What Is Transesterification?

Transesterification, that is, the reaction of an ester with an alcohol / acid / ester (different ester) to form a new ester and a new alcohol / acid / ester under the catalysis of an acid or a base.

The esterification reaction is

Fatty acid methyl esters are mainly prepared by transesterification of triglycerides and methanol.

1 Amount ratio of alcohol and oil

The ratio of alcohol and oil is one of the main factors affecting the transesterification conversion. According to calculations, 1 mol of triglyceride is required for complete transesterification, and 3 mol of fatty acid ester and 1 mol of glycerol are generated. If n (alcohol) Bn (oil) is too large, it will seriously affect the severe separation of glycerol and increase the cost of separation. At the same time, it cannot increase the conversion rate and can only increase the cost of alcohol recovery. Therefore, in order to make the reaction the most economical, the result is the best, and the reaction mixture is easier to post-process, the amount ratio of methyl (ethyl) alcohol to rapeseed oil is 6B1 is the best. For partial transesterification, the amount of methanol added has a great impact on the performance of the final product modified rapeseed oil. The lower the amount of addition, the lower the transesterification depth), the lower the introduction of OH, and the poorer the water solubility of the product;

2 Catalyst dosage

During the transesterification reaction, if no catalyst is added, or a small amount of catalyst is added, the reaction with vegetable oil is extremely slow, even if there is a large excess of methanol.As the amount of catalyst increases, the transesterification

The solid base LDH / LDO has higher activity in the transesterification reaction, and the yield and conversion rate are above 98.5%. The process is simple in operation, and can directly obtain fatty acid methyl esters, diglycerides, monoesters, and by-product glycerin without refining treatment. The catalyst can be recycled and regenerated, and there is no three waste pollution in the whole process, and the industrialization prospect is broad. The best reaction conditions for complete transesterification of rapeseed oil and methanol are: the reaction temperature is 65 ~ 70 , the reaction time is 3h, the amount ratio of alcohol and oil substance is 6: 1, and the amount of catalyst is 2% of the mass of rapeseed oil. The transesterification reaction is of great significance for the synthesis and development of leather fatliquors, which can broaden the source of raw materials and develop fatliquors with excellent properties.

At present, acid-catalyzed transesterification processes are rarely used in biodiesel generating units abroad. Acidic catalysts are mainly used to pre-esterify oils with higher acid values, followed by alkali-catalyzed transesterification. Existing biodiesel plants in China mainly use waste oils with high acid value as raw materials, and they are small in scale. Most of the catalysts used are liquid acids, and a few of them use solid acids. It is a good process route to use a solid acid catalyst to pre-esterify high acid value vegetable oil, and then use alkali-catalyzed transesterification to prepare biodiesel. ^[4]