Extraction conditions supercritical carbon dioxide

In some cases, components extracted with supercritical carbon dioxide are immediately dissolved in a solvent after extraction. Under what conditions might this be advisable ... 

As seen in Table 2 the PET-oligomers - mainly cyclic trimers - are not extracted by supercritical carbon dioxide at dyeing conditions. This was also confirmed by other authors [9], The surface content of oligomers depends on the dyeing temperature whereas the total amount of cyclic trimers does not change. 

Topal, U. et al.. Extraction of lycopene from tomato skin with supercritical carbon dioxide effect of operating conditions and solubility analysis, J. Agric. Food Chem., 54, 5604, 2006. 

Supercritical fluids (e.g. supercritical carbon dioxide, scCCb) are regarded as benign alternatives to organic solvents and there are many examples of their use in chemical synthesis, but usually under homogeneous conditions without the need for other solvents. However, SCCO2 has been combined with ionic liquids for the hydroformylation of 1-octene [16]. Since ionic liquids have no vapour pressure and are essentially insoluble in SCCO2, the product can be extracted from the reaction using CO2 virtually uncontaminated by the rhodium catalyst. This process is not a true biphasic process, as the reaction is carried out in the ionic liquid and the supercritical phase is only added once reaction is complete. 

Supercritical carbon dioxide modified with 10 vol% methanol has been employed for the removal of the amine surfactant in hexagonal mesoporous silica (HMS). The effects of temperature and pressure on the extraction efficiency have been extensively studied. It has been found that within an hour, as high as 96% of the amine surfactant can be extracted at a relatively mild condition of 85°C and 100 bar. At constant pressure, high extraction efficiencies are obtained at 50 and 85°C while at constant temperature, high efficiencies occur at 100 bar and 250 bar. This work establishes the feasibility of using supercritical fluid extraction (SFE) for the removal of the amine surfactant. In fact, it has been discovered that SFE produces EIMS of more enhanced mesoporosity as compared to that of calcination. 

We have demonstrated in this paper that two and four samples can be extracted in parallel with supercritical carbon dioxide without significant impact on data quality. Modifications made to an off-line extractor involved addition of a multiport manifold for the distribution of supercritical fluid to four extraction vessels and of a 12-port, two-way switching valve that allowed collection of two fractions per sample in unattended operation. The only limitation that we have experienced with the four-vessel extraction system was in the duration of the extraction. When working with 2-mL extraction vessels and 50-/zm restrictors, and using the pressure/temperature conditions mentioned above, the 250-mL syringe pump allows us a maximum extraction time of 60 min. During this time, two 30-min fractions can be collected with the present arrangement. 

In contrast to alkamides, alternative extraction solvents such as SF carbon dioxide appear to be ineffective as an extraction solvent for CAP removal (Catchpole et al., 2002 Sun et al., 2002). Conditions evaluated by these researchers include pressures of 31 - 55 MPa and temperatures between 41 and 60°C. In both studies, ethanol was used as a solvent modifier, but the supercritical carbon dioxide was not modified sufficiently to promote the extraction of CAP. The addition of 10% methanol to the supercritical carbon dioxide at 25 MPa and 60°C was sufficient to promote the extraction of rosmarinic acid, a compound with similar structure features as cichoric acid (Bicchi et al., 2000). Thus, additional work is needed to determine if SFE can be used as a method to remove CAP. 

Caredda et al. (2002) described the extraction conditions for leaf oil by supercritical carbon dioxide extraction as follows pressure, 90 bar temperature, 50°C and carbon dioxide flow, Phi = l.Okg/h. Waxes were entrapped in the first separator... 

Supercritical fluid extraction (SFE) is a suitable process for many separation problems. The regeneration of the supercritical fluid is as important as the extraction step itself Therefore this paper presents a method to do this in a more isobaric way than the customary pressure reduction regeneration. For the example of soil remediation we have investigated the activated carbon regeneration of supercritical carbon dioxide loaded with the low-volatile polycyclic aromatic hydrocarbon (PAH) pyrene. Characteristics of supercritical fluid extraction for soil remediation are elevated temperatures and pressures up to 370 K and 300 bar. For this reason adsorption isotherms of pyrene on activated carbon up to these conditions are measured first. Subsequently this method is used to regenerate carbon dioxide in a closed solvent cycle plant with a 4 1 extractor. An economic analysis using these results indicate that the soil remediation costs will decrease for about 20 - 30 % by means of an activated carbon adsorber. 

