The kinetics of reactions of carbon dioxide with monoethanolamine, diethanolamine and triethanolamine by a rapid mixing method

Modeling, Simulation, and Membrane Wetting Estimation in Gas-Liquid Contacting Processes Including Shell-Side Reaction: Biogas Upgrading Using DEA Solution

The basic principles of a steady-state mass transfer model and the resistance-in-series film model are assessed with the aid of a series of experiments in a gas-liquid contact membrane mini-module (3 M Liqui-Cel MM-1.7 × 5.5) using an aqueous solution of diethanolamine (DEA) of 0.25 M (mol/L) for biogas upgrading. Experimental data show that CO2 removal may exceed 67% and reach 100% in combination with the highest possible recovery of CH4 when employing biogas flow rates in the range of 2.8 × 10-5 - 3.6 × 10-5 m3/s and solvent flow rates within 0.47 × 10-5 - 0.58 × 10-5 m3/s. For the experimental data set, a correlation has been developed, effectively interpolating CO2 removal with the gas and liquid flow rates. The wetting values calculated are concentrated close to each other for the same liquid flow rate without considerably depending on the gas flow rate, especially when applying the Hikita-Yun (reaction rate-shell-side correlation) compared with the Hikita-Costello pair. Furthermore, the calculated wetting diminishes with increasing liquid flow rate, a result that is consistent with previous modeling attempts and relevant literature indications. The assumption of enhanced mass transfer in the liquid-filled part of the membrane pores due to the reaction is scrutinized, leading to objectionable computational wetting values. It is shown that for a concentration of DEA equal to 0.25 M the Hatta numbers and the enhancement factors are not equal in the whole reaction path; thus, the choice of the shell-side correlation has an appreciable impact on the overall analysis, especially for the determination of the wetting values.

Kinetics of Carbon Dioxide Removal Using N-Acetylglucosamine

Glucosamine, the amino sugar made from glucose, is a safe and natural reagent for post-combustion carbon dioxide capture. Its most plentiful derivative, N-acetylglucosamine (or NAG), was studied in this work with respect to its reaction kinetics in aqueous solutions. A stirred cell reactor with a flat gas-liquid interface was used, and it was found that CO₂ reacts with NAG via a pathway similar to that with alkanolamines. In the 20-100 mM range of NAG concentration, the second-order rate constant at T = 308 K was 125 kmol m^-3 s^-1. For the 303-313 K range, the activation energy was 42 kJ mol^-1. In a study on vapor-liquid equilibrium, it was found that the loading capacity of NAG (100 mM) at 303 K was 0.6 mol CO₂/mol NAG, while the equilibrium partial pressure of CO₂ was 0.8 kPa. Three rate promoters were tested, and piperazine showed better efficacy than monoethanolamine and 2-amino-2-methyl-1-propanol in aqueous NAG solutions. This work is expected to stimulate further interest in this new, green CO₂ capturing solvent.

High-level production in a plant system of a thermostable carbonic anhydrase and its immobilization on microcrystalline cellulose beads for CO2 capture

KEY MESSAGE

Plant-produced SazCA and its application to CO2 capture. Technologies that rely on chemical absorption or physical adsorption have been developed to capture CO2 from industrial flue gases and sequester it at storage sites. Carbonic anhydrases (CAs), metalloenzymes, that catalyze the reversible hydration of CO2 have recently received attention as biocatalysts in the capture of CO2 from flue gases, but their cost presents a major obstacle for use at an industrial scale. This cost, however, can be reduced either by producing a long-lasting enzyme suitable for CO2 capture or by lowering production costs. High-level expression, easy purification, and immobilization of CAs from Sulfurihydrogenibium azorense (SazCA) were investigated in a plant system. Fusion of the 60-amino acid-long ectodomain (M-domain) of the human receptor-type tyrosine-protein phosphatase C increased the levels of SazCA accumulation. Fusion of the cellulose-binding module (CBM3) from Clostridium thermocellum resulted in tight binding of recombinant protein to microcrystalline cellulose beads, enabling easy purification. The chimeric fusion protein, BMC-SazCA, which consisted of SazCA with the M and CBM3 domains, was expressed in tobacco (Nicotiana benthamiana), giving a recombinant protein yield in leaf extracts of 350 mg/kg fresh weight. BMC-SazCA produced in planta was active in the presence of various chemicals used in CO2 capture. Immobilization of BMC-SazCA on the surface of microcrystalline cellulose beads extended its heat stability, allowing its reuse in multiple rounds of the CO2 hydration reaction. These results suggest that production of SazCA in plants has great potential for CA-based CO2 sequestration and mineralization.

