CO2 Separation Process Research Articles

Electrochemical Conversion of Bicarbonate Using Proton Exchange Membrane-Based Electrolyzer

Direct electrochemical conversion of captured carbon dioxide (CO2) is gaining interest as an efficient method for capturing and utilizing CO2, eliminating the need for energy-intensive CO2 separation process.[1] The integrated electrolyzer with bicarbonate feed operates on the principle of spontaneous reduction of CO2 released from bicarbonate within the electrolyzer. The key to the on-site decomposition of bicarbonate into CO2 is to acidify the bicarbonate within the electrolyzer through the deliberately generated pH gradient. Bipolar membrane has been extensively used to generate pH gradient and acidify the bicarbonate feed.[2] However, the high ionic resistivity of bipolar membrane and slow kinetic of water dissociation reaction can result in a high operation cell voltage.In this study, we demonstrate proton exchange membrane based-bicarbonate electrolyzer which produces carbon monoxide from bicarbonate feedstock with high CO production selectivity and low cell voltage that are comparable to the conventional gas fed CO2 electrolyzer. To achieve highly selective CO production selectivity, a nickel single atom catalyst (Ni SAC) where the atomically dispersed nickel active sites decorated on the nitrogen doped carbon was prepared and utilized. Ni-SAC showed high CO production selectivity even in bicarbonate feed electrolyzer. To further improve the performance of this integrated electrolyzer, significant attention was given to the optimization of electrode structures. Due to the complexity of the reaction environment within the integrated electrolzyer, the performance of the electrolyzer is heavily dependent on the porosity of electrodes and distribution of catalyst on the electrodes. By optimizing the fabrication of electrodes with Ni-SACs, the optimal catalyst coated electrode showed high CO production selectivity over 90% with current density of 100 mA/cm2 at low operating cell potential of 3 V.

Hierarchically porous carbon foams coated with carbon nitride: Insights into adsorbents for pre-combustion and post-combustion CO2 separation

Adsorption is fundamental to many industrial processes, including separation of carbon dioxide from other gases in pre- or post-combustion gas mixtures. Adsorbents should have high capacity and selectivity, which are both intimately linked with surface area, pore size distribution, and surface energy. Porous carbons are cheap and scalable adsorbents, but greater understanding of how their textural properties and surface chemistry affects their performance is needed. Here, we investigate the effect of nitrogen doping on CO2 adsorption. Microporous carbon foams with large surface area (>2500 m2 g−1) and pore volume (1.6 cm3 g−1) are synthesized, then coated with varying amounts of carbon nitride (up to 17 at% nitrogen) to achieve high CO2 uptake (25.5 mmol g−1) and selectivity (CO2:N2 = 21), whilst also giving insights into the relationship between structure and function. At low pressure (relevant to post-combustion capture), moderate carbon nitride loading leads to enhanced uptake and selectivity by combining large ultramicropore volume with the introduction of Lewis base sites, leading to high isosteric heat of adsorption. Higher carbon nitride loading further increases selectivity but lowers uptake by blocking micropores. Conversely, at high pressure (relevant to pre-combustion capture) the uncoated carbon foam displays superior uptake, because mesoporosity is the dominant factor in this regime, rather than the presence of ultramicropores. Finally, the samples displayed excellent regeneration under repeated adsorption–desorption cycles, and breakthrough curves were measured. These results underscore the delicate balance required for optimal material design when applying porous carbon adsorbents to CO2 separation processes. Moving forward, improved adsorbents will contribute to the proliferation of carbon capture and storage (CCS) and carbon capture and utilisation (CCU) technologies, ultimately contributing reduced anthropogenic CO2 emissions.

