Chemical absorption using aqueous amine-based solutions is the leading method for large-scale CO2 capture in industrial plants. This technology, however, still faces many challenges, in particular the high-energy requirements for solvent regeneration, which limit the economic viability of the technology. To guide the development of more energy-efficient amine solvents, this work studied the effect of molecular characteristics of diamines, including carbon chain length and type of amino functional group, on CO2 absorption and desorption performances. Six linear terminal diamines [NH2CH2CH2–R, where R = NH2, NHCH3, N(CH3)2, CH2NH2, CH2NHCH3, and CH2N(NH3)2] were investigated, and two monoamines, monoethanolamine (NH2CH2CH2OH, MEA) and 3-aminopropanol (NH2CH2CH2CH2OH, 3AP), were also tested as benchmarks. The CO2 absorption capacity in each amine was measured at 40 °C under atmospheric pressure using different CO2 gas partial pressures. 13C and 1H nuclear magnetic resonance spectroscopies were used to identify and quantify species present in the CO2–amine–H2O system. Computational modeling was also carried out using Gaussian software to explain the effect of the chain length change on the stability of monocarbamate. The experimental results showed that the chain length extension from C2 to C3 led to a higher CO2 absorption capacity and more bicarbonate formation during the CO2 absorption process, and the computational study results supported this conclusion. In addition, the experimental results also demonstrated that increasing the substitution on one N atom in the tested diamines is favorable for a higher CO2 absorption capacity and more bicarbonate formation under a CO2 partial pressure of 101 kPa. Both chain length extension from C2 to C3 and an increase in the number of substituents on one N atom yield better performance in the CO2 desorption with regard to the CO2 higher cyclic capacity and faster initial CO2 release rate for the tested amines.

In this work, the pH values of 1-dimethylamino-2-propanol (1DMA2P) solution were measured over a CO2 loading range of 0–0.8 mol CO2/mol amine, 1DMA2P concentration range of 1.5–4.0 mol/L, and a temperature range of 298–303 K. Two-dimensional (2D) vapor–liquid equilibrium (VLE) plots of the 1DMA2P–H2O–CO2 system were established by calculating ion concentrations in the 1DMA2P solution using the pH method. A three-dimensional (3D) VLE surface representing the concentrations of ions in the 1DMA2P solution was also obtained. In addition, equations were generated and used to predict CO2 loading in 1DMA2P solution, based on knowledge of amine concentration, temperature, and pH of the solution. The results showed that these equations performed very well in predicting the CO2 loading of a 1DMA2P solution, with an absolute average deviation (AAD) of 9.2%.

Exact and reliable estimation of mass transfer performance is very important for the design, simulation, and optimization of CO2 absorption in a packed column. In this study, two types of artificial neural networks (ANNs), namely back-propagation neural network and radial basis function network, were applied to predict the mass-transfer performance of CO2 absorption into aqueous monoethanolamine (MEA) in packed columns (containing Berl saddles, Pall rings, IMTP random packing, and 4A Gempack, Sulzer DX structured packing, respectively) from input variables. These variables were inert gas flow rate, liquid flow rate, solution concentration, liquid CO2 loading, CO2 mole fraction, temperature, and total packing area, which were considered to predict the targeted output mass transfer variables. The predicted results from ANN were validated against experimental data as well as compared with results from well-known correlations in terms of the volumetric mass flux, CO2 mole fraction, and temperature profiles along the height of the packed column. The comparisons between the predicted and experimental results showed that the proposed ANN models performed very well in predicting mass transfer performance of CO2 absorption into aqueous MEA in a packed column.

In this work, three promising tertiary amines—1-(2-hydroxyethyl)piperidine (1-(2-HE)PP), 3-(diethylamino)-1,2-propanediol (DEA-1,2-PD), and N-(2-hydroxyethyl)pyrolidine (1-(2-HE)PRLD)—were experimentally studied and the results presented in terms of pKa, the protonation calibration curves, and ion speciation plots. The pKa of these amines were determined in the temperature range of 294–320 K. The protonation calibration curves for the three amines were also developed based on 13C NMR detection. In addition, ion (amine, amineH+, HCO3–, and CO32–) speciation plots for the three tertiary amines were developed at the temperature of 298 K, at the amine concentration of 1.0 M, over the CO2 loading ranges of 0–0.897 mol CO2/mol amine for 1-(2-HE)PP, 0–0.915 mol CO2/mol amine for DEA-1,2-PD, and 0–0.927 mol CO2/mol amine for 1-(2-HE)PRLD by using the pH method, the 13C NMR method, and the pH + 13C NMR method. By comparing the ion (amine, amineH+, HCO3–, and CO32–) concentrations of the three tertiary amines obtained from these three methods, it can be concluded that each of these three methods could be used to develop the ion speciation plots of amine–CO2–H2O systems, but there are some significant differences between them.

