Physical Absorption Of CO2 Research Articles

A study of nano-micro-bubble process for CO2 absorption in water for biogas upgrading application

The work proposed a novel micro-bubble system using swirling jet flow method for improving the physical absorption of CO2 in water. The effects of operating conditions; e.g. gas flow rate (from 500 to 2000 mL/min), inlet pressure (2 and 3.5 bar) and inlet CO2 concentration (from 5 to 60% v/v in CO2/N2 gas mixture) on the physical absorption of CO2 were studied. It was found that the CO2 absorption system reached to steady state after 30 minutes with the outlet CO2 concentrations of 2.9% and 8.8% at 40% and 60% of inlet CO2 concentrations, respectively. These outlet CO2 concentrations demonstrated the standard of bio-methane for replacing natural gas in vehicle use, from which less than 10% CO2 is required. Moreover, the increase of gas flow rate resulted in increase of outlet CO2 concentration. The rising of inlet pressure from 2 to 3.5 bars let to reduction of the outlet CO2 concentration together with enhancing the dissolved CO2 concentration in water from 49.1 to 51.7 mg/L at gas flow rate of 2000 mL/min and 60% of inlet CO2 concentration. The highest efficiency of CO2 removal was 98.41% under gas flow rate at 500 mL/min with 60% of inlet CO2 concentration. Under the optimized conditions, this system was tested with real biogas as raw material containing mainly 57.7% of CH4 and 40.3% of CO2 which achieved to remove the 95.1% of CO2 removal and no significant loss of CH4. This highlight demonstrated the potential application of this technology for biogas upgrading or purification further.

An environmentally friendly deep eutectic solvent for CO2 capture

A leading cause of global warming is the increase of carbon dioxide (CO2) emissions due to anthropogenic activities which prompts an urgent need for substantial reduction. Recently, CO2 absorption in deep eutectic solvents (DESs) has attracted scientific attention, because of their adaptability compared to traditional ionic liquids and aqueous amine solutions. This study employs the heating method to synthesize DESs using tetrapropylammonium bromide (TPAB) and formic acid (Fa) with molar ratios of TPAB-Fa (1:1) and TPAB-Fa (1:2). Absorption experiments by static method quantified CO2 solubility in the DESs under varied pressures and temperatures. TPAB-Fa (1:2) at 25.0 °C was the most efficient with the CO2 solubility of 0.218. Thermodynamic modeling was performed by employing the nonrandom two liquids activity coefficient model and the Peng–Robinson equation of state for the liquid and gas phases, respectively. The Henry’s law constant was determined from experimental data. CO2 physical absorption was confirmed via nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) analyses. TPAB-Fa (1:2), as the superior DES, exhibited regeneration efficiency of 99% after five absorption/desorption cycles.

CFD simulation and experimental study of CO2 absorption in a rotating packed bed

The rotating packed bed (RPB), a process intensification equipment, has been widely studied and applied to chemical engineering processes such as gas absorption, nanomaterial preparation, and polymer devolatilization. In this study, we presented a typical RPB model to study the intensification mechanism of high gravity on gas-liquid mass transfer. Based on this, three-dimensional computational fluid dynamics (CFD) simulations and experiments of CO2 physical absorption were conducted to investigate the gas-liquid mass transfer characteristics in the RPB. The predicted and experimental values of CO2 saturation rates of the liquid phase showed good agreement, and the errors were within ± 15 % under various operating conditions. Moreover, detailed flow field and mass transfer information that are difficult to measure experimentally, such as the distribution of CO2 mass fraction in the liquid, liquid holdup, turbulent kinetic energy dissipation rate, and gas-liquid interfacial area, were analyzed by CFD simulation results. These results provide a solid foundation for the further development and application of RPB.

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.

Density, viscosity, and CO2 solubility in ether-functionalized phosphonium-based bis(trifluoromethanesulfonyl)amide ionic liquids

