Experimental Research On Upgrading Of Biodiesel By Selective Hydrogenation Based On DBD Reaction Technology

As a kind of high-quality clean energy,biodiesel has broad prospects in replacing traditional fossil fuels and has received widespread attention.Biodiesel contains a large amount of polyunsaturated fatty acid esters,resulting in poor oxidation stability and low cetane number,which limits the large-scale application of biodiesel.Selective catalytic hydrogenation of biodiesel to partially hydrogenate polyunsaturated fatty acid esters to monounsaturated fatty acid esters can significantly improve the oxidation stability,cetane number and lubrication performance of biodiesel without big loss of low temperature fluidity,at the same time,it helps reduce hydrogen consumption and cost.In view of the high cost of equipment,harsh reaction conditions,catalyst coking and complicated process flow,a technical scheme based on dielectric barrier discharge reaction technology for partial hydrogenation and upgrading of biodiesel under normal temperature and pressure conditions was proposed.Soybean biodiesel was used as raw material,hydrogen was used as hydrogen donor,and Raney-Ni was used as catalyst to carry out research on partial hydrogenation and upgrading of biodiesel.The influences of system operating parameters such as voltage,frequency and gas flow on the load characteristics and working performance of the reactor were discussed systematically.The orthogonal experiment of hydrogenation and upgrading of soybean oil biodiesel was carried out in a dielectric barrier discharge reactor.The effects of various operating parameters on the depth and selectivity of biodiesel hydrogenation were studied.Based on the results of GC-MS,the hydrogenation reaction mechanism of biodiesel was analyzed,and the physicochemical properties of biodiesel before and after hydrogenation were compared and analyzed.The main research work and contents of the paper are as follows:?1?Construction and performance study of soybean biodiesel-hydrogen plasma-catalyst three-phase discharge reaction system.According to the principle of dielectric barrier discharge and plasma chemical reaction,a coaxial cylindrical vapor phase discharge biodiesel hydrogenation upgrading reactor was designed.The effects of operating parameters such as voltage,frequency and length of discharge zone on the load characteristics and working performance of DBD reactor were discussed.The results show that with the increase of discharge frequency,the load voltage first increases and then decreases,reaching the maximum at the resonance frequency point.At this time,the discharge power also reaches the maximum value,and the energy input density of the reaction device is the highest.The fit of the equivalent capacitance and the air gap equivalent capacitance curve of the dielectric layer at different lengths of the discharge region are good,indicating that the discharge mainly occurs in the inner effective area of the discharge tube and is evenly distributed in the axial length of the discharge tube.?2?DBD discharge reactor electrode evaluation and optimization.The working electrode is preferably considered in consideration of the discharge power,the electron density,and the effective energy conversion efficiency of the device.The results show that the DBD reactor with large diameter electrode has higher discharge power,higher electron density and higher specific electron density at the same load voltage,which indicates that under the input power of the unit,more active particles can be produced,and the overall performance of the discharge device is better.?3?Hydrogenation catalyst performance evaluation and preference.The experimental study on the selective hydrogenation of biodiesel was carried out,and the reaction catalyst was comprehensively optimized with the hydrogenation depth and the selectivity of low unsaturated components.The results show that the iodine value of biodiesel has the largest decline rate under the action of Co-Mo/Al₂O₃,but the polyunsaturated component is mainly converted into fully saturated product,which is not conducive to the low temperature fluidity of biodiesel.Raney-Ni has the highest conversion of polyunsaturated components in biodiesel,and the formation of low unsaturated components of products is more selective.?4?Study on the influence of operating parameters on the depth and selectivity of biodiesel hydrogenation.Four factors four-level orthogonal test were carried out with input voltage,gas flow rate,liquid phase circulation flow and reaction time as independent variables.The effects of various reaction parameters on the depth and selectivity of biodiesel hydrogenation were studied.The results show that the depth of hydrogenation of biodiesel increases rapidly with the increase of input voltage and gas flow rate,and then decreases slowly with the increase of liquid phase circulation flow and reaction time.The low unsaturation of biodiesel The composition formation selectivity tends to increase rapidly and then slowly decreases with the increase of input voltage,gas flow rate,liquid phase circulation flow rate and reaction time.The maximum iodine value reduction rate of the sample obtained by the test was 58.3%,the content of high unsaturated component was decreased by 36.54%,and the content of low unsaturated component was increased by 28.41%.?5?Research on hydrogenation reaction mechanism and kinetics of biodiesel.The iodine value and composition of biodiesel before and after hydrogenation were measured,and the hydrogenation reaction mechanism of biodiesel was discussed.The results show that under the action of dielectric barrier discharge,the strong inelastic collision between hydrogen molecules and high-energy electrons produces a hydrogen plasma containing active substances such as hydrogen radicals,positive and negative ions and excited states,and hydrogen plasma is in contact with biodiesel.The addition reaction of unsaturated C=C bond,hydrodeoxygenation reaction and hydrodecarboxylation reaction occur.The hydrogenation reaction of the main components of biodiesel can be described by the pseudo first-order reaction model,and the polyunsaturated fatty acid methyl ester is converted into low.The reaction rate of unsaturated fatty acid methyl ester is higher than that of low unsaturated fatty acid methyl ester to fully saturated fatty acid methyl ester.Under the conditions of gas phase discharge reaction,the hydrogenation reaction of biodiesel has better selectivity for methyl ester formation of low unsaturated fatty acids.?6?Study on the influence of hydrogenation on the physical and chemical properties of biodiesel.The results show that the cetane number of biodiesel is increased from 47.9 to 61.2after partial hydrogenation,and the low calorific value is increased from 37.6MJ/kg to39.1MJ/kg.The ignition performance is improved and the energy density is improved.The improvement of diesel engine power and economic performance;the comprehensive thermal analysis of biodiesel before and after hydrogenation shows that the initial weight loss temperature of biodiesel after hydrogenation is 20.53?higher than that of crude oil,but the peak of heat release rate is increased by 4.22W/g,the peak temperature of the exothermic rate is reduced by 25.23?,and the combustion duration is shortened,and the exothermic period is more concentrated.After the hydrogenation and upgrading,the kinematic viscosity of biodiesel increased,and the low temperature flow performance decreased slightly,but it was still better than 0#diesel.The oxidation stability and low temperature flow performance of biodiesel were well balanced when the reaction time was 1.5h and the comprehensive quality of biodiesel has been significantly improved.