Gas Liquid Membrane Contactor Research Articles

Hollow Fiber Contactors with Improved Hydrophobicity for Acid Gas Removal: Progress and Recent Advances

The gas–liquid membrane contactor technology, which integrates the absorption process with membranes, is a developing membrane technology that is especially pertinent to acid gas absorption. When it comes to removing acid gases from natural gas or after combustion, membrane technology has demonstrated potential as a substitute for conventional absorption columns. The membrane contactor offers exceptional operating flexibility and a high mass transfer area. In addition to summarizing the key elements of membrane materials, absorbents, and membrane contactor design, this paper presents the working principle and wetting mechanism of hollow membrane contactors and focuses the most recent advancements in membrane contactor research in gas separation from gas mixtures. The state-of-the-art overview of highly hydrophobic microporous membranes is presented after a discussion of the main challenges to the preparation of superhydrophobic membranes.

Experimental study of hollow fiber membrane contactor process using aqueous amino acid salt-based absorbents for efficient CO2 capture

Gas–liquid membrane contactors are a promising alternative to packed columns that suffer from channeling, bubble formation, and flooding problems. In this study, potassium serinate + piperazine (PSZ) and potassium alaninate + piperazine (PAZ), which are amino acid salts with good CO2 absorption performances and high surface tensions, are investigated to determine the effects of the operating parameters on the CO2 removal efficiency, CO2 absorption flux, CO2 loading, and overall mass-transfer coefficient in the membrane contactor process. The experimental results demonstrate that the 2.5 M PSZ and 2.5 M PAZ absorbents outperform 2.5 M monoethanolamine (MEA) under various operating conditions, including the gas flow rate, liquid flow rate, CO2 concentration, and CO2-loaded absorbent. Based on these results, an expression for predicting the CO2 loading from the pH is proposed. The amount of cross-over confirmed that amino acids with high surface tension have better resistance to membrane wetting than 2.5 M MEA. In addition, empirical correlation expressions were established from the results of several operating parameters. The absolute average deviation (AAD) values were 6.50 %, 2.95 %, and 4.71 % for 2.5 M MEA, 2.5 M PSZ, and 2.5 M PAZ, respectively, suggesting good agreement between the theoretical and experimental results.

Mitigated CH4 release of anaerobic waste fermentation is enabled through effluent degassing system equipped with a polydimethylsiloxane membrane contactor

In this study, first, a fed-batch biogas fermenter was established using anaerobic digester sludge treating secondary sludge from a municipal wastewater treatment plant and operated for 120 days on glycerol as the sole substrate. Then, the prefiltered effluent of the anaerobic digester unit was loaded subsequently into a stirred-tank coupled with a hollow-fibre, polydimethylsiloxane (PDMS) gas-liquid membrane contactor and a dissolved methane sensor for studying the gas recovery process under continuous biogas supply, consisting of CH4 and CO2 in different proportions (70/30 CH4/CO2 vol.%; 50/50 CH4/CO2 vol.%; 30/70 CH4/CO2 vol.%.). Experiments showed that besides the actual composition of the internal biogas, the ratio (0.5–2) of sweep gas (N2) and effluent (liquid) volumetric flow rates (G/L) could be a crucial operating factor with influence on the degassing efficiency attainable by the 1 m2 PDMS membrane module. Results were compared to the performance of the same PDMS membrane module working with synthetic anaerobic digester effluents, indicating the dissolved methane recoveries observed with the synthetic effluents (>50 %) considerably surpassed those with the real effluent (<20 %) where the dissolved methane concentrations, at G/L of 1, were in the range of 12.4 to 17.3 mg L−1.

Carbon dioxide absorption in a gas-liquid membrane contactor: Influence of membrane properties and absorbent chemistry