We measured the densities and viscosities of two ionic liquids, triethyl(methoxymethyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P222(1O1)][TFSA]) and triethyl(2-methoxyethyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P222(2O1)][TFSA]), at atmospheric pressure and 273.15–363.15 K. The high-pressure density at the pressures up to 50 MPa was also measured at 298.15–353.15 K. Meanwhile, CO2 solubility in these phosphonium-based ionic liquids was determined using a magnetic suspension balance at 303.15–333.15 K and pressures up to 6 MPa. The experimental density and viscosity at atmospheric pressure were fitted using quadratic and Vogel-Fulcher-Tammann equations, respectively. The high-pressure density was fitted using the Tait equation and Sanchez-Lacombe equation of state. The properties of the two ether-functionalized ionic liquids were compared to those of triethylpentylphosphonium bis(trifluoromethanesulfonyl)amide [P2225][TFSA]. The density at atmospheric pressure increased in the order [P2225][TFSA] < [P222(2O1)][TFSA] < [P222(1O1)][TFSA]. The introduction of the ether group effectively reduced viscosity in the following order: [P222(1O1)][TFSA] < [P222(2O1)][TFSA] < [P2225][TFSA]. The CO2 solubilities in [P222(1O1)][TFSA] and [P222(2O1)][TFSA] were slightly lower than those in [P2225][TFSA]. In contrast, the molality of CO2 (m1) increased in the order [P2225][TFSA] < [P222(2O1)][TFSA] < [P222(1O1)][TFSA]. Ether functionalized phosphonium-based cations are effective in enhancing the physical absorption of CO2, particularly the molality of CO2.

Intensification of absorption rate of carbon dioxide and ammonia in a simulated packed (Stephens–Morris) column using pulsed gas phase under optimized parametric conditions

BackgroundReducing gas emissions is a significant challenge in our ecosystem. Gas-liquid absorption is used in chemical industry to remove components from gas streams. Stephens–Morris tube, known for liquid-liquid and gas-liquid systems, has gained attention for gas absorption columns utilizing disc-shaped packing elements to improve mass transfer by creating tortuous flow path. MethodsThis investigation focuses on physical absorption of CO2 and NH3 in gas-liquid systems based on various process parameters vis. liquid flow rate (0.24–0.60 L/min), gas flow rate (6–60 L/min), pulsation frequency (0–9.06 Hz), pulsation amplitude (0–26 mm), effect of solute gas concentration (0–100 %), and effect of varying the number of discs in the disc column (15, 20, 25, 33). Response Surface Methodology (RSM) was used to predict maximum absorption efficiency under optimized conditions. Significant FindingsPulsation frequency and amplitude proportionally increased absorption coefficient, while liquid flow rate affected it differently in pulsed and unpulsed absorption. In gas film-controlled system, mass transfer coefficient was proportional to the gas flow rate. RSM yielded R2 of 0.975 while relative error and dwill was 0.097 and 0.96, respectively. Understanding system characteristics and operations at optimal pulsation frequencies and amplitudes can maximize absorption effectiveness, particularly for low-solubility gases dominated by liquid phase resistance.

Prediction and optimization of liquid dispersion of monoethanolamine in a rotating packed bed for CO2 absorption

Rotating packed bed (RPB) has recently gained traction as a preferred technology for the absorptive removal of CO2. In this device, solvent dispersion is the most crucial hydrodynamic parameter that directly affects the liquid-side mass transfer coefficient. The current study focuses on the optimization of the dispersion of monoethanolamine (MEA), a commonly used CO2 absorption solvent, in the RPB. Computational fluid dynamics (CFD) model was developed and validated against the published experimental data. The validated model was used to investigate the effect of operational parameters such as solvent concentration, rotational speed of the packed bed, inlet velocity, and the contact angle of packing material on MEA dispersion. The liquid dispersion of MEA was modeled using response surface methodology (RSM), artificial neural network (ANN) and adaptive neuro-fuzzy inference systems (ANFIS). The comparison of the modeled data revealed that ANN has the least mean square error (0.16) and is, therefore, the most capable model to predict the liquid dispersion of MEA in the RPB. Based on the ANOVA analysis, the inlet velocity of MEA is found to be an insignificant parameter and, therefore, does not contribute significantly to the liquid dispersion of MEA in the RPB. At optimized operating conditions, the MEA dispersion increased from 5346 to 10485 m−1, thus enhancing the physical absorption of CO2 up to eight times. CFD coupled with ANN for the prediction and RSM for the optimization of liquid dispersion can be employed to optimize industrial-scale RPB for the effective absorptive removal of CO2.