This work has investigated CO2 absorption using 3-(diethylamino)propylamine (DEAPA), a diamine that contains one primary and one tertiary amine in the same molecule. The results are compared with those for the blended amine system of monoethanolamine and methyldiethanolamine (MEA–MDEA), a mixed amine solvent with an equal number of moles of primary and tertiary amine. The 2 M DEAPA, 2 M MEA, and 4 M MEA–MDEA (1:1 mole ratio) were tested for their CO2 absorption performance. The experimental results show that the intramolecular tertiary amino group of DEAPA can promote the CO2 absorption rate of the intramolecular primary amino group and enhance its CO2 absorption capacity. The results using 13C nuclear magnetic resonance also showed that the intermolecular tertiary amine in the MEA–MDEA system was more favored for the promotion of the primary amine in the blend to form bicarbonate at an earlier CO2 equivalent loading stage and produced less carbamate than the intramolecular tertiary amino group of DEAPA did with respect to its primary amine. Furthermore, the CO2 equilibrium solubility of DEAPA was measured at different temperatures with various CO2 partial pressures, and then an empirical model based on these experimental data was developed. The results predicted by this model were fitted well with the experimental results. The Gibbs–Helmholtz equation was used to estimate the CO2 absorption heat of the DEAPA system, and the results showed that DEAPA has a CO2 absorption heat (−36.4 kJ/mol) lower than those of MEA, MDEA, and DEA. The results demonstrate that DEAPA has the potential to be an alternative solvent with a high absorption rate, a high CO2 capacity, and a low heat of absorption in CO2 capture processes.

In this present work, the absorption kinetics of CO2 into aqueous 1-(2-Hydroxyethyl) piperidine (1-(2-HE)PP) solutions with respect to observed pseudo-first-order rate constant (k0) and second order reaction rate constant (k2), were determined using the stopped-flow apparatus within the 1-(2-HE)PP concentration range of 0.20–1.00 kmol/m3 and a temperature range of 293–313 K. The values of k0 were then represented using the correlation based on the base-catalyzed hydration mechanism. The results show that the correlated values of k0 matched well with the experimental values with an acceptable AAD of 8.3%, which indicates that the base-catalyzed hydration mechanism can satisfactorily describe the experimental kinetics data of the1-(2-HE)PP reaction with CO2. In order to comprehensively understand the kinetics, the ion speciation plots of 1-(2-HE)PP-H2O–CO2 system were developed using the pH method. In addition, the Brønsted plots between k2 (obtained from stopped-flow apparatus) and pKa (obtained from experimental measurement) for 1-(2-HE)PP were developed, and then used to predict k2 using the values of pKa.

The physical properties of densities, viscosities, and refractive indices, which are important in kinetics and mass transfer processes were measured for aqueous CO2-loaded and -unloaded (EAE) solutions applied in CO2 absorption in the temperature range from 293.15 to 323.15 K at atmospheric pressure. Due to the limitation of the instrument and corrosive behavior with increasing concentration, the mass fractions (w1) of aqueous EAE solutions selected were: as 0.089, 0.178, 0.267, and 0.356, which correspond to the molar concentrations of 1, 2, 3, and 4 mol·L–1, respectively. The determined density, viscosity and refractive index data for binary EAE+H2O and ternary CO2+EAE+H2O systems were correlated using Weiland et al. model, Redlich–Kister equation, extended Arrhenius equation, and a new proposed empirical function. All the calculated density, viscosity, and refractive index data fitted well with experimental values at all operational conditions.

•Two different solid acid catalyst SAPO-34 and SO42−/TiO2 were found and characterized.•The two catalysts were firstly used for rich MEA solution regeneration.•The effect of the catalyst/MEA ratio and the lifetime of SAPO-34 were studied.•The possible catalytic reaction mechanism was proposed.•B/L ratio and MSA of catalyst had the most positive impact on rich MEA solvent regeneration.In this work, the regeneration of rich CO2-loaded monoethanolamine (MEA) solvent with two catalysts (e.g. SAPO-34 and SO42−/TiO2) was investigated in order to reduce the energy requirement for solvent regeneration. The regeneration behavior with and without catalyst of a 5M MEA solution with an initial CO2 loading of 0.5 mol CO2/mol amine at 96 °C was studied to compare their CO2 desorption rate and heat duties. The results show that the two solid acid catalysts can reduce the heat duty for solvent regeneration and increase the CO2 desorption rate in comparison with blank test. The mechanism of CO2 desorption with catalyst in 5M MEA was proposed based on the result of catalyst characterization (e.g. N2 absorption/desorption experiment, Py-IR, NH3-TPD, FT-IR and XRD) to better understand the desorption process. The results indicate that SAPO-34 with the higher joint value of Brϕnsted/Lewis acid sites ratio (B/L) and mesopore surface area (MSA) shows the faster CO2 desorption rate and lower heat duty than SO42−/TiO2. Based on the experimental results, the addition of solid acid catalysts into amine solution could be considered as one of choices to reduce the heat duty for CO2 desorption from CO2-loaded amine solvent.

