 "C for 5 h. This support was impregnated with Pt, Ni, and Ce in the same manner of the fiberfrax. The composition of the catalyst was 8.2% Ni-4.2% CeO2-0.41% Pt/Si02. A compression molding was made, which was then crushed and pulverized. The crushed 10-20-mesh pieces of the catalyst were used for the reaction. Before each run, the catalyst was reduced in situ with a stream of 10% H2 and 90% N 2 at 400 "C for 30 min to reduce the Ni and Pt surfaces which were partly oxidized by air during the packing of the catalyst into the reactor. Apparatus and AI Flow Reactor System. A transparent quartz tube of 8-mm inner diameter was used as the reactor. Reactor control methods by computers were reported by some researchers (Nakamura et al., 1982, 1984), but in practice, they were not easy to apply to the catalytic reaction system since variables for control were too many or data treatment was too difficult to search for optimum conditions of operation. In our laboratory, already, an automatic control system was applied to the catalyst life test for the reaction of paraffin conversion to
0888-5885/89/2628-1285$01.50/0 0 1989 American Chemical Society
1286 Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 Table I. Effect of Space Velocity on the Performance of MeOH Conversion" product MeOH catalyst sheet no. GHSV, h-' time on stream, h conv, 70 HZ co 41.9 21.0 4 28 000 4 92.0 32.7 62.3 3 37 300 5 70.5 63.1 33.4 2 56 000 6 54.7 33.9 3 36.1 63.0 1 112 000 68.7 31.1 1 200 OOOb 5 8.2
distribution, vol 90;dry gas base CH, co2 HCHO 17.3 12.4 0.00 2.0 0.00 0.00 1.1 0.00 0.05 1.3 0.00 0.02 0.06 0.00 0.09
MeOMe 0.00 0.00 0.00 0.00 0.14
OReaction condition; 400 "C, P M ~ =o 0.46 ~ atm, N2 = 3 Lab-'. bN2 = 5.4 Lab-'; catalyst 1, 7.8% Ni-4.4% Ce02-0.44% Pt/15.8% Si02/ fiberfrax.
aromatics involving regeneration (Inui et al., 1987). This system was operated more than 1000 h, but its details have not yet been reported. In the present study, an AI flow reactor system controlled by a personal computer was applied to a catalytic reaction involving a deactivation-regeneration process, and we attempted to operate the system by minimum control variables (Nakazaki and Inui, 1988). The following points put emphasis on the design of the AI flow reactor system. (1)Measurement, control, recording, data storage, and data treatment are performed systematically. (2) A decentralization control system is introduced. If a personal computer is troubled, the system can be operated by a manual operation. (3) The system is independent on performances of a specific personal computer. Even if a personal computer is replaced, the reactor system fulfills its function. (4) Countermeasures for several emergencies are fully considered. The schematic diagram of the AI flow reactor system is shown in Figure 1. This system is divided into the following sections: (A) flow lines for reactants (solid line); (B) electrical signal lines (broken line); and (C) lines for converters from signals to the signals for the computer (dotted lines). Section A consists of mass flow controllers (circled 13), solenoid valves (circled 12, two-way; circled 5 and 11, three-way), pneumatic power driven three-way cock (circled 6, attached a heater), a microtube pump (circled 7 , two channel), and autosampler (circled 14). Section B consists of thermocontrollers (circled 2, 3, 4; circled 4 is attached to the RS-232C interface), a gas chromatograph (circled 17), a integrator (circled 20, attached to the RS232C interface), a inflammable gas sensor (circled lo), and a relay actuator (circled 16, eight-channel attached to a GP-IB interface). This section is used with section C. Section C consists of section B and a personal computer (circled 19, attached to the GP-IB and RS-232C interfaces) for the system control. The program for this system was written by the BASIC language on MS-DOS. The machine language was used for the GP-IB interface control program. Regeneration of deactivated catalyst was performed in an air flow or a N2 flow. The regeneration operation was automatically determined by the computer when the Hz STY decreased down to the preset programmed value. At several emergencies, for example, the reactor temperature rose unusually or inflammable gases leaked from the reactor system; all power sources of the system were cut off, and then the reactant gases are replaced by a N2 stream. In addition, when the reactor system overheated, a fire extinguisher automatically came on. Reaction Method. The AI flow reactor system mentioned above was applied to the MeOH decomposition on the Ni-CeO,-Pt composite catalysts. The reactor packed with the catalyst was heated in a Nz flow from room temperature to 400 "C. The N2 flow was changed to the re-
2 WAY S.1'.
'
L
. I
_____
Figure 1. Schematic diagram of AI flow reactor system. (-) and/or liquid; ( - - - ) signal line; (-.-) GP-IB I/F bus line; RS-232C I / F line.
