Certain relationships in deposition of coke on zeolitic cracking catalyst

Abstract

This article investigates coke deposition in a single-pass flow unit with a stationary fluidized bed of catalyst with a cracking period of 1.25-20 min., feedstock mass velocity 1-6 h/sup -1/, and various cracking temperatures. Vacuum gasoils from different crudes were used as the feedstocks. Voorhie's equations are used for a quantitative description of coke deposition. The coke deposition on the catalyst is presented as a power function of the catalyst operating time and is independent of the feedstock mass velocity, and coke yield on feed is a power function of the conversion of feed and is likewise independent of the feedstock mass velocity. It is determined that the coke yield in the course of cracking on zeolitic catalyst varies exponentially with the feedstock conversion, regardless of the particular set of process conditions used to reach this conversion. The dependence of coke deposition on the catalyst of the feedstock conversion is also exponential, but each value of the catalyst: feedstock ratio (C:F) gives a different curve. Larger values of C:F correspond to less deposition of coke on the catalyst, and larger values of the latter correspond to more highly aromatic feedstocks.