CO2 In Aqueous Solutions Research Articles

Living Atomically Dispersed Cu Ultrathin TiO2 Nanosheet CO2 Reduction Photocatalyst.

Supported atomically dispersed metals are proving to be efficacious photocatalysts for CO2 reduction to solar fuels. While being atom efficient, they suffer from being noble, rare, and costly (Pt, Pd, Au, Ag, Rh) and lacking in long‐term stability. Herein, all of these problems are solved with the discovery that atomically dispersed Cu supported on ultrathin TiO2 nanosheets can photocatalytically reduce an aqueous solution of CO2 to CO. The atomically dispersed Cu can be recycled in a straightforward procedure when they become oxidatively deactivated. This advance bodes well for the development of a solar fuels technology founded on abundant, low‐cost, nontoxic, atomically dispersed metal photocatalysts.

Physicochemical Properties of the System N,N-Dimethyl-dipropylene-diamino-triacetonediamine (EvA34), Water, and Carbon Dioxide for Reactive Absorption

Aqueous solutions of N,N-dimethyl-dipropylene-diamino-triacetonediamine (EvA34) are promising solvents for CO2 capture. Therefore, in the present work, a comprehensive experimental study was carried out to determine data on physicochemical properties of EvA34 and its mixtures with H2O and CO2. The liquid density and the dynamic viscosity were studied for pure EvA34, as well as for unloaded and CO2-loaded aqueous solutions of EvA34. The liquid heat capacity was studied for pure EvA34 and unloaded aqueous solutions of EvA34. Furthermore, data on the vapor pressure of pure EvA34 was recorded. The pH value was measured for unloaded and CO2-loaded aqueous solutions of EvA34, and the dissociation constants of EvA34 were determined from titration curves. Moreover, data on the solubility of CO2 in aqueous solutions of EvA34 and data on the CO2-containing species in the liquid phase of these solutions were recorded. Most of the new data were taken at temperatures between 293 and 393 K. The mass fraction of EvA34 i...

One-Pot Multienzymatic Transformation of NH3, CO2, and Ornithine into the Organic Nitrogen Plant Fertilizer Citrulline Using a Single Recombinant Lysate of E. coli

Biocatalytic transformation of carbamate formed readily from CO2 and NH3 provides attractive green routes for mitigation of these important environmental pollutants. Accordingly, a coupled-enzyme system was developed for the one-pot production of citrulline through carbamoylation of ornithine in aqueous solutions of CO2 and NH3. Hyperthermophilic ornithine carbamoyltransferases are produced recombinantly in E. coli with carbamate kinases known to have a propensity for carbamoyl phosphate synthesis. Importantly, in vitro biocatalysis is carried out by E. coli cell lysate prepared through coexpression of the required recombinant enzymes in a single bacterial culture, greatly reducing limitations normally associated with protein production and purification. Acetate kinase that is endogenous in the lysate also recycles the required ATP cofactor, which would otherwise have been required in costly stoichiometric amounts. Recombinant lysates catalyze the production of carbamoyl phosphate with substoichiometric A...

Experimental Study of Density, Viscosity and Equilibrium Carbon Dioxide Solubility in Some Aqueous Alkanolamine Solutions

In this work, equilibrium solubility of CO2 in aqueous blends of different amines is examined. The amines used are methyldiethanolamine (MDEA), N,N-dimethylaminoethanol (DMAE), N,N-diethylaminoethanol (DEAE), 2-(2-aminoethylamino)ethanol (AEEA), and 3-methylamino propylamine (MAPA). New equilibrium solubility data for CO2 in aqueous solutions of DMAE + MAPA, DMAE + AEEA, MDEA + MAPA, MDEA + AEEA, DEAE + MAPA and DEAE + AEEA over a range of low pressures are obtained. Each of the solutions contains 40 wt% of a tertiary amine (DMAE, MDEA, DEAE) and 5 wt% of a primary/secondary amine (MAPA, AEEA). The experimental temperature was set to 313.15 K and the measured CO2 loading was in the range of 0.274–4.563 (mol CO2 per kg of solution). In order to make a better comparison, viscosities and densities of the amine solutions were also measured at 303.15–353.15 K. Experiments show that the aqueous DMAE + MAPA blend has the highest absorption capacity, and at the same time, its viscosity and density are in a desirable range.

