Silver Nitrate Impregnated Pellet-Type Adsorbents ... - ACS Publications

Ind. Eng. Chem. Res. 2006, 45, 9129-9135

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Silver Nitrate Impregnated Pellet-Type Adsorbents for Propylene/Propane Separation Chang Hyun Ko, Sang-Sup Han, Jong-Ho Park, Soon-Haeng Cho, and Jong-Nam Kim* Separation Technology Research Center, Korea Institute of Energy Research, 71-2, Jang-dong, Yuseong-gu, Daejon 305-343, Korea

Adsorptive separation of propylene from propane using adsorption has attracted much attention due to its energy efficiency compared to distillation. We prepared propylene-selective adsorbents suitable for pressure swing adsorption (PSA) separation by impregnating AgNO3 on high-surface-area pellets such as silica, clay, and aluminosilica as substrates. Considering adsorption capacity, selectivity, desorption rate, and pellet crush strength before and after impregnation, AgNO3/aluminosilica was the most suitable adsorbent among the three adsorbents. A large portion of the AgNO3 was located inside micropores in the aluminosilica after impregnation. The propylene adsorption capacity of AgNO3/aluminosilica was 2.3 mmol/g, and the selectivity of propylene over propane was 3.1 at 298 K and 3 kgf/cm2. However, the adsorption capacity of AgNO3/ aluminosilica for propylene decreased by exposing the adsorbent to hydrogen. 1. Introduction In the petrochemical industry, olefin/paraffin separation by distillation is a highly energy-consuming process. Such low energy efficiency mainly comes from the slight difference of boiling point between olefins and their corresponding paraffins.1,2 Recently, propane/propylene separation using adsorption has attracted much attention as an alternative technology for distillation. Among adsorptive separation methods, kinetic separation uses the size difference between propylene and propane, which results in an adsorption and desorption rate difference. NaA zeolite and partially Li+ exchanged NaA (NaLiA), whose pore sizes were around 4 Å, showed high propylene/propane selectivity (>10) and fast adsorption equilibrium at 423 K.3-6 AlPO4-14 was a better adsorbent than NaA or NaLiA considering selectivity and adsorption rate.3 CaA (5 Å), NaX (13 Å), and carbon molecular sieves (CMS) revealed poor selectivity due to the larger pore sizes of CaA and NaX compared to propane and propylene, or the broad pore size distribution of CMS.7-9 Apart from kinetic separation, equilibrium separation uses a specific interaction between adsorbate and adsorbent: π-complexation. Propylene has a double bond (π-bonding), which propane does not have. Cu+ and Ag+ are able to form complexes with propylene by donating a d-electron to the π*-orbital in propylene and accepting a π-electron from propylene to their outer s-orbitals.10 Mouljin and co-workers dispersed CuCl on the faujasite zeolite and obtained the propylene adsorption capacity of 2.77 mol/kg at 400 kPa and 338 K. However, the desorption rate of propylene was very slow.11 Yang and coworkers reported highly propylene-selective adsorbents using AgNO3 and CuCl as olefin-selective ingredients and alumina, silica, polymeric ion exchange resin, and mesoporous material as substrates.12-14 They also reported that equilibrium separation using AgNO3/silica showed higher propylene productivity at the same propylene recovery than that of kinetic separation using NaA.15 Most of the previously reported data were obtained using powder-type adsorbents. Considering practical pressure swing adsorption (PSA) applications, adsorbents must be of pellet type * To whom correspondence should be addressed. Tel.: +82-42-8603112. Fax: +82-42-860-3102. E-mail: [email protected].

