Free glycerol removal from monoglyceride using TiO2-ZrO2 nanofiltration membranes

Abstract In this work, membrane technology was applied to the removal of free glycerol from a glycerol/monoglyceride mixture that contained 13–19 wt% of glycerol. Experiments were performed using tubular TiO 2 -ZrO 2 ceramic membranes with average pore-sizes of 2.2, 1.76 and 1.17 nm. Membrane performance was evaluated based on the mass percentage of glycerol in the permeate and on the amount of permeate flux. Results showed that a smaller membrane pore-size corresponded to a higher mass percentage of glycerol in the permeate, which indicated that the molecular-sieving mechanism was dominant in membrane separation. In most experiments, the permeate flux decreased with the passage of filtration time. The best performance was achieved, however, by adjusting the filtration temperature and the transmembrane pressure. For example, the permeate flux remained stable during a standard amount of filtration time at 120 °C and 7 MPa for the membrane with an average pore-size of 1.17 nm, which resulted in 97 wt% of free glycerol in the permeate from a mixture that contained 12.9 wt% of glycerol. Importantly, membrane performance recovered to a large extent after being washed with methanol. For instance, permeate flux recovered to more than 55% of the level of initial flux for the membrane with an average pore-size of 1.17 nm at 100 °C and 7 MPa.