2024
Ind. Eng. Chem. Res. 1987,26, 2024-2028
Antunes, C.; Tassios, D. Ind. Eng. Chem. Process Des. Deu. 1983,22, 457. Chang, R. F.; Morrison, G.; Levelt Sengers, J. M. H. J . Phys. Chem. 1984, 88, 3389. Dymond, J. H.; Smith, E. B. The Virial Coefficients ofPure Gases and Mixtures; Clarendon: Oxford, 1980. Eubank, P. T.; Kreglewski, A.; Hall, K. R.; Holste, J. C.; Mansoorian, H. AIChE J . 1985,31, 849. Fredenslund, A,; Jones, R. L.; Prausnitz, J. M. AIChE J . 1975, 21, 1086. Fredenslund, A.; Gmehling, J.; Rasmussen, P. Vapor-Liquid Equilibria Using UNIFAC; Elsevier: New York, 1977. Hayden, J. G.; O'Connell, J. P. Ind. Eng. Chem. Process Des. Deu. 1975, 14, 209.
Joffe, J. J . Chem. Eng. Data 1977, 22, 348. Jonah, D. A. Fluid Phase Equilib. 1983, 15, 173. Kim, E. S. M.S. Thesis, Texas A&M University, College Station, 1984 (Eubank, P. T., Thesis Director). Lugo, R. M.E. Report, Texas A&M University, College Station, 1982. Lyckman, E. W.; Eckert, C. A.; Prausnitz, J. M. Chem. Eng. Sei. 1965, 20, 685. Orbey, H.; Vera, J. H. AIChE J . 1983, 29, 107. Tsonopoulos, C. AIChE J. 1974, 20, 263. Received for review August 4, 1986 Accepted June 30, 1987
Separation of Diethylbenzene Isomers by Column Adsorption and Desorption Tsan-Sheng L u and Ting-Yueh Lee* National Tsing Hua University, Department of Chemical Engineering, Hsinchu, Taiwan 30043, R.0.C
An experimental study of the separation of diethylbenzene (DEB) isomers was performed on a bench-scale column, using zeolites, X, Y, ZSM-6, and DZ and their ion-exchanged forms as adsorbents with various desorbents. It was found that CDZ zeolite was the most appropriate for the separation of DEB mixture in the temperature range 120-190 "C. T h e effects of particle size and feed rate on separations, as well as the process feasibility through consecutive injection of the isomer mixture, were also studied. Diethylbenzene (DEB) has many industrial applications: used as organic solvent precursor for cross-linking agents of resins, and specialty chemicals. In particular, p-DEB is the main desorbent used in the parex process (Derosset et al., 1980) for the separation of p-xylene from xylene isomers. Three isomers of DEB were produced as a byproduct of benzene alkylation process. These isomers have approximately the same boiling points. Their boiling points are 183.4, 181.0, and 183.8 O C for o, m-, and p-DEB, respectively. It is almost impossible to separate them by distillation. It is conceivable that the cryogenic separation is also very costly. The current market price for p-DEB is about U.S. $6500/ton. There is extreme price incentive for developing an efficient separation process to obtain high-purity p-DEB. Several patents dealt with the separation of p-alkyl aromatic isomers (Neuzil and Korous, 1977; Taniguchi and Iwata, 1979; Toray Industries, Inc., 1981); however, very little usable information is disclosed. Santacesaria et al. (1985), Morbidelli et al. (1985), and Storti et al. (1985) studied the vapor-phase separation of xylenes on Y zeolites. They claimed that propylbenzene was the most suitable desorbent in the operation temperature range 150-200 "C. Seko et al. (1979, 1982) reported on the separation of ethylbenzene and p-xylene from the mixed xylenes by improved zeolites X and Y and their exchanged cations. They carried out the separation in a form of displacement chromatography and claimed low cost and high recycle use of the desorbent. They also developed the technology for the process scale-up, deviced means of packing a large column, and improved the hardness as well as the sorption capacity of the adsorbent. In this paper, vapor- and liquid-phase adsorption and desorption on X, Y, ZSM-5, and DZ (a faujasite) zeolites and their ion-exchanged forms packed in a column were employed for separating p-DEB from DEB isomers. The * T o whom correspondence should be addressed.
