Ind. Eng. Chem. Res. 1992, 31, 2122-2721
2722
Press, W. H.; Flannery, B.; Teukolsky,S.;Vetterling, W. Numerical Recipee-The Art of Scientific Computing Cambridge University Press: New York, 1988, Chapter 14. Ritcey, G. M.; Ashbrook, A. W. Solvent Extraction, Principles and Applications to Process Metallurgy, Part Elsevier: New York, 1984; p 26. Seeley, F.; Crow, D. Extraction of Metala from Chloride Solutions with Amines. J . Chem. Eng. Data 1966,11, 424-429. Siepak, J.; Shishkiv,A. The Influence of Donor Atoms of Ligand on the Selectivity of Some PhosphoroorganicExtractante. 2.Chem. 1990,30,413-415. Singh, J.; Gogia, S.; Tandon, S. Equilibrium studies on solvent extraction of zinc(I[), cadmium(I[), and mercury(lI) with naphthenic acid. Indian J. Chem. Eng. 1982,21A, 333-335. Tanaka, M.; Niinomi, T. Extraction of Copper(II) with Capric Acid Dissolved in Benzene. J. Ziwrg. Nucl. Chem. 1965,27,431-439.
Tanaka, M.; Nakasuka, N.; Sasane, S. Extraction of Nickel with Capric Acid. J. Inorg. Nucl. Chem. 1969,31, 2591-2598. Tavlarides, L.; Bae, J.; Lee,C. Solvent Extraction,Membranes, and Ion Exchange in Hydrometallurgical Dilute Metala Separation. Sep. Sci. Technol. 1987,22, 581-616. Web, S.;Grigoriev, V. The Liquid Membrane Process for the S e p aration of Mercury from Waste Water. J. Membr. Sci. 1982,12, 119-129. Wiencek, J. M. Liquid Membrane Separations Employing Non-ionic Microemulsions. Ph.D. Dissertation, Case Western Reserve University, 1990. Wiencek, J.; Qutubuddin, S. Microemuleion versus Macroemuleion. J. Membr. Sci. 1989,45, 311-312. Received for review May 11, 1992 Accepted September 16, 1992
Sorption Kinetics of Cobalt in Chelating Porous Membrane Satoshi Konishi, Kyoichi Saito,* and Shintaro Furusaki Department of Chemical Engineering, University of Tokyo, Hongo, Tokyo 113, Japan
Takanobu Sugo Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Watanuki, Takasaki 370-12, Japan
Glycidyl methacrylate was grafted onto a microfiltration hollow-fiber membrane. Subsequently, the produced epoxide group was converted into an iminodiacetate (IDA) group. The cobalt solution was permeated across the chelating porous membrane through the submicron-diameter pores. The efficient removal of cobalt ion during permeation was demonstrated by the resulting breakthrough curve. Furthermore, the profile of the amount of cobalt sorbed a c r m the membrane was determined as a function of the effluent volume by X-ray microanalysis ( X U ) . The shape of the breakthrough curves was not dependent on the liquid residence time, and the regular propagation of the XMA line profile equivalent to that of sorbed cobalt demonstrated that the overall sorption rate was not governed by the diffusional resistance of cobalt ion to the IDA group of the chelating porous membrane. Introduction Collection of ions and proteins during liquid permeation across a modified microfiltration membrane through the pores is extremely effective with regard to mass-transfer rate. For example, a module charged with affinity membranes, where biomolecules are transported by convection driven by the pressure difference, is superior to a bed charged with affinity beads, where biomolecules are transported by diffusion driven by the concentration difference (Brandt et al., 1988). In most conventional ion-exchange and adsorption beds, the overall adsorption rate of ions and proteins is governed by their diffusion rate in the pores of the bead. We have thus far introduced functional groups, i.e., the chelate-forming group (Tsuneda et al., 1991; Yamagishi et al., 1991), ion-exchange group (Saito et aL, 1989a,b), and affinity ligand (Iwata et al., 1991; Kim et al., 19911, into a commercially available microfiltration membrane. The effectiveness of the resultant porous membranes was verified under criteria of liquid permeability, adsorption rate, and capacity. Removal of cobalt is a critical problem for water chemistry in nuclear engineering, since trace amounts of cobalt ion dissolved in pure water used as recirculating water are converted into radioactive species in the reactor of an atomic power plant. Tsuneda et al. (1991) selected an iminodiacetate (IDA, -N(CHZCOOH)~)group among the chelate-forming groups suitable for removal of cobalt ion from pure water. Yamagishi et al. (1991)discovered a method of introduction for a high-density IDA group
