1382
Ind. Eng. Chem. Res. 1988,27, 1382-1387
Prasad, R.; Tsai, H. L.; Kennedy, L. A.; Ruckenstein, E. Combust. Sci. Technol. 1981a, 25,71-84. Prasad, R.; Tsai, H. L.; Kennedy, L. A.; Ruckenstein, E. Combust. Sci. Technol. 1981b, 26,51-64. Prasad. R.: Kennedv. L. A.: Ruckenstein. E. Combust. Sei. Technol. issic, 27,45-& ' Fkdcliffe, S. W.; Hickqan, R. G. J. Inst. Fuel 1975, 208,208-214. Trimm, D.L.Appl. Catal. 1983, 7,249-282. Trimm, D. L.;Lam, C . W . Chem. Eng. Sei. 1980, 35, 1405-1413.
Wampler, F. B.; Clark, D. W.; Galhes,F. A. Combust. Sei. Technol. 1976,14, 25-31. Westbrook, C. K.; Pitz, W. J. Combust. Sei. Technol. 1983, 33, 315-319.
Received for review August 17, 1987 Revised manuscript received February 23, 1988 Accepted March 11, 1988
Phenylacetonitrile Alkylation with Different Phase-Transfer Catalysts in Continuous Flow and Batch Reactors Vittorio Ragaini,* Giovanni Colombo, and Paolo Barzaghi Dipartimento di Chimica Fisica ed Elettrochimica, Uniuersitd di Milano, via Golgi 19, 20133 Milano, Italy
Emo Chiellini and Salvatore D'Antone Dipartimento di Chimica e Chimica Industriale, Universitd di Pisa, via Risorgimento 35, 56100 Pisa, Italy
T h e monoalkylation of phenylacetonitrile (PAN), in phase-transfer (PT) conditions, with butyl bromide in aqueous organic medium as catalyzed by both quaternary ammonium salts bound t o an insoluble polymer and soluble low molar mass analogues has been studied by using different experimental apparatus. Batch slurry r e a d o n or fiied bed reactors under continuous flow conditions and different stirring modes have been adopted within the scope of a basic investigation of the performance of different phase-transfer catalytic systems. A classification is provided of the different catalytic systems and apparatus in terms of specifie activity, and an optimization of experimental conditions useful for further kinetic investigations has been performed. The ethylation of phenylacetonitrile (PAN) with tetrabutylammonium bromide (TBAB) as a soluble catalyst in phase-transfer (PT).conditions in an aqueous organic system, has been studied (Komeili-Zadeh et al., 1978;Sol a r ~et al., 1980;Balakrishnan and Ford, 1981,1983)with the aim of analyzing the reaction kinetics. In particular, parameters such as stirring rate and base (NaOH) and Brconcentrations were analyzed. For the utilization of insoluble PT catalysts in fixed bed reactors (Ragaini and Saed, 1980,Ragaini et al., 1986),a fairly detailed study has been undertaken of the monoalkylation reaction of PAN (Scheme I), as catalyzed both by insoluble polymer-supported quaternary ammonium groups or glymes and soluble low molar mass analogues. The ultimate goal of the study was the evaluation of the specific activities of the different catalysts when used in either slurry (SR) or fixed bed (FB) reactors under different stirring modes such as ultrasound mixer (UM), turbine stirrer (TS), and in-line turbine mixer with recirculating pump (TP).
Experimental Section Catalysts. In Table I the chemical and physical characteristics are collected for the catalysts whose structures are illustrated in Scheme 11. The low molar mass quaternary ammonium derivatives either in the salt or in the hydroxide forms as well as the insoluble polymeric catalysts IRA 904 and Duolite A101, A161,and A171 were from commercial sources. The other polymeric catalysts containing quaternary ammonium groups or glymes as active groups were prepared according to a general procedure as represented in Scheme 111. Styrene/divinylbenzene polymer matrices with different degrees of cross-linking were prepared by suspension polymerization of the two comonomers in the presence of n-octane as porogenic agent. The successive chloro-
* To whom correspondence should be addressed.
