Improvement Of Cold Flow Fluidity And Oxidative Stability Of Biodiesel Blends By Polymethacrylic Acid High Carbon Ester Polymers And Its Mechanism

Along with the implementation of the dual carbon strategy,clean energy sources such as nuclear,solar,wind,geothermal and biomass are being researched and developed worldwide.Biodiesel is a blend of long-chain esters with physicochemical properties similar to diesel,which can be obtained through the esterification of vegetable oils,animal fats or waste grease with short-chain alcohols.Biodiesel has more advantages than traditional fossil fuels,including renewability,excellent lubricity,and lower emissions of carbon monoxide,hydrocarbons,and other particulate matter.Biodiesel and its mixture with fossil fuels can be directly used in diesel engines without the need for major modifications to the engine.Therefore,it has always been considered an ideal alternative to transportation fuels,and its development is an effective way to achieve the"dual carbon goal".However,biodiesel applications have always been limited by poor cold flow properties（CFPs）and oxidative stability（OS）.Currently,the addition of cold flow improvers or antioxidants to biodiesel blends has proven to be the most effective and economical strategy to improve poor low temperature performance and oxidative stability.In order to improve the CFPs and OS of biodiesel,rapeseed oil biodiesel and waste cooking oil biodiesel were blended with 0#diesel,respectively.A series of high carbon methacrylate ester polymers with different structures were designed and prepared as cold flow improvers（CFIs）and bifunctional additives for biodiesel blends,and the crystallisation inhibition mechanism was investigated by polarised light microscopy,viscosity temperature curves and differential scanning calorimetry.The mechanism of OS enhancement was investigated by DPPH radical scavenging experiments and Rancimat method.The main studies and conclusions are as follows:（1）A series of copolymers of hydroxyethyl methacrylate-methyl methacrylate(RMC-HEMA,R=-C₁₂,-C₁₄,-C₁₆,-C₁₈)with different molar ratios were synthesized as CFIs for B20（20 vol%rapeseed oil biodiesel+80 vol%diesel）.C₁₄MC-HEMA（9:1）at 1000 ppm exhibited better improvement performance,reducing the solid point（SP）and cold filtration point（CFPP）of B20 by 14°C and 6°C,respectively.To improve the CFPs of B20 efficiently,two polymers of poly-alpha-olefin（PAO）and ethylene vinyl acetate copolymer（EVA）were used as additives in combination with C₁₄MC-HEMA（9:1）at different mass ratios.The results showed that when the weight ratio of C₁₄MC-HEMA（9:1）to PAO was 5:1 and1000ppm was added,the SP and CFPP of B20 decreased by 18°C and 14°C,respectively.Compared with the single C₁₄MC-HEMA（9:1）,SP and CFPP further decreased by 4°C and8°C,respectively.（2）To address the poor CFPs and OS factors of biodiesel blends,a series of high carbonyl methacrylate-cyclohexyl vinyl ether(RMC-CVE,R=-C₁₂,-C₁₄,-C₁₆,-C₁₈),tetradecyl methacrylate-cyclohexyl vinyl ether(C₁₄MC-CVE)（3:1,5:1,7:1,9:1,11:1 and13:1）and tetradecyl methacrylate-cyclohexyl vinyl ether-vanilla acrylate(C₁₄MC-CVE-VAA（9:1:1）)copolymers were synthesised.The copolymer C₁₄MC-CVE-VAA containing antioxidant groups was used as a bifunctional additive to improve the CFPs and OS of B20（20 vol%used cooking oil biodiesel+80 vol%diesel）.When the dose of C₁₄MC-CVE-VAA（9:1:1）was 2000 ppm,the SP and CFPP values of B20 were reduced by 17°C and 11°C,respectively.The IP increased from 1.50 h to 7.46 h,meeting ASTM D6751 and EN14214standards.The binary polymer C₁₄MC-HEMA,obtained by introducing hydroxyl polar groups into high carbon methacrylate,and combined with the additive poly-alpha-olefin to further enhance the CFPs of biodiesel blends.Additionally,the ternary polymer C₁₄MC-CVE-VAA obtained by introducing phenolic hydroxyl groups and cyclic monomers into C₁₄MC,enables the biodiesel blends to have good CFPs and also to meet the relevant standards ASTM D6751and EN14214 for OS.This provides a new direction for the development and research of graft modification of high carbon methacrylate polymers as multifunctional additives.