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New Adsorbents Based on Principles of Chemical Complexation: Monolayer-Dispersed Nickel(II) for Acetylene Separation by π-Complexation Ralph T. Yang*,† and Robert Foldes Department of Chemical Engineering, State University of New York at Buffalo, Buffalo, New York 14260
A sorbent was prepared by dispersing a monolayer of Ni2+ ions (by spreading a monolayer of NiCl2‚6H2O) on a high-surface-area γ-Al2O3. This sorbent showed high selectivities for acetylene (C2H2) over other hydrocarbons, by forming a weak π-complexation bond between Ni2+ and C2H2. For example, at 60 °C, the equilibrium amounts of hydrocarbons adsorbed at 1 atm were (in mmol/g) C2H2 ) 1.56, C2H6 ) 0.043, C2H4 ) 0.061, C3H6 ) 0.42, and C3H8 ) 0.30. The bond energy for the Ni2+-C2H2 complex was approximately 9.3 kcal/mol, and the adsorption was reversible. The stoichiometry of the complex was Ni2+(C2H2)n where n ) 1-3 at 25 °C and subatmospheric pressure. The π-complexation bond was formed by the donation of the C2H2 π-electrons to the vacant hybridized dsp2 orbitals of Ni2+ and the back-donation of electrons from the filled d (or dp-hybrid) orbitals of Ni2+ into the antibonding orbitals of C2H2. This work demonstrates that new sorbents can be designed and prepared by exploiting the weak, reversible π-complexation bonds, and, consequently, conventional separation/purification processes can be replaced by more efficient adsorption processes. Introduction Separation of acetylene is important in two types of industrial processes: acetylene production and the removal of acetylene and its derivatives as a preseparation for other separation processes. These are discussed as follows. Acetylene is produced from hydrocarbons by various thermal cracking processes followed by its separation from other hydrocarbon cracking products at nearambient temperatures. The separation is presently accomplished by costly solvent extraction processes employing liquid solvents such as DMF (dimethylformamide). Separation by gas-solid adsorption would be highly desirable, particularly by the efficient pressure swing adsorption processes (Yang, 1987). However, no appropriate sorbents are available since the known sorbents either do not have the high selectivities for acetylene (over other hydrocarbons) or adsorb acetylene irreversibly. Olefin-paraffin separations represent a class of most important and also most costly separations in the chemical and petrochemical industry. Cryogenic distillation has been used for over 60 years for these separations (Keller et al., 1992). They remain to be the most energy-intensive distillations because of the close relative volatilities. For example, ethane-ethylene separation is carried out at about -25 °C and 320 psig (2.306 MPa) in a column containing over 100 trays, and propane-propylene separation is performed by an equally energy-intensive distillation at about -30 °C and 30 psig (0.308 MPa) (Keller et al., 1992). Separation by using π-complexation has been discussed as a promising alternative (Gilliland et al., 1941; Long, 1972; Hirai, 1985; Ho et al., 1988; Keller et al., 1992; Blytas, 1992; Eldridge, 1993). The π-complexation is a subgroup of chemical complexation where the mixture is contacted with a second phase containing a complexing agent (King, 1987). The advantage of chemical complexation * To whom all correspondence should be addressed. † Present address: Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109.
