Acid In Supercritical CO2 Research Articles

Solubility of solid carnosic acid in supercritical CO 2 with ethanol as a co-solvent

The present study is devoted to the experimental measurement and thermodynamic modeling of solid carnosic acid solubility in supercritical CO 2 + ethanol as a co-solvent. Measurements were carried out at temperatures in the range of 313.15 and 333.15 K, pressures ranging from 280 to 400 bar, and at different content of the modifier ethanol (from 0.7 to 10%). The Group Contribution Associating Equation of State (GCA-EoS) [H.P. Gros, S.B. Bottini, E.A. Brignole, High pressure phase equilibrium modeling of mixtures containing associating compounds and gases, Fluid Phase Equilibria 139 (1997) 75–87] was applied in this work to represent the experimental solubility data obtained. Due to the lack of information in the literature about pure carnosic acid parameters, its solid volume, critical properties, and sublimation pressures were estimated in this work. The key step in the thermodynamic modeling proved to be the introduction of a solute hard-sphere parameter in the Carnahan–Starling repulsive term of the model, which depends on both temperature and pressure.

Solubilities of benzoic acid in supercritical CO 2 with mixed cosolvent

The solubilities of benzoic acid in supercritical CO 2 with pure and mixed cosolvent were measured at pressures from 8.0 to 23.0 MPa and 328.15 K for pure cosolvent, and 308.15, 318.15 and 328.15 K for mixed cosolvent. The experiments were carried out by using a flow-type phase equilibrium apparatus. The effect of cosolvents, ethyl acetate, ethanol and ethyl acetate + ethanol (molar ratio 1:1) was studied at the concentration of 2.0 mol%. The results show that the solubility enhancement follows the order: ethanol > ethyl acetate + ethanol > ethyl acetate. The measured solubilities were correlated using a modified Chrastil equation, and the calculated results are in good agreement with the experimental data.

Micellar catalysis for partial oxidation of toluene to benzoic acid in supercritical CO 2: effects of fluorinated surfactants

One of the key hindrances on development of solid catalysts containing cobalt species for partial oxidation of organic molecules at mild conditions in conventional liquid phase is the severe metal leaching. The leached soluble Co species with a higher degree of freedom always out-performs those of solid supported Co species in oxidation catalysis. However, the homogeneous Co species concomitantly introduces separation problems. We have recently reported for the first time, a new oxidation catalyst system for the oxidation of organic molecules in supercritical CO 2 using the principle of micellar catalysis. [CF 3(CF 2) 8COO] 2Co· xH 2O (the fluorinated anionic moiety forms aqueous reverse micelles carrying water-soluble Co 2+ cations in scCO 2) was previously shown to be extremely active for the oxidation of toluene in the presence of sodium bromide in water–CO 2 mixture, giving 98% conversion and 99% selectivity to benzoic acid at 120 °C. In this study, we show that the effects of varying the type of surfactant counterions and the length of the surfactant chains on catalysis. It is found that the use of [CF 3(CF 2) 8COO] 2Mg· yH 2O/Co(II) acetate is as effective as the [CF 3(CF 2) 8COO] 2Co· xH 2O and the fluorinated chain length used has a subtle effect on the catalytic rate measured. It is also demonstrated that this new type of micellar catalyst in scCO 2 can be easily separated via CO 2 depressurisation and be reused without noticeable deactivation.

Measurement of solubilities of palmitic acid in supercritical carbon dioxide and entrainer effect of water by FTIR spectroscopy

The solubilities of palmitic acid in supercritical CO 2 and supercritical CO 2+water were measured by using a static recirculation method combined with on-line Fourier transform infrared (FTIR) spectroscopy. Experiments were carried out at 15.0 MPa and 313.2 K. The peak of CH 2 symmetric stretching band for palmitic acid was used to measure the solubilities of palmitic acid. The solubility of palmitic acid in supercritical CO 2 saturated with water was found to be 16% larger than that in supercritical CO 2. The interaction between palmitic acid and water was investigated, and the amount of interaction species was determined by using FTIR spectroscopy. The noticeable bands were the CO stretching bands for palmitic acid. It was also found that the solubility of palmitic acid in supercritical CO 2 increased with increasing molarity of water, because of the interaction between water and carboxyl group in palmitic acid.

