Acid In Supercritical Carbon Dioxide Research Articles

High-yield production of lactide isomers from depolymerization of polylactic acid in supercritical carbon dioxide

Chemical depolymerization of polylactic acid (PLA) was demonstrated in supercritical carbon dioxide medium. No catalyst, organic solvent or water was employed in the reaction. The primary feedstocks used in ring opening polymerization of PLA, lactide isomers, were produced with high yield. More specifically, lactides were produced as the sole nongaseous products with a 93 % yield based on the initial polymer mass at 200 °C and 310 bar in 120 min. The influences of the reaction temperature, time, and pressure on PLA depolymerization products were investigated. While the lactide yield and distribution were highly influenced by the reaction temperature and time, further improvement was attained with an increase in the pressure. The results demonstrate that supercritical CO2 can be applied as a promising reaction medium for PLA degradation, providing a high-yield production of its feedstock. The process can enable green depolymerization of polylactic acid and promote its circular economy with a closed loop production.

Precipitation copolymerization of methyl methacrylate/meth‐acrylate acid in supercritical carbon dioxide

AbstractUtilizing 2,2′‐azobis(isobutyronitrile) (AIBN) as the initiator, the copolymerization of methyl methacrylate/methacrylate acid is performed by precipitation copolymerization. The effects of pressure, initiation concentration, the methacrylic acid (MA) concentration, and small amount of water are investigated separately. The morphology and molecular weight are analyzed by scanning electron microscopy and gel permeation chromatography, respectively. The results indicates that the concentration of MA or AIBN affects the molecular weight greatly, and the maximum molecular weight reaches 213 kDa. The morphology of samples exhibits a certain degree of agglomeration. Most samples are obtained as free‐flowing powder with numerous spherical bulges under a proper polymerization condition.

Solubility studies on 2-hydroxyisobutyric acid in supercritical carbon dioxide: Solubility evaluation and application to actinide extraction

• First report on solubility of 2-hydroxyisobutyric acid in SCCO 2. • Solubility correlated with semi-empirical/empirical and equation of state models. • Development of supercritical method for recovery of actinide ions. • Demonstration of recovery of U and Th from aqueous/solid/cellulose matrix. The solubility of 2-hydroxyisobutyric acid in supercritical carbon dioxide is experimentally determined using a flow saturation technique. The experimental solubility data was generated at 308, 313, 318 and 323 K with pressures ranging from 10 to 20 MPa. The solubility data was found to range from 0.4 × 10 −3 mol·mol −1 to 5.7 × 10 −3 mol·mol −1 . The solubility data was correlated with two semi-empirical equations, Mendez-Santiago and Chrastil equation. The self-consistency of the data is verified with Mendez-Santiago model. Peng-Robinson equation of state combined with van der Walls mixing rules was also employed to correlate the solubility data. All three models have successfully correlated the solubility data with an average deviation of < 7%. Based on the solubility data, supercritical fluid extraction based method was developed for the recovery of uranium and thorium from solid/liquid matrices (cellulose matrix, uranyl and thorium nitrates, aqueous medium) using 2-hydroxyisobutyric acid as a ligand.

Solubility of pyridine-2,6-dicarboxylic acid in supercritical carbon dioxide and its application for removal of lead and nickel in simulated matrices

The solubility of pyridine-2,6-dicarboxylic acid in supercritical carbon dioxide was measured at 313–333 K and 10–20 MPa, using a flow-saturation technique. The influence of methanol on solubility behavior is investigated. The solubility in neat supercritical carbon dioxide ranged from 0.44 × 10−6 mol·moltot−1 to 3.4 × 10−6 mol·moltot−1, while its solubility in presence of methanol ranged from 0.17 × 10−5 mol·moltot−1 to 18.1 × 10−5 mol·moltot−1. The solubility data was modeled with Chrastil, Mendez-Teja, Garlapati equations and Peng-Robinson equation of state model. The solubility in the presence of methanol was correlated using modified Chrastil, modified Mendez-Teja and Thakur models. Among the models employed, Chrastil model (binary system) and modified Mendez-Teja model (ternary system) shown highest accordance with experimental data. Pyridine-2,6-dicarboxylic acid was employed as a chelating agent for development of a supercritical fluid extraction method for removal of Pb2+ and Ni2+ from simulated aqueous/soil matrices.

