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Modeling and experimental study on the solubility and Mass transfer of CO2 into aqueous DEA solution using a stirrer bubble column
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In this research, the chemical absorption rate and solubility of carbon dioxide into DEA aqueous solutions were investigated in a stirrer bubble column. Experiments envelopment the molarity of DEA, CO2 partial pressures and stirrer speed are 0.2-2.0 M, 300-450 kPa and 0-600 rpm, respectively. The DEA and CO2 concentration and gas-liquid flow rate effects on the mass transfer performance were measured in terms of CO2 capture efficiency, loading, mass transfer flux and mass transfer coefficient. A thermodynamic model, according to the Pitzer's GE model is provided for the equilibrium solubility of CO2 in DEA aqueous solutions. The results have shown that the CO2 loading in range of 0.16-0.40 and mass transfer rate in range of 0.36 × 10⁻⁵ to 0.97 × 10⁻⁵ kmol m⁻² s⁻¹ increases with DEA concentration and CO2 partial pressure. Also the results indicate that the quantity of kl increases with addition of DEA concentration, liquid and gas flow rate. Film parameter increases with increasing of DEA concentration and decreases with increasing of CO2 partial pressure. Absorption percent of CO2 was varied in range of 30-57%. The maximum absorption rate of CO2 at partial pressure of 45 kPa has been obtaining 1.8 g min⁻¹ when the DEA concentration is 2.0 M.
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... In the next step, due to the large input data and disparities in weights and slopes, normalization operations must be performed; otherwise, learning in neural networks will be slow [44]. To avoid this issue, Eq. (2) can be used for normalization [45]. ...
... In the next step, the learning algorithm for the network is determined. Training data is utilized to estimate network parameters, and weights, and enhance performance [45]. During the network training process, the validation data is used to improve the model based on a set of training data, and then the model is tested using the test data. ...
... (4) to assess the accuracy and performance of the model based on ANN. These measures evaluate the accuracy between the predicted values and the actual values [45]. ...
In this research, artificial neural networks (ANNs) were used to predict the mass transfer flux of CO2 in K2CO3/Piperazine solutions (NCO2). ANN models including multilayer perceptron (MLP) and radial basis function (RBF) networks were used in the modelling. response surface methodology (RSM) was used to assess the impact of the process variables to achieve the optimal conditions. The optimal values of the input parameters, including temperature, loading means and predicted, coefficient of gas and liquid mass transfer, partial pressure of CO2, and equilibrium partial pressure of CO2 were obtained 56.94, 0.472, 0.787, 3.321, 0.843, 55786.409 and 32334.814 respectively. The maximum CO2 mass flux at optimum conditions was obtained 449.915 (kmol/m2.s. It has been observed that reducing CO2 loading and PCO2* and increasing PCO2-b have a greater effect on NCO2 increase. The experimental data on CO2 absorption in K2CO3/Piperazine solutions were used as a case study to learn, test, and evaluate the 0.8, 0.1, and 0.1 values, respectively. The optimal structure of a MLP includes 4 and 5 neurons in two hidden layers, and for RBF it is equal to 50. The comparison of R2 values for MLP, RBF, and RSM shows that they were 0.9953, 0.9944, and 0.9819, respectively. This indicates that MLP has high accuracy and compatibility, as evidenced by its high R2 value. In addition, the results of the RSM and the MLP were compared, and they demonstrated the desired accommodation.
... When the DES is stirred, convection becomes a relevant factor and facilitates/boosts the transport of CO 2 molecules from the interface to the bulk of the liquid. The facilitated mass transfer can be understood based on the two-film theory [18,19], and by understanding that stirring reduces the thickness of the stagnant liquid film that the CO 2 molecules must cross by molecular diffusion before reaching well-mixed zones of the fluid. ...
... When the DES is stirred, convection becomes a relevant factor and facilitates/boosts the transport of CO2 molecules from the interface to the bulk of the liquid. The facilitated mass transfer can be understood based on the two-film theory [18,19], and by understanding that stirring reduces the thickness of the stagnant liquid film that the CO2 molecules must cross by molecular diffusion before reaching well-mixed zones of the fluid. The values of CO2 absorption capacity measured under stagnant conditions in this work are approximately similar to the ones reported by Ullah et al. at low pressures [15]. ...
Amine absorption (or amine scrubbing) is currently the most established method for CO2 capture; however, it has environmental shortcomings and is energy-intensive. Deep eutectic solvents (DESs) are an interesting alternative to conventional amines. Due to their biodegradability, lower toxicity and lower prices, DESs are considered to be “more benign” absorbents for CO2 capture than ionic liquids. In this work, the CO2 absorption capacity of choline-chloride/levulinic-acid-based (ChCl:LvAc) DESs was measured at different temperatures, pressures and stirring speeds using a vapour–liquid equilibrium rig. DES regeneration was performed using a heat treatment method. The DES compositions studied had ChCl:LvAc molar ratios of 1:2 and 1:3 and water contents of 0, 2.5 and 5 mol%. The experimental results showed that the CO2 absorption capacity of the ChCl:LvAc DESs is strongly affected by the operating pressure and stirring speed, moderately affected by the temperature and minimally affected by the hydrogen bond acceptor (HBA):hydrogen bond donator (HBD) molar ratio as well as water content. Thermodynamic properties for CO2 absorption were calculated from the experimental data. The regeneration of the DESs was performed at different temperatures, with the optimal regeneration temperature estimated to be 80 °C. The DESs exhibited good recyclability and moderate CO2/N2 selectivity.
... Among different technologies of CO 2 capture, including absorption, adsorption, membrane separation, cryogenic distillation, etc. post-combustion CO 2 absorption is the most mature process. This technology is widely used in the commercial applications due to its higher efficiency and lower cost [3][4][5][6][7][8][9]. Since the cost of CO 2 separation is a limiting factor for large-scale applications, reducing the cost of CO 2 separation process by improving the process and solvent is a major priority of the CO 2 absorption process. ...
... The constants values of Eq. (12) for expressed reactions (Eqs. (6)(7)(8)) are given in Table 2. ...
In this work, the CO2 absorption by potassium hydroxide aqueous solution was studied. The response surface methodology (RSM) based on central composite design (CCD) was used to design experiments, make models, and find the optimum operating conditions for attaining desirable responses in the range of temperature, pressure and absorbent concentration of 25–65 °C, 2–10 bar and 0.01–1.21 mol/lit, respectively. The effects of process variables and their interactions on the responses were investigated with the numerical model, obtained from experimental data fitting to a second-order polynomial model, to achieve the optimal conditions. The experiments and numerical model indicated that the increase in temperature and absorbent concentration decrease CO2 loading, and an increase in pressure increase CO2 loading. Optimum conditions were found to be the temperature of 35 °C, pressures of 4 bar and, KOH concentration of 0.412 mol/lit. The CO2 loading of 0.745 and CO2 removal efficiency of 32.221% were achieved in the optimal conditions. The modified Pitzer’s GE model was used for CO2 + KOH + H2O system, in order to investigate the species concentration in the liquid phase. The average relative error between predicted CO2 loading and experimental CO2 loading was 7.4%.
... Greenhouse gases are intended as a significant origin for universal warming of the ground in recent years. [1][2][3][4] Among the greenhouse gases (GHG), carbon dioxide is the most significant contributor to global warming, and its uptake from the atmosphere is continuously affecting the earth's heat balance. [5][6][7] Environmental issues due to pollutant emissions from fossil fuel combustion have become global problems, [8] including air toxins and greenhouse gases. ...
... [5][6][7] Environmental issues due to pollutant emissions from fossil fuel combustion have become global problems, [8] including air toxins and greenhouse gases. Further removal of acid gases, e.g., CO 2 and H 2 S, from natural gas, which is known as natural gas sweetening process, is an essential part of refinery plants. The CO 2 removal may be utilized to enhance oil recovery, urea production, and beverage carbonation purposes. ...
In this work, hydrodynamic and mass transfer of CO2 absorption into metal oxide nanofluid includes TiO2, ZnO, and ZrO2 nanoparticles at Piperazine (Pz) solution in the bubble column was studied. The novel rigorous correlations were extended based on the variable parameters for the calculation of gas holdup, enhancement factor, and mass transfer coefficients in the reactive absorption processes using the π-Buckingham method. The correlations were constructed based on dimensionless numbers, including nanoparticle loading, film parameter, CO2 partial pressure ratio to the total pressure, the film thickness of phases, CO2 loading, and ratio of diffusion coefficients of CO2 in the gas and liquid phases. Experimental data were used to calculate the correlations, consisting of Pz concentration, CO2 partial pressure, nanoparticle loading, and stirrer speed in the range of 0.1–0.5 mol/l, 16.0–35.2 kPa, 0.0–0.1 wt%, and 0–300 rpm, respectively. The film parameter was applied to exert the influence of chemical reactions on the performance of absorption. The mean squared error (RMSEP), the average absolute error (%AARD), and the coefficient of correlation of the results (R²) for the correlations were in the range 0.021–2.604, 3.78–18.14, and 0.861–0.980, respectively, which represents the excellent accuracy of the proposed correlation.
... The chemical reaction in these processes is reversible by changing the temperature and pressure of the system. Therefore, the chemical solvents can be revived by varying these operational parameters and circulate within a closed system [12]. Amine solutions are weak bases that are classified according to the number of organic groups bonded to nitrogen atoms. ...
... Reaction constants are considered as a function of temperature depicted in Eq. (12). Also, Henry's constant is calculated based on Eq. (13), the constants of which are reported in DeCoursey and Thring [29]. ...