Scheme I PT Catalyst
+ C&Br
Toluene
NoOH/H20
+ (NaBrl
aq
Stirring
Scheme I1
methylation of the basic resins followed by quaternization with tertiary amines or etherificationwith the monomethyl ether of tetraethylene glycol or tetraethylene glycol led to 0 1988 American Chemical Society
Ind. Eng. Chem. Res., Vol. 27, No. 8, 1988 1383 Table I. Characteristics of Styrene/Divinylbenzene Polymeric Catalysts and Low Molar Mass Analogues Utilized in the Alkylation of Phenylacetonitrile ion-exchange capacity, mequiv/g specific activity, morphology of sample DVB, mol % functional group anal. method elemental anal. mequiv/ga the orig. polymer TEBA-PB1 TEGPB TEBA-PB2 TBBA-PB TBBA-TEG-PB MTEG-PB IRA 904 Duolite A161 Duolite A171 Duolite A101 TBA TEBA
N(CzHd3 (OCZH~),OH N(GHd3 N(C4H& N(C4HAb (OCzHd4OCH3 N(CH3)3 N(CHJ3 N(CHJ3 N(CH3)3 (C4H9)4N+OH(C2H6)4NCC1-
2 2 2 12 12 12 20 20 20 20
-
0.9
1.3
1.3 1.3 0.6
1.7 2.0 0.8
1.3 1.0 1.7 2.0 1.8 1.5 1.0c 1.2'
gel gel macroporous macroporous macroporous macroporous macroporous macroporous macroporous macroporous
1.1c
1.4' 3.7 6.0
Evaluated as millimole of bound reagent per gram of dry polymeric product if not otherwise indicated. *Containing 18% (mol/mol) of methoxytetraethylene glycol residues, (OC2H4)40CH3. Referred to a wet product containing 50% water.
Scheme I11 CHi=CH
CH,=CH
-CH2-CH-CHi-
CH
I
,
CH2-CH-CHi-CH-CH;CH,
I
/
the polymer-supported catalysts active in phase-transfer reactions. Apparatus. The experimental apparatus that have been used for the alkylation of PAN are classified according to the conditions in which reactions have been performed. Notations and relevant experimental conditions adopted are as follows: (I) batch reactors (BR) with (a) magnetic stirrer (BR-MS) and (b) ultrasonic mixer and magnetic stirrer (BR-UM) (soluble catalysts); (11)slurry reactors (SR) with (a) ultrasonic mixer and magnetic stirrer (SR-UM) and (b) turbine stirrer (at about 10000 rpm) (SR-TS) (insoluble catalysts); also the reactions carried out under the reported conditions can be classified as batch reactions; (111) fixed bed reactors (FB) with (a) recirculating pump, ultrasonic mixer, and magnetic stirrer (FBUM), (b) recirculating pump and turbine stirrer (FB-TS), and (c) recirculating pump and turbine stirrer acting partially as a pump (FB-TP) (insoluble catalysts); the reactions performed under these conditions can be classified as continuous flow-type reactions. As examples of prototype apparatus, Figures 1 and 2 represent the configurations used for FB-UM and FB-TP modes, respectively. The reactor in Figure 1 includes a three-necked, jacketed, Pyrex glass flask with a volume of about 250 mL (R), a catalyst holder (C), a flow meter (F), a recirculating pump (P),an ultrasonic mixer tip (UM), a magnetic stirrer bar (MS), and a thermostatic bath (T). When the UM is replaced with a turbine stirrer (TS),the reactor is designed as FB-TS, and in this case magnetic stirring is not used. Reactor R has also been used as either a two-phase batch reactor or slurry reactor when soluble or insoluble catalysts have been used, respectively. In that case, parts C, F, and P were not included in the apparatus. In Figure 2, a fixed bed apparatus is represented in which the catalyst (C) is separated from the mixing
I/
v
R
n
I
I
I
Figure 1. Reaction apparatus with fixed-bed reactor and ultrasonic mixer (FB-UM).
