Hydrogenation Of Vanadyl Porphyrin Compounds And The Hindered Diffusion In Catalysts

With the intensification of petroleum resources,the hydrotreating technology of residues plays an increasingly important role in the process of reducing the weight of heavy oil.Residue hydrodemetallization(HDM)is an important part of the heavy oil hydrotreating process,and plays a key role in protecting subsequent hydrogenation catalysts.Due to the large molecular size of metal compounds in heavy oil,and most of them have high reactivity,the hydrogenation reaction process in the catalyst pores is seriously affected by diffusion.Therefore,studying the reaction and diffusion law of metal compounds in the catalyst pores provides guidance for optimizing the design of HDM catalysts and improving the utilization rate.At present,most of the studies on the hydrogenation reaction and diffusion of heavy oil in the literature use heavy oil as a raw material and commercial alumina-based catalysts for reaction research.When the heavy oil system is taken as the research object,there are problems such as easy association of asphaltenes,complicated molecular structure,wide pore size distribution of alumina material,and irregular pore structure,etc,which cannot accurately reflect the true reaction performance and diffusion of metal compounds in the catalyst pores.Therefore,in this paper,two different configurations of vanadyl porphyrin,VO-OEP and VO-TPP,are selected as probe molecules.Hydrogenation reaction and diffusion rules were studied in regular but different pore size Ni Mo/Zr-SBA-15 catalysts and an alumina-based commercial hydrodemetallization catalyst.The experimental results show that as the pore size of the catalyst increases,the effective diffusion coefficient of the reactant molecules in the catalyst pores gradually increases,and the diffusion resistance gradually decreases.Although commercial catalysts have higher reactivity and larger average pore diameter,due to the bending and shrinkage of their pores,the molecules are subjected to more serious diffusion resistance in their pores,so the phenomenon of hindered diffusion is more significant.The comparison of the two vanadium compounds shows that VO-TPP has higher intrinsic reactivity due to the electron-donating effect of four phenyl groups,and the presence of four benzene ring side chains also leads to more severe steric hindrance.Therefore,for VO-TPP,the effect of its diffusion on the reaction is also more obvious.This thesis also studies the hydrogenation intermediates of VO-OEP and VO-TPP by combining HPLC and FT-ICR MS.The hydrogenation intermediates of the vanadyl porphyrin model compound were found to contain 2H products(VO-TPPH₂and VO-OEPH₂)and 4H products(VO-TPPH₄),and the hydrogenation reaction process of vanadyl porphyrin was determined as follows:The first step is hydrogenation to generate 2H intermediate product,and then hydrogenation is continued to obtain 4H intermediate product.Finally,a porphyrin ring-opening reaction occurs,and vanadium atoms fall off and are deposited as sulfides on the catalyst surface and pores.