Ind. Eng. Chem. Process Des. Dev. 1986, 25, 12-17
12
Randolph. T. W.; Blanch, H. W.; Prausnitz, J. M.; Wilke, C. R. Biotech. Lett. 1985, 7, 325. Rowlinson, J. S.;Swlnton, F. L. “Liquids and Liquid Mixtures”, 3rd ed.: Butterworth: Boston, 1982: Chapter 6. Saltiel, J.; Charlton, J. L. “Rearrangements in Ground and Excited States”; Academic Press: New York, 1980; Vol. 3, p 25. Scott. R. L. Ber. Bunsenges, Wys. Chem. 1972, 76, 296. Scott, R. L.; van Konynenburg, P. 8. Discuss. Faraday Soc. 1970, 4 9 , 87. Simmons, G. M.; Mason, D. M. Chem. Eng. Sci. 1871, 27, 89. Squires, T. G.; Venier, C. G.; Ada, T. F/uM Phase €qul/ib. 1983, 10, 261. Stahl. E.: Quirin. K. W. NuM Phase Eouiib. 1983. 10. 269. Streett, W. B. I n “Chemical Engineerhg at Supercrltikl Conditions”, Pauiaitis, M. E., Penninger, J. M. L., Gray. R. D., Davldson, P., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; p 3. Takahashi, T.; Ehrlich, P. Macromolecules 1982, 75, 714.
Tiltscher, H.; Schelchshorn, J.; Wolf, H.; Dialer. K. Oer. Chem. Eng. 1979. 2 , 313. Tlltscher, H.; Wolf, H.; Schelchshorn, J. Angew. Chem., Int. Ed. Engl. 1981, 20, 892. Tiitscher, H.; Wolf, H.: Schelchshorn, J. Ber. Bunmnws. W y s . Chem. 1984, 88,897. Wheeler, J. C. Ber. Bunsenges. Phys. Chem. 1972, 76, 308. Williams, D. F. Chem. Eng. Sci. 1981, 36, 1769. Winkler, D. E. U.S. Patent 2845461, 1958. Wlnkler. D. E.; Hearne, G. W. Ind. €ng. Chem. 1961, 5 3 , 655.
Received for review May 6 , 1985 Revised manuscript received September 30, 1985 Accepted October 13, 1985
ARTICLES Simultaneous Pyrolysis of Ethane-Propane Mixture in Pulsed Microreactor System Zou Renjun” Hebei Academy of Sciences, Sh#azhuang, China and Hebei Institute of Technomy, Tianjin, China
Lou Olangkun, Zhang Blngchang, CUI Hongwu, Guo Zhushan, and Song Xlaorul Hebei Institute of Technomy, Tlanjin, China
This paper concerns the simultaneous pyrolysis of an ethane-propane mixture in a pulsed microreactor system designed and assembled personally at the fobwing reaction condition ranges: temperature, 759-925 OC;residence time, 0.038-1.1 s; fractional composition, 0-1 .O mole fraction. The ethylene peak yield showed a maximum, up to 57.39 mol % at 880 OC, 0.216 s, in the pyrolysis of a mixture composed of N2:C2H6:C3H8= 0.4975:0.3077:0.1948. The synergistic effect of components of mixed feedstocks has been studied and the deviations of conversion and selectivity from the pure additivity behavior have been correlated and observed. The opposite views of different authors in the chemical literature are then discussed and explained. There are positive deviations of the overall selectivity of ethylene as well as both real and overall selectivities of propylene in simultaneous pyrolysis from these in individual pyrolysis. The results of this paper are of academic and economic significance to the utilization of oil field gas and natural gas resources as well as recycling ethane from ethylene plants using naphtha or AGO as feedstock.