Solubility of the diarrheic shellfish toxin okadaic acid in supercritical CO2

AbstractThe solubility of okadaic acid (OA) in supercritical CO2 was measured using a flow‐type apparatus with sequential sampling during dynamic nonrecirculating experiments at saturation conditions. Methanol and water were used as solvent modifiers of CO2. Collected OA was measured by high‐performance liquid chromatography with fluorimetric detection after derivatization with 1‐bromoacetylpyrene to obtain the labeled ester of the toxin. Solubility results were obtained with methanol concentrations ranging from 0 to 8.5% volume in the CO2 density range of 0.495 to 0.913 g/mL at 40, 60, and 73°C. Measured solubility of OA ranged from 0 to 15×10−6 mol/L, increasing with methanol concentration and fluid density and diminishing with temperature. Experiments with water‐modified CO2 up to 0.3% volume (near saturation) were done at 60°C; solubilities of OA up to 5×10−6 mol/L were measured. This is the first approach to handle the liposoluble diarrheic shellfish toxins with supercritical CO2. The study, with pure OA, provides useful information regarding the effects of pressure, temperature, and addition of modifiers on its solubility. Obtained results show that the toxin can be solubilized in this media and potential applications are suggested and being currently investigated.

Assessment of Solubility of Ketoprofen and Vanillic Acid in Supercritical CO2 under Dynamic Conditions

The use of supercritical fluids, and in particular supercritical carbon dioxide (SC-CO2), can be foreseen in a wide range of techniques and processes within pharmaceutical sciences. When dealing with both drugs and formulation adjuvants, the determination of the relevant solubilities in SC-CO2 represents a mandatory prerequisite, underlying the development of industrial scale operations. The aim of this work concerned the experimental determination of the solubility in SC-CO2 of vanillic acid and ketoprofen by means of an easy-to-use plant designed and assembled to operate in dynamic conditions. Its reliability was preliminarily checked by comparing solubility data obtained for salicylic acid and naphthalene with literature ones. Solubility measurements for ketoprofen and vanillic acid were carried out at 313 and 328 K in the 9−25 MPa pressure range. Crossover pressures of 16 MPa and 15 MPa were found for ketoprofen and vanillic acid, respectively. The solubility data were worked out according to a thermodynamic approach, which relies on the Peng−Robinson equation of state.

Solubilities of lactic acid and 2-hydroxyhexanoic acid in supercritical CO 2

Solubilities of lactic acid and 2-hydroxyhexanoic acid in supercritical CO 2 have been measured at T=(311 or 313, 318, 328 K) in the pressure range from 50 to 200 bar. The measurements have been performed using a flow-type apparatus. The solute solubility in compressed carbon dioxide increased with pressure at all investigated temperatures. At pressures below 130 bar, a solubility decrease on temperature increase was observed. An accurate correlation method for the solubility of low volatile substances in supercritical CO 2 has been applied for the interpolation of the experimental results.

Solubility of stearic acid in supercritical CO2‐acetonitrile mixtures

AbstractThe solubility of stearic acid in supercritical CO2 with acetonitrile (CH3CN) cosolvent was measured at 318. 15 K in the pressure range hm 9.5 to 16.5 MPa, and the cosolvent concentration ranges from 0. 0 to 5.5 mol%. The solubility increases with acetonitrile concentration and pressure, and it also increases with the apparent density of CO2 d1 (moles of CO2 in per liter of fluid) at higher co solvent concentrations. At lower d1, however, the solubility of the acid at lower acetonitrile concentrations is lower than that in pure CO2 provided that d1 is fixed, which is discussed qualitatively based on the clustering of the components in the system.

Solubility of behenic acid in supercritical carbon dioxide with ethanol

The solubilities of behenic acid in supercritical CO 2 with and without ethanol cosolvent were determined at 308.15 K and 318.15 K in the pressure range from 8.0 to 16.0 MPa, and the concentration of cosolvent ranged from 0 to 6.5 mol%. The corresponding density of the fluid phase was also determined. The effects of the cosolvent concentration, fluid density, pressure, and temperature on the solubility are discussed. The solubility increases with ethanol concentration, pressure, and the apparent density d 1 (moles of CO 2 per liter of the fluid) of CO 2 at higher ethanol concentrations.

Solvent effect on monomer–dimer equilibrium in supercritical fluid: Spectroscopic and thermodynamic studies

The monomer–dimer equilibrium of lauric acid in supercritical CO2 was studied at different temperatures and pressures using FTIR spectroscopy. The equilibrium constant and thermodynamic properties of the dimerization were obtained based on the spectroscopic determinations. It has been found that fluid density plays an important role on the dimerization. Thermodynamic studies on the equilibrium suggested that there may be differential solvent effects on the monomer and dimer. At lower density, the solvent aggregates about the solute and, therefore, the differential solvent effect is significant. With increase in density the solvent–solute clustering and differential solvent effect decrease, and the supercritical solution becomes more homogeneous.

