Measurements of the solubilities of derivatized amino acids in supercritical carbon dioxide

The solubilities of phenylalanine and tyrosine in supercritical carbon dioxide (SCCO₂) were measured after derivatization as the N-acetyl amino acid ethyl ester, N-carbobenzoxy amino acid and N-acetyl amino acid. Using an SCCO₂ flow system, a measuring method of the saturated solubilities of the derivatized amino acids was established in which the contact height of the extraction cell, i.e. a packed column, is increased till the concentration of a derivatized amino acid at the exit of the cell reaches a plateau. The solubilities of N-acetyl phenylalanine ethyl ester (APEE) exceeded 0.001 mole fraction, which is higher than those of caffeine produced in industrial SCCO₂ processes. A possible way of separating the amino acid mixtures using polarity differences in different amino acid side chains was demonstrated using the solubility data of the N-acetyl-amino acid ethyl esters in SCCO₂, as the solubilities of APEE are higher than those of N-acetyl tyrosine ethyl ester by two orders of magnitude.     

Temperature effects on supercritical carbon dioxide extractions of hydrocarbons from geological samples

The extraction of aliphatic and aromatic hydrocarbons from New Albany Shale by supercritical carbon dioxide at different extraction temperatures is described. The main goal of this work was to determine the effect of the temperature on the extraction process (i.e. relative extraction rate and efficiency). The data suggest that temperature changes of 20 and 40 degrees for the relatively moderate extraction temperatures tested (55, 75, and 95°C), can have significant effects on both relative extraction rates and yields. While lower molecular weight aromatics presented exponential extraction profiles, similar to those of the aliphatic hydrocarbons, higher molecular weight aromatics, such as the phenanthrenes, showed a linear extraction profile. This behavior cannot be explained by solubility differences in the supercritical fluid alone, and are, therefore, most likely based on differences in the speciation of the hydrocarbons within the sample matrix. Extractions at elevated temperatures (300°C) resulted in significant increments in the relative recoveries of all compounds, but particularly for the aromatic hydrocarbons. This may be caused by structural rearrangement of the sample matrix with subsequent release of trapped hydrocarbons and possibly by C-S and S-S bond breakage.     

Mathematical modelling for extraction of oil from Dracocephalum kotschyi seeds in supercritical carbon dioxide

Extraction of oil from Dracocephalum kotschyi Boiss seeds using supercritical carbon dioxide was designed using central composite design to evaluate the effect of various operating parameters including pressure, temperature, particle size and extraction time on the oil yield. Maximum extraction yield predicted from response surface method was 71.53% under the process conditions with pressure of 220 bar, temperature of 35 °C, particle diameter of 0.61 mm and extraction time of 130 min. Furthermore, broken and intact cells model was utilised to consider mass transfer kinetics of extracted natural materials. The results revealed that the model had a good agreement with the experimental data. The oil samples obtained via supercritical and solvent extraction methods were analysed by gas chromatography. The most abundant acid was linolenic acid. The results analysis showed that there was no significant difference between the fatty acid contents of the oils obtained by the supercritical and solvent extraction techniques.     

Dispersion polymerization of styrene in supercritical carbon dioxide using monofunctional perfluoropolyether and silicone-containing fluoroacrylate stabilizers

The free radical dispersion polymerization of styrene was carried out in supercritical carbon dioxide (scCO₂) using two different stabilizers. The polymerizations are performed in the presence of poly(heptadecafluorodecyl acrylate-co-tris(trimethylsilyloxy)silyllpropyl methacrylate) p(HDFDA-co-SiMA) and a commercially available carboxylic acid-terminated perfluoropolyether (Krytox^® 157FSL) as polymerization stabilizers. Dry, fine powdered spherical polystyrene particles were produced under optimised conditions. The resulting high yield of spherical and relatively uniform micron-size polystyrene particles were formed utilizing various amounts of p(HDFDA-co-SiMA) random copolymer. However, it was observed that Krytox^® 157FSL was not a good stabilizer as p(HDFDA-co-SiMA) for the dispersion polymerization of styrene. The particle diameter was shown to be dependent on the type of the stabilizer and the weight percent of the stabilizer added to the system. The effect of varying the concentrations of stabilizers and initiator, reaction time and reaction pressure upon the polymerization yield, molar mass and morphology of polystyrene have been investigated.     