4
TP
P
Figure 2. Reaction apparatus with fixed-bed reactor and in-line turbine stirrer acting partially as a pump (FB-TP).
1384 Ind. Eng. Chem. Res., Vol. 27, No. 8, 1988
Table 11. Preparation of Cross-Linked Styrene Copolymers under Suspension Polymerization Conditions comonomers,O mol % polymeric product sample St DVB Est wt, g conversn,b % RS1 96.5 2.0 1.5 294 98 RS2 77.5 12.5 10.0 291 97 a St, Styrene; DVB, divinylbenzene; E s t , ethylstyrene. Evaluated as (polymer weight/comonomers weight)100.
Table 111. Chloromethylation of Cross-Linked Styrene Copolymers poly(St) matrix reacted polymer DVB, transformed samDle samale mol % wt, P units," mol % wt, P 93 140 100 RS1 2.0 RC1 100 135 100 RS2 12.5 RC2 Evaluated by elemental analysis.
chamber as previously illustrated [Figure 2 in Ragaini et al. (1986)]. The notations C, F, MS, P, and T are the same as in Figure 1,and TP is an in-line mixer, which includes a turbine (about 10000 rpm) acting also as a pump with a low lift that is coupled to the pump (P). A is the vessel for feeding the two liquid phases, and TC is the thermocouple for temperature control. Low Molecular Weight Compounds. Reagents. PAN, butyl bromide, toluene, sodium hydroxide, TBA, and TEBA were pure grade, commercially available products from Carlo Erba or Fluka. Commercial styrene (Fluka) was distilled under vacuum prior to use. Divinylbenzene (Fluka) consisting of 35% p-divinylbenzene, 15% m-divinylbenzene, 35 % m-ethylstyrene, and 15% p-ethylstyrene was made inhibitor free by elution through an anion-exchange resin (IRA 400, OH form). Tetraethylene glycol, chloromethyl methyl ether (chloromethyl methyl ether and (bischloromethyl) methyl ether have been demonstrated to be carcinogenic; handling and disposal of the quoted compounds, glassware, and waste derived therefrom have been done according to the recommendations and guidelines suggested by Steere (1975)),triethylamine, tri-n-butylamine, and tetra-n-butyl ammonium bromide were all commercial products used without further purification. Benzoyl peroxide (BPO Fluka) was crystallized from ethanol. Zinc dichloride (C. Erba) was used without further purification. Methoxytetraethylene Glycol. Tetraethylene glycol from Fluka was reacted with 1/5 equiv of CHJ (mol/mol) in T H F and 5% aqueous NaOH (1/1vol/vol mixture) in
the presence of tetra-n-butyl ammonium bromide. The reaction product was distilled under vacuum, collecting the central fraction of the distillate that contained 2% dimethoxytetraethylene glycol as evaluated by GLC. Polymerization and Chemical Transformation of Cross-Linked Polymers. Data for the preparation and chemical modifications of preformed polymers are summarized in Tables 11-V. Suspension Copolymerization of Styrene and Divinylbenzene (Table 11). A mixture of 720 mL of water; 27.0 g of 5% aqueous solution of poly(sodium methacrylate), molecular weight (mean numerical) = 5 X lo6, 4.5 g of aluminum silicate, 0.7 g NaC1, 262 g (2.52 mol) of styrene; 38 g (0.29 mol) of divinylbenzene as contained in a 1/1 mixture with ethylstyrene; 330 mL of n-octane; and 1.6 g (1.2 mmol) of BPO was placed in a 2-L cylindrical reactor. The reaction mixture was heated to 70 "C for 24 h under mechanical stirring. After cooling the solid was collected by filtration, washed with water, and extracted with ethanol. After