operating temperature range, specific metal cation, particle size, and the most appropriate desorbent were determined. Furthermore, the cyclic operation of the column and the efficiency of the separation, as well as the optimal use of the desorbent, were also investigated. Experimental Section Materials. The DEB mixture was premixed by using each research grade pure isomer according to the following compositions: p-DEB, 45.3 wt % (CPC, TSM Corp.); m-DEB, 43.8 wt % (TSM Corp.); o-DEB, 6.5 wt % (TSM Corp.). The compositions were confirmed by GC analysis. Research grade o-xylene, m-xylene, p-toluene, ethylbenzene, and propylbenzene were used as the desorbent. Zeolites X (Davison), Y (Strem), ZSM-5 (synthesized in this laboratory), and DZ (a faujasite) as well as their ionexchanged forms of Ba, Cs, H, and K were chosen as the adsorbent. The adsorbent pellets were crushed into smaller particles (0.2-1.6-mm diameters) and packed in a column for the separation study. The chemical analysis and the physical properties of the sorbents were listed in Table I. Apparatus. The adsorption column is a 0.70 cm inside diameter by 120 cm long stainless steel pipe. The outside diameter of the pipe was enlarged with an additional solid copper layer coaxial with the stainless steel pipe to a total outside diameter of 2.54 cm. It can facilitate better heat conduction and ensure a uniform temperature inside the column. Along the column there were five heating zones controlled by a five-port temperature controller (Eurotherm, England). Details of the whole setup where shown in Figure 1. The DEB mixture and the desorbent were fed into the column from the top, using two separate high-pressure metering pumps (Eldex Labs Inc.). The amount of feed was controlled manually. A t the outlet of the column, there was a fraction collector for taking Samples continuously at a specific time interval. A purge system is provided for the purpose of degas, regeneration, and purge of the column.
0888-5885/87/2626-2024.$01.50/0 G3 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 10, 1987 2025 Table I. Elemental Analysis of Adsorbent element, % method 13X” Na-Yb Na AA 9.41 f 0.10 5.78 f 0.10 K AA Ca AA cs Ba weight Me A1 volumetric Mf 12.17 f 0.06 14.63 f 0.10 Si weight M 17.93 f 0.03 18.31 f 0.03
K-13Xc 2.66 f 0.10 11.22 f 0.05
12.17 f 0.06 17.93 f 0.03
(Ba,K)YC
C,-13XC 8.50 f 0.30
C,-Y‘ 4.20 f 0.20
5.80 f 0.20
10.70 f 0.30
12.17 f 0.06 17.93 f 0.03
14.63 f 0.10 18.31 f 0.03
ZSM-5d 2.82 f 0.05
0.13 f 0.02
1 T I
Figure 4. Concentration profiles: adsorbent, CDZ; desorbent, mxylene; T = 170 "C; DEB mixture, 2 cm3. d
48
2s
Figure 7. Concentration profiles: adsorbent. CDZ; desorbent, oxylene; T = 170 "C; DEB mixture, 2 cm3. rr31 "I,
,lo
L"
'5
t 1 5 10
~
P-DEE
2 t
T N r
20
43
5:
I t( Tiin
Figure 5. Concentration profiles: adsorbent, HZSM-5; desorbent, propylbenzene; T = 150 "C; DEB mixture, 2 cm3.
Figure 8. Concentration profiles: adsorbent, (Ba,K)Y; desorbent, n-xylene; T = 150 "C; DEB mixture, 2 cm3.
