Hollow fiber gas-liquid membrane contactors for acid gas capture: a review

External ceramic membrane contactor for in-situ H2 assisted biogas upgrading

Biological H2-assisted biogas upgrading has gained significant attention as an environmentally friendly substitute to common physico-chemical upgrading techniques, but is largely limited by the low solubility of H2. This study evaluated the design of a ceramic membrane contactor module for H2 injection. H2 dissolution was maintained at high efficiency by controlling gas supply and sludge recirculation rate, achieving a biogas quality of average 98.8% CH4 during the stable operation phase with a 108% increase in the CH4 production rate. This also outperforms conventional H2 injection using diffuser sparging which could only achieve a biogas quality of 84% CH4 content. Microbial community analysis found high Methanobacterium spp. abundance within the archaea at 95.2% at the end of the operation, allowing the dominance of the hydrogenotrophic methanogenesis pathway for high upgrading efficiencies. The system is a high-performance external membrane connector module coupled to common anaerobic digestion systems for biogas upgrading.

Graphene Oxide Enhanced Monoethanolamine and Ethylenediamine Nanofluids for Efficient Carbon Dioxide Uptake from Flue Gas

The addition of nanoparticles in amine solutions to produce a stable amine-based nanofluid provides a high surface area for absorption and improves the absorption rate. In this work, nanofluids were prepared by dispersing graphene oxide (GO) in monoethanolamine (MEA) and ethylenediamine (EDA) solutions for adsorption of carbon dioxide (CO2) to further improve their absorption performance by providing more reaction sites on the GO framework. GO was synthesized using the modified Hummers method and characterized for physicochemical properties using SEM, EDS, FTIR, Raman analysis, and TGA. The FTIR spectra for the GO nanoparticles before absorption showed peaks attributed to C-C, H-C, and C-O bonding. After the absorption experiments, the FTIR spectra of GO showed peaks due to C-O-NH2, N-O-N, and N-H bonding. The BET analysis further confirmed the decrease in the surface area, pore volume, and pore diameter of the GO recovered from the nanofluids after the CO2 experiment, indicating an interaction between GO and amine molecules. The absorption process of CO2 by the nanofluid was performed in a custom-made pressure chamber whereby the CO2 gas was in direct contact with the absorption fluids. The obtained adsorption rate constant (k) for the reaction between CO2 and 30% MEA and EDA solutions was 0.113 and 0.131, respectively. Upon addition of 0.2 mg/mL GO in the base solution, k increased to 0.16854 and 0.17603 for the MEA and EDA nanofluids, respectively. The proposed mechanism involves GO nanoparticles interacting with the amine groups through the oxygen-rich groups of GO. This results in the formation of a zwitterion that readily reacts with CO2, resulting in a carbamate.

Modeling, Simulation, and Membrane Wetting Estimation in Gas-Liquid Contacting Processes Including Shell-Side Reaction: Biogas Upgrading Using DEA Solution

The basic principles of a steady-state mass transfer model and the resistance-in-series film model are assessed with the aid of a series of experiments in a gas-liquid contact membrane mini-module (3 M Liqui-Cel MM-1.7 × 5.5) using an aqueous solution of diethanolamine (DEA) of 0.25 M (mol/L) for biogas upgrading. Experimental data show that CO2 removal may exceed 67% and reach 100% in combination with the highest possible recovery of CH4 when employing biogas flow rates in the range of 2.8 × 10-5 - 3.6 × 10-5 m3/s and solvent flow rates within 0.47 × 10-5 - 0.58 × 10-5 m3/s. For the experimental data set, a correlation has been developed, effectively interpolating CO2 removal with the gas and liquid flow rates. The wetting values calculated are concentrated close to each other for the same liquid flow rate without considerably depending on the gas flow rate, especially when applying the Hikita-Yun (reaction rate-shell-side correlation) compared with the Hikita-Costello pair. Furthermore, the calculated wetting diminishes with increasing liquid flow rate, a result that is consistent with previous modeling attempts and relevant literature indications. The assumption of enhanced mass transfer in the liquid-filled part of the membrane pores due to the reaction is scrutinized, leading to objectionable computational wetting values. It is shown that for a concentration of DEA equal to 0.25 M the Hatta numbers and the enhancement factors are not equal in the whole reaction path; thus, the choice of the shell-side correlation has an appreciable impact on the overall analysis, especially for the determination of the wetting values.

