420
Ind. Eng. Chem. Fundam. 1983, 22, 420-425
Schwaha, K.; Bethtold, E. Swl. Scl. 1977. 65, 277. SlnEIC, D.; Balky, J. E. Chem. Eng. Scl. 1977. 32,281. Taylor, K. C.; Sinkevltch. R. M. Ind. Eng. Chem. Rod. Res.D e v . 1983, 22, 45. Unni, M. P.; Hudglns, R. R.; Sihreston, P. L. Can.J . Chem. €ng. 1973, 30, 299. Weinberg, W. H.;Lambert, R. M.; Comrie, C. M.; Linnett. J. W. Sod. Sci.
1972, 30. 299. Wilf, M.: Dawson, P. 1. Surf. Sci. 1977, 65, 399. Wllson, G. R.; Hall, W. K. J . Catal. 1972, 24, 306.
Received for review August 2, 1982 Accepted June 16, 1983
Desorption of Phenol from Activated Carbon by Solvent Regeneration T. Sutlknot and Kenneth J. Hlmmelsteln'~ Department of Chemlcal and Petroleum Englneerlng, University of Kansas, Lawrence, Kansas 66045
Acthrated carbon saturated with phenol has been regenerated with acetone extraction followed by low-pressure steaming, in batch or continuous mode. The regenerated adsorptive capacities are close to that of virgin carbon and stable even at high regeneratlon cycles. A mathematical model Is developed to Characterize the desorption of phenol during the extraction; agreement between the experimental desorption data and the desorption data predicted by the model is good when the governing equation for phenol desorption is assumed to be linear. Experimental data suggest that the rate of desorption increases as the extraction velocity is increased: however. the rate-controlling step of the phenol desorption from the carbon remains to be determined.
Introduction The ability of activated carbon to adsorb compounds at low concentrations has made it a common sorbent in water treatment and other industrial applications. However, the economics of the carbon adsorption process depends very much on the method of regeneration. In the case of the spent carbon with a large quantity of sorbate, regeneration with solvent extraction is economically more attractive than the commonly employed thermal method (Winter et al., 1973). A schematic diagram of solvent regeneration is shown in Figure 1. Early uses of solvent regeneration have been reported by Smisek and Cerny (1970) and Hassler (1963). Recent studies on solvent regeneration of activated carbon have been reported by Wankat and Partin (1980) and Yehaskel (1979). The desorption of a sorbate from the carbon surface by solvent extraction is a partitioning process. When the solubility of a sorbate is higher in a solvent than in the water, the presence of the solvent in the sorption system can reduce the solid-to-liquid equilibrium concentration ratio of the sorbate; thus desorption takes place as the solvent is displacing or mixing with the water. However, Little if anything has been done to investigate the transport phenomena during the solvent extraction process. The desorption process during solvent extraction is important to the effectiveness and economics of regenerating spent carbon with solvent extraction. "his paper presents an experimental study and mathematical models to investigate the characteristics of desorption during solvent extraction of spent carbon. A time-dependent model is developed in this paper to simulate the experimental desorption data from batch and continuous solvent extractions of activated carbon. Experimental Section Materials. Phenol was used as the sorbate in this study since it is representative of compounds used as pesticides Midwest Research Institute, Kansas City, MO 64110. t I n t e r e x Research Corp., Lawrence, KS 66044.
and herbicides and is often a constituent of industrial waste. An aqueous solution at 5000 mg/L phenol concentration was used as the "waste" throughout this study as this concentration was assumed to reasonably represent strong industrial phenolic wastes. Many properties determine whether or not a given solvent is applicable for the desorption of a given sorbate; these properties include solubility of sorbate in the solvent, relative ease of solvent recoverability from the solventsorbate mixture, miscibility or solubility of solvent in water, and other properties such as density and latent heat of vaporization. Acetone is a possible solvent for phenol desorption and is used as the solvent in this study. Analytical. An ultraviolet spectrophotometer was used to analyze aqueous phenol solutions; a gas chromatograph was used to analyze phenol, acetone, and water mixtures. Procedure. Two experiments of solvent regeneration were conducted in this study. One is batch-mode solvent extraction of the spent carbon and the other is continuous (or column) regeneration of activated carbon. Experiments on batch-mode solvent extraction were conducted to generate desorption rate data important to the development or a mathematical model for desorption kinetics. Of course, the conventional basis for analyzing the rate of adsorption or desorption is the isotherm data of the sorbate, solvent, and sorbent system. However, in the actual application of solvent regeneration, the intergranular and intrapore spaces of carbon are filled with water or with other solvent before the regenerant is added. When the regenerant (acetone in this present study) is added to the water-filled carbon, the acetone (regenerant) mixes with and gradually displaces the water before the sorbate can be desorbed from the carbon. Because of this complexity, isotherm data for phenol-acetone-carbon system are not meaningful to characterize the phenol desorption phenomena unless the presence of water in the system is quantitatively taken into consideration. As acetone is added to the water-saturated spent carbon, the concentrations of water in the intergranular and intrapore spaces are constantly changing and are difficult to quan-
0196-4313/83/1022-0420$01.50/00 1983 American Chemical Society
Ind. Eng. Chem. Fundam., Vol. 22, No. 4, 1983
I
Steam.
