Study On Calcium-based Solid Alkali Catalyzed Transesterification Reaction And Biodiesel Production Process

In recent years,the massive consumption of fossil fuels and the increasingly harsh environment have forced us to look for new"green energy".Biodiesel has attracted more and more attention due to its renewability and environmental protection.In the method of preparing biodiesel,the transesterification method is the most widely used,and the choice of catalyst in this method is very important.The solid alkali catalyst represented by CaO has the characteristics of a wide range of raw materials,mild reaction conditions,low price,and simple preparation process,and has become the focus of biodiesel catalyst research in recent years.However,the specific surface area of CaO is small,it is easy to absorb water and CO₂in the air,and metal ions are easy to leach out during the reaction,which leads to the deactivation of the catalyst,so its application is greatly restricted.In order to improve these drawbacks,this thesis uses Ca(OH)₂and methacrylic acid(C₄H₆O₂)as raw materials to design a CaO solid alkaline nano catalyst with simple preparation process and excellent catalytic performance.And through different methods to improve it,used in soybean oil transesterification to produce biodiesel.The biodiesel process is a systemtic engineering,which needs to evaluate the energy,environmental and economic impacts of the whole process,and use life cycle methods to evaluate different biodiesel projects in order to make more appropriate decision.Therefore,this study systematically investigated the influence of different metals-improved CaO catalyst on the biodiesel production process,and evaluated biodiesel projects based on the life cycle method.In addition,the industrial development of biodiesel is also particularly important,but alkali catalysts are very sensitive to acidic substances and water in the feedstock oil,and are easy to cause saponification and emulsification.Therefore,it is necessary to establish a biodiesel production process in Aspen Plus software,simulate the reaction process,and optimize the operating conditions of the equipment to provide a theoretical basis for the industrial development of biodiesel.(1)A bimetallic CaO/Ag nanocatalyst was developed.Calcium and silver were introduced into methacrylic acid through coordination bonds.The successful loading of Ag particles changed the distribution of active sites of CaO,thereby improving the catalytic performance and stability.The CaO/Ag catalyst exhibits abundant strong basic sites,with larger specific surface area(7.02 vs 2.05 m²/g),pore size(58.84 vs37.08 nm)and pore volume(0.070 vs 0.016 cm³/g),and more conducive to the transfer of triglycerides in the channel.RSM-CCD was used to study the factors affecting the transesterification reaction and optimize the reaction conditions.The results show that under the catalysis of CaO/Ag,the reaction time is shortened by half,and the biodiesel yield is also significantly improved.The catalyst can still maintain high catalytic activity after being recycled for 5 times.The kinetic and thermodynamic analysis results show that Ag cooperated with CaO catalysis effectively reduces the mass transfer resistance of triglycerides in the transesterification reaction,thereby reducing the activation energy of the reaction,increasing the mass transfer constant,and accelerating the reaction rate.(2)Based on the research of CaO,cheap Cumetal was introduced,and the bimetallic oxide CaO/CuO and hydrophobic CaO/CuO/BN nanocatalysts were prepared by co-precipitation method.Research on different ratios of CaO/CuO catalysts shows that the best ratio of CaO:CuO is 4:1,and the largest biodiesel can be obtained.XRD characterization analysis shows that CuO can effectively inhibit the formation of CaCO₃in the catalyst,and is better than Ag metal in protecting CaO.The addition of BN further modified the CaO/CuO catalyst,which changed the morphology and structure of the catalyst,and showed good performance in the transesterification reaction.The transesterification reaction of soybean oil containing0.1 wt%moisture,when CaO:CuO:BN=4:1:0.5,the yield of biodiesel can still be as high as 82.24%,and the addition of BN can resist the moisture in the feedstock oil.(3)Using LCA(Life Cycle Assessment)and LCC(Life Cycle Cost)life cycle methods,the energy consumption,environmental emissions,and economic of the biodiesel production process from different feedstock oils are evaluated.The results show that the total energy consumption of soybean oil biodiesel in the life cycle is about 2.65 times that of waste cooking oil,and compared with soybean oil,the emissions of CO₂,SO₂,NO_x,CO and dust during the life cycle of waste cooking oil biodiesel are reduced by 82.92%,45.68%,94.91%,53.40%and 90.61%,respectively.Economic analysis shows that the costs of soybean oil biodiesel and waste cooking oil biodiesel are 7851.05 and 7334.30 RMB/t,respectively.Among them,the cost of feedstock accounts for the largest proportion,61.75%and 54.14%,respectively,followed by catalyst costs,which account for 11.26%and 13.61%respectively.(4)Select waste cooking oil with higher acid value as raw material,and use Aspen Plus software to design,simulate and optimize the biodiesel production process.The two-step method is used to pretreat the waste cooking oil first,and then use CaO to catalyze the transesterification reaction,and effectively recover the raw materials and products of the production process.Using sensitivity analysis tools to optimize reaction equipment and operating conditions,high-quality biodiesel and by-product glycerin were obtained in each process,which verified the feasibility of the model.In this way,the scope of use of feedstock oil can be broadened,and it can provide a basis for the development of biodiesel industry in waste cooking oils.