The mass transfer parameters of both gas and liquid phases affect the mass transfer flux of CO2 in absorption processes. In this study, an accurate correlation was proposed to calculate CO2 mass transfer flux in an absorption‐reactive process by methyldiethanolamine (MDEA) solution using the Buckingham π theorem. The various parameters include film parameter, CO2 loading, concentration ratio, partial to total pressure ratio, film thickness ratio, and diffusion ratio are incorporated in the model. The operating conditions are in the ranges of 293–313K, 0.1–100kPa, 0.001–0.7, and 10–50 wt% for the temperature, total pressure, loading, and amine concentration, respectively. The results showed the average absolute relative error of 4.4% for the calculation of mass transfer flux.
... Alkano-amines in forms of an aqueous solution is one of the chemical solvents, which are more efficient at low partial pressures. The convectional amines are monoethanolamine (MEA), diethanolamine (DEA), methyl-diethanolamine (MDEA), and 2-amino-2-methyl-1-propanol (AMP) which are widely used in these processes (Ghaemi 2017;Mirzaei and Ghaemi 2018;Mondal et al. 2017;Pashaei et al. 2016). Due to low absorption capacity, foaming tendency, equipment corrosivity, and less absorption rate, the applications of amines are limited when they are used alone. ...
... The equilibrium Henry's and extended Raoult's laws are used for the CO 2 and H 2 O, respectively. The VLE equations for the CO 2 and H 2 O describe as (Pashaei et al. 2016 ...
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.
... Greenhouse gases have caused environmental problems, including increased temperature, damage to the ozone layer and changes in sea levels (Li et al., 2013;Mondal et al., 2012; emissions of greenhouse gases in the atmosphere, which is increasing with human activities (Leung et al., 2014;Pashaei et al., 2016). To reduce the environmental impacts of greenhouse gases, these gases should be prevented from entering the atmosphere. ...
... Generally, CO 2 removal is limited to four technologies such as cryogenic distillation, membrane purification, absorption using amine solutions and adsorption using solid adsorbents (Bansiwal et al., 2014;Norouzbahari et al., 2016;Pashaei et al., 2016;Shafeeyan et al., 2014;Wilcox, 2012). Cryogenic distillation and membrane purification were used less than other techniques for carbon dioxide capturing because of some problems and limitations. ...
Activated alumina (AA) was modified with sodium hydroxide and potassium hydroxide solutions to enhance carbon dioxide adsorption capacity. The process optimization was carried out using response surface methodology (RSM) based on central composite design (CCD) with two variables, the temperature and pressure in the range of (20–80 °C) and (2–10 bar), respectively. In addition, the effect of operating parameters including adsorbent amount, percentage of hydroxide solution, temperature and pressure on the CO2 adsorption process were investigated. The optimum CO2 adsorption capacities for modified activated alumina adsorbents with 30% NaOH and KOH at temperature of 20 °C and pressure of 6 bar were found to be 146.70 and 130.84 mg/g adsorbent, respectively. The Freundlich isotherm model was showed the best accordance with the experimental data and the kinetic modeling results indicated that the Elovich model is well-fitted for adsorption process by modified activated alumina. As well as thermodynamic parameters revealed that the adsorption process for the studied three adsorbents is exothermic and spontaneous.
... . Diethanolamine (DEA) is a commonly used solvent in the industrial gas sweetening process due to its high reaction rate with CO 2 and low volatility 7 . It is a primary amine that contains two hydroxyl groups, making it a good candidate for reacting with acid gases such as CO 2 and H 2 S 8,9 . ...
This research focuses on modeling CO2 absorption into alkanolamine solvents using multilayer perceptron (MLP), radial basis function network (RBF), Support Vector Machine (SVM), networks, and response surface methodology (RSM). The parameters, including solvent density, mass fraction, temperature, liquid phase equilibrium constant, CO2 loading, and partial pressure of CO2, were used as input factors in the models. In addition, the value of CO2 mass flux was considered as output in the models. Trainlm, trainbr, and trainscg algorithms trained the networks. The results showed that the best number of neurons for MLP with one layer is 16; with two layers, 5 neurons in the first layer and 12 neurons in the second layer; and with three layers, 9 neurons in the first layer, 5 neurons in the second layer, and 1 neuron in the third layer. The best spread in RBF was found to be 2.202 for optimal network performance. Furthermore, statistical data analysis revealed that the trainlm function performs best. The coefficients of determination for RSM, MLP, RBF, and SVM for optimized structures are obtained at 0.9802, 0.9996, 0.9940, and 0.8946, respectively. The results demonstrate that MLP and RBF networks can model CO2 absorption using the trainlm, trainbr, and trainscg algorithms.
... This reflects the heterogeneous nature of the surface which is supported by values greater than one obtained for the n parameter in Freundlich isotherms. Also, the affinity constant b indicates a reducing trend with temperature increasing, verifying the exothermic nature of the CO 2 uptake process 73,74 . ...
Deep eutectic solvents (DES) are a generation of ionic liquids that benefit from low cost, good stability, and environmental-friendly features. In this research, a porous silica gel was impregnated with a eutectic Choline Chloride-Monoethanolamine solvent (ChCl-MEA) to greatly improve its CO2 capture performance. In the impregnation, the weight percentages of ChCl-MEA were used in the range of 10–60 wt% at a temperature of 25 °C. The effect of ChCl-MEA loading on the structural properties of the DES-modified silica samples was studied by BET, FTIR, and TGA analyses. Investigation of the CO2 adsorption performance at different operational conditions showed that the modified silica gel with 50 wt% ChCl-MEA (Silica-CM50) presents the highest CO2 capture capacity of 89.32 mg/g. In the kinetic modeling, the fractional order model with a correlation coefficient of 0.998 resulted in the best fit with the experimental data. In addition, the isotherm data for Silica-CM50 were well-fitted with the Dual site Langmuir isotherm model with a correlation coefficient of 0.999, representing two distinct sites for the adsorption process. Moreover, the thermodynamic parameters including Enthalpy, Entropy, and Gibbs free energy at 25 °C were obtained to be − 2.770, − 0.005 and − 1.162, respectively. The results showed the exothermic, spontaneous and feasibility of the adsorption process.
... According to the zwitterion mechanism [34,35], the rate of CO 2 absorption is affected by the concentration of the hydroxyl ion as well as the amine and CO 2 concentration. In this mechanism, as the concentration of the hydroxyl ion decreases, the rate of CO 2 absorption also decreases. ...
Chemical absorption of CO2 into aqueous amine solutions using a nonstirred bubble column was experimentally investigated. The performance of CO2 absorption of four different primary and secondary amines including monoethanolamine (MEA), piperazine (PZ), 2-piperidineethanol (2PE), and homopiperazine (HPZ) were compared. The effects of initial concentration of amine, the inlet mole fraction of CO2, and solution temperature on the rate of CO2 absorption and CO2 loading (mol CO2/mol amine) were studied in the range of 0.02-1 M, 0.10-0.15, and 25-40 °C, respectively. The effect of the presence of copper ions in the amine solution on CO2 loading was also studied. By comparison of the breakthrough curves of the amines at different operational conditions, it was revealed that the shortest and longest time for the appearance of the breakthrough point was observed for MEA and HPZ solutions, respectively. CO2 loading of MEA, 2PE, PZ, and HPZ aqueous solutions at 25 °C, 0.2 M of initial concentration of amine, and 0.15 of inlet mole fraction of CO2 were 1.06, 1.14, 1.13, and 1.18 mol CO2/mol amine, respectively. By decreasing the inlet mole fraction of CO2 from 0.15 to 0.10, CO2 loading slightly decreased. As the initial concentration of amine and temperature decreased, CO2 loading increased. Also, the presence of copper ions in the absorbent solution resulted in a decrease in the CO2 loading of MEA and HPZ aqueous solutions. In case of PZ and 2PE amines, adding copper ions led to precipitation even at low copper ion concentrations.
... Bubble diameter (m) d 32 Sauter [15] MDEA Analysis of the effect of contactor, operation conditions, liquid phase nature and chemical reaction upon the mass transfer coefficient and gas-liquid interfacial area [16] Triethanolamine (TEA) Study of hydrodynamic behavior and mass transfer of CO2 removal process Analysis of the influence of operation conditions, liquid phase nature and chemical reaction on the mass transfer coefficient and gas-liquid interfacial area [17] MEA-based nanoparticle suspensions Adding nanoparticles (SiO 2 , TiO 2 and Al 2 O 3 ) to enhance CO 2 absorption rate [18] DEA Effect of gas and liquid flow rates, amine concentration and CO 2 partial pressure upon the absorption efficiency, mass transfer flux and CO 2 loading [19] PZ Analysis of mass transfer and hydrodynamics parameters including CO 2 loading, removal efficiency, absorption flux and mass transfer coefficients at various gas and liquid flow rate, absorbent concentration, and stirrer speed [20] PZ-based nanoparticle suspensions Investigation of the effect of nano heavy metal oxide particles (TiO 2 , ZnO and ZrO 2 ) on the hydrodynamic and absorption characteristics [21] PZ Study of reaction rate, film parameter, overall mass transfer coefficient, gas holdup, gas-liquid interfacial area and Sauter mean diameter the interpenetrating continuum assumption. The number of bubbles in computational cells is represented by the gas volume fraction and bubble-liquid interaction is accounted for through the interphase momentum exchange terms [25,26]. ...