because powder-type adsorbents might cause an additional pressure drop during the PSA process. Cho and co-workers used AgNO3-impregnated pellet-type clay as an adsorbent and achieved more than 88% recovery and 99.5% purity of propylene from the feed containing 94.5% propylene in the benchscale PSA separation process operating at 3 kgf/cm2.16 In this study, olefin-selective adsorbents were prepared for propylene/propane separation by impregnating AgNO3 on pellettype substrates such as clay, silica, and aluminosilica. The propylene adsorption capacity and selectivity of each adsorbent were strongly dependent on its surface area and pore volume. The effect of hydrogen on propylene adsorption capacity of the adsorbent was also investigated. 2. Experimental Section 2.1. Preparation of Adsorbents. AgNO3 was impregnated on pellet-type aluminosilica, silica, and clay by the incipient wetness method. AgNO3 was purchased from Junsei Chemical Co. As a typical example, the preparation of 39.4 wt % AgNO3/ aluminosilica involved four steps: First, the pellet-type substrate was heated to 573 K under inert atmosphere (N2 or Ar) to remove adsorbed impurities and moisture. Second, 0.5 mL of 7.65 M AgNO3 solution was slowly added on 1.0 g of aluminosilica substrate with vigorous shaking until the solution was absorbed completely on the substrate. Third, the resultant AgNO3-containing substrate was dried to remove excess liquid. Finally, AgNO3-impregnated substrate was activated by heat treatment in inert atmosphere at 383 K. We denote AgNO3impregnated samples depending on the AgNO3 concentration and substrates, for example, 37.5 wt % AgNO3/silica, 39.4 AgNO3/aluminosilica, 28.5 wt % AgNO3/clay, and so on. 2.2. Characterization of Adsorbents. The surface area, pore volume, and pore diameter were measured by adsorptiondesorption study using nitrogen at 77 K, and pore size distribution for micropores was obtained by argon desorption at 87 K, with a Micromeritics ASAP 2010 analyzer. Before each measurement, about 0.2 g of the sample was degassed at 383 K and below 1.33 mPa for 16 h. The pellet crush strength was defined by the applied force with a corn-type press on the pellet just before pellet crush. The applied force was measured by the digital force gauge DPS20 purchased from Imada Inc.

10.1021/ie051119p CCC: $33.50 © 2006 American Chemical Society Published on Web 11/14/2006

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Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006

Figure 1. Adsorption and desorption measurement apparatus using magnetic suspension balance system.

2.3. Measurements of Adsorption/Desorption Isotherm. Adsorption and desorption isotherms were measured by a magnetic suspension balance (MSB) as shown in Figure 1. Constant-temperature bath I maintained the temperature of injected adsorbate to a given temperature with (0.1 °C precision. Constant-temperature bath-II protected magnetic balance from thermal stress during the heat treatment of sample. The prepared adsorbent was degassed and regenerated in the balance under the flow of ultrahigh purity helium gas at 383 K, then adjusted to the measuring temperature and evacuated to 1.33 mPa using a turbo molecular pump. After each adsorption isotherm measurement, desorption isotherm was also measured to check the reversibility. The purity and providing company for each adsorbate were as follows: propylene (minimum purity: 99.5%, Air Products & Chemical Co.), propane (minimum purity: 99.5%, Liquid Carbonic Co.). Partial pressure of adsorbate was displayed based on the pressure unit kgf/cm2, and 1 kgf/cm2 was considered to be 98 kPa for the conversion of SI unit. 2.4. Measurements of Adsorption Isotherm in Hydrogen Environment. A 300 mg sample of 39.4 wt % AgNO3/ aluminosilica was placed in the MSB chamber to measure propylene/propane adsorption at 298 K. Then, high-purity hydrogen (99.995 vol %) was provided in this MSB chamber at a given temperature with 1 atm for 1 h. After the temperature of MSB chamber decreased to 298 K and hydrogen was evacuated, the propylene adsorption isotherm was measured again at 298 K. Hydrogen contact temperature was changed from 298 to 343 K. 3. Results and Discussion To prepare highly efficient adsorbent, a substrate with a high surface area must be used in order to contain a large amount of AgNO3. High-surface-area substrates may maximize the contact area between adsorbate and AgNO3. In the selection of substrate, the surface area, pore size, and pore volume of various pellettype substrates were considered. Powder-type substrates such as zeolites (NaX, NaY) and mesoporous materials (MCM-41, MCM-48, SBA-15) were excluded because powder might cause an additional pressure drop during the PSA process. Even if these powder materials were synthesized as pellets, binder materials, which helped pellet formation, might change the adsorption properties of the adsorbent. As shown in Table 1, aluminosilica and silica pellets seem to be better substrates for

Table 1. Physical Properties of Pellet-Type Substrates properties [m2

aluminosilica g-1]

BET surface area total pore volume [cm3 g-1] average pore diametera [nm]

698 0.52 2.9

Silica

clay

489 0.84 1.8

392 0.42 2.2

a Average pore diameter was calculated with the equation 4V/A, where V is total pore volume at p/p0 ) 0.98 and A is BET surface area.