without lowering the liquid permeability of the porous membrane. They have demonstrated that a modified hollow fiber exhibited a relatively sharp breakthrough curve of cobalt during permeation. In order to both improve the properties of the functional membrane and determine the operating conditions of cobalt removal by the membrane, further details of the kinetica of cobalt sorption during permeation across the chelating porous membrane are required. The objective of our study was to experimentally elucidate the kinetica of efficient removal of cobalt ion during permeation by means of two measurements: measurement of the breakthrough curve of the liquid permeated across the membrane and determination of the profile of the metal sorbed a c r w the membrane by X-ray microanalysis. Experimental Section Prepnration of Chelating Porous Membrane. Figure 1 shows the chemical structure of an iminodiacetate (IDA)-group-containing hollow fiber, as compared with commercial IDA beads based on a poly(styrendiviny1benzene) network. The chelating porous membrane prepared here bears its share of functions: polyethylene as a trunk polymer has high chemical stability, whereas an IDA-groupcontaining graft chain as a branch polymer has a high affinity for metal ions. The preparation scheme of the chelating porous membrane consists of four steps: (1) irradiation of electron beams onto a trunk polymer, (2) grafting of glycidyl methacrylate (GMA, CHz= CCH3COOCHzCHOCH2)in a GMA/methanol medium,
0888-5885/92/2631-2722$03.00/00 1992 American Chemical Society
Ind. Eng. Chem. Rea., Vol. 31, No. 12, 1992 2723 I
- - --CH-CH,-CH-CH,-I
-
-
"=0
-
0- COCH,CHCH,OH
9110
I OH
I 0
O-. 0
I
I
COCH,CHCH,OH I 0 OH
211 I
( a ) conventional poly(styrene-divinylbenzenel-based bead
.
I 0
I 0-
.
1
O-.
. .
0
I
(b) novel polyethylene-based membrane
Figure 1. Comparison of chemical structures of chelating materials.
(3) conversion of the produced epoxide group into the IDA group, and (4) hydrolysis of the remaining epoxide group into a diol group. Commercially available hollow fiber (Asahi Chemical Industry Co., Ltd., Japan) was used as a trunk polymer for grafting. The inner and outer diameters of this hollow fiber were 1.95 and 3.01 mm, respectively. This hollow fiber was made of a porous polyethylene with nominally 0.34-rm-diameter pore size and 72% porosity, and was industrially used as a microfiltration membrane. Detailed reaction conditions are described in our previous publication (Yamagishi et al., 1991). The degree of GMA grafting, defined by eq 1, was set a t 200%. dg = lOo[(W,- WO)/WOl (1) where Wo and W1 are the weights of the original and GMA-grafted hollow fibers. The conversion of the epoxide group into the IDA group, X, and the density of the IDA group per kilogram of the product were defined as follows: w, = wo + (W1 - WJ[X(142 133) + (1- X)(142 + 18)]/142 (2) By converting the above equation, X is obtained as X = [142(W2 - Wo)/(W,- Wo)- 160]/115 (3) and the density of IDA group per kilogram of the product is [X(W,- Wo)/1421/Wz (4) where Wzis the weight of the hollow fiber containing the IDA group. The values 142,133, and 18 are the molecular weights of GMA, iminodiacetic acid, and water, respectively, and the values 142 133and 142 18 in eq 2 mean that the epoxide group of GMA graft chains reacts with the IDA and water, respectively. The resulting chelating porous hollow fiber was referred to as an IDA-T fiber, where T denotes tubular. Properties of IDA-T Fiber. The inner and outer diameters and length of the GMA-grafted hollow fiber and IDA-T fiber in the wet state were determined with a microscope and a scale. After the IDA-T fiber was dried under reduced pressure, the pore volume was determined by the mercury intruaion method. The cross section of the