Oil field gas and wet natural gas are composed of light hydrocarbons. These light hydrocarbons, especially ethane and propane, act as excellent feedstocks for olefin plants in petrochemical industry and are receiving worldwide interest. For the sake of economizing on ethane and propane, enhancing ethylene and propylene, saving energy, and making greatest profit, several questions have to be resolved: Which alternative do they prefer, simultaneous pyrolysis (the so called “co-cracking” appearing in some papers) of unseparated ethane-propane mixture or individual pyrolysis of separated ethane and propane? How do the variations in composition of ethane-propane mix-
* In accordance with the authors’ wishes, their family names are listed first. 0196-4305/86/1125-0012$01.50/0
ture and in operating condition of pyrolysis affect the process economics? What is the optimum operating condition for saving ethane and propane and enhancing ethylene and propylene? These questions have to be answered not only at the beginning of an olefin plant project based on ethane and propane feedstock but also for existing ethylene plants using naphtha or AGO feedstock, because they have the problem concerning recyclic ethane and propane returning to ethane cracker and propane cracker. In present paper, the simultaneous pyrolysis of ethane-propane mixtures is studied and compared with the individual pyrolysis of ethane and propane, and there are naturally the answers to above-mentioned questions. Experimental Section The flow diagram of pulsed microreactor system is shown in Figure 1. I t includes the following units.
0 1985 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986 wmnerature
13
1nteRrator
I
4
10
0
20
30
Reactor tube length, cm
Figure 2. The axial temperature profiles of microreactor. Delay c o i l
Figure 1. Flow diagram of the modified pulsed microreactor system. Table I. Propane Pyrolysis at Different Pulses' yield, mf propane no. of pulse C2H4 CIHB convn,mfb 1 0.3925 0.1072 0.7910 2 0.3921 0.1078 0.7865 0.3927 0.1092 0.7909 3 4 0.3845 0.1074 0.7918 0.3924 mean value 0.1079 0.7900 std mean variance 0.0040 0.0009 0.0024 "40 OC, 0.1 s, C3HB:N2= 1:l (mole fraction). bmf = mole fraction.
A. Reactant Sampling Unit. This includes 4-port and 6-port valves, a sampling coil, needle regulating valve, metering valve, manometer, and rotameter. B. Pyrolysis Reaction Unit. The microreactor is made of narrow stainless steel tubing (i.d. of reactor tube 0.198 cm, 0.d. of inner tube of thermocouple 0.163 cm, annular area 0.00992 cm2) and placed in an electrically heated furnace, silicon-controlled regulator ZK-50, thermocouple EU-2, pyrometer XCT-191, potentiometer UJ31, and signal alarm equipment. C. Product Pulse Capturing Unit. This consist of a 6-port valve, delay coil, and pulse-signalyzer. D. ChromatographyUnit. The unit is a dual-channel chromatograph SP-2305 with digital integrator. The operating condition ranges of experiments for studying individual and simultaneous pyrolysis of ethane and propane are shown as below: the composition of the mixture is 0-1.0 (propane mole fraction), dilution ratio nitrogen:hydrocarbons = 1:l (mole fraction), reaction temperature 759-925 "C, residence time 0.038-1.1 s. This system is characterized by some features: the axial temperature profile of the microreactor tube is practically ungradient in the reaction zone (see Figure 2), so for the residence time distribution, the flow pattern for the system as a whole is close to the plug-flow pattern (see Figure 3). As to the operation reproducibility, the experimental data are essentially reproductive; see Table I. The carbon balance is almost closed; see Table 11. The combination of test value reproducibility and carbon balance closure shows the reliability of the equipment and the validity of
J
level
Stirmlur
Response
Figure 3. The stimulus and response curves of the residence time distribution test for microreactor system as a whole.
the analytical techniques by and large. Reaction Mechanism and Data Processing The free-radical reaction scheme for pyrolysis of ethane-propane mixtures had been derived by Froment et al. (1979). The simplified molecular reaction scheme for this pyrolysis system is given as C3H8 C2H4 + CH4 (1) C3H8 + C3H6 + H2 (11) C3H8 C2H4 C2H6 + C3H6 (111) C2H6 + C2H4 + H2 (IV) C2H4 + C& C3H6 + CH4 (V) 2C3H6 3C2H4 (VI) There is a point worthy of note that in simultaneous pyrolysis systems ethane is both a reactant in reactions IV and V and a product in reaction 111. In view of this particular fact in chemistry, in data processing we have to distinguish clearly two kinds of ethane conversions: real and overall conversion, and two kinds of ethylene selectivities: real and overall selectivity. This distinction has not yet been considered by other authores in the chemical literature. A. Overall Conversion. Let us define the overall conversion of reactant component i in simultaneous pyrolysis as - Vbi cy,. = (1)
-
+
-b
v,
vRi
The equation for calculating overall conversion of component i may be written as
Table 11. Carbon Balance in Ethane Pyrolysis" c , 90 in out coking and loss
0.1 100.0 100.0
0.2 100.0 100.0
0
0
" 800 OC, C2Hs:N2= 3 7 (mole fraction).
residence time, s 0.25 0.3 100.0 100.0 98.9 97.7 2.3 1.1
0.4 100.0 97.3 2.7
0.5 100.0 96.5 3.5
14
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986
B. Real Conversion. Let us define the real conversion of reactant component A in simultaneous pyrolysis of an A-B mixture as
3077:O. 1948
N p :C.p6:C+i85O.4975:0.