In this study, numerical simulation of the removal process of CO2 using aqueous solutions of piperazine (PZ) in a bubble column has been done. The main focus of this work is to investigate the applicability of the space-time conservation element and solution element (CESE) method for the numerical solution of the coupling of hydrodynamics, mass transfer and chemical reactions. The reactive absorption process has been investigated by means of experiments and numerical simulation. A two-dimensional computational fluid dynamics (CFD) model in the Eulerian framework has been used to describe the gas-liquid system. To obtain the numerical solution, the CESE method based on a uniform rectangular mesh has been implemented by developing a computer code. Experimental study and CFD simulations have been carried out at different conditions of CO2 partial pressure (20 and 36 kPa) and solution concentration (0.1, 0.3 and 0.5 M). The simulation results were in reasonable agreement of 5.226 % and 4.575 % with the experimental values for gas holdup and mass transfer flux, respectively. The comparisons prove that the CESE method can be considered as a proper numerical method for the simulation of complex multiphase flows due to its simplicity, accuracy and low computational costs.
... According to our previous studies, 11 numerous chemical reactions happen in a bubble column. The possible reactions are summarized in Table 4. ...
The present work evaluates and optimizes CO2 absorption in a bubble column for the Pz-H2O–CO2 system. We analyzed the impact of the different operating conditions on the hydrodynamic and mass-transfer performance. For the optimization of the process, variable conditions were used in the multivariate statistical method of response surface methodology. The central composite design is used to characterize the operating condition to fit the models by the least-squares method. The experimental data were fitted to quadratic equations using multiple regressions and analyzed using analysis of variance (ANOVA). An approved experiment was carried out to analyze the correctness of the optimization method, and a maximum CO2 removal efficiency of 97.9%, an absorption rate of 3.12 g/min, an NCO2 of 0.0164 mol/m²·s, and a CO2 loading of 0.258 mol/mol were obtained under the optimized conditions. Our results suggest that Pz concentration, solution flow rate, CO2 flow rate, and speed of stirrer were obtained to be 0.162 M, 0.502 l/h, 2.199 l/min, and 68.89 rpm, respectively, based on the optimal conditions. The p-value for all dependent variables was less than 0.05, and that points that all three models were remarkable. In addition, the experiment values acquired for the CO2 capture were found to agree satisfactorily with the model values (R² = 0.944–0.999).
... Shahedi Asl). Hamborg and Versteeg, 2012;Kierzkowska-Pawlak, 2012;Luo et al., 2015;Mathews and Panda, 2012;Oh et al., 2011;Panda and Mathews, 2014;Pashaei et al., 2016;Tizaoui and Grima, 2011;Zhu et al., 2017). ...
The present study aimed to propose a general model for absorption with a non-elementary chemical reaction. The modeling of the system was conducted within the stagnant liquid film surrounding bubbles in the bubble column reactor. The finite difference method was used to solve the governing differential equations. The model was solved for the general reaction orders of components with a general boundary condition. Therefore, it includes all kinetic regimes based on the film theory and is capable of predicting the absorption system with a complex reversible or irreversible chemical reaction. Further, the effects of different parameters such as the equilibrium constant, the concentration of components, and chemical reaction orders on the absorption enhancement were investigated. The results indicated that the initial concentration and reaction order of components can significantly influence the absorption enhancement. Finally, In order to validate the model, the results were compared with those of the previous studies.
... Although water was used as absorbent owing to the easy access, the method exhibits a low capture efficiency. Afterward, amine solutions were applied worldwide (Amrei et al. 2014;Nakhjiri et al. 2018;Pashaei et al. 2016;Stowe and Hwang 2017;Yuan et al. 2017). Marzouk et al. (2010) conducted an experimental study on CO 2 capture in a mixed gas (9.5% CO 2 /90.5% CH 4 ). ...
Coalbed methane is an abundant form of natural gas extracted from coal beds. Coalbed methane is viewed as a cleaner energy source versus petroleum and coal combustion because methane extraction, transport and use are more efficient and less polluting. However, coalbed methane contains high amounts of CO2 that induce solidification during liquefaction. Therefore, CO2 has to be reduced below 2% to meet the pipeline transportation standards. In addition, CO2 capture would reduce the amount of gas emissions to the atmosphere, thus mitigating global warming. Here, we review membrane absorption, which is an advanced method for CO2 capture from coalbed methane, by controlling the gas and liquid phases separately during the operation process. We compare CO2 removal methods for various coalbed methane sources. Parameters influencing CO2 removal by membrane absorption are discussed to conclude that CO2 capture efficiency is improved by increasing the flow rate, temperature, and absorbent concentration, reducing the gas flow rate, and selecting a mixed absorbent. We also explain the principles, processes and applications of CO2 membrane absorption.
... The CO 2 absorption properties of different chemical absorbents were observed in this study. Sun et al. [29,30] studied the absorption of CO 2 by TEA, DEA and MEA aqueous solution through experiments. The absorption process was accompanied by chemical reaction, which enhanced the absorption of CO 2 . ...
... Reactive absorption is an important unit of several chemical and petrochemical industries. Chemical reactions in the absorption of undesirable gases bring many advantages in terms of operating conditions such as increasing mass transfer while decreasing the operating total pressure (Schneider et al., 2003;Khan et al., 2011;Pashaei et al., 2016). ...
In this research, the reactive absorption of carbon dioxide in an aqueous solution of NH3, H2O, and NaOH has experimentally been investigated. The experiments were carried out in an absorption pilot plant in different operational conditions. The composition and temperature of both gas and liquid phases were obtained during the column height. The concentration of molecular and ionic species in the liquid phase was calculated using the principles of electrolyte and Pitzer model. In the experiments, the effect of sodium hydroxide concentration on carbon dioxide absorption was considered. The results revealed that the concentrations of ionic and molecular species in the liquid phase drastically influence the absorption rate of carbon dioxide. Also, the results showed that the absorption rate of carbon dioxide was increased by increasing ammonia and sodium hydroxide concentration.
Burning fossil fuels releases toxic gases into the environment and has negative effects on it. In this study, Persian gum@Graphene oxide (Pg@GO) was synthesized and used as a novel adsorbent for CO2 capture. The characterization of materials was determined through XRD, FTIR, FE-SEM, and TGA analysis. The operating parameters including temperature, Pressure, and adsorbent weight were studied and optimized by response surface methodology via Box–Behnken design (RSM-BBD). The highest amount of CO2 adsorption capacity was 4.80 mmol/g, achieved at 300 K and 7.8 bar and 0.4 g of adsorbent weight. To identify the behavior and performance of the Pg@GO, various isotherm and kinetic models were used to fit with the highest correlation coefficient (R²) amounts of 0.955 and 0.986, respectively. The results proved that the adsorption of CO2 molecules on the adsorbent surface is heterogeneous. Based on thermodynamic results, as the value of ΔG° is − 8.169 at 300 K, the CO2 adsorption process is exothermic, and spontaneous.
Chemical vapour deposition (CVD) was used to produce multi-walled carbon nanotubes (MWCNTs), which were modified by Fe-Ni/AC catalyst to enhance CO2 adsorption. In this study, a new realm of possibilities and potential advancements in CO2 capture technology is unveiled through the unique combination of cutting-edge modelling techniques and utilization of the recently synthesized Fe-Ni/AC catalyst adsorbent. SEM, BET, and FTIR were used to analyze their structure and morphology. The surface area of MWCNT was found to be 240 m2/g, but after modification, it was reduced to 11 m2/g. The modified MWCNT showed increased adsorption capacity with higher pressure and lower temperature, due to the introduction of new adsorption sites and favorable interactions at lower temperatures. At 25°C and 10 bar, it reached a maximum adsorption capacity of 424.08 mg/g. The optimal values of the pressure, time and temperature parameters were achieved at 7 bar, 2646 S and 313 K. The Freundlich and Hill models had the highest correlation with the experimental data. The Second-Order and Fractional Order kinetic models fit the adsorption results well. The adsorption process was found to be exothermic and spontaneous. The modified MWCNT has the potential for efficient gas adsorption in fields like gas storage or separation. The regenerated M-MWCNT adsorbent demonstrated the ability to be reused multiple times for the CO2 adsorption process, as evidenced by the study. In this study, a feed-forward MLP artificial neural network model was created using a back-propagation training approach to predict CO2 adsorption. The most suitable and efficient MLP network structure, selected for optimization, consisted of two hidden layers with 25 and 10 neurons respectively. This network was trained using the Levenberg-Marquardt backpropagation algorithm. An MLP artificial neural network model was created, with a minimum MSE performance of 0.0004247 and an R2 value of 0.99904, indicating its accuracy. The experiment also utilized the blank spreadsheet design (BSD) within the framework of response surface methodology (RSM) to predict CO2 adsorption. The proximity between the Predicted R2 value of 0.8899 and the Adjusted R2 value of 0.9016, with a difference of less than 0.2, indicates a high level of similarity. This suggests that the model is exceptionally reliable in its ability to predict future observations, highlighting its robustness.
In this research, artificial neural networks (ANN) and response surface methodology (RSM) were applied for modeling and optimization of carbon dioxide (CO2) absorption using KOH-Pz-CO2 system. In the RSM approach, the central composite design (CCD) describes the performance condition in accordance with the model using the least-squares technique. The experimental data was placed in second-order equations applying multivariate regressions and appraised applying analysis of variance (ANOVA). The p-value for all dependent variables was obtained to be less than 0.0001, indicating that all models were significant. Furthermore, the experimental values obtained for the mass transfer flux satisfactorily matched the model values. The R² and Adj-R² models are 0.9822 and 0.9795, respectively, which, it means that 98.22% of the variations for the NCO2 is explained by the independent variables. Since the RSM does not create any details about the quality of the solution acquired, the ANN method was applied as the global substitute model in optimization problems. The ANNs are versatile utensils that can be utilized to model and anticipate different non-linear and involved processes. This article addresses the validation and improvement of an ANN model and describes the most frequently applied experimental plans, about their restrictions and generic usages. Under different process conditions, the developed ANN weight matrix could successfully forecast the behavior of the CO2 absorption process. In addition, this study provides methods to specify the accuracy and importance of model fitting for both methodologies explained herein. The MSE values for the best integrated MLP and RBF models for the mass transfer flux were 0.00019 and 0.00048 in 100 epochs, respectively.
