Removal and Recovery of Phenols from Industrial Waste Effluents with Amberlite XAD Polymeric Adsorbents Evan H.Crook,* Roger P. McDonnell, and James T. McNulty Rohm and Haas Company, Phdadelphia, Pennsylvania 19137
Industrial waste effluents containing 280-6700 ppm of phenol, condensed phenol (bisphenol A) or substituted phenol (p-nitrophenol) were passed through columns containing Amberlite XAD polymeric sorbents in order to remove the phenolic compounds. Using Amberlite XAD-4 a total of 87 g/l. of phenol could be removed from a waste effluent containing 6700 pprn of phenol with the resultant effluent from the resin containing < I ppm of phenol leakage. Regeneration of the resin could be effected by an acetone or MeOH treatment. Acetone for recycle in the regeneration step and phenol (99Y0purity) could be recovered by distillation. Bisphenol A may be removed from a waste stream (280-910 pprn of BPA) by passage through columns of Amberlite XAD-4 and XAD-7. The capacity of XAD-4 and XAD-7 for BPA was 34 and 16 g/l., respectively. The resin was efficiently (95-100%) regenerated with 4 % NaOH. p-Nitrophenol (1248 mg/l.) was removed from an industrial waste stream by pa'ssage of the effluent through a bed of Amberlite XAD-7. The resin had a capacity of 40 g/l. at a breakpoint of 7.0 mg/l. The resin was efficiently regenerated with ethanol.
Introduction The presence of phenol and phenolic compounds in industrial waste effluents has become an increasingly important source of stream pollution due to the direct discharge of such wastes into our waterways. With increased governmental pressure to reduce phenol concentration in effluent streams to 0.1 mg/l. or less it has become increasingly important to develop processes which can accomplish this objective and a t the same time permit the recovery of phenol in a useful form. Recently it has been demonstrated that Amberlite XAD polymeric adsorbents can remove substantial quantities of phenolic compounds (Paleos, 1969) from aqueous solution and also have the added benefit of being easily regenerable with nonaqueous solvents or caustic solution. In many cases this permits the recovery of the phenolic material in a useable form. The Amberlite XAD adsorbents are hard, insoluble beads of porous polymer characterized by a spectrum of surface polarities and by a variety of surface areas, porosities, and pore size distributions (Gustafson, 1970; Albright, 1972). Because of the difference in surface properties, the polymeric sorbents display a wide range of sorption (via van der Waals forces) behavior and can be employed in both aqueous and nonaqueous systems. The individual 0.5-mm diameter resin beads are highly porous structures which consist of many small microspheres whose diameter is as small as l o T 4mm. This macroporous structure coupled with normal ion-exchange bead particle size results in good hydraulic properties coupled with rapid kinetics of adsorption. The physical properties of the Amberlite polymeric sorbents are presented in Table I. Of the adsorbents presented in Table I the first two are nonpolar and the latter two are of intermediate polarity. In general the nonpolar adsorbents are very effective for adsorbing nonpolar solutes from polar solvents. Conversely, the highly polar adsorbents are most effective for adsorbing polar solutes from nonpolar solvents. In general practice one uses the adsorbent with the highest surface area having a suitable polarity. A basic limitation, however, is the size of the molecule being adsorbed. Since the average pore diameter of the sorbents decreases as the surface area increases, one must recognize that with large molecules i t will be necessary to use an adsorbent with
larger pores and consequently less surface area so that molecular diffusion may occur more rapidly. The following describes some of our experience in which Amberlite XAD-4 and XAD-7 polymeric sorbents have demonstrated excellent phenol removal from waste streams and have permitted substantial recovery of phenol for recycle in industrial processes. Experimental Section Exhaustion runs were carried out in either buret (1-cm diameter) or 1-in. diameter columns containing 20 or 400 ml, respectively, of polymeric sorbent. The flow of waste effluent in all cases was downflow. Regeneration of the resins was also carried out in a downflow fashion. Resins. Amberlite XAD-4 and XAD-7 polymeric sorbents were preconditioned before use by passing 5-7 BV of methanol through beds of the resins and rinsing the beds with deionized water (4-5 BV). Results a n d Discussion Phenol. An acidic (pH 1.5) waste stream which contained 3000-6700 ppm of phenol (also small quantities of other phenolic compounds and ca. 5000 ppm of NaCl) was studied for phenol removal using Amberlite XAD-4 polymeric sorbent. Before passage through the XAD-4 resin the partially neutralized (pH 3-7) effluent was pumped through cartridge fiber filters to remove trace