CO2 Absorption Performance Research Articles

Investigating the influence of CaCO3 nanoparticles on the performance of CO2 absorption in the PVC membrane contactors

The membrane contactor application to purify acid gases is a significant advancement in environmental protection and engineering processes. Notwithstanding the numerous privileges of membrane contactors, the wetting of the polymeric membrane is considered the main worry in developing the mentioned technology. The polymeric membrane wetting by liquid absorbents increases the membrane mass transfer resistance and decreases the gas absorption. In this study, hydrophobic PVC membranes including various amounts of CaCO3 nanoparticles were manufactured to reduce the wetting problem. The prepared membranes were evaluated using AFM, TEM, XRD, contact angle, SEM, and tensile strength measurements. The contact angle results illustrated that adding the nanoparticles enhanced the membrane contact angle; so that for nanocomposite membranes comprising 1.5 wt.% nanoparticles, the contact angle increased from about 77°–94°. Investigating the tensile strength results showed that the nanoparticle presence in the membrane structure raised the tensile strength by 10 MPa. Finally, the nanocomposite and pure membrane performance in CO2 absorption was evaluated in the system of membrane contactors. The findings exhibited that after 25 days of the gas absorption process, the permeate flux of pure membranes significantly decreased. However, the gas absorption flux in nanocomposite membranes containing 1.5 wt.% nanoparticles remained constant during this period.

Influence of Absorbent Composition and Operating Parameters on CO2 Removal Efficiency Using Aqueous Blends of 1-Dimethylamino-2-propanol in Tray Column

The CO2 absorption performance in aqueous blends of monoethanolamine (MEA)—1-dimethylamino-2-propanol (DMA2P) and piperazine (PZ)—DMA2P was investigated using a bench-scale tray column under atmospheric pressure. The removal efficiency of CO2 (ηCO2) and the overall volumetric mass transfer coefficient (KGav) in DMA2P-MEA and DMA2P-PZ solutions were determined at 313.2 K. The simulated flue gas was composed of 15% (mole fraction) CO2 and 85% N2. The effects of inlet gas flow rate (G), absorbent composition (w), inlet liquid flow rate (L), and plate number (NP) on ηCO2 and KGav were demonstrated. Our results showed that the absorption of CO2 in DMA2P aqueous solution can be accelerated by the addition of MEA/PZ in a tray column, and both ηCO2 and KGav can be significantly improved.

CO2 absorption performance of biogas slurry enhanced by biochar as a potential solvent in once-through CO2 chemical absorption process

Carbon capture, utilization, and storage (CCUS), offers a promising avenue for mitigating CO2 emissions, in which the big challenge is the high CO2 capture cost. A novel CCUS technology called once-through CO2 chemical absorption using biogas slurry, could potentially reduce the CO2 capture cost through decreasing the energy consumption greatly during CO2 capture. This technology, however, is constrained by the CO2 absorption capacity of biogas slurry. To enhance the CO2 capture capacity of this innovative technology, we proposed a method to enhance CO2 absorption by integrating biochar into biogas slurry. Results indicated that the CO2 absorption capacity of biogas slurry improved by biochar varied with the type of biochar adopted. Among all the investigated biochar, the wood biochar like sea buckthorn and sand willow exhibited the lowest CO2 capture enhancement, with 0.82±0.19 mmol/g and 0.81±0.30 mmol/g, respectively. Biochar from C4 plants like corn stalks and cobs demonstrated the highest enhancement, with 2.11±0.24 mmol/g and 2.47±0.86 mmol/g, respectively. The enhancement driven by C3 plant biochar like millet stalks and shells was intermediate, with 1.62±0.47 mmol/g and 1.62±0.46 mmol/g, respectively. The primary factor for promoting CO2 absorption in the biochar-based biogas slurry was the increase in pH of biogas slurry. The total pore volume of biochar was the principal material property that enhanced CO2 absorption, followed by the EC and BET surface areas of biochar. Increasing the carbonization temperature of biochar could also enhance the CO2 absorption capacity by biogas slurry. In CO2-rich biochar-based biogas slurry, CO2 primarily existed as HCO3− and carbamate. However, for the influence of the biochar's pore structure, CO2 in the CO2-rich biochar-based biogas slurry was more stable than that in CO2-rich biogas slurry.

