Aqueous Carbonate Solution Research Articles

Methanation of syngas over coral reef-like Ni/Al 2O 3 catalysts

Coral reef-like Ni/Al 2O 3 catalysts were prepared by co-precipitation of nickel acetate and aluminium nitrate with sodium carbonate aqueous solution in the medium of ethylene glycolye. Methanation of syngas was carried out over coral reef-like Ni/Al 2O 3 catalysts in a continuous flow type fixed-bed reactor. The structure and properties of the fresh and used catalysts were studied by SEM, N 2 adsorption-desorption, XRD, H 2-TPR, O 2-TPO, TG and ICP-AES techniques. The results showed that the coral reef-like Ni/Al 2O 3 catalysts exhibited better activity than the conventional Ni/Al 2O 3-H 2O catalysts. The activities of coral reef-like catalysts were in the order of Ni/Al 2O 3-673> Ni/Al 2O 3-573> Ni/Al 2O 3-473> Ni/Al 2O 3-773. Ni/Al 2O 3-673-EG catalyst showed not only good activity and improved stability but also superior resistance to carbon deposition, sintering, and Ni loss. Under the reaction conditions of CO/H 2 (molar ratio) = 1:3, 593 K, atmospheric pressure and a GHSV of 2500 h −1, CH 4 selectivity was 84.7%, and the CO conversion reached 98.2%.

Experimental study of concentration dependence of Ta2O5 and Nb2O5 solubility in the alkaline and carbonate solutions at T=550oC, P=500 bar and low oxygen fugacity (Co-CoO buffer)

This study is a continuation of long-term work to build a quantitative model of genesis of deposits of Ta, Nb and Li, connected with granites. Importance of the problem is the need to use the available experimental data to estimate quantitatively a possible role of hydrothermal transport and redeposition of tantalum and niobium under physical-chemical conditions typical for Ta and Nb deposits, generally connected with alkaline rocks. Earlier we investigated concentration and temperature dependence of the tantalum and niobium oxides solubility in the sodium alkaline and carbonate solutions in a wide range of temperature, compositions and concentrations of solutions at P=1000 bar [Kotova and Zaraisky, 2009; Zaraisky et al., 2009]. The choice of sodium specificity of the solutions is related to the fact, that Ta-Nb mineralization in lithium-fluoric granites (“apogranites”), alkaline granites, alkaline metasomatites, sienites and carbonates is closely associated with sodium metasomatism (albitization, ribektization, egirinization). In order to practically cover the entire range of conditions for the formation of Ta-Nb deposits the experimental studies of Та2О5 and Nb2O5 solubility were carried out in aqueous alkaline solutions at P=500 bar. The tantalum and niobium oxides- chemical reagents Та2О5 and Nb2O5, being the analogues of tantite and nioboxide, seldom occurring in nature, were used as initial material in the runs. The concentration dependence of the Та2О5 and Nb2O5 solubility at T=550 o C, P=500 bar in the solutions of Na2CO3 and NaOH with the concentration (0.01; 0.1; 0.5, 1.0 и 2.0 m) in the presence of oxygen buffer Co–CoO was studied. Run duration was 21 days. Experiments were performed on a hydrothermal line. The capsules and the container with buffer were sealed into cold-seal pressure vessel of Tuttle type with big working volume that gives possibility to isolate the capsules from the container with buffer. The same technique was used to study Та2О5 solubility in fluoride and chloride solutions. After the run, the quenched aqueous solutions and the solid products were separated using a centrifuge. The solutions were then analyzed using ICP/MS (Inductively Coupled Plasma Mass Spectrometry) and ICP/AES (Atomic Emission Spectroscopy) for Nb, Ta, Mn, and Fe and admixture elements Ti, W, and Sn,. The composition of the solid product was characterized using optical microscopy, X-ray diffraction, and electron microprobe analysis (Cam Scan MV 2300 (VEGA TS5130MM). Experimental data are shown in fig. 1, 2, 3 and 4. The Ta2O5 solubility isotherms was found to have a negative trend in all studied alkaline and carbonate solutions at P=1000 bar. The concentration dependence of the Та2О5 was found to be more complicated at P=500 bar. In NaOH solutions a pressure decrease from 1000 bar to 500 leads to a decrease of tantalum content by a factor of 1 between 0.01 and 0.05 m NaOH. However, the Ta2O5 solubility increases by a factor of 1 in aqueous solutions with NaOH concentrations of 1 m and greater (fig. 1). In the Na2CO3 solutions with decreasing pressure from 1000 bar to 500 the tantalum content decreases by a factor of 1 (fig. 2). Experimentally established fact of the weak solubility of tantalum oxide in aqueous alkaline and carbonate solutions is fundamentally important for understanding of genesis of Ta deposits. The experimental data show that, for the range of concentrations, temperatures and pressures considered in this study, the Ta2O5 solubility is very low with concentrations on the order of 10 -5 to 10 -7 m in aqueous alkaline and carbonate solutions. The investigations have shown that at such low concentrations it is difficult to speak about possibility of Ta hydrothermal transport by alkaline and carbonate solutions. In NaOH and Na2CO3 solutions oxide tantalum has incongruent solubility. As solid phases wonderfully cut crystals of Na-tantite Na2Ta4O11 with the hexaoctahedric form typical for pyrochloride are formed in 0.01 and 0.1m NaOH and