An accurate model for the solubilities of quartz in aqueous NaCl and/or CO2 solutions at temperatures up to 1273 K and pressures up to 20,000 bar

A simple and general relation between the solubility of quartz and the density of solution is derived rigorously. Based on this relation and the pressure-volume-temperature-composition model of Mao et al. (2010), an accurate density-based model is developed for the solubility of quartz in aqueous NaCl and/or CO2 solution up to 1273 K and 20,000 bar. The model parameters are regressed with carefully assessed experimental data. Compared to a large number of experimental data, the average absolute deviations of calculated quartz solubilities in water, aqueous NaCl solution and aqueous CO2 solution are 5.50%, 5.24% and 7.55%, respectively, which are within experimental uncertainties, and are much better than the most competitive models in literature. Particularly, this model can predict the experimental solubility of quartz in aqueous NaCl and CO2 solution without using any additional parameter. This model can be incorporated in software for accurate geochemical modeling. The strategy of this model should be promising for the solubilities of other minerals in water or multicomponent aqueous solutions.

SDS‐modified Nanoporous Silver as an Efficient Electrocatalyst for Selectively Converting CO2 to CO in Aqueous Solution

Summary of main observation and conclusionSelectively electrochemical conversion of CO2 into organic fuel using renewable electricity is one of the most sought‐after processes. In this paper, we report the electrochemical reduction of CO2 (CO2RR) on the nanoporous Ag electrodes made of compacted Ag nanoparticles (AgNPs), which were prepared by one‐step reduction in the water phase with or without the surfactant sodium dodecyl sulfate (SDS). The scanning electron microscope (SEM) characterizations show that the compacted Ag electrodes have the nanoporous morphology formed by stacking AgNPs. Compared with the nanoporous Ag electrode without SDS modification (C‐AgNPs), the SDS‐modified AgNPs electrode (C‐AgNPs‐SDS) is highly effective in improving selective CO production in a wide range of potentials (–0.69 V — –1.19 V, vs. RHE), with a Faradaic efficiency of 92.2% and a current density of –8.23 mA·cm–2 for CO production at –0.79 V (vs. RHE). C‐AgNPs‐SDS is also catalytically stable with only less than 7% deactivation after 8 h of continuous electrolysis.

Photocatalytic Reverse Semi-Combustion Driven by Ionic Liquids.

The simple photolysis of CO2 in aqueous solutions to generate CO and/or hydrocarbons and derivatives in the presence of a catalyst is considered to be a clean and efficient approach for utilizing CO2 as a C1 building block. Despite the huge efforts dedicated to this transformation using either semiconductors or homogeneous catalysts, only small improvements of the catalytic activity have been achieved so far. This article reports that simple aqueous solutions of organic salts-denominated as ionic liquids-can efficiently photo-reduce CO2 to CO without using photosensitizers or sacrificial agents. The system relies on the formation of the [CO2 ].- intermediate through homolytic C-C bond cleavage in a cation-CO2 adduct of imidazolium-based ionic liquids (ILs). The system continuously produced CO up to 2.88 mmol g-1 of IL after 40 h of irradiation by using an aqueous solution of 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIm.CO2 ) IL, representing an apparent quantum yield of 3.9 %. The organophotocatalytic principles of our system may help to develop more simple and efficient organic materials for the production of solar fuels from CO2 under mild conditions, which represents a real alternative to those based on semiconductors and homogeneous metal-based catalysts.

