Pressure, temperature, and extraction

As a case-study, the decaffeination process for tea will be considered, where in every case the extraction parameters (pressure, temperature and extraction cycle) are maintained. In the... 

For preparative and industrial scale separations of enantiomers the supercritical fluid extraction (SFE) seems very promising. The process of SFE with carbon dioxide allows variations in extraction parameters (pressure, temperature and extraction time) to find an optimal range both for maximum quantity and maximum optical purity of the product[4]... 

PSE was applied to the rapid extraction of cocaine and benzoylecgonine from coca leaves [31]. Several parameters including the nature of the extracting solvent, the pressure, temperature, extraction, addition of alkaline substances, and sample granulometry were investigated. Critical parameters were pressure, temperature, and extraction time. They were optimized by means of a central composite design. It was demonstrated that an extraction time of 10 min was sufficient to extract cocaine quantitatively at 80 °C and 20 MPa. 

Numerous applications have been developed for a wide variety of compounds from different matrices, but surprisingly, only a few reviews dedicated to the extraction of medicinal plants have been pubhshed in the last few years [37-39]. ASE of cocaine and benzoylecgonine from coca leaves has been reported by Brachet et al. [40]. The influence of several extraction parameters such as the nature of the extracting solvent, the addition of alkaline substances, the pressure, the temperature, the extraction time, and the sample granulometry on cocaine recovery was systematically investigated. Methanol was fotmd to be the most suitable solvent. Critical parameters were found to be pressure, temperature, and extraction time. A central composite design has been used to optimize these 3 parameters and to assess the robustness of the extraction method. The optimal conditions for the quantitative extraction of cocaine from leaves were the following 20 MPa, 80 °C, 1 mL min , 10 min extraction time, with a particle size distribution between 90 and 150 pm. 

Benzoyl piperidine. In a 1-litre three-necked flask, equipped with a mechanical stirrer, separatory funnel and a thermometer, place 85 g. (99 ml.) of redistilled piperidine (b.p. 105-108°) and a solution of 53 g. of sodium hydroxide in 400 ml. of water. Stir the mixture and introduce during the course of 1 hour 140 g. (115-5 ml.) of redistilled benzoyl chloride maintain the temperature at 35-40°, Cool to room temperature and extract the benzoyl piperidine with ether. Wash the ethereal solution with a little water to remove any dissolved sodium hydroxide, and dry with anhydrous potassium carbonate. Remove the ether on a water bath and distil the residue under diminished pressure (Fig. II, 20, 1). Collect the benzoyl piperidine at 184—186°/15 mm. it is an almost colourless viscous liquid and crystallises on standing in colourless needles m.p. 46°. The yield is 170 g. 

B. 2,2-(Trimethylenedithio)cyclohexanone. A solution of 3.02 g. (0.02 mole) of freshly distilled 1-pyrrolidinocyclohexene, 8.32 g. (0.02 mole) of trimethylene dithiotosylate4 (Note 2), and 5 ml. of triethylamine (Note 3) in 40 ml. of anhydrous acetonitrile (Note 4), is refluxed for 12 hours in a 100-ml., round-bottom flask under a nitrogen atmosphere. The solvent is removed under reduced pressure on a rotary evaporator, and the residue is treated with 100 ml. of aqueous 0.1 N hydrochloric acid for 30 minutes at 50° (Note 5). The mixture is cooled to ambient temperature and extracted with three 50-ml. portions of ether. The combined ether extracts are washed with aqueous 10% potassium bicarbonate solution (Note 6) until the aqueous layer remains basic to litmus, and then with saturated sodium chloride solution. The ethereal solution is dried over anhydrous sodium sulfate, filtered, and concentrated on a rotary evaporator. The resulting oily residue is diluted with 1 ml. of benzene and then with 3 ml. of cyclohexane. The solution is poured into a chromatographic column (13 x 2.5 cm.), prepared with 50 g. of alumina (Note 7) and a 3 1 mixture of cyclohexane and benzene. With this solvent system, the desired product moves with the solvent front, and the first 250 ml. of eluent contains 95% of the total product. Elution with a further 175 ml. of solvent removes the remainder. The combined fractions are evaporated, and the pale yellow, oily residue crystallizes readily on standing. Recrystallization of this material from pentane gives 1.82 g. of white crystalline 2,2-(trimethylenedithio)cyclo-hexanone, m.p. 52-55° (45% yield) (Note 8). 

Extraction of 25 different binary mixtures of racemic acids (2-(4-isobutylphenyl)-propionic acid (1), and cis- and trans-chrysanthemic (2)), and various chiral bases with supercritical carbon dioxide permitted the conclusion that molecular chiral differentiation in a supercritical fluid is more efficient than in conventional solvents. In the majority of cases, however, complete separation could not be achieved. In five cases, remarkable partial resolutions were realized (30-75% ee) and resolution was possible on a preparative scale. The pair ds-chrysanthemic acid and (S)-(-i-)-2-(benzylamino)-1-butanol (3) was studied in detail. Pressure, temperature, and time, as well as the molar ratio of base and acid, had a marked influence on the quantity and quality of the products. Increasing pressure or decreasing temperature resulted in higher ee values. (-)-cw-Chrysanthemic acid in 99% ee was obtained from the raffinate in a single extraction step. Multiple extractions produced the (-i-)-cA-acid in 90% ee (see fig. 6.3) (Simandi et al., 1997). 

