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1.
Essential oil was extracted from yarrow flowers (Achillea millefolium) with supercritical CO2 at pressure of 10 MPa and temperatures of 40–60 °C, and its composition and yield were compared with those of hydrodistillate. The yield of total extract, measured in dependence on extraction time, was affected by extraction temperature but not by particle size of ground flowers. CO2-extraction of cuticular waxes was lowest at 60 °C. Major essential oil components were camphor (26.4% in extract, 38.4% in distillate), 1,8-cineole (9.6% in extract, 16.2% in distillate), bornyl acetate (16.7% in extract, 4.3% in distillate), γ-terpinene (9.0% in extract, 9.4% in distillate), and terpinolene (7.6% in extract, 3.9% in distillate). Compared to hydrodistillation, the yield of monoterpenes was lower due to their incomplete separation from gaseous CO2 in trap but the yield of less volatile components like monoterpene acetates and sesquiterpenes was higher. Hydrolysis of γ-terpinene and terpinolene, occuring in hydrodistillation, was suppressed in supercritical extraction, particularly at extraction temperature of 40 °C. 相似文献
2.
Ali Zeinolabedini HezaveAmir Mowla Feridun Esmaeilzadeh 《The Journal of Supercritical Fluids》2011,58(2):198-203
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. 相似文献
3.
In situ measurements of the ionic conductivity were performed on polyethers, poly(ethylene oxide) (PEO) and poly(oligo oxyethylene methacrylate) (PMEO), with lithium triflate (LiCF3SO3) as crystalline and amorphous electrolytes, and at CO2 pressures up to 20 MPa. Both PEO and PMEO systems in subcritical and supercritical CO2 increased more than five fold in ionic conductivity at 40 °C composed to atmospheric pressure. The pressure dependence of the ionic conductivity for PEO electrolytes was positive under CO2, and increased by two orders of magnitude under pressurization from 0 to 20 MPa, whereas it decreases with increasing pressure of N2. The enhancement is caused by the plasticizing effect of CO2 molecules that penetrate into the electrolytes. 相似文献
4.
Monomer mixture of styrene (St) and N-cyclohexylmaleimide (ChMI) and initiator benzoyl peroxide (BPO) were first impregnated into isotactic polypropylene (iPP) films simultaneously using supercritical carbon dioxide (SC CO2) as a solvent and swelling agent at 35.0 °C. The composites were obtained after the monomers were grafted onto the iPP matrix at 70 °C. The effects of various conditions, such as pressure, monomer concentration, and the molar ratio of the two monomers in the soaking process, on the composition of the composites were determined. The molar ratios of St to ChMI in the composites were estimated by Fourier transform infrared spectroscopy. The thermal properties, the morphology, and the mechanical properties of the composites were characterized by different techniques. The results demonstrated that the phase size of the grafted St-ChMI was very small and the phase boundary was very ambiguous. The composites had better thermal stability than the original iPP film. The Young's modulus and tensile strength of the film increased continuously with increasing grafting percentage. The two grafted monomers in the composites had good synergetic effect. 相似文献
5.
Yong XiangZhe Wang Chao XuChengchuan Zhou Zheng LiWeidou Ni 《The Journal of Supercritical Fluids》2011,58(2):286-294
The corrosion behavior of X70 steel and iron in water-saturated supercritical CO2 mixed with SO2 was investigated using weight-loss measurements. As a comparison, the instantaneous corrosion rate in the early stages for iron in the same corrosion environment was measured by resistance relaxation method. Surface analyzes using SEM/EDS, XRD and XPS were applied to study the morphology and chemical composition of the corroded sample surface. Weight-loss method results showed that the corrosion rate of X70 steel samples increased with SO2 concentration, while the corrosion rate increased before decreasing with SO2 concentration for iron sample. Comparing resistance relaxation method results with weight-loss method results, it is found that the instantaneous corrosion rate of iron is much higher than the uniform corrosion rate of the iron tablet specimens which are covered with thick corrosion product films after a long period of corrosion. The corrosion product films were mainly composed of FeSO4 and FeSO3 hydrates. The possible reaction mechanism under such environment was also analyzed, and the electrochemical reaction between the dissolved SO2 in the condensed water film with iron is the critical reaction step. 相似文献
6.
