A comparative method for estimating the membrane mass transfer resistance of a ceramic hollow fiber membrane contactor using a Wetted‐Wall Column
Graphical abstract
Introduction
Carbon Capture and Storage (CCS) is a technology for the capture and safe storage of CO2 [1], [2]. Research into hollow fiber membrane contactors (HFMC) has recently been conducted to increase the CO2 absorber efficiency [3]. HFMC is an advanced device in which the packing material of the absorption column is replaced by a hollow fiber membrane module. It is important to highlight that a large phase contact area through the membrane pores is the key factor providing high efficiency of ceramic HFMCs compared to conventional absorption processes [4]. The main advantages are that not only the gas and absorbent can be independently increased to reach high productivities but also high membrane areas per unit volume of the membrane module and high self-mechanical supports are achievable [4], [5], [6], [7], [8], [9], [10]. However, since the thin ceramic hollow fiber membrane can be broken with mechanical force, its thickness and outer diameter are generally larger than that of the common polymeric membrane and this means that, in turn, the overall mass transfer resistance () associated with the ceramic HFMC is more important than the polymeric HFMC. It is of particular importance to quantify and then reduce the of the CO2 absorption process by optimizing the micro-structures (i.e., pore structure) of the ceramic HFMC [5], [6], [9]. One of the aims of the investigation was to estimate the resistance contributions to the overall CO2 absorption process of ceramic HFMCs by experimental comparison with a wetted-wall column (WWC). The novelty of this work is that we suggest a new comparative method to study the ceramic HFMC utilizing a simple WWC, as will be described in detail in the next section.
Section snippets
Theory and methodology
The overall mass transfer coefficient () was defined as follows [11], [12]:where , , and are the gas volumetric flow rate, the concentration of CO2 in the inlet gas phase, and the outlet gas phase, respectively. is the mass-transfer area based on the surface area of gas-liquid contact and is the mean pressure difference of CO2 in the gas phase. The overall mass transfer resistance () is defined, in turn, as inversely
Fabrication of two different hydrophobic ceramic hollow fiber membranes
Alumina powder was purchased from Kceracell Co. Ltd., Korea (99.9% α-Al2O3; average particle size: 0.5 μm; BET specific surface area: 6.4 m2/g; Model number LSC-235C). 1-Methyl-2-pyrrolidone (NMP, 99.5%, Sanchun Pure Chemical Co. Ltd., Korea) was used as a solvent for preparing the dope solution. Polyethersulfone (PESf, Ultrason® E6020P, BASF, Germany) was used as a binder. Polyvinylpyrrolidone (PVP, Sigma Aldrich, USA) was used to prepare a homogeneous spinning dope solution.
The reagents were
Characterization of ceramic HFMCs
Fig. 3 shows the SEM images at different magnifications for the ceramic hollow fiber membranes prepared by the non-solvent induced phase separation method. It is observed that both membranes consist of three layers of different morphologies arranged concentrically, namely: 1) finger-like pore layer on the inner side, 2) intermediate sponge-like layer, and 3) lumen-side finger-like pore layer. Keeping all the other variables constant, the obtained morphology is strongly dependent on the internal
Conclusions
Based on the resistance-in-series model, we described a novel experimental method for estimating the relative membrane mass transfer resistance () of ceramic hollow fiber membrane contactors (HFMC). In this work, the relative contribution expressed as a percentage of the overall mass transfer resistance () can be determined experimentally by a comparative method using a wetted-wall column (WWC) performed in the same configuration and experimental conditions of the tested
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
This research was supported by Research and Development Program of the Korea Institute of Energy Research (C1-2428-01). E. Magnone and H.J. Lee should be considered co-first authors.
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