I
I
Cycle
Second Cycle A Third Cycle 0 Fourth Cycle
t
I
It
0 Firit
f-T
Solvent
I
t
421
I Solvent Decanter
Fresh Adrorber hlvent-Loden Cande mate Time, Minuter
Figure 3. Effluent profiles of phenol desorption in continuous solvent regeneration of activated carbon.
Waste Solvent Recovery Still
Recovered Orgonicr Adsorption Cycle
Solvent Regeneration Cycle
Figure 1. Schematic diagrams of adsorption and solvent-regeneration cycles of activated carbon adsorbers.
r
ixi0-3
* *
8
8 W i t h Stirring
0 Without Stirring
0 0
0
0
0
0
0 I
I
20
IO
0
I
30
Time, Minuter
Figure 2. Phenol concentration in acetone during batch mode extraction.
tify. Therefore, in the present analysis of phenol desorption, the governing equation for phenol desorption is based on the rate data instead of equilibrium isotherm data The procedure for the generation of rate data is described as follows. Two hundred milliliters of 5000 mg/L phenol aqueous solution was added to a bottle containing 1 g of virgin acid-washed carbon. The bottle was agitated on a mechanical shaker until there was no further reduction of phenol concentration. The solution was then drained by gravity and the phenol concentration of the solution was measured to calculate the amount of phenol adsorbed by the 1 g of carbon; 100 mL of acetone was added to the drained carbon in a clean bottle. The bottle was vigorously shaken and l-mL samples were taken a t 2 or 3-min intervals. A similar experiment was conducted without mixing. Figure 2 shows the results of these experiments. The experiment on continuous mode resembles the common process of solvent regeneration (see Figure 1). This experiment was conducted to investigate the phenol desorption process in a realistic mode of solvent regener-
ation. This experiment was also made to generate phenol effluent data with which the mathematical model developed later in this paper could be verified. The procedures for this experiment are described next. The apparatus used in these processes consisted of a jacketed glass column (2.5 cm o.d., and 105 cm long) and a positive displacement pump. Glass wool was used for the support of the activated carbon bed in the column. The column was filled with 216 g of acid-washed virgin carbon (Witco 940,12 X 30 mesh). The adsorption process was started by pumping 5000 mg/L of phenol aqueous solution upward through the carbon column. The flow rate was kept constant at 30 mL/min. About 10 L of 5000 mg/L phenol solution was passed through the column to achieve phenol breakthrough. After the carbon column had been saturated with phenol, the pump was turned off, but the carbon bed was kept submerged in the phenol solution by closing the stopcock a t the bottom of the column. The desorption was started by opening the top stockcock to let the regenerant (acetone) flow into the carbon bed and by simultaneously opening the bottom stopcock such that the effluent was maintained a t the desired flow rate. Samples of the effluents were taken from time to time (at 2-min intervals maximum) for the generation of time-dependent phenol effluent data. All of the effluent was collected to check the overall phenol mass balance during the adsorption and desorption processes. After about 750 mL of acetone (2.7 g of acetone/g of carbon) had been passed through the carbon bed, the bed was drained of all remaining acetone by opening the bottom stopcock. Steam (at 5 psig) was passed through the carbon bed to remove the acetone remaining in the bed. A thermometer was attached in the steam outlet at the bottom of the column. The steaming was stopped when the outlet temperature of the column was about 98 OC.