+
+
+
IDA-T fiber was observed by scanning electron microscopy (SEM). Ultrafiltered water was forced to permeate radially from the inside to the outside of the hollow fiber at a filtration preasure of 0.1 MPa The flow rate of the effluent was converted into the pure water flux (PWF) based on the inside area of the hollow fiber. Breakthrough Curve of Cobalt Ion. Sorption of cobalt ion to the chelating porous hollow fiber was examined by permeation mode. Figure 2a shows the experimental apparatus used for measuring the breakthrough curve, i.e., the concentration change of cobalt in the effluent as a function of effluent volume. The 14-cm-long hollow fiber was positioned in a U-configuration. A CoC1, aqueous solution was used as the feed solution. The feed solution was applied to the inside of the hollow fiber and forced to permeate across the membrane through the pores. The inlet concentration of the CoClZ solution ranged from 5 to 30 mg of Co/L (pH 5.6). The filtration pressure ranged from 0.025 to 0.1 MPa. The effluent penetrating the outside of the hollow fiber was sampled continuously, and its cobalt content was determined by atomic absorption spectroscopy. All experiments were performed at 303 K. X-ray Microanalysis of Sorbed Cobalt. After a prescribed volume of effluent was obtained, the hollow fiber was washed with deionized water and immediately freeze-dried in order to freeze the diffusion of sorbed cobalt. The distribution of the amount of cobalt sorbed across the IDA-T fiber was determined by measuring the characteristic X-ray of cobalt using an X-ray microanalyzer, JEOL JXA-733 model. Elution Curves of Cobalt and Durability for Repeated Use. The 20 mg of Co/L CoClZsolution was fed to the 14-cm-long IDA-T fiber to reach equilibrium. After the fiber was washed with deionized water, the feed was switched to 1 M HC1 to elute cobalt. The flow rate of 1 M HCl was set at 90 mL/h using a syringe pump, as shown in Figure 2b. In addition, to examine the durability of the IDA-T fiber, sorption and elution during permeation were repeated eight times and the amount of sorbed cobalt at each cycle was determined.
Results and Discussion Properties of Chelating Porous Membrane. Figure 3 shows the amount of glycidyl methacrylate (GMA)
2724 Ind. Eng. Chem.
Res., Vol. 31, No. 12,1992
1 FeedTank 2 Flow Controller 3 Pressure Gauge
4 Hollow Fiber
3 Hollow Fiber 4 Micro Test Tube
1 Syringe 2 infusion Pump
5 Measuring Cylinder
( a i hid^ elor me l b l lower Plow rate Figure 2. Experimental appmatus for measuring the sorption and elution of cobalt ion during permeation across the chelating porous membrane. T h e feed wan forced to permeate from the inaide to the outside of the hollow fiber through the porn. The cobalt concentration of the effluent penetrating the outside BCIOBB the hollow fiber wan determined.
Table I. Properties of Chelating Porous Membrane starting IDA-T fiber hollow fiber denree of =aftinn (%), 2w conversion 0.60 IDA group density (mol/!@) 2.0 IDA group density (mol/!&) 8.5 inner diameter (mm) 2.69 1.95 outer diameter (mm) 4.39 3.01 porasity 67 72 flux of pure w a W (m/h) 2.41 2.49 flux of CoCI, solution' (mlh) 3.18 2.54 pore vo~ume-(cma/g) 1.12 2.6 I
I
I .
.
-on
time [min]
figure3. D~ and swelling v8 grafting The swelling ratio wan defined 88 the volume of the Gm-grafted hollow fiber divided by that of the original hollow fiber in the wet state.
grafted onto the microfiltrationhollow-fiber membrane 88 a function of reaction time. The volume swelling of the hollow fiber accompanied b y graft polymerization is also shown in this f w e . Here, the volume swelling ratio was defmed 89 the volume of GMA-grafted hollow fiber divided by that of the original hollow fiber i n t h e wet state. The
I
.
