Supercritical Carbon Dioxide Solutions Research Articles

The effect of different wear on superhydrophobic wax coatings

Wear resistance of superhydrophobic coatings made by spraying a crystallizing wax from supercritical carbon dioxide solutions was evaluated using several methods. Scratch tests were performed using ...

Determining the Solubility of Nifedipine and Quinine in Supercritical Fluid Carbon Dioxide Using Continuously Stirred Static Solubility Apparatus Interfaced with Online Supercritical Fluid Chromatography

A high pressure vessel equipped with continuous magnetic stirring has been interfaced directly online with supercritical fluid chromatography (SFC). The interface consists of an oven housing a recirculation pump that maintains a constant flow of supercritical fluid solution from the vessel through a sample injection valve for online SFC analysis. The method involves increasing the vessel pressure in controlled steps to produce a series of progressively more saturated supercritical fluid carbon dioxide solutions for online SFC solubility measurements. The integrated static solubility system provides a convenient means to ensure equilibrium is established prior to performing online SFC solubility measurements and also facilitates a self-validation accuracy check procedure. For nifedipine, solubility data was obtained at 333.15 and 353.15 K through the pressure range from 12.5 to 27.5 MPa using 2.5 MPa steps. For quinine, solubility data was obtained at 323.15 and 343.15 K through the pressure range from 12....

Estimating the solubility of different solutes in supercritical CO2 covering a wide range of operating conditions by using neural network models

A new neural network-based model is proposed for solute solubility in supercritical carbon dioxide (CO2). The solubility of fifteen solutes in supercritical carbon dioxide at different temperatures and pressures are estimated. Four neural network models have been tested to investigate the generalize-ability of each network. The results from different semi-empirical models, namely Chrastil, Kumar and Johnston, Bartle, Mendez-Santiago and Teja, the Peng–Robinson and Soave–Redlich–Kwong equation of state models are compared to the one estimated by using the proposed neural network model. The average absolute deviation (AAD) of 5.42% compared to those of density-based and equation of state models, representing the reasonable accuracy of the developed model for estimating the solubility of solutes in supercritical fluid extraction process.

A predictive approach for thermodynamic modeling of solubility in supercritical fluids using genetic algorithm

The interaction parameter kij used in various mixing rules is not always available. The present work deals with its determination using a group contribution approach which itself is based on group interaction parameters. To date the interaction parameters matrix concerns twelve groups only. Therefore new parameters were determined by optimizing a well defined objective function by means of the genetic algorithm (GAs) and using the Predictive Soave Equation of State (PSEOS) with the van der Waals mixing rule (VDW MR), considering the solubility of organic solutes in supercritical carbon dioxide at elevated pressure ranging from 60 to 350 bar.

Properties of thin Teflon AF 2400 coatings deposited onto carbon fabric from solutions in supercritical carbon dioxide

For the design of hydrophobized conductive gas diffusion layers of the electrodes of polymercontaining fuel cells, of great interest is the method for the formation of a fluoropolymer film from fluoropolymer solution in supercritical carbon dioxide. The present work describes the systematic studies on the carbon-fabric-deposited Teflon AF 2400 coatings obtained by this method. The electrical and geometric characteristics of the coatings, their elemental compositions, and stabilities are studied. It is shown that supercritical carbon dioxide allows the deposited fluoropolymer to penetrate homogeneously into the depth of carbon fabric to form a uniform coating around single individual fibers. The optimum limits of variation in the Teflon AF 2400 amount upon production of the gas diffusion layers of polymer electrolyte, alkaline, and phosphoric acid fuel cells are determined.

Investigation of low-molecular fluoraparifin solution in supercritical carbon dioxide by IR-spectroscopy method

Investigation of low-molecular fluoraparifin solution in supercritical carbon dioxide by IR-spectroscopy method

Simplified calculation of solubility of solid solutes in supercritical carbon dioxide by EoS models

Equations of State (EoSs) have been widely used in calculating solubility of solutes in supercritical carbon dioxide (SCCO2). However, the traditional EoS models, need the data of sublimation vapor pressure and critical parameter of solutes, which are difficult to obtain, and the calculation procedure is also complicated. In this study, simplifications and approximations were made towards combinations of three EoSs (Soave-Redlich-Kwong, Peng-Robinson, and modified Esmaeilzadeh-Roshanfekr) and five mixing rules (Huron-Vidal, van der Waals one and two, modified covolume-dependent, and Wong-Sandler) to overcome the above limitations. After simplifications and approximations, the modified models have been reduced into two groups, including two and three parameter models. At last, the models in the work of Yazdizadeh et al. (2012) and four semi-empirical models (Chrastil, Valle and Aguilera, Sung and Shim, and Sparks) were used for comparison, and comparative analysis suggests that the new models in this work are better.

