Equilibrium conditions of clathrate hydrates formed from carbon dioxide and aqueous acetone solutions

Hydration of carbon dioxide in water solution is the rate limiting step for the CO2 mineralization process, a process which is at the base of many carbon capture and utilization (CCU) technologies aiming to convert carbon dioxide to added-value products and mitigate climate change. Here, we present a combined experimental and computational study to clarify the effectiveness and molecular mechanism by which nickel nanoparticles, NiNPs, may enhance CO2 hydration in aqueous solutions. Contrary to previous literature, our kinetic experiments recording changes of pHs, conductivity, and dissolved carbon dioxide in solution reveal a minimal effect of the NiNPs in catalyzing CO2 hydration. Our atomistic simulations indicate that the Ni metal surface can coordinate only a limited number of water molecules, leaving uncoordinated metal sites for the binding of carbon dioxide or other cations in solution. This deactivates the catalyst and limits the continuous re-formation of a hydroxyl-decorated surface, which was a key chemical step in the previously suggested Ni-catalyzed hydration mechanism of carbon dioxide in aqueous solutions. At our experimental conditions, which expand the investigation of NiNP applicability toward a wider range of scenarios for CCU, NiNPs show a limited catalytic effect on the rate of CO2 hydration. Our study also highlights the importance of the solvation regime: while Ni surfaces may accelerate carbon dioxide hydration in water restricted environments, it may not be the case in fully hydrated conditions.

The solvation of carbon dioxide in solution represents a key step for the capture and fixation CO2 in nature, which may be further influenced by the formation of (bi)carbonate species and/or the formation of CO2 clusters in solution. The latter processes are strongly dependent on the exact environment of the liquid state (e.g., pH value, solvated ions, etc.) and may interfere with the experimental determination of structural, dynamical, and thermodynamic properties. In this work a hybrid quantum mechanical/molecular mechanical (QM/MM) simulation approach at correlated ab initio level of theory resolution-of-identity second-order Møller-Plesset Perturbation Theory (RI-MP2) has been applied in the framework of thermodynamic integration (TI) to study structure, dynamics, and the hydration free energy of a single carbon dioxide molecule in aqueous solution. A detailed analysis of the individual QM/MM potential energy contributions demonstrate that the overall potential remains highly consistent over the entire sampling phase and that no artificial contributions are influencing the determination of the hydration free energy. The latter value of 0.01 ± 0.92 kcal/mol was found in very good agreement with the values of 0.06 and 0.24 kcal/mol obtained via quasi-chemical theory and experimental measurements, respectively. In order to obtain detailed information about the C- and O C-water interaction, conically restricted regions with respect to the main axis of the CO2 molecule have been employed in structural analysis. The presented data not only provide detailed information about the hydration properties of CO2 but act as a critical validation of the simulation technique, which will be beneficial in the study of nonaqueous solvents such as pure and aqueous NH3 solutions, which have been suggested as potential candidates to capture CO2 from anthropogenic sources.

CHAPTER 26 - SOME BIOLOGICAL ANALYTICAL METHODS

A POLAROGRAPHIC depolarization effect due to carbon dioxide in aqueous solutions occurring at − 2.2 V. (from the normal calomel electrode) has been described by Van Rysselberghe1 and v. Stackelberg2. This effect is, however, indistinct. When using absolute (99.8 per cent) ethyl alcohol with 0.3 M tetramethyl ammonium chloride in electrolysis with the dropping mercury cathode, a well-defined wave with a maximum at − 2V. (Fig. 1) is formed on the current-voltage curve. The behaviour shows it to be due to the evolution of hydrogen from carbonic acid, the carbon dioxide molecule being regarded as not reducible. Here nitrogen containing 4 vol. per cent of carbon dioxide was bubbled through the solution for 3–4 min. at room temperature. The equilibrium concentration of carbon dioxide dissolved under its pressure in the gaseous phase is attained very quickly (in about 2 min.). The ensuing limiting current is strictly proportional to the partial pressure of carbon dioxide.

Utilization of carbon dots from jackfruit for real-time sensing of acetone vapor and understanding the electronic and interfacial interactions using density functional theory

