Modelling Catalyst Deactivation by External Coke Deposition during Fluid Catalytic Cracking

Abstract

Although the Fluid Catalytic Cracking (FCC) is an economic important process, simulation of its kinetics is rather empirical—mainly it is a consequence of the complex interactions among operating variables and the complex kinetics that take place. A crucial issue is the inevitable catalyst reversible deactivation, consequence of both, coke (by-product) deposition on the catalyst surface (external) and inside the catalytic zeolite (internal). In order to tackle this problem, two main proposals to evaluate deactivation rate by coking have been extensively applied, both use a probability distribution function called "the negative exponential function"—one of them uses the time that catalyst has been in the reacting stream (named Time-on-Stream), and the other is related to the coke amount on/inside the catalyst (denoted as Coke-on-Catalyst). These two deactivation models can be unified by tracking catalyst activity as function of the decrease on effective diffusivity due to pore occlusion (external) by coke—this situation leads to an increase of Thiele modules and consequently a decrease of the effectiveness factor of each reaction. This tracking of catalyst activity incorporates, implicitly, rates of reaction and transport phenomena taking place in the catalyst pores and is therefore phenomenological rather than statistical. In this work, the activity profiles predicted previously are reproduced at MAT laboratory reactor. The same approach is used to model an industrial riser and the results are in agreement with previous reports.

Catalytic Cracking of Hydrocarbons in a CREC Riser Simulator Using a Y-Zeolite-Based Catalyst: Assessing the Catalyst/Oil Ratio Effect

“…Fluidized catalytic cracking (FCC) is one of the most valuable processes in petroleum refineries − and the best example of large-scale application of Y-zeolites. Every day, more than 10 million barrels of gasoline are produced in FCC units throughout the world. , VGO or vacuum gas oil is the typical feedstock used in FCC units.…”

A Model of Catalytic Cracking: Catalyst Deactivation Induced by Feedstock and Process Variables

“…Other studies take into account catalyst deactivation by diffusion restrictions arising from pore clogging by coke using the effectiveness factor [17] or by a function of heavy aromatics adsorption formed from various reactions paths [18]. Special attention has been paid to the assessment of different types of coke deposited and their chemical nature (physical and chemical) on the basis of the experimental dependence of coke yield on catalyst-to-oil ratio [19].…”

Model based analysis of the effect of 2-ethylphenol addition to n-decane in fluid catalytic cracking over a series of zeolites

“…This process also results in the formation of heavy secondary products on the catalyst, referred to as coke, leading to catalyst activity decay by covering the acid sites and, in a later stage, by blocking the pore network. Apart from its deactivating effect on the catalyst, coke influences also the product selectivity [5,6]. The FCC industrial unit consists mainly of the riser reactor, where cracking reactions take place, the fluid bed regenerator, used to burn off the coke deposited on the catalyst, and the distillation column(s), for the separation of the products.…”