Experimental Results and Discussion As indicated earlier, Figure 2 shows the results of experiments in batch mode phenol desorption. The bottom line represents the change in phenol concentration without mixing. The top line is the phenol concentration changes under vigorous mixing. As shown, the desorption rate of phenol from the activated carbon varies greatly depending on the convective motion of fluid surrounding the carbon granules. Figure 3 shows phenol effluent profiles from four desorption cycles of the column operation. In the first and second cycles, the acetone flow rate was not constant. Two additional sets of phenol effluent data (third and fourth
422
Ind. Eng. Chern. Fundarn., Vol. 22, No. 4, 1983 0.3 r
R
0
1
2
3
4
5
6
7
Number of C y c l e
Figure 4. Adsorption capacities of solvent-regenerated carbon column during six cycles of operation.
cycles) were generated at a constant acetone flow rate (16 mL/min) . The stability of the regenerated adsorption capacity of the carbon column during the first few cycles of operation are shown in Figure 4. As shown in Figure 4, the adsorption capacities of the acetone regenerated carbon are stable except for the first cycle, which shows a slightly lower capacity than the capacity of virgin carbon. In the first cycle, however, more than 93% of phenol adsorbed in the virgin carbon was desorbed during the acetone extraction. The amounts of acetone and steam used in each of these cycles were kept constant. Despite the differences in acetone flow rates during these cycles Figures 3 and 4 suggest that regeneration Capacities during these cycles are constant as long as the amounts of acetone and steam used in each cycle are the same. However, it is also apparent from Figure 3 that higher flow rates, which mean higher velocities in the carbon-packed column, result in a faster desorption rate as indicated by the higher peak, faster tailing off, and the earlier phenol breakthrough in the first cycle (average flow rate of 20 mL/min) relative to the second cycle (average flow rate of 10 mL/min). This effect of velocity on the desorption rate is in agreement with the effect of mixing in the batch mode desorption result shown in Figure 2, thus confirming that convective transport surrounding the carbon granular directly affects the rate of desorption. The stability of the regenerated capacity after many regeneration cycles is shown in Figure 5. As shown, the regenerated capacity is stable a t higher cycles. Mathematical Model Development Mathematical models for batch and continuous desorption of phenol during regeneration are presented and discussed in this section. These models are developed to simulate the experimental data and to analyze the desorption characteristics. Since the desorption of the adsorbed sorbate is the critical step in the solvent regeneration, a mathematical model for the desorption would be helpful to the design and operation of a solvent regeneration system. The model for column desorption is presented first, followed by the development of model for batch-mode desorption. Mathematical models for sorption and transport phenomena in porous media have been well developed. However, most of the available models and their solutions are derived for the cases where fluid density, fluid velocity, and porosity are constant. The desorption of phenol from carbon by acetone extraction is different from these cases and is more complicated. First, fluid density along the carbon column is not constant as acetone is displacing the
1 10
0
I
I
I
I
20
30
40
50
Cycle
Figure 5. Adsorption capacities of solvent-regenerated carbon column at high cycles. Acetone
1/ /
Z
L A2
= +AZt -
Acetone Dirploc:ingWater Region Water Region
I
1 Water
Figure 6. Acetone extraction in the wet, spent carbon column.
remaining water and as phenol is being desorbed. Second, the phenol desorption occurred only at the column section where the acetone has displaced the remaining water. Third, the accessible void space (integranular and intrapore) for the fluid flow in the carbon column is not constant during the course of desorption because a relatively large amount of phenol was adsorbed on the carbon. Because of these constraints, the use of the available models and their solutions to describe the present case of phenol desorption would not be appropriate without modifications. A simplified model suitable for phenol desorption is discussed next. Development of the mathematical model is based on a phenol mass balance. Consider a volume element (AAz) of a 2r-inside-diameter carbon column (see Figure 6) where the fluid is flowing through the element of the carbon column; the phenol flow rate into the cross section is M d c N I where A = d, Mp = phenol molecular weight, e = voic/%action, and N y signifies the 2 directed flux and (N,,)z its value a t location 2. Similarly, assuming a homogeneous and isotropic void fraction in all sections of the column, the phenol rate of flow out of the element is Mfie(Npz)lz+b. Total phenol in the void space of the element ISAAzC e and its rate of accumulation is therefore Ae(aC,/dt) Az wiere C, is the concentration of phenol in the fluid and t is time. In addition, loss by sorption is -\kAa(l - e ) A z where )I is the flux of phenol per unit external area of the granular carbon and a is the external area of granular carbon per unit volume of the solid carbon. Since in general, rate out - rate in + rate of accumulation + loss by sorption = 0, then
Ind. Eng.
