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SEPARATIONS Adsorption of Light Hydrocarbon Gases on Alkene-Selective Adsorbent Nettem V. Choudary, Prakash Kumar, and Thirumaleshwara S. G. Bhat* Research Centre, Indian Petrochemicals Corporation Ltd., Vadodara 391 346, India
Soon H. Cho, Sang S. Han, and Jong N. Kim Korea Institute of Energy Research, 71-2 Jangdong, Yusongku, Taejon, Korea
Equilibrium adsorption isotherms of ethylene (C2H4), ethane (C2H6), propylene (C3H6), and propane (C3H8) were measured on a Ag+-impregnated clay-based alkene-selective adsorbent, Olesorb-1, in the temperature range of 293-363 K. The heats of adsorption estimated with the Clausius-Clapeyron equation were higher for ethylene (13.5 kcal/mol) and propylene (14.3 kcal/ mol) than for the corresponding alkanes, indicating π-bond interactions. A sharp decrease in the ethylene and propylene heats of adsorption was observed with increasing coverage. The isotherm data correlated well with the Langmuir-Freundlich isotherm model for all of the systems. Predicted mixture adsorption for ethylene/ethane and propylene/propane systems showed high adsorption selectivity for the alkenes over the corresponding alkanes. The selectivity decreased with increasing alkene composition in the gas phase. The diffusion of the alkenes was rapid compared to that of the corresponding alkanes. Twenty percent of the alkene was irreversibly adsorbed. The adsorbent was evaluated for its performance in a four-bed vacuum swing adsorption process. Ethylene could be separated from ethane with over 85% recovery and 99.8% purity. 1. Introduction Ethylene and propylene, the two most important building blocks of the petrochemical industry, are also the two chemicals produced in the largest quantities in the world. The current global ethylene production capacity is 93 million tons per annum (tpa).1 The demand for ethylene is expected to increase at a rate of 4.5% per annum during the period 2000-2010. Ethylene and propylene are produced by naphtha/gas cracking or by dehydrogenation of alkanes. The separation of ethylene from ethane and propylene from propane has been achieved conventionally by low-temperature/highpressure distillation.2 These separation processes are quite energy-intensive because of the similar relative volatilities of the components.3 The high capital and operating costs associated with conventional cryogenic distillation processes provide an incentive for ongoing research into the development of alternative energyefficient separation technologies.4 One of the most promising alternative separations is by adsorption based on π complexation between alkene molecules and transition metal ions. Although stronger than van der Waals forces, this interaction is sufficiently weak to be broken by simple engineering operations such as raising the temperature or decreasing the pressure. The early attempts at separating alkene/alkane mixtures based * To whom all correspondence should be addressed. Phone: 91-265-272011 Ext. 3673. Fax: 91-265-272098. E-mail:
[email protected].
on π complexation2,4,7-9 employed liquid solutions containing silver (Ag+) or cuprous (Cu+) ions with limited success. There have been a number of studies with gas/ solid systems based on π complexation.10-16 Gas/solid operations can be simpler as well as more efficient, particularly with pressure/vacuum swing adsorption processes. However, the attempts so far at developing solid adsorbents based on π complexation have not been very satisfactory. Various solid adsorbents reported during the past several years have lacked the required adsorption capacity and selectivity or diffusivity. CuCl, considered as early as in 1941 by Gilliland et al.17,18 for alkene/alkane separation, lacks adsorption capacity because of its low surface area. Silver salt supported on anion-exchange resins19,20 also has a low adsorption capacity. The zeolite-based adsorbents CuY21 and AgY13 exhibit either low selectivity or poor reversibility. The only commercially viable adsorbent based on π complexation that has been reported is CuCl/γ-Al2O3 for CO removal.12 More recently, several new alkene-selective adsorbents based on π complexation have been reported by Yang et al.13-16 These include Ag+/resins,13,16 monolayer CuCl/γ-Al2O3,16 monolayer CuCl/pillared clays,22 and monolayer AgNO3/SiO2.14 Ag+/resin adsorbent, though it exhibits a high adsorption capacity and selectivity for alkene, suffers from low diffusivities. In the process recently patented by BOC, 23,24 Ramchandran et al. used Cu-modified 4A zeolite to separate ethylene and propylene from the corresponding alkanes at elevated temperatures in the range of 125-200 °C.
