H-ZSM-5/cobalt/silica capsule catalysts with different crystallization time for direct synthesis of isoparaffins: simultaneous realization of space confinement effect and shape selectivity effect

Abstract

Publisher Summary Fischer–Tropsch synthesis (FTS) as one option to produce hydrocarbons has been known since 1925. FTS products are sulfur free, aromatic free, and nitrogen free compared to conventional petroleum-derived products, which decide them as ideal fuel candidates. The FTS hydrocarbon products obtained on the traditional FTS catalysts can only be used as the substitute of diesel oil because of their high cetane number and linear structure. Currently, more attention has been focused on the production of hydrocarbons rich in isoparaffin because of their wide foreground as synthetic gasoline. Zeolites, one of the crystalline aluminosilicate, have special pores, cavities, and regular channels on molecular dimensions. Some zeolites are excellent hydrocracking and hydroisomerization acidic catalysts for the conversion of heavy oil to light hydrocarbons in petroleum industry. Integrating the acidic zeolite membrane with an FTS catalyst, a novel zeolite capsule catalyst was successfully designed and used for the direct synthesis of light isoparaffins from syngas (CO + H 2 ). In the FTS reaction using these zeolite capsule catalysts, syngas passed through the zeolite membrane and reached Co active sites on the core part of capsule catalysts. Then the formed FTS products with linear structure entered the zeolite membrane to receive the hydrocracking and isomerization on the acidic sites of the zeolite. As a result, the selectivity of light isoparaffins increased and all the long-chain hydrocarbons disappeared in the final products. The three zeolite capsule catalysts constructed by growing H-ZSM-5 zeolite membrane on the external surface of Co/SiO 2 pellets with different crystallization time were tested for the direct synthesis of isoparaffins via FTS reaction.