Water-gas shift reaction on alumina-supported Pt-CeOx catalysts prepared by supercritical fluid deposition

Alumina-supported platinum catalysts, both with and without ceria, were prepared by supercritical fluid deposition and evaluated for activity for water-gas shift reaction. The organometallic precursor, platinum(II) acetylacetonate, was deposited from solution in supercritical carbon dioxide. Analysis of the catalysts by high resolution scanning transmission electron microscopy indicated that platinum was present in the form of highly dispersed metal nanoparticles. Pretreatment of the alumina-supported ceria in hydrogen prior to the deposition of the platinum precursor resulted in more platinum nucleated on ceria than non-pretreated alumina-supported ceria but varied in both particle size and structure. The ceria-containing catalyst that was not pretreated exhibited a more uniform particle size, and the Pt particles were encapsulated in crystalline ceria. Reaction rate measurements showed that the catalyst was more active for water-gas shift, with reaction rates per mass of platinum that exceeded most literature values for water-gas shift reaction on Pt-CeOx catalysts. The high activity was attributed to the significant fraction of platinum/ceria interfacial contact. These results show the promise of supercritical fluid deposition as a scalable means of synthesizing highly active supported metal catalysts that offer efficient utilization of precious metals.

Experimental and theoretical analysis of the diffusion behavior of chromium(III) acetylacetonate in supercritical CO2

The tracer diffusion coefficients, D12, of solutes in supercritical carbon dioxide (SC-CO2), modified or not with cosolvents, are necessary for industrial and research applications. In this study, the determination and analysis of D12 values of chromium(III) acetylacetonate in SC-CO2 are presented. The measurements were carried out by the chromatographic impulse response (CIR) method from 308.15 to 333.15K at pressures from 125 to 250bar, and yield diffusivities between 0.570ÿ10⿿4 and 1.529ÿ10⿿4cm2⿿s⿿1 The experimental trends of D12 with temperature, pressure, density, and Stokes-Einstein coordinates are also presented. Eleven equations were evaluated for modeling the new data, and the best results were achieved using the semi-empirical correlations of Magalhães et al. (error of 1.95% and 1.90%), the universal model of Lito et al. (2.01%), and the predictive modified Stokes⿿Einstein equation (3.16%) and Vaz et al. expression (3.27%). Finally, a comparison between the diffusivities of this work and those reported in the literature for other metal acetylacetonates (Co(acac)3, Cr(acac)3, Pd(acac)2 and Pt(acac)2) was accomplished, being possible to conclude that the correct interpretation of the diffusive phenomenon of these systems requires not only the molecular weight but also solute diameter.

Semi-empirical models and a cubic equation of state for correlation of solids solubility in scCO2: Dyes and calix[4]arenes as illustrative examples

Knowledge of a compound's solubility in the supercritical solvent is crucial to the definition of the optimal operating conditions and consequently to the development of supercritical applications.The present paper examines the performance of two of the most widely used groups of models for correlating the solubility of solid solutes in supercritical carbon dioxide – equations of state (EoSs) and semi-empirical density based models. The Soave-Kwong-Redlich (SRK) EoS with the one-fluid van der Waals mixing rule represents cubic EoSs, while the group of the density-based models includes Chrastil, Kumar and Johnston, Bartle et al., Méndez-Santiago and Teja, Garlapati and Madras, Nejad et al. and Khansary et al. models.The seven solutes chosen as illustrative examples are compounds of interest to the dry dyeing processing techniques and biotechnological processes and have diverse structural complexity.The results obtained reveal that the more recently advocated density-based models (Garlapati and Madras, Nejad et al. and Khansary et al. models) perform better with overall average absolute deviations, AARD, of 6.5, 9.0 and 9.3%, respectively. The 6.7% overall AARD for the SRK CEoS is acceptable and it can be used as a reliable thermodynamic model to predict the solubility of any compound for which there is no sufficient experimental data available.

