Raschig process

In the Raschig process, ammonia is oxidized with sodium hