Sterically-hindered Amines Research Articles

Recent Progress on CO2 Capture Based on Sterically Hindered Amines: A Review

Recent Progress on CO₂ Capture Based on Sterically Hindered Amines: A Review

A hybrid chemo-biocatalytic system of carbonic anhydrase submerged in CO2-phillic sterically hindered amines for enhanced CO2 capture and conversion into carbonates

The present study highlights a hybrid approach to capture and convert carbon dioxide (CO2) from exhaust gases using bovine carbonic anhydrase (CA) submerged into aqueous amine solvents. Particularly, the sterically hindered amines have unique properties to absorb CO2 and also play a key role in wide range of industrial applications. In this work, the reaction kinetics of CO2 were studied in the aqueous phase of sterically hindered amines (SHAs), 2-amino-2-hyroxymethyl-1,3-propanediol (AHPD) and 2-amino-2-methyl-1-propanol (AMP), mixed with bovine CA as test and without CA as control using the stopped flow technique. The results showed a significant improvement in the rate of reaction between SHAs (either aqueous AHPD or aqueous AMP) and CO2 in the presence of CA. Moreover, the absorption capacity of SHA for CO2 and its initial absorption rate in presence of CA was significantly enhanced. The rate constants of pseudo first-order reaction of CO2 reacting with AHPD and AMP (each 0.5 kmol/m3) with varied concentration of CA were determined at temperature range of 298- 353 K. The aqueous AHPD and AMP systems in the presence of CA and control retained 65% of absorption capacity after 5 repetitive cycles. Also, the amine solvent captured CO2 was converted into calcium carbonate (CaCO3) which is white powder materials. The synthesized CaCO3 was characterized for its morphological and physicochemical properties using scanning electron microscopy (SEM) and Fourier transformer infrared spectroscopy (FTIR) etc. Overall, as the CA present is the amine solvent can efficiently convert the CO2 and that can be removed easily in the form of CaCO3 precipitates.

The enhanced enzymatic performance of carbonic anhydrase on the reaction rate between CO2 and aqueous solutions of sterically hindered amines

AbstractThe kinetics of the reactions of carbon dioxide (CO2) with aqueous solutions of two different sterically hindered amines (SHAs), 2‐amino‐2‐ethyl‐1,3‐propanediol (AEPD) and 2‐amino‐2‐methyl‐1,3‐propanediol (AMPD), in the presence and absence of carbonic anhydrase (CA) was investigated experimentally using stopped‐flow conductimetry. The amine concentration, CA concentration, and temperature were varied within the ranges of 0.1–0.5 kmol·m–3, 0–125 g·m–3, and 298–353 K, respectively. Based on pseudo first‐order reaction conditions, the intrinsic reaction rate (ko) was obtained according to a modified termolecular reaction mechanism. The obtained results showed that the reaction rate between the SHA solutions (either aqueous AEPD or aqueous AMPD) and CO2 was enhanced significantly upon adding small amounts of CA as a promoter. Such a result supports the use of the aforementioned solvent system as a candidate for CO2 capture. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Selective removal of hydrogen sulfide from simulated biogas streams using sterically hindered amine adsorbents

Three silica supported sterically hindered amines, two moderately hindered amines (containing primary and secondary amine groups) and one severely hindered amine (containing a secondary amine group), are evaluated for removal of H2S from mixed CH4/CO2/H2S streams akin to those found in natural gas deposits or in biogas streams. The results from in-situ infrared spectroscopy and both calculated and simulated heats of adsorption suggest a hydrogen bonding sorption mechanism for H2S, involving two amine molecules on all sterically hindered amine (SHA) adsorbents. Basicity calculations with a sterically hindered Lewis acid suggest that steric hindrance is responsible for the limited amine-CO2 interactions on the hindered amines, but has less effect on the amine-H2S interactions. Using a multicomponent gas mixture of H2S/CO2/CH4, a range of experiments confirm that moderately sterically hindered amines can simultaneously remove CO2 and H2S while the most severely sterically hindered amine, based on a tert-butylaminopropylsilyl-grafted species, is the best adsorbent for the selective removal of H2S in the presence of low and high CO2 concentrations, offering facile regeneration. The H2S selectivity achieved, with essentially no measurable CO2 uptake, is the highest H2S selectivity reported to date amongst similar gas mixtures for solid sorbents.

