The shape selectivity of paraffin hydroconversion on TON-, MTT-, and AEL-type sieves

Based on a comparison between simulated and measured adsorption properties, we demonstrate that both normal and monomethylparaffins are able to fully enter the pores of TON-, MTT-, and AEL-type molecular sieves. This disprove s the theory that monomethylparaffins only partially enter these pores and that normal paraffins are predominantly hydroisomerized at the pore mouths of these sieves. Instead, we attribute the high selectivity for paraffins w ith terminal methyl groups to product shape selectivity, and the low select ivity for paraffins with neighboring methyl groups to transition state sele ctivity. These traditional shape selectivity concepts explain not only the detailed product distribution of n-heptane hydroconversion, but also that o f longer-chain n-paraffins. (C) 1999 Academic Press.