Supercritical Extraction Process Research Articles

96/04933 A new two-stage process for supercritical fluid extraction of coal with tetralin pretreatment

96/04933 A new two-stage process for supercritical fluid extraction of coal with tetralin pretreatment

PARTIAL OIL EXTRACTION EXTENDS THE SHELF LIFE OF PECAN HALVES

Pecans, because of their high oil and polyunsaturated fatty acid content, have a relatively short shelf life due to oxidation of the oil. Using a nondestructive supercritical CO2 extraction process, we evaluated oil reduction as a means for pecan shelf life extension. Pecan halves were extracted under sufficient conditions for 22% and 28% oil reduction, and then stored in modified-atmosphere packages with 21% O2 at 22C for up to 37 weeks. Kernel hexanal content and sensory rancid flavor were monitored at various times throughout the study. The resistance of oils to oxidation, indicated by the onset of sustained hexanal production, was increased from 6 weeks for full-oil halves, to 18 weeks for 22% reduced-oil halves, to 22 weeks for 28% reduced-oil halves. Objectionable rancid flavor was detected by the 22nd week of storage for full-oil pecans. Reduced-oil pecans never developed objectionable rancid flavor. Supported by USDA grant 93-341508409, OCAST grant AR4-044, and the Oklahoma Agricultural Experiment Station.

A new two-stage process for supercritical fluid extraction of coal with tetralin pretreatment

A new two-stage process for supercritical toluene extraction of coal is proposed that achieves conversion of 60 wt% and a liquid yield of 45 wt%. The first stage consists of pretreatment of the coal with tetralin liquid and vapour with a prescribed temperature-pressure-solvent programme (TPSP). In this stage, coal is pretreated with liquid tetralin up to 460 K and tetralin vapour from 460 to 653 K. In the second stage, the coal is extracted with supercritical toluene at 653 K and 20 MPa. Extractions were compared with other TPSPs including toluene-tetralin (70 : 30 w/w) mixtures and it was found that the new process could achieve similar conversions and liquid yield but with much less tetralin. The pretreatment TPSP is explained in terms of coal swelling during liquid tetralin pretreatment and inhibition of radical recombination in the pyrolysis during tetralin vapour pretreatment.

Molecular simulation of the desorption process on solid surfaces under vacuum and supercritical conditions

The applicability of molecular dynamics (MD) and computer graphics (CG) methods to investigating the dynamics of isolated adsorbed species on a MgO(001) surface under vacuum and supercritical conditions was demonstrated. The migration process of the adsorbed species was greatly affected by the morphology of the MgO(001) surface, and the desorption process of the adsorbed species was influenced by the thermal vibration of atoms of the MgO(001) surface under the vacuum condition. The supercritical extraction process from the MgO(001) surface could be reproduced by the MD simulation. In the co-existence of supercritical fluids, the desorption of adsorbed species occurred at lower temperatures compared to the situation under the vacuum condition. Furthermore, we clarified that the collision of the supercritical fluid with the adsorbed species has a significant role on the mechanism of the supercritical extraction process.

A Rapid Supercritical Extraction Process for the Production of Silica Aerogels

AbstractSilica aerogels are a special class of porous materials in which both the pore size and interconnected particle size have nanometer dimensions. This structure imparts unique optical, thermal, acoustic, and electrical properties to these materials. Transmission electron microscopy and small angle x-ray scattering show that this nanostructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Recently, Lawrence Livermore National Laboratory (LLNL) has demonstrated that a Rapid Supercritical Extraction (RSCE) process can be used to prepare near-net shape silica aerogels in hours rather than days. Preliminary data from RSCE silica aerogels show that they have improved mechanical properties and slightly lower surface areas than their conventionally dried counterparts, while not compromising their optical and thermal performance.

Comparison of Models for Supercritical Fluid Extraction of Seed and Essential Oils in Relation to the Mass-Transfer Rate

A general dimensionless model was developed for a sensitivity analysis of the supercritical extraction process of vegetable oils and essential oils. Two dimensionless parameters, Γ, a dimensionless partition coefficient, and ϑ, a dimensionless characteristic time, appeared as the most important parameters to monitor the evolution of the extraction process. Some limiting values of these two parameters within the general model yielded simpler models which are often used in the literature. The numerical solutions of both the complete model and the simpler cases were compared to assess the range of relevance of the simpler models in terms of Γ and ϑ values. These results were compared with the experimental data found in the literature to assess the correctness of the assumption used to model supercritical fluid extraction in single cases. The implications of this analysis on the development of scale-up procedures were also discussed.