Dividing by Az and A , and taking the limit of Az to zero, we get
Since
M$J,z = UZC, + Jpz
(3)
according to Fick’s law
Chem.
Fundam., Vol. 22, No. 4, 1983
423
persion was assumed to be negligible because experimental data showed that the breakthrough curves of acetone and phenol were very sharp. Thus,the downward displacement of water by acetone can be considered as plug flow, and eq 6 becomes
where m = e / ( l - e). Phenol desorption does not take place in the section of the column where acetone had not displaced the water, mathematically, aS,/at = 0 at z > Uzt. Furthermore, a uniform initial concentration of phenol on activated carbon along the column, zero phenol concentration at the acetone inlet, and homogeneous initial Dhenol concentration in fluid phase of tge column are assumed. Hence
as,-- 0 _
De is the effective diffusivity of phenol in acetone-water mixture, and U, is the actual fluid velocity in the z direction. Combining eq 2 with eq 3 and assuming De is constant, we get these results
at
(at z
> Uzt)
C, = Cp0 (at t = 0, z = z ) (initial condition)
S, = S,
(at t = 0, z = z ) (initial condition)
C, = 0 (at t = t, z = 0) (boundary condition) *a(l - e) = 0 (4)
A mass balance of phenol in the solid phase is accumulation =
a(i - e
)
~
~
p
~
at
where S, is the concentration of phenol on activated carbon (g of phenol adsorbed/mL of solid carbon). Since sorption equals *a(l - c)AzA and accumulation sorption = 0, then
+
q A ( 1 - e)
+
a(i - e at
) ~ ~ ,
-V,dS,
..
0 (6) For the case of constant effluent velocity and fluid head, the aUz/az term is approximately zero. In the case where the fluid volume of the carbon bed was kept constant by maintaining constant level of fluid head, then ( UiA - UJ) t = 0 (7) and Vi = U,, where Vi = inlet acetone velocity and U, = outlet effluent velocity. Moreover, since the volume of the acetone-water mixture is approximately equal to the volume of pure acetone added to the volume of water, and assuming the volume of the phenol, acetone, and water mixture is the same as summation of pure volume of each component added, at any section of the column UzIzAt- Uzz+bAt= 0 and az Although the diffusivity of phenol in the acetone-water mixture may be an important term in eq 6, phenol dis-
VdC,
(14)
where V, is the volume of solid carbon excluding the pore volume and Vf is the fluid volume. If V, is the total volume, V, = (1 - e)Vt, and Vf = tVt, eq 14 then becomes -dS, = + mdC,
(5)
Summing up the phenol balances in fluid phase and on solid phase
-auz - -0
As mentioned earlier, the results of the phenol batch desorption rate experiment (Figure 2) are used as the basis for the development of a mathematical expression for continuous phenol desorption rate in the column. In batch desorption of phenol by acetone, the phenol mass balance can be written as eq 14
(15)
Dividing both sides by dt, one obtains
--dS, dt
- m-dCP dt
(16)
At t = 0, S, = a, C, = b, a is the phenol concentration in the solid carbon before extraction; b is the phenol concentration in the liquid remaining in the container. For most time-dependent sorption processes, it is generally known that there exists an equilibrium, fluid-interface sorbate concentration which is in equilibrium with the sorbate concentration on the sorbent. By assuming linear driving force for the mass transfer, the dS,/dt can be expressed as
-dSP- - k(C* - C,)
dt where k is the desorption rate coefficient and C* is the fluid concentration of phenol in equilibrium with S,. As mentioned earlier, the presence of water in the phenol-acetone-carbon system made it difficult to use isotherm data to characterize the equilibrium relationship between C* and S,. Therefore, a linear relationship was assumed and eq 17 can be written as
c* = ps,
(18)
and (19)
Id.Eng. Chem. Fundam., Vol. 22, No. 4, 1983
424
r .E
5x1~-4
1
t- /.
-
m Desorption Effluent Doto i n the Fourth C y c l e
Colculated from Eq. 20
0
0
0
0
0
0
I
0
0
I 30
I
IO
20 Time. Minuter
Figure 7. Phenol concentration in acetone during batch mode extraction. c
where P = the equilibrium ratio between S, and C,. With the Laplace transform method, the solution to S,(t) and C,(t) can be obtained as C, =
("")+ Pm
1 exp[ -(kP
+ k ) t ] + P(
*) + Pm
1
s, =
-,--.-.-.--i' 0
I
I . I1
2.0
3.0
Dimenrionleir Time, I ( = qt/Vp)
Figure 8. Experimental and calculated phenol effluent concentrations.
