Non-oxidative thermal degradation of amines: GCMS/FTIR spectra analysis and molecular modeling

Aqueous amino solvents, such as monoethanolamine (ETA/MEA), methyl diethanolamine (MDEA) or amine blends, are the most widely used solvents in commercial CO₂ or acid gas separation applications. These commercial solvents have various disadvantages, such as the possibilities of the solvent to be degraded. This research examines the impact of non-oxidative thermal degradations on the performance of the CO₂ absorption and the degradation mechanism of amine solvents. The impact of degradation was conducted by measuring the CO₂ solubility of solvent that had been heated to 120°C for 2 h. Although the performance of CO₂ absorption was not significantly reduced, the degradation of amines was found. Supported by Fourier Transform Infrared (FTIR) and Gas Chromatography/Mass Spectrometer result, the suspected products of non-oxidative thermal degradation of MDEA were MEA and acetone.     

Antioxidative degradation mechanism of 2-mercaptobenzimidazole modified TEPA-MCM-41 adsorbents for carbon capture from flue gas

Solid amine adsorbents can efficiently adsorb CO₂, but a significant problem is that amine groups are oxidized. In this research, tetraethylenepentamine-impregnated MCM-41 adsorbents (TEPA-MCM-41) were functionally modified with sulphur-containing antioxidant 2-mercaptobenzimidazole (described as antioxidant MB) and tns-(2.4-di-tert-butyl)-phosphite (defined as antioxidant 168), respectively. The antioxidative degradation mechanism of 8% MB–50% TEPA-MCM-41 was analyzed by in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectrum and high-performance liquid chromatography/mass spectrometry (HPLC/mass). The CO₂ adsorption capacity of 50% TEPA-MCM-41 was 4.30 mmol/g under 15% CO₂/85% N₂, but decreased to 1.38 mmol/g after oxidation at 100°C for 42 h under 95% N₂/5% O₂ certain condition. The CO₂ capacity of 8% MB–50% TEPA-MCM-41 reduced from 3.90 to 2.86 mmol/g. After 30 adsorption cycles under 5% O₂/15% CO₂/80% N₂, the capacity of 8% MB–50% TEPA-MCM-41 also only decreased by 16.8%, while 50% TEPA-MCM-41 decreased by 63.2%. The reason for the excellent antioxidant stability of 8% MB–50% TEPA-MCM-41 is that MB scavenged free radicals from amine oxidation and decomposed the hydroperoxides produced by free radical reactions. The hydroperoxides were decomposed into alcohols (non-radical products), which were eventually oxidized to sulphonic compounds. The MB modification inhibited the oxidative degradation of solid amine adsorbents guided for the production of antioxidant-efficient adsorbents.     

Effects of exchanged ammonium cations on structure characteristics and CO2 adsorption capacities of bentonite clay

Different alkali and alkaline earth cation forms of bentonite clay were exchanged with protonated mono-, di- and triethanolamine compounds, to study the effect of the exchanged ammonium cations on the structure characteristics, thermal behavior, surface properties and CO₂ adsorption capacities of bentonite clay. The revolution of the interlayer structure characteristics, thermal properties, the specific surface area and elemental analysis were characterized by XRD, FTIR, TGA, BET and CHNS techniques respectively, while the CO₂ adsorption capacities were gravimetrically measured by using magnetic suspension balance (MSB) equipment. It was found that the intercalation of ammonium cations into the interlayer space of bentonite clay induced a step change in its basal spacing, depending on their molar mass and the interlayer molecular arrangement. The presence of the characteristic IR peaks of amine compounds in the spectra of bentonite clay adsorbents modified by amines was qualitatively supported by the incorporation of ammonium cations in the interlayer space of bentonite, while the presence of C, H and N elements using CHNS technique was quantitatively confirmed by the intercalation process of amine compounds. It was also found that the molar mass of amines has an inverse effect on the amount of the adsorbed water (intensity), its desorption temperature (position) and the specific surface area of the synthesized materials. The CO₂ adsorption capacities on all the studied bentonite clay adsorbents modified by amines were found to increase between 2.68 and 3.15 mmol/g, compared to 0.93 mmol/g for untreated bentonite at the studied temperature and pressure. As expected, bentonite clay modified with di- and triethanolammonium cations showed lower CO₂ adsorption capacities than that treated with monoethanolammonium cations, due to their low specific surface area.     