drying under vacuum, 291 g of cross-linked polymer was obtained as small beads (100-300 wd. Chloromethylation of Poly(styrene-co-divinylbenzene) (Table 111). To a suspension of 100 g of poly(styrene) in 1 L of a 1:1 (v/v) mixture of 1,2-dichloroethane and chloromethyl methyl ether, 66 g (0.48 mol) of ZnC1, was slowly added at room temperature under mechanical stirring. The resulting suspension was stirred at 40 "C for 3 h. After cooling, the largest part of the solvent was removed under vacuum and the polymer washed with 500 mL of methanol. After drying under vacuum, 135 g of polymeric product (containing 100% of chloromethylated units) was obtained. No evidence was gained on the formation of additional cross-links due to the parasite alkylation involving chloromethyl groups introduced on the phenyl rings. It is, however, worth mentioning that the chloromethylation reaction was performed in a large excess of chloromethyl methyl ether (9/1 mol/mol) with respect to styrene units. Etherification of Poly(chloromethy1styrene-costyrene-co-divinylbenzene) with Methoxytetraethylene Glycol (Table IV). Twenty-three grams (1.2 mol) of NaH was added to a solution of 208 g (1.0 mol) of methoxytetraethylene glycol in 1 L of THF. When hydrogen evolution was over, 100 g of poly(chloromethy1styrene-co-styrene-co-divinylbenzene) was added, and the mixture was heated at reflux for 70 h under mechanical stirring. After cooling, the resin was filtered and washed several times with ethanol. After drying under vacuum,
Table IV. Etherification of Cross-Linked Chloromethylated Styrene Copolymers reaction conditions NaH poly(St) matrix H(°C2H4)40R sample sample DVB, mol % wt, g R amt, mol amt, mol TEG-PB RC 1 2.0 100.0 H 1.0 1.2 MTEG-PB RC2 12.5 100.0 CH, 1.0 1.2 ~~~~~~
(I
Evaluated by elemental analysis.
reacted polymer transformed specific activity,* units," mol % mequiv/g 23.0 1.5 18.0 1.0
Evaluated as millimole of bound reagent per gram of polymeric product.
Table V. Quaternation of Cross-Linked Chloromethylated Styrene CoDolymers reaction conditions samale TEBA-PB1 TEBA-PB2 TBBA-PB TBBA-TEG-PB a Evaluated
samale RC1 RC2 RC2 MTEG-PB
by elemental analysis.
poly(St) matrix DVB,mol% 2.0 12.5 12.5 12.5
w t , ~
4.2 100.0
100.0 20.0
amine (C,H,),N (C,HJ,N (CJ%)J'J (C&),N
wt,
4.8 116.7 134.8 22.6
reacted polymer quaternary group,a mequiv/g 1.3 1.7 2.0 0.8
Ind. Eng. Chem. Res., Vol. 27, No. 8, 1988 1385 Table VI. Kinetic Constants for PAN Monoalkylation with Butyl Bromide in the Presence of Different PT Catalysts in Fixed Bed (FB) Reactor or in Batch Reactor (BR) with Ultrasonic Mixer" temp, catalyst TBAd TEBAd TBBA-PB
"C 70
Cf
TBA-PB(2 % )
60
TBBA-TEG-PB
7o
MTEB-PB TEG-PB Duolite A101 Duolite A171 Duolite A161 IRA 904
70 70 60 60 60 60
k, min-' mor2 L2 rb 30.43 0.996 2.02 X lo-' (6.60 X 10-2)c 5.76 X lo-' (1.32 X 0.993 6.89 X lo-' (2.90 X 0.991 1.44 X lo-' 0.996 2.55 X 0.996 4.21 x 0.994 6.54 X 0.989 2.15 X 0.994 run 1 no conversn run 2 5.72 X 0.968 0.985 run 4 1.17 X lo-' 0.958 run 2 6.48 X
0.978
run 4 1.12 x lo-'
0.991
run 2 6.32 X 2.26 X 1.61 X 1.28 X 1.24 X 5.37 x 10-3 9.86 x 10-4
0.989 0.953 0.974 0.980 0.980 0.999 0.945
"If not otherwise indicated. *Correlation coefficient for -[ln (1y)] vs time plots. Data referred to the apparatus BR-MS. dThis soluble catalyst has been added as the last component.
