Solubility In Supercritical CO2 Research Articles

A new optimization method for parameter determination in modeling solid solubility in supercritical CO2

For reliable design of supercritical extraction processes, it is necessary to have a sound knowledge of the solute solubilities and their representations by mathematical models so that the solute-supercritical fluid behavior can be predicted accurately. In this work, a new optimization method, the pattern search method, was used to optimize binary interaction parameters for correlating solute solubilities in supercritical CO2 with cubic EOS models. For this purpose, experimentally measured solubility data collected for 10 binary systems were used to examine this parameter optimization method. The results show that the calculated solubility values agree very well with the corresponding experimental data. The average absolute relative deviations between calculated and experimental data are mostly found to be less than 10% and some even less than 1%. Meanwhile, a comparison between the pattern search method and genetic algorithm reflects that the former gives better correlation performance and more significant reduction of computing times than the latter.

Effects of polymers as direct CO2 thickeners on the mutual interactions between a light crude oil and CO2

In this paper, two commercial polymers with relatively low molecular weights, poly vinyl ethyl ether (PVEE) and poly 1-decene (P-1-D), are tested as direct thickeners for CO2 and their detailed effects on the mutual interactions between a light crude oil and polymer-thickened CO2 are experimentally studied under different reservoir pressures. More specifically, the polymer cloud-point pressures are measured at different known polymer solubilities in supercritical CO2. The equilibrium interfacial tensions (IFTs) and onset pressures of quick polymer dissolution into CO2 are measured for the polymer−pure CO2 systems. The polymer-swelling effect due to pure CO2 dissolution is observed and examined. To study the mutual interactions between the light crude oil and polymer-thickened CO2, their equilibrium IFTs are measured and their so-called minimum miscibility pressures (MMPs) and onset pressures of the initial quick light-hydrocarbons extraction by CO2 are determined. The oil-swelling effect due to polymer-thickened CO2 dissolution is also visualized and analyzed. All the experimental data for polymer-thickened CO2 are compared with those for pure CO2.

A bulky phosphite modified rhodium catalyst for efficient hydroformylation of disubstituted alkenes and macromonomers in supercritical carbon dioxide

The hydroformylation of disubstituted alkenes and related macromonomers in supercritical CO2 is demonstrated. Higher turnover frequencies were observed for the 1,2-disubstituted alkenes than for the 1,1-disubstituted alkenes. The turnover frequency for poly(styrene) macromonomer hydroformylation compares well with that observed for cyclohexene. The turnover frequency observed for poly(methyl methacrylate) macromonomer hydroformylation is considerably lower than that observed for methyl methacrylate. Unprecedented turnover frequencies are observed in comparison with previous studies where CO2 has been applied as a solvent. This is achieved using rhodium modified with a readily available bulky phosphite ligand without the need of ligand modification to improve solubility in supercritical CO2.

Smooth and Conformal TiO2 Thin-Film Formation Using Supercritical Fluid Deposition

Conformal TiO2 having a smooth surface was deposited using a flow-type reactor for supercritical fluid deposition (SCFD). Ti(O-iPr)2(tmhd)2 was selected as the best candidate for SCFD from among three candidates because it exhibited the best results according to the following criteria: solubility in supercritical CO2 (scCO2), carbon impurities in the TiO2, and surface morphology of the deposited film. The growth rate increased with increasing temperature from 200 to 300°C. The activation energy in this temperature range was measured to be about 46.3 kJ/mol. Compared with conventional methods, such as chemical vapor deposition (CVD; activation energy of 85 kJ/mol, decomposition temperature above 450°C), TiO2-SCFD had a much lower activation energy owing to the solvent effect of scCO2. We also examined the growth-rate dependence on the precursor concentration and found first-order reaction kinetics such that the surface reaction rate constant (ks) was as low as 2.0 × 10−6 m/s at 300°C. This process resulted in good step coverage during film formation on trenches with an aspect ratio of 12.5.

Distinctive Features of Solubility of RAFT/MADIX-Derived Partially Trifluoromethylated Poly(vinyl acetate) in Supercritical CO2

Well-defined statistical copolymers of vinyl acetate and 1-(trifluoromethyl)vinyl acetate were synthesized by RAFT/MADIX polymerization. These copolymers exhibited enhanced solubilities in supercritical CO2 compared to poly(vinyl acetate). A copolymer composition–solubility optimum was observed, which resulted from a subtle interplay between polymer–polymer interactions and entropy of mixing.