Visible light photocatalytic conversion of CO2 in aqueous solution using 2D-structured carbon-based catalyst-coated β,γ-AgI nanocomposite

Solar-light-driven carbon-based photocatalysts have been widely used for CO2 conversion reaction. In this work, silver iodide (AgI)-decorated 2D structure graphitic carbon nitride (GCN) composite was prepared using nitrogen-rich melamine precursor and the characterization results reveal that the mixture of hexagonal wurtzite and cubic phases of β,γ-AgI are incorporated on GCN surface. Consequently, the photoconversion of CO2 over AgI/GCN composite was tested under visible light irradiation in triethanolamine medium. The main products from CO2 conversion were methane, acetone and ethanol. Besides, the effects of metal AgI loading (0.5–1.5%), the amount of photocatalyst (1–4 g/L) and irradiation time for CO2 photoconversion were evaluated. Furthermore, the charge separation mechanism associated with the AgI/GCN composite for CO2 photoconversion was also discussed.

CO2 Corrosion Behavior of Calcite-Covered API 5L X52 Carbon Steel in Aqueous Solutions

The CO2 corrosion of API 5L X52 steel in the presence and absence of calcite scale has been investigated. The scale was precipitated from a supersaturated solution at temperatures of 25 and 80 °C. The crystalline phase, cross section and surface morphologies of scale were studied by x-ray diffraction and scanning electron microscopy, respectively. It was found that the scale deposit mostly consisted of calcite. The corrosion behavior of bare and calcite-covered samples was investigated by electrochemical impedance spectroscopy and cyclic polarization techniques in aqueous CO2 solutions at 30, 50 and 70 °C. The presence of calcite scale on carbon steel surface decreased the adsorption of intermediate corrosion products as the scale uniformly covered the bare surface which resulted in reduction of general CO2 corrosion rate. The results of cyclic polarization tests revealed that the bare and calcite-covered samples were not susceptible to localized CO2 corrosion under conditions studied in this research.

Influence of Cr content on corrosion performance of middle Cr alloy steel in CO2 environment

The corrosion behavior of three medium-Cr alloys in CO2 aqueous solution environment was studied by high temperature autoclave accelerated test and electrochemical means (including micro-potential test). In this environment, the corrosion rate of the 5Cr sample was 1.5023 mm/a, 7Cr was 0.2471 mm/a, and 9Cr was 0.0540 mm/a. The CO2 corrosion product film consisted of two layers. The inner film was amorphous FeCO3 and Cr(OH)3, and the outer layer was granular FeCO3 and CaCO3. The dense inner film was rich in Cr, which provided effective protection for the tested steel in the CO2 corrosive environment. Increasing the Cr element content helped to increase the self-corrosion potential of the steel, reduced the corrosion current, and helped to improve the corrosion resistance of the steel. On the other hand, the increase of Cr content inhibited the transformation of pearlite, the pearlite content decreased, the proportion of acicular ferrite increased, and the microstructure was more uniform and single. Meanwhile the uniform microstructure reduced the potential difference between different regions, and the corrosion resistance of steel was improved.

Comparative Study between Pristine Ag and Ag Foam for Electrochemical Synthesis of Syngas with Carbon Dioxide and Water

The electrosynthesis of syngas (H2 + CO) from CO2 and H2O can reduce greenhouse gas emissions and address the energy crisis. In the present work, silver (Ag) foam was employed as a catalytic electrode for the electrochemical reduction of CO2 in aqueous solution to design different syngas ratios (H2:CO). In addition to H2 and CO, a small amount of formic acid was found in the liquid phase. By contrast, the planar polycrystalline Ag yields CO, formic acid, methane and methanol as the carbon-containing products. During the potential-controlled electrolysis, the Ag foam displayed a relatively higher activity and selectivity in the electroreduction of aqueous CO2 to CO compared with its smooth surface counterpart, as evidenced by the lower onset potential, higher partial current density and Faradic efficiency at the same bias voltage. Moreover, the electrode remained stable after three successive cycles. Based on the characterization using X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, potential step determination and density functional theory calculations, superior performance was credited to the three-dimensional structure of Ag foam constructed with coral-like Ag particles, in which the numerous edge sites are beneficial for the stabilization of the surface adsorbed COOH species and the exposed {111} facets favor the desorption of adsorbed CO species.

