Hydrophobic Air-Gap Membrane Distillation

An apparatus for air-gap distillation comprising:

• a feed-liquid source including a feed liquid;
• a distillation module comprising:
• a) a first feed-liquid chamber in fluid communication with the feed-liquid source, the first feed-liquid chamber including a heat-transfer plate with a condensing surface, wherein the condensing surface is sufficiently hydrophobic to produce a contact angle with water of at least 90°;
• b) a conduit coupled to the first feed-liquid chamber to extract the feed liquid after the feed liquid flows through the first feed-liquid chamber;
• c) a heat source configured to heat the feed liquid in the conduit;
• d) a second feed-liquid chamber coupled to the conduit and configured to receive the feed liquid after the feed liquid flows through the conduit and is heated by the heat source, wherein the second feed-liquid chamber includes a selectively permeable material that allows a component of the feed liquid to pass through the selectively permeable material and exit the second feed-liquid chamber in vapor form but not in liquid form, wherein one side of the selectively permeable material faces the condensing surface of the heat-transfer plate;
• and
• e) a gap between the condensing surface and the selectively permeable material;
• and
• a condensate collection receptacle in fluid communication with the gap.

A method for air-gap distillation, comprising:

• flowing a feed liquid through a first feed-liquid chamber of a distillation module, wherein the first feed-liquid chamber includes a condensing surface that is sufficiently hydrophobic to produce a contact angle of at least 150° with water;
• heating the feed liquid;
• flowing the heated feed liquid through a second feed-liquid chamber of the distillation module, wherein the second feed-liquid chamber includes a selectively permeable material that includes an outer surface in fluid communication with a gap between the selectively permeable material and the first feed-liquid chamber;
• permeating a vapor component from the feed liquid in the second feed-liquid chamber through the selectively permeable material into a gap between the selectively permeable material and the condensing surface;
• condensing the vapor component of the feed liquid as a jumping droplet from the condensing surface in the gap to produce a liquid condensate in the gap;
• removing the liquid condensate from the liquid-gap chamber;
• and
• removing from the second feed-liquid chamber a brine remaining from the feed liquid after the vapor component permeates through the selectively permeable material.