Antiradical Efficiency of Essential Oils from Plant Seeds Obtained by Supercritical CO2, Soxhlet Extraction, and Hydrodistillation

The effect of supercritical CO2 (SCCO2) extraction conditions (pressure and temperature) on the system performance as well as the antiradical efficiencies of the essential oils from Japanese pepper (Xanthoxylum piperitum DC.), cardamom (Elettaria cardamomum Maton), and fennel (Foeniculum vulgare) seeds were investigated. A control study with the conventional Soxhlet extraction and hydrodistillation was also conducted to compare the performance of those processes. Antiradical efficiencies were investigated by utilizing 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay with a UV-vis spectrophotometer. Higher pressure and temperature had positive effects on the supercritical process performance due to higher CO2 density and substrate solubility in SCCO2. Antiradical efficiencies of cardamom and pepper were almost the same, being significantly higher than that of fennel seeds. However, this effect decreased dramatically for all the spices when the extraction method was changed to Soxhlet extraction and hydrodistillation. SCCO2 extraction was found to yield more quality and effective essential oils than Soxhlet extraction and hydrodistillation.

Three-dimensional optofluidic waveguides in hydrophobic silica aerogels via supercritical fluid processing

Optofluidic components enable flexible routing and transformations of light beams in integrated lab-on-a-chip systems with the use of carefully shaped fluid parcels. For structural integrity reasons, the working fluid is typically contained within a solid-material chip. One of the outstanding challenges in optofluidics is the preparation and processing of optofluidic waveguides. These require solid cladding materials that are sufficiently strong to contain the fluid while possessing optical properties that allow efficient confinement of light within fluidic channels. Here, we report on a new technique to obtain liquid-core optofluidic waveguides based on total internal reflection of light in three-dimensional water-filled channels embedded in hydrophobic silica aerogel. To form the channels, we employ a fiber made of cage-like silicon-oxygen compound – trifluoropropyl polyhedral oligomeric silsesquioxane (trifluoropropyl POSS) – which has high solubility in supercritical CO2 (scCO2). A U-shaped fiber made of trifluoropropyl POSS is obtained by melt/freeze processing of POSS powder and subsequently placed in a silicate sol. After gelation of the sol and aging of the gel, scCO2 extraction is used to dry the wet gel and extract the POSS fiber, yielding a dry silica aerogel with a U-shaped empty channel inside it. Finally, the silanol groups at the surface of the aerogel are reacted with hexamethyldisilazane (HMDS) in the presence of scCO2 to render the aerogel surface hydrophobic and the channel is filled with water. We demonstrate efficient waveguiding by coupling light into the water-filled channel and monitoring the channel output. The presented procedure opens up new possibilities for creating complex three-dimensional networks of liquid channels in aerogels for optofluidic applications.

Measurement and correlation solubility of cefixime trihydrate and oxymetholone in supercritical carbon dioxide (CO2)

The equilibrium solubilities of cefixime trihydrate and oxymetholone in supercritical carbon dioxide (CO2) were measured using a “static method”. Cefixime trihydrate is a cephalosporin antibiotic drug and Oxymetholone is a 17alpha-alkylated anabolic-androgenic steroid drug. The experimental measurements for cefixime trihydrate were performed at temperatures of 308, 318 and 328K as well as pressure range from 183 to 335bar. The solubility of oxymetholone was determined at 308, 318 and 328K and pressure range from 121 to 305bar. The experimental solubility data (mole fraction) for cefixime trihydrate and oxymetholone was greater than 1.6×10−7 and 1.6×10−5 and less than 3.02×10−7 and 1.49×10−4, respectively. The solubilities for two drugs in CO2 were correlated by using four semi-empirical models such as Bartle, Kumar and Johnstone (K–J), Mendez-Santiago and Teja (M–T) and Chrastil models. The results obtained from the semi-empirical models show that there is good agreement between the experimental data and the results of semi-empirical models. By using the correlation results, the heat of drug–CO2 solvation and heat of drug vaporization for cefixime–CO2 and oxymetholone–CO2 systems may be approximately estimated. Also, the Peng–Robinson (PR) cubic equation of state (CEOS) along with the van der Waals combining rule was applied to correlate the drugs solubilities in supercritical CO2. The average absolute deviation between the experimental data and the results of PR equation for cefixime trihydrate and oxymetholone was 11.92% and 11.74%, respectively.