Elodie Naveau Christophe Detrembleur Christine Jérôme Michaël Alexandre 《Polymer》2009,50(6):1438-1446
In this study, the preparation of organoclays via a new process using supercritical carbon dioxide is described. This method turns out to be very efficient with various surfactants, in particular nonwater-soluble alkylphosphonium salts. The influence of the surfactant as well as of the clay nature on the thermal stability of the organoclay is evaluated by thermogravimetric analysis. Phosphonium-based montmorillonites are up to 90 °C more stable than ammonium-based montmorillonites. Moreover, the use of hectorite adds another 40 °C of thermal stability to the phosphonium-modified clays. These organomodified clays have been melt-blended with polyamide 6 and morphology as well as fire properties of the nanocomposites are discussed, in terms of influence of the stability of organoclays. For the first time, comparison of nanocomposites based on clay organomodified by ammonium and phosphonium salts of the very same structure is reported. 相似文献
7.
M. Díez-MunicioA. Montilla M. HerreroA. Olano E. Ibáñez 《The Journal of Supercritical Fluids》2011,57(1):73-79
Nowadays, the application of green chemistry principles in the production of new polymeric materials is receiving an increasing attention. In the present work, we have investigated the impregnation of chitosan with lactulose using supercritical fluids under various operating conditions, in order to improve the solubility of this natural polymer at neutral or basic pH. A comparison between chitosan scaffolds and microspheres is also presented; both chitosans were characterized using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and Fourier transform infrared spectroscopy (FTIR). The degree of impregnation was evaluated by quantitative gas chromatography (GC-FID) analysis and interactions chitosan-lactulose by ninhydrin method. The supercritical carbon dioxide impregnation proved to be feasible for both chitosan forms. The highest impregnation yield (8.6%) was obtained for chitosan scaffolds using the following impregnation parameters: continuous process, 60 min contact time, 14% (v/v) of co-solvent ethanol:water (95:5), depressurization rate equal to 3.3 bar/min, 100 bar of pressure and 100 °C. Under these conditions, Maillard reaction also occurred. 相似文献
8.
Jinyao Wang Meiyan Wang Jianmin Hao Shin-ichiro Fujita Zhijian Wu Fengyu Zhao 《The Journal of Supercritical Fluids》2010,54(1):9-13525
The interactions between CO2 and carbonyl compounds at different CO2 pressures have been studied both experimentally and theoretically. In situ high-pressure FTIR on carbonyl compounds, i.e., acetaldehyde, acetone, and crotonaldehyde, in supercritical CO2 have been measured at various CO2 pressures varying from 6 to 22 MPa. In order to get insights into the mechanism, theoretical study has been conducted concerning the effect of CO2 on frequency shift of CO in acetaldehyde, acetone, benzaldehyde, crotonaldehyde and cinnamaldehyde at different CO2 pressures. It has been shown that the experimental frequency shifts can be well simulated by the theoretical model calculations using particular structures, in which a carbonyl compound interacts with a few CO2 molecules, depending on the carbonyl compounds examined, except for acetaldehyde.The interaction energies between CO2 and those carbonyl compounds are also given. In addition, the effect of CO2 on hydrogenation of crotonaldehyde and benzaldehyde has been discussed by means of the local softness (s+) calculated at CO2 pressures of 0-22 MPa, which can explain the reactivity difference in the crotonaldehyde and benzaldehyde hydrogenations in supercritical CO2. 相似文献
9.