Estimating speciation of aqueous ammonia solutions of ammonium bicarbonate: application of least squares methods to infrared spectra

The knowledge of the speciation and of the supersaturation of aqueous solutions of CO2 and NH3 is pivotal for the design and optimization of unit operations, e.g. absorption or crystallization, in the framework of ammonia-based CO2 capture systems.

The Impact of Field Measurements and Data-Handling Procedures on Carbonate- and Sulfide-Scale Prediction

Summary Carbonate and sulfide scales are directly coupled together and differ from other inorganic scales because they are intimately linked to the in-situ concentrations of carbon dioxide (CO2) and hydrogen sulfide (H2S), which influence the local pH and availability of reactive species. The CO2 in aqueous solutions has the most significant effect on the system pH, on the solution content of bicarbonate ion (HCO3–), and on the final alkalinity. However, the presence of H2S in the system also has a direct and important effect on the total-system alkalinity. When calcium carbonate deposition occurs in a depressurized aqueous fluid, the amount of scale (CaCO3) that forms depends on the initial (prescaling) solution alkalinity. Thus, the occurrence and severity of carbonate scale are linked to both the solution carbonate system (CO2/HCO3–/CO32–) and the sulfide system (H2S/HS–/S2–). In previous publications, we have described a rigorous work flow (step-by-step procedure) to accurately predict carbonate- and sulfide-scaling profiles from reservoir to separator using commonly available field data (Verri et al. 2017a). Although, with perfect data, the work flow is rigorous [i.e., it will correctly predict the types and amounts of scale that can occur in some carbonate systems (e.g., CaCO3, FeCO3, FeS)], the numerical results produced are, of course, subject to errors of different types. In this paper, we identify and describe three key categories of data and procedures that must be correctly gathered and used to obtain accurate carbonate- and sulfide-scale predictions: These relate to field measurements, data-handling procedures, choice of software, model equations, and parameters. Moreover, in this work, the impact of unreliable field measurements on the final carbonate and sulfide scaling profiles is estimated, with a specific focus on gas- and water-chemistry errors. By varying important parameters such as Ca2+ concentration and gas-phase CO2 and H2S, it is possible to assess the impact that errors in these measurements have on the final scale-prediction profiles. Because of the closely coupled nature of the carbonate and sulfide systems, it is essential to consider “groups” of variables that change together.

Heat of absorption of CO2 in aqueous N,N-diethylethanolamine + N-methyl-1,3-propanediamine solutions at 313 K

Abstract Differential heat of absorption of CO2 in aqueous solutions of N,N-diethylethanolamine (DEEA) and activated DEEA solutions up to a total concentration of 2 mol·L−1 was measured as a function of CO2 loading at 313.15 K using a reaction calorimeter. In order to analyze the performance of N-methyl-1,3-propanediamine (MAPA) as an activator, DEEA blended solutions containing 0.05, 0.1 and 0.2 mol·L−1 MAPA were studied. The heat of CO2 absorption in single DEEA solutions was unaffected by changing the DEEA concentration in the range of (0.5–2) mol·L−1. On the other hand, increasing the concentration of MAPA in aqueous amine mixtures of (DEEA + MAPA) raised the heat of absorption.