Synthesis and Electrical Conductivity of La1−xSrxAl0.9Mg0.1O3−δ (x = 0.1–0.4) Perovskite Solid Solution

Perovskite solid solution powders of (La1−xSrx)(Al0.9Mg0.1)O3−δ (x = 0.1−0.4) were prepared by a coprecipitation method using corresponding aqueous solutions and ammonium carbonate solution. The X-ray diffraction patterns for the compositions of x = 0.1−0.4 were identified as those of hexagonal LaAlO3 solid solutions. The bulk conductivity of (La0.6Sr0.4) (Al0.9Mg0.1)O3−δ by AC method at 1 V was independent of the oxygen partial pressure and 2.33 ×10−3 Scm−1 at 800°C, suggesting the oxide ion conduction. The activation energy of bulk conductivity was 111 kJmol−1 at 300–500 °C. The grain boundary conductivity increased from 2.02×10−6 Scm−1 at Po2 = 10−15 Pa to 1.11×10−5 Scm−1 at Po2 = 2.1×104 Pa at 800 °C. Hole conduction contributed to the increased conductivity. DC conductivity of (La0.6Sr0.4)(Al0.9Mg0.1)O3−δ depended on the applied voltage and temperature. In N2 atmosphere, hole conductivity overlapped oxide ion conductivity at a high applied voltage (E > 1 V) because of the chemical reaction between positively charged oxide vacancy and N2 gas (Vo·· + N2 → 2No′ + 4h·).

Liquid–Liquid Equilibrium for Fuel Oxygenate Systems Containing Dialkyl Carbonate in Aqueous Solution

Experimental tie-line data were investigated for two quaternary systems of water + n-hexane + diethyl carbonate + dimethyl carbonate and water + toluene + isooctane + dimethyl carbonate, and two related ternary systems of water + n-hexane + diethyl carbonate and water + n-hexane + dimethyl carbonate at 298.15 K and ambient pressure. The experimental tie-line data have been correlated using a modified UNIQUAC model and an extended UNIQUAC model, both with multicomponent interaction parameters in addition to the binary ones.

Intrinsic dissolution of lithium carbonate in aqueous solutions.

Intrinsic dissolution rate studies were carried out on lithium carbonate discs that were prepared with the disc in a component on the final support. This overcame the problem of further handling of the fragile discs. Dissolution media employed were similar to those used for the routine evaluation of lithium carbonate dosage forms. Linear dissolution rate profiles were found in simulated gastric fluid (SGF), Tris buffer and water. Data in SGF and water showed positive intercepts with the Levich model. The dissolution process of lithium carbonate was considered to be complex. Dissolution profiles in simulated intestinal fluid (SIF) containing phosphate showed a marked initial curvature and a subsequent reduced dissolution rate. This was due to the precipitation of trilithium phosphate onto the disc. Dissolution rate studies on lithium carbonate dosage forms could be invalidated where a phosphate buffer system has been used.