Novel rate-based modeling and mass transfer performance of CO2 absorption in rotating spiral contactor

For the process of CO2 absorption, existing gas-liquid contactors suffer from low mass transfer performance and low gas-liquid ratios. In this study, a rotating spiral contactor was developed to overcome these drawbacks and a novel rate-based model was developed to predict the CO2 absorption performance. The effective interfacial area (ae), overall volumetric mass transfer coefficient (KGae) and CO2 absorption efficiency (η) were investigated. The results showed that the ae was 913–1125 m2/m3 superior to the conventional contactor. In the range of gas–liquid ratio of 200–1800, the KGae and η were 1.4–10.1 kmol.m-3.h-1.kPa-1 and 40.5–99.6 %, respectively. The rate-based model predicted the KGae and η with the AARD of 6.71 % and 1.90 %, respectively. Also, it has better robustness even in highly nonlinear temperature and composition distributions. This study provides a potential contactor and a new modeling tool for CO2 capture and other gas-liquid separation.

Deciphering the transfer mechanisms for CO2 absorption into binary blended solutions

A thorough understanding of the mechanisms involved in CO2 chemical absorption is crucial for the development of efficient CO2 capture technologies. Due to the insufficient insight into the interaction mechanism of different components in blended solutions, CO2 absorption reactions were often categorized as unidirectional transfer between absorption products. In this study, the CO2 absorption performance of binary blended solutions, including piperazine (PZ)/n-methyldiethanolamine (MDEA), ethanolamine (MEA)/MDEA, ammonia (NH3)/MDEA, PZ/potassium carbonate (K2CO3), and NH3/K2CO3, was investigated using a combination of experimental and computational methods. The CO2 absorption mechanisms of “competitive reaction”, “transfer reaction” and “parallel reaction” in the binary blended solution system were proposed. Kinetic experiments revealed that different blended solutions had varying impacts on the process of CO2 absorption. Among them, PZ/MDEA and MEA/MDEA solutions reduced the absorption rates by an average of 8% and 25%, respectively, compared to PZ or MEA component solutions. NH3/MDEA and PZ/K2CO3 solutions had absorption rates similar to those of single NH3/PZ component solutions. NH3/K2CO3 solutions, on the other hand, exhibited an average increase of 17% in absorption rates compared to NH3 solutions. Quantum mechanical (QM) methods were employed to evaluate of the absorption products and key processes in terms of kinetics and thermodynamics. Quantitative 13C NMR analyses were conducted to further investigate the interactions between components and the pathways of mass transport in blended solutions, which demonstrated proton transfer and CO2/-COO transfer between adsorption products. This study highlights an accurate description of the transfer mechanisms of various blended systems for the enhanced CO2 capture.

Zinc (II)-1,4,7,10-tetraazacyclododecane complexes catalyzed tertiary amine-based CO2 capture in a rotating packed bed

A novel tertiary amine-based CO2 absorption process using zinc (II)-1,4,7,10-tetraazacyclododecane complexes (CN) as a catalyst in a rotating packed bed was proposed for energy-efficient CO2 capture. The CN-catalysis reaction mechanism was first studied by density functional theory calculation, and the Gibbs Free Energy profile was established. Furthermore, the effects of various operation conditions for the tertiary amine-CN-CO2 systems on the CO2 removal efficiency (η), the overall gas-phase volumetric mass transfer coefficient (KGa), and the efficiency enhancement factor (Φ) were investigated. It was found that η and KGa with adding 4 wt% CN were 1–3 folds than those uncatalyzed. The absorption performance of CO2 in DEEA solution with CN was superior to that in 10 wt% DEA solution. Finally, an artificial neural network model was established to predict KGa, and the predicted data agreed well with experimental results with the average absolute relative deviation of 5.07 %.

Study on Shipboard Carbon Capture Technology with the MEA-AMP-Mixed Absorbent Based on Ship Applicability Perspective.

Ocean-going ships powered by diesel engines were the main source of CO2 emissions in the marine environment, and it was imperative to study shipboard carbon capture technology. Based on this, the whole process of CO2 absorption and desorption was studied with a mixed amine (MEA + AMP). The effective cycle time, CO2 absorption capacity, desorption efficiency, energy consumption, foaming and volatilization characteristics, and other key parameters were compared and analyzed under the conditions of required capture efficiency by ships. The MEA20% + AMP10% solution showed good CO2 absorption performance. At 80% capture efficiency, the desorption efficiency was more than 50%. The absorption capacity was close to that of the MEA30% solution, and the cycle time was basically the same. The effective cycle time under the reaction time of 2 s was also determined, which was an important parameter for setting the desorption frequency and had a great effect on reducing the desorption energy consumption. This work can provide an important reference value for the real ship application of carbon capture devices.