The market for biogas production has been increasing every year all over the world. The use of biogas as an energy vector is accomplished through the most diverse applications, such as direct burning (thermal energy), internal combustion engines, and fuel cells. Besides direct applications, biogas can be used as a raw material for producing high added‐value products, such as molecular hydrogen and renewable hydrocarbons, through a new enterprise concept, the biorefineries. Purity and quality control are determinant factors that enable the decision‐making regarding the end use of biogas. Physical, chemical, and biological methods can be used in biogas upgrading processes as well as the combination of different techniques. This review aims to deepen the knowledge about relevant technologies for biogas purification. It also addresses the most efficient and feasible methods, challenges to be overcome, and main demands for future studies. Therefore, the presentation, in a detailed way, of the synergistic effects caused by components contained in in natura biogas and the combinatorial methods for removing these contaminants, differentiates this from other works that approach only the purification techniques, but do not point out their problems and the causes more comprehensively. Thus, studies related to the combined effects of contaminants would be interesting in future works. This article is protected by copyright. All rights reserved.
This study aimed to investigate CO2 absorption using chemical solvent of amine H2O-TEA-CO2 in presence of activated carbon (AC) particles. The studied experimental range includes the temperature in range of 293–333 K, pressure in range of 3.5–9.5 bar, the concentration of solvents in range of 2.5–8.5 wt%, and amount of activated carbon in range of 0.3–0.9 kg/m³. The central composite design (CCD) with four parameters of temperature, pressure, amine concentration, and active carbon was applied in 5 levels. The physical solubility CO2 in amine solutions decreases with the increasing temperature that indicates the process is exothermic. The optimal values of temperature, pressure, concentration, and active carbon are 303.0 K, 8.00 bar, 7.00 M, 0.75 g, respectively, and 25.99% for the input variables and desirability index of 0.732. The CO2 loading, absorption capacity, and absorption percentage are obtained in the range of 0.572–1.180 molCO2/molTEA, 0.208–0.506 wt%, and 12.73–32.61% in Triethanolamine (TEA) solutions in activated carbon, respectively. All dependent variables had a p value of less than 0.05, indicating that models were significant and substantial. The result showed that the addition of solid particles to chemical solvents effectively enhances CO2 absorption.
In this study, carbon dioxide (CO2) absorption is investigated in blended sulfolane (TMS) and piperazine (PZ) aqueous solution in a stirrer reactor. The response surface methodology (RSM) was applied to design the experiments. The experiments were carried out in operating conditions, including PZ in range of 2–8 wt%, TMS in range of 10–30 wt%, temperature in range of 20–70 °C and CO2 partial pressure in range of 2–8 bar. The results show that CO2 loading in aqueous TMS-PZ solution increases with PZ concentration while decreases with TMS concentration. Since the studied pressure is low, the presence of TMS decreases CO2 loading in mixed solvent compared to aqueous PZ solution under the same conditions. Optimum parameters were obtained 3.95 wt% PZ, 15.01 wt% TMS, temperature of 32.5 °C and pressure of 3.5 bar. The maximum value of CO2 loading and absorption percentage under these optimal conditions were obtained 0.194 and 54.386%, respectively. In addition to experimental study, concentration of species in TMS + PZ + CO2 + H2O electrolyte system is obtained using modified Pitzer thermodynamic model. The trend of concentration is in good agreement with previous studies which obtained species concentration in PZ + CO2 + H2O system. By adding VLE equations to chemical equilibrium constant, charge and mass balances equations, it is possible to predict equilibrium CO2 loading by the model; calculated relative error between experimental and predicted loading was obtained 1.1–23.3%.
Volatile organochlorine compounds (VOXs) presented in biogas can cause many technological and environmental problems. During the combustion of biogas containing VOXs, the corrosion of installation, as well as the formation of toxic by-products (polyhalogenated dioxins and furans) and further emission to the atmosphere, may occur. Therefore, in this study, a new procedure based on physical absorption was developed. In order to meet the requirements of green chemistry and green engineering, new deep eutectic solvents (DESs) composed of natural components were used in the absorption studies. Several physical properties of new DESs were determined, followed by an explanation of the absorbents formation mechanism, by means of spectroscopic analysis, and density functional theory. The most important absorption parameters i.e. type of DES, gas flowrate, kind of matrix gas, temperature, and initial concentrations of VOXs were optimized. The obtained results indicate that DES composed of syringol and levulinic acid in 1:1 molar ratio could absorb VOXs efficiently. In addition, the DES regeneration studies demonstrated that the absorption capacities of DES did not change after ten absorption-desorption cycles. Studies on the absorption mechanisms indicate that the H-bonding and van der Waals interactions are the main driving force for the VOXs removal from biogas.
Understanding the mass-transfer kinetics of CO2 in novel hybrid absorbents with physical
and chemical contributions is essential for process design and evaluation. In this study, the liquid-side mass-transfer coefficients (kL) and second-order reaction rate constants (k2) of CO2 in hybrid absorbents (namely, choline-2-pyrrolidine-carboxylic acid salt/polyethylene glycol/water ([Cho][Pro]/PEG200/H2O)) were determined. The kL values for the hybrid absorbents were obtained from the CO2 diffusion coefficients (DCO2) and the kL values in PEG200/H2O. The DCO2 value was calculated from the density and viscosity of the hybrid absorbents, whereas the kL values in PEG200/H2O were measured experimentally. The k2 values of CO2 in the hybrid absorbents were estimated according to the reaction mechanism, the enhancement factor, and the kL values, and compared with those of other commercialized absorbents. The results showed that 30 wt% [Cho][Pro]+70 wt% H2O had the highest kL and k2 values at atmospheric pressure, whereas the values of kL and k2 of CO2 in 30 wt% [Cho][Pro]/H2O+PEG200 were comparable to those in diethanolamine aqueous and amino-functionalized ILs. The hybrid absorbent of [Cho][Pro]/PEG200/H2O could be promising for CO2 separation considering its thermodynamic and kinetic properties.
In this study, to appraise the performance of hybrid Diethanolamine-methanol solvent for the CO2 absorption process in the packed bed, the volumetric overall gas phase mass transfer coefficient (KGaV) and the absorption percentage (η) under different operating conditions were investigated including inlet solvent temperature 25-65 °C, reboiler temperature 75-115 °C, the inlet CO2 concentration 5-15 vol.%, solvent flow rate 0.50- 1.50 lit/min, gas flow rate 50-100 lit/min and solvent concentration 10-30 wt.%. The results show that by reducing the reboiler temperature from 115 to 95 °C, the mass transfer coefficient reduces 1%, but the reboiler temperature reduces 17% instead. This issue has a great effect on energy saving in the desorption section. Moreover, by adjusting the operating condition, the maximum KGaV and η were 4.69 (kmol.m⁻³.h⁻¹.kPa⁻¹) and 99.9%, respectively. The results of this study indicate that the use of DEA-methanol solution had equal and even higher absorption percentage (up to 99.9%) than the conventional MEA aqueous solution in addition to the lower regeneration temperature.
In this study, the absorption of carbon dioxide (CO2) in a microchannel reactor by use of the three solvents monoethanolamine (MEA), diethanolamine (DEA) and activated methyldiethanolamine (a-MDEA) was investigated under different operating conditions, including temperature, solvent and gas flow rates, and amine concentration. The results show that increasing solvent flow rate or amine concentration has effect of increasing the mass transfer flux. Raising the gas flow rate increased the mass transfer flux for MEA and DEA, while for a-MDEA it initially increased and then reduced the flux. The temperature was found to be a less effective parameter. Additionally, the performance of the microreactor in the enhancement of the absorption rate was demonstrated. The optimum molar flux of volumetric mass transfer was determined to be 12,826, 11,374 and 8241 kmol per cubic meter-hour for MEA, DEA and a-MDEA respectively.
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.
In this work, absorption of CO2 into nanofluid of TiO2, ZnO, and ZrO2 at Piperazine solution was investigated experimentally in a continuous stirrer bubble column. The dosage range of nanofluids was 0.01 to 0.1 wt% in the experiments. The process parameters such as nanoparticles type, solid loading, and stirrer speed were varied to the hydrodynamics and absorption performance including gas holdup, Sauter mean diameter, CO2 loading, CO2 removal efficiency, absorption rate, mass transfer flux and overall mass transfer coefficients. The results showed that the nanoparticle mass fraction and range of stirrer speed have an optimum value for the above-mentioned performance. The optimum value of TiO2, ZnO, and ZrO2 nanoparticles were 0.05 wt%, 0.1 wt%, and 0.05 wt%, respectively. The maximum absorption rate of TiO2, ZnO, and ZrO2 in comparison with pure Pz solution were 14.7% (0.05 wt%), 16.6% (0.1 wt%), and 3.7% (0.05 wt%), respectively. And also, with an increase of the stirring speed, the absorption performance increased first up to 200 rpm and it starts to decrease after 200 rpm. The hydrodynamics studies indicate that the gas hold-ups increase and the Sauter mean diameter decrease in the bubble column with increasing nanoparticles to the base fluid.
In this research, thermodynamic and absorption rate of carbon dioxide in monoethanolamine (MEA) solution was investigated. A correlation based on both liquid and a gas phase variable for carbon dioxide absorption rate was presented using the π-Buckingham theorem. The correlation was constructed based on dimensionless numbers, including carbon dioxide loading, carbon dioxide partial pressure, film parameter and the ratio of liquid phase film thickness and gas phase film thickness. The film parameter is used to apply the effect of chemical reactions on absorption rate. A thermodynamic model based on the extended-UNIQUAC equations for the activity coefficients coupled with the Virial equation of state for representing the non-ideality of the vapor phase was used to predict the CO
In the present work, absorption of carbon dioxide into Piperazine solution was investigated experimentally in a pilot scale stirrer bubble column. In the experiments, mass transfer and hydrodynamics parameters including loading, removal efficiency, absorption flux and mass transfer coefficients at various volumetric liquid and CO2 flow rate, absorbent concentration, and stirrer speed were studied. The experiments were carried out at 295.15 K temperature and atmospheric pressure under the Piperazine concentration in range of 0.1–0.5 mol l⁻¹, CO2 partial pressure range 16.0–35.2 kPa, stirrer speed range in range of 0–300 rpm and liquid flow rate in range of 0.5–2.0 l h⁻¹.The results showed that mass transfer flux, overall mass transfer coefficient, driving force and CO2removal efficiency were varied in the range of (6.18–15.99) × 10⁻⁶ kmol m⁻² s⁻¹, (2.39–2.58) × 10⁻⁶ kmol m⁻² s⁻¹ kPa⁻¹, 200–1400 Pa, and 65.5–82.1%, respectively. The hydrodynamics studies indicate that the gas holdups and the Sauter mean diameter in the bubble column increase with increasing CO2 partial pressure. CO2 partial pressure influence depends on the Piperazine concentration. This positive influence of partial pressure emanates from the smaller bubbles formation. Also increasing the CO2 partial pressure in the range of 16.0–35.2 kPa, increases the gas holdup and Sauter mean diameter up to about 48%.
The present study investigates the absorption of CO2, into novel bis(3-aminopropyl)amine (APA)-activated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP), using a wetted-wall column absorber. The physicochemical and transport properties of these solvents were measured over a temperature (T) range of 298–323 K and a partial pressure (pCO2) range of 5–15 kPa. APA is used as an activator with molar concentration varying from 0 to 1.1 kmol m⁻³ while maintaining the total (APA + AMP) concentration to 3.0 kmol m⁻³. Details on uncertainty analysis of property measurements are provided in order to analyse the kinetics data. The effect of thermodynamic properties on liquid–liquid interactions are discussed and assessed. Following the reaction mechanism of primary and secondary amines with CO2, the reaction mechanism of aqueous APA was described by the zwitterion mechanism. Based on this mechanism, the overall reaction scheme for (APA + AMP + H2O)–CO2 system was established. According to the pseudo-first-order condition, the reaction rate parameters were estimated for the (APA + AMP + H2O)–CO2 system from the kinetics measurement. A substantial enhancement of the reaction rate in comparison to the single AMP solution was observed upon the addition of a small amount of APA to the blend. Furthermore, it was prominent from the parity plot that the model fitted and experimental rate data were in close agreement with each other.
Tannery industry in Pakistan occupies an important place in the national economy. The magnitude of chrome effluent waste generated by the industry has rapidly multiplied during the past decade. This has caused an irreversible damage to the 'flora and fauna', which demands immediate remedial action. An effort has been made to develop indigenous means to combat chromium pollution with humic acids. Humic acids (HA) are polymeric, brown complex of compounds occurring in the aquatic, terrestrial and sedimentary environments. Soft brown coals and leonardite are major sources of humic acids, which contain up to 80% extractable humic acids. These economical, coal-derived humic acids are useful for soil and water remediation. The process reported in the present study for this purpose is simple, economical and avoids the problems associated with the disposal of bulky chromium waste produced using coagulation and other techniques.
In this research, kinetics and absorption rate of CO2 were studied using partially carbonated ammonia solutions. A correlation was proposed to calculate CO2 absorption rate based on two dimensionless parameters: conversion film parameter and carbonation ratio. Absorption rate experiments have been performed employing a laboratory absorption packed column. More than 60 items of experimental data were used for obtaining the correlation parameters. In the experiments, total ammonia concentration range was 30 to 750 (mol · m−3), carbonation ratio range was 0.22 to 0.785, and CO2 partial pressure in the gas mixture was 10, 14, or 18 (kPa). A comparison of the predictions indicated that the proposed correlation was more accurate than other correlations reported in the literature.
The rate law for reaction of amines with carbon dioxide is rate = kamine(R2NH)(CO2) + kamine′(R2NH)· (OH)(CO2), where the first and second terms are for uncatalyzed and hydroxide-catalyzed pathways. The latter reaction, which involves proton abstraction in the rate-determining step, is not observed with all amines. Values for kamine at 10° follow the Brønsted relationship log kamine (M-1 sec-1) = mpK + Y, with values of m and Y equal to 0.43 and -1.50 for reactions of primary and secondary amines, and 0.48 and -0.20 for the reactions of hydrazine and hydroxylamine derivatives. Second-order rate constants for hydrogen ion catalyzed decarboxylation of carbamates formed from amines of pK -1.05 to approximately 5 may be fitted to a Brønsted relationship log kH + (M-1 sec-1) = 0.77pK + 3.6 at 10°. Rates for carbamates formed from more basic amines are virtually independent of basicity and are approximately 108 M-1 sec-1. The rate-limiting step in carbamate formation and breakdown with weakly basic amines involves carbon-nitrogen bond formation and cleavage. It is suggested that proton transfer may be rate limiting in the synthesis and breakdown of carbamates formed from basic amines.
Carbon dioxide (CO2) separation by chemical absorption is widely regarded as the most effective method for its mitigation in natural gas streams or flue gas of the fossil fuel power plants. In this paper, CO2 loading (αCO2) in aqueous solution of piperazine (PZ: C4H10N2), a high reactive cyclic secondary diamine, is modeled over extensive ranges of operational conditions: temperature (287–395 K), PZ concentration (0.1–8 mol kg H2O−1) and CO2 partial pressure (0.0215–9510.3 kPa). To achieve this goal, a feed-forward back-propagation multilayer perceptron artificial neural network (FFANN) was developed and tested via employing the Levenberg–Marquardt training algorithm, enhanced through combination with Bayesian regularization technique. Regression analysis results (R2 = 0.9977) and comparison of the ANN predicted values with corresponding experimental data (%AARD = 2.3927) as well as with some correlations in the literature, have revealed high prediction ability and robustness of the developed neural network.
The present study aims to analyze the carbon dioxide absorption process in a chemical solvent based on 2-(ethylamino)ethanol, which is not commonly used in industry for this purpose, but it allows extracting interesting conclusions about the influence of absorption regime, physical properties or reagent chemical structure upon both hydrodynamic and mass transfer behavior in a bubble reactor. The influence of gas flow-rate upon bubble size distribution or gas hold-up allows understanding how the behavior of this type of reactors is and how they can influence the overall process. In this way, in analyzing the predominant reaction mechanism, the behavior of mass transfer coefficient can be known and understood as to why, for this kind of chemical solvent, a dramatic decrease of this coefficient is produced only with the presence of a small amount of amine.
The effect of different surfactants (n-octyltrimethylammonium bromide (OTABr), sodium dodecyl benzene sulfonate (SDBS) and Tween 80) with different critical micelle concentrations (CMC) on the CO2 absorption into aqueous solutions in a bubble column is analyzed in the present work. The presence of these surfactants increased the gas-liquid interfacial area, and decreased the liquid phase mass transfer coefficient, but with significant different extent. The results indicated that the CMC can be a key parameter affecting the mass transfer of CO2 absorption into a dilute aqueous solution of a surfactant. Sardeing’s model was used to fit the experimental data successfully by re-correlating the parameters.
Solubility information for CO2 in different ionic liquids, ILs, in part can potentially be used to select a specific IL for the separation of CO2 from hydrocarbon fluids. Unfortunately, not all CO2–IL systems have been experimentally described at similar temperatures and pressures; therefore, a direct comparison of performance by process simulation is not always possible. In the extreme cases, the design of a CO2 separation process may require predicting the CO2–IL equilibria for which there are no available solubility data. To address the need for this information, a semi-empirical correlation was developed to estimate the dissolution of CO2 in CO2–IL solvent systems. The theoretical COSMO–RS calculation method was used to calculate the chemical potential of CO2 in a wide variety of ILs and the Soave–Redlich–Kwong equation was used to calculate the fugacity coefficient of the CO2 vapour phase. The model was correlated with available literature data, yielding an average error of AAR = 23% and small bias. © 2012 Canadian Society for Chemical Engineering
In this work, new solubility data of CO2 in aqueous piperazine (Pz) solutions were measured over a temperature range from T = (287.1 to 313.1) K and for amine concentrations from m = (0.10 to 2.00) mol·kg−1. The CO2 partial pressure was kept within PCO2 = (0.11 to 525.17) kPa using a vapor−liquid equilibrium (VLE) apparatus based on a static-synthetic method. These experimental data and those found in the literature for the ternary system Pz−CO2−H2O were correlated using a model combining the virial equation of state to calculate the fugacity coefficients with a modified Pitzer's thermodynamic model for the activity coefficients. With the new extended interaction parameters βi,j0 and βi,j1 that cover a wide range of temperature, CO2 partial pressure, and amine concentration, the model is able to correlate satisfactorily the available reliable experimental solubility data.