0888-5885/96/2635-1006$12.00/0
is that the bonds formed are stronger than those by van der Waals forces alone, so it is possible to achieve high selectivity and high capacity for the component to be bound; at the same time, the bonds are still weak enough to be broken by using simple engineering operations such as raising the temperature or decreasing the pressure. Highly efficient solid π-complexation sorbents have been developed recently for olefin-paraffin separations (Yang and Kikkinides, 1995). These sorbents contain highly dispersed Ag+ or Cu+ cations and have high selectivities, high capacities, fast rates, and reversibility. However, acetylene chemisorbs on Ag+ and Cu+ cations to form acetylides (e.g., HC ≡ CAg and C2Ag2), and the acetylides are highly unstable and are susceptable to detonation (Keller et al., 1992). Therefore, acetylene must be preseparated prior to olefin-paraffin separations. Also for safety reasons, the trace amount (ppm level) of acetylene contained in air must be preseparated prior to all air separation processes. In this work, it was found that Ni2+ cations form weak and reversible π-complexation bonds with acetylene and that Ni2+ cations do not form π-complexation bonds with hydrocarbons containing single and double bonds. A sorbent containing dispersed Ni2+ ions was prepared. It exhibited high selectivities for acetylene over other hydrocarbons as well as other superior adsorption properties for acetylene separation. Experimental Section Preparation of Sorbent. A high-surface-area γ-Al2O3 was used as the support. In order to introduce metal ions on γ-Al2O3, a known technique for monolayer dispersion was employed. The phenomenon of spontaneous dispersion of metal oxides and salts in monolayer or submonolayer forms onto surfaces of inorganic supports with high surface areas has been studied extensively in the literature (e.g., Xie and Tang, 1990). Bonds formed between the monolayer and the substrate surface need to be strong enough to make the process of spreading spontaneous. A theoretical value for mono© 1996 American Chemical Society
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layer coverage capacity can be estimated by assuming the monolayer to be close-packed. The surface area of the support can be estimated from the nitrogen adsorption isotherm at the liquid nitrogen temperature (77 K). By preparing several samples with different salt/support ratios and by measuring the amounts of residual crystalline salt after heat treatment (when the process of spreading occurs), one can determine the threshold (monolayer) dispersion capacity. The threshold dispersion capacity is the maximum amount of salt that can be spread onto the surface of the support by heat treatment, such that no residual amount of salt exists in the crystalline form. The temperature of the heat treatment should be high enough to overcome the kinetic resistance but below that for chemical reaction which would alter the structure of the surface. The γ-Al2O3 support used in this study was PSD-350 activated alumina from Alcoa Separations Technology, Inc. The BET surface area was 340 m2/g with a pore volume of 0.57 cm3/g, and it had a trimodal pore size distribution with a significant fraction of the pores larger than 2 nm. NiCl2‚6H2O was used as the source for Ni(II) cations. The procedure for spreading NiCl2‚ 6H2O on γ-Al2O3 was taken from Xie and Tang (1990). They spread 0.18 g of salt on 1 g of a γ-Al2O3 of a 170 m2/g surface area at 70 °C for 78 h. The fact that the salt was spread in the form of a monolayer was verified by XRD analysis. Since the surface area of our γ-Al2O3 was twice as high, we used twice the amount of NiCl2‚ 6H2O (0.36 g/g of Al2O3) and heat-treated the sample in air at 70 °C for 5 days. This procedure ensured monolayer spreading of the salt on γ-Al2O3 (as shown by Xie and Tang, 1990). Equilibrium Isotherm and Uptake Rate Measurements. Isotherms and uptake rates were measured gravimetrically employing a Cahn 2000 System 113 microbalance in the same manner as described in detail by Ackley and Yang (1991). Each adsorption experiment was followed by desorption to check the reversibility. Helium (high-purity grade; Linde Division; minimum purity 99.95%) was used as the inert carrier gas and the environment for regeneration. The following hydrocarbons were used: acetylene (purified grade; Matheson; minimum purity 99.6%), ethane (CP grade; Matheson; minimum purity 99.5%), ethylene (CP grade; Matheson; minimum purity 99.0%), propane (CP grade; Matheson; minimum purity 99.0%), and propylene (CP grade; Matheson; minimum purity 99.0%). These gases were used without further purification. Results and Discussion Monolayer Dispersion: Further Evidence and Its Effects on Adsorption. Equilibrium adsorption isotherms were measured on both a pure γ-Al2O3 support and that spread with NiCl2‚6H2O. Figure 1 shows the isotherms for acetylene, ethylene, and ethane at 60 °C. In addition, the desorption isotherm for C2H2 on γ-Al2O3 is also shown in Figure 1. The surface chemistry of aluminas is not fully understood. However, it is know that strong Lewis acid sites exist on their surfaces and that the pretreatment temperature strongly influences both the amount and strength of the acid sites (Tanabe et al., 1989; Gates, 1992; Pines, 1981). Hydrocarbon molecules can be chemisorbed on the surface by coordination to the positive Al sites. The γ-Al2O3 used in this study was pretreated at 200 °C (in He) prior to isotherm measurements at 60 °C. The results in Figure 1 show strong
Figure 1. Equilibrium adsorption isotherms of C2 hydrocarbons on γ-Al2O3 and monolayer NiCl2‚6H2O/γ-Al2O3 at 60 °C. (Curves are fittings by eqs 1, 4, and 5.)
