Glycerol Esterification For Biodiesel Preparation

As a kind of renewable and clean energy,biodiesel is of great significance to protect the environment and reduces the dependence on petroleum.Nowadays,the main method for biodiesel production is acid catalytic esterification-alkali catalytic transesterification.However,the method also has many deficiencies.Sulfuric acid,the catalyst for the esterification reaction,could form waste acid water which will pollute the environment.In addition,the cost of methanol recovery is large.Moreover,the raw materials used for biodiesel production usually have high acid value,which is difficult to be reduced to below 1 mg KOH/g through the acid catalytic esterification,and hence the product yield would be reduced.In order to solve the above issues,a new glycerol esterification method for biodiesel preparation was proposed in this paper.It is easy to reduce the acid value to below 1 mg KOH/g without any catalyst.The main research contents and conclusions are as follows:(1)For glycerol esterification reaction,the soybean oil mixed with oleic acid was used as the raw material,with the acid value of 100 mg KOH/g.The effects of reaction temperature,stirring speed,the amount of glycerol and reaction time on glycerol esterification process were investigated.Based on the results,a dynamics model was built and a high temperature reaction kettle system was developed to carry out the scaling up tests,and the effect of distributor location in the kettle on the glycerol esterification process was investigated.The results showed that the influence degree of reaction parameters on the glycerol esterification followed the order:temperature>glycerol>stirring speed.The optimal temperature,stirring speed,and glycerol to fatty acid mole ratio were 240?,500 rpm,and 1.1:1,respectively,with the reaction time of 3 h,and the final acid value was 0.33 mg KOH/g.It can be inferred from the decline trend of acid value that the macroscopic reaction was the first order reaction under the experimental conditions.The results from the scaling up device were as expected,the final acid value was 0.8 mg KOH/g when the temperature,glycerol to fatty acid mole ratio were 240? and 1:1.Moreover,better results were obtained when the distributor was located above the liquid level.(2)The oil after glycerol esterification was used as the raw material for transesterification to get fatty acid methyl ester(FAME).The effects of catalyst type,catalyst amount,reaction time and transesterification reaction steps on the transesterification process were investigated.Monoglyceride,diacylglycerol,triacylglycerol and FAME were semi-quantitatively determined by Thin Layer Chromatography method.The results showed that the glyceride was not completely converted into FAME during the first order transesterification,and hence the secondary transesterification reaction was needed.The catalytic effect of KOH was the best for the transesterification reaction.Better results were obtained when 25%methanol and 0.5%KOH were added in the first order reaction,and 5%methanol,0.5%KOH in the second order reaction,the FAME content was 95.1%.(3)The solubilities of glycerol in biodiesels with different compositions were determined by gas chromatography in the temperature range of 50 to 120?.The effects of carbon chain length,iodine value and the biodiesel type on the solubilities of glycerol in biodiesel were investigated.Based on the solubilities of glycerol in biodiesel at different temperatures,the temperature of the glycerol extraction process was optimized.Experimental results showed that the solubility of glycerol in biodiesel decreased with the increase in carbon chain length and decrease in iodine value.In addition,the solubility of glycerol in biodiesel increased with temperature.The experiment results showed that the optimal temperature for the glycerol extraction process was suitable around 50?.(4)Glycerol is both the reactant for the esterification reaction and also the byproduct of the transesterification process.Recycle of the crude glycerol can realize the virtuous cycle of glycerol in the process of biodiesel production.Neutral salty crude glycerol,salt-free crude glycerol and refined glycerol were obtained through purification of the raw crude glycerol.The three types of glycerol was used in the esterification process and compared with the fresh glycerol on the reduction of acid value.The results showed that the acid value was reduced to be below 0.5 mg KOH/g when the waste oil was used as raw material.The performance of purified crude glycerol was similar to that of fresh one.