•MEA-MDEA-PZ can reduce 15.22–49.92% energy cost for CO2 capture.•The energy cost was analysised based on the carbamate and bicarbonate.•The heat of CO2 absorption in MEA-MDEA-PZ with different mix ratio were studied.•More MDEA and less PZ in MEA-MDEAPZ benefits bicarbonate formation.The blends of monoethanolamine (MEA), N-methyl-diethanolamine (MDEA) and piperazine (PZ) as a solvent for CO2 capture were investigated in terms of CO2 absorption-desorption performance. The total concentration of the blends was 6M mixed with different amine molar ratios, 3M MEA-2.5M MDEA-0.5M PZ (Blend-1), 3M MEA-2M MDEA-1M PZ (Blend-2) and 3M MEA-1.5M MDEA-1.5M PZ (Blend-3). The CO2 equilibrium solubility, absorption capacity, initial absorption rate, speciation, relative energy consumption and heat of absorption for each blend were investigated in this work. The results showed that Blend-3 had the best CO2 absorption performance in terms of the CO2 equilibrium solubility, initial CO2 absorption rate and CO2 absorption capacity compared to Blend-1 and Blend-2 and 5M MEA. 13C NMR spectroscopy was used to quantify species formed in the CO2-loaded MEA-MDEA-PZ solution and the results shows that Blend-1 system produced more bicarbonate and less carbamate compared to Blend-2 and Blend-3 systems. The heat of CO2 absorption was calculated using Gibbs-Helmholtz equation and the results showed that MEA-MDEA-PZ systems had lower absorption heat than that of MEA, DEA, AMP, PZ and trio-amine blends of MEA-AMP-PZ. For the CO2 desorption performance, three blends studied in this work had lower relative energy consumption for the solvent regeneration compared to 5M MEA and Blend-1 showed the best desorption performance. Among these blends, an increase in molar ratio of MDEA/PZ in the blends led to a decrease in energy consumption and an increase in cyclic capacity and the CO2 desorption rate. In addition, the blend of MEA-MDEA-PZ reduced the energy consumption by 15.22–49.92% compared to 5M MEA.

In the present work, the density and viscosity of 2-(methylamino)ethanol (MAE) solution were measured over the temperature range of 293.15 to 323.15 K with MAE mass fractions of w1 = 0.075, 0.15, 0.225, and 0.30 and CO2 loadings varying between 0 and 0.677 mol CO2/mol MAE. The physical solubility of N2O in aqueous MAE solution was measured in a stirred cell reactor over the temperature range of 289.31–348.18 K with MAE mass fraction w1 = 0.075, 0.15, 0.225, 0.30, 0.375, 0.45, 0.60, 0.75, and 1. The experimental density data for both CO2 loaded and unloaded aqueous MAE solutions were fitted by Redlich–Kister equation. The Weiland’s model was used to correlate the viscosity data of aqueous MAE solution. Finally, N2O solubility data were correlated by using an empirical polynomial model and compared with both the semiempirical model and the Redlich–Kister equation.

•The ANN models were used to correlate the CO2 equilibrium solubility of 3DMA1P.•The ANN models were superior in term of absolute average deviation to other thermodynamic models.•The vapor-liquid equilibrium data was essential for the development of theoretical models and correlations.In this work, the CO2 equilibrium solubility of 3-dimethylamino-1-propanol (3DMA1P) is presented over the concentration range of 1–3 mol/L, the temperature range of 298–333 K, and the CO2 partial pressure of 3–101 kPa. Several thermodynamic models (i.e. Kent-Eisenberg model, Austgen model, Hu-Chakma model, Liu et al. model) were used to correlate and predict the CO2 equilibrium solubility of 3DMA1P solution. It was found that the Liu et al. model could be considered to be an appropriate model to predict the CO2 equilibrium solubility in 3DMA1P solutions with an absolute average deviation (ADD) of 9.4%. In addition, the ANNs models (BPNN and RBFNN model) were developed and used to correlate the CO2 equilibrium solubility of 3DMA1P. It was found that the ANNs models could predict the experimental values very well with excellent ADDs of 3.0% for the BPNN model and 4.4% for the RBFNN model, respectively. In addition, a comparison of thermodynamic models and ANN models was presented in terms of prediction of CO2 solubility in 3DMA1P solution.

•The kinetics of CO2 reaction with MAE, EAE, IPAE and TBAE were investigated.•The termolecular mechanism and base-catalyzed hydration mechanism were studied.•The CO2 capacity in aqueous solutions was following the order: MAE < EAE < IPAE < TBAE.In this work, pseudo first-order reaction rate constants (k0) for the reaction of CO2 with sterically hindered secondary amines at temperatures of 293–313 K and various amine concentrations were studied using the rapid-mixing stopped-flow technique. It was found that the values of k0 increased as the concentration of amine in aqueous solution increased and as solution temperatures were increased. The second order rate constant (k2) at 293–313 K was also determined based on the proposed reaction mechanisms. The termolecular mechanism was able to fit the experimental data with predicted CO2 absorption rates of MAE and EAE with an absolute average deviation (AAD) of 2.81% and 14.96%, respectively. However, the base-catalyzed hydration mechanism is more precise in terms of the hindered amines (IPAE and TBAE) in predicting the CO2 absorption rates with AAD of 7.97% and 5.15%. The combined data for the CO2 loading showed that all four amines have good properties for the post-combustion CO2 capture process in comparison with MEA. In comparison with the amine reference MEA (CO2 loading = 0.58 mol CO2/mole of amine), the CO2 loading of the four amines is between 0.66 and 0.93 mol of CO2/mole amine. These results show that IPAE and TBAE are good candidates for CO2 capture as alternatives to MEA because of their good CO2 absorption and high reaction rate with CO2.