10.1021/ie010546+ CCC: $22.00 © 2002 American Chemical Society Published on Web 05/02/2002
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The principle separation mechanism involves different adsorption rates for alkenes and alkanes. BOC developed a commercial three-bed PSA/TSA system to recover alkenes from feed mixtures containing 80-85% alkenes, with a recovery of 80%. We have recently developed25-29 alumina- and clay-based alkene-selective adsorbents containing Ag+ ions. Employing these adsorbents, a vacuum swing adsorption process has been developed for the separation of light alkene/alkane mixtures. The present paper describes adsorption studies of ethylene, ethane, propylene, and propane on one of these adsorbents (named Olesorb-1). The performance of the adsorbent in a four-bed vacuum swing adsorption system is also briefly discussed. 2. Experimental Section 2.1. Adsorbent Preparation and Characterization. The alkene-selective adsorbent used in the present study was obtained from the CATAD Division of IPCL (Indian Petrochemicals Corporation Ltd.) and was produced by employing a proprietary process28,29 wherein AgNO3 was impregnated on modified clay support. The adsorbent was characterized for surface area, pore volume, and pore size distribution by nitrogen adsorption using Micromeritics ASAP2010 instrument at 77 K. 2.2. Adsorption Measurements. Gravimetric and volumetric methods were employed for the measurement of adsorption/desorption uptakes and equilibrium adsorption, respectively. For gravimetric measurements, Cahn 1100 microbalance system was used. The volumetric setup used for adsorption/desorption measurements was a glass metal assembly fitted with MKS absolute pressure transducers in two ranges, viz., 0-100 and 0-1000 Torr, with auto-range facility. The adsorbent sample was activated in situ at 200 °C under vacuum (1 × 10-5 Torr). The sample was then cooled to the desired temperature and was maintained within (0.01 °C by employing a Julabo F12 circulating thermostatic bath. The hydrocarbon gases used in the present study, viz., ethylene (99.7%) and propylene (99.6%), were obtained from Indian Petrochemicals Co. Ltd., India, whereas ethane (99.99%) and propane (99.5%) were supplied by M/s Chemtron Science Laboratory, India. 3. Theoretical Section Adsorption isotherm data were fitted to the three isotherm equations given below
Freundlich equation v ) kpn
(1)
(2)
Langmuir-Freundlich equation v ) vmbpn/(1 + bpn)
∑(vcal - vexp)2/(n - p)
σ)x
(4)
where vcal and vexp are the calculated and experimental adsorption values, respectively, in mmol/g; n is the total number of experimental points; and p is the number of parameters in the equation. Mixture adsorption was predicted from the measured pure-component adsorption isotherm data using the extended Langmuir-Freundlich (L-F) model given below. On extending the L-F model to binary gas mixture, we obtain
v1 ) (vm)1b1p1n1/(1 + b1p1n1 + b2p2n1)
(5)
where b1 and n1 are the Langmuir and Freundlich constants, respectively, for component 1. p1, v1, and (vm)1 are the partial pressure, amount adsorbed, and monolayer capacity, respectively. Similarly, for component 2
v2 ) (vm)2b2p2n2/(1 + b1p1n1 + b2p2n1)
(6)
The total volume adsorbed for a binary gas mixture is given by
v ) v1 + v2 ) [(vm)1b1p1n1 + (vm)2b2p2n2]/(1 + b1p1n1 + b2p2n1) (7) Dividing eq 5 by eq 7, we obtain the adsorbed-phase composition with respect to component 1
