Evaluation of multi-channel ceramic tubular membranes for high-salinity water desalination by vacuum membrane distillation

Membrane distillation (MD) is a separation technique capable of treating hypersaline brines produced by oil and gas extraction and seawater desalination and could assist in achieving near zero-liquid discharge. Although polymeric membranes are conventionally used for this process, ceramic membranes possess higher mechanical robustness & chemical stability and have successfully been modified by hydrophobic coatings for use in MD. In this study, we developed and evaluated the performance of surface-modified ceramic membranes in manufacturable form factors for vacuum membrane distillation (VMD) applications. Tubular membranes with pore sizes ranging from 100 nm to 250 nm composed of titanium oxide or aluminum oxide were treated with fluoroalkylsilanes (FAS) to enhance hydrophobicity. The performance of membranes with 1, 7, and 19 channels was tested to determine the effect of the number of channels on flux and selectivity. NaCl rejection was >99 wt% across both materials and all geometries. Moreover, single-channel membranes outperformed multi-channel ones, demonstrating area-normalized fluxes as high as 39 kg/(m²h) and NaCl rejections >99.5 % at 80 °C. The exponential increase in flux with temperature predicted by the Antoine equation was validated with a temperature-swing test up to 110 °C, where measured flux exceeded 200 kg/(m²h). The performance and resilience of these ceramic membranes in treating brines across a range of temperatures demonstrate their viability for practical applications.