Extraction vessels

Supercritical CO2 is used to extract fat from candy bars. Samples are placed in an extraction vessel and its weight determined before and after extraction. The %w/w fat content is determined by difference. The volume of CO2 needed to effect a complete extraction is determined experimentally. Variations in results for different samples illustrate the importance of sampling. 

Immersion-type extractors have been made continuous through the inclusion of screw conveyors to transport the soHds. The Hildebrandt immersion extractor (18) employs a sequence of separate screw conveyors to move soHds through three parts of a U-shaped extraction vessel. The helix surface is perforated so that solvent can pass through the unit in the direction countercurrent to the flow of soHds. The screw conveyors rotate at different speeds so that the soHds are compacted as they travel toward the discharge end of the unit. Alternative designs using fewer screws are also available. 

The coupling of supercritical fluid extraction (SEE) with gas chromatography (SEE-GC) provides an excellent example of the application of multidimensional chromatography principles to a sample preparation method. In SEE, the analytical matrix is packed into an extraction vessel and a supercritical fluid, usually carbon dioxide, is passed through it. The analyte matrix may be viewed as the stationary phase, while the supercritical fluid can be viewed as the mobile phase. In order to obtain an effective extraction, the solubility of the analyte in the supercritical fluid mobile phase must be considered, along with its affinity to the matrix stationary phase. The effluent from the extraction is then collected and transferred to a gas chromatograph. In his comprehensive text, Taylor provides an excellent description of the principles and applications of SEE (44), while Pawliszyn presents a description of the supercritical fluid as the mobile phase in his development of a kinetic model for the extraction process (45). 

Extraktions-anlage, /. extraction plant, -ap-parat, m. extraction apparatus, -dauer, /. time of extraction. -flUssigkeit, /. extraction liquid, liquid extract. -gef ss, n. extraction vessel, -hiilse, /. extraction shell or thimble. -kolben, m. extraction flask, -mittel, n. extracting agent, extraction solvent. -miihle,/. extraction mill, -rtickstand, m. extraction residue. 

SEE extraction pressures of 500 bar at 80 to lOO C combined with countercurrent cascading mode of extraction using four extraction vessels, the rate of oleoresin extraction doubles again rate of oleoresin extraction under these conditions is four times that of traditional batch extraction at 300 bar and 60°C... 

Plant material is macerated using two volumes of 2-propanol as the extraetion solvent. The 2-propanol solvent is then deeanted and filtered. Any solid material in the filter is returned to the extraction vessel, and the entire proeedure is reiterated until the extract produced is colorless. A small volume of dioxane, 15% of the total extraeted volume, is added to the combined extracts. The chlorophyll-containing solution is then triturated with water until it is turbid, and then it is placed in a refrigerator for 2 to 3 h. 

Volumes Vl and Vq of the two immiscible liquid phases, are added to the extraction vessel and a single solute distributes itself between the phases as concentrations X and Y, respectively, at a rate, Q, as shown in Fig. 3.30. 

Accelerated solvent extraction (ASE) is a technique which attempts to merge the beneficial solvation properties of SFE with traditional organic solvents. Specifically, the sample is placed in an extraction vessel which can withstand high pressures while being maintained at a constant temperature. Extraction is carried out by pumping the extraction solvent through the samples for a limited time. As an example of the use of ASE, Richter and Covino extracted PCBs from a 10-g fish tissue sample with hexane... 

The solvent, microwave energy applied, and extraction time selected are the main parameters controlled in MAE. The user should use proper extraction vessels and equipment in MAE because very high pressures can be achieved and explosions may result if appropriate precautions are not taken. 

SEE is an instrumental approach not unlike PLE except that a supercritical fluid rather than a liquid is used as the extraction solvent. SFE and PLE employ the same procedures for preparing samples and loading extraction vessels, and the same concepts of static and dynamic extractions are also pertinent. SFE typically requires higher pressure than PLE to maintain supercritical conditions and, for this reason, SFE usually requires a restrictor to control better the flow and pressure of the extraction fluid. CO2 is by far the most common solvent used in SFE owing to its relatively low critical point (78 atm and 31 °C), extraction properties, availability, gaseous natural state, and safety. 

Cucumbers and potato tubers are washed, then cut into portions (5-cm pieces and quarters, respectively), and frozen. Grapes are washed, stemmed, and frozen. Frozen pieces were homogenized using a cutter portions (100-g for cucumbers and grapes, 50-g for potatoes) are weighed into the extraction vessels (screw-top jars) and stored at less than -18 °C until sample fortification and extraction. 