Carbonylation of methanol in supercritical CO2 catalysed by a supported rhodium complex

A rhodium complex supported on polyvinylpyrrolidone catalyses the carbonylation of methanol to methyl ethanoate and ethanoic acid in supercritical CO2 at rates up to ca. 50% those in liquid solution but with minimal catalyst leaching.

Effect of acetic acid+acetonitrile and ethanol+acetonitrile mixed cosolvents on the solubility of stearic acid in supercritical CO 2

The solubility of stearic acid in supercritical (SC) CO 2 with acetic acid+acetonitrile (molar ratio 1:1) and ethanol+acetonitrile (molar ratio 1:1) mixed cosolvents was measured at 318.15 K in the pressure range from 95 to 160 bar, and the total cosolvent concentrations range from 0 to 6 mol%. The density of the fluid phase was also determined, and the effects of pressure, cosolvent concentration, and apparent density of CO 2 on the solubility have been discussed. The solubility data for the solute in CO 2+pure cosolvent binary mixtures was combined. It is known that enhancement of the solubility by the cosolvents follows the order: acetic acid>acetic acid+acetonitrile>acetonitrile, and ethanol>ethanol+acetonitrile>acetonitrile. In other words, the effect of each binary cosolvent on the solubility lies between those of the two pure cosolvents.

Solubility of stearic acid in supercritical CO 2-acetic acid and CO 2- n-octane mixtures at 308.15 K

The solubility of stearic acid in supercritical CO 2 with n-octane and acetic acid cosolvents was measured at 308.15 K in the pressure range from 80 to 160 bar and the cosolvent concentrations range from 0.0 to 3.5 mol%. The density of the fluid phase was also determined. The solubility increases with the concentrations of the cosolvents (Y 3) and pressure. However, the solubility increases very slowly with Y 3 at higher Y 3 when acetic acid is used as a cosolvent, mainly because acetic acid can associate with itself. In CO 2-acetic acid mixture, the solubility increases with Y 3 provided that the apparent density of CO 2 d 1 (moles of CO 2 per liter of fluid) is fixed. In CO 2- n-octane mixture, the solubility also increases with Y 3 at higher d 1. However, at lower d 1 and Y 3 the solubility decreases with Y 3 at fixed d 1. It was found that clustering between CO 2 and the cosolvent reduces the efficiency of CO 2 to dissolve the solute.

Hydrogen bonding of some organic acid in supercritical CO 2 with polar cosolvents

FTIR spectroscopy was used to study the hydrogen bonding of benzoic acid and salicylic acid with ethanol and methanol in supercritical CO 2. The extent of hydrogen bonding was estimated from the hydrogen-bonded and nonhydrogen-bonded infrared absorption bands. It was found that the solutes and the cosolvents can form hydrogen bondings even their concentrations are very low. At constant solute concentrations, the extent of hydrogen bonding increases with cosolvent concentrations.

Effect of ethanol and n-octane on the solubility of stearic acid in the supercritical CO 2

Solubilities of stearic acid in supercritical CO 2 with ethanol and n-octane cosolvents were determined at 318.15 K in the pressure range from 96 to 165 bar, and the cosolvent concentrations range from 0.0 to 3.7 mol%. The corresponding densities of the fluid phases were also measured. It was observed that both of the cosolvents enhance the solubility significantly. The solubility increases with pressure noticeably at lower pressures, especially at lower cosolvent concentrations. The effect of pressure on the solubility is very limited at higher pressures or higher cosolvent concentrations.

Solubility of stearic acid in supercritical CO 2 with cosolvents

The solubility of stearic acid in CO 2 + acetic acid and CO 2 + methyl acetate binary mixtures was measured at 318.15 K in the pressure range 90–165 bar and the cosolvent concentration range 0.0–5.1 mol%. The solubility data are discussed qualitatively on the basis of the chemical association principle, which indicates that the larger solubility enhancement by acetic acid is primarily caused by the stronger hydrogen bond between the solute and acetic acid.

Asymmetric hydrogenation of α,β-unsaturated carboxylic acids in supercritical carbon dioxide

Hydrogenation of tiglic acid in supercritical CO 2 catalyzed by a chiral H 8-BINAP-Ru(II) complex proceeds cleanly with cis stereochemistry to afford 2-methylbutanoic acid in up to 89% ee and over 99% yield.