Effect of surfactant hydrophobicity and charge type on membrane distillation performance

YZ Tan and S Velioglu and L Han and BD Joseph and LG Unnithan and JW Chew, JOURNAL OF MEMBRANE SCIENCE, 587, 117168 (2019).

DOI: 10.1016/j.memsci.2019.117168

Membrane distillation (MD) is a promising green technology that can utilize waste heat to concentrate nonvolatile solutes, or remove volatiles and dissolved gases from an aqueous feed. The primary reason for the limited commercial implementation of MD is membrane pore- wetting, which deteriorates the separation performance. For oily wastewater, the surfactants are particularly detrimental due to the inherent nature to lower surface tension, which reduces the liquid entry pressure (LEP) and thereby increases the likelihood for porewetting. Unfortunately, the understanding on the influence of surfactants on MD performance is limited. To contribute to the knowledge base, we systematically investigated five surfactants with different hydrophobicities and charge types, in the absence and presence of salt, both via experiments and molecular dynamics simulations. The results show that surfactants adversely affect MD performance, and different surfactants exert different influences. Among the anionic surfactants of different hydrophobicities, the most hydrophobic exhibited the worst MD performance, which is tied to greatest surfactant-membrane attraction. However, when comparing surfactants of different charge types, the greatest surfactant-membrane attraction is not linked to the worst MD performance, suggesting factors like water-membrane affinity that underlies wetting propensity have to be considered too. This study provides more mechanistic insights into the role of surfactants in affecting MD performance.

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