3D-CFD Modeling of Hollow-Fiber Membrane Contactor for CO2 Absorption Using MEA Solution

Membrane technology is considered an innovative and promising approach due to its flexibility and low energy consumption. In this work, a comprehensive 3D-CFD model of the Hollow-Fiber Membrane Contactor (HFMC) system for CO2 capture into aqueous MEA solution, considering a counter-current fluid flow, was developed and validated with experimental data. Two different flow arrangements were considered for the gas mixture and liquid solution inside the HFMC module. The simulation results showed that the CO2 absorption efficiency was considerably higher when the gas mixture was channeled through the membranes and the liquid phase flowed externally between the membranes, across a wide range of gas and liquid flow rates. Sensitivity studies were performed in order to determine the optimal CO2 capture process parameters under different operating conditions (flow rates/flow velocities and concentrations) and HFMC geometrical characteristics (e.g., porosity, diameter, and thickness of membranes). It was found that increasing the membrane radius, while maintaining a constant thickness, positively influenced the efficiency of CO2 absorption due to the higher mass transfer area and residence time. Conversely, higher membrane thickness resulted in higher mass transfer resistance. The optimal membrane thickness was also investigated for various inner fiber diameters, resulting in a thickness of 0.2 mm as optimal for a fiber inner radius of 0.225 mm. Additionally, a significant improvement in CO2 capture efficiency was observed when increasing membrane porosity to values below 0.2, at which point the increase dampened considerably. The best HFMC configuration involved a combination of low porosity, moderate thickness, and large fiber inner diameter, with gas flow occurring within the fiber membranes.

Unveiling the potential of membrane in climate change mitigation and environmental resilience in ecosystem

Carbon capture technologies are becoming increasingly crucial in addressing global climate change issues by lowering CO2 emissions from industrial and power generation activities. Post-combustion carbon capture, which uses membranes instead of adsorbents, has emerged as one of promising and environmentally friendly approaches among these technologies. The operation of membrane technology is based on the premise of selectively separating CO2 from flue gas emissions. This provides a number of different benefits, including improved energy efficiency and decreased costs of operation. Because of its adaptability to changing conditions and its low impact on the surrounding ecosystem, it is an appealing choice for a diverse array of uses. However, there are still issues to be resolved, such as those pertaining to establishing a high selectivity, membrane degradation, and the costs of the necessary materials. In this article, we evaluate and explore the prospective applications and roles of membrane technologies to control climate change by post-combustion carbon capturing. The primary proposition suggests that the utilization of membrane-based carbon capture has the potential to make a substantial impact in mitigating CO2 emissions originating from industrial and power production activities. This is due to its heightened ability to selectively absorb carbon, better efficiency in energy consumption, and its flexibility to various applications. The forthcoming challenges and potential associated with the application of membranes in post-carbon capture are also discussed.

Numerical Simulation of Membrane Separation Characteristics of Supercritical Carbon Dioxide and Water

To solve the problem of water carryover in the supercritical CO2 separation and mining process in the CO2 plume geothermal system, a three-dimensional shell-tube hollow fiber membrane absorption separator is designed in this study. A coupled species transport model, a porous medium model, and an absorption mathematical model are established, and the flow field and separation characteristics in the circular and flat tubes are analyzed using numerical simulation. The results show that the membrane separation efficiency increases with an increase in the flatness and membrane tube length. When the inlet velocity of the mixture is 0.1 m/s, the separation efficiency can reach 75.92%. Selecting a smaller flow Reynolds number and a more significant membrane tube flatness will reduce the water mass fraction at the outlet. When adding baffles of different shapes to the membrane tube, the mixture fluid in the membrane tube meanders forward and flows in the shape of "Z" under the blocking effect of the arcuate baffles. With an increase in the number of arcuate baffles in the membrane tube, the membrane separation efficiency of the separator increases continuously. The mixture fluid flows in the membrane tube with the built-in torsional baffles in a spiral manner, and the separation efficiency of the membrane separator increases with a torsion ratio reduction in the membrane tube.

A critical review in recent progress of hollow fiber membrane contactors for efficient CO2 separations

Among wide range of membrane-based operations, membrane contactors, as they reify comparatively modern membrane-based mechanism are gaining quite an attention in both pilot and industrial scales. In recent literature, carbon capture is one of the most researched applications of membrane contactors. Membrane contactors have the potential to minimize the energy consumption and capital cost of traditional CO₂ absorptions columns. In a membrane contactor, CO₂ regeneration can take place below the solvent boiling point, resulting into lower consumption of energy. Various polymeric as well as ceramic membrane materials have been employed in gas liquid membrane contactors along with several solvents including amino acids, ammonia, amines etc. This review article provides detailed introduction of membrane contactors in terms of CO₂ removal. It also discusses that the main challenge that is faced by membrane contactors is membrane pore wetting caused by solvent that in turn can reduce the mass transfer coefficient. Other potential challenges such as selection of suitable solvent and membrane pair as well as fouling are also discussed in this review and are followed by potential ways to reduce them. Furthermore, both membrane gas separation and membrane contactor technologies are analysed and compared in this study on the basis of their characteristics, CO₂ separation performances and techno economical transvaluation. Consequently, this review provides an opportunity to thoroughly understand the working principle of membrane contactors along its comparison with membrane-based gas separation technology. It also provides a clear understanding of latest innovations in membrane contactor module designs as well as challenges encountered by membrane contactors along with possible solutions to overcome these challenges. Finally, semi commercial and commercial implementation of membrane contactors has been highlighted.

