And 2-amino-2-methyl-1-propanol Research Articles

PDU-Scale Experimental Results of CO2 Removal With Amp/Pz Solvent

Abstract :This paper provides a discussion concerning results of CO2 removal from a gas mixture by the application of aqueous solutions of ethanoloamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) promoted with piperazine (PZ). The studies were conducted using a process development unit. Research of such a scale provides far more reliable representation of the actual industrial process than modelling and laboratory tests. The studies comprised comparative analyses entailing identical energy supplied to a reboiler as well as tests conducted at similar process efficiencies for both solvents. The results thus obtained imply that using AMP/PZ enables reduction of the solvent heat duty. Moreover, while using AMP/PZ temperature decrease was also observed in the columns.

CO2 absorption into aqueous amine blended solutions containing monoethanolamine (MEA), N,N-dimethylethanolamine (DMEA), N,N-diethylethanolamine (DEEA) and 2-amino-2-methyl-1-propanol (AMP) for post-combustion capture processes

Presently monoethanolamine (MEA) remains the industrial standard solvent for CO2 capture processes. Operating issues relating to corrosion and degradation of MEA at high temperatures and concentrations, and in the presence of oxygen, in a traditional PCC process, have introduced the requisite for higher quality and costly stainless steels in the construction of capture equipment and the use of oxygen scavengers and corrosion inhibitors. While capture processes employing MEA have improved significantly in recent times there is a continued attraction towards alternative solvents systems which offer even more improvements. This movement includes aqueous amine blends which are gaining momentum as new generation solvents for CO2 capture processes. Given the exhaustive array of amines available to date endless opportunities exist to tune and tailor a solvent to deliver specific performance and physical properties in line with a desired capture process. The current work is focussed on the rationalisation of CO2 absorption behaviour in a series of aqueous amine blends incorporating monoethanolamine, N,N-dimethylethanolamine (DMEA), N,N-diethylethanolamine (DEEA) and 2-amino-2-methyl-1-propanol (AMP) as solvent components. Mass transfer/kinetic measurements have been performed using a wetted wall column (WWC) contactor at 40°C for a series of blends in which the blend properties including amine concentration, blend ratio, and CO2 loadings from 0.0–0.4 (moles CO2/total moles amine) were systematically varied and assessed. Equilibrium CO2 solubility in each of the blends has been estimated using a software tool developed in Matlab for the prediction of vapour liquid equilibrium using a combination of the known chemical equilibrium reactions and constants for the individual amine components which have been combined into a blend.From the CO2 mass transfer data the largest absorption rates were observed in blends containing 3M MEA/3M Am2 while the selection of the Am2 component had only a marginal impact on mass transfer rates. Overall, CO2 mass transfer in the fastest blends containing 3M MEA/3M Am2 was found to be only slightly lower than a 5M MEA solution at similar temperatures and CO2 loadings. In terms of equilibrium behaviour a slight decrease in the absorption capacity (moles CO2/mole amine) with increasing Am2 concentration in the blends with MEA was observed while cyclic capacity followed the opposite trend. Significant increases in cyclic capacity (26–111%) were observed in all blends when compared to MEA solutions at similar temperatures and total amine concentrations. In view of the reasonable compromise between CO2 absorption rate and capacity a blend containing 3M MEA and 3M AMP as blend components would represent a reasonable alternative in replacement of 5M MEA as a standalone solvent.

Development of a thermodynamic identification tool for CO2 capture by chemical absorption

AbstractThe extended UNIQUAC model has been used for the representation of the thermodynamic behaviour of CO2 absorption in aqueous amine solutions. Based on available experimental data, an identification methodology has been developed to fit the extended‐UNIQUAC model parameters. In the scope of providing a robust methodology, a combination of two successive optimization methods has been chosen: a genetic algorithm and a quasi‐Newton method. The first quasi‐global method allows to screen the entire search space without a precise initialization, and provides an approximate solution which is then refined by the second local method.The developed multi‐step regression strategy has been successfully applied to the H2O‐ monoethanolamine(MEA)‐CO2 system. The model gives a good agreement with the experimental vapour‐liquid equilibria for CO2 partial pressures and total pressures for all MEA concentrations and for a wide range of temperature with an average absolute relative deviation of around 20 %. Furthermore, the model predicts accurately literature data on excess enthalpy and bubble point of the system.This identification procedure has been successfully extended on several ternary H2O‐amine‐CO2 solvent systems such as methyldiethanolamine (MDEA) and 2‐amino‐2‐methyl‐1‐propanol (AMP).The wide variety of operating configurations and solvent types used and presented in this work proves the robustness and the efficiency of the developed identification method.