Sampling considerations in supercritical fluid chromatography

Summary Packed column supercritical fluid chromatography, like HPLC, utilizes a sample loop to introduce materials onto the column for analysis. Unlike HPLC the mobile phase in SFC cannot be used to dissolve the sample. In practice, this causes a solvent peak, which can create a problem in the chromatographic interpretation. This paper describes one approach to solving this problem. A valving scheme is used to extract materials with the supercritical CO₂ mobile phase and introduce them onto the column with no external handling. The viability of this method is demonstrated and separations of the CO₂ extracts for several materials are shown on various columns. Comparisons are made for coal and coffee extracts using this on-line method and conventional off-line CH₂Cl₂ extracts. Advantages of the on-line procedure as they apply to chromatography and high information detectors are also discussed.     

Effect of titanium dioxide solubility on the formation of BaTiO3 nanoparticles in supercritical water

Fine BaTiO₃ nanoparticles were prepared by hydrothermal synthesis under supercritical condition (400 °C and 30 MPa) from mixture of barium hydroxide and titanium dioxide as starting precursors. First, conditions for synthesizing BaTiO₃ were examined by using batch reactors. High pH condition, pH > 13, is necessary to obtain phase pure BaTiO₃. The reason was discussed based on the solubility of titanium dioxide, which that dissolution–recrystallization process is essential for the synthesis of BaTiO₃ nanoparticles. Rapid heating of the starting precursors by mixing with high temperature water in a flow reactor is effective to synthesize smaller size and narrower particle size distribution for the BaTiO₃ nanoparticles, compared with the case of slow heating with a batch reactor.     

Use of various filters for generating modified supercritical fluid mobile phases

Summary Adding various components to supercritical carbon dioxide in supercritical fluid chromatography can extend or significantly alter the solvating properties. Polar samples which are difficult to analyze with pure supercritical CO₂ because of their high polarity can be separated by addidng polar modifiers. In this paper, a new mixing method using an HPLC filter for adding polar modifier to CO₂ is described. Although several filters were tried, only one could keep the amount of modifier in the mobile phase constant for a long time. The amount of water or methanol dissolved in supercritical CO₂ was measured by an amperometric microsensor made of a thin film of perfluorosulfonate ionomer (PFSI).     

Solubility of iodopropynyl butylcarbamate in supercritical carbon dioxide

Supercritical carbon dioxide has been considered an appropriate alternative for extraction and purification process of cosmetics, pharmaceuticals, food supplements and natural products. Solubility information of biological compounds is essential for choosing supercritical fluid (SCF) processes. The solubility of iodopropynyl butylcarbamate (IPBC), a fungicide and anti-dandruff agent, was measured in supercritical carbon dioxide with a high pressure apparatus equipped with a variable volume view cell at 313.15, 323.15, and 333.15 K and at pressure between 80 and 35 MPa. The experimental data were correlated well with Peng–Robinson equation of state (PR EOS) and quasi-chemical nonrandom lattice fluid model.     

Supercritical fluid chromatography of imidazole derivatives

Summary The aim of this work was to use SFC to separate simple, slightly basic, imidazole derivatives which are used for the synthesis of more complex molecules with therapeutic properties. Control of their purity utilizes separation techniques and this paper shows what SFC can do in comparison with LC which requires derivatization before detection and with GC where peak tailing can be a problem. Our results concern the use of sub-critical mixtures of CO₂ and polar modifiers because imidazole derivatives react with neat CO₂, thus failing to elute from packed columns, and are only partially resolved on capillary columns with neat N₂O. Therefore, separations with CO₂-alcohol-amine-water mixtures on aminopropyl-bonded silica with UV detection are discussed. The resolution and sensitivity limits allow real sample analysis within a very short time.     