2.0
The equation for calculating real conversion of reactant component A may be written as a ,= ~ + (*B/*A)NB-A (4)
t
800 o c
C. Yield. We define the yield of product component j in individual pyrolysis of pure reactant component i as
The equation for calculating the yield of product component j in individual pyrolysis may be written as -
0 0
I
0.2
I
I
0.4
I
0.6
I
I
I
Reaidence time 0 ,
I
1 .o
0.8
1
I
1.2
sec
We define the yield of product component j in simulataneous pyrolysis as
Figure 4. First-order plots for simultaneous pyrolysis of ethanepropane mixture.
(7)
paper, the residence time is calculated according to the real flow rate of carrier gas under the reaction condition
The equation for calculating the yield of product component j in simultaneous pyrolysis may be written as Njm=
(APj/APT)
- (ARj/ART)
(8) CSji(ARi/ART)
The equation for calculating the yield of product component j in simultaneous pyrolysis of A-B mixture may be written as
D. Overall Selectivity. The overall selectivity equation of product component j in simultaneous pyrolysis may be written as
Experimental Results and Discussion A. Reaction Order. Figure 4 presents first-order plots of conversion function -In (1- arl)vs. residence time 0. In this figure, arirefers to real conversion of ethane, propane, and ethane-propane mixtures, arC2o, arc30, and am,respectively. The relationship between -In (1 - arl)and 8 in the figure looks very much like a straight line, so that the quasi-first-order reaction could be treated, although the simultaneous pyrolysis is rather complicated. B. Conversion Prediction. The equation for predicting conversion in simultaneous pyrolysis is shown as a, = 1 - (1 - a 1 ) k l ~ / k p
(15)
Zou (1979) has developed the equation for calculating the rate constants of reactant component i in simultaneous pyrolysis as The overall selectivity equation of product component j in the simultaneous pyrolysis of an A-B mixture may be written as Ya; =
Njm
*Aad
+ (1 - *A)&aB
(11)
E. Real Selectivity. The real selectivity equation of product component j in simultaneous pyrolysis may be written as Njm
Yrj = z*ia,i
(12)
The real selectivity equation of product component j in the simultaneous pyrolysis of an A-B mixture may be written as (13) The experimental data were printed by a micro-data processor in accordance with the information from on-line chromatography . F. Residence Time. Zou (1981) has described various definitions of residence time in detail. In the present
k , = exp[a, flJ*llT
+ b,*, + c,T + dll*l,2 + e , P + gl]*ZJ3 + h l ] p
+ ‘L]$lITz
+
+ ml]*i]2T]
(16)
Figure 5 presents the relationship between real conversions of ethane and propane in simultaneous pyrolysis. The calculated propane conversion by eq 15 and 16 are rather close to the experimental results of Froment et al. (1976) denoted by the line. The experimental propane conversions of this paper are higher than both former values. It is thus seen that propane conversion obtained from the pulsed mode is higher than that from the continuous mode. Even if the experimental results obtained from a pulsed microreactor are not yet reproduced closely in commercial flow reactors, the pulsed microreactor system may after all be accepted as a powerful tool for choosing pyrolysis feedstock, comparing relative pyrolysis effects of mixture with different compositions, and seeking better operating conditions in view of simplicity, quickness, and relative validity. The conversions of ethane and propane in simultaneous pyrolysis and different from those in individual pyrolysis due to mutual effects. Figure 6 clearly shows that there are negative synergies of both propane real conversion and
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986 15 0.6
a c t:
1.0
r-
:Tm%
I-
112 : C$i6
O O
0.8
Y
0.5
?a d
-8
d A
X Calculated
0.2
d
0.4
0.3
drc;
3
0.5
-
0.4
i
Figure 5. Experimental and calculated real conversion of propane for various real conversion of ethane: Nz:CzH6:CSH8 = 0.4975:0.3077:0.1948.