Efficient CO2 capture over N2 in flexible MOFs: Pressure driven breathing effect

Developing efficient CO2 adsorbents is imperative to mitigate excessive CO2 emission. This study employs density functional theory (DFT), Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations to investigate CO2 capture performance in x-pcu-n via pressure-driven breathing effect at 195 K. The breathing effect is influenced by the ligand length and predominantly achieved through ligand twisting under 20–40 kPa. Longer ligands facilitate greater breathing effect, expanding dimensions by 1.04–1.24 times, thereby enhancing available space and exposing additional adsorption sites for selective CO2 uptake. The resulting capacities are measured at 10.48, 9.44, 9.30, and 5.23mmol/g, with CO2 over N2 selectivity of 1714.44, 1368.84, 1784.15, and 1224.59, respectively, in x-pcu-n (n = 4, 3, 2, and 1) at 100 kPa. This study elucidates the pressure-driven breathing effect and their applicability in CO2 capture and separation processes, offering theoretical insights for the development of efficient CO2 adsorption materials utilizing pressure-driven flexible MOFs.

Cationic Imidazolium-Urethane-Based Poly(Ionic Liquids) Membranes for Enhanced CO2/CH4 Separation: Synthesis, Characterization, and Performance Evaluation.

The escalating emissions of CO2 into the atmosphere require the urgent development of technologies aimed at mitigating environmental impacts. Among these, aqueous amine solutions and polymeric membranes, such as cellulose acetate and polyimide are commercial technologies requiring improvement or substitution to enhance the economic and energetic efficiency of CO2 separation processes. Ionic liquids and poly(ionic liquids) (PILs) are candidates to replace conventional CO2 separation technologies. PILs are a class of materials capable of combining the favorable gas affinity exhibited by ionic liquids (ILs) with the processability inherent in polymeric materials. In this context, the synthesis of the IL GLYMIM[Cl] was performed, followed by ion exchange processes to achieve GLYMIM variants with diverse counter anions (NTf2-, PF6-, and BF4). Subsequently, PIL membranes were fabricated from these tailored ILs and subjected to characterization, employing techniques such as SEC, FTIR, DSC, TGA, DMA, FEG-SEM, and CO2 sorption analysis using the pressure decay method. Furthermore, permeability and ideal selectivity assessments of CO2/CH4 mixture were performed to derive the diffusion and solubility coefficients for both CO2 and CH4. PIL membranes exhibited adequate thermal and mechanical properties. The PIL-BF4 demonstrated CO2 sorption capacities of 33.5 mg CO2/g at 1 bar and 104.8 mg CO2/g at 10 bar. Furthermore, the PIL-BF4 membrane exhibited permeability and ideal (CO2/CH4) selectivity values of 41 barrer and 44, respectively, surpassing those of a commercial cellulose acetate membrane as reported in the existing literature. This study underscores the potential of PIL-based membranes as promising candidates for enhanced CO2 capture technologies.

Metal-Organic-Frameworks Based Mixed-Matrix Membranes for CO2 Separation: An Applicable-Conceptual Approach.

A promising class of porous crystalline materials, metal-organic frameworks (MOFs), have recently emerged as a potential material in fabricating mixed matrix membranes (MMMs) for gas separation applications. Their unique chemistry and structural versatility offer substantial advantages over conventional fillers. This review gives an in-depth exploration of MOF chemistry, focusing on strategies to manipulate their adsorption behavior to enhance separation properties. We scrutinize the impact of various MOF-based MMM components, including polymer matrix, MOFs fillers and polymer/filler interface, on the overall gas separation performance. This involves a detailed analysis of key parameters associated with MMM preparation. Additionally, we offer a comprehensive overview of the determining factors in MOF-based MMM development for gas separation, including MOF structure, synthesis, and chemistry. Moreover, the most advances in modification strategies of MOF for CO2 separation, such as a wide variety of hybrid MOFs will be outlined, which opens the door to an improved CO2 separation process. Finally, the gas transport mechanisms of MMMs are thoroughly discussed to understand the factors affecting the gas permeation through the polymer matrix, MOFs and interface between them.