CO2 capture performance, kinetic and corrosion characteristics study of CO2 capture by blended amine aqueous solutions based on 1-(2-hydroxyethyl) piperidine

The chemical absorption method using amine-based aqueous solutions as absorbents is considered a critical technology in the mitigation of CO2 emissions. However, the trade-off between absorption performance and energy consumption presents a significant challenge for large-scale industrial applications. In this study, we propose using N-(2-hydroxyethyl)ethylenediamine (AEEA), 1-(2-amino Ethyl)piperazine (AEP) and piperazine (PZ) to regulate the CO2 capture characteristics of 1-(2-hydroxyethyl)piperidine (HEP) aqueous solution. We found that the addition of promoter AEEA/AEP/PZ increases the CO2 absorption and desorption performance of HEP aqueous solution. We established the CO2 capture mechanism, which involves the generation of HEPH+, carbamate, and bicarbonate during the absorption of CO2. During the desorption process, the bicarbonate can be decomposed, while the carbamate remains in the solution. Furthermore, we obtained data on the kinetics and corrosion characteristics of the blended absorbents. The absorption resistance of the three blended amine aqueous solutions is concentrated on the gas film, accounting for approximately 77 %. The corrosion rate of blended amine-enriched solutions on 20# carbon steel decreases with the increasing mass fraction of promoters or CO2 loading. SEM-EDS analysis revealed the presence of a dense FeCO3 oxide film on the surface of 20# carbon steel, which protects the carbon steel sheet from further corrosion. Overall, the proposed absorbents indicated a promising potential in the CO2 capture applications.

EXPERIMENTAL INVESTIGATION OF AMINE-BASED GRAPHENE NANOSUSPENSION FOR CO2 ABSORPTION

Absorption is the most widely used carbon dioxide (CO2) removal technology. The CO2 absorption performance of monoethanolamine (MEA), the most commonly used CO2 absorbent, can be improved by suspending nanoparticles. This work examined the performance of graphene nanoplatelets (GNPs) as additives to enhance CO2 absorption in MEA. The GNPs were characterized by HRTEM, FTIR, and XRD. The study examined the influence of GNP concentrations on CO2 absorption at room temperature. The images from HRTEM confirmed that the implemented graphene consists of several layers of graphene sheets. Increasing the loading of particles increased the solubility of CO2 until the optimum concentration was reached. From this work, it is evident that incorporating GNPs into MEA enhances the CO2 absorption performance of MEA. Thus, the addition of nanoparticles to the absorbent can enhance its CO2 absorptivity.

A novel non-aqueous tertiary amine system for low energy CO2 capture developed via molecular dynamics simulation

The current technology for capturing CO2 using alkanolamine aqueous solutions is known for its high energy and capital costs. As a result, developing new absorbents for low-energy CO2 removal remains a challenge. An additional activator can promote CO2 absorption performance. However, it is based on experimental screening. In this study, based on molecular dynamic simulation, we have successfully developed a novel and energy-efficient CO2 absorbent by combining N, N-Dimethylethanolamine (DMEA), and ethylene glycol (EG), with different activators, including ethanolamine (MEA), ethylenediamine (EDA), and piperazine (PZ). The addition of these activators significantly enhances the CO2 absorption performance of DMEA-based absorbents. Among them, DMEA-PZ-EG exhibits the maximum CO2 absorption rate and capacity, achieving 6.35 (g-CO2/(kg-soln.·min.)) and 96.5 (g-CO2/kg-soln.), respectively, representing a 230.1 % and 206.35 % improvement over 2M DMEA-EG absorbent. Moreover, compared to a 30 wt% MEA solution, the energy consumption of DMEA-based absorbents is reduced by 33.93–51.56 %. The reaction products were characterized using various spectroscopic techniques, including Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR), and 1D and 2D Nuclear Magnetic Resonance spectroscopy (1H and 13C NMR). The NMR results confirmed that DMEA becomes protonated after CO2 absorption in the DMEA-EG mixture. The deprotonation of EG promote its reaction with CO2, resulting in the forming of EG carbonates. This assumption has been confirmed by the IR spectrum. Furthermore, the effect of activators on CO2 absorption has been analysed at the molecular level through molecular dynamics simulation and a new method is proposed to predict the CO2 absorption performance of non-aqueous solvents. Using non-aqueous DMEA absorbents presents a promising approach for improving CO2 capture efficiency, reducing energy consumption, and facilitating regeneration.

