Solubility In scCO2 Research Articles

Bright nickel film deposited by supercritical carbon dioxide emulsion using additive-free Watts bath

This paper is aimed on studying film smoothening effect of supercritical carbon dioxide emulsion (Sc-CO2-E) on nickel film electroplated using an additive-free Watts bath. Morphology of nickel film electroplated with Sc-CO2-E was found to be similar to that of nickel film prepared from electroless plating. Surface roughness (Ra) of nickel film electroplated with Sc-CO2-E was lower than that of nickel film electroplated through conventional method. A minimum Ra was found for nickel film electroplated through conventional method and Sc-CO2-E when increasing current density from 0.010 to 0.150 A/cm2. The minimum Ra was 69.8 nm at 0.020 A/cm2 and 14.0 nm at 0.030 A/cm2, respectively for conventional and Sc-CO2-E case. After the minimum point, increasing rate of Ra increased was lower for Sc-CO2-E case; this was because of higher hydrogen solubility in Sc-CO2. Grain size of nickel film electroplated with Sc-CO2-E was found to be finer than that of conventional case.

Assessment of scCO 2 techniques for surface modification of micro- and nanoparticles: Process design methodology based on solubility

In order to effectively exploit the remarkable properties of fine particles to form hybrid nanostructured composites with applications in the biomedical area, one essential step is their surface functionalization. The overall objective of the present work was to use supercritical carbon dioxide (scCO 2) for the design of the surface of inorganic particles by depositing thin and ultrathin films. Two scCO 2 routes were proposed to modify the surface of micro- (SiO 2, 5 μm) and nanometric (TiO 2, 20–30 nm) oxide particles: antisolvent methods for polymers that are non-soluble in CO 2 (polymethylmethacrylate), and the use of compressed CO 2 as a solvent for modifiers with certain solubility in scCO 2 (octadecylsilane, salicylic acid). In the antisolvent technique, solid particles were dispersed in a solution containing the polymer and mixed with scCO 2; polymer precipitation, induced by the presence of CO 2, occurred preferentially onto the available surface offered by the oxide particles. For CO 2-soluble modifiers, the molecules were transferred from the compressed phase to the surface of the solid particles by diffusion; reactivity between adequate moieties permitted to form covalently grafted films. Vibrational ATR-FTIR spectroscopy was used to evaluate potential interactions between samples components. The wettability of the produced systems was analyzed by dispersion experiments in water and toluene.

Partitioning of drug model compounds between poly(lactic acid)s and supercritical CO 2 using quartz crystal microbalance as an in situ detector

Quartz crystal microbalance (QCM) was used as an in situ detector to investigate the potential application in the phase equilibrium determination of supercritical CO 2-drug-polymer systems. CO 2 solubility in two biodegradable polymers, poly( d, l-lactic acid) ( d, l-PLA) and poly( l-lactic acid) ( l-PLA) was primarily measured at 313.15 K and pressures up to 10.0 MPa. d, l-PLA showed a better CO 2 absorption ability due to its amorphous structure. Four drug model compounds of poor solubility in water, ibuprofen, aspirin, salicylic acid and naphthalene were selected as representatives for the examination of drug uptake in PLA matrices, as well as partition coefficient during supercritical impregnation. It was found that partition coefficients of drugs can reach as high as 10 3–10 4 orders of magnitude and greatly affected by the intermolecular interactions between drugs and PLA. Aspirin exhibited the best partitioning during the supercritical impregnation at pressures of 8.0–10.0 MPa due to the existence of carboxylic acid and acetyl groups. Drug partitioning is additionally related to the drug concentration in ScCO 2, i.e. salicylic acid showed little absorption in PLA according to its poor solubility in ScCO 2 at 7.5–8.0 MPa, whereas the well CO 2-soluble compound, naphthalene, exhibited a moderate partition coefficient although its polarity was different from l-PLA.