Ruthenium(0)-sequential catalysis for the synthesis of sterically hindered amines by C-H arylation/hydrosilylation.

We report sequential ruthenium(0)-catalysis for the synthesis of sterically-hindered amines via direct C-H arylation of simple imines and imine hydrosilylation. The method involves direct C-H arylation under neutral conditions with organoboranes enabled by ruthenium(0) catalysis. The catalytic hydrosilylation was performed in a one-pot fashion using Et3SiH. The reaction is compatible with a broad range of electronically- and sterically-varied imines, enabling rapid production of valuable biaryl amines in good to excellent yields. The method constitutes a two-step, one-pot procedure to synthesize sterically-hindered amines from aldehydes. The utility of this atom-economic strategy is demonstrated in one-pot, three-component coupling, direct in situ aldehyde arylation and the use of transfer hydrogenation.

Carbon steel corrosion in piperazine-promoted blends under CO2 capture conditions

Aqueous amine promoter blends have improved CO2 absorption capacity and uptake. Tertiary (3°) and sterically-hindered (SH) amines are favoured for their molar absorption ratio, (i.e. CO2 absorption capacity). With a promoter, namely piperazine (PZ), the ordinarily slow reaction kinetics of a 3°/SH amine is accelerated. Amine blends of 30 and 50% by weight, MDEA+PZ and AMP+PZ, were tested using immersion corrosion techniques at 120°C. In all cases, a siderite (FeCO3) product layer was formed on the surface of the carbon steel coupons. Aqueous PZ solutions produced thin layers with comparatively lower Fe ion concentrations than blended solutions. The fast CO2 capture kinetics of PZ, and therefore carbonate formation, makes the rapid reaction possible due to readily available Fe ions oxidised on the surface. The replacement of PZ content in a blend, by MDEA or AMP, resulted in slower formation of siderite and variably poorer corrosion protection. Critically, the use of AMP in the blend offers better protection against corrosion, shown by lower concentration of Fe ions in the bulk solution than parallel MDEA solutions. This can be attributed to the faster formation of carbonate species by AMP, as a SH amine, which also results in more imperfect crystals.

The Kinetic Effect of Adding Piperazine Activator to Aqueous Tertiary and Sterically-hindered Amines Using Stopped-flow Technique

Abstract Aqueous amines as the solvents for CO 2 removal in low concentration streams have been exhaustively studied. This work focuses on the blending of piperazine (PZ) activator with aqueous tertiary amines (Methyldiethanolamine, MDEA) across concentration range of 200-900 mol/m3 for MDEA and 5-41 mol/m3 for PZ and sterically-hindered amines (2-amino-methyl-1-propanol, AMP) across concentration range of 6-24 mol/m3 for AMP and 7-48 mol/m3 for PZ at temperature range of 298-313 K using stopped-flow technique to determine the direct pseudo first-order reaction kinetics of the blends. The different proposed reaction mechanisms such as base-catalyzed hydration, zwitterion and termolecular reaction mechanisms for the reaction of CO 2 with aqueous solutions of amines were used to calculate the second-order reaction rate constants k 2 , (m3·mol-1s-1). Zwitterion mechanism correlated the stand-alone AMP perfectly while base catalysis mechanism correlated the stand-alone MDEA successfully. Hybrid of zwitterion mechanism correlated the blend of AMP/PZ while a hybrid of zwitterion and base catalysis mechanisms correlated the experimental data of MDEA/PZ system.

