Use Of Supercritical Fluids Research Articles

Fine particle formation using supercritical fluids

The use of supercritical fluids as solvents for the formation of micro- and nano-particles has shown tremendous over the past few years due to increased demands from industry for materials with high performance specifications and high or unique functionality. Supercritical fluids allow synthesis of many types of particles since the solvent's chemical and physical properties can be varied with temperature or pressure, both of which can affect the degree of supersaturation and nucleation. In this review, we describe methods for the formation of fine particles using supercritical fluids CO 2 and water. Basic principles and specific features of each solvent are described, and the advantages and limitations are discussed.

Supercritical fluid-mediated alumination of mesoporous silica and its beneficial effect on hydrothermal stability.

We have investigated the use of supercritical fluids (SCFs) as carriers/solvents during the postsynthesis alumination of mesoporous silica. SCFs were found to be ideally suited for transport of Al into mesoporous silica and to lead to Al-grafted aluminosilicate materials that exhibit exceptional hydrothermal (steam) stability even for highly aluminated materials. The improvements in steam stability arising from the use of SCFs as grafting media (as compared to aqueous or organic solvents) are remarkable, especially for Al-grafted MCM-41 materials with high (Si/Al < or = 10) Al contents. It is proposed that under supercritical fluid conditions Al is sorbed on the surface of the pore walls of the host Si-MCM-41 with little penetration into the pore wall region, that is, the low solvating power of SCFs ensures the deposition of Al onto rather than into the silica framework. This is because the host silica framework cannot undergo any significant hydrolysis (to allow penetration of Al into the pore wall region) during the SCF-mediated alumination. Removal of the Al (i.e., dealumination) which occurs during steaming is therefore less detrimental to the structural integrity of SCF-grafted Al-MCM-41 materials since any dealumination that occurs will not involve removal of Al from deep within the pore walls.

Supercritical Fluids and the Food Industry.

This paper reviews the use of supercritical fluids in various aspects of the food industry, and is divided into six different areas: modeling of supercritical fluids, separation of extracted material, supercritical carbon dioxide as a solvent for extraction, supercritical fluids and analytical uses, and supercritical fluids and novel methods of food processing. An assortment of solutes are covered in the extraction section of the paper, including antineoplastic agents and lipids. The analytical methods section covers supercritical fluid chromatography, pesticide detection, and lipid analysis. The novel methods section discusses supercritical fluid extrusion and a new method of eliminating hexane from soybean oil.

Basis for a new procedure to eliminate diarrheic shellfish toxins from a contaminated matrix.

The natural contamination of shellfish with diarrheic shellfish toxins (DSP) has important public health implications. To avoid the economic effects of toxic episodes on shellfish farmers and the related industry, research on artificial methods alternative to the natural detoxification of shellfish is needed. Because the usual thermal processes are not efficient, alternative technologies have to be studied. Here preliminary results are presented about the lability of the DSP toxin okadaic acid in a supercritical atmosphere of carbon dioxide with acetic acid. Most of the toxin is eliminated (up to 90%), and the biological activity against its target enzyme is also severely affected (up to 70% reduction). Detoxification of contaminated shellfish requires a partial dehydration, and the detoxification yield is lower than that obtained with free toxin. Mass spectrometry experiments suggest that acetylation of the toxin molecule is not the basis of the inactivating mechanism, but a conformational change is suggested. This is the first report of the use of supercritical fluids to inactivate toxins.

Supercritical resist drying for isolated nanoline formation

Supercritical resist drying enables the formation of fine resist patterns with a nanometer-scale resolution. Fine isolated and dense lines of resist collapse when dried by conventional methods after development, thereby lowering the useful resolution of resist patterns. For nanolines, the collapse is due to the swelling of the resist that results from development and rinsing. To prevent collapse, the cause of the swelling must be removed from the resist before drying. The use of supercritical fluid is the most suitable way to do that because such fluid has a diffusion coefficient as large as that of a gas. Supercritical resist drying with carbon dioxide prevents the collapse of isolated lines and enables the formation of nanolines with a width of about 7 nm and a high aspect ratio of over 10 in the case of the negative tone resist of hydrogen silsesquioxane and 100 kV electron beams.

Supercritical fluid extraction of ethoxyquin from a beef matrix

The extraction and determination of ethoxyquin is becoming increasingly important as products, which are labeled as “natural” are becoming more common. This manuscript investigates gates the use of supercritical fluids in the extraction of ethoxyquin from lean beef and beef fat. Three fluids were examined: carbon dioxide, trifluoromethane, and 1,1,1,2-tetrafluoroethane. Carbon dioxide appeared to react with ethoxyquin during the extraction. Methanol modified hydrofluorocarbons provided more complete extractions over pure hydrofluorocarbon fluids. Methanol modified 1,1,1,2-tetrafluoroethane was used in the extraction of ethoxyquin from lean beef and beef fat, and provided a quantitative extraction at the 0.5 ppm level.