Rapid CO2 absorption into aqueous benzylamine (BZA) solutions and its formulations with monoethanolamine (MEA), and 2-amino-2-methyl-1-propanol (AMP) as components for post combustion capture processes

Our recent studies have identified benzylamine (BZA) as a promising candidate for CO2 capture processes, however the formation of stable and insoluble BZA-carbamate salts in highly concentrated unblended BZA solutions, and at high CO2 loadings, severely restricts the working concentration of the unblended BZA solvent. Thus, BZA is ideally placed as a candidate for use in a formulated solvent to improve the overall amine concentration and CO2 loading which can be used.The current work focuses on the investigation of CO2 absorption into aqueous solutions of BZA as well as formulations of BZA incorporating MEA and AMP as the second amine components, respectively. Mass transfer/kinetic measurements using a wetted wall column (WWC) at 40°C have been performed for a series of unblended BZA solutions as well as a series of amine concentrations and ratios in the formulations. Overall mass transfer coefficients as a function of total CO2 loading in the solutions (0.0–0.4mol CO2/total mole amine in solution) have been determined for the unblended BZA solutions and formulations. CO2 absorption rates into unblended BZA solutions are significantly faster than in MEA solutions at similar concentrations and zero CO2 loading. The majority of the BZA formulations investigated here can be considered promising candidates for CO2 capture and possess larger or comparable mass transfer rates (up to 30% increase at low loadings) when compared to the corresponding unblended 5.0 and 6.0M MEA solutions under similar conditions. Formulations containing BZA and MEA demonstrated the fastest CO2 absorption rates overall due to the presence of two fast reacting amines, both of which can actively and directly contribute to the absorption of CO2.

Stripping of CO2 from different aqueous solvents using PVDF hollow fiber membrane contacting process

The stripping of carbon dioxide from liquid absorbents is an important task in the operation of gas–liquid membrane contacting processes. In order to gain a better understanding on the role of various absorbents on CO2 stripping, potassium glycinate (PG), monoethanolamine (MEA), diethanolamine (DEA), and 2-amino-2-methyl-1-propanol (AMP) were applied as absorbent/stripping solutions. The membrane used for the experiments was hollow fiber polyvinylidenefluoride (PVDF) membrane fabricated via thermally induced phase separation method. The performances of various amine solutions on the CO2 stripping capability were investigated. CO2 stripping experiments revealed that regardless of type of solvent the CO2 stripping flux and efficiency rapidly increases with liquid temperature, pressure and initial CO2 concentration. In addition, the gas–liquid contact time was a key factor to enhance the stripping flux at low temperature while liquid phase boundary layer thickness and associated mass transfer resistance is important at elevated temperatures. Moreover the comparison stripping experiments between shell and tube side liquid flow revealed that for low packing density tube side flow gives better stripping performance.

Absorption characteristics of carbon dioxide into an O/W emulsion absorbent containing N-methylcyclohexylamine/2,6-dimethylpiperidine

A novel absorbent was developed using an oil/water (O/W) emulsion absorbent with lipophilic amine. N-methylcyclohexylamine (MCHA) and 2,6-dimethylpiperidine (DMPD) were selected as the absorbents and Tween 80 was used as the emulsifier. The absorption rate and equilibrium were measured using a wetted wall column and vapor–liquid equilibrium apparatus, respectively, to investigate the carbon dioxide (CO2) absorption performance of each absorbent. The monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) solutions were used for comparison. The absorption rate of CO2 into the emulsion absorbent was higher than that into the aqueous MEA solution. The CO2 loading ratio of the MCHA and DMPD were 0.87 and 0.72 at 313K, respectively. Additionally, the effective CO2 loading in MCHA and DMPD were 0.31 and 0.4 CO2/mol amine respectively, which is higher than that in the MEA and AMP solutions. These results show that the emulsion absorbent containing the lipophilic amine may show effective CO2 absorption performance.

