Wetted Wall Contactor Research Articles

Measuring CO2 and N2O Mass Transfer into GAP-1 CO2–Capture Solvents at Varied Water Loadings

This paper investigates the CO2 and N2O absorption behavior in the water-lean gamma amino propyl (GAP)-1/TEG solvent system using a wetted-wall contactor. Testing was performed on a blend of GAP-1 aminosilicone in triethylene glycol at varied water loadings in the solvent. Measurements were made with CO2 and N2O at representative lean (0.04 mol CO2/mol alkalinity), middle (0.13 mol CO2/mol alkalinity), and rich (0.46 mol CO2/mol alkalinity) solvent loadings at 0, 5, 10, and 15 wt % water loadings at 40, 60, and 80 °C and N2O at (0.08–0.09 mol CO2/mol alkalinity) at 5 wt % water at 40, 60, and 80 °C. CO2 flux was found to be nonlinear with respect to log mean pressure driving force (LMPD). Liquid-film mass transfer coefficients (k′g) were calculated by subtracting the gas film resistance (determined from a correlation from literature) from the overall mass transfer measurement. The resulting k′g values for CO2 and N2O in GAP-1/TEG mixtures were found to be higher than that of 5 M aqueous monoethanolamine u...

Measuring Nitrous Oxide Mass Transfer into Non-Aqueous CO2BOL CO2 Capture Solvents

This paper investigates CO2 absorption behavior in CO2BOL solvents by decoupling the physical and chemical effects using N2O as a nonreactive mimic. Absorption measurements were performed using a wetted-wall contactor. Testing was performed using a “first generation” CO2-binding organic liquid (CO2BOL), composed of an independent base and alcohol. Measurements were made with N2O at a lean (0.06 mol CO2/mol BOL) and rich (0.26 mol CO2/mol BOL) loading, each at three temperatures (35, 45, and 55 °C). Liquid-film mass transfer coefficients (kg′) were calculated by subtracting the gas film resistance-determined from a correlation from literature–from the overall mass transfer measurement. The resulting kg′ values for N2O in CO2BOLs were found to be higher than that of 5 M aqueous MEA under comparable conditions, which is supported by published measurements of Henry’s coefficients for N2O in various solvents. These results suggest that the physical solubility contribution for CO2 absorption in CO2BOLs is great...

Absorption of carbon dioxide in piperazine activated concentrated aqueous 2-amino-2-methyl-1-propanol solvent

In this work new experimental data on the rate of absorption of CO 2 into piperazine (PZ) activated concentrated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) over the temperature range 303–323 K are presented. The absorption experiments have been carried out in a wetted wall contactor over CO 2 partial pressure range of 5–15 kPa. PZ is used as a rate activator with a concentration ranging from 2 to 8 wt% keeping the total amine concentration in the solution at 40 wt%. The physical properties such as density and viscosity of concentrated aqueous AMP+PZ, as well as physical solubility of CO 2 in concentrated aqueous AMP+PZ, are also measured. New experimental data on vapor liquid equilibrium (VLE) of CO 2 in these concentrated aqueous solutions of AMP+PZ in the temperature range of 303–323 K have also been presented. The VLE measurements are carried out in an equilibrium cell in CO 2 pressure range of 0.1–140 kPa. A thermodynamic model based on electrolyte non-random two-liquid (eNRTL) theory is used to represent the VLE of CO 2 in aqueous AMP+PZ. Liquid phase speciations are estimated considering the nonideality of concentrated solutions of the amines and the calculated activity coefficients by eNRTL model. The CO 2 absorption in the aqueous amine solutions is described by a combined mass transfer-reaction kinetics model developed according to Higbie's penetration theory. The model predictions have been found to be in good agreement with the experimental results of the rates of absorptions of CO 2 into aqueous AMP+PZ.