For wine, 50-g portions are weighed into the extraction vessels just prior to fortification and extraction. 

A significant advance was made in this field by Watarai and Freiser [58], who developed a high-speed automatic system for solvent extraction kinetic studies. The extraction vessel was a 200 mL Morton flask fitted with a high speed stirrer (0-20,000 rpm) and a teflon phase separator. The mass transport rates generated with this approach were considered to be sufficiently high to effectively outrun the kinetics of the chemical processes of interest. With the aid of the separator, the bulk organic phase was cleanly separated from a fine dispersion of the two phases in the flask, circulated through a spectrophotometric flow cell, and returned to the reaction vessel. 

The instrumental requirements for supercritical fluid extraction are quite simple. A pump is essential to generate the extraction pressure in a themostated extraction vessel. The soluble sample components are then swept from the vessel through a flow restrictor into a collection device that is normally at ambient pressure. The fluid used for supercritical fluid... 

Figure 3.3 Apparatus for intermittent extraction of solids 1, boiler vessel 2, extraction vessel 3, cooler 4, heating coil 5, transformer 6, contact-block 7, timer. Reproduced by permission of DSM Research, Geleen...

SFE can be carried out in three different ways. In a static extraction (no flow-rate), the extraction vessel is pressurised to the desired pressure with the extracting fluid and then simply left for a certain length of time. The main benefit of this method is that the fluid has time to penetrate the matrix. It is most applicable when the analyte has a high affinity for the solvent and a low affinity for the matrix and also when the solubility limit of the analyte in the fluid is much higher than the actual level reached during the extraction [89]. This method was popular in early SFE experiments but has declined in favour of dynamic SFE. Here, fresh SCF is continuously passed over the sample, extracting soluble compounds and depositing them in a suitable solvent or on a solid trap. The dynamic mode is particularly useful when the concentration of the solute... 

Special nonmicrowave absorbing extraction vessels required... 

Extraction oven Extraction vessel Flow restricter... 

A 1-g sieved, air-dry soil sample is placed in a polytetrafluoroethylene (PTFE)-lined extraction vessel, with a mixture of hexane and acetone, and microwaved at full power for 10 minutes (adapted and condensed from Reference 14). 

In Procedure 12.4, sample and solvent are added to the extraction vessel at room temperature and are heated to 130°C during the extraction process [9], The extraction time is short when compared to other extractions procedures, being only 10 minutes. Microwave extraction is used when a rapid analysis is desired and the analyte of interest is not affected by high temperature and pressure. 

The prepared mixtures were placed in the extraction vessel, and stirred for 2 h and then left to settle for 4 h. Samples were taken by a syringe (Gaschromatographic s Hamilton 0.4 p,L) from both the upper (methylcyclohexane) phase and lower layers (aromatic phase). Both phases were analyzed using Konik gas chromatography (GC) equipped with a thermal conductivity detector (TCD) and Shimadzu C-R2AX integrator. A 2 m x 2 mm column was used to separate the components... 

The apparatus is shown in Fig. 4.1. The body of the extraction vessel is made from Pyrex. Separation is effected by absorption of a batch containing both phases into a porous 2 cm diameter nickel-chrome alloy disc (A), the upper surface of which is domed. The disc is mounted on the end of a stainless-steel shaft (B) turned by a geared high-torque electric motor. The disc-shaft-motor assembly can he transported along its axis of rotation to any of three stations. The assembly is shown at its bottom station, with the porous disc within the inner vessel (C), around which is a collar (D) forming the first annular pocket (E). The collar itself forms the inner wall of the second annular pocket (F), the outer wall of which extends upwards to support a Perspex Hd (G) on which the rotor (H) is situated. The inner vessel and both annular pockets are fitted with drain valves. A stiff piece of platinum wire is passed through the Hd into the glassware as far as the level of the first annular pocket. 

A schematic diagram of the automatic system is shown in Fig. 4.12. It consists of five component modules a sample introduction unit, a digestion unit, a neutrafization vessel, a chelation and extraction vessel and an extract collection unit. The sy stem is controlled by a series of interacting cam and electronic process timers. 

The extraction vessel outlet valve can be controlled either manually from the control unit or automatically by the phase boundary detector unit. The operation of this detector is based on the difference in refractive index between the organic and aqueous phases, and has been described elsewhere [34]. 

The organic phase is removed by applying a positive air pressure to the extraction vessel, thus forcing the extract up a PTFE tube and through a probe into a glass, or polypropylene, extract collection vessel situated in the extract collection module. During the washing cycle, the tube and probe are washed out with ethanol—water and then blown dry with air. 

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