•Equilibrium CO2 solubility of aqueous 1-Dimethylamino-2-propanol solution.•Current and new developed models representing the equilibrium CO2 solubility in 1DMA2P.•Guidelines about effective screening of solvents based on three absorption parameters.In this work, the CO2 equilibrium solubility in 1-dimethylamino-2-propanol (1DMA2P) solution was determined as a function of 1DMA2P concentration (over the range of 1–5 M), temperature (in the range of 298–333 K), and CO2 partial pressure (in the range of 8–101 kPa), and the data used to fit the correlations for K2 using Kent-Eisenberg, Austgen, Li-Sheng and Hu-Chakma models. A new K2 correlation model was also developed to predict the CO2 equilibrium solubility in 1DMA2P solution. It was found that all of the models could fit the CO2 equilibrium solubility in 1DMA2P solution data with absolute average deviations (ADDs) for the models by Kent-Eisenberg, Austgen, Li-Sheng, Hu-Chakma and Liu et al. of 14, 15, 12, 6.3 and 10%, respectively. In addition, the heat of CO2 absorption in 1DMA2P solution estimated using Gibbs-Helmholtz equation was found to be −31.67 kJ/mol. Information or guidelines about effective utilization of data of screened solvents is provided based on three absorption parameters, namely, CO2 equilibrium solubility, second order reaction constant, and CO2 absorption heat.

•The CO2 fracturing fluid has not need of flowback.•The influence of different factors on the rheology characteristics was systematically analyzed.•The correlations of rheological parameters were obtained.In this study, the macro properties of a CO2 fracturing fluid were studied experimentally. A detailed experimental investigation has been conducted on the rheology of the CO2 clean-fracturing fluid by using a large scale experiment system. A fluid model using Fluent software was adopted to simulate the gas distribution and fully developed state of the CO2 fracturing fluid. The experimental results show that the CO2 fracturing fluid is shear thinning and the rheological properties can be described by the power-law model. As well, the character of this fluid differs greatly from that of single phase non-Newtonian fluid because of its formation of foam and the structure of its external phase. It was also found that the viscosity of CO2 fracturing fluid was proportional to the increment of foam quality and pressure, which, however, was inversely proportional to the increase of temperature and shear rate. Moreover, through analysis of the effects of different factors on the rheology characteristics, correlations of its rheological parameters were obtained.

•Reaction kinetics between CO2 and blends of MEA and DEA are studied.•Two possible situations are discussed based on the ratio of blends.•DEA barely reacts with CO2 in blends at low concentration.•The proposed mechanisms explain all experimental data very well with excellent AADs less than 5%.The stopped-flow technique was applied on the measurement of the kinetics of carbon dioxide (CO2) absorption into aqueous blends of monoethanolamine (MEA) and diethanolamine (DEA) over the temperature range of 293–313 K. The investigation of blended MEA + DEA with various molar ratios of DEA to MEA revealed that the reaction mechanism between CO2 and blended absorbents could be different at different ratio of DEA to MEA. Consequently, the kinetic data obtained in this work was split into two groups with respect to the different molar ratios of DEA to MEA in order to study the different mechanisms. In group A, the concentration of MEA was in the range of 5–15 mol/m3 and the concentration of DEA was low (varied between 5 and 15 mol/m3), while in group B, the DEA concentration was high (varied between 140 and 240 mol/m3) and the concentration of MEA remained in the range of 5–15 mol/m3. Modified models based on the termolecular mechanism were developed for each group and used to interpret the experimental kinetic data. Results showed that the models could explain the data well with an AAD of 4.71% for group A at low concentration of DEA and 3.33% for group B at high concentration of DEA. It is interesting to point out that DEA barely reacts with CO2 at low molar ratios (i.e. group A) whereas at high DEA concentration (i.e. group B), both MEA and DEA reacted with CO2.