Absorption of carbon dioxide into piperazine activated aqueous N-methyldiethanolamine

This work presents a theoretical and experimental investigation on the absorption of CO 2 into piperazine (PZ) activated aqueous N-methyldiethanolamine (MDEA) solvent. A comprehensive mathematical model which is based on Higbie's penetration theory has been developed to analyze the experimental data. The model involving coupled mass transfer–reaction kinetics–chemical equilibrium incorporates the important reversible reactions in the liquid phase. The model is validated with the experimental results of steady state absorption measurements of CO 2 in a 2.81 × 10 −2 m o.d. stainless steel wetted wall contactor. The rates of absorption of CO 2 into this solvent have been measured over the CO 2 partial pressure range of 2–14 kPa and temperature range of 298–313 K under atmospheric pressure. The absorption experiments are performed over the MDEA concentration range of 1.89–2.41 kmol m −3 along with PZ concentrations of 0.24, 0.60 and 0.95 kmol m −3. The predicted absorption rates and enhancement factors based on the model have been found to be in good agreement with the experimental results, the average absolute deviation between the model predicted and experimental results being 6.8%. The values of the rate constants, k 23 and k 25 for the PZ-carbamate and PZ-dicarbamate formation reactions determined in this work have been found to be about 17,500 m 6 kmol −2 s −1 and 15,500 m 6 kmol −2 s −1 at 298 K, respectively. Good agreement between the model predicted and experimental results validates the mathematical model developed in this work to represent CO 2 mass transfer in PZ activated aqueous MDEA.

Absorption of carbon dioxide into aqueous solutions of piperazine activated 2-amino-2-methyl-1-propanol

In this work, new experimental data on the rate of absorption of CO 2 into piperazine (PZ) activated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) are reported. The absorption experiments using a wetted wall contactor have been carried out over the temperature range of 298–313 K and CO 2 partial pressure range of 2–14 kPa. PZ is used as a rate activator with a concentration ranging from 2 to 8 wt%, keeping the total amine concentration in the solution at 30 wt%. The CO 2 absorption into the aqueous amine solutions is described by a combined mass transfer-reaction kinetics-equilibrium model, developed according to Higbie's penetration theory. Parametric sensitivity analysis is done to determine the effects of possible errors in the model parameters on the accuracy of the calculated CO 2 absorption rates from the model. The model predictions have been found to be in good agreement with the experimental results of rates of absorption of CO 2 into aqueous (PZ+AMP). The good agreement between the model predicted rates and enhancement factors and the experimental results indicates that the combined mass transfer-reaction kinetics-equilibrium model with the appropriate use of model parameters can effectively represent CO 2 mass transfer in PZ activated aqueous AMP solutions.

Kinetics and modeling of carbon dioxide absorption into aqueous solutions of piperazine

In this work, the kinetics of the reaction between CO 2 and aqueous piperazine (PZ) have been estimated over the temperature range of 298–313 K from the absorption data obtained in a wetted wall contactor. The absorption data are obtained for the PZ concentrations of 0.2– 0.8 kmol m - 3 and for CO 2 partial pressures up to 5 kPa. A coupled mass transfer-kinetics-equilibrium mathematical model based on Higbie's penetration theory has been developed with the assumption that all reactions are reversible. The model is used to estimate the rate constants from the experimental data for absorption of CO 2 in aqueous PZ. The estimated rate constants of this study are in good agreement with those reported in the literature.

Absorption of [formula omitted] in aqueous blends of diglycolamine [formula omitted] and morpholine

The rate of CO 2 absorption in aqueous morpholine (MOR), and aqueous mixtures of MOR and diglycolamine ® (DGA) was measured in a wetted wall contactor. 23.5 wt% MOR and 11 wt% MOR/53 wt% DGA were studied at 298–333 K. The second order rate constant for MOR at 25 °C, 22000 L/mol s, is four times greater than DGA. The MOR reaction with CO 2 was found to be catalyzed by DGA, consistent with the zwitterion mechanism. Predictions made with a rigorous eddy diffusivity theory suggest that 11 wt% MOR/53 wt% DGA absorbs CO 2 50% faster than 65 wt% DGA of the same CO 2 loading.

