Carbon Dioxide Mole Research Articles

Quality control of eddy covariance fluxes of two ecosystem types with local flux-variance similarity functions in West Africa

Ecosystem capacity studies for carbon sequestration and water extraction are largely conditioned by Eddy Covariance (EC) measurement availability and quality. Our study aims at evaluating several procedures of EC data qualification. Indeed, quality control of EC data is generally ensured by stationarity and well-developed turbulence tests. The latter is based on integral turbulence characteristic (ITC) models. In this study, we revisited the quality control procedure using locally established ITC models for wind speed components and atmospheric scalars (temperature, humidity and carbon dioxide molar densities) in unstable and stable conditions. We also considered the interdependence of flux qualities because of the corrections applied to fluxes during their preprocessing. The analyses were carried out using one year of data collected above a woodland forest and mixed crop sites, both situated in Northern Benin, West Africa. From these analyzes we note that the quality flags vary depending on the use of local or existing ITC models. Also, the test of turbulence development on atmospheric scalars, previously neglected, is of great importance in the quality control of data. Thus, taking into account the ITC models associated with the atmospheric scalars established locally in the well-developed turbulence test as well as taking into account the interdependence of the flux quality have considerably improved the standard quality control procedure used in effectively filtering unrealistic flux data while keeping a considerable percentage of good and medium quality data.

Thermodynamically Efficient, Low-Emission Gas-to-Wire for Carbon Dioxide-Rich Natural Gas: Exhaust Gas Recycle and Rankine Cycle Intensifications

Onshore gas-to-wire is considered for 6.5 MMSm3/d of natural gas, with 44% mol carbon dioxide coming from offshore deep-water oil and gas fields. Base-case GTW-CONV is a conventional natural gas combined cycle, with a single-pressure Rankine cycle and 100% carbon dioxide emissions. The second variant, GTW-CCS, results from GTW-CONV with the addition of post-combustion aqueous monoethanolamine carbon capture, coupled to carbon dioxide dispatch to enhance oil recovery. Despite investment and power penalties, GTW-CCS generates both environmental and economic benefits due to carbon dioxide’s monetization for enhanced oil production. The third variant, GTW-CCS-EGR, adds two intensification layers over GTW-CCS, as follows: exhaust gas recycle and a triple-pressure Rankine cycle. Exhaust gas recycle is a beneficial intensification for carbon capture, bringing a 60% flue gas reduction (reduces column’s diameters) and a more than 100% increase in flue gas carbon dioxide content (increases driving force, reducing column’s height). GTW-CONV, GTW-CCS, and GTW-CCS-EGR were analyzed on techno-economic and environment–thermodynamic grounds. GTW-CCS-EGR’s thermodynamic analysis unveils 807 MW lost work (79.8%) in the combined cycle, followed by the post-combustion capture unit with 113 MW lost work (11.2%). GTW-CCS-EGR achieved a 35.34% thermodynamic efficiency, while GTW-CONV attained a 50.5% thermodynamic efficiency and 56% greater electricity exportation. Although carbon capture and storage imposes a 35.9% energy penalty, GTW-CCS-EGR reached a superior net value of 1816 MMUSD thanks to intensification and carbon dioxide monetization, avoiding 505.8 t/h of carbon emissions (emission factor 0.084 tCO2/MWh), while GTW-CONV entails 0.642 tCO2/MWh.

Critical cluster composition from homogeneous nucleation data: application to water in carbon dioxide\u2013nitrogen carrier gases

