Homogeneous Process for the Production of Biodiesel

Conventional industrial biodiesel processes are based on homogeneous alkaline catalysts. Sodium hydroxide or sodium methylate are the most often used catalyst in 

Notably, the fast separation of the glycerol from the reacting mixture also removes most of the catalyst from the reaction mixture, even in the reaction phase, thus increasing the need of high initial catalyst make up. 

The refined oil is mixed with the methanol/alkaline catalyst-mixture, reacting at mild temperature and low pressure and left in a settler for phase separation by gravity. 

Most of the catalyst is recovered after the transesterification reaction as sodium glycerate, sodium methylate and sodium soaps in the glycerol phase. An acidic neutralization step with, for example, aqueous hydrochloric acid is required to neutralize these salts sodium soaps are thus converted into free fatty acids, which can be removed from glycerol by decantation. In this case, glycerol is obtained as an aqueous solution containing sodium chloride. Depending on the process, the final glycerol purity is about 80%. 

When sodium hydroxide is used as catalyst, side reactions forming sodium soaps generally occur. This type of reaction is also observed when sodium methylate is employed and traces of water are present. The sodium soaps are soluble in the glycerol phase and must be isolated after neutralization by decantation as fatty acids. 

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