SBIR Phase I: Carbon Nanotube Enhanced Membrane Distillation for Sea and Brackish Water Desalination, and the Treatment of Saline Waste Water

The broader impact/commercial potential of this small business Innovative Research Phase 1 project is the possibility of inexpensive clean water generation from sea and brackish water. With rapidly increasing world population, portable water will be one of the most important technological challenges of this century. There is no unique ?one size fits all? approach to desalination. Many factors such as salt concentration, the presence of specific ions, energy cost, pretreatment requirements and capital investments are important considerations in selecting the desalination technology to be implemented. The carbon nanotube enhanced membrane distillation proposed here is a relatively low temperature process where industrial waste heat and solar heating can be used for desalination. Small water heaters such as the natural gas heaters used in homes can be used to generate high quality drinking water along with what is needed for domestic consumption. Another major application of this technology is in oil and gas drilling. Hydraulic fracturing or fracking is a water-intensive process. A typical frack well uses several million gallons of water over its lifetime and generates a highly saline ?produced water?. With its ability to handle high salt concentrations, the proposed approach is a viable alternative for treating this waste. The technical objectives in this project are to utilize carbon nanotubes (CNTs) to create breakthrough membrane properties for desalination via membrane distillation (MD). In MD, a hydrophobic porous membrane separates a hot salt water feed and a cold permeate stream. As the heated brine passes on the membrane and is partially transformed to water vapor. The hydrophobicity of the membrane prevents the aqueous solution from entering the pores. However, freed from hydrogen bonding the water vapor passes through and is condensed on the permeate side of the membrane. The novel membranes referred to as carbon nanotube immobilized membranes (CNIM) will be developed by immobilizing CNTs into membrane pores where they will serve as molecular transporters and sorbents, thus providing additional pathways for water vapor transport. The other major advantage of CNIM is that it is less prone to fouling than conventional membranes. Key innovations of the proposal include the functionalization of CNTs for maximization of water vapor transport while minimizing fouling. Additional objectives include the study of fouling behavior of some commercially important water samples such as sea water, power plant effluents and produced water. Finally, a process optimization tool will be developed to optimize CNIM-MD design.