CO2 Absorption Flux Research Articles

Improving O₂ Absorption in PVDF Membrane with Cross-Linked Polymer Coatings

Surface modification of polyvinylidene fluoride (PVDF) membranes using various polymers, including chitosan, nylon, dopamine, and EDA, was examined through SEM and FTIR analyses. SEM imaging unveiled the preservation of membrane porosity post-modification, affirming successful polymer integration without pore obstruction. Nylon coatings induced alterations in surface morphology, with enlarged pore apertures and roughened surfaces attributed to formic acid exposure during dissolution. FTIR spectroscopy confirmed the presence of the respective polymers, exhibiting characteristic peaks for each. Notably, membranes coated with EDA exhibited enhanced CO2 absorption flux owing to their inherently hydrophilic nature and larger pore dimensions. Optimization of EDA coating parameters, including deposition time and concentration, revealed a direct correlation between increased EDA deposition and enhanced CO2 absorption flux, emphasizing the significant impact of these parameters on membrane performance in gas absorption. Consequently, tailored surface modifications offer a promising avenue for enhancing membrane functionality in gas separation applications

Effects of Varying Spiral-Ring Pitches on CO2 Absorption by Amine Solution in Concentric Circular Membrane Contactors.

The CO2 absorption flux while using monoethanolamide (MEA) solution in a spiral-wired channel was significantly enhanced by optimizing both the descending and ascending spiral ring pitch configurations within the filled channel. In this study, two distinct spiral ring pitch configurations were integrated into concentric circular membrane contactors to augment CO2 absorption flux. Spiral rods were strategically inserted to mitigate concentration polarization effects, thereby reducing mass transfer boundary layers and increasing turbulence intensity. A theoretical one-dimensional model was developed to predict absorption flux and concentration distributions across varying MEA absorbent flow rates, CO2 feed flow rates, and inlet CO2 concentrations in the gas feed. Theoretical predictions of absorption flux improvement were validated against experimental results, demonstrating favorable agreement for both ascending and descending spiral ring pitch operations. Interestingly, the results indicated that descending spiral ring pitch operations achieved higher turbulent intensity compared to ascending configurations, thereby alleviating concentration polarization resistance and enhancing CO2 absorption flux with reduced polarization effects. Specifically, under conditions of a 40% inlet CO2 concentration and 5 cm3/s MEA feed flow rate, a notable 83.69% enhancement in absorption flux was achieved compared to using an empty channel configuration. Moreover, a generalized expression for the Sherwood number was derived to predict the mass transfer coefficient for CO2 absorption in concentric circular membrane contactors, providing a practical tool for performance estimation. The economic feasibility of the spiral-wired module was also assessed by evaluating both absorption flux improvement and incremental power consumption. Overall, these findings underscore the effectiveness of optimizing spiral ring pitch configurations in enhancing CO2 absorption flux, offering insights into improving the efficiency and economic viability of CO2 capture technologies.

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.

Study on design strategies and on new structure-performance relationships for CO2 capture in gas-liquid hollow fiber membrane contactors

The urgent need for carbon dioxide (CO2) capture technologies motivates this chemical engineering study, which systematically investigates the influence of macroscopic and microscopic structure on the CO2 absorption performance of hydrophobic alumina (Al2O3) hollow fiber membrane (A-HFMs) contactors. Six different A-HFMs prepared using the non-solvent-induced phase separation (NIPS) method with select solvents followed by sintering at 1300°C were then tested for chemical CO2 absorption in an A-HFM contactor using a monoethanolamine (MEA) solution. The hydrophobicity of the coatings applied on the A-HFM surfaces was confirmed by the water contact angle and thermogravimetric (TGA) analysis. Pearson's statistical analysis of a correlation matrix revealed the strength of relationships between nine variables, including outer diameter (mm), inner diameter (mm), percentage of sponge layer (%), pore size (nm), maximum pore size (nm), mechanical strength (MPa), surface porosity (m−1), overall porosity (%), and CO2 absorption flux (mol m−2 s−1). Building upon these findings, this study unveils a novel non-linear function linking three specific microscopic characteristics— pore size, surface porosity, and a geometric sponge layer factor—to CO2 absorption flux, offering valuable insights for optimizing hydrophobic A-HFM design and enhancing CO2 capture efficiency. The A-HFM, characterized by the combination of three factors (higher pore size, increased surface porosity, and a thicker sponge layer), achieved a CO2 absorption flux of 6.36 ×10−3 mol m−2 s−1 at room temperature, showcasing its exceptional performance in capturing CO2. The resulting empirical morphological factor provides a novel approach for enhancing the performance of CO2 absorption through A-HFM design optimization.