•Mass transfer of DEEA/MEA was investigated in DX structured packed column.•The KGaV was evaluated by the orthogonal analysis.•Effect of concentration, temperature, CO2 loading, liquid and gas flow rate.•Order of importance for the contribution to KGaV of operational factors.The mass transfer performance of CO2 absorption into blended DEEA/MEA solutions was investigated in a lab-scale absorber packed with Sulzer DX structured packing using a standard orthogonal array with an L25(56) matrix. The volumetric overall mass transfer coefficient (KGaV) was evaluated at various key operating conditions over a amine concentration range of 2.00–5.00 kmol/m3, CO2 lean loading of 0.15–0.35 mol CO2/mol amine, over a wide CO2 partial pressure range of 6–18 kPa, a liquid feed temperature range of 303.15–343.15 K, with liquid flow rate 3.90–11.70 m3/m2·h, and 30.47–47.87 kmol/m2·h inert gas flow rate. The results show that these key operating parameters have significant effects on KGaV. Also, based on orthogonal analysis, it was clear that the order of importance for the contribution to KGaV of the six investigated factors was as follows: CO2 lean loading > CO2 partial pressure > Liquid feed temperature > Amine concentration > Liquid flow rate > Inert gas flow rate and the optimization of the experimental combination was B1C1D2A3E3F2.

In this work, the CO2 absorption performance in aqueous amine solutions have been investigated in hollow fiber membrane contactor. The overall mass transfer coefficients (Kol) was evaluated at different operating conditions, including absorbent type, liquid velocity, gas velocity and concentration of amine. The experimental results reveal that the overall mass transfer coefficient increase with liquid velocity, gas velocity and concentration of amine increasing. DEEA, as a promising tertiary amine, has a higher Kol value compared to that of MDEA.

•An improved screening method was developed with initial lean loading and time limitation for absorption/desorption process.•Screening result of single amines was validated by simulation experiments in Aspen Plus.•The method was applied for optimal molar ratio selection for blended amine systems.An improved fast screening method, i.e. the multiple fast screening method, was developed to quickly screen high efficiency solvents for post combustion CO2 capture, especially for the existing amine-based CO2 capture processes. The method was based on an integrated CO2 absorption-desorption process, where the absorption process was performed at 40 °C with a certain initial lean loading, obtained by a pretreatment process, and desorption process is done at the temperature of 80 °C. The duration of each of the two processes was set to be 60 min. This screening method, taking into account the CO2 absorption capacity as well as the absorption and desorption efficiency, was tested on five single alkanolamines in aqueous solutions with concentration of 30 wt%, and blended MEA/DEEA solutions with different ratio at a certain total molar concentration of 5 mole/L. The repeatable screening results of the single amines by this improved method show that the cyclic capacities of the amines are different from the experimental results obtained by using the equilibrium-based screening method, the experimental results of single amine solutions were finally further validated by a simulation process in Aspen Plus and show good agreement. For the blended amine systems screening, the molar ratio of MEA/DEEA of 2.5:2.5 presents the highest cyclic capacity, while no optimal ratio is found by using traditional equilibrium-based screening method. The absolute average difference (AAD) of mass balance between gas and liquid phases for both the single and blended amines screening experiments was calculated, and it turns out to be reliable with the value of 2.65% and 2.80%, respectively.

In this work, the reaction kinetics of carbon dioxide (CO2) with diethylenetriamine (DETA) and 1-amino-2-propanol (1-AP) in methanol and ethanol systems were measured using the stopped flow technique over a temperature range of 293–313 K in terms of pseudo-first-order rate constant (k0). Concentration in the range of 10 to 50 mol/m3 for diethylenetriamine, and 20 to 100 mol/m3 for 1-amino-2-propanol were studied. The experimental data show that the pseudo-first-order rate constants (k0) increase with the increase of both amine concentration and temperature. The zwitterion mechanism and the termolecular mechanism were used to represent the data for DETA in methanol and ethanol systems with excellent ADDs of 3.5% and 2.4%, respectively, and 1-AP in methanol and ethanol systems with excellent ADDs of 2.4% and 2.6%, respectively. In comparison with EDA and AEEA in terms of k2, DETA exhibits a better reaction kinetics performance for capturing CO2. Those results will be useful in finding an efficient method for the removal of CO2 from industrial gases.

The formation of bicarbonate ions in an amine solution during CO2 absorption results in lowering the heat duty for amine solvent regeneration in the CO2 capture process because bicarbonate breakdown needs the lowest energy input to release CO2. In this study, bicarbonate formation was conducted for two mixed solvents consisting of tertiary amines (1DMA2P (1 M) or MDEA (1 M)) blended with MEA in order to determine both formation rate and capacity of bicarbonate ions as compared to MEA alone. The amines and concentrations used in the study were MEA (5 M), MEA–MDEA (5:1 molar ratio, 6 M total), and MEA–1DMA2P (5:1 molar ratio, 6 M total) at various CO2 loadings. The formation of bicarbonate ions was evaluated using 13C NMR technique at 293.15 K. The results show that for the single tertiary amine system higher concentrations of bicarbonate ions were formed for MDEA than for 1DMA2P for the same CO2 loading. The results for the blended amine systems showed that bicarbonate ions were generated at CO2 loadings lower with MEA alone than with MEA–1DMA2P generating bicarbonate ions at a CO2 loading (0.34 mol CO2/mol amine) lower than that with MEA–MDEA (0.38 mol CO2/mol amine). Thus, as an additive in MEA, 1DMA2P has a better potential than does MDEA to generate bicarbonate ions at a leaner CO2 loading with the attendant lowering of the regeneration energy.

