Abstract
Membrane distillation (MD) is a rapidly developing field of research and finds applications in desalination of water, purification from nonvolatile substances, and concentration of various solutions. This review presents data from recent studies on the MD process, MD configuration, the type of membranes and membrane hydrophobization. Particular importance has been placed on the methods of hydrophobization and the use of track-etched membranes (TeMs) in the MD process. Hydrophobic TeMs based on poly(ethylene terephthalate) (PET), poly(vinylidene fluoride) (PVDF) and polycarbonate (PC) have been applied in the purification of water from salts and pesticides, as well as in the concentration of low-level liquid radioactive waste (LLLRW). Such membranes are characterized by a narrow pore size distribution, precise values of the number of pores per unit area and narrow thickness. These properties of membranes allow them to be used for more accurate water purification and as model membranes used to test theoretical models (for instance LEP prediction).
Highlights
According to the World Health Organization, 1 billion people currently do not have access to clean tap water, and this number may increase to 3.5 billion by 2025 [1,2,3,4,5,6]
The effective use of track-etched membranes (TeMs) in membrane distillation (MD) and in the processes of direct osmosis and filtration requires the expansion of the range of their characteristics
The studies presented in this review allow us to say that TeMs have the prospect of being used in membrane distillation
Summary
According to the World Health Organization, 1 billion people currently do not have access to clean tap water, and this number may increase to 3.5 billion by 2025 [1,2,3,4,5,6]. Membranes made from electrospun fibers showed high appropriate membrane structure, design and fabrication method are important to improve values for salt rejection and water flux. The basic principles, configurations and required characteristics for membranes in MD were discussed to achieve the best results in water flux and salt rejection. Most of the reviews indicate that the limitations of membranes for large-scale MD consist in fouling, relatively high thermal conductivity of most popular hydrophobic polymers used in MD (PVDF, PTFE and PP) in comparison with PET or PS, high energy cost, expansion of production and improvement of water fluxes and purification degree. TeMs are characterized by regular pore geometry with the ability to control them per unit area, a narrow pore size distribution, a narrow thickness and a tortuosity of 1 Such membranes have potential to be used as model membranes for development and confirmation of theoretical mass, heat transfer, LEP and fouling. As mentioned above, the unique properties of TeMs can increase the accuracy of water purification
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