Enzymatic synthesis of short‐chain esters in n‐hexane and supercritical carbon dioxide: Effect of the acid chain length

AbstractEnzymatic synthesis is the preferred way to produce so‐called “natural products.” Hydrolases have been used for short‐chain ester synthesis. These esters present a pleasant flavor and they have a lot of applications in different industries. Novozym 435 from Candida antarctica (EC 3.1.1.3, triacylglycerol lipase) was used for hexyl ester synthesis in n‐hexane and supercritical carbon dioxide (SCCO2). Direct esterification provided higher yields than transesterification for the synthesis of esters. Several carboxylic acids of different chain lengths were tested for the esterification reactions: acetic, propionic, butyric, caproic and caprylic acids. The reactions were carried out at 40°C and the amount of enzyme used was 13.8 g/mol alcohol. Substrates were added at equimolar concentrations, with sufficient stirring to avoid external diffusion control. Different substrate concentrations up to 1.5 M were used. The working pressure was 14 MPa in the case of SCCO2 and atmospheric pressure in the case of organic solvent. The results in both solvents show that the reaction rate increases with the chain length of the acid, but the final yields were similar. However, some of the reactions prove to be faster in SCCO2, except for hexyl acetate and propionate synthesis, in which acetic and propionic acid presented a lower solubility in SCCO2 due to its high polarity. Moreover, an acetic acid concentration of 1.5 M brought about a strong inhibition of the enzyme activity.

Metal Ion Extraction with Bipyridine Derivatives as Chelating Ligands in Supercritical Carbon Dioxide

AbstractThree fluorinated bipyridine ligands have been designed and synthesized as chelating agents for the extraction of metal ions in supercritical CO2 (sc‐CO2). The ligand solubilities in sc‐CO2 were investigated at different temperatures and pressures, and the measured data have been correlated using a semiempirical model. The calculated results showed satisfactory agreement with the experimental data. Based on these data, metal ion extraction with the three compounds as chelating agents in sc‐CO2 was performed from spiked filter paper, whereby ligand 1 showed the highest extraction efficiency, especially for Ni2+ and Cu2+. The extraction constants, Kex, of the three chelating ligands were seen to increase with increasing extraction efficiency for the same metal ion in the same extraction system.

Supercritical carbon dioxide, a new medium for aerobic alcohol oxidations catalysed by copper-TEMPO

The copper catalysed aerobic oxidation of selected alcohol substrates in supercritical carbon dioxide (scCO(2)), employing a range of simple copper(II) catalyst compounds, is here described. The copper acetate complex of polydimethylsiloxane (PDMS) functionalised pyridine (1), compound 2, has previously been synthesised and characterised by us and its solubility in scCO(2) demonstrated. Due to this solubility we anticipated that the selective aerobic oxidation of alcohols to aldehydes could be homogeneously catalysed by this compound in scCO(2) in combination with the co-catalyst 2,2,6,6-tetramethylpiperidin-1-yloxy free radical (TEMPO). Our initial results showed that complete oxidation of 4-nitrobenzyl alcohol was achieved within 4 h of reaction. However, the activities of analogous copper derivatives containing simpler pyridine substituents, [Cu(AcO)(2)(py)](2) and [Cu(AcO)(2)(4VP)](2) (4VP = 4-vinylpyridine), were shown to be similar, in spite of their negligible solubility in scCO(2). When we repeated the reactions in highly non-polar hexane rather than scCO(2) similar observations were made. In both cases, as 2 is soluble and the pyridine analogues are not, a much higher reaction rate was anticipated for 2 as it is the only compound capable of homogeneous catalysis. However, in some cases slightly better activities were observed for [Cu(AcO)(2)(py)](2) rather than for the PDMS functionalised analogue, 2. Thus, despite poor catalyst solubility typically being very inhibitory in this type of catalytic process, in this system solubilisation of the catalyst is not necessary. In continuation the activity of silica supported copper complexes was therefore investigated. Employing such catalysts the 4-nitrobenzyl and benzyl alcohol substrates were completely oxidised to the corresponding aldehydes in scCO(2), this time employing lower catalyst loadings. Other types of alcohol substrate showed more limited conversions however. To conclude, alcohol oxidation in the non-conventional green solvent scCO(2), with the benign terminal oxidant, dioxygen, and simple, cheap, easily prepared metal catalyst compounds was demonstrated. This is the first copper-TEMPO catalysed alcohol oxidation system in scCO(2) to be described.