Solid Oil Particles Formation of Ginger Rhizome Using Rapid Expansion Supercritical Carbon Dioxide Solution (RESS) as an Environmentally Friendly Method

Particles formations of ginger rhizome were successfully produced by using Rapid expansion supercritical solution (RESS). In this study, effect of extraction temperature (40,45,55 and 65 °C) and constant extraction pressure 4000 Psi were investigated on the particle size of the produced particles. Based on the different experimental conditions, the smallest particle size of ginger after processing via the RESS process was obtained at extraction temperature of 40 °C and extraction pressure, 4000 Psi. Temperature is the one factor that can affect the average particle size of the solid oil particle. The size of the ginger particles were monitored by scanning electron microscopy (SEM).

Modification of polymethylmethacrylate by means of diffusion introduction of single-walled carbon nanotubes in supercritical carbon dioxide

Amorphous polymethylmethacrylate has been modified by means of impregnation suspension of single-walled carbon nanotubes in alcoholic solution in supercritical carbon dioxide. Properties of the so formed composite have been studied. Thermal stability of the polymer has increased after the modification.

Interfacing supercritical fluid reaction apparatus with on-line liquid chromatography: Monitoring the progress of a synthetic organic reaction performed in supercritical fluid solution

An interface has been developed that connects a supercritical fluid reaction (SFR) vessel directly on-line to a liquid chromatograph. The combined SFR-LC system has enabled the progress of the esterification reaction between phenol and benzoyl chloride to synthesize phenyl benzoate in supercritical fluid carbon dioxide solution to be dynamically monitored. This was achieved by the periodic SFR-LC analysis of samples directly withdrawn from the esterification reaction mixture. Using the series of SFR-LC analysis results obtained for individual esterification reactions, the reaction progress profile for each esterification reaction was obtained by expressing the measured yield of phenyl benzoate as a function of reaction time. With reaction temperature fixed at 75°C, four sets (n=3) of SFR-LC reaction progress profiles were obtained at four different SFR pressures ranging from 13.79 to 27.58MPa. The maximum SFR yield obtained for phenyl benzoate using a standard set of reactant concentrations was 85.2% (R.S.D. 4.2%) when the reaction was performed at 13.79MPa for 90min. In comparison, a phenyl benzoate yield of less than 0.3% was obtained using the same standard reactant concentrations after 90min reaction time at 75°C using either: heptane, ethyl acetate or acetonitrile as conventional organic reaction solvents.

Development of a Semicontinuous Spray Process for the Production of Superhydrophobic Coatings from Supercritical Carbon Dioxide Solutions

Superhydrophobic surfaces have been fabricated in a continuous spray process, where an alkyl ketene dimer (AKD) wax is dissolved in supercritical carbon dioxide (scCO2) and sprayed onto the substrate. The mass of extracted AKD from scCO2 has been investigated as well as the pressure, temperature, and flow of CO2 at the steady-state spray conditions. Several different substrates such as glass, aluminum, paper, poly(ethylene terephthalate) (PET), and polytetrafluoroethylene (PTFE) have been successfully coated, and the superhydrophobic properties have been evaluated by measurement of water contact angle, water drop friction, scanning electron microscopy (SEM), and surface topography. The most efficient spray process, considering surface properties and mass of extracted AKD, is obtained at the lowest temperature investigated, 67 °C, and the highest pressure evaluated in this study, 25 MPa. We also show that the influence of preexpansion conditions (p, T) on the surface temperature at the selected spray distance (3 cm) is negligible by measurement with an infrared camera during spraying.

Experimental study of water (Micro) droplet formation from its saturated solution in supercritical carbon dioxide

The formation of micron-size water droplets in supercritical carbon dioxide (SC-CO2) in a high-pressure cell with sapphire windows is studied experimentally using in situ laser diffractometry. According to the analysis of diffraction patterns of laser radiation scattered on water droplets in SC-CO2 and optical microscopy data at 10.0 MPa and 40°C, the mean diameter of water droplets is 55 ± 3 μm.

Synthesis of highly dispersed silver nanoparticles or nano-network modified KIT-6 using supercritical carbon dioxide

Mesoporous KIT-6-supported highly dispersed silver nanoparticles and nano-networks were successfully synthesized in supercritical carbon dioxide and co-solvent solution using AgNO3 as a precursor, followed by calci- nations. The nanocomposites were characterized by XRD, TEM, ICP, and N2 adsorption-desorption isotherms. Three kinds of co-solvents were investigated including ethanol, the mixture of ethanol and ethylene glycol, and the mixture of ethanol and water. It was found that when only ethanol was used as a co-solvent, a small amount of AgNO3 was deposited onto the complex nanochannels of KIT-6 even if the deposition time was 12 h. However, it took a short deposition time of 1 h to deposit a large amount of pre- cursors onto the substrates when the mixture of ethanol and ethylene glycol and the mixture of ethanol and water were used as co-solvents. The large solubility of AgNO3 in ethylene glycol or water had a positive effect on the dis- solution of precursor in scCO2, which was beneficial to the adsorption of precursor on the substrates.

