Economic alkali process

The starting material for all industrial chlorine chemistry is sodium chloride, obtained primarily by evaporation of seawater. The chloride ion is highly stable and must be oxidized electrolytically to produce chlorine gas. This is carried out on an industrial scale using the chlor-alkali process, which is shown schematically in Figure 21-15. The electrochemistry involved in the chlor-alkali process is discussed in Section 19-. As with all electrolytic processes, the energy costs are very high, but the process is economically feasible because it generates three commercially valuable products H2 gas, aqueous NaOH, and CI2 gas. 

Four chapters address alternatives to throwaway slurry scrubbing. The development of the limestone dual alkali process is reviewed. Two chapters present results related to dry scrubbing with nahcolite or lime. A conceptual design and economics are given for MgO scrubbing using a spray dryer. 

Because pervaporation is suitable for separation azeotropic mixtures, such as dehydration of an azeotropic mixture of ethanol-water (ca. 94%), economic comparison of the process with distillation has been reported.228 Besides separation of azeotropic mixtures of organic solvents, dehydration of nitric acid (azeotropic point ca. 68 wt.%) has been tried using a perfluorocarbon ion exchange membrane for the chlor-alkali process nitric acid is concentrated up to... 

Potassium hydroxide is a by-product of chlorine production in the chlor-alkali process. Its low relative market value (chlorine 37.5 /kg Ha 123.8 /kg KOH 0.65 /kg) makes economic allocation seem sensible. The process would run without the KOH by-product but not for KOH production exclusively. 

Hydrolysis, although a simple method in theory, yields terephthalic acid (TPA), which must be purified by several recrystallizations. The TPA must be specially pretreated to blend with ethylene glycol to form premixes and slurries of the right viscosities to be handled and conveyed in modern direct polyesterification plants. Hie product of the alkaline hydrolysis of PET includes TPA salts, which must be neutralized with a mineral acid in order to collect the TPA. That results in the formation of large amounts of inorganic salts for which commercial markets must be found in order to make the process economically feasible. There is also the possibility that the TPA will be contaminated with alkali metal ions. Hydrolysis of PET is also slow compared to methanolysis and glycolysis.1... 

The catalytic system used in the Pacol process is either platinum or platinum/ rhenium-doped aluminum oxide which is partially poisoned with tin or sulfur and alkalinized with an alkali base. The latter modification of the catalyst system hinders the formation of large quantities of diolefins and aromatics. The activities of the UOP in the area of catalyst development led to the documentation of 29 patents between 1970 and 1987 (Table 6). Contact DeH-5, used between 1970 and 1982, already produced good results. The reaction product consisted of about 90% /z-monoolefins. On account of the not inconsiderable content of byproducts (4% diolefins and 3% aromatics) and the relatively short lifetime, the economics of the contact had to be improved. Each diolefin molecule binds in the alkylation two benzene molecules to form di-phenylalkanes or rearranges with the benzene to indane and tetralin derivatives the aromatics, formed during the dehydrogenation, also rearrange to form undesirable byproducts. 

Lindley, A.A. (1997) An Economic and Environmental Analysis of the Chlor-Alkali Production Process Mercury Cells and Alternative Technologies. Prepared for the European Commission (DG III C-4, Chemicals, Plastics, Rubber). See also OSPAR Document WOCAI 99/5/8 (Madrid, 1999). 

The process flow sheet was first tested for direct leaching of steel mill flue dust and production of zinc metal by electrowinning. The tests were performed in a continuously operating pilot plant, producing 10-20 kg/day zinc metal. The same pilot plant was then used for treating copper/zinc-rich brass mill flue dust in a closed loop operation, recycling all the zinc solvent extraction raffinate to the copper circuit leach section. In the zinc circuit leach section, only the amount of zinc rich dust necessary for neutralization of the copper solvent extraction raffinate was used. The results obtained from the pilot plant tests indicated contamination problems within the solvent extraction loops. The estimation of economic data showed a weak return on the assets compared with the alkali route, and sensitivity toward the raw material price. 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

Hence, although the hydroxide can be made by the action of water on the oxide, it is far more economical to employ a method of preparation based on that described by Albertus Magnus. The chloride is first converted into carbonate by Leblanc s or Solvay s process, and the carbonate is subsequently converted into the hydroxide by causticization with lime. If the alkali chloride could be transformed directly into the hydroxide, without the intermediate formation of the carbonate, by a cheap enough process, the waste of industrial energy, so to speak, involved in this roundabout procedure would be avoided. Numerous patents 7 have been obtained for decomposing common salt by steam or superheated steam, but without any useful result. 

The alkali sulphates can also be made by neutralizing, say, a soln. of 5 grms. of sulphuric acid in 30 c.c. of water with the alkali hydroxide or carbonate, and evaporating the soln. until crystals begin to form. The process is not economical except on a small scale. It is used mainly for lithium, rubidium, and caesium sulphates. H. Erdmann 20 treated a hot soln. of crude rubidium iron alum with milk of lime made from purified lime, and filtered the liquid from the excess of lime, calcium sulphate, and ferric hydroxide, by suction. The small amount of lime in soln. is precipitated by adding rubidium carbonate. The filtrate is neutralized with sulphuric acid, and evaporated to the point of crystallization. 

Sulfonation of Benzene and Alkylbenzenes. Since the main utilization of ben-zenesulfonic acid was its transformation to phenol, the importance of the sulfonation of benzene has diminished. The process, however, is still occasionally utilized since it is a simple and economical procedure even on a small scale. Excess sulfuric acid or oleum is used at 110-150°C to produce benzenesulfonic acid.97,102 Sulfonation of toluene under similar conditions yields a mixture of isomeric toluenesul-fonic acids rich in the para isomer. This mixture is transformed directly to cresols by alkali fusion. 

Beryllium reacts with fused alkali halides releasing the alkali metal until an equilibrium is established. It does not react with fused halides of the alkaline-earth metals to release the alkaline-earth metal. Water-insoluble fluoroberyllates, however, are formed in a fused-salt system whenever barium or calcium fluoride is present. Beryllium reduces halides of aluminum and heavier elements. Alkaline-earth metals can be used effectively to reduce beryllium from its halides, but the use of alkaline-earths other than magnesium [7439-95 4] is economically unattractive because of the formation of water-insoluble fluoroberyllates. Formation of these fluorides precludes efficient recovery of the unreduced beryllium from the reaction products in subsequent processing operations. 

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