Modified Metal-organic Frameworks Catalyzed Microalgal Biodiesel Into Jet-fuel Range Hydrocarbon Products

Using biolipid as raw material to deoxygenate and crack to produce bio-jet fuel as a substitute for fossil jet fuel is of great significance to achieve the goal of ‘double carbon’.Microalgae have the technical advantages of rapid growth and high oil content,which is expected to solve the problem of raw material shortage in the production of bio-jet oil.The preparation of bio-aviation oil from microalgae oil has become an international research hotspot in the field of new energy.However,molecular sieve is usually used as catalyst to deoxygenate and crack,and the process requires hydrogen as atmosphere,which increases the risk and economic cost,and also the metal particles loaded on molecular sieve tend to agglomerate and deactivate,resulting in low selectivity of jet fuel products.In this paper,a nickel-based metal-organic framework of terephthalic acid（Ni-BDC）catalyst was developed for the synthesis of bio-jet fuel,and meanwhile,the greenhouse gas CO₂,which is safe and environmentally friendly and promotes bond breaking reaction,was directly used as the reaction atmosphere.Ligand group modification method and carbonization method were used to improve the selectivity and composition quality of hydrocarbon products in jet-fuel range.Metal-organic framework catalysts were prepared by group modified ligand method to catalyze methyl palmitate for the production of bio-jet oil and the product selectivity was improved.The specific surface area of metal-organic framework catalyst was increased from 55 to 901 m2/g after hydroxyl modification.NH3-TPD analysis showed that the content of strong acid sites increased from 0 to 0.77 mmol/g and XPS analysis showed that the content of active metal sites on catalyst surface increased from5.05 to 5.70%.Studies showed that deoxygenate occurs prior to bond cracking reaction,resulting in higher yield of deoxygenated C15 alkanes than cracking C8^C14 alkanes.The selectivity of hydrocarbon products in jet-fuel range of Ni-DOBDC reached 82%from 68% and the selectivity of n-alkanes increased to 65%.Carbonization of the metal-organic framework enhanced its acid and the quality of jet-fuel catalyzed from methyl palmitate was improved.The deoxygenation capacity of the nickel-based metal-organic framework catalyst was enhanced,and the selectivity of the direct-deoxygenation product n-pentadecane was increased from 14.01% to 24.79%.After carbonization at 600°C,the number of strong acid sites of the obtained catalyst（BDC-600）increased to 0.8352 mmol/g.The selectivity of hydrocarbon products in jet-fuel range increased to 83.5% and the selectivity of alkenes decreased from 10.59%to 5.39%,while cycloalkanes increased from 4% to 8%,which improved the composition quality of hydrocarbon products in jet-fuel range.Modified metal-organic framework catalyzed algal biodiesel to produce jet-fuel products with high selectivity.The results showed that the C=C double bond could promote the formation of cycloalkanes through double bond migration and inner esterification,and the selectivity of the ring products obtained by catalyzing unsaturated fatty acid methyl ester was 2.4 times higher than that from saturated fatty acid methyl ester.The deoxygenation and cracking abilities of two modified nickel-based catalysts（Ni-DOBDC,BDC-600）for converting microalgal biodiesel were investigated.The selectivity of hydrocarbon products in jet-fuel range increased from 60.38% to 72.18%and 75.56%.The selectivity of paraffin increased by 26% and 53.2%,while the selectivity of olefin decreased by 14% and 47.7%,which enhanced the corrosion resistance of jet-fuel products.