Glycerol as a sustainable solvent for green chemistry

Glycerol, an organic waste generated by the biodiesel industry, has been recently proposed as a valuable green solvent. This review summarizes the advantages, disadvantages and potential uses of glycerol as a green solvent for catalysis, organic synthesis, separations and materials chemistry. In particular, through selected examples we show here that glycerol may combine the advantages of water (low toxicity, low price, large availability, renewability) and ionic liquids (high boiling point, low vapour pressure, low solubility in scCO2). More generally, all these reported works contribute to increase the portfolio of available green solvents and afford innovative solutions to the substitution of the conventionally used volatile organic solvents.

Solubility of bio-sourced feedstocks in ‘green’ solvents

A group of 14 different bio-sourced, renewable feedstocks (homoserine, 1; glutamic acid, 2; aspartic acid, 3; 2,5-furandicarboxylic acid, 4; fumaric acid, 5; oxalacetic acid, 6; tartaric acid, 7; malic acid, 8; succinic acid, 9; levulinic acid, 10; γ-hydroxybutyrolactone, 11; xylitol, 12; mannitol, 13; sorbitol, 14) have been examined for their solubility/miscibility in a variety of ‘green’ solvents, including water, supercritical carbon dioxide (scCO2), and ionic liquids. Two other bio-based compounds 5-hydroxymethylfurfural, 15, and D-xylose, 16, were studied in selected solvents. Trends in solubility have been assessed so that these data may be extrapolated to help predict solubilities of other related compounds. For example, 10, 11 and 15 all demonstrated appreciable solubility in scCO2, as they possess weak intermolecular interactions. The dicarboxylic acids studied (4–9) all proved soluble in modified scCO2 (by use of MeOH as a cosolvent). While the polyols (12–14) and 1 were insoluble in scCO2 but water of various pHs and ionic liquids proved adept at their dissolution. Some of the amino acids studied (2 and 3) were only soluble in water with an adjustment of pH.

Catalytic supercritical fluid extraction: selective hydroformylation of olefin mixtures using scCO2 solubility for differentiation

A new reaction concept that allows one to control the substrate selectivity of a catalytic reaction by supercritical fluid extraction is demonstrated for the hydroformylation of long-chain olefins as a prototypical example.

Robust modelling of solubility in supercritical carbon dioxide using Bayesian methods

Two sparse Bayesian methods were used to derive predictive models of solubility of organic dyes and polycyclic aromatic compounds in supercritical carbon dioxide (scCO(2)), over a wide range of temperatures (285.9-423.2K) and pressures (60-1400 bar): a multiple linear regression employing an expectation maximization algorithm and a sparse prior (MLREM) method and a non-linear Bayesian Regularized Artificial Neural Network with a Laplacian Prior (BRANNLP). A randomly selected test set was used to estimate the predictive ability of the models. The MLREM method resulted in a model of similar predictivity to the less sparse MLR method, while the non-linear BRANNLP method created models of substantially better predictivity than either the MLREM or MLR based models. The BRANNLP method simultaneously generated context-relevant subsets of descriptors and a robust, non-linear quantitative structure-property relationship (QSPR) model for the compound solubility in scCO(2). The differences between linear and non-linear descriptor selection methods are discussed.

