Developing Janus Filters for Real-World Separation of Oil from Surfactant-Stabilized Emulsions

Abstract

A major industrial problem that directly impacts our water quality is the difficulty in separating oil and/or water from contaminated, surfactant-stabilized, oil-in-water emulsions. Lacking the appropriate technology to separate these industrial emulsions on site, they are either sent away for tedious, expensive treatment processes, or as a last resort disposed of directly into our environment. Janus filters, named after the Roman God of Two Faces to depict their asymmetrical structure, have shown tremendous potential as a low-cost, green alternative for rapid emulsion separation. Existing Janus filters that bear a demulsifier on one side and a hydrophobic polymer on the opposite side can break oil-in-water emulsions and selectively separate the coalesced oil. Though effective, the early generations of Janus filters were not ideal for real-world application due to the tedious syntheses of the polymers used, the troublesome fabrication protocols of the coatings as well as lack of perfect control in the structures and properties of the produced filters. This thesis covers the development of a portfolio of Janus filters for real-world applications and focuses on integrating features to address common membrane challenges, such as biofilm formation, as well as improving the practicality and reproducibility of procedures. First, a trifunctional Janus filter was developed that not only offers demulsification and oil separation performance but also exhibits antimicrobial activity. Hydrophobic and demulsifying polymers were synthesized via free radical polymerization and attached to opposite sides of a cotton fabric through transesterification chemistry. The demulsifying face was subjected to quaternization enhancing the demulsification capabilities, improving the o/w separation performance, and bestowing the fabric with antimicrobial properties. Next, the feasibility of developing a multi-substrate Janus filter with a well-controlled structure, fabricated by combining glass wool and cotton fabric, through facile coating methods based on sol gel chemistry was investigated. The effect of varying the distribution of hydrophilic and hydrophobic layers within a Janus filter on the separation performance of o/w emulsions was also studied. To broaden our understanding, the commercial viability of the portfolio of Janus filters was assessed through a case study with industrial samples and supplementary techno-economic analysis, market research and customer discovery.