Degradations‐ und Energieverhalten reaktiver Amin‐Lösungen bei der CO2‐Absorption/Desorption

Reactive absorption using aqueous amine solutions is the technically most feasible retrofit option for the separation of CO₂ from flue gases. Frequently discussed issues are the realization of a cost‐effective increase in efficiency in the sophisticated overall absorption process and the minimization of the energy demand for solvent regeneration under operating conditions. However, the influence of degradation phenomena on capacity and energy efficiency during the absorption‐regeneration cycles using blended monoethanolamine solutions has been less considered so far. The decrease in capacity depends in particular on time, temperature, O₂‐ and SO₂ concentration in the flue gas and has to be considered in plant design. Addition of degradation inhibitors decreases the energy requirements.     

Reduction of amine mist emissions from a pilot-scale CO2 capture process using charged colloidal gas aphrons

In the CO₂ capture process from coal-derived flue gas where amine solvents are used, the flue gas can entrain small liquid droplets into the gas stream leading to emission of the amine solvent. The entrained drops, or mist, will lead to high solvent losses and cause decreased CO₂ capture performance. In order to reduce the emissions of the fine amine droplets from CO₂ absorber, a novel method using charged colloidal gas aphron (CGA) generated by an anionic surfactant was developed. The CGA absorption process for MEA emission reduction was optimized by investigating the surfactant concentration, stirring speed of the CGA generator, and capture temperature. The results show a significant reduction of MEA emissions of over 50% in the flue gas stream exiting the absorber column of a pilot scale CO₂ capture unit.     

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

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

Reduction of CO2 emissions by a membrane contacting process☆

A membrane-based gas–liquid contacting process was evaluated in this work for CO₂ removal from flue gases. The absorption of CO₂ from a CO₂–N₂ mixture was investigated using a commercial hollow fiber membrane contactor and water or diethanolamine as absorbing solvents. Significant CO₂ removal (up to 75%) was achieved even with the use of pure water as absorbent. By using aqueous amine solutions and chemical absorption, mass transfer improved, and CO₂ removal was nearly complete (∼99%). A mathematical model was developed to simulate the process and it was validated with experimental data. Results show that membrane contactors are significantly more efficient and compact than conventional absorption towers for acid gas removal.     

Carbon dioxide absorption into biphasic amine solvent with solvent loss reduction

The main challenge in the CO₂ capture from flue gases is to reduce the energy consumption required for solvent regeneration. Lipophilic amines exhibit a thermomorphic phase transition upon heating, giving rise to autoextractive behaviour, which enhances desorption at temperatures well below the solvent boiling point. The low regeneration temperature of less than 80 °C together with the high cyclic CO₂ loading capacity (c. 0.9 mol-CO₂/mol-absorbent) of such biphasic amine systems permit the use of low temperature and even waste heat for desorption purposes. In order to improve the capture process and reduce the commensurate energy demand still further, desorption experiments were carried out at 70-80 °C and techniques for enhancing CO₂ release without gas stripping were also studied. The comparison of various amines at a concentration of 3 M and for a 15 mol% CO₂ feed gas demonstrates the considerable potential of lipophilic amines for the CO₂ absorption process. Chemical stability is a decisive factor for the industrial application of amine absorbents. Degradation of the novel lipophilic amine absorbents was shown to be minor, while volatility losses represent a major shortcoming of the biphasic solvent systems. Appropriate countermeasures to limit solvent losses were examined experimentally.     

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

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

CO2 Absorption into Aqueous Solutions of Monoethanolamine,Methyldiethanolamine, Piperazine and their Blends

The removal of carbon dioxide from industrial gases, e.g. in thermal power stations to meet the discharge limits for CO₂ in flue gases, is usually achieved with a reactive absorption technique using aqueous solutions of alkanolamines. From the absorption performance point of view, primary and secondary amines are preferred. However, in case the costs of the solvent regeneration are also taken into account, tertiary amines are much more attractive. In order to combine the specific advantages of tertiary and primary/secondary alkanolamines, both types of solvents are mixed. In this paper, mixtures of monoethanolamine and methyldiethanolamine with piperazine as absorption activator are experimentally compared with respect to CO₂ removal performances at 25 °C. The absorption process in a special packed column has also been simulated with the use of published data on reaction kinetics, physicochemical properties (densities, viscosities, diffusivities, Henry coefficients) of the CO₂‐amines systems, including experimentally determined hydrodynamic and mass transfer characteristics of the CO₂ scrubber.     

