Absorption of carbon dioxide in aqueous colloidal silica solution with NaOH

The absorption rate (R _A ) of carbon dioxide was measured into an aqueous nanometer-sized colloidal silica solution of 0–31 wt% and NaOH of 0–2 kmol/m³ in a flat-stirred vessel for various sizes and speeds of 25 °C and 101.3 N/m² to obtain the volumetric liquid-side mass transfer coefficient (k _L a _L ) of CO₂. The film theory accompanied by chemical reaction between CO₂ and NaOH was used to estimate the theoretical value of absorption rate of CO₂. The empirical correlation formula containing the relationship between k _L a _L and rheological property of the aqueous colloidal silica solution was presented. The value of R _A in the aqueous colloidal silica solution was decreased by the reduction of k _L a _L due to elasticity of the solution.     

Mass transfer of carbon dioxide in aqueous colloidal silica solution containing <Emphasis Type="Italic">N</Emphasis>-methyldiethanolamine

The absorption rate (R _A ) of carbon dioxide was measured into an aqueous nanometer sized colloidal silica solution of 0–31 wt% and N-methyldiethanolamine of 0–2 kmol/m3 in a flat-stirred vessel for the various sizes and speeds of at 25 °C and 0.101 MPa to obtain the volumetric liquid-side mass transfer coefficient (k _L a) of CO₂. The film theory accompanied by chemical reaction between CO₂ and N-methyldiethanolamine was used to estimate the theoretical value of absorption rate of CO₂. An empirical correlation formula containing the relationship between k _L a and rheological property of the aqueous colloidal silica solution was presented. The value of R _A in the aqueous colloidal silica solution was decreased by the reduction of k _L a due to elasticity of the solution.     

Absorption of Carbon Dioxide into Aqueous Xanthan Gum Solution Containing Monoethanolamine

Abstract

Carbon dioxide was absorbed into the aqueous xanthan gum (XG) solution in the range of 0–0.151 wt% containing monoethanolamine (MEA) of 0–2 kmol/m³ in a flat‐stirred vessel with the impeller of 0.05 m and agitation speed of 50 rpm at 25°C and 0.101 MPa to measure the absorption rate of CO₂. The volumetric liquid‐side mass transfer coefficient (k_La_L) of CO₂ decreased with increasing XG concentration, and was correlated with the empirical formula having the rheological behavior of XG solution. The chemical absorption rate of CO₂ was estimated by the film theory using the values of k_La_L and physicochemical properties of CO₂ and MEA. The aqueous XG solutions made the rate of absorption of CO₂ accelerated compared with the Newtonian liquid based on the same viscosity of the solution.     

Chemical Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution with Diethanolamine

Abstract

The chemical absorption rate (R_A) of CO₂ was measured into the aqueous nanometer sized colloidal silica solution of 0–31 wt% and diethanoleamine of 0–2 kmol/m³ in the flat‐stirred vessel with the impeller size of 0.034 m and its agitation speed of 50 rev/min at 25°C and 0.101 MPa, and compared with the values estimated from the model based on the film theory accompanied by chemical reaction. The value of the volumetric liquid‐side mass transfer coefficient (k_La) of CO₂, which was used to estimate the value of R_A, was obtained by the empirical correlation formula presenting the relationship between k_La and the rheological behavior of the aqueous colloidal silica solution. The value of R_A in the aqueous colloidal silica solution was decreased by the reduction of k_La due to the elasticity of the solution.     

Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution

Abstract

On the basis of experimental data for carbon dioxide absorption into aqueous nanometer sized colloidal silica solution as a non‐Newtonian fluid, a dimensionless correlation for volumetric liquid‐side mass transfer coefficient (k_La) of CO₂ in the flat‐stirred vessel was proposed. In addition to ordinary liquid properties and operating parameters such as impeller size and speed in the vessel, Deborah number, which is defined as the product of the characteristic material times of the liquid and agitation speed in the flat‐stirred vessel and represents the viscoelastic behavior of non‐Newtonian fluid, was used to present unified expressions for k_La in Newtonian as well as non‐Newtonian liquid. The values of k_La in the aqueous colloidal silica solution were reduced due to elasticity of the solution.     