Figure 2. Change of pellet crush strength before and after impregnation of 7.65 M AgNO3 solution on each substrate: (a) clay; (b) silica; (c) aluminosilica.

adsorbent due to their larger pore volume and high surface area compared to clay. In addition to surface area, the mechanical strength of the pellet must be considered because pellet crush might cause a pressure drop during the PSA process. The comparison among substrates for the change of strength before and after AgNO3 impregnation is shown in Figure 2. Prior to impregnation, silica was the hardest among the three substrates. The mechanical strength order of the pellets is as follows: silica > aluminosilica > clay. After impregnation of AgNO3, however, pellet crush strength of silica decreased drastically as shown in Figure 2. The decrease of mechanical strength in silica pellets might come from the formation of the cracks during the impregnation step. Soaking of salt solution swollen silica pellets, subsequent drying, and thermal treatment might cause the formation of cracks inside the silica pellets. On the other hand, there was almost no strength change for aluminosilica despite swelling and contraction. This means that aluminosilica is a better substrate for adsorbent than silica as far as the metal impregnation step is concerned. The adsorption isotherms of propane and propylene on aluminosilica are displayed in Figure 3. Aluminosilica adsorbed

Ind. Eng. Chem. Res., Vol. 45, No. 26, 2006 9131

Figure 3. Propylene and propane adsorption isotherms of aluminosilica at 298 K: (9) propylene; (O) propane. Table 2. Optimum Adsorption Capacity of AgNO3-Impregnated Adsorbents for Propane and Propylene Depending on Substrates adsorption capacity (mmol/g) adsorbent AgNO3/ aluminosilica AgNO3/silica AgNO3/clay a

AgNO3 concn (wt %)

propylenea

propanea

selectivity (propylene/ propane)

39.4

2.30

0.70

3.29

37.5 28.5

2.70 1.75

0.70 0.95

3.86 1.84

Adsorption capacity was measured at 3 kgf/cm2 and 298 K.

and desorbed propane reversibly. However, aluminosilica adsorbed quite a large amount of propylene and did not desorb propylene the same amount. Aluminosilica adsorbed propylene irreversibly. This indicates that strong bond formation occurred between the aluminosilica substrate and adsorbed propylene at ambient conditions. As AgNO3 provides reversible adsorption sites by π-complexation between AgNO3 and propylene, the impregnation of AgNO3 prevents irreversible adsorption and enables reversible adsorption. The impregnation amount of AgNO3 in aluminosilica was changed in order to maximize propylene adsorption capacity and propylene/propane selectivity as shown in Figure 4. The adsorption capacity was measured at 3 kgf/cm2 and 298 K. To maximize the propylene adsorption capacity on the alumino-

silica, the amount of AgNO3 should be maximized on the substrate surface while at the same time remaining in the form of monolayer dispersion. Up to a AgNO3 concentration of 39.4 wt %, an increase of the AgNO3 concentration resulted in an increase of the propylene adsorption sites on the surface of aluminosilica. At a AgNO3 concentration of 39.4 wt %, a maximum propylene adsorption capacity of 2.3 mmol/g is thus reached. Up to 39.4 wt %, AgNO3 is supposed to be evenly distributed on the surface of aluminosilica in the form of monolayer dispersion of AgNO3. The evidence for the formation of AgNO3 monolayer on the substrate is the effectiveness of AgNO3 for propylene. The molar ratio of propylene over AgNO3 (propylene/AgNO3) was maintained at 1 up to the AgNO3 concentration of 39.4 wt %. This means that every molecule of AgNO3 takes part in the adsorption of propylene up to this concentration. At 41.2 wt %, however, the amount of propylene adsorption decreased compared to that at 39.4 wt %. Thus, the addition of AgNO3 above 39.4 wt % decreased propylene adsorption sites. This also means that excess amount of AgNO3 might induce the agglomeration of monodispersed AgNO3 into large particles which result in a decrease of propylene adsorption capacity and propylene/Ag+ above 39.4 wt %. The optimized AgNO3 concentrations that also maximized the propylene adsorption capacities of clay and silica are reported in Table 2. Figure 5 shows the adsorption isotherms of pure propylene and propane at 298 K on various types of adsorbents using the optimized AgNO3 concentration reported in Table 2. For all adsorbents, propylene was more strongly adsorbed than propane in entire pressure range 0-5 kgf/cm2. Such propylene-preferred adsorption comes from AgNO3: 39.4 wt % AgNO3/aluminosilica and 37.5 wt % AgNO3/silica had higher propylene adsorption capacities and propylene/propane selectivities than 28.5 wt % AgNO3/clay because aluminoslica and silica contained larger amounts of AgNO3 than clay did. As AgNO3 was selected as a common propylene-selective material, the surface area and pore volume of the substrate governed the properties of the adsorbent for propylene/propane separation; 37.5 wt % AgNO3/silica had a slightly higher propylene capacity than 39.4 wt % AgNO3/aluminosilica had. However, the mechanical strength of silica pellet decreased drastically after impregnation.

