Study On The Catalytic Cracking Of Non-edible Oil By Monolithic Zeolite

The issue of energy shortage and environmental pollution has aroused widespread concern worldwide.Production of renewable,carbon neutral biofuels is becoming a hot research topic as an alternative to traditional fossil fuels.Efficient energy conversion of non-edible vegetable oil can improve energy security,reduce CO₂ and atmospheric pollutant emissions,and promote the upgradation of agricultural structure,which is of great strategic significance.Catalytic cracking is an important pathway for energy conversion of non-edible vegetable oils,which requires the catalysts to drive a series of parallel and serial reactions such as cracking,deoxygenation and isomerization.HZSM-5 zeolites with unique three-dimensional pore structure,large specific surface area,controllable acidity,and shape selection effects,are widely used in catalytic cracking processes.However,the microporous structure of traditional HZSM-5 zeolite will restrict the entry of triglyceride macromolecules into the micropore channel,which will result in difficulties such as low accessibility of active site in the channel,difficulty in control of liquid product selectivity,and fast carbon deposition and deactivation.On the other hand,in practical applications,powdered HZSM-5 zeolite requires tablet pressing or adhesive molding,which can easily lead to adverse effects such as poor fluidity of reactants and products,poor thermal conductivity,and high pressure drop.Structural design and modification of HZSM-5 zeolite can significantly optimize the mass/heat transfer and fluid mechanics behavior of the catalyst bed,while regulating the pore structure and acid properties of the catalyst,thus effectively improving the above problems.The research content and results of this paper are as follows:（1）Study on preparation and catalytic performance of monolithic SS-fiber@HZSM-5catalystsMonolithic SS-fiber@HZSM-5 catalyst with different Si O₂/Al₂O₃ ratios was successfully prepared by seed coating followed by hydrothermal crystallization on stainless steel fiber felt.With the increase of the Si O₂/Al₂O₃ ratio,the growth of HZSM-5 zeolite becomes easier,with a more regular coffin-like morphology,a gradual increase in specific surface area and pore volume,and a gradual decrease in acid strength.Above catalysts were applied to the catalytic cracking of castor oil with powder HZSM-5 as comparison test.Under the same reaction conditions,the hydrocarbon content in the gasoline and diesel fractions obtained from monolithic SS-fiber@HZSM-5 catalyst is 4-5times higher than that of the powder HZSM-5 catalyst.In conjunction with its much lower rate of coke deposition,structural design of the catalyst indicates a significant intensification on the catalytic cracking process.Under the optimal reaction conditions of cracking temperature of 510°C,N₂ gas flow rate of 20 m L min^-1,and weight hourly space velocity of4 h^-1,the catalyst with a silicon aluminum ratio of 200 in shell HZSM-5 provided a gasoline fraction yield of 32.3%and a diesel fraction yield of 38.6%,with hydrocarbon content of 78.13%and 58.71%,respectively.After continuous operation for 13 h,the activity and deoxygenation ability of the monolithic SS-fiber@HZSM-5 catalyst decreased significantly,which was still better than the powder HZSM-5 catalyst.（2）Study on preparation and catalytic performance of metal-modified monolithic M/SS-fiber@HZSM-5 catalystsIn order to enhance the deoxygenation performance of the catalyst and effectively reduce the acid value of the oil product,monolithic M/SS-fiber@HZSM-5 catalysts modified by metal Ni,Co,Mg,Fe,Al,and Cu were prepared by a wet impregnation method based on monolithic SS-fiber@HZSM-5（200）catalyst.Catalyst characterization showed that the supported metals were converted into Ni O,Co₃O₄,Mg O,Fe₂O₃,Al₂O₃,and Cu O,which were distributed on the surface of the HZSM-5 shell without affecting the zeolite framework.After metal loading,the weak acid content in HZSM-5 decreases while the strong acid content increases（except for Mg-modified samples）.Among them,Ni-modified samples generated new Br（?）nsted acid sites.Ni/SS-fiber@HZSM-5 catalysts with different Ni loading was prepared.With the increase of Ni loading,the intensity of Ni O diffraction peaks in XRD pattern was continuously increase,as well as the specific surface area and pore volume.Excess Ni loading（>10 wt%）resulted in complete coverage of the zeolite surface by oxides,but without damage of original HZSM-5 structure.The modified M/SS-fiber@HZSM-5 catalysts were used for the catalytic cracking of castor oil,in which Ni and Co modified catalysts showed high gasoline fraction yields.The gasoline and diesel fractions obtained from Ni-modified samples exhibited the highest hydrocarbon content,i.e.,97.89%and 98.79%,respectively.However,the rate of carbon deposition in Ni-modified sample is also highest.Ni modification increases the proportion of B/L acid in the catalyst,which could promote cracking,aromatization,and deoxygenation,but also promote coking reaction to a certain extent.The effect of Ni loading on reaction performance was investigated.Higher yields of gasoline and diesel fractions can be obtained simultaneously（39.9%and 24.6%,respectively）over the Ni/SS-fiber@HZSM-5 with a Ni loading of 10 wt%.Excessive Ni content will exacerbate the coking behavior in the catalyst and cause rapid deactivation,leading to a decrease of hydrocarbon content in gasoline and diesel fractions.After continuous operation for 20 h,the activity of the 10%Ni/SS-fiber@HZSM-5 catalyst significantly decreased,which was still better than that of the unmodified SS-fiber@HZSM-5 catalyst.