Carbon chemical solvents

Much useful information on these and other solvents will be found in the booklet Synihtiic Oryanic Chemicals issued by the Carbide and Carbon Chemicals Corporation. 

Natural Products. Various methods have been and continue to be employed to obtain useful materials from various parts of plants. Essences from plants are obtained by distillation (often with steam), direct expression (pressing), collection of exudates, enfleurage (extraction with fats or oils), and solvent extraction. Solvents used include typical chemical solvents such as alcohols and hydrocarbons. Liquid (supercritical) carbon dioxide has come into commercial use in the 1990s as an extractant to produce perfume materials. The principal forms of natural perfume ingredients are defined as follows the methods used to prepare them are described in somewhat general terms because they vary for each product and suppHer. This is a part of the industry that is governed as much by art as by science. 

The Carbitol (monoethyl ether of diethylene glycol) was the Carbide and Carbon Chemicals Company product, which was distilled before use, b.p. 192-196°. It is a suitable solvent to render the reactants mutually soluble. Aqueous alkali with an ether solution of the nitrosamide does not yield diazomethane. 

The absorption occurs as a result of the driving force of the partial pres-Miie from the gas to the liquid. The reactions involved are reversible bv changing the system temperature or pressure, or both. Therefore, die at[ueous base solution can be regenerated and thus circulated in a contin nous cycle. The majority of chemical solvent processes use either an amine or carbonate solution. 

Steam stripping Air stripping Biological nitrification Chemical oxidation Ion exchange Solvent extraction Biological oxidation (aerobic) Wet oxidation Activated carbon Chemical oxidation Chemical precipitation Ion exchange Adsorption Nano-filtration Reverse osmosis Electrodialysis... 

The proton and carbon chemical shifts of twenty-one and twenty different anthocyanins are presented in Table FI. 4.4 and Table FI. 4.5, respectively. These anthocyanins are chosen to illustrate the chemical shifts of the majority of anthocyanin building blocks reported. The linkage positions of the various anthocyanin building blocks may be conspicuous through shift comparison. However, be aware of shift effects caused by variation in solvent, pigment concentration and temperature. Table FI.4.6 contains typical H- H coupling constants of the most common anthocyanidins. 

Carbide and Carbon Chemicals Corp., Cellosolve and Carbitol Solvents, Jan. 1, 1947. 

The metabolism of carbon tetrachloride (a chemical solvent that was formerly in common use) attracts attention as well. Its bioactivation appears to involve consecutive one-electron reduction and the formation of chloride ion and the trichloromethyl radical. The latter radical then reacts with oxygen, giving rise to an oxygenated radical and, eventually, to highly toxic phosgene (Mico Pohl 1983). Scheme 3-70 (below) describes these reactions ... 

Typically, a solvent that is chemically similar to the target solute or that reacts with it will provide high solubility. Water is often used for polar and acidic solutes (e.g., HCl), oils for light hydrocarbons, and special chemical solvents for acid gases such as C02, S02, and H2S. Solvents are classified as physical and chemical. A chemical solvent forms complexes or chemical compounds with the solute, while physical solvents have only weaker interactions with the solute. Physical and chemical solvents are compared and contrasted by examining the solubility of C02 in propylene carbonate (representative physical solvent) and aqueous monoethanolamine (MEA representative chemical solvent). 

The propylene carbonate data are from Zubchenko et al. [Zhur. Prik-lad. Khim., 44, 2044-2047 (1971)], and the MEA data are from Jou, Mather, and Otto [Can. J. Chem. Eng., 73, 140-147 (1995)]. The two figures have the same content, but Fig. 14-2 focuses on the low-pressure region by converting both composition and pressure to the logarithm scale. Examination of the two sets of data reveals the following characteristics and differences of physical and chemical solvents, which are summarized in the following table ... 

Avery, D. A. Tracey, D. H. "The Application of Fluidized Beds of Activated Carbon to Solvent Recovery from Air or Gas Streams," Institution of Chemical Engineers Symposium Series, No. 30, 1968. 

Scheme 3.18 provides some pertinent proton and carbon chemical shift and coupling constant data for trihalomethanes, including what data are available for fluorodihalomethanes. There are potentially significant solvent effects on proton chemical shifts of all trihalomethanes,... 

As was the case for the monofluoro series, halogens attached directly to the CF2 carbon deshield the fluorine nuclei (Tables 4.2 and 4.3). Iodine has the greatest deshielding effect on fluorine chemical shifts I > Br > Cl > F. In contrast, iodine has its usual shielding effect upon carbon chemical shifts. When considering proton chemical shifts for the fluoromethanes, again one must keep in mind the significant solvent effects observed for all di- and trihalomethanes. 

In the chemical absorption process, the C02 reacts with chemical solvents to form a weakly-bonded intermediate compound that is then broken down by the application of heat. The heat regenerates the original solvent and produces a CO2 stream. Typical solvents are amine- or carbonate-based. Examples are MEA, diethanolamine (DEA), ammonia and hot potassium carbonate. These processes can be used at low C02 partial pressures, but the feed gas must be free of S02, 02, hydrocarbons and particulates. Hydrocarbons and particulates cause operating problems in the absorber199. 

Absorption is indeed a standard technique for C02 removal. Physical absorption in water under pressure is applicable for recovery below 90%. Chemical solvents are preferred for advanced recovery, such as amine solutions, hot carbonate, cold methanol, Selexol, etc. 

To produce pure hydrogen, the carbon dioxide must be removed. The gas passes through a carbon dioxide removal system, which contains a chemical solvent that selectively absorbs the carbon dioxide as the gas passes through the solvent.12 Heat then is added to the solvent to discharge the carbon dioxide. The regenerated solvent is returned to the system to continue the removal of carbon dioxide. 

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