Gas (-.e-)
action gas flow containing 46% MeOH vapor. The GHSV was varied by changing the amounts of catalyst. Reaction temperatures were 350-550 "C. The gaseous products were analyzed by a gas chromatograph equipped with the integrator. Deactivated catalyst was regenerated using a flow of air or Nz at a rate of 3 LSh-l, and the amount of COz formed was analyzed. Properties of the Catalyst. BET surface areas of the catalysts were measured by a gas chromatography. The metal surface area in the catalyst was measured by a CO adsorption technique (Inui and Suehiro, 1982). Temperature-programmed desorption for adsorbed H2 (H, TPD) was measured by the following flow method. A 100-mg portion of the catalyst was heated in a 10% H2 stream from room temperature to 400 "C with a constant heating rate of 10 "C-min-l and was then kept at that temperature for 30 min. The catalyst was cooled to room temperature in the same H, flow. The adsorption gas was then substituted by an argon stream at a flow rate of 50 cm3.min-' for 30 min followed by heating at a rate of 5 "Csmin-l up to 500 "C. The change in H2 was measured by a TCD cell. Results and Discussion Catalytic Activity for MeOH Decomposition. The effect of GHSV on the performance of MeOH conversion on catalyst 1 is shown in Table I. A t 28000 h-' of GHSV, MeOH conversion immediately attained 92 % after introduction of the feed gas. However, CHI and CO, were produced at 17.3% and 12.4%, respectively. Hydrogen reacted with CO to form CH4 and HzO, and then CO re-
Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 1287 1000 r G .-
Table 11. Amounts of C O , Produced during the Regeneration converted produced produced GHSV, MeOH, COZ, COz/converted catalyst h-l mol/L cat. mol/L cat. MeOH ratio, % 2210 0.70 0.032 1 28000 4000 3.06 0.077 37300 112000 1290 9.75 0.76 11700 1.96 0.017 2 28000
1
800
0 50
100
150
250
200 Time o n stream l h )
'Catalyst 1, 7.8% Ni-4.4% Ce02-0.44% Pt/15.8% SiO,/fiberfrax; catalyst 2, 8.2% Ni-4.2% Ce0,4.41% Pt/SiOz. Regeneration conditions: 400 "C, air = 3 L-h-'.
Figure 2. Change in the catalyst activity during the reaction involving the regeneration. Catalyst 1, 7.8% Ni-4.4% CeO2-0.44% Pt/15.8% Si02/fiberfrax; reaction temperature, 400 "C; GHSV, 28000 h-l; feed gas, 46% MeOH and 54% Nz; (4) regeneration by air flow; (1) regeneration by N2 flow. 1000
8550'C
L
t-
LOO'C
, w 100
I
I
1
I
I
I
20 30 LO 50 60 Time on stream(h1 Figure 3. Effect of temperature on the space-time yields of H, and CO after the initial retardation. Catalyst 2, 8.2% Ni-4.2% Ce0,0.41% Pt/SiO,; GHSV, 28000 h-l; feed gas, 46% MeOH and 54% Nz; (0) HP; (0)CO.