x1a ) (vm)1b1p1n1/[(vm)1b1p1n1 + (vm)2b2p2n2]
(8)
x1a ) 1/[1 + (vm)2b2p2n2/(vm)1b1p1n1]
(9)
or
For a given gas-phase composition, x1a can be calculated with eq 9 from the values of L-F constants for the two pure gases. The adsorption selectivity in a binary mixture can be calculated from the adsorbed-phase and gas-phase compositions of the two gases using the relation
selectivity R1/2 ) x1ax2g/x1gx2a
(10)
Diffusion Constant, D/r2. The adsorption uptake data were used to calculate apparent diffusivity, D/r2 using the well-known equation30
Mt/Ma ) 1 - 6/π2Σ[1/n2 exp(-n2π2tD/r2)] (11)
Langmuir equation v ) vmbp/(1 + bp)
regression coefficient r2 and the standard deviation of fit σ, defined by
(3)
where v is amount adsorbed at pressure p, k, and n are Freundlich constants, vm is monolayer capacity, and b is the Langmuir constant. The constants of eqs 1-3 were obtained by a nonlinear regression of the experimental data, along with the
where Mt and Ma are the amounts adsorbed at time t and at infinite time, respectively. By a nonlinear fitting of the sorption curve to the solution of the above equation, the values of D/r2 were calculated. 4. Results and Discussion The physical properties such as particle size distribution and bulk density of the Olesorb-1 adsorbent are given in Table 1. Nitrogen adsorption and desorption isotherms measured at 77 K are shown in Figure 1. The
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Figure 1. Nitrogen adsorption-desorption isotherms at 77 K and BJH pore size distribution plot (inset) for Olesorb-1. Table 1. Physical Properties of Clay Support and Olesorb-1 Adsorbent property (kg/m3)
bulk density BET surface area (m2/g) pore volume (cm3/g)
Olesorb-1
clay support
968 165 0.28
610 385 0.46
nitrogen isotherm exhibited a well-defined hysteresis loop. The estimated surface area and pore volume of the adsorbent (Table 1) are 165 m2/g and 0.28 cm3/g, respectively. The pore size distribution curve obtained from the desorption branch based on the BJH approach (inset in Figure 1) shows a mean pore size of about 45 Å. 4.1. Equilibrium Adsorption Isotherms. Adsorption isotherms of ethane and ethylene were measured at various temperatures in the range between 293 and 363 K and are plotted in Figure 2. Sorption isotherms of ethane and ethylene measured at 303 K on the starting clay support are also shown in the figure. It can be seen that the ethylene adsorption is higher on Olesorb-1 than on the virgin clay whereas the ethane adsorption capacity is suppressed on the former. Table 2 gives the equilibrium adsorption capacities of the various adsorbates at different temperatures and 1 atm. At 760 Torr and 303 K, the ethylene and ethane equilibrium capacities were 1.17 and 0.32 mmol/g, respectively, and those of propylene and propane were 1.39 and 0.47 mmol/g, respectively. The enhanced adsorption capacity of ethylene is due to the presence of Ag+ ions for π complexation. The corresponding adsorption capacities on virgin clay for ethylene and ethane were 0.40 and 0.29 mmol/g respectively. On impregnation, the alkane capacities decreased by about 25%. This can be attributed to the drop in the surface area of the clay support.
Figure 2. Adsorption isotherms of ethylene and ethane at various temperatures on Olesorb-1: symbols, experimental data, solid line, L-F fit.
