Aqueous mixtures of AMP,HMDA-N,N′-dimethyl and TEG for CO2 separation: a study on equilibrium and reaction kinetics

Abstract

The hindered amine 2-amino-2-methyl-1-propanol (AMP) is a capable CO₂ separation solvent. HMDA-N,N′-Dimethyl (or HMDA-N,N′), which is the dimethyl derivative of 1,6-hexamethyl diamine, is a prospective activator of the absorption rate in AMP/H₂O mixtures. If a less volatile co-solvent such as triethylene glycol (TEG) is used in AMP-based solutions, the regeneration energy constraint will be lowered. In this work, a formulated blend of AMP (2-3?M), HMDA-N,N′ (0.1–0.5 M), TEG (0.7–2?M) and water was suggested for improved CO₂ capture from flue gas in thermal power stations. Kinetics of the CO₂ reaction with the suggested blend was studied in a stirred cell at 35, 40, and 45?°C. The pathway was elucidated using the renowned zwitterion mechanism. Overall, it was envisaged that both AMP and HMDA-N,N′ react with CO₂ in parallel. The values of the pseudo-first order rate constant were determined. It was found that HMDA-N,N′ reacts with CO₂ according to a second-order reaction (rate constant k_2,HMDA-N,N^′ = 79,525?M^?1 s^?1 at 35?°C), whose energy of activation is 38?kJ mol^?1. Lastly, the loading capacity of the suggested blend was measured in an ambient-pressure equilibrium setup. Its highest value was 1.4?mol CO₂/mol amine, when equilibrium CO₂ pressure was 4?kPa.     

Kinetics of carbon dioxide absorption in aqueous solution of diethylenetriamine (DETA)

A string of discs contactor was used to measure the kinetics CO₂ absorption in unloaded aqueous solution with the diethylenetriamine (DETA) concentrations ranging between 1.0 and 2.9 kmol m⁻³ and at temperatures ranging between 298.1 and 332.3 K. The reaction rates strongly increase as the increasing the concentrations and temperatures. Both the termolecular and the zwitterion models were applied to interpret the experimental data and gave identical results for all practical purposes. The reaction order with respect to the DETA concentration is found to vary slightly with temperature between 1.71 and 1.76 with an average of about 1.73. Both DETA and water contribute as a base in carbamate formation. It was found that fitting of experimental data to the termolecular mechanism gave statistically more robust results than fitting to the zwitterion mechanism.     

DEGRADATION OF AQUEOUS SOLUTIONS OF ALKANOLAMINE BLENDS AT HIGH TEMPERATURE, UNDER THE PRESENCE OF CO2 AND H2S

An experimental study on the degradation of aqueous solutions of alkanolamine blends, under the presence of carbon dioxide and hydrogen sulfide, was carried out. The studied alkanolamines were: diethanolamine (DEA), methyldiethanolamine (MDEA), and 2-amino-2-methyl-1-propanol (AMP). Degradation experiments were carried out at a temperature of 200°C. The mass fraction of DEA and MDEA in the studied aqueous solutions was 10% and 35%, respectively. AMP was incorporated into the MDEA-DEA aqueous solutions, with concentrations of (0-8) mass fraction. Partially degraded alkanolamine aqueous solutions were analyzed, after about 90 hours, by gas chromatography.

It was found that in all the studied alkanolamine aqueous solutions the MDEA degrades more slowly than DEA under the same experimental conditions. Degradation of both alkanolamines was found to be almost independent of the AMP concentration. AMP exhibits an intermediate stability; it is more resistant to degradation than DEA but less than MDEA. In addition, thermal degradation of DEA and MDEA is minimal up to 200°C.     