Nanoparticle-Embedded Polymers and Their Applications: A Review

There has been increasing interest in the study and development of nanoparticle-embedded polymeric materials and their applications to special membranes. Nanoparticle-embedded polymeric materials have been observed to have a desirable compatibility with commonly used membrane matrices, a wide range of functionalities, and tunable physicochemical properties. The development of nanoparticle-embedded polymeric materials has shown great potential to overcome the longstanding challenges faced by the membrane separation industry. One major challenge that has been a bottleneck to the progress and use of membranes is the balance between the selectivity and the permeability of the membranes. Recent developments in the fabrication of nanoparticle-embedded polymeric materials have focused on how to further tune the properties of the nanoparticles and membranes to improve the performance of the membranes even further. Techniques for improving the performance of nanoparticle-embedded membranes by exploiting their surface characteristics and internal pore and channel structures to a significant degree have been incorporated into the fabrication processes. Several fabrication techniques are discussed in this paper and used to produce both mixed-matrix membranes and homogenous nanoparticle-embedded polymeric materials. The discussed fabrication techniques include interfacial polymerization, self-assembly, surface coating, and phase inversion. With the current interest shown in the field of nanoparticle-embedded polymeric materials, it is expected that better-performing membranes will be developed soon.

A Simplified Kinetic Modeling of CO2 Absorption into Water and Monoethanolamine Solution in Hollow-Fiber Membrane Contactors

The absorption of CO₂ from CO₂-N₂ gas mixtures using water and monoethanolamine (MEA) solution in polypropylene (PP) hollow-fiber membrane contactors was experimentally and theoretically examined. Gas was flowed through the lumen of the module, whereas the absorbent liquid was passed counter-currently across the shell. Experiments were carried out under various gas- and liquid-phase velocities as well as MEA concentrations. The effect of pressure difference between the gas and liquid phases on the flux of CO₂ absorption in the range of 15-85 kPa was also investigated. A simplified mass balance model that considers non-wetting mode as well as adopts the overall mass-transfer coefficient evaluated from absorption experiments was proposed to follow the present physical and chemical absorption processes. This simplified model allowed us to predict the effective length of the fiber for CO₂ absorption, which is crucial in selecting and designing membrane contactors for this purpose. Finally, the significance of membrane wetting could be highlighted by this model while using high concentrations of MEA in the chemical absorption process.

Computational fluid dynamics comparison of prevalent liquid absorbents for the separation of SO2 acidic pollutant inside a membrane contactor

In recent years, the emission of detrimental acidic pollutants to the atmosphere has raised the concerns of scientists. Sulphur dioxide (SO₂) is a harmful greenhouse gas, which its abnormal release to the atmosphere may cause far-ranging environmental and health effects like acid rain and respiratory problems. Therefore, finding promising techniques to alleviate the emission of this greenhouse gas may be of great urgency towards environmental protection. This paper aims to evaluate the potential of three novel absorbents (seawater (H₂O), dimethyl aniline (DMA) and sodium hydroxide (NaOH) to separate SO₂ acidic pollutant from SO₂/air gaseous stream inside the hollow fiber membrane contactor (HFMC). To reach this goal, a CFD-based simulation was developed to predict the results. Also, a mathematical model was applied to theoretically evaluate the transport equations in different compartments of contactor. Comparison of the results has implied seawater is the most efficient liquid absorbent for separating SO₂. After seawater, NaOH and DMA are placed at the second and third rank (99.36% separation using seawater > 62% separation using NaOH > 55% separation using DMA). Additionally, the influence of operational parameters (i.e., gas and liquid flow rates) and also membrane/module parameters (i.e., length of membrane module, hollow fibers' number and porosity) on the SO₂ separation percentage is investigated as another highlight of this paper.

