Search results for "supercritical fluid"
showing 10 items of 166 documents
Solubility of quercetin in supercritical CO2 + ethanol as a modifier: measurements and thermodynamic modelling
2004
Abstract Grape seeds extracts have shown a broad range of pharmacological activities including, among others, antiulcer and antioxidant properties, which are mainly attributed to the phenolic compounds present. To date, the most abundant phenolic compounds isolated from grape seeds are catechins and their derivatives, e.g. quercetin. The present study is devoted to the experimental measurement and thermodynamic modelling of the solubility of quercetin in supercritical CO 2 + ethanol as a co-solvent. The solubility of quercetin was measured at 313.15 K, pressures ranging from 80 to 120 bar, and at different content of the modifier ethanol—from 5 to 30%. Two types of thermodynamic models were…
Solubility of solid carnosic acid in supercritical CO2 with ethanol as a co-solvent
2005
Abstract The present study is devoted to the experimental measurement and thermodynamic modeling of solid carnosic acid solubility in supercritical CO 2 + ethanol as a co-solvent. Measurements were carried out at temperatures in the range of 313.15 and 333.15 K, pressures ranging from 280 to 400 bar, and at different content of the modifier ethanol (from 0.7 to 10%). The Group Contribution Associating Equation of State (GCA-EoS) [H.P. Gros, S.B. Bottini, E.A. Brignole, High pressure phase equilibrium modeling of mixtures containing associating compounds and gases, Fluid Phase Equilibria 139 (1997) 75–87] was applied in this work to represent the experimental solubility data obtained. Due t…
In Vitro Bioactivity of Astaxanthin and Peptides from Hydrolisates of Shrimp (Parapenaeus longirostris) By-Products: From the Extraction Process to B…
2021
Non-edible parts of crustaceans could be a rich source of valuable bioactive compounds such as the carotenoid astaxanthin and peptides, which have well-recognized beneficial effects. These compounds are widely used in nutraceuticals and pharmaceuticals, and their market is rapidly growing, suggesting the need to find alternative sources. The aim of this work was to set up a pilot-scale protocol for the reutilization of by-products of processed shrimp, in order to address the utilization of this valuable biomass for nutraceutical and pharmaceuticals application, through the extraction of astaxanthin-enriched oil and antioxidant-rich protein hydrolysates. Astaxanthin (AST) was obtained using …
Supercritical fluid extraction and HPLC determination of relevant polyphenolic compounds in grape skin.
2005
The polyphenols determined are: (+)-catechin, (-)-epicatechin, rutin, quercetin and trans-resveratrol. Suitable conditions of supercritical fluid extraction were established using ethanol as a modifier of the polarity solvent (supercritical carbon dioxide). Final extraction conditions were: 20% v/v ethanol, 60degreesC, 250 bars and flow rate 2 mL/min. Static step time and dynamic step time were established using a selected grape skin sample. The extract was collected in water; the more polar polyphenols ((+)-catechin and (-)-epicatechin) remain in solution but rutin, quercetin and trans-resveratrol precipitate in this medium, thereby the solution of the extracted polyphenols was filtered. (…
Evaluation of methods aimed at complete removal of template from molecularly imprinted polymers
2001
Polymers imprinted with clenbuterol were used to study the influence of various post-polymerization treatments [e.g., thermal annealing, microwave assisted extraction (MAE), Soxhlet extraction and supercritical fluid template desorption] on the bleeding of residual template. The aim of the study was to reduce the bleeding to levels that would allow the use of the materials as affinity phases for extraction of clenbuterol from bovine urine at concentrations below 1 ng ml−1. After treatment, the clenbuterol imprinted polymers were packed into solid-phase extraction columns and the bleeding was estimated by quantifying the amount of template released in 10 ml of methanol–acetic acid (9 + 1 v/v…
Non-conventional methods and media for the activation and manipulation of carbon nanoforms
2013
Very often, chemical transformations require tedious and long procedures, which, sometimes, can be avoided using alternative methods and media. New protocols, enabling us to save time and solvents, allow us also to explore new reaction profiles. This Tutorial Review focuses on the physical and chemical behavior of carbon nanoforms, CNFs (fullerenes, nanotubes, nanohorns, graphene, etc.) when non-conventional methods and techniques, such as microwave irradiation, mechano-chemistry or highly ionizing radiations are employed. In addition, the reactivity of CNFs in non-conventional media such as water, fluorinated solvents, supercritical fluids, or ionic liquids is also discussed.
Chromatography-mass spectrometry: Recent evolution and current trends in environmental science
2020
The coupling of chromatography to mass spectrometry has been a very important step in environmental science that has changed routine workflows opening a horizon of new and impressive possibilities. This hyphenated technique benefits from coupling as chromatography offers great separation power and comprises various techniques and mechanisms. In turn, chromatography exploits the identification capability of mass spectrometry and is able to provide nominal or exact mass charge ration (m/z) not only of the intact molecule but also of several characteristic fragments. The sensitivity, selectivity, specificity, and rapidity in chromatography–mass spectrometry make this technology highly powerful…
Synthesis of dimethyl carbonate in supercritical carbon dioxide
2006
The reactivity of carbon dioxide with methanol to form dimethyl carbonate was studied in the presence of the n-butylmethoxytin compounds n-Bu3SnOCH3, n-Bu2Sn(OCH3)2 , and [n-Bu2(CH3O)Sn]2 O. The reaction occurred under solventless conditions at 423 K and was produced by an increase in CO2 pressure. This beneficial effect is primarily attributed to phase behavior. The mass transfer under liquid-vapor biphasic conditions was not limiting when the system reached the supercritical state for a CO2 pressure higher than 16 MPa. Under these conditions, CO2 acted as a reactant and a solvent.
Transesterification of rapeseed oil over acid resins promoted by supercritical carbon dioxide
2011
The methanolysis of rapeseed oil catalyzed by commercial styrene-divinylbenzene macroporous acid resins was performed in a batch reactor at 100-140 °C and 10-46 MPa to study the effect of supercritical carbon dioxide (scCO2) on the performances of the process. Reaction temperatures of 120-140 °C were necessary to obtain high enough yields of fatty acid methyl esters. Upon addition of scCO2 faster transesterification kinetics was obtained also at the lowest investigated operating pressure (10-11 MPa), working in two fluid phase systems. Experiments performed changing the reaction time indicated that most of the esters were formed during the first 3 h. When the pressure was increased at 38-46…
Supercritical Carbon Dioxide: A Promoter of Carbon-Halogen Bond Heterolysis
2013
as the leaving groupdeparts from the carbon atom prior to the entrance of thenucleophile. Polar protic solvents with high dielectric con-stants promote polar bond heterolysis by providing effectiveH-bonding and electron-pair donation interactions to theleaving group and the incipient carbocation, respectively.Then, the solvent captures the carbocation intermediate togive the corresponding S