10
acted with H 2 0 to form C02. Above 28000 h-' of GHSV, CHI decreased rapidly and a very small amount of HCHO was found. A t 200000 h-' of GHSV, a small amount of dimethyl ether was found in the initial stage. The H2 selectivity reached as high as 99% at the low MeOH conversion. Hence, the selectivity was considered to increase through suppression of secondary reactions by nonreacting MeOH adsorbed on the catalyst. The performance of MeOH decomposition on catalyst 1 is shown in Figure 2. The space-time yield of CO for catalyst 1 is not shown in Figure 2, however, since CO produced just a half of H2 STY. Although a considerable amount of CHI in the case of catalyst 1was formed at the initial stage of time on stream, it gradually decreased and after 60 h on stream almost completely disappeared. It was found that both H2 and CO STYs decreased gradually with irregular autooscillations of relatively short periods of time. The performance of MeOH decomposition on catalyst 2 is shown in Figure 3. Methane was produced slightly in the initial ca. 4 h on stream; however, after that, the formation of CHI stopped. The yields of H2 and CO rapidly decreased within the initial 4 h and then reached a stable state. The reaction temperature was then raised to 550 "C by a stepwise manner. The variation of H2 and CO STYs was small. When MeOH conversion reached even as high as 89.470, Le., 975 mo1.L-l-h-l H2 STY, with 96.2% Hzselectivity at 550 "C, only a small amount of CH, was produced. Regeneration. When H2 STY for catalyst 1 decreased by about half of that at the initial stage on stream, air was allowed to flow with an air flow of 3 L-h-' for 2 h at 400 "C. With this treatment, the catalytic activity recovered almost completely. The space-time yield of Hz decreased down to ca. 160 mol.L-'.h-'; then it was maintained at this level. A small amount of C 0 2 generated during the regeneration treatment (Table 11) indicates that organic
200 300 400 Temperature ( ' C )
500
Figure 4. Hydrogen T P D spectrum for various catalysts. (- - -) Catalyst 1 (7.8% Ni-4.4% Ce0,-0.44% Pt/15.8% SiO,/fiberfrax); (-) catalyst 2 (8.2% Ni-4.2% Ce024.41% Pt/SiOp); (---) 8.3% Ni-4.0% CeO2-0.41% Pt/A1203.
substances remained on the catalyst surface. The ratios of C02produced/MeOH converted for both catalysts 1and 2 were very small. On the basis of the assumption that HCHO, which is one of the possible intermediates of MeOH decomposition, covered the catalyst surface with a monolayer, the area per gram of catalyst and the area per gram of metal were calculated from the amounts of COz generated. The surface areas per unit weight of catalyst and per unit weight of metal of catalyst 1were 154 and 1880 m2.g of metal-' and of catalyst 2 were 443 and 5140 m2.g of metal-', respectively. These values were remarkably large compared with the BET surface areas of the fresh catalysts. The metal surface area of catalyst 1 decreased 7.5 m2-gof metal-' from 12.5 to 5 m2-gof metal-' during the reaction. The quotient 1880/7.5, i.e., 251, is so large that HCHO could not exist with a monolayer. The BET surface area of catalyst 1 also decreased 29 m2.g of catalyst-1 from 42 to 13 m2-gof catalyst-' during the reaction. Accordingly, a considerable amount of HCHO could have accumulated on the surface of the support in a polymer state. On the other hand, C 0 2 produced for catalyst 2 was 1.8 times as much as for catalyst 1. Nevertheless, the BET surface area, 307 m2.g of cat-', did not change during the reaction. Therefore, the polymerized HCHO would be in a kind-of whiskerlike state. The catalytic activity of catalyst 1 was recovered to five-sixths of the initial activity by using merely N2 flow at a rate of 3 Lsh-' for 2 days at room temperature. Only H2 was found in the effluent gas from the reactor, indicating that the catalyst would be deactivated to one-sixth of the initial activity by polymerized HCHO. The H2 T P D spectra with the flow method are shown in Figure 4. The ratios of hydrogen atoms desorbed/metal atoms of catalyst were 0.07 for catalyst 1 and 0.37 for catalyst 2, respectively. The amount of H2 desorbed by catalyst 2 was much larger than that by catalyst 1. In addition, the ratios of hydrogen atoms desorbed/CO molecules adsorbed were 4.03 for catalyst 1 and 8.87 for catalyst 2, respectively. According to the aforementioned results, hydrogen was not only adsorbed but also partially solved in a metal and spilled over a support.
1288 Ind. Eng. Chem. Res., Vol. 28, No. 9, 1989 1000 I
- 0
0
0
10 20 30 LO I n t e g r a t e d time on stream ( h ]
Figure 5. Computer-controlled reaction test involving the regeneration treatment. Catalyst 2,8.2% Ni-4.2% CeO2-0.41% Pt/SiO,; (1) regeneration; reaction condition; GHSV, 28 000 h-l; reaction temperature, 400 "C; feed gas, 46% MeOH and 54% N,; (0) H2; (0) CO; ( A ) CH,; regeneration temperature, 25 "C; feed gas for regeneration, 3 L-h-' of NS.
