Reactions, Adsorption and Diffusion in FCC Catalysts

Abstract

The objective of this MS thesis is to study the reactions, adsorption and diffusion in FCC catalysts. The effects of different parameters on catalytic cracking are studied. Three main cases are considered: isothermal reactions with adsorption and diffusion, nonisothermal reactions with adsorption and diffusion and isothermal reactions with adsorption and diffusion in an active matrix. In each case, the conditions are varied and the effects of different parameters are studied. It is concluded that for an isothermal process the conversion increases with Thiele modulus and Biot number and decreases with the ratio of bulk to solids volumes and degree of nonlinearity. For a nonisothermal process, the conversion decreases if the heat transfer resistance is the controlling step. When diffusion and adsorption processes occur simultaneously in the macropore and micropore, macropore processes slow the diffusion and therefore reduce the conversion. The conversion is further decreased if the three resistances are significant: external fluid film resistance, macropore and micropore diffusion. The models developed are applied to gas oil data and to 1,3,5-triisopropylbenzene (1,3,5-TIPB) data at two different temperatures. The finite volume model with external fluid film resistance gives the best fit for the gas oil data. Different reaction sets are considered for 1,3,5-TIPB and it is found that the parallel reactions of 1,3-diisopropylbenzene (1,3-DIPB) at 400 ℃ gives the best fit while the second order reaction for cumene gives the best fit at 550℃. It was checked that the optimized Thiele moduli follow Arrhenius equation. To find the reaction constants, diffusivities and adsorption constants should be measured experimentally.