Study On Water-free Purification Process Of Methyl Ricinoleate Preparation

Castor oil-based biodiesel made from castor oil is a green renewable fuel with excellent performance and environmental friendliness.As the main component of castor oil-based biodiesel,methyl ricinoleate is an important raw material for the production of undecaenoic acid,heptanal,sebacic acid,sec-octanol and other chemical intermediates.At present,homogeneous alkali-catalyzed transesterification is the main method to produce biodiesel.The preparation process of methyl ricinoleate is as follows.Firstly,transesterification reaction between castor oil and methanol occurs under the catalysis of homogeneous base(KOH or NaOH dissolved in methanol).Then,a series of purification processes such as methanol removal,glycerol removal,alkali removal by water washing,and distillation were used to obtain the high purity products.However,in the purification process of methyl ricinoleate,several problems exist.First,the transesterification reaction is a reversible reaction,so in the process of methanol removal,the transesterification reaction will go in the reverse direction,affecting the yield of methyl ester and the subsequent purification process.Second,due to the presence of a small amount of glycerin and the hydrophilicity of methyl ricinoleate,the issues of water-oil emulsification,separation difficulties and relatively low yield of methyl ester exist in the alkali removal process of methyl ester,with a large amount of wastewater generated.In order to solve these problems,methyl ricinoleate was prepared by water-free purification in this paper.The main research contents and conclusions are as follows:(1)Methanol removal process is the key to the yield of methyl ester and the subsequent purification process,so it is necessary to study and optimize the methanol removal process.The effects of temperature,time and pressure on the contents of methyl ricinoleate and glycerin in methanol removal process were investigated.The effects of temperature and time on the contents of methyl ricinoleate and glycerin in reverse transesterification were analyzed.Results show that the optimal temperature for methanol removal was 40 ℃.About 90% of methanol was removed by rotating evaporation using circulating water vacuum pump(5 kPa)for 1 hour,with the residual methanol removed by high vacuum freeze drying machine(80 Pa).The methanol removal rate was 98.16% and the content of methyl ricinoleate was 70.91%.When the temperature was below 40 ℃,although the methyl ricinoleate content was higher,the methanol cannot be fully removed and the time was long.When the temperature was higher than 40 ℃,the time was shorter,but the methyl ricinoleate content was significantly reduced.The results of transesterification reverse reaction showed that the degree of transesterification increased with the increase in temperature,and the content of methyl ricinoleate and glycerin in the reaction system decreased.(2)The removal of homogeneous base catalyst in methyl ricinoleate was studied.Glycerol was selected as the extraction agent to investigate the phase equilibrium relationship of glycerol,methyl ricinoleate and KOH at different temperatures and ratios,and the extraction equilibrium diagram of KOH in methyl ricinoleate and glycerol was obtained.The removal of KOH from methyl ricinoleate by glycerol extraction was studied.The results show that the best extraction effect was achieved at 30 ℃ and alkali: glycerol = 2%.The content of KOH in methyl ricinoleate was reduced to 0.047% after single stage extraction.The content of KOH in methyl ricinoleate was decreased to 20 ppm after three stage extraction.For water extraction,the content of KOH in methyl ricinoleate was only decreased to 0.09% after six stage extraction.It can be seen that the effect of glycerol extraction was significantly higher than the water washing method,with the amount of glycerol used was also far lower than that of water.Finally,the methyl ricinoleate was purified by distillation and glycerol produced from the extraction agent glycerol and transesterification was recoverd.The results showed that the methyl ricinoleate distillation rate was 78.4% and the purity of methyl ricinoleate reached 97.5%.It indicated that methyl ricinoleate in the process can be obtained as a high purity product.The glycerol recovery rate reached 90.6%.The purity of glycerol after distillation reached 96.3%.It proved that the recycling of glycerol from glycerol extraction was feasible.