Lactic acid recovery by membrane technology using niosomes as extraction agents

Abstract

Lactic acid recovery from dilute aqueous solutions by membrane extraction technology using niosomes of Span 80 (sorbitan monooleate) modified by SDS (sodi-um dodecyl sulphate) as extraction agents was studied. Experiments were conducted at a transmembrane pressure of 0.3 bar using a 0.20 mm pore size TiO2 microfiltration flat-disc membrane. The effect of the feed composition (lactic acid concentration, pH, dispersed phase volume, and SDS content in niosomes) on the extraction rate and extraction degree at the equilibrium conditions, and membrane behavior during the subsequent concentration stage were investigated. SDS contained in niosomes, SDS to lactic acid molar ratio in the dispersion, and pH were the main factors affecting the lactic acid extraction degree. The best conditions were achieved with niosomes for-mulated with Span 80 (20 mol/m3) and SDS (4 mol/m3), a SDS to lactic acid molar ra-tio of 0.010, and pH lower than the pKa of the lactic acid: 33% of lactic acid extraction degree at the equilibrium and a constant permeate flux of 26 L/m2h was kept during the dispersion concentration. A two-step process increased the extraction degree up to about 43%. Back-extraction was made by NaOH addition until a pH > 12, where niosome breakup was observed.