3D models guide the design of hollow fiber membrane contactors with complex internal structures for CO2 capture

AbstractMembrane contactors have good prospects in the field of CO2 capture. In this study, the effects of operation conditions (gas velocity, liquid flow, CO2 pressure, amine concentration, and CO2 loading) on CO2 absorption flux (JCO2) for CO2 absorption into N‐methyl‐4‐piperidinol (MPDL) solution in membrane contactors were investigated through experiments and simulations. A three‐dimensional (3D) model was developed using COMSOL Multiphysics software to study the comprehensive CO2 mass transfer process in the multifiber membrane contactor and the effect of the number of fibers on the flow and CO2 concentration distribution without simplifying the geometry compared with those of traditional one‐dimensional (1D) and two‐dimensional (2D) models. Non‐ideal effects occurring in hollow fiber membrane contactors can be explained using a 3D modeling. By comparing the simulated with the experimental , the effectiveness of the model was determined. The simulation results emphasize that the spatial concentration distribution has a great correlation with the corresponding velocity distribution. Additionally, reducing the uneven velocity distribution of gas and liquid is a very important factor to improve the mass transfer performance of CO2. Increasing the number of fibers with a constant total volumetric flux can reduce the thickness of the boundary layer and promote the mass transfer.

Investigation of CO2 Absorption Rate in Gas/Liquid Membrane Contactors with Inserting 3D Printing Mini-Channel Turbulence Promoters.

The CO2 absorption by Monoethanolamine (MEA) solutions as chemical absorption was conducted in the membrane gas absorption module with inserting 3D mini-channel turbulence promoters of the present work. A mathematical modeling of CO2 absorption flux was analyzed by using the chemical absorption theory based on mass-transfer resistances in series. The membrane absorption module with embedding 3D mini-channel turbulence promoters in the current study indicated that the CO2 absorption rate improvement is achieved due to the diminishing concentration polarization effect nearby the membrane surfaces. A simplified regression equation of the average Sherwood number was correlated to express the enhanced mass-transfer coefficient of the CO2 absorption. The experimental results and theoretical predictions showed that the absorption flux improvement was significantly improved with implementing 3D mini-channel turbulence promoters. The experimental results of CO2 absorption fluxes were performed in good agreement with the theoretical predictions in aqueous MEA solutions. A further absorption flux enhancement up to 30.56% was accomplished as compared to the results in the previous work, which the module was inserted the promoter without mini channels. The influences of the MEA absorbent flow rates and inlet CO2 concentrations on the absorption flux and absorption flux improvement are also illustrated under both concurrent- and countercurrent-flow operations.

Enhancing performance of ceramic membrane in CO2 membrane absorption: Single-to multi-channel

Membrane absorption technology has received high attention for CO2 capture, but the brittleness of ceramic membranes limits its miniaturization. Here, founding that ceramic membrane with multi-channel geometry can not only have high specific surface area but also maintain high mechanical strength with small size. In this work, a four-channel ceramic membrane was used to test and compare performance with several single-channel membranes. This four-channel membrane had highest CO2 absorption flux of 4.83 mol m−3 s−1 and KOG of 1.26 mm s−1 among them. Then membrane phase resistance and its contribution to overall mass transfer resistance were analyzed to evaluate the impact of the membrane thickness or geometry. Owing to the undetermined thickness of multi-channel membrane, the absorption performance equivalent thickness was obtained through the simulation to be 0.23 mm using 2 M MEA. Moreover, a preliminary geometric design was attempted and CO2 absorption performances of different multi-channel membranes were compared based on above model.