Carbon dioxide (CO2) stripping from CO2-loaded aqueous N,N-diethylethanolamine solution (DEEA) was comprehensively investigated in a laboratory scale regeneration column packed with Dixon ring random packing. The regeneration heat duty (Qreb) of DEEA was evaluated as a function of various operating parameters, including rich CO2 loading, lean CO2 loading, solution flow rate, feed temperature, and DEEA concentration, as well as synergistic parameters (e.g., Δα × L and C × L). The experimental results showed that the Qreb was sensitive to these operating parameters. For example, the Qreb decreased significantly as the lean CO2 loading, rich CO2 loading, and DEEA concentration increased, indicating that the Qreb can be reduced by adjusting these operating parameters. In addition, CO2-loaded aqueous DEEA solution was observed to have a lower Qreb (of 2.17 GJ/t CO2) as compared to those of aqueous MEA and DETA solutions. Based on heat duty alone, DEEA can be considered to be an attractive solvent for amine-based postcombustion CO2 capture.

A series of sand pack flood tests are carried out on Court heavy oil using different alkali solutions to evaluate the influence of different factors on enhanced oil recovery of heavy oil, such as interfacial tension (IFT), emulsification effect, and pressure drop. These alkali solutions include NaOH, Na2CO3, NaOH–surfactant, Na2CO3–surfactant, and the mixtures of NaOH and Na2CO3 at different ratios. The results demonstrated that using NaOH solution to displace heavy oil obtained the best oil recovery efficiency but without the lowest IFT and the most effective emulsification. By correlation of the enhanced oil recovery efficiencies with IFTs, emulsification effects, and pressure drops, it was found that the oil recovery efficiency corresponded better with the increments in pressure drop than other factors after chemical slug injection. In combination with the discovery of micromodel tests, it was deduced that the improvement on the heavy oil recovery efficiency was mainly due to the formation of an oil bank, which plugged the water channel. The formation of the oil bank for the NaOH displacing process is due to the accumulation of oil droplets. While for the NaOH–surfactant flooding process, the formation of the oil bank is mainly because of the emulsification. OH– exerts a special influence on the separation of trapped oil into oil droplets and the accumulation of oil droplets. A certain amount of OH– is required to reduce the IFT, which is beneficial to the formation of oil droplets, while excessive OH– can promote the accumulation of oil droplets, which is also detrimental to the formation of oil droplets.

Blended absorbents composed of N,N-diethylethanolamine (DEEA) and amine activator were comprehensively studied using an improved rapid screening method. A total of nine amine activators, including MEA, DEA, EEA, AMP, AEEA, MAPA, DETA, TETA, and PZ, were assessed based on absorption rate, stripping rate, and cyclic CO2 capacity. The rapid screening experiments for the absorption and stripping were conducted at 40 and 80 °C, respectively. Results revealed how the absorption/stripping performance is affected by the number and structure of −NH– groups in the activators. In addition, all of the 3 M DEEA-based solutions showed improved absorption rate and regeneration rate as well as cyclic CO2 capacity with the use of 3 M DEEA and 5 M MEA individually. Furthermore, experimental results showed that the highest average absorption rate, average desorption rate, and cyclic CO2 capacity of 1.6272 mol CO2/L were achieved by an aqueous DEEA-PZ solution.

Amine scrubbing is regarded as one of the most suitable technologies for postcombustion CO2 capture. However, data on regeneration energy and performance is limited in literature. In this study, the reboiler heat duties of triethylenetetramine (TETA) and triethylenetetramine (TETA) + N-methyldiethanolamine (MDEA) were experimentally evaluated in a bench-scale stripper packed with Dixon ring random packing. The effects of various operating parameters on the desorption performance (presented in terms of reboiler heat duty, Qreboiler) were investigated, including lean loading, rich loading, amine concentration, solvent flow rate, and amine type. The experimental results showed that the Qreboiler was very sensitive to these process parameters. In addition, a comparison of the Qreboiler of TETA, monoethanolamine (MEA), and diethylenetriamine (DETA) was conducted to evaluate the potential for TETA’s application in the CO2 capture process. The results obtained in this work showed that the Qreboiler of TETA, as a function of amount of CO2 released, is lower than that of MEA and DETA.

