Membrane distillation (MD) is a thermal separation process that distills water. Warm seawater is separated from cold feed-water with a hydrophobic (water repellent) membrane. The liquid streams remain separated by surface tension, while higher vapour pressure drives steam molecules across the membrane.
In application, various layers separate the warm seawater, the product distillate, and the cooling water. A temperature difference of 5 to 10 K is sufficient to drive the MD process.