using ion-exchanged zeolites CsX, KX, (Ba,K)Y, CsY, HZSM-5, and CDZ (an ion-exchanged form of DZ) and by m-xylene as desorbent in the temperature range 120-190 "C indicated that zeolite CDZ offered the best efficiency. The residence time difference (At,,) of p-DEB and m-DEB (or o-DEB) on this sorbent is 61.2 min, and the efficiency of separation is 2.92. Figures 2-4 indicated the results of the runs representatively. A summary of the separation by CDZ was tabulated in Table I1 which included t (residence time), R (total recovery), ES (efficiency of separation), tg, (time on stream to obtain 95% p-DEB), REg5(the corresponding 95 % component recovery), and w (weight of desorbent used). Effect of Desorbent on Separation. Three series of experiments were carried out to elucidate the effects of desorbent on separation. Desorbents of m-xylene and propylbenzene on HZSM-5 did not show any positive re-
sults on separation of the DEB mixture as indicated in Figures 3 and 5. Neither solvents m-xylene nor p-xylene on (Ba, K)Y showed any impact on separation as indicated in Figures 2 and 6. A very extensive study was carried out on CDZ zeolite with a series of desorbents: m-, p-, and o-xylenes, ethylbenzene, and propylbenzene. The best of them was o-xylene, and the efficiency of separation was 3.11. The representative result is shown in Figure 7. Effect of Temperature. Effects of temperature (at 150, 170, and 190 OC) on the separation by sorbent (K, Ba)Y and desorbent m-xylene are plotted in Figures 8, 2, and 9, respectively. It clearly showed that the increase in temperature would improve the separation slightly but not drastically. It is of interest to know that below 130 "C, both DEB mixture and desorbent are in the liquid state. For temperatures between 140 and 180 OC, the mixture to be separated is in the liquid state and the desorbent
Ind. Eng. Chem. Res., Vol. 26, No. 10, 1987 2027 Table 11. Results of Column Separation with CDZ Adsorbent and Several Different Desorbents (DEB Mixture Injection Amount = 2 cm')
T, OC 170
t , min 135
p-xylene
170
100
m-xylene
190
92
m-xylene
170
190
m-xylene
180
130
m-xylene
190
180
o-xylene
170
134
D DroDvlbenzene . -
I
" For p-DEB.
For m-DEB.
For o-DEB.
R, wt % 95.47" 104.86b 88.4gC 99.30d 92.75" 92.74b 87.41' 92.3gd 80.64" 80.13' 79.77c 80.35d 96.82" 87.62b 87.69' 91.98d 82.21" 90.67b 89.87c 86.61d 87.64" 88.60' 84.67c 87.88d 90.46" 92.47b 88.4lC 91.24d
t, min 92.98" 60.23b
ES 1.81
64.86" 40.98b
2.18
0
25.56
55.10" 33.86b
2.02
0
23.87
115.50" 54.30b
2.92
89.44
85
62.20
89.55" 45.28'
2.86
79.76
74
91.06
110.52" 56.68b
1.29
75.94
90
50.30
85.66" 46.7gb
3.11
93.62
64
32.16
RE95, % 0
tg5,min
w ,g 38.93
Total.
rPo1 'io
103 >!
r---
I
m-xylene
80
;Oi 40
WDEB p-DEB
0
10
20
30
40
50
60
'0
t(m)
Figure 9. Concentration profiles: adsorbent, (Ba,K)Y; desorbent, m-xylene; T = 190 OC; DEB mixture, 2 cm3.
m-xylene is in the vapor state. At 190 "C,both mixture and desorbent are in the vapor state, but the separation is not appreciably better than at 170 "C; as demonstrated in Figures 2 and 9. Effect of Amount of Sorbates on Separation. Increasing the sorbates flow rate tends to decrease the efficiency of separation due to the fact that the column was overwhelmed by the sorbates. The separation results for runs of 2- and 8-cm3 mixture injections are plotted in Figures 7 and 10. Excellent result was obtained for the 2-cm3mixture injection, and a somewhat mediocre result was obtained for the 8-cm3 injection. Nevertheless, the REg5for 8- and 2-cm3injections were 30.8% and 93.6% or 2.4 and 1.9 cm3 of 95% pure p-DEB were recovered, respectively. Effect of Particle Size. Three sizes of adsorbent with average particle diameters of 1.6, 0.7, and 0.2 mm were packed into the column for separation study. Results of the runs are shown in Figures 7, 11, and 12, respectively. The operational pressure had to be increased as the particle size was decreased. It was of interest to observe that the smallest particle did not necessarily give a better
0
43
12C
80
2 00
160
I'm4
Figure 10. Chromatography of mixed DEB: adsorbent, CDZ; desorbent, o-xylene; T = 170 OC; DEB mixture, 8 cm3. WOI
5Ir
2 0 12
4k p.3EB 0-DEB
0
40
80
160
2
Vmir)
Figure 11. Chromatography of mixed D E B adsorbent particle size, D, = 0.7 mm; T = 170 "C; P = 0.17 MPa; DEB mixture, 2 cm3; adsorbent, CDZ; desorbent, o-xylene.
separation but would take much longer time to flush out the mixture from the column at a much higher pressure of 0.29 MPa. From the smaller sizes of elution peak, it
2028 Ind. Eng. Chem. Res., Vol. 26, No. 10, 1987 mol ''*
mixture in the tkihperatwe range 120-190
Acknowledgment
'i
We are gratefdfor the financial support on this research from Taiwan Styrene Monomer Corp. and for the comments and suggestions on the work by Prof. I. Wang.
