The Pt-catalyzed direct dehydrogenation of intermediate chain length paraffins is a highly desirable production method for valuable olefins. This study deals with the industrially relevant effects of internal diffusion processes and of carbonaceous deposits on the olefin formation in the complex reaction network of n-octane dehydrogenation.
The effect of particle size as well as of coke formation on conversion of intermediate chain length paraffins (C6–C9) to the corresponding olefins was investigated on a promoted Pt catalyst with the model substance n-octane. Increasing the particle size leads to pore diffusion limitations and thus to a reduction of the activity for paraffin conversion and of the octene selectivity caused by more pronounced formation of consecutive products (aromatics, octadienes). Both effects are adequately predicted by the developed kinetic model. The activity of dehydrogenation declines with the content of coke, but to a lesser extent than the rate of coke formation, which is beneficial regarding the catalyst lifetime. The initial activity is fully recovered by mild coke burn-off (T < 470 °C).Zum Volltext