Biosorption of Dyes by Natural and Activated Vine Stem. Interaction between Biosorbent and Dye

In the present study, the vine stem and modified vine stem were used as low cost adsorbents for the removal of acidic and basic dyes from aqueous solutions. A comparative study was also carried out with activated carbon obtained from vine stem and then the adsorption capacities of all adsorbents were evaluated by batch adsorption process. The effects of various adsorption parameters (initial pH, particle size, and contact time) were investigated. The modification of the vine stem with nitric acid increased its adsorption capacity for the basic dye. Both, vine stem and modified vine stem exhibited higher adsorption capacities than activated carbon. The adsorption capacities were found to be 322.58, 250, and 200 mg g ―1 for modified, natural vine stem, and activated carbon, respectively. In the case of acidic dye, the pH strongly affected the adsorption capacity and the maximum dye uptake was observed at pH 2 for all adsorbents. The acidic dye adsorption was lower compared to basic dye on both biosorbents and activated carbon tested. The maximum acidic dye adsorption values (58.82 and 59.88 mg g ―1 ) were obtained with the vine stem and activated carbon, respectively. In the case of lignocellulosic adsorbents, both surface charge and surface groups had main effect on the adsorption of basic dye, while adsorption mechanism in activated carbon was mainly through the physical adsorption. The results of comparative adsorption capacity of adsorbents indicated that vine stem or modified vine stem can be used as a low cost alternative to activated carbon in aqueous solution for basic dye removal.

Adsorption of cadmium(II) from aqueous solutions by thiol-functionalized activated carbon

Thiol groups of adsorbent surfaces offer strong affinities for heavy metal ions, such as Hg(II), Pb(II), Cd(II), and so on. In this study, thiol group was impregnated to activated carbon by a series of treatments of oxidation and chlorination followed by 1,2-ethanedithiol introduction in order to investigate the adsorption properties of Cd(II) in aqueous solution. Batch sorption experiments were carried out to study kinetics, and the effect of Mg(II) and different pH conditions on Cd(II) sorption. Sequential extraction experiments were performed to understand binding characteristics. In general, thiol-functionalization improved the removal of Cd(II) by activated carbon in aqueous solution. Compared to untreated activated carbon, over a factor of four of the maximum sorption capacity enhancement was achieved. The presence of Mg(II) interfered Cd(II) sorption, but the degree of the sorption interference was alleviated significantly. Cd(II) sorption occurred more rapidly due to more involvement of ion exhchange by thiol- functionalization.

Synthesis and electrical conductivity of La–Sr–X–Mg–O (X = Ti, Zr, Al) perovskite solid solution

Perovskite solid solutions of (La 0.6Sr 0.4)(X 1− y Mg y )O 3− δ (X = Ti, Zr, Al) were prepared by a coprecipitation method using corresponding aqueous solutions and ammonium carbonate solution. The freeze-dried powders were sintered in air at 1000–1500 °C for 1–36 h. Single phase solid solutions were produced in the compositions of (La 0.6Sr 0.4)(Zr 0.6Mg 0.4)O 3− δ and (La 0.6Sr 0.4)(Al 0.9Mg 0.1)O 3− δ where (3 − δ) < 3. For the compositions of X = Ti and Zr for y = 0.1 where (3 − δ) > 3, two phases including perovskite solid solution were produced at 1400–1500 °C. The stability of perovskite solid solution was closely related to the fraction of lattice oxygen atom (3 − δ). A relatively high conductivity was measured for (La 0.6Sr 0.4)(Al 0.9Mg 0.1)O 3− δ ( σ = 4.15 × 10 −4 S/cm at 600 °C, activation energy 113.4 kJ/mol). The influence of fraction of oxide ion vacancy on the activation energy was small for δ = 0.1–0.3 of perovskite solid solution.

Effect of Content of Mg(NO3)2·6H2O on Fabrication of α-Alumina Nanopowders by Thermal Decomposition of Ammonium Aluminum Carbonate (AACH)

An alpha-Al2O3 and MgAl2O3 spinel phase doped alpha-Al2O3 nanopowders were fabricated by the thermal decomposition and synthetic of ammonium aluminum carbonate hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, 8 degrees C, and the highest [NH4+][AlO(OH)2-][HCO3] ionic concentration of pH 10 from the ammonium hydrogen carbonate (AHC) aqueous solution. The phase transformation of amorphous-s, theta-, alpha-Al2O3, MgAl2O3 spinel phases was examined at each temperature according to the amount of Mg(NO3)2 x 6H2O and AACH. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical alpha-Al2O3 nanopowders with a particle size of 60 nm were obtained by firing the crystallites, which had been synthesized from AACH at pH 10 and 8 degrees C, at 1050 degrees C for 6 h in air.