Equilibrium solubility of CO<Subscript>2</Subscript> in aqueous binary mixture of 2-(diethylamine)ethanol and 1, 6-hexamethyldiamine

CO₂ solubility data are important for the efficient design and operation of the acid gas CO₂ capture process using aqueous amine mixture. 2-(Diethylamino)ethanol (DEEA) solvent can be manufactured from renewable sources like agricultural products/residue, and 1,6-hexamethyldiamine (HMDA) solvents have higher absorption capacity as well as reaction rate with CO₂ than conventional amine-based solvents. The equilibrium solubility of CO₂ into aqueous binary mixture of DEEA and HMDA was investigated in the temperature range of 303.13-333.13 K and inlet CO₂ partial pressure in the range of 10.133-20.265 kPa. Total concentration of aqueous amine mixtures in the range of 1.0-3.0 kmol/m³ and mole fraction of HMDA in total amine mixture in the range of 0.05-0.20 were taken in this work. CO₂ absorption experiment was performed using semi-batch operated laboratory scale bubble column to measure equilibrium solubility of CO₂ in amine mixture, and CO₂ absorbed amount in saturated carbonated amine mixture was analyzed by precipitation-titration method using BaCl₂. Maximum equilibrium CO₂ solubility in aqueous amine mixture was observed at 0.2 of HMDA mole fraction in total amine mixture with 1.0 kmol/m³ total amine concentration. New solubility data of CO₂ in DEEA+HMDA aqueous mixtures in the current study was compared with solubility data available in previous studies conducted by various researchers. The study shows that the new absorbent as a mixture of DEEA+HMDA is feasible for CO₂ removal from coal-fired power plant stack gas streams.     

Potential of different additives to improve performance of potassium carbonate for CO<Subscript>2</Subscript> absorption

The performance of potassium carbonate (K₂CO₃) solution promoted by three amines, potassium alaninate (K-Ala), potassium serinate (K-Ser) and aminoethylethanolamine (AEEA), in terms of heat of absorption, absorption capacity and rate was studied experimentally. The experiments were performed using a batch reactor, and the results were compared to pure monoethanolamine (MEA) and K₂CO₃ solutions. The heat of absorption of K₂CO₃+additive solution was calculated using the Gibbs-Helmholtz equation. In addition, a correlation for prediction of CO₂ loading was presented. The results indicated that absorption heat, absorption rate and loading capacity of CO₂ increase as the concentration of additive increases. The blend solutions have higher CO₂ loading capacity and absorption rate when compared to pure K₂CO₃. The heat of CO₂ absorption for K₂CO₃+additive solutions was found to be lower than that of the pure MEA. Among the additives, AEEA showed the highest CO₂ absorption capacity and absorption rate with K₂CO₃. In conclusion, the K₂CO₃+AEEA solution with high absorption performance can be a potential solvent to replace the existing amines for CO₂ absorption.     

A Single Stage Membrane Process for CO2 Capture from Flue Gas by a Facilitated Transport Membrane

Carbon dioxide is the most important anthropogenic greenhouse gas and it accounts for about 80% of all greenhouse gases (GHG). The global atmospheric CO₂ concentrations have been increased significantly and have become the major source responsible for global warming; the greatest environmental challenge the world is facing now. The efforts to control the GHG emissions include the recovery of CO₂ from flue gas. In this work, feasibility analysis, based on a single stage membrane process, has been carried out with an in-house membrane program interfaced within process simulation program (AspenHysys) to investigate the influence of process parameters on the energy demand and flue gas processing cost. A novel CO₂-selective membrane with the facilitated transport mechanism has been employed to capture CO₂ from the flue gas mixtures. The results show that a membrane process using the facilitated transport membrane can also be considered as an alternative CO₂ capture process and it is possible to achieve more than 90% CO₂ recovery and 90% CO₂ purity in the permeate with reasonable energy consumption compared to amine absorption and other capture techniques.     

Simulation of CO<Subscript>2</Subscript> removal in a split-flow gas sweetening process

Split-flow gas sweetening is known to consume less energy than a conventional gas sweetening process when the inlet sour gas contains a high concentration of acid gases. In this work, a computer simulation of a split-flow natural gas sweetening process based on absorption/stripping process with alkanoamine (MEA and DGA) solutions, using Aspen plus, was performed. The input of parameters such as the concentration of sour gases (CO₂, H₂S) in the feed gas has been examined. Simulation results show that the split-flow gas sweetening process can reduce the reboiler duty of a stripping tower better than the conventional gas sweetening process according to the concentration of CO₂ in the feed gas.     