Molecular investigation into the effect of carbon nanotubes interaction with CO2 in molecular separation using microporous polymeric membranes

The use of nanofluids has been recently of great interest to separate acidic contaminants such as CO₂. The main objective of this research is to assess the influence of carbon nanotubes (CNTs) addition to distilled water on enhancing the CO₂ molecular separation through a porous membrane contactor (PMC). For this aim, a comprehensive model is developed based on non-wetted and counter-current operational modes to evaluate the principal mass and momentum transport equations in tube, membrane and shell compartments of PMC. Consequently, a CFD-based axisymmetrical simulation is implemented according to finite element technique (FET) to prognosticate the results. It is found from the results that the addition of 0.1 wt% carbon nanotubes (CNTs) particles to water significantly enhances the mass transfer and consequently the CO₂ molecular separation efficiency from 38 to 63.3%. This considerable enhancement can be justified due to the existence of two momentous phenomena including Brownian motion and Grazing effect, which enhance the mass transport of CO₂ molecules in the PMC. Moreover, the effect of CNTs concentration, some membrane's parameters such as number of hollow fibers and porosity and also some module's design parameters including module radius and length on the CO₂ separation performance are investigated in this paper as another highlight of the current work.

Carbon dioxide capture in 2,2'-iminodiethanol aqueous solution from ab initio molecular dynamics simulations

The reaction of carbon dioxide (CO₂) with aqueous 2,2'-iminodiethanol (trivial name is diethanolamine: DEA) has been investigated using both blue moon ensemble and metadynamics approaches combined with ab initio molecular dynamics (AIMD) simulations. A spontaneous direct proton transfer from DEA zwitterion (DEAZW) to DEA but not to H₂O has been observed in straightforward AIMD simulation in the time scale of ps. The ab initio free-energy calculations reproduced the overall free-energy difference, predicting the ionic products DEA carbamate ion (DEAC) and the protonated DEA (DEAH). The computed free-energy barrier for the first reaction step, which is the CO₂ binding (48 kJ mol^-1), is found to agree reasonably well with the available experimental data (52-56 kJ mol^-1). By contrast, the barriers for the next step, the deprotonation of zwitterion realized either via reaction with DEA or H₂O, are underestimated by 25-35 kJ mol^-1 compared to the experimental reference. A part of this error is attributed to the neglected reversible work needed to bring two reactants together, which might significantly contribute to the free-energy of activation of bimolecular reactions in a dilute solution. The computed free-energy profile is compared with our results [Y. Kubota et al., J. Chem. Phys. 146, 094303 (2017)] for the same reaction in 2-aminoethanol (trivial name is monoethanolamine: MEA).

Role of Hydrogen-Bond Interactions in CO2 Capture by Wet Phosphonium Formate Ionic Liquid: A Raman Spectroscopic Study

The mechanism of CO₂ absorption by a formate ionic liquid, [P₄₄₄₄ ]HCOO, was studied by Raman spectroscopy. The band area for the symmetric CO₂ stretching of the formate anion linearly decreases with the CO₂ loading. From the slope of the decrease, 1 : 1 stoichiometry is proven between CO₂ and the formate anion. The result favors the mechanism we proposed in a preceding work [J. Chem. Eng. Data 61, 837 (2016)]: HCOO^- +CO₂ +H₂ O→HCOOH+HCO₃^- →[HCOOH…HCO₃^- ]. Further support for the mechanism is obtained by the observation of antisymmetric vibration of CO for the proposed hydrogen-bonded complex between HCOOH and HCO₃^- . The bands appeared as a doublet (1677 and 1730 cm^-1 ) as this complex has two carbonyl groups. Based on DFT calculations, the [HCOOH…HCO₃^- ] complex is supposed to be the most abundant form of chemisorbed CO₂ .