•CO2 solubility in 1DMA2P was measured at various T   and PCO2PCO2.•The CO2 absorption heat of 1DMA2P was got and was lower than MEA and MDEA.•The ion speciation plots were generated using the pH calculation method.•The overall mass transfer coefficient of 1DMA2P was investigated and compared.In this work, the CO2 absorption performance of aqueous 1-dimethylamino-2-propanol (1DMA2P) was comprehensively investigated in terms of CO2 equilibrium solubility, CO2 absorption rate, CO2 absorption heat, and mass transfer efficiency. The CO2 equilibrium solubility in 2 M 1DMA2P was measured over the temperature range of 298–333 K and CO2 partial pressure range of 8–101 kPa. The results showed that the CO2 equilibrium solubility of 1DAM2P was higher than those of conventional amines, MEA and MDEA. The CO2 absorption heat of 1DMA2P based on the Gibbs–Helmholtz equation was found to be −30.5 kJ/mol, which suggests that 1DMA2P needs a lower regeneration energy as compared with MEA and MDEA. Ion speciation (including 1DMA2P, 1DMA2PH+, HCO3−, CO32−) plots obtained from the pH method were also generated at the temperatures of 298 K and 313 K. In addition, the overall mass transfer coefficient (KGav) of 1DMA2P in a packed column was also experimentally obtained and compared with those of MEA and MDEA. The ranking was: MEA > 1DMA2P > MDEA.

•Kinetics in the system of DEAB–CO2–H2O was studied using stopped-flow technique.•Reaction kinetics can be ranked as: DEAB > DEMEA > DMMEA > MDEA.•The Brønsted correlation for predication k2 of DEAB was also developed.In the present work, a stopped-flow apparatus was used to determine the CO2 absorption kinetics of 4-diethylamine-2-butanol (DEAB) in terms of observed pseudo-first-order rate constant (k0) and second order reaction rate constant (k2). The experiments were done using DEAB in the concentration range of 0.10–0.90 kmol/m3, and a temperature range of 293–313 K. The pKa of DEAB was also experimentally determined over a temperature range of 278–333 K. The Brønsted relationship between the reaction rate constant obtained from the stopped-flow apparatus and pKa obtained from experimental determination was then evaluated. The results showed that the Brønsted correlation could predict the absorption rate constant with an AAD of 8.6%, which is within an acceptable range of 10%. By comparing through different evaluation techniques such as k2, pKa and ΔrGm°ΔrGm°, it was observed that DEAB has faster reaction kinetics than those of conventional tertiary amines, namely, DEMEA, DMMEA and MDEA.

•GA-BPNN model is applied to predict both pure and impure MMPs in CO2-EOR process.•GA-BPNN model shows excellent outperformance over the literature correlations.•The variation trends of MMPs alter with the gradual change of input variables.In this study, a genetic algorithm based back propagation artificial neural network model was developed and used to predict the minimum miscibility pressure, i.e. MMP, for both pure and impure CO2 injection cases. Ten parameters that affecting the MMP were chosen as input variables, while the MMP was selected as output parameter. These parameters were reservoir temperature-TR, mole fraction of volatile oil components-xvol, mole fraction of intermediate oil components-xint, mole fraction of C5–C6 oil components-xC5-C6, molecular weight of C7+ components-MWC7+, mole fraction of CO2 in solvent-xCO2, mole fraction of C1 in solvent-xC1, mole fraction of N2 in solvent-xN2, mole fraction of H2S in solvent-xH2S, and mole fraction of C2–C4 in solvent-xC2–C4. The performance of the newly developed model was evaluated by calculating the deviations between the predicted and the target values, and was compared with four well known correlations in published literature. Through the comparison, it can be found that our new model outperformed those four correlations with the lowest average absolute relative error of 5.51% and mean square error of 7.01%. The influence degrees of each factor on MMP were also analyzed qualitatively and quantitatively by sensitivity analysis. It was found that xint, xC5–C6, and xH2S have positive effects on MMP, while TR, xvol, MWC7+, xCO2, xC1, and xN2 have negative effects on MMP. In addition, the effect of xC2–C4 on MMP can be neglected. Furthermore, the variations of MMP with the increase of each factor were also considered, and it can be found that the slopes of these curves are not constant all the time and change with the variations of the influence factors.

In the present work, ion speciation studies in solutions of the novel amine 4-(diethylamine)-2-butanol (DEAB), at various CO2 loadings (0–0.8 mol of CO2/mol of amine) and amine concentrations (0.52–1.97 M), were determined by 13C nuclear magnetic resonance (NMR) spectroscopy. In addition, the dissociation constant K of DEABH+ was determined at 24.5, 35, and 45 °C using a pH meter. The ion speciation plot, which contains various sets of concentrations of DEAB, protonated DEAB, bicarbonate, and carbonate, was successfully generated. Because DEAB is a novel solvent, this is the first time that the ion speciation plots of the DEAB–CO2–H2O system have been developed. It is also the first time that the 13C NMR calibration technique was applied to develop the vapor–liquid equilibrium (VLE) model for an amine–CO2–H2O system. The results obtained from the present work can be a great help for the further analysis of the DEAB VLE model, as well as CO2 absorption and kinetics studies. Furthermore, it was found that the novel 13C NMR calibration technique developed in this work provides higher accuracy than the conventional technique.