"Kilogram of the IDA-T fiber. 'Kilogram of the starting hollow fiber, where the weight of the starting hollow fiber (W,) can be hy inserting q 1 into q 3 Converted into that of IDA-T fiber (W,) to eliminate WL: wd Wo = 1 + (dg/100)(160 115X)/142. (Filtration pressure = 0.1 MPa
+
entire swelling induced by grafting of GMA in a methanol medium prevented the f f i g of the pores with the grafted
branches. The properties of the IDA-T fiber are summarized in Table I. The IDA group density of the IDA-T fiber amounted to 2 mol/kg of the product, which was twice the
-iurn (a) original membrane
( b ) chelating membrane
Figure 4. SEM picture of em88 section of chelating porous membrane. The dark areas of the photograph indieate the pores (marker = 1 Inn).
Ind. Eng. Chem. Res., Vol. 31, No. 12, 1992 2725
r 1 1 1 1 1 1 1 1 1 1
-1
1 303K
303K
.5 0 0.025 A 0.050 0 0.100
1
0
-
Dimensionless time [-I Figure 5. Effect of filtration pressure on breakthrough curve. The cobalt solution was applied to the inside of the 14-cm-longIDA-T fiber at the inlet concentration of 20 mg of Co/L. The abscissa is dimensionless time defined by eq 5.
density of the commercial poly(styrene-divinylbenzene)-based beads (Mibubishi Kasei Co., 1975). Figure 4 shows the SEM pictures of the cross sections of the original hollow fiber and the IDA-T fiber. Obviously, the IDA-T fiber had a larger pore diameter than the original hollow fiber. The flux of the cobalt solution across the IDA-T fiber increased by 25%, as compared to the original hollow fiber. Breakthrough Curves. As a preliminary experiment, the effect of hollow-fiber length on the shape of breakthrough (BT) curves was examined. A longer hollow fiber produces a larger difference in the pressure along the fiber and leads to a wider distribution in the residence time across the fiber. This resulta in a larger dispersion in the BT curve. The hollow fibers whose length ranged from 3 to 14 cm had no effect on the BT curves because the pressure drop along the fiber lumen was much smaller than the pressure drop across the fiber wall in this range. Figure 5 shows the BT curves as a function of the filtration pressure. In this figure, the ordinate is the concentration ratio of the effluent to the inlet. The dimensionless time as the abscissa, 7 , is defined as 7
= 4diUiCot/(d2 - d:)pbqo
(6)
where C is the concentration of the effluent. V and V, are the effluent volume and the volume whose concentration reaches Cotrespectively. Variation of filtration pressure corresponds to that of residence time of the liquid in the membrane. The mean residence time, t,, can be calculated as t, =
E(d2 - d3/4diUi
2
Dimensionless time [-I Figure 6. Effect of inlet concentration on the breakthrough curve. The cobalt solution was fed at a filtration pressure of 0.05 MPa.
m - ,,
,
I
'
"
'
1
'
j o l a r ratio Co I IDA =I11 -
--- -------------100-
n
"
-
303K I
,
,
.
.
,
,
Figure 7. Sorption isotherm of the IDA-T fiber at 303 K.
itMembrane thickness mm = 0.85
(5)
where di, do,pb, and ui are the inner and outer diameters, density, and flux based on the inside area, respectively, of the IDA-T fiber, and t and Coare the permeation time and concentration of the inlet. The amount of sorbed cobalt, qo, is defined as qo = L"*(CO- C ) dV/W,
1
0
2
(7)
where t is the porosity of the IDA-T fiber. The value t, ranged from 0.86 to 3.45 s, corresponding to pressures of 0.1-0.025 MPa. The shape of the BT curve was constant irrespective of filtration pressure. The lack of dependence of the shape of the BT curves on t , is indicative of negligible diffusional resistance of cobalt ion to the IDA group. Figure 6 shows the dependence of the BT curve on the inlet concentration of cobalt. The BT curves overlapped for the inlet concentration ranging from 5 to 30 mg of
Figure 8. Profiles of amount of sorbed cobalt across the IDA-T fiber. The inlet concentration and filtration pressure were 20 mg of Co/L and 0.05 MPa, respectively.
