Study On The Enzymatic Synthesis Of Biodiesel From Rapeseed Oil

Biodiesel,as an environmentally friendly,renewable and clean liquid fuel,is being greatly concerned and widely developed in the world.Its main raw material is vegetable oil.Rapeseed oil,which has many unique advantages as one of the main vegetable oil in China and Hunan province,will become the better raw material of biodiesel than other oils.Enzymatic method is the most promising method in the various methods for biodiesel production.But there is a series of fatal shortcomings in the most of developed enzymatic production methods,such as high cost,slow reaction,short life of lipase,low yield of methyl ester and so on.All these problems has greatly restricted us to achieve industrialization of biodiesel produced by enzymatic method.So,it is greatly in need of developing a new technology to make the industrialization become reality.In order to lower the cost of biodiesel and improve enzyme reaction system,a series of research about enzymatic production of biodiesel from rapeseed oil has been done.At first,gas chromatography analysis method was established to rapidly and accurately judge the reaction degree.Secondly,the reaction mechanism and process conditions of enzymatic transesterification of rapeseed oil was studied in the water-bearing organic solvent system,water-little organic solvent system and solvent-free system.Thirdly,a new technology about how to renew lipase used in the solvent-free alcoholysis of rapeseed oil,as well as a new enzymatic interesterification technology,was developed.At last,the optimal refining process condition of crude biodiesel was obtained,the refined product can almost meet the demands of the relative biodiesel standard. 1.The established gas chromatography analysis methodThe main component of rapeseed oil biodiesel are palmitic ME,stearic ME, methyl oleic ME,linoleic ME,linolenic ME,cis-11-eicosenoic ME,erucic ME.The best separation condition in the GC apparatus with HP-innowax capillary column (30m* 0.25mm*0.25μm)was that the initial column temperature was 170℃keeping 0.5min,then the column was heated to 200℃by 5℃per minute,and then to 240℃by 15℃per minute and keeped for 5min.Under these conditions,the transesterification degree of rapeseed oil can be detected rapidly and accurately with methyl tridecanoate as the internal standard.2.The reaction mechanism and process conditions of enzymatic transesterification of rapeseed oil in the two liquid phase system with composition of water and organic solvent.The lipozyme TLIM lipase is more effective catalyst than Novozym 435 lipase for transesterification of rapeseed oil.When the molar ratio of methanol to oil is 4:1, the temperature is 40℃,and the methanol is added with three interval batches,the optimal reaction condition was that 3 mL/g petroleum ether,7%(w/w)TLIM and 20%(w/w)water based on the oil weight were added to react for 18h.There are highly significant third-order polynomial regression relationship between the methanolysis degree and the various affecting factors.Because of the accompanying with the hydrolysis of triglyceride,the methanolysis rate is not more than 75%.3.The reaction mechanism and process conditions of enzymatic transesterification of rapeseed oil in water-little organic solvent system.we took Lipozyme TLIM enzyme as a catalyst,rapeseed oil with different quality grades as raw materials,different short-chain alcohol as acyl acceptors in the organic solvent-little water system.The orthogonal experimental results showed that alcoholysis reaction of triglyceride was accompanied with hydrolysis of triglyceride and esterification of fatty acid.The fourth grade oil is a better biodiesel feedstock than the first,second and the third grade oil;ethanol is a better acyl acceptor than methanol. The optimal reaction condition for biodiesel production was that the fourth grade oil reacted with 20%(w/w)Lipozyme TLIM and 4 molar ethanol per molar oil for 10h at the temperature of 40℃.Under the optimal condition,a transfer rate of 86.2%was obtained.4.A new technology to renew lipase used in the solvent-free alcoholysis of rapeseed oil and its optimal process conditions.When the fourth grade rapeseed oil was used as raw material,immobilized lipase lipozyme TLIM is more effective catalyst than Novozym 435,ethanol is a better acyl receptor than methanol,ZSJ1 has the better renewing effect on the enzyme activity than ZSJ2,30℃is most appropriate temperature to stimulate enzyme activity and to keep it stable.When the enzyme in the reaction was periodically renewed,the reaction time was shortened to 9 hours,a transesterification rate of more than 90% was obtained,and the relative activity of the lipase being repeatedly used 15 batches was remained more than 96%.5.A new enzymatic interesterification technology for biodiesel productionBecause of that the transesterification rate is not high enough,enzymatic activity is not stable enough,the renewing operation is troublesome in the alcoholysis reaction, a new e enzymatic interesterification technology for biodiesel production from rapeseed oil was developed.The main factors of effecting interesterification reaction rate were the enzyme type,enzyme quantity,substrate molar ratio,temperature and time.After the enzyme type was determined as Lipozyme TLIM,other factors were optimized according to the quadratic regression orthogonal rotation test design,a regression model obtained was as following.Y=91.9417+1.1125X₁+0.5458X₃-2.6490X₁²-3.3740X₂² -2.7990X₃²-2.7490X₄²The results shows that,in the interesterification system,the immobilized enzyme Lipozyme TLIM demonstrated better catalytic behavior than Novozym 435;the best enzymatic interesterification conditions of the fourth grade rapeseed oil were:40℃, 40%(w/w)Lipozyme TLIM quantity,14:1 substrate molar ratio,the reaction time 12 hours/batch.Under the optimal condition,an interesterification rate of 91.7%was obtained,and the enzyme can be repeatedly used with little activity loss,which provided technical basis for the industrialization of enzymatic biodiesel.6.the optimal refining conditions of crude biodiesel and the properties of the refined productsThe best conditions for crude biodiesel alkali refining process was obtained by orthogonal design optimization.excess of alkali is 0.35%,alkaline concentration is 15%,initial alkali refining temperature is 50℃.Under these conditions,the biodiesel refining rate was 94.5%,and acid value of product was 0.40mg KOH/g.IR and GC analysis showed that the C18 and C16 fatty acid methyl ester content in rapeseed biodiesel account for more than 60%of total fatty acid methyl ester,the chemical composition and molecular structure could almost meet the request of mineral diesel substitutes.The characteristics inders of rapeseed oil biodiesel was according to the German biodiesel standards and Chinese biodiesel standard(draft)requirements,except the higher viscosity and the smaller cetane number.High vacuum distillation and cetane improver can be taken to lower viscosity and improve the cetane number.