Study On Preparation Of Biodiesel Catalyzed By Choline Amino Acid Ionic Liquids And Ionic Liquid-mediated Enzyme Catalysis

Ionic liquid is a kind of green and renewable solvent,which can replace the traditional acid-base catalyst and organic solvent to synthesize biodiesel.Ionic liquid has the dual properties that it can be used as catalyst and non-aqueous enzyme catalyzed reaction medium.In this study,nineteen bioderived and renewable choline amino acid ionic liquids（[Cho][AA]-ILs）were synthesized using amino acids and choline hydroxide as raw materials and used for preparing biodiesel.Firstly,the molecular structure of[Cho][AA]-ILs was characterized,and some of their physicochemical properties were determined.Then,the synthesis of biodiesel from soybean oil transesterification catalyzed by[Cho][AA]-ILs was studied.Finally,the application of[Cho][AA]-ILs as reaction medium in the production of biodiesel from waste cooking oil by coupled immobilized lipase catalyzed in hydrolyzation-esterification two-step process was investigated.The results were as follows:（1）FT-IR and NMR data show that[Cho][AA]-ILs has been successfully synthesized.Thermogravimetric data show that the thermal decomposition temperatures of[Cho][Arg]and[Cho][Val]are 102 and 137°C,respectively.Most of the p H values of[Cho][AA]-ILs are greater than 10 in methanol and water solution,among them,the p H value of[Cho][Arg]is 13.17 in methanol solution with ILs concentration of 0.1 mol.L^-1,which is similar to the KOH（p H is 13.56）.The p H value of[Cho][Asp]is 7.74 in methanol solution at same concentration.[Cho][Arg]was chosed as the most suitable catalyst for the synthesis of biodiesel from oil and methanol.（2）Using[Cho][Arg]as a catalyst to catalyse soybean oil transesterification,response surface（RSM）parameters were optimized based on the Box Behnken design（BBD）for molar ratio of methanol to oil,reaction temperature,catalyst load and reaction time.The optimal parameters of the four factors were obtained as 9.13:1,81°C,14.75 wt.%and 56.44 min.Under these conditions,the highest biodiesel conversioncatalyzed by the[Cho][Arg]achieved 98.58%.（3）The kinetics of transesterification of soybean oil and methanol catalyzed by[Cho][Arg]was evaluated.The results showed that the reaction was consistent with the quasi-first-order kinetic model,and the activation energy Ea and pre-exponential factor A were 10.06 k J·mol^-1 and 1.1707 min^-1,respectively.（4）Lipases Lipozyme RM,Novozym 435 and Lipozyme TL IM were used as catalysts,and the[Cho][AA]-ILs was used as the enzymatic reaction medium to carry out the hydrolysis of waste cooking oil and oleic acid esterification catalyzed by[Cho][AA]-ILs mediated enzyme.The results showed that[Cho][AA]-ILs promoted the catalytic activities of three immobilized enzymes in Wahaha water system to varying degrees when mediating the hydrolysis of waste cooking oil.In the phosphoric acid buffer liquid system,[Cho][AA]-ILs inhibited the hydrolytic activity of Novozym435,but did not promote or inhibit the Lipozyme RM and Lipozyme TL IM.When mediating fatty acid esterification,[Cho][Arg]showed excellent performance in catalyzing oleic acid esterification coupled with Lipozyme TL IM lipase.The addition of reaction medium[Cho][Arg]significantly improved the biodiesel conversion of the enzymatic reaction.（5）The experimental conditions of Lipozyme TL IM enzymatic hydrolyzation-esterification reaction were optimized.The hydrolysis reaction parameters were obtained as follows:reaction temperature 55°C,p H=7.0,enzyme dosage 3 wt.%,oil-water volume ratio 1:1.Under the condition of reaction time 18 h and shaking speed200 rpm,the hydrolysis rate is 86.99%.The esterification reaction parameters were as follows:[Cho][Arg]loading 2 wt.%,enzyme dosage 10 wt.%,molar ratio of methanol to oil 4:1,200 rpm and 25°C for 150 min,and the esterification rate of biodiesel was96.87%.Lipozyme TL IM enzyme itself has high catalytic hydrolysis activity,and is intolerant to short chain alcohols,so it is difficult to catalyze esterification.However,the addition of[Cho][Arg]as reaction medium enables Lipozyme TL IM to obtain high catalytic esterification ability of fatty acids.Under the[Cho][Arg]coupled Lipozyme TL IM system,the green process of Lipozyme TL IM hydrolyzation-esterification was established successfully.In this study,[Cho][Arg]showed excellent catalytic activity and great potential as a non-water-mediated enzyme for esterification.Therefore,alkaline ionic liquid[Cho][Arg]is a promising catalyst and reaction medium that is easy to synthesize and sustainable to regenerate raw materials,and can be well biodegradable,and can be used as a substitute for traditional alkali catalyst to synthesize biodiesel,and as a high efficiency medium for esterification reaction to prepare biodiesel.