Knowledge on critical cluster composition is important for improving the nucleation theory. Thus, homogeneous water nucleation experiments previously carried out in nitrogen and 0%, 5%, 15% and 25% of carbon dioxide ( Campagna et al. 2020a, 2021) are analyzed. The tests were conducted at 240 K and 0.1 MPa, 1 MPa and 2 MPa. The observed nucleation rates are strongly dependent on supersaturation, pressure, temperature and mixture composition. These experimentally found dependencies can be used to derive the composition of critical clusters by means of the nucleation theorem. In this way, a macroscopic quantity, nucleation rate, reveals properties of critical clusters consisting of a few tens of molecules. Two novel methods are presented for the detailed application of the nucleation theorem. The first method extends to mixtures of ,,,,,,,N>2,,,,,, components the approach used in literature for two components. The second method not only applies to N>2 mixtures in a more straightforward manner, but it can also be used for unary as well as for binary and multi-component nucleation cases. To the best of our knowledge, for the first time the critical cluster composition is computed for high pressure nucleation data of a vapor (here water) in mixtures of two carrier gases (here carbon dioxide–nitrogen). After a proper parameterization of the nucleation rate data, both methods consistently lead to the same critical nuclei compositions within the experimental uncertainty. Increasing pressure and carbon dioxide molar fraction at fixed supersaturation leads to a decrease in the water content of the critical cluster, while the adsorbed number of nitrogen and carbon dioxide molecules increases. As a consequence, the surface tension decreases. This outcome explains the observed increase in the nucleation rate with increasing pressure and carbon dioxide molar fraction at constant supersaturation.Graphic abstract

Evaluation of the property methods for pure and mixture of CO2 for power cycles analysis

The use of a binary cycle coupled to the complete reinjection of non-condensable gases could provide a valid answer to the improvement of the sustainability of geothermal plants. In recent years, the interest in the use of CO2 as a working fluid in transcritical cycles has increased. However, the low critical temperature of carbon dioxide (≈30 °C) requires the cooling cycle, temperatures below 15 °C, which are not always available. In this work, to overcome this limitation and obtain a higher critical temperature and a lower maximum pressure for more flexible applications of transcritical binary cycles, the possibility of using a second component, mixed with CO2, has been evaluated. For this purpose, the following fluids have been proposed: R1234yf, R1234ze(E), n-butane, n-hexane, n-pentane, and propane, with a minimum considered carbon dioxide molar content of 60%. To carry out a cycle analysis, the knowledge of the thermodynamic properties of CO2-mixtures is fundamental; however, suitable equations of state under the appropriate conditions for these blends have not been clearly defined yet. Therefore, in the first part of this paper, different EoS for predicting thermodynamic properties of pure CO2 and CO2-based mixtures are analyzed and compared with reference data obtained from works published in the literature. However, because of the lack of experimental data of the selected blends, the values of density, enthalpy and entropy, obtained with the selected EoS, are compared with NIST REFPROP results. The EoS involved in the evaluation are cubic-type (PR, PR-Twu, PRSV, RK, SRK, GCEOS), Virial-type (LKP, BWRS), Helmholtz-type (SW), and SAFT-type (PC-SAFT). In a power cycle, the fluid works under different conditions, involving several possible states across the components. So the influence of the different EoS on each power cycle's key component for pure CO2 and two selected CO2-based mixtures has been investigated. The thermodynamic results show that the CO2-based mixtures, in a transcritical configuration, can achieve efficiencies higher than the sCO2 power cycle.

Upgrading exergy utilization and sustainability via supersonic separators: Offshore processing of carbonated natural gas

Offshore processing of natural gas with 44%mol carbon dioxide at remote deep-water oil-and-gas fields is invariably characterized by low-efficiency power generation via gas-fired turbines releasing hot flue-gas and entailing high degradation of resources, high carbon emissions and low sustainability. This work demonstrates how to upgrade exergy utilization and consequently process sustainability by using supersonic separators in some gas processing steps; namely: (i) water dew-point adjustment; (ii) hydrocarbon dew-point adjustment; and (iii) carbon dioxide abatement to 20%mol. To accomplish this, the exergy performance of two supersonic separator gas processing alternatives are compared with conventional gas processing comprising triethylene-glycol absorption for water dew-point adjustment, Joule-Thomson expansion hydrocarbon dew-point adjustment and membrane-permeation carbon dioxide removal. Since exergy is measured relatively to a reference environmental reservoir, two such reference reservoirs are used: RER-1: standard atmosphere with 2%mol water containing hydrocarbons at combustion chemical equilibrium with air species; and RER-2: 1atm water-saturated raw natural gas in equilibrium with liquid water. Aspen-HYSYS simulations are used to solve mass/energy balances and thermodynamic property calculations. With RER-2 the conventional gas processing conserves 63.3% of the inlet exergy, while the two alternative supersonic separator processes attain 66.5% and 72.4% of exergy conservation, proving the associate gains of exergy efficiency and sustainability.

