Effect of methanol addition on water–CO2–diethanolamine system: Influence on CO2 solubility and on liquid phase speciation

The aim of this study is the characterisation of VLE and chemical equilibria for the system CO₂/diethanolamine (DEA)/H₂O/methanol. The effect of MeOH composition has been studied using four compositions (from 0 to 30 wt% of methanol with a fixed composition (30 wt%) of DEA), the measurement being made at T = 298.15 K and at various CO₂ loadings (from 0.2 to 0.8). An original experimental device was used. This device combines a FT-IR spectroscopy analysis of the liquid phase with a VLE measurement cell.The data base obtained, including the new solubility data and the liquid phase composition, allows the modelling of the system CO₂/DEA/H₂O/methanol using an electrolyte equation of state [Fürst, W., Renon, H., 1993, Representation of excess properties of electrolyte solutions using a new equation of state, AIChE J, 39(2): 335–343] representing the equilibrium properties of the system and the liquid phase speciation.     

Thermodynamic modeling of CO2 solubility in aqueous solutions of NaCl and Na2SO4

A thermodynamic model based on the electrolyte NRTL activity coefficient equation and PC-SAFT equation-of-state is developed for CO₂ solubility in aqueous solutions of NaCl and Na₂SO₄ with temperature up to 473.15 K, pressure up to 150 MPa, and salt concentrations up to saturation. The Henry's constant parameters of CO₂ in H₂O and the characteristic volume parameters for CO₂ required for pressure correction of Henry's constant are identified from fitting the experimental gas solubility of CO₂ in pure water with temperature up to 473.15 K and pressure up to 150 MPa. The NRTL binary parameters for the CO₂-(Na⁺, Cl⁻) pair and the CO₂-(Na⁺, SO₄²⁻) pair are regressed against the experimental VLE data for the CO₂-NaCl-H₂O ternary system up to 373.15 K and 20 MPa and the CO₂-Na₂SO₄-H₂O ternary system up to 433.15 K and 13 MPa, respectively. Model calculations on solubility and heat of solution of CO₂ in pure water and aqueous solutions of NaCl and Na₂SO₄ are compared to the available experimental data of the CO₂-H₂O binary, CO₂-NaCl-H₂O ternary and CO₂-Na₂SO₄-H₂O ternary systems with excellent results.     

Experimental study of methane and carbon dioxide solubility in 1,4 butylene glycol at pressures up to 11 MPa and temperatures ranging from 303 to 423 K

This work reports solubility data of methane and carbon dioxide in 1,4 butylene glycol and the Henry's law constant of each solute in the studied solvent at saturation pressure. The measurements were performed at 303, 323, 373, 398 and 423.15 K and pressures up to 3.8 MPa for mixtures containing carbon dioxide and pressures up to 10.9 MPa for mixtures containing methane. The experiments were performed in an autoclave type phase equilibrium apparatus using a technique based on the total pressure method (synthetic method). All investigated systems show an increase of gas solubility with the increase of pressure. A decrease of carbon dioxide solubility with the increase of temperature and an increase of methane solubility with the increase of temperature were observed. From the variation of solubility with temperature, the partial molar enthalpy and entropy change of each mixture were calculated.     

Activity of carbided molybdena–alumina for CO2 hydrogenation

The relationship between the catalytic activity of carbided molybdena–alumina and the methane desorption from carbidic carbon through temperature-programmed surface reaction (TPSR) were studied. The effects of passivation and hydrogen treatment on the catalytic activities of molybdenum carbides for CO₂ hydrogenation were determined. When the 973 K-carbided catalyst was reduced at 773 K with hydrogen, the catalyst exhibited the highest activity for the reaction, the activity decreasing with increasing H₂ pretreatment temperature. Passivation of this catalyst decreased the reaction rate by 20%. TPSR results were correlated with the activity to reveal that molybdenum carbide with slightly deficient carbidic carbon (Mo₂C_0.962C_1.0) serves as an active site for CO₂ hydrogenation.     