amounts of suspended solids. Effect of Flow Rate a n d Concentration. Waste effluents containing 3000 ppm of phenol and 6700 ppm of phenol, respectively, were passed through Amberlite XAD-4 (1-in. diameter, 400 ml, 32-in. bed depth) a t flow rates of 2, 3, and 4 BV/hr. In all cases the resultant phenol leakage was 0.1 ppm or less (limit of phenol detectibility with the aminoantipyrene method) up to the break point. The pH of the influent varied only between 6.4 and 6.8 in all the runs and thus was not a major factor in determining leakage or capacity. The data obtained are presented in Figure 1. At 6700 ppm influent phenol concentration the capacity of Amberlite XAD-4 polymeric sorbent for phenol is (to 1 ppm leakage) 87 g/l., while a t 3000 ppm influent concentration the capacity decreases to 72 g/l. At influent concentrations of 12) and contained 51% dry solids. The p-ntrophenol content of the stream varied from 700 to 1300 ppm. Since the raw waste stream was highly alkaline it was necessary to adjust its pH to a lower value in order that polymeric sorbents might remove maximum quantities of the residual p-nitrophenol. Also, before pH adjustment was carried out solid precipitated materials had to be removed by settling since such insoluble materials would restrict flow through the sorbents. A final clarification of the settled, pH adjusted solution was carried out by passing the stream through a ys in. thick pad of diatomaceous earth. The resultant intense yellow aqueous stream was then passed through a 20-ml bed (ca. 9 in. bed height) of Amberlite XAD-7 adsorbent a t a flow rate of 8 BV/hr and a t a temperature of 50°C. The results of this study are presented in Figure 6. Three cycles of loading runs a t 50°C with the same resin are shown. The data show a n average leakage of 5-6 ppm of p-nitrophenol over the major portion of the run (ca. 32 BV). There is no decrease in capacity due to organic fouling within the scope of the three-cycle loading studies. Also shown for comparison in Figure 6 is a loading curve (for the p-nitrophenol waste) which was carried out a t 25°C. There is no significant advantage to reducing the temperature of the effluent from 50 to 25'C in order to improve either leakage or resin capacity. In order to determine if increased bed depth would improve the leakage of p-nitrophenol through the Amberlite XAD-7 resin, a run was carried out using 200 ml of resin contained in a 1-in. diameter column (bed depth = 38 cm = 15 in.). The waste effluent was passed through the Amberlite XAD-7 adsorbent a t the same flow rate as was used in the burette column studies. The results are also presented in Figure 6. Use of the 1-in. diameter, 15-in. bed depth column of XAD-7 does not afford a substantial improvement in either leakage or capacity a t the flow rate of effluent studied. Comparison of the leakage curves (Figure 6) predicts that in order to meet an effluent cumulative leakage of 7 ppm it will be necessary to load the bed to a 20 ppm endpoint through 32 BV (leakage 1.6% of influent concentraInd. Eng. Chern., Prod. Res. Dev., Vol. 14, No. 2, 1975
115
6000 P P M PHENOL
I
TO S E W E R
500
-
/
I
1
I I
I
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I
0 I6O o O
I
ii
400
t
< 300
200
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Figure 7. Regeneration of Amberlite XAD-7 loaded with p-nitrophenol using ethanol; flow rate = 2 BV/hr.
Figure 6. Removal of p-nitrophenol from a waste effluent using Amberlite XAD-7; p-nitrophenol concentration = 1248 ppm; 0, cycle 1, 50°C, 0 , cycle 2, 50°C; 0 , cycle 3, 50°C; A, cycle 1, 2 5 T , 0 ,1 in. column, 50°C.
tion). The calculated capacity for this loading is 40.0 gm/l. ofp-nitrophenol(2.49 lb/ft3). Regeneration. Because of the high level of dissolved solids in the influent and the desire to regenerate the Amberlite XAD-7 resin with a nonaqueous solvent it was necessary to wash the resin with deionized water before the regeneration took place. 116
Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 2, 1975
Ethanol was chosen as a regenerant for the XAD-7. The elution of the p-nitrophenol from Amberlite XAD-7 with ethanol is shown in Figure 7. A regeneration efficiency of 97% was calculated for the Amberlite XAD-7 resin (from the 1-in. diameter column run). This result coupled with the multi-cycle (3) results obtained from the buret columns assures us that Amberlite XAD-7 can be used in this application without concern about irreversible organic fouling. In summary, Amberlite XAD-7 can remove substantial quantities of p-nitrophenol (1248 ppm) from a waste effluent with a resultant cumulative leakage of 7 ppm of p-nitrophenol through 32 BV of treated effluent. An or-
1
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I GaL_
I
10
30
20 BV
L-_ 40 50 60
EFFLUENT
Figure 8. Removal of bisphenol A from waste effluent using Amberlite sorbents; concentration of BPA = 910 ppm, flow rate = 2 BVjhr, pH 10.0 and 11.4.
