Reactive Absorption Of CO2 Research Articles

Physical and reactive absorption of CO2 in capillaries: Mass transfer, modelling and produced chemical species

In a circular economy and sustainability context, CO2 utilization is key. For photochemical or electrochemical transformations, CO2 absorption in liquids has become crucial and even a limiting step. This work aimed to establish an average mass transport coefficient (k̅La) characteristic of the CO2 absorption in water and in alkaline solutions in capillary absorbers (2–4 mm) under Taylor flow and recirculation mode. A correlation among prevailing dimensionless numbers (Sh, Re, Ca and Sc) was also established. To achieve so, the absorption of CO2 was conducted in both, water and NaOH solutions (0.5 mol/dm3), and its concentration was monitored by measuring total inorganic carbon and pH. The gas and liquid flowrates used for the tests were 1.66×10−4 L/s and 2.5×10−4 L/s, respectively. The effect of temperature was investigated in the range of 283 and 308 K. The highest k̅La was found to be 12 × 10−2 and 2.1 × 10−2 s−1, for water and NaOH solutions, respectively. The modelling and simulation of the carbon species formation and production was also conducted and a determination coefficient (R2) of 0.99 was found.

Immobilization of carbonic anhydrase for CO2 capture and utilization.

Carbonic anhydrase (CA) is an excellent candidate for novel biocatalytic processes based on the capture and utilization of CO2. The setup of efficient methods for enzyme immobilization makes CA utilization in continuous bioreactors increasingly attractive and opens up new opportunities for the industrial use of CA. The development of efficient processes for CO2 capture and utilization (CCU) is one of the most challenging targets of modern chemical reaction engineering. In the general frame of CCU processes, the interest in the utilization of immobilized CA as a biocatalyst for augmentation of CO2 reactive absorption has grown consistently over the last decade. The present mini-review surveys and discusses key methodologies for CA immobilization aimed at the development of heterogeneous biocatalysts for CCU. Advantages and drawbacks of covalent attachment on fine granular solids, immobilization as cross-linked enzyme aggregates, and "in vivo" immobilization methods are presented. In particular, criteria for optimal selection of CA-biocatalyst and design of CO2 absorption units are presented and discussed to highlight the most effective solutions. Perspectives on biocatalytic CCU processes that can include the use of CA in an enzymatic reactive CO2 absorption step are eventually presented with a special focus on two examples of CO2 fixation pathways: hybrid enzyme-microalgae process and enzyme cascade for theproduction of carboxylic acids. KEY POINTS: • Covalent immobilization techniques applied to CA are effective for CO2 ERA. • Biocatalyst type and morphology must be selected considering CO2 ERA conditions. • Immobilized CA can offer novel routes to CO2 capture and direct utilization.

3D multiphase flow simulation of Marangoni convection on reactive absorption of CO2 by monoethanolamine in microchannel

The Marangoni convection leads to variation in the CO 2 loading distribution, and causes deformation of the phase interface. Moreover, it can promote interface renewal and enhance the reaction absorption process of MEA and CO 2 . A multiphase flow 3D numerical simulation method employing the coupled volume of fluid (VOF) and level set model is established to study the reactive absorption of CO 2 by the monoethanolamine (MEA) aqueous solution in a falling film microchannel. Based on the flow-reaction-mass transfer model of the MEA-CO 2 system in the falling film microchannel, the enhancement effect of the Marangoni convection in this reactive absorption process is analyzed. The enhancement factor of the Marangoni convection obtained in this work is in good agreement with experimental results in the literature. With consideration of the absorption ratio as well as the enhancement effect of the Marangoni convection, the influence of different MEA concentrations on absorption of CO 2 is investigated. Furthermore, the appropriate MEA concentration for absorption enhanced by the Marangoni convection is acquired.