Carbon dioxide sensing using a PEI-Cr2O3-rGO nanocomposite sensor with patterned copper clad as a substrate

ABSTRACT The focus of this work is on carbon dioxide sensing using a nanocomposite sensor composed of PEI, Cr2O3, and rGO, with a patterned copper-clad substrate. Study explores how sensors with varying weight percentages of Cr2O3 and rGO in PEI perform in terms of sensitivity when exposed to carbon dioxide gas. Furthermore, the study probed into exploring the correlation between the fluctuations in electrical resistance of the sensors and the levels of CO2 gas concentration. This examination delves into the sensitivity, repeatability, response time, and recovery time of the sensors. At 1000 ppm of CO2, the sensor with 0.25 wt% of Cr2O3-rGO in PEI demonstrated the lowest sensitivity percentage of 1.71, while the highest sensitivity of 2.13 was achieved by the sensor with 1.0 wt% of Cr2O3-rGO in PEI. The repeatability of the sensors containing 0.25, 0.50, 0.75, and 1.00 wt% of Cr2O3-rGO in PEI was found to be comparable at 8 minutes. However, the repeatability of the sensor with 1.00 wt% of Cr2O3-rGO in PEI was especially noteworthy. A PEI nanocomposite with 0.25 wt% Cr2O3-rGO demonstrated the quickest response time of 33 seconds and recovery time of 36 seconds compared to the other sensors. The sensing mechanism involves the physical absorption of CO2, the effective interactions of the amino groups with CO2 to form carbamates, and the electrical response changes of the PEI-Cr2O3-rGO nanocomposite at room temperature. This mechanism provides a reliable and efficient means of sensing CO2 gas for various applications at equal to or less than 1000 ppm.

A novel approach based on detailed structural and molar free volume analyses to characteristics of deep eutectic solvents specialized for CO2 absorption

This study presents a novel approach based on structural and molar free volume analyses to characterize deep eutectic solvents (DESs) with functional groups possessing CO2 affinity based on analytical prediction and data. Although DESs have garnered attention due to their high tunability and applicability in various fields, there is paucity of literature containing their detailed analyses. In this investigation, HBDs with amino (–NH2), carbonyl (CO), and ether (R-O-R') groups were chosen to determine the effect of functional groups on the CO2 absorption capacity and structural properties of DESs. Based on FT-IR and 1D/2D NMR measurements on DESs, it was confirmed that the hydrogen used for the formation of hydrogen bonds exhibited a distinct property and that DESs were successfully formed. In addition, the DES including tetraethylammonium bromide, 3-amino-1-propanol, and water with an amino group exhibited a high capacity for chemical CO2 absorption. In the case of the DES, structural configuration prediction was proposed using the chemical CO2 absorption capacity. The proportional relationship between the physical CO2 absorption and molar free volume of DESs was also confirmed using analytical data. Finally, these novel approaches to DESs can be used as a guide for applying and developing new DESs with structural properties.

Theoretical Analysis of Physical and Chemical CO2 Absorption by Tri- and Tetraepoxidized Imidazolium Ionic Liquids.

The efficient capture of CO2 from flue gas or directly from the atmosphere is a key subject to mitigate global warming, with several chemical and physical absorption methods previously reported. Through polarizable molecular dynamics (MD) simulations and high-level quantum chemical (QC) calculations, the physical and chemical absorption of CO2 by ionic liquids based on imidazolium cations bearing oxirane groups was investigated. The ability of the imidazolium group to absorb CO2 was found to be prevalent in both the tri- and tetraepoxidized imidazolium ionic liquids (ILs) with coordination numbers over 2 for CO2 within the first solvation shell in both systems. Thermodynamic analysis of the addition of CO2 to convert epoxy groups to cyclic carbonates also indicated that the overall reaction is exergonic for all systems tested, allowing for chemical absorption of CO2 to also be favored. The rate-determining step of the chemical absorption involved the initial opening of the epoxy ring through addition of the chloride anion and was seen to vary greatly between the epoxy groups tested. Among the groups tested, the less sterically hindered monoepoxy side of the triepoxidized imidazolium was shown to be uniquely capable of undergoing intramolecular hydrogen bonding and thus lowering the barrier required for the intermediate structure to form during the reaction. Overall, this theoretical investigation highlights the potential for epoxidized imidazolium chloride ionic liquids for simultaneous chemical and physical absorption of CO2.