The present work demonstrates the performance of hollow fibre membranes fabricated using polyvinyl chloride, polystyrene (EPS) and polydimethylsiloxane (PDMS) coupled with 30% monoethanolamine (MEA) in a gas liquid membrane contactor (GLMC) for the absorption of carbon dioxide. A gas mixture with a composition of (50/50 v/v%) methane (CH4) and (CO2) was used to assess the efficiency of the prepared membranes in the removal of carbon dioxide. Then HFM 3 which showed high CO2 removal was used to separate a mixture of nitrogen (N2)/oxygen(O2)/carbon dioxide (CO2) with a composition of (73/18/9 v/v%), respectively. Four different absorption liquids: 30 % MEA solution, 30 % EDA solution, 30 % MEA – graphene oxide (GO) and 30 % EDA-GO nanofluids were coupled with HFM3 to analyse the efficiency of the different amine liquids in CO2 absorption in GLMC. The 30 % EDA-GO solution showed an increase in the efficiency of CO2 absorption. The nanofluids showed an enhancement factor for CO2 absorption in the nanofluid was 121 % and 117 % for MEA-GO and EDA-GO, respectively. This enhancement was attributed to the hydrodynamic effects and Brownian motion of graphene oxide in the amine liquids. 30 % EDA solution infused with 0.2 mg/ml graphene oxide nanoparticles achieved the highest loading of carbon dioxide 0.25 mol/ cm3.

Preparation of amino-functionalized polyethylene-silica composite membrane and FDH immobilization

Enzymatic CO2 conversion represents a highly efficient, energy-conserving, and environmentally sustainable approach to mitigating the increasing pressure caused by huge carbon emissions and generating valuable products. However, several challenges associate with the process including the instability and recovery difficulty of free enzyme, as well as low solubility of CO2 in mild conditions. Immobilizing enzyme on the amino-functionalized supports presents a viable solution to these issues. Considering the wide application of polymer hollow fiber membranes in the field of CO2 gas–liquid membrane contactor and the characteristics of hydrophilic, biocompatible, and high specific surface area of silica nanoparticles, the amino-functionalized polyethylene (PE)-silica (APS) composite membranes were fabricated via different routes. The morphologies, the loading rates of modified SiO2 and reusability of APS membranes were characterized for a crude screening. Following that, seven kinds of APS membranes were used as the carriers of formate dehydrogenase (FDH) that could catalyze the reduction of CO2 to formate, and their immobilization efficiency and catalytic performance were compared. The results show that 1# and 2# membranes based on carboxyl-modified PE with a loading rate of 5.5 %∼5.6 % and the reusability of above 99 % were more ideal carriers than others. The enzyme activity recovery rate of APS-immobilized FDH (FDH-APS) was separately 367 % and 256 %, proving the intensification action of carriers on the enzymatic reaction. After 10 cycles of use, the relative activity of two kinds of FDH-APS was around 70 % and 78 %, much higher than corresponding particles or membrane attached FDH (25.3 % and 20.4 %). After storage at 4 °C for 20 days, the relative activity of FDH-APS was 82.7 % and 81.0 %, while it was only 61.4 % for free enzyme.

Deoxygenation of CO2 Absorbent Based on Monoethanolamine in Gas–Liquid Membrane Contactors Using Composite Membranes

Deoxygenation of CO2 Absorbent Based on Monoethanolamine in Gas–Liquid Membrane Contactors Using Composite Membranes

Deoxygenation of CO&lt;sub&gt;2&lt;/sub&gt; Solvent Based on Monoethanolamine in Gas–Liquid Membrane Contactors Using Composite Membranes

This work is devoted to the removal of dissolved oxygen from a model solvent based on monoethanolamine (MEA) to prevent its oxidative degradation during the absorption purification of flue gases from carbon dioxide. Composite membranes based on porous ceramic and polymer substrates with a thin selective layer of poly[1-(trimethylsilyl)-1-propyne] and its mixture with polyvinyltrimethylsilane have been developed. Gas-liquid membrane contactors have been created on their basis. It is shown that with their use in the vacuum mode, up to 60% of dissolved oxygen can be removed from the model solvent.

Surface modification of polypropylene hollow fiber membranes using fluorosilane for CO2 absorption in a gas-liquid membrane contactor

Conventional methods for improving the hydrophobicity of polypropylene (PP) membranes to prevent wetting phenomena require complex pretreatment procedures in order to activate the surface for enabling the reaction with fluorosilane (FS)-based materials. This study successfully prepared PP membrane contactors with enhanced hydrophobicity through a simple single-step dip-coating method using perfluoroether-grafted silanes for CO2 capture. The FS coating layer on the PP membrane surface was confirmed through ATR-FTIR spectroscopy, XPS, FE-SEM, and EDS. Furthermore, the evaluation of the CO2 absorption performance and long-term stability of the FS-coated PP membrane according to the variation of the gas flow rate (50, 100, 200, 400, and 800 mL/min) confirmed the superior chemical stability and durability of our membranes to those of previously reported hydrophobic membranes. The as-prepared FS-coated PP membrane expands the application scope of gas-liquid membrane contactors for CO2 capture from the flue gas of coal-fired power plants.