Dissolution of olivine in the presence of oxalate, citrate, and CO2 at 90 °C and 120 °C

In this article, we report the results from a study of olivine dissolution kinetics under operating conditions suitable for ex situ aqueous mineral carbonation for CO₂ storage. We studied the effect of oxalate and citrate ions on the dissolution of gem-quality San Carlos olivine (Mg_1.82Fe_0.18SiO₄). Flow-through experiments were performed at 90 °C and 120 °C, at f_CO2 between 4 and 81 bar, with a solution containing either sodium oxalate or sodium citrate in a molality range between 10⁻³ and 10⁻¹. The pH was varied between 2 and 7 by adding HCl, LiOH, and adjusting f_CO2. At all investigated temperatures and for pH values in a broad range, both sodium oxalate and sodium citrate increased dissolution rate with the strongest effect up to one order of magnitude in presence of 0.1 m of oxalate, at 120 °C, and above pH 5. The enhancement effect was primarily ascribed to the oxalate or citrate ions that are the dominant species in this pH range. The overall dissolution process was described using the population balance equation (PBE) coupled with a mass balance equation to account for the evolution of the particle size distribution (PSD) of olivine. Far from equilibrium conditions for dissolution were established in all the experiments in order to achieve a surface-reaction controlled mechanism. We described the reaction with a surface complexation model, which assumes adsorption of a proton and of an oxalate (citrate) ions (proton and oxalate) on adjacent sites in order to enhance dissolution, and we derived a dissolution rate equation in presence of oxalate:where r^? is the specific dissolution rate commonly used in absence of organic compounds, and K_H, K_X, and β are thermodynamic and kinetic parameters. The values of these parameters have been estimated from the experimental data and the agreement between the model results and the experiments is very good.     

Effect of CO2, HCO3 and CO3 on oxygen reduction in anion exchange membrane fuel cells

The effect of carbonate and bicarbonate anions on the oxygen reduction reaction was investigated in four alkaline solutions (pH ∼ 14) on a Pt disk type electrode with varying concentrations of carbonate and bicarbonate. The addition of carbonate and bicarbonate had two primary effects on the observed voltammetric behavior: i) The Tafel slope shifts positive with increasing carbonate/bicarbonate concentration, indicating that the carbonate anions may compete for surface adsorption sites; and ii) The dissolved oxygen concentration and diffusion coefficient are depressed with increasing anion concentration. Finally, adding CO₂ to the cathode stream of an anion exchange membrane fuel cell caused an improvement in the device performance under fully hydrated conditions, suggesting that the fuel cell was operating at least partially under the carbonate cycle.     

The effect of [bmim][Br] on the solubility of carbon dioxide and methane in glycols at pressures up to 14 MPa and temperatures ranging from 303 to 423 K

Solubility data of methane in ethylene glycol and 1-4 butylene glycol and carbon dioxide in ethylene glycol and 1-2 propylene glycol in the presence of the ionic liquid 1-butyl-3-methylimidazolium bromide have been measured in the temperature range (303–423) K at pressures up to 14 MPa. Henry's law constant of each solute in the studied solvent at saturation pressure is given. The experiments were performed in an autoclave type phase equilibrium apparatus using the total pressure method. For mixtures containing carbon dioxide and ethylene glycol no influence was observed. For mixtures containing carbon dioxide and 1-2 propylene glycol it was observed salting-out effect at 303.2 K and 323.2 K and salting-in effect at the remaining temperatures. For mixtures containing methane and ethylene glycol or 1-4 butylene glycol salting-in effect was observed.     

