Preparation and characterization of silicon nitride hollow fiber membranes for seawater desalination

Porous silicon nitride hollow fiber membranes have been successfully prepared by a combined phase-inversion and sintering method. First, stable Si3N4 suspensions were prepared by correlating the rheological properties with the type and concentration of dispersant, powder pretreatment and solids loading. Then the powders/binder ratio was optimized, considering the morphology, structure, permeation and mechanical properties of the hollow fiber membranes. When the ceramic powders/binder ratio was fixed at 7/1, the hollow fiber membranes showed a good combination of gas and water flux, bending strength, porosity and average pore size, which is very suitable for membrane distillation (MD) application. After the obtained membranes were chemically modified from hydrophilic to hydrophobic by grafting fluoroalkylsilane (FAS), their water desalination performances were tested using vacuum membrane distillation (VMD) and direct contact membrane distillation (DCMD). Both methods lead to satisfactory membrane distillation performances with a high flux and a salt rejection rate of 99–100%. The membranes also exhibited superior long-term stabilities in terms of the water flux and salt rejection rate. The novel Si3N4 hollow fiber membranes developed in this paper are promising for industrial applications.