A 13C NMR study of carbon dioxide absorption and desorption in pure and blended 2-(2-aminoethylamine)ethanol (AEEA) and 2-amino-2-methyl-1-propanol (AMP) solutions

Quantitative 13C nuclear magnetic resonance (NMR) spectroscopy was used to study carbon dioxide (CO2) absorption and desorption, at 313 and 393K, respectively, from 30wt% aqueous 2-(2-aminoethylamine)ethanol (AEEA), 30wt% 2-amino-2-methyl-1-propanol (AMP) and 20wt% AEEA+10wt% AMP solutions. The 13C NMR results indicate that the main AEEA species are free amine, protonated amine, primary carbamate and secondary carbamate, and the main AMP species are free amine and protonated amine. There is no evident indication that dicarbamate species of AEEA and carbamate of AMP are formed. When AEEA absorbs CO2, the formation of AEEA carbamate on primary amine is comparatively faster than that on secondary amine. During the CO2 desorption process, the AEEA carbamate on secondary amine is produced by an endothermic reaction, which reduces the overall efficiency of desorption. Six cycles of absorption–desorption tests are performed to measure the feasibility of regenerated amine solutions for reuse and the absorption amount of them remains essentially constant during the second to the sixth absorption–desorption experiments. Compared with pure AEEA solution, the recyclability of blended amines, AEEA+AMP, improves while the mol CO2/mol amine (CO2 loading) of the blended amines decreases.

Amine neutralized amino acid as CO2 absorbents: A quantitative 13C-NMR study

Amino acids, fully or partially neutralized with amines, are a new class of CO2 absorbents that have the possibility to combine the ionic character of amino acids with the better CO2 absorbing properties of the amines to form a more energy efficient solvent with improved environmental footprint. This work studies the effect of differences in pKa and structural properties between the amine and amino acid on the resulting active amino group in the blend. Equimolar mixtures of the amino acids, glycine, l-alanine, l-proline, taurine and l-serine, with alkanolamines, monoethanoamine (MEA) and 2-amino-2-methyl-1-propanol (AMP), were quantitatively studied by 13C nuclear magnetic resonance spectroscopy (NMR) at 25°C. The amino acids tested in the present work were chosen based on their solubility in water and on their relative basicity (pKa) to that of the amines.It is observed that in amino acid-MEA blended systems, carbamate formation from both MEA and the amino acids occur and that generally, the amine group with highest pKa value is most favored when neutralizing the amino acid carboxylic group. If this is the amino acid an amino acid zwitterion may be formed, or, if amine has the highest pKa value, an amine–amino acid complex may be formed, rendering the amino acid amine group active toward CO2 absorption. However, the experimental data show that not only the pKa value of the amino acid is important but that also steric effects play a role in determining the preferred carbamate forming position. In the amino acid-AMP systems almost all carbamate is formed on the amino acid amine group due to the steric hindrance in AMP.Generally, addition of amine to an aqueous amino acid solution increases the amino acid solubility. In this work solid precipitation was only observed at higher CO2 loadings for l-alanine blended with both MEA and AMP. NMR spectroscopy analysis showed that the precipitate consists mainly of amino acid and bicarbonate/carbonate with very small amounts of amine.

