Heterogeneous and homogeneous effects of hydrogen sulfide on light-hydrocarbon pyrolysis

The pyrolysis of ethane, propane, isobutane, n-butane, and n-decane has been studied with H/sub 2/S added in the 0-10% range under conditions in which the surface/volume (S/V) ratio was varied over approximately 6 orders of magnitude. In the absence of H/sub 2/S the pyrolysis rates and product selectivities remained virtually constant over large changes in S/V ratio. At low S/V ratios H/sub 2/S can either inhibit or accelerate the rate of hydrocarbon decomposition depending upon the nature of the intermediate radicals. Under high S/V conditions, H/sub 2/S caused an increase in pyrolysis rate for all hydrocarbons tested. The results are consistent with a mechanism and kinetic analysis in which the effect of high surface area is to catalyze the decomposition of H/sub 2/S into intermediate radicals. The effects of H/sub 2/S on product selectivity appear as a large increase in propylene yield from n-butane feed, increased isobutene from isobutane feed, and little or no change in selectivity with n-decane, propane, or ethane feed.