The advantage of this extraction method is that the parameters pressure, temperature and solvent to feed ratio can be varied in each extraction step. By this way a very accurate fractionation of the different compounds included in the feed can be achieved. The solubility of the compounds in the supercritical fluid, depending on pressure and temperature, can be changed in each extraction step. The highly soluble substances are extracted in the first step at low fluid density. Increasing the density in the following extraction steps leads to the removal of the less soluble substances. Further, the flow rate of the supercritical fluid can be adjusted in each extraction step, either constant flow for each step or different flow rates, depending on the separation to be achieved. 

S Lacorte, C Molina, D Barcelo. Temperature and extraction voltage effect on fragmentation of organophosphorus pesticides in liquid chromatography atmospheric pressure chemical ionization mass spectrometry. J Chromatogr A 795 13-26, 1998. 

Supercritical fluid extraction conditions were investigated in terms of mobile phase modifier, pressure, temperature and flow rate to improve extraction efficiency (104). High extraction efficiencies, up to 100%, in short times were reported. Relationships between extraction efficiency in supercritical fluid extraction and chromatographic retention in SFC were proposed. The effects of pressure and temperature as well as the advantages of static versus dynamic extraction were explored for PCB extraction in environmental analysis (105). High resolution GC was coupled with SFE in these experiments. 

When the experiments were performed at the same pressure, temperature, and moisture content but with toluene as modifier and with a static extraction time of 15 or 30 min prior to the dynamic extraction step, then recovery was most affected by moisture content (sum of ranks 88) followed by pressure (sum of ranks 70) and the toluene volume (sum of ranks 68). The fourth variable to influence was the static extraction time (sum of ranks 57). Temperature, volume of collection solvent, and the presence/absence of glass beads were the least important. Figure 6 shows the relative changes in recovery for each compound and for each of the seven variables investigated in Test 2. 

Undecanedione (92.1 g, 0.5 mol) is added to a solution of 16.0 g (0.4 mol) of sodium hydroxide in 800 mL of water and 200 mL of ethanol in a 2000-mL round-bottomed flask. The mixture is refluxed for 6 hr, cooled to room temperature, and extracted with ether. The combined ether phases are dried with magnesium sulfate, and the solution is separated from the drying agent and concentrated at room temperature under reduced pressure. The residual oil is distilled through a 30-cm Vigreux column. The pure compound boils at 65-67°C/0.5 mm and weighs 70-73 g (84-88% based on the diketone) (Note 8). 

A solution of 2-(4,4-dimethyl-2-oxazolin-2-yl)-4 -trifluoromethylbiphenyl (3.5 g, 0.011 mole) in 60 mL 6 N hydrochloric acid was stirred at vigorous reflux for 2 hr. The reaction mixture was then cooled to room temperature and extracted with methylene chloride. The organic extracts were dried and concentrated under reduced pressure to yield a solid. Recrystallisation from ethyl ether/pentane afforded 4 -(trifluoromethyl)-2-biphenyl carboxylic acid, yield 86% (melting point 167-169°C). 

A separation process is sought that can satisfy both our present economic and enviromental constraints. It would also provide an alternative to present practice that relies on expensive azeotropic or extractive distillation processes used in the recovery of products from low relative volatility streams. As an example, virtually all industrial butadiene recovery processes now rely on extractive distillation using acetonitrile or other equivalent agent to enhance the relative volatility of the C4 components. The use of supercritical or near critical separation of these streams may satisfy these requirements provided certain pressure, temperature and recompression criteria can be met. Such a process would also reduce the need for a complex train of distillation towers. 

The experimental design was made with three independent variables [17]. Thus the total number of experiments is 8. These independent variables are extraction temperature (Uj), extraction pressure (U2) and extraction time (U3) the dependent variable (Ye) is extraction yield (g/1). Maximum and minimum values for the temperature, pressure and time were selected as 333 and 313 K, 160 and 80 atmospheres, 90 and 30 minutes, respectively. 

The experimental phase equilibria and mass transfer data were then used to solve the mass balances over the whole unit. The mass flows, pressures, temperatures and compositions of each stream are listed in Table 1. We can see that there is a relatively large amount of carbon dioxide flowing through the extraction column. This is due to the high solvent to feed flow ratio (Ssolvent loading on free fatty acids. 

One promising way to seperate halogenated flame retardents out of polymer composites seems to be the extraction by supercritical fluids like C02.. Main objective of this paper is to find the suitable conditions for high extraction efficiencies. For model mixtures involving the flame retardents TBBA, TBPA and HBCD the extraction efficiency from the inert matrix MgS04 was examined in relation to extraction pressure, temperature and time. The data form the basis for realistic tests on ABS composites with different flame retardents. 

An automated SFE option has been utilized by Montanari et al. (47) and Taylor et al. (37,48) to develop the conditions most amenable to isolating PPL concentrates from deoiled soy meal. In the former case, a set of conditions was tested by programming the microprocessor controller of the automated SFE to run a large number of extractions on common samples at various pressures, temperatures, and cosolvent (ethanol) levels. The results showed that at 70°C and 40.7 MPa with 10 mol% ethanol, phosphatidylcholine could be extracted preferentially relative to the other phospholipids in the soya meal. By utilizing higher pressures, it was found that the total amount of phospholipids extracted could be substantially increased at the slight reduction of the phosphatidylcholine content in the final extract. 

SFE parameters such as CO2 pressure, flow rate, extraction temperature, and extraction time were varied in order to estimate the best extraction conditions. Figure 1 shows the relationship between CO2 pressure and percent recovery. At a constant temperature (45°C), as the density increased from 0.87 g/mL (250 atm) to 0.97 g/mL (450 atm), the percent recovery increased dramatically from 11.5% to 87.2%. Since the density of CO2 at 450 atm is greater than the density of CO2... 

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