Aqueous Amine Research Articles

Using carbon steel in the stripper and reboiler for post-Combustion CO2 capture with aqueous amine blends

Aqueous amine solutions loaded with CO2 show a range of corrosion behaviour when in contact with carbon steels. Primary (1°) and secondary (2°) amines undergo corrosion, including the formation of iron oxide surface layers. By contrast, tertiary (3°) and sterically-hindered (SH) amines produce an excess of carbonate ions, leading to FeCO3 formation, and thereby reducing corrosion. Four amines were tested under challenging conditions (1–5M at 120°C) to confirm these behaviors. Due to recent interest in blended amine solvents (1° or 2° with 3° or SH) for improved reaction kinetics, CO2 absorption capacity and recoverability, four binary amine combinations (MEA+MDEA, MEA+AMP, AEPZ+MDEA, AEPZ+AMP) were tested in a range of compositions. Blends containing low concentrations of 1° or 2° amine show promise for use with carbon steel due to the formation of a siderite product layer and low corrosion levels. An increase in concentration of 1° or 2° amines, shows higher Fe ion concentrations initially as well as significant weight change to the coupon. However, the formation of more diverse product layers at longer time intervals reduces the Fe ion concentration in the bulk. Blends generally offer reduced corrosion compared to 1° or 2° amines alone, another benefit towards deployment.

Carbon dioxide (CO2) capture: Absorption-desorption capabilities of 2-amino-2-methyl-1-propanol (AMP), piperazine (PZ) and monoethanolamine (MEA) tri-solvent blends

In this study, highly concentrated tri-solvent blends containing 2-amino-2-methyl-1-propanol (AMP), piperazine (PZ) and monoethanolamine (MEA) were experimentally investigated for their potential capabilities in carbon dioxide (CO2) capture. The concentration of both AMP and PZ were varied but their combined concentration (AMP + PZ) was kept at 3 kmol/m3 to limit the possibility of precipitation, the maximum PZ concentration (1.5 kmol/m3), and the total aqueous amine solution concentration (6 kmol/m3). At atmospheric pressure condition, the absorption process was carried out at 313 K and 15.1%v/v CO2 while 363 K was used for the desorption analysis. Experimental results indicated that all the AMP – PZ – MEA tri-solvent blends possessed higher cyclic capacities, initial desorption rates, and lower heat duties (50–54.5%) compared to the standard 5 kmol/m3 MEA. For the initial absorption rates, only the tri-solvent blends with AMP/PZ molar ratios of 1 and 2 were higher than 5 kmol/m3 MEA. These findings, most especially the significant reduction in heat duty by halve reveal the prospects of AMP – PZ – MEA tri-solvent blends for CO2 capture applications.

Infrared Spectroscopic Study of Reaction of Carbon Dioxide with Aqueous Monoethanolamine Solutions

Increasing levels of atmospheric CO2 emissions from fossil fuel combustion is altering global climate, and several strategies are being examined for CO2 capture and sequestration. Aqueous amine solutions, in particular, monoethanolamine (MEA) is extensively used for CO2 adsorption. Our objective in this study was to follow the reaction of CO2 with 15 wt % monoethanolamine (MEA) by horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR), with particular focus on the evolution of MEA, protonated MEA (MEAH+), MEA carbamate, and carbonate/bicarbonate species. Since the path length in HATR-FTIR is well-defined, by use of standards and Beer’s law, the molar absorptivity was calculated. This allowed us to monitor the concentrations of MEA and MEAH+ quantitatively. Using the characteristic infrared bands of the various amine-derived species, influence of SO2 (151 ppm) on CO2 absorption by MEA was studied, including the cycling process of adsorption (40 °C) and desorption (100 °C...

