Boosting vapor flux in osmotic distillation: A comprehensive evaluation of operating conditions and membrane properties

Abstract

Osmotic distillation (OD) presents a promising technique for desalination in seawater electrolysis, but its effectiveness is hindered by low vapor flux and limited operational efficiency. This study employs a theoretical model to evaluate how operating conditions and membrane properties impact OD vapor flux. For conventional membranes, optimizing parameters mitigates concentration and temperature polarization but provides only modest increase in vapor flux, as the membrane contributes the majority of mass transfer resistance. With 0.6 M NaCl/3.5 M K₂CO₃ as feed/draw solutions, regardless of operating condition, the vapor flux of conventional membranes cannot exceed 0.94 kg m^-2 h^-1. In contrast, improving membrane properties, which leads to vapor permeability ($B_m$) enhancement, offers significantly more potential for increasing vapor flux. However, this improvement must be paired with an increased thermal conduction coefficient ($K_{m,d}$) to avoid severe temperature polarization. Furthermore, our modeling results further indicate that operating condition optimization has a markedly larger impact on advanced membranes with improved $B_m$ and $K_{m,d}$ than conventional membranes (60.7 % vs. 8.3 % vapor flux increase). These findings underscore the necessity for research efforts to prioritize the advancement of membrane design, while subsequent studies can focus on optimizing operating conditions alongside these improved membranes. This approach will significantly improve OD vapor flux and provide critical insights for the future development of OD technology, thereby facilitating its application in seawater electrolysis.