Structural tailoring of hierarchical fibrous composite membranes to balance mass transfer and heat transfer for state-of-the-art desalination performance in membrane distillation

Abstract

Membrane distillation (MD) displays superior characteristics to other technologies to alleviate the ever-increasing freshwater crisis through seawater desalination and/or wastewater recycling.

Porous evaporators with special wettability for low-grade heat-driven water desalination

“…[82][83][84] The thickness of membranes also significantly impacts the efficiency of MD because thicker membranes have higher mass transfer resistance, resulting in a lower permeate flux. 85,86 Generally, the vapor flux initially increases with decreasing membrane thickness. However, a thinner membrane also reduces the thermal resistance resulting in a lower interface temperature difference, and the heat loss becomes dominant, which starts declining as a result of conduction losses when thickness goes below an optimal value.…”

“…However, a thinner membrane also reduces the thermal resistance resulting in a lower interface temperature difference, and the heat loss becomes dominant, which starts declining as a result of conduction losses when thickness goes below an optimal value. 86,87 Despite that the MD membrane has no strict requirement in mechanical strength, super-thin membranes can be easily destroyed by liquid flow. Thus, the adequate thickness of MD membranes should be strictly controlled to balance between permeate flux, thermal resistance as well as mechanical strength.…”

“…92 In the above configurations, the introduction of hydrophilic layers can effectively reduce the thickness of the hydrophobic vapor transfer layer, but meanwhile, bring a slight influence on the mechanical properties and thermal resistance of the whole membrane evaporators. 86 In other words, the design of the asymmetrical superwettable MD membrane aimed at simultaneously solving the contradiction between the thickness of the active layer, heat conduction and the mechanical strength of the MD membrane. In addition to controlling the pore structure, membrane porosity, and membrane thickness, decreasing the thermal conductivity of the MD membrane may become a viable direction to improve the thermal efficiency of MD technology further.…”

Mechanically improved superhydrophobic nanofibrous polystyrene/high‐impact polystyrene membranes for promising membrane distillation application

“…Also, by using the nanofiltration (NF) process, considerable rejection for multivalent salts (such as MgSO 4 ) is expected 6,7 . However, excessive energy consumption and fouling/scaling problems deteriorate separation performance 8,9 . Membrane distillation (MD) has been emerged as a decent thermal‐based desalination process in recent years owing to its attractive characteristics such as the ability to use low‐grade waste heat, employing renewable energy sources like solar, wind, and geothermal energies, treating highly saline brine with lesser dependence on feed concentration and osmotic pressure and so on 10 .…”

Transport Analysis of Anti-Wetting Composite Fibrous Membranes for Membrane Distillation

“…CFMs with a modified structure (TiO 2 [ 32 , 33 ], SiO 2 [ 34 , 35 , 36 ], carbon nanotubes [ 37 , 38 ], and silver nanoparticle [ 39 , 40 ]) can achieve anti-fouling or anti-bacterial performance. The membranes with different pore sizes of PVDF-HFP skin layer and polyethylene terephthalate (PET) supporting layer can increase the membrane strength and enhance the MD performance [ 41 ]. Except for hydrophilic and hydrophobic membranes [ 42 , 43 ], most of the studies on the CFMs are always found in direct contact MD (DCMD) [ 28 , 44 , 45 ].…”