Comparing CO2 removal characteristics of aqueous solutions of monoethanolamine, 2-amino-2-methyl-1-propanol, methyldiethanolamine and piperazine through absorption process

The gradual increase in concentration of anthropogenic CO2 in the atmosphere and its potential threat to the environment has become a matter of worldwide concern towards exploration of energy-efficient, cost effective and promising technique of CO2 capture from industrial flue gases. The present experimental investigation is a kind of comparative assessment of CO2 capturing capabilities of four different aqueous amine solvents viz. monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), methyldiethanolamine (MDEA) and piperazine (PZ) from flue gas through post combustion technique. The absorption study has been performed in a packed column over the temperature range of 298–313K and the CO2 partial pressure range of 10–15kPa. CO2 absorption performances have been studied under the influence of process variables such as solvent concentration (10, 20 and 30wt%), gas flow rate, absorbent (solvent) flow rate. The regeneration performances of amine solution are studied over the temperature range of 368–383K. The specific rate of absorption of all four different aqueous amine solution, CO2 loading capacity of each and every individual amine after absorption and regeneration performance and the percentage of CO2 absorbed have been examined. The absorption performance follows an increasing trend of MDEA<AMP<MEA<PZ on the basis of specific absorption rate and the regeneration performance follows an increasing manner of MEA<PZ<MDEA<AMP based on regeneration efficiency.

Prediction of VLE for aqueous blended amines using VLE models of single amines

The possibility of the vapor-liquid equilibrium (VLE) prediction of aqueous blended amines using Kent-Eisenberg (KE) VLE models of single amines has been investigated in this study. The VLE data of five different types of single amine and seven types of aqueous blended amine as mixtures of the selected single amines were collected first. The VLE of the single amines was fit to the KE models, and the VLE of the aqueous blended amines was predicted using the KE models of single amines without introducing any interaction terms between the amines. As a result, it was found that the VLE of the aqueous blended amines could be satisfactorily predicted using only the VLE models of single amines. Finally, VLE prediction ability as a function of temperature and the possible uses of the proposed method in the development of new aqueous blended amines were discussed.

A comparison of Raman and IR spectroscopies for the monitoring and evaluation of absorbent composition during CO2 absorption processes

The separation of CO2 from flue gases by reactive chemical absorption using aqueous amines is likely to be a critical technology in the mitigation of global CO2 emissions. The operation of large-scale CO2 capture plants requires close monitoring of the absorbent composition to maintain the plant water balance and efficient CO2 removal, and avoid excessive amine loss. Traditionally monitoring of composition is done offline by analytical methods that are manually intensive, with turn-around times of hours to days. This can lead to costly delays in changes to process operation. In this work the use of Raman and infrared (IR) spectroscopies coupled with Partial Least-Squares Regression are compared for the determination of absorbent composition in a binary amine mixture. These methods can be used online, or offline with an analysis time of minutes. Both laboratory and pilot plant samples were assessed. Both Raman and IR spectroscopies were found capable of determining the individual amine and CO2 concentration of laboratory samples. However, only IR proved successful with pilot plant samples as Raman spectroscopy induced fluorescence that made the Raman technique (as used here) impractical.