Co/L. This indicates that the amount of sorbed cobalt in equlibrium with the inlet concentration was constant in this range, as shown in Figure 7. A favorable rectangular isotherm was obtained. This result is reasonable with respect to the much higher stability constant of iminodiacetatecobalt complex of 106.95in 0.1 M KC1 solution at 300 K (Chaberek and Martell, 1952). The equilibrium amount of sorbed cobalt was 89% of the value calculated from the IDA group density assuming the chelation ratio of the IDA group to cobalt ion is unity. XMA Profiles across the Membrane. The intensity of the X-ray characteristic of cobalt, which was proportional to the amount sorbed, and measured across the fiber wall by X-ray microanalysis (XMA). Figure 8 shows XMA line profiles as a function of the dimensionless time ( 7 ) . The XMA line profiles include two features: (1)the line height of the plateau is constant at each 7; (2) the line front regularly proceeds from the inside to the outside with increasing 7. This observation agrees well with the con-
2726 Ind. Eng. Chem. Res., Vol. 31, No. 12, 1992
a
Ideal sorption line,
m
30000r---t
P
I
C
0
0.5
1
1.5
Dimensionless time [-I Figure 9. Comparison of amount of sorbed cobalt between measurements of BT curves and XMA line profile.
centration change of cobalt ion in the effluent, which is indicative of negligible diffusional resistance of the cobalt ion to the IDA group. Figure 9 shows the amount of sorbed cobalt vs the dimensionless time together with an ideal sorption line. Here the amount of sorbed cobalt was calculated from the BT curve as follows:
On the other hand, the line profile of cobalt determined by XMA was converted to the total amount of cobalt sorbed over the membrane:
where y ( r ) is the height of the line profile from the base line as a function of radial distance and y o is the height corresponding to q0 in equilibrium with Co. Five points obtained from the integration of the line profile showed excellent agreement with the values obtained from the BT curves. Deviation from the ideal sorption curve was limited between T = 0.8and 1.4, which was equivalent to the deviation from the ideal BT curve in Figure 6. A complex pore distribution and tortuosity of the porous membrane did not result in an XMA line profile which was completely perpendicular to the base line. The skirt of the line front reached the outside of the membrane at T = 0.9 and the shoulder at T = 1.4. Elution Curves and Durability for Repeated Use. Figure 10 shows an elution curve of cobalt for the IDA-T fiber. The flow rate of 1M HC1 was set at 90 mL/h, which corresponded to t , = 33 s. The amount of sorbed cobalt, 102 g of Co/kg, was eluted quantitatively with 1M HC1. The peak and averaged concentrations of cobalt in the eluate were 22 300 and 10400 mg of Co/L, respectively. All cobalt was eluted by four membrane volumes (about 1.3 mL) of the eluate because there was virtually no dead volume in the chelating porous membrane. Kim et al. (1991) and Briefs and Kula (1992) have demonstrated that the affiiity porous membrane showed efficient elution of the proteins adsorbed in permeation mode. The following two possibilities of chemical instability by acidic eluate were examined (1) the decomposition of the ester group of the GMA graft chain; (2) the conversion of the IDA group into another group. Hrudkova et al. (1977) have reported that a poly-GMA-based bead showed high stability to acid and alkaline solution at ambient temperature. After nine cycles of sorption and elution, no decrease in the equilibrium loading was observed.
(Effluent volume)/(Membranevolume) 1-1 Figure 10. Elution curve. HCl(1 M) wae applied at a constant flow rate of 90 mL/h to the inside of the 14-cm-long IDA-T fiber equilibrated with 20 mg of Co/L CoCl, solution.
The desired kinetics of cobalt removal during permeation across the chelating porous membrane was experimentally elucidated by two independent determinations.
Acknowledgment We wish to thank Kazuo Toyomoto of the Industrial Membrane Division of Asahi Chemical Industry Co., Ltd., Japan for his help in providing the original hollow fiber. Also, special thanks go to Hiroshi Ito of Takasaki Radiation Chemistry Research Institute of JAERI for his valuable advice in performing XIMA. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture, Japan, and from the Kurata Foundation Fund of 1991.