Yang et al.13 represented adsorption selectivity by the ratio of the equilibrium adsorption capacities of alkene and alkane at 1 atm. Given in Table 2 are similar ratios for Olesorb-1. The ethylene/ethane and propylene/ propane adsorption ratios were 8.6 and 4.6, respectively, which are substantially higher than the values for supported Cu adsorbents given in Table 2. The ethylene/ ethane ratio increased with increasing temperature. For example, the ethylene/ethane ratio at 760 Torr increased from 8.6 at 303 K to 10.6 at 333 K. Equilibrium adsorption data for C3H6 and C3H8 on Olesorb-1 in the temperature range 293-363 K are shown in Figure 3. The adsorption capacity and propylene/propane ratio are also high. At 760 Torr and 303 K, the C3H6 equilibrium capacity was 1.39 mmol/g, and the adsorption ratio increased with increasing temperature. For example, at 760 Torr, the ratio increased from 4.6 to 5.9 with an increase in temperature from 293 to 333 K. The adsorption capacity and selectivity ratios for ethylene/ethane and propylene/propane on Olesorb-1 compare well with those reported in the literature13 and given in Table 2. The adsorption isotherm data were fitted to the Langmuir, Freundlich, and Langmuir-Freundlich equa-
Table 2. Comparison of Adsorption Capacity of the Present Work with Literature Data adsorption capacity at 1 atm (mmol/g)
pure gas adsorption selectivity ratio
adsorbent
T (K)
C2H4
C3H6
C2H4/C2H6
C3H6/C3H8
ref
CuCl/γ-Al2O3
298 333 303 333
0.72 0.48 1.17 0.85
0.77 0.52 1.39 1.00
7.7 9.5 8.6 10.6
3.5 4.3 4.6 5.9
13 13 present work present work
Olesorb-1
Ind. Eng. Chem. Res., Vol. 41, No. 11, 2002 2731 Table 3. Fitted Constants, Regression Coefficients r2, and Standard Deviations σ for Adsorption Isotherm Data Fitted to the Langmuir, Freundlich, and Langmuir-Freundlich Equations (a) Freundlich Constants for Olesorb-1 gas ethylene
ethane
propylene
propane
T (K)
K [mmol/(g Torr)]
n
r2
σ (mmol/g)
293 303 313 333 363 293 303 313 333 293 303 313 333 363 293 303 313 333
0.1963 0.1680 0.1100 0.0813 0.0851 0.1984 × 10-2 0.1489 × 10-2 0.0686 × 10-2 0.0598 × 10-2 0.2631 0.2325 0.1871 0.1075 0.0529 0.5238 × 10-2 0.3877 × 10-2 0.3854 × 10-2 0.1795 × 10-2
0.2867 0.2923 0.3382 0.3536 0.2820 0.6851 0.6710 0.7564 0.7401 0.2651 0.2698 0.2855 0.3360 0.4108 0.6385 0.6537 0.6283 0.6884
0.9995 0.9999 0.9999 0.9983 0.9976 0.9997 0.9994 0.9997 0.9988 0.9978 0.9972 0.9978 0.9979 0.9995 0.9985 0.9994 0.9998 0.9997
0.009 0.004 0.004 0.010 0.007 0.001 0.001 0.001 0.001 0.020 0.020 0.016 0.014 0.006 0.006 0.003 0.002 0.001
(b) Langmuir Constants for Olesorb-1 gas ethylene
Figure 3. Adsorption isotherms of propylene and propane at various temperatures on Olesorb-1: symbols, experimental data, solid line, L-F fit.
ethane
tions. The fitted constants, regression coefficients r2, and standard deviations σ are given in Table 3. As can be seen from these data, the isotherm data are wellcorrelated by the Langmuir-Freundlich (L-F) model for most of the systems. It can be seen from Table 3 that the values of the Langmuir-Freundlich constant b, which is a measure of the interaction between the adsorbate and the adsorbent, are substantially higher for the alkenes than for the corresponding alkanes, thus suggesting a stronger interaction of the former molecules with the adsorbent surface. 