Supercritical carbon dioxide is a good solvent for a variety of substances. Due to low temperatures and pressures being necessary to achieve supercritical conditions, production techniques work under relatively mild conditions III. Another important feature of supercritical carbon dioxide is the gaslike viscosity causing favourable transport porperties, so that for example supercitical fluid extractions (SFE) are achieved faster than with traditional methods. Carbon dioxide is intoxic and so incurs less costs for disposal than conventional organic solvents 111. 

Picture 1 shows the device for extracting samples using supercritical carbon dioxide/modifier mixtures. Extractions were made at 300 bar, 50 °C in 30 minutes and with modifier concentrations not exceeding 4 mol%, thus ensuring supercritical conditions (tab. 1). 

An industrially spent hydrotreating catalyst from naphtha service was extracted with tetrahydrofuran, carbon dioxide, pyridine and sulfur dioxide under subcritical and supercritical conditions. After extraction, the catalyst activity, coke content, and pore characteristics were measured. Tetrahydrofuran was not effective in the removal of coke from catalyst, but the other three solvents could remove from 18% to 54% of the coke from catalyst. 

Supercritical fluid extraction can be used to remove carbonaceous material from spent catalysts. De Filippi and Robey (2) used supercritical carbon dioxide extraction to regenerate adsorbents. Abel (3) tried supercritical carbon dioxide extraction to regenerate a certain catalyst. Tiltscher et al. (4,5) studied the isomerization of 1-hexene on an alumina catalyst and showed that under supercritical conditions, 1-hexene was able to remove the oligomeric compounds (C -C q) from t ie catalyst surface and prevent coking. 

In closing, this paper was not intended to represent an exhaustive process development effort in flavors extraction from natural materials nor a development of the quantitative analytical capabilities of supercritical carbon dioxide. However, even though the examples and the conditions of extraction were somewhat arbitrary, they point out some of the interesting features of the pressure dependent dissolving power properties of supercritical fluids. They can be further refined by virtue of more narrow ranges and ratios of pressure and temperature to accomplish still more narrow separations. 

In addition to fluorous solvents and ionie liquids, supercritical fluids sc-fluids, scf s), sueh as supercritical carbon dioxide (se-C02), constitute a third class of neoteric solvents that can be used as reaction media. Although sc-fluids have been known for a long time and have been advantageously used as eluants in extraction and chromatography processes (see Sections A.6 and A.7 in the Appendix), their application as reaction media for chemical processes has become more popular only during the last decade. Some of their physical properties and the supercritical conditions necessary for their existence have already been described in Section 3.2 (see Figure 3-2 and Table 3-4) see also references [209, 211-220, 224-230] to Chapter 3 for reviews on sc-fluids and their applications (particularly for SC-CO2 and SC-H2O). 

Although several studies have been made on the extraction of oil from seed by supercritical fluids, few are about sunflower oil (91). Reports on supercritical carbon dioxide (SC-CO2) over a wide range of pressure (20-70 Mpa) and temperature (40-80°C) show a maximum solubility of sunflower oil in supercritical CO2 at 80°C and 70 Mpa, conditions similar to those obtained for other seed oils. Over 90% of the oil content of seed can be removed under these conditions (92). 

In addition to extraction from solids, supercritical fluids can be used to extract aromatic molecules from liquids. Senorans et al. have utilized carbon dioxide to extract high-quality brandy aroma using a countercurrent supercritical fluid extractor. The aroma quality is influenced by the extraction conditions. Medina and Martinez studied alcohol removal from beverages using supercritical carbon dioxide, to produce beverages with low-alcohol content but sufficient flavor, because of three key benefits 1) water and salts are not appreciably removed by the carbon dioxide 2) proteins and carbohydrates are not extracted or denatured and 3) there is a good control in the aroma recovery. The alcohol removal efficiency increases with the extraction pressure raffinate alcohol concentration can be reduced up to 3 wt.% at 250 bar and 40°C, from 6.2 wt.% in the feed. " ... 

The shape of the curves indicate that the initial stage of the extraction is limited by solubility. Note the initial rise was greatest at 40 C (0.95 g/mL) at those conditions the recovery reached 82 % when only 60 mL of supercritical carbon dioxide had passed through the extraction thimble. For the same volume of the supercritical fluid (60 mL), the recovery was only 78 % for 80°C(0.81 g/mL), and 58 % for 120 C (0.67 g/mL). However, as the analyte flux begins to diminish (the easy-to-extract solutes are removed, and the more difficult solutes deeper within the matrix are now being removed), the extraction mechanism is no longer limited by saturation solubility. Rather, the extraction mechanism in the later stages of SFE is diffusion limited for... 

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