4.8 Article

Enhanced Flux and Electrochemical Cleaning of Silicate Scaling on Carbon Nanotube-Coated Membrane Distillation Membranes Treating Geothermal Brines

Journal

ACS APPLIED MATERIALS & INTERFACES
Volume 9, Issue 44, Pages 38594-38605

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsami.7b12615

Keywords

membrane distillation; silicate scaling; carbon nanotubes; electrochemical cleaning

Funding

  1. U.S. Department of Energy's National Renewable Energy Laboratory (NREL) [XEU-6-62543-01, DE-AC36-08GO28308]
  2. Office of Naval Research [n00014-14-1-0809]
  3. National Science Foundation CAREER [1553756]
  4. Directorate For Engineering [1553756] Funding Source: National Science Foundation
  5. Div Of Chem, Bioeng, Env, & Transp Sys [1553756] Funding Source: National Science Foundation

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The desalination of inland brackish groundwater offers the opportunity to provide potable drinking water to residents and industrial cooling water to industries located in arid regions. Geothermal brines are used to generate electricity, but often contain high concentrations of dissolved salt. Here, we demonstrate how the residual heat left in spent geothermal brines can be used to drive a membrane distillation (MD) process and recover desalinated water. Porous polypropylene membranes were coated with a carbon nanotube (CNT)/poly(vinyl alcohol) layer, resulting in composite membranes having a binary structure that combines the hydrophobic properties critical for MD with the hydrophilic and conductive properties of the CNTs. We demonstrate that the addition of the CNT layer increases membrane flux due to enhanced heat transport from the bulk feed to the membrane surface, a result of CNT's high thermal transport properties. Furthermore, we show how hydroxide ion generation, driven by water electrolysis on the electrically conducting membrane surface, can be used to efficiently dissolve silicate scaling that developed during the process of desalinating the geothermal brine, negating the need for chemical cleaning.

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