Homogeneous water nucleation in carbon dioxide–nitrogen mixtures: Experimental study on pressure and carrier gas effects

New homogeneous nucleation experiments are presented at 240 K for water in carrier gas mixtures of nitrogen with carbon dioxide molar fractions of 5%, 15%, and 25%. The pulse expansion wave tube is used to test three different pressure conditions, namely, 0.1, 1, and 2 MPa. In addition, a restricted series of nucleation experiments is presented for 25% carbon dioxide mixtures at temperatures of 234 and 236 K at 0.1 MPa. As pressure and carbon dioxide content are increased, the nucleation rate increases accordingly. This behavior is attributed to the reduction in the water surface tension by the adsorption of carrier gas molecules. The new data are compared with theoretical predictions based on the classical nucleation theory and on extrapolations of empirical surface tension data to the supercooled conditions at 240 K. The extrapolation is carried out on the basis of a theoretical adsorption/surface tension model, extended to multi-component mixtures. The theoretical model appears to strongly overestimate the pressure and composition dependence. At relatively low pressures of 0.1 MPa, a reduction in the nucleation rates is found due to an incomplete thermalization of colliding clusters and carrier gas molecules. The observed decrease in the nucleation rate is supported by the theoretical model of Barrett, generalized here for water in multi-component carrier gas mixtures. The temperature dependence of the nucleation rate at 0.1 MPa follows the scaling model proposed by Hale [J. Chem. Phys. 122, 204509 (2005)].

Total Oxidation of Methane on Oxide and Mixed Oxide Ceria-Containing Catalysts

Methane, discovered in 1766 by Alessandro Volta, is an attractive energy source because of its high heat of combustion per mole of carbon dioxide. However, methane is the most abundant hydrocarbon in the atmosphere and is an important greenhouse gas, with a 21-fold greater relative radiative effectiveness than CO2 on a per-molecule basis. To avoid or limit the formation of pollutants that are dangerous for both human health and the atmospheric environment, the catalytic combustion of methane appears to be one of the most promising alternatives to thermal combustion. Total oxidation of methane, which is environmentally friendly at much lower temperatures, is believed to be an efficient and economically feasible way to eliminate pollutants. This work presents a literature review, a statu quo, on catalytic methane oxidation on transition metal oxide-modified ceria catalysts (MOx/CeO2). Methane was used for this study since it is of great interest as a model compound for understanding the mechanisms of oxidation and catalytic combustion on metal oxides. The objective was to evaluate the conceptual ideas of oxygen vacancy formation through doping to increase the catalytic activity for methane oxidation over CeO2. Oxygen vacancies were created through the formation of solid solutions, and their catalytic activities were compared to the catalytic activity of an undoped CeO2 sample. The reaction conditions, the type of catalysts, the morphology and crystallographic facets exposing the role of oxygen vacancies, the deactivation mechanism, the stability of the catalysts, the reaction mechanism and kinetic characteristics are summarized.

High-pressure vapor + liquid equilibria for the binary system CO2 + (E)-2-hexenal

The isothermal vapor + liquid equilibria of carbon dioxide + (E)-2-hexenal (a key apple aroma) was measured using a visual equilibrium cell with an analytic methodology. The selected isotherms were (313.2, 323.2 and 333.2) K, and the pressures assessed ranged from (2.2–9.8) MPa. The thermodynamic consistency of the experimental data was verified, and the uncertainties of the molar fractions of the vapor and liquid phases were estimated. The density and dynamic viscosity of pure (E)-2-hexenal were measured at 101.13 kPa and temperatures from (292.2–353.2) K. Two equations of state were selected to model the vapor + liquid equilibria. The Peng-Robinson with two different mixing rules, and the Perturbed Chain - Statistical Associating Fluid Theory. The phase envelopes showed a critical pressure, detected at carbon dioxide molar fractions ≥ 95 % mol∙mol−1.