A pilot plant at laboratory scale for absorption of CO2 has been constructed and operated to test the CO2 removal by aqueous ammonia solutions. The design of the pilot plant is based on a standard absorption and desorption flow sheet and partial or complete separation of gas mixtures. Pilot plant data for CO2 removal efficiencies, effects of CO2 loading, and temperature profiles are obtained. A rate-based model, RateFrac in Aspen Plus simulator, is used to simulate the CO2 absorption of the pilot plant. The simulation results of the CO2 capture predicted by the rate-based model are in good agreement with the experimental data of the pilot plant. Further, the optimization covering operational parameters is carried out using the rate-based model.
The dissolution of single bubbles of gases of low solubility kept stationary in a downward stream of water was studied. In “clean” water, two regimes are identified. Initially, the process is fast, consistent with the theory for circulating bubbles. Then, the mass-transfer rate falls sharply to that predicted for solid spheres. Transition times and transition diameters vary widely with experimental conditions. In untreated water, only the second regime is found. Results are explained in terms of the kinetics of trace surfactant accumulation at the interface. An adaptation of the stagnant-cap model is proposed, with surface immobilization expressed in terms of interface dynamics. The model yields good prediction of the transition point for a very large set of conditions, including different gases at various concentrations in the liquid stream and a wide range of initial bubble diameters.
We determined interfacial areas, A, and individual mass transfer coefficients, kL, for the absorption of CO2 in a bubble column, with an anionic surfactant in the absorbent liquid. The results of experiments to determine the dependence of kL on surface tension of the liquid phase and the superficial velocity of the gas were fitted to within a 10% error by expressions of the form where K4 depends exclusively on the kind of bubbling device.Likewise, the experimental values of specific area, a, were correlated with the column diameter dc and the physical properties by means the following equation: that reproduces satisfactorily the experimental values.
N-ethylmonoethanolamine (EMEA), a secondary alkanolamine linked to an ethyl group, represents an especially promising absorbent for CO2 capture, because it can be prepared from renewable resources. Up to now, there is no reliable information on the reaction between CO2 and EMEA in the literature. In this work, the reaction mechanism and kinetics were investigated using a stirred-cell reactor at 298, 303, and 308 K. The reaction pathway was described using both the zwitterion and the termolecular mechanism. From our kinetic data at low amine concentration (0.02–0.1 M), we deduced that the absorption process occurs in the fast reaction regime with second-order kinetics for EMEA and first-order kinetics for CO2. Besides, a comparison with the efficacy of two other secondary amines, diethanolamine (DEA) and diisopropanolamine (DIPA) was performed, and it was found that the absorption rate in aqueous EMEA was faster than that in DEA and DIPA at high amine concentration (0.5–2 M). Thus, the performance of EMEA as a CO2 absorbent appears encouraging.
Physicochemical properties of aqueous amino acid salt (AAS), potassium salt of sarcosine (KSAR) and aqueous amine amino acid salt (AAAS), 3-(methylamino)propylamine/sarcosine (SARMAPA) have been studied. Densities of KSAR were measured for sarcosine mole fraction 0.02 to 0.25 for temperature range 298.15 K to 353.15 K, the viscosities were measured for 0.02 to 0.10 mole fraction sarcosine (293.15 K to 343.15 K) while the N2O solubilities were measured from 0.02 to 0.10 mole fraction sarcosine solutions (298.15 K to 363.15 K). Densities of SARMAPA were measured for sarcosine mole fraction 0.02 to 0.23 for temperature range (298.15 K to 353.15 K), viscosities were measured for 0.02 to 0.16 mole fraction sarcosine (293.15 K to 343.15 K) while the N2O solubilities were measured from 0.02 to 0.16 mole fraction sarcosine solutions (298.15 K to 343.15 K). Experimental results were correlated well with empirical correlations and N2O solubility results for KSAR were predicted adequately by a Schumpe model. The solubilities of N2O in AAS and AAAS are significantly lower than values for amines. The solubilities vary as: amine > AAAS > AAS.
In this paper, we have attempted to validate a transient, two-dimensional axisymmetric simulation of a laboratory-scale cylindrical bubble column, run under bubbly flow and churn turbulent conditions. The experimental data was obtained via gamma-radiation based non-invasive flow monitoring methods, viz., computer automated radioactive particle tracking (CARPT) provided the data on liquid velocity and turbulence, and computed tomography (CT) determined the gas holdup profiles. The numerical simulation was done using the FLUENT software and compares the results from the algebraic slip mixture model, and the two-fluid Euler–Euler model. Reasonably, good quantitative agreement was obtained between the experimental data and simulations for the time-averaged gas holdup and axial liquid velocity profiles, as well as for the kinetic energy profiles. The favorable results suggest that the simple two-dimensional axisymmetric simulation can be used for reasonable engineering calculations of the overall flow pattern and gas holdup distributions.
A small wetted wall column (WWC) was used to study the kinetics of CO2 absorbed in PZ and NH3/PZ blended solution. The experiments of CO2 absorption into 0.1–0.4 M PZ and 0.53–4 M NH3/0.1–0.4 M PZ mixed solution at 10–40 °C have been done in wetted wall column under the driving force of 8–25 kPa in this paper. The ‘interface concentration corrected-pseudo first order’ mass transfer model and ‘Ternary-termolecular’ reaction mechanism were proposed to describe the CO2 absorption into NH3/PZ system for the high driving force and low PZ concentration condition. Both of the models in this study used for CO2 with NH3/PZ blended solution were in a good agreement with the experimental results.
Literature data on the rates of reaction between CO2 and alkanolamines (MEA, DEA, DIPA, TEA and MDEA) in aqueous solution are discussed. These data induced us to carry out absorption experiments of CO2 into aqueous DEA, DIPA, TEA and MDEA solutions from which the respective rate constants were derived. The experimental technique was similar to that used by Laddha and Danckwerts[30].The results for DEA and DIPA were analysed by means of a zwitterion-mechanism which was derived from the mechanism originally proposed by Danckwerts[16The reaction rate of CO2 with aqueous TEA and MDEA solutions shows a significant base catalysis effect which is also reported by Donaldson and Nguy
Literature data on the rates of reaction between CO2 and alkanolamines (MEA, DEA, DIPA, TEA and MDEA) in aqueous solution are discussed. These data induced us to carry out absorption experiments of CO2 into aqueous DEA, DIPA, TEA and MDEA solutions from which the respective rate constantsThe results for DEA and DIPA were analysed by means of a zwitterion-mechanism which was derived from the mechanism originally proposed by Danckwerts [1The reaction rate of CO2 with aqueous TEA and MDEA solutions shows a significant base catalysis effect which is also reported by Donaldson and Nguy
Aqueous solutions of alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), N-methyldiethanolamine (MDEA), di-2-propanolamine (DIPA), and bis[2-(hydroxyamino)ethyl] ether (DGA) are good solvents for the removal of acid gases such as CO[sub 2] and H[sub 2]S from the gas streams of many processes in the natural gas, petroleum, ammonia synthesis, and some chemical industries. The viscosity of aqueous solutions of methyldiethanolamine (MDEA) and of diethanolamine (DEA) have been measured at five temperatures in the range 25--80 C throughout the whole concentration range. The viscosity has been correlated as a function of composition for use in industrial calculations.
An equation has been developed with the guidance of recent statistical theories of electrolytes which is designed for convenient and accurate representation and prediction of the thermodynamic properties of aqueous electrolytes including mixtures with any number of components. The three previous papers have given the theoretical background and the evaluation of parameters for pure electrolytes of various charge types. The equation is here applied to a wide variety of mixed aqueous electrolytes at room temperature and at ionic strengths up to 6 M in many cases and occasionally even higher. The first objective is the prediction of properties of mixed electrolytes using only the parameters for pure electrolytes; on this basis standard deviations in ln ..gamma.. or phi for 69 sets of mixtures are less than 0.01 in 36 cases and above 0.05 in only seven cases all involving Cs/sup +/ or OH/sup -/. A second objective is the determination of parameters giving the differences in short-range interaction of ions of the same sign where these differ significantly from zero. As expected, these difference terms, while always small, are relatively most important for singly charged ions (and especially for OH/sup -/ and Cs/sup +/) and less important for ions of higher charge. The equations, including difference terms where known from binary mixtures with a common ion, were finally tested on 17 sets of mixtures involvingfour or more ions without any further adjustment of parameters. The standard deviation is less than 0.01 in all cases and is 0.003 or less in 11 cases. Thus these equations appear to yield accurate predictions of properties of mixed aqueous electrolytes. 5 tables.
Absorption of acid gases such as CO{sub 2} and H{sub 2}S from natural and process gases is of great industrial importance. The kinetics of the reaction between CO{sub 2} and aqueous diethanolamine (DEA) were estimated over the temperature range of 293--343 K from absorption data obtained in a laminar-liquid jet absorber. The absorption data were obtained over a wide range of DEA concentrations and for CO{sub 2} partial pressures near atmospheric. A rigorous numerical mass-transfer model based on penetration theory in which all chemical reactions are considered to be reversible was developed and used to estimate kinetic rate coefficients from the experimental absorption data. The kinetic data were found to be consistent with the zwitterion mechanism. The scarce zwitterion rate coefficient estimates reported in the literature are in fair agreement with the results of this work.