A molecular insight into poly(methyl methacrylate) impregnation with mefenamic acid in supercritical carbon dioxide: A computational simulation

The process of poly(methyl methacrylate) (PMMA) matrix impregnation with mefenamic acid (MFA) in a supercritical carbon dioxide medium has been studied by the full atomistic classical molecular dynamics method. Simulations have been performed for two systems that differ in the polymer sample size (≈270 kDa and ≈1080 kDa) at 333 K and 40 MPa. The characteristics of the systems, such as the radius of gyration, end-to-end distance, mean squared displacement, radial distribution functions, average number of hydrogen bonds, and number of close contacts, have been analyzed and discussed. It has been found that by the end of the simulation (15 ns), the MFA loadings reach about 1.43 w/w % and 1.14 w/w % for the small and big PMMA samples, respectively. It was shown that the solute was distributed in the molecular form inside the polymer matrix. At the same time, when the CO2 molecules were removed from the systems and the simulation was performed in a canonical ensemble with the same cell length as in the previous isobaric-isothermal ensemble, the MFA molecules began to self-associate and get adsorbed on the polymer surface as hydrogen-bonded aggregates. In order to estimate the strength of the intermolecular interaction between the system components, ab initio calculations were performed. The calculated energies of the electron donor–acceptor (EDA) and hydrogen-bonded (HB) complexes can be arranged in the following order (in absolute value): ΔEEDA(PMMA-CO2)≈ΔEHB(MFA-CO2) < ΔEHB(PMMA-MFA) < ΔEHB(MFA-MFA).

Surface modification of TiO2 nanoparticles with terephthalic acid in supercritical carbon dioxide

This paper presents a supercritical CO2 strategy for surface modification of TiO2 nanoparticles with carboxylic acids. The reaction between TiO2 nanoparticles and terephthalic acid molecules in sc-CO2 provides carboxylic acid-modified TiO2 nanoparticles with a modification efficiency much higher than the conventional solvent immersion method. From the statistical method of response surface methodology, modifier ratio 4.04 (mol/mol), temperature 401.5 K, and pressure 14.8 MPa resulted in an optimum modification rate of 25.34%. The modified TiO2 was characterized by FTIR, TG-DTA, FE-SEM, TEM-EDS, and zeta potential analysis. The results showed the surface modification of TiO2 in sc-CO2 is made of modifier molecules bonding chemically. Surface modification by terephthalic acid affects the surface electrical property of TiO2 nanoparticles in water, leading to a positive charge surface. Since this method is ecologically and environmentally friendly, it can be applied in precursor composites for the synthesis materials of biomedical application.

Experimental measurement and correlation of phase equilibria of palmitic, stearic, oleic, linoleic, and linolenic acids in supercritical carbon dioxide

Supercritical carbon dioxide (SC-CO2) represents a promising solvent in the synthesis of biodiesel given its enhanced mass transfer properties as well as its high affinity to the fatty acids. In this work, the phase equilibria data of 5 major fatty acids: palmitic, stearic, oleic, linoleic, and linolenic acid in SC-CO2 were studied experimentally at temperature between 343.15 to 373.15K and pressures between 8 to 24MPa. The experimental data were correlated using Peng–Robinson Equation of State with van der Waals (PR-vdW), Panagiotopoulos-Reid (PR-PR), and Stryjek-Vera (PR-SV) combining rules. The fitting result by PR-PR was shown to be more accurate and consistent than those of PR-vdW and PR-SV. From these data, we found that oleic acid has the greatest solubility in SC-CO2, followed by linoleic acid, palmitic acid, stearic acid, and lastly, linolenic acid.