Cyclic Operation of Deactivation-Regeneration Processes. Although catalyst 1 had a high activity, it was difficult to control it by the personal computer, owing to the frequent self-oscillation of its activity. As catalyst 2 was deactivated smoothly, the cyclic operation of the deactivation-regeneration processes of MeOH decomposition on catalyst 2 could be applied. The result is shown in Figure 5 . The H2 STY at the initial stage of the reaction reached as high as 700 mo1.L-Ish-'. When the difference in the H2 STY for a period of 30 min on stream was less than 5 mol.L-'.h-', the reaction gas was automatically replaced with 3 Lsh-' N2 flow by judgment of the computer. The reactor was then cooled to 25 "C. Ten hours later, N2 flow replaced the reaction gas after the temperature was raised to 400 "C. The deactivation-regeneration processes were repeated five times during 42-h total reaction time on stream. The H2 STY always reached as high as ca. 700 molL-'.h-l with regeneration. There was a tendency to extend the time until the regeneration increased. This would be due to the change in a catalyst property such as redistribution of the metal. If the regeneration was carried out before the catalytic activity decreased completely, the time for the catalyst regeneration would be able to shorten. With the intention of searching for the proper regeneration conditions, the deactivation-regeneration processes were performed at 400 "C. The various times and levels for regeneration were selected in advance. The result is shown in Figure 6. The arrows indicate the regenerations. The numbers above the arrows indicate the time for the regeneration (minutes). For the first step, as the catalytic activity decreased to 600 mol-L-'-h-' H2 STY, the reaction gas was replaced by 3 L-h-' N2 flow. However, since the time of N2 treatment was too short, the catalytic activity did not reach 600 mol.L-'.h-', which was the level for the regeneration. For the second step, the level for the regeneration was lowered to 550 mol-L-'-h-' H2 STY. A t this level, the catalyst was regenerated scarcely by 30 min of N2 treatment. Further, the level for the regeneration was lowered to 500 mol.L-'.h-' H2 STY. A t this level, there was a tendency for the catalytic activity to increase with an increase of time of the regeneration. As mentioned above, the catalyst was regenerated by 60-80 min of N2 treatment a t 400 "C after 120 min of reaction. An operation containing deactivation-regeneration processes would be performed with two reactors with enough time for the regenerations, reciprocally. Conclusions (1)The 8.2% Ni-4.2% Ce02-t).41% Pt/Si02 composite catalyst has a very high activity, as high as 700 mol-L-l-h-'
5 10 15 20 I n t e g r a t e d time on s t r e a m ( h i
Figure 6. Cyclic operation for deactivation-regeneration with the intention of searching for the regeneration conditions. Catalyst 2, 8.2% Ni-4.2% Ce0,-0.41% Pt/SiO,; (1) regeneration; numbers above 1 indicate the time for the regeneration (min). Reaction condition; GHSV, 28 000 h-l; reaction temperature, 400 "C; feed gas, H,; (0)CO; (A)CH,; regeneration 46% MeOH and 54% N,; (0) temperature, 400 "C; feed gas for regeneration, 3 L-h-' N,.
H2 STY, with high selectivity for the MeOH decomposition. (2) A large part of the deactivation would be caused by suppression by absorbed H, which was removable with N2 flow. (3) Deactivation-regeneration processes were repeated on the composite catalyst. The AI control reactor system performed correctly and safely, as mentioned above. Registry No. MeOH, 67-56-1; H2, 1333-74-0; CO, 630-08-0; CH,, 74-82-8; COz, 463-79-6; Ni, 7440-02-0; CeOz, 1306-38-3; Pt, 7440-06-4.
