Showing papers on "Carbonic acid published in 2016"

Degradation of well cement in HPHT acidic environment: Effects of CO2 concentration and pressure

Abstract: Application of cement in high-pressure high-temperature (HPHT) carbonic acid containing environment poses serious well integrity issues. HPHT condition facilitates acid attack on well cement resulting in the loss of structural integrity. This paper presents the results of an experimental study conducted to investigate the effects of CO 2 concentration (mole fraction) and pressure on mechanical integrity of degraded Classes G and H cements after exposure to carbonic acid environment. Cement cores were prepared and aged in autoclave filled with 2% NaCl solution saturated with mixture of methane and carbon dioxide gases for durations up to 28 days. Experiments were performed by varying test pressure and CO 2 concentration. Compressive strength, porosity and permeability of unaged and aged samples were measured to assess the level of degradation. Besides, analysis of the mineralogy, the microstructure, and the morphology of specimens was conducted. After exposure, incomplete hydration of clinker materials, carbonation of cement hydrates, leaching of by-products of carbonation, and structural transformation of amorphous calcium silicate hydrate to its crystalline form were observed. Generally, compressive strength increased with CO 2 concentration due to carbonation of calcium hydroxide (CH) and calcium silicate hydrate (C-S-H). Correspondingly, porosity and permeability decreased. Furthermore, degree of degradation is greatly influenced by pressure.

The fate of carbon dioxide in water-rich fluids under extreme conditions.

Abstract: Investigating the fate of dissolved carbon dioxide under extreme conditions is critical to understanding the deep carbon cycle in Earth, a process that ultimately influences global climate change. We used first-principles molecular dynamics simulations to study carbonates and carbon dioxide dissolved in water at pressures (P) and temperatures (T) approximating the conditions of Earth's upper mantle. Contrary to popular geochemical models assuming that molecular CO2(aq) is the major carbon species present in water under deep Earth conditions, we found that at 11 GPa and 1000 K, carbon exists almost entirely in the forms of solvated carbonate ([Formula: see text]) and bicarbonate ([Formula: see text]) ions and that even carbonic acid [H2CO3(aq)] is more abundant than CO2(aq). Furthermore, our simulations revealed that ion pairing between Na+ and [Formula: see text]/[Formula: see text] is greatly affected by P-T conditions, decreasing with increasing pressure at 800 to 1000 K. Our results suggest that in Earth's upper mantle, water-rich geofluids transport a majority of carbon in the form of rapidly interconverting [Formula: see text] and [Formula: see text] ions, not solvated CO2(aq) molecules.

How Acidic Is Carbonic Acid

Abstract: Carbonic, lactic, and pyruvic acids have been generated in aqueous solution by the transient protonation of their corresponding conjugate bases by a tailor-made photoacid, the 6-hydroxy-1-sulfonate pyrene sodium salt molecule. A particular goal is to establish the pKa of carbonic acid H2CO3. The on-contact proton transfer (PT) reaction rate from the optically excited photoacid to the carboxylic bases was derived, with unprecedented precision, from time-correlated single-photon-counting measurements of the fluorescence lifetime of the photoacid in the presence of the proton acceptors. The time-dependent diffusion-assisted PT rate was analyzed using the Szabo–Collins–Kimball equation with a radiation boundary condition. The on-contact PT rates were found to follow the acidity order of the carboxylic acids: the stronger was the acid, the slower was the PT reaction to its conjugate base. The pKa of carbonic acid was found to be 3.49 ± 0.05 using both the Marcus and Kiefer–Hynes free energy correlations. This ...

