Subcritical carbon dioxide extraction

Field and Monohan [430] sequentially extracted Dacthal and its mono-and diacid metabolites from soils by first performing a supercritical carbon dioxide extraction to recover Dacthal, followed by a subcritical (hot) water extraction step to recover metabolites. Dacthal was recovered from soil in 15 minutes by supercritical carbon dioxide at 150 °C and 400 bar. The mono-and diacid metabolites were extracted from soil in 10 minutes under the sub-... 

With an increased interest and awareness of the impact of society and industry on the environment, there has been a significant attempt in recent years to reduce or replace the usage of organic solvents. Much early work in this area concentrated on the application of supercritical and subcritical carbon dioxide, but in recent years superheated (or subcritical/pressurized hot) water (SHW) has become of interest for both chromatography and extraction [43,54], The earliest work was reported by GuUlemin et al. [55], who used the term thermal aqueous liquid chromatography. As well as using SHW for the separation of... 

The most important extraction technique nowadays is simple solvent extraction. The traditional solvent for extraction was benzene, but this has now been superseded by other solvents because of concern over possible toxic effects of benzene on those working with it. Petroleum ether, acetone, hexane and ethyl acetate, together with various combinations of these, are typical solvents for extraction. Recently, there has been a great deal of interest in the use of carbon dioxide as an extraction solvent. Both supercritical carbon dioxide and subcritical liquid carbon dioxide are used, depending on circumstances. The pressure required to liquify carbon dioxide at ambient temperature is considerable and thus the necessary equipment is expensive. This is reflected in the cost of the oils produced but carbon dioxide has the advantage that it is easily removed and there are no concerns about residual solvent levels. The major applications of liquid carbon dioxide extraction are in decaffeination of coffee and extraction of hops. 

Another important application is microwave-assisted extraction of natural products in combination with subcritical and supercritical-fluid (carbon dioxide) extraction. This complex installation (Fig. 2.31) was designed, built, and tested at the... 

Supercritical CO2 is used for carbon dioxide explosion pretreatment. CO2 is cheap, nontoxic, inflammable, and easy to extract after explosion (Taherzadeh and Karimi, 2008). Due to the release of carbon dioxide at high pressure, lignocelluloses are disturbed, which increases the surface area for further hydrolysis. Glucose release was observed to increase with increasing pressure and temperature of the carbon dioxide was applied in supercritical carbon dioxide explosion. However, using subcritical carbon dioxide results in opposite scenario. 

If, on the other hand, the equilibrium solute concentration C is very low, leading to a correspondingly low value for Cj in equation (10.1), the energy and capital costs associated with the recompressor can become major factors in determining the separation cost. This will be seen to be the case, for example, in the hypothetical process for extracting crushed rape seed with subcritical carbon dioxide which is considered in section 10.6. It would also be true of the extraction of caffeine from coffee beans if pressure reduction was used to recover the caffeine. In cases such as these the most economic flow conditions and tower dimensions will be such that Ct is quite close to the equilibrium value C. ... 

The worked example for the extraction of material from a solid matrix with marginally subcritical carbon dioxide complements a similar example for the extraction of an ethanol/water solution given in an earlier paper [1]. The intention of the example was to illustrate the way in which a proposed near-critical extraction process can be costed from bench data and to highlight aspects in the design which are important in dictating the energy consumption and overall economics of such a process. 

Green extraction processes (viz., subcritical water and sub- and supercritical carbon dioxide extraction) are the most promising methods for industrial implementation. In fact, these methods are excellent for isolating anthocyanins and other polyphenols from grape processing wastes [196]. 

The current trend of consumer preference towards natural products requires new processing methods for spice-oils and extracts, without the addition of external material. In recent years there has been an increased interest in supercritical and subcritical extraction [26,27], which use carbon dioxide as a solvent [34,35,36]. Carbon dioxide (CO2) is an ideal solvent for the extraction of natural products because it is non-toxic, non-explosive, readily... 

Organophosphorus insecticides including diazinon, ronnel, parathion ethyl, methiadathion and trichlorovinphos have been extracted from soil by subcrit-ical carbon dioxide containing 3% methyl alcohol. At a pressure of 35.5 MPa and 50 °C, recoveries of 85% were obtained [280,315]. 

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. 