Convective‐Reactive CO2 Dissolution in Aquifers With Mass Transfer With Immobile Water

AbstractThe objective of this paper is to study the impact of immobile water, its fraction, and its mass transfer with the flowing region on efficiency of CO2 dissolution in aquifers with an immobile water zone. A continuum scale code is developed with underlying assumptions of spatially homogeneous and temporally invariable partitioning fraction of the porous media, first‐order mass transfer between the mobile and immobile zones, and simplified reaction of CO2 aqueous solution with calcium carbonate rock. Using ranges of values for Damköhler number (Da), fraction of the total pore volume, and mass transfer coefficient rate (α), 96 simulations are conducted. It is shown that due to a lower intensity of reaction in the mobile region, intermediate values of α serve as a threshold below which the mass transfer coefficient is not affecting the overall CO2 storage and above which overall CO2 storage increases as a function of mass transfer coefficient. Additionally, we found that (i) when α is high and geochemistry is intensive (high Da), the overall CO2 storage decreases with increase in fraction of mobile water. This is because CO2 storage through consumption of rock in immobile water with higher geochemistry is reduced. (ii) When α is high but Da is low, the system is effectively a single porosity medium with no chemistry‐influenced discrimination between mobile and immobile zones, and therefore, overall CO2 storage increases with fraction of mobile water. (iii) When α is low, the magnitude of Da does not influence the overall CO2 storage.

Reversible flocculation of nanoparticles by a carbamate surfactant

Fatty alkyldiamine readily reacts with CO2 in aqueous solution at pH 12 to reversibly form surface active carbamate species. The carbamate can be reverted to the amine by exposure to N2 and heat. In this work, a carbamate-based surfactant (Y12-carbamate) has been used to disperse and stabilize hydrophobic nanoparticles. This state could be regarded as the “on” state of a series of cycle. The nanoparticles were then flocculated when the carbamate groups were cleaved by exposure to N2 and heating, corresponding to the “off” state. In a subsequent cycle, the nanoparticles were re-dispersed by exposure to CO2, while the pH remained at 12. This cycle of re-dispersion and flocculation could be repeated two times without impairing the particle size. However, further cycles increased the particle size, indicating that all particles could not be completely re-dispersed. In addition, we also investigated the effect of pH on the colloidal stability with sodium Y12-carbamate, by measuring particle size and electrophoretic mobility. The results showed that pH strongly influenced the stability of the nanoparticles. Sodium Y12-carbamate stabilized the particles with a negative electrophoretic mobility at pH well above pKa whereas at pH close to pKa of Y12-amine (pKa = 9.0), the particles quickly flocculated, as a result of an ion-pair formation between Y12-ammonium and Y12-carbamate.

Corrosion behavior of 20# steel in aqueous CO2 solution under stratified gas-liquid two-phase flow condition

PurposeThis paper aims to investigate the corrosion rate, surface morphology and composition of corrosion products of 20# seamless steel in aqueous CO2 solution under stratified gas-liquid two-phase flow condition. The development of a corrosion products layer has also been discussed.Design/methodology/approachThe following methods were used: weight loss method, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction.FindingsThe corrosion rate curve presents an irregular zigzag change trend with a gradual increase in time. The peak value of the corrosion rate appears when the corrosion time is 4 h and 8 h. The corrosion products layer is composed of two sub-layers: the inner dense layer that is about 6 µm thick and the outer loose layer that is about 9 µm thick when the corrosion time is 8 h. The main corrosion product are FeCO3 and Fe2O3.Originality/valueThe atomic ratio of Fe/C/O is relatively stable for the inner dense layer, but changes in thickness for the outer loose layer. There is a densification stage after a loose corrosion products layer forms, and it is periodic.