4.2. Heats of Adsorption. The isosteric heats of adsorption (∆H) for various adsorbates were estimated using the Clausius-Clapeyron equation (Table 4), and their dependence on adsorption coverage is shown in Figure 4. The heats of adsorption of ethylene and propylene are substantially higher than those for the corresponding alkanes. For example, at 0.1 mmol/g loading, the heats of adsorption of ethylene, propylene, ethane, and propane are 13.5, 14.3, 4.7, and 5.8 kcal/ mol, respectively. Furthermore, the isosteric heats of ethylene and propylene decreased with increasing degree of coverage with a logarithmic decay, whereas those of ethane and propane remained constant after an initial decrease with increasing coverage. The heats of adsorption reported in the literature for various π-complexbased adsorbents are compiled in Table 4, which shows that the present data compare well with the reported values. The high heats of adsorption for alkenes indicate the presence of π interactions with Ag+ ions on the surface of the adsorbent. The difference in heats of adsorption between the pairs ethane/ethylene and propane/propylene are comparable. For example, at 0.1 mmol/g sorbate loading, the difference in heats of
propylene
propane
T (K)
vm (mmol/g)
b x 103 (1/Torr)
r2
σ (mmol/g)
293 303 313 333 363 293 303 313 333 293 303 313 333 363 293 303 313 333
1.414 1.309 1.237 1.025 0.657 0.328 0.290 0.314 0.225 1.642 1.525 1.397 1.183 1.035 0.984 0.677 0.503 0.410
11.430 10.081 6.580 6.202 5.997 1.166 1.066 0.661 0.757 13.058 11.775 9.753 7.080 4.570 1.176 1.051 1.321 0.978
0.915 0.958 0.963 0.928 0.823 0.993 0.996 0.998 0.999 0.920 0.927 0.929 0.961 0.968 0.984 0.989 0.989 0.995
0.109 0.093 0.074 0.068 0.063 0.005 0.003 0.002 0.001 0.117 0.103 0.091 0.059 0.049 0.019 0.013 0.011 0.005
(c) Langmuir-Freundlich Constants for Olesorb-1 gas ethylene
T (K)
293 303 313 333 363 ethane 293 303 313 333 propylene 293 303 313 333 363 propane 293 303 313 333
vm B x 103 (mmol/g) (1/Torr) 8.524 8.406 8.194 7.984 7.800 2.305 0.939 0.842 0.355 4.619 3.707 3.663 2.891 4.583 12.143 9.988 7.497 2.253
21.548 18.703 12.217 9.410 10.246 0.754 1.158 0.586 0.879 48.359 49.955 39.832 25.957 9.425 0.409 0.367 0.485 0.675
n
r2
σ (mmol/g)
0.3216 0.3248 0.3728 0.3825 0.3027 0.6846 0.7412 0.8267 0.8784 0.3497 0.3738 0.3855 0.4546 0.4706 0.6510 0.6670 0.6424 0.7258
0.9997 0.9999 0.9997 0.9972 0.9966 0.9997 0.9998 0.9999 0.9999 0.9998 0.9999 0.9999 0.9999 0.9999 0.9982 0.9992 0.9997 0.9998
0.007 0.004 0.006 0.014 0.009 0.001 0.001 0.001 0.003 0.006 0.002 0.004 0.002 0.001 0.006 0.004 0.002 0.005
adsorption for C2 hydrocarbon gases, ∆HC2H4 - ∆HC2H6, was 8.8 kcal/mol compared to 8.5 kcal/mol for propylene and propane. This difference in heats of adsorption can be attributed to the interaction between the Ag+ ion and the π-electron cloud of the carbon-carbon double bond. 4.3. Prediction of Binary Mixture Adsorption. The binary mixture adsorption for ethylene/ethane and
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Table 4. Comparison of Heats of Adsorption on Olesorb-1 with Those Reported in the Literature -∆H (kcal/mol) adsorbenta Ag+ resin CuCl/γAl2O3 CuCl/TiO2-PILC CuCl/Al2O3-LP CuCl/Al2O3-PILC CuCl/ZrO2-PILC CuCl/Fe2O3-PILC Ag+-Amberlyst 35 Ag+-Amberlyst 35 Ag+-Dowex88 Olesorb-1
ethane ethylene propane propylene 4.8 5.3 4.8 5.4 5.5 5.7 5.5 4.6 5.6 5.9 4.7
10.0 11.7 13.7 12.2 11.4 11.0 11.2 9.4 9.0 6.6 13.5
5.1 5.6 5.2 6.3 6.4 6.9 6.6 5.8
10.3 14.2 13.0 11.9 11.2 10.7 10.8 14.3
ref 13 13 22 22 22 22 22 16 16 16 present work
a PILC, pillared clay; LP, Laporte pillared clay; heat data from the present work are reported at an adsorption loading of 0.1 mmol/g of sorbate.
