Process for preparing light-coloured lower alkyl esters of fatty acids with reduced content of free and combined glycerine

摘要

Recovery of light-coloured lower alkyl esters (I) of fatty acids with a reduced content of free and combined glycerol comprises: (a) feeding crude (I) to the sump of a vacuum fractionating column containing substance exchange packing arranged in 2 separate segments, where it is vaporised; (b) separating the resultant vapour in condenser(s); (c) separating the condensate into a denser glycerol phase and a less dense (I) phase; (d) recycling the (I) phase as reflux to the upper packing; and (e) discharging purified (I) below the upper column packing. Preferably (I) is fed to the sump of the column, which has 2 separate chambers fed by 2 separate falling film evaporators by forced circulation. The vapour from both is introduced below the lower substance exchange packing and a side stream of purified (I) is added to this segment as reflux. The high boiling residue is discharged from at least one of the falling film evaporators. Also, part of the vapour is condensed in a partial con denser between the 2 segments; and/or a side stream of vapour is discharged between the 2 segments and condensed in a total condenser outside the vacuum column. One or both condensates are passed to the phase separator with the top condensate.