(360c) Isolation of Fatty Acids from Industrial Effluents

Reactive separations offer a promising tool for process intensification in effluent treatment. While facilitating the separation of multicomponent mixtures which are regarded as being inseparable via conventional rectification, they also allow for exploitation of valuable constituents present only in minor concentrations in aqueous solutions. Acetic acid and formic acid, for instance, are representative byproduct constituents of pulping processes. Low concentrations of the fatty acids and the fact that aqueous formic acid-acetic acid mixtures form a binary azeotrope and a ternary saddle point azeotrope render effluent treatment and fatty acid isolation uneconomic and result in the waste of valuable bulk products at present.

Implementation of reactive separation techniques in combination with alternative unit operations open up a wide range of alternative process options for effluent treatment. The separation is based on the esterification of the fatty acids and their transformation into low boiling esters. Change of the substance properties through chemical reaction allow for overcoming distillation boundaries and facilitate product isolation under less stringent operation conditions. Process concepts include selective esterification of formic acid due to its pronounced acid strength or combined esterification of both formic acid and acetic acid.

Different options which combine the process intensifying building blocks reactive distillation and pervaporation are discussed and compared. Application of membrane separation methods, namely pervaporation, is beneficial when it comes to separation of excess alcohol from esters in the distillate phase. Accordingly high grade quality of the isolated constituents is achieved.  Within the technological limits of chemical reaction, product separation by distillation and product separation by pervaporation the process design may be optimised and adjusted to the specific needs for integration, targeting economic feasibility.