Determination of partial molar volumes at critical end points

There has been considerable interest in the volumetric behavior of supercritical binary (and higher) fluid mixtures near the solvent critical point. It is in the vicinity of this critical point that supercritical extraction processes are generally considered to be most effective. In the case of a solvent + solute system that exhibits liquid-liquid-vapor (llg) partial miscibility, properties of the dense gas phase near an ll = g upper critical end point are most interesting. The partial molar volumes of the solvent and solute at these conditions are difficult to measure directly. In this note, we show that the solvent and solute partial molar volumes of the critical phase of a binary critical end point are readily determined from the associated three-phase liquid-liquid-vapor (llg) volume-composition data.

Canola paste extrusion for feeding supercritical extractors

A custom-built, single-screw extruder (barrelf 0.44 m long, 36.75 mm ID; screw flight angles: 5.98°, 7.97°; or 9.94°; average screw flight: 4.9 mm high, 3 mm wide; flight-top to barrel clearance: 0.0254 mm) was developed for continuously feeding precrushed Canola seed pastes into supercritical fluid extractors. The screw was driven by two variable-speed hydraulic motors and rotated typically at 66.5, 88.5, or 100.5 rpm. The pressures and temperatures along the extruder barrel were measured with six iron–Constantan thermocouples and four pressure transducers, respectively. The discharge rate of the paste was determined gravimetrically and was found to vary from approximately 1.7 to 9.5 kg h−1 for average discharge pressures ranging from 30 to 10 MPa. The average pressure along the barrel was found to increase almost linearly. A three-component velocity model was developed to simulate the extruder performance and verified by comparison with experimental data obtained by using a Newtonian fluid having a viscosity of 130 Pa s. The model over predicted the discharge rates of Canola pastes unless allowance is made for slip. The practical implications for supercritical extraction processes are discussed.

Caracterización del aceite de semilla de uva extraído con dióxido de carbono supercrítico

The present work is based on a comparative study of the borage seed's oil obtained with supercritical carbon dioxide by means of the conventional extraction using hexane as a solvent. In the optimal working conditions, the results obtained in the extraction with carbon dioxide are comparable to those obtained in the extraction with hexane, although the oil's quality is higher. Therefore, the process of supercritical extraction with carbon dioxide could be more effective than conventional extraction because the solvent removal is not necessary and several steps of the oil refining process can be reduced notably.

Multiphase equilibrium behavior of the mixture carbon dioxide + ethane + methanol

There is considerable interest in the use of methanol, ethanol, and other polar molecules as cosolvents in super-critical extraction processes, wherein the cosolvent methanol would enhance the ability of a solvent gas, carbon dioxide, e.g., to solubilize a liquid- or solid-phase species. The three-phase liquid-liquid-vapor (11g) phase equilibrium behavior of the mixture carbon dioxide + ethane + methanol was experimentally studied. The boundaries of the three-phase 11g region in pressure-temperature space are delineated. Compositions and molar volumes of the two liquid phases and the vapor phase along the 288.15 and 298.15 K isotherms are reported.

Production of calorie-reduced almonds by supercritical extraction

Diced and flaked almonds were extracted by a supercritical-extraction process. The oil content of diced almonds was reduced by 48% on a weight basis (56% on the volume basis) during 12 h of extraction with supercritical C02 flowing through the extraction vessel at an average rate of about 3.3 kg h-1 at 7000 psi and 50 °C. In case of flaked almonds an oil reduction of 87% by weight and 89% on a volume basis was achieved under similar conditions. Screen analysis of extracted almonds confirmed that the process did not cause breakage of almond particles during extraction. Being considerably enriched in protein (the diced by 35% and flaked by 82%, respectively, on a weight basis), minerals (by 33 and 89%), and carbohydrates including dietary fiber (by 48 and 100%), the extracted almonds are nutritionally more balanced due to fewer calories coming from fat. The derived products also have considerably lower bulk densities. Since the bulk volume is considerably more important than the weight of almonds used in many food applications, this greater relative bulk volume of extracted almonds could translate into significant benefits for both the consumers and processors.

CHARACTERIZATION OF DESULFURESATION EXTRACTS FROM MIDWESTERN U.S. COALS

ABSTRACT Coals from Midwestern States were extracted using two different processes, viz., a supercritical extraction process and a perchloroethylene coal refining process. The objectives of these processes are the selective removal of sulfur and nitrogen compounds from high-sulfur coals. The solvent extracts were analyzed using gas chromatography/mass spectrometry as well as wet chemical analysis. The extracted organosulfur compounds varied, depending upon the extraction process, extraction conditions, type of solvent, type of coal, and degree of weathering. The experimental results are compared among the types of coal as well as among the different processes, from viewpoints of chemical and molecular interaction.

Effect of retrograde solubility on the design optimization of supercritical extraction processes

Application d'une strategie generale de conception des procedes d'extraction supercritique a un procede de deshydratation de l'acetone par du dioxyde de carbone supercritique. Simulation, dans le schema de fabrication, de l'extracteur, de la colonne de distillation, des echangeurs de chaleur et des compresseurs et utilisation d'un programme non lineaire de determination de la conception optimale

Distribution of cholesterol in milk fat fractions.