Improvement in CO2 absorption and reduction of absorbent loss in aqueous NH3/triethanolamine/2-amino-2-methyl-1-propanol blends

Changes in the CO₂ absorption rates and capacities of the absorbent 2-amino-2-methyl-1-propanol (AMP), blended with NH₃ and other additives, were investigated toward performance improvement. The NH₃-blended absorbent removed CO₂ more efficiently than the AMP absorbent alone. However, absorbent loss through NH₃ evaporation was observed under these conditions. A second absorbent, the tertiary amine triethanolamine (TEA), which has a low vapor pressure, was selected and blended with the NH₃/AMP system to reduce NH₃ evaporation. Its effects on NH₃ loss and the absorption rate and capacity of the NH₃/AMP system were investigated, and the optimum blending ratios were determined. In addition, the absorbent blend at the optimum blending ratio was compared to AMP alone and the commercially available absorbent monoethanolamine at the same weight ratio. The thermal stabilities of the absorbents, under conditions used in the CO₂ absorption process, were compared by thermogravimetric analysis.     

Influence of process operating conditions on solvent thermal and oxidative degradation in post-combustion CO2 capture

The CO₂ post-combustion capture with amine solvents is modeled as a complex system interconnecting process energy consumption and solvent degradation and emission. Based on own experimental data, monoethanolamine degradation is included into a CO₂ capture process model. The influence of operating conditions on solvent loss is validated with pilot plant data from literature. Predicted solvent consumption rates are in better agreement with plant data than any previous work, and pathways are discussed to further refine the model. Oxidative degradation in the absorber is the largest cause of solvent loss while thermal degradation does not appear as a major concern. Using a single model, the process exergy requirement decreases by 10.8% and the solvent loss by 11.1% compared to our base case. As a result, this model provides a practical tool to simultaneously minimize the process energy requirement and the solvent consumption in post-combustion CO₂ capture plants with amine solvents.     

Degradation of alkanolamine blends by carbon dioxide

Aqueous solutions of MDEA, MDEA + DEA and MDEA + MEA containing 4.2 kmol/m³ total amine, were contacted with CO₂ at a partial pressure of 2.58 MPa and temperatures ranging from 120 to 180°C, in a stainless steel batch reactor. The reaction products include the known degradation compounds of the amines as well as products formed from secondary interactions in the amine blends. The rate of degradation was first order in the amines and, in magnitude, followed the sequence MDEA < MEA < DEA. Furthermore, the rate constant for MDEA was independent of amine substitution level and blend constituents. From a practical standpoint, MDEA + DEA blends would require frequent DEA make-up to maintain treating efficiency.     

Degradable epoxy resins based on bisphenol A diglycidyl ether and silyl ether amine curing agents

A series of silyl ether amine curing agents were synthesized by selective substitution reactions of chloroalkylsilanes or the transetherification of alkoxysilanes. Crosslinked networks were prepared by mixing a stoichiometric ratio of bisphenol A diglycidyl ether (D.E.R 331) with the amine curing agents. The networks were characterized by ATR‐FTIR spectroscopy, TGA, DSC, and DMA. The onset of thermal degradation, glass transition temperatures, and storage moduli for the networks were 350 °C, 70–108 °C, and 5–25 MPa, respectively. The degradation behavior of the cured samples was monitored for 30 days in PBS, NaOH 5% (w/v), and HCl 5% (v/v) solutions and the degradation products were characterized by spectroscopic methods. The thermal, mechanical, and degradation studies indicated that crosslink density, T_g, storage modulus, and the rate of degradation were affected by the functionality of the amine curing agents and the number of hydrolyzable silyl ether bonds present per mole of curing agent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44620.     