The finite difference approximation to eq 23 and 24 is listed below. ac - Cin+l- Cin _ ai AI
/3m + 1 { a + bm + m (ab - b) exp[ -(kP + 3 t ] ) 2 (21)
Comparison between the experimental values of C, and C, calculated from eq 20 is shown in Figure 7. As shown, the agreement between the experimental and computed values is fair; thus the expression for dS,/dt is adequate to describe the desorption of phenol by acetone extraction. The expression for dS,/dt in eq 19 is used in eq 9, which becomes
To solve eq 22 numerically, it is converted to a dimensionless equation as
-ac+ - + ac - - = o 1 as
aI
azd
m aI
where I = qt/V, (dimensionless time), q = flow rate of acetone, Vp = pore volume of the carbon bed, zd = z / L (dimensionless length), C = C,/S (dimensionless), S = S,/S, (dimensionless), and L = ged length.
The explicit method of Barakat and Clark (1966)was used for the numerical solution of eq 23. This method is an unconditionally stable explicit procedure for the diffusion equation. It uses forward and backward difference equations, but Satter et al. (1977) have pointed out that from experience the solution of forward difference equation alone is not much different from that of forward and backward difference equations. Only a forward difference equation was used in solving eq 23, for the use of the backward difference equation requires boundary values (at z = U,t) which are not known in the desorption system, when t is less than z/U,.
The superscript n represents the nth increment of dimensionless time, and AI is the dimensionless time interval. The subscript i represents the ith increment of the dimensionless distance zd, and Azd is the dimensionless distance interval. A computer program was developed and the convergence of the solution was checked, allowing a tolerance of less than 1% discrepancy in the computed results Azd and hzd/2. The A I was not changed during each convergence test, but different values of A I were entered to check the stability. The result of computation was plotted in Figure 7 with K1 = 3.2, Kz = 0.9, AI = 0.01, and aZd = 0.0003125. Values of K1 and K 2 were arbitrarily selected and changed until the agreement between the measured data and the computed results is reasonable. The numerical solution of the computer program converged at hzd = 0.0003125; the stability of solution was checked by using a AI value of 0.005, and the results computed with AI = 0.005 agree very well with those computed with A I = 0.01 indicating stability. It can be seen that agreement between the experimental data and computed results is reasonable as shown in Figure 8; this indicates the expression d S /at, (eq 151, is adequate, as a first approximation, to descrige the phenol desorption. It must be noted that an effective void fraction ( E = 0.6) was used and kept constant in the simulation. The void fraction of the carbon column consists mainly of the intergranular spaces. Due to the highly porous nature of the carbon granules, the internal pore spaces of the carbon constitute a significant part of the total void volume. About 40 g of phenol was adsorbed in the carbon column after each adsorption cycle. The phenol is adsorbed on
Ind. Eng. Chem. Fundam., Vol. 22, No. 4, 1983
Scheme I
the carbon surface, especially the intrapore surface of the carbon granule. The carbon column is 419 mL of absolute volume and contains 217 g of activated carbon. The density of phenol in solid phase is about 1g/mL. It can be expected that about 40 mL of the void volume in the carbon column was occupied by the adsorbed phenol. As the adsorbed phenol is dissolved by the acetone, the void volume of the carbon column should increase. This changing void volume is probably the reason why the latter time data points in Figure 8 do not match exactly with the results of the mathematical simulation in which the void volume was assumed constant. By definition, I = qt/ V and V, = tAL; hence, an increase in V, will decrease somewhat. Discussion of the Simulation Results Although the expression chosen for dS/dt adequately fits both column and batch desorption data, physical interpretation of the expression is difficult and the ratecontrolling step in the desorption remains unclear. The dS,/dt expression can be interpreted as external diffusion control or intrapore diffusion control; these interpretations depend on how C* of eq 17 is defined. If C* is assumed to be the phenol fluid concentration at the exterior surface of the carbon granule and C* in equilibrium with S, as defined by eq 18, then eq 19 can be derived and the desorption is controlled by external diffusion. Equation 19 can also be derived if one assumes intrapore