Nomenclature C = cobalt concentration in the effluent, g m-3 Co = cobalt concentration at the inlet, g m-3 di = inner diameter of the hollow fiber, m do = outer diameter of the hollow fiber, m q = amount of cobalt sorbed to the IDA-T fiber, g kg-' q0 = amount of sorbed cobalt in equilibrium with Co, g kg-l r = radial distance, m t = time, s t , = residence time defined by eq 7, s ui = flux based on the inside area of the hollow fiber, m s-l V = effluent volume, m3 V , = effluent volume where C reaches Co, m3 Wo = weight of the original hollow fiber, kg W1= weight of the GMA-grafted hollow fiber, kg W , = weight of the hollow fiber containing the IDA group, kg X = conversion of the epoxide group into the IDA group yo = height of XMA line profile Corresponding to qo y ( r ) = height of XMA line profile Greek Symbols 6 = porosity of hollow fiber Pb = density of IDA-T fiber, kg m-3
T
= dimensionless time defined by eq 5 Registry No. GMA, 106-91-2; Co, 7440-48-4.
Literature Cited Brandt, S.; Gaffe, R. A.; Kessler, S. B.; O'Connor, J. L.; Zale, S. E. Membrane-Based Affmity Technology for Commercial Scale Purifications. Bia/Technology 1988,6, 779-782. Briefs, K.-G.; Kula, M.-R. Fast Protein Chromatography on Analytical and Preparative Scale Using Modified Microporous Membranes. Chem. Eng. Sci. 1992, 47, 141-149. Chaberek, S.; Martell, A. E. Stability of Metal Chelates. I. Iminodiacetic and IminodipropionicAcids. J. Am. Chem. SOC.1952,74, 5052-5056.
Ind. Eng. Chem. Res. 1992,31, 2727-2731 Hrudkova, H.; Svec, F.; Kalal, J. Reactive Polymers. XIV. Hydrolysis of the Epoxide Groups of Copolymer Glycidyl Methacrylate-Ethylene Dimethacrylate. Br. Polym. J. 1977,9,238-340. Iwata, H.; Saito, K.; Furusaki, S.; Sugo, T.; Okamoto, J. Adsorption Characteristics of an Immobilized Metal Affinity Membrane. Biotechnol. B o g . 1991, 7, 412-418. Kim, M.; Saito,K.; Furusaki, S.; Sato, T.; Sugo, T.; Ishigaki, I. Adsorption and Elution of Bovine Gamma-Globulin Using an Affmity Membrane Containing Hydrophobic Amino Acids as Ligands. J. Chromatogr. 1991,585, 45-51. Mitsubishi Kasei Manual Zon-Exchange Resin DZAION; Mitsubishi Kasei Co.: Tokyo, 1975. Saito, K.; Ito, M.; Yamagishi, H.; Furusaki, S.; Sugo, T.; Okamato, J. Novel Hollow Fiber Membrane for the Removal of Metal Ion during Permeation: Preparation by Radiation-Induced Cografting
2727
of a Cross-Linking Agent with Reactive Monomer. Znd. Eng. Chem. Res. 1989a, 28, 1908-1812. Saito, K.; Kaga, T.; Yamagishi,H.; Furueaki, S.; Sugo, T.; Okamoto, J. Phosphorylated Hollow Fibers Synthesized by Radiation Grafting and Cross-Linking. J. Membr. Sci. 1989b, 43,131-141. Tsuneda, S.; Saito,K.; Furusaki, S.; Sugo, T.; Okamoto, J. Metal Collection Using Chelating Hollow Fiber Membrane. J. Membr. Sci. 1991,58, 221-234. Yamagishi, H.; Saito,K.; Furusaki, S.; Sugo, T.; Ishigaki, I. Introduction of a High-Density Chelating Group into a Porous Membrane without Lowering the FLUX. Znd. Eng. Chem. Res. 1991, 30,2234-2237.
