Chapter 1
Nanostructured Polymer Membranes: Applications, State-of-the-Art, New Challenges and Opportunities

Visakh. P. M

Research Associate, Tomsk Polytechnic University, Department of Ecology and Basic Safety, Tomsk, Russia

Corresponding author: visagam143@gmail.com

Abstract

This chapter is a brief account of the various topics presented in Nanostructured Polymer Membranes: Applications. Different topics are discussed such as membrane technology; gas and vapor separation of membranes; membranes for wastewater treatment; polymer electrolyte membrane; methanol fuel cell membrane; polymer membranes for water desalination; polymer membrane (optical, electrochemical and anion/polyanion sensors); phosphoric acid-doped polybenzimidazole membranes; natural nanofibers in polymer membranes for energy applications; potential interest of carbon nanoparticles for pervaporation polymeric membranes; mixed matrix membranes for nanofiltration application; and the fundamentals, applications and future prospects of nanofiltration membrane technique.

Keywords: Polymer membranes, nanostructured polymer membranes, polymer membrane applications, vapor separation of membranes, nanofiltration application, mixed matrix membranes

1.1 Membranes: Technology and Applications

Membrane technologies have gained an important place and made great progress in numerous industries and are used in a broad range of applications. Commercial markets have been spreading very rapidly and throughout the world the most important industrial applications of membranes are pure water production and wastewater treatment. Membrane science and technology is interdisciplinary, involving polymer chemistry to develop new membrane materials and structures. There are many membrane applications other than wastewater treatments such as artificial kidneys (hemodialysis), artificial lungs (blood oxygenators), and controlled drug delivery and release and other medical applications [1, 2]. In recent years, membranes and membrane separation techniques have grown from a simple laboratory tool to an industrial process with considerable technical and commercial impact. Reverse osmosis is regarded as the most economical desalination process, which has played a crucial role in water treatment such as ultrapure water makeup, pure boiler water makeup in industrial fields, seawater and brackish water desalination in drinking water production, and wastewater treatment and reuse in industrial, agricultural, and indirect drinking water production [3].

Nanofiltration (NF) membranes are mostly of porous structure. The typically excellent performance of NF membrane, such as high flux, small investment and low cost for operation, brings it wider and larger applications [4]. Ultrafiltration (UF) membranes have been widely expanded further, such as in the water treatment field, food and beverage production, the automobile industry, the pharmaceutical industry, the electronic industry, etc. [5]. Chitosan and polyelectrolyte (Nafion) membrane also provide equivalent performance in PV dehydration of organics. One major challenge in the chemical industry is the complex separation problem of organic mixtures forming zaeotrope with water. Polyether-polyamide block copolymers (PEBA), combining permeable hydrophilic and stabilizing hydrophobic domains within one material, are successfully used as the organic-water PV separation membrane. Applications for hydrophobic membranes are numerous, such as wastewater treatment, removal of organic traces from ground and drinking water, removal of alcohol from beer and wine, recovery of aromatic compounds in food industries, and separation of compounds from fermentation broth in biotechnology, etc.

Some kind of membrane has been developed for the removal and recovery of metals [6-9], including chromium, copper, zinc, cobalt, nickel, strontium and lanthanides, from wastewaters and industry streams. Ceramic membranes have a lot of advantages, conditions under which polymer membranes fail: they are autoclavable, allow sterilization by superheated water, steam, or oxidizing agents, show high temperature resistance, acid and base resistance, solvent resistance, excellent mechanical resistance, and have a long working life and are environment friendly.

Zeolites are crystalline microporous silicalite or aluminosilicate materials with a regular three-dimensional pore structure, charge-balanced by cations, which is relatively stable at high temperatures. They are currently used as catalysts or catalyst supports for a number of high temperature reactions. Membrane technologies are best suited in this context as their basic aspects well satisfy the requirements of process intensification for a sustainable industrial production. In fact, they are precise and flexible processing techniques.

