Manufacturing of Distillation Membranes with Controlled Microstructure Based on Atomistic and Continuum Theories

With access to clean water becoming a global concern, the need for an efficient, sustainable, and affordable water purification method is now greater than ever. Desalination is the production of freshwater from saltwater (e.g., seawater). The investigators have proposed a novel approach to fabricate fibrous membranes for saltwater desalination via a process called Direct Contact Membrane Distillation (DCMD).

The fabrication method enables the development of desalination membranes for potential use in individual household systems, where rooftop sunlight can be used to heat the saltwater and produce purified water for the negligible cost of pumping a small volume of water to the roof. The fabricated DCMD membranes can also be used in other existing or potential applications such as food and beverage production and in the chemical and pharmaceutical industries.

STEM education and outreach activities are planned to raise public awareness about climate change and the need for sustainable water purification methods. Many of the investigators’ outreach activities will focus on developing courses and modules for autistic students in collaboration with the Science House at North Carolina State University (the Catalyst Program).

Boiling is the easiest way to desalinate saltwater. However, boiling water requires a significant amount of energy. Alternatively, readily available industrial waste heat or solar energy can heat the saltwater enough to initiate evaporation.

The rate of water evaporation from warm saltwater is limited by the rate at which vapor travels away from the warm water (heat source) to the cold surroundings (heat sink). The rate of water evaporation can be increased by bringing the heat sink as close as possible to the heat source, which shortens the distance that the vapor needs to travel, i.e., increases the thermal and concentration gradients.

Separating the sink and source with a thin membrane that is permeable to vapor but impermeable to liquid water is the most practical way to shorten the distance. This is called Direct Contact Membrane Distillation (DCMD). The major problem with the current DCMD membranes is that their porosities are generally very low, resulting in low water-vapor transport across the membrane.

This problem can potentially be addressed by using high-porosity electrospun fibrous membranes, but the increased porosity is often accompanied by a higher chance of membrane wetting failure (i.e., liquid water penetrating the membrane). The investigators have identified the root causes of membrane wetting failure and have proposed a novel approach to address them.

The goal of this project is to design and produce a DCMD membrane that is very thin and porous and is simultaneously impermeable to liquid water. These high-efficiency DCMD membranes have the potential to successfully desalinate saltwater even when the saltwater is only slightly warmer than the environment. The research approach will apply first-principles computer simulations (molecular dynamics and finite element simulations) and neural network modeling coupled with a unique manufacturing method to engineer the microstructure of electrospun fibrous membranes against wetting failure.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.