Immobilization of carbonic anhydrase on poly(ionic liquid) composite membranes for CO2 absorption by gas-liquid membrane contactors

In our current climate crisis, an impressive global effort is being deployed to develop and implement technologies to mitigate CO2 emissions. For instance, CO2 capture and storage/utilization (CCUS) will be fundamental during the energy transition. In the context of CCUS, the enzyme carbonic anhydrase (CA) has gained growing attention because it acts as a green catalyst in CO2 capture by absorption. A few works investigated the preparation of membranes with immobilized CA for CO2 capture by gas-liquid membrane contactors. Although these biocatalytic membranes exhibited improvements in the CO2 capture rate, limited immobilization strategies and carriers have been investigated so far. This work describes the fabrication, characterization, and testing of novel composite membranes with immobilized CA for CO2 capture. The membranes were comprised of a hydrophilic poly(ionic liquid) (PIL) top layer coated on a porous poly(vinylidene fluoride) (PVDF) support. The layer was prepared by in-situ polymerization of an ionic liquid monomer solution cast on the PVDF. CA was easily immobilized on the PIL layer by physical adsorption. The immobilized enzyme's catalytic activity was evaluated to identify the optimum formulation of the PIL layer (monomer and cross-linker concentrations) and immobilization protocol (enzyme concentration in the buffer solution and pH). Despite the immobilization protocol's simplicity, the enzyme was strongly bonded as the enzyme-loaded membranes could be reutilized 10 times while retaining above 90% of their initial activity. These membranes were further characterized by SEM, EDX, ATR-FTIR, TGA, DSC, zeta potential, and water contact angle. Moreover, the biocatalytic composite membranes were tested in a gas absorption set-up to demonstrate their applicability. They showed an increase in the overall mass transfer coefficient with respect to the pristine support by a factor of 2.5, making them interesting candidates for promoting CO2 capture.

CO2/CH4 separation performance of SiO2/PES composite membrane prepared by gas phase hydrolysis and grafting coating in gas-liquid membrane contactor: A comparative study

The gas-liquid membrane contactor (GLMC) is a new and promising kind of gas separation technique, but still exhibits limitations, especially in membrane performance. In order to solve the above problems, we fabricated and characterized novel OH/SiO2/PES composite membranes using gas phase hydrolysis and graft coating methods, respectively. In the preparation process, whether to use alkali to pretreat the membrane was used as an evaluation index. The CO2/CH4 separation performance was tested using the modified OH/SiO2/PES hollow fiber membrane as the membrane contactor in GLMC. In the experiment, we conducted a single factor experiment with diethanolamine (DEA) as the adsorbent to analyze the effect of the flow rate and concentration of DEA on the separation of CO2/CH4. The collected gas had a CH4 content of 99.92% and a CO2 flux of 10.1059 × 10−3 mol m−2 s−1 while DEA at a concentration of 1 mol/L was flowing at a rate of 16 L/h. The highest separation factor occurred at this moment, which was 833.67. Overall, the CO2/CH4 separation performance in GLMC was enhanced with the use of the fluorinated OH/SiO2/PES composite membrane.

An electrolytic bubble column with an external hollow fiber membrane gas–liquid contactor for effective microbial electrosynthesis of acetate from CO2

Currently, almost all microbial electrosynthesis (MES) reactors were biofilm-driven whether the cathode electron transfer was direct or indirect. It has been proven that cathode biofilm formation is time-consuming, and the current density achieved on these biofilms was relatively low. However, the main challenge for the non-biofilm-driven MES is how to maintain a good Columbic efficiency (CE) at high current densities. Here, we report a novel electro-H2 bubble column reactor with an external hollow fiber membrane gas–liquid contactor to tackle the challenge. The electrolyzer was placed at the bottom of the reactor to produce H2 micro-bubbles (mean diameter 169 ± 7 µm) at a current density of 156 A/m2. The bubble column was put on the top of the cathodic chamber of the electrolyzer to extend the H2 retention time, while the hollow fiber membrane gas–liquid contactor in the external loop was used to recover the unused gas. Consequently, the homoacetogens in reactor could efficiently convert the electrolytically-produced H2 and the externally-supplied CO2 into acetate. The volume of the catholyte (5.5 L) in this reactor is one order of magnitude higher than all reported MES reactors. Batch tests with enriched homoacetogens demonstrated a maximum acetate production rate (1.15 g/Lcatholyte/d, 898 g/m2cathode/d), acetate titer (34.5 g/L) could be achieved in this setup, and the average (maximum) CE of the electron to acetate efficiency was 64% (92%). Besides, dissolved H2 measurement and bacteria community analysis indicated the high acetate titers were likely caused by the H2 oversaturation situation and good substrate/product mass transfer rather than the selection of certain types of homoacetogens. The electro-H2 bubble reactor seems to be a promising MES setup for scale-up and practical application.