Carrier-driving CO2 separation by amine-rich membranes with intercalated graphene oxide

Amine-rich facilitated transport membranes (FTMs) attract great interest in intensifying the membrane-based CO2 separation processes. The high-molecular-weight polyvinylamine (PVAm) polymers containing fixed-site carriers of the amino groups were used to prepare highly CO2-permeable membranes. The sterically hindered PVAm polymers of poly(N-methyl-N-vinylamine) and poly(N-isopropyl-N-vinylamine) were obtained by functionalization of PVAm to provide superior CO2 solubility. By loading the mobile carriers of amino acid salt (AAS) and CO2-philic graphene oxide (GO), the prepared FTMs render enhanced CO2 permeance and CO2/N2 selectivity. The d-spacing of 8.8 Å and the ultramicropores of 3.5 Å from GO nanosheets provide the combination of both selective surface flow and molecular sieving mechanisms to achieve improved CO2 permeance and CO2/N2 selectivity. In addition, the intercalation of GO hinders N2 transport through the membrane due to a longer pathway, while the mobile carriers of AAS introduced into the PVAm matrix facilitate CO2 transport through the selective layer. Therefore, the CO2/N2 selectivity of the prepared FTMs was significantly enhanced to 171 based on the intensified carrier-driving transport mechanism. It can be concluded that amine-rich membranes based on both fixed and mobile carriers of the amino groups together with intercalated GO can synergistically improve the CO2/N2 separation performance, and be potentially applied for CO2 capture from flue gas.

Cerium-MOF-Derived Composite Hierarchical Catalyst Enables Energy-Efficient and Green Amine Regeneration for CO2 Capture.

The excessive energy consumed restricts the application of traditional postcombustion CO2 capture technology and limits the achievement of carbon-neutrality goals. Catalytic-rich CO2 amine regeneration has the potential to accelerate proton transfer and increase the energy efficiency in the CO2 separation process. Herein, we reported a Ce-metal-organic framework (MOF)-derived composite catalyst named HZ-Ni@UiO-66 with a hierarchical structure, which can increase the CO2 desorbed amount by 57.7% and decrease the relative heat duty by 36.5% in comparison with the noncatalytic monoethanolamine (MEA) regeneration process. The composite catalyst of the CeO2 coating from the UiO-66 precursor on the HZ-Ni carrier shows excellent stability with a long lifespan. The HZ-Ni@UiO-66 catalyst also shows a universal catalytic effect in typical blended amine systems with a large cyclic capacity. The HZ-Ni@UiO-66 catalyst effectively decreases the energy barrier of the CO2 desorption reaction to reduce the time required to reach thermodynamics, consequently saving the energy consumption generated by water evaporation. This research provides a new avenue for advancing amine regeneration with less heat duty at low temperatures.

Laser Patterning of Porous Support Membranes to Enhance the Effective Surface Area of Thin-Film Composite-Facilitated Transport Membranes for CO2 Separation.

Although thin-film composite membranes have achieved great success in CO2 separation, further improvements in the CO2 permeance are required to reduce the size and cost of the CO2 separation process. Herein, we report the fabrication of composite membranes with high CO2 permeability using a laser-patterned porous membrane as the support membrane. High-aspect-ratio micropatterns with well-defined micropores on their surface were carved on microporous polymer supports by a direct laser writing process using a short-pulsed laser. By using a Galvano scanner and optimizing the laser conditions and target materials, in-plane micropatterns, such as microhole arrays, microline grating, microlattices, and out-of-plane hierarchical micropatterns, were created on porous membranes. An aqueous suspension of hydrogel microparticles doped with an amine-based mobile carrier was sprayed onto the patterned surface to form a defect-free thin separation layer. The surface area of the separation layer on the patterned support is up to 80% larger than that of flat pristine membranes, resulting in a 52% higher CO2 permeance (1106 GPU) with a CO2/N2 selectivity of 172. The laser-patterned porous membranes allow the development of inexpensive and high-performance functional membranes not only for CO2 separation but also for other applications, such as water treatment, cell culture, micro-TAS, and membrane reactors.