The role of CT and MRI in the diagnosis of sigmoid volvulus

Carbon dioxide (CO2) capture has attracted great interest these days due to the role of CO2 in global warming and its effects in industrial processes. Thus, higher energy efficient and affordable technologies are required for its removal so as to address these problems. In this work, the reaction kinetics of CO2 with 2-amino-2-hyroxymethyl- 1,3-propanediol (AHPD), a sterically hindered amine (SHA), was studied by direct stopped flow method. The aim was to research CO2 absorbent with better CO2 absorption capacity and reaction kinetics than the commonly applied amine solvents. The study was carried out at 288, 298, and 303 K in a concentration range of 0.5-2.0 kmol/m3 of AHPD. Based on the pseudo-first-order for the reaction of CO2, it was found that the reaction can be modeled by a single termolecular reaction mechanism. The reaction rate between CO2 and aqueous solution of AHPD was 9.99, 12.03, and 16.05 m3/kmol.s at 288, 298, and 303 K, respectively, while its activation energy was 31.59 kJ/mol. The results obtained were compared with published reaction rate data of other amines. The present study shows that AHPD is a potential SHA as CO2 absorbent if the reaction rate is enhanced by an additional amine.

Carbamate Stabilities of Sterically Hindered Amines from Quantum Chemical Methods: Relevance for CO2 Capture

The influence of electronic and steric effects on the stabilities of carbamates formed from the reaction of CO2 with a wide range of alkanolamines was investigated by quantum chemical methods. For the calculations, B3LYP, M11-L, MP2, and spin-component-scaled MP2 (SCS-MP2) methods were used, coupled with SMD and SM8 solvation models. A reduction in carbamate stability leads to an increased CO2 absorption capacity of the amine and a reduction of the energy required for solvent regeneration. Important factors for the reduction of the carbamate stability were an increase in steric hindrance around the nitrogen atom, charge on the N atom and intramolecular hydrogen bond strength. The present study indicates that secondary ethanolamines with sterically hindering groups near the N atom show significant potential as candidates for industrial CO2-capture solvents.

Photoinduced Oxidation of Sterically Hindered Amines in Acetonitrile Solutions and Titania Suspensions (An EPR Study)

The reactions of sterically hindered amines (SHA) were investigated in acetonitrile solutions and TiO(2) suspensions upon exposure to monochromatic radiation, λ=365 nm, by means of in situ EPR spectroscopy. The formation of singlet oxygen, as one of the possible oxidation agents for SHA, in these systems is affected significantly by solvent used and the experimental conditions. Experiments in homogeneous media evidenced alternative pathways for the SHA oxidation with a variety reactive oxygen species involved. In anhydrous acetonitrile solutions containing KO(2), the SHA oxidation was negligible not only in the dark but also on continuous exposure. However, the presence of water, even at low concentrations, led to the transformation of O(2)(•-) to singlet oxygen and hydrogen peroxide, which served as a source of hydroxyl radicals. These species participated in oxidation of SHA resulting in the generation of nitroxide radicals. To investigate the influence of different competitive reactions of SHA with other ROS formed upon TiO(2) photoexcitation, a series of experiments using different additives (e.g. KO(2), H(2)O(2), NaN(3), dimethylsulfoxide, methanol as organic cosolvents) under air or argon were performed. The detailed analysis of paramagnetic intermediates formed upon the irradiation of the studied systems was accomplished using EPR spin trapping technique.

