Benzene Propylene Alkylation Modified Beta Zeolite Catalyst Coke

Modified zeolite Beta catalyst, synthesized in our group, named BPA-9711, exhibits high activity, selectivity and stability under the optimal operating conditions for benzene alkylation with propene to produce cumene in pilot plant. The catalyst was deactivated after 8000 hours' run due to coke deposition.In this dissertation, the nature of the carbonaceous deposit (coke) on BPA-9711 was studied in details. The amount and characters of the coke was determined by Thermal Gravimetric (TO) analysis and Temperature Programmed Oxidation (TPO), the ingredients of the coke was distinguished by 13C CP-MAS NMR, FT-IR and GC-MS. Solvent extraction and N2 physical adsorption were conducted to gain a clear understanding of the effect of coking on pore structure of the catalyst. It is clear that there are two types of deposit, soft coke and hard coke. The former, which can be removed either by benzene flush at the reaction temperature and or by oxidation, contributes a little effort to deactivation, while the latter, which can only be minimized by oxidation in high temperature, play a dominant role in the catalyst deactivation. The deposit on the decayed BPA-9711 consists mainly of multi-isopropyl benzene, alkyl-tetrahydronaphthalene, and a little amount of organic matters with high molecular weight. It is deduced that (multi-)isopropyl benzene underwent hydrogen transfer, condensation, and cyclation to form polynuclear aromatics which prevents reactants to access intracrystal active sites, and blocks products to diffuse outside. The deposit is located in pores and channels of the crystal instead of on the surface. The coke on BPA-99H, new catalyst for trans-alkylation was also investigated.