Consistent with the latest experimental data and the recent internationally recommended values for the critical parameters, we have developed compact and accurate representative equations for the following properties on the saturation line of ordinary (light) water substance: vapor pressure, density, enthalpy and entropy of both the saturated liquid and the saturated vapor. These equations form the basis of a ‘‘Supplementary Release on Saturation Properties of Ordinary Water Substance’’ issued by the International Association for the Properties of Steam (IAPS).
The effect of inner diameter and clearance on gas holdup in a bubble column with a draft tube was simulated by CFX software. Simulation was done by using three- dimensional two-phase Euler-Euler model. Shear Stress Transfer (SST) model was used as a turbulent model. Gas holdup by the simulation showed a fairly good agreement with the correlation of Yamashita (1999).
CO2 capture and storage has gained widespread attention as an option for reducing greenhouse gas emissions. Chemical absorption and stripping of CO2 with hot potassium carbonate (K2CO3) solutions has been used in the past, however potassium carbonate solutions have a low CO2 absorption efficiency. Various techniques can be used to improve the absorption efficiency of this system with one option being the addition of promoters to the solvent and another option being an improvement in the mass transfer efficiency of the equipment. This study has focused on improving the efficiency of the packed column by replacing traditional packings with newer types of packing which have been shown to have enhanced mass transfer performance. Three different packings (Super Mini Rings (SMRs), Pall Rings and Mellapak) have been studied under atmospheric conditions in a laboratory scale column for CO2 absorption using a 30wt% K2CO3 solution. It was found that SMR packing resulted in a mass transfer coefficient approximately 20% and 30% higher than that of Mellapak and Pall Rings, respectively. Therefore, the height of packed column with SMR packing would be substantially lower than with Pall Rings or Mellapak. Meanwhile, the pressure drop using SMR was comparable to other packings while the gas flooding velocity was higher when the liquid load was above 25kgm−2s−1. Correlations for predicting flooding gas velocities and pressure drop were fitted to the experimental data, allowing the relevant parameters to be estimated for use in later design.
The velocity constant k″, of the reaction CO2 + OH - → HCO3- has been determined by the rapid thermal method over the range 0 to 40°C, by mixing together CO2 solutions with NaOH solutions of concentrations, 0.005 to 0.05 M. The effect of large variations of ionic strength has also been studied. The present thermal results are considerably more extensive than any hitherto available, but check satisfactorily with the more limited data obtained by Faurholt's carbamino method and by the manometric method. The velocity constant is related to temperature by the equation log k″ = 13.635 - (2895/T). The energy of activation is 13,250 cal. Previous manometric figures for the velocity constant ku of the reaction CO2 + H2O → H 2CO3 have been corrected with the aid of the present values of k″. The corrections were very slight at 0°C but quite appreciable at 25-38°C.
The objective of this study is to investigate the potential process for the removal of carbon dioxide (CO2) from flue gas using fundamental membrane contactor, which is a membrane gas absorption (MGA) system. The experiments consisted of microporous polyvinylidenefluoride (PVDF) flat sheet membrane with 0.1μm (as module I) and 0.45μm (as module II) pore size. 2-Amino-2-methyl-1-propanol (AMP) solution was employed as the liquid absorbent. The effect of AMP concentration was studied with variation in the range 1–5M. In addition, the experiments were carried out with 10%, 20%, 30% and 40% gas ratio of CO2 to N2 and pure CO2 as well. Through contact angle measurement, membranes for module I and module II were obtained with CA values of around 130.25° and 127.77°, respectively. The mass transfer coefficients for module II are lower than those of module I for 1–5M of AMP. Furthermore, the increase in CO2 concentration in the feed gas stream enhanced the CO2 flux as the driving force of the system was increased in sequence from 1M to 5M of AMP. However, after the particular percentage (40%) of CO2 inlet concentration, the CO2 fluxes seem saturated. The combination of AMP as liquid absorbent and PVDF microporous membrane in MGA system has shown the potential to remove the CO2 from flue gas. In addition, the higher AMP concentration gave higher mass transfer coefficient at low liquid flow rates.
The effect of kind of gas sparger, outer diameter Do and length Ld of draft tube, lower clearance, superficial gas velocity and clear liquid height HL on gas holdup εG in a 0.16 m I.D. bubble column with a draft tube for gas dispersion into the annulus and for an air-water system was experimentally studied.εG depended on the kind of gas sparger in the range of φ ≤ 0.713, but hardly depends on them at φ = 0.875. φ is the ratio of (Do/DT) and DT is the inner diameter of the bubble column.At a given HL and in the range of φ ≤ 0.713, εG hardly depends on φ and Ld. But εG decreases clearly with increasing Ld at φ = 0.875.εG decreases with increasing HL. The effect of HL is well expressed by the modified three-region model.The experimental data for εG is correlated.
Alkanolamine solutions are frequently used as solvent for the removal of acid compounds from industrial gases (Kohl and Riesenfeld, 1979). Depending on the process requirements, e.g., selective removal of H2S, CO2-bulk removal, several options for alkanolamine based treating solvents with varying compositions of the solution have been proposed.In this paper an overview is presented of the mechanisms that have been proposed in literature and the kinetic data for the various reactions are critically evaluated. Conclusions on the applicability and restrictions are discussed along with perspectives. In addition white spots in the present knowledge are indicated.The reaction between CO2 and primary/secondary amines both in aqueous and non-aqueous solutions can be described over a wide range of conditions and amine concentrations with the zwitterion-mechanism as originally proposed by Caplow (1968) and reintroduced by Danckwerts (1979). All published results, both non-aqueous and aqueous solutions, amine-promoted carbonate processes, blends of amines and sterically hindered amines can be satisfactorily explained with this mechanism. The validity of the kinetic relations that are derived is restricted to about 313 K. Above this temperature the results are severely affected by the limitations of the used experimental techniques. Both stopped flow or rapid mixing and absorption techniques show their limitations because the rates of the reactions are too fast and because of the reversibility (for absorption experiments) of the reaction. For the formation of the zwitterion, an acid-base reaction, a Brønsted relation exists between the rate constant for this step of the reaction, k2, and the basic strength, pKa, of the amine.The reaction between CO2 and tertiary amines can be described with the base catalysis of the CO2 hydration as proposed by Donaldson and Nguyen (1981). The formation of monoalkylcarbonate is not responsible for the reactivity measured in aqueous tertiary amine solutions at low pH as can be concluded from the results published for TREA. In non-aqueous solvents no reaction occurs for tertiary amines.The determination of reaction mechanism and reaction rate constants from mass transfer experiments can be substantially affected by effects of reversibility of the absorption reactions. The condition of pseudo first order irreversible reaction cannot always be met, e.g., in those cases where the conversion is relatively high or the equilibrium constant is low as is the case for e.g., AMP. If this condition is not fulfilled the interpretation of the mass transfer experiments neglecting reversibility can lead to erroneous conclusions. For tertiary amines also the presence of even small amounts of fast reacting contaminants, e.g., primary or secondary amines has a pronounced effect
We determined interfacial areas, A, and individual mass transfer coefficients, kL, for the absorption of CO2 in a bubble column, with an anionic surfactant in the absorbent liquid. The results of experiments to determine the dependence of kL on surface tension of the liquid phase and the superficial velocity of the gas were fitted to within a 10% error by expressions of the form kL=K4σ1.35uG0.5 where K4 depends exclusively on the kind of bubbling device.Likewise, the experimental values of specific area, a, were correlated with the column diameter dc and the physical properties by means the following equation: adc=K·Re0.98·Sc0.57·Fr0.09·Bo−0.70dpdc−0.19 that reproduces satisfactorily the experimental values.
The present design practice of the bubble column reactors is still closer to an art than science because of the complexity of the fluid mechanics. In view of this, there have been continuous attempts to understand the complex three-dimensional turbulent two-phase flow. The present paper reviews the modelling efforts on the flow patterns published in the last 30 years with relatively more focus on the last 10 years. Over this period, there have been sustained efforts to improve our understanding of the governing equations of the change (equations of continuity and motion) for two-phase flows. Both Eulerian and Lagrangian approaches have been extensively used. The development has been mainly on three fronts: (i) formulation of interfacial forces (ii) closure problem for the eddy viscosity and (iii) modelling of the correlations arising out of Reynolds averaging procedure.
Measurements of the rates of homogeneous reaction of mono-, di- and tri-ethanolamine by various workers are critically compared. Some discrepancies remain unexplained but it seems probable that a zwitterion is the intermediate in the formation of carbamate and that the reaction of DEA (but not of MEA) is catalysed by bases.
Equilibrium data of CO2 in aqueous solutions of DEA and AMP for a range of CO2 partial pressure (0.5-100 k Pa) and temperature (25-80°C) obtained using a stirred cell reactor is presented in this paper. The data were analyzed using the Deshmukh and Mather Model. It has been found that this model is able to predict results which are close to the experimental data in terms of the total CO2 loadings and the pH of the solution, an additional parameter which was monitored in this work. Comparison was also made with other published results using the different interaction parameters generated in this work. Good agreement between predicted and experimental values were also observed.
The equilibrium of CO2 and carbamate concentration data for the absorption of CO2 in aqueous solutions of single and mixed amines was analyzed using the Deshmukh–Mather model. Data on CO2 loading in aqueous solutions of DEA and MDEA and their mixtures at various temperature (303–323 K) and CO2 partial pressure (0.09–100 kPa) together with carbamate concentrations in case of DEA and its mixtures with MDEA were fitted simultaneously to generate the different interaction parameters required to calculate the activity coefficients in the model. Using the generated interaction parameters, the model was applied to correlate the CO2 loading in solutions of DEA and MDEA and their mixtures reported in the literature as well as those obtained in our laboratory and was found to be able to give a good estimation of CO2 loading and carbamate concentration over a wide range of operating conditions in both single and mixed amine solutions.