Characterisation of microcellular foams produced from semi-crystalline PCL using supercritical carbon dioxide

Microcellular foams were produced from polycaprolactone (PCL) using a method based on the rapid release of supercritical CO₂. The average pore size in the structure was found to vary with the selected vent time and the final microstructure was a combination of open and closed cells. Thermal analysis showed that the degree of crystallinity of all foams was in the region of 70%. This was found to be consistent with the observation of lamellar textures on the inner surface of the pores. There was also a pronounced decrease in compressive modulus with increasing vent time and average pore size.     

Effect of the carbon dioxide modifier on the lipid composition of wool wax extracted from raw wool

Wool wax or lanolin is a unique substance secreted by sheep and forms a natural protective coating on wool fibres. It is widely used in pharmaceutical and cosmetic formulations. However, different systems of wool wax recovery from scouring liquour provide a dark impurified greasy product. This product has a lipid composition that differs from the wool wax present on wool fibres. The wool wax extraction method from raw wool with pressurised CO₂ and different modifiers at constant pressure and temperature was studied. Thin-layer chromatography coupled to an automated flame ionisation detection system (TLC/FID) was used to analyse the different lipid classes present in the collected extracts. Moreover, a detailed structural comparison of the cholesteryl esters and hydroxycholesteryl esters was carried out by means of sub-ambient pressure chromatography mass spectrometry in the electron impact and in the ammonia positive chemical ionisation modes. For comparison, qualitative and quantitative analyses of the lanolin extracted in Soxhlet with dichloromethane and commercial cosmetic lanolin were carried out. Differences in the quantity of wool wax extraction and in the lipid composition of different wool wax extracts were detected by changing the modifier polarity.     

Extraction of atabron residues from cabbage with supercritical carbon dioxide

Summary In this work we present a new procedure for extraction of Atabron residues from cabbage samples using supercritical carbon dioxide. The results obtained with this procedure were compared with those obtained using traditional extraction methods for Atabron residues. The extraction yields found by both procedures are similar but SFE has several advantages, especially higher speed, greater economy, better selectivity and greater reproducibility.     

Solubility of carbon dioxide in pentaerythritol tetraoctanoate

In this paper, solubility measurements of CO₂ in pure pentaerythritol tetraoctanoate (PEC8) between 273 and 343 K are presented. The experiments were performed according to the static, synthetic method. The data are represented using the Peng–Robinson equation of state with the Huron–Vidal mixing rules and the UNIQUAC equation for the excess Gibbs Energy (g^E) at infinite pressure. This system shows immiscibility in liquid phase, with lower critical end point (LCEP) at T = 268 ± 0.1 K and xCO₂=0.98±0.001$x_{\text{C}{\text{O}}_2}=0.98\pm 0.001$ and upper critical end point (UCEP) at the critical point of pure CO₂.     

Effect of acid-base properties on copper catalysts for hydrogenation of carbon dioxide

Acidic or basic components as co-catalysts were added to the Cu-based catalysts for hydrogenation of CO₂. Effects of acid-base properties on the catalytic activity and methanol selectivity are discussed.     

Nanofiltration membrane behavior in a supercritical medium

The permeability values of “TN” organomineral nanofiltration membranes to water, L, and to supercritical CO₂, G, were compared. The resulting values for G were an order of magnitude higher than for L. The difference may be directly related to the viscosity difference between the two fluids. Temperature- and pressure-related variations in G were also analyzed; for this purpose, Poiseuille's model satisfactorily accounts for experimental behavior, while Knudsen's model is unsuitable. A hysteresis effect was observed on the isotherms corresponding to variations in G versus pressure, suggesting partially irreversible CO₂ adsorption on the micropore walls, that would diminish the radius. This phenomenon could be enhanced by an increased fluid density and viscosity.     

Synthesis of polylactide/clay nanocomposites by in situ intercalative polymerization in supercritical carbon dioxide

Polylactide (PLA)/clay nanocomposites have been prepared by in situ ring-opening polymerization in supercritical carbon dioxide. Depending on the type of organoclay used, polylactide chains can be grafted onto the clay surface, leading to an exfoliated morphology. Nanocomposites with high clay contents (30-50 wt.%), called masterbatches, have also been successfully prepared and were recovered as fine powders thanks to the unique properties of the supercritical fluid. Dilution of these masterbatches into commercial l-polylactide by melt blending has led to essentially exfoliated nanocomposites containing 3 wt.% of clay. The mechanical properties of these materials have been assessed by flexion and impact tests. Significant improvements of stiffness and toughness have been observed for the PLA/clay nanocomposites compared to the pure matrix, together with improved impact resistance.     

