Study On The Esterification Of Soybean Deodorizing Distillate By Stepwise Acid Catalysis

Deodorizing distillate is produced in the processing of edible oil.Deodorizing distillate is the main raw material for the extraction of natural vitamin E and phytosterols.The main way to extract natural vitamin E and phytosterol is through esterification,which convert fatty acids in deodorizing distillate to methyl esters,and then further separated by molecular distillation or supercritical CO₂ fluid extraction and so on.Therefore,the study of esterification of fatty acids in deodorizing distillate is an important link in the comprehensive utilization of deodorizer distillate.In this thesis,soybean deodorizer distillate was used to study the esterification process of stepwise acid catalyzed esterification.The emphasis was placed on the establishment of process flow,the determination of parameter control points,the optimization of conditions,and the wide use of stepwise acid catalysis in the process of esterification.The specific research content and results are as follows:The first part,the equilibrium relationship between methanol phase and oil phase and water content in methanol phase were determined by esterification experiment by acid catalyzed esterification,and a intial two step and three step acid catalyzed esterification process route was established.Three parallel experiments were carried out on two kinds of esterification process routes respectively.By comparing the two step and three step acid esterification process routes,it was proved that the three step acid catalyzed esterification process was feasible.The three step acid catalyzed esterification is to divide the whole esterification process into three steps.The esterification process of free fatty acids is controlled by controlling the end point of each step.The first step is about 60 mgKOH/g as the end point of the reaction,the end point of the second step is around 30 mgKOH/g,and the end of the third step was reduced to less than 3 mgKOH/g.The second part,the process optimization of the three stepwise catalysis experiment was carried out.In the experiment,the methanol was used recycling,that is,the methanol produced by the second step reaction was used in the first step.The methanol produced by the third step reaction was used in the second step,and the third step we use fresh methanol.The sulfuric acid catalyst is added with fresh methanol in proportion,and the intermediate process is not added again.Though the experiment,we get the best process conditions of stepwise acid catalyzed esterification of soybean deodorizer distillate.The optimum reaction condition is61?,ratio of H₂SO₄ to raw material is 0.9%,and ratio of methanol is 20%.We also studied the effect of moisture content in methanol with stepwise acid catalysis in soybean deodorized esterification,experiments shows that the higher water content in methanol the higher end point of acid value in soybean deodorizer distillate esterification reaction,when the moisture content in methanol is under the condition of 1%-3%,the reaction can be achieved,but when content reached 4%,the end point of acid value in soybean deodorizer distillate esterification reaction is significantly enhanced.Therefore,the methanol can be used to complete the stepwise esterification reaction within the water content of 1%-3%.The third part,stepwise acid catalyzsis is used to research the esterification reaction of different acid value of soybean deodorizer distillate range 70mgKOH/g to130mgKOH/g.The experiment shows the the end value of the soybean deodorizer distillate,which is 70 mgKOH/g,is greater than 3.5 mgKOH/g after stepwise esterification,such soybean deodorizer distillate which acid value is in this range,can be apply on stepwise acid catalyzsis esterification reaction by mixed with high acid value of soybean deodorizer distillate.While the other acid value of soybean deodorizer distillate can applied to stepwise acid catalyzsis esterification by adjust the end point acid value of the first step according to the acid value of the raw material.When the raw material acid value within the 100 mgKOH/g-130 mgKOH/g range,the acid value of the end point acid value of the first step must be controled in 70mgKOH/g,and when the raw material acid value within the 80 mgKOH/g-100mgKOH/g range,the acid value of the end point of the first step must be controled in60 mgKOH/g.The fourth part,the rate of natural vitamin E retention by stepwise acid catalyzed and the traditional mathod of esterification were compared,the rate of VE retention are 96.10%and 98.14%.The experiment show that the method of stepwise acid catalyzsis can effectively enhance the rate of natural vitamin E retention in esterification action.At the same time,the experiment also studied the way of natural vitamin E protected by nitrogen,which can also effectively reduce the loss of natural vitamin E in esterification process.Under the protection of nitrogen,the rate of VE retention in stepwise esterification of soybean deodorizer distillate is 99.24%.