Extraction of ferulic acid from Angelica sinensis with supercritical CO2

Extraction of pharmacologically active ingredient of ferulic acid from the root of Angelica sinensis with supercritical CO2 was investigated. The experimental results show that the extract yields were 0.87-4.06% at temperatures from 45 to 65 degrees Celsius and pressures from 30 to 50 MPa, and the maximum content of ferulic aicd in the extracts was about 0.35-0.37%, which is lower than that of 0.61-0.85% by conventional percolation methods. Ethanol was used as co-solvent in different ratios to raw materials in order to increase the content of ferulic acid in the extracts. The experimental results show that both the extract yields and the content of ferulic acid in the extracts increase greatly compared with pure CO2 extraction. When the ratio of ethanol to the raw material was 1.6, the content of ferulic acid in the extracts was 0.91-1.27%, indicating that supercritical fluid extraction (SFE) with CO2 in the presence of suitable co-solvent is superior to percolation in extracting polar ferulic acid from Angelica sinensis.     

Optimization of extraction of evodiamine and rutaecarpine from fruit of Evodia rutaecarpa using modified supercritical CO(2)

Evodiamine and rutaecarpine have been intensively studied due to their pharmacological actions and clinical applications. In this report, supercritical fluid was used to extract evodiamine and rutaecarpine from the unripe fruit of Evodia rutaecarpa. Response surface methodology using Box-Behnken experimental design was utilized to optimize parameters for supercritical carbon dioxide extraction with methanol as co-solvent. The effect of various values of dynamic extraction time (30-90min), temperature (50-70°C) and pressure (200-400bar) on extraction yields of the two compounds was evaluated. Determinations of the extracts were performed by high-performance liquid chromatography. The experimental data obtained were fitted to second-order polynomial equations and analyzed by analysis of variance. The highest yields predicted were 1.217mg/g for evodiamine and 0.969mg/g for rutaecarpine at the optimal values (time 78min, temperature 62°C, pressure 280bar and co-solvent flow rate 0.4mL/min), based on the selected range of experimental conditions.     

Why do co-solvents enhance the solubility of solutes in supercritical fluids? New evidence and opinion

The effects of two polar co-solvents, chlorodifluoromethane and acetone, on the solubility and enthalpy of a solution of 1,4-naphthoquinone in supercritical (SC) CO2 were studied. We found that the dissolution process becomes less exothermic in the presence of the co-solvents relative to that in pure CO2, although the solubility is enhanced significantly by the co-solvents. This indicates that the increase in the solubility by adding co-solvents results from the increase of the entropy of solution. On the basis of the unexpected results we propose a new mechanism for the solubility enhancement of the solute by the co-solvents in supercritical fluids (SCF); this should be applicable to cases in which the local density of the SC solvent around the solute and the co-solvent is larger, and the co-solvent associates preferentially with the solute. The results are also very important for the understanding of other fundamental questions of SCF science, such as the effect of co-solvents on the thermodynamic and kinetic properties of the reactions in SCFs.     

Oxidation of n-Butanol and 2-Pentanol with Molecular Oxygen in Supercritical CO2

Oxidation of n-butanol and 2-pentanol using molecular oxygen in supercritical (SC) CO2 with and without co-solvent is investigated. The results showed that the reaction selectivity is high when the reaction is carried out in SC CO2. It has been observed that co-solvent affects conversion and selectivity of the reaction considerably.     

Investigation of AOT reverse microemulsions in supercritical carbon dioxide

Bis(2-ethylhexyl) sodium sulphosuccinate (AOT) was successfully solubilised in supercritical carbon dioxide (scCO₂), with ethanol or pentanol as co-solvent. Three molecular spectroscopic probes: methyl orange (MO), 8-hydroxy-1,3,6-pyrenetrisulphonic acid trisodium salt (HPTS), and riboflavin (RF) were used to examine the solubilisation characteristics of the water/scCO₂ microemulsions formed with AOT. MO was extracted at various operating conditions, although the wavelength of its solvatochromic absorption maximum was not indicative of bulk water properties. Instead, the spectral results imply that MO may be located at the surfactant/water interface. The highly water-soluble dye HPTS was unable to be extracted into scCO₂/AOT/water systems, suggesting that the water in the reverse micelle core was not as polar under supercritical conditions as those at ambient conditions. Finally, RF was extracted into the supercritical phase (40°C, 175 bar) with pentanol co-solvent, with an apparent enhanced uptake compared with the value at 40°C and ambient pressure in bulk water. This appears to be due to the presence of microcrystals dispersed in the supercritical phase.     