Figure 4. Propane and propylene adsorption capacity, propylene selectivity over propane, and molar ratio of propylene to Ag+ according to AgNO3 concentration at 298 K and 3 kgf/cm2.

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Figure 5. Propane and propylene adsorption isotherms on AgNO3-impregnated adsorbents at 298 K depending on substrates: (b) propylene on 39.4 wt % AgNO3/aluminosilica; (O) propane on 39.4 wt % AgNO3/aluminosilica; (9) propylene on 37.5 wt % AgNO3/silica; (0) propane on 37.5 wt % AgNO3/silica; (2) propylene on 28.5 wt % AgNO3/clay; (4) propane on 28.5 wt % AgNO3/clay. AgNO3 concentration for each substrate was based on those given in Table 2.

Considering the propylene adsorption capacity, selectivity, and pellet hardness, AgNO3/aluminosilica was the most suitable adsorbent for propylene/propane separation among all three AgNO3-impregnated pellet-type substrates. The distribution of AgNO3 on the aluminosilica surface was also investigated by measuring the surface area, pore volume using nitrogen adsorption at 77 K, and pore size distribution using argon at 87 K, before and after metal salt impregnation. When 1.0 g of aluminosilica was impregnated with 0.65 g of AgNO3 (39.4 wt % AgNO3), the surface area and pore volume, obtained by nitrogen adsorption, decreased from 698 to 268 m2/g and from 0.43 to 0.22 cm3, respectively. On the other hand, the average pore size increased slightly after impregnation from 2.9 to 3.2 nm. Such an increase of average pore size after AgNO3 impregnation suggests that AgNO3 places in the small pore rather than the large pore. In the analysis of pore size distribution by argon adsorption-desorption, as shown in Figure 6, a large portion of pore volume in aluminosilica comes from small pores whose size is less than 2.0 nm. After AgNO3 impregnation, differential pore volume decreased drastically. The decrease of differential pore volume mainly comes from the occupation of

Figure 6. Pore size distribution of aluminosilica and AgNO3-impregnated aluminosilica (39.4 wt % AgNO3/aluminosilica) using Ar adsorptiondesorption isotherms at 87 K.

AgNO3 inside the pores. The pore volume from small pores (less than 2 nm) decreased much more than that from large pores


Figure 7. Comparison of desorption rate between 28.5 wt % AgNO3/clay and 39.4 wt % AgNO3/aluminosilica. Table 3. Equilibrium Isotherm Parameters for AgNO3/ Aluminosilica Using Toth’s Isotherm (Eq 1) adsorption temp (K)

adsorbate

298

propylene propane propylene propane propylene propane

323 343

qm (mmol/g) b ((kgf/cm2)-1) 2.4426 1.6612 2.2659 0.5770 1.8332 0.4658

38.966 2.3551 4.777 1.2522 2.2579 0.633

n 0.4984 0.5618 0.6686 1.4788 0.895 2.6824

(more than 2 nm). This means that large portions of AgNO3 particles are located inside the pores whose size is less than 2 nm. The desorption rate of 39.4 wt % AgNO3/aluminosilica was compared to that of 28.5 wt % AgNO3/clay. As shown in Figure 7, the desorption of propane and propylene from 28.5 wt % AgNO3/clay was slower than that from 39.4 wt % AgNO3/ aluminosilica. Such slow desorption might induce the decrease of productivity in the PSA process. Not only the propylene adsorption capacity and selectivity, but also the desorption rate of AgNO3/aluminosilica, is better than that of AgNO3/clay. Figure 8 shows the change of propylene and propane adsorption isotherms for 37.5 wt % AgNO3/aluminosilica depending on the adsorption temperature from 298 to 343 K. The equilibrium adsorption isotherms are correlated by Toth’s isotherm parameters, as shown in eq 1. Calculated parameters depending on adsorption temperatures are summarized in Table 3.

bP q ) qm [1 + (bP)n]1/n

(1)

q is the amount adsorbed, P is the equilibrium partial pressure of the adsorbate, and qm, b, and n are constants. Figure 9 describes the isosteric heats of adsorption for propylene and propane obtained from the temperature-dependent adsorption isotherms using the Clausius-Clapeyron equation