Sensitivity analysis of the rate-based CO2 absorber model using amine solutions (MEA, MDEA and AMP) in packed columns

The modeling and simulation of CO2 capture processes with amine solutions are considered as important developments toward the detailed study and analysis of these processes. In the literature, the application of rate-based models for the modeling of CO2 capture processes by amine solutions has been proved superior to equilibrium-stage models. The results of rate-based models, however, depend strongly on the selection of model parameters such as physical properties, transport properties, kinetic models, and mass transfer correlations. In this study, sensitivity analysis was performed to investigate the effect of mass transfer correlations in combination with kinetic models on the performance of an absorber column. The reason for this investigation is to establish appropriate correlations that can be used for design of the CO2 capture process. Sensitivity analysis was performed using a rate-based model for capture of CO2 in monoethanolamine (MEA), methyldiethanolamine (MDEA), and 2-amino-2-methyl-1-propanol (AMP) solutions in packed columns containing structured and random packing. The model was successfully validated by comparison of obtained results with published experimental data. The sensitivity analysis revealed that the mass transfer correlations developed by Hanley and Chen (2012) to simulate a structured packing absorption column, obtained the best results in comparison with the other tested and analyzed correlations in this study. For a randomly packed column, the correlations suggested by Onda et al. (1968) exhibited the best results. The kinetic models tested and examined in this study had a determinant role in the results of the sensitivity analysis in a manner that reflected the assumptions used in development of the model such as the temperature and amine concentration ranges. Therefore, careful selection of the mass transfer correlations and kinetic models to be used in the rate-based absorber model is required for modeling of the CO2 capture process. Otherwise, serious errors in design of the CO2 capture process may result.

Theoretical Investigation on the Different Reaction Mechanisms of Aqueous 2-Amino-2-methyl-1-propanol and Monoethanolamine with CO2

A fundamental understanding on the inherent mechanisms leading to the different reactivity of the representative systems for unhindered and hindered families of amines, monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) in CO2 capture, is important for the rational design of novel amines. In this work, a comparative study on the reaction mechanisms between AMP + CO2 and MEA + CO2 was investigated at the B3LYP/6-311++G(d,p) level with the appropriate treatment of solvent effects. Two channels that lead to carbamate and bicarbonate were considered. The total reaction rate coefficients were computed using a microkinetic model. The results indicate that the formation of bicarbonate for AMP + CO2 is more favorable in kinetics than the formation of carbamate. However, the case is reversed for MEA + CO2. This explains well the experimental observation of different product distributions between the AMP + CO2 and MEA + CO2 reactions. The complementary results from QM/MM molecular dynamics simulations wit...

Solubility of carbon dioxide gas in some 2.5 M tertiary amine aqueous solutions

Solubility of carbon dioxide (CO2) acid gas in aqueous solutions in 2.5mol/l tertiary amines, such as 2-(2-(dimethylamino) ethoxy) ethanol [DMAEOE], 3-dimethyl amino-1-propanol [DiMAP], 1,2-bis (dimethyl amino) ethane [TEMED], pyridine and methyl-4-morpholine has been measured at [313 and 353] K, and over the pressure range (0–200) kPa, using a specifically built apparatus based on the static method. The vapor pressures and the densities of these aqueous solutions, also, have been measured by a static method and picnometry, respectively. For validation of the experimental procedure, solubility of acid gas CO2 in 2.5mol/l aqueous solutions of mono-ethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) has been measured at 313.15K. The experimental solubility results are presented in the form of the partial pressure of CO2 versus the mole ratio α (mol CO2/mol amine), at each temperature. The solubility of gas CO2, in all the investigated aqueous amines, decreases with an increase of the temperature and increases with increasing partial pressure of CO2 gas at a given temperature. The values of the solubility of CO2 gas are in the following sequence: Pyridine<Methyl morpholine<DMAEOE<TEMED<DiMAP.

Comparisons of amine solvents for post-combustion CO2 capture: A multi-objective analysis approach

Amine solvents are of great interest for post-combustion CO2 capture applications. Although the development of new solvents is predominantly conducted at the laboratory scale, the ability to assess the performance of newly developed solvents at the process scale is crucial to identifying the best solvents for CO2 capture. In this work we present a methodology to evaluate and objectively compare the process performance of different solvents. We use Aspen Plus, with the electrolyte-NRTL thermodynamic model for the solvent CO2 interactions, coupled with a multi-objective genetic algorithm optimization to determine the best process design and operating conditions for each solvent. This ensures that the processes utilized for the comparison are those which are best suited for the specific solvent. We evaluate and compare the process performance of monoethanolamine (MEA), diethanolamine (DEA), and 2-amino-2-methyl-1-propanol (AMP) in a 90% CO2 capture process from a 550MW coal fired power plant. From our analysis the best process specifications are amine specific and with those specific, optimized specifications DEA has the potential to be a better performing solvent than MEA, with a lower energy penalty and lower capital cost investment.