Highly Fluorous Complexes of Ruthenium and Osmium and Their Solubility in Supercritical Carbon Dioxide

A series of ruthenium and osmium complexes containing highly fluorous diphosphine ligands (F)P(wedge)P(F) = (F(13)C(6)C(6)H(4)-p)(2)P(CH(2))(2)P(p-C(6)H(4)C(6)F(13))(2) (dfppe) and (F(13)C(6)C(6)H(4)-p)(2)P(CH(2))(3)P(p-C(6)H(4)C(6)F(13))(2) (dfppp) has been prepared. The fluorous diphosphine ligands incorporate four C(6)F(13) "fluoro-ponytails", and these have been effective in solubilizing the complexes in supercritical carbon dioxide (scCO(2)). Precise solubility measurements in scCO(2) were performed for some of the complexes. The new complexes [MX(2)((F)P(wedge)P(F))(2)] and [MX((F)P(wedge)P(F))(eta-C(5)H(5))], M = Ru, Os, X = Cl, Br, have been characterized by a number of spectroscopic techniques and their electrochemical properties measured, three of the ruthenium complexes also being characterized by single-crystal X-ray studies. The noncovalent interactions observed in the X-ray structures have been analyzed by the Hirshfeld surface approach, putting them on a more solid footing. The fluorinated complexes show significantly different solvation properties from those of the analogous unfluorinated compounds, particularly with respect to their behavior in common organic solvents and their good scCO(2) solubility.

Impregnation of vitamin E acetate on silica mesoporous phases using supercritical carbon dioxide

Impregnation of a drug model (α-tocopheryl acetate) into mesoporous host matrices has been carried out using supercritical carbon dioxide (SC CO 2) as impregnation solvent at 15 MPa and 313 K with a flow rate of 500 g h −1. The operating conditions were defined following the solute concentration in the fluid phase as a function of pressure and carbon dioxide flow rate. Solubility measurements of α-tocopheryl acetate were first performed at 313 K for pressures ranging 10–20 MPa. High values of solubility in SC CO 2 were measured: 6 wt% at 10 MPa and 14 wt% at 20 MPa. Measurements of the concentration of the solute in SC CO 2 in the experimental conditions of impregnation in dynamic mode showed than it was ten times lower than the solubility. The variations of this concentration have been studied at 313 K, for a pressure varying from 8 to 15 MPa, and for a carbon dioxide flow rate varying from 120 to 600 g h −1. Two different host matrices were used: a commercial chromatographic silica support and a MCM-41-type mesoporous organized silica synthetized at the laboratory. This latter showed the best drug loading of 1.14 g per gram of adsorbent. The drug loadings obtained in supercritical media were similar to the ones obtained in liquid media using hexane as impregnation solvent. Nevertheless, the maximum loading was obtained after 1 h of impregnation in SC media while 4 h were needed in liquid media.

Supercritical CO2/Ionic Liquid Systems: What Can We Extract from Infrared and Raman Spectra?

Infrared (IR) spectroscopy has been successfully applied to study the solubility of supercritical (sc) CO2 in an ionic liquid (IL), the swelling of the IL under scCO2, the diffusion of CO2 in the IL, and the molecular interaction between the IL and scCO2 using a single defined experimental setup. The study has been performed using 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and scCO2 with a pressure of up to 150 bar at 313 K. The solubility of scCO2 in the IL was calculated via the intensity of the CO2 antisymmetric stretching mode, which was measured using the attenuated total reflection (ATR) method. This approach allowed to determine also the swelling of the IL under scCO2 using several IL bands. The knowledge gained about the solubility and swelling allowed the calculation of the molar fraction of CO2 in the IL and the attainment of similar data as previously determined by other methods. The kinetic measurement of the infrared spectra also offered the opportunity to observe the evolution of the concentration of CO2 in the IL and allowed an estimation of the diffusion coefficient of CO2 in IL under high pressure. Finally, information about the molecular interactions between the IL and scCO2 could also be gained in situ using both infrared and Raman spectroscopy.