Offshore decarbonation of CO2-rich natural gas intensified via gas-liquid membrane contactors with blended aqueous-amines

A battery of high-pressure countercurrent gas-liquid membrane contactors (GLMC) using aqueous-methyl-diethanolamine(39% w/w)-piperazine(5% w/w) solvent is demonstrated for offshore decarbonation of 5MMNm3/d carbon-dioxide-rich natural gas. To accomplish this, a Gas-Liquid Membrane Contactor Unit Operation Extension (GLMC-UOE) was built for HYSYS simulator. Mass/energy balances, pressure-drop, vapor/liquid equilibrium properties are solved by GLMC-UOE with rigorous thermodynamics provided by the HYSYS Acid-Gas Chemical-Solvents Package appropriate for high-pressure carbon dioxide chemical-absorption. GLMC-UOE discretizes a countercurrent GLMC module as a cascade of countercurrent GLMC elements, which are solved via adapted simultaneous corrections of variables. Each GLMC element adopts a multicomponent interfacial heat/mass transfer model based on logarithmic-mean of transmembrane temperature-difference and component fugacity-differences for vapor-to-liquid or liquid-to-vapor transfers. The transferable species comprehend carbon dioxide, methane, ethane, propane, water, methyl-diethanolamine and piperazine. GLMC-UOE was validated against the literature. The process comprises the high-pressure GLMC battery, reboilered low-pressure stripping column, heat exchangers, multi-staged carbon dioxide compression and triethylene-glycol dehydration unit. A stripper heat-ratio of 167.7 kJ/molCO2 was required for solvent regeneration, a value compatible with the literature. The process dispatches dry dense carbon dioxide for enhanced oil recovery in the same offshore field. GLMC-UOE correctly predicts GLMC temperature effects, gas hydration, methane losses in the solvent and pressure-drop.

Stability of Porous Polymeric Membranes in Amine Solvents for Membrane Contactor Applications.

Membrane gas-liquid contactors have great potential to meet the challenges of amine CO2 capture. In this case, the most effective approach is the use of composite membranes. However, to obtain these, it is necessary to take into account the chemical and morphological resistance of membrane supports to long-term exposure to amine absorbents and their oxidative degradation products. In this work, we studied the chemical and morphological stability of a number of commercial porous polymeric membranes exposed to various types of alkanolamines with the addition of heat-stable salt anions as a model of real industrial CO2 amine solvents. The results of the physicochemical analysis of the chemical and morphological stability of porous polymer membranes after exposure to alkanolamines, their oxidative degradation products, and oxygen scavengers were presented. According to the results of studies by FTIR spectroscopy and AFM, a significant destruction of porous membranes based on polypropylene (PP), polyvinylidenefluoride (PVDF), polyethersulfone (PES) and polyamide (nylon, PA) was revealed. At the same time, the polytetrafluoroethylene (PTFE) membranes had relatively high stability. On the basis of these results, composite membranes with porous supports that are stable in amine solvents can be successfully obtained to create liquid-liquid and gas-liquid membrane contactors for membrane deoxygenation.

Biocatalytic Membranes for Carbon Capture and Utilization.