Comprehensive studies on polyethylenimine filled polypropylene and its potential application in carbon dioxide sequestration

Polypropylene (PP) was blended with branched polyethylenimine (PEI) with the aim to prepare blends having CO₂ adsorption property. The CO₂ adsorption properties will be conferred due to the presence of variety of amine functionality in PEI. PEI contains primary, secondary as well as tertiary amine groups. Before testing CO₂ adsorption, PP–PEI blends were characterized using variety of techniques, for example, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, scanning electron microscopy, and polarized light optical microscopy. In this work, we have studied in detail both compatibilized as well as noncompatibilized blends of PP and PEI. The compatibilization was achieved via addition of maleic anhydride grafted PP. Finally, all the compatibilized as well as noncompatibilized blends were studied for CO₂ adsorption. The compatibilized blends showed better thermal, mechanical as well as CO₂ adsorption properties as compared to the noncompatibilized blends. POLYM. ENG. SCI., 59:2092–2102, 2019. © 2019 Society of Plastics Engineers     

Promoting the CO2 adsorption in the amine-containing SBA-15 by hydroxyl group

Novel CO₂ capturer with a high efficiency is fabricated through dispersing the amine mixture of tetraethylenepentamine (TEPA) and diethanolamine (DEA) or glycerol within the as-synthesized mesoporous silica SBA-15, and the resulting sample is characterized by low angle X-ray diffraction and N₂ adsorption to evaluate the distribution of the guest. The influence of hydroxyl group on the CO₂ adsorption capacity of the composite is investigated by using CO₂-TPD and TG–MS techniques. The hydroxyl group of the P123 ((EO)₂₀(PO)₇₀(EO)₂₀, template preserved in as-synthesized SBA-15) and the guest could promote the capture of CO₂ by the amine through changing the interaction mechanism. In addition, the presence of hydroxyl group promotes the formation of the intermediate between CO₂ and the amine with a lower thermal stability hence the CO₂ trapped by the composite is easier to be desorbed and thus the regeneration of adsorbent is facilitated. Therefore, using this mixed amine (TEPA and DEA) modified as-synthesized SBA-15 as CO₂ capturer not only saves the energy for removal of template, but also cut down the cost in the preparation and regeneration of CO₂ capturer, which is critical in CO₂ separation and capture.     

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.     

Chemical kinetics of the reaction of CO2 with amines in pseudo m–nth order conditions in polar and viscous organic solutions

The specific rate of absorption for five gas-liquid systems: CO₂-monoethanolamine (MEA) in ethanol solution, CO₂-diethanolamine (DEA) in ethanol, CO₂-MEA in ethylenglycol, CO₂-DEA in ethylenglycol and CO₂-cyclohexylamine (CHA) in ethylenglycol was measured in a laboratory wetted wall contactor. Reactions were found to be first order with respect to CO₂ and second order with respect to amine for the first four ones and first order with respect to amine for the last one. The values of the specific rate of absorption are such that these reactions may be used to determine interfacial areas and mass transfer coefficients in gas-liquid reactors working with polar and viscous organic liquids.     

Effect of amine degradation products on the membrane gas absorption process

The effect of the presence of monoethanolamine (MEA) degradation products on membrane hollow fibers was investigated using untreated polypropylene (PP) as a model material. Common amine oxidative degradation products were added to MEA to simulate a degraded solution. The effect of these degradation products on the membrane gas absorption process using PP hollow fiber membrane was quantified. When PP membrane which has been exposed to amine degradation products is used in a membrane gas absorption contactor, the mass transfer rate of CO₂ is reduced relative to the use of unexposed PP. It was found that the presence of oxalic acid reduced the mass transfer rate of CO₂ in MEA most significantly followed by formic acid and then acetic acid. These acids are believed to adsorb into the PP, altering the surface properties and reducing the hydrophobicity of the membrane. This in turn increases the degree of wetting of the membrane pores. The membrane was characterized before and after use in a membrane gas absorption contactor containing degraded MEA solvent and studies showed that membrane pore wetting increased by 22-31% after 69 h of use. SEM images and XPS spectra of exposed PP membrane indicate that wetting may be due to both morphological and chemical changes in the membrane due to contact with the solvent. This study highlights the need to consider reductions in the mass transfer rate of membrane gas absorption processes associated with inevitable changes in the solvent composition that comes with prolonged use.     

