Fabrication of cross-linked hydrogel-coated membrane for microalgal lipid separation via photoinitiated chemical vapor deposition

Abstract

Due to the uncertainty in the petroleum-based energy supply, research interest on alternative energy sources such as microalgal biofuels has grown rapidly. However, the high production cost for biofuel had hampered its mass production with economic feasibility. Especially, the dewatering for harvesting and extracting bio-lipid from aquatic microalgae is responsible for greater than one third of production cost for microalgal biofuel. Here, we fabricated a cross-linked hydrogel-coated membrane to achieve low-cost, simple but highly efficient separation of bio-lipid from aqueous microalgal culture medium. The membrane is composed of stainless steel mesh coated conformally with a cross-linked hydrogel, poly(2-hydroxyethyl methacrylate) (pHEMA) synthesized in one-step manner by photoinitiated chemical vapor deposition (piCVD) process. The pHEMA-coated membrane showed hydrophilic and underwater oleophobic properties and its selective wettability allowed for the selective the water permeation through the membrane while blocking the oil penetration, leading to an efficient separation of bio-lipid-in-hexane/water mixture solely driven by gravity. The conformal coating of hydrophilic and underwater-oil-repellent pHEMA film membrane enabled extremely high oil rejection performance with the intrusion pressure of 6.1 kPa and water permeation flux of 0.65 × $10^4$ L $m^-2$ $h^-1$, which resulted in the excellent separation efficiency greater than 97.95%. The cross-linked hydrogel-coated membrane also showed an outstanding mechanical and chemical stability, which was confirmed by the reusability of the membrane up to 5 times. The outstanding results exemplify an easily commercializable downstream process for microalgal biofuels.