Solubility of Triphenylmethyl Chloride and Triphenyltin Chloride in Supercritical Carbon Dioxide

The solubility of triphenyltin chloride (TPT) and triphenylmethyl chloride (TPC) in supercritical carbon dioxide (SC-CO 2 ) was measured with a dynamic method at temperatures from 308.15 K to 338.15 K and pressures ranging from 15 MPa to 40 MPa. The two compounds displayed a similar mole fraction solubility in SC-CO 2 of about 10- 3 to 10 ―4 with a relative uncertainty of about 6 % over the range of experimental conditions. The experimental solubility data were correlated with both empirical Gordillo and semiempirical Chrastil models. The correlation results indicated that the values of average relative deviations (ARD) with the Gordillo model for TPT and TPC were 5 % and 12 %, and those of with the Chrastil model were 9 % and 6 % respectively.

SANS study of the self-organization of gradient copolymers with ligand groups in supercritical CO2

We report on a small-angle neutron scattering study of the self-organization of new gradient fluorinated copolymers with ligand groups in supercritical carbon dioxide (scCO2). Poly(1,1,2,2-tetrahydroperfluorodecyl acrylate-co-acetoacetoxyethyl methacrylate) (poly(FDA-co-AAEM)), poly(1,1,2,2-tetrahydroperfluorodecyl acrylate-co-vinylbenzylphosphonic acid diethylester) (poly(FDA-co-VBPDE)) and poly(1,1,2,2-tetrahydroperfluorodecyl acrylate-co-vinylbenzylphosphonic diacid) (poly(FDA-co-VBPDA)) gradient copolymers synthesized by controlled radical polymerization exhibit a very good solubility in scCO2. We investigated their conformation and aggregation as a function of composition and molecular weight of the copolymer, concentration, pressure and temperature. Generally, the gradient copolymers form small aggregates with low mean aggregation numbers between 1 and 10 and radii of gyration in the range 24 to 54 A. Because of the nature of the AAEM CO2-phobic moiety, the effect of pressure on the aggregation of poly(FDA-co-AAEM) is more important than the one of temperature: CO2 density alone is not sufficient to describe the thermodynamic state. The ability of poly(FDA-co-VBPDA) to solubilize water inside aggregates dispersed in CO2 is also demonstrated.

Measurement and Correlation of Solubility of Uracil in Supercritical Carbon Dioxide

The solubility of uracil in supercritical carbon dioxide (SC-CO2) was determined with dynamic method at temperatures (308, 318, 328, 338, and 348) K and various pressures in the range of (15 to 40) MPa. The mole fraction solubilities of uracil ranged from (0.769 to 14.98)·10−8. The solvent capacity of SC-CO2 to dissolve uracil increases by increasing the pressure at a constant temperature. The crossover point was observed around a pressure of 15 MPa. Experimental data of the solubility of uracil were correlated by the Chrastil model and the modified Chrastil model. The results indicated that the two models were able to successfully correlate the experimental solid uracil + SC-CO2 solubility data, and the values of average absolute relative deviation (AARD) were 12.8 % and 10.1 %, respectively.

Swelling, melting point reduction and solubility of PEG 1500 in supercritical CO 2

The knowledge of the solubility of PEG 1500 as well as the swelling and melting point variation in supercritical CO 2 in a relatively high-pressure range is a necessary prerequisite to set-up pharmaceutical processes dealing with the polymer in the molten state. Experiments carried out in a pressurized view cell indicated that the PEG 1500 progressively decreases its melting point and increases its volume as a consequence of the absorption of the CO 2. The melting point depression was pronounced (from 46 to 28 °C) up to 8.7 MPa. Thereafter a constant value was attained. Analogously, under CO 2 the polymer increased its volume (about 34%) until 10 MPa; after this pressure, the polymer volume no longer increased. PEG 1500 showed solubility in SC-CO 2 at 35 and 55 °C in the 10–40 MPa range in the order of 10 −6 mole fraction. An empirical model based on solubility parameters was used to fit the experimental data and to predict the maximum concentration achievable by the polymer in the dense gas, as well as to quantify the polymer concentration at low pressures where the experimental determination may be extremely difficult.

