Chlorine economic importance

The book explores the invention of new chemical reactions for use in the synthesis of biologically and economically important compounds. It begins with a mechanistic study of the industrial importance of the pyrolysis of chlorinated alkanes. It continues with a theory on the biosynthesis of phenolate derived alkaloids involving phenolate radical coupling. Included in the book is a description of the work on nitrite photolysis (the Barton Reaction) which involved the invention of new radical chemistry leading to a simple synthesis of the hormone, aldosterone. In two final chapters Dr Shyamal Parekh views Professor Barton s pioneering work from the modern perspective, with a review of recent applications in industry and research. 

Halides are compounds that include one of the halogen elements fluorine, chlorine, bromine, or iodine. The simplest halides are combinations of one element, such as sodium (Na), with a halogen element, such as chlorine (Cl). Complex halides combine two or more elements with a halogen, and some contain water. Some halides are economically important minerals, such as halite (common salt), fluorite (fluorine), and chlorargyrite (silver ore). 

C. W. Scheele in 1774 and has been extensively studied since because of its economic importance (see below) and its intrinsic physicochemical interest. Direct chlorination of molten S followed by fractional distillation yields disulfur dichloride (S2CI2) a toxic, golden-yellow liquid of revolting smell mp —76°, bp 138°, d(20°) 1.677 gcm . The molecule has the expected C2 structure (like S2F2, H2O2, etc.) with S-S 195 pm,... 

Since the economic importance of para-chlorotoluene is considerably greater than that of ortAfl-chlorotoluene, catalytic systems have been developed to increase the para-selectivity of the chlorination. Since the early 1930s addition of sulfur or disulfur dichloride [129] to FeClj as a cocatalyst has been known to shift the isomer ratio in... 

The chlorophenoxyalkanoic acids constitute yet another economically important group of halogenated aromatic hydrocarbons. They are widely used as herbicides to control dicotyledonous weeds. The most important of them are 2,4-D and its propionic and butyric acid homologs, 4-chloro> 2-methylphenoxyacetic acid (MCPA), and 2,4,5>trichlorophenoxyacetic add (2,4,5-T). In all the cases studied, aerobic biodegradation proceeds by removal of the aliphatic side chain with the formation of the corresponding chlorinated phenoL Thus, formation of 2,4 chlorophenol from both 2,4-D and 4-(2,4-dichlorophenoxy)-butyric acid, 4-chloro-o-cresol from MCPA, and 2,4,5-trichlorophenol from 2,4,5-T has been... 

These figures demonstrate the economic importance of the chlorine industry. 

Comparison to the Raschig Process. The economics of this peroxide process in comparison to the Raschig or hypochlorite—ketazine processes depend on the relative costs of chlorine, caustic, and hydrogen peroxide. An inexpensive source of peroxide would make this process attractive. Its energy consumption could be somewhat less, because the ketazine in the peroxide process is recovered by decantation rather than by distillation as in the hypcochlorite process. A big advantage of the peroxide process is the elimination of sodium chloride as a by-product this is important where salt discharge is an environmental concern. In addition to Elf Atochem, Mitsubishi Gas (Japan) uses a peroxide process. 

Anhydrous stannous chloride, a water-soluble white soHd, is the most economical source of stannous tin and is especially important in redox and plating reactions. Preparation of the anhydrous salt may be by direct reaction of chlorine and molten tin, heating tin in hydrogen chloride gas, or reducing stannic chloride solution with tin metal, followed by dehydration. It is soluble in a number of organic solvents (g/100 g solvent at 23°C) acetone 42.7, ethyl alcohol 54.4, methyl isobutyl carbinol 10.45, isopropyl alcohol 9.61, methyl ethyl ketone 9.43 isoamyl acetate 3.76, diethyl ether 0.49, and mineral spirits 0.03 it is insoluble in petroleum naphtha and xylene (2). 

Two variables of primary importance, which are interdependent, are reaction temperature and ch1orine propy1ene ratio. Propylene is typically used ia excess to act as a diluent and heat sink, thus minimising by-products (eqs.2 and 3). Since higher temperatures favor the desired reaction, standard practice generally involves preheat of the reactor feeds to at least 200°C prior to combination. The heat of reaction is then responsible for further increases in the reaction temperature toward 510°C. The chlorine propylene ratio is adjusted so that, for given preheat temperatures, the desired ultimate reaction temperature is maintained. For example, at a chlorine propylene molar ratio of 0.315, feed temperatures of 200°C (propylene) and 50°C (chlorine) produce an ultimate reaction temperature of approximately 500°C (10). Increases in preheat temperature toward the ultimate reactor temperature, eg, in attempts to decrease yield of equation 1, must be compensated for in reduced chlorine propylene ratio, which reduces the fraction of propylene converted and, thus aHyl chloride quantity produced. A suitable economic optimum combination of preheat temperature and chlorine propylene ratio can be readily deterrnined for individual cases. 