Novel Thermomorphic Biphasic Amine Solvents for CO2 Absorption and Low‐Temperature Extractive Regeneration

The key challenge in amine‐based CO₂ capture from flue gases is to reduce the energy consumption required for solvent regeneration. Lipophilic amines exhibit a thermomorphic phase transition upon heating, giving rise to autoextractive behavior, which intensifies desorption at temperatures well below the boiling point of aqueous solutions. The low regeneration temperature of less than 80 °C together with the high cyclic CO₂ loading capacity of ～0.9 mol mol_absorbent^–1 of such thermomorphic biphasic solvent (TBS) systems permit the use of low‐value and even waste heat at temperatures below 100 °C for desorption. In order to reduce the exergy demands still further, techniques for enhancing CO₂ release using extractive regeneration with inert solvent addition were investigated at temperatures of 40–50 °C to permit the use of waste heat at temperatures of ～70 °C or less. The regeneration of 3 M absorbed lipophilic amine solutions with 0.93 mol mol^–1 CO₂ loading by using various additional solvents and the evaluation of the extractive performance in multiple‐stage crosscurrent and countercurrent configurations indicated the promise of adding certain hydrophobic solvents to enhance the low‐temperature regeneration of TBS absorbents.     

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

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

Effect of addition of weak acids on CO<Subscript>2</Subscript> desorption from rich amine solvents

Experiments were conducted to study the effect of addition of four weak acids (adipic, suberic, phthalic and sebacic acids) on the regeneration of three types of CO₂-loaded rich solvents (Monoethanolamine (MEA), Diethanolamine (DEA) and Methyldiethanolamine (MDEA)). It was found that CO₂ could be released faster and in a larger quantity when the amount of acid added to the solvent was increased while other desorption conditions were maintained unchanged. Adipic acid appeared to be more effective than phthalic, suberic and sebacic acids in enhancing solvent regeneration rate. Among the three amines investigated, MEA had the highest CO₂ desorption rate, while DEA saved the most energy. The effect of adipic acid residue in the MEA solvent on CO₂ absorption was also investigated. The residue acid reduced the absorption capacity of the MEA solvent significantly when the solvent concentration was low and slightly when the concentration was high.     

Investigation on kinetics of carbon dioxide absorption in aqueous solutions of monoethanolamine + 1, 3-diaminopropane

ABSTRACT

Environmental concerns from global warming and climate change demand carbon dioxide separation from post-combustion gases. Important parameters are involved in choosing the suitable solvent for carbon dioxide separation, including the reaction rate of carbon dioxide and the solvent. In this paper, the kinetics of carbon dioxide (CO₂) absorption in aqueous solutions of Monoethanolamine (MEA) + 1,3-Diaminopropane (DAP), a diamine containing two primary amino group, was developed. The measurements were performed in a stirred cell with a horizontal gas-liquid interface in the temperature range of 313.15–333.15 K and aqueous solutions of 10 wt% MEA + 5 wt% DAP and 12.5 wt% MEA + 2.5 wt% DAP. Experiments were conducted in an isothermal batch reactor with a horizontal gas-liquid interface under pseudo-first-order conditions, enabling the determination of the overall kinetic rate constant from the pressure drop method. Second-order reaction rate constants of CO₂ absorption in amine solutions were estimated using the calculated initial absorption rate. It was found that the rate constants in MEA+ DAP solutions were greater than in MEA solutions which means that DAP increases the reaction rate.     

Kinetics study of carbon dioxide absorption in aqueous solutions of 1,6-hexamethyldiamine (HMDA) and 1,6-hexamethyldiamine, N,N′ di-methyl (HMDA, N,N′)

A study towards the kinetics of CO₂ in aqueous solutions of 1,6-hexamethyl diamine (HMDA) and 1,6-hexamethyl diamine, N,N′ di-methyl (HMDA, N,N′) was performed at concentrations ranging from 0.5 to 2.5 mol/L and temperatures from 283 up to 303 K. The kinetics data were determined by CO₂ absorption experiments using a stirred cell reactor with a flat interface between gas and liquid. These new CO₂ solvents were identified in earlier work for their high CO₂ capacity and limited corrosiveness. The experimental technique was validated using kinetic experiments for a 2.5 mol/L monoethanolamine solution. In view of double amine functionality and the six carbon chain between the amine groups, attention was paid to whether the amine groups acted independently and whether or not internal cyclisation would affect the carbamate forming mechanism. The reaction order with respect to HMDA was found to vary from 1.4 to 1.8 with increasing temperature. Absorption experiments in an equimolar solution of HMDA with HCl showed that the two amine groups react independently from each other towards CO₂. The reactivity of both diamines was more than five times larger than for monoethanolamine. The secondary diamine HMDA, N,N′ was found to be even more reactive towards CO₂. Additionally, the effect of CO₂ loading on the kinetics was studied for 0.5 mol/L aqueous solutions of HMDA and HMDA, N,N′ at 293 K. Both solvents are from absorption kinetics point of view good candidates for further evaluation as solvent (-component) for CO₂ capture.     