A cleaner and more sustainable decarbonation process via ionic-liquid absorption for natural gas with high carbon dioxide content

Ionic-liquids are considered alternatives to conventional aqueous-amines absorption solvents due to their carbon dioxide affinity, low vapor-pressure, high thermal stability and low heat-ratio. In this context, this work firstly approaches a new natural gas decarbonation process based on ionic-liquid [Bmim][NTf2] absorption and selective solute stripping at high-pressure and high-temperature (2-staged-stripping initiating at 50 bar and 250 °C) taking advantage of the high thermal resistance of halogenated ionic-liquids. Its strong points have to do with its high-pressure stripping (50 bar) which impressively lowers carbon dioxide compression power for enhanced oil recovery destinations. Consequently, such new process burns less fuel for power production and is a cleaner production alternative to traditional aqueous-amine-based decarbonation processes which strip carbon dioxide at only 1–2 bar. Secondly, the positive aspects of new ionic-liquid decarbonation process were confirmed in two new multi-criterial sustainability-related implemented procedures: (i) new ionic-liquid multi-criterial screening for natural gas decarbonation; and (ii) new multi-criterial sustainability assessment of natural gas decarbonation processes. The new multi-criterial screening confirmed the same [Bmim][NTf2] as the most suited ionic-liquid from environment/engineering relevant properties (e.g., carbon dioxide loading, absorption-related properties, toxicology and cost), while the multi-criterial sustainability assessment proved that the new [Bmim][NTf2] decarbonation process is five times cleaner and more sustainable than the amine-based counterpart, both respectively attaining sustainability degrees of 5.17 and 1.0. In this sustainability assessment, the two decarbonation processes were designed for cleaning natural gas with 45%mol carbon dioxide at 60 bar. Processes were scored in terms of compliance to qualitative heuristic criteria and quantitative sustainability metrics for environmental-economic-social aspects. Metrics were aggregated into one indicator, the sustainability degree, evoking a sustainability-based process ranking.

Supersonic separator for cleaner offshore processing of supercritical fluid with ultra-high carbon dioxide content: Economic and environmental evaluation

Offshore gas processing presents challenges, especially when high flow rates, high-pressure and high carbon dioxide contents are involved. The present scenario comprehends offshore processing of high flow rate of high-pressure natural gas with 68%mol carbon dioxide, which results from oil production and behaves as a dense supercritical fluid. The processing goals with this fluid comprise: [A] water dew-point adjustment; [B] hydrocarbon dew-point adjustment; [C] decarbonation of a small part to 20%mol carbon dioxide fuel-gas for power production; and [D] compression/pumping of the remaining fluid enriched with carbon dioxide from decarbonation for enhanced oil recovery. For these tasks the industry considers traditional well established processes such as molecular-sieves adsorption for water dew-point adjustment, Joule-Thompson expansion for hydrocarbon dew-point adjustment and membrane-permeation for carbon dioxide removal. However, conventional technologies can become cumbersome in such awkward conditions. Thus, unconventional solutions are sought for reliability, lower equipment size/weight, and better power consumption, emissions and environmental sustainability. Recently, supersonic separators have been analyzed in proof-of-concept researches for natural gas processing. In this regard, this work quantitatively proves that goals [A],[B],[C] are achievable using only supersonic separators, attaining 33% higher net value, 40% greater oil production, 10% lower investment and economic leverage to reach lower carbon emission relatively to conventional counterparts.