Fluidos supercríticos em química analítica. I. Cromatografia com fluido supercrítico: conceitos termodinâmicos

Under the chromatographic point of view, the physico-chemical properties of a supercritical fluid are intermediate to those of the gases and liquids. Many times they approach the best features of each one, as for example, the solubilization power of liquids and low viscosity of gases. The thermodynamic definitions and main physico-chemical features of a supercritical fluid will be presented in this article. The use of supercritical fluids in analytical chemistry has been extremely modest in Brazil, even considering the enormous potential of their applications, and their use in several techniques, such as chromatography (SFC) and supercritical fluid extration (SFE). This article series is intended to discuss the historical evolution, instrumentation features and potential and limitations of the supercritical fluid use in analytical chemistry. A special focus will be centered on chromatography and extration techniques using supercritical fluids.

The Use of Supercritical Fluids as Alternative Solvents

The Use of Supercritical Fluids as Alternative Solvents

Thin film coating of photocatalytics on ultra light ceramic tile by use of supercritical fluid

Although sol-gel method is an easy procedure to form a thin film, it's extremely difficult to coat on the surface of small size particles, fibers, and fiber ceramics, because concentration occurs by capillary phenomena and causes peeling or breakage of film. In order to solve this problem, we use supercritical CO2 rapid expansion from supercritical solution (RESS), nano-sized particles of TiO2 with high intensity can be sprayed out of a nozzle, then collected on the surface of substrates, but can be absorbed into fibers or porous materials, being not interfered by viscosity of a solution. TiO2 sol made by hydrolysis process is set in a pressure cell and mixed together with super-critical CO2. Controlling the pressure and the temperature, we could obtain TiO2 sol and super critical fluid mixture, and then discharge to the substrate. At this point, Titania sol viscosity is so low that a surface wettability of the substrate becomes negligible. By the use of the characteristics of the supercritical fluid, without constraint condition of viscosity or capillarity, this sol can penetrate into the interstices of the substance's structure. Thus, clearing obstruction of capillary phenomena, supercritical fluid coating method shows its capability to penetrate deep into inside of entangled fiber of the three-dimensional structure so as considered to be a heat resistant filter with 95% porosity.

Transition Metal (53Cr, 59Co, 91Zr, and 95Mo) and 14N NMR Spectroscopy of Coordination Compounds Containing Nitrogen Donor Ligands in Low-Viscosity Fluids

Appreciable decreases of the line widths of NMR resonances of the quadrupolar nuclei 14N, 53Cr, 59Co, 91Zr, and 95Mo have been obtained in supercritical solvents and in low-viscosity liquefied gases. Several α-diimines R1N=C(R2)−C(R2)=NR1 and their coordination compounds have been studied. Regarding the solubility of two α-diimines and some Cr, Zr, and Mo complexes it appears that the addition of small amounts of a modifier (acetone, CH2Cl2, THF) results in enhanced solubility of compounds without detrimental effects on the line widths. The use of HP NMR tubes (with and without pressure sensor) is very appropriate for measurements of NMR spectra under high pressure in supercritical fluids and liquefied gases of low viscosity. In several cases it appeared that the use of liquefied gases is more straightforward than the use of supercritical fluids, and gives similar or better results in terms of reduction of line widths.

The use of supercritical fluids in synthetic organic chemistry

Download options Please wait... Article information DOI https://doi.org/10.1039/B101219N Article type Review Article Submitted 06 Feb 2001 First published 23 Mar 2001 Download Citation J. Chem. Soc., Perkin Trans. 1, 2001, 917-941 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions The use of supercritical fluids in synthetic organic chemistry R. S. Oakes, A. A. Clifford and C. M. Rayner, J. Chem. Soc., Perkin Trans. 1, 2001, 917 DOI: 10.1039/B101219N To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author R. Scott Oakes Anthony A. Clifford Christopher M. Rayner

Mordant dyeing of wool by supercritical processing

Few studies have reported the use of supercritical fluids as solvents in dyeing of textile fibers. Studies on synthesis of new dyestuff that can be used in this technique and their solubility in the supercritical fluid are attracting increasing attention. In this study, wool fibers were dyed with mordant dyes dissolved in supercritical carbon dioxide. We used three mordant dyes that have chelating ligand properties, 2-nitroso-1-naphthol (C.I. Mordant Brown), 5-(4-aminophenylazo) salicylic acid (C.I. Mordant Yellow 12) and 1,2-dihydroxyanthraquinone (C.I. Mordant Red 11 also called Alizarin) which were dissolved in supercritical carbon dioxide, and five different mordanting metal ions, Cr(III), Al(III), Fe(II), Cu(II) and Sn(II). Wool fibers were mordanted by the metal using conventional techniques and dyed at 333-353 K temperature and at 150–230 atm pressure. Dyed materials had excellent wash fastness properties.