Solubilities and partial molar volumes of three bis(2-ethoxyethyl) ethanedioate derivatives in supercritical carbon dioxide

Three new CO₂-philic bis(2-ethoxyethyl) ethanedioate derivatives, bis(2-(2-methoxyethoxy)ethyl) ethanedioate (compound 1), bis(2-(2-ethoxyethoxy)ethyl) ethanedioate (compound 2), and bis(2-(2-butoxyethoxy)ethyl) ethanedioate (compound 3), were designed and synthesized and their solubilities in supercritical carbon dioxide (scCO₂) were then measured at different temperatures (313, 323, 333) K over the pressure range (8.9 to 13.9) MPa. The measured solubility data were correlated with five different theoretical semi-empirical models (Chrastil, kJ, SS, MST, JCF) and satisfactory agreements were obtained. The JCF model provided the best fit and the lowest average absolute relative deviation (AARD) varied from (3.58 to 6.80)%. Furthermore, the partial molar volumes of three compounds in the supercritical phase were also calculated according to the Kumar and Johnston theory, and the values were between −(19105 and 3510) cm³ · mol⁻¹.     

Measurement and correlation of solubility of artemisinin in supercritical carbon dioxide

Artemisinin is an effective antimalarial drug isolated from the herbal medicine Artemisia annua L. Supercritical fluid extraction is an environment-friendly method for the extraction of artemisinin. In this work, the solubility of artemisinin in supercritical carbon dioxide was determined by static method at three temperatures of 313 K, 323 K, 333 K and pressures from 11 to 31 MPa. The range of experimental solubility data was from 0.498 × 10⁻³ to 2.915 × 10⁻³ mol/mol under the above-mentioned conditions. Two density-based models (Chrastil and Mendez–Santiago–Teja models) were selected to correlate the experimental data of this work, and the average absolute relative deviation (AARD) was 8.32% and 8.33%, respectively. The correlation results showed good agreement with the experimental data.     

Polybutadiene-coated zirconia packing materials in solvating gas chromatography using carbon dioxide as mobile phase

Summary In this paper, practical considerations of column efficiency, separation speed, thermal stability, and column polarity of capillary columns packed with polybutadiene-coated zirconia were investigated under solvating gas chromatography (SGC) conditions using carbon dioxide as mobile phase. When compared with results obtained from conventional porous octadecyl obtained from conventional porous octadecyl bonded silica (ODS) particles, PBD-zirconia particles produced greater change in mobile phase linear velocity with pressure than conventional ODS particles under the same conditions. The maximum plate number per second (N_t) obtained with a 30 cm PBD-zirconia column was approximately 1.5 times higher than that obtained with an ODS column at 100 °C. Therefore, the PBD-zirconia phase is more suitable for fast separations than conventional ODS particles in SGC. Maximum plate numbers per meter of 76,900 and 63,300 were obtained using a 57 cm×250 μm i.d. fused silica capillary column packed with 3 μm PBD-zirconia at 50 °C and 100 °C, respectively. The PBD-zirconia phase was stable at temperatures up to 320 °C under SGC conditions using carbon dioxide as mobile phase. Polarizable aromatic compounds and low molecular weight ketones and aldehydes were eluted with symmetrical peaks from a 10 cm column packed with 3 μm PBD-zirconia. Zirconia phases with greater inertness are required for the analysis of more polar compounds by SGC.     

Evaluation of attraction terms in equations of state on the prediction of solubility of some biomolecules in supercritical carbon dioxide

In the present work,effect of theattr action terms of four recently modified Peng-Robinson(MPR)equations of state on the prediction of solubility of caffeine,cholesterol,uracil and erythromycin was studied.The attraction terms of two of these equations are linear relative to the acentric factor and for the other two are exponential.It is found that the later show less deviation.Also interaction parameters for the studied systems are obtained and the percentage of average absolute relative deviation(%AARD)in each calculation is displayed.