An experimental/computational study of steric hindrance effects on CO2 absorption in (non)aqueous amine solutions

The reaction kinetics and molecular mechanisms of CO₂ absorption using nonaqueous and aqueous monoethanolamine (MEA)/methyldiethanolamine (MDEA)/2-amino-2-methy-1-propanol (AMP) solutions were analyzed by the stopped-flow technique and ab initio molecular dynamics (AIMD) simulations. Pseudo first-order rate constants (k₀) of reactions between CO₂ and amines were measured. A kinetic model was proposed to correlate the k₀ to the amine concentration, and was proved to perform well for predicting the relationship between k₀ and the amine concentration. The experimental results showed that AMP/MDEA only took part in the deprotonation of MEA-zwitterion in nonaqueous MEA + AMP/MEA + MDEA solutions. In aqueous solutions, AMP can also react with CO₂ through base-catalyzed hydration mechanism beside the zwitterion mechanism. Molecular mechanisms of CO₂ absorption were also explored by AIMD simulations coupled with metadynamics sampling. The predicted free-energy barriers of key elementary reactions verified the kinetic model and demonstrated the different molecular mechanisms for the reaction between CO₂ and AMP.     

Reaction kinetics of 2‐((2‐aminoethyl) amino) ethanol in aqueous and non‐aqueous solutions using the stopped‐flow technique

Observed pseudo‐first‐order rate constants (k_o) for the reaction between CO₂ and 2‐((2‐aminoethyl) amino) ethanol (AEEA) were measured using the stopped‐flow technique in an aqueous system at 298, 303, 308 and 313 K, and in non‐aqueous systems of methanol and ethanol at 293, 298, 303 and 308 K. Alkanolamine concentrations ranged from 9.93 to 80.29 mol m^?3 for the aqueous system, 29.99–88.3 mol m^?3 for methanol and 44.17–99.28 mol m^?3 for ethanol. Experimentally obtained rate constants were correlated with two mechanisms. For both the aqueous‐ and non‐aqueous‐AEEA systems, the zwitterion mechanism with a fast deprotonation step correlated the data well as assessed by the reported statistical analysis. As expected, the reaction rate of CO₂ in the aqueous‐AEEA system was found to be much faster than in methanol or ethanol. Compared to other promising amines and diamines studied using the stopped‐flow apparatus, the pseudo‐first‐order reaction rate constants were found to obey the following order: PZ (cyclic‐diamine) > EDA (diamine) > AEEA (diamine) > 3‐AP (primary amine) > MEA (primary amine) > EEA (primary amine) > MO (cyclic‐amine). The reaction rate constant of CO₂ in aqueous‐AEEA was double that in aqueous‐MEA, and the difference increased with an increase in concentration. All reaction orders were practically unity. With a higher capacity for carbon dioxide and a higher reaction rate, AEEA could have been a good substitute to MEA if not for its high thermal degradation. AEEA kinetic behaviour is still of interest as a degradation product of MEA. © 2012 Canadian Society for Chemical Engineering     

Fine Bubble‐based CO2 Capture Mediated by Triethanolamine Coupled to Whole Cell Biotransformation

Carbon capture technology can be set up in combination with biocatalysis to utilize the bound CO₂ as substrate in the Kolbe‐Schmitt like enzymatic reaction. The exemplary whole cell biotransformation of catechol to 2,3‐dihydroxybenzoic acid in a triethanolamine‐mediated multiphase system shows increased equilibrium conversion. Apart from the beneficial thermodynamics, the inherent fluid properties of triethanolamine is enabling easy application of CO₂ fine bubbles as highly efficient gassing method to minimize the CO₂ demand and CO₂ emissions.     

An experimental and theoretical study on the effects of amine chain length on CO2 absorption performance

To explore the effect of amine chain length on CO₂ absorption performance, the reaction kinetics of CO₂ absorption in aqueous 1-dimethylamino-2-propanol (DMA2P), 1-diethylamino-2-propanol (DEA2P), 2-(methylamino)ethanol (MAE), and 2-(ethylamino)ethanol (EAE) solutions with different concentrations were explored using the stopped-flow apparatus. Additionally, Density Functional Theory (DFT) calculations were conducted to examine the reaction mechanism and the free energy barrier of the elementary reactions underlying CO₂ absorption in these four aqueous amine solutions. Kinetic models for CO₂ absorption in tertiary amines and secondary amines were established, based on the base-catalyzed hydration mechanism and the zwitterion mechanism, respectively, both of which perform well in predicting the relationship between k₀ and the amine concentration. The free energy barrier obtained by DFT is consistent with the activation energy barrier trend obtained by experiment. In addition, the effect of chain length on the free energy barrier was investigated through the chemical bond and weak interaction analysis.     