Innovative carbon capture technologies that capture CO2 from large point sources and directly from air are urgently needed to combat the climate crisis. Likewise, corresponding technologies are needed to convert this captured CO2 into valuable chemical feedstocks and products that replace current fossil-based materials to close the loop in creating viable pathways for a renewable economy. Biocatalytic membranes that combine high reaction rates and enzyme selectivity with modularity, scalability, and membrane compactness show promise for both CO2 capture and utilization. This review presents a systematic examination of technologies under development for CO2 capture and utilization that employ both enzymes and membranes. CO2 capture membranes are categorized by their mode of action as CO2 separation membranes, including mixed matrix membranes (MMM) and liquid membranes (LM), or as CO2 gas-liquid membrane contactors (GLMC). Because they selectively catalyze molecular reactions involving CO2, the two main classes of enzymes used for enhancing membrane function are carbonic anhydrase (CA) and formate dehydrogenase (FDH). Small organic molecules designed to mimic CA enzyme active sites are also being developed. CO2 conversion membranes are described according to membrane functionality, the location of enzymes relative to the membrane, which includes different immobilization strategies, and regeneration methods for cofactors. Parameters crucial for the performance of these hybrid systems are discussed with tabulated examples. Progress and challenges are discussed, and perspectives on future research directions are provided.

Helical-Ridge-Membranes from PVDF for enhanced gas–liquid mass transfer

New membrane geometries have the potential to increase mixing at the feed and permeate side to counteract concentration polarization and fouling. Such membrane geometries can be of very different architecture. Here, we address a new class of hollow fiber membranes having helical ridges. We focus on gas–liquid mass transfer, which is significantly slowed down by a liquid-side diffusion resistance. We present hydrophobic polyvinylidene fluoride (PVDF) helical ridge hollow fiber membranes produced by a rotating needle spinneret. Conceptually, the wet spinning methodology builds upon our Rotation-in-a-Spinneret platform technology, featuring customized microstructured rotating needles. The microstructured needle orifice includes two grooves to initiate ridge formation on the lumen side of the hollow fiber, while the ridges twist helically upon needle rotation. The new generation spinneret device produces hollow fiber membranes with reduced fiber diameter as compared to previous versions. It is specifically designed such that rotating spinning parameters enable an adjustable helical ridge pitch. Ridge formation and ridge shape strongly depend on rotational speed. The latter affects characteristic membrane properties such as membrane permeability and molecular selectivity. The helical ridges induce secondary flow in the lumen of the hollow fiber membranes, proven by pressure drop manipulation and experimental flow streamline visualization. In-depth analysis by flow simulation identifies rotational flow patterns as the governing flow phenomena. Ultimately, application in gas–liquid membrane contactors for oxygenation and CO2 capture revealed up to 10-fold improved transmembrane gas fluxes. Hence, the helical ridges cause turbulence promotion to introduce significant mass transfer enhancement.

Preparation of OH/TiO2/PES composite membrane by a novel gas-phase hydrolysis method in gas-liquid membrane contactor to improve the separation efficiency of CO2 and CH4

Conventional gas separation methods are very limited for CO2 separation in terms of separation efficiency and cost. In this study, We obtained fluorinated TiO2/polyethersulfone (PES) composite membranes by gas-phase hydrolysis and compared the characterization results with the composite membranes prepared by the graft coating method. In the mixed gas separation experiment, we used diethanolamine (DEA) as the absorbent to test the separation performance of CO2/CH4 using the composite membranes prepared by gas phase hydrolysis in a gas-liquid membrane contactor (GLMC) system. DEA flow rate and concentration and feed gas flow were found to have a significant effect on separation performance. When the feed gas flow rate was kept constant at 30 ml/min and the DEA flow rate and concentration were 16 L/h and 1 mol/L, respectively, the collected CH4 concentration was 99.4 %. Meanwhile, the CO2 flux was 10.096 × 10−3 mol m−2 s−1, and the separation factor reached 110.444. Collectively, the application of TiO2/PES composite membranes in GLMC is an efficient method for CO2 capture and mixed gas separation.

CO2 capture based on Al2O3 ceramic membrane with hydrophobic modification

In this paper, Al2O3 ceramic membrane is modified to hydrophobicity by grafting 1 H,1 H,2 H,2 H-perfluorodecyltriethoxysilane. And its properties are characterized in detail. CO2 capture performance of ceramic membrane is investigated by experiments. Results show that wetting resistance after modification is significantly improved, and contact angle increases from the initial 49.8–130.9°. However, hydrophobic modification has no significant effect on the crystalline phase, surface morphology and pore size distribution of the ceramic membrane. With ethanolamine (MEA) as absorbent, CO2 mass transfer rate and capture efficiency using modified hydrophobic ceramic membrane are 46.6 × 10−3 mol/(m2·s) and 98.0%, showing significantly increase compared to the original membrane. After 72 h immersion in MEA solution, quality of ceramic membrane does not change significantly. And there is almost no change in average pore size. We believe this study will provide a reference for the industrial application for CO2 capture by gas-liquid membrane contactor with ceramic membrane.