Ammonia as an efficient catalyst for decomposition of carbonic acid: a quantum chemical investigation

Abstract: Electronic structure calculations using M06-2X, MP2 and CCSD(T) methods have been employed to show ammonia as an efficient catalyst for decomposition of carbonic acid. The results predict that ammonia can catalyze the reaction as both a monomer and dimer, the latter being more efficient as it makes the reaction nearly barrierless. It has been shown that monomeric ammonia makes the process significantly faster compared with the water monomer (the rate constant being 104 to 105 times higher) as well as the water dimer (10–20 times faster). Dimeric ammonia has been shown to be a better catalyst than its monomeric counterpart (the rate constant being 103 to 104 times higher). Its efficiency as a catalyst was found to be close to that of formic acid. Owing to the fact that ammonia is present in the Earth's atmosphere at a significant trace level, it is expected to play a nontrivial, if not pivotal, role in atmospheric chemistry as a catalyst.

Stable solid and aqueous H2CO3 from CO2 and H2O at high pressure and high temperature.

Abstract: Carbonic acid (H2CO3) forms in small amounts when CO2 dissolves in H2O, yet decomposes rapidly under ambient conditions of temperature and pressure. Despite its fleeting existence, H2CO3 plays an important role in the global carbon cycle and in biological carbonate-containing systems. The short lifetime in water and presumed low concentration under all terrestrial conditions has stifled study of this fundamental species. Here, we have examined CO2/H2O mixtures under conditions of high pressure and high temperature to explore the potential for reaction to H2CO3 inside celestial bodies. We present a novel method to prepare solid H2CO3 by heating CO2/H2O mixtures at high pressure with a CO2 laser. Furthermore, we found that, contrary to present understanding, neutral H2CO3 is a significant component in aqueous CO2 solutions above 2.4 GPa and 110 °C as identified by IR-absorption and Raman spectroscopy. This is highly significant for speciation of deep C-O-H fluids with potential consequences for fluid-carbonate-bearing rock interactions. As conditions inside subduction zones on Earth appear to be most favorable for production of aqueous H2CO3, a role in subduction related phenomena is inferred.

In Situ Carbonic Acid from CO2: A Green Acid for Highly Effective Conversion of Cellulose in the Presence of Lewis acid

Abstract: Converting cellulose to renewable energies and chemicals is the most promising and sustainable route to solving the crisis of fossil fuel resources. Up to now, however, it is still a big challenge to effectively transform recalcitrant cellulose into targeted compounds. For the first time, this study proposes a new and highly effective catalysis system with a synergy effect to convert cellulose into formic acid and levulinic acid simultaneously by using in situ carbonic acid from CO2 as a green acid in the presence of CrCl3. The synergy effect of in situ carbonic acid and CrCl3 could highly effectively hydrolyze cellulose to glucose, isomerize glucose to fructose, dehydrate fructose to HMF, and rehydrate HMF to formic acid and levulinic acid in a one-pot way. Here, 49% formic acid and 32% levulinic acid could be obtained from cellulose at a moderate condition. Our results demonstrated that this new catalysis system is comparable to other catalysis systems, and in situ carbonic acid can be used as a low-cos...

Effects of inorganic carbon and pH on growth kinetics of Synechocystis sp. PCC 6803

Abstract: Growth pH and the concentration of bioavailable inorganic carbon (Cib) are two essential factors controlling the rate of photoautotrophic growth of microalgae. We developed a novel experimental strategy to determine the effects of pH and Cib independently by a pH-Stat and the use of NH4NO3 as the N source. We grew Synechocystis sp. PCC 6803 at pH values of 7.5, 8.5, and 9.5, with a stable inorganic carbon (Ci) concentration ranging from 0.08 to 3.3 mM, and a light intensity of ~ 202 μE m− 2 s− 1. Among the pH values tested, pH 8.5 supported the highest maximum specific growth rate (μmax), 2.4/day that was statistically larger than μmax values at pH 7.5 and 9.5, about 2.0/day. Using the sum of dissolved CO2, carbonic acid, and bicarbonate (i.e., Cib) to fit Monod kinetics, we found the half-maximum-rate concentrations (KCib) were in a narrow range: 86 μM for pH 8.5, 84 μM for pH 7.5, and 96 μM for pH 9.5, values that were statistically indistinguishable. All KCib values were small, indicating that Synechocystis has a high affinity for Cib, attaining μmax by ~ 1 mM. Analyzing the kinetics individually for each Ci species supports that bicarbonate best represented the rate of Ci uptake.

Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics.

Abstract: Protonation by carbonic acid H2CO3 of the strong base methylamine CH3NH2 in a neutral contact pair in aqueous solution is followed via Car–Parrinello molecular dynamics simulations. Proton transfer (PT) occurs to form an aqueous solvent-stabilized contact ion pair within 100 fs, a fast time scale associated with the compression of the acid–base hydrogen-bond (H-bond), a key reaction coordinate. This rapid barrierless PT is consistent with the carbonic acid-protonated base pKa difference that considerably favors the PT, and supports the view of intact carbonic acid as potentially important proton donor in assorted biological and environmental contexts. The charge redistribution within the H-bonded complex during PT supports a Mulliken picture of charge transfer from the nitrogen base to carbonic acid without altering the transferring hydrogen’s charge from approximately midway between that of a hydrogen atom and that of a proton.

Kinetics of carbonate mineral dissolution in CO2-acidified brines at storage reservoir conditions

Abstract: We report experimental measurements of the dissolution rate of several carbonate minerals in CO2-saturated water or brine at temperatures between 323 K and 373 K and at pressures up to 15 MPa. The dissolution kinetics of pure calcite were studied in CO2-saturated NaCl brines with molalities of up to 5 mol kg−1. The results of these experiments were found to depend only weakly on the brine molality and to conform reasonably well with a kinetic model involving two parallel first-order reactions: one involving reactions with protons and the other involving reaction with carbonic acid. The dissolution rates of dolomite and magnesite were studied in both aqueous HCl solution and in CO2-saturated water. For these minerals, the dissolution rates could be explained by a simpler kinetic model involving only direct reaction between protons and the mineral surface. Finally, the rates of dissolution of two carbonate-reservoir analogue minerals (Ketton limestone and North-Sea chalk) in CO2-saturated water were found to follow the same kinetics as found for pure calcite. Vertical scanning interferometry was used to study the surface morphology of unreacted and reacted samples. The results of the present study may find application in reactive-flow simulations of CO2-injection into carbonate-mineral saline aquifers.

Experimental investigation of the impact of rock dissolution on carbonate rock properties in the presence of carbonated water

Abstract: Carbon dioxide (CO2) storage in aquifers or injection to petroleum reservoirs for enhanced oil recovery purposes are the ways of mitigation of global warming. Dissolution of carbon dioxide in water forms carbonic acid. This acid would react with the carbonate components in carbonate rocks (i.e., CaCO3, MgCO3) and cause dissolution of salts thereafter changing carbonate rocks intrinsic properties. Dissolution changes the properties of carbonate rocks. To investigate these phenomena, two carbonate rock samples were saturated with brine and brought in contact with carbonated water for about 12 days. After each 72-h period, porosity, permeability, the mass of the cores and concentration of released ions in brine were measured. Concentrations of released ions were calculated by titration in each period. A considerable change on rock properties was observed. Porosity and permeability changes were about +8.09 and ±9.73 %, respectively, and core weight loss was about 0.82 Wt %. Besides, intensity of the concentration of released magnesium ions in brine with comparison to calcium ions indicates that the core samples are dolomite. The results of this study show that carbonate rock dissolution should be considered in water alternative CO2 injection, carbonated water injection and CO2 storage projects.