Chemical Absorption of Carbon Dioxide into Aqueous PEO Solution of Monoethanolamine

Abstract

Carbon dioxide was absorbed into aqueous polyethylene oxide (PEO) solution containing monoethanolamine (MEA) in a flat‐stirred vessel to investigate the effect of non‐Newtonian rheological behavior of PEO on the rate of chemical absorption of CO₂, where the reaction between CO₂ and MEA was assumed to be a first‐order reaction with respect to the molar concentration of CO₂ and MEA, respectively. The liquid‐side mass transfer coefficient (k_L), which was obtained from the dimensionless empirical equation containing the properties of viscoelasticity of the non‐Newtonian liquid, was used to estimate the enhancement factor due to chemical reaction. PEO with elastic property of non‐Newtonian liquid made the rate of chemical absorption of CO₂ accelerate compared with Newtonian liquid based on the same viscosity of the solution.     

An experimental/computational study of steric hindrance effects on CO2 absorption in (non)aqueous amine solutions

The reaction kinetics and molecular mechanisms of CO₂ absorption using nonaqueous and aqueous monoethanolamine (MEA)/methyldiethanolamine (MDEA)/2-amino-2-methy-1-propanol (AMP) solutions were analyzed by the stopped-flow technique and ab initio molecular dynamics (AIMD) simulations. Pseudo first-order rate constants (k₀) of reactions between CO₂ and amines were measured. A kinetic model was proposed to correlate the k₀ to the amine concentration, and was proved to perform well for predicting the relationship between k₀ and the amine concentration. The experimental results showed that AMP/MDEA only took part in the deprotonation of MEA-zwitterion in nonaqueous MEA + AMP/MEA + MDEA solutions. In aqueous solutions, AMP can also react with CO₂ through base-catalyzed hydration mechanism beside the zwitterion mechanism. Molecular mechanisms of CO₂ absorption were also explored by AIMD simulations coupled with metadynamics sampling. The predicted free-energy barriers of key elementary reactions verified the kinetic model and demonstrated the different molecular mechanisms for the reaction between CO₂ and AMP.     

Comparison of the rate of CO2 absorption into aqueous ammonia and monoethanolamine

Aqueous ammonia has been proposed as an absorbent for use in CO₂ post combustion capture applications. It has a number of advantages over MEA such as high absorption capacity, low energy requirements for CO₂ regeneration and resistance to oxidative and thermal degradation. However, due to its small molecular weight and large vapour pressure absorption must be carried at low temperature to minimise ammonia loss. In this work the rate of CO₂ absorption into a falling thin film has been measured using a wetted-wall column for aqueous ammonia between 0.6 and 6 mol L^?1, 278–293 K and 0–0.8 liquid CO₂ loading. The results were compared to 5 mol L^?1 MEA at 303 and 313 K. It was found that the overall mass transfer coefficient for aqueous ammonia was at least 1.5–2 times smaller than MEA at the measured temperatures. From determination of the second-order reaction rate constant k₂ (915 L mol^?1 s^?1 at 283 K) and activation energy E_a (61 kJ mol^?1) it was shown that the difference in mass transfer rate is likely due to both the reduced temperature and differences in reactivity between ammonia and MEA with CO₂.     

Surfactant adsorption onto activated carbon and its effect on absorption with chemical reaction

The effects of surfactant contaminations and activated carbon addition on physical gas absorption, and absorption with fast and instantaneous reaction (sulphite oxidation, carbon dioxide absorption into sodium hydroxide and monoethanol amine (MEA) solutions) have been studied in a stirred cell with a flat gas/liquid interface. Surfactants significantly decrease the liquid-side mass transfer coefficient k_L even at very small concentrations. The surfactants can be removed by adsorption onto activated carbon (“surfactant grazing”).In absorption with fast chemical reaction of the gas (sulphite oxidation), the liquid side mass transfer coefficient k_L has no effect on the absorption rate and, consequently, there are no effects of surfactant and activated carbon. CO₂ absorption into sodium hydroxide solution may occur in the instantaneous absorption regime; then, any change in k_L causes a proportional change in the absorption rate. In CO₂ absorption into MEA solution, however, in the instantaneous regime, much stronger effects of surfactant and of its removal by activated carbon are observed. It is suggested that in the absence of surfactants surface convection (Marangoni instability) may occur in MEA solutions.     

