Rejection of lactic acid solutions by dynamically formed nanofiltration membranes using a statistical design method

Nanofiltration studies using zirconium (IV) hydrous oxide poly(acrylic acid) dynamically formed membranes for solutions containing lactic acid, with employing a statistical experimental design, are reported. The aim of the research was experimental attainment of range of optimum conditions for nanofiltration resulting in low lactic acid rejection. For this purpose the effect of operating parameters such as cross-flow velocity, pH in the feed solution, pressure difference across the membrane and lactic acid concentration in the feed solution on lactic aid rejection was investigated using an experimental design technique. Lactic acid rejection was recorded for a series of experiments at different values of real operating parameters. The standardized values of operating parameters were fixed at two levels, +1 and -1. Experimental data were used for evaluation of regression coefficients of polynomial equation. The polynomial equation as an interpolation formula gives information on non-conjugated as well as conjugated effects of four inlet variables of the membrane process on outlet variable, lactic acid rejection by dual-layer membrane dynamically formed on stainless steel support TiO2 coated supplied by DuPont Separation Systems (Seneca, SC, USA). The developed polynomial equation can be a tool for control of the nanofiltration process. With increasing lactic acid concentration in the feed solution, low rejection can be maintained by decreasing the crossflow velocity and pressure difference across the membrane at fixed pH. Experimental data and results of calculations using polynomial equation showed that examined membrane at the appropriate levels of operating parameters could work as a separation medium in applications where removal of lactic acid is realized.