Ocean Acidification: Investigation and Presentation of the Effects of Elevated Carbon Dioxide Levels on Seawater Chemistry and Calcareous Organisms

Abstract: Ocean acidification refers to the process by which seawater absorbs carbon dioxide from the atmosphere, producing aqueous carbonic acid. Acidic conditions increase the solubility of calcium carbonate, threatening corals and other calcareous organisms that depend on it for protective structures. The global nature of ocean acidification and the magnitude of its potential impact on marine ecosystems and the industries they support make it an important and engaging topic to explore in the undergraduate laboratory. In this multiweek experiment, designed for second year analytical and environmental chemistry courses, artificial seawater samples containing pieces of seashell or coral were prepared. One sample was pressurized with carbon dioxide and stirred for 1 week, while the other was stirred without carbonation. Mass and pH measurements and carbonate, bicarbonate, calcium(II), and magnesium(II) titrations were performed on samples before and after treatment. Through data analysis and a rigorous consideration...

Formation of Carbonic Acid in Impact of CO2 on Ice and Water

Abstract: A new mode of formation is proposed for carbonic acid in the atmosphere. It involves impact of vibrationally excited gas-phase CO2 molecules on water or ice particles. This is a first mechanism that supports formation on ice as well as on liquid water surfaces. Results of ab initio molecular dynamics simulations are presented on collisions of CO2 with (H2O)n clusters (n = 1, 4, 8, 12). Efficient formation of carbonic acid is seen with product lifetimes exceeding 100 ps. The reaction is feasible even for collision of CO2 with a single water molecule but in a different mechanism than for larger clusters. For clusters, the transition state shows charge separation into H3O+···HCO3–, which transforms into neutral carbonic acid as the product, hydrated by the remaining waters. Possible atmospheric implications of the results are discussed.

In vitro Evaluation of the Efficacy of 2% Carbonic Acid and 2% Acetic Acid on Retrieval of Mineral Trioxide Aggregate and their Effect on Microhardness of Dentin.

Abstract: INTRODUCTION In this in vitro study, the efficacy of 2% carbonic acid and 2% acetic acid on the surface, microhardness of white mineral trioxide aggregate (MTA) and dentin after 1 day of setting and 21 days of setting of MTA is measured. MATERIALS AND METHODS Tooth molds were made using 60 single-rooted premolars by slicing them to 4 mm in the mid-root region. White MTA (Angelus) was mixed and packed in the molds. Three experimental groups were formed and exposed to 2% carbonic acid, 2% acetic acid, and saline for 10 minutes on 1 and 21 days of setting respectively. Vickers hardness test of white MTA and dentin was done before and after exposure. Data were subjected to analysis of variance (ANOVA) and post hoc tests. RESULTS The results show that 2% acetic acid was significantly effective in reducing the microhardness of white MTA compared to 2% carbonic acid and saline on exposure for 10 minutes. CONCLUSION The results of the present study indicate that 2% acetic acid has maximum efficacy in reducing the surface microhardness of partial and completely set MTA, followed by 2% carbonic acid. CLINICAL SIGNIFICANCE The following study will help find an adjunct for retrieval of MTA, which was found difficult with the existing methods.

Method for preparing of carbonate minerals and removing acidic gases from exhaust fumes of ship and a device therefor

Abstract: The present invention relates to a method for manufacturing carbonate ore and removing acidic gas from ship exhaust gas and an apparatus therefor, and more particularly, to a method and apparatus, wherein in a single reactor, an electrolysis of a NaCl-containing material for generating a NaOH aqueous solution and a reaction between a NaOH aqueous solution and a carbon dioxide-containing acidic gas for generating negative ions of carbonic acid or bicarbonate are performed together, and then the negative ions of carbonic acid or bicarbonate are introduced into a mineralization reactor together with marine water to thereby carbonate ore, and thus carbon dioxide-containing acidic gas is mineralized and carbonized in a more compact scale on a ship and the acidic gas can be removed at the same time

