Preparation Of Biodiesel Via Two-step Catalyzed Process

Biodiesel,a generic name of both plant diesel and animal diesel,is produced as alternative diesel fuel from renewable resources.Biodiesel is characterized by excellent properties such as biodegradation,less contamination,wide source of raw material,etc.Developing biodiesel,not only let out less of contamination,but also alleviates the energy crisis in our nation,strengthens the energy safe,which has profound meaning for promoting the comprehensive development of agriculture products.The study selects the acid rapeseed oil as raw material and adopts two-step process to make biodiesel.Firstly,acid is reduced by esterification rapeseed oil with methanol under cation exchange resin to meet the requirement of transesterification (acid number below 1mgKOH/g) subsequently.Secondly,the rapeseed oil free of FFA was reacted with methanol by transesterification in the presence of solid base catalyst.Several kinds of cation exchange resins were applied to catalyze esterification for acid reduction.The activities of these resins are in order as follows: CD-552＞HD-8＞001×7,001×4＞D113.The results show that the resin CD-552 is the best catalyst for FFA reduction.Acid number of the oil is reduced from 10.97mgKOH/g to 0.689mgKOH/g under the following reaction conditions:the molar ratio of alcohol to FFA 30:1,reaction time 5 hours,reaction temperature 60℃and amount of catalyst 5wt%.The resin HD-8 needs 12 hours reaction time meet the requirement of transesterification on the same condition.But after add 1wt%sodium chloride,it needs only 4 hours,and amount of catalyst reduce to 2wt%,the acid number of the oil is reduced from 11mgKOH/g to below 1mgKOH/g.After esterification,the resins are easy to be separated and recycled for 3～4 times.After acid was removed,self-made Mg-Al hydrotalcite solid base was used to catalyze the transesterification.The preferred preparation conditions are as follows: the molar ratio of Mg-Al 0.33:1,crystallization time 12 hours;calcinations temperature 500℃;calcinations time 5 hours;and it has better catalytic activity.XRD spectrum show that when the molar ratio of Mg-Al 0.33:1,the catalyst has a single MgO phase,and at the angle of 2θ=29.23°has an obvious characteristic apex.At the same time,it exists Mg-O-Al phase,so Mg-Al can be well combined,Mg is well-proportioned dispersed on the surface of Al,and solid base center has been formed,leading to good catalytic activity.On this condition,glycerin yield reach 92.97%,and it can be recycled for 2 times.The Specifications of self-made biodiesel meet foreign standards.