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

Equilibrium conditions of clathrate hydrates formed from carbon dioxide and aqueous acetone solutions were experimentally measured at temperatures between 269.2 and 281.4 K and pressures up to 3.98 MPa. The acetone concentrations in solutions were investigated from 0.04 to 0.40 mass fractions. The experimental results suggested a transition in hydrate structure from structure I to another structure for acetone solutions between 0.04 and 0.12 mass fractions of acetone. The hydrate structure was suggested to be structure II which was the most stable with a 0.16 mass fraction acetone solution. For more than 0.16 mass fraction of acetone, the equilibrium conditions of the hydrate were shifted to lower temperatures as acetone concentrations increased.

Adsorption Behavior of Chromium(VI) on Activated Carbon and Quantitative Interpretation of Its Reductive Desorption

The adsorption and desorption of chromium(VI) ion on activated carbons in aqueous solution were studied. Adsorption experiments of Cr(VI) on pretreated activated carbons showed that the pH dependence of adsorption rates can be explained by the difference of the adsorbed species. Also, the reduction rates of Cr(VI) to Cr(III) by activated carbons in acidic solutions were quantitatively determined. In desorption experiments, a high recovery rate (90%) was obtained for activated carbons treated with adsorption at pH = 6 and elution by a 0.1 mol L−1 NaOH solution.

CO2 capture by improved hot potash process

Abstract Global climate warming caused by emission of greenhouse gas including CO 2 is one of serious problems nowadays. In an effort to mitigate CO 2 emissions, one of most effectively clean energy plan is to produce power from coal using the integrated gasification combined cycle (IGCC). However, the cost of existing CO 2 capture technologies is still too high. Utilization of large-solubility and low-cost absorbent for CO 2 capture in IGCC can effectively reduce the electricity price increase caused by addition of CO 2 removal unit. As it needs to trap CO 2 before combustion under high pressure in IGCC absorption is considered to be a better choice. HPP (Hot Potash Process) uses aqueous solution of potassium carbonate as the absorbent. Compared to physical solvent absorption method Rectisol and Selexol, HPP has relatively low investment and relatively high CO 2 recovery. Even in comparison with other chemical absorbent amine method HPP still has advantages as good chemical stability and low vapor pressure. In this paper several activators piperidine, piperozine, pyrazine, morpholine, imidazole, N-hydroxyethyl piperozine, Naminoethyl piperozine, AMP was tested respectively at 70 °C. As a result, piperidine activation works best, followed by N-(2-hydroxyethyl)piperazine, N-(2-aminoethyl) piperazine, 2-amino-2-methyl-1 -propanol and piperazine, pyrazine and imidazole is at its worst. Among them, N-(2-hydroxyethyl)piperazine is less volatile, more stable and suitable as the activator. Absorbing capacity and absorbing rate of CO 2 in carbonate aqueous solution with HPZ increases by 5% or more than those with PZ. An improved HPP process is presented adopting the new activator. In this process two de-absorption two columns is designed operating at different pressure. This makes it possible to reuse the heat of condensation during high pressure de-sorption in reboiler of low pressure de-sorption. By preliminary calculating the novel process can save energy consumption obviously. The steam consumption, cooling water consumption and power consumption declines by 43.30%, 31.81% and 10.57%, respectively. It is expected to develop a low-cost technology for capture CO 2 from IGCC in the future.

Synthesis of nearly monodispersed metal oxide nanoparticles in water

We report a generalized aqueous route for the synthesis of a variety of nearly monodisperse nanostructured metal oxides with controllable sizes and shapes using aqueous metal ammonium carbonate solution as a precursor and decanoic acid under reflux as well as hydrothermal conditions. The procedure is based on direct formation of metal oxide through hydrolysis followed by dehydration of a metal ammonium carbonate complex in basic medium, in situ dissolution and surface modification of an oxide nanoparticle by decanoic acid through the formation of ammonium salt of decanoic acid. All the synthesized metal oxide nanostructures were characterized by transmission electron microscopy, powder X-ray diffraction and IR spectroscopy. The characterization result shows that all the particles are monodispersed in size and shape, and highly crystalline in nature. A probable formation mechanism is proposed to explain the formation of the size and shape selective CeO2.

