Coking in pulse and flow microreactors

Abstract

Abstract A relation is obtained for coke deposition in pulse microreactors. The relation has three parameters: an initiation rate constant, a chain-growth rate constant, and an asymptotic deposition amount. The relation can be easily extended to apply to coke deposition in continuous-flow reactors. The derived form for continuous-flow reactors is sufficiently general to be reduced to the same qualitative nature as different special cases more-or-less emperically obtained in the literature. The model is fitted to data from pulse or continuous-flow reactors on the craking of cumene, hexadecane or styrene over silica—alumina or Y zeolite of various acidities and exposed to various steam treatments. Increasing the acidity increases the chain-growth rate. Steaming the catalyst affects primarily the initiation rate. The asymptotic deposition is not appreciably affected in either case. The rate parameters depend upon the time interval between pulses, for time intervals less than eight minutes. The chain-growth rate is the most affected, and appears to tend to zero with decreasing time intervals. This is consistent with the fit obtained from data using continuous-flow reactors (zero time between pulses) where the chain-growth rate constant is vanishingly small. The results imply that both the type and the amount of coke formed depend upon the reactor used.