| Abstrakt: |
Steady C8 alkylate production, lasting several days, was observed on a SiO2-supported Nafion catalyst during 1-butene + isobutane alkylation in dense CO2-based reaction mixtures (358−368 K; I/O = 5). Pressure-tuning studies reveal that C8 alkylate selectivity is favored at near-critical pressures (79 bar), decreasing by fourfold at higher pressure (131 bar). The selectivity enhancement at the lower pressures was partly due to retention of heavier (C12+) products in the catalyst pores, which break through when the pores are filled. By periodic increases of the pressure prior to this breakthrough, pore cleaning is demonstrated. Effective rate constants, estimated from the steady conversion data, decrease at increased pressures, implying enhanced pore-diffusion limitations in denser media. The rate constants for butene dimerization are roughly 3 orders of magnitude greater than those for alkylation. Consistent with model predictions, operating the reactor at lower space velocities with nearly total butene conversion enhances the C8 alkylate selectivity. However, the maximum value attained was only around 40%, underscoring the need to design more active alkylation catalysts. |