Carbon dioxide absorption using a phase transitional alkanolamine–alcohol mixture

Some alkanolamine–alcohol mixtures separate into a CO₂ rich phase and a CO₂ lean phase after the absorption of CO₂, which makes possible a new approach to CO₂ capture. In this study, CO₂ absorbent solutions with various concentrations of monoethanolamine (MEA) and diethanolamine (DEA) were prepared by mixing them with alcohol. The CO₂ absorption capacities of the alkanolamine–alcohol mixtures were investigated by using a semi-batch reactor at 313 K. The species distributions of the absorbents were identified in order to determine the CO₂ absorption mechanism of these solutions. Although the CO₂ absorption capacities of the phase transitional absorbents are lower than that of aqueous solutions, we conclude from our experimental results that the phase transitional solutions have the economic advantages, and in particular lower regeneration energies, because only the CO₂-rich phase needs to be transported to the stripper.     

二氧化碳催化还原成碳的进展

介绍了二氧化碳催化还原成碳的最新研究成果和发展趋势，以及它的基本反应原理和应用，并对这方面的开发研究提出了建议。     

An evaluation of autotrophic microbes for the removal of carbon dioxide from combustion gas streams

Carbon dioxide is a greenhouse gas that is believed to be a major contributor to global warming. Studies have shown that significant amounts of CO₂ are released into the atmosphere as a result of fossil fuels combustion. Therefore, considerable interest exists in effective and economical technologies for the removal of CO₂ from fossil fuel combustion gas streams. This work evaluated the use of autotrophic microbes for the removal of CO₂ from coal fired power plant combustion gas streams. The CO₂ removal rates of the following autotrophic microbes were determined: Chlorella pyrenoidosa, Euglena gracilis, Thiobacillus ferrooxidans, Aphanocapsa delicatissima, Isochrysis galbana, Phaodactylum tricornutum, Navicula tripunctata schizonemoids, Gomphonema parvulum, Surirella ovata ovata, and four algal consortia. Of those tested, Chlorella pyrenoidosa exhibited the highest removal rate with 2.6 g CO₂ per day per g dry weight of biomass being removed under optimized conditions. Extrapolation of these data indicated that to remove CO₂ from the combustion gases of a coal fired power plant burning 2.4 × 10⁴ metric tons of coal per day would require a bioreactor 386 km² × 1 m deep and would result in the production of 2.13 × 10⁵ metric tons (wet weight) of biomass per day. Based on these calculations, it was concluded that autotrophic CO₂ removal would not be feasible at most locations, and as a result, alternate technologies for CO₂ removal should be explored.     

超临界二氧化碳化学

本文简要介绍了在超临界条件下，二氧化碳化学的新进展，开发研究动向及其发展趋势。     

无机碱催化胺与CO2有效转化制备有机脲化合物

本文直接以CO2和有机胺为原料制备有机脲类化合物,反应过程中无任何脱水剂参与,通过优化反应的温度、压力、浓度、时间、溶剂、催化剂与助剂种类及用量等因素,获得了最佳反应条件：在温度为190℃、二氧化碳压力为4.5MPa、以无机碱Cs2CO3为催化剂、Bu4NBr为助剂、N-甲基吡咯烷酮(NMP)为溶剂,反应浓度为6.67 mmol/mL的条件下反应6小时,以良好的产率制备了15种对称型不同烷基或芳基取代的有机脲类化合物,分离产率可达42%~80%,采用1H NMR和13C NMR对其结构进行了表征,并分析了反应可能的机理。该方法具有方便高效、环境友好和原子经济的特点。关键词：二氧化碳;有机胺;无机碱;对称型有机脲;机理中图分类号：O622 文献标识码： A 文章编号：1003-5214 (2020) 01-0000-00     

EFFECTS OF COMPOSITION ON THE PERFORMANCE OF ALKANOLAMINE BLENDS FOR GAS SWEETENING

The use of amine blends to harness the desirable qualities of the constituent amines in order to reduce operating costs and/or improve product quality is becoming increasingly attractive to operators of alkanolamine-basedgas sweetening units. A number of parameters, all of which have economic implications, can be used to monitor the performance of amine blends. These include absorption rates, equilibrium solubility, corrosion, solution degradation and reclamation. This paper evaluates the influence of blend composition and components on some of the above parameters for aqueous blends of MDEA + MEA, MDEA + DEA and MDEA + DIPA     