1.2 Polymer Membranes: Gas and Vapor Separation

Various separation technologies have been developed over the years and used in order to respond to the required demands. Polymeric membranes have also been extensively utilized for separation and purification of hydrogen and helium as valuable light gases. It should be noted that the recovery of hydrogen in refineries is a key approach to meet the increased demand for hydrogen owing to new environmental regulations. Gas and vapor separation using polymeric membranes is an area of growing interest with a variety of prominent applications, particularly in the chemical and petrochemical sector. Polymeric membranes used for air separation typically provide higher permeation rates for oxygen, and as a result, the permeate stream is comprised of oxygen-enriched gas. The main feature of organic vapors that facilitates their separation from a gas stream is their high solubility. Accordingly, rubbery polymers, such as PDMS or silicone rubber, has been introduced and examined as a viable candidate for this purpose [10-12].

Hydrocarbon recovery is considered the largest market for membranes after acid gas removal and this position is expected to remain for the foreseeable future. Olefin/paraffin separation is an application with considerable potential opportunity for practical applications. One of the most important applications of olefin/paraffin separation is the recovery of propylene vent gas from propylene reactor [13]. Polysulfones are one of the most widely used commercial membrane materials, particularly for a variety of gas separation applications, including hydrogen and air separation [14]. Polyethersulfone is one of the most important polymeric materials for use in gas separation and filtration applications due to its mechanical, chemical and thermal resistances, introducing it as an ideal candidate for asymmetric membranes [15, 16]. Applicability of PESf membrane-based pilot plants for CO2 recovery from LNG-fired boiler flue gas showed that 90% recovery of CO2 with 99% purity was possible.

Polyimides are the largest group of organic polymers used for the synthesis of membranes for gas and vapor separation due to their high thermal and chemical stability and mechanical strength [17]. These materials are composed of aromatic dianhydride and diamine monomers and a wide variety of PIs and therefore exist according to varying both dianhydride and diamine [18]. Visser et al. [19] proposed the concept of mutual plasticization in mixed gas studies as opposed to auto-plasticization in pure gas condition. Duthie et al. [20] and Lin and Chung [21] demonstrated that nitrogen, and to a lesser extent oxygen permeability, increased with temperature. However, carbon dioxide permeability decreased with temperature, showing that in this case the relative magnitude of solubility decline was higher than the diffusivity augmentation with temperature increase. Substituted polyacetylenes have large oxygen permeability (>1000 Barrer) due to high free volume and unusual free volume distribution derived from their low cohesive energy structure, stiff main chain and bulky substituents [22]. The gas separation performance of polymers depended on the degree of the conversion which was affected by the film thickness [23]. It was shown that greater chain mobility occurred in thin films due to the proximity of the free surfaces and reduced diffusional resistance for removal of the volatile compounds of the rearrangement reaction. Moreover, it was revealed that thin films of TR membranes derived from 6FDA-HAB polyimides, experienced a greater extent of aging than thick films after 1000 h exposure to different gases such as H2, O2, N2 and CH4.

1.3 Membranes for Wastewater Treatment

Synthetic polymer membranes are used mostly in the case of wastewater treatment because it is possible to select a polymer suitable for the specific separation problem from the existing enormous categories of polymers. In comparison with conventional wastewater treatment processes, membrane technology offers the advantage of selectively removing contaminants based on their sizes. Membranes with different pore-size distributions and physical properties remove a wide range of pollutants. The success of membrane operations in wastewater treatment is attributed to the compatibility between different membrane operations in integrated systems. The synergy resulting from this integration is the specific feature of hybrid systems, enhancing the process effectiveness for a particular scenario of wastewater treatment. The wastewater treatment by integrated systems nowadays suggests reducing environmentally harmful effects, decreasing groundwater consumption and energetic requirements, and recovering valuable compounds as a byproduct. Membrane bioreactor (MBR), combining membrane...