114 g of a polymeric product containing 18% etherified units was obtained. Amination of Poly(chloromethy1styrene-co styrene-co -divinylbenzene) with Tri-n -butylamine (Table V). A mixture of 100 g of polymeric product, 100 mL of 1,2-dichloroethane, 0.4 g of NaOH, and 100 mL of tri-n-butylamine was heated at reflux for 24 h. After cooling, the solid was filtered, washed with water and dichloromethane in this order, and dried under vacuum to give 134.8 g of product containing 44.1% quaternary ammonium groups. Analyses. Gas chromatographic analyses were carried out with a Packard 438 flame-ionization gas chromatograph equipped with a stainless steel column (2 m x in.) filled with 3% silicon oil SE 30 or Chromosorb WHP, 8O/lOO mesh. The initial column temperature (60 "C) was increased after 4 min at a rate of 20 "C/min to 200 "C. Nitrogen at 3 atm was used as carrier gas with a flow rate of 20 mL/min. Detector and injector were maintained at 300 "C. Calibration factors (referred to PAN) were determined with two standard mixtures. The retention times (min) and calibration factors for the different reaction components are, respectively, PAN 10, 1; butyl bromide 2.8, 1.57; toluene 3.95, 1.02; monoalkylated PAN 13.15, 0.649; and dialkylated PAN 17.2, 0.508. Alkylation Experiments. The following standard procedure, if not otherwise indicated, has been adopted to perform kinetic experiments with FB reactors. The catalyst was placed in tubular reactor C (Figures 1 and 2) between two quartz wool layers; then reagents were added: a NaOH aqueous solution (50/50 w/w) and PAN were stirred and heated at the reaction temperature, recirculated for 2 h through the catalytic bed and then toluene and butyl bromide were added. At this point the kinetic experiment was considered started. The experiments with a slurry reactor (SR) were performed in the same way with the catalyst suspended in the reaction mixture and con-
Table VII. Kinetic Constant Values for PAN Monoalkylation Obtained in the Presence of TEBA-PB(12%) Catalyst Using Different Reactors apparatus temp, O C k, min-' m o P L2 X lo2 SR-UM 70 5.45 . ~. 4.21 FB-UM 2.55 70 SR-TS 1.63 1.59 FB-TS 70 1.19 FB-TP 0.72
1;:
2.56 I
I
I
I
I
I
FB-UM TEBA- PB (12%)
c
1
0
66 7
I
I
I
133
200
267
time ( m i d
Figure 3. Pseudo-first-order plot for catalyst I1 (TEBA-PB) used in a fixed-bed reactor with ultrasonic mixer (FB-UM).
ditioned as above under magnetic stirring. The recycling experiments in series 1-3 (Table VI) were carried out in the same way by washing, at each run end, the catalyst with a water/toluene mixture and reusing it without any further treatment in the successive run. Typical PAN/catalyst and butyl bromide/catalyst molar ratios of 50-100 and 250-500 were used, respectively. For the most active catalysts (TBA and TEBA), the molar ratios PAN/catalyst were 8000 and 200, respectively.
