Hydrodeoxygenation Isomerization Bifunctional Catalysts For Vegetable Oils

The alkane products?second-generation biodiesel?derived from the hydrodeoxygenation of vegetable oils are an ideal alternative to fossil fuels,but the use of biodiesel is limited due to the poor low-temperature fluidity of these n-alkanes.In order to improve the low-temperature flow performance of biodiesel,a feasible and promising method is to convert the n-alkanes into iso-paraffins.That is,vegetable oils undergo hydrodeoxygenation and isomerization,and biodiesel with better performance can be obtained.The technologies that have been developed to produce biodiesel from vegetable oils are mostly composed of two steps,namely the first step of hydrodeoxygenation of vegetable oils,and then the isomerization of the products obtained in the first step.The process of this kind of technology is not only complicated,but also is a high cost in the investmen.Therefore,if the vegetable oil is subjected to hydrodeoxygenation and isomerization to produce low-condensation point biodiesel in one step,the economic benefit of the process can be greatly improved,and the key to this technology is to develop a hydrodeoxygenation/isomerization bifunctional catalyst.In this paper,SAPO-11 zeolites were prepared by hydrothermal synthesis method,and MoNi/SAPO-11 catalysts were prepared by using the SAPO-11 as the carrier to support MoNi active components.The zeolite and catalysts were characterized by SEM,Py-IR,NH₃-TPD and other methods.The hydrodeoxygenation and alkane isomeric performance of the catalysts were evaluated in a continuous fixed bed reactor using jatropha curcas oil as feed.The effects of Si/Al ratio and synthetic media on the properties of SAPO-11 zeolite and the perforance of the corresponding catalysts were investigated.The micro-mesoporous SAPO-11 zeolite was prepared by the addition of pore-foaming agent,and the influence of the pore-foaming agent and synthetic media on the catalytic performance of the catalyst was also investigated.Experimental results of the Si/Al ratio effect showed that the SAPO-11 prepared with Si/Al=0.4 has suitable amount of acid,and the corresponding catalyst shows good hydrodeoxygenation activity/alkane isomerization performance.The effect of synthetic media on the properties of SAPO-11 zeolite and the catalytic performance of the corresponding catalysts showed that compared with aqueous monophasic media,isopropanol-water two-phase media can reduce the degree of silica condensation and promote more silicon atoms into the zeolite framework,resulting in the as prepared SAPO-11 with more B acid sites?especially medium B acid sites?;In addition,the zeolite synthesized in the two-phase media also has a certain amount of mesoporous pores.The alkane isomer fraction of vegetable oils hydrodeoxygenation over the corresponding catalysts increased from 0.20 to 0.38.The results of the addition of pore-foaming agent to prepare SAPO-11 with micro-mesoporous pores showed that compared with the zeolite without pore-foaming agen addition,using CTAB as a pore-foaming agen and CTAB/ethyl orthosilicate mass ratio0.05,SAPO-11 zeolite synthesized has typical micro-mesostructure characteristics,and the SAPO-11's mesopore specific surface area increased from 137.5 m²·g^-1 to 200.5 m²·g^-1 and mesopore volume increased from 0.18 cm³·g^-1 to 0.25 cm³·g^-1.The alkane isomer fraction of vegetable oils hydrodeoxygenation over the corresponding catalysts increased from 0.20to 0.30.Using the SAPO-11 prepared under the conditions of n?isopropanol?:n?Al₂O₃?=10 and the CTAB/ethyl orthosilicate mass ratio of 0.1 as the support,the alkane isomer fraction of vegetable oils hydrodeoxygenation over the MoNi/SAPO-11 catalyst increased from 0.20to 0.45.This should be attributed to the synergistic effect of isopropanol and CTAB on the as prepared SAPO-11 with a more appropriate micro-mesoporous structure and a larger amount of B acid.