Thermodynamics and Equilibrium Solubility of Carbon Dioxide in Diglycolamine/Morpholine/Water

Carbon dioxide solubility was studied in 3.5 m (23.5 wt %) morpholine (MOR), 17.7 m (65 wt %) 2-aminoethoxyethanol (diglycolamine or DGA), and 3.6 m MOR + 14.7 m DGA (11 wt % MOR + 53 wt % DGA). CO2 solubility was determined by dynamic measurements with a wetted wall contactor. Carbamate and bicarbonate concentrations were determined by 13C NMR in solutions loaded with 13CO2. The data are represented by the electrolyte NRTL model. At a given CO2 loading (mol/mol amine), the CO2 vapor pressure over 3.5 m MOR is 10 to 1000 times greater than 17.7 m DGA. In 3.6 m MOR + 14.7 m DGA, the CO2 vapor pressure is 5 to 7 times greater than in 17.7 m DGA at high CO2 loading, but the same below 0.2 loading. MOR carbamate is less stable than DGA carbamate by a factor of 7 to 10 from (300 to 333) K. The model predicts that MOR vapor pressure is 100 times greater than DGA over 3.6 m MOR + 14.7 m DGA from (313 to 333) K. The heat of CO2 absorption in the blend is equivalent to 17.7 m DGA up to 0.35 loading but is 40 % lower at 0.5 loading. The working capacity of the blend is 17 % less than 17.7 m DGA.

Absorption of carbon dioxide in aqueous piperazine/methyldiethanolamine

AbstractCarbon dioxide absorption in 0.6 M piperazine (PZ)/4 M methyldiethanolamine (MDEA) was measured in a wetted wall contactor. The data were simulated using a model that accounts for chemical reactions and transport effects with the eddy diffusivity theory. PZ/MDEA blends absorb CO2 faster than monoethanolamine (MEA) or diethanolamine (DEA) blends with MDEA at similar concentrations. The reaction of PZ to form a monocarbamate is dominant at low loading (<0.14). The reaction of the monocarbamate to form dicarbamate is dominant at high loading. The absorption rate did not follow pseudo first‐order behavior except at very low loading. All carbamate and dicarbamate formation reactions approached instantaneous behavior at high loading. The series resistance due to pseudo first‐order reaction and instantaneous carbamate formation matched data throughout the entire loading range. A typical ammonia plant absorber was simulated at isothermal conditions using the rigorous model. Gas film limitations were dominant (>50%) only at the top of the absorber.

Thermodynamics of Piperazine/Methyldiethanolamine/Water/Carbon Dioxide

Vapor−liquid equilibrium, speciation, and amine solubility were studied for the piperazine (PZ)/methyldiethanolamine (MDEA)/water/carbon dioxide system. Solubility data for carbon dioxide in these solutions were obtained using a wetted-wall contactor. Solubility data for anhydrous PZ solid in water were obtained by adding PZ flakes to an agitated flask. In a 0.6 M PZ/4 M MDEA solution at 313 K, the partial pressure of carbon dioxide approaches one-tenth of the value in 4 M MDEA at low loading. This performance is between that of monoethanolamine (MEA) blends and diethanolamine (DEA) blends. The solubility data are modeled using the electrolyte NRTL model. The model is verified using 13C and 1H NMR data at high loading. The resulting model shows that the piperazine carbamate is the major reaction product at low loading (<0.1) while the protonated piperazine carbamate is the major reaction product at high loading. The piperazine dicarbamate species is present in higher concentration than in the simple PZ/H2O/CO2 system. Comparison to other blends (MEA/MDEA and DEA/MDEA) show that the dicarbamate and protonated carbamate species have a negative effect on the solubility of CO2 at moderate loading. Amine volatility predictions are made using the Dortmund modification of the UNIFAC model to predict the activity coefficient of PZ in aqueous solutions. PZ volatility is very high; this model predicts PZ losses of the same magnitude as MDEA in a blend indicative of industrial concentrations, even though MDEA is present at much higher concentrations.