Milk fat was fractionated into liquid (m.p. congruent to 12 degrees C), intermediate (m.p. congruent to 21 degrees C) and solid (m.p. congruent to 39 degrees C) fractions by three different processes--melt crystallization, short-path distillation and supercritical CO2 extraction--and the cholesterol content of these fractions determined. Cholesterol was enriched in the liquid fractions from all three processes, in particular about 80% of the cholesterol being found in the liquid fraction obtained by short-path distillation. The basis of migration of cholesterol into various milk fat fractions was explained by its affinity to various triglycerides (melt crystallization) and by vapour pressure and molecular weight (short-path distillation). It was more complex in the supercritical CO2 extraction process; the interplay of cholesterol affinity toward CO2 and its molar volume, and its vapour pressure enhancement under applied pressure play a role.

Evaluation of separation and purification processes in the antibiotic industry. Scientific note.

Antibiotic production is a complex capital intensive process, which divides naturally into two segments, fermentation and separation/purification. The separation and purification section is very large as a result of the number of processing steps required (up to 60) and the need to purify and recycle large quantities of organic solvents. Separation and purification is not generic within the antibiotic industry. Not only does each individual antibiotic require a different separation process, but also there are many different separation schemes in use for the same antibiotic. Much research is currently in progress on three relatively new separation techniques on a commercial level, which may lead to substantial reductions in the complexity of the process; chromatography (both conventional preparative HPLC and annular chromatography), supercritical extraction, and various membrane processes.

Supercritical phase behavior: The entrainer effect

One of the keys to lowering the cost of supercritical extraction processes is to find appropriate cosolvents (entrainers) that maintain or improve selectivity while increasing the solubility. This solubility enhancement is of great commercial interest; however until recently there was no way to predict either for which systems or under what conditions it would occur. We show that the entrainer effect is caused by a chemical association between the cosolvent and the solute. Further, we present a model that explicitly accounts for these chemical associations. Finally, we show that data and analysis techniques already established for associations in liquid solvents (especially spectroscopic and solvatochromic techniques) can be used to make qualitative predictions of the entrainer effect in a supercritical fluid.

Process synthesis concepts for supercritical gas extraction in the crossover region

AbstractA procedure is presented for designing supercritical gas extraction processes using a pure solvent fluid to effect the separation. The necessary conditions for the procedure to be applicable are the existence of crossover behavior and separable crossover pressures in the fluid phase mixture. Data are presented to support the existence of such phenomena in ternary systems, and an actual separation process has been designed and operated based upon the data. For systems exhibiting this behavior, process synthesis principles are developed to illustrate the evolution of a process flowsheet for the separation of a mixture into its pure components.

CRITICAL POINT PREDICTION USING A MULTI-FLUID GENERALIZED CORRESPONDING STATES PRINCIPLE

Abstract The Generalized Corresponding States Principle (GCSP), based on the properties of two non-spherical reference fluids, offers flexibility and ease of computation for the prediction of thermodynamic and transport properties of pure fluids and fluid mixtures. In this work, the multi-fluid GCSP is used for the calculation of the critical properties of mixtures. Classes of mixtures studied include those containing: (1) simple spherical molecules; (2) large quasi-spherical molecules such as the cyclosiloxanes; (3) both spherical and large nonspherical molecules such as those important in supercritical extraction and hydrocarbon processing; and (4) molecules exhibiting strong dipole moments. The advantages of the GCSP method are outlined, particularly for fluids not usually amenable to conventional corresponding states treatments.

High pressure extraction of oil seed

AbstractFor calculation of phase equilibria of the system seed oil/CO2, an equation of state published in the literature has been fitted to experimental data of that system. The results thus obtained are of only limited use in designing a supercritical extraction process. The experimental investigation of the mass transfer kinetics is much more significant. Mechanical processing of the oil seed's cell wall structure has been shown to be of great importance. The best specific yields were achieved with material that had been mechanically pre‐deoiled and thereby broken open. Yields are increased considerably by use of the gas mixture CO2/propane or other special gas mixtures or by the addition of refrigerants. However, the extraction times achieved in batch operation, together with the mass product nature of oil seed, make a continuous supercritical extraction essential if operation is to become economic relative to the conventional hexane extraction. To this end, the energetics of the process have been calculated, and practical possibilities for continuous operation are discussed.

Supercritical Fluid Extraction Applied to Coal Liquefaction

In principle, supercritical fluid extraction should increase the solubility of high-molecular-weight components of coal. This article discusses experiments that explore effect of hydrogen donors, organic solvents, supercritical water, hydrogens, and carbon monoxide in coal conversion. A two-stage process for supercritical extraction of softening coal is presented. The use of supercritical water for coal conversion also is being explored by a number of coal scientists. (DP)