Resistance-in-series model for flux decline and optimal conditions of Stevia extract during ultrafiltration using novel CAP-PAN blend membranes

• 80–90% flux decline occurs due to pore blocking during filtration.
• Irreversible resistance increases several folds with TMP.
• The phase space plot is generated to evaluate the optimal operating conditions.
• Recovery and purity of glycosides were strong functions of TMP and Re.

Tailor made polymeric blend membrane (cellulose acetate phthalate–polyacrylonitrile (Roy and De, 2014)) was used to extract Steviol glycosides from dry Stevia leaf powder. A detailed study was carried out by varying the applied transmembrane pressure and Reynolds number during the separation. Owing to the complexity in composition of Stevia extract, a resistance in series model was proposed to depict the flux decline. The model exhibited enough versatility to estimate the polarization resistance and flux decline profile for wide set of operating conditions. The polarization resistance and pore blocking resistance were found to be a strong increasing function of transmembrane pressure and a decreasing function of Reynolds number. The limiting and threshold operating conditions were also identified. From theoretical calculation, a phase space plot of transmembrane pressure and Reynolds number was generated to identify the optimal operating conditions that would result the maximum productivity. The obtained Stevia recovery and purity was found to have inverse relationship, exhibiting higher recovery and lower purity at higher transmembrane pressures and Reynolds number.

The phase space plot shows the optimal transmembrane pressure and Reynolds number to have the limiting permeate flux.Figure optionsDownload high-quality image (80 K)Download as PowerPoint slide