Catalytic Hydrodeoxygenation And Hydroisomerization Of Biolipid Over Hierarchical ZSM-22 With Core-shell Structure

The technology of producing alternative clean biofuels from fatty acids has obtained a long-scale development due to the more serious energy and environment crisis. Produce the high-graded biodiesel with high cetane number and low freezing point from one-step hydrodeoxygenation and hydroisomerization of feedstock oil has become a potential energy strategy, which sets higher demands for the development of novel catalysts. Classic ZSM-22 zeolites as selected, hierarchical and core-shell zeolites with a dual structures model were controllably prepared. Acidity of catalysts and dispersion of metal Pt were inproved with the adjustment of porous properties in order to obtain the highly active catalysts for one-step hydrodoxygenation and hydroisomerization.Hierarchical HZSM-22 zeolites were prepared by alkali-treatment and/or subsequent acid washing. It was found the sample with alkali to solid ratio of 13:1 and also acid washing treatment possessed the highest external surface area and relative crystallinity and also lowest acidity. The improved structure property favored the diffusion of both reactants and products in the channels and hydroisomerization on zeolites surface area. Comparing with parent ZSM-22 zeolites, the selectivity to target alkanes and isomerized alkanes was improved over as-prepared hierarchical catalysts.Core-shell zeolites with disordered meso-SiO2 as shell were prepared by surfactant-directed recrystallization with the hieraechical zeolites as core. Increasing the thickness of the shell, higher external surface area and Pt metal dispersion improved the hydrodeoxygenation conversion but restrained the subsequent hydroisomerization of long-chain n-paraffins due to the shielding of mesoporous structure and acitive sites on the core. Finally, the sample with suitable shell thickness and acidity showed the highest selectivity for the isomerized products of ca.70%, which is better than that on hierarchical zeolites.Core-shell zeolites with ordered Al-MCM-41 as shell were synthesized with template in alkaline solutions. The hierarchical zeolites with relatively high crystallinity were surrounded uniformly by ordered mesoporous shell under NaOH concentration of 0.2 mol/L, and then resulted in higher acid sites accessibility. For sample with not only higher external surface area and Pt metal dispersion improved the hydrodeoxygenation conversion, the highly ordered mesoporous channels also favored the diffusion of n-paraffins produced from external surface to decrease the cracking degree of products and then obtain the highest isomers selectivity of ca.81%.