Carbonic Anhydrase Promotes the Absorption Rate of CO2 in Post-Combustion Processes

The rate of carbon dioxide (CO2) absorption by monoethanol amine (MEA), diethanol amine (DEA), N-methyl-2,2'-iminodiethanol (MDEA), and 2-amino-2-methyl 1-propanol (AMP) solutions was found to be enhanced by the addition of bovine carbonic anhydrase (CA), has been investigated using a vapor-liquid equilibrium (VLE) device. The enthalpy (-ΔHabs) of CO2 absorption and the absorption capacities of aqueous amines were measured in the presence and/or absence of CA enzyme via differential reaction calorimeter (DRC). The reaction temperature (ΔT) under adiabatic conditions was determined based on the DRC analysis. Bicarbonate and carbamate species formation mechanisms were elucidated by (1)H and (13)C NMR spectral analysis. The overall CO2 absorption rate (flux) and rate constant (kapp) followed the order MEA > DEA > AMP > MDEA in the absence or presence of CA. Hydration of CO2 by MDEA in the presence of CA directly produced bicarbonate, whereas AMP produced unstable carbamate intermediate, then underwent hydrolytic reaction and converted to bicarbonate. The MDEA > AMP > DEA > MEA reverse ordering of the enhanced CO2 flux and kapp in the presence of CA was due to bicarbonate formation by the tertiary and sterically hindered amines. Thus, CA increased the rate of CO2 absorption by MDEA by a factor of 3 relative to the rate of absorption by MDEA alone. The thermal effects suggested that CA yielded a higher activity at 40 °C.

Comparison of Carbon Dioxide Absorption in Aqueous MEA, DEA, TEA, and AMP Solutions

The separation and capture process of carbon dioxide from power plants is garnering interest as a method to reduce greenhouse gas emissions. In this study, aqueous alkanolamine solutions were studied as absorbents for CO2 capture. The solubility of CO2 in aqueous alkanolamine solutions was investigated with a continuous stirred reactor at 313, 333 and 353 K. Also, the heat of absorption (−ΔHabs) between the absorbent and CO2 molecules was measured with a differential reaction calorimeter (DRC) at 298 K. The solubility and heat of absorption were determined at slightly higher than atmospheric pressure. The enthalpies of CO2 absorption in monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and 2-amino-2-methyl-1-propanol (AMP) were 88.91, 70.44, 44.72, and 63.95, respectively. This investigation showed that the heat of absorption is directly related to the quantity of heat for absorbent regeneration, and is dependent on amine type and CO2 loading.

Amine-based absorbents selection for CO2 membrane vacuum regeneration technology by combined absorption–desorption analysis

A novel membrane vacuum regeneration (MVR) technology was developed to achieve lower regeneration energy demand for CO2 absorption process. Sixteen different amine-based absorbents including primary, secondary, tertiary amines, polyamines, diamines, and sterically hindered amines were analyzed by combined absorption–desorption screening experiments for selecting the most effective absorbents for CO2 membrane vacuum regeneration (MVR) technology. The CO2 absorption experiments were conducted in a hollow fiber membrane contactor (HFMC) at 25°C and 12.5kPa CO2 partial pressure. The CO2 rich solvent was regenerated at 75°C and 20kPa regeneration pressure by using the MVR technology. The chain length, number of functional groups, side chain, and number of hydroxyl groups of amines were investigated to get a better understanding on the effects of the structure in the MVR process. The results show that the tertiary amines have greater regeneration performances than the primary amines, but the CO2 absorption rates of the tertiary amines are worse than the primary amines. For the polyamines, the absorption performance of polyamines can be improved by increasing the number of amine groups while the MVR performance of the polyamines can be reduced. Steric hindered amines exhibited greater MVR performances. In addition, amines with steric hindrance effect caused by the substitution of hydroxyl group or methyl group to amine group in structure has also shown good performance in the MVR process for CO2 desorption. The overall performance of amine-based absorbents was also investigated by an absorption–desorption characters analysis. It shows triethylenetetramine (TETA) and N-methyldiethanolamine (MDEA) have great average CO2 absorption rates and relatively high cyclic capacities per mole absorbent, and ethylenediamine (EDA) is considered to be the promising absorbent as cyclic capacity in mol CO2/kg absorbent. Diethanolamine (DEA) and 2-Amino-2-methyl-1-propanol (AMP) are found to have the best overall performances in terms of CO2 absorption rate at lean loading and cyclic capacity in mol CO2/mol absorbent. In terms of overall performance, MDEA is mostly recommended for using in MVR process. Sweeping steam can significantly improve MVR performance in most selected absorbents except AMP and 2-amino-2-hydroxymethyl-1,3- propanediol (THAM) absorbents which present the potential to reduce the regeneration energy demand by operating without sweeping steam. The study also finds that MVR shows better regeneration performance as compared to traditional thermal regeneration process at the same regeneration temperature.