Taylor flow bubble transport characteristics of low partial pressure CO2 absorption in a serpentine micro contactor

Due to small axial back-mixing, wide operating range and simple control, Taylor flow in microfluidic system has potentially used in many fields including chemical processing, environment control, biomedical engineering and thermal management. Quantifying and manipulating absorption characteristics is significant for Taylor flow during the mass transfer process, especially for CO2 purification or CO2 enrichment under low partial pressure CO2. Firstly, a physical model for the liquid film distribution around the bubble is raised, and a more applicable equation of liquid film thickness is established in case of low partial pressure CO2 in a serpentine micro contactor. Secondly, bubble transport characteristics during absorption process including bubble velocity, gas holdup and net leakage flow are systematically determined in the serpentine micro contactor. The influences of the physical properties, inertial effect and configuration of the micro contactor on the bubble transport characteristics are analyzed simultaneously. Thirdly, the prediction is also made for net leakage flow within the experimental scope of 0.001 < CaTP <0.055, 0.06 < WeTP < 9.10, 18 < ReTP < 460, 10 < Dn < 155. Thus, this work provide equations to quantify the absorption characteristics quickly and accurately based on the liquid film distribution model in the serpentine micro contactor, which is of fundamental importance for the low partial pressure CO2 physical absorption.

Synergetic effect and mechanism between propylene carbonate and polymer rich in ester and ether groups for CO2 physical absorption

Polymers rich in ester and ether groups may have excellent behavior for CO2 absorption. However, these polymers are not widely used in industry due to their high kinematic viscosities. The introduction of a small-molecule solvent is supposed to reduce kinematic viscosity of the polymer and help the polymer to be the excellent CO2 absorbent, but the effect and related mechanism remain unknown. This work proposed propylene carbonate (PC) + poly(ethylene glycol) bis(2-ethylhexanoate) (PEGB) as potential CO2 capture absorbent and carried out a theoretically and experimentally integrated study for CO2 capture using high-molecule polymer. Firstly, quantum chemistry calculation based on the density functional theory (DFT) attributes the strong PEGB-CO2 interaction to the large amount of effective binding sites including ester and ether groups. Secondly, the DFT simulation shows the synergetic effect of PC and PEGB: CO2 absorption of PC+PEGB is obviously easier than that of pure PC or PEGB. The synergetic effect is verified by thermodynamic experiment, the relatively high and positive value of excess CO2 absorption capacity of the PC+PEGB mixture is obtained. Thirdly, the synergetic mechanism is assessed to be the stronger Lewis acid-base and hydrogen-bond interaction offered by the mixed absorbent based on charge transfer behavior analysis. Finally, 0.2513 PC+0.7487 PEGB may be the optimum mass ratio for promising CO2 capture because of its high CO2 absorption capacity (0.3276 mol-CO2/mol-solution) and appropriate kinematic viscosity (2.5721 × 10−5 m2 s−1, about 60% decrease compared with PEGB).

Thermal Behavior of Alkanolamine-Based Deep Eutectic Solvents: Towards Carbon Dioxide Capture Applications

In this study, the specific heat capacities, heat of absorption, extent of chemical absorption of CO2 and thermal stability of amine based deep eutectic solvents (DESs) namely, choline chloride-monoethanolamine (ChCl-MEA), choline chloride-diethanolamine (ChCl-DEA), and choline chloride methyl-diethanolamine (ChCl-MDEA) were determined experimentally and compared with aqueous amine solution and solid adsorbents. The estimation of these quantities would aid in the determination of the regeneration energy and thermal stability requirements of the amine based DESs. This study is significant because the conventional aqueous amines are known to exhibit a prohibitive regeneration energy, and the instability of the solvents under CO2 absorption conditions has been widely reported. It is notable to point out that the specific heat capacity of the amine based deep eutectic solvents are all lower than that of the aqueous amine solution of MEA 30% weight. Moreover, when compared to solid adsorbents, e.g. polyethylenimine (PEI) impregnated mesoporous precipitated silica, amine based DESs exhibited a good level of closeness in the specific heat capacity and sometimes having less specific heat as in the case of ChCl-MDEA. Furthermore, HPLC analysis of the DESs before and after CO2 absorption showed that only part of the amine in the DES reacted with CO2. This is an indication that both chemical and physical absorption of CO2 existed. This result is of great importance since physical absorption of the carbon dioxide will significantly reduce the regeneration energy requirements for the capture process. The Thermo-Gravimetric Analysis (TGA) results showed that amine based DESs are more thermally stable compared to the corresponding aqueous solution of amines. The degradation temperature of amine based DESs is higher than that of stand-alone amines. For instance, the degradation temperature of ChCl-MEA 1:6 is around 140 °C while that aqueous solution of MEA is 65 °C. This result is of great importance in the CO2 capture using aqueous amine solution, especially in the regeneration step where the temperature is about 120-140 °C.