chemisorption of C2H2 on γ-Al2O3: a high Henry’s constant and the irreversibility of isotherm. Upon desorption at 60 °C in pure He, the residual amount of C2H2 on γ-Al2O3 was 3.4 mmol/g, equivalent to 6 × 1014 molecules/cm2. The total amount of Al ions is on the order of 1014/cm2 (Tanabe et al., 1989). Thus, essentially a monolayer of C2H2 was chemisorbed on the alumina (with possibly more than one C2H2 bonded to each Al ion). Heating failed to desorb C2H2. Coking began at 120 °C as observed visually by color change, due to cracking on the acid sites. The concentration of the Ni2+ ions dispersed on the surface was, assuming monolayer Ni(II) salt dispersion, 1.24 mmol/g. This corresponded well to the amount of C2H2 that was adsorbed on the Ni2+/Al2O3 surface; i.e., the C2H2/Ni2+ ratio was approximately 1 for the C2H2 capacity at 60 °C. The C2H2 isotherm was totally reversible, as to be discussed shortly. The amounts of adsorbed C2H4 and C2H6 (Figure 1) were substantially lower than that of C2H2. The deposition of Ni(II) salt on the alumina surface also decreased the adsorption for both C2H4 and C2H6. This result indicated a weak coordination of the C2H4 and C2H6 molecules to the positive Al sites on the alumina (Tanabe et al., 1989) and a lack of interactions with the Ni salt covered surface. All isotherms other than C2H2/ γ-Al2O3 shown in Figure 1 were reversible. The results in Figure 1 show a high selectivity of the NiCl2‚6H2O/γ-Al2O3 sorbent for C2H2 over C2H4 and C2H6. Moreover, it provided further evidence (Xie and Tang, 1990) for the monolayer dispersion of the Ni salt as no bare Al2O3 surface remained. C2H2-Ni2+ π-Complexation: Bond Strength, Reversibility, and Selectivities over Other Hydrocarbons. The equilibrium isotherms of C2H2 on NiCl2‚ 6H2O/γ-Al2O3 at four temperatures (25, 45, 60, and 70 °C) are shown in Figure 2. The amounts adsorbed at 1 atm were 3.28, 2.26, 1.56, and 1.46 mmol/g, respectively, at these temperatures. The isosteric heat of adsorption was calculated from the temperature dependence of the fitted isotherms (the fitting will be discussed shortly). The value at 1 mmol/g was 9.3 kcal/mol. The isosteric heats of adsorption of olefins (C2H4 and C3H6) on sorbents with Ag+ and Cu+ ions were on the order of 14 kcal/mol (Yang and Kikkinides, 1995), and these were considerably stronger π-complexation bonds in comparison with the C2H2-Ni2+ bond.
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Figure 2. Equilibrium isotherms of C2H2 on monolayer NiCl2‚ 6H2O/γ-Al2O3. (Curves are fittings by eqs 1, 4, and 5.)
Figure 4. Selective adsorption for C2H2 over other hydrocarbons on monolayer NiCl2‚6H2O/γ-Al2O3 at 60 °C. (Curves are fittings by eqs 1, 4, and 5.)
sure swing adsorption of C2 mixtures by π-complexation, the maximum temperature rise was 50 °C (Sikavitsas et al., 1995). This is not high enough to cause a problem. Equilibrium Isotherm Model. The isotherm derived by Yang and Kikkinides (1995) was taken as the starting point for fitting our experimental data. The isotherm has the following form:
q)
Figure 3. Reversibility for adsorption of C2H2 on monolayer NiCl2‚6H2O/γ-Al2O3 at 60 °C.