Modeling and optimization of an integrated membrane – P/VSA separation process for CO2 removal from coal plant flue gas

This work presents a mathematical framework for the simulation and optimization of an integrated membrane – Pressure/Vacuum Swing Adsorption (P/VSA) process for CO2 removal from coal plant flue gas. The integrated process includes a membrane module in the first stage and a P/VSA unit in the second stage and it is optimized to minimize energy requirement for 95% and 90% total CO2 purity and recovery, respectively. Three membrane specifications, with CO2/N2 selectivity of 75, 50 and 25, and two adsorbents, zeolite 13X and MOF UTSA-16, are examined. The configuration which includes a membrane module with a CO2/N2 selectivity of 75 followed by a P/VSA unit with a UTSA-16 adsorbent leads to a minimum energy demand of 163 kWh/tn CO2, which is lower than the energy requirements of competitive CO2 separation processes, such as a two-stage P/VSA and multi-stage membrane processes. In addition, lowering the CO2/N2 selectivity from 75 to 50, leads to a minimum energy requirement of 177 kWh/tn CO2, which is still competitive to the other CO2 capture technologies. Furthermore, a comparison between different operating temperatures demonstrates that although a higher temperature increases the total energy demand, it has no impact on the optimal operating conditions and separation efficiency.

Breakthrough applications of porous organic materials for membrane-based CO2 separation: a review.

Over the last decades, porous organic materials (POMs) have been extensively employed in various industrial approaches including gas separation, catalysis and energy production due to possessing indisputable advantages like great surface area, high permeability, controllable pore size, appropriate functionalization and excellent processability compared to traditional substances like zeolites, Alumina and polymers. This review presents the recent breakthroughs in the multifunctional POMs for potential use in the membrane-based CO2 separation. Some examples of highly-selective membranes using multifunctional POMs are described. Moreover, various classifications of POMs following with their advantages and disadvantages in CO2 separation processes are explained. Apart from reviewing the state-of-the-art POMs in CO2 separation, the challenges/limitations of POMs with tailored structures for reasonable application are discussed.

Tungsten-doped high-silica CHA zeolite membranes with improved hydrophobicity for CO2 separation

High-silica CHA (SSZ-13) zeolites membranes, with pore size between the molecular size of CO2 and N2 or CH4, are promising for some industrial CO2 separation process. Considering water is typically present in these industrial gas feed and the negative impact of moisture on the membranes’ gas permeation, it is highly desirable to increase the surface hydrophobicity of membranes to reduce the adsorption of water. In this paper, a W-doping strategy was proposed to increase the hydrophobicity of SSZ-13 membranes by eliminating the silanols on the surface, and the W-doped high-silica CHA (W-SSZ-13) zeolite membranes were prepared for the first time. Characterizations such as SEM, XRD, and XPS confirmed the successful incorporation of W into CHA membrane. The incorporation of W reduced the pore mouth size, and the W-SSZ-13 zeolite membranes showed improved CO2/N2 and CO2/CH4 separation performance. After W-doping, the maximum separation factors (αmax) for the CO2/N2 mixture with equimolar composition under dry conditions increased from 8.8 to 16.9, and for the equimolar CO2/CH4 mixture, the value increased from 105.9 to 176. The W-SSZ-13 membranes also showed better separation performance under wet conditions. For both systems, the W-SSZ-13 membrane showed higher αmax and less CO2 permeance reductions, indicating a more resistance in wet conditions.