Aqueous amine solution characterization for post-combustion CO2 capture process

This article presents a thermodynamic and kinetic characterization of CO2 absorption by 30 aqueous amine solutions. A solvent screening setup (S.S.S.) was used to find the CO2 loading (α) for 30 different aqueous amine solutions (30wt%) at a pressure of 1bar with feed gas containing 15vol% CO2 and 85vol% N2 at 313.15K to provide reliable absorber parameters. The structures of various amines (linear, non-linear, polyamines, sterically hindered, etc.) were tested and the S.S.S. results showed that hexamethylenediamine (HMD) has higher CO2 loading at 1.35moles of CO2/mole of amine, and triethanolamine (TEA) has the lowest at 0.39mole of CO2/mole of amine. The heat of absorption indicates that MDEA has the lowest and HMD has the highest at −52.51kJ/mole of CO2 and −98.39kJ/mole of CO2, respectively. The combined data for the CO2 loading and the absorption heat generated 6 amines that have good properties for the post-combustion CO2 capture process in comparison with that of MEA. These amines are made up of one secondary amine (2-ethylaminoethanol, 2EAE) and 5 tertiary amines (N-methyldiethanolamine, MDEA, 1-dimethylamino-2-propanol, 1DMA2P, 2-dimethylaminoethanol, 2DMAE, 3-dimethylamino-1-propanol, 3DMA1P and N,N,N′,N′-tetramethyl-1,3-propanediamine, TMPDA). In comparison with the amine reference MEA (ΔH=−85.13kJ/mole of CO2 and α=0.58mole CO2/mole of amine), the 6 amines have heats of absorption that are between −68.95kJ/mole of CO2 and −52.51kJ/mole of CO2, and their CO2 loading is between 0.52 and 1.16mole of CO2/mole amine. The third important parameter, namely the reaction kinetics between aqueous amine solutions and CO2, was studied by using stopped-flow equipment to measure the pseudo-first order reaction (k0, s−1) at different amine concentrations. A determination of the second order rate constants (k2, m3mole−1s−1) at 298.15, 303.15, 308.15 and 313.15K was performed by using the proposed reaction mechanisms. The base catalysis mechanism was used to correlate the experimental data of the tertiary amines and the zwitterion mechanism was used to correlate the experimental data of the primary/secondary amines. The kinetics results show that 2EAE, a secondary amine, was very high in comparison with MDEA, 1DMA2P, 2DMAE, 3DMA1P and TMPDA, all of which are tertiary amines that are very close to MEA, which is the reference case. This result shows that 2EAE is a good candidate for CO2 capture as an alternative to MEA because it has good CO2 absorption, a low heat of absorption and high kinetic reaction with CO2. Moreover, the outcomes for the thermodynamic and kinetic properties indicate that the following 5 amine blends have emerged from this study: 2EAE/MDEA, 2EAE/1DMA2P, 2EAE/2DMAE, 2EAE/3DMA1P and 2EAE/TMPDA.

Anticorrosion Protection by Amine–Ionic Liquid Mixtures: Experiments and Simulations

The mixtures of aqueous amines and ionic liquids (ILs) are considered as potential solvents for CO2 capture. We report corrosion and CO2 absorption behavior of the mixed IL–amine solutions. The absorption tests were performed at 318.15 K under 0.1–2.7 MPa. The corrosion tests were carried out at 318.15 K under 2.7 MPa. Addition of [bmim][BF4] in aqueous alkanolamine solutions reduces corrosion rate for MEA by up to 72%. The CO2 absorption capacity in the mixtures falls between those of aqueous MDEA and pure IL. These results allow to choose the working pressure range as a function of other parameters, such as gas pressure and mixture viscosity. According to the simulations, [bmim][BF4] participates in the gas capture through H-bonding, although the number of amine molecules is enough to capture all supplied CO2 molecules. The equilibrium of the chemisorption reaction is, therefore, modified upon the stepwise IL addition. An ideal IL content for preventing corrosion is 10% w/w.

Study of Formation of Bicarbonate Ions in CO2-Loaded Aqueous Single 1DMA2P and MDEA Tertiary Amines and Blended MEA–1DMA2P and MEA–MDEA Amines for Low Heat of Regeneration

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 l...

Viscosity and density measurements of aqueous amines at high pressures: MDEA-water and MEA-water mixtures for CO2 capture

Viscosity and density are thermophysical properties crucial to characterizing any kind of fluid such as aqueous amines. These blends are becoming more and more relevant for their CO2 capture potential, such that having accurate viscosity and density measurements would prove useful. Densities and viscosities of these mixtures at atmospheric pressure may be found in the literature although it is more difficult to find values at high pressures, these potentially proving interesting when seeking to provide a full description of these fluids.Viscosity and density measurements at high pressures (up to 120MPa) and at temperatures between 293.15K and 353.15K of MDEA+water and MEA+water mixtures (both from 10% to 40% amine mass fraction) are presented in this work. Density measurements were performed with an Anton Paar DMA HPM densimeter with an expanded uncertainty (k=2) less than ±0.7kg·m−3. A falling body technique was used to measure viscosities at high pressures due to its sturdiness in terms of corrosion. Details of this latter equipment are presented, including calibration using n-dodecane and uncertainty calculations, which give a relative expanded uncertainty (k=2) of less than ±2.4% for the highest viscosity and ±2.9% for the lowest.