Cyclic adsorption-desorption isotherms for C2H2 on the Ni2+-sorbent were measured at 60 °C and are shown in Figure 3. Nearly complete reversibility was seen in this experiment. The olefin-Ag+ (or Cu+) complexation, in comparison, did not exhibit such high reversibilities (Yang and Kikkinides, 1995), probably due to the stronger bonds, i.e., 14 vs 9.3 kcal/mol. The residual amount of C2H2 that could not be desorbed at 60 °C was slightly less than 2% of the amount adsorbed at 1 atm (or about 2% of that corresponding to C2H2/ Ni2+ ) 1). This was likely due to sites that form strong π-complex or bare Al sites. Figure 3 also shows a small hysteresis loop, possibly due to capillary condensation in very fine pores. Cyclic adsorption-desorption was also measured at 70 °C, and 100% reversibility (and no hysteresis) was observed at this temperature. Apparently no capillary condensation occurred at 70 °C. The fact that 70 °C was also the temperature at which the Ni salt was dispersed was probably a coincidence. Figure 4 displays isotherms of the five hydrocarbons on the NiCl2‚6H2O/γ-Al2O3 sorbent at 60 °C. At 1 atm, the equilibrium amounts and the pure-component selectivity ratios were C2H2 ) 1.56 mmol/g, C2H6 ) 0.043 mmol/g, C2H4 ) 0.061 mmol/g, C3H6 ) 0.42 mmol/g, and C3H8 ) 0.30 mmol/g and C2H2/C2H4 ) 36.3, C2H2/C2H6 ) 25.6, C2H2/C3H6 ) 3.7, and C2H2/C3H8 ) 5.2. These are indeed excellent selectivities and C2H2 capacity for industrial separation processes (Yang, 1987). For pres-
1+b h cP exp(s) qmc qmpbpP + ln 1 + bpP 2s 1+b h cP exp(-s)
(1)
The two terms express two contributions, physical and chemical adsorption (denoted respectively by subscripts p and c). This model also takes into account the energetic heterogeneity of the surface ion sites for complexation. The second term in eq 1 is the Langmuir isotherm on a surface with a uniform energy distribution. The parameter, s, is a heterogeneity parameter indicating the spread of the energy distribution (Honig and Reyerson, 1952). For the limiting cases s f 0, the second term in eq 1 is reduced to the Langmuir isotherm. The parameters b h c and s depend on temperature as follows:
b h c ) b0 exp(j/RT)
(2)
s ) x3σ/RT
(3)
where j and σ are the mean and square root of variance of the uniform energy distribution. Except for acetylene, all isotherms were fitted well by using only the first term in eq 1 with two parameters, qpm and bp. However, the adsorbed amounts of ethane and ethylene with molecular weights similar to that of acetylene were very small compared to those of acetylene. This suggested strong domination of chemisorption over physical adsorption for the adsorption of acetylene. Consequently, the acetylene isotherms were fitted with only three parameters of the second term of eq 1; i.e., the contribution to adsorption of C2H2 by van der Waals forces was neglected. In this manner we obtained excellent fittings, but some of the parameters did not have physical meaning (e.g., the strong variation of s with temperature). To correct for this inconsistency, we decided to carry out the regression for all experimental points of the adsorption of acetylene at four different temperatures at once. The four acetylene isotherms were
Ind. Eng. Chem. Res., Vol. 35, No. 4, 1996 1009
Figure 5. Uptake rates on NiCl2‚6H2O/γ-Al2O3 at 60 °C.
Figure 6. Uptake rates of C2H2 on NiCl2‚6H2O/γ-Al2O3.