Figure 4. Heats of adsorption of ethylene, ethane, propylene, and propane on Olesorb-1 as a function of adsorbent loading.
propylene/propane mixtures was predicted using purecomponent adsorption isotherm data and the mixed Langmuir-Freundlich (L-F) model. The predicted adsorbed-phase composition and selectivity (R1/2) in a binary mixture at 303 and 333 K for ethylene over ethane and propylene over propane are shown in Figure 5. The adsorbent showed a high binary mixture selectivity R1/2 for ethylene and propylene at all compositions. However, the selectivity R1/2 was very high at low alkene gas compositions and decreased with increasing alkene gas-phase composition. For example, for ethylene, R1/2 at 303 K decreased from 42.1 at 10 mol % gas-phase composition to 5.4 with an increase in composition to 90 mol %. Similarly, for propylene, R1/2 decreased from 29.5 to 3.6 with an increase in alkene gas-phase composition from 10 to 90 mol %. There was a marginal effect of temperature on R1/2. At lower alkene compositions, there was a reduction in adsorption selectivity with increasing temperature, whereas at higher alkene compositions, there was a slight increase in the selectivity. The binary mixture adsorption selectivity R1/2 at about 50 mol % alkene composition in Figure 5 compares well with the adsorption selectivity obtained from equilibrium adsorption data for the ethylene/ethane and propylene/propane adsorption isotherms given in Table 2. At lower concentrations of alkene, the π interactions dominate, giving rise to higher R1/2 values.
Figure 5. Mixture adsorption for ethylene/ethane and propylene/ propane predicted by extended L-F model: (a) alkene adsorbed composition as a function of gas-phase composition; (b) adsorption selectivity of ethylene/ethane and propylene/propane as a function of alkene gas-phase composition.
4.4. Sorption Uptakes and Reversibility. The sorption uptakes of ethylene, ethane, propylene, and propane studied at 303 K on this adsorbent are shown in Figure 6. The diffusion coefficient, D/r2, was calculated from the uptake data and is given in Table 5; simulated curves for diffusivity are also shown in Figure 6. The data show that the diffusion of ethylene and propylene was rapid. Over 90% of adsorption equilibrium was attained within a couple of minutes. The uptake rates of ethylene and propylene are faster than those of the corresponding alkanes. The desorption rates were also high. However, about 20% of the sorbate (ethylene/propylene) was retained on the adsorbent. When the sample was heated to about 100 °C, complete desorption occurred. To verify the adsorption reproducibility, uptake measurements were repeated for 10 cycles. The repeated adsorption-desorption cycling was done only by evacuation at 303 K. During the first cycle, about 20% of the sorbate remained on the sorbent. However, during the subsequent cycles, no additional retention of sorbent was observed. From the third cycle
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adsorption selectivities for ethylene and propylene over the corresponding alkanes. The adsorption selectivity was ascribed to the interaction between the silver ions and the π electrons of the alkene molecules. The isotherm data correlated well with the LangmuirFreundlich isotherm model for all of the systems studied. The predicted adsorption data for ethylene/ ethane and propylene/propane mixtures also showed very high adsorption selectivities for the alkenes over the corresponding alkanes. The alkene selectivity decreased with an increase in its concentration in gas phase. The diffusion of alkene was rapid compared to that of the corresponding alkane. Twenty percent of the alkene was irreversibly adsorbed. Ethylene could be separated from ethane with over 85% recovery and 99.8% purity using Olesorb-1 adsorbent and a four-bed vacuum swing adsorption process. Acknowledgment
Figure 6. Sorption uptakes of ethylene, ethane, propylene and propane on Olesorb-1 at 303 K: symbols, experimental data; lines, simulated diffusivity curves. Table 5. Diffusion Time Constant (D/r2) for Diffusion in Olesorb-1 at 303 K sorbate
D/r2 (s-1)
ethylene ethane propylene propane
2.9 × 10-3 0.6 × 10-3 1.3 × 10-3 0.5 × 10-3
