Study On The Characteristics Of Biodiesel Prepared By Calcium-based Solid Base Catalytic Transesterification Based On MOFs

Biodiesel is a renewable and degradable green liquid fuel,which is considered as an ideal substitute for fossil energy due to its advantages of good environmental friendliness and safety.Currently,homogeneous bases are mainly used as catalysts for biodiesel production,but homogeneous bases catalysts cannot be recycled and the products need to be washed,resulting in high production costs.As a typical representative of solid base catalysts,Ca O catalyzed transesterification with high activity,easy separation after reaction and widely existed in nature,has become a research hotspot in the field of catalytic transesterification for biodiesel preparation in recent years.However,common Ca O suffers from the problems of easy Ca²⁺loss,small specific surface area（<5 m~2/g）and poor pore structure,and the above problems limit the useful life of the catalyst and reduces the reusability of Ca O.Metal Organic Frameworks（MOFs）are a class of crystalline porous materials with periodic network structure formed by inorganic metal ions or metal clusters interconnected with organic ligands containing nitrogen or oxygen through self–assembly.MOFs have the characteristics of high porosity,large specific surface area and controllable functional groups.Therefore,this thesis proposes a research idea to synthesize calcium–based solid base catalysts based on MOFs materials through two strategies of post–functionalization and in–situ construction,and test the catalyst activity in the transesterification of palm oil and methanol for biodiesel preparation.The preparation and transesterification conditions were optimized and the stability performance was investigated to reveal the conformational relationship between the physicochemical properties and catalytic activity of the catalysts.（1）The post–functionalization strategy was adopted to functionalize and modify UiO–66（Zr）with calcium acetate,so as to realize the loading of Ca O,increase the specific surface area of calcium–based solid base,while the interaction between Ca and Zr improved the stability of the catalyst.The characterization results showed that the catalyst UCN650 with a calcium acetate amount of 40 wt.%and calcination temperature of 650℃under nitrogen atmosphere had a specific surface area of 24.06 m~2/g,which was higher than that of UCA700,and the high specific surface area improved the catalytic activity of the catalyst.The biodiesel conversion of96.99%at catalyst amount of 6 wt.%,molar ratio of alcohol to oil of 9,reaction temperature of65℃and reaction time of 1 h,and the conversion still exceeded 90%after reuse for three times.The catalyst with reduced activity could be regenerated by cyclohexane scrubbing,and the regenerated catalyst activity was comparable to the original catalyst activity.（2）A metal organic frameworks Ca–BTC with Ca as the central metal ion was synthesized by hydrothermal method,and the in–situ construction of calcium–based solid base was realized by high–temperature activation.Investigate the effects of calcination temperature and heating rate on the catalyst activity and pore structure.The characterization results showed that the catalyst Ca–800N–5 prepared at heating rate of 5℃/min and calcination temperature of800℃/min presents a rod–like structure composed of nano–carbon sheets.Ca O was embedded in the nano–like carbon layer,and the unique structure provided a huge specific surface area（369.66 m~2/g）.The conversion of 97.50%was obtained under the conditions ofζ=8 wt.%,γ=12,T_r=65℃and t=2 h,and the conversion remained above 80%after 6 times of reuse.（3）A bimetallic organic frameworks CaCe–BTC with Ce and Ca as the center metal ions was synthesized by the hydrothermal method,combined with high–temperature pyrolysis to achieve the in situ ordered doping of Ca O by Ce.Investigate the effect of Ce/Ca molar ratio on the reusability of the catalyst.The characterization results showed that the substitution between Ca²⁺and Ce⁴⁺produced strong interactions and lattice distortion to improve the stability of the catalyst.Among them,C3–800N prepared under the condition of Ca/Ce molar ratio of 3:10 and calcination temperature of 800℃had the highest basicity（0.51 mmol/g）.The biodiesel conversion of 96.05%atζ=8 wt.%,γ=9,T_r=65℃and t=1 h and the conversion was only reduced by 2.14%after 8 times of reuse.The results of anti–water/acid experiments showed that when the water/acid amount was 5 wt.%,the conversion of 83.43%and 86.45%,respectively.