Bioremediation also has its limitations. Some chemicals are not amenable to biodegradation, for instance, heavy metals, radionuclides, and some chlorinated compounds. In some cases, the microbial metabolism of the contaminants may produce toxic metabolites. Bioremediation is a scientifically intensive procedure that must be tailored to site-specific conditions, and usually requires treatability studies to be conducted on a small scale before the actual cleanup of a site.13 The treatability procedure is important, as it establishes the extent of degradation and evaluates the potential use of a selected microorganism for bioremediation. A precise estimate on vessel size or area involved, speed of reaction, and economics can therefore be determined at the laboratory stage. 

There are many natural sources of chlorine compounds, which is not surprising considering that it is the 20th most abundant element. Salt and salt water are widely available the Great Salt Lake contains 23% salt, and the Dead Sea contains about 30%. Because salt is so abundant, most minerals that contain chlorine are not important sources for economic reasons. Bromine is found in some salt brines and in the sea, as are some iodine compounds. 

It should also be noted that there are some producers that have used the concept in this chapter where the chlorine production is combined with EDC production. The VCM plant would then be designed in the so-called unbalanced mode where the feedstocks are EDC and ethylene, not chlorine and ethylene. Effectively, all of the chlorine and one-half of the ethylene come into the unbalanced VCM plant as EDC. Frequently, the reason for this strategy is that EDC is very much easier and safer to store and transport than liquid chlorine. An additional important reason for this configuration is that chlorine can then be produced economically in areas of low-cost power. Often, these are the very same areas where low-cost ethylene is also available. Examples of areas of both low-cost power and low-cost ethylene are the United States Gulf Coast (see Fig. 21.4) and the Middle East. 

There are two important methods for the manufacture of propylene oxide, each accounting for one half the total amount produced. The older method involves chlorohydrin formation from the reaction of propylene with chlorine water. Before 1969 this was the exclusive method. Unlike the analogous procedure for making ethylene oxide from ethylene, which now is obsolete, this method for propylene oxide is still economically competitive. Many old ethylene oxide plants have been converted to propylene oxide synthesis. 

CO is derived from a variety of feedstocks such as petroleum gas, fuel oil, coal, and biomass. The industrial scale production of PO starts from propylene, which is mainly obtained from crude oil. However, due to the high importance of this compound, many pathways from renewable sources have additionally been developed [54]. PP is converted to PO by either hydrochlorination or oxidation [55]. The use of chlorine leads to large amounts of salts as by-products, therefore oxidation methods are more important, such as the co-oxidation of PP using ethylbenzene or isobutene in the presence of air and a catalyst. However, this process is economically dependent on the market share of these by-products, thus new procedures without significant amounts of other side-products have been developed, such as the HPPO (hydrogen peroxide to propylene oxide) process in which propylene is oxidized with hydrogen peroxide to give PO and water [56, 57] (Fig. 14). 

Accdg to PCUK s Dr J.P. Schirmann, the new method in addn to having a decided economic edge over existing methods, has the important advantage that chlorine compds are not involved in the reaction... 

Chlorination of Alkanes. The most direct and economical method for the manufacture of chloromethanes is the thermal free-radical chlorination of methane.176 177 Whereas in the 1940s and 1950s photochlorination was practiced in some plants, thermal chlorination is the principal industrial process today. The product chloromethanes are important solvents and intermediates. Commercial operations perform thermal chlorination at about 400-450°C. Vapor-phase photochemical chlorination of methane may be accomplished at 50-60°C. Fast and effective removal of heat associated with thermally induced free-radical substitution is a crucial point. Inadequate heat control may lead to explosion attributed to the uncontrollable pyrolysis liberating free carbon and much heat ... 

Prior to the discovery of a-sulfonation of anthraquinone, nitration was the only useful method for preparing a-substituted anthraquinones. The nitro group of a-nitroanthraquinones can be replaced in a manner similar to the sulfonic acid moiety, e.g., by chlorine atoms and amino, hydroxy, alkoxy, or mercapto groups. Reduction readily yields aminoanthraquinones. Nitration of anthraquinone has gained increasing importance because of environmental considerations, this method offering an economical alternative to a-sulfonation... 

---