A MODEL FOR THE DISTRIBUTION OF ACID GASES BETWEEN AN AQUEOUS ALKANOLAMINE SOLUTION AND LPG

The model of Deshmukh and Mather (1981) is a popular method for correlating and predicting the vapor-liquid equilibria in systems containing acid gases (hydrogen sulfide and carbon dioxide) and aqueous solutions of alkanolamines. The model includes phase equilibrium between an aqueous liquid and a gas as well as chemical equilibrium in the aqueous phase. A recent review by Weiland et al. (1993) demonstrated the accuracy of the correlation. Presented here is a model based on that of Deshmukh and Mather (1981) for calculating the distribution of acid gases between two liquid phases - an aqueous phase and a non-aqueous liquid (typically a propane- or butane-rich liquid)

In the new model the phase equilibrium is modeled using a modified Henry's law approach. Fugacities of the components in the non-aqueous phase are calculated using the Peng and Robinson (1976a) equation of state. All of the parameters in the model are taken from the literature. Thus the model represents a prediction of the behavior. It is demonstrated that the predictions are in good agreement with the available experimental data     

Electrospinning zwitterion-containing nanoscale acrylic fibers

Free radical copolymerization of n-butyl acrylate and a sulfobetaine methacrylamide derivative provided high molecular weight zwitterionic copolymers containing 6-13 mol% betaine functionality, and the electrospinning of low T_g zwitterionomers was explored for the first time. Copolymerizations were performed in dimethylsulfoxide (DMSO) rather than fluorinated solvents previously reported in the literature. Dynamic mechanical analysis of zwitterionomer films revealed biphasic morphology and featured a rubbery plateau and two distinct thermal transitions. Electrospinning from chloroform/ethanol (80/20 v/v) solutions at low concentrations between 2 and 7 wt% afforded nanoscale polymeric fibers with diameters near 100 nm. The presence of only 6 mol% zwitterion allowed the formation of low T_g, free-standing, non-woven mats, and we hypothesize that zwitterionic aggregation rather than chain entanglements facilitated electrospinning at these relatively low solution concentrations. To our knowledge, this is the first report of electrospun zwitterionic polymers and these non-woven membranes are expected to lead to new applications for sulfobetaine copolymers.     

Recent developments on carbon capture and storage: An overview

The Intergovernmental Panel on Climate Change assumes the warming of the climate system, associating the increase of global average temperature to the observed increase of the anthropogenic greenhouse gas (GHG) concentrations in the atmosphere. Carbon dioxide (CO₂) is considered the most important GHG, due to the dependence of world economies on fossil fuels, since their combustion processes are the most important sources of this gas. CO₂ concentrations are increasing in the last decades mainly due to the increase of anthropogenic emissions. The processes involving CO₂ capture and storage is gaining attention on the scientific community as an alternative for decreasing CO₂ emission, reducing its concentration in ambient air. However, several technological, economical and environmental issues as well as safety problems remain to be solved, such as the following needs: increase of CO₂ capture efficiency, reduction of process costs, and verification of environmental sustainability of CO₂ storage. This paper aims to review the recent developments (from 2006 until now) on the carbon capture and storage (CCS) methodologies. Special attention was focused on the basic findings achieved in CCS operational projects.     

CHEMICAL ABSORPTION OF CO2 AND SO2 INTO Ca(OH) 2 SLURRY

Chemical absorption of CO₂ and SO₂2 as single gases and as a mixture into slurries of Ca(OH) ₂ was studied in a stirred vessel with a flat gas-liquid interface. In the case of CO₂, the reaction product interrupted the subsequent gas absorption in the absence of a surface active agent. With single gases, the enhancement factor for SO₂ was much larger than that for CO₂, though both were larger than that into saturated solution. With the mixed gases, the enhancement factor for S02 was almost equal to that for the single gas absorption, but for CO₂ it was only slightly larger than that into the saturated solution     

Polyethercarbonate-silica nanocomposites synthesized by copolymerization of allyl glycidyl ether with CO2 followed by sol-gel process