Energy-efficiency analysis of industrial CO2 removal system using nanoabsorbents

Abstract CO2 physical absorption process is typically operated at a low temperature as low as −40 °C and high pressure. In this study, nanoabsorbents are applied to increase the operating temperature by improving the absorption performance. Herein, CO2 absorption performance is analyzed in a column absorber based on the Eulerian-Eulerian and population balance models. The computational results are verified experimentally under the same conditions and flow regimes can be classified into two regions in terms of the Reynolds numbers of the CO2 gas and absorbent. Dimensionless correlations are developed to predict the CO2 mass transfer coefficient for each region, which can be scaled up for industrial applications of the nanoabsorbents. The input power of the CO2 absorption system is calculated by considering each component. Finally, an operational map of the CO2 absorption and regeneration system, including both CO2 mass transfer coefficient and the input power, is presented. The operational map will be a guideline to optimize operating conditions. Specifically, when the CO2 absorption/regeneration industrial system is optimally designed, energy consumption can be reduced by approximately 40.5% with the CO2 mass transfer coefficient of 0.475 m/s. When SiO2/MeOH nanoabsorbents are used as a working fluid of CO2 absorption system, the operational energy can be additionally saved by 23.2%. In addition, CO2 mass transfer coefficient can be improved by 11.9% using nanoabsorbents for same Reynolds number. It is expected that the energy consumption in the industrial MeOH-based CO2 absorption system will be greatly reduced by using the nanoabsorbents and the present optimization methods.

Prediction of CO2 chemical absorption isotherms for ionic liquid design by DFT/COSMO-RS calculations

Ionic liquids with an aprotic heterocyclic anion (AHA-ILs) is a promising family of compounds to overcome the challenge of CO2 capture. In this work, a computational methodology has been developed to predict CO2 chemical absorption isotherms in AHA-ILs without the need of experimental data. This methodology combines DFT and COSMO-RS calculations allowing the design of new chemical absorbents for CO2 capture. The CO2 physical absorption equilibrium constants (Henry's law constants), chemical equilibrium constants and reaction enthalpies were reliably predicted by proposed computational approach, by means of comparison to available experimental data of 9 different AHA-ILs. Finally, 15 newly designed AHA-ILs were evaluated to demonstrate the flexibility of the DFT/COSMO-RS tool by predicting their CO2 absorption isotherms. The evaluated absorbents compromise very different behaviors: from physical absorption to reactions completely displaced toward products at very low CO2 partial pressure, emphasizing the extremely tunable character of AHA-ILs. Current results will definitively contribute to link molecular and processes scales in the research of new CO2 capture technology based on ILs.

Physical absorption of CO2 in betaine/carboxylic acid-based Natural Deep Eutectic Solvents

The ability of some zwitterionic natural deep eutectic solvents (NADESs) based on N,N,N-trimethylglycine (TMG) and carboxylic acids (oxalic, glycolic and phenylacetic) to act as environmentally friendly solvents for CO2 capture has been investigated. The solubility of CO2 in the NADESs was measured gravimetrically at different temperatures in the range 298.15–333.15 K, and at different pressures in the range 0.1–4 MPa. The effect of the adopted experimental conditions has been discussed. The highest uptake has been observed for phenylacetic acid/TMG DES at 313.15 K and 4 MPa (45.5 mg CO2/g DES). The efficiency of this NADES as CO2 sorbent when reused in subsequent capture cycles has been evaluated. This work might open new perspectives in developing the most appropriate combination of HBA and HBD components of the DESs and the most appropriate operative conditions for an environmentally friendly CO2 capture.

The effect of liquid viscosity and modeling of mass transfer in gas–liquid slug flow in a rectangular microchannel

AbstractBoth chemical (by adding 0.05 M NaOH) and physical absorption of CO2 into aqueous glycerol solutions with viscosity up to 45.6 mPa·s in a microchannel are investigated. The concentration distribution pattern, absorption time, and mass transfer coefficient are analyzed and discussed. A new concentration distribution pattern is observed with the lowest concentration locating at the channel center. It is shown for the first time that presents a positive relationship with liquid viscosity, which is explained by the essential role of the mass exchange between the liquid film and bulk liquid slug. This mass exchange may lead to a rise in k L when increasing the liquid viscosity under some cases in chemical absorption. A mass transfer model is successfully applied to predict the bubble size evolution in physical absorption. The model also shows about 10–46% of the mass transfer contribution from liquid films before saturation.