Experimental cloud-point data up to 478 K and 248.0 MPa are reported for binary and ternary mixtures of poly(2-ethylhexyl methacrylate) (1) + carbon dioxide (2) + 2-ethylhexyl methacrylate (3) and poly(2-ethylhexyl acrylate) (1) + carbon dioxide (2) + 2-ethylhexyl acrylate (3) systems. High-pressure cloud-point data are also reported for poly(2-ethylhexyl methacrylate) and poly(2-ethylhexyl acrylate) in supercritical propane, propylene, butane, 1-butene, and dimethyl ether. Cloud-point behavior for the poly(2-ethylhexyl methacrylate) (1) + carbon dioxide (2) + 2-ethylhexyl methacrylate (3) system were measured in changes of the pressure, temperature (p, T) slope and with 2-ethylhexyl methacrylate mass fraction of w3 = 0.0, 0.201, 0.303, and 0.564. With w3 = 0.666 2-ethylhexyl methacrylate to the poly(2-ethylhexyl methacrylate) (1) + carbon dioxide (2) solution, the cloud-point curves take on the appearance of a typical lower critical solution temperature boundary. The poly(2-ethylhexyl acrylate) (1) + carbon dioxide (2) + w3 = 0.0, 0.097, 0.206, 0.409, 0.552, and 0.604 2-ethylhexyl acrylate (3) systems change the (p, T) curve from upper critical solution temperature region to lower critical solution temperature region as the 2-ethylhexyl acrylate mass fraction increases. For w3 = 0.709 2-ethylhexyl acrylate, the poly(2-ethylhexyl acrylate) (1) + carbon dioxide (2) solution significantly changes the phase behavior. Also, the impact by dimethyl ether mass fraction for the poly(2-ethylhexyl methacrylate) (1) and poly(2-ethylhexyl acrylate) (1) + carbon dioxide (2) + dimethyl ether (3) system is measured at temperatures to 455 K and a pressure range of (4.3 to 248.0) MPa. Pressure, composition (p, x) isotherms are obtained for the carbon dioxide (1) + 2-ethylhexyl methacrylate (2) systems at (313.15, 333.15, 353.15, 373.15, and 393.15) K and pressure up to 20.5 MPa. The carbon dioxide (1) + 2-ethylhexyl methacrylate (2) systems exhibit type-I phase behavior with a continuous mixture critical curve. The experimental results for carbon dioxide (1) + 2-ethylhexyl methacrylate (2) mixtures are modeled using the Peng−Robinson equation of state with two adjustable parameters.

Equilibrium conditions of clathrate hydrates formed from xenon and aqueous solutions of acetone, 1,4-dioxane and 1,3-dioxolane

This study analyzes the contraction and concentration positions of the peculiar points in aqueous and mutual solutions of acetone and isopropanol at a temperature of 25 °C. The concentration positions of contraction maxima are located at 0.25 for acetone solutions and 0.17 for isopropanol solutions. It has been shown that the maximum contraction value of acetone-2-propanol solutions is positive and does not exceed 0.004. This indicates the absence of clusters and microinhomogeneous structures in these solutions, allowing us to consider them as close to ideal. The special points of aqueous solutions of acetone and isopropanol are close to each other, at 0.064 and 0.05, respectively. In this case, the maximum contraction value of aqueous solutions of acetone exceeds that of aqueous solutions of 2-propanol by no more than 25%. The concentration positions of the contraction maxima are located at 0.25 for acetone solutions and 0.17 for isopropanol solutions.

BackgroundAcetone and tetrahydrofuran are commonly used as solvents in the chemical industry. The separation of acetone–tetrahydrofuran mixtures is often faced in the pharmaceutical and special chemical industries. As acetone and tetrahydrofuran can form a minimum azeotrope, they cannot be separated by conventional distillation. But acetone and tetrahydrofuran are important organic raw materials and solvents, so the mixture should be separated for reuse.ResultsThe process of continuous extractive distillation was used to separate the mixture of acetone (62% mass fraction) and tetrahydrofuran (38% mass fraction) using butyl ether as solvent. The characteristics of the continuous extractive distillation were simulated via ASPEN and experiments also showed the feasibility of separating the acetone–tetrahydrofuran mixture. Effects of the reflux mass ratio (R), mixture feed stage (FS), the solvent feed stage (SFS) on the extractive distillation column and the volume ratio of solvent to mixture (S/F) on the distillate mass fraction of acetone and bottom product mass fraction of acetone were investigated. The results of the extractive distillation simulation were verified by experiment data. With the following operation conditions for the extractive distillation column: number of theoretical plates 53; mixture feed at 24th plate; solvent feed at 7th plate, solvent to mixture ratio 3 and reflux mass ratio 3, the mass fraction of acetone in the distillate can reach 99%.ConclusionsThe process of continuous extractive distillation using butyl ether as solvent can separate the acetone–tetrahydrofuran mixture. The solvent to mixture ratio and reflux mass ratio are important factors that affect the mass fraction of the product. © 2013 Society of Chemical Industry

Increasing energy demand in the world leads to more electricity generation mainly at fossil fuel power plants. Greenhouse gases are thus produced and mostly emitted to the atmosphere directly, resulting in global warming and climate change. Carbon dioxide is believed to be a main pollutant among greenhouse gases responsible from global warming. Conventional systems using mostly amine solutions to capture carbon dioxide at the source have some disadvantages, and alternatives are constantly being searched. In this work, a benign system of aqueous calcium acetate solution was investigated for this purpose. Calcium acetate is easy to produce, relatively cheap, environmentally friendly, nonhazardous, and noncorrosive. These properties make it a great alternative for use in capturing carbon dioxide. This absorption process is accompanied by chemical reaction. Therefore, the reaction kinetics needs to be investigated before its use in absorbers. A stirred cell reactor was used in the experiments using aqueous calcium acetate solution of different concentrations (2‐20% w/w) and different carbon dioxide concentrations in gas mixtures (4.5‐100% v/v dry carbon dioxide) at temperatures ranging from 286 to 352 K. The Gibbs free energy change for the overall reaction between carbon dioxide and aqueous calcium acetate solution was found to be –2.75 kJ/mol that shows the reaction is exergonic and occurs spontaneously. It was also found out that the reaction is pseudo–first order with respect to carbon dioxide which was also proven by calculating the Hatta number. Activation energy and Arrhenius (frequency) constant were also determined experimentally.

