ChemInform Abstract: Kinetics of Reactions of C8 Olefins on HY Zeolite

Abstract

Abstract Reactions of two C 8 olefins ( n -octene and 2,4,4-trimethylpentene) have been studied on HY at 300 °C. Skeletal isomerization is the dominant reaction of n -octene (initial selectivity 0.98), while cracking is the dominant reaction of 2,4,4-trimethylpentene (initial selectivity 0.80). Conversion rates of both olefins can be fitted by a kinetic expression previously applied to the cracking of n -paraffins on HY at 400 °C. The kinetic rate constants for reaction of these olefins, independent of adsorption parameters, have been calculated, and show that the sum of the rate constants for cracking 2,4,4-trimethylpentene is ~160 times greater than that for skeletal isomerization of n -octene. The parameters obtained show that adsorption of olefins on HY decreases with an increased degree of branching. Methylheptenes are less strongly adsorbed than linear octenes. Trimethylpentenes are less strongly adsorbed than isobutene. This trend is also observed by comparing initial coke formation on HY from the two olefin feedstocks, which shows that n -octenes are adsorbed to a significantly higher extent than 2,4,4-trimethylpentene. Catalyst decay was accounted for by the time-on-stream theory of decay. The decay parameters show that aging occurs much more rapidly for 2,4,4-trimethylpentene than for n -octene. There appears to be no simple relationship between total coke deposited and catalyst deactivation. A correlation may exist between deactivation and the degree of dehydrogenation of the coke, but it would appear to be specific to the feed used. In both these reactions no molecular hydrogen was present in the initial products, or indeed up to 50% conversion. Methane and ethane were also absent in the initial product and do not appear in significant quantities even at 50% conversion.