Literature Cited
,
Aquild, A.; Alder, J. S.; Freeman, D. N.; Voorhoeve, R. J. H. Focus on C1 Chemistry. Hydrocarbon Process. 1983, 62 (March), 57. Cheng, W. H.; Akhter, S.; Kung, H. H. Structure Sensitivity in Methanol Decomposition on ZnO Single-Crystal Surfaces. J . Catal. 1983,82, 341. Foyt, D. C.; White, J. M. Thermal Decomposition of Methanol Adsorbed on Magnesia. J. Catal. 1977,47, 260. Inui, T.; Suehiro, M. Steam Reforming of Methanol over Different Size Cu Catalysts Supported on Alumina. J . Jpn. Petrol. Inst. 1982, 25, 63. Inui, T.; Suehiro, T.; Yamamoto, S.; Ohmura, K.; Takegami, Y. Synthesis-Gas Formation from Methanol over Ni Based Composite Catalysts. J . J p n . Petrol. Inst. 1982, 25, 121. Inui, T.; Miyamoto, Y.; Takegami, Y. Low Temperature Oxidation of Hydrogen Enhanced by Spillover on A Ni-Based Composite Catalyst. Stud. Surf. Sci. Catal. 1983, 17, 189. Inui, T.; Makino, Y.; Okazumi, F.; Nagano, S.; Miyamoto, A. Selective Aromatization of Light Paraffins on Platinum Ion-Exchanged Gallium-Silicate Bifunctional Catalysts. Ind. Eng. Chem. Res. 1987, 26, 647. Kasaoka, S.; Shiraga, T. Catalytic Thermal Decomposition and Steam Reforming of Methanol over Alumina Supported Metal of VI11 group. J . Fuel Scz. Jpn. 1980, 59, 40. Kikuchi, E.; Kunitomo, Y.; Morita, Y. Catalyst for On-board Reforming of Methanol. J . Jpn. Petrol. Inst. 1980, 23, 328. Nakamura, R.; Sasamoto, K.; Sato, K.; Niiyama, H.; Echigoya, E. Fully Automatic Computer-Operated Reaction System in Laboratory (Part 1). Design and Development of the System and Example of Feed-back Optimization Experiments. J . Jpn. Petrol. Inst. 1982, 25, 286. Nakamura, R.; Sasamoto, K.; Sato, K.; Niiyama, H.; Echigoya, E. Fully Automatic, Computer-Operated Laboratory Reaction System. (Part 1). I. Design and Development of the System and Feedback Optimization Experiments. Int. Chem. Eng. 1984,24, 536. Nakazaki, Y.; Inui, T. Highly Selective Synthesis-Gas Formation from Methanol over Ni-Based Composite Catalysts. Chem. Express 1988, 3, 323. Niiyama, H.; Tamai, S.;Kim, J.; Echigoya, E. Catalytic Conversion of Methanol (Part 1). Decomposition of Methanol over Supported Metal and Metal Oxide Catalysts. J . Jpn. Petrol. Inst. 1981,24, 322. Nissan Motors. Jpn. Patent Appl. 67344, 1983.
I n d . E n g . C h e m . Res. 1989, 28, 1289-1292
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Tawarah, K. M.; Hansen, R. S. Kinetics and Mechanism of Methanol Decomposition over Zinc Oxide. J. Catal. 1984, 87, 305.
Perrard, A.; Joly, J.; Germain, J. RBactivit6 de l'oxyg6ne labile de l'oxyde chromique Cr203avec les gaz r6ducteurs. 11. M6thanol. Bull. Sci. Chim. Fr. 1984, I , 208. Sherwin, M. B. Chemicals from Methanol. Hydrocarbon Process. 1981, 60 (March), 79.