Gas–liquid mass‐transfer properties in CO2 absorption system with ionic liquids

The deficiency of mass‐transfer properties in ionic liquids (ILs) has become a bottleneck in developing the novel IL‐based CO₂ capture processes. In this study, the liquid‐side mass‐transfer coefficients (k_L) were measured systematically in a stirred cell reactor by the decreasing pressure method at temperatures ranging from 303 to 323 K and over a wide range of IL concentrations from 0 to 100 wt %. Based on the data of k_L, the kinetics of chemical absorption of CO₂ with mixed solvents containing 30 wt % monoethanolamine (MEA) and 0–70 wt % ILs were investigated. The k_L in IL systems is influenced not only by the viscosity but also the molecular structures of ILs. The enhancement factors and the reaction activation energy were quantified. Considering both the mass‐transfer rates and the stability of IL in CO₂ absorption system, the new IL‐based system MEA + [bmim][NO₃] + H₂O is recommended. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2929–2939, 2014     

Carbon dioxide absorption in a cross-flow rotating packed bed

This work investigates the feasibility of applying the cross-flow rotating packed bed (RPB) to the removal of carbon dioxide (CO₂) by absorption from gaseous streams. Monoethanolamine (MEA) aqueous solution was used as the model absorbent. Also, other absorbents such as the NaOH and 2-amino-2-methyl-1-propanol (AMP) aqueous solutions were compared with the MEA aqueous solution. The CO₂ removal efficiency was observed as functions of rotor speed, gas flow rate, liquid flow rate, MEA concentration, and CO₂ concentration. Experimental results indicated that the rotor speed positively affects the CO₂ removal efficiency. Our results further demonstrated that the CO₂ removal efficiency increased with the liquid flow rate and the MEA concentration; however, decreased with the gas flow rate and the CO₂ concentration. Additionally, the CO₂ removal efficiency for the MEA aqueous solution was superior to that for the NaOH and AMP aqueous solutions. Based on the performance comparison with the conventional packed bed and the countercurrent-flow RPB, the cross-flow RPB is an effective absorber for CO₂ absorption process.     

己二酸对MEA吸收-解吸CO2过程的影响<

实验研究了己二酸对MEA水溶液吸收-解吸CO₂的影响。在0.4 mol·L-1 MEA的CO₂吸收富液解吸过程加入一定量的己二酸并分析了其对CO₂解吸能耗和解吸速率的影响,发现解吸速率明显升高,析出单位体积CO₂的能耗显著降低;对解吸还原后的贫液进行了CO₂二次吸收的实验,发现因加酸引起的CO₂二次吸收量变化小于7%;为去除不确定因素对CO₂相似文献   

Simultaneous absorption of CO<Subscript>2</Subscript> and SO<Subscript>2</Subscript> into aqueous AMP/NH<Subscript>3</Subscript> solutions in binary composite absorption system

To enhance the absorption rate for CO₂ and SO₂, aqueous ammonia (NH₃) solution was added to an aqueous 2-amino-2-methyl-1-propanol (AMP) solution. The simultaneous absorption rates of AMP and a blend of AMP+ NH₃ for CO₂ and SO₂ were measured by using a stirred-cell reactor at 303 K. The process operating parameters of interest in this study were the solvent and concentration, and the partial pressures of CO₂ and SO₂. As a result, the addition of NH₃ solution into aqueous AMP solution increased the reaction rate constants of CO₂ and SO₂ by 144 and 109%, respectively, compared to that of AMP solution alone. The simultaneous absorption rate of CO₂/SO₂ on the addition of 1 wt% NH₃ into 10 wt% AMP at a p _A1 of 15 kPa and p _A2 of 1 kPa was 5.50×10⁻⁶ kmol m⁻² s⁻¹, with an increase of 15.5% compared to 10 wt% AMP alone. Consequently, the addition of NH₃ solution into an aqueous AMP solution would be expected to be an excellent absorbent for the simultaneous removal of CO₂/SO₂ from the composition of flue gas emitted from thermoelectric power plants.     

Combined Absorption and Self-Decomposition of Ozone in Aqueous Solutions with Interfacial Resistance

A theoretical analysis is performed employing the film model for the isothermal absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance, which is inversely proportional to the interfacial mass transfer coefficient k_s. A closed-form solution has been obtained. The effects of system parameters on the ozone mass transfer rate are examined. These parameters include the interfacial resistance (1/k_s), the acidic and basic self-decomposition reaction rate parameters (M_m ^0.5, M_n ^0.5.; M_m = [2D_Ak_mC_Ai ^m-1/(m+1)]/(k_L ⁰)², M_n=(2D_Ak_nC_Ai ^n-1/(n+1))/(k_L ⁰)², the reaction orders (m,n), the pH value of solution, and the liquid-phase mass transfer coefficient (k_L ⁰). The results indicate that the reduction effect of the interfacial resistance on the absorption rate is most significant for the situation with the larger values of M_m and M_n as well as with higher pH values. Also, for any particular finite value of k_L ⁰/k_s, the reduction effect encountered is greater for a gas liquid contactor with a lower k_L ⁰. The reduction effect should be avoided in order to maintain a higher mass transfer rate of ozone in aqueous solution. This analysis is of importance for the efficient use of ozone in water/wastewater treatment processes in the presence of interfacial resistance substances such as surface active agents. For some known special cases (for example, cases with no interfacial resistance), the present solution reduces to the previous works of other investigators.     

