Kerry C. Pratt

A study of nickel-molybdate coal-hydrogenation catalysts using model feedstocks

Abstract A model feedstock consisting of dibenzothiophene, dibenzofuran, quinoline, and phenanthrene dissolved in heptane has been hydroprocessed in a flow reactor at 6.89 MPa and 400 °C over a series of nickel-molybdate catalysts. Under simultaneous processing, the main product of dibenzothiophene hydrodesulphurization was diphenyl, the main product of quinoline hydrodenitrogenation was propylcyclohexane, and that of dibenzofuran hydrodeoxygenation was cyclohexyl benzene. Sulphur was removed without the need for saturation of the sulphur-containing ring. For both nitrogen and oxygen removal, the ring containing the hetero atom was saturated before scission of the CN or CO bond. The main products of the hydroprocessing of phenanthrene were hydroderivatives of varying degrees of saturation. Very little hydrocracking took place under our conditions, and this occurred predominantly by successive saturation and cracking of terminal rings. With increasing catalyst acidity, the rates of all reactions studied increased, as did the degree of hydrocracking relative to hydrogenation. Coke formation on the catalyst also increased markedly with acidity.

Catalytic reactions in transport reactors

Abstract By assuming plug flow of both gas and solids phases, and simple kinetics, a model of the transport reactor has been prepared which accounts for the unsteady state behaviour of the catalyst particles. Computational results are presented to show the influence of the major variables. As in a steady state analysis, the Thiele modulus serves to indicate the catalyst effectiveness.

Catalyst activity decay functions in liquid and vapour phase xylenes isomerization over H-Y zeolite

Abstract A kinetic comparison of the deactivation of a zeolite catalyst in vapour and liquid phase isomerization of xylenes has been made. Quantitative data confirm the more rapid deactivation in the vapour phase. The liquid phase deactivation was best expressed by an exponential function, while the vapour phase was best expressed by a power law. Both systems correlated best using time on stream as the variable. Changes in isomerization selectivity were shown to result from differing variation of deactivation parameters with temperature. The faster deactivation of mordenite compared with Y zeolite was confirmed, and is consistent with the structural characteristics of the two zeolites.

Optimal temperature policy in a riser reactor

Abstract The nature of the optimal axial temperature distribution in a riser reactor to maximise the yield of the intermediate B, in the reaction sequence A→B→C was investigated by way of the selective oxidation of naphthalene to phthalic anhydride. For this case, imposition of an axial profile could not improve the yield over that obtainable by operating at the optimum isothermal temperature. This result appears to be general, and suggests that optimal yields could be obtained by operation at the optimum isothermal temperature, which should prove easier to implement in practice than a specified temperature distribution.