A state-of-the-art review on capture and separation of hazardous hydrogen sulfide (H2S): Recent advances, challenges and outlook

Hydrogen sulfide (H₂S) is a flammable, corrosive and lethal gas even at low concentrations (ppm levels). Hence, the capture and removal of H₂S from various emitting sources (such as oil and gas processing facilities, natural emissions, sewage treatment plants, landfills and other industrial plants) is necessary to prevent and mitigate its adverse effects on human (causing respiratory failure and asphyxiation), environment (creating highly flammable and explosive environment), and facilities (resulting in corrosion of industrial equipment and pipelines). In this review, the state-of-the-art technologies for H₂S capture and removal are reviewed and discussed. In particular, the recent technologies for H₂S removal such as membrane, adsorption, absorption and membrane contactor are extensively reviewed. To date, adsorption using metal oxide-based sorbents is by far the most established technology in commercial scale for the fine removal of H₂S, while solvent absorption is also industrially matured for bulk removal of CO₂ and H₂S simultaneously. In addition, the strengths, limitations, technological gaps and way forward for each technology are also outlined. Furthermore, the comparison of established carbon capture technologies in simultaneous and selective removal of H₂S-CO₂ is also comprehensively discussed and presented. It was found that the existing carbon capture technologies are not adequate for the selective removal of H₂S from CO₂ due to their similar characteristics, and thus extensive research is still needed in this area.

Emerging Trends in Porogens toward Material Fabrication: Recent Progresses and Challenges

Fabrication of tailor-made materials requires meticulous planning, use of technical equipments, major components and suitable additives that influence the end application. Most of the processes of separation/transport/adsorption have environmental applications that demands a material to be with measurable porous nature, stability (mechanical, thermal) and morphology. Researchers say that a vital role is played by porogens in this regard. Porogens (i.e., synthetic, natural, mixed) and their qualitative and quantitative influence on the substrate material (polymers (bio, synthetic), ceramic, metals, etc.) and their fabrication processes are summarized. In most cases, porogens critically influence the morphology, performance, surface and cross-section, which are directly linked to material efficiency, stability, reusability potential and its applications. However, currently there are no review articles exclusively focused on the porogen pores' role in material fabrication in general. Accordingly, this article comprises a review of the literature on various types of porogens, their efficiency in different host materials (organic, inorganic, etc.), pore size distribution (macro, micro and nano), their advantages and limitations, to a certain extent, and their critical applications. These include separation, transport of pollutants, stability improvement and much more. The progress made and the remaining challenges in porogens' role in the material fabrication process need to be summarized for researcher's attention.

Effects of Operating and Structural Parameters on Removal of Nitric Oxide by Oxidation in a Ceramic Hollow Fiber Membrane Contactor

A numerical study on the oxidation removal of nitric oxide in a ceramic hollow fiber membrane contactor was performed. To represent the transport and absorption process, the model was created by combining multiphase, species, reaction, and porous models. The numerical results were verified by comparing them with experimental data. The tube and lumen sides both have laminar parabolic velocity distributions. The nitric oxide concentration decreases gradually from the membrane wall to axis at the cross-section except on the inner and outer sides of the membrane tube. The equivalent diffusion length was proved useful for evaluating the entrance effect. At low concentrations, the reduction efficiency was proportional to the absorbent concentration, and at large concentrations, it neared a maximum value. The reduction efficiency was positively affected by elevated operating temperature and pressure. With a gas channel width of 13 mm, the reduction flow rate achieves its maximum. The efficiency of NO reduction per area decreases as the effective membrane length increases. Increasing the operating temperature and membrane length are recommended as design priorities due to high relative enhancements. It is not recommended to improve reduction efficiency by increasing membrane tube diameter and operating pressure in design. Changing the gas flow rate, absorbent concentration and gas channel width are moderate recommended as well.

Removing of the Sulfur Compounds by Impregnated Polypropylene Fibers with Silver Nanoparticles-Cellulose Derivatives for Air Odor Correction

The unpleasant odor that appears in the industrial and adjacent waste processing areas is a permanent concern for the protection of the environment and, especially, for the quality of life. Among the many variants for removing substance traces, which give an unpleasant smell to the air, membrane-based methods or techniques are viable options. Their advantages consist of installation simplicity and scaling possibility, selectivity; moreover, the flows of odorous substances are direct, automation is complete by accessible operating parameters (pH, temperature, ionic strength), and the operation costs are low. The paper presents the process of obtaining membranes from cellulosic derivatives containing silver nanoparticles, using accessible raw materials (namely motion picture films from abandoned archives). The technique used for membrane preparation was the immersion precipitation for phase inversion of cellulosic polymer solutions in methylene chloride: methanol, 2:1 volume. The membranes obtained were morphologically and structurally characterized by scanning electron microscopy (SEM) and high resolution SEM (HR SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectrometry (FTIR), thermal analysis (TG, ATD). Then, the membrane performance process (extraction efficiency and species flux) was determined using hydrogen sulfide (H2S) and ethanethiol (C2H5SH) as target substances.