CO2 capture by membrane absorption coupling process: Experiments and coupling process evaluation

An experiment system composed of a membrane absorption unit and three regeneration units was set up. The membrane absorption unit could be equipped with single and multiple modules in single cycle absorption mode. The three regeneration units included a hot regeneration, a vacuum desorption and an inert gas sweep. An efficient blended absorbent comprised of potassium glycinate (PG) and 2-amino-2-methyl-1-propanol (AMP) was developed in this work. Coupling process of membrane module-blended absorbent was evaluated by various operation modes such as single and multiple modules, single cycle absorption and regeneration, and continuous circulation of absorption and regeneration. Results show that performance of the blended absorbent (PG+AMP) was better than that of single ones (PG or AMP). The hot regeneration could give a high circular absorption capacity and a high regeneration efficiency while the vacuum desorption and the inert gas sweep gave a poor circular absorption capacity and a poor regeneration efficiency. Membrane flux of the coupling process increased as the gas and liquid flowrates increased. The absorption and regeneration time would greatly reduce by the assembly of multiple modules in consecutive and parallel modes. The circular absorption capacity and the regeneration efficiency by the hot regeneration were far larger than that by the membrane regeneration in the continuous circulation of absorption and regeneration. The membrane absorption process by coupling membrane and absorbent could be scale-up linearly. The parallel assembly mode of multiple modules was more effective than the consecutive assembly mode for CO2 capture.

Characterization of Piperazine/2-Aminomethylpropanol for Carbon Dioxide Capture

In this work, two blends of piperazine (PZ) and 2-amino-2-methyl-1-propanol (AMP) (5 m PZ/2.3 m AMP and 2 m PZ/4 m AMP) were characterized for use in CO2 capture by amine scrubbing. Experimental results on solid solubility, CO2 solubility, mass transfer rate, viscosity, volatility and thermal degradation are given. The 2/4 blend has the advantages of low viscosity (6 cP at 40°C when the loading is 0.45) and no precipitation over a wide loading range. The heat of CO2 absorption is 72kJ/mol (PCO2=1.5kPa, 40°C), about 10kJ/mol higher than 8 m PZ. The 2/4 blend maintains the performance of 8 m PZ in terms of high CO2 absorption rate and CO2 capacity. The 5/2.3 blend has a better solid solubility window (0°C) than 8 m PZ, but does not perform as well with other criteria.

Screening and Characterization of Advanced Amine Based Solvent Systems for CO2 Post-Combustion Capture

Carbon dioxide chemical absorption with amine based solvents is currently the state-of-the-art technology for post-combustion carbon capture. However, many technical challenges still remain that need to be addressed to make it cost-effective. Through bench-scale tests, this research work is focused on developing and characterizing advanced amine-based solvents. Screening of amine solvents is performed to identify suitability on the basis of solvent maximum concentration, rich CO2 loading, lean CO2 loading, cyclic CO2 loading and energy requirement. The five alkanolamine solvents which are experimented upon in this work are: monoethanolamine (MEA), diethanolamine (DEA), N-methyldiethanolamine (MDEA), Piperazine (PZ) and 2-Amino-2-methyl-1-propanol (AMP). These solvents are taken as reference solvents to allow comparison with literature data and to establish confidence in the experimental methods used for solvent evaluation. CO2 outlet concentration curves from the absorption experiments show that piperazine reaches equilibrium faster than any other solvent and the CO2 loading capacity from phosphoric acid titration method is highest in piperazine with a value of 0.92.