An energy-efficient cyclic amine system developed for carbon capture from both flue gas and air

High energy consumption is a major barrier to the large-scale deployment of carbon capture processes from flue gases or air (direct air capture, DAC). The non-aqueous amines reported in literature possess a high energy efficiency for CO2 capture from flue gases, they struggle with gas streams containing ultra-dilute CO2, like air, due to poor absorption kinetics. This study developed novel 2-PE (2-piperidineethanol)/APZ (Aminoethylpiperazine) based CO2 absorbents to address these problems. The experiments and MD simulation results showed that the 2-PE/APZ-based absorbents possessed a superior absorption performance both in flue gas and air. Among the developed absorbents, when 2-PE/APZ mixed with DMF (Dimethylformamide), the CO2 loading reached to 1.004 mol/mole, as the theoretical maximum. In DAC tests, 87.31 % CO2 from the air was captured in 24 h experiments. The regeneration heat duty of 2-PE/APZ/DMF decreased to 1.694 KJ/g CO2, a 55.89 % reduction compared to the benchmark 30 wt% MEA. The CO2 absorption/desorption mechanism was analysed by NMR, In-situ FT-IR, and DFT calculation. It indicated that this significant improvement in CO2 absorption performance and the reduction in energy consumption are due to the synergistic effect of 2-PE and APZ. During CO2 absorption, CO2 reacts with APZ forming APZ zwitterion rapidly, then deprotonation to the 2-PE. The formation of protonated 2-PEH+ ion pairs with APZCOO- reduces hydrogen bonds and van der Waals forces among the amine-CO2 complex, facilitating easy regeneration at mild conditions while maintaining high reactivity. The combination of theoretical and experimental results indicates that 2-PE/APZ-based absorbents can serve as a promising alternative for carbon capture from flue gas to air with low energy usage.

Performance of a novel CO2 absorption and reverse electrodialysis system with different amine solutions for simultaneous energy and bicarbonate recovery

In this study, the performance of a novel integrated carbon dioxide (CO2) capture and reverse electrodialysis (RED) system was evaluated. The optimal operating conditions and carbon dioxide absorption and desorption mechanisms were identified. The proposed system utilizes a RED device to recover energy from the desorption step of the CO2 capture process, which is known to have high energy requirements in conventional processes. It has the potential as a hybrid process capable of recovering absorbent, energy, and bicarbonate through RED. To verify the performance of the system, CO2 loading, power density, and absorbent regeneration were evaluated using primary (monoethanolamine, MEA), secondary (diethanolamine, DEA), and tertiary (N-methyldiethanolamine, MDEA) amines. In the case of primary and secondary amines, carbamates, intermediate products, are formed and pass through the ion exchange membrane of RED, thereby achieving high power density. However, they are re-substituted with amines after passing through the ion exchange membrane (IEM), leading to the loss of absorbent. Conversely, in the case of tertiary amines, no intermediate products were formed, and excellent absorbent regeneration performance of more than 99.9% was demonstrated through multi-stage RED. Through this, the feasibility of future applications of this technology was confirmed.

Study on CO2 absorption by EmimCl-MEA deep eutectic solvent in microchannel

Carbon dioxide (CO2) is widely acknowledged as the primary contributor to the greenhouse effect. Microchannel reactors can be used for enhancing chemical processes, solving the problems of limited gas-liquid mass transfer, and have significant advantages in CO2 capture. In this study, the deep eutectic solvent (DES) prepared by mixing ionic liquid (1-ethyl-3-methylimidazolium chloride, EmimCl) and Ethanolamine (MEA) in a molar ratio of 1:1 was selected for CO2 capture in a microchannel. The structure and physical properties of the DES were investigated, and the effects of gas and liquid flow rates, water content, and CO2 concentration on the CO2 absorption properties were analyzed. The increase of the water content not only significantly reduces the viscosity of DES, but also improves the CO2 absorption performance. In addition, the CO2 absorption mechanism of this DES has been obtained by the NMR spectrum, showing that the absorption process is a rapid chemical absorption process between CO2 and MEA. The Cl- of EmimCl could stabilize the protonated amine and prevent it from further reacting with MEACO2-, furthermore increasing the CO2 absorption rate.