0
0.3 -
4
841 'C
.
-
+i
,mol.fr.
CF8 =
0.4975:O. 3077: 0.1948
e"
o,/x
Boo'c
:
,!:::::---
.I
X
0.2
1 .o
I
I
I
I
I
I
I
I
I
l
'
0.1' 0
I 0.2
' ' ' ' '
I
0.6
0.4
Residence time
I
0.8
6,
I
1 .o
sec
Figure 7. Variation of the ethylene fractional yield with the residence time at different temperature.
I n d i v i d u a l conversion
0.6
0.4
,-I a
841 O C N2 :
Cp6 : C f 8
=
0.4975:0.3077:0.1948
0 0
I
I
-
4 A
0.2 sec
I
I
0.2 0.4 Composition
I
I
I
I
y:
5
4
\ I *
ethane overall conversion as well as there is positive synergy of ethane real conversion in simultaneous pyrolysis with respect to their individual conversion, respectively. It will be seen from the above-mentioned mechanism that an amount of ethane is produced from propane, so ethane real conversion is larger than overall conversion as seen clearly by checking curve 3 against curve 5 and comparing eq 1with eq 3. Therefore, there is a positive synergy with respect to ethane real conversion (compare curve 3 with 4) and a negative synergy with respect to ethane overall conversion (compare curve 5 with 4). C. Yield. The ethylene yield varies with reaction temperature and residence time. Figure 7 presents this variation. Figure 8 shows the relationship between ethylene peak yield, optimum residence time, and pyrolysis temperature. These results shown in Figures 7 and 8 are confirmed by the author's previous paper; see Zou (1979). As for the problem concerning the deviation of ethylene simultaneous yield from individual yield, different authors held different points of view (Zou, 1981). Minet and Hammond (1975) held the view of negative deviation; Ross and Shu (1977) held the opposite view. This paper presents the view that there is essentially positive deviation, but sometime negative. This result agrees with that of Froment et al. (1979). Figure 9 presents conversion of ethane and propane and yield of methane and propylene at different temperature. D. Selectivity. There are deviations of ethylene selectivity in simultaneous pyrolysis from that in individual pyrolysis and opposite views of the deviation values in the literature. Froment et al. (1979) held the view of negative deviation. Mol (1981) held the contrary view to them. Goossens (1979) also did not agree with Froment's view,
-
E
-
1 0.2
-
U
0.4
0.2
&
0.6 0.8 1 .o 'fq , propene mol.fr.
Figure 6. Deviation of simultaneous conversion from individual conversion of ethane and propane pyrolysis.
0.4
780
820
900
860
Temperature,
C
Figure 8. Relationship of the ethylene peak yield and the optimum residence time vs. the Pyrolysis temperature: N2:C2Hs:C3Hs = 0.4975:0.3077:0.1948. N2:C$i6:C+18
P
0.4975:O .307710.1948
r
1.0
w-~x-x----x
rl .L(
4 h
0.6
.s' I i!
0.4
$
5
V
0.2
0
740
780
820
Temperature,
860
900
940
O c
Figure 9. Variation of conversion and product distribution with reaction temperature at fixed residence time.
but Hofmann (1980) has supported him. All of them have not made the distinction of these two kinds of ethylene selectivities. The results of the present paper clearly indicate that there is a negative deviation with respect to real selectivity and a positive deviation with respect to overall selectivity; see Figure 10. There are also opposite views of the deviation value of propylene selectivity in simultaneous pyrolysis from that
18
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 1, 1986
I""" 0.1
" ' 1
aec
Table 111. Surface Effect to Ethylene Selectivity in Ethane Pyrolysis at Different Residence Time (800 " C )
ethylene
0.7
residence time, s
i
Y
i t .8
0.4
1 0
0.2
0.4
Composition
0.6
Ys,
0.8 1.0 propane r,ol.fr.
Figure 10. Real and overall ethylene selectivity in simultaneous pyrolysis of ethane-propane mixture: 1, overall selectivity; 2, real selectivity; 3, additive selectivity.
0
0.2 0.4 conpoaition
0.6 Yc;,
0.8 1 .o propane mol. f r .