The mass-transfer performance of CO2 absorption into aqueous diethylenetriamine (DETA) solutions was investigated in an absorption column randomly packed with Dixon rings at 303–303 K and atmospheric pressure, and compared with that of monoethanolamine (MEA), which is widely considered as a benchmark solvent for CO2 absorption. The mass-transfer performance was presented in terms of volumetric overall mass-transfer coefficient (KGav). In particular, the effects of operating parameters, such as inlet CO2 loading, solvent concentration, liquid flow rate, inert gas flow rate, and liquid temperature, were investigated and compared for both MEA and DETA. Over 40 runs of absorption experiments were carried out in this study. The results showed that KGav of DETA was found to be higher than that of MEA. Also, inlet CO2 loading, solvent concentration, liquid flow rate, and liquid inlet temperature had significant effect on KGav for both systems. However, the inert gas flow rate had an insignificant effect on KGav. Lastly, predictive correlations for KGav for DETA–CO2 and MEA–CO2 systems in randomly Dixon ring packed columns were successfully developed. The predicted results were found to be in relatively good agreement with the experimental results, with average absolute deviations (AADs) of 16% and 14%, respectively.

Hierarchical mesostructures of poly(ε-caprolactone)-b-poly(ethylene oxide)-b-poly(ε-caprolactone) (PCL-PEO-PCL) triblock copolymers have been grown from evaporation-induced self-assembly directed by alkali metal ions. The self-assembly process began with a dilute homogeneous solution of the triblock copolymers in a mixture of tetrahydrofuran (THF) and water. THF preferentially evaporated under reduced pressure and induced the formation of amphiphilic polymer micelles. The spherical polymer micelles formed both in deionized water and NaOH aqueous solution. However, different mesostructures were discovered during the film depositing process for scanning electron microscopy observation. The polymer micelles were observed for the deposition sample in deionized water while sisal-like hierarchical mesostructures resulted from the film deposition of polymer micelles in NaOH aqueous solution. The sisal-like mesostructures and their formation process were observed through scanning electron microscopy, transmission electron microscopy, fluorescent microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Detailed study revealed that during evaporation-induced self-assembly of PCL-PEO-PCL amphiphilic triblock copolymer directed by alkali metal ions, the sodium ions and polymer micelles increasingly concentrated in NaOH aqueous solution and the solvent quality for the diblock progressively decreased, which resulted in the stronger coordination between alkali metal ions and PEO ligands in the block copolymer and PEO segment crystallization.

Among the current technologies for post-combustion CO2 capture, amine-based chemical absorption appears to be the most technologically mature and commercially viable method. This review highlights the opportunities and challenges in post-combustion CO2 capture using amine-based chemical absorption technologies. In addition, this review provides current types and emerging trends for chemical solvents. The issues and performance of amine solvents are reviewed and addressed in terms of thermodynamics, kinetics, mass transfer, regeneration and solvent management. This review also looks at emerging and future trends in post-combustion CO2 capture using chemical solvents in the near to mid-term.Carbon dioxide absorption into aqueous amines is the most attractive approach for carbon dioxide capture from fossil fuel-fired power plants. Since no solvent currently exists that will possess all excellent features for carbon dioxide capture, an appropriate selection of an attractive solvent is of great importance. It requires comprehensive understanding of performance in terms of absorption solubility, kinetics, mass transfer, regeneration, as well as its thermal and chemical stabilities, since these directly affect the capture performance and operating conditions.Download high-res image (124KB)Download full-size image

•Reaction kinetics of 1-(2-HE)PRLD with CO2 is presented using stopped-flow technology.•CO2 absorption heat of 1-(2-HE)PRLD is shown.•The plot of the kinetics versus heat absorption is created.The CO2 absorption performance of aqueous 1-(2-hydroxyethyl)pyrrolidine (1-(2-HE)PRLD) was studied with respect to kinetics (i.e., in terms of the pseudo-first-order rate constant (ko) and second-order reaction rate constant (k2), obtained using the stopped-flow apparatus). CO2 equilibrium solubility and heat of CO2 absorption were evaluated at the temperature range of 293–313 K in the 1-(2-HE)PRLD concentration range of 0.20–1.00 mol/L for kinetics and at 2 M for CO2 solubility. The values of ko were then represented using the base-catalyzed hydration mechanism, which gave an acceptable AAD of 10%. In addition, Brønsted plots of k2 vs. pKa were developed to predict k2 using pKa values of various tertiary amines. In addition, the CO2 equilibrium solubility and CO2 absorption heat were obtained in this work. Based on a comparison with other amines such as MEA, MDEA and 1DMA2P, 1-(2-HE)PRLD showed better performance in terms of CO2 equilibrium solubility (DEAB > 1-(2-HE)PRLD > 1-(2HE)PP > 1DMA2P > MDEA > MEA > DEA), kinetics (MEA > DEA > DEAB > 1-(2-HE)PRLD > 1-(2-HE)PP > DMMEA > 1DMA2P > MDEA.) and CO2 absorption heat (MEA > DEA > MDEA > DEAB > 1-(2-HE)PRLD > 1-(2HE)PP > 1DMA2P). Therefore, 1-(2-HE)PRLD could be considered as a good alternative solvent for CO2 capture. A correlation between kinetics and heat of CO2 absorption has been developed to guide the design of what can be considered to be ideal amine solvents for CO2 capture.