A magnetically levitated sphere rheometer (MLSR) designed to measure viscosity of fluids exposed to high-pressure carbon dioxide has been developed. This device consists of a magnetic sphere submerged inside a test fluid within a high-pressure housing and levitated at a fixed point. The housing is constructed from an optically transparent sapphire tube. The cylindrical tube can be moved vertically to generate a shear flow around the levitated sphere. The difference in magnetic force required to levitate the sphere at rest and under fluid motion can be directly related to fluid viscosity. Rheological properties, specifically zero shear viscosities, of transparent high-pressure materials can be measured to a precision of about 5% and over a wide range of viscosities. In addition, operation at constant pressure, in concentration regimes from a pure polymer to an equilibrated polymer/supercritical fluid solution, and at shear rates over several orders of magnitude is possible, eliminating many of the disadvantages associated with other high-pressure rheometers. Experiments performed at different temperatures with a poly(dimethylsiloxane) melt at atmospheric pressure are compared with data from a commercial Couette rheometer to demonstrate device sensitivity and viability. Measurements of a PDMS melt plasticized by high-pressure CO2 are performed to illustrate the utility of the new rheometer under high-pressure conditions. Experimental data are obtained at 30 °C, for pressures up to 20.7 MPa and CO2 concentrations reaching 30 wt%. Viscosity reductions of nearly two orders of magnitude compared with the pure polymer viscosity at atmospheric pressure are observed. Additionally, the effects of pressure on a polymer/CO2 system are directly investigated taking advantage of the constant pressure operation mode of the MLSR. This allows us, for the first time in experiments of polymers with supercritical fluids, to decouple the effects of CO2 concentration and pressure in a single device. 相似文献
10.
A novel one-shell high temperature and high pressure semi-continuous reactor has been developed for the study of the Boudouard reaction at temperatures up to 820 °C and pressures up to 32.5 MPa. Semicontinuous gasification of charcoal using supercritical CO2 has been achieved at conversions up to 90.8% (w/w) at LSHV between 20 and 30 h−1 after 5–9 h. A gasification model is proposed and validated. Effective rates of gasification (1.32 ± 0.12) × 10−6 to (6.10 ± 2.03) × 10−5 s−1 were obtained. The results indicated that this method is technically feasible for the on-line production of high pressures streams of CO/CO2 in the lab for carrying out further chemistries, avoiding the use of CO high pressure bottles. 相似文献
11.
S. CardeaE. Reverchon 《Chemical Engineering and Processing: Process Intensification》2011,50(7):630-636
Polymeric catalytic membrane reactors offer a larger flexibility over conventional reactors. The most-used method to generate polymer-based catalytic membranes is the phase inversion that, however, presents some limitations; in particular, the difficulty in generating a uniform distribution of the loaded materials.In this work, we use two new processes for the formation of membranes loaded with catalyst for potential applications in catalysis: supercritical assisted phase inversion and supercritical assisted gel drying, applied to formation of poly(vinylidene fluoride-co-hexafluoropropylene) membranes loaded with palladium nanoparticles. We analyzed the effect of process parameters (polymer concentration, catalyst concentration, pressure, temperature) on the membranes morphology. The supercritical phase inversion process produced cellular asymmetric structures with cell size ranging between 3 and 6 μm and nanoporous homogeneous networks, depending on the process conditions. Palladium nanoparticles homogeneous distributions were obtained only operating at selected process conditions, i.e., pressures larger than 150 bar and temperatures lower than 45 °C.Supercritical gel drying allowed homogeneous nanoporous membranes formation at all the tested process conditions: they were characterized by very high porosity (higher than 90%) and a very uniform catalyst distribution. 相似文献
12.
Ekaterina S. Lokteva Aleksey E. LazhkoElena V. Golubina Vadim V. TimofeevAlexander V. Naumkin Tatiana V. YagodovskayaSergey N. Gaidamaka Valery V. Lunin 《The Journal of Supercritical Fluids》2011,58(2):263-271
Carbonaceous deposits formation was established as the primary reason of Pd/TiO2 catalyst deactivation during reductive processing of CCl4 to form hydrodechlorination and oligomerization products. Three methods of carbonaceous deposits elimination were tested: (1) extraction by supercritical CO2, (2) oxidation by ozone in supercritical CO2, and (3) low-temperature glow-discharge oxygen plasma treatment. Synchronic thermal analysis confirms effective carbonaceous deposits removal during regeneration by ozone or low temperature glow-discharge oxygen plasma; by XPS deep oxidation of surface Pd after oxidative treatment (by ozone or oxygen plasma) was found. Thus H2 reduction was proposed as the second step making possible full regeneration of initial catalytic activity of Pd/TiO2. 相似文献
13.
