Nanocomposite pervaporation membrane for desalination
Introduction
Water is one of the fundamental conditions required for organisms to survive. However, during the last few decades, the rapid world population, rising living standard, consumption pattern changes, climate change, extension of irrigated agriculture and industrialization are driving for an escalating global demand for clean water, which leads to water scarcity (Vörösmarty et al., 2000; Ercin and Hoekstra, 2014; Elimelech and Phillip, 2011). Encouraging efforts to overcome the lack of clean water have been made by the development of water treatment processes in the 20th century; however, water scarcity is much more pressing today than before. The World Water Council (WWC) has estimated that 3.9 billion people in the world will live in water-scarce areas by 2030 (WWC, Urban Urgency, Water Caucus Summary, 2007). Along similar lines, the World Health Organization (WHO) predicted that 2.1 billion people lack of safe drinking water supply (WHO, Water, Sanitation and Hygiene strategy 2018–2025, 2018) (Li et al., 2019). Therefore, the provision of clean water has become a major issue for public and government. Water resources on earth comprise conventional water resources (CWRs) and unconventional water resources (UCWRs). CWRs are groundwater, rivers and lakes, while UCWRs involve seawater, brackish water and wastewater, which evidently requires much more purification before it can be used.
The total water supply (both salt and freshwater) on the earth is 1.4 billion km3, of which 97.5% is saltwater, which cannot be used directly for human consumption (Hameeteman, 2013). Hence desalination, which converts salty water to fresh water from the almost limitless source of seawater, has become an attractive solution to deliver clean water to the community. There are two major types of technologies for desalination: thermal desalination and membrane technology. In recent years membrane technology has become the most attractive option for desalination due to its advantages, such as its high efficiency and energy saving (Semiat, 2008; Drioli et al., 2011), high operational stability, low chemical costs, easy to integrate and control within industrial processes (Drioli et al., 2011). Since reverse osmosis (RO) membranes were developed in the1960s, membrane technology has taken over the desalination market with installed 73% membrane-based desalination while 27% is thermal desalination (Ahmed et al., 2019). RO is a mature technology for supplying fresh water from seawater (salinity of 3.5 wt%) and brackish water (salinity of 0.05−3 wt%) primarily due to its low cost and high salt rejection of over 99.5% (Li, 2016). RO has so far maintained its leadership among alternative membrane processes such as membrane distillation (Hsu et al., 2002), electrodialysis (Sadrzadeh and Mohammadi, 2008), capacitive deionization (Oren, 2008) and forward osmosis (McGinnis and Elimelech, 2007) that have been proposed (Lee et al., 2011). However, RO has certain drawbacks: the driving force needs to be increased to handle highly concentrated salt water, which leads to higher cost, and RO membrane elements are sensitive to fouling. To address these issues, innovative membrane technologies are proposed to improve the established membrane processes for desalination.
Pervaporation (PV) is a thermal driven membrane processes (Xue et al., 2020), in which the chemical potential difference acts as driving force (Cannilla et al., 2017; Slater et al., 2006). PV has attracted many researchers to be developed as a potential desalination method due to some advantages such as a potential low energy, high salt selectivity, limited effects of fouling, and the capability to handle feed waters with high salinity (Prihatiningtyas et al., 2020a; Wang et al., 2016). Limited information on the application of pervaporation for desalination and wastewater treatment might be due the lack of a high water flux in PV compared to RO. Most efforts of researchers are devoted to searching the right PV desalination membrane material to achieve the preferred separation in an efficient way. An ideal PV membrane should have a high water flux and selectivity, good mechanical and thermal resistance, and have a good fouling resistance, leading to a long lifetime. A study reported that chlorination to prevent biofouling of RO membranes is an issue due to the active chlorine attacks polymer network of RO (Al-Abri et al., 2019), for example the applications of polyamide thin film composite (PA-TFC RO) membranes for desalination (Xu et al., 2013). Typical PV membranes are hydrophilic membrane which the dense selective layer is a good fouling resistance, however Li et al. found that PV desalination membranes showed gradually deteriorated desalination properties due to a fouling (Li et al., 2017). Hence, Zhao et al. studied to modify polyvinyl alcohol (PVA) polymer with a fluorine based crosslinker (FS-3100) to increase the chlorine resistance. They reported that the fabricated composite membranes showed much better chemical resistances to acid, alkali, and also chlorine solutions (Zhao et al., 2020).
PV membranes are dense; they are made of polymers such as polyether amide, sulfonated polyethylene, poly(vinyl alcohol), and cellulose-based material (Wang et al., 2016); however, they have some limitations such as low permeability, high energy consumption, low resistance to fouling, and short life span (Alaei Shahmirzadi and Kargari, 2018). Hence the development of new membrane materials to obtain a PV membrane with desired properties, energy efficient, and cost effective is needed for desalination. Researchers have been introducing nanoparticles into a polymer matrix to overcome the challenges of the present polymeric PV membranes. Nanoparticles such as silica, zeolite, alumina, clay, TiO2, MoS2, graphene oxide, carbon dots, carbon nanotubes (CNTs), and multi-walled carbon nanotubes (MWNTs) have been employed to prepare desalination membranes (Prihatiningtyas et al., 2020a). Although nanoparticles provide extraordinary benefits, there are some challenges in membrane fabrication for industrial development. Therefore, this article reviews the current research progress in nanocomposite pervaporation membranes for desalination from the viewpoints of membrane materials and membrane fabrication procedures.
Section snippets
Pervaporation desalination
Pervaporation is a membrane process developed to separate liquid mixtures based on selective sorption and diffusion of one of the species through the dense membrane. The term pervaporation was defined by Kober as a contraction of ‘permeation’ and ‘evaporation’, after observing the selective permeation of water through a collodion and parchment membrane at the 1910s (Kober, 1917). In pervaporation, a liquid mixture in the feed is contacted with one side of a membrane, then the product in the
Fabrication method
Membranes are a selective barrier in a separation process that is permitting a certain compound through their structures by a combination of sieving and diffusion mechanisms. Membrane can be in the form of a solid or a liquid. Solid membranes are classified as shown in Fig. 5 (Purkait et al., 2018).
Symmetric membranes can be of three types, based on the membrane structure (Purkait et al., 2018):
- 1
Porous membranes: These membranes are defined as having pores. In general, the separation is a
Conclusion
Desalination by pervaporation has gained much attractiveness due to its performance in terms of water flux, salt rejection, and its reduced thermal requirements. The PV desalination performance depends on the nature and selectivity of the membrane and the nanofiller, diffusivity of the filler, and operating conditions. Current research shows that incorporating nanoparticles in the membrane enhances the performance of PV desalination. Many studies on laboratory and pilot scale have struggled to
Conflict of interest
None declared.
Acknowledgement
This work was supported by the Indonesia Endowment Fund for Education (LPDP). The authors would like to thank to Yusak Hartanto for the fruitful discussions (UCLouvain).
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