Separation of Dissolved Gases from Aqueous Anaerobic Effluents Using Gas-Liquid Membrane Contactors

This study aimed to evaluate a gas-liquid membrane contactor for recovering the dissolved gases of methane (CH4) and carbon dioxide (CO2) from model aqueous anaerobic effluents. For this purpose, synthetic effluents were prepared by using the gas mixtures of SE-1: 100/0, SE-2: 0/100 and SE-3: 50/50 CH4/CO2 vol.% as well as DI water. The units in which the synthetic effluent was prepared were coupled with a dense hollow fiber membrane module by employing argon gas at atmospheric pressure. The desorption of the gases CH4 and CO2 dissolved in the effluents was investigated with a countercurrent flow of the liquid on the lumen side. The effect of the sweep gas flow rate on the removal rate was also investigated. The results showed that the recovery rate of CH4 was slightly affected by increasing the sweep gas flow rate, while the recovery rate of CO2 was enhanced considerably. By applying a sweep gas flow rate of 20 mL/min, the recovery rate of both gases from SE-3 exceeded 50%.

Hydrophobic Modification of Polyetherimide Hollow Fiber Membrane Contactor by 2-(Perfluoroalkyl) Ethanol Coating for Carbon Dioxide Absorption

Highly porous polyether imide (PEI) hollow fiber membranes were fabricated through a phase-inversion process. Surface modification of the membranes was performed by coating an ultra-thin layer of 2-(perfluoroalkyl) ethanol (ZONYL). The properties of the prepared membranes were evaluated through field emission scanning electronic microscopy (FESEM), water contact angle, N2 permeation, overall porosity, critical water entry pressure (CEPw) and collapsing pressure experiments. From FESEM, the PEI membrane showed an open structure with large finger-likes cavities. By coating the ZONYL layer, the modified membrane presented improved outer surface water contact angle (105 °), CEPw (450 kPa), and collapsing pressure (750 kPa). The improved PEI-ZONYL membrane presented an almost stable CO2 absorption flux (6.8×10-4 mol/m2 s) during 72 h of the gas-liquid membrane contactor operation while a significant flux reduction was observed for the plain PEI membrane. Therefore, the improved membrane with high surface hydrophobicity and porosity can be a promising candidate for high performance gas-liquid membrane contactors.

Two-Dimensional Conjugated Mass Transfer of Carbon Dioxide Absorption in a Hollow-Fiber Gas-Liquid Membrane Contactor.

The absorption efficiencies of CO2 in hollow-fiber membrane contactors using an ethanolamine (MEA) solvent under both concurrent- and countercurrent-flow operations were investigated theoretically and experimentally. Two-dimensional mathematical modeling was developed by Happel’s free surface model, and the resultant partial differential equations were solved analytically using the separated variables method with the use of an orthogonal expansion technique. A simplified expression of Sherwood number variations was reported by employing the relevant operations conditions and expressed in terms of the computed eigenvalues for predicting concentration distribution and absorption efficiency. It is emphasized that, in comparing various fiber packing configurations, both theoretical predictions and experimental results should be compared to find the absorption flux increment accomplished by the CO2/N2 stream passing through the fiber cells under the same mass flow rate. The value of the present mathematical treatment is evident to propose a simplified expression of the averaged Sherwood number variations, and provides the predictions of the absorption flux, absorption efficiency, average Sherwood number with the absorbent Graetz number, inlet CO2 concentration, and absorbent flow rates as parameters. The availability of such concise expressions, as developed directly from the analytical formulations, is the value of the present study. The experiments of the CO2 absorption using MEA with alumina (Al2O3) hollow fiber membranes are also set up to confirm the accuracy of the theoretical predictions. The accuracy derivations between the experimental results and theoretical predictions for concurrent- and countercurrent-flow operations are and , respectively. The operations of the hollow-fiber membrane contactor implementing N = 7 fiber cells and N = 19 fiber cells offer an inexpensive method of improving absorption efficiency by increasing fiber numbers with consideration of device performance.