Figure 8. Adsorption equilibrium isotherms of propylene and propane on 37.5 wt % AgNO3/aluminosilica depending on the adsorption temperature: (b) propylene at 298 K; (O) propane at 298 K; (9) propylene at 323 K; (0) propane at 323 K; (2) propylene at 343 K; (4) propane at 343 K. The experimental data were fitted using Toth’s isotherm equation.

appearing in eq 2.

d(ln p) ∆H ) R d(1/T)

(2)

The heats of adsorption for ethylene and ethane, already reported by Son et al.,17 are also displayed in Figure 9, to be compared with those for propylene and propane. The adsorptions of propane and ethane are mainly related with weak physical interactions such as van der Waals forces. Thus, the heat of adsorption for propane is higher than that for ethane due to the higher polarizability. On the other hand, heats of adsorption

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Figure 9. Isosteric heats of adsorption for propylene, propane, ethylene, and ethane on 37.5 wt % AgNO3/aluminosilica depending on adsorption amount.

for propylene and ethylene on AgNO3/aluminosilica are almost the same, because their interactions are dominated by π-complexation. The olefin-rich stream in petrochemical processes frequently contains hydrogen. Hydrogen in the olefin-rich stream is able to reduce silver ion in AgNO3/aluminosilica. The change of adsorption capacity on 39.4 wt % AgNO3/aluminosilica after exposure to hydrogen at several adsorption temperatures is shown in Figure 10. A sample of 39.4 wt % AgNO3/ aluminosilica was placed in the reaction chamber with high-

purity hydrogen (99.995 vol %) at 1 atm for 1 h with given temperature. Before and after hydrogen contact, the propylene adsorption capacity was measured. At the exposure temperature of 298 K, the difference of adsorption capacity before and after hydrogen contact was negligible. At 323 K, the propylene adsorption capacity decreased drastically and the selectivity of propylene over propane was less than 2. At 343 K, the propylene adsorption capacity became similar to that of propane. Hydrogen contact to AgNO3/alulminosilica at high temperature decreased the propylene adsorption capacity due to the reduction of Ag+ to metallic Ag. Yang and co-workers also reported a similar phenomenon.18 They used Ag+-exchanged Y zeolite (Ag+-Y) as adsorbent and placed the adsorbent in 50% hydrogen environment at 393 K for 1 h. After hydrogen contact, Ag+-Y was not able to adsorb olefin. Ag+ inside the Y zeolite might be completely reduced to metallic Ag at their experimental conditions. However, in the present experiment, although the propylene adsorption capacity decreased compared to the original capacity, 39.4 wt % AgNO3/aluminosilica still adsorbed propylene. This indicates that Ag+ in aluminosilica is not reduced completely. This difference might come from the Ag+ environment inside the adsorbent. In the Y zeolite, the framework of zeolite was a counteranion and Ag+ cation was attached on the framework inside the pore. Thus, partial surface of Ag+ cation opened freely for hydrogen. On the other hand, Ag+ cation in aluminosilica was surrounded by nitrate anion (NO3-), because AgNO3 would maintain as a metal salt in aluminosilica. Although AgNO3 is slightly more tolerant than Ag+-Y, hydrogen is also detrimental to AgNO3/aluminosilica for olefin adsorption. These results show that hydrogen in the propylene/

Figure 10. Adsorption isotherms of 39.4 wt % AgNO3/aluminosilica for propylene and propane at 298 K, depending on hydrogen exposure temperature: propylene isotherm without hydrogen exposure (a) and with hydrogen exposure at 298 K (b), 323 K (c), and 343 K (d); propane isotherm without H2 exposure at 298 K (e). Filled symbols mean adsorption of propylene, and empty symbols represent desorption of propylene. Hydrogen pressure was 1 atm.