Supersonic separator for cleaner offshore processing of natural gas with high carbon dioxide content: Environmental and economic assessments

Supersonic separators offer a cleaner offshore processing of natural gas with carbon dioxide content from deep-water oil-gas fields. Conventional offshore gas processing comprises water dew-point adjustment via glycol-absorption, hydrocarbon dew-point adjustment via Joule-Thomson expansion, and carbon dioxide removal via membrane-permeation. Alternative processing contemplates the use of supersonic separators for adjusting gas dew-points followed by carbon dioxide capture via membrane-permeation (so-called SS-MP scheme); or for adjusting gas dew-points and also accomplishing carbon dioxide abatement (so-called SS-SS scheme). The conventional process is environmentally and economically compared with SS-MP and SS-SS for application in offshore rigs treating raw gas (44%mol carbon dioxide) to produce exportable fuel-gas (≈20%mol carbon dioxide), while dispatching carbon dioxide rich fluid (≈75%mol carbon dioxide) for enhanced oil recovery in the oil-gas field. Results show that SS-MP requires 7.8% less power than the conventional process. Moreover, implementing SS-SS deepens the advantage against the conventional operation because SS-SS produces carbon dioxide rich fluid at high-pressure, requiring much less compression power for enhanced oil recovery than the low-pressure permeate from membrane-permeation. SS-SS has lowest carbon emission (−28.3%), lowest power consumption (−21.3%) and best economic performance: lowest manufacturing cost and lowest compressor investment. Thus, SS-SS is the overall best and cleanest solution, with highest 20 years net value (+860 MMUSD) and lowest environmental impact.

Kinetics of Methanol Synthesis from Carbon Dioxide Hydrogenation over Copper–Zinc Oxide Catalysts

Kinetics of methanol synthesis from carbon dioxide hydrogenation is studied on two noncommercial catalysts: a copper–zinc oxide catalyst on alumina (CuZA) and a copper–zinc oxide catalyst on zirconia (CuZZ). The experiments have been performed in an isothermal fixed bed reactor with a temperature range between 200 and 230 °C, a total pressure comprised between 50 and 80 bar, a gas hourly space velocity (GSHV) between 7800 and 23 400 h–1 and for different hydrogen:carbon dioxide molar ratios (between 2 and 6). Unlike other works in the literature, no carbon monoxide is contained in the feed which corresponds to the conditions of some recent industrial applications, the influence of the catalyst support has been tested to improve the methanol selectivity. The experimental data were modeled using the kinetic laws and adsorption coefficients determined by Graaf et al. based on a Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism. The reactor model was based on an isothermal pseudo-homogeneous plug flow model...

Upgrading of natural gas ultra-rich in carbon dioxide: Optimal arrangement of membrane skids and polishing with chemical absorption

Water depths in oil and gas offshore production are moving from shallow to deep and ultra-deepwaters. Floating Production Storage and Offloading platforms are preferred in such frontier offshore enterprises. However, ultra-deepwaters natural gas processing imposes challenges in the design of floating units, limited in area and weight of processing equipment. Oil reserves with high gas/oil ratio (>250 sm3/m3) and high carbon dioxide content create additional challenges due to the impacts in the deck area of the gas plant. Among other natural gas processing operations, removal of carbon dioxide is required to meet sales gas specification, being skid-mounted membrane modules well suited for this purpose. To avoid emissions and to increase oil production, the separated acid gas is injected for enhanced oil recovery, creating a changing scenario due to increasing carbon dioxide content in the reservoir along production lifetime. In this context, this work optimizes arrangements of membranes modules and operational conditions via nonlinear programming formulations to optimize total membrane area for minimum footprint of membrane skids, with either carbon dioxide content in the treated natural gas less than 3%mol (Type 1 Constraint) or methane losses in the injection gas limited by imposing carbon dioxide content in the injection gas greater than 75%mol (Type 2 Constraint). To reduce computational effort, surface response models are employed, regressed from data simulated with a rigorous phenomenological model of spiral-wound membrane modules. Optimization results – total and stage area, carbon dioxide contents in retentates and permeates and natural gas production – are obtained for three feed scenarios: 10%mol, 30%mol and 50%mol carbon dioxide in raw natural gas. Type 1 Constraint leads to higher methane losses while Type 2 Constraint demands a polishing Chemical Absorption to comply with carbon dioxide specification of sales gas, configuring a hybrid process. Life cycle costs and total footprint area point to superiority of carbon dioxide separation design resulting from Type 2 Constraint, with optimal service distribution between bulk removal in Membrane Permeation and polishing operation in Chemical Absorption, considering time-varying composition of the raw natural gas.

