Study On The Catalytic Synthesis Of Glycerol To Alkyl Glycerol Ethers

Recently,with the rapid development of biodiesel production,the production of by-product glycerol is increasing rapidly.How to utilize the excess glycerol effectively has became a hot research.Among the high value-added applications of glycerol,it is a good choice to convert the glycerol into alkyl glycerol ethers and to use these ethers as fuel additives,which has been favored by more and more researchers.In the process of catalytic synthesis of glycerol to alkyl glycerol ethers,there are few studies about comparison between glycerol dehydration with alcohols(methanol,ethanol and tert-butyl alcohol).Most literature only study on the dehydration of single alcohol with glycerol,and mainly use the batch reactor.In addition,there are also few studies on the preparation alkyl glycerol ethers by fixed-bed reactor.Therefore,in this paper,alcohols(methanol,ethanol and tert-butyl alcohol)and glycerol were used as raw materials.And the stainless steel autoclave and fixed-bed reactor were used to study and compare the catalytic synthesis of alkyl glycerol ether by alcohols dehydration with glycerol.Firstly,in the study of synthesis alkyl glycerol ethers in stainless steel autoclave,Amberlyst-35 was employed as the catalyst.The effects of catalyst amount(1-15 wt.%),reaction temperature(50~140℃),reaction time(5~10h)and molar ratio of alcohol to glycerol(3:1~8:1)on the catalytic performance were investigated,and the experimental results obtained are as follows:(1)In the process of glycerol dehydration with methanol,the optimum reaction conditions are as follows: catalyst amount 5wt.%,reaction time 10 h,reaction temperature120℃ and methanol to glycerol molar ratio of 6:1.Through the analysis of water content in the system,the results show that a large amount of by-product water will be produced in the reaction process,which may lead to the aim-product hydrolysis,and restrict the right-hand movement of the reaction equilibrium.(2)In the process of glycerol dehydration with ethanol or tert-butyl alcohol,when the catalyst amount is more than 10 wt.%,it is found that the glycerol conversion and product selectivity show no obvious change.The optimum conditions for glycerol dehydration withethanol are as follows: the molar ratio of ethanol to glycerol is 5:1,the reaction temperature is90℃ and the reaction time is 8h.The selectivity to MAGE is 63%.(3)The optimum molar ratio of glycerol to tert-butyl alcohol is 1:6.The optimum reaction temperature and time are 70℃ and 6 h,respectively.Due to the influence of steric hindrance,the main product of this process is MAGE,and the highest selectivity runs up to95.6%.However,the selectivity of DAGE and TAGE are both less than 10%;(4)Through comparative analysis of yield,if considering MAGE as the target product,the glycerol dehydration with tert-butyl alcohol is a better choice.If the target product is di-ether(DAGE)or tri-ether(TAGE),ethanol and glycerol are the most suitable raw material for dehydration.Secondly,in the study of catalytic synthesis alkyl glycerol ethers by the continuous reaction on the fixed bed reactor.The phosphotungstic acid supported on silica catalyst was prepared by sol-gel method,and the catalyst was characterized by Fourier transform infrared spectroscopy.It is found that the HPW is successfully loaded on silica support.However,the HPW supported on the catalyst has been leached after the reaction.The catalyst was fixed on a fixed-bed reactor after being compressed and sieved.The reaction conditions are as follows:catalyst amount 3.0g,preheater temperature 290℃ and feed rate of 0.14ml/min.The effects of reaction temperature,reaction time and raw materials molar ratio on the catalytic performance were investigated.The results were as follows:(1)In the glycerol dehydration with methanol,the optimum reaction conditions are as follows: reaction time 4h,reaction temperature 260℃ and the molar ratio of methanol to glycerol 8:1.When the temperature is 300℃,the catalyst shows deactivation and the yields of DAGE and TAGE are close to 0;(3)In the glycerol dehydration reaction with ethanol,the optimum reaction conditions are follows: reaction time 3h,reaction temperature 240℃ and methanol/glycerol molar ratio8:1.With the temperature rising to 300℃,the glycerol conversion decreases obviously and the product selectivity decreases to the bottom;(4)During the glycerol dehydration with tert-butyl alcohol,the yield of MAGE and DAGE reach the maximum when the reaction temperature is 240℃,the reaction time is 3h and the molar ratio of raw materials is 6:1.However,the temperature almost shows no effect on the TAGE selectivity,and the steric hindrance still has a great influence on the productselectivity even in a fixed-bed continuous reactor;(5)Compared with the stainless steel reactor,the product yield has been improved when glycerol dehydration with alcohols on the fixed-bed reactor.However,there are some problems that the raw materials exist side reactions and the catalyst exhibits a short life.Besides,the leaching of the HPW and the carbon deposition of catalyst are the main reasons for the catalyst deactivation.