8
tinid
Figure 12. Chromatography of mixed DEB: adsorbent particle size, D = 0.2 mm; T = 170 O C ; P = 0.29 MPa; DEB mixture, 2 cm3; aisorbent, CDZ; desorbent, o-xylene. ro
OC.
'IC
Nomenclature CPC = Chinese Petroleum Company D = desorbent D = adsorbent particle size ~ ! 4= efficiency of separation R = recovery RE = component recovery t = time on stream A t l z = difference of elution time of components 1 and 2 T = temperature TSM Corp. = Taiwan Styrene Monomer Corporation w = weight of desorbent used wi = weight percent in the effluent of component i Greek Symbols
aij = mean standard deviation oft, and tl from mean residence time 4 = mass flow rate of the mixture 0
40
80
120 163 200 2 4 3 280 320 360 ;XI
i L 0 480 520 560 6co G O 580 '20
Figure 13. Elution curve of consecutive feed of DEB mixture: adsorbent, CDZ; desorbent, o-xylene; T = 170 "C.
probably indicated that the material went into the pores and a certain amount of the mixture might still be trapped inside the intra- or inter-spaces of the zeolite. Finally, the feasibility of continuous operation of the process was demonstrated. Identical separation results were obtained from four intermittent feeds as shown in Figure 13. In a programmable predetermined time interval, a high purity of p-DEB could be taken out as product and the remaining mixture of adsorbates and desorbent could be channeled into a distillation or crystallization unit where the desorbent could be separated and recycled back to the column and the mixture returned to the feed stream.
Conclusions A column adsorption and desorption method was employed to separate DEB isomers. Zeolites X, Y, ZSM-5, and DZ and their ion-exchanged forms were employed as adsorbents. Xylenes, toluene, and propylbenzene served as the desorbent. The operation temperature ranged from 120 to 190 OC,and pressure was about 0.2-0.3 MPa. The effects of sorbent, desorbent, temperature, particle size, and cation were investigated. It was found that CDZ zeolite was the most appropriate for the separation of DEB
Superscript - = mean value Subscripts 95 = purity of 95% p-DEB
i = component i j = component j Registry No. p - D E B , 105-05-5; m-DEB, 141-93-5; o-DEB, 135-01-3.
Literature Cited Derosset, A. J.; Neuzil, R. W.; Tajbl, D. G.; Braband, J. M. Sep. Sci Technol. 1980, 15(3),637. Morbidelli, M.; Santacesaria,E.; Storti, G.; Carra, S. Ind. Eng. Chem. Process, Des. Dev. 1985, 24(1), 83. Neuzil, R. W.; Korous, D. J. (UOP Inc.) US.Patent 4051 192, 1977; Chem. Abstr. 1977,87, 1841875. Santacesaria,E.; Gelosa, D.; Danise, P.; Carra, S. Ind. Eng. Chem. Process Des. Dev. 1985, 24(1), 78. Seko, M.; Heroshi, T.; Tsutomu, I. Znd. Eng. Chem. Prod. Res. Dev. 1982, 21(4), 656. Seko, M.; Tetsuya, M.; Koji, I. Ind. Eng. Chem. Prod. Res. Dev. 1979, I8(4), 263. Storti, G.; Santacesaria,E.; Morbidelli, M.; Carra, S. Ind. Eng. Chem. Process Des. Dev. 1985, 24(1), 89. Taniguchi, K.; Iwata, K. (Mitaue Petrochemical Industries Ltd.) Jpn. Tokkyo Koho Patent 79 122 229, 1979; Chem. Abstr. 1980, 92, 94030j. Toray Industries, Inc. Jpn. Tokkyo Koho Patent 8 149 891, 1981; Chem. Abstr. 1982, 96, 180921q. Received for review June 2, 1986 Accepted May 12, 1987
