New microporous polymers for carbon dioxide selective membranes

Energy security and climate change are pressing global concerns. In this context, high performance carbon dioxide selective gas separation membranes are required for purification of biogas, natural gas and efficient carbon capture technology. Carbon dioxide removal using a polymer membrane system offers advantages over alternative processes, most notably energy efficiency, as membranes do not require thermal regeneration, a phase change or active moving parts in their operation. For any gas separation membrane, it is desirable to have good selectivity for the desired gas component combined with high permeability (i.e. flux), to minimise the required size of the system. Unfortunately, current highly permeable polymers possess insufficient selectivity and conversely highly selective polymers possess low permeability. Therefore, the goal of enhancing the selectivity of highly permeable polymers, such as Polymers of Intrinsic Microporosity (PIMs), is an important challenge in chemical engineering. We propose an integrated, multi-skilled and multi-national programme of research that will combine molecular modelling, computational simulation of polymer packing, polymer synthesis, gas adsorption and gas permeability studies to develop polymers for use as highly carbon dioxide-selective membranes. PIMs will be prepared with the direct incorporation of benzimidazole and pyrrolone heterocyclic units into the polymer chains. Calculations show that these heterocyclic units possess a high affinity for carbon dioxide. The proposed polymer design conforms to the concept of PIMs, which requires polymers chains that are both rigid and contorted to frustrate space-efficient packing in the solid state. The combined use of molecular modelling and polymer packing simulations to understand gas permeability and, ultimately, predict performance of PIMs as membrane materials will enable the design of further optimised polymers. Achieving the objective of the proposed research programme would be an important first step towards providing carbon dioxide selective membranes of real utility in biogas and natural gas purification, carbon capture and for several niche applications.

We propose a highly focused programme of fundamental research with the specific objective of preparing new polymers that will provide enhanced performance for carbon dioxide-selective membranes. Achieving this objective would be an important first step towards providing membranes of real utility in natural gas purification or carbon capture. Bridging the gap between the successful synthesis and evaluation of promising new materials (the end-point of the proposed research programme) and commercial exploitation would involve the development of thin-film or hollow-fibre membranes, module design, fabrication of pilot-scale modules, further scale-up, etc. Such development is not formally within the scope of the proposed research programme, however, all promising carbon dioxide selective polymers will be studied further by our international collaborators at ITM (contact: Dr. John Jansen), Frauhoffer IAP (contact: Dr. Detlev Fritsch) and TIPs (contact: Prof. Yuri Yampolskii) who would perform initial follow-on studies (e.g. small-scale, flat-sheet composite membrane fabrication and testing). These collaborators have good contacts with membrane manufacturers so that larger scale evaluation could be carried out if initial membrane studies are encouraging. Ultimately, a highly permeable polymer with good selectivity may provide membranes that offer a cheaper alternative to current forerunner technologies for CCS and, therefore, will be of global environmental and economic impact. Importantly, carbon dioxide is becoming a valuable commodity with an increasing market value due to its demand for enhancing the yield from oil and gas wells, for carbonation of beverages and as a chemical feedstock. This has resulted in the ironic situation of increasing commercial supply of carbon dioxide from wells in the US and Italy that tap into deep geological reservoirs (i.e. the opposite process to CCS!). Hence, in the short-to-medium term, efficient carbon dioxide-selective membranes may have environmentally beneficial and economically feasible niche applications (e.g. recycling of carbon dioxide from brewing or cement manufacture), in addition to biogas and natural gas purification and CCS. The development of Polymers of Intrinsic Microporosity (PIMs) starting from the first EPSRC grant being awarded in 1999, through the patent application process (2003-10), to the agreement of the first commercial license (2010), offers a realistic example as a pathway to impact. It is one that we will try to emulate with the polymers resulting from the present proposal. As a first step, patent protection will be sought for successful carbon dioxide selective membranes in collaboration with the Research and Contracts Division of Cardiff University. However, as demonstrated by the commercial uptake of PIMs, the eventual impact cannot always be planned or predicted at the proposal stage of the programme and is often dependent upon the right people finding out about the research. Hence, dissemination in high-impact journals and seeking accompanying publicity will play an important role in finding industrial partners for technological exploitation. Due to the topical nature of carbon capture, high-impact journals (e.g. Science, Nature Materials) will be realistic targets for the dissemination of high performing materials that are generated by the research programme. Presentation of the research at suitable international membrane conferences will also assist dissemination. Such publicity is likely to generate interest from membrane companies, especially those with current development programmes based on PIMs.