Optimization of carbon dioxide supply in raceway reactors: Influence of carbon dioxide molar fraction and gas flow rate

Influence of CO2 composition and gas flow rate to control pH in a pilot-scale raceway producing Scenedesmus sp. was studied. Light and temperature determined the biomass productivity whereas neither the CO2 molar fraction nor the gas flow rate used influenced it; because pH was always controlled and carbon limitation did not take place. The CO2 molar fraction and the gas flow rate influenced carbon loss in the system. At low CO2 molar fraction (2–6%) or gas flow rate (75–100l·min−1) the carbon efficiency in the sump was higher than 95%, 85% of the injected carbon being transformed into biomass. Conversely, at high CO2 molar fraction (14%) or gas flow rate (150l·min−1) the carbon efficiency in the sump was lower than 67%, 32% of the carbon being fixed as biomass. Analysis here reported allows the pH control to be optimized and production costs to be reduced by optimizing CO2 efficiency.

Synthesis of novel amino-functionalized ionic liquids and their application in carbon dioxide capture

In this study, four novel amino-functionalized ionic liquids, 1-(2-aminoethyl)-1-methylpiperazin-1-ium amino acid salts ([AEMP][A], wherein [A]− = [Gly]−, [Ala]−, [Pro]−, [Leu]−), have been synthesized and characterized, and their physicochemical properties, such as glass transition and thermal decomposition temperatures, were determined. These amino-functionalized ionic liquids, dissolved in solution or supported on SiO2, were applied for carbon dioxide absorption. The results showed that the absorption rate is faster when ionic liquid is supported on silica gel than dissolved in the solution. The absorption capacity reached about 1.5 mol carbon dioxide per mol ionic liquid at ambient pressure, as verified by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Moreover, the amino-functionalized ionic liquid can be recycled under vacuum.

Combined Application of High-Field Diffusion NMR and Molecular Dynamics Simulations To Study Dynamics in a Mixture of Carbon Dioxide and an Imidazolium-Based Ionic Liquid

Self-diffusion and related short-time dynamic and structural properties were investigated for mixtures of carbon dioxide and the ionic liquid 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [bmim](+)[Tf2N](-) for a broad range of carbon dioxide molar fractions and at different temperatures. The studies were performed by a novel multinuclear pulsed field gradient (PFG) NMR technique, which combines the advantages of a high magnetic field (17.6 T) and a high magnetic field gradient (up to 30 T/m), in combination with molecular dynamics simulations. In general, a satisfactory agreement was observed between the experimental and simulation diffusion data. Under all conditions examined, the self-diffusion coefficients of carbon dioxide were found to be approximately an order of magnitude larger than the corresponding self-diffusion coefficients of the ions. It was observed that an increase in temperature and in the amount of carbon dioxide in the ionic liquid led to an increase in the ion self-diffusivities without changing the relationship between the self-diffusion coefficients of the cations and anions. An observation of a slightly higher diffusivity of the cations in comparison to that of the anions is attributed to the preferential mobility of the cations in the direction of the ring plane. The diffusion activation energies of the ions were found to decrease gradually with an increase of the carbon dioxide content in the ionic liquid. The activation energy of the carbon dioxide diffusion in all cases was found to be smaller than those of the ions.

