In order to mitigate deleterious anthropogenic effects of emitted carbon dioxide (CO2), various systems for CO2 capture and storage (CSS) have been developed. Among a wide range of methods such as adsorption, absorption or cryogenic distillation, membrane-based separation processes have attracted a significant interest, due to their mild operating conditions, easy scale-up and low energy consumption [1].
Apart from CO2 separation, utilization of CO2 and its conversion into value-added products can be considered as a promising way to reduce the CO2 level in the atmosphere [2]. Thus, combining the catalytic CO2 conversion together with the membrane-based separation process, appears as the most comprehensive strategy towards the independence from fossil raw materials and energy sources.
There are several types of membrane modules available, namely plate- and frame- module, spiral wound module, tubular module and hollow fiber module. The most relevant advantage of the hollow fiber module is the possibility of having a very large surface area. Commonly, polymeric hollow fiber membranes are fabricated in the process called non-solvent induced separation (NIPS). NIPS is a well-established method, which allows for the development of fibers with the desired properties, tailored to the specific application. A wide spectrum of polymeric materials can be utilized for the formation of a membrane [3]. Coating of a membrane is one of the most prominent ways to enhance its gas separation performance. Moreover, it is beneficial not only in terms of the gas separation, but the coating may serve also as the immobilization medium for the catalyst [4].
The overall goal of our research is the development of polymeric hollow fiber membranes, followed by their functionalization with catalytically active species for CO2 conversion. Subsequently, the modified membranes may be applied in the membrane-based reactors, where both separation and catalyzed CO2 conversion take place simultaneously. In such systems, the equilibrium restrictions can be overcome, resulting in the higher yield of the reaction.
In our experiments we prepared hollow fiber membranes under various spinning conditions. For the polymer dope polyethersulfone (PES) was chosen due to its superior capability for CO2 separation. Hollow fiber membranes were coated with a solution of Pebax 1657, a block copolymer which is commonly known to improve the separation performance of the membrane. Moreover, the effect of the addition of various ionic liquids to the coating solutions was tested, since they are known to promote the gas separation performance of membranes [5].
Ultimately, morphologies of the coated membranes were characterized by scanning electron microscopy (SEM). Gas separation properties were investigated by the single gas permeation tests. For the reference, the flat sheet membranes have been coated with the analogous coating solutions.
References
1. R.S.K. Valappil, N. Ghasem, M. Al-Marzouqi, J. Ind. Eng. Chem., 2021, 98, 103-129.
2. A.A. Khan, M. Tahir, J. CO2 Util., 2019, 29, 205-239.
3. N. Peng, N. Widjojo, P. Sukitpaneenit, M.M. Teoh, G.G. Lipscomb, T.S. Chung, J.Y. Lai, Prog. Polym. Sci., 2012, 3(10), 1401-1424.
4. M. Baniamer, A. Aroujalian, S. Sharifnia, Int. J. Energy Res, 2020, 45(2), 2353-2366
5. M. Zia ul Mustafa, H. bin Mukhtar, N.A.H. Md Nordin, H.A. Mannan, R. Nasir, N. Fazil, Chem Eng Technol, 2019, 42(12), 2580-2593