CO2separation using bipolar membrane electrodialysis

Caustic solvents such as sodium or potassium hydroxides, converted viaCO2 capture to aqueous carbonates or bicarbonates, are a likely candidate for atmospheric CO2 separation. We have performed a comprehensive experimental investigation of CO2 gas regeneration from aqueous potassium carbonate and bicarbonate solutions using bipolar membrane electrodialysis (BPMED). This system allows the regeneration of pure CO2 gas, suitable for subsequent sequestration or reaction to synthetic hydrocarbons and their products, from aqueous carbonate/bicarbonate solutions. Our results indicate that the energy consumption required to regenerate CO2 gas from aqueous bicarbonate (carbonate) solutions using this method can be as low as 100 kJ (200 kJ) per mol of CO2 in the small-current-density limit.

An evidence for conversion of A-PW9O349− derivatives to A-PW10O379− derivatives. Synthesis and characterization of [(A-PW9O34)2(H2OM)3CO3]11− (M = Sm(III), Eu(III) and Gd(III)) and [(PW10Sm2O38)4(W3O8(H2O)2(OH)4)]22− (M = Sm(III) and Gd(III))

In this study, we show that the A-PW9O349− anion reacts with aqueous carbonate solutions of samarium(III), europium(III) and gadolinium(III), and yields different products. Under heating to 80°C, the main products for Eu(III) and Gd(III) are new sandwich type polyoxometalates, [(A-PW9O34)2(H2OM)3CO3]11−, while a samarium(III) derivative analogous to [(A-PW9O34)2(H2OSm)3CO3]11− is produced when the reaction is maintained under room temperature (30°C). Under heating, the main product for Sm(III) is a new tetramer species of [(PW10Sm2O38)4(W3O8(H2O)2(OH)4)]22−. We obtained a gadolinium(III) derivative analogous to [(PW10Gd2O38)4(W3O8(H2O)2(OH)4)]22− as by-product from the filtrate of the respective sandwich type polyoxometalate synthesis. On the other hand, 31P NMR shows decomposition of the sandwich type compound to a tetramer species for the Eu(III) derivative in aqueous solution. The structures of sandwich type polyoxometalates consist of a (MOH2)3CO3 belt encapsulated by two A-PW9O34 groups. The structure of the tetramer species consist of four PW10O379− units each incorporating two Sm(III) ions to create four Keggin-like anions that are further tied together by three additional tungstate units. The new complexes in these two categories have been isolated and characterized by elemental analysis, IR, 31P NMR spectroscopy thermogravimetric analysis (TGA) and X-ray single crystal structure analysis.

Insights on natural gas purification: Simultaneous absorption of CO2 and H2S using membrane contactors

Natural gas plays a critical role in today's energy supply. However, before it can be utilized as a fuel for chemical processing or energy generation, it must undergo extensive treatment to remove all contaminants such as CO2 and H2S. This paper presents the simultaneous absorption of CO2 and H2S from natural gas using aqueous potassium carbonate solutions as the absorbent solvent while utilizing hollow fiber membrane contactors. The reaction mechanisms of CO2 and H2S absorption into aqueous carbonate solutions are considered complicated due to the several species involved in the reaction scheme that undergo reversible reactions. A comprehensive 2D mathematical model has been developed for the simultaneous absorption of CO2 and H2S while considering reversible and equilibrium reactions rates. The model results showed that lower concentrations of carbonate solutions resulted in higher absorption rates, while the presence of high bicarbonate concentrations in the solution was the main incentive for the enhanced reversible reactions and thus, lower absorption rates were achieved. A complete removal of CO2 and H2S in a gas mixture containing 5% CO2, 5% H2S, and 90% CH4 was possible by using two membrane modules in series while using fresh 1M carbonate solution in each module. The first module removes all H2S in the system and small amounts of CO2, while the second module removes the remaining CO2 coming out from the first module. This scheme is favorable than using only one membrane module, because the majority of bicarbonate ions that favors the reversible reaction, are generated from the consumption of H2S with carbonate solution. Therefore in the second module, CO2 can be consumed significantly due to the absence of bicarbonate ions.

