In most cases the catalyst is sodium hydroxide or sodium
methylate. It 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. In that case
glycerol is obtained as an aqueous solution containing sodium
chloride. Depending on the process, the final glycerol purity is about
80% to 95%.