MCM-41 catalyst preparation and hydroisomerization evaluation

The low-carbon linear alkanes in the Fischer-Tropsch synthesis product can be used for high-quality high-octane gasoline after hydroisomerization, which is an important means to realize the clean utilization of coal resources. By adjusting the alkali solubility of MOR zeolite crystals, mesoporous MCM-41 was synthesized using zeolite solution as the source of silica and aluminum, and a series of MOR/ MCM-41 micro-mesoporous composite materials were prepared by recrystallization method, which was combined with metal active component ions. After the exchange, a Pt-based catalyst with MOR/MCM-41 as the carrier was obtained, and n-hexane was selected as the Fischer-Tropsch low-carbon hydrocarbon model compound to evaluate the hydroisomerization performance.

The morphology, pore structure, and physical and chemical properties of the composite material were characterized by SEM, TEM, pyridine infrared, XRD, BET, nitrogen absorption and desorption, etc., and the characterization results showed that after in-situ recrystallization modification, the MOR grain size decreased Small, the outer surface is successfully coated with MCM-41 material, and the adsorption performance is improved. Appropriate alkali treatment can improve the easy aggregation phenomenon of MOR zeolite particles, and adjust the ratio of Brønsted acid to Lewis acid. The amount of weak acid is basically the same while that of medium strong acid. The amount is significantly reduced. The evaluation results of hydroisomerization performance show that at the reaction temperature of 200 ~ 280 ℃, the conversion rate increases with the increase of the reaction temperature, and at the same conversion rate level, it has a higher level of n-hexane hydroisomerization Selective. With the increase of alkali treatment concentration, the selectivity of isomerized products is improved, and the degree of cracking is weakened, mainly due to the dispersion effect of composite material alkali treatment on MOR particles and the pore expansion effect brought by the synthesis of MCM-41 by recrystallization. Adjust the pore structure of the catalyst, shorten the mass transfer path between the reactant molecules and the active center, and improve the catalytic performance of isomerization.

By preparing micro-mesoporous composite materials and establishing a modification system, the selectivity of n-hexane hydroisomerization can be improved at a similar conversion rate.

This study provides a reference for the preparation of low-carbon n-paraffin hydroisomerization catalyst supports, and it is expected that the efficient conversion of isomerized products can be achieved by regulating the mesoporous complex.