Ionic liquids for CO2 capture—Development and progress

Innovative off-the-shelf CO₂ capture approaches are burgeoning in the literature, among which, ionic liquids seem to have been omitted in the recent Intergovernmental Panel on Climate Change (IPCC) survey. Ionic liquids (ILs), because of their tunable properties, wide liquid range, reasonable thermal stability, and negligible vapor pressure, are emerging as promising candidates rivaling with conventional amine scrubbing. Due to substantial solubility, room-temperature ionic liquids (RTILs) are quite useful for CO₂ separation from flue gases. Their absorption capacity can be greatly enhanced by functionalization with an amine moiety but with concurrent increase in viscosity making process handling difficult. However this downside can be overcome by making use of supported ionic-liquid membranes (SILMs), especially where high pressures and temperatures are involved. Moreover, due to negligible loss of ionic liquids during recycling, these technologies will also decrease the CO₂ capture cost to a reasonable extent when employed on industrial scale. There is also need to look deeply into the noxious behavior of these unique species. Nevertheless, the flexibility in synthetic structure of ionic liquids may make them opportunistic in CO₂ capture scenarios.     

Mass transfer investigation and operational sensitivity analysis of amine-based industrial CO2 capture plant

In this article, the industrial process of CO₂ capture using monoethanolamine as an aqueous solvent was probed carefully from the mass transfer viewpoint. The simulation of this process was done using Rate-Base model, based on two-film theory. The results were validated against real plant data. Compared to the operational unit, the error of calculating absorption percentage and CO₂ loading was estimated around 2%. The liquid temperature profiles calculated by the model agree well with the real temperature along the absorption tower, emphasizing the accuracy of this model. Operational sensitivity analysis of absorption tower was also done with the aim of determining sensitive parameters for the optimized design of absorption tower and optimized operational conditions. Hence, the sensitivity analysis was done for the flow rate of gas, the flow rate of solvent, flue gas temperature, inlet solvent temperature, CO₂ concentration in the flue gas, loading of inlet solvent, and MEA concentration in the solvent. CO₂ absorption percentage, the profile of loading, liquid temperature profile and finally profile of CO₂ mole fraction in gas phase along the absorption tower were studied. To elaborate mass transfer phenomena, enhancement factor, interfacial area, molar flux and liquid hold up were probed. The results show that regarding the CO₂ absorption, the most important parameter was the gas flow rate. Comparing liquid temperature profiles showed that the most important parameter affecting the temperature of the rich solvent was MEA concentration.     

Preliminary analysis of process flow sheet modifications for energy efficient CO2 capture from flue gases using chemical absorption

The energy penalty associated with solvent based capture of CO₂ from power station flue gases can be reduced by incorporating process flow sheet modifications into the standard process. A review of modifications suggested in the open and patent literature identified several options, primarily intended for use in the gas processing industry. It was not immediately clear whether these options would have the same benefits when applied to CO₂ capture from near atmospheric pressure combustion flue gases. Process flow sheet modifications, including split flow, rich split, vapour recompression, and inter-stage cooling, were therefore modelled using a commercial rate-based simulation package. The models were completed for a Queensland (Australia) based pilot plant running on 30% MEA as the solvent. The preliminary modelling results showed considerable benefits in reducing the energy penalty of capturing CO₂ from combustion flue gases. Further work will focus on optimising and validating the most relevant process flow sheet modifications in a pilot plant.     

Removal of CO2 and/or SO2 from gas streams by a membrane absorption method

Studies were made on the membrane absorption of CO₂ and/or SO₂ using hydrophobic microporous hollow-fibre (HF) membrane modules. The absorbent liquids used were aqueous solutions of NaOH, K₂CO₃, alkanolamines and Na₂SO₃, flowing on the lumen side of the HF in laminar flow. A semi-empirical correlation was derived for the gas-phase mass-transfer coefficient on the shell side, by including geometrical factors of the HFs and the shell tube in the general correlation for mass transfer. It was found that the CO₂ absorption rate in various aqueous solutions of alkalis and alkanolamines is successfully described by a model based on gas diffusion through the membrane pores subsequent to gas absorption accompanied by chemical reaction. The simultaneous membrane absorption of SO₂ and CO₂ was also studied using aqueous Na₂SO₃ solution, the selective removal of SO₂ to CO₂ being successfully achieved when both the liquid flow rate and solute concentration are low. This suggests that this membrane absorption method provides an energy saving process for SO₂ removal from flue gases.