Kinetics of an Air- and Water-Stable Ruthenium(IV) Catalyst for the Deprotection of Allyl Alcohol in Water

Kynurenic allyl ester reacts readily with [CpRu(NCCH3)3]PF6 in dry acetone to yield the RuIV allyl. The complex is an effective catalyst for the hydrolysis of methyl allyl carbonate in aqueous solution in air yet decomposes rapidly in aerobic solutions of methanol. Kinetic studies are consistent with rate-limiting attack of water (or methanol) on the RuIV allyl as a key step. A polystyrene-supported version of the catalyst was active for the catalytic hydrolysis of methylallyl carbonate, but kinetic studies indicate that the Ru leaches from polystyrene upon repeated catalytic cycles.

Tailor-made microdevices for maximizing process intensification and productivity through advanced heating

For the Kolbe–Schmitt synthesis from resorcinol, large process intensification was achieved recently, using a simple continuous set-up comprising a capillary reactor. However, the productivity of such capillary is low and the design less convenient for scale-up to the pilot or even production scale. Consequently, a tailor-made electrically heated microdevice was developed and successfully tested for the pilot scale using the internal numbering-up approach and enabling external numbering-up. For the Kolbe–Schmitt synthesis in aqueous potassium hydrogen carbonate solution, a productivity of 225kg/h at 4s residence time and 32% yield was achieved, corresponding to a space-time yield of 38,250kg/(m3h). As alternative heating approach, continuous microwave heating applying both multi-mode and single-mode devices and using capillary reactors of different dimensions and shapes was investigated and revealed the benefits of a compact design with respect to microwave absorption and of small dimensions for higher space-time yields up to 32,550kg/(m3h). The first attempt of developing a microstructured plate reactor made of PEEK for continuous microwave heating did not lead to the expected performance. The detected reasons are discussed.

Neural model for the leaching of celestite in sodium carbonate solution

A neural model for computing the conversion kinetics of SrSO 4 to SrCO 3 was investigated in sodium carbonate solution, based on the multilayered perceptrons was presented. For this purpose the artificial neural network (ANN) method was used. The effects of stirring speed, temperature, mole ratio Na 2CO 3:SrSO 4 and particle size of the celestite on leaching kinetics were studied. The surface transformation of celestite to strontium carbonate in aqueous carbonate solutions was also supported by FT-IR spectroscopy. The conversion rate of celestite increases systematically with increasing temperature (up to 70 °C). Furthermore, the feasibility of replacing the SO 4 2− ions with CO 3 2− ions in the structure of the leached solid was also investigated by FT-IR. FT-IR results showed that the replacement of SO 4 2− ions in celestite by CO 3 2− ions in leaching conditions was nearly completed at 60 °C with a mole ratio Na 2CO 3:SrSO 4 = 4:1, solid to liquid = 5:500, −212+106 μm particle size, and 400 rpm stirring rate for an interval of 240 min. The first (up to 90 min) conversion result obtained was trained with an extended delta-bar-delta algorithm (EDBD), which is in the multilayered perceptrons and is a neural model structure. Results of other conversion times (90–240 min) results were predicted. Results predicted by the neural model were in very good agreement with the experimental results.

Polymeric Functionalized Stationary Phase for Separation of Ionic Compounds by IC

Synthesis and properties are described of multilayered stationary phases containing quaternary amine functional groups used for the analysis of inorganic anions by ion chromatography. The bonded phases were characterized by elemental analysis, solid state 13C NMR spectroscopy and chromatographic methods. The surface of polyhydroxyethyl methacrylate (solid support) was coated with polymeric layers formed by condensation polymerization of primary amine with diepoxide. Each layer of the anion exchange stationary phase consisted of methylamine and 1,4-butanedioldiglycidyl ether copolymer. A series of stationary phases with different number of polymerized layers were tested. Separation of inorganic anions, such as F−, Cl−, NO2 −, Br−, NO3 −, were performed. Aqueous hydroxide, carbonate and bicarbonate solutions were used as mobile phases.