Lower-temperature preparation of SiC ceramic membrane using zeolite residue as sintering aid for oil-in-water separation

Due to their excellent attributes of high water permeance, good stability and antifouling properties, silicon carbide (SiC) membranes have achieved widespread application in industrial wastewater treatment facilities. However, the high sintering temperature (usually beyond 2000 °C) during the preparation of porous silicon carbide is a challenge for the transfer of the technology from the laboratory to industry. An efficient sintering additive method was proposed herein to address this issue. Inexpensive residues (containing oxides of sodium, aluminum and silicon) from an NaA zeolite production line were used as the sintering additives to make the SiC particles more tightly connected due to the formation of new phases. Thus, a SiC network could be formed during an in-situ reaction at lower sintering temperature (e.g., 1000 °C) in air without inert gas protection. The as-prepared SiC membranes exhibited a high pure water permeance of 3700 L m^-2 h^-1 bar^-1 and open porosity of 46%. The mechanical strength of the membrane reached 45 MPa. After alkali corrosion or thermal shock resistance tests, the bending strength was maintained at least 38 MPa. The membrane with a mean pore size of 0.4 μm exhibited a high rejection rate to oil droplets (˃ 90%) in various oil-in-water emulsions with a high water permeance. Membrane cleaning with an ultrasonic treatment resulted in good stability in long-term filtration tests. The utilization of zeolite residues successfully reduced the operational cost of heating during ceramic membrane fabrication with recycled solid wastes. Hence, the proposed preparation method for SiC membranes has good sustainability and is scalable for oil-water separation applications.