이산화탄소 흡수제의 화학구조별 반응열량 특성 연구

반응열량계를 사용하여 1, 2, 3차 아민 수용액과 이산화탄소의 반응열을 각각 측정하였다. 이를 통해 MEA(monoethanolamine, 1차 아민), EAE(2-(ethylamino) ethanol, 2차 아민), MDEA (N-methyldiethanolamine, 3차 아민) 30 wt% 수용액이 <TEX>$40^{\circ}C$</TEX>에서 이산화탄소와 반응시 발생하는 반응열을 측정하고 이를 <TEX>$CO_2$</TEX>의 loading ratio에 따라 어떻게 변화하는지 평가하였다. 또한, 입체장애 구조를 가지는 AMP(2-amino-2-methyl-1-propanol, 1차 아민), DEA(diethanolamine, 2차 아민), TEA(triethanolamine, 3차 아민) 30 wt% 수용액의 반응열을 각각 측정하여 입체장애 구조가 반응열에 미치는 영향을 살펴보았다. 그 결과, 흡수제의 입체장애 유무와 관계없이 1차 > 2차 > 3차 아민 순으로 반응열이 증가함을 확인하였다. 그리고 입체장애 아민이 동일 차수의 비 입체장애 아민보다 상대적으로 반응열이 낮지만 그 차이는 크지 않음을 확인하였다. In this study, the heats of absorption of <TEX>$CO_2$</TEX> with aqueous solutions of primary, secondary and tertiary amine aqueous solutions were measured in the commercial reaction calorimeter SIMULAR (HEL, UK). The heats of absorption of 30 wt% amine aqueous solutions of MEA (monoethanolamine, primary amine), EAE(2-(ethylamino)ethanol, secondary amine), and MDEA (methyldiethanolamine, tertiary amine) were measured as function of the <TEX>$CO_2$</TEX> loading ratio at <TEX>$40^{\circ}C$</TEX>, in each case. In addition, the heats of absorption of sterically-hindered amine aqueous solutions of AMP(2-amino-2-methyl-1-propanol, primary amine), DEA(diethanolamine, secondary amine) and TEA(triethanolamine, tertiary amine) were measured to observe the steric hindrance effect. The heat of absorption is high in the following order regardless of the steric hindrance: primary amine > secondary amine > tertiary amine. The heats of absorption of amines having sterically-hindered substituents surrounding nitrogen atoms are relatively low compare to that of sterically-free amines, although the difference is very small.

Reaction kinetics of carbon dioxide with 2-amino-2-hydroxymethyl-1,3-propanediol in aqueous solution obtained from the stopped flow method

Carbon dioxide (CO_2) capture has attracted great interest these days due to the role of CO_2 in global warming and its effects in industrial processes. Thus, higher energy efficient and affordable technologies are required for its removal so as to address these problems. In this work, the reaction kinetics of CO_2 with 2-amino-2-hyroxymethyl- 1,3-propanediol (AHPD), a sterically hindered amine (SHA), was studied by direct stopped flow method. The aim was to research CO_2 absorbent with better CO_2 absorption capacity and reaction kinetics than the commonly applied amine solvents. The study was carried out at 288, 298, and 303 K in a concentration range of 0.5-2.0 kmol/m^3 of AHPD. Based on the pseudo-first-order for the reaction of CO_2, it was found that the reaction can be modeled by a single termolecular reaction mechanism. The reaction rate between CO_2 and aqueous solution of AHPD was 9.99, 12.03, and 16.05 m^3/kmol.s at 288, 298, and 303 K, respectively, while its activation energy was 31.59 kJ/mol. The results obtained were compared with published reaction rate data of other amines. The present study shows that AHPD is a potential SHA as CO_2 absorbent if the reaction rate is enhanced by an additional amine.

Creating a Biocatalyst for the Production of an Optically Pure Sterically Hindered Amine

Creating a Biocatalyst for the Production of an Optically Pure Sterically Hindered Amine

ChemInform Abstract: Functionalized Organolithium Reagents. Part 10. Synthesis of Amines via Carbon-Sulfur Bond Cleavages of Substituted Aminomethyl Sulfides with Organolithium Reagents: Aminocarbene Route to Enamines and Sterically Hindered Amines.

ChemInform Abstract: Functionalized Organolithium Reagents. Part 10. Synthesis of Amines via Carbon-Sulfur Bond Cleavages of Substituted Aminomethyl Sulfides with Organolithium Reagents: Aminocarbene Route to Enamines and Sterically Hindered Amines.