Results The activities of the different catalysts and the performance of the experimental apparatus were evaluated from the kinetic measurements. In particular, the constant k for the reaction (Scheme I) was obtained through integration of the kinetic equation, expressed in the forms d[PAN]/dt = k[Cat][BuB][PAN] (1) d[PAN]/dt = kqPAN]
(2)
where [Cat], [BuB], and [PAN] are the molar concentrations (mol/L) of catalyst, alkylation agent, and phenylacetonitrile, respectively. The kinetic constant k' = k[Cat][Sub], as derived from eq 2, represents the pseudo-first-order rate constant (l/min) when [Cat] and [BuB] are taken as practically constant. According to the previous suggestions (Solar0 et al., 1980; Dehmlow and Dehmlow, 1980),the alkylation should occur in the organic phase and concentrations are referred to the volume of this phase. The values of k , as evaluated from k'values, are reported in Table VI for the different catalysts at 40-80 "C. In Table VI1 the kinetic constant values obtained in the different apparatus with the same catalytic system, TEBA-PB(12%) are collected. In Figures 3-5, the values of -[ln (1- y ) ] vs time ( t )are plotted, y being the relative molar conversion of PAN at a certain time t as defined by (3) Y = ([PAN],=, - [PANlt)/[PANlt
1386 Ind. Eng. Chem. Res., Vol. 27, No. 8, 1988 5 33
I
I
I
I
BR-UM TEBA
'/ /?-'
1
/
I!
5
-
2 67
L
I
.
A/-///-L
II
/"I
-
/ -/-
L(,=/-_-Y
,
,
,
,
,
1
,
/-
0
48
96
144
192
240
time ( m i d
Figure 4. Pseudo-first-order plot for catalyst I11 (TEBA) used in a batch reactor with ultrasonic mixer (BR-UM).
FB - UM TBBA-TEG-PB (70°C)
I
time ( m i d
Figure 5. Pseudo-first-order plot for catalyst IV (TBBA-TEGPB) used in a fixed-bed reactor with ultrasonic mixer (FB-UM).
For the catalyst TBBA-TEG-PB, three sets of data are reported as collected on experiments carried out at 7 0 "C by reusing the catalyst recovered from the reaction medium.
Discussion The interpretation of the experimental results according to pseudo-first-order kinetics (eq, Figures 3-5) does not provide a satisfactory interpretation of the experimental trends. However, considering that the correlation coefficients ( r ) of the linear plots of -[ln (1- y)] vs t are sufficiently close to 1 (Table VI), the use of kinetic constants (k)to compare both the activities of the catalysts and the performances of the experimental apparatus can be considered as a valuable tool. In a forthcoming paper, a more detailed kinetic analysis of PAN monoalkylation both in the absence and in the presence of a catalyst, under different conditioning procedures for the catalyst, will be reported (Ragaini et al., 1988). Before making a comparison of the catalysts, it is necessary to note (see Table VI) that the TBBA-TEG-PB activity as tested in three different series of experiments is very sensitive to its preconditioning history. In fact, the first experiment in each series carried out with the original catalyst did not show any appreciable conversion of PAN, whereas, the fourth experiment of series 1 and 2 exhibits a very high and comparable rate constant.
Within the limits of the fairly low number of sets of experiments performed and the uneven trend in the absolute rate in going from the second to the fourth experiment in series 1 and 2 , we may conclude that self-activation of the catalyst occurs in reuse because of better accessibility or proper solvation of the catalytic sites caused by a TEG neighboring effect. A better understanding of that behavior will require a more detailed study of the effects exerted by the bulk morphology (porosity and surface area) of the polymer matrices, the relative content and the distribution of quaternary ammonium groups and TEG residues. Taking into account only the experiments where maximum activity was observed, the following relative order of catalytic activity can be drawn: TBA >> TEBA > TBBA-PB > TBBA-TEG-PB > TEBA-PB(12%) > TEBA-PB(2%) > M T E G P B > T E G P B > Duolite A101 Duolite A171 > Duolite A161 > IRA 904. The performances of the different reactor configurations as evaluated using TEBA-PB( 12% ) as catalyst (Table VII) were in the following order: SR-UM > FB-UM > SR-TS FB-TS > FB-TP. From the data reported in Table VI, the activation energies (hE *, kcal/mol) have been evaluated for the following catalytic systems: TEBA in BR-UM mode, 9.1 f 0.9; TEBA in BR-MS mode, 9.97 f 1.2; TEBA-PB(12%) in FB-UM mode, 11.0 f 0.1. The use of an ultrasonic mixer as a stirring system decreases by about 10% the value of hE* (Ragaini et al., 1986).