Electrochemical performance of fuel cell catalysts prepared by supercritical deposition: Effect of different precursor conversion routes

Supercritical deposition (SCD) is used to prepare carbon-supported Pt nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me2) is adsorbed from supercritical carbon dioxide (scCO2) solutions onto Vulcan VX-72 at 13.2MPa and 50°C. The adsorbed metal precursor is converted to its metal form via three different routes: thermal conversion in N2 at ambient pressure (route 1), thermal conversion in scCO2 (route 2), or chemical conversion in H2 at ambient pressure (route 3). Sequential SCD is used in routes 1 and 3. The mean diameters of the synthesized Pt nanoparticles are smallest for route 1 and largest for route 3. Nano-scale morphology of the electrocatalysts is characterized using transmission electron microscopy (TEM), revealing narrower Pt particle size distributions for the catalyst prepared via route 1 than for those synthesized by routes 2 and 3. Electrocatalyst prepared using route 1 showed the best performance both in specific activity (measured via cyclic voltammetry) and in PEMFC tests among electrocatalysts prepared using different routes.

Codeposition of Cu/Ni thin films from mixed precursors in supercritical carbon dioxide solutions

In this article, we report on the codeposition of Cu and Ni thin films in supercritical CO2 solutions to gain a general understanding of alloy deposition in a supercritical medium as well as the interdiffusion between Cu and Ni. Films were deposited directly onto TiN films supported on SiO2/Si wafers in a supercritical CO2 solution using a batch reactor. Cu and Ni deposited as separate films, where Cu deposited initially. Alloying upon annealing was also investigated. During an in situ X-ray diffraction measurement above 300 °C, both Cu and Ni diffused through each other and formed an alloy that further improved adhesion at the copper/insulator interface.

A NEW SIMPLE CORRELATION FOR CALCULATING SOLUBILITY OF DRUGS IN SUPERCRITICAL CARBON DIOXIDE

During the past 20 years, supercritical fluid (SCF) based technologies have been gaining an increasing attention through the academic and industrial communities due to its advantages. One of the most important parameter for any supercritical-based technologies is the knowledge of the solute solubility at different pressures and temperatures. But, due to several concerns e.g. time and expense, measuring the solubility of all compounds in wide ranges of temperature and pressure is not possible. Respect to this, a new empirical correlation with four fitting parameters has been proposed to correlate the solubility of pharmaceuticals in different temperatures and pressures. The obtained results compared with four widely used density based correlations including Mendez-Santiago and Teja (MST), Bartle et al., Chrastil, Kumar and Johnston (KJ) revealed rather good capability of the proposed simple correlation for predicting the solubility of solutes in supercritical carbon dioxide (SC- CO 2). At last, the obtained results compared with the results of three Equations of State (EoS's) with three different mixing rules.

Improved hydrodynamic equations for the accurate prediction of diffusivities in supercritical carbon dioxide

The tracer diffusion coefficients are fundamental quantities in simulation and design. Due to the increasing interest upon biorefinery and sustainability in general, green solvents and processes, like carbon dioxide and supercritical fluid extraction, are attracting relevance in both chemistry and chemical engineering research and development. In this work, tracer diffusion coefficients at infinite dilution are focused aiming to propose reliable models for their pure estimation. Four predictive hydrodynamic models were proposed on the basis of modifications introduced in the original expressions of Wilke–Chang, Scheibel, Lusis–Ratcliff, and Tyn–Calus. The modified equations provide reliable results with average absolute errors between 7.86% and 8.56%, and inferior dispersion around the averages. On the contrary, the original correlations taken from the literature achieve errors between 11.89% and 27.25%, along with higher scattering of results. Furthermore, the new expressions offer average errors between 0.47% and 0.53%, while the original ones provide systematic overestimations between 2.95% and 27.23%. In the whole, the new expressions proposed in this work are equally able to predict accurately tracer diffusion coefficients of any solutes in supercritical carbon dioxide.