Solubility and diffusivity of N//2O and CO//2 in water were determined as a function of temperature from the results published in the open literature, and new data were measured in the present work. The solubility of N//2O in several aqueous alkanolamine (DEA, DIPA, DMMEA, and DIPA) solutions at various temperatures was measured and correlated over a wide range of conditions. For both the diffusivity of N//2O and the alkanolamine in aqueous alkanolamine solutions a modified Stokes-Einstein relation was derived. With the aid also of the 'N//2O analogy' the diffusivity of CO//2 in these solutions can be estimated.
A system of equations for the thermodynamic properties of electrolytes is developed on the basis of theoretical insights from improved analysis of the Debye-Hückel model as well as recently published numerical calculations for more realistic models. The most important result is the recognition of an ionic strength dependence of the effect of short-range forces in binary interactions. By modifying the usual second virial coefficients to include this feature, one obtains a system of equations which are only slightly more complex than those of Guggenheim but yield agreement within experimental error to concentrations of several molal instead of 0.1 M. If one compares instead with the recently proposed equations of Scatchard, Rush, and Johnson, the present equations are very much simpler for mixed electrolytes (and somewhat simpler for single electrolytes) yet appear to yield comparable agreement with experimental results for both single electrolytes and mixtures.
Expressions for predicting pure-component and cross second virial coefficients for simple and complex systems have been developed from the bound-pair formalism of Stogryn and Hirschfelder. For pure components, the generalized correlation requires the critical temperature and pressure, Thompson's mean radius of gyration or the parachor, dipole moment, and, if appropriate, a parameter to describe chemical association which depends only in the type of group (hydroxyl, amine, ester, carboxylic acid, etc.). Mixing rules have been developed for predicting cross coefficients and solvation effects can be accounted for in a similar manner to association. Agreement with experimental data on 39 nonpolar and 102 polar and associating compounds, 119 mixed nonpolar systems, and 73 mixed systems involving polar compounds, is comparable to or better than that of several other correlations including those which require data to obtain parameters. The method should be most accurate for systems of complex molecules where no data are available.
Alkanolamines are the most popular absorbents used to remove CO2 from process gas streams. Therefore, the CO2 reaction with alkanolamines is of considerable importance. The aim of this article is to provide an overview on the kinetics of the reaction of CO2 with aqueous solutions of alkanolamines. The various reaction mechanisms that are used to interpret experimental kinetic data – zwitterion, termolecular and base-catalyzed hydration – are discussed in detail. Recently published data on reaction kinetics of individual amine systems and their mixtures are considered. In addition, the kinetic behavior of several novel amine-based solvents that have been proposed in the literature is analyzed. Generally, the reaction of CO2 with primary, secondary and sterically hindered amines is governed by the zwitterion mechanism, whereas the reaction with tertiary amines is described by the base-catalyzed hydration of CO2.
The electrolyte nonrandom two-liquid (NRTL) model proposed by Chen et al. (1982) is generalized to represent the excess Gibbs energy of aqueous multicomponent electrolyte systems. Using only binary parameters, the model correlates and predicts the deviation from ideality of aqueous multicomponent electrolyte systems over the entire range of temperature and concentration.
As part of an ongoing project dealing with the measurement and correlation of phase equilibria in aqueous solutions containing a weak base like ammonia and acid gases like carbon dioxide, sulfur dioxide and hydrogen cyanide, the solubility of carbon dioxide was measured in aqueous solutions containing the single salts sodium sulfate and ammonium sulfate as well as in a solution containing both salts. The temperature ranged from 313.15 K to 433.15 K and pressures up to 10 MPa. Pitzer's semiempirical model is used to correlate the new data. From the results for the solubility of carbon dioxide in the single salt aqueous solutions, interaction parameters were determined. With these parameters the solubility of carbon dioxide in an aqueous mixture containing both salts is predicted quantitatively.
The kinetics of the reaction between carbon dioxide (CO2) and mixed solutions of methyldiethanolamine (MDEA) and piperazine (PZ) was investigated experimentally in a laminar jet apparatus. The experimental kinetic data were obtained under no interfacial turbulence and over a temperature range from 313 to 333 K, MDEA/PZ wt% concentration ratios of 27/3, 24/6 and 21/9, and CO2 loadings from 0.0095 to 0.33 mol CO2/mol amine. In addition, a new absorption-rate/kinetics model for the kinetics of the mixed of solvents was developed, which takes into account the coupling between chemical equilibrium, mass transfer, and all possible chemical reactions involved in the CO2 reaction with MDEA/PZ solvent. The partial differential equations of this model were solved by the finite element numerical method (FEM) based on COMSOL software. The obtained experimental kinetics data were used to obtain the kinetic parameters of CO2 absorption into MDEA/PZ solutions. The reaction-rate constant obtained for PZ blended with MDEA was kPZ = 2.572 × 1012 exp(−5211/T). The 2D model for the blended amines MDEA/PZ has revealed the concentration profiles of all the species in both the radial and axial directions of the laminar jet which has enabled a better understanding of the correct sequence in which the reaction steps involved in the reactive absorption of CO2 in aqueous mixed MDEA/PZ solution occur. It also revealed that PZ may be depleted by the time the solvent blend of MDEA/PZ with a loading greater than 0.015 mol/mol amine is exposed to CO2 from the top of the laminar jet absorber.
A computer-operated static apparatus for the experimental measurement of gas solubility data by the synthetic method was recently installed. It was used for the determination of carbon dioxide solubility data in aqueous N-methyldiethanolamine (MDEA), diethanolamine (DEA) solutions and aqueous solution of a mixture of MDEA/DEA. For all the systems, temperatures between 298 and 348 K and pressures up to ca. 4.5 MPa were investigated. For one aqueous MDEA solution at 313 K, two other experimental static set-ups were applied to check the reliability of the measured data. The first one, which is manually operated, also uses the synthetic method, while in the second apparatus, the phases were analyzed by gas chromatography. Consistency of the obtained data with literature has been analyzed.
Axial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn-turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid-phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid-phase turbulence. The scale-up effect on liquid mixing reduces as the pressure increases.
A molecular-thermodynamic correlation is established for calculating vapor-liquid equilibria in aqueous solutions containing one or more volatile electrolytes: ammonia, carbon dioxide, hydrogen sulfide, sulfur dioxide, and hydrogen cyanide. The correlation is similar to that presented in 1975, but the domain of application has been increased. The present correlation holds from about 0° to 170°C and for ionic strengths of about 6 molal; for the weak electrolytes considered here, this corresponds to total concentrations between 10 and 20 molal. To represent activities at these high concentrations, activity coefficients are expressed as a function of molality by Pitzer's equation. Required parameters are estimated from data reduction or from correlations.
Special attention is given to the ternary systems ammonia-carbon dioxide-water and ammonia-hydrogen sulfide-water. Calculated equilibria are in satisfactory agreement with the severely limited experimental data now available.
Analytical solution of models for gas–liquid reactors is restricted to a few asymptotic cases, while most numerical models make use of the physically less realistic stagnant film model. A model was developed that simulates the dynamic behaviour of gas–liquid tank reactors by simultaneously solving the Higbie penetration model for the phenomenon of mass transfer accompanied by chemical reaction and the dynamic gas and liquid phase component balances. The model makes it possible to implement an alternative for the well known Hinterland concept, which is usually used together with the stagnant film model. In contrast to many other numerical and analytical models the present model can be used for a wide range of conditions, the entire range of Hatta numbers, (semi-)batch reactors, multiple complex reactions and equilibrium reactions, components with different diffusion coefficients and also for systems with more than one gas phase component. By comparing the model results with analytical asymptotic solutions it was concluded that the model predicts the dynamic behaviour of the reactor satisfactorily. It is shown that under some circumstances substantial differences exist between the exact numerical and existing approximate results. It is also shown that for some special cases, differences can exist between the results obtained using the stagnant film model with Hinterland concept and the implementation of the Higbie penetration model.
The reaction kinetics of the absorption of CO2 into aqueous solutions of piperazine (PZ) and into mixed aqueous solutions of 2-amino-2-methyl-l-propanol (AMP) and PZ were investigated by wetted wall column at 30–40 °C. The physical properties such as density, viscosity, solubility, and diffusivity of the aqueous alkanolamine solutions were also measured. The N2O analogy was applied to estimate the solubilities and diffusivities of CO2 in aqueous amine systems. Based on the pseudo-first-order for the CO2 absorption, the overall pseudo first-order reaction rate constants were determined from the kinetic measurements. For CO2 absorption into aqueous PZ solutions, the obtained second-order reaction rate constants for the reaction of CO2 with PZ are in a good agreement with the results of Bishnoi and Rochelle (Chem. Eng. Sci. 55 (2000) 5531). For CO2 absorption into mixed aqueous solutions of AMP and PZ, it was found that the addition of small amounts of PZ to aqueous AMP solutions has significant effect on the enhancement of the CO2 absorption rate. For the CO2 absorption reaction rate model, a hybrid reaction rate model, a second-order reaction for the reaction of CO2 with PZ and a zwitterion mechanism for the reaction of CO2 with AMP was used to model the kinetic data. The overall absolute percentage deviation for the calculation of the apparent rate constant kapp is 7.7% for the kinetics data measured. The model is satisfactory to represent the CO2 absorption into mixed aqueous solutions of AMP and PZ.