Comparative analysis of the oil and supercritical CO(2) extract of Cymbopogon citratus Stapf

Dried and ground leaves of lemon grass (Cymbopogon citratus Stapf.) were used as a matrix for supercritical extraction of essential oil with CO(2). The objective of this study was to analyze the influence of pressure on the supercritical extraction. A series of experiments were carried out, for 360 min, at 50 degrees C and at different pressures: 90, 100, 110 and 120 bar. Extraction conditions were chosen to maximize citral content in the extract oil. The collected extracts were analysed by GC-MS and their composition was compared with that of the essential oil isolated by hydrodistillation and by steam distillation. At higher solvent density the extract aspect changes passing from a characteristic yellow essential oil to yellowish semi-solid mass because of the extraction of high molecular mass compounds. The optimum conditions for citral extraction were 90 bar and 50 degrees C, at these conditions citral represent more than 68% of the essential oil and the extraction yield was 0.65% while the yield obtained from hydrodistillation was 0.43% with a content of citral of 73%.     

Cosolvent Effect on the Tautomerism of Ethyl Acetoacetate in Supercritical CO_2

There are some unique advantages for chemical reactions in SCFs. For example, reaction rates, yields, and selectivity can be tuned by pressure or small amount of cosolvent. SCFs can be used to replace environmentally undesirable solvents. It is not surprised that in recent years the use of SCFs as solvents for chemical reaction media has received much attention. However, mechanism for the effect of pressure and cosolvents on chemical reactions is not very clear. Tautomeric reactions are id…     

Minimizing UV noise in supercritical fluid chromatography. I. Improving back pressure regulator pressure noise

Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO(2)) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40 °C and 100 bar), compared to 0.0045%/bar for water (CO(2) IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO(2) decreases 8-fold at 200 bar, compared to 100 bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN(p-p)) as low as 0.1 bar, at 200 bar, and 20Hz, compared to older equipment that attempted to maintain PN(p-p)<1bar, at <5Hz. With this lower PN(p-p), changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1 bar at 100 bar, common with some older BPR's, produced a UV baseline offset >0.5 mAU. A pressure change of ±0.5 bar representing the previous state-of-the-art, resulted in a UV offset of 0.3m AU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN(p-p) of 0.1 bar, demonstrated UV peak to peak noise (N(p-p))<0.02 mAU with a >0.03 min (10Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time.     

Effects of different extraction methods and conditions on the phenolic composition of mate tea extracts

A simple and rapid HPLC method for determination of chlorogenic acid (5-O-caffeoylquinic acid) in mate tea extracts was developed and validated. The chromatography used isocratic elution with a mobile phase of aqueous 1.5% acetic acid-methanol (85:15, v/v). The flow rate was 0.8 mL/min and detection by UV at 325 nm. The method showed good selectivity, accuracy, repeatability and robustness, with detection limit of 0.26 mg/L and recovery of 97.76%. The developed method was applied for the determination of chlorogenic acid in mate tea extracts obtained by ethanol extraction and liquid carbon dioxide extraction with ethanol as co-solvent. Different ethanol concentrations were used (40, 50 and 60%, v/v) and liquid CO? extraction was performed at different pressures (50 and 100 bar) and constant temperature (27 ± 1 °C). Significant influence of extraction methods, conditions and solvent polarity on chlorogenic acid content, antioxidant activity and total phenolic and flavonoid content of mate tea extracts was established. The most efficient extraction solvent was liquid CO? with aqueous ethanol (40%) as co-solvent using an extraction pressure of 100 bar.     

Electrodeposition of germanium from supercritical fluids

Several Ge(II) and Ge(IV) compounds were investigated as possible reagents for the electrodeposition of Ge from liquid CH(3)CN and CH(2)F(2) and supercritical CO(2) containing as a co-solvent CH(3)CN (scCO(2)) and supercritical CH(2)F(2) (scCH(2)F(2)). For Ge(II) reagents the most promising results were obtained using [NBu(n)(4)][GeCl(3)]. However the reproducibility was poor and the reduction currents were significantly less than the estimated mass transport limited values. Deposition of Ge containing films was possible at high cathodic potential from [NBu(n)(4)][GeCl(3)] in liquid CH(3)CN and supercritical CO(2) containing CH(3)CN but in all cases they were heavily contaminated by C, O, F and Cl. Much more promising results were obtained using GeCl(4) in liquid CH(2)F(2) and supercritical CH(2)F(2). In this case the reduction currents were consistent with mass transport limited reduction and bulk electrodeposition produced amorphous films of Ge. Characterisation by XPS showed the presence of low levels of O, F and C, XPS confirmed the presence of Ge together with germanium oxides, and Raman spectroscopy showed that the as deposited amorphous Ge could be crystallised by the laser used in obtaining the Raman measurements.     