Conclusions The alkylation of PAN performed in the presence of conventional PT catalysts and ion-exchange-type catalysts under different experimental conditions supports the following remarks. Soluble, low molar mass catalysts (TBA and TEBA) were more reactive than the corresponding polymer-supported catalysts under all the adopted experimental conditions. Among the insoluble polymer catalysts, however, those specifically synthesized were more active than the corresponding commercial insoluble anion exchangers. Comparing the polymer-supported catalysts and the soluble low molar mass quaternary ammonium salts, the following order of activity was detected: TBA >> TEBA > TBBA-PB > TBBA-TEG-PB > TEBA-PB(lB%) > TEBA-PR(2%) > M T E G P B > T E G P B > Duolite A101 = Duolite A171 > Duolite A161 > IRA 904. For all the insoluble catalysts, the ultrasound mixer system (UM) was 2-4-fold more efficient than the conventional magnetic or mechanical stirring modes and turbine stirrer. A better performance in terms of specific activity for insoluble catalysts was obtained in reactions carried out under slurry conditions (SR). The relative efficiency for different experimental configurations and apparatus as evaluated in the presence of the same insoluble catalyst (TEBA-PB(12%)) was as follows: SR-UM > FB-UM > SR-TS FB-TS > FB-TP. The polymer-bound tributylbenzyl ammonium chloride catalyst used in the FB apparatus with an ultrasonic mixer of suitable geometry (Figure 1)can reach a reactivity close to that shown by the soluble analogue TEBA in the monoalkylation of PAN. Therefore, the advantage and the potential of the FB technique in the use of insoluble phase-transfer catalysts (Ragaini et al., 1980, 1986) is confirmed. At present, the technique allows for easy recycling of the catalyst, which does not suffer any appreciable loss of activity through thermal decomposition. The contemporary presence of tetraethylene glycol (TEG) and triethylbenzyl ammonium groups within the same polymeric matrix seems to decrease the specific ac-
Ind. Eng. Chem. Res. 1988,27, 1387-1390
tivity of the quaternary ammonium groups. Interestingly, the activity, started from an almost zero value increased during recycle experiments and reached values close to that of the fully quaternized polymer after three experiments. FB reactors with ultrasonic mixer, on the other hand, reached a level of performance comparable to those obtained in a slurry reactor. The latter system possesses the drawback of uneven recycle of the catalyst because of the grinding and collapsing of the catalytic particles. It has been confirmed that the substitution of conventional stirring modes by an ultrasonic mixer decreases the activation energy of the reaction by at least 10%. Acknowledgment The authors thank the Italian National Research Council (C.N.R.) Fine and Secondary Chemistry Finalized Project for partial financial support. Registry NO.PAN, 140-29-4;TBA, 2052-49-5; TEBA, 56-34-8; C4H$r, 109-65-9NaOH, 1310-73-2;CBH,CH(C4H9)CN, 3508-983;
1387
IRA 904, 9050-98-0; Duolite A161, 64427-61-8; Duolite A171, 75366-89-1;Duolite A101, 92307-93-2. Literature Cited Balakrishnan, T.; Ford, W. T. Tetrahedron Lett. 1981, 44, 4377. Balakrishnan, T.; Ford, W. T. J . Org. Chem. 1983, 48, 1029. Dehmlow, E. V.; Dehmlow, S. S. Phase Transfer Catalysis; Verlag Chemie: Weinheim, 1980; p 32. Komeili-Zadeh, H.; Dou, H. J.-M.; Metzger, J. J . Org. Chem. 1978, 43, 156. Ragaini, V.; Saed, G. 2.Phys. Chim. N . F. 1980, 119, 85. Ragaini, V.; Verzella, G.; Ghignone, A.; Colombo, G. Znd. Eng. Chem. Process Des. Deu. 1986, 25, 878. Ragaini, V.; Chiellini, E.; D'Antone, S.; Colombo, G.; Barzaghi, P. Universiti di Milano, Department of Physical Chemistry & Electrochemistry, unpublished results, 1988. Solaro, R.; D'Antone, S.; Chiellini, E. J. Org. Chem. 1980,45, 4179. Steere, N. V. J . Chem. Ed. 1975, 52, A419.