Solubilities and partial molar volumes of 1-methypropanedioate derivatives in supercritical carbon dioxide

In present study, five new CO2-philic 1-methypropanedioate derivatives containing nonfluorous alkyl groups had been designed and synthesized. The solubilities of these compounds in supercritical carbon dioxide (scCO2) were investigated with a static analytical method at the temperature from 323K to 343K and in the pressure range of 9.3–13.7MPa. All compounds showed high solubilities in supercritical CO2 at easily accessible temperatures and pressures. To correlate the experimental data, two density-based models proposed by Bartle and Chrastil were investigated. The correlation results showed good self-consistency between the calculated and the measured values, which were in the range of 7.79–21.99% by Bartle model and 4.09–11.15% by Chrastil model. Additionally, according to the Kumar and Johnston theory, the partial molar volume V¯2 of each compound in scCO2 was also calculated and the results were between −10788.4 and −1585.84.

Enhancement of Poly(vinyl ester) Solubility in Supercritical CO2 by Partial Fluorination: The Key Role of Polymer–Polymer Interactions

An enhancement of poly(vinyl ester) solubility in supercritical carbon dioxide (sc-CO(2)) can be achieved by decreasing the strength of the polymer-polymer interactions. To demonstrate this, a library of statistical copolymers of vinyl acetate and vinyl trifluoroacetate was synthesized by RAFT/MADIX polymerization with varying compositions at a given number-average molecular weight. These copolymers exhibited unprecedentedly low cloud-point pressures in sc-CO(2) at 40 °C compared with previously reported poly(vinyl esters). Surface tension measurements combined with a computational approach evidenced the prominent role played by polymer-polymer interactions.

Correlation of the Solubility of Some Organic Aromatic Pollutants in Supercritical Carbon Dioxide Based on the UNIQUAC Equation

The ability to correlate and predict the solubility of solids in supercritical fluids is of utmost importance in different applications, including environmental pollution, extraction and purification of pharmaceuticals, food and natural products, and natural gas industry. The environmental field includes desorption of many organic compounds such as naphthalene and phenanthrene from soil, and detoxification of hazardous wastes. In this work, a new methodology is proposed to correlate and predict the solubility in supercritical CO2 of some polycyclic aromatic hydrocarbons. This methodology uses the expanded liquid theory, which the solid±fluid equilibrium is modeled using the UNIQUAC model. The regressed coefficients of the model are calculated using an empiric equation that relates the interaction parameters to the solvent density. Robustness of proposed model was assessed by testing it on a database consisting of more than 1400 solubility data. The experimental solubility of acenaphtene, anthracene, chrysene, fluoranthene, fluorene, naphthalene, phenanthrene, pyrene, perylene and triphenylene were used for evaluating this new methodology. The results obtained using the proposed technique showed good agreement with the experimental data used.

MICRONIZATION AND ENCAPSULATION OF FUNCTIONAL PIGMENTS USING SUPERCRITICAL CARBON DIOXIDE

ABSTRACTThis research involves experimental studies of supercritical fluid (SCF)‐based micronization and encapsulation processes exploiting both solvent and antisolvent properties of supercritical CO2 for diverse functional pigments to extend the application of these natural functional pigments. First, the reliability of homemade experimental apparatuses designed and constructed by our research group was tested. Quercetin and β‐carotene were used as model substances in the micronization process via supercritical antisolvent (SAS). Bixin‐rich extract with polyethylene glycol (PEG) 10,000 as encapsulant material was used in the encapsulation process via SAS, while rutin and anthocyanin‐rich extract with PEG 10,000 and ethanol as cosolvents were applied to the formation of polymeric microcapsules via rapid expansion of supercritical solutions (RESS). The processing parameters and the used levels were based on the literature data. SAS process successfully reduced the particle size of quercetin by 4.1 times, while conventional micronization process only reduced the particle size by 1.8 times. Furthermore, it was demonstrated that SAS process can be successfully utilized to coprecipitate microparticles of PEG loaded with bixin‐rich extract. RESS process using ethanol as cosolvent was employed effectively to encapsulate rutin and anthocyanin‐rich extract in the PEG matrix. The data obtained in this study are in good agreement with the previous values reported by several authors using similar operational conditions and equipment. Core material : encapsulant material ratio, core material physical properties, such as solubility in supercritical CO2 and in CO2 + ethanol, and viscosity were key parameters for these processes.PRACTICAL APPLICATIONSThe application of natural food colorants with relevant antioxidant activities, such as carotenoids and flavonoids, as food additives in various food products is seriously hampered by their fast degradation triggered by light, temperature, presence of oxygen, insolubility in aqueous systems and low dispersibility, among others. Their particle size reduction and/or encapsulation have been successfully used to overcome all these drawbacks. SCFs have become an attractive alternative solvent due to their environmentally friendly properties. SCFs may be conveniently used for various applications such as extraction, reactions, micronization and encapsulation, among others. Studies showing the use of SCFs and/or the construction of apparatuses that use these green solvents for solubility enhancement of functional pigments with poor water solubility and/or avoiding degradation of these compounds are extremely important.