Using a manometric experimental setup, high-pressure sorption measurements with CH4 and CO2 were performed on three Chinese coal samples of different rank (VRr = 0.53%, 1.20%, and 3.86%). The experiments were conducted at 35, 45, and 55 °C with pressures up to 25 MPa on the 0.354-1 mm particle fraction in the dry state. The objective of this study was to explore the accuracy and reproducibility of the manometric method in the pressure and temperature range relevant for potential coalbed methane (CBM) and CO2-enhanced CBM (CO2-ECBM) activities (P > 8 MPa, T > 35 °C). Maximum experimental errors were estimated using the Gauss error propagation theorem, and reproducibility tests of the high-pressure sorption measurements for CH4 and CO2 were performed. Further, the experimental data presented here was used to explicitly study the CO2 sorption behaviour of Chinese coal samples in the elevated pressure range (up to 25 MPa) and the effects of temperature on supercritical CO2 sorption isotherms.The experiments provided characteristic excess sorption isotherms which, in the case of CO2 exhibit a maximum around the critical pressure and then decline and level out towards a constant value. The results of these manometric tests are consistent with those of previous gravimetric sorption studies and corroborate a crossover of the 35, 45, and 55 °C CO2 excess sorption isotherms in the high-pressure range. The measurement range could be extended, however, to significantly higher pressures. The excess sorption isotherms tend to converge, indicating that the temperature dependence of CO2 excess sorption on coals at high-pressures (>20 MPa) becomes marginal. Further, all CO2 high-pressure isotherms measured in this study were approximated by a three-parameter excess sorption function with special consideration of the density ratio of the “free” phase and the sorbed phase. This function provided a good representation of the experimental data.The maximum excess sorption capacity of the three coal samples for methane ranged from 0.8 to 1.6 mmol/g (dry, ash-free) and increased from medium volatile bituminous to subbituminous to anthracite. The medium volatile bituminous coal also exhibited the lowest overall excess sorption capacity for CO2. However, the subbituminous coal was found to have the highest CO2 sorption capacity of the three samples. The mass fraction of adsorbed substance as a function of time recorded during the first pressure step was used to analyze the kinetics of CH4 and CO2 sorption on the coal samples. CO2 sorption proceeds more rapidly than CH4 sorption on the anthracite and the medium volatile bituminous coal. For the subbituminous coal, methane sorption is initially faster, but during the final stage of the measurement CO2 sorption approaches the equilibrium value more rapidly than methane. 相似文献
14.
Ana M. Lpez-Periago Julio Fraile Carlos A. García-Gonzlez Concepcin Domingo 《The Journal of Supercritical Fluids》2009,50(3):305-312
scCO2 technology was used for the impregnation of microporous zeolites with organic molecules. Specifically, faujasite Y was impregnated with 1,3,5-triphenyl-2-pentene-1,5-dione that after reacting with the acid sites of the zeolite large cavities, formed the 2,4,6-triphenylpyrylium cation. Since the triphenylpyrylium cation has a size higher than the diameter of the zeolite channels, the fabrication method was considered as a ship-in-a-bottle procedure. To optimize the loading, different pressures and temperatures were tested in both the diffusion and cyclisation steps used in the impregnation supercritical process. The obtained impregnated samples were purified either by conventional Soxhlet extraction with dichloromethane or by cleaning with a scCO2 continuous flow. Loaded amounts of ca. 4–7 wt% were obtained following the supercritical procedure, which resulted more time-effective than the conventional procedure based in the use of organic solvents. Samples obtained were analyzed by thermal analysis, UV–vis and IR spectroscopy and characterization of surface area and micropore volume. 相似文献
15.
Supercritical CO2 extraction of Plumula nelumbinis oil was investigated at temperatures of 308–338 K and pressures of 15–45 MPa. The yield of the extracted oil was 0.128 g/g material at optimal conditions, in which gamma-sitosterol, unsaturated fatty acids and gamma-tocopherol had higher relative concentrations as determined by GC–MS. The broken and intact cell (BIC) model, with reduced adjustable parameters, was utilized to simulate the SFE process. The values of average absolute relative deviation (AARD) were in the range 2.34–10.9%, indicating that the improved method had a similar effect to the BIC model when three parameters were adjusted. The parameters obtained during the modeling had clear physical meanings and were used to gain an in-depth understanding of the SFE process theoretically. 相似文献
16.