Influence of five model parameters on the performance of a CO2 absorber column by a loaded aqueous MEA solution

Rigorous packed-bed absorber modeling and simulation are significant for post-combustion CO2 capture processes design. Hence, a good knowledge and judicious selection of model parameters are essential to ensure reliable predictions. In this paper, the reactive absorption of CO2 into loaded aqueous monoethanolamine solution was modeled, furthermore, the effects of five different parameters (kinetic model, enhancement factor, enthalpy of absorption, CO2 diffusivity, and vapor pressure) were investigated. Finally, this study revealed that some model parameters have a large influence on the column performance, contrary to others. In addition, methods and correlations that generally provide more accurate predictions of the empirical data relative to the other cases involved in this research were determined for each model parameter. It was also found that the model deviation was reduced by 18% and 4% for the liquid temperature and liquids CO2 loading profiles, respectively, while comparing between the worst and the best case.

Accurately Predicting CO2 Reactive Absorption Properties in Aqueous Alkanolamine Solutions by Molecular Simulation Requiring No Solvent Experimental Data

We present a general atomistic simulation framework for efficient reactive equilibrium calculations in dilute solutions, and its application to CO2 reactive absorption in aqueous alkanolamine solutions. No experimental data of any kind are required for the solvents, and no empirical adjustments are required for its implementation. This hybrid methodology calculates reaction equilibrium constants by combining high-level quantum chemical calculations of ideal-gas standard reaction Gibbs energies (ΔG0) with conventional solvation free energy calculations obtained from classical force field methodology. For these quantities we use explicit solvent molecular dynamics simulations with the General AMBER Force Field (GAFF). The resulting equilibrium constants are then coupled with a macroscopic Henry Law based ideal solution model to calculate the solution speciation and the CO2 partial pressure, PCO2. We show results for seven primary amines: monoethanolamine (MEA), 2-amino-2-methylpropanol (AMP), 1-amino-2-propanol (1-AP), 2-amino-2-methyl-1,3-propanediol (AMPD), 2-aminopropane-1,3-diol (SAPD), 2-(2-aminoethoxy)ethanol or diglycolamine (2-AEE or DGA, respectively), and 2-amino-1-propanol (2-AP). Experimental speciation and PCO2 data for some of these are available, with which we validate our methodology. We predict new results for others in cases when such data are unavailable, and provide explanations for the experimental inability to detect carbamate solution species in relevant cases. Our results for the pK value of the carbamate reversion reaction are within the chemical accuracy limit of 218.546/T units (corresponding to 1 kcal·mol–1 in the corresponding free energy change) in comparison with experimental results when such data exist, which at 298.15 K corresponds to 0.73 pK units. The precision of our pK predictions is comparable to that which can be obtained from conventional experimental methodologies for these quantities. Our results suggest that the presented molecular simulation methodology may provide a robust and cost-efficient tool for solvent screening in the design of post-combustion CO2 capture processes.

CO2 Reactive Absorption into an Aqueous Blended MDEA and TMS Solution: Experimental and Modeling

In this research, the significant environmental process of CO2 capture is investigated into an aqueous blended MDEA + TMS solution using a stirrer reactor experimentally and numerically. The experiments were designed based on the response surface methodology (RSM) under operating conditions of a pressure range of 2–8 bar, a temperature range of 20–70 °C, MDEA, and TMS concentration range of 10–20 wt%. The results indicated that by enhancing the initial pressure from 3.5 to 8 bar, the equilibrium CO2 loading increases by 17.8%. Based on RSM and central composite design method, the maximum values of CO2 loading and absorption percentages were 0.308% and 72.73%, respectively, at appropriate conditions of the temperature of 32.5 °C, the pressure of 3.5 bar, and MDEA and TMS concentrations of 12.5 wt%. A new relation for CO2 loading was correlated with a correlation coefficient of 0.994, as a function of studied independent variables.