Facile fabrication of FAS-PDMS/PEEK composite hollow fiber membrane with honeycomb-like structure for CO2 capture from flue gas by membrane absorption

In this study, as an efficient technology membrane absorption was applied with newly developed polyetheretherketone (PEEK) hollow fiber membrane (HFM) to remove CO2 from flue gas. To alleviate membrane wetting issue, 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS) was integrated into polydimethylsiloxane (PDMS) and then crosslinked FAS-PDMS was coated on porous PEEK membranes to prepare composite membranes. Surface characterization verified that PDMS layer containing fluoroalkylsilane had been successfully formed on membrane surface. As mass ratio of FAS to PDMS in coating solution raised, an interesting honeycomb-like structure was observed dispersing on composite membrane surface. Meanwhile, water contact angle was improved from 90.0° to 133.5° indicating enhanced membrane hydrophobicity. The effects of gas and liquid flow velocities on CO2 absorption performance of FAS-PDMS/PEEK HFM were systematically studied. The highest CO2 removal efficiency of 99.6% was achieved when gas and liquid velocity were 0.027 and 0.019 m s−1. When gas velocity raised to 0.110 m s−1, the maximum absorption flux of 1.22 × 10-4 mol m−2 s−1 and overall mass-transfer coefficient of 2.69 × 10−5 m s−1 could be obtained. Compared with the original membrane, the CO2 absorption flux of FAS-PDMS-0.6 HFM was increased by 50.9%, and the performance had no degradation in 36 h test. This study provides a novel strategy to alleviate the membrane wetting problem during CO2 membrane absorption process.

Reusability of Discarded Tubular Ceramic Membranes for CO2 Removal: A Case Study for Membrane Circularity.

Discarded polymeric or ceramic membranes are currently in need of appropriate and sustainable management. In the present study, the direct reuse of discarded ceramic membranes in membrane contactor (MC) systems for CO2 removal was investigated for the first time. The hydrophobic surface modification of the discarded ceramic membrane was done by using macromolecule additive coating. The influence of operational parameters (absorbent liquid flow rate (QL), feed gas flow rate (Qg), and different NaOH concentrations) of the MC on CO2 removal was investigated to prove the technical feasibility of reused ceramic membranes. The CO2 absorption flux was 7.9 × 10-4 mol/m2 s at optimal conditions of 2 M NaOH, QL (20 mL/min), and Qg (300 mL/min) with a removal efficiency of 98%, which lasted for 8 h. This study demonstrates a potential alternative for the reuse of discarded ceramic membranes and avoids their disposal in landfills. The proposed approach will also bring membrane technology into the circular economy and achieve sustainability goals by reducing the amount of waste from discarded ceramic membranes in the future and combating global warming by absorbing CO2.

Functionalized cross-linking mechanism of biochar “adsorption-reaction microunit” on the promotion of new ammonia-based CO2 capture

Ammonia-based CO2 capture technology has crucial impacts on power plants carbon emission reduction, which has become one of the most concerning issues. However, there are limitations faced by traditional capture technology in the absorption rate, ammonia escape and regeneration energy consumption. The functionalized biochar (with a specific surface area of up to 2835.36 m2/g, micropores volume of 77.4 %) was used to enhance the mass transfer process of new ammonia-based (ammonia-ethanol mixed absorbent) CO2 capture by the bubbling absorption experiment system, combined with Monte Carlo simulations, which explored the adsorption and release characteristics of CO2/NH3 molecules in biochar with different pore sizes. The results show that the CO2 absorption flux added biochar RH-900 is 59.67 L·min, increased by 16.16 % compared with pure absorbent. And the volume mass transfer coefficient is 1.226 × 10-4mol/m2·s·Pa, increased by 15.3 % compared with the SiO2. The addition of RH-900 also promotes the CO2 load capacity of the carbonated solution up to 0.5255 mol/L, enhancing the CO2 absorption capacity and CO2 capture efficiency significantly. The ultra-micropores adsorb CO2, while the surface of larger pores distributes and achieves the adequate fixation of NH3. Besides, the mesopores and macropores provide space where the CO2 is transported and diffused, and the free ammonia concentration is maintained. The study provides an innovative thought for improving the ammonia-based CO2 capture method and significantly reducing of harmful carbon emissions by biomass energy-carbon capture and storage (BECCS) technology.

Investigation on the Performance of CO2 Absorption in Ceramic Hollow-Fiber Gas/Liquid Membrane Contactors.

