Methanol Dehydration Method Of High Acid Oil Drop Acid Esterification Process Of Moisture

The raw material must be free of water and the acid value of it is less than1.0mgKOH·g-1when biodiesel is prepared with alkali catalyzed transesterification. With the oil of high acid value as feedstock for biodiesel, it need reduce the acid value through esterification because of its high acid value. Traditional process mainly adopts homogeneous acid catalyzed esterification method, but it mainly exist the following problems:as the esterification reaction of free fat in material and methanol is a reversible reaction, the reaction reached chemical equilibrium after a period of time. So it is difficult to react completely and the acid value of material could not achieve requirements by base-catalyzed transesterification produce biodiesel. How to promote the reaction move to the positive direction is the key to reduce the acid value of feedstock through esterification. The best way is remove the water of esterified product continuously for promoting the reaction toward the positive direction.In this paper, the simple and fast measuring method of water content in methanol was established through the conductivity method, colorimetric method, and copper sulfate method were studied. The removing effect of the water was studied with molecular sieve and copper sulfate in methanol and in reducing the acid value through esterification, and the condition of the reagent of removing water was optimized. The optimum reaction conditions of reducing high-acid of biodiesel feedstock with high acid value with circulating gaseous esterification were studied under adding copper sulfate. The following result was obtained through research:1) The results of the measuring method of water content in methanol show that:①The error of methanol solution of sodium nitrate, methanol solution of ammonium nitrate and methanol solution of ammonium chloride was19.5%,25%and1.0%with the conductivity method, respectively. The degree of accuracy of methanol solution of ammonium chloride was best in these methanol solutions of salt. Therefore, the more suitable salt was cobalt nitrate for the conductivity.②The error of methanol solution of cobalt nitrate and methanol solution of cobalt chloride was0.833%and1.291%with the colorimetric method, respectively. The degree of accuracy of methanol solution of cobalt chloride was best in these methanol solutions of salt. Therefore, the more suitable salt was cobalt choride for the colorimetric.③The maximum error was1.0%and the minimum was0.48%with the copper sulfate method, the method of copper sulfate was a simple and accurate for the measuring method of water content.2) The results of the removing effect of the water in methanol show that:①The best removing effect of water in methanol was the4A molecular sieve in3A,4A,5A and13X sieves. Along with the smaller water content in methanol and the larger the amount of molecular sieve, the better the removing effect of water in methanol.②The best time for removing the water of anhydrous copper in methanol was30min, and with the larger the amount of anhydrous copper sulfate, the better the removing effect of water, the water content in methanol had little effect on the removing effect of water in methanol.3) The oleic acid as raw materials to simulate the high acid value,4A molecular sieve and copper sulfate as the reagent of removing water for removing water in methanol in reducing the acid value through esterification shows that:①Using the4A molecular sieves as the reagent of removing water, the conversion rate of high acid oil in esterification is95.43%by following optimum reaction conditions: molar ratio of methanol to oil was8:1, dosage of catalyst was1.4%(W/W), dosage of4A molecular sieve was40%(W/W), and reaction time was90min.②sing the copper sulfate as the reagent of removing water, the conversion rate of high acid oil in esterification is88.21%by following optimum reaction conditions: dosage of anhydrous copper sulfate was10%(W/W), molar ratio of methanol to oil was4:1,dosage of catalyst was3%(W/W), reaction temperature was75℃and reaction time was120min.③The results of the conversion rate of high acid oil through gas phase esterification is affected by the water content in methanol show that:the conversion rate is88.44%when the water content in methanol is7.25%, and the conversion rate was69.98%when the water content in methanol is9.0%, Accordingly, the critical water content in methanol that has a significant impact in circulating gaseous esterification reaction was7.25%.④sing the water content in methanol is9.0%, the conversion rate of high acid oil in circulating gaseous esterification reaction is90.28%by following optimum reaction conditions:dosage of anhydrous copper sulfate was40%(W/W), reaction temperature was80℃,dosage of catalyst was1.2%(W/W) and reaction time was90min.The research achievements of the paper provide the basic data for removing the water in methanol containing water timely in the process of high acid value oil esterification reducing the acid value, and provide a basis for the further application of technology.