Equilibrium solubility of carbon dioxide in (2-amino-2-methyl-1-propanol + piperazine + water)

In this work, a new set of values for the solubility of carbon dioxide in aqueous mixture containing different concentrations of 2-amino-2-methyl-1-propanol (AMP), a sterically-hindered amine, and piperazine (PZ), an activator, are presented. The results were carefully determined using a 1.0 dm 3 stainless steel vapour-recirculation equilibrium cell at T = (313.2, 333.2, and 353.2) K, and pressures up to 152 kPa. The AMP concentrations in the ternary (solvent) mixture were (2 and 3) kmol · m −3; those of PZ’s were (0.5, 1.0, and 1.5) kmol · m −3. The measured equilibrium loading (solubility)/partial pressure pairs at different temperatures and concentration levels were generally consistent with the corresponding values correlated from the Kent–Eisenberg model that has been adapted for the system in the study, where the parameters of the models were determined using the results from this study and relevant data from literature.

A simple and efficient method for sulfonylation of amines, alcohols and phenols with cupric oxide under mild conditions

Cupric Oxide efficiently catalyzed the synthesis of sulfonamides and sulfonic esters. This method has been applied to a variety of substrates including nucleophilic and sterically-hindered amines, alcohols and phenols with excellent yields of sulfonamides and sulfonic esters. The remarkable selectivity under mild and neutral conditions of this commercially available inexpensive catalyst is an attractive feature of this method.

Crowded piperidines with intramolecularly hydrogen-bonded nitrogen: synthesis and conformation study.

2,2,6,6-Tetramethyl substituted piperidines with a beta-branched N-alkyl substituent were synthesized by the photoreaction of N-Me precursors with ketones. The main conformation features of these sterically-hindered amines (established by NMR and IR spectroscopy) are a ring in the chair form, an eclipsed conformation for the N-substituent and an intramolecular OH...N bond. High barriers for the geminal substituent topomerization were measured for these piperidines at different temperatures by means of line-shape analysis of the temperature-dependent 13C and 1H NMR spectra. An MM3-derived conformation scheme indicated that, for one of the studied analogues, the rotation of the N-substituent determines a slow topomerization rate. A new mechanism of nitrogen inversion--a concerted hydrogen-bond dissociation/nitrogen inversion process--is considered for hydrogen-bonded amines.

Reactions of Singlet Oxygen with Olefins and Sterically Hindered Amine in Mixed Surfactant Vesicles

The photosensitized oxidations of the olefins, trans-1,2-dimethoxystilbene (DMOS), trans-stilbene (TS), and trans,trans-1,4-diphenyl-1,3-butadiene (DPB) as well as the amine 2,2,6,6-tetramethylpiperidine (TMP) in mixed surfactant vesicles were investigated. The sensitizer was either a hydrophobic dye, tetraphenylporphyrin (TPP), or a cationic dye, methylene blue (MB). The substrate molecules were solubilized in the bilayer membranes of one set of vesicles, and the sensitizers were incorporated in the bilayers or the aqueous inner compartments of another set of vesicles. The irradiation samples were prepared by mixing the above two sets of vesicle dispersions. Photoirradiation of the oxygen-saturated samples resulted in the oxidation of the substrates, as evidenced by the isolation of the end products in the olefin oxidation and by the detection of the ESR spectrum of the nitroxide radical in the amine oxidation. The quantum yields for the product formation were enhanced significantly in D2O dispersions co...

Sterically-Hindered Amines for Acid-Gas Absorption

Abstract This paper reviews sterlcally-hindered amines for removal of add gases such as CO2 and H2S from gaseous streams. Steric hindrance of amines reduces carbamate stability. Moderately hindered amines are characterized by high rates of CO2 absorption and high capacities for CO2. The moderately hindered amine in use with organic solvent has considerably higher capacity than the conventional amine-solvent system for simultaneous removal of CO2and H2S from synthesis gas and natural gas. A severely-hindered-amine absorbent, characterized by a very low rate of CO2absorption, has much higher capacity and selectivity than the current industry standard, methyldiethanolamine, for selective removal of H2S from CO2-containing streams. Use of hindered amines represents new advances in gas treating. Hindered amines save energy and capital in gas treating significantly. In addition, hindered amines used commercially have much better stability than conventional amines. As of today, fourteen commercial plants use hindered amines.