The absorption efficiencies of CO2 in ceramic hollow-fiber membrane contactors using monoethanolamine (MEA) absorbent under both cocurrent- and countercurrent-flow operations were investigated theoretically and experimentally; various MEA absorbent flow rates, CO2 feed flow rates, and inlet CO2 concentrations were used as parameters. Theoretical predictions of the CO2 absorption flux were analyzed by developing the mathematical formulations based on Happel's free surface model in terms of mass transfer resistances in series. The experiments of the CO2 absorption were conducted by using alumina (Al2O3) hollow-fiber membranes to confirm the accuracy of the theoretical predictions. The simplified expression of the Sherwood number was formulated to calculate the mass transfer coefficient of the CO2 absorption incorporating experimental data. The data were obtained numerically using the fourth-order Runge-Kutta method to predict the concentration distribution and absorption rate enhancement under various fiber packing configurations accomplished by the CO2/N2 stream passing through the fiber cells. The operations of the hollow-fiber membrane contactor encapsulating N = 7 fiber cells and N = 19 fiber cells of different packing densities were fabricated in this work to examine the device performance. The accuracy derivation between experimental results and theoretical predictions for cocurrent- and countercurrent-flow operations were 1.31×10-2≤E≤4.35×10-2 and 3.90×10-3≤E≤2.43×10-2, respectively. A maximum of 965.5% CO2 absorption rate enhancement was found in the module with embedding multiple fiber cells compared with that in the device with inserting single-fiber cell. Implementing more fiber cells offers an inexpensive method of improving the absorption efficiency, and thus the operations of the ceramic hollow-fiber membrane contactor with implementing more fiber cells propose a low-priced design to improve the absorption rate enhancement. The higher overall CO2 absorption rate was achieved in countercurrent-flow operations than that in cocurrent-flow operations.

Preparation and characterization of PPO/ SiO2 mixed matrix membrane for CO2 separation using membrane contactor

This study presents CO2 separation using PPO/SiO2 mixed matrix membranes (MMMs) in a membrane contactor. The non-solvent induced phase separation (NIPS) method was used to prepare flat sheet membranes using a commercial grade of PPO (polyphenylene oxide) polymer and 2-Ethyl-1-hexanol as a non-solvent additive. Mixed matrix membranes were fabricated via two approaches; adding the hydrophobic silica into casting solution (approach 1) and into coagulation bath (approach 2). The results showed that the addition of 2-ethyl-1-hexanol (5wt%) to the casting solution improved the membrane porosity by 74.7% while reducing the contact angle from 106.3 to 95.2°. Water contact angle of prepared MMMs by approaches 1 and 2 were found to be around 117.8 and 142.9°, respectively indicating that silica could enhance the membrane hydrophobicity in both methods. The maximum CO2 absorption flux and removal efficiency were attained about 5.8 × 10−3 (mol.m−2.s−1) and 64.8 % for MMM with 2 wt.% silica in approach 1. Meanwhile, MMM obtained with silica content (2 g.L−1) from approach 2, indicated CO2 flux of 5 × 10−3 (mol.m−2.s−1) and removal efficiency around 55.8 %. The long-term performance of prepared MMMs was evaluated during 20 days of operation. The results confirmed the long term stability of prepared samples and good interaction between the silica particles and the PPO polymer in scenario of approach 2.

Study on robust absorption performance of hydrophilic membrane contactor for direct air capture

Increased atmospheric carbon dioxide (CO2) concentration constitutes a growing environmental and health concern. The absorption of CO2 from air requires a large gas–liquid contact area due to low driving force. Here, the membrane absorption was proposed to the removal of atmospheric CO2 using a ceramic membrane contactor, while NaOH serves as absorbent, performance of ceramic membrane absorption was study. In hydrophilic membrane, NaOH concentration of 2 mol⋅L−1 has the best absorption performance, which serves as initial concentration in absorption cyclic process, and when NaOH utilization reaches 75 %, it still has great absorption performance. In addition, suitable gas and liquid operating parameters of this work were also confirmed as 1000 mL⋅min−1 and 1 mL⋅min−1, respectively, corresponding mass transfer coefficient and CO2 absorption flux is 2.6 mm⋅s−1 and 0.096 mol⋅m−2⋅h−1, respectively. The great absorption stability shows the huge potential of ceramic membrane contactor application for direct air capture.