Novel CO 2-soluble pyridine derivatives and the extraction of heavy metals into Sc-CO 2

New CO 2-soluble, 4-aminopyridine derivatives ( 3a– f) for use as chelating agents were designed and synthesized from the parent compound 4-aminopyridine ( 1) by simple chemical modifications and tested for solubility and metal ion extraction ability in supercritical CO 2 (Sc-CO 2). All of the newly prepared derivatives showed much higher solubility in Sc-CO 2 than the corresponding 4-aminopyridine parent compound, and good or moderate extraction efficiencies for several metal ions (Cu 2+, Co 2+, Zn 2+, and Sr 2+) in 50–90% yield under different conditions, such as temperature, ligand:co-ligand ratio, extraction time, and CO 2 pressure. Interestingly, it was observed that N-(4-pyridyl)pentadecafluorooctanamide ( 3f) with the ‘CO 2-philic’ fluoroalkyl moiety had the lowest CO 2 solubility among the new amide-group-containing pyridine derivatives ( 3a– f), possibly owing to stronger self-interaction. The highest extraction efficiency, especially for copper ions (91%), was achieved with N-hexyl- N-(4-pyridyl)octanamide ( 3e) including a tertiary amide group with only nonfluorous alkyl chains. It is proposed that a tertiary amide group can be considered as a new ‘CO 2-philic’ moiety.

Limiting Partition Coefficients of Solutes in Biphasic Trihexyltetradecylphosphonium Chloride Ionic Liquid−Supercritical CO2 System: Measurement and LSER-Based Correlation

Limiting partition coefficients of a selection of low-to-medium volatility solutes between both phases in a biphasic trihexyltetradecylphosphonium chloride ([thtdp][Cl]) ionic liquid (IL)-supercritical carbon dioxide (scCO2) system were obtained by capillary column chromatography with [thtdp][Cl] as the stationary liquid and scCO2 as the carrier fluid. It is shown that supercritical fluid chromatography can be used to probe the partitioning behavior of solutes in biphasic IL-scCO2 systems even when the IL has nonzero solubility in scCO2. Relative partition coefficients of solutes at a particular temperature and density of CO2 can be correlated within Abraham's linear solvation energy relationships. Compared with our previous results in a [bmim][BF4]-scCO2 system, the solute partition coefficients in the [thtdp][Cl]-scCO2 system are more sensitive to the solute hydrogen bond acidity descriptor.

Acetylation of Soybean Lecithin and Identification of Components for Solubility in Supercritical Carbon Dioxide

There is a growing interest to develop environmentally friendly surfactants for utilization with supercritical carbon dioxide (scCO2), which is a "green" solvent with many industrial applications. The goal of the present work was to separate the commonly used soybean lecithin into a phospholipid-rich fraction, acetylate this fraction, and then test its solubility in scCO2 to gauge its suitability as a surfactant for potential scCO2-based applications. Soybean lecithin was first purified by fractionation using acetone and ethanol and then acetylated with acetic anhydride. The acetylated lecithin was further purified by fractionation with acetone to separate the acetylated fraction from the nonacetylated fraction. High-performance liquid chromatography and electrospray ionization mass spectrometry were utilized to characterize these fractions. The various acetylated phospholipid fractions were then tested for solubility in scCO2 under various pressures and temperatures using both a cloud-point and a Fourier transform infrared apparatus. Acetylation was found to increase the solubility of the phospholipids in scCO2, and N-acetylated phosphatidylethanolamine (NAc-PE) was found to be the most soluble component of the acetylated phospholipids.