Computer-aided molecular design of imidazole-based absorbents for CO2 capture

Reactive absorption of CO2 by aqueous amine solutions is widely used in the oil, gas and petrochemical industries. However, the energy cost associated with CO2 capture is still a major hurdle to global implementation. Finding new absorbent systems with improved properties is therefore critical to the safety and efficiency of the carbon capture process. Owing to a wide range of tunable properties, imidazoles or imidazoles/amine mixtures have recently been identified as promising to address some of these challenges. In this work, evolutionary de novo design is used to propose new imidazole-based compounds suitable for carbon capture. At the core of this scheme is a genetic algorithm that optimizes the acid dissociation constant (pKa), an important factor governing the performance of solvents. Calculation of the pKa using quantum chemical methods may produce accurate results but is often too computationally demanding to be suitable for a de novo design setup, where thousands of structures are evaluated over many iterations. To improve the efficacy of the evolutionary process while maintaining high accuracy, we apply a quantitative structure–property relationship (QSPR) model that relates molecular structure descriptors calculated at the semi-empirical level to experimentally determined pKa values. Several promising compounds with high pKa (>10) were identified by the evolutionary design approach and further validated using density functional theory calculations. QSPR models for equally relevant physical properties (such as density, viscosity, vapour pressure) and biodegradability were used as additional filters to ensure that the high pKa structures also have favourable values for these properties.

Reaction dynamics of $$\hbox {CO}_2$$ CO 2 in aqueous amines from ab initio molecular dynamics: 2-amino-2-methyl-1,3-propanediol (AMPD) compared to monoethanolamine (MEA)

We present Car–Parrinello molecular dynamics simulations—combined with metadynamics—of the reactions accompanying the capture of $$\hbox {CO}_2$$ in an aqueous amine solution. The selected amine is 2-amino-2-methyl-1,3-propanediol, which has been investigated experimentally in the search for optimum absorbents. In analogy with the empirical search, we use as reference aqueous monoethanolamine (MEA) at 30 wt%, namely the chemical absorbent most frequently used for the removal of $$\hbox {CO}_2$$ from combustion gases. In particular, we refer to our own results which have led to a detailed characterization of several reaction paths for the absorption of $$\hbox {CO}_2$$ and the amine regeneration (Ma et al. in J Chem Theory Comput 11:3189, 2015). Our simulations refer to the zwitterion mechanism leading to the formation of a carbamate or carbamic acid and to the release of the molecule in solution. The scenario established for the reactions in MEA is confirmed, and in particular the role of the zwitterion mechanism also for $$\hbox {CO}_2$$ release. We find that the difference in the structure of the two molecules does not influence the dynamics of either the formation or the dissociation of the zwitterion. However, it affects its interaction with water in a significant way, thus reducing the probability of carbamate formation and its stability in solution.

Contrasting mechanisms for CO2 absorption and regeneration processes in aqueous amine solutions: Insights from density-functional tight-binding molecular dynamics simulations

CO2 chemical absorption and regeneration processes in aqueous amine solutions were investigated using density-functional tight-binding molecular dynamics simulations. Extensive analyses of the structural, electronic, and dynamical properties of 100 independent trajectories supported the contrasting mechanisms in the absorption and regeneration processes. In the CO2 absorption process, bicarbonate formed where the hydroxyl anion migrated through the hydrogen-bond network of water molecules, namely, by a Grotthuss-type mechanism. On the other hand, direct proton transfer from the protonated amine to the hydroxyl group of bicarbonate, which is called the ion-pair mechanism, was the key step to the release of CO2.

Solubility of heptane in aqueous solutions of methyldiethanolamine (MDEA)

New experimental solubility data of heptane in aqueous amine solutions is presented. Simple equilibrium cells were used to measure the solubility of heptane in aqueous amine systems in the range: 298–328 K. Aqueous liquid samples were analyzed using a gas chromatograph. It was observed that heptane solubility in Methyldiethanolamine (MDEA) solutions increased with increasing temperature. Also, increasing amine concentration in the tested solution, the solubility of heptane increased. Simple models were developed in order to represent the activity coefficient of heptane in the aqueous MDEA solution in the range of 40–50 wt % MDEA. The Henry's law-based model allowed for a more direct comparison between the solubilities in pure water and in the aqueous solution of MDEA. The obtained heptane solubility data were compered to predicted data using group contribution equation of state model (GCA-EoS).

