Reductive cleaning methods

Various processes that result in a reduction of the mineral matter and sulfur content can be employed to clean coal. The ash content of raw coal is often used to select the best cleaning method, and the ash content of the cleaned coal is used to measure the effectiveness of the cleaning process. In the commercial pulverization of coals, the amount and nature of ash is considered carefully before selecting pulverizing equipment or setting up the process. 

These reagents open the oxirane ring at the sterically more hindered side, and the reductions are accompanied by retention of the configuration. The alkali metal procedures can be employed as a comparatively simple and clean method of reducing sterically hindered oxiranes. A general synthetic method has been developed with this procedure for the preparation of 2-ethynylcycloalkanols. ... 

Electrochemical oxidation and reduction [104] can be a simple, clean method for the generation of a wide variety of radicals, for example, radical anions from quinones and nitrocompounds. 

The equipment required is simple and existing controls can be modified to accommodate the Auxiliary gas so capital costs are low. Indications are that there will be no energy penalty and possible an improvement in efficiency. It may be that the process can be optimised for energy saving and NOx reduction. The method also eliminates the additional energy and CO2 emissions associated with almost aU post-furnace clean up techniques. Glass quality and puU rates do not appear to be affected by the process. 

Cleaning Methods. The principal benefit of cleaning is the reduction in ash content. With ash content reduced, shipping costs and the requirements for storage and handling decrease because of the smaller quantity of coal necessary per unit of heating value. 

In assessing the performance of cleaning methods, it is not only the percent reduction that is important but also the ability to clean down to very low levels. Several studies have demonstrated that reducing lead loadings from relatively high levels to about 100 pg/ft is more readily accomplished than reductions below 100 pg/ft and becomes progressively harder at lower levels. 

Yujiro Hayashi of Tokyo University of Science and Temaki Mukaiyama of the Kitasato Institute developed (Chem. Lett. 2008, 37, 592) a reduction-oxidation method for converting primary, secondary (such as 1, with clean inversion) and tertiary alcohols to sulfides. Peter A. Crooks of the University of Kentucky found Chem. Lett. 2008, 37, 528) that tet-rabenzylpyrophosphate 5 was an effective agent for condensing an acid 4 with an amine 6 to give the amide 7. This protocol, that runs in near quantitative yield in an hour at room temperature, with all impurities readily removable by washing with aqueous base and aqueous acid, appears to be well-suited both for scale-up, and for solid-phase synthesis. 

The most common method of converting iron ore to metallic iron utilizes a blast furnace wherein the material is melted to form hot metal (pig iron). Approximately 96% of the world s iron is produced this way (see Iron). However, in the blast furnace process energy costs are relatively high, pollution problems of associated equipment are quite severe, and capital investment requirements are often prohibitively expensive. In comparison to the blast furnace method, direct reduction permits a wider choice of fuels, is environmentally clean, and requires a much lower capital investment. 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

Electrolytic Reductions. Both nitro compounds and nitriles can be reduced electrochemically. One advantage of electrochemical reduction is the cleanness of the operation. Since there are a minimum of by-products, both waste disposal and purification of the product are greatiy simplified. However, unless very cheap electricity is available, these processes are generally too expensive to compete with the traditional chemical methods. 

Other methods which should be mentioned because they show potential benefits for pollution reduction from utility stacks include (1) coal cleaning... 

Oxidation-reduction potential Because of the interest in bacterial corrosion under anaerobic conditions, the oxidation-reduction situation in the soil was suggested as an indication of expected corrosion rates. The work of Starkey and Wight , McVey , and others led to the development and testing of the so-called redox probe. The probe with platinum electrodes and copper sulphate reference cells has been described as difficult to clean. Hence, results are difficult to reproduce. At the present time this procedure does not seem adapted to use in field tests. Of more importance is the fact that the data obtained by the redox method simply indicate anaerobic situations in the soil. Such data would be effective in predicting anaerobic corrosion by sulphate-reducing bacteria, but would fail to give any information regarding other types of corrosion. 

A completely different method of synthesis of azo compounds from diazonium salts involving radical intermediates was found by Citterio et al. (1980, 1982 c), Cit-terio and Minisci (1982), and Fontana et al. (1988). It is a new general synthesis of arylazoalkanes based on the addition of an alkyl radical to an arenediazonium ion followed by reduction of the intermediate azo radical cation adduct by a metal salt (Scheme 12-80). The preferred source for the alkyl radical R in this reaction is an alkyl iodide, which gives rise to alkyl radicals cleanly in the presence of an arenediazonium salt and a Ti3+ or Fe2+ salt as in Scheme 12-81. The overall stoichiometric equation is therefore as given in Scheme 12-82. The yields vary between 36% and 79% (with respect to alkyl iodide). 

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