Rigorous Modeling of Solubility of Acid in Supercritical Carbon Dioxide Using Connectionist approach: Comparison between ANN and density based modeling

ABSTRACT Recently, supercritical fluid has a wide application in different industries; due to this fact, researchers have a great tendency to investigate these types of fluids and their properties. The solubility, as the important properties of supercritical, is a function of different parameters. Since the experimental tests and investigations are costly and requires lots of time, a computational investigation was designed to estimate the solubility acids with different characteristic in supercritical CO2 (SC-CO2). A well-trained multilayer network was used to estimate the solubility of different acids in SC-CO2 as a function of various parameters. These factors or parameters are pressure, temperature, molecular weight of acid, carbon number, hydrogen number, and values of constant for acid dissociation. For the training and testing step of the modeling, 180 data points from the literature were utilized. The comparison between experimental data and estimated values of acid solubility illustrated that the predicting connectionist model for acid solubility estimation of acids in SC-CO2 has high accuracy based on reported statistical parameters, so the aforementioned model is reliable for estimation of solubility. This model also was compared with the density-based model, and the ANN results demonstrate that the proposed model is reliable than the density-based model. R2 (coefficient of determination) and average relative absolute deviation (AARD) corresponded to ANN and density-based modeling are 0.9125 and 1.2688, 0.9989, and 0.9759, respectively. The mentioned parameters are the statistical witness for the superiority of ANN against the density-based model.

Solubility of Phenylphosphinic Acid in Supercritical Carbon Dioxide and the Influence of Methanol on the Solubility Behavior

The solubility of phenylphosphinic acid (PPA) was measured for the first time in supercritical carbon dioxide (SCCO2) at 313, 323, and 333 K with pressure ranging from 10–20 MPa using a dynamic flo...

Polymorphism and conformations of mefenamic acid in supercritical carbon dioxide

In this paper we have studied the conformations of mefenamic acid molecules in its saturated solution in supercritical carbon dioxide being in contact with bottom phase containing different polymorphs of mefenamic acid under isochoric heating conditions in the temperature range of 80–220 °C. For this purpose, we used in situ IR and Raman spectroscopy as well as micro IR and micro Raman spectroscopy and quantum chemical calculations. We have found that there is a correlation between the polymorphic modifications of the crystalline form of mefenamic acid and its conformers in CO2 fluid phase. The results of this work have shown that it is possible to monitor the polymorphic transformation of the crystalline phase of mefenamic acid by screening its molecular conformations in a fluid solution. This finding opens up the possibilities to manage the obtaining of certain polymorph of mefenamic acid with high purity degree from its fluid solution by means of variation of thermodynamic parameters of this solution.

Solubility measurement and RESOLV-assisted nanonization of gambogic acid in supercritical carbon dioxide for cancer therapy

Despite the captivating interest for its potential anticancer efficacy against multiple types of cancer and ability to overcome multidrug resistance, the practical application of gambogic acid (GA) has been hampered by its poor water solubility. Herein, the fabrication of nanosized GA particles (251.2 nm ± 85.6 nm) using eco-friendly supercritical fluid (SCF)-assisted rapid expansion of a supercritical solution into a liquid solvent (RESOLV) process was demonstrated. The equilibrium solubility of GA in supercritical carbon dioxide (SC−CO2) was initially determined at altered supercritical conditions (P: 10.0 MPa to 30.0 MPa, T: 308.15 K–328.15 K) and the obtained data points were then correlated using various density-based models including Méndez-Santiago and Teja, Bartle as well as Chrastil models. The solubility of GA in SC−CO2 was found to be between 1.63 × 10−6 and 22.62 × 10−6 in terms of GA mole fraction, and considerably good correlation agreement was obtained with all the applied models and being the lowest deviations obtained with the Méndez-Santiago and Teja model. Furthermore, the fabricated GA nanoparticles (NPs) through benign RESOLV technique, were systematically characterized. Subsequently, in vitro antiproliferation tests resulted in its augmented antitumor efficacy due to enhanced solubility of GA. Together, the results have suggested that the benign RESOLV process has successfully fabricated nanosuspensions of GA with enhanced bioavailability and antineoplastic efficacy and may have great potential in pharmaceutics.