The salt-based catalytic enhancement of CO2 absorption by a tertiary amine medium

An improved CO2 sequestration method is proposed that uses new catalysts, specifically a series of tertiary amine nitrate salts, in an aqueous tertiary amine medium.

Investigation on CO2 Solubility in Aqueous Amine Solution of MDEA/PZ with SiO2 Nanoparticles Additive as Novel Solvent

Conventional industrial processes for CO2 capturing include gas absorption by solvent. The most common solvent consisting of an aqueous solution of methyl di-ethanol amine (MDEA) activated with Piperazine (PZ). This research however examines CO2 solubility in absorption and desorption process using the above mentioned solvent that reinforced by nanoparticles additives at concentrations of 12, 25, 50, and 100 ppm, respectively. In this novel solvent Carbon dioxide solubility was studied at 40 and 120°C. These tests conducted at 0.1 to 26 atm partial pressure of CO2 and Vapor–Liquid Equilibrium (VLE) data were obtained from laboratory setup. The results indicate an increase in CO2 loading and changing on solubility equilibrium curve to more concentration of CO2 in liquid phase for solvent containing nanoparticles. The solvent CO2 loading was enhanced up to 37.5% by introducing 25 ppm of our novel nanoparticles.

Thermodynamic and Experimental Study of the Energetic Cost Involved in the Capture of Carbon Dioxide by Aqueous Mixtures of Commonly Used Primary and Tertiary Amines.

The capture of carbon dioxide with chemical solvents is one solution to mitigate greenhouse gas emissions from anthropogenic sources and thus tackle climate change. Recent research has been focused on optimizing new kinds of advanced absorbents including aqueous amine blends, but critical downsides such as the large energetic cost involved with the industrial process remain. To address this issue, a better understanding of the energetic interactions existing in solution is necessary. In this paper, we report direct experimental measurements of the energy cost involved in the solvation of CO2 in two aqueous amine blends at different temperatures. The chemical solvents were designed as aqueous mixtures of commonly used primary and tertiary amines to study the influence of the different chemical properties inferred by the amine class. We have also applied a thermodynamic model to represent the energetic effects that take place in solution during CO2 dissolution in these mixtures, where all parameters were taken from previous studies focused on single amine absorbents. The noteworthy agreement observed with the reported experimental heats of absorption and with literature vapor liquid equilibrium properties confirmed the relevance of the underlying molecular mechanisms considered in our model, and suggest that this model would prove useful to investigate CO2 dissolution in other amine blends.

Experimental investigation of sorption characteristics of capturing carbon dioxide into piperazine activated aqueous 2-amino-2-methyl-1-propanol solution in a packed column