Production method of light magnesium carbonate

Abstract: The invention discloses a production method of light magnesium carbonate The production method comprises the following steps of by using magnesium which is stacked for many years and is carbonized to generate magnesium carbonate components, magnesium alloy flux residues, and high-concentration CO2 waste gas exhausted from chemical fertilizer industry, petroleum industry, biological and chemical industry and the like, as raw materials, forming carbonic acid under high pressure, converting and dissolving magnesium carbonate in residues so that the magnesium carbonate is converted into water-soluble magnesium bicarbonate, enabling the water-soluble magnesium bicarbonate and other water-insoluble impurities such as calcium carbonate to be subjected to filtration and separation in a vacuum filter, then performing pyrolysis, and performing drying to obtain finished products; and when chlorine salt and magnesium ions in filtrate do not have a recovery value, discharging the chlorine salt and the magnesium ions into a circulation fluid tank for recovery utilization

Synthesis of macrocyclic tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane in carbonic acid solution

Abstract: The possibility to synthesize stereoregular tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane (tris-cis-tris-trans-[PhSi(O)OH]12) in an inorganic liquid medium – aqueous carbonic acid solution – was shown. The interaction of polyhedral phenylcoppersodiumsiloxane, {[(C6H5Si(O)O−]12(Cu2+)4(Na+)4}*(L)m (L = Bun OH, H2O), with carbonic acid can be considered as a new ‘green’ method to obtain functional organosiloxane macrocycles. In contrast to the known methods, no organic solvents were used during the reaction. The identification of the structure of the end compound was performed by means of NMR and Infrared spectroscopy as well as X-ray crystallography.

The Simultaneous Determination of Silicic, Boric and Carbonic Acids in Natural Water via Ion-Exclusion Chromatography with a Charged Aerosol Detector

Abstract: The simple and simultaneous determination of silicic, boric and carbonic acids was made using ion-exclusion chromatography (IEC) and a Corona™ charged aerosol detector (C-CAD). Silicic and boric acids were separated by the column packed with a weakly acidic cation-exchange resin in H+-form and ultra-pure water eluent, and the detector responses were improved by the addition of acetonitrile to eluent. Under the optimized conditions, the simultaneous determination of weak inorganic acids, except for carbonic acid, was successfully performed. When the conversion column packed with a strong acidic cation-exchange resin in Na+- or K+-form was inserted between the separation column and the detector, weak inorganic acids including carbonic acid could be detected by the C-CAD. The calibration curves were linear in the range of 0.5–10 mg·L−1 as Si for silicic acid (r2 = 0.996), 10–100 mg·L−1 as B for boric acid (r2 = 0.998) and 1.3–21 mg·L−1 as C for carbonic acid (r2 = 0.993). The detection limits based on three times the standard deviation were 0.03 mg·L−1 as Si for silicic acid, 0.40 mg·L−1 as B for boric acid and 0.08 mg·L−1 as C for carbonic acid. This method was applicable to river, hot spring and drinking water.

Regeneration cycling method of flue gas desulfurizing agent

Abstract: The invention relates to a regeneration cycling method of a flue gas desulfurizing agent, which comprises the following steps: filling an exchange column with HCO3 type anion exchange resin by a wet method, passing a sodium bicarbonate desulfurization product, namely a sodium sulfate and sodium bicarbonate mixed solution through a resin bed layer, and collecting a sodium bicarbonate effluent at the column bottom; crystallizing the effluent to obtain sodium bicarbonate, thereby finishing regeneration of a sodium bicarbonate desulfurizing agent; and leaching the ion exchange resin out of work, which is contained in the exchange column, with deionized water, ammonium bicarbonate or carbonic acid solution for regeneration, and washing the resin with deionized water to obtain HCO3 type resin. According to the method, the anion exchange resin is introduced to finish the regeneration of the sodium bicarbonate desulfurizing agent, the loaded resin can be recycled after regeneration, the resin regeneration effluent has commercial value, no waste residue or waste liquid is discharged, the green economic property and utilization rate of the process are improved, and a reasonable way is provided for recycling.