Cetirizine solubility in supercritical CO 2 at different pressures and temperatures

A simple static technique was used to obtain the solubility of cetirizine in supercritical carbon dioxide. The solubility measurements were performed at temperatures and pressures ranging from 308.15 to 338.15 K and 160 to 400 bar, respectively; resulting in mole fractions in the 1.05 × 10 −5 to 4.92 × 10 −3 range. The Chrastil, Bartle, Kumar & Johnston and the Mendez-Santiago and Teja (MST) models were used to correlate the experimental data. The calculated solubilities showed good agreement with the experimental data in the temperature and pressure ranges studied.

Evaluation of Polymers as Direct Thickeners for CO2 Enhanced Oil Recovery

In this paper, two commercial polymers, poly(vinyl ethyl ether) (PVEE) and poly(1-decene) (P-1-D), are tested to thicken CO2 for CO2 enhanced oil recovery (EOR). First, a series of laboratory tests are conducted to measure the cloud-point pressures of either polymer at different polymer solubilities in supercritical CO2 and the equilibrium interfacial tensions (IFTs) of a light crude oil-pure or polymer-thickened CO2 system under different reservoir conditions. Second, a capillary viscometer is used to measure the viscosities of polymer-thickened CO2 at different test pressures. Third, a total of six high-pressure CO2 coreflood tests are performed to examine the effects of polymer-thickened CO2 on the total CO2 EOR. It is found that at the same and low polymer solubility in pure CO2, the measured cloud-point pressure of PVEE is much lower than that of P-1-D. The measured equilibrium IFT for polymer-thickened CO2 at a high pressure is much lower than that for pure CO2. The PVEE- or P-1-D-thickened CO2 viscosity is approximately (13 to 14) times higher than the pure CO2 viscosity. The CO2 coreflood test results show that PVEE- or P-1-D-thickened CO2 flooding can further enhance oil recovery after a pure CO2 breakthrough. The CO2 breakthrough can be significantly delayed if polymer-thickened CO2 is injected directly.

High Solubility and Partial Molar Volume of 2,2′-Oxybis(N,N-bis(2-methoxyethyl)acetamide) in Supercritical Carbon Dioxide

2,2′-Oxybis(N,N-bis(2-methoxyethyl)acetamide) was synthesized and confirmed by IR, NMR, and elemental analysis. The solubility of this compound was measured at temperatures ranging from (313 to 333) K and pressures from (9.2 to 15.2) MPa in supercritical carbon dioxide. The synthesized compound showed high solubility in supercritical CO2 at easily accessible temperatures and pressures (e.g., 1.84 × 10−3 mol·L−1 at 9.2 MPa and 313 K). To confirm the tested solubility, the density-based correlations proposed by Bartle and Chrastil were investigated for the synthesized compound. The results showed good self-consistency of the data calculated using the Bartle semiempirical equation, which differed from the measured values by between (0.96 and 41.22) %. Better agreement with the experimental solubility data was obtained with the Chrastil model, for which average absolute relative deviations of less than 6 % were observed. The solubility data were also used to estimate the partial molar volume V2 for the compo...

