Catalytic Pyrolysis Of Non-edible Oils For The Production Of Aromatics Over Metal-modified HZSM-5 Catalysts

Aromatics are very important basic organic raw materials,which are widely used in pharmaceutical,chemical and energy industries,and the demand is increasing year by year.Traditional aromatics production technologies include high temperature dry distillation of coal,catalytic reforming of naphtha,hydrogenated gasoline,aromatization of light hydrocarbons.However,with the excessive consumption of petrochemical resources and environmental pollution,biomass has received more attention as a new renewable resource.Compared with other biomasses,non-edible oils have two major advantages of being similar in structure to fossil fuels and avoiding competition with food,which make them more preferable to become green raw material sources for the production of bio-aromatics.In the catalytic cracking of biomass,catalysts play a key role.HZSM-5 zeolite is commonly used as the catalyst for aromatics production because of its good acid properties and ordered pore structure,which exhibits good aromatization activity.However,there are problems such as low aromatic yield,low selectivity and rapid catalyst deactivation during the reaction process.Therefore,the metal modification of HZSM-5 zeolite to modulate the acidic sites and pore structure are the key to improve the catalytic performance of HZSM-5 zeolite.The metal-modified catalysts were also used to produce aromatic hydrocarbons by catalytic cracking of biomass non-edible oils.The main contents and results of experiments are as follows.The HZSM-5（25）zeolite was used as the parent material to prepare a series of metal-modified catalysts by wet impregnation method.The prepared catalysts were also characterized by Fourier transform infrared spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy,N₂adsorption-desorption and ammonia temperature-programmed desorption.The results showed that the introduction of metal species（Zn,Ga,In,Ni,Mo）had no significant effect on the skeleton and crystalline structure of the parent HZSM-5 zeolite,but increased the specific surface area and pore volume of the catalyst.The addition of metal species regulated the acidic sites of the catalyst,resulting in a decrease in the Br（?）nsted acid sites,an increase in the Lewis acid sites and a decrease in the Br（?）nsted/Lewis.The loaded metals were present in the parent HZSM-5 in the form of metal oxides,acting as metal active sites.The catalytic performance of metal-modified HZSM-5 catalysts were investigated by the catalytic cracking of glycerol trioleate as a model compound.It was found that aromatic formation was closely related to the type of loaded metal and the acidic nature of the catalyst,the trend of aromatic promotion was in the order of Zn>Ga>Mo>HZSM-5>In>Ni.And then the physicochemical properties and catalytic activity of the modified HZSM-5 catalyst with different zinc loadings were investigated.It was shown that the loading state and acid properties of zinc metal in HZSM-5 catalyst were closely related to its loading amount,with the increase of loading amount,the Lewis acid sites increased,the Br（?）nsted acid sites decreased,and the Br（?）nsted/Lewis decreased.When the zinc loading amount was1.3 wt.%,the Br（?）nsted and Lewis acid sites maintained a balance,and the Br（?）nsted/Lewis was 0.97,which was favorable for the transfer of cyclic alkanes formed in the Br（?）nsted acid sites to the Lewis acid sites for deoxygenation and aromatization and other reactions to form aromatics,thus improving the yield of aromatics with an activity of 1.3%Zn>0.5%Zn>2.6%Zn>HZSM-5.When the reaction temperature was 515°C,the catalyst dosage was2 g,the weight hourly space velocity was 2.7 h^-1 and the carrier gas rate was 50 m L/min,the yields of the organic liquid product and the total aromatics obtained from the catalytic cracking of glycerol trioleate over 1.3%Zn/HZSM-5 catalyst reached 60.17%and 56.13%,respectively.The aromatic yield was increased by 18.01%compared to the aromatic product obtained over the parent HZSM-5 catalyst.The effects of process conditions（oil feedstock type,reaction temperature,catalyst loading,nitrogen flow rate and weight hourly space velocity）on the composition distribution of products were investigated by catalytic cracking of biomass non-edible oils over 1.3%Zn/HZSM-5 catalyst.The results showed that the composition of oil feedstock had a close relationship with the distribution of the products and the selectivity of the aromatics.Waste acidified oil and waste cooking oil have lower aromatic yields than woody oils due to the presence of more free fatty acids.Rubber seed oil and tung oil contain more unsaturated long-chain fatty acids and promoted the formation of polycyclic aromatic hydrocarbons.Jatropha curcas oil is a more suitable feedstock for the production of aromatic hydrocarbons than the other four oils.The experimental results showed that the optimal pyrolysis conditions of jatropha curcas oil over 1.3%Zn/HZSM-5 catalyst were pyrolyzed at 515℃,catalyst loading of 2 g,weight hourly space velocity of 2.7 h^-1 and carrier gas flow rate of 50 m L/min,and the yield of organic liquid product reached 52.57%and the yield of aromatics reached 50.33%.