Molecular investigation into the effect of carbon nanotubes interaction with CO2 in molecular separation using microporous polymeric membranes

The use of nanofluids has been recently of great interest to separate acidic contaminants such as CO₂. The main objective of this research is to assess the influence of carbon nanotubes (CNTs) addition to distilled water on enhancing the CO₂ molecular separation through a porous membrane contactor (PMC). For this aim, a comprehensive model is developed based on non-wetted and counter-current operational modes to evaluate the principal mass and momentum transport equations in tube, membrane and shell compartments of PMC. Consequently, a CFD-based axisymmetrical simulation is implemented according to finite element technique (FET) to prognosticate the results. It is found from the results that the addition of 0.1 wt% carbon nanotubes (CNTs) particles to water significantly enhances the mass transfer and consequently the CO₂ molecular separation efficiency from 38 to 63.3%. This considerable enhancement can be justified due to the existence of two momentous phenomena including Brownian motion and Grazing effect, which enhance the mass transport of CO₂ molecules in the PMC. Moreover, the effect of CNTs concentration, some membrane's parameters such as number of hollow fibers and porosity and also some module's design parameters including module radius and length on the CO₂ separation performance are investigated in this paper as another highlight of the current work.

Determination of fast gas–liquid reaction kinetics in flow

A flow concept is developed to measure fast gas–liquid reaction kinetics based on a tube-in-tube reactor.

Carbon Dioxide (CO2) Fixation: Linearly Bridged Zn2 Paddlewheel Nodes by CO2 in a Metal-Organic Framework

When the reaction of zinc nitrate with 4',4‴,4‴″,4‴‴'-(ethene-1,1,2,2-tetrayl)tetrakis[(1,1'-biphenyl-3-carboxylic acid)] (H₄tmpe) in dimethylformamide (DMF) under hydrothermal condition is performed in air or carbon dioxide (CO₂), [Zn₄(tmpe)₂(H₂O)₂(μ₂-CO₂)]·8DMF·18H₂O (1) crystallizes out. However, if it is in dioxygen, argon, or carbon monoxide, [Zn₂(tmpe)(DMF)]·2DMF·8H₂O (2) is the product. Both compounds are chemically stable coordination polymers. 1 contains zinc carboxylate paddlewheels as nodes linearly bridged by CO₂ into two interpenetrating lattices, and 2 has an infinite single framework formed by a tetranuclear node. 1 is the second example containing the linear CO₂-bridged paddlewheel node. Interestingly, CO₂ fixation in a μ₂-η²_O,O bridging mode is observed in 1, which is rarely characterized structurally and has been confirmed using IR and gas chromatography analysis. The stability of 1 is further verified by density functional theory calculations, which found an energy minimum with a Zn-O═C angle of 180°. Both compounds display strong emission around 490 nm and excited-state lifetimes around 2.4 ns.

Mixed matrix membrane contactor containing core-shell hierarchical Cu@4A filler for efficient SO2 capture

Achieving high flux membrane contactor is significantly important for hazardous gas removal. In this study, we prepared poly(vinylidene fluoride) (PVDF)-based mixed matrix membrane contactor (MMMC) that contained a core-shell hirarchical Cu@4A composite filler (Cu@4A). On one hand, the Cu@4A regulated the physical structure of MMMC, which enhanced gas permeation and thus resulted in the increment of physical SO₂ absorption flux. On the other hand, Cu@4A changed the chemical environment of MMMC by remarkably increased SO₂ facilitated transport sites, which elevated SO₂ concentration around Cu@4A by the enhancement of adsorption and oxidation of SO₂, resulting in the increase of chemical SO₂ absorption flux. Moreover, the copper nanosheets on 4A helped to construct facilitated transport pathways along the Cu@4A fillers at polymer-filler interface. The results showed that Cu@4A loaded MMMC exhibited increased SO₂ removal efficiency and SO₂ absorption flux compared with PVDF control membrane. Specifically, the M₁₀⁴⁰ MMMC loaded with 40 wt% Cu@4A and PVDF concentration 10 wt% exhibited the highest SO₂ removal efficiency and SO₂ absorption flux, which was up to 73.6% and 9.1 × 10^-4 mol·m^-2·s^-1 at the liquid flow rate of 30 L/h. Besides, the overall SO₂ mass transfer coefficient (K_o) and membrane mass transfer resistance (H/K_m) were investigated.