Removal of carbon dioxide by absorption in mixed amines: modelling of absorption in aqueous MDEA/MEA and AMP/MEA solutions

This work presents an investigation of CO 2 absorption into aqueous blends of methyldiethanolamine (MDEA) and monoethanolamine (MEA), as well as 2-amino-2-methyl-1-propanol (AMP) and monoethanolamine (MEA). The combined mass transfer–reaction kinetics–equilibrium model to describe CO 2 absorption into the amine blends has been developed according to Higbie's penetration theory following the work of Hagewiesche et al. (Chem. Eng. Sci. 50 (1995) 1071). The model predictions have been found to be in good agreement with the experimental rates of absorption of CO 2 into (MDEA+MEA+H 2O) of this work and into (AMP+MEA+H 2O) reported by Xiao et al. (Chem. Eng. Sci. 55 (2000) 161), measured at higher contact times using wetted wall contactor. The good agreement between the model predicted rates and enhancement factors and the experimental results indicate that the combined mass transfer–reaction kinetics–equilibrium model with the appropriate use of model parameters can effectively represent CO 2 mass transfer for the aqueous amine blends MDEA/MEA and AMP/MEA.

Absorption of carbon dioxide into aqueous piperazine: reaction kinetics, mass transfer and solubility

This work studies the absorption of carbon dioxide into aqueous solutions of piperazine in a wetted wall contactor. Absorption was studied from 298 to 333 K in solutions of 0.6 and 0.2 M aqueous piperazine. The apparent reaction rate is first order in both carbon dioxide and piperazine with a value of 53,700 m 3/ kmol s at 25°C. The apparent second-order rate constant follows an Arrhenius temperature dependence over the range studied with an activation energy of 3.36×10 4 kJ/ kmol . Solubility in 0.6 M PZ was measured by bracketing absorption and desorption in the wetted wall contactor at 313 and 343 K . Chemical and phase equilibrium was modeled by considering the following piperazine species: piperazine carbamate, dicarbamate, protonated carbamate, and protonated piperazine. Henry's law and the dissociation of carbon dioxide to form bicarbonate and carbonate were also considered. The carbamate stability constant and p K a for piperazine carbamate were regressed from the VLE data. Although shown to be present by NMR, the dicarbamate is not the dominant reaction product at any loading. The carbamate stability constant is comparable to other secondary amines such as diethanolamine (DEA) but the apparent second-order rate constant is an order of magnitude higher than primary amines such as monoethanolamine (MEA) or diglycolamine (DGA ®). The second-order rate constant obtained in this work is much higher than previously published values for the piperazine/carbon dioxide reaction. These previous studies were limited by mass transfer limitation of products and reactants and were not a true measurement of the kinetics of carbon dioxide/piperazine. There is some evidence that the reactivity of piperazine is due to its cyclic and diamine characteristics.

Chemical kinetics of the reaction of CO 2 with amines in pseudo m– nth order conditions in polar and viscous organic solutions

The specific rate of absorption for five gas-liquid systems: CO 2-monoethanolamine (MEA) in ethanol solution, CO 2-diethanolamine (DEA) in ethanol, CO 2-MEA in ethylenglycol, CO 2-DEA in ethylenglycol and CO 2-cyclohexylamine (CHA) in ethylenglycol was measured in a laboratory wetted wall contactor. Reactions were found to be first order with respect to CO 2 and second order with respect to amine for the first four ones and first order with respect to amine for the last one. The values of the specific rate of absorption are such that these reactions may be used to determine interfacial areas and mass transfer coefficients in gas-liquid reactors working with polar and viscous organic liquids.