CO and CO2 hydrogenation study on supported cobalt Fischer–Tropsch synthesis catalysts

The conversion of CO/H₂, CO₂/H₂ and (CO+CO₂)/H₂ mixtures using cobalt catalysts under typical Fischer–Tropsch synthesis conditions has been carried out. The results show that in the presence of CO, CO₂ hydrogenation is slow. For the cases of only CO or only CO₂ hydrogenation, similar catalytic activities were obtained but the selectivities were very different. For CO hydrogenation, normal Fischer–Tropsch synthesis product distributions were observed with an of about 0.80; in contrast, the CO₂ hydrogenation products contained about 70% or more of methane. Thus, CO₂ and CO hydrogenation appears to follow different reaction pathways. The catalyst deactivates more rapidly for the conversion of CO than for CO₂ even though the H₂O/H₂ ratio is at least two times larger for the conversion of CO₂. Since the catalyst ages more slowly in the presence of the higher H₂O/H₂ conditions, it is concluded that water alone does not account for the deactivation and that there is a deactivation pathway that involves the assistance of CO.     

Hematite and iron carbonate precipitation-coexistence at the iron–montmorillonite–salt solution–CO2 interfaces under high gas pressure at 150 °C

The hydrothermal reactivity of swelling clays has relevant implications on the geological storage of radioactive waste and greenhouse gases because the clay geo-materials have been proposed as engineered or natural barriers due to their low permeability in confined systems and their high capacity to sequester ions. In the present study, the iron–montmorillonite–salt solution–CO₂ interactions were investigated under high gas pressure (200 bar) at 150 °C.Various chemical processes were characterized at the solid–fluid interfaces such as the dissolution of montmorillonite fine particles and oxidative-dissolution of elemental iron. The ionic supersaturation of solution and possibly the surface complexation in the system produced the precipitation of hematite nanoparticles (< 200 nm) after 15 days of solid–fluid contact. The hematite nanoparticles dispersed and/or coagulated on the clay matrix caused a stable red coloration of the montmorillonite composite. We assume that initial dissolved oxygen was progressively consumed in this closed-stirred system favouring the presence of divalent iron (in-situ change of redox conditions) and then leading the surface precipitation of iron carbonate nanocrystals (< 500 nm) after 60 days of solid–fluid contact. Thus, an atypical mineral coexistence of hematite–iron carbonate was observed in our system. A qualitative comparison with the blank experiment, i.e. at the same P–T conditions, but without CO₂ injection, suggested that the carbon dioxide increased the hydrothermal reactivity of montmorillonite because the hematite and iron carbonate formation were not observed after the same reaction time.     

Food treatment with high pressure carbon dioxide: Saccharomyces cerevisiae inactivation kinetics expressed as a function of CO2 solubility

Experimental survival curves of Saccharomyces cerevisiae cells exposed to high pressure carbon dioxide (HPCD) treatments under several constant temperatures (35, 40 and 50 °C), pressures (7.5, 10.0 and 13.0 MPa) and suspended in distilled water with different sodium phosphate monobasic buffer concentrations (0.02, 0.10, 0.20 and 0.40 M) were obtained. The Peleg model was applied to the isobaric and isothermal conditions described by the power law equation log[S(t)] = −btⁿ, where S(t) is the momentary survival ratio and ‘b’ and ‘n’ are the rate and the shape parameters, respectively. The values of the coefficients ‘b’ and ‘n’ were calculated for each experiment at fixed pressure and temperature. For each suspending medium the power law model was proposed to describe the combined effects of pressure and temperature. Taking into account the CO₂ solubility as a function of the sodium phosphate monobasic concentration, ‘b’ and ‘n’ were correlated to the CO₂ solubility values and temperature. An equation was proposed for ‘b’ as a function of CO₂ solubility and temperature while ‘n’ was a weak function of temperature. The resulting equation was much simpler that the one obtained correlating the microbial inactivation to pressure and temperature and, more important, it was independent of the suspending medium. The results indicate that the coupling of carbon dioxide solubility, also predicted with commercial software, and the use of inactivation models referred to solubility and temperature may provide a powerful instrument for the interpretation of microbial inactivation experiments and for the design of HPCD processes and equipments.     

