Potential of extraction of Steviol glycosides using cellulose acetate phthalate (CAP) – polyacrylonitrile (PAN) blend hollow fiber membranes

Abstract

Cellulose acetate phthalate (CAP) – Polyacrylonitrile (PAN) blend hollow fibers were spun in the present work and their efficacy in extraction of Steviol glycosides was investigated. Various compositions of blend hollow fibers were characterized in terms of scanning electron microscopy (SEM), permeability, contact angle, pore size distribution and breaking stress. Concentration of CAP was varied up to 5 wt.% in a total polymer concentration of 20 wt.%. It was observed from SEM images that finger like pores in the cross-section became tear drop like with decrease in concentration of CAP, making them denser. Pure PAN membrane showed the highest permeability around 238 l/m².h.bar and the lowest molecular weight cut off (MWCO) 12 kDa and the highest pore density 2.8 × 10¹⁸ m^-2. CAP-PAN (4:16) blend membrane of MWCO 30 kDa was found to be the most suitable for extraction of Steviol glycosides. At 34 kPa transmembrane pressure drop (TMP) and cross flow rate (CFR) 10 l/h, glycoside recovery was 55 % and purity was 30 % under total recycle mode of operation. Steady state permeate flux was 8 l/m².h at 102 kPa TMP. A three stage diafiltration was carried out at 34 kPa TMP and 5 l/h flow. Enhanced 94 % recovery and 54 % purity of the Steviol glycosides was obtained under these conditions.