propane mixture must be removed prior to use of Ag/aluminosilica as an adsorbent. 4. Conclusion AgNO3-impregnated propylene-selective adsorbents were prepared using pellet-type materials, such as aluminosilica, silica, and clay, as substrates. The comparison of propylene adsorption capacity and selectivity among them shows that AgNO3/ aluminosilica was the most suitable adsorbent for propylene/ propane separation due to its higher adsorption capacity and selectivity for propylene, desorption rate, and pellet crush strength. The optimized AgNO3 concentration on aluminosilica was 39.4 wt %. At this concentration, the adsorption capacity of propylene was 2.3 mmol/g and the propylene/propane selectivity was 3.1 at 298 K and 3 kgf/cm2. Hydrogen exposure to AgNO3/aluminosilica reduced the adsorption capacity and selectivity for propylene. To maintain the adsorption capacity and selectivity, hydrogen in the propylene/propane mixture must be removed prior to separation. Literature Cited (1) Keller, G. E.; Marcinkowsky, A. E.; Verma, S. K.; Williamson, K. D. Olefin RecoVery and Purification Via SilVer Complexation in Separation and Purification Technology; Li, N. N., Calo, J. M., Eds.; Marcel Dekker: New York, 1992. (2) Eldridge, R. B. Olefin/Paraffin Separation Technology: A Review. Ind. Eng. Chem. Res. 1993, 32, 2208. (3) Padin, J.; Rege, S. U.; Yang, R. T.; Cheng, L. S. Molecular sieve sorbents for kinetic separation of propane/propylene. Chem. Eng. Sci. 2000, 55, 4525. (4) Patino-Iglesias, M. E.; Aguilar-Armenta, G.; Jimenez-Lopez, A.; Rodriguez-Castellon, E. Kinetics of the total and reversible adsorption of propylene and propane on zeolite 4A (CECA) at different temperatures. Colloids Surf., A.: Physicochem. Eng. Aspects 2004, 237, 73. (5) Da Silva, F. A.; Rodrigues, A. E. Vacuum swing adsorption for propylene/propane separation with 4A Zeolite. Ind. Eng. Chem. Res. 2001, 40, 5758.

(6) Grande, C. A.; Rodrigues, A. E. Propane/propylene separation by pressure swing adsorption using zeolite 4A. Ind. Eng. Chem. Res. 2005 44, 8815. (7) Grande, C. A.; Gigola, C.; Rodrigues, A. E. Adsorption of propane and propylene in pellets and crystals of 5A Zeolite. Ind. Eng. Chem. Res. 2002, 41, 85. (8) Da Silva, F. A.; Rodrigues, A. E. Propylene/propane separation by vacuum swing adsorption using 13X zeolite. AIChE J. 2001, 47, 341. (9) Grande, C. A.; Silva, V. M. T. M.; Gigola, C.; Rodrigues, A. E. Adsorption of propane onto carbon molecular sieve. Carbon 2003, 41, 2533. (10) Chen, J. P.; Yang, R. T. Molecular orbital study of selective adsorption of simple hydrocarbons on Ag(I) and Cu(I) exchanged resins and halides. Langmuir 1995, 11, 3450. (11) van Miltenburg, A.; Zhu, F.; Kapteijn, W.; Moulijn, J. A. Adsorptive separation of light olefins and paraffins. Abstracts, 8th International Conference on Fundamentals of Adsorption, Sedona, AZ, May 23-28, 2004; International Adsorption Society; Plenary-8. (12) Cheng, L. S.; Yang, R. T. Monolayer cuporous chloride dispersed on pillared clays for olefin-paraffin separations by π-complexation. Adsorption 1995, 11, 61. (13) Yang, R. T.; Kikkinides, E. S. New sorbents for olefin/paraffin separations by adsorption via π-complexation. Ind. Eng. Chem. Res. 1995, 41, 509. (14) Padin, J.; Yang, R. T. New sorbents for olefin/paraffin separations by adsorption via π-complexation: synthesis and effects of substrates. Chem. Eng. Sci. 2000, 55, 2607. (15) Rege, S. U.; Padin, J.; Yang, R. T. Olefin/paraffin separations by adsorption: π-complexation vs. kinetic separation. AIChE J. 1998, 44, 799. (16) Han, S.-S.; Park, J.-H.; Kim, J.-N.; Cho, S.-H. Study on propylene/ propane separation by gaseous adsorption technology. Abstracts, 6th International Symposium on Separation Technology between Korea and Japan, Tokyo, Japan, October 4-6, 2002; The Society of Separation Process Engineers, Japan and The Korean Institute of Chemical Engineers; AD121. (17) Son, Y.; Han, S.-S.; Park, J.-H.; Kim, J.-N.; Cho, S.-H.; Lee, T. Study on the adsorption characteristics of ethane and ethylene on aluminosilica based sorbent. Hwahak Konghak 2003, 41, 749. (18) Takahashi, A.; Yang, R. T. Cu(I)-Y zeolite as a superior adsorbent for diene/olefin separation. Langmuir 2001, 17, 8405.

ReceiVed for reView October 7, 2005 ReVised manuscript receiVed August 31, 2006 Accepted September 7, 2006 IE051119P

Silver Nitrate Impregnated Pellet-Type Adsorbents ... - ACS Publications

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