[Mechanisms of separating lignin from black liquid by inorganic microfiltration]

The effects of rejection to lignin from black liquid were carried out by inorganic membranes which had pore size 50 nm, 0.2 micron and 0.8 micron, respectively. The results show that MF membranes can effectively separate lignin from black liquid. The flux of 0.2 micron alpha-Al2O3 and ZrO2 membranes were larger than the flux of 50 nm and 0.8 micron membranes. The flux of each membrane drops deeply as the SS concentration increased under the conditions of low SS in black liquid. However, the flux dropping had the linear relationship with SS concentration when it was high. 2 g/L polyethylene glycol 4000 solution can not affect the fluxes of 0.2 micron and 50 nm membranes, effectively, instead of decreasing the flux of 0.8 micron membrane about 60%. 2 g/L polyethylene glycol 20,000 solution can sharply decrease the flux of each membrane. Reason that provoke flux decreasing and change the rejective ability was the cake formation on the surface membrane and the lignin aggregation.