Investigations of primary and secondary amine carbamate stability by 1H NMR spectroscopy for post combustion capture of carbon dioxide

Carbamate formation is one of the major chemical reactions that can occur in solution in the capture of CO2 by amine-based solvents, and carbamate formation makes a significant enthalpy contribution to the absorption-desorption of CO2 that occurs in the absorber/stripper columns of the PCC process. Consequently, the formation of carbamates of selected series of primary and secondary amines over the temperature range (288 to 318)K has been investigated by equilibrium 1H NMR studies, and the stability constants (K9) for the equilibrium:RNH2+HCO3-⇄K9RNHCOO-+H2Oare reported. van’t Hoff analyses have resulted in standard molar enthalpies, ΔHmo, and entropies, ΔSmo, of carbamate formation. A ΔHmo-ΔSmo plot generates a linear correlation for carbamate formation (providing a mean standard molar free energy, ΔGmo, for carbamate formation of about −7kJ·mol−1), and this relationship helps provide a guide to the selection of an amine(s) solvent for CO2 capture, in terms of enthalpy considerations. A linear ΔHmo-ΔSmo plot also occurs for carbamate protonation.The formation of the carbamates has been correlated with systematic changes in composition and structure, and steric effects have been identified by comparing molecular geometries obtained using density functional B3LYP/6-311++G(d,p) calculations. Trends in steric effects have been identified in the series of compounds monoethanolamine (MEA), 1-amino-2-propanol, 2-amino-1-propanol (AP) and 2-amino-2-methyl-1-propanol (AMP). In the case of 2-piperidinemethanol, 2-piperidineethanol and 3-piperidinemethanol, strong intramolecular hydrogen bonding is shown to be the likely cause for lack of carbamate formation, and in the ring systems of pyrrolidine, morpholine, piperidine and thiomorpholine trends in carbamate formation (as given by K9) have been correlated with the internal ring angle at the amine nitrogen, as well as the planarity of the environment around the nitrogen atom.

Equilibrium solubility of H2S in aqueous solutions of 1-amino-2-propanol as function of concentration, temperature, and pressure

Experimental values for the gas solubility of hydrogen sulphide (H2S) in aqueous solutions of 1-amino-2-propanol (MIPA) were measured at T=(313.15 and 393.15)K, over the pressure range of (51.4 to 1467.6)kPa. The concentrations of the aqueous MIPA solutions studied were (0.20, 0.30, 0.40, and 0.50) mass fraction. The results of gas solubility are reported as partial pressure of H2S, pH2S, against its liquid mole ratio, aH2S (mol H2S·mol−1 MIPA), and against its mole fraction in the solvent, xH2S. The experimental results show that the solubility of H2S increases as the concentration of MIPA in solution increases, at a given temperature throughout the pressure range considered; also the solubility values increase, under constant temperature, as the pressure increases in the studied concentration range of MIPA.The physicochemical model of Kent and Eisenberg was used to regress simultaneously all the experimental results of the solubility of H2S in the four studied aqueous solutions of MIPA. The model correlates satisfactorily the experimental results. The standard deviation of the regression for pressure is 68.0kPa using 69 experimental solubility points.The new experimental solubility results of H2S were compared with those reported in the literature for aqueous solutions of diethanolamine (DEA), diisopropanolamine (DIPA), N-methyldiethanolamine (MDEA), and 2-amino-2-methyl-1-propanol (AMP), under similar conditions of temperature and amine concentration. From this comparison, it is concluded that aqueous solutions of MIPA are a good solvent alternative to use in industrial gas purification processes at relatively high pressures, since the magnitude of the H2S solubility results in MIPA solutions was found to be higher than that in aqueous solutions of MDEA, DEA, and DIPA.