onward, the adsorption capacity of the adsorbent remained almost constant. 4.5. Adsorbent Performance. The adsorbent was evaluated in a four-bed vacuum swing adsorption unit employing feed containing 83.1% ethylene; 16.8% ethane; and traces of propylene C4’s, CO, CO2, N2, and CH4. Each bed was filled with about 7.5 L of Olesorb-1 adsorbent. The process steps employed included adsorption, cocurrent rinse with product gas, countercurrent product extract by evacuation, and repressurization with raffinate alkane gas and/or rinse gas from the bed outlet that is undergoing product rinse step. The unit operation was at ambient temperature (290-300 K) . Ethylene was selectively adsorbed during the adsorption step, followed by a product gas rinse to remove unadsorbed ethane from the gas phase. The adsorbed ethylene was extracted by evacuation and collected in a product tank. The bed was partially repressurized with raffinate before pressurization with feed gas. Each bed was subjected to the above steps in a cyclic manner. The sequencing was done with the help of solenoid valves and programmable logic control (PLC). In a typical experiment, the overall cycle time was about 760 s. The feed flow was about 28-30 L/min, and the pressure ranged up to 950 Torr. The evacuation pressure was about 50 Torr, and the ethylene productivity was 1.4 mol per kilogram of adsorbent per hour. By employing Olesorb-1 adsorbent and the above process cycle, over 85% of the ethylene could be recovered with 99.8% purity. 5. Conclusions The alkene-selective adsorbent Olesorb-1 exhibited very high adsorption capacities, heats of adsorption, and
The authors are thankful to Ministry of Commerce, Industry and Energy (Korea); KOSEF (Korea); Korea Institute of Energy Research (Korea); and Indian Petrochemicals Corporation Ltd. (India) for financial support, for providing various facilities, and for necessary approvals. The authors also thank Mr. S. P. Patel (IPCL) for his assistance during experimental work. Literature Cited (1) Chang, T. Oil Gas J.. 2000, April 3, 56-67. (2) Keller, G. E.; Marcinkowsky, A. E.; Verma, S. K.; Williamson, K. D. Separation and Purification Technology; Li, N. N., Calo, J. M., Eds.; Marcel Dekker: New York, 1992; p 59. (3) Humphrey, J. L.; Seibert, A. F.; Koort, R. A. Separation TechnologiessAdvances and Priorities; DOE Report 12920-1; U.S. Department of Energy, U.S. Government Printing Office: Washington, DC, 1991. (4) Eldridge, R. B. Ind. Eng. Chem. Res. 1993, 32, 2208. (5) King, C. J. Separation Processes Based on Reversible Chemical Complexation. In Handbook of Separation Process Technology; Rousseau, R. W., Ed.; Wiley: New York, 1987; Chapter 15. (6) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 2nd ed.; Interscience: New York, 1966; Chapters 25 And 28. (7) Quinn, H. W. Hydrocarbon Separations with Silver(I) Systems. In Progress in Separation and Purification; Perry, E. S., Ed.; Interscience: New York, 1971; Vol. 4, p 133. (8) Ho, W. S.; Doyle, G.; Savage, D. W.; Pruett, R. L. Alkene Separation via Complexation with Cuprous Diketonate. Ind. Eng. Chem. Res. 1988, 27, 334. (9) Safarik, D. J.; Eldridge, R. B. Alkene/Alkane Separations by Reactive Absorption: A Review. Ind. Eng. Chem. Res. 1998, 37, 2571. (10) Long, R. B. Separation of unsaturates by complexing with solid copper salts. In Recent Developments in Separation Science; Li, N. N., Ed.; CRC Press: Boca Raton, FL, 1972. (11) Xie, C.; Tang, Y.-Q. Spontaneous Monolayer Dispersion of Oxides and Salts onto Surfaces of Supports: Applications to Heterogeneous Catalysis. Adv. Catal. 1990, 37, 1. (12) Kumar, R.; Golden, T. C.; White, T. R.; Rokicki, A. Novel Adsorption Distillation hydrid Scheme for Propane/Propylene Separation. Sep. Sci. Technol. 1992, 27, 2157. (13) Yang, R. T.; Kikkinides, E. S. New Sorbents for Alkene/ Alkane Separations by Adsorption via π-Complexation. AIChE J. 1995, 41 (3), 509. (14) Rege, S. U.; Padin, J. Yang, R. T. Alkene-Alkane Separations by Adsorption: Equilibrium Separation by π-Complexation vs Kinetic Separation. AIChE J. 1998, 44, 799. (15) Padin, J.; Yang, R. T.; Munson, C. L. New Sorbents for Alkene Alkane Separation and Alkene Purification from C4 Hydrocarbons. Ind. Eng. Chem. Res. 1999, 38 (10), 3614.
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Received for review June 26, 2001 Revised manuscript received March 14, 2002 Accepted March 18, 2002 IE010546+