A fuel gas waste heat recovery-based multigeneration plant integrated with a LNG cold energy process, a water desalination unit, and a CO2 separation process

Development of the multigeneration plants based on the simultaneous production of water and energy can solve many of the current problems of these two major fields. In addition, the integration of fossil power plants with waste heat recovery processes in order to prevent the release of pollutants in the environment can simultaneously cover the environmental and thermodynamic improvements. Besides, the addition of a carbon dioxide (CO2) capturing cycles with such plants is a key issue towards a sustainable environment. Accordingly, a novel waste heat recovery-based multigeneration plant integrated with a carbon dioxide separation/liquefaction cycle is proposed and investigated under multi-variable assessments (energy/exergy, financial, and environmental). The offered multigeneration system is able to generate various beneficial outputs (electricity, liquefied CO2 (L-CO2), natural gas (NG), and freshwater). In the offered system, the liquified natural gas (LNG) cold energy is used to carry out condensation processes, which is a relatively new idea. Based on the results, the outputs rates of net power, NG, L-CO2, and water were determined to be approximately 42.72 MW and 18.01E+03, 612 and 3.56E+03 kmol/h, respectively. Moreover, the multigeneration plant was efficient about 32.08% and 87.72%, respectively, in terms of energy and exergy. Economic estimates indicated that the unit product costs of electricity and liquefied carbon dioxide production, respectively, were around 0.0466 USD per kWh and 0.0728 USD per kg-CO2. Finally, the total released CO2 was about 0.034 kg per kWh. According to a comprehensive comparison, the offered multigeneration plant can provide superior environmental, thermodynamic, and economic performances compared to similar plants. Moreover, there was no need to purchase electricity from the grid.

A low-carbon polygeneration system based on a waste heat recovery system, a LNG cold energy process, and a CO2 liquefaction and separation unit

Abstract Expanding energy conversion plants that simultaneously produce water and energy can address multiple issues in these two major fields. Additionally, utilizing waste heat energy from fossil fuel-driven plants rather than releasing it into the atmosphere can provide both thermodynamic and environmental benefits. A new polygeneration plant that integrates a waste heat recovery process and a CO2 liquefaction and separation process is developed and analyzed through a multi-criteria assessment (thermodynamic, economic, and environmental). The plant is capable of producing several advantageous products, including power, natural gas, desalinated water, and liquefied CO2. The polygeneration plant employs cold energy of liquefied natural gas (LNG) for condensation processes, a novel approach. Results indicate a net power rate of ~41.96 MW, with 166.8, 4912.8, and 972.6 mol/s for liquefied CO2, natural gas, and desalinated water, sequentially. The plant exhibits energy efficiency and exergy efficiency of ~31.6% and ~86.5%, respectively. The cost feasibility shows that electricity production carries a unit cost of 0.0474 US$/kWh, while liquefied CO2 production cost was about 0.0742 US$/kgCO2. The plant is estimated to emit roughly 0.0343 kg/kWh of carbon dioxide. The energy and exergy efficiencies decrease by ~9% and 2%, respectively, as the seawater feed rate increases from 13 to 23 kg/s. A comprehensive comparison indicates that the studied polygeneration plant yields superior economic, thermodynamic, and environmental performance compared to similar facilities. Furthermore, the proposed plant is capable of meeting its own power demands and does not require electricity from the grid.

The potential of mangosteen peel as a biosorbent: A review

AbstractThe high productivity of mangosteen and its utilization in various industries produce the mangosteen peel as a waste of the process. Mangosteen peel as a lignocellulose‐based material has great potential to be utilized as a biosorbent, especially in the separation process of wastewater pollutants. Previous studies on mangosteen peel biosorbent are limited to the adsorption of heavy metal ions, dyes, and CO2 separation process. These studies show that the separation efficiency can reach above 90%, which indicates the potential to be expanded for the usage of other compounds as the adsorbate. The gradual diffusion process of adsorbate molecules into biosorbent pores depends specifically on the suitability of the materials and the operating conditions of the adsorption process. Materials suitability can be modified by the biosorbent pretreatment process to enhance its adsorption capacity. The mangosteen peel biosorbent, which still performs well in the adsorption process even after being regenerated for a few cycles, is an added value for its potential to be utilized as a biosorbent in various applications because it can reduce costs and process waste; also expand the possibility to reuse the desorbed adsorbate compound.