In this project, the feasibility of catalyst regeneration by supercritical fluid extraction was studied. A spent catalyst from an industrial naphtha hydrotreater was extracted with tetrahydrofuran, pyridine, carbon dioxide, and sulfur dioxide under subcritical and supercritical conditions. The coke reduction and changes in the catalyst pore characteristics were measured and to a limited extent the catalyst activity was evaluated. It is shown that by supercritical extraction, the coke content of spent hydrotreating catalysts can be reduced and the catalyst pore volume and surface area can be increased. 

The effectiveness of tetrahydrofuran, pyridine, carbon dioxide, and sulfur dioxide as solvents to remove the coke from catalyst under supercritical and subcritical conditions was studied. The critical properties of these solvents are listed in Table I and the extraction conditions are shown in Table II. 

Toward this end, we have investigated tandem or coupled processes that embodied the use of pressurized fluids, namely carbon dioxide, for both extraction, fiactionation and reaction. Related exanqrles to the work described here are coupling supercritical fluid extraction (SFE) with production scale supercritical fluid chromatography (SFC) for the enrichment of high value tocopherols from natural botanical sources (/0), or subcritical water hydrolysis of vegetable oils (77) followed 1 partition into dense carbon dioxide to produce industrially-useM mixtures of tty acids. 

Three distinct processes were experimentally studied a coupled process for deacidi%ing and enriching the plqrtosterol content of rice bran oil (RBO) by continuous countercurrent colnitmar fiactionation, a scale up of a coupled supercritical fluid extraction (SFE)/ supercritical fluid chromatogr hy (SFC) process for the enrichment of phytosterol in com bran oil, and a unit process involving the snbcritical water extraction of berry substrates. The e q)erimental aspects of the first two processes are described in the literature (36, 37), and will not be repeated here. Research is currently underw to couple the described process below with other unit processes involving both subcritical water and siq)ercritical carbon dioxide. 

Analysis of process development data - The following illustrates how PDU data can be used to develop a commercial SCFCO2 plant s process design. This data is provided by Marc Sims on pyrethrins, a natural insecticide extracted with subcritical and supercritical carbon dioxide from pyrethrum flowers (a species of chrysanthemum). 

Lai et al. [58], in a combined process of permeation of soybean oil with reverse osmosis NF membranes in combination with extraction by subcritical liquid pressurized carbon dioxide, obtained a preferential permeation of oleic acid in relation to triglycerides. From a system model of 40% of oleic acid and 60% of triglycerides (soybean oil), the permeation through the reverse osmosis membrane (BW 30) resulted in a permeate above 80% w/w of oleic acid, while the permeation through the membrane for NF (NF 90, MWCO = 200 Da) resulted in a permeate with approximately 50% w/w of oleic acid. However, the last membrane showed a significantly high permeate flux compared with that obtained with the BW 30. 

Other properties, in particular, the solubility of various nonvolatile solutes, are often found to be quite enhanced compared to the subcritical region. As an example, the enhanced solubility of caffeine in supercritical carbon dioxide (Tc = 304.1 K, Pc = 73.8 bar) makes it possible to use carbon dioxide as a solvent to extract caffeine from coffee, thus avoiding the use of other solvents with potential toxic effects. 

Figure 24 shows other possibilities for linking up these individual critical fluid-based options into tandem processes. Here the previously discussed option is shown initially as well as the supercritical fluid extraction and chromatographic separation of phospholipids which was noted in Section 3.2.3. Also, our previously-cited example of subcritical water synthesis of fatty acids from natural oil feedstocks is noted, the end product in this case is a mixture of fatty acids contained in an aqueous emulsion. These can be separated from water via a membrane process or counter currently into supercritical or liquid carbon dioxide. Further rectification of the fatty acid mixtures would also be amenable to fractionation via the thermal gradient fractionation column mentioned previously. 

Costs for the isolation of flavour and perfume ingredients by solvent extraction with liquid CO2 compared with solvent extraction with supercritical carbon dioxide and steam distillation. Because of the higher pressures involved, the extraction equipment required for supercritical extraction with CO2 costs more (typically IV2 times as much) than that required for subcritical extraction. In some applications this factor is more than offset by the higher loadings of extract in the solvent phase obtained in the supercritical case which result in lower compressor and separator costs (see chapter 10). For this... 

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