Table 1. Equilibrium Isotherm Parameters (Eqs 1, 4, and 5)
Table 2. Diffusion Time Constants on NiCl2‚6H2O/γ-Al2O3
qmp (mmol/g)
bp (1/atm)
qmc (mmol/g)
bc (1/atm)
D/R2 (1/s) s
On γ-Al2O3 3.32 2.70
C2H4 (60 °C) C2H6 (60 °C)
0.335 0.330
C2H4 (60 °C) C2H6 (60 °C) C3H6 (60 °C) C3H8 (60 °C) C2H2 (25 °C) C2H2 (45 °C) C2H2 (60 °C) C2H2 (70 °C)
On NiCl2‚6H2O/γ-Al2O3 0.107 1.38 0.063 2.27 0.564 2.50 0.461 1.59 10.19 6.13 3.72 3.13
0.062 0.161 0.305 0.453
7.56 7.08 6.76 6.57
coupled through the temperature dependencies of s and b h c. The four s’s plus four bh c’s were replaced by three new parameters C1, C2, and C3:
b h c ) C1 exp(C2/T)
(4)
s ) C3/T
(5)
The nonlinear regression was performed by employing the IMSL implementation of the Levenberg-Marquardt algorithm. The final values of all fitting parameters were physically acceptable, and the fitting was only slightly less satisfactory than that by fitting each isotherm separately. The fitted curves are shown in Figures 1, 2, and 4. Table 1 lists the values of qm’s obtained from regression and the calculated values of bh c and s from eqs 4 and 5, respectively, using C1 ) b0 ) 2.5 × 106 1/atm, C2 ) -4521 K (j ) -8.98 kcal/mol), and C3 ) 2252 K (σ ) 2.85 kcal/mol). The values for j (i.e., the mean heat of adsorption) and σ as well as those for s were physically realistic values. The values for s of 6-8 corresponded to relatively high heterogeneity but were well within empirical values for a large number of gas-solid systems (Valenzuela and Myers, 1989). Uptake Rates. Uptake rates for all five hydrocarbons on NiCl2‚6H2O/γ-Al2O3 were measured at 60 °C and 0.26 atm. For C2H2, the uptake rates at 26, 45, and 70 °C and 0.26 atm were also measured. The uptake curves of ethylene, propylene, and acetylene are compared in Figure 5. The diffusion of ethylene and propylene in NiCl2‚6H2O/γ-Al2O3 was rapid and was dominated by Knudsen diffusion. In the case of acetylene the rate was significantly slower. However, approximately 80% completion was achieved in 5 min.
C2H4 (60 °C) C2H6 (60 °C) C3H6 (60 °C) C3H8 (60 °C)
1.8 × 2.4 × 10-2 1.2 × 10-2 1.7 × 10-2 10-2
D/R2 (1/s) C2H2 (26 °C) C2H2 (45 °C) C2H2 (60 °C) C2H2 (70 °C)
9.1 × 10-5 2.0 × 10-4 3.8 × 10-4 5.0 × 10-4
Two rate control mechanisms might be responsible for the slower acetylene uptake: surface diffusion and chemical reaction (forming π-complex). Sladek et al. (1974) extended the hopping mechanism for surface diffusion to chemisorbed species. They assumed that the surface diffusion in chemisorption systems was qualitatively similar to the surface diffusion of physically adsorbed molecules. Thus, the small mobilities of chemisorbed molecules were associated with their stronger bonding to the surface. Since a very large adsorbed amount as in the case of π-complexation can cause a large gradient in the surface concentration, hence a large-flux, surface diffusion could be a controlling step in the uptake. It is not possible with the available data to eliminate either of the possible steps as the controlling one. The temperature dependence of the acetylene uptake rates is shown in Figure 6. The desorption rates were only slightly slower than the adsorption rates. The overall diffusion time constants, D/R2, were calculated from the uptake curves by nonlinear regression as described elsewhere (Ackley and Yang, 1991). The results are listed in Table 2. It should be noted that the values of D/R2 for acetylene should be considered only as an empirical fitting parameter (indicating the rates) since the rate mechanism is not fully understood. Nature of π-Complexation Bonding. The first satisfactory explanation of π-complexation bonds involving transition metals was provided by Dewar (1951) in terms of molecular orbital theory. The bonding was interpreted based on a donor-acceptor model, illustrated (for the case of acetylene) in Figure 7. The model was subsequently generalized by Chatt et al. in a series of publications including one on acetylene (Chatt et al., 1957), and it was later extended by Blizzard and Santry (1968). The Ni2+ ion usually forms hybridized dsp2 orbitals, and the remaining four 3d orbitals are filled by its own eight electrons. When forming a bond with C2H2, as shown by Figure 7, π electrons of C2H2 are donated to the vacant hybridized dsp2 orbitals of Ni2+ and the
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Figure 7. Schematic of the metal-acetylene π-complexation bond, showing the donation of π-electrons of acetylene into vacant metal hybrid orbitals and the back-donation of electrons from a filled d (or dp-hybrid) orbital of the metal into an antibonding orbital of acetylene.