Figure 9. Removal of bisphenol A from a pH adjusted waste effluent using Amberlite XAD-4; concentration of BPA = 280 ppm, flow rate = 2 BV/hr, pH 6.9.
ganic solvent (in this case ethanol) can efficiently regenerate the Amberlite XAD-7 resin.
Bisphenol A Loading. Waste streams containing bisphenol A were investigated for BPA removal using polymeric sorbents. The first stream contained ca. 900 ppm of BPA, 9% NaCl, 1% Na2C03, 0.4% NaOH, and 85% of the BPA was recovered Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 2, 1975
117
Table 111. Capacities of Amberlite XAD-4 and XAD-7 Polymeric Adsorbents for Bisphenol A Resin
Capacity, g of B P A / ~ .
XAD-4 (280 ppm BPA influent, pH 6.9) XAD-4 (910 ppm BPA influent, pH 10.0) XAD-7 (910 ppm BPA influent, pH 10.0) from the resin. It is likely that with further cycling of the resin better accountability of the BPA would be obtained. Also with further study a more efficient regenerant procedure could be defined. Acknowledgment The authors thank Messrs. N. Borenstein, T. L. 0’Neill, S. J . Guogas, J . C. Fanelli, M. C. Bode, N . Golin, and Ms. M. Musella and M. E. Walker for their valuable contributions to this study.
34.0 (50 ppm leakage) 33.4 (71 ppm leakage)
15.8 (47 ppm leakage) Literature Cited Albright, R. L., (to Rohm and Haas Co.), U.S.
Patent 3,663,467 (May 16,
1972).
Gustafson, R. L., (to Rohm and Haas C o . ) , U.S.
Patent 3,531,463 (Sept
29, 1970).
Paleos, J., J. Coiloid Interface Sci.. 31, 7 (1969).
Received f o r review December 19, 1974 Accepted March 11,1975
Presented at the Division of Organic Coatings and Plastics Chemistry, 168th National Meeting of the American Chemical Society, Atlantic City, N.J., September 1974.
Methylcyclopentane Reforming with Platinum-Rhenium Catalyst. Mechanism Studies Douglas M. Selrnan* Exxon Chemical Company, Baton Rouge, Louisiana 70827
Alexis Voorhies, Jr. Louisiana State University. Baton Rouge. Louisiana 70803
The catalytic reforming of methylcyclopentane (MCP) with a commercial platinum-rhenium reforming catalyst has been investigated in an integral, fixed-bed reactor. The catalyst was equilibrated with a virgin naphtha at rather severe reforming conditions. Data were then obtained over a range of pressures (100-400 psig) at each of three temperatures: 800, 850, and 900°F. An extensive investigation of contact time was also made at 850”F, 200 psig, and 10 mol of hydrogen/mpi of MCP and resulted in MCP conversions from 10 to 90%. These tests were all conducted in the a b s m c e of either pore diffusion or external mass transfer limitations. Fresh catalyst had a high hydrogen6lysis activity and produced a large amount of MCP ring-opening products. During equilibration, the hydrogenolysis activity rapidly declined and approached a low, constant value. The data suggest that ring-opening proceeds through at least two different mechanisms, one primarily responsible for isohexanes while the other results in nearly selective formation of normal hexane. Experimental data support the theory that the reaction to benzene proceeds through olefin intermediates with the rate-limiting step being the isomerization of methylcyclopentene to cyclohexene. The data also indicate that the highest selectivity to benzene is obtained when operating at high temperatures and low hydrogen partial pressures.
Introduction The conversion of cyclopentane homologs to aromatic compounds is an important reforming reaction because of the large amounts of the former in reforming feeds and the significant octane improvements to be gained by their conversion. A reaction of this type is the conversion of methylcyclopentane (MCP) to benzene. This particular reaction proceeds through several steps and is accompanied by a considerable number of side reactions which occur on both acidic and hydrogenation-dehydrogenation catalytic sites (Mills et al., 1953; Hindin et al., 1958). 118
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Since its introduction in the early 1950’s, the dual-function platinum-alumina-halogen catalyst has been the standard for commercial reforming. However, this role has in some cases been lessened by the development of “bimetallic” reforming catalysts which contain two metals dispersed on a halogenated alumina. The platinum-rhenium catalyst is one example of this type which has achieved industrial importance. Commercial tests have shown that this catalyst is more resistant to deactivation than the standard platinum catalyst (Jacobson et al., 1969). The objective of the work presented in this paper is a