Analysis of the heat of reaction and regeneration in alkanolamine-CO<Subscript>2</Subscript> system

The estimation of regeneration heat of absorbent is important because it is a key factor that has an effect on the process efficiency. In this study, thermal stability and regeneration heat of aqueous amine solutions such as monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), N-methyldiethanolamine (MDEA), and 1,8-diamino-pmenthane (KIER-C3) were investigated by using TGA-DSC analysis. The thermal characteristics of the fresh and CO₂ rich amine solutions were estimated. The CO₂ rich amine solutions were obtained by VLE experiments at T=40 °C. The regeneration heat of aqueous MEA solution was 76.991–66.707 kJ/mol-CO₂, which is similar to heat of absorption. The reproducibility of the results was obtained. The regeneration heat of aqueous KIER-C3 20 wt% solution (1.68 M) was lower than that of aqueous MEA 30 wt% solution (4.91 M). Therefore, the KIER-C3 can be used as an effective absorbent for acid gas removal.     

Kinetics and new mechanism study of CO2 absorption into water and tertiary amine solutions by stopped-Flow technique

The objective of the present work was to find the accurate kinetic models and mechanism for CO₂ absorption into tertiary amine solution, aiming at understanding the contribution of the CO₂ reaction with H₂O, OH⁻, and tertiary amines on the overall reaction rate. First, the kinetics of CO₂ absorption into water instead of a buffer solution were studied using the stopped-flow technique at 293–313 K, with initial CO₂ molar concentration of 1.1–37.3 mM. The experimental first-order reaction rate constant () was determined to be about 1000 times larger than the value for CO₂ absorption into buffer solution reported in the reference. The was then correlated by a proposed semiempirical model and a simplified theoretical model, giving the activation energy for CO₂ reacting with H₂O as fitted by the simplified theoretical model in good agreement with the value of previous research. Also, the pH values and hydroxyl ion concentrations of aqueous Diethylaminoethanol (DEEA) solutions were determined at 293–313 K, with DEEA molar concentration of 0.1–0.4 M and CO₂ loading of 0–0.626 mol/mol. In addition, the observed first-order reaction rate constant ( k_{0_DEEA} ) of binary DEEA-H₂O solution with DEEA molar concentration of 0.1–0.4 M reacting with CO₂ was determined at 293–313 K. It should be pointed out that the kinetic experiments of CO₂ absorption into DEEA solution was done with the molar ratio of DEEA to CO₂ fixed at 20. The values of k_{0_DEEA} were then fitted and predicted by four models (i.e., termolecular model, base-catalyzed model, the improved model, and Khalifah model). The results show the improved model and Khalifah model can predict k_{0_DEEA} well with an average absolute relative difference (AARD) <5%. The predicted results indicate that the contribution of OH⁻ to k_{0_DEEA} cannot be ignored for the absorption of CO₂ into tertiary amine solutions, and could be responsible for 50–70% of the total absorption reaction rate. Furthermore, the k₀ value of CO₂ absorption into aqueous triethanolamine and CO₂-loaded DEEA solution were further investigated and comprehensively discussed, suggesting that both pK _a and the CO₂ solubility affect k₀ , with pK _a having a much more significant effect. © 2018 American Institute of Chemical Engineers AIChE J, 65: 652–661, 2019     

The development of kinetics model for CO2 absorption into tertiary amines containing carbonic anhydrase