electrons in the filled d (or dp-hybrid) orbitals of Ni2+ are back-donated into the π-antibonding orbital of acetylene. CNDO/2 molecular orbital theory calculations done by Blizzard and Santry (1968) sugtest that there is a strong mixing between the π-antibonding orbital and σ-antibonding orbital of acetylene. Thus, both of these orbitals are involved in the back-donation. A discussion on the formations, structures, and stabilities of transition-metal complexes of acetylene was presented by Hopkinson (1979). The most important factor affecting the stability of the complex (or strength of the bond) is the back-donation from the filled orbitals of the metal. There are other factors having an influence on the stability of the complex, such as the strongly electron-withdrawing groups (usually bulky ones), referred to as π acids. The presence of these groups in the complex close to the carbon-carbon triple bond has a strong stabilizing influence. Conversely, a more nucleophilic transition-metal ion usually forms a more stable complex. Since earlier transition metals and those of higher oxidation states are less nucleophilic, they are less liable for back-donation when forming a π-complexation bond with C2H2. It should be noted that this model is for free metal ions and does not account for any influence of the support on which the metal ion is spread nor the influence of the anion that is bonded to the transition-metal ion. As mentioned, Ag+ and Cu+ bond too strongly with C2H2 and are not suitable as sorbents. An attempt to use Cu+2, in order to weaken the back-donation to C2H2, also failed because the bond formed was still too strong. Literature information shows that there exist many stable monomeric complexes of metals (Mo and M+2) of Ni, Pd, and Pt (Nelson and Johansen, 1971; Greaves et al., 1968). These metals have been investigated extensively because they are superior catalysts for reactions of unsaturated hydrocarbons (Eisch et al., 1990). The stability of these complexes decreases in the direction from Pt to Ni. Upon considering all of these facts, the choice was made in favor of Ni2+. NiCl2‚6H2O was chosen because it was known to spread in monolayer on γ-Al2O3, as already discussed. The weakly chemisorbed acetylene on the surface Ni2+ ions can be represented by Ni2+(C2H2)n. The values of n can be obtained from the data shown in Figure 2. The average values of n at 1 atm of C2H2 (i.e., the C2H2/Ni ratios ) were approximately 2.4 (at 25 °C), 1.6 (at 45 °C), 1.2 (at 60 °C), and 1.1 (at 70 °C). Thus, n was in the range of 1-3. Further work is in progress in our laboratory on molecular orbital theory calculations in order to obtain a basic understanding of the π-complexation bonds between acetylene and transition metals. Particular attention is being paid to the effects of different counteranions and substrates, for the purpose of sorbent design. Work is also in progress on other transition metals. Preliminary results on Co2+, in the monolayer
form of Co(NO3)2‚6H2O/γ-Al2O3, are encouraging. Co2(CO)6 is known to selectively form a coordinated bond with the carbon-carbon triple bond over the double bond, so the double bond (in the same molecule that contains the triple bond) is free to undergo further reactions while the triple bond is protected (Nicholas and Pettit, 1971). Results on Co2+ and molecular orbital calculations will be reported shortly. Acknowledgment This work was supported by NSF under CTS9212279. Nomenclature b ) Langmuir constant D ) diffusivity P ) pressure q ) equilibrium amount adsorbed qm ) monolayer or saturated amount adsorbed R ) gas constant or particle radius in D/R2 s ) heterogeneity parameter T ) absolute temperature Greek Letters ) bond energy for adsorption σ ) square root of variance of uniform energy distribution Subscripts c ) chemisorption or π-complexation p ) physical adsorption