Competitive H2S – CO2 absorption in reactive aqueous methyldiethanolamine solution: Prediction with ePC-SAFT

Reactive absorption of CO2 and H2S in aqueous methyldiethanolamine (MDEA) solutions is considered within the ePC-SAFT equation of state. We demonstrate that ePC-SAFT can be employed in a predictive manner without regression of additional temperature-correlated terms. Mixed system predictions are tested using a consistent set experimental data covering a wide range of temperatures (313 K–413 K), partial pressures (0.001 kPa–1000 kPa), and MDEA mass fractions (0.05–wMDEA 0.75 wMDEA). Predicted partial pressures for acid gas absorption show good agreement for low MDEA fractions (wMDEA< 0.5). Absorption selectivity in binary H2S + CO2 absorption is correctly predicted, with absolute average deviations of 57.18% and 79.32% for partial pressures of CO2 and H2S. We identify a significant deterioration in ePC-SAFT predictive power for the high-MDEA regime (wMDEA > 0.5), likely originating from underlying assumptions in the Debye-Hückel electrolyte free energy treatment and representation of ionic species.

Prediction of Alkanolamine pKa Values by Combined Molecular Dynamics Free Energy Simulations and ab Initio Calculations

Knowledge of aqueous protonation constants (pKa) of chemical species is of significant importance in CO2 reactive absorption system design. Their theoretical prediction has mainly relied on implici...

Reactive absorption of CO2 into Piperazine aqueous solution in a stirrer bubble column: Modeling and experimental

The present work focuses on CO2 reactive absorption using Piperazine aqueous solutions in a stirrer bubble column. A stirrer bubble column has been applied for operating conditions, including CO2 partial pressures in the range of 16.0–35.2 kPa, stirrer speed in the range of 0–300 rpm and CO2 loading in the range of 0.01–0.3 mol CO2.mol Pz−1. The results reveal that the absorption reaction rate increases with increasing the CO2 partial pressure and Pz concentration. The film parameter increases with increasing the Pz concentration and decreasing the CO2 partial pressure. Experimental results show that mass transfer flux, overall mass transfer coefficient and removal efficiency of CO2 are varied in the range of (0.35–4.32)×10−6 kmol.m−2.s−1, (2.39–2.58)×10−6 kmol. m−2.s−1.kPa−1 and 65.5–82.1%, respectively. Hydrodynamic studies illustrate that gas holdup, gas-liquid interfacial area, and Sauter mean diameter increases with increasing CO2 partial pressure and decreasing Pz concentration. Also, it was found that gas holdup, Sauter mean diameter and interfacial area values obtained in this work are within the range of 0.06–0.076, 10–13 mm and 44.0–46.1 m2 m−3, respectively.

A Novel Approach to the Modelling of Transport Phenomena in Random Packings

The separation characteristics of absorption columns are commonly predicted by simplified stage models (equilibrium or rate-based). Such models employ several parameters which have to be determined by experiments. This represents a major weakness of stage models, as, generally, these parameters are not directly transferable to different chemical systems or geometries. An alternative approach to the modelling of transport phenomena in fluid separation processes is based on so-called hydrodynamic analogies. Hereby, the actual flow in a packing is replaced by a combination of different, simplified flow patterns depending on the specific geometry of column internals. The transport of heat and mass in such flows can be described by rigorous conservation equations. As a consequence, the use of most of the above mentioned experimental parameters can be avoided. In this work, the hydrodynamic analogy approach is applied to random packings. To validate the model, the separation efficiency of Pall rings for the reactive absorption of CO2 into aqueous sodium hydroxide solution was investigated experimentally in an industrial-scale column. In this paper, the modelling method is described in detail and the validation of the simulation results is presented.