Supercritical carbon dioxide processing of fluorinated surfactant templated mesoporous silica thin films

The effect of processing mesoporous silica thin films with supercritical CO2 immediately after casting is investigated, with a goal of using the penetration of CO2 molecules in the tails of fluorinated surfactant templates to tailor the final pore size. Well-ordered films with two-dimensional hexagonal close-packed pore structure are synthesized using a cationic fluorinated surfactant, 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)pyridinium chloride, as a templating agent. Hexagonal mesopore structures are obtained for both unprocessed films and after processing the cast films in CO2 at constant pressure (69-172 bar) and temperature (25-45 degrees C) for 72 h, followed by traditional heat treatment steps. X-ray diffraction and transmission electron microscopy analysis reveal significant increases in pore size for all CO2-treated thin films (final pore diameter up to 4.22 +/- 0.14 nm) relative to the unprocessed sample (final pore diameter of 2.21 +/- 0.20 nm) before surfactant extraction. Similar pore sizes are obtained with liquid and supercritical fluid treatments over the range of conditions tested. These results demonstrate that combining the tunable solvent strength of compressed and supercritical CO2 with the "CO2-philic" nature of fluorinated tails allows one to use CO2 processing to control the pore size in ordered mesoporous silica films.     

共溶剂对超临界CO2注入技术制备聚丙烯/SiO2纳米复合材料的影响

采用超临界CO2注入技术制备聚合物-无机纳米粒子复合材料, 以乙醇作为共溶剂, 在超临界CO2中将正硅酸乙酯(TEOS)注入到聚丙烯(PP)中, 重点研究共溶剂乙醇对TEOS在PP中注入率的影响. 实验结果表明注入率随着共溶剂加入先增加后减小. 同时研究了在共溶剂的存在下其他实验条件对注入率的影响. 并采用卢瑟福背散射能谱法(RBS)分析了聚丙烯/SiO2纳米复合材料的注入元素深度分布, 发现Si元素在PP中的浓度分布不均匀, 随着深度的增加而减小.     

共溶剂对超临界CO_2注入技术制备聚丙烯/SiO_2纳米复合材料的影响(英文)

采用超临界CO2注入技术制备聚合物-无机纳米粒子复合材料,以乙醇作为共溶剂,在超临界CO2中将正硅酸乙酯(TEOS)注入到聚丙烯(PP)中,重点研究共溶剂乙醇对TEOS在PP中注入率的影响.实验结果表明注入率随着共溶剂加入先增加后减小.同时研究了在共溶剂的存在下其他实验条件对注入率的影响.并采用卢瑟福背散射能谱法(RBS)分析了聚丙烯/SiO2纳米复合材料的注入元素深度分布,发现Si元素在PP中的浓度分布不均匀,随着深度的增加而减小.     

Structural and adsorptive properties of Ba or Mg oxide modified zirconia

Zirconia nanoparticles modified by barium oxide or magnesium oxide were synthesized by using a co-precipitation process followed by ethanol supercritical drying. The nanoparticles obtained were further calcined at 873 K. BET surface area, XRD, and TGA were used to characterize the prepared samples. Isotherms of N2 and CO2 adsorption on these modified zirconia nanoparticles were measured at various temperatures. Additions of BaO or MgO resulted in an increase in CO2 adsorption capacity of the modified zirconia particles. Results also show that BaO as a modifier is more effective than MgO in enhancing the CO2 adsorption capacity of zirconia. At 1 bar and 473 K, Ba modified zirconia adsorbs approximately 0.25 mmol/g of CO2.     