The chemical absorption of carbon dioxide by a laminar jet of ethylenediamine has been studied at 25.5°C under pseudo‐first‐order kinetic conditions. The reaction was found to be second‐order with a rate constant of 1.0 x 105 1/g. mole sec. Equilibrium calculations at 18°C indicate that the partial pressure of carbon dioxide is very low, even over highly carbonated ethylenediamine solutions. The effects of amine concentration and carbonation ratio on the physical solubility and diffusivity of carbon dioxide in solution were inferred from corresponding results for nitrous oxide

A comparative study of the photokinetic behaviors of aliphatic alcohols and related substrates was made for the photooxidation with uranyl ions. Ethylene glycol, glucose, sucrose and some other substrates showed abnormal results compared to a series of simple aliphatic alcohols: the photoredox quantum yields φ for the former substrates decreased with substrate concentration (at their higher concentrations) and temperature rise, in contrast to simple aliphatic alcohols. In aqueous acetone solution φ increased with the increase in acetone content, the reaction constant ρ* being more negative than in aqueous solution. In 40% aqueous acetone solution the φ values for simple aliphatic alcohols varied in a complicated way with temperature. The abnormal results were interpreted in terms of the relative importance of physical quenching competing with the primary chemical process.

For practical applications of gas hydration (formation of gas hydrates) in environmental and technological processes, considerable knowledge regarding the thermodynamic stability and structural features of these hydrates, as well as the occupation behavior of specific components of gas mixtures within them, is essential. Herein, the hydrate phase equilibria of a system comprising CH4/CO2/N2 (55/40/5) + aqueous acetone solutions (1, 3, and 5.56 mol %) were determined in the temperature range 273–285 K and under pressures up to 4.5 MPa. Gas compositions in the hydrate phase were also obtained by evaluating the following variables: (1) hydrate-formation temperature and pressure, (2) concentration of acetone, and (3) type of hydrate structure: (a) structure I or (b) structure II. The crystal structures of the gas hydrates formed from the acetone and CH4 + CO2 + N2 mixture gas were also evaluated by both X-ray diffraction and Raman spectroscopy. In addition, structural identification of the CH4 + CO2 + N2 + acetone hydrates formed by varying the concentration of acetone (0, 1, 3, and 5.56 mol %) was performed. Further evaluation of the temperature-dependent occupation behavior of CH4 and CO2 in structure II hydrate cages in the temperature range 150–290 K indicates that CH4 and CO2 gradually escaped from the hydrate frameworks with increasing temperature, up to 255 K, at which point the CH4 + CO2 + N2 + acetone hydrate completely decomposed.

Methane hydrate exists in huge amounts in certain locations, in sea sediments and the geological structures below them, at low temperature and high pressure. Production methods are in development to produce the methane to a floating platform. There it can be reformed to produce hydrogen and carbon dioxide, in an endothermic process. Some of the methane can be burned to provide heat energy to develop all needed power on the platform and to support the reforming process. After separation, the hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform can be separated from other gases and then sequestered in the sea as carbon dioxide hydrate. In this way, hydrogen is made available without the release of carbon dioxide to the atmosphere, and the hydrogen could be an enabling step toward a world hydrogen economy.

The present article reports the development of a novel electrochemical carbon dioxide minisenso based on hemoglobin which is incorporated into self‐assembled bilayer lipid membranes (s‐BLMs) on a metal support. The presence of carbon dioxide in solution was found to modulate the ion conductivity of BLMs containing hemoglobin, when using a lipid composition containing egg phosphatidylcholine (egg PC) and dipalmitoylphosphatidic acid (DPPA). The use of stabilized metal‐supported BLMs has allowed the electrochemical investigation of the reversibility of the response to carbon dioxide and of hemoglobin binding to lipid membranes. The effects of hemoglobin concentration, composition of BLMs in DPPA and pH on the sensitivity of the response were examined. The sensor provides the advantages of fast response times (on the order of ca. 10 s) to alterations of carbon dioxide concentration, low detection limits (ca. 0.4 × 10−6 M) and capability of analysing small sample volumes. Semisynthetic platelet‐activating factor (PAF; 1‐O‐alkyl‐2‐acetyl‐sn‐glyceryl‐3‐phosphorylcholine, AGEPC) was found to improve the response characteristics of the carbon dioxide sensor (i.e., decrease of the detection limit to nM range and increase of the dynamic range of carbon dioxide determination). The biosensor was routinely mechanically stable and functional for over 48 h. During this time it showed reproducible sensitivity and response to a given concentration of carbon dioxide in solution.