Hydroxycinnamic acids in supercritical carbon dioxide. The dependence of cosolvent-induced solubility enhancement on the selective solvation

Simulation of hydroxycinnamic acids (caffeic, p-coumaric, ferulic, synapic) in pure and modified by polar cosolvents (methanol, acetone) supercritical carbon dioxide has been carried out using classical molecular dynamics. Dependences of solvation free energies of the acids on the pressure and cosolvent mole fraction have been calculated using Bennett’s acceptance ratio method. When a polar cosolvent is added, the solvation free energy decreases sharply, and with a subsequent increase in its concentration, it changes slightly. The cosolvent-induced effect decreases with increasing pressure. The structural parameters characterizing the selective solvation of the acids have been calculated. A correlation between the cosolvent-induced solubility enhancement and the average number of solute – cosolvent hydrogen bonds has been found.

Solubilities of Binary Systems α-Tocopherol + Capsaicin and α-Tocopherol + Palmitic Acid in Supercritical Carbon Dioxide

Solubilities of two binary mixtures (α-tocopherol + capsaicin and α-tocopherol + palmitic acid) in supercritical carbon dioxide (CO2) are reported in this work. Measurements were done in a semiflow...

Solvation of Hydroxybenzoic and Hydroxycinnamic Acids in Supercritical Carbon Dioxide: Formation of Hydrogen Bonds with a Polar Cosolvent

Selective solvation of ortho-hydroxybenzoic, meta-hydroxybenzoic, para-hydroxybenzoic, protocatechal, gallic, lilac, para-coumaric, and caffeic acids with a polar cosolvent (methanol) in supercritical carbon dioxide was studied at 318 K at a density of 0.7 g/cm3 and a methanol concentration of 3.5 mol % with conventional molecular dynamics. We studied the localization of a cosolvent in the nearest environment of a solute, the formation of cosolvent clusters around the solute, and the number and nature of hydrogen bonds between molecules of the solute and cosolvent. We also considered the structural features of hydrogen-bound complexes associated with a molecular structure of a solute (the number and the arrangement of hydroxyl groups, the substitution of hydroxyl hydrogen atoms with methyl moieties, and the presence of an ethylene group).

Features of solvation of phenolic acids in supercritical carbon dioxide modified by methanol and acetone

The study of solvation of three phenolic acids, 3,4,5-trihydroxybenzoic acid (gallic acid), 3,4-dihydroxybenzoic acid (protocatechuic acid), and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid), in pure, methanol-modified and acetone-modified (0.03 and 0.06mol fraction) supercritical (SC) carbon dioxide has been carried out by computational methods. Structural features of hydrogen-bonded complexes formation in modified SC media have been researched by using classical molecular dynamics at different densities corresponding to the experimental pressures 20 and 30MPa and temperatures from 313 to 333K. The results obtained have revealed that an increase of fluid density and cosolvent concentration provide increasing the average number of hydrogen bonds formed by the solute with cosolvent. Ab initio calculations of formation energy of hydrogen-bonded complexes solute – cosolvent have been performed. Solvation free energy of the phenolic acids in SC CO2 with and without cosolvents was evaluated by means of the Bennett’s acceptance ratio method. The solvation free energy has been found to be strongly dependent on the number of hydrogen bonds solute – cosolvent. Cosolvent-induced solubility enhancement values were also calculated. The results indicate that the increase in solubility of the phenolic acids is observed by passing from the pure SC CO2 through acetone-modified to methanol-modified solvent. Moreover the order of cosolvent-induced solubility enhancement magnitude depends on the number of hydrogen bonds solute – cosolvent and greatly on the concentration of the latter.

An investigation of the dissolution of acetylsalicylic acid in supercritical carbon dioxide

The dissolution of acetylsalicylic acid in supercritical carbon dioxide (SC–CO2) is investigated using Fourier transform IR spectroscopy. Temporal dependences of integrated intensities of the absorption band of acetylsalicylic acid (ASA) near 1199 cm–1 are measured for various ASA charges placed into a cuvette. Molar fractions of ASA in the saturated solution in SC–CO2 are determined at a temperature of 40°C and pressures of 10.0 and 15.0 MPa, and the components are 2.10 ± 0.25 × 10–4 and 11.0 ± 1.5 × 10–4, respectively.

