Development of an experimental protocol to evaluate FCC stripper performance in terms of coke yield and composition

Tests have been conducted in a microactivity test (MAT) and a fluidized bed reactor to develop an experimental protocol to determine how the yield and composition of coke and the associated catalyst surface area vary as a fun ction of stripper conditions in fluid catalytic cracking (FCC). In both rea ctors, the use of rapid quenching has allowed the relatively short strippin g times encountered in FCC units to be simulated. Low sulphur vacuum gas oi ls (VGO) with a low metal equilibrium catalyst (E-cat) were used for stripp ing periods of up to 20 minutes. Significant variations occur in the struct ure of both hard and soft coke during stripping. Although the hard coke bec omes more highly condensed with prolonged stripping, the surface area reduc tion by the hard coke remains fairly constant for stripping periods in exce ss of ca. 5-10 minutes and is small (10 m(2) g(-1)) in relation to the loss of surface area from the soft coke. The use of about 70 g of catalyst in t he fluidized bed provides sufficient sample for demineralization to recover sufficient of the hard coke for C-13 NMR analysis after the initial extrac tion of the soft coke. Indeed, it has been found that a further pool of sof t (chloroform-soluble) coke is physically entrapped within the catalyst por e structure and is only released after demineralization. In fact, this seco nd soft coke fraction is much more highly aromatic than the first and ultim ately controls the final coke yield. For the combination of E-cat and VGOs investigated here, typically about half of the final hard coke content of n early 1% w/w catalyst is derived from this second soft coke fraction by car bonization. The structural information obtained has been used to formulate a model for the stripping process where the soft coke II fraction undergoes cracking in competition with coke formation and evaporative removal from t he catalyst.