A systematic approach for the thermodynamic modelling of CO2-amine absorption process using molecular-based models

The development of new amine systems for CO2 capture is a topic of high interest because of the limitations current aqueous amine systems have for capturing CO2 at large scale. Having a robust and systematic approach for describing the absorption of CO2 would help accelerating the discovery of high performance amine solvents. In this contribution, a molecular-based equation of state is applied to describe the absorption of CO2 in aqueous solutions of single and blended amines at conditions of relevance for post-combustion CO2 capture. A scheme of implicit reactions is used to describe the formation of carbamate and/or bicarbonate products resulting from the chemical reactions between CO2 and five amines of practical industrial interest. This procedure eliminates the need to specify the detailed equilibrium reactions and significantly reduces the number of parameters required to represent the absorption process. A maximum of two adjustable model parameters (one of which with a linear temperature dependence), optimised for a fixed amine concentration, suffices to represent the absorption of CO2 in aqueous solutions of single amines over a broad range of temperatures (298–413 K) and partial pressures of CO2 (0.1–1000 kPa). The extrapolation capabilities of the model are tested by predicting the absorption of CO2 in aqueous solutions of single amines for different amines concentrations (∼8.5–35 wt%), with modelling results showing good quantitative agreement with solubility, speciation and enthalpy of absorption data available in literature. Furthermore, without introducing any new model parameter, the absorption of CO2 in various amine blends is satisfactorily predicted by considering competing interactions for the reactive sites in the model of CO2. The developed models are then used to assess the CO2 capture performance of selected amine systems in terms of two key process parameters: solvent cyclic capacity and regeneration energy. Results for systems with the same total amine mass concentration show that the highest molar cyclic capacities are obtained for 30 wt% piperazine (0.45 molCO2.molAmine-1), whereas the greatest energy savings for solvent regeneration are estimated for 30 wt% methyldiethanolamine (2.3 GJ.tCO2-1). Moreover, two piperazine–promoted blends showed the potential for reducing up to ∼26% the energy consumption for solvent regeneration and separating up to ∼41% more CO2 in a molar basis when compared to the benchmark 30 wt% monoethanolamine. Altogether, these results demonstrate the feasibility of the developed approach as a reliable platform for the screening of amine solvents as function of key process parameters, and as a valuable tool for process modelling.

Modification of porphyrin/dipyridine metal complexes on the surface of TiO2 nanotubes with enhanced photocatalytic activity for photoreduction of CO2 into methanol

Abstract

Self-Inhibitory Electron Transfer of the Co(III)/Co(II)-Complex Redox Couple at Pristine Carbon Electrode.

Applications of conducting carbon materials for highly efficient electrochemical energy devices require a greater fundamental understanding of heterogeneous electron-transfer (ET) mechanisms. This task, however, is highly challenging experimentally, because an adsorbing carbon surface may easily conceal its intrinsic reactivity through adventitious contamination. Herein, we employ nanoscale scanning electrochemical microscopy (SECM) and cyclic voltammetry to gain new insights into the interplay between heterogeneous ET and adsorption of a Co(III)/Co(II)-complex redox couple at the contamination-free surface of electron-beam-deposited carbon (eC). Specifically, we investigate the redox couple of tris(1,10-phenanthroline)cobalt(II), Co(phen)32+, as a promising mediator for dye-sensitized solar cells and redox flow batteries. A pristine eC surface overlaid with KCl is prepared in vacuum, protected from contamination in air, and exposed to an ultrapure aqueous solution of Co(phen)32+ by the dissolution of the protective KCl layer. We employ SECM-based nanogap voltammetry to quantitatively demonstrate that Co(phen)32+ is adsorbed on the pristine eC surface to electrostatically self-inhibit outer-sphere ET of nonadsorbed Co(phen)33+ and Co(phen)32+. Strong electrostatic repulsion among Co(phen)32+ adsorbates is also demonstrated by SECM-based nanogap voltammetry and cyclic voltammetry. Quantitatively, self-inhibitory ET is characterized by a linear decrease in the standard rate constant of Co(phen)32+ oxidation with a higher surface concentration of Co(phen)32+ at the formal potential. This unique relationship is consistent not with the Frumkin model of double layer effects, but with the Amatore model of partially blocked electrodes as extended for self-inhibitory ET. Significantly, the complicated coupling of electron transfer and surface adsorption is resolved by combining nanoscale and macroscale voltammetric methods.