Immobilization of carbonic anhydrase for enhancement of CO2 reactive absorption

Cleaning workers experience occupational hazards, such as skin diseases and respiratory illness, due to their exposure to the ingredients of cleaning chemicals. To control chemical exposure through inhalation route, airborne concentration of the chemicals is maintained within its occupational exposure limits (OELs). However, universally accepted OELs for dermal exposure are lacking. Unavailability of experimentally determined values of dermal absorption parameters is one of the reasons behind it. Herein, we estimated the dermal absorption parameters (e.g., octanol–water partition coefficient, skin permeability coefficient and maximum flux of chemical across the skin) of a number of cleaning chemical ingredients. Atom/Fragment Contribution (AFC) method was used to estimate octanol–water partition coefficients. The skin permeability coefficients were estimated using the Potts and Guy correlation equation. The estimated skin permeability coefficients were used to estimate maximum flux of the chemicals across the skin. Estimated values of these parameters were compared to that of the chemicals for which ACGIH assigned a “skin” notation. The skin permeability coefficients of the cleaning chemical ingredients were found as similar to that of the chemicals having ACGIH “skin” notation. However, the maximum fluxes of the chemicals were found as lower than that of the chemicals having ACGIH “skin” notation. The estimated dermal absorption parameters of the ingredients are expected to help in evaluating dermal exposure hazard of the cleaning chemicals.

An experimental correlation for mass transfer flux of CO2 reactive absorption into aqueous MEA‐PZ blended solution

AbstractIn this study, the thermodynamics and mass transfer of CO2 absorption in the aqueous monoethanolamine‐piperazine blended solution have been studied. A correlation is proposed for the mass transfer flux of CO2 reactive absorption. The effective parameters on the mass transfer flux are considered in both the liquid and gas phases using dimensional analysis Pi‐Buckingham theorem. The effective variables were extracted as a dimensionless parameter. The dimensionless parameters are calculated from experimental data presented in the literature. The unknown constants of the mass transfer flux correlation are obtained using nonlinear regression. In the proposed correlation, the effect of operating parameters including the partial pressure, temperature, and also the dimensionless parameters of the film parameter, enhancement factor, and loading are investigated. The results showed that by increasing the loading and film parameter, the mass transfer flux was reduced. The mean absolute deviation in the proposed correlation for mass transfer flux was about 4.5%, which indicates the high accuracy of the predicted equation.

Investigating the performance and thermodynamic efficiency of CO2 reactive absorption – A solvent comparison study

The capture of the CO2 released in the atmosphere by various sources is a key issue included in all environmental related European new legislation and roadmaps. Among Carbon Capture Systems (CCS), post-combustion reactive absorption is one of the most efficient and easily deployable methods. In specific, amine aqueous solvents ensure high absorption efficiency due to their reactivity with CO2. Monoethanolamine (MEA) and a mixture of Monoethanolamine and Piperazine, 30 MEA/18 PZ % wt., were found to achieve very satisfying levels of CO2 capture. For these solvents, a simulation of the entire CO2 capture unit was performed in Aspen Plus software. For the MEA case, a parametric analysis was performed to determine the impact of the absorber inlet liquid temperature, gas and liquid flow rates on CO2 mole fraction, reboiler heat duty and stripper temperature profile. The absorber inlet liquid temperature was found to be the most important factor influencing the absorption performance as well as the reboiler heat duty required for regeneration. The absorber inlet gas and liquid flow rates had also impact on the liquid temperature profiles in the absorber and on the energy cost. Comparing the two solvents, the MDEA/PZ solvents captured 99% of the CO2 of the flue gas while MEA only 80% for the conditions of the simulation. For the reference system with MEA, overall exergy efficiency was calculated considering the carbon capture unit as an integrated thermodynamic system. The overall exergy efficiency of the MEA system was calculated 23.8%, while the respective value for the MDEA/PZ system was calculated 26.1%. Evaluating the two main columns of the system in terms of exergy efficiency, the absorber showed low values of efficiency for both solvents, in specific 16.3% for MEA and 22.6% for MDEA/PZ, while the desorber had higher efficiencies, 27.8% for MEA and 34.3% for MDEA/PZ. In general, MDEA/PZ system was characterized by higher thermodynamic efficiencies both in system and individual column level. Furthermore, the analysis for the MDEA/PZ system resulted to a 5% lower reboiler heat duty than in the MEA case.