Solubility of Perfluoropentanoic Acid in Supercritical Carbon Dioxide: Measurements and Modeling

The solubility of perfluoropentanoic acid in supercritical carbon dioxide was investigated for a broad range of pressures (10 to 26 MPa) and at three temperatures: 314, 324, and 334 K. A dynamic gravimetric device was used for the high pressure measurements. The solubility ranges from (24.7 ± 0.3) kg·m–3 at 334 K to 10.2 MPa to (103.9 ± 7.7) kg·m–3 at 314 K and 20.1 MPa. Density-based models, notably the dimensionless version of the Adachi-Lu model, fit the experimental data accurately. The latter model was employed to calculate the solubility over a wide range of CO2 densities.

Solubility of Binary and Ternary Systems Containing Vanillin and Vanillic Acid in Supercritical Carbon Dioxide

Experimental solubility data of binary and ternary systems containing vanillin and vanillic acid in supercritical carbon dioxide were carried out in equipment based on the static-synthetic method. Compositions of dissolved solids were determined online via high-performance liquid chromatography with a diode array detector. The carbon dioxide + vanillin, carbon dioxide + vanillic acid, and carbon dioxide + vanillin + vanillic acid systems were studied at (315.00, 324.90, and 334.71) K, (314.91, 324.91, and 334.71) K, and (314.13, 323.67, and 333.17) K, respectively. For all systems the measurements were carried out at pressure range between 8.00 and 30.00 MPa. For binary systems the maximum solubilities were 5.215 × 10–3 and 2.911 × 10–5 in mole fraction for vanillin and vanillic acid, respectively. For ternary systems the maximum solubilities were 4.669 × 10–3 and 2.213 × 10–5 for vanillin and vanillic acid, respectively. The expanded uncertainties (k = 2) for the measured properties are estimated to be U...

Numerical simulation of the solvate structures of acetylsalicylic acid in supercritical carbon dioxide containing polar co-solvents

Hydrogen-bonded complexes of acetylsalicylic acid with polar co-solvents in supercritical carbon dioxide, modified by methanol, ethanol, and acetone of 0.03 mole fraction concentration, are studied by numerical methods of classical molecular dynamics simulation and quantum chemical calculations. The structure, energy of formation, and lifetime of hydrogen-bonded complexes are determined, along with their temperature dependences (from 318 to 388 K at constant density of 0.7 g cm−3). It is shown that the hydrogen bonds between acetylsalicylic acid and methanol are most stable at 318 K and are characterized by the highest value of absolute energy. At higher supercritical temperatures, however, the longest lifetime is observed for acetylsalicylic acid–ethanol complexes. These results correlate with the known literature experimental data showing that the maximum solubility of acetylsalicylic acid at density values close to those considered in this work and at temperatures of 318 and 328 K is achieved when using methanol and ethanol as co-solvents, respectively.

Determination and modelling of solubility of o-aminobenzamide and its mixture with o-nitrobenzoic acid in supercritical carbon dioxide

To research functional group effect on the solubility of o-aminobenzamide (o-AB) and o-nitrobenzoic acid (o-NBA) for each other, solubility of o-AB and its mixture with o-NBA in supercritical carbon dioxide (SCCO2) was measured with dynamic method at temperatures ranging from 308 to 328K and pressures ranging from 10.0 to 21.0MPa. Then solubility of o-AB and o-NBA was correlated with four commonly used expanded liquid models. In addition, 2365 solubility data of 90 kinds of solid solute, coupled with solubility of o-AB and o-NBA in this work (2425 data points in total), were used to compare the correlation accuracy of the four expanded liquid models, and the best correlation accuracy was obtained by δ2∼δ1/v1 model.To evaluate the effect of heat capacity terms that is usually ignored during the derivational process of expanded liquid models, a new expanded liquid method (M-δ1/v1 model) was proposed based on δ2∼δ1/v1 model and tested by the above mentioned 2425 groups of solubility data. The correlated results showed that M-δ1/v1 model achieved the minimum average absolute relative deviation (AARD, %) 9.72% among the five models of 30.05%, 14.22%, 13.91%, 15.07% for δ2∼ρ, δ2∼ρd, δ2∼δ1/v1, and β12∼ρ2 models, respectively. Furthermore, the result of statistical tests of δ2∼δ1/v1 and M-δ1/v1 models indicated that the best correlation accuracy of M-δ1/v1 model could be attributed to the additional consideration of the heat capacity terms, rather than the more adjustable parameters.