New insight into impact of humidity on direct air capture performance by SIFSIX-3-Cu MOF.

Removal of CO2 from air is one of the key human challenges in battling global warming. SIFSIX-3-Cu is a promising metal-organic framework (MOF) suggested for carbon capture even at low CO2 concentrations. However, the impact of humidity on its performance in direct air capture (DAC) is poorly understood. To evaluate the MOF performance for DAC application under humid conditions, we investigate the adsorption of H2O, CO2, and N2 using density functional theory (DFT), grand canonical Monte Carlo (GCMC), and molecular dynamics (MD) simulations. The simulation results show a higher tendency of SIFSIX-3-Cu towards H2O adsorption rather than CO2 (and N2). The results agree with the adsorption isotherms for the pure compounds from the Sips model. The extended Sips model shows 1.34 mmol g-1 CO2 adsorption at the atmospheric pressure and 298 K for the CO2/N2 mixture containing 400 ppm CO2, and low CO2 adsorption (less than 0.75 mmol g-1) at a low relative humidity (RH) of 20%. This finding highlights the efficiency of SIFSIX-3-Cu for DAC in dry air and the negative impact of humidity on the CO2 selective adsorption. Therefore, we suggest to consider the impairing of humidity effects when designing a SIFSIX-3-Cu-based CO2 separation process and removal of any water vapor before introduction of the air to SIFSIX-3-Cu.

Synergy tetraethylenepentamine and diethanolamine impregnated within silica nanotubes derived from natural halloysite for efficient CO2 capture

Amine-impregnated porous solid adsorbents are promising commercial CO2 capture adsorbents for CO2 mitigation due to relatively large CO2 capacity and high CO2 selectivity. However, the intrinsic viscosity and aggregation of the polyamine leads to low amine efficiency and greatly limits its further development. In this work, a facile and efficient approach was carried out to manipulate the porosity of natural halloysite (HNTs) support with hollow tubular structure and impregnate mixed-polyamines, i.e., both tetraethylenepentamine (TEPA) and diethanolamine (DEA) to synergistically enhance CO2 adsorption capacity, fast adsorption kinetics and thermal/chemical stability compared to the individual supported TEPA and DEA. The effects of the blend amount for TEPA and DEA, adsorption temperature and CO2 partial pressure on CO2 adsorption capacity and adsorption kinetics were specifically discussed. Due to the auxiliary effect of DEA, the chemical reaction between non-hydroxylated TEPA and CO2 was altered thus improving amine efficiency and the agglomeration layer between protonated TEPA molecules and carbamate, which existed due to electrostatic interaction when TEPA was loaded alone, was loosened thus improving amine efficiency and adsorption kinetics. Therefore, the maximum CO2 adsorption capacity of MHNTs loaded with 20 wt% TEPA and 20 wt% DEA was 3.25 mmol/g at 75 °C in the flow of 40 vol% N2/60 vol% CO2. Compared with loading individual TEPA with multiple amino groups on MHNTs, individual DEA with hydroxyl groups could increase the utilization efficiency of the amino groups of TEPA and ultimately obtain excellent CO2 capture capacity and adsorption kinetics. The experimental results show that the adsorbents obtained in this study using mixed amine impregnated silica nanotubes derived from natural minerals have a promising application in practical CO2 capture and separation processes.

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.

Polyimide/Ionic Liquids Hybrid Membranes with NH3-Philic Channels for Ammonia-Based CO2 Separation Processes.

