A molecular to macro level assessment of direct contact membrane distillation for separating organics from water
Type
ArticleAuthors
Pillai, Sreekiran
Santana, Adriano
Das, Ratul

Shrestha, Buddha R.
Manalastas, Edelberto
Mishra, Himanshu

KAUST Department
Biological and Environmental Sciences and Engineering (BESE) DivisionEnvironmental Science and Engineering Program
Interfacial Lab
Water Desalination and Reuse Center, Division of Biological and Environmental Science and Technology, King Abdullah University of Science and Technology, Thuwal, Jeddah, Saudi Arabia
Water Desalination and Reuse Research Center (WDRC)
Date
2020-04-12Online Publication Date
2020-04-12Print Publication Date
2020-08Submitted Date
2020-01-09Permanent link to this record
http://hdl.handle.net/10754/662735
Metadata
Show full item recordAbstract
The removal of water-soluble organics from aqueous feeds is required in numerous practical applications, including bioresource processing, fermentation, and wastewater treatment. To this end, direct contact membrane distillation (DCMD) has been proposed as a separation technology. DCMD utilizes hydrophobic membranes – typically, comprising perfluorocarbons – which, when placed between a warm feed and a cold permeate, prevent mixing due to the robust entrapment of air inside the (membranes') pores. Thus, the membranes allow only pure water vapor to transport across, following the thermal gradient. Here, we assessed DCMD for separating organics from aqueous feeds in light of organic fouling by utilizing ethanol and perfluorodecyltrichlorosilane (FDTS) as the surrogate organic and hydrophobic coating, respectively. We investigated the adsorption of ethanol onto FDTS-grafted surfaces and membranes exposed to alcohol-water mixtures. Using the surface force apparatus, we found that the magnitude of hydrophobic forces between ultra-smooth FDTS-grafted mica surfaces in water-alcohol mixtures decreased with the increasing alcohol content. To simulate a practical DCMD scenario, we utilized FDTS-grafted polycarbonate membranes to separate a pure water reservoir from another containing 0.6 M NaCl and alcohol. For the 0% alcohol case, the membranes robustly separated the reservoirs for over a week, whereas even for ≥0.1% ethanol content, the membranes leaked within <5 h. After the leakage, the membranes’ hydrophobicity could not be recovered by rinsing them with pure water and blow-drying; a heat treatment at 363 K for 1 h proved to be successful, however. Our molecular dynamics simulations revealed that ethanol molecules in water got preferentially stabilized at the interfaces of water and hydrophobic surfaces. Furthermore, this stabilization is significantly enhanced at higher alcohol concentrations due to the emergence of II-D interfacial networks comprising adsorbed alcohol molecules. Thus, this micro to macro-scale assessment demonstrates that DCMD with hydrophobic membranes is not suitable for separating organics from water, even at low alcohol concentrations. We also compare the efficacies of apparent advancing and receding contact angles towards a reliable characterization of fouled surfaces.Citation
Pillai, S., Santana, A., Das, R., Shrestha, B. R., Manalastas, E., & Mishra, H. (2020). A molecular to macro level assessment of direct contact membrane distillation for separating organics from water. Journal of Membrane Science, 608, 118140. doi:10.1016/j.memsci.2020.118140Sponsors
HM acknowledges KAUST for funding. SP acknowledges Dr. Andrea Farinha and Dr. Krishna Katuri (KAUST) for assistance with gas chromatography; Mr. Sankara Arunachalam (KAUST) and Muhammed Ghifari Ridwan (KAUST) for assistance with contact angle measurements.Publisher
Elsevier BVJournal
Journal of Membrane ScienceAdditional Links
https://linkinghub.elsevier.com/retrieve/pii/S0376738820307183ae974a485f413a2113503eed53cd6c53
10.1016/j.memsci.2020.118140