Figure 11. Real and overall propylene selectivities in simultaneous pyrolysis of ethane-propane mixture: 1, overall selectivity; 2, real selectivity; 3, additive selectivity.
in individual pyrolysis in the literature. Froment et al. (1976) and Zou (1979) held the view of positive deviation, but Mol (1981) held just the contrary. Figure 11 shows the positive deviation and supports the former view. E. Surface Effect. Surface reactions producing coke can be expected to be of relatively greater importance in the case of a microreactor tube because of the smaller diameter and hence higher surface to volume ratio. For this reason, the two cases of treatment of the inside wall of stainless microreactor tube are compared (1)hydrogen sulfide treatment: the fresh tube is inactivated by passing H2S through for 15 min at 700 OC; (2) air decoking: the coked reactor tube is decoked by passing air through the 600-700 "C. The reactor is not used formally in research work until the composition of effluent gas from the tube outlet is constant by running the informal pyrolysis reaction at constant conditions. The experimental results mentioned above in the present paper are obtained in case (2), because the situation of a commercial reactor is similar to case (2) rather than case (1). Although it is so, we have compared the surface effect to ethylene selectivity in both case; see Table 111. The experimental results listed in Table 111coincide with change tendency of curve C-H in Figure 4 of Froment
0.1 0.2 0.3 0.4
selectivity, mP case 1, case 2, deactivated coked surface surface 1.0 0.62b 1.0 0.876 0.868
"mf = mole fraction. bSee Figure 10.
et al. (1976) and that of curves in Figure 6 of Dunkleman and Albright (1974).
Conclusion The present paper advances a new point of view: there are two conversions in the simultaneous pyrolysis of ethane-propane mixtures due to the dual status of ethane which acts as both reactant and product component. Therefore we must distinguish the ethane real conversion from its overall conversion as well as ethylene real selectivity and its overall selectivity. From this, the present paper has explained and cleared from the opposite even contradictory points of view of different authors in the literature. This paper has pointed out a new way to economically utilize ethane and propane from natural gas or oilfield gas. The simultaneous pyrolysis in appropriate operating conditions has an advantage over the individual pyrolysis in the fact that it not only may save energy for separating ethane from propane but also may save feedstock ethane and propane together with enhanced product ethylene and propylene because the ethylene and propylene overall selectivities in simultaneous pyrolysis are higher than those in individual pyrolysis (see Figures 10 and 11). The present results are also of value for reference to utilizing recycling ethane and propane in ethylene plants using heavier hydrocabons and feedstocks. Acknowledgment Zou Jin and Liu Zhiyong are gratefully acknowledged for having done the carbon balance experiment on this equipment. Nomenclature A = chromatographic peak area aij, b,, ...,mij = coefficients in eq 16, see Zou (1979) Fo = flow rate of reaction carrier gas at vent, mL/s k = pyrolysis reaction rate constant N = yield .of product component, mole fraction = yield of component A from component B in individual pyrolysis at the same operating condition as in simultaneous pyrolysis, mole fraction P = reaction pressure, atm Po = atmospheric pressure, atm Sij = relative response value of i to j T = reaction temperature, K To= ambient temperature, K V = captured volume, standard volume V' = volume of product formed from reactant, which is contained in captured volume V , standard volume VO = reactor volume, mL Y = selectivity of product component, mole fraction Greek Letters a = conversion of reactant component, mole fraction 6 = dilute ratio, mole ratio 19 = residence time, s * \k =
content of reactant in feedstock, mole fraction
Ind. Eng. Chem. Process Des. Dev. 1986, 25, 17-21
Subscripts A, B = component A and B, respectively, in feedstock
cIo,czO,Cz',
C3O, c3== CHI, CzH6,CzH4, C3H8,C3H6, respectively i = component j = component m = mixture or simultaneous pyrolysis P = product R = reactant T = tracer, nitrogen in this experiment Registry No. CzH4,74-85-1; C3H6,115-07-1;CzHs,74-84-0; CSHS, 74-98-6. Literature Cited Dunkbman. J. J.; Albright, L. F. ACS Symp. Ser. 1974, 3 2 , 241. Van Damme, P. S.; Narayanan, S.; Froment, G. F.; Van de Steene, 8. 0.; Ooossens, A. G. Ind. Eng. Chem. Process Des. Dev 1078, 15, 495.