An efficient separation technology involving ammonia (NH3) and carbon dioxide (CO2) is of great importance for achieving low-carbon economy, environmental protection, and resource utilization. However, directly separating NH3 and CO2 for ammonia-based CO2 capture processes is still a great challenge. Herein, we propose a new strategy for selective separation of NH3 and CO2 by functional hybrid membranes that integrate polyimide (PI) and ionic liquids (ILs). The incorporated protic IL [Bim][NTf2] is confined in the interchain segment of PI, which decreases the fractional free volume and narrows the gas transport channel, benefiting the high separation selectivity of hybrid membranes. At the same time, the confined IL also provides high NH3 affinity for transport channels, promoting NH3 selective and fast transport owing to strong hydrogen bonding interaction between [Bim][NTf2] and NH3 molecules. Thus, the optimal hybrid membrane exhibits an ultrahigh NH3/CO2 ideal selectivity of up to 159 at 30 °C without sacrificing permeability, which is 60 times higher than that of the neat PI membrane and superior to the state-of-the art reported values. Moreover, the introduction of [Bim][NTf2] also reduces the permeation active energy of NH3 and reverses the hybrid membrane toward "NH3 affinity", as understood by studying the effect of temperature. Also, NH3 molecules are much easier to transport at high temperature, showing great application potential in direct NH3/CO2 separation. Overall, this work provides a promising ultraselective membrane material for ammonia-based CO2 capture processes.

Multiobjective optimization of membrane in hybrid cryogenic CO2 separation process for coal-fired power plants.

Post-combustion carbon dioxide (CO2) capture is considered a potential method to mitigate CO2 emissions from fossil fuels burned in power plants. In recent years, combining two different methods of post-combustion CO2 capture such as membrane and cryogenic distillation has been explored for availing the advantages of each method. This study focuses on the optimization of membranes for developing the membrane-cryogenic distillation process. For this purpose, a process flow sheet is developed, and simulation with model components such as compressor, heat exchanger, turbo expander, and distillation column is carried out using Aspen Plus. A membrane model is developed using in-house MATLAB code, and optimization is done to achieve higher concentration and recovery of CO2 using the MOJAYA algorithm. The membrane model is coupled to Aspen Plus through component object model (COM) technology. In this investigation, a hollow fiber membrane is considered. The optimized specifications of membrane modules are length, number of hollow fibers, feed pressure, and permeate pressure which are 0.3 m, 100,000, 5.76 bar, and 0.1 bar, respectively. This analysis results in the purity and recovery of the process of 99.8 and 90%, respectively, and an energy penalty of around 1.74 MJ/kg of CO2. A comparison of other processes available in the literature reveals that the current study renders maximum purity and recovery with a minimum energy penalty.

Perspectives on the green hybrid blend of diethanolamine-glycerol for post-combustion carbon dioxide capture via a Y-type micro-reactor

CO2 capture by aqueous primary and secondary alkanolamine solutions is a recognized technology in industrial CO2 separation processes. Yet, certain obstacles caused by high-energy consumption due to the amine regeneration demands, and the formation of thermally stable salts require to be overcome for the development of these solvents. In this paper, glycerol, as a beneficial by-product of biodiesel production, has been introduced as a second promising CO2 absorbent for aqueous diethanolamine solution in a Y-type micro-reactor with dimensions of 800 µm × 4 cm × 19 cm. The experiments of CO2 capture into the hybrid blend of DEA-Glycerol were investigated at ambient pressure and the operating temperature of 25–45 °C, volumetric gas flow rate of 100–300 ml/min, DEA concentrations of 1.5–2.5 M, and glycerol concentrations of 5–15%wt. Experimental results demonstrated that adding 10 wt% glycerol in the aqueous blend of 2.5 M DEA-Glycerol boosts the CO2 removal percentage, RP, up to 96.89%, and enhances the volumetric overall gas-phase mass transfer coefficient, KGaV, and volumetric mass transfer flux, NAaV, to 34.89 kmol/m3.h.kPa and 88.04 kmol/h.m3, respectively. Furthermore, based on the Box-Behnken statistical responses, under the constant concentration of 2 M of DEA, increasing the presence of glycerol from 5 to 10 wt% in the hybrid blend of DEA-Gly can intensify the CO2 RP, KGaV, and NAaV values by 2.12% and 8.66%, and 1.80%, respectively, illustrating the glycerol contribution on the CO2 capture process.