Hydrogenation of CO2 to formic acid on supported ruthenium catalysts

We report on the preparation and application of novel heterogeneous supported ruthenium catalysts. The catalysts are active in the synthesis of formic acid from the hydrogenation of carbon dioxide and are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction analysis and transmission electron microscopy. Abundant hydroxyl groups, which interact with the ruthenium components, play an important role in the catalytic reactions. Highly dispersed ruthenium hydroxide species enhance the hydrogenation of CO₂, while crystalline RuO₂ species, which are formed from the relatively high ruthenium content or the pH of the solution during preparation of the catalyst, restrict the production of formic acid. Optimal activity of ruthenium hydroxide as a catalyst for the hydrogenation of CO₂ to formic acid is achieved over a γ-Al₂O₃ supported 2.0 wt% ruthenium catalyst, which is prepared in a solution of pH 12.8 with NH₃·H₂O as a titration solvent. A possible hydrogenation mechanism for the hydroxide ruthenium catalyst is proposed.     

Microstructure, kinetics and mechanisms of CO2 catalytic decomposition over freshly reduced nano-crystallite CuFe2O4 at 400–600 °C

The decomposition of CO₂ was investigated as a process of both industrial and environmental importance. Copper ferrite was obtained by the thermal decomposition of acetate precursors. CuFe₂O₄ were isothermally reduced in H₂ flow at 400–600 °C, the isothermal reduction profiles obtained in this study show that a topochemical mode of reduction is done by which the reduction process proceeds. The nano-wires metallic phase of iron (106 nm) and copper (56 nm), produced from the complete reduction of CuFe₂O₄, were subjected to the direct reoxidation in CO₂ flow at 400–600 °C. The reoxidation process was found to be controlled by both the reduction and reoxidation temperatures. CO₂ decomposes to carbon nano-tubes during the reoxidation of the freshly reduced CuFe₂O₄. The prepared, completely reduced and reoxidized CuFe₂O₄ compacts, were characterized by XRD, SEM, TEM and reflected light microscope. For the reoxidation process, it is found that at the initial stages the reaction is controlled by the interfacial chemical reaction mechanism with some contribution to the gaseous diffusion mechanism. On the other hand at the intermediate and final stages the mechanism by which the reoxidation process proceeds was found to be the solid-state diffusion.     

Effect of cultivation mode on microalgal growth and CO2 fixation

The biofixation of carbon dioxide (CO₂) by marine microalgae cultivation has been regarded as one of the potential to diminish the greenhouse effect and produce the biomass. To compare and select the high efficiency cultivation mode, the effect of two different cultivation modes on the performances of growth and CO₂ biofixation from air for energy marine microalgae Chlorella sp. was determined in this work. In one mode the microalga was cultivated using static (open) method and in the other mode it was cultivated using aerated (closed) method. It was found that, under the experimental conditions, the specific growth rate and CO₂ fixation rate of the aerated (closed) cultivation were 0.5121 (d⁻¹) and 1.3784 g CO₂/l d, and are 1.78 and 5.39 times that of the static (open) cultivation, respectively. In addition, the effects of pH value and dissolved oxygen (DO) concentration of the culture medium were analyzed and compared in two cultivation modes. The result indicates the aerated (closed) mode can effectively enhance the performance on microalgal growth and CO₂ biofixation.     

The simultaneous activation of methane and carbon dioxide to C2 hydrocarbons under pulse corona plasma over La2O3/γ-Al2O3 catalyst

The pulse corona plasma has been used as an activation method for reaction of methane and carbon dioxide, the product was C₂ hydrocarbons and by-products were CO and H₂. Methane conversion and the yield of C₂ hydrocarbons were affected by the carbon dioxide concentration in the feed. The conversion of methane increased with increasing carbon dioxide concentration in the feed whereas the yield of C₂ hydrocarbons decreased. The synergism of La₂O₃/γ-Al₂O₃ and plasma gave methane conversion of 24.9% and C₂ hydrocarbons yield of 18.1% were obtained at the power input of plasma was 30 W. The distribution of C₂ hydrocarbons changed by using Pd-La₂O₃/γ-Al₂O₃ catalyst, the major C₂ product was ethylene.     