Literature Cited Ackley, M. W.; Yang, R. T. Diffusion in Ion-Exchanged Clinoptilolites. AIChE J. 1991 37, 1645. Blizzard, A. C.; Santry, D. P. Geometries and Charge Distributions of Organic Ligands I. Metal-Carbon π-Bonding and the Geometry of Acetylene. J. Am. Chem. Soc. 1968, 90, 5749. Blytas, G. C. Separation of Unsaturates by Complexing with Nonaqueous Solutions of Cuprous Salts. In Separation and Purification Technology; Li, N, N., Calo, J. M., Eds.; Marcel Dekker: New York, 1992; Chapter 2. Chatt, J.; Rowe, G. A.; Williams, A. A. A. Series of Stable Acetylene Complexes. Proc. Chem. Soc. 1957, 208. Dewar, M. J. S. A Review of the π-Complex Theory. Bull. Soc. Chim. Fr. 1951, 18, C79. Eisch, J. J.; Sexsmith, S. R.; Fitcher, K. C. Molecular Hydrogen and Aluminum Hydride Transfers Mediated by Nickel(0) Complexes. J. Organomet. Chem. 1990, 382, 273. Eldridge, R. B. Olefin/Paraffin Separation Technology: A Review. Ind. Eng. Chem. Res. 1993, 32, 2208. Gates, B. C. Catalytic Chemistry; Wiley: New York, 1992. Gilliland, E. R.; Bliss, H. L.; Kip, C. E. Reactions of Olefins with Solid Cuprous Halide. J. Am. Chem. Soc. 1941, 63, 2088. Greaves, E. O.; Lock, C. J. L.; Maitlis, P. M. Metal-Acetylene Complexes. II. Acetylene Complexes of Nickel, Paladium, and Platinum. Can. J. Chem. 1968, 46, 3879. Hirai, H.; Hara, S.; Komiyama, M. Polystyrene-Supported Aluminum Silver Chloride as Selective Ethylene Adsorbent. Angew. Makromol. Chem. 1985, 130, 207. Ho, W. S.; Doyle, G.; Savage, D. W.; Pruett, R. L. Olefin Separations via Complexation with Cuprous Diketonate. Ind. Eng. Chem. Res. 1988, 27, 334. Honig, J. M.; Reyerson, L. H. Adsorption of Nitrogen, Oxygen and Argon on Rutile at Low Temperatures; Applicability of the Concept of Surface Heterogeneity. J. Phys. Chem. 1952, 56, 140. Hopkinson, A. C. Acidity, Hydrogen Bonding and Complex Formation. In The Chemistry of the Carbon-Carbon Triple Bond; Wiley: New York, 1979; Part 1, Chapter 4. Keller, G. E.; Marcinovsky, 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; p 59.
Ind. Eng. Chem. Res., Vol. 35, No. 4, 1996 1011 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. Long, R. B. Separation of Unsaturates by Complexing with Solid Copper Salts. In Recent Developments in Separation Science; Li, N. N., Ed., CRC Press: Cleveland, 1972; Vol. 1, p 35. Nelson, J. H.; Johanssen, H. B. Mono-olefin and Acetylene Complexes of Nickel, Paladium, and Platinum. Coord. Chem. Rev. 1971, 6, 27. Nicholas, K. M.; Pettit, R. An Alkyne Protecting Group. Tetrahedron Lett. 1971, 3475. Nieuwland, J. A.; Vogt, R. R. In The Chemistry of Acetylene; Reinhold: New York, 1945; p 51. Pines, H. The Chemistry of Catalytic Hydrocarbon Conversion; Academic Press: New York, 1981. Sikavitsas, V. I.; Yang, R. T.; Burns, M. A.; Langenmayr, E. J. Magnetically Stabilized Fluidized Bed for Gas Separations: Olefin-Paraffin Separations by π-Complexation. Ind. Eng. Chem. Res. 1995, in press. Sladek, K. J.; Gilliland, E. R.; Baddour, R. F. Diffusion on Surfaces. II. Correlation of Diffusivities of Physically and Chemically Adsorbed Species. Ind. Eng. Chem. Fundam. 1974, 13, 100.
Tanabe, K.; Misono, M.; Ono, Y.; Hattori, H. New Solid Acids and Bases; Elsevier: Amsterdam, The Netherlands, 1989. Valenzuela, D. P.; Myers, A. L. Adsorption Equilibrium Data Handbook; Prentice-Hall: Englewood Cliffs, NJ, 1989. Xie, Y.-C.; Tang, Y.-Q. Spontaneous Monolayer Dispersion of Oxides and Salts onto Surfaces of Supports: Application to Heterogeneous Catalysis. Adv. Catal. 1990, 37, 1. Yang, R. T. Gas Separation by Adsorption Processes; Butterworth: Boston, 1987. Yang, R. T.; Kikkinides, E. S. New Sorbents for Olefin-Paraffin Separations by Adsorption via π-Complexation. AIChE J. 1995, 41, 509.
Received for review March 10, 1995 Revised manuscript received June 16, 1995 Accepted July 3, 1995X IE950169Z
X Abstract published in Advance ACS Abstracts, February 15, 1996.