Reactive absorption of CO2 in NaOH: An Euler-Euler simulation study

Recently, a new model for the reactive mass transfer during absorption of CO2 in aqueous NaOH was developed, based on using a rather generally applicable expression for the enhancement factor and taking into account the reaction of CO2 with water in addition to that with hydroxide ions (Krauß and Rzehak, 2017). By substituting the interfacial area concentration estimated from experimental data, good agreement was found for the pointwise measurement of time-dependent pH-value in a bubble column taken from the literature (Darmana et al., 2007). In the present contribution, this mass transfer model is implemented in an Euler-Euler/RANS framework including also the hydrodynamic part of the problem. Hydrodynamic closures were taken the same as applied successfully for a range of different conditions in previous work. However, the accuracy of the coupled model in predicting the measured pH-value is seen to fall behind that of the simple pointwise approximation. This suggests that for the present application, the hydrodynamic part of the model requires further improvement. Possible directions to this end are discussed.

Study of Ion Speciation of CO2 Absorption into Aqueous 1-Dimethylamino-2-propanol Solution Using the NMR Technique

In this work, the speciation (i.e., 1DMA2P molecule as well as 1DMA2PH+, HCO3–, and CO32– ions) for the CO2 reactive absorption of CO2 in aqueous 1-dimethylamino-2-propanol solution (i.e., into a 1DMA2P–H2O–CO2 system) was studied using the 13C nulcear magnetic resonance (NMR) technique at a temperature of 301 K over the 1DMA2P concentration range of 0.5–2.0 mol/L and CO2 loading range of 0–1.0 mol CO2/mol amine. Also, in addition to other material conservation laws, a new criterion for selection of the protonation calibration curves, the charge balance of the 1DMA2P–H2O–CO2 system, was added in order to generate results with better accuracy. In addition, the equilibrium constants, K1 and K5, were also obtained using the NMR technique, which had good agreement with those from other works with absolute average deviations of 2.2% and 3.5%, respectively.

Reactive absorption of CO2 in NaOH: Detailed study of enhancement factor models

In a pioneering study, Darmana et al. (2007), considered the reactive absorption of CO2 in aqueous NaOH in a bubble column. Although quite good agreement was obtained between an Euler-Lagrange simulation and measured pH-values at a single point, a number of aspects of the model deserve further discussion. This will be provided in the present work by using a simplified treatment that applies at the measurement location. Particularly relevant is the enhancement factor, which describes the effect of the chemical reaction on the mass transfer. An investigation of alternative expressions for this quantity is given, based on which an improved match with the data can be obtained. Furthermore, the complete network of possible reactions in this system has to be considered.

Parametric analysis using AMP and MEA as aqueous solvents for CO2 absorption

Chemical absorption (or reactive absorption) is a common technique used for gas sweetening purposes, capturing acid components from point source emissions or even from ambient air (Cheng and Tan, 2011). CO2 reactive absorption is extensively studied as it is a very effective process, targeting to the emissions reduction of this dangerous greenhouse gas, with wide perspective for further optimization. Reactive absorption combines physical absorption and reaction between acid components and basic solvents, thus the modelling of these mechanisms is challenging and requires a multi-component design (Koronaki et al., 2013).In this work, a rate-based, steady state model, based on the two-film theory, is presented and it is validated for two alkanolamine based aqueous solvents, Mono-ethanolamine (MEA) and 2-Amino-2-methyl-1-propanol (AMP). The model predictions are validated against data extracted by experiments conducted in a pilot scale absorption column with random packing. The comparisons between the model results and the experimental data reveal satisfactory predictions of the various parameters’ profiles along the column.A parametric analysis is performed, investigating the effect of inlet gas and liquid flow rates, the initial liquid loading, the type of packing, the initial amine solution concentration and the gas and liquid inlet temperatures on the CO2 absorption efficiency and on the temperature of the liquid getting out the column. The sensitivity analysis shows that the gas flow rate entering the column is the most important factor influencing the CO2 removal efficiency. In addition, inlet liquid temperature has the greater statistical significance on the outlet liquid temperature. The comparison of the two solvents under the same reference conditions shows that MEA is more efficient as solvent for CO2 absorption.