Received for review April 15, 1992 Accepted August 17,1992
Triphase Catalysis for Recovery of Phenol from an Aqueous Alkaline Stream Narendra N. Dutta,* Somiran Borthakur, and Gajanan S. Patil Chemical Engineering Division, Regional Research Laboratory, Jorhat 785 006,Assam, India
Use of a polymer-supported phase-transfer catalyst for the removal/recovery of phenol from an aqueous alkaline stream has been demonstrated. Phenol was extracted into the organic phase as phenyl benzoate via reaction with benzoyl chloride dissolved in toluene using two types of catalysts. Catalyst with a tributylphosphonium ion as the active centre was found to be more effective than Amberlite IRA 401(C1) resin catalyst. The apparent reaction rates were found to obey pseudofirst-order kinetics under suitable conditions.
Introduction In a previous communication (Dutta et al., 1992), we presented the results of the esterification reaction between benzoyl chloride and phenols in a two-phase system using hexadecyltributylphosphonium bromide (HTPB) as the phase-transfer catalyst (PTC). Conversion of phenols as high as 99.85% could be achieved within 10-15 min using HTPB and Aliquat 336 (Krishnakumarand Sharma, 1984) as well. Phase-transfer-catalyzed esterification of phenol with various aliphatic acid chlorides gives good quantitative yields of products (Direktor and Effenburger, 1985). Various other classes of reactions under phase-transfer conditions are feasible, and a comprehensive review on the same has been published (Dutta, 1990). Certain products such as benzoates which have commercial value are insoluble in water, and they can be recovered by simple phase separation and evaporation of organic phase. Such an extractive reaction scheme was shown to be quite promising for a phenolic wastewater treatment process. However, for industrial applications, a heterogeneous catalyst in the so-called phenomenon of “triphase catalysis” (Regen, 1975) would be desirable in order to simplify catalyst separation and reuse. Though activity of immobilized PTC is generally low, considerable efforts have been made toward its improvement. For instance, activity can be dramatically improved by using a long spacer chain between the polymer matrix (Tomoi et al., 1986) and the active ion. The most commonly used polymer matrix tested as support for P T C is polystyrene cross-linked with divinylbenzene. A number of commercially available ion-exchange resins such as IRA 401; Dowex 1 x 8 and 1x2; and AGMP-1 contain quaternary ammonium groups. Such resins have been studied as heterogeneous PTCs for al-
* T o whom correspondence should be addressed. 0888-5885/92/2631-2727$03.00/0
kylation (Ragaini et al., 1986,1988) and oxidation (Ido et al., 1986) reactions. In this paper, we report a comprehensive study on the use of a typical ion-exchange resin and a freshly prepared polymer-supported PTC containing phosphonium ion for reaction of phenol with benzoyl chloride.
Experimental Section Materials. Phenol (ArOH), benzoyl chloride (RC1 or RX), and all other reagents were of analytical grade and were procured from reputed firms. Two catalyst types were used. One is a gel-type Amberlite IRA 401(C1) manufactured by BDH Chemical Co. This resin contains quaternary ammonium radical in the matrix consisting of styrene-divinylbenzene copolymer with 8% degree of cross-linking. Pretreatment of the resin was made by NaOH and HC1 to obtain in the final chloride form. The major size fraction, 150-210 pm, obtained by seiving was used for reaction. The other catalyst was prepared as described below. Procedure. A. Preparation of Immobilized Phase-Transfer Catalyst: Immobilizing Tri-n -butylphosphine on Polymer Support. A mixture of 25 g of microporous chloromethylpolystyrene (3.5 mequiv of Cl-/g and 2% divinylbenzene cross-linked), 40 g of tri-nbutylphosphine, and 400 mL of 1,2-dichloropropanewere heated under refluxing condition in Nz atmosphere for about 8 h. After thorough washing in sequence with methanol, acetone, and methanol and drying under vacuum a t 60 OC, the chloride content was determined by a Volhard titration. It has a titer value of 1.15 mequiv of c1-/g. B. Triphase Reaction. Reaction was carried out in a 300-mL fully baffled cylindrical vessel provided with a four-bladed turbine impeller of 1-cm width, sampling port, and feed inlet. The impeller to vessel diameter ratio was 1992 American Chemical Society