diffusion control. If C* is hypothesized as the phenol fluid concentration in the intrapore of the carbon granule and is linearly in equilibrium with S,, then eq 19 can be obtained. Illustrations of these diffusion controls are presented in Scheme I. Since the dSp/dt expression can be regarded either as external diffusion control or intrapore diffusion control, the actual diffusion-controlling step remains unclear. However, the simulated desorption rate constant is significantly larger in the batch desorption under vigorous mixing than in the column desorption. Moreover, the batch desorption rate without any mixing is negligible as shown in Figure 4. Therefore, considering that the desorption rate is dependent upon the degree of mixing, one can deduce that the desorption is controlled by or significantly affected by external diffusion. Further desorption studies at several velocity ranges should be useful to evaluate the extent of the mixing effect and thus may lead to the determination of the rate-controlling step. In any event, the desorption of phenol by acetone extraction can be described by a linear mass transfer driving force equation as shown in eq 17. Conclusions Regeneration of phenol-saturated carbon by acetone extraction has been experimentally investigated and mathematically analyzed. The rate of phenol desorption by batch mode acetone extraction is dependent upon the convective motion between the regenerant and the carbon granules. When there is no convection, the desorption rate is almost negligible. Mathematical models for batch and continuous modes of phenol desorption have been developed. The models simulate the desorption data reasonably well, and the
f
425
desorption of the phenol by acetone extraction can be described by a linear mass transfer driving force equation. However, the diffusion-controlling step of the desorption remains to be investigated. Nomenclature A = cross-sectional area, cm2 a = initial value of S in extraction, g/mL b = initial value of c‘, in extraction, g/mL C = C /C , dimensionless phenol fluid concentration C* = hi8concentration of phenol in equilibrium with S,, g/mL C = phenol concentration in fluid phase, g/mL c‘, = initial value of c,, g/mL Ci” = dimensionless phenol fluid concentration at nth dimensionless time increment and ith dimensionlessdistance increment De = effective diffwionity of phenol in acetonewater mixture, cm2/min I = g t / V , , dimensionless time k = desorption rate coefficient, g/g min L = bed length, cm Mp = molecular weight of phenol, g/g-mol m = e / ( l - E) Npz= 2-directed flux of phenol, g-mol/(min cm2) q = flow rate of regenerant, mL/min S = S,/S,, dimensionless phenol concentration on solid carbon S, = phenol concentration on solid carbon, g of phenol/mL of solid carbon = initial value of S,, g/mL Ss$ i = dimensionlessphenol concentration on solid carbon at nth dimensionless time increment and ith dimensionless distance increment t = time, s U,= fluid velocity in z direction V f = volume of fluid, mL V = pore volume of the carbon bed, mL = volume of solid carbon (includingthe pore volume), mL V , = total volume, mL 2, = a directional parameter, cm
4
Greek Letters a = external area of granular carbon per unit volume of the
solid carbon, l/cm
= equilibrium ratio between S, and C+, dimensionless E = void fraction 9 = flux of phenol per unit external area of the granular
carbon, g/(cm2 s) Registry No. Carbon, 7440-44-0;phenol, 108-95-2;acetone, 67-64-1. Literature Cited Barkat, H. 2.; Clark, J. A. J . Mat Transfer, Trans. A S . M . E . . Ser. C 1888.
as.
Hassier, J. W. “Activated Carbon,” 2nd ed.; Chemical Publisher Co.: New York, 1963. Satter, A.; Shum, Y. M.f Adama, W. T.; Davis, L. A. “Chemical Transport in Porous Medla”,52nd Annual Fail Technical Confergnmce and Exhibition of Society of Petroleum Engineers of America, Instltute of Mining. MetaiiurgIcal, and Petroleum Engineers (AIME). Denver, CO. Oct 1977; AIME: New York. Smisek, M.; Cerny, S. “Activated Carbon, Topics In Organic and General Chemistry”; Robinson, P. L., Ed.; Elsetvier Co.: New York, 1970. Wankat. P. C.; Partin. L. C. Ind. Eng. Chern. Process Des. Dev., 1880. 19. 446. Wlnter, T. H.; Fox, R. D.; Himmeistein, K. J. “Economic Comparison of P h a nolk Waste Treatment”. Internatlonai Environmental Conference, InstiMe of the Engineers at Western Pennsylvania, Pktsburg, PA, Nov 1973. Yehaskel, A. “Activated Carbon-Manufactured and Regenerations”. Noyes Data Co.: New Jersey, 1979.
Received for review August 13, 1982 Revised manuscript received June 21, 1983 Accepted August 3,1983
This research was supported in part by the General Research Fund, University of Kansas.
