Catalytic activity and kinetic studies for the hydrodesulphurisation of thiophene.

Abstract

The dissertation describes a study of the catalytic hydrode-sulphurisation (hds) reaction over a series of lithium added cobalt-molybdate catalysts supported on y-alumina. Attempts have been made to interpret the change in catalytic activity in terms of the results of physico-chemical studies on a series of different catalyst preparations. Studies on the kinetics of hds of thiophene were also undertaken on two catalysts having different atomic ratios of lithium and cobalt (Li/Co = 0.0; Li/Co = 1.63). A continuous flow tubular fixed-bed microcatalytic reactor at 400° C and atmospheric pressure was employed to study catalytic activities. It was found that small lithium additions to the cobalt-molybdate catalyst increased the catalytic activity. Results also indicated that lithium addition to the hds catalyst affects the isomerisation of but-1-ene which occurs simultaneously with hydrogenolysis. Various characterisation techniques were also applied to the lithium series of catalysts. Among them, physisorption and electron spin resonance (e.s.r.) spectroscopic studies were found to be the most useful. Characterisation by physisorption indicated that, for catalysts with low lithium content (Li/Co <6.53), the surface area and the pore structure were not significantly altered. However, for catalysts with higher lithium contents the surface area decreased sharply. The results of e.s.r. studies indicated that lithium addition to the cobalt-molybdate catalyst affects the reducibility of molybdenum and a correlation was observed between the catalytic activity and the reducibility. The chemical kinetics of hds of thiophene were also studied in a tubular differential reactor at atmospheric pressure and in the temperature range 260-320° C. The hds of thiophene was found to be less than first order with respect to thiophene, while both thiophene and hydrogen sulphide were found to have an inhibiting effect on the thiophene hds conversion. Empirical power function, Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) type of kinetic models were used to correlate the data on thiophene hydrogenolysis. Although the empirical power function analysis did not yield a unique rate expression which describes the experimental data, nevertheless two alternative rate expressions of the LH type were found, which describe the experimental data with reasonable precision.

Date of Award	1983
Original language	English
Awarding Institution	University of Bath