The catalyst system consisting of Y(CF₃CO₂)₃, Zn(Et)₂, and pyrogallol in the solvent of 1,3-dioxolane was found to be effective for the copolymerization of allyl glycidyl ether with carbon dioxide at 60 °C and 400 psi. The IR, ¹H-NMR, and ¹³C-NMR spectra as well as the element analysis indicated that the resulting copolymer was an alternating polyethercarbonate with the carbonate content higher than 97.5%. The resulting polyethercarbonate could react with 3-(trimethoxysilyl)propyl methacrylate via a free radical reaction to generate the alkoxysilane-containing copolymer precursors that were used in the subsequent sol-gel process to result in the polyethercarbonate-silica nanocomposite. The generated nanocomposite was characterized by ¹³C-NMR, ²⁹Si-NMR, SEM, DSC, TGA, ESCA, and UV-Vis. The mechanical properties were also measured. A good compatibility between polyethercarbonate and silica and a SiO₂ network with silica particles less than 100 nm in the nanocomposite were observed. Both the thermal and mechanical properties of the resulting polyethercarbonate-silica nanocomposite were found to enhance with silica content. The optical transparency of the generated nanocomposite was comparable to that of the based polyethercarbonate.     

Selective production of poly(carbonate–co–ether) over cyclic carbonate for epichlorohydrin and CO2 copolymerization via heterogeneous catalysis of Zn–Co (III) double metal cyanide complex

Epichlorohydrin (ECH), as a cheap raw chemical material, is an ideal monomer for copolymerization with CO₂ to produce biodegradable polycarbonates. This work describes the selective ECH–CO₂ copolymerization via heterogeneous catalysis of nanolamellar zinc–cobalt double metal cyanide complex (Zn–Co (III) DMCC), affording a poly(carbonate–co–ether) with carbonate content up to 70.7%. Remarkably, the cyclic carbonate contents in the product are 5.0%–11.3% at 25–60 °C, better than those from homogeneous catalysis. Moreover, the copolymer with 70.7% carbonate content presents high thermal decomposition temperature of 250 °C and relatively high glass-transition temperature (T_g) of 31.2 °C.     

Block copolymerization of carbon dioxide with cyclohexene oxide and 4-vinyl-1-cyclohexene-1,2-epoxide in based poly(propylene carbonate) by yttrium-metal coordination catalyst

The coordination system, Y(CF₃CO₂)₃ (I)-Zn(Et)₂ (II)-m-hydroxybenzoic acid (III), was found to be the most active catalyst to generate poly(propylene carbonate) (PPC) from carbon dioxide and propylene oxide (PO) in 1,3-dioxolane. A high yield and a high molecular weight could be obtained at the conditions of a II/I molar ratio of 20, a III/II molar ratio of 1.0, a temperature of 60 °C, and a pressure of 2.76 MPa. The carbonate content in the resultant PPC was found to be nearly 100%.The block copolymerization in the based PPC was carried out by in situ introducing an epoxide other than PO right after the copolymerization of carbon dioxide with PO using the same catalyst system. The IR and ¹H NMR spectra as well as the measured molecular weights verified the resulting copolymers were block copolymers. For the block copolymerization of CO₂ with cyclohexene oxide and CO₂ with 4-vinyl-1-cyclohexene-1,2-epoxide in the based PPC, the yield as well as the cyclohexene carbonate and the 4-vinyl-1-cyclohexene carbonate contents were found to increase with increasing temperature. The most appropriate temperature was around at 80 °C. The weight-average molecular weights of the block copolymers lay in a range from 2.44×10⁵ to 3.16×10⁵, the polydispersity in a range from 5.0 to 6.3, and the 10% weight loss temperature in a range from 226 to 253 °C. The thermal and mechanical properties of the resultant block copolymers lay between those of PPC, poly(cyclohexene carbonate), and poly(4-vinyl-1-cyclohexene carbonate), indicating the desired properties of a polymer can be achieved via block copolymerization.