Received for review July 20, 1987 Revised manuscript received January 21, 1988 Accepted March 21, 1988
Conversion of Methane to Oxygen-Containing Compounds by the Photochemical Reaction K o t a r o Ogura,* C a t h a r i n a T. Migita, and M i n o r u F u j i t a Department of Applied Chemistry, Yamaguchi University, Ube 755, Japan
The oxidative photolysis of methane was studied in the presence of water vapor and air a t 100 "C and in atmospheric pressure. The major products were oxygen-containing compounds involving methanol, formaldehyde, acetic and peracetic acids, formic acid, and carbon dioxide. The reactions gave 4-16% conversions with a selectivity in methanol exceeding 33%. Hydroxyl radicals which are formed by the photolysis of water vapor activate methane by hydrogen abstraction in the first step in the synthesis, and the reaction pathway of the products is discussed. The activation of methane is a prevailing subject that commands considerable attention derived from interest in conversion of methane to a more worthy substance. Methane is the dominant ingredient of natural gas and occurs more widely throughout the world than raw petroleum. It is then desired to open up new avenues of use for methane except that as an energy source. Many approaches have been tried for methane activation, but a technologically promising process in which methane is directly used as a raw material under mild condition has not been developed. Recently, the monohalogenation of methane has been catalytically achieved over supported solid acid such as FeO,ClY/Al2O3at temperatures between 180 and 250 "C (Olah et al., 1985). Kitajima and Schwartz (1984) employ silica-supported rhodium complexes in the catalytic chlorination of methane, and their products were methyl chloride and hydrogen chloride with lesser amounts of other chlorinated methane. Photoactivation of methane has been paid attention to from the fundamental as well as the technological points of view. The mercury-sensitized photolysis of methane gives H2, C2H4, C2Hs,C3H8,etc., for which a mechanism involving "hot" hydrogen atoms is proposed due to the very small value of the temperature coefficient obtained (Mains and Newton, 1961). Rebbert and Ausloos (1968) have photolyzed methane with a helium resonance lamp and observed that about 95% of the protons absorbed lead to ionization according to CH4 + hv [CH4+]*+ e-. [CH,]* may dissociate into CH3+or
-
CH2+ or react with CHI to give CH6+and CH3. In the economic application of methane, however, photochlorination is one of the most encouraging processes of activation (Dumas, 1840; Chaktravarty and Dranoff, 1984; Ogura and Takamagari, 1986). However, this process lacks selectivity and generally yields mixtures of chloromethanes, which is similar to the case in thermal chlorination. Methyl chloride is chlorinated more rapidly than methane itself; so if methyl chloride is the desired product, a ratio of methane to chloride of at least 1O:l is required (Jones and Allison, 1919). Although the partial oxidation of methane is very important in the technological aspect, little fundamental work has been reported on the process. Liu and Lunsford (1982) and Liu et al. (1984) found that nitrous oxide is a fitting oxidant and molybdenum supported on silica is an operative catalyst for the conversion of methane to methanol and formaldehyde. Solymosi et al. (1985) report the partial oxidation of methane by N20 over a Sn02-Bi20, catalyst which leads to formaldehyde with a selectivity of 95-84% at 1.7-2.7% conversion at 550 "C. The direct conversion processes of methane to a more valuable compound practiced industrially and proposed so far are confronted with many problems if methane is designed as a raw material on an extensive scale. The following points may be indicated: (i) severe reaction conditions; (ii) low selectivity and conversion efficiency; (iii) not a very worthy product; Le., oxygen-containing C2 species are seldom obtained.
0888-5S85/88/2627-1387$01.50/0 0 1988 American Chemical Society
