Performance manipulations of a composite membrane of low thermal conductivity for seawater desalination

Membranes of low thermal conductivity (thermal insulation) but high moisture permeability are highly desired in membrane-based humidification-dehumidification (MHDD) seawater desalination technology. The porous membranes with thermal insulation could decrease the heat losses in humidification, thus the system energy performance can be improved. To satisfy this purpose, in this study, a PVDF/SiO2 (Si aerogel) composite bilayer membrane of low heat conductivity is prepared and analyzed. To solve the problem of cracking in forming SiO2 layer, the casting solution (TEOS, H2O) is doped with a drying control chemical additive (DCCA) N, N-dimethylformamide (DMF) to decrease the surface tensions in the gel. Then performance analysis of the developed membranes are conducted and the membranes are characterized. The results found that the heat conductivity is decreased from 0.08199 W m−1 K−1 to 0.04487 W m−1 K−1, with a penalty of effective moisture diffusivity sacrificed from 4.93 × 10−6 m2/s to 2.42 × 10−6 m2/s. They are superior to the available SiO2 blend insulation membranes. Further, the membranes can be optimized by facile structural manipulations such as adjusting the SiO2 layer thickness to realize the desired performance while balancing the paradox between the permeability and heat conductivity. This is the first time that heat conductivity of membranes can be manipulated for seawater desalination.