Gradual increase in concentration of CO2 in the atmosphere and its potential threat to the global climate has become the matter of widespread anxiety and significant research over the last few decades in order to find out the promising techniques for CO2 capture. The present study investigates a post-combustion technique of capturing CO2 from flue gas using aqueous amine blend of 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). The absorption experiments have been performed in a packed column over the temperature range of 298–308K and the CO2 partial pressure range of 10–15kPa. CO2 absorption characteristics are examined with process variables viz. different solvent blend (wt% AMP+wt% PZ), gas flow rate, absorbent flow rate and different CO2 partial pressures. Piperazine is used mainly as reaction rate activator with a concentration range of 2–10wt% maintaining the total amine concentration of 30wt%. The regeneration performances of amine blend are studied over the temperature range of 368–383K. The specific rate of absorption of different (AMP+PZ) blends, CO2 loading capacity of individual blends after absorption performance and percentage of CO2 absorbed have been examined. The specific rate of absorption for the four (AMP+PZ) blends have been found to be (14.6–26.8)×10−6kmolm−2s−1. The maximum percentage of CO2 absorbed has been estimated to be 99.63% when the PZ concentration is maximum i.e. 10wt% in the blend. The highest CO2 loading capacity has been observed to be 0.978 for the case of maximum PZ contribution in the blend solvent such as 10wt%. Regeneration efficiencies of individual blend and the residual CO2 after stripping are studied. The regeneration efficiency of every individual amine blend is within the range of 90.93–98.93% and the maximum efficiency of 98.93% is observed for the case of highest AMP contribution in the (AMP+PZ) blend i.e. 28wt% with addition of this blend also has the better regeneration performance which is represented as residual CO2 (0.026moles per mole of amine blend) left in the regenerated amine blend. The cyclic CO2 loading capacity ranges from 0.858 to 0.978moles of CO2 for entire four aqueous amine blends as compared to 30wt% MEA which ranges from 0.405 to 0.524moles of CO2 per mole of amine. The reboiler heat duty requirement to regenerate the CO2 rich aqueous amine solvent has been estimated for entire four different (AMP+PZ) blends and found to be within the range of 3.4–4.8MJ/kg CO2 as compared to 30wt% MEA which has the range of 3.6–4.5MJ/kg CO2. The experimental rate data are compared with the model predicted rate data and the parity plot shows an excellent agreement with the experimental results. Hence, sorption of CO2 into piperazine activated aqueous 2-amino-2-methyl-1-propanol solution in a packed bed column could be an efficient technique of entrapping CO2 from flue gas.

CO2 absorption by binary mixture of ionic liquids-monoethanolamine at lower pressure

We studied the absorption capability for CO2 of four binary mixtures of [BMIM][BF4]-MEA, [EMIM][BF4]-MEA, [BMIM][PF6]-MEA and [EMIM][PF6]-MEA at 298–318K and 0.1–0.6MPa, where BMIM is 1-butyl-3-methylimidazolium, EMIM is 1-ethyl-3-methylimidazolium, BF4 is tetrafluoroborate, PF6 is hexafluorophosphate, and MEA is monoethanolamine. Some factors such as ILs nature, MEA concentration, temperature, pressure, absorption rate and regeneration and recycling of absorbent were investigated. Compared with traditional aqueous amine, such water-free ILs-MEA does not suffer from water volatile loss and resulting corrosion that are typical problems in traditional aqueous amine process. With the addition of MEA, CO2 absorption capacity in such ILs-MEA is much larger than that in the pure ILs and is comparable to that in some aqueous amines and tertiary mixture of ILs-amine-H2O, typically, the CO2 absorption capacity of [BMIM][BF4]-MEA (50v% MEA) is 0.519mol CO2/mol MEA at 298K and 100KPa. ILs nature has important effect, and the absorption capacity of BF4 ILs-MEA for CO2 is about 30% higher than that of PF6 ILs-MEA where a precipitate is observed for the former while the absorption product of carbamate is soluble for the latter. Reasonable lower temperature and higher MEA concentration is favorable for CO2 absorption. The absorbents can be regenerated and recycled with no remarkable change in CO2 absorption.

Foaming Prevention in Absorption Columns through Removal of Contaminants from Amine-Based Solutions Using a Solvent Resistant Nanofiltration (SRNF) Membrane

An environmentally friendly removal method based on a membrane process for the purification of aqueous amine solution for use in carbon dioxide absorption was analyzed. Two kinds of commercial solvent resistant nanofiltration (SRNF) membranes (Desal-DL and SR100, polymeric) were chosen, and their capabilities in removing three common contaminants from diethanolamine (DEA) solution were examined. These contaminants that caused foaming of DEA solution include sodium chloride, sodium sulfite, and acetic acid. From the two tested solvent resistant nanofiltration (SRNF) membranes, it had been found that Desal-DL membrane provided promising results and performance that can be an alternative to conventional separation, including distillation, for purification of amine solution. Experiments were also conducted to test the foaming tendency and stability of the untreated and treated amine solution. The untreated DEA with sodium sulfite had the highest foaming tendency. However, after NF treatment, there was substantial decrease of the foaming tendency. The results obtained confirmed the potential of using SRNF-membranes to reduce foaming tendency and stability in DEA solution.