CO2 absorption intensification using novel DEAB amine-based nanofluids of CNT and SiO2 in membrane contactor

Recent developments in nanotechnology have a great impact to improve the mass transfer in gas-liquid systems. The effect of nanoparticles was taken into account considering Grazing effect and Brownian motion as main phenomena of mass transfer enhancement in nanofluids. In the present study, a sensitivity analysis was performed to evaluate the influence of nanoparticles on the CO2 absorption inside a hollow fiber membrane contactor (HFMC). The distilled water and chemical system of 4-diethylamino-2-butanol (DEAB)-water nanofluid for CO2 absorption was studied. The considered drops were nanofluids containing carbon nanotube (CNT) and nanosilica (SiO2). A rigorous two-dimensional mathematical model for CO2 absorption from a N2/CO2 gas mixture was developed. The predicted results indicated that the injection of nanoparticles to distilled water and DEAB amine solution improves the CO2 absorption efficiency. Nanofluid of CNT represented better separation performance than nanosilica. Also, the CO2 absorption efficiency of nanofluids was enhanced with the increasing amine and nanoparticle concentration, liquid flow rate and also, decreasing the gas flow rate. Although increasing the liquid temperature decreased the physical absorption of CO2, it enhanced the chemical absorption of CO2 due to improvement of the reaction rates and diffusion coefficients.

Various CO2-to-CO Electrolyzer Cell and Operation Mode Designs to avoid CO2-Crossover from Cathode to Anode

Abstract The electrochemical CO2 reduction reaction (CO2RR) towards CO allows to turn CO2 and renewable energy into feedstock for the chemical industry. Previously shown electrolyzers are capable of continuous operation for more than 1000 h at high faradaic efficiencies and industrially relevant current densities. However, the crossover of educt CO2 into the anode gas has not been investigated in current cell designs: Carbonates (HCO3 − and CO3 2−) are formed at the cathode during CO2RR and are subsequently neutralized at the anode. Thus, CO2 mixes into the anodically evolved O2, which is undesired from commercial perspectives. In this work this chemical transport was suppressed by using a carbonate-free electrolyte. However, a second transport mechanism via physically dissolved gases became apparent. A transport model based on chemical and physical absorption of CO2 and O2 will be proposed and two solutions were experimentally investigated: the use of an anode GDL (A-GDL) and degassing the anolyte with a membrane contactor (MC). Both solutions further reduce the CO2 crossover to the anode below 0.1 CO2 for each cathodically formed CO while still operating at industrially relevant current densities of 200 mA/cm2.

Thermodynamic and kinetic evaluation of ionic liquids + tetraglyme mixtures on CO2 capture

The mixture of ionic liquids (ILs) with a low viscous solvent such as tetraglyme (TGM) may be interesting to reach new absorbent formulations with improved performance in CO2 capture technologies. In this work, CO2 absorption by IL/TGM mixtures was analyzed by equilibrium and kinetic gravimetric measurements and packed column simulations in Aspen Plus. Four ILs with remarkable different absorbent properties were employed. The ILs 1-butyl-methylimidazolium tricyanomethanide ([Bmim][TCM]) and 1-butyl-methylimidazolium methylsulfate ([Bmim][MeSO4]) present CO2 physical absorption, with remarkably different viscosity values. On the other hand, the ILs trihexyltetradecylphosphonium 2-cyanopyrrolide ([P66614][CNPyr]) and1-butyl-methylimidazolium acetate ([Bmim][Acetate]) were selected as CO2 chemical absorbents, being the former significantly less viscous. CO2 absorption experiments were carried out in a magnetic suspension microbalance using a wide composition range of IL/TGM mixtures, measured at 303 K and at different pressures, from 1 up to 20 bar. The results were analyzed considering thermodynamics (CO2 solubility in IL/TGM) and kinetics (CO2 diffusivity in IL/TGM) features. ILs with physical absorption presented higher CO2 solubilities and diffusivities when increasing TGM composition. In fact, the neat TGM shows higher CO2 physical absorption capacity and rate than IL/TGM mixtures at any studied opeating conditions. In contrast, ILs with CO2 chemical absorption generally present higher CO2 absorption capacity than TGM/IL mixtures, but a certain amount of TGM improves drastically the CO2 absortion kinetics with a slight decrease of the solubility. The simulation analysis of IL/TGM performance in the absorption column reveals that: i) TGM is better physical absorbent for CO2 capture than IL/TGM mixtures and neat ILs; and ii) it is possible to select finest IL/TGM mixtures which minimize the solvent and energy expenses in CO2 capture by chemical absorption.