Determination of the Solubility of Copper with Three Commercial Ligands and One Novel Ligand in Supercritical CO2

The solubility of four copper ligand systems in supercritical (SC) CO2 was studied. Three of the ligand systems studied were commercial ligands, while the last one was a new Schiff base reduced macrocyclic ligand. The three commercial ligands were ethylenediaminetetraacetic acid (EDTA), diisooctylphosphinic acid (DiOPA), and the anion-exchanger Aliquat 336 (methyltrioctylammonium chloride). The Schiff base reduced macrocyclic ligand was 3,6,9,12-tetraaza-4(1,2),11(1,2)-dibenzena-1(1,3)-pyridinacyclotridecaphane (TeDiPyDeca), which forms a very stable 1 + 1 copper complex (Keq = 2.42 × 106). This article presents the synthesis, Fourier transform infrared spectroscopy (FT-IR) studies, and crystal structure of the new copper complex Cu(TeDiPyDeca) as well as experimental data of solubility fitting with a Peng Robinson equation and van der Waals mixing rules. The molar volume of the solid (Vs), the vapor pressure (Pvap), and the binary interaction coefficient (k ij ) of the four metal complexes were found. The physical effects of the molecular forms of the studied copper complexes were the most important factors in regard to solubility in SC CO2.

Solubility and Self-Assembly of Amphiphilic Gradient and Block Copolymers in Supercritical CO2

This work aims at demonstrating the interest of gradient copolymers in supercritical CO(2) in comparison with block copolymers. Gradient copolymers exhibit a better solubility in supercritical CO(2) than block copolymers, as attested by cloud point data. The self-assembly of gradient and block copolymers in dense CO(2) has been characterized by Small-Angle Neutron Scattering (SANS), and it is shown that it is not fundamentally modified when changing from block copolymers to gradient copolymers. Therefore, gradient copolymers are advantageous thanks to their easier synthesis and their solubility at lower pressure while maintaining a good ability for self-organization in dense CO(2).

Perfluoroalkyl bile esters: a new class of efficient gelators of organic and aqueous–organic media

A new class of fluorinated gelators derived from bile acids is reported. Perfluoroalkyl chains were attached to the bile acids through two different ester linkages and were synthesized following simple transformations. The gelation property of these derivatives is a function of the bile acid moiety, the spacer and the fluoroalkyl chain length. By varying these parameters, gels were obtained in aromatic hydrocarbons, DMSO and DMSO/DMF–H2O mixtures of different proportions. Several derivatives of deoxycholic and lithocholic acids were found to be efficient organogelators, while the reported bile-acid based organogelators are mostly derived from the cholic acid moiety. The efficient gelators among these compounds formed gels well below 1.0% (w/v) and hence they can be termed as supergelators. The mechanical properties of these gels could be modulated by changing either the bile acid moiety or by varying the length of the fluoroalkyl segment. The presence of CO2-philic perfluoroalkyl groups is also expected to enhance their solubility in supercritical CO2 and hence these compounds are promising candidates for making aerogels.

Micronization and characterization of drug substances by RESS with supercritical CO2

A RESS (rapid expansion of supercritical solution) process for the preparation of ultra-fine drug particles with no organic solvent has been developed with supercritical CO2. Three drug substances with different solubility in supercritical CO2 were used, and orifice disks and capillary tubes were adapted as an expansion device. The solubilities of drug substances in supercritical CO2 and the effects of various operating parameters on the characteristics of the particles prepared by RESS process were experimentally investigated. The solubility of the drug substance in supercritical CO2 had a major effect on the average diameter of the particle prepared by RESS process, and the particle diameter decreased with the solubility for all the drugs and operating conditions. The particle diameter also decreased with preexpansion temperature and increased with the hole diameter of the orifice nozzle and aspect ratio (L/D) of the capillary tube.

Impregnation of Ibuprofen into Polycaprolactone using supercritical carbon dioxide

Polycaprolactone (PCL) is a Food and Drug Administration (FDA) approved biodegradable polyester used in tissue engineering applications. Ibuprofen is an anti-inflammatory drug which has good solubility in supercritical CO2 (SCCO2). The solubility of CO2 in PCL allows for the impregnation of CO2-soluble therapeutic agents into the polymer via a supercritical fluid (SCF) process. Polymers impregnated with bio-active compounds are highly desired for medical implants and controlled drug delivery. In this study, the use of CO2 to impregnate PCL with ibuprofen was investigated. The effect of operating conditions on the impregnation of ibuprofen into PCL was investigated over two pressure and two temperature levels, 150bar and 200bar, 35°C and 40 °C, respectively. Polycaprolactone with drug-loadings as high as 27% w/w were obtained. Impregnated samples exhibited controlled drug release profiles over several days.