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.

Physical absorption and thermodynamic modeling of CO2 in new deep eutectic solvents

Due to the advantages of deep eutectic solvents (DESs), such as good CO2 absorption performance, excellent biodegradability, low cost, and simple synthesis, attention has been drawn to selecting DESs with high efficiency for capturing CO2 in a green and environmentally compatible context. In the present study, acetamide as the hydrogen bond acceptor (HBA) and diethylene glycol, 1,2-propanediol, and 1,3-propanediol as the hydrogen bond donors (HBD) for the synthesis of DESs. First, the density and viscosity of these prepared DESs were measured under standard ambient pressure and at temperatures ranging between 293 K and 343 K. Subsequently, the CO2 solubility in DESs was ascertained by the isovolumetric saturation experimental method. The results indicated that all synthesized DESs exhibited physical absorption of CO2 and the diethylene glycol-based DESs had the highest dissolvability for CO2. For the DES with diethylene glycol and 1,2-propanediol as HBD, the CO2 solubility increased as the molar ratio of HBD decreased. On the contrary, the amount of CO2 adsorbed by 1,3-propanediol-based DES increased with increasing 1,3-propanediol content. The semi-empirical Jou and Mather model allows for an efficient correlation to be made among experimentally determined CO2 solubilities, temperatures, and the CO2 partial pressures. Comparing the deviations between the experimental and fitted values, the average relative deviation is small. By estimating the Henry constants and Manuscript File Click here to view linked References comparing them with the literature, it was demonstrated that the synthesized DESs are competitive in absorbing CO2.

Adopting green absorbent for CO2 capture and agricultural utilization: Biogas slurry and biomass ash case

Previously, the once-through CO2 chemical absorption process by biogas slurry was experimentally verified to offer the unique advantages like low energy consumption, cost-effectiveness, and feasibility of CO2 fixation in plants. However, this technology also faces some challenges and limitations, including a low CO2 absorption rate and performance. To improve the effectiveness and reliability of this innovative carbon capture, utilization, and storage (CCUS) technology, this study proposes a novel method to enhance the CO2 absorption performance without affecting agricultural applications of CO2 by mixing biogas slurry with biomass ash as the green CO2 absorbent. The results indicate that when the solid-liquid mass ratio of biomass ash to biogas slurry is 5:10, the CO2 loading of the biomass ash and biogas slurry mixture (BA-BS) reaches 936.7 ± 59.1 mmol/kg. Furthermore, the pH of the BA-BS remains stable at 6.9, meeting the rhizosphere pH requirements for plant cultivation. The CO2 absorption of the BA-BS liquid phase, referred to as improved biogas slurry (IBS), reaches its maximum at 230.4 ± 3.5 mmol/L, which is 126.8% higher than that of the unimproved biogas slurry. The nitrogen content in the BA-BS solid phase, calling improved biomass ash (IBA), also reaches its maximum at 4.24 ± 0.74 mg/g, thereby expanding the agricultural utilization of biomass ash. The most reasonable and effective way of utilizing CO2-rich mixed biogas slurry and biomass ash involves use IBA as the base fertilizer for tomato cultivation, supplemented later with IBS to promote growth. This optimal application allows for substantial utilization of CO2, introduced into the tomato cultivation environment by IBA and IBS. The carbon fixation of a single tomato has improved by 108.2%. This study thus provides a feasible solution for high-value negative carbonization of biogas slurry and biomass ash.

