Vacuum gas oil hydrocracking performance of bifunctional Mo/Y zeolite catalysts in a semi-batch reactor

• Hydrocracking of VGO studied in a batch reactor for different NiMoS and zeolite loadings.
• Products distributions analyzed using two dimensional chromatography.
• Overall activity in hydrocracking is determined by zeolite loading.
• Selectivity to middle distillate improves with the increase of metal to zeolite ratio.

A new approach has been developed to characterize bifunctional catalysts in a complex matrix of hydrotreated vacuum gas oil using a batch reactor test. Triphasic reactions were carried out in a reactor equipped with a stationary basket, hydrogen injection and products sampling systems. Bifunctional catalysts containing different relative amounts of alumina-supported NiMo sulfide and zeolite were tested at 400 °C under 120 bars over different reaction times. The repeatability of the test conditions was validated and the lack of mass transfer limitations at phase interfaces was confirmed. Gas and liquid samples were analyzed by one and two-dimensional gas chromatography (GC × GC) respectively to obtain quantitative distributions of linear and branched paraffins, naphthenes and aromatics. The details of the products distribution provided by chromatography were explained using mechanisms of bifunctional catalysis. It has been established that the limiting step defining the total conversion is the scission of the hydrocarbon chains on acid sites of the zeolite. The increase of the molybdenum to zeolite ratio provided an improvement of middle distillate selectivity.

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