Accurate (p, ρ, T) data for two new (carbon dioxide + nitrogen) mixtures from (250 to 400) K at pressures up to 20 MPa

Recently our group published a set of (p,ρ,T) data for two (carbon dioxide+nitrogen) mixtures with a low carbon dioxide content (xCO2=0.10,0.15). These data showed larger relative deviations from the GERG-2008 equation of state than expected, specially at low temperatures, high pressures, and for the mixture with higher carbon dioxide content (xCO2=0.15). In order to analyze whether the mentioned deviations from the equation of state increase with the carbon dioxide content, it was decided to measure the (p,ρ,T) behavior of two additional mixtures with higher carbon dioxide molar fractions (xCO2=0.20,0.50). The new experimental data show again an appreciable disagreement with the GERG-2008 equation of state at low temperatures and high pressures. Relative deviations, which depend on temperature, arise to 0.4% at 250K and 20MPa and to 0.24% at 275K and 20MPa for the xCO2=0.20 and xCO2=0.50 mixture, respectively. Second virial coefficients are calculated for the two new mixtures presented in this work and also for those presented in our previous paper.

Modeling of Droplet Composition in Supercritical Antisolvent Process: Part A

Supercritical fluids (SCF) are the fluids at the temperature and pressure above the critical temperature and critical pressure respectively. One of the important applications of these fluids is the precipitation of micro to nano range of particles. The aim of this work is to develop a mathematical model of the droplet moving in a supercritical carbon dioxide environment. The solvent chosen in this study is ethanol. The two film theory is used to calculate the mass transfer rate of carbon dioxide and solvent. Due to the mass transfer phenomena, the size of the droplet changes as it moves downwards in a chamber. The density of the droplet is also changing because its composition is changing. The droplet diameter, carbon dioxide mole fraction and moles of carbon dioxide & ethanol are calculated.

Simultaneous solubility of carbon dioxide and hydrogen in the ionic liquid [hmim][Tf 2N]: Experimental results and correlation

The solubility of a single gas as well as the simultaneous solubility of several gases in an ionic liquid is of great interest in many areas of chemical engineering, particularly in heterogeneous catalysis. One of the most interesting features involved in the study of the simultaneous solubility of several gases in a pure ionic liquid is the difference between experimental data and predictions for the simultaneous solubility (based on experimental data for the solubility of the single gases). The well soluble gas might act as a cosolvent or as an antisolvent for a sparsely soluble second gas. New experimental results and a correlation are presented for the simultaneous solubility of hydrogen (i.e., a sparsely soluble gas) and carbon dioxide (a well soluble gas) in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf 2N]) at temperatures between 293 K and 373 K and pressures up to about 9.2 MPa. The experimental results reveal that carbon dioxide acts as a cosolvent for hydrogen in that particular ionic liquid. A correlation shows that the cosolvency effect can be modeled by considering interaction parameters between hydrogen and carbon dioxide in liquid [hmim][Tf 2N]. The correlation can also be used to quantify that cosolvency effect: one mole of carbon dioxide in 1000 g of [hmim][Tf 2N] increases the solubility of (small amounts of) hydrogen by about 20%.

Analysis of the supercritical antisolvent mechanisms governing particles precipitation and morphology by in situ laser scattering techniques

A general description of the mechanisms governing the supercritical (sc) antisolvent (SAS) process is given. It simplifies the complex interactions of phase equilibria, jet fluid dynamics and mass transfer by two characteristic and competing times. One of them characterizes the time for the disappearance of the interface between the liquid and the fluid phase (liquid/fluid interface) where the fluid phase is represented either by a liquid or by a sc fluid phase depending on the pressure and the mixture composition. The second one is the time for particle precipitation. This description is experimentally supported by the investigation of the SAS process at various process conditions using in situ light scattering measurements which allow the access to both, to the liquid/fluid (droplets) and to the solid/fluid (particles) interface. SAS experiments were conducted by injecting the solution – yttrium acetate dissolved in dimetylsulfoxide – into the antisolvent carbon dioxide with different flow rates at a constant carbon dioxide molar fraction. The variation of the liquid flow rate did not affect the morphology of the precipitate. As a consequence, the occurrence of nano particles, micro particles and expanded micro particles can be assigned to the precipitation of the particles from a single-phase mixture, a two-phase mixture of short lifetime and a two-phase mixture of long lifetime, respectively. These particular precipitation regimes have been experimentally attained by varying either the pressure or the solute concentration.