Nanotechnology against industrial emissions
The use of fossil fuels has created a number of problems for which countries are intensively developing solutions to increase sustainability. All solutions require some form of separation and purification, which is currently accomplished through primarily energy-intensive processes such as absorption, cryogenic separation and distillation. Polymer membranes are considered one of the most energy-efficient methods for separating gases. However, most polymers either have low permeability or are not selective toward one gas over another. The EU-funded project DOUBLENANOMEM (Nanocomposite and nanostructured polymeric membranes for gas and vapour separations) developed novel polymers that efficiently separate gas mixtures. The project looked at appropriate combinations of nanofillers with microcavities inside them that have well-defined size and porosity dispersed in advanced nanoporous polymers. Addition of nanofillers such as carbon nanotubes, zeolites, mesoporous oxides and metal-organic frameworks allowed increasing the polymer-free volume and creating preferential channels for mass transport. Other than developing high volume polymers such as polynorbornenes, scientists also produced polymers of intrinsic microporosity. Such polymers are unable to pack efficiently in the solid state and therefore trap sufficient free volume. Due to their contorted structure, they enable fast transport of small gas molecules. Scientists developed a new polymerisation reaction based on old chemistry – Tröger's base formation – that allowed them to prepare an extremely stiff polymer structure. Potential applications of this method should extend far beyond preparing polymers only for gas separation membranes. Due to its extreme rigidity, the polymer acts as a molecular sieve, hindering transport of larger gas molecules. To become an attractive alternative, pervaporation membranes need to be improved to become highly selective for ethanol over water. The project significantly enhanced understanding of fouling processes occurring at the membranes to improve ethanol recovery from fermentation broth. The project's innovative membrane technology should also offer an alternative to traditional processes for CO2 separation in power stations. Despite their potential, the polymer materials need to be scaled to allow further evaluation of the separation process.
Keywords
Industrial emissions, gas separation, polymer membrane, nanofillers, microporosity
