|Process||Gas separation with dense membrane||Membrane condenser||Transport membrane condenser|
|Membrane morphology||Dense||Porous hydrophobic||Porous hydrophilic|
|Parameter determining process performance||High pressure difference between the membrane sides for promoting water vapor permeation.||
-Cooling of the feed for increasing the amount of liquid water to be recovered, depending on the temperature and relative humidity of the feed gaseous stream.|
-Low pressure difference (0.01–0.1 bar) between the membrane sides for promoting the gases permeation.
-High temperature difference between the membrane sides for promoting water vapor condensation within membrane pores.|
-Low pressure difference (around 0.3 bar ) between the membrane sides for promoting the permeation of condensed species.
|Transport mode||Solution diffusion mechanism||Knudsen-molecular diffusion transition||Capillary condensation|
|Water collection side||Permeate||Retentate||Permeate|
|Permeating species||Mainly water vapor; a small fraction of other gaseous feed species||Permanent gases, a small fraction of water vapor||Mainly water vapor|
|Retained species||Low permeable species||Condensed water and condensable gaseous species (whose amount strongly depends on operating conditions)||Non-condensable feed components, a small fraction of water vapor|
|Advantages||High purity of the recovered water ((H2O/N2) and H2O permeability up to 105 barrer [41, 42]).||
-Possibility to control the liquid water vapor composition by opportunely tuning the operating conditions.|
-Possibility to recover condensable components.
-Low energy consumption
-Preferential water permeation, owed to the strong affinity of the hydrophilic materials to the water, which limits the permeation of the other species|
|Drawbacks||High energy consumption (because the evaporated water through the cooling tower and stack leaves at near atmospheric pressure, requiring additional vacuum to apply the necessary driving force for separation).||
- Quality of liquid water eventually effected by the presence of contaminants.|
- Limited process performance (in terms of recovered water) in the case of gaseous streams at low temperature and relative humidity.
-High temperature gradient across the membrane.|
-Increase of the temperature at the membrane surface and within the membrane pores.
-Membrane pore size influences membrane selectivity .
- Heat and water flux must be carefully balanced to maximize the transport membrane condenser performance.