Received for review October 20, 1988 Accepted May 25, 1989
Investigation of Phase-Transfer Reactions Catalyzed by Poly(ethy1ene glycol) Bound to Macroporous Polystyrene Supports Ying Shan,* Ru-hong Kang, and Wei Li Department of Chemistry, Hebei Teachers' University, Shijiazhuang, Hebei, People's Republic of China
Several macroporous polystyrene-resin-supported poly(ethy1ene glycols) and comparable microporous analogues were prepared. These polymer catalysts were used t o catalyze various organic reactions such as esterification, etherification, and alkylation. The results show that the macroporous polymers exhibit significantly greater activity than the comparable microporous analogues and that the catalytic activity of macroporous polymers was influenced greatly by the cross-link density, PEG chain length, ring substitution, dielectric constant of solvents, and recovery of catalysts. The establishment of the triphase catalysis has brought about further development of phase-transfer catalysis (PTC). The triphase catalysts are usually synthesized by polymer-supported ammonium salts, phosphonium salts, crowns, cryptands, and poly(ethy1ene glycols) (PEG). Mostly divinylbenzene (DVB) cross-linked styrene (STY) resins have been used as supports. A few inorganic supports have been used (Tundo, 1977; Sawicki, 1982). Resins are mostly low cross-linked (Regen, 1979). Though these catalysts are very active, their mechanical strength is low. In order to discuss the effect of catalytic activity on the resin structure, Gui et al. (1986) used double-layer reticulate polystyrene resin to support PEG, and Regen and Durgadas (1981) used macroporous resin to support quaternary salts. These changed the structure of the catalyst, and the strength of the catalyst became stronger. It was found that the catalytic activity of the macroporous resin to support quaternary salts is lower than that of the microporous resin. The organic phase diffuses into the pore of the macroporous resin, which is unfavorable to ion exchange (Tomoi et al., 1984). Eight macroporous resin-supported PEG catalysts were synthesized. The results are different from those of polymer-supported quaternary salts. Experiment and Results Potassium acetate was melted and powdered; n-decane (internal standard) was of GC purity. Other reagents were of AR or CP purity. I. Synthesis of Catalysts (Regen and Durgadas, 1981; He et al., 1984; Qian, 1984). 1. Cross-Linked Macroporous Poly(styrene-co -(chloromethyl)styrene) and 2% Divinylbenzene. A solution of 1.0 g of gelatin and 0.6 mL of 0.1'70 methylene blue in 100 g of water was added to a 250-mL round-bottom flask fitted with a reflux condenser, a magnetic stirrer, and a water bath temperature controller. A solution of 13.4 g of styrene, 5.7 g of (chloromethyl)styrene, 0.9 g of 43.2% divinylbenzene, 6.0 g of isooctyl alcohol, and 0.2 g of BPO was added. The flask was purged with nitrogen for 30 min, and a nitrogen atmosphere was maintained throughout polymerization. Stirring was started at room temperature.
* Author t o whom
correspondence should be addressed.
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The size of the organic droplet suspended in water can be determined by sampling the mixture and examining it under a microscope. If smaller droplets are desired, the stirring speed can be increased. After the droplet size was established, the mixture was heated with stirring to 72 f 1 "C for 2 h and then to 95 "C for 4 h. Insoluble polymer was collected on sieves and washed thoroughly with water. Particles of 100-200 mesh were used. The other macroporous resins were prepared as follows: for 4 % , 6%, 8%, 1070 cross-linked polymers (cross-link density, styrene (g), (chloromethy1)styrene (g), divinylbenzene (g)), 470, 13.4, 5.7, 1.8; 6%, 12.7, 5.5, 2.7; 8%,12.7, 5.5, 3.6; 1070, 12.7, 5.5, 4.6. The reactants used the above amount specifications. The resins were prepared with the procedure described above. Preparation of Microporous Polymer. Microporous polymer was synthesized as before except that no isooctyl alcohol existed. 2. Preparation of Graft Copolymers. Poly(ethy1ene glycol) was added to a 20-cm X 3-cm tube equipped with a no-air stopper and Teflon-coated magnetic stirring bar. A solution of 0.5 g of NaH dispersed in 16 mL of freshly distilled diglyme was dropped in the tube for 2-5 h during vigorous stirring. After the solution was stirred under nitrogen a t room temperature for 1 h, 1.0 g of chloromethylated polystyrene (ring substitution 30%) was added. The tube was then placed in an oil bath maintained at 90 "C, and the mixture was stirred for a certain time under nitrogen. The resulting resin was collected by filtration, washed successively with 200 mL of 4:l THF/water and 200 mL of THF, extracted (Soxhlet) with T H F for 24 h, and dried under vacuum to give the catalyst. Chlorine analysis indicated complete replacement of chloride ion by the polyether (Table I). The IR peaks of every catalyst are as follows: 3500 cm-' (0-H); 3000 cm-I (Ar-H); 2900 cm-' (C-H); 1600, 1490 cm-' (Bz); 1450 cm-' (CH-CH); 1100 cm-l (C-0-C). 3. Titration of OH in Catalysts. Use the technique of Regen (1979) (see Table 11). 4. Determination of Catalysts' Porosity and Swelling. The samples were covered with EPON 815/812 and cut into slices. The porosity was detected by HITACHI-500 emission electron microscope. The data are in Table 111. 0 1989 American Chemical Society