17
Froment, G. F.; Van de Steene, B. 0.;Sumedha, 0. Oil Gas J . 1970, 77(16), 87. Goossens, A. G. Kinetics Technology International, B. V., The Hague, The Netherlands, personal communication, Aug 14, 1979. Hoffmann, H. University of Erlangen, 8520 Erlangen, West Germany, personal communlcation. Nov 25, 1980. Minet. R. G.; Hammond, J. D. 011Gas J . 1075, 73(31), 80. Mol, A. Hydrocarbon Process. 1981. 60(2), 129. Ross, L. L.; Shu, W. R. Oil Gas J . 1977, 75(43), 58. Sundaram, K. M.; Froment, G. F. Ind. Eng. Chem. Fundam. 1978, 17, 174. Zou Renjun Sci. Sin. 1979, 22(1), 53. Zou Renjun Sci. Sin. 1079, 22(6), 637. Zou Renjun "Principles & Techniques of Pyrolysis in Petrochemical Industry", 1st ed.; Chemical Industry Press: Beijing, 1981.
Received for review September 21, 1983 Revised manuscript received August 17, 1984 Accepted August 28, 1984
Adsorption of Water from Aqueous Ethanol Using 3-A Molecular Sieves Wah Koon Teo and Douglas M. Ruthven' Department of Chemical Engineering, National University of Singapore. Kent Ridge, Singapore 05 11
The adsorptive dehydration of aqueous ethanol using 3-A molecular sieve adsorbent has been studied experimentally by following the uptake curves for a closed batch system and by measuring breakthrough curves for a packed column. This system is potentially attractive for the dehydration of rectified spirit in the production of fuel alcohol. The equilibrium isotherm is almost rectangular, and the kinetic data for both systems can be satisfactorily Correlated in terms of simple kinetic models. The resuits of experiments in which particle size and fluid velocity were varied show that intraparticle diffusion is the main resistance to mass transfer with some contribution from external film resistance at low fluid velocities and/or water concentrations.
The production of fuel alcohol from rectified spirit requires almost complete removal of the residual moisture. This has traditionally been accomplished by azeotropic or extractive distillation, but the high energy costa of these processes have stimulated a search for a more efficient method of separation. Dehydration by adsorption on a 3-A molecular sieve has been suggested as a promising alternative to the conventional processes (Hartline, 1979). The 3-A sieve has the advantage that the micropores are too small to be penetrated by alcohol molecules so the water is adsorbed without competition from the liquid phase. In order to obtain the basic data required to assess the economic viability of such a process, we have studied the kinetics and equilibrium of dehydration of rectified spirit on a 3-A molecular sieve in both batch and column experiments. Since adsorption is noncompetitive and the isotherm for water is highly favorable, the data can be accurately correlated in terms of a very simple mathematical model. Experimental Section Material. A type 3-A molecular sieve in 1/16-in.cylindrical pellet form (Sigma Chemical Co.) was used exclusively in the experimental work. Smaller particle sizes of molecular sieve were obtained by crushing and screening
* Permanent address: Department of Chemical Engineering, University of New Brunswick, Fredericton, N.B., Canada. 0196-4305/86l1125-0017$01.50l0
the 1/16-in.pellets. The molecular sieves were preconditioned by thermal activation in a furnace at 300 "C for 24 h and then stored in a vacuum desiccator for use in adsorption studies. Mixtures of ethanol and water were prepared from deionized water and analytical grade absolute alcohol (0.79 g/L, minimum purity 99,9 wt %) supplied by Merck. Concentrations of ethanol-water mixtures were determined by gas chromatography by using a Perkin-Elmer Model F-17 gas chromatograph with a Chromosorb-102 column and a hot-wire detector. Equilibrium Data. The equilibrium isotherm was determined at 24 "C over a range of water concentrations in the fluid phase from 1.3 to 7.3 w t %. The solid-liquid mixtures were allowed to equilibrate for 3 days with periodic gentle swirling. The concentration in the adsorbed phase was found by mass balance from the initial and final concentrations in the fluid. Batch Kinetic Studies. Batch uptake experiments were carried out in closed circulating system sketched in Figure 1. The ethanol-water mixture containing 5.915 wt % H,O from a reservoir (42 mL) maintained at constant temperature was circulated continuously through a small packed bed of molecular sieve particles (8 g). Such a system proved superior to a stirred vessel used in preliminary experiments, since it gave better solid-liquid contact and eliminated the solid-solid attrition problem encountered in the latter system. Rates of sorbate uptake by the adsorbent from the ethanol-water mixtures were moni0 1985 American Chemical Society
