Extraction of Citric Acid by Liquid Surfactant Membranes: Bench Experiments in Single and Multistage Operation

The extraction of citric acid by liquid surfactant membranes (LSM) was performed using W/O/W emulsions, composed of sodium acetate aqueous solutions (inner phase), mixtures of Alamine 336 and ECA 4360 dissolved in Exxsol D240/280 (membrane phase), and citric acid aqueous solutions (feed phase). Two factorial designs (2(5-1) and 23) were used to define suitable operating conditions, in a single stage, producing citric acid solutions at 0.25 g mL(-1) from aqueous feed solutions at 0.10 g mL(-1). The parameters investigated and the best operating conditions obtained were pH of the feed phase (pH = 1.5), surfactant (w(s) = 2 %) and carrier concentrations in the membrane phase (w(c) = 20 %), stirring speed (v = 145 rpm), and permeation time (t = 10 minutes) and the response variables were the citric acid concentration in the inner and feed phases and inner phase swelling. Under these conditions, an extraction greater than 50 % and swelling equal to 80 % were obtained. Use of recycled membranes as well as extraction in multiple stages was also evaluated. Experiments of recycling revealed that the membranes can be reused for at least three times with good performance. Extraction in multiple stages showed high efficiency for the citric acid separation (similar to 100 %) after three steps of operation.