Date of Award
Doctor of Philosophy (PhD)
Professor R.B. Anderson
In the hydrogenolysis of hydrocarbons, iron is unique among the transition metals since it breaks molecules extensively and produces large quantities of methane even at low conversion. Hydrogenolysis of propane, isopentane and n-hexadecane were studied at 325 and 355ºC over reduced Fe and carbided Fe catalysts prepared from a commercial NH₃ synthesis catalyst. Reaction network analysis applied to the selectivity data yielded a quantitative estimate of the relative importance, for an adsorbed species, of desorbing or undergoing C-C bond splitting; this method indicated that product desorption is the slow step in the reaction mechanism. Power rate expressions were obtained for hydrogenolysis of propane and isopentane at 325ºC. Used catalysts, characterized by Mössbauer spectroscopy, contained α-Fe at high feed ratios of H₂ to hydrocarbon, and Fe₃C, at low ratios. The formation of bulk iron carbides led to changes in selectivity, yielding less methane and more intermediate hydrocarbons. In hydrogenolysis of n-hexadecane, the analysis of the C₇-C₁₅ products by gas chromatography-mass spectrometry showed the presence of alkylbenzenes, alkenes and branched alkanes, which account altogether for as much as 20 mole % of the heavier hydrocarbons. The data also suggest that the breaking of paraffins on iron possibly occurs by rapid demethylation. Hydrogenolysis of hydrocarbons is completely inhibited when carbon monoxide is added to the feed, even at concentration as low as 4 mole %; CO is presumably more strongly adsorbed on the catalyst than hydrocarbons. The products obtained were similar to those found in the Fischer-Tropsch synthesis. Traces of water in the feed reduce the rate of hydrogenolysis. An increase in the K₂O content of Fe catalyst decreases its activity but does not affect its selectivity. A new method of deriving selectivity equations from reaction networks is presented. Network analysis is shown to apply to irreversible reactions for hydrogenolysis and isomerization.
Monnier, Jacques, "Hydrogenolysis of Hydrocarbons on Iron Catalysts" (1983). Open Access Dissertations and Theses. Paper 1398.