17.
Poly(acrylic acid)/nylon6 and polystyrene/nylon6 blends were prepared using supercritical CO2 as substrate-swelling agent and monomer/initiator carrier. Both supercritical CO2/nylon6 binary system and SC CO2/monomer/nylon6 ternary system were studied. Virgin nylon6 and synthesized blends were characterized through differential scanning calorimetry, infrared spectroscopy, and polarizing microscopy. Supercritical CO2-induced crystallization was found in modified nylon6. 相似文献
18.
Hongliu Sun 《Polymer》2005,46(20):8872-8882
A method is reported to improve creep resistance in tension for polytetrafluoroethylene (PTFE) and modified PTFE (M-PTFE). PTFE and M-PTFE from different sources were annealed in air, N2 or supercritical CO2 (scCO2) at a range of temperatures, pressures and time intervals. Annealing PTFE in scCO2 increases crystallinity from 9 to 53%, depending on the material and annealing conditions. No corresponding increase occurs for samples annealed in air or N2. In comparison to as-received PTFE, significant improvements in tensile creep resistance (18-60%) are observed also dependent upon the material and annealing conditions. For a given temperature and duration, the increase in PTFE tensile creep resistance after annealing in air or N2 is greater than after annealing in scCO2 despite the higher crystallinity for post-scCO2 processed PTFE. Density measurements indicate that the effect of increased crystallinity is counterbalanced by scCO2-generated microvoids, particularly at higher pressures, leading to smaller creep resistance. In contrast, thermal annealing in air or N2, which does not significantly change the density or enhance the crystallinity of PTFE or M-PTFE, yields better tensile creep resistance. The detailed morphological origin of improved resistance to tensile creep is unknown, but stress relief by thermal annealing is evident. 相似文献
19.
K. Ko
í L. Obalov L. Matjov D. Plach Z. Lacný J. Jirkovský O. olcov 《Applied catalysis. B, Environmental》2009,89(3-4):494-502
Pure TiO2 anatase particles with a crystallite diameters ranging from 4.5 to 29 nm were prepared by precipitation and sol–gel method, characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis and scanning electron microscopy (SEM) and tested in CO2 photocatalytic reduction. Methane and methanol were the main reduction products. The optimum particle size corresponding to the highest yields of both products was 14 nm. The observed optimum particle size is a result of competing effects of specific surface area, charge–carrier dynamics and light absorption efficiency. 相似文献
20.
Pathumthip Tonthubthimthong Peter L. Douglas Supaporn Douglas Wilai Luewisutthichat Wittaya Teppaitoon La-eid Pengsopa 《The Journal of Supercritical Fluids》2004,30(3):287-301
Nimbin, a component found in neem seeds, which is reported to have several valuable medicinal properties including: anti-inflammatory, anti-pyretic, anti-fugal, antihistamine and antiseptic was extracted from neem seeds using supercritical CO2 and CO2 with a methanol modifier.Nimbin extraction yields using supercritical carbon dioxide were found to be approximately 85% at 308 K, 23 MPa and a CO2 flow rate of 0.62 cm3/min for a 2-g sample of neem. An optimum extraction pressure appears to exist at ≈23 MPa and 328 K. Although extraction using a methanol modifier did improve the extraction somewhat, methanol was not found to be an effective modifier for extracting nimbin.Dynamic extraction curves were predicted using three empirical models and a theoretical model. The three empirical models were: a Langmuir gas adsorption model, a first order plus dead time (FOPDT) model and a so-called tn cyclone model used to incorporate sigmoidal curves. The parameters in the empirical models were fitted to the experimental data. The Goto et al. [J. Chem. Eng. Jpn. 31 (1998) 171] theoretical model was compared to the experimental results and was found to fit the data well. The theoretical model shows that the extraction yield depends strongly on the solvent flow rate, that is, external mass transfer or equilibrium is the controlling step of this process. 相似文献