Optimized Preparation Of Lanthanum Modified Calcium Based Solid Base Catalyst And Molecular Simulation Of Catalytic Transesterification

Biodiesel is an ideal alternative fuel for petrodiesel proven by many researches,which is renewable,wide source of raw materials,and environmentally friendly.At present,the actual catalysts used in biodiesel production are homogeneous base catalysts which are wasting much water cleaning,and unfavor reactions such as saponification are easily occur when oils have higher acid value.The La-Ca solid base catalyst has excellent performance,good stability and excellent acid resistance in transesterification.But it has the disadvantages of complicated preparation method,high preparation cost and poorer pore structure.This research is financially supported by the National Natural Science Foundation of China(51876106),Primary Research&Development Plan of Shandong Province,China(2018GGX104027)and Young Scholars Program of Shandong University(YSPSDU,2015WLJH33),La-dolomite and HNTs-La/Ca catalyst are prepared by impregnation and hydrothermal methods and used in transesterification to produce biodiesel,respectively.The preparation conditions of the catalyst are optimized,the XRD,XRF,XPS,ATR-FTIR,N2-sorption and desorption,CO2-TPD,NH3-TPD,SEM-EDS,Hammett indicator and other characterization methods are used to explain the performance of the catalyst.At the same time,the reaction parameters of catalyst in transesterification are optimized and reusable performance of catalyst is studied.Finally,the mechanism of lanthanum doped calcium solid base catalysts for methanol and acetic acid adsorption are researched based on the density functional theory.The conclusions obtained in this paper can enrich and develop the basic theory of calcium-based solid base catalyst,and provide theoretical guidance for the industrialization process of biodiesel in China.(1)La-dolomite solid base catalyst is prepared by impregnation method.The preparation conditions of the La-dolomite solid base catalyst are optimized and the molar ratio of La to dolomite is 1 when activation temperature is 800?.As raction conditions of catalyst addition of 7 wt.%,methanol to oil molar ratio of 18,reaction temperature of 65? and reaction duration of 180 min,the biodiesel yield reached 98.7%,and the activation energy of the La-dolomite in transesterification is 57.68 kJ/mol.The La-dolomite solid base catalyst has excellent reusability,and biodiesel yield in the fifth cycle is 95.9%.At the same time,the main physical and chemical properties of biodiesel obtained meet the requirements of GB/T 20828-2015.(2)Halloysite nanotubes loaded La Ca(HNTs-La/Ca)is prepared by hydrothermal method,and its performance in transesterification to produce biodiesel is studied.Firstly,catalysts are prepared by using fumed silica,y-Al2O3,MCM-41 and HNTs as carriers,respectively,and the catalyst with HNTs has the strongest activity.The most suitable mass ratio of La2O3 to CaO in the HNTs-La/Ca catalyst is 1.5.The performance of HNTs-La/Ca catalyst in transesterification against fatty acid poisoning is studied.As reaction conditions are 7 wt.%of catalyst addition,the molar ratio of methanol to oil is 18,reaction temperature is 150?,reaction duration is 120 min,and oil acid value is 0.34 mg KOH/g,the biodiesel yield reaches 97.5%,and biodiesel yield can still reach 88.7%when it is reused for the fifth time.The physical and chemical indexes of biodiesel obtained by transesterification meet the requirements of ASTM-D6751.In addition,the HNTs-La/Ca catalyst can maintain a high biodiesel yield(>72%)for 3 reuse cycles under high acid value(>10 mg KOH/g).(3)The effect of La doping CaO in adsorption of methanol and acetic acid is studied by molecular simulation.The adsorption model of methanol on CaO(100)and La-CaO(100)surfaces is constructed,and La modification can improve the stability of CaO surface.The adsorption energy and dissociation activation energy of methanol and the adsorption energy of acetic acid on CaO(100)surface and La-CaO(100)surface are calculated.The density of the bonding state and Mulliken charge layout of methanol and acetic acid CaO(100)surface and La-CaO(100)surface are analyzed.When adsorbs methanol,the adsorption energy changes very small after La doping,but the dissociation activation energy is significantly reduced.When adsorbs acetic acid,acetic acid dissociates on pure CaO(100)surface while does not dissociate after La doping,and the adsorption energy is significantly reduced.