Search results for "Supercritical"
showing 10 items of 236 documents
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
Novel Food Processing and Extraction Technologies of High-Added Value Compounds from Plant Materials
2018
Some functional foods contain biologically active compounds (BAC) that can be derived from various biological sources (fruits, vegetables, medicinal plants, wastes, and by-products). Global food markets demand foods from plant materials that are “safe”, “fresh”, “natural”, and with “nutritional value” while processed in sustainable ways. Functional foods commonly incorporate some plant extract(s) rich with BACs produced by conventional extraction. This approach implies negative thermal influences on extraction yield and quality with a large expenditure of organic solvents and energy. On the other hand, sustainable extractions, such as microwav…
Inclusion complexes of triphenylphosphine derivatives and peracetylated-β-cyclodextrin in supercritical carbon dioxide
2008
The supramolecular chemistry of peracetylated-β-CD (perAc-β-CD) as a host for triphenyphosphine derivatives has been studied in supercritical (scCO2) using UV absorption spectroscopy. It was found that the association constant in scCO2 at 40°C and 300 bar is 10 to 1000 times smaller compared to analogous systems in aqueous solvent. Studies of the thermodynamics of the inclusion process found an enthalpy of association of -30 kJ/mole and an entropy of -55 J/moleK. This difference with respect to water is attributed to the absence of the hydrophobic effect in scCO2 due to the much smaller polarity of scCO2 versus water. To further explore the effect of the solvent on the association constant,…
Supercritical water gasification of microalgae and their constituents in a continuous reactor
2016
The supercritical water gasification of Nannochloropsis gaditana microalgae has been studied in term of process development at 24 MPa and 663 °C. Gasification has been investigated using a 200 cm3 down flow reactor working continuously. The effect of microalgae slurry concentration, with or without alkali catalysts, was studied. Moreover, the role played by different constituents of microalgae on gasification was investigated. Particularly, gasification of amino acids, carbohydrates and model mixtures among them was studied. Nannochloropsis gaditana was successfully gasified up to 97.4 wt% as gasification efficiency and 86.0 wt% as carbon efficiency. The product gas is mainly composed of hy…
Effects of Dietary Supplementation with Honeybee Pollen and Its Supercritical Fluid Extract on Immune Response and Fillet’s Quality of Farmed G…
2022
The awareness of the correlation between administered diet, fish health and products’ quality has led to the increase in the research for innovative and functional feed ingredients. Herein, a plant-derived product rich in bioactive compounds, such as honeybee pollen (HBP), was included as raw (HBP) and as Supercritical Fluid Extracted (SFE) pollen (HBP_SFE) in the diet for gilthead seabream (Sparus aurata). The experiment was carried out on 90 fish with an average body weight of 294.7 ± 12.8 g, divided into five groups, according to the administration of five diets for 30 days: control diet (CTR); two diets containing HBP at 5% (P5) and at 10% (P10) level of inclusion; two diet…
Determination of pesticide residues in fruit and vegetables.
1996
A review concerning the determination of pesticide residues in fruit and vegetables is presented. The basic principles and recent developments in the extraction and quantitation of pesticides are discussed. Consideration is given to solid phase and supercritical extraction techniques, automation and robotic systems, and immunoassay procedures.