Analysis of volume expansion mechanism of CO2-acetate systems at 40 °C

We measured the density and liquid phase CO₂ mole fraction (xCO₂) of CO₂-expanded acetates (methyl acetate, ethyl acetate, propyl acetate, butyl acetate, i-propyl acetate, and t-butyl acetate) at 40 °C and carried out molecular dynamics (MD) simulations. The pressure dependence of xCO₂ was almost the same for all measured acetates. The expansion coefficient and the partial molar volume estimated using the Peng-Robinson equation of state was found to have regions: a nearly constant region and a rapidly changing region that seem to be caused by the interspaces. When the length of the alkyl chain increased, the interspaces became larger. CO₂ molecules existed in the interspaces while the volume remains nearly constant in the lower xCO₂ region. However, there were no interspaces in the higher xCO₂ region where volume expanded rapidly and these trends were supported by the MD simulations. The fraction from the center of mass of CO₂ to the carbonyl oxygen atom was highest in regions of lower xCO₂, while the distance from the center of mass of CO₂ to the carbonyl oxygen atom was shortest regardless of region or mixture. The results show that CO₂ molecules tend to aggregate around the carbonyl oxygen in the acetate.     

Measurement and prediction of CO2 solubility in sodium phosphate monobasic solutions for food treatment with high pressure carbon dioxide

Two experimental systems were designed and tested to measure the CO₂ solubility in pure water and sodium phosphate monobasic solutions (0.240, 2.40 and 4.80 g/100 g water) at different pressures (7.5 and 15.0 MPa) and temperatures (35, 40 and 50 °C).The solubility experimental results were compared with the equilibrium conditions evaluated by applying three different thermodynamic models by means of the process simulation software Aspen Plus^®: (1) the Peng-Robinson equation of state (EOS), with the Wong and Sandler mixing rules (PRWS) and the excess Gibbs free energy calculated according to the UNIFAC method; (2) the Electrolytic Non-Random Two Liquids (ELECNRTL) with the Redlich-Kwong equation of state for aqueous and mixed solvent applications; (3) the completely predictive Soave-Redlich-Kwong (PSRK) equation of state.CO₂ solubility appeared to be a strong function of sodium phosphate monobasic concentrations. The predictions of the PRWS EOS agreed well with the experimental data in the pressure and temperature ranges tested. Larger differences between experimental and predicted results were observed for conditions close to the CO₂ critical point and for low sodium phosphate monobasic concentrations. Predictions of thermodynamic models 2 and 3 had much larger deviations from experimental data.     

Effect of ceria on the structure and catalytic activity of V2O5/TiO2–ZrO2 for oxidehydrogenation of ethylbenzene to styrene utilizing CO2 as soft oxidant

The present study was undertaken to investigate the influence of ceria on the physicochemical and catalytic properties of V₂O₅/TiO₂–ZrO₂ for oxidative dehydrogenation of ethylbenzene to styrene utilizing CO₂ as a soft oxidant. Monolayer equivalents of ceria, vanadia and ceria–vanadia combination over TiO₂–ZrO₂ (TZ) support were impregnated by a coprecipitation and wet impregnation methods. Synthesized catalysts were characterized by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction, transmission electron microscopy and BET surface area methods. The XRD profiles of 550 °C calcined samples revealed amorphous nature of the materials. Upon increasing calcination temperature to 750 °C, in addition to ZrTiO₄ peaks, few other lines due to ZrV₂O₇ and CeVO₄ were observed. The XPS V 2p results revealed the existence of V⁴⁺ and V⁵⁺ species at 550 and 750 °C calcinations temperatures, respectively. TEM analysis suggested the presence of nanosized (<7 nm) particles with narrow range distribution. Raman measurements confirmed the formation ZrTiO₄ under high temperature treatments. TPR measurements suggested a facile reduction of CeO₂–V₂O₅/TZ sample. Among various samples evaluated, the CeO₂–V₂O₅/TZ sample exhibited highest conversion and nearly 100% product selectivity. In particular, the addition of ceria to V₂O₅/TZ suppressed the coke deposition and allowed a stable and high catalytic activity.     