Surface modified single-step nanofluid for improved CO2 absorption and storage Prospects at pore-scale in micromodels: CO2 utilization for saline porous media

The utilization (absorption and areal sweep) of injected carbon dioxide (CO2) can be enhanced if a viscous and agglomeration free nanofluid is used as most of the nanoparticles (NPs) prefer to stay in bulk phase rather than adsorbing on CO2 surface. NP adsorption can be improved if non-participating NPs are surface modified with a suitable surface modifying agent e.g., triethoxy (vinyl)silane (TVS). Thus, in this study, single-step approach was used to synthesize agglomeration free TiO2 nanofluid whose surface modification was carried out in varying proportion of TVS (1–5% v/v) followed by the discussion on comparative CO2 absorption and storage performance by different tools such as DLS, IFT, Rheology, Contact-angle, and Micromodel flow. The basic nanofluid (To) showed greater CO2 absorption after surface modification as demonstrated by molality results. However, surface modification also decreased dispersion stability of surface modified nanofluids (T1, T2, and T3) and T2 was regarded as the most stable nanofluid with −64.4 mV (ζ-potential) and 153 nm (NP size). After surface modification, increase in NP size and settlement was higher for surface modified nanofluids than To, which exhibited dispersion stability of 84 d with −53.4 mV and 15 nm. Contact angle results also showed that surface modified nanofluids possess greater affinity for CO2 absorption than basic nanofluid (To). Rheological analysis was also consistent with other tests where viscosity was found dependent on both storage period and temperature, and NP settlement was found to be the most influential parameter on flow properties of nanofluid. Finally, pore scale analysis was performed to understand areal sweep of injected CO2 in micromodel with and without nanofluid, where nanofluid imparted greater CO2 storage by diverting it in un-swept pore networks of micromodel which were untapped by CO2 without nanofluid.

A mass transfer study of CO2 absorption in aqueous solutions of isomeric forms of sodium alaninate for direct air capture application

Direct air capture (DAC) of CO2 is a critical emerging technology required to achieve ambitious net-zero emissions. Aqueous amino acid absorbents are ideal candidates for DAC and this work describes the investigation of the CO2 absorption performance of sodium salts of β- and α-alaninate under relevant conditions for DAC by utilising synthetic CO2 gas streams at concentrations levels found in the atmosphere (200–600 ppm). The effects of solution concentration, temperature, gas flowrate, liquid flowrate, and dissolved CO2 concentration (i.e., CO2 loading) on CO2 mass transfer coefficients were investigated. The overall mass transfer coefficient was found to be independent of the gas and liquid flowrates, with larger values determined for β-alaninate solutions (0.75–1.16 mmol m−2 s−1 kPa−1) than that of α-alaninate (0.65–0.87 mmol m−2 s−1 kPa−1), under similar experimental conditions. The results showed that the overall mass transfer coefficient increases with increasing temperature, conversely decreasing steadily with increasing CO2 loading. The maximum CO2 loading capacity of the 5.0 M solutions was ∼10 % higher for β-alanine (0.651 mol CO2/mol alaninate) than α-alanine (0.607 mol CO2/mol alaninate) at 25.0 °C. Precipitation was found to play an important role in the CO2 absorption processes here. Interestingly, beyond CO2 loadings >0.12 mol CO2/mol α-alaninate, the 5.0 M solution of α-alaninate begins to develop precipitate(s) while precipitation in the β-alaninate solution is only initiated at much higher CO2 loadings >0.52 mol CO2/mol β-alaninate. This study provides valuable insights into the suitability of β-alanine and α-alanine for CO2 capture directly from the ambient air.

Nanoporous hypercrosslinked polymers as cost-effective catalysts to significantly promote the CO2 absorption performance of water-lean solvents for post-combustion CO2 capture

In most cases, the slow CO2 sorption kinetics of water-lean solvents—which include low-volatile organic diluents—are the limiting factor when it comes to post-combustion CO2 capture. This study offers a solution by suggesting the use of catalysts based on nanoporous hypercrosslinked polymers (HCPs) to improve the removal efficiency of water-lean solvents based on diethanolamine (DEA) and to increase CO2 mass transfer. Simple and inexpensive monomers were used to prepare three HCPs: HCP-C, HCP-S, and HCP-B, which stand for benzene, polystyrene, and carbazole, respectively. Blends of DEA and Glycerol (Gly) were used to disperse these polymers. Addition of 0.5 wt% HCP to a solvent mixture of 20% DEA and 30% Gly considerably boosts removal efficiency and increases the amount of CO₂ that can be absorbed until the breakthrough point by as much as 3000%, according to the results. Additionally, various gas flow rates, DEA concentrations, and glycerol concentrations were also investigated to determine the HCP-C catalytic effect on the CO2 absorption. A volumetric overall mass transfer coefficient enhancement of up to 319 % is possible in the investigated ranges when using HCP-C, according to the findings. Moreover, a possible catalytic mechanism was suggested.