Fractionation of Peace River Bitumen Using Supercritical Ethane and Carbon Dioxide

The purpose of this work was to provide valuable data for the use of supercritical fluids in both surface and in situ bitumen and heavy oil recovery operations. Experiments were conducted using a semibatch extractor packed with a mixture of bitumen and sand, and the experiments were performed such that thermodynamic equilibrium governed the extraction process. Experimental temperatures and pressures were varied in order to observe their impact on the ability of supercritical ethane and carbon dioxide to recover oil from the bitumen-sand mixture. The results showed that ethane consistently outperformed carbon dioxide in terms of its ability to extract oil from the bitumen-sand mixture. In all cases, supercritical ethane produced yields that were much greater than those obtained with supercritical carbon dioxide. Analysis of the extracted material revealed that the bitumen extracted using ethane was much heavier and contained a wider range of hydrocarbons.

Manufacture of Submicron Particles via Expansion of Supercritical Fluids

The RESS (rapid expansion of supercritical solutions) process offers interesting possibilities for producing submicron solid particles for high-value materials used, in particular, in the food and pharmaceutical industries. Despite extensive models and experimental data on the use of supercritical fluids in extraction processes, there are still uncertainties about the fundamental processes that contribute to particle formation in the RESS process. In the present research, the effect of the nozzle diameter and preexpansion conditions on particle size and morphology of a model system of carbon dioxide/cholesterol has been examined.

Applications of supercritical fluid extraction and chromatography in forensic science

Supercritical fluid technology is a rapidly expanding analytical technique. Here we give a brief insight into the background of supercritical fluid technology and how supercritical fluid extraction and supercritical fluid chromatography work in analysis. The applications of these two techniques in forensic science are known to be important. The main area of forensic use of supercritical fluid technology is in the sample preparation and separation of drugs of abuse particularly opiates, cannabinoids, cocaine and sedatives. Supercritical fluid technology can be used for both time-of-death-related drug analysis and for obtaining information relating to long term drug abuse. We also give a review of the use of supercritical fluids in two other major forensic areas, fingerprinting and the extraction and separation of explosives from both bombing events and gunshot residues. Overall we show that supercritical fluid technology is fast becoming a major part of forensic investigations and that it is an invaluable analysis technique.

Assessment of Solubility of Ketoprofen and Vanillic Acid in Supercritical CO2 under Dynamic Conditions

The use of supercritical fluids, and in particular supercritical carbon dioxide (SC-CO2), can be foreseen in a wide range of techniques and processes within pharmaceutical sciences. When dealing with both drugs and formulation adjuvants, the determination of the relevant solubilities in SC-CO2 represents a mandatory prerequisite, underlying the development of industrial scale operations. The aim of this work concerned the experimental determination of the solubility in SC-CO2 of vanillic acid and ketoprofen by means of an easy-to-use plant designed and assembled to operate in dynamic conditions. Its reliability was preliminarily checked by comparing solubility data obtained for salicylic acid and naphthalene with literature ones. Solubility measurements for ketoprofen and vanillic acid were carried out at 313 and 328 K in the 9−25 MPa pressure range. Crossover pressures of 16 MPa and 15 MPa were found for ketoprofen and vanillic acid, respectively. The solubility data were worked out according to a thermodynamic approach, which relies on the Peng−Robinson equation of state.

Supercritical Fluids; Opportunities in Heterogeneous Catalysis

The use of supercritical fluids (SCFs) in technology and research has been triggered by several unique features of these media. SCFs allow improvement of technical processes such as extraction, separation, particle formation and chemical reactions. However, it has been just in the last decades that SCFs have gained their importance in science and industrial applications, due to the relatively high pressures usually required when working with these media and the rigorous demands on the equipment used. Opportunities provided by the use of supercritical media in chemical reaction design have been the focus of several reviews(1-17). Here, we concentrate on a discussion of opportunities that SCFs provide in heterogeneous catalysis. First, we will consider the intrinsic properties of SCFs, then discuss the effect of these properties on chemical reactions, especially focusing on heterogeneously catalyzed reactions. Finally, we illustrate some of the opportunities of SCF applications in heterogeneously catalyzed reactions, using pertinent case studies.

Use of supercritical fluids for different processes including new developments—a review

Supercritical fluids have a great potential for wide fields of processes. Extraction processes with supercritical fluids are established even in industrial scale and become again more interesting for industry. Beside this, developments like fractionation of products, dyeing of fibres, treatment of contaminated soils, production of powders in micron and submicron range and reactions in or with supercritical fluids are only a rough extract of possible investigations which will be covered in this paper.

Powders elaboration in supercritical media: comparison with conventional routes

The use of supercritical fluids as media for the formation of powdered materials is a recent development. After a brief presentation of supercritical fluid properties and fundamentals of crystallization, this paper describes two routes to particle formation: the rapid expansion of supercritical solutions and the supercritical antisolvent. Advantages that fluids may offer are discussed through comparison with equivalent conventional processes.

Chemiluminescence detection systems in supercritical fluid methods

This review covers chemiluminescence detection systems in techniques making use of supercritical fluids (supercritical fluid chromatography and supercritical fluid extraction), focussing mainly on the last ten years. The article is divided into two main sections, the applications of chemiluminescence detection systems for nitrogen and sulfur. Practical considerations are discussed, and the possibilities and limitations are evaluated.