Hydrocracking and isomerization of n-paraffin mixtures and a hydrotreated gasoil on Pt/ZSM-22: confirmation of pore mouth and key-lock catalysis in liquid phase

A mixture of n-paraffins as well as a hydrotreated gasoil were hydrocracked over a Pt/ZSM-22 and a Pt/USY zeolite catalyst in a three phase reactor wi th complete internal mixing operated under industrially relevant conditions . The distribution of the isomerization products obtained from the n-paraff in mixture and the hydrotreated gasoil on Pt/ZSM-22 shows that pore-mouth a nd key-lock catalysis are operative, although the selective formation of br anching at the end of the carbon chain is less pronounced. Ethylbranching i s suppressed in liquid as well as vapor phase conditions. The cracked produ cts obtained on Pt/ZSM-22 for both feedstocks contain a high amount of line ar paraffins in comparison to the amount observed for hydrocracking on Pt/U SY. This indicates that similar to vapor phase operations, the scission of the bond in the beta position of the positively charged secondary carbon at om towards a new secondary carbenium ion (s,s beta-scission) is also the do minant cracking mechanism for operations in liquid phase. The differences b etween vapor and liquid phase operations of Pt/ZSM-22 are attributed to dif ferences in the adsorption modes of the molecules. (C) 2000 Elsevier Scienc e B.V. All rights reserved.