CO₂ absorption into aqueous solutions of two tertiary alkanolamines, namely, MDEA and DMEA with and without carbonic anhydrase (CA) was investigated with the use of the stopped‐flow technique at temperatures in the range of 293–313 K, CA concentration varying from 0 to 100 g/m³ in aqueous MDEA solution with the amine concentration ranging from 0.1 to 0.5 kmol/m³, and CA concentration varying from 0 to 40 g/m³ in aqueous DMEA solution with the amine concentration ranging from 0.05 to 0.25 kmol/m³. The results show that the pseudofirst‐order reaction rate (k_{0, amine}; s^?1) is significantly enhanced in the presence of CA as compared with that without CA. The enhanced values of the kinetic constant in the presence of CA has been calculated and a new kinetics model for reaction of CO₂ absorption into aqueous tertiary alkanolamine solutions catalyzed by CA has been established and used to make comparisons of experimental and calculated pseudo first‐order reaction rate constant (k_{0, with CA}) in CO₂‐MDEA‐H₂O and CO₂‐DMEA‐H₂O solutions. The AADs were 15.21 and 15.17%, respectively. The effect of pKa on the CA activities has also been studied by comparison of CA activities in different tertiary amine solutions, namely, TEA, MDEA, DMEA, and DEEA. The pKa trend for amines were: DEEA > DMEA > MDEA > TEA. In contrast, the catalyst enhancement in amines was in the order: TEA> MDEA> DMEA> DEEA. Therefore, it can be seen that the catalyst enhancement in the amines decreased with their increasing pKa values. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

CO<Subscript>2</Subscript> capture using aqueous solutions of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>+2-methylpiperazine and monoethanolamine: Specific heat capacity and heat of absorption

The specific heat capacity, heat of CCO₂ absorption, and CCO₂ absorption capacity of aqueous solutions of potassium carbonate (K₂CO₃)+2-methylpiperazine (2-MPZ) and monoethanolamine (MEA) were measured over various temperatures. An aqueous solution of K₂CO₃+2-MPZ is a promising absorbent for CCO₂ capture because it has high CCO₂ absorption capacity with improved absorption rate and degradation stability. Aqueous solution of MEA was used as a reference absorbent for comprison of the thermodynamic characteristics. Specific heat capacity was measured using a differential scanning calorimeter (DSC), and heat of CCO₂ absorption and CCO₂ absorption capacity were measured using a differential reaction calorimeter (DRC). The CCO₂-loaded solutions had lower specific heat capacities than those of fresh solutions. Aqueous solutions of K₂CO₃+2-MPZ had lower specific heat capacity than those of MEA over the temperature ranges of 303-353 K. Under the typical operating conditions for the process (CCO₂ loading=0.23mol-CCO₂·mol^?1-solute in fresh solution, T=313 K), the heat of absorption (?ΔHabs) of aqueous solutions of K₂CO₃+2-MPZ and MEA were approximately 49 and 75 kJ·mol-CO₂, respectively. The thermodynamic data from this study can be used to design a process for CCO₂ capture.     

Transfer rate measurement of lysozyme by liquid-liquid extraction using reverse micelles with dense CO2

Lysozyme was extracted from aqueous solution into i-octane using reverse micelles in the presence of pressurized CO₂. A squat vessel with two independent stirrers was used to measure the mass transfer of the lysozyme across a planar interface. Mass transfer coefficient, k _L of the lysozyme from the aqueous to the organic phase was measured at selected ionic strengths, pH, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant concentrations, temperatures and pressurized CO₂. The mass transfer rate of lysozyme was higher in high temperature (318 K) and pressure (20MPa). pH of 9 in aqueous phase showed highest mass transfer rate of lysozyme. The application of pressurized CO2 markedly increased the mass transfer rate of lysozyme comparing to conventional non-pressurized system.     

Reaction between Hydrosulfide and Iron/cerium (hydr)oxide: Hydrosulfide Oxidation and Iron Dissolution Kinetics

Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N₂) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide initial concentration (0.90–3.30 mmol/L), oxide initial surface area (16–143 m²/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by means of capillary electrophoresis, while iron dissolution was monitored through atomic absorption spectroscopy. Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments. The hydrosulfide oxidation by the iron/cerium (hydr)oxide was found to be surface-controlled, with rates (R_i) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: R_i = k_i[HS⁻]_t=0^−0.5[A]_t=0[H⁺]_t=0^−0.5 , where k_i represents the apparent rate constants for the oxidation of HS⁻ (k_HS) or the dissolution of Fe(II) (k_Fe), [HS⁻]_{t = 0} is the initial hydrosulfide concentration, [A]_{t = 0} is the initial Fe/Ce (hydr)oxide surface area and [H⁺]_{t = 0} is the initial proton concentration. The rate constant, k_HS, for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 ± 0.65) × 10⁻⁴ mol² L⁻¹ m⁻² min⁻¹, with the rate of hydrosulfide oxidation being ca. 10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric ratio between HS⁻ oxidized and Fe(II) produced; k_Fe = (3.9116 ± 0.41) × 10⁻⁵ mol² L⁻¹ m⁻² min⁻¹).