Mixed-matrix membranes: Preparation and characterization for biorefining

In the past two decades, many researchers have tried to produce energy from renewable sources, considering its enormous demand in the world. The use of biomass may help mitigate the request for different energy sources such as fuels, chemicals, and materials and also reduce the climate change problem. Biomass is a biological material derived from living or recently living organisms. It is used directly via combustion to produce heat or indirectly after its conversion into different biofuel forms (Heinimo and Junginger, 2009; Naik et al., 2010). The term "biofuel" or "biorenewable fuel" refers to any solid, liquid, or gaseous fuel derived from biomass (terrestrial or aquatic carbon-containing matter). In particular, solid biofuel is referred to pellets and wood chips; liquid biofuel refers biodiesel, bioethanol, and oil fuel; biogas and syngas are considered to be gas-biofuel. The biorefinery concept is often considered for the production of fuels from biomass feedstocks (He et al., 2012). Several separation technologies are part of this process. In this field, membrane separation processes are more attractive because of different advantages such as low energy consumption, greater separation efficiency, the reduced number of processing steps, and the high quality of the final product (de Morais Coutinho et al., 2009). In the biorefinery process, when separations are performed by means of membranes, the most commonly used are polymeric. However, they have different drawbacks such as low stability at high temperature and pressure and low permselectivity properties (Ozturk and Demirciyeva, 2013). To solve these problems, different routes are followed such as functionalization of existing polymers, synthesis of new ones, and the development of membranes using more selective materials (eg, carbon, metals, perovskites) (Clarizia et al., 2004). An alternative is represented by the preparation of mixed-matrix membranes (MMMs), in which inorganic fillers are dispersed into the polymeric matrix (Fig. 3.1). These membrane-types combine the easy processability of the polymers and the peculiar properties of the inorganic particles. In this chapter, the main strategic methods used to prepareMMMs will be discussed in depth. Afterward, the application of these membranes in biorefinery processes will be illustrated.