Development of opposing surface wettability PVDF membrane to improve CO2 capture in membrane gas absorption

Membrane gas absorption (MGA) is a hybrid CO2 capture technology. However, the membrane wetting problem and the low CO2 permeability membrane constraint the MGA performance. Therefore, the development of PVDF membrane with opposing surface wettability is significant to increase the CO2 absorption performance. In this work, superhydrophobic membrane was first synthesised by templated method. The patterned surface of the membrane (tPVDF) demonstrated water contact angle (WCA) 152° and sliding angle (SA) 8.6°. Then, the opposite surface of the patterned surface was modified with ethylenediamine (tPVDF/EDA) and polydopamine (tPVDF/PDA). From the FTIR analysis, tPVDF/EDA and tPVDF/PDA have successfully deposited with amine and hydroxyl functional groups. By comparing with tPVDF, tPVDF/EDA and tPVDF/PDA showed smaller membrane average pore size of 0.29um and 0.25um respectively. However, the surface porosity of the membranes is almost unchanged at 50 % (tPVDF), 48 % (tPVDF/EDA) and 47 % (tPVDF/PDA). In the MGA performance, tPVDF/EDA and tPVDF/PDA improved CO2 absorption flux to 0.088 and 0.090 mol/m2s respectively from 0.005 mol/m2s. The results indicates that the improvement of MGA performance was mainly due to the NH2 and OH functional groups deposited on the membrane surface that enhanced the membrane affinity to polar CO2 and the superhydrophobic patterned surface inhibited the intrusion of absorbent into membrane pores. The CO2 absorption flux obtained in the work is reasonably good and comparable to the literatures.

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.

Simulation Assessment of Inlet Parameters and Membrane-Surface-Structure Effects on CO2 Absorption Flux in Membrane Contactors

The management of global carbon dioxide (CO2) emissions is considered one of the main environmental problems facing the modern world. One of the potential techniques for CO2 capture is absorption, using membrane contactor modules. Most of the previous research that dealt with membrane contactor simulations considered the whole membrane surface as the active reaction surface. However, in this paper, a more realistic model of the membrane-contactor module is presented, taking into account the effects of the pore size and surface porosity. CO2 absorption into the monoethanolamine (MEA) solution in hollow fiber membrane-contactor modules was numerically investigated. A computational fluid dynamics simulation was established using essential basic fluid dynamics and mass transfer equations in reactive mode. An algorithmic function was used to present the relations between the CO2 absorption flux and the hollow fiber length, membrane surface pore size, and porosity. The simulation results were compared to previously obtained experimental results without using any fitting parameters, and a good agreement was found with an average error of 8.5%. The validated simulation was then used to predict the effects of the MEA inlet velocity and concentration, the membrane surface pore size, and porosity on the total CO2 absorption flux. A maximum absorption flux of about 1.8 mol/m2·s was achieved at an MEA concentration of 4 M with a pore size of 0.2 microns, a surface porosity of 1%, and an inlet velocity of 0.25 m/s. The extrapolation technique was then used to predict the values of the absorption flux at longer fiber lengths. The concentration profiles around the pores at the gas–liquid contact surface of the membrane were obtained and presented. The proposed model exhibited excellent potential to evaluate the effective reaction surface in hollow fiber membrane contactors. This model could be considered the first step to obtaining accurate predictions of the membrane contactor gas absorption performance based on its surface structure.

CO2 absorption using benzylamine as absorbent and promoter in a hollow fiber membrane contactor: A numerical study

Benzylamine (BZA) is a novel amine that indicates a promising potential for CO2 absorption. In this work, a mathematical model has been presented to investigate the CO2 absorption using aqueous BZA compared to aqueous monoethanolamine (MEA), diethanolamine (DEA), and 4-diethylamino-2-butanol (DEAB) in a hollow fiber membrane contactor (HFMC). Several factors such as CO2 partial pressure, amine concentration, gas velocity, liquid velocity, temperature, wettability, and mass transfer resistance of phases have been studied. According to the results, increment in the amine concentration, CO2 partial pressure, liquid velocity, gas velocity, and temperature have enhanced the CO2 absorption flux. Also, adding BZA to aqueous MDEA and K2CO3 significantly increases the CO2 absorption flux in both solutions. Moreover, the mass transfer resistance of individual phases reveals that the liquid phase mass transfer resistance is the controlling phase in non-wetted mode, while with membrane wetting, contribution of membrane side mass transfer resistance increases and become the controlling phase. In general, BZA could be a prominent potential choice as absorbent and promoter for CO2 absorption in HFMCs.