Methyl-diethanolamine degradation — Mechanism and kinetics

Methyl-diethanolamine (MDEA) degradation reactions between aqueous solutions of MDEA and CO₂ have been carried out in a 600 mL stirred autoclave under the following conditions: initial MDEA solution concentration 20-50 mass%, solution temperature 100-200°C, CO₂ partial pressure 1.38-4.24 MPa. It was found that MDEA degrades quite rapidly (although more slowly than diethanolamine under comparable conditions) at elevated temperatures and CO₂ partial pressures. Degradation products are identified by gas chromatography and mass spectrometry (GC/MS). An MDEA degradation reaction mechanism and kinetic model predicting concentration changes is proposed and verified.     

Chemical modification of carbon powders with aminophenyl and aryl-aliphatic amine groups by reduction of in situ generated diazonium cations: Applicability of the grafted powder towards CO2 capture

Aminophenyl, p-aminobenzyl and p-aminoethylphenyl groups were grafted at the surface of carbon Vulcan XC72R by spontaneous reduction of the in situ generated diazonium cations from the corresponding amine. X-ray photoelectron spectroscopy and elemental analysis confirmed an amine loading of about 1 mmol/g. The grafting of amine functionalities leads to a decrease of specific surface area from 223 to about 110 m²/g with a drastic loss of microporosity. Acid-base properties of the surface are also affected by the modification. Aminophenyl grafted groups make the surface more acidic while aryl-aliphatic amines groups tends to render it more basic. The grafted layer shows in each case a good thermal stability up to 250 °C. The affinity of the modified powder towards CO₂ and N₂ has been evaluated by thermal swing adsorption. The maximum adsorption capacity of CO₂ of modified carbons is lower than the unmodified carbon but the presence of the amine functionalities involves a better selectivity of the material towards CO₂ adsorption in comparison of N₂ adsorption.     

Liquid crystalline H-bonded polymers influenced by chiral and achiral spacers

La₂O₃/polybenzoxazine composite was prepared through incorporating La₂O₃ into benzoxazine based on phenol and 4,4??-diaminodiphenyl methane (BB) to study the effect of La₂O₃ on the thermal stability of crosslinked polybenzoxazines. The ring-opening polymerization of BB benzoxazine was analyzed by DSC and measurement of viscosity. The structure and the thermal stability of BB polybenzoxazine were characterized by FTIR, TGA and DMA. The thermal degradation processes of polybenzoxazine were investigated using TGA-FTIR. The results showed that La₂O₃ could form coordination interaction with the nitrogen atoms of BB and thus promoted the polymerization of BB benzoxazine. The coordination interaction could not influence the volatilization of the amine degradation gases during the thermal degradation process of BB polybenzoxazine due to the amine structure existing in the chemical crosslinking network of polybenzoxazine and being stable. Furthermore, the coordination interaction weakened the C-N and C-C bonds in CH₂-NR-CH₂- of BB polybenzoxazine and thus accelerated the appearance and volatilization of the phenolic gases during the thermal degradation process, resulting in the decrease of the thermal stability and char yield at 800?°C of BB polybenzoxazine.     

Characterization of polyaniline via pyrolysis mass spectrometry

In this work, direct insertion probe pyrolysis mass spectrometry technique was applied to investigate the thermal and the structural characteristics of electrochemically prepared HCl and HNO₃‐doped polyaniline (PANI) films. It has been determined that the thermal degradation of both samples showed three main thermal degradation stages. The first stage around 50–60°C was associated with evolution of solvent and low‐molecular‐weight species adsorbed on the polymer, the second stage just above 150°C was attributed to evolution of dopant‐based products, and the final degradation stage at moderate and elevated temperatures was associated with evolution of degradation products of the polymer. Chlorination and nitrolysis of aniline during the electrochemical polymerization were detected. Extent of substitution increased as the electrolysis period was increased. Furthermore, for the HNO₃‐doped PANI, the evolution of CO₂ at elevated temperatures confirmed oxidation of the polymer film during electrolysis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008