Monolayer cuprous chloride dispersed on pillared clays for olefin-paraffin separations by π-complexation

New adsorbents containing cuprous chloride dispersed on pillared interlayered clays (PILC) have been prepared and studied for olefin-paraffin separations. High surface-area PILC's were synthesized with different metal oxide (Al₂O₃, Fe₂O₃, TiO₂ and ZrO₂) as the intercalating pillars. Cuprous chloride was dispersed in a submonolayer form on these PILC's. Pure-component isotherms were measured for C₂H₄, C₂H₆, C₃H₆ and C₃H₈ at 25°C and 60°C. All sorbents exhibited high C₂H₄/C₂H₆ and C₃H₆/C₃H₈ ratios with significantly high amounts of olefins adsorbed. The best sorbent was CuCl/TiO₂-PILC which showed a C₂H₄/C₂H₆ ratio of 5.3 and C₃H₆/C₃H₈=2.9 at 25°C. In all cases, olefins adsorbed by π-complexation with Cu(I) ion, reflected by heats of adsorption in the range 10.7-13.7 kcal/mol, as compared to 4.8-6.9 kcal/mol for the physical adsorption of the paraffins. The π-complexation was fully reversible, limited only by the rates of pore diffusion. Diffusion of C₂'s was rapid while for C₃'s the diffusion reached 60% completion in approximately 6 min. Comparing these results with those of CuCl/γ-Al₂O₃, the olefin/paraffin adsorption ratios were not as high as those of the later. However, the olefin isotherms on the PILC-supported CuCl displayed the desirable feature of having a steeper portion above the knee of the isotherm (the knee occurred at below 0.1 atm). This was a useful feature for separation because it yielded a larger working capacity. The steeper isotherm was attributed to a higher degree of energy heterogeneity as the PILC contained both surfaces of pillars and clay layers as opposed to only γ-Al₂O₃.