Modeling of the chemical behavior of sodium fire aerosols during atmospheric dispersion

ABSTRACTThe use of liquid sodium as a coolant in sodium-cooled fast reactors (SFR) circuits requires studying the consequences of a sodium fire for safety analysis, and particularly the toxicological impact of sodium fire aerosols. More particularly, the carbonation of sodium fire aerosols from sodium hydroxide (NaOH) to sodium carbonate (Na2CO3) is investigated. A new kinetic model, based on the CO2 reactive absorption and the two-film theory, is developed to describe the carbonation process of NaOH solutions, taking into account the NaOH aerosols' initial characteristics in equilibrium with the atmosphere. This model is applied for the case of NaOH aerosols considering the CO2 absorption at the particle external surface. The estimation for the model parameters is detailed as function of NaOH degree of conversion, relative humidity (RH), and temperature. By comparisons with available experimental data, the absorption interfacial area is empirically estimated over the studied range of RH and initial parti...

Computer-aided molecular design of imidazole-based absorbents for CO2 capture

Reactive absorption of CO2 by aqueous amine solutions is widely used in the oil, gas and petrochemical industries. However, the energy cost associated with CO2 capture is still a major hurdle to global implementation. Finding new absorbent systems with improved properties is therefore critical to the safety and efficiency of the carbon capture process. Owing to a wide range of tunable properties, imidazoles or imidazoles/amine mixtures have recently been identified as promising to address some of these challenges. In this work, evolutionary de novo design is used to propose new imidazole-based compounds suitable for carbon capture. At the core of this scheme is a genetic algorithm that optimizes the acid dissociation constant (pKa), an important factor governing the performance of solvents. Calculation of the pKa using quantum chemical methods may produce accurate results but is often too computationally demanding to be suitable for a de novo design setup, where thousands of structures are evaluated over many iterations. To improve the efficacy of the evolutionary process while maintaining high accuracy, we apply a quantitative structure–property relationship (QSPR) model that relates molecular structure descriptors calculated at the semi-empirical level to experimentally determined pKa values. Several promising compounds with high pKa (>10) were identified by the evolutionary design approach and further validated using density functional theory calculations. QSPR models for equally relevant physical properties (such as density, viscosity, vapour pressure) and biodegradability were used as additional filters to ensure that the high pKa structures also have favourable values for these properties.

Rigorous correlation for CO2 mass transfer flux in reactive absorption processes

Mass transfer flux of CO2 in reactive absorption processes depends on mass transfer variables of both liquid and gas phases. In this work, a new rigorous correlation for calculation of CO2 mass transfer flux in reactive absorption processes was developed based on the variables. The correlation parameters including film parameter, CO2 loading, concentration ratio, pressure ratio, film thickness ratio and diffusion coefficient ratio were determined using Buckingham Pi-theorem. Experimental data of CO2 reactive absorption in piperazine solution were used to evaluate the correlation. The data used in calculating the correlation constants are temperature in range of 40–100°C, partial pressure of CO2 in range of 18–66,330Pa, CO2 loading in range of 0.226–0.412mole of CO2 per mole of amine and amine concentration of 2–8molal (Dugass, 2009). The average absolute relative error for the presented correlation is 5.8% which infers high accuracy of this correlation compared to the previous correlations reported based on enhancement factors. The results showed that increasing the temperature and CO2 loading has negative effect on CO2 mass transfer flux. Also the results indicated that on increasing partial pressure of CO2 and piperazine concentration, the rate of mass transfer was increased.