Efficient conversion of CO2 to formic acid by formate dehydrogenase immobilized in a novel alginate–silica hybrid gel

The efficient utilization of CO₂ will not only help to alleviate greenhouse effect, but also to obtain useful chemicals as well. A novel bio-pathway has been explored to convert CO₂ into formic acid by the aid of formate dehydrogenase (FateDH) as the biocatalyst and reduced nicotinamide adenine dinuncleotide (NADH) as the terminal electron donor. In order to simplify subsequent separation of the enzyme and improve its catalytic stability, the enzyme FateDH was encapsulated in a novel alginate–silica (ALG–SiO₂) hybrid gel. This hybrid gel was prepared by in situ hydrolysis and polycondensation of tetramethoxysilane (TMOS) in alginate solution followed by gelation of alginate with Ca²⁺. The leakage of the enzyme was significantly reduced by hybridization compared to pure alginate. The optimum reaction condition was found to be at pH 7.0 and 37 °C. Under these conditions, the highest yield of formic acid catalyzed by the immobilized FateDH was up to 95.6%, only a little lower than that of the free form enzymatic reaction (98.8%). The relative activity of immobilized FateDH after 10 cycles could be maintained as high as 69%. Storage stability test showed that the relative activity of FateDH in hybrid gel was about fourfold higher than that in pure alginate gel after being kept at 4 °C for 1 month.     

High-pressure phase equilibrium for the hydroformylation of 1-octene to nonanal in compressed CO2

The hydroformylation reaction in supercritical carbon dioxide or CO₂-expanded liquids (CXLs) has many advantageous properties. However, accurate phase behavior and equilibrium must be known to properly understand and engineer these systems. In this investigation, the vapor-liquid equilibrium and mixture critical points of CO₂ systems with 1-octene, nonanal, 1-octene and nonanal mixtures, and mixtures of 1-octene, nonanal and syngas (CO/H₂) were measured at 60 °C up to 120 bar of pressure. The Peng-Robinson equation of state with van der Waals two-parameter mixing rule was employed successfully to correlate the binary mixture data and predict the ternary mixture data. The presence of CO/H₂ pressure increased the mixture critical points and decreased the volume expansion at any given pressure. In an actual reaction, the mixture critical point would increase throughout the reaction, while the volume of the liquid phase would decrease. These data will aid the understanding and reaction engineering for the hydroformylation reaction in CO₂-expanded liquids and supercritical fluids.     

Impact of thickness on CO2 concentration profiles within polymer films swollen near the critical pressure

The isothermal swelling of polymer thin films by a supercritical fluid does not increase monotonically with increasing chemical potential (pressure), but rather a maximum in swelling is generally observed near the critical pressure. A reactive templating approach utilizing the condensation of silica within hydrophilic domains of a swollen amphiphilic polymer film enables visualization of the qualitative concentration profile of CO₂ by the changes in the size of hydrophobic domains (pores) with cross sectional TEM microscopy; specifically, isothermal swelling of poly(ethylene oxide-propylene oxide-ethylene oxide) films by CO₂ at 60 °C is examined. Films that contain thickness gradients are used to avoid any uncertainties in the impact of thickness due to variations in the temperature or pressure during the silica modification. A uniform pore size (local swelling) is observed for all film thicknesses when the pressure is outside of the anomalous maximum in the film swelling, except for a small increase at the buried interface due to preferential adsorption of CO₂ to the native silicon oxide surface of the substrate. However at this swelling maximum, a gradient in the pore size is observed at both interfaces. These swelling gradients at interfaces appear to be responsible for the anomalous maximum in thin films. As the film thickness increases beyond 350 nm, there is a decrease in the maximum swelling at the free interface.