Direct Contact Membrane Distillation-Based Desalination:  Novel Membranes, Devices, Larger-Scale Studies, and a Model

Abstract

We report here direct contact membrane distillation results from modules having 0.28 m2 of membrane surface area employing porous hydrophobic polypropylene hollow fibers of internal diameter (330 μm) and wall thickness (150 μm) with a porous fluorosilicone coating on the outside surface. The brine salt concentration and temperature and the distillate temperature and velocity were varied. Water vapor fluxes approach values obtained earlier in much smaller modules. As the brine temperature was increased from 40 to 92 °C, water vapor flux increased almost exponentially. Increasing the distillate temperature to 60 from 32 °C yielded reasonable fluxes. Salt concentration increases to 10% led to a small flux reduction. An extended 5-day run did not show any pore wetting. A model using the mass transfer coefficient k m as an adjustable parameter predicted the brine temperature drop, distillate temperature rise, and water vapor flux well for the large module and the smaller module of 119-cm2 surface area.

Performance improvement of PVDF hollow fiber-based membrane distillation process

“…The presence of larger pores is a possible reason causing membrane wetting even though the membranes are highly hydrophobic [8]. To improve the applicability of these membranes for the MD processes, there are two approaches to minimize wetting; one is a finely porous hydrophobic coating which helps to minimize the pores size while maintaining suitable porosity [9][10][11]; the other is to apply a dense hydrophilic coating which can protect the effective membrane pores from wetting [12][13][14][15][16][17].…”

“…Generally, in order to increase membrane area and reduce module fabrication costs, larger module housings, higher packing density and/or longer fiber length are preferred in industry [32]. However, it has been observed in MD studies that the thermal efficiency can be impacted negatively by increasing packing density and fiber length because the distillate tends to be heated up along the fibers [10,33]. In addition, the risk of membrane pore wetting increases with the increasing fiber length due to the imposed hydrostatic pressure drop along the module length [22].…”

Identification of material and physical features of membrane distillation membranes for high performance desalination

“…Hydrophobic materials, such as polypropylene (PP), PTFE, PVDF, etc., can be used to fabricate MD membranes [3]. In this paper, PVDF and PTFE membranes were employed.…”

Effect of coagulation pretreatment on membrane distillation process for desalination of recirculating cooling water

“…DCMD has been applied for water desalination, heavy metal recovery, waste water reuse and food concentration processing, and so on. The theory and application of DCMD have been described in many papers [8][9][10][11]. Further more, DCMD process not only was applied for the desalination of RCW, but also was coupled with RCW system for pure water production.…”