A vibrational spectroscopic study of structure evolution of water dissolved in supercritical carbon dioxide under isobaric heating

A combination of Raman scattering spectroscopy and infrared absorption was applied to investigate the structural evolution of water dissolved in supercritical carbon dioxide under isobaric heating (T=40-340 degrees C, P=250 bar). Quantitative analysis of experimental spectra allowed us to determine that at relatively moderate temperatures water dissolved in CO(2)-rich phase exists only under monomeric form (solitary water surrounding by CO(2) molecules), but hydrogen-bonded species, namely, dimers, begin to appear upon heating. At the same time, the ratio of dimers to monomers concentration increases with further temperature increase and at temperatures close to the temperature of total miscibility of the mixture (T=366 degrees C, P=250 bar), water dimers only are present in the CO(2)-rich phase.     

Transesterification of palm oil using supercritical methanol with co-solvent HCFC-141b

The transesterification of palm oil in supercritical methanol has been investigated without using any catalyst. HCFC-141b was used as co-solvent to reduce the molar ratio of methanol to palm oil under the milder conditions. The reaction was carried out in a flow-type tubular reactor. The residence time was fixed at 40 min. When the molar ratio of methanol to palm oil was set to 20:1 at 325 °C and 35 MPa, the optimum molar ratio of methanol to co-solvent was found to be 20:1. Addition of HCFC-141b increased FAME production even at the lower molar ratio of methanol to palm oil. In addition, a similar FAME content was obtained under the milder conditions (5 MPa lower pressure) compared with conditions without co-solvent at higher pressure. The role of HCFC-141b in the transesterification reaction under supercritical conditions was investigated.     

Spectrophotometric measurement of uranium(VI)-tributylphosphate complex in supercritical carbon dioxide

UV-visible absorption spectra of uranium(VI)-tributylphosphate (U(VI)-TBP) complex dissolved in supercritical CO(2) at 40-60 degrees C and 100-250 kg cm(-2) were recorded. Wavelengths and molar extinction coefficients for the absorption peaks of U(VI)-TBP were determined and confirmed to be in good agreement with those of UO(2)(NO(3))(2)(TBP)(2) complex dissolved in organic solvents such as n-hexane. The absorbance at a given wavelength was proportional to the concentration of U(VI) species in supercritical CO(2), indicating a feasibility of in-situ determination of U(VI) concentration in CO(2) phase. A lower detection limit of U(VI)-TBP complex was estimated to be ca. 1x10(-3)M. The molar extinction coefficient of U(VI)-TBP in supercritical CO(2) decreased slightly with an increase of the density of CO(2) medium, suggesting that the solute-solvent interaction of U(VI)-TBP complex with CO(2) was affected by the density. On the basis of the spectra obtained, phase behavior and solubility of UO(2)(NO(3))(2)(TBP)(2)+H(NO(3))(TBP)+TBP in supercritical CO(2) were elucidated.     

Steric Stabilization of Colloids by Poly(dimethylsiloxane) in Carbon Dioxide: Effect of Cosolvents

Steric stabilization and flocculation of colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO(2) at pressures up to 345 bar at 25 degrees C and 517 bar at 65 degrees C without stirring. The addition of 15 wt% hexane to CO(2) led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1-2 μm PMMA particles. The critical flocculation pressure of the colloids in the hexane/CO(2) mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS-CO(2) system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO(2) with PDMS-based surfactants. Copyright 2000 Academic Press.     

超临界二氧化碳介质中钯催化末端炔烃羰基化反应的影响因素

在超临界二氧化碳介质的钯催化末端炔烃羰基化反应中 ,研究了助溶剂、压力和温度等因素对反应的影响。发现末端炔烃羰基化反应生成炔酸酯的最佳条件为 :醇 3～ 4mL ,CO2 压力 7.5MPa和温度 4 0℃。     

Supercritical CO2-ionic liquid mixtures for modification of organoclays

The use of supercritical CO(2) as solvent in the modification of montmorillonite by imidazolium and phosphonium ionic liquids bearing long alkyl chains (C(18)) known for their excellent thermal stability is described. The objective is to combine the environmentally friendly character of ionic liquids and supercritical carbon dioxide for the organophilic treatment of lamellar silicates. Dialkyl imidazolium and alkyl phosphonium salts were synthesized to be used as new surfactants for cationic exchange of layered silicates. Then, the synthesized phosphonium (MMT-P) or imidazolium (MMT-I) modified montmorillonites, cationically exchanged under supercritical carbon dioxide with or without co-solvent, have been analyzed by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) and compared to montmorillonites treated by conventional cationic exchange.