Active site accessibility of resid cracking catalysts

It is well understood that pore structure is important in designing FCC catalysts. For residue cracking, the pore structure of catalyst matrix should be accessible for precracking the large hydrocarbon molecules so that the resulting smaller molecules can transfer into the zeolite channels and can be converted to value-added products over the zeolite sites. However, pore parameters such as pore volume and pore size distribution are insufficient for selecting an appropriate matrix. A method for testing the active site accessibility of resid cracking catalysts has been developed on currently widely used MAT equipped with the unstripped hydrocarbon burned off in place, with an online measurement of the CO₂ and H₂O that are produced. The effect of pore distribution of the FCC catalyst matrix on the active site accessibility of several catalysts has been tested tentatively in terms of bottoms conversion and strippable coke yield. The results showed that the yields of HCO and strippable coke increase when the matrix small pores increase, and decrease when the catalyst matrixes are highly accessible. These test observations are in agreement with commercial results.