(558k) Effective Diffusion Coefficient of Isobutane, 2,3 Dimethyl-Butane, Hexane and Decalin in Ternary Blends of Adsorbates (Liquid Phase): Spent PtSOxZrTi and CeNax Catalysts

Diffusion and adsorption of isobutene, hexane, dimethyl-butane, dimethyl-pentane, hexyl-cyclohexane and pyridine in PtSOxZrTi/Silice structured alkylation catalyst were studied in presence of a solvent and hydrogen at 1.4 MPa. Rate of diffusion of binary and ternary blends were studied in a batch reactor at different temperature using fresh and spent catalysts with different level of coke; on spent catalyst coke were build-up during isobutane alkylation in presence of hydrogen. Heat of adsorption were experimentally measured and predicted by DFT simulation. Modified Peng-Robinson EOS equations were used to determine the excess of volume of the liquid phase, hydrogen solubility and hydrocarbon vaporization at different temperatures. Catalysts were characterized by nitrogen adsorption, FTIR and 13CNMR analyses. A simulation program for diffusion and adsorption in meso-micropores was developed to determine the effective diffusivity and the amounts of adsorbates on surface taking in account counter-diffusion of sorbents and the presence of hydrogen at medium pressure. The results show that difference in the rate of counter-diffusion resides in the pore structure and the presence of acid sites on these solids. It was found important interactions sorbents-adsorbates and sorbent-sorbents that occurred in solution and on surface; they modified the effective counter diffusion rate. On fresh catalyst all hydrocarbon after 20 minutes of contact time the adsorption in mesopores arrive to equilibrium. In micropores only lineal-paraffins and small iso-paraffins are able to diffuse on free of coke free of solvent micropores. They take days to diffuse and adsorbe at equilibrium. On spent catalyst micropores were blocked by the presence of strong adsorbed hydrocarbons and coke that restrain the diffusion to and out of this pores. Coke and adsorption at the mouth of micropores impede the alkylation reactions. Adsorbate-adsorbate interactions and adsorbate pore intersections are discussed as well as the effect of coke on adsorption and desorption results. Heat of adsorption obtained for single sorbent, binary and ternary blends are different due to hydrocarbons interactions. The equilibrium of adsorption at different temperature and pressures were simulated using Langmuir isotherm for mesopores and Elovich equations for micropores. Effective diffusivity of hydrocarbons in ternary blends is in the order of 10^-6 cm/s in mesopores and 10^-10 cm/s in micropores. These values takes in account the competition for adsorption.