Thermally rearranged nanofibrous composite membranes for carbon dioxide absorption and stripping

We develop thermally rearranged (TR) nanofibre membranes for the capture of CO2 using membrane gas absorption. The porous nature of the electrospun nanofibre membranes and the hydrophobicity of the TR polymers provide ideal properties for both CO2 absorption and stripping. The use of thermal rearrangement after fabricating the nanofibre composite structures (TR-NFM) also interconnects the nanofibres and greatly improves mechanical strength. Surface hydrophobicity is further increased by electrospraying of nanoparticles onto the nanofibre membrane surface to increase roughness (TR-NCM), leading to higher breakthrough pressures and stable CO2 stripping performance for up to 270 h at 100 °C without membrane wetting. The TR-NFM and TR-NCM membranes both show an order of magnitude increase in CO2 absorption flux compared to a standard polytetrafluoroethylene (PTFE) membrane, offering strong potential for commercial application.

Cyclic olefin polymer membrane as an emerging material for CO2 capture in gas-liquid membrane contactor

Porous flat sheet membranes were prepared with a commercial grade of cyclic olefin polymer (COP) for CO2 capture using membrane contactor (MC). The membranes were prepared via non-solvent induced phase separation technique using different types of additives, namely, polyvinylpyrrolidone (PVP), polyethylene glycol (PEG400) and sorbitan monooleate (Span 80), and coagulants (acetone and 70/30 wt% acetone/water mixture) were investigated. The prepared membranes were characterized in terms of the thickness (70–85 µm), porosity (50–80%), mean pore size (158–265 nm), bubble pore size (~ 0.6–12 µm), liquid entry pressure (1.67–4.55 bar), water contact angle (~ 94° - 111°), monoethanolamine (MEA) contact angle (~ 67° - 73°) and mechanical properties (tensile strength: 4.53 – 5.15 MPa, elongation at break: 4 – 8% and Young´s modulus: 190 – 232 MPa). The thermodynamic study of COP membranes proved that a fast phase inversion of the proposed system resulted in a more porous structure. The addition of PEG400 and Span 80 caused delayed demixing and influenced the morphological structure and MC performance. The structural and topographical characteristics of the membranes were also studied. The CO2 absorption test performed at 27 °C showed that the maximum CO2 absorption flux was around 16 × 10−5 mol/m2.s using 1 M MEA aqueous solution as absorbent with fixed liquid and gas flow rates at 150 L/h and 8.4 L/h, respectively. It was found that the considered additives enhanced the MC performance and affected the CO2 absorption flux.

Theoretical and Experimental Studies of CO2 Absorption in Double-Unit Flat-Plate Membrane Contactors.

Theoretical predictions of carbon dioxide absorption flux were analyzed by developing one-dimensional mathematical modeling using the chemical absorption theory based on mass-transfer resistances in series. The CO2 absorption into monoethanolamine (MEA) solutions was treated as chemical absorption, accompanied by a large equilibrium constant. The experimental work of the CO2 absorption flux using MEA solution was conducted in double-unit flat-plate membrane contactors with embedded 3D turbulence promoters under various absorbent flow rates, CO2 feed flow rates, and inlet CO2 concentrations in the gas feed stream for both concurrent and countercurrent flow operations. A more compact double-unit module with embedded 3D turbulence promoters could increase the membrane stability to prevent flow-induced vibration and enhance the CO2 absorption rate by overwhelming the concentration polarization on the membrane surfaces. The measured absorption fluxes with a near pseudo-first-order reaction were in good agreement with the theoretical predictions for the CO2 absorption efficiency in aqueous MEA solutions, which was shown to be substantially larger than the physical absorption in water. By embedding 3D turbulence promoters in the MEA feed channel, the new design accomplishes a considerable CO2 absorption flux compared with an empty channel as well as the single unit module. This demonstrates the value and originality of the present study regarding the technical feasibility. The absorption flux enhancement for the double-unit module with embedded 3D turbulence promoters could provide a maximum relative increase of up to 40% due to the diminution in the concentration polarization effect. The correlated equation of the average Sherwood number was obtained numerically using the fourth Runge–Kutta method in a generalized and simplified expression to calculate the mass transfer coefficient of the CO2 absorption in the double-unit flat-plate membrane contactor with turbulence promoter channels.