Extraction, commercial processes liquid-solid

Because of its low cost, nonhazardous chemical nature, and low critical temperature, carbon dioxide has been used in many applications. A commercial process to remove caffeine from coffee, using supercritical C02 as the solvent, is shown in Fig. 17. While actually a liquid-solid extraction process, it demonstrates principles involved in SCFE. A commercial SCFE process has been reported for recovery of hydrocarbon liquid from heavy oil. As compared with conventional propane deasphalting, this SCFE process can reduce capital and energy costs. 

A pivotal step in the analytical process is sample preparation. Frequently liquid-liquid extractions (LLEs) are used. Solvents, pH, and multiple back extractions are all manipulated to increase selectivity and decrease unwanted contaminants before injection on the GC system. Solid phase extraction (SPE) is more convenient than it used to be because of an increase in commercially available SPE columns. SPE columns are packed with an inert material that binds the drug of interest, allowing impurities to pass through. As with LEE, solvent choices and pH affect retention and recovery. There are three commercially available types of SPE columns, diatomaceous earth (which uses the same principles as LLE), polystyrene-divinylbenzene copolymer, and mixed mode bonded silica (Franke and de Zeeuw, 1998). 

Primary recovery of the active ingredient from the solid or liquid phase to remove large quantities of unwanted waste materials, which may themselves be processed further. Suitable techniques include solvent extraction, precipitation by chemical or physical changes to the product-containing solution, and ultrafiltration or microfiltration to separate products above a particular size. Work done on combined biomass separation-primary product recovery processes such as expanded-bed adsorption are now being commercialized in the pharmaceutical industry. 

Due to its unique characteristics and physicochemical properties such as being less toxic, nonflammable, and having the extraction power tuned by temperamre and pressure, SC CO2 can be used as a green solvent for extraction of substances especially from solid or liquid substrates. Such extraction has been carried out on commercial scale for more than two decades and applications like decaffeination of coffee beans and black tea leaves and hops extraction are involved in large-scale processes [17]. Other extractions such as extraction of flavors, spices, and essential oils from plant materials are under investigation. An overview of published data for different materials is given in the review of Marr and Gamse [18]. 

We thus reduce the number of alternatives to 2. In both options the incineration will be carried out at the nearest, EPA approved, commercial incinerator located in Chicago and operated by Chemwaste Management Company. Based on the physical properties presented in Table 1 and the quantity of material to be incinerated, estimates of incineration cost were obtained as 0.64/kg of liquid and 22/kg of solid [ 8 ]. If one wishes to use the solvent extraction process, one realizes a considerable economic savings in incineration costs due to the substantial difference between the costs of incinerating liquids and solids. The estimated cost of incinerating solids includes ash disposal. If the solid, upon incineration, does not... 

New phases will continue to be introduced to take full advantage of specific interactions. The commercialization of immunoaffinity SPE will no doubt occur, especially for compounds that are polar and difficult to recover by the available sorbents of today. Polymers will be refined to enhance the recovery of polar compounds and more new phases will be introduced. Finally, other uses of SPE will be developed and optimized, such as derivatization on disks, and products will no doubt be introduced that make this process routine. At last sampling handling and solid-phase extraction will reach the level of sophistication that its relatives in liquid chromatography have reached, and perhaps go beyond. 

For reasons of completeness it should be pointed out that polymeric sulfur is also obtained if sulfur vapor is quenched from very high temperatures (e.g., 600 °C) to very low temperatures (liquid nitrogen) followed by warming the condensate to -1-20 °C and extraction with carbon disulfide. Up to 60% S have been obtained in this way [53]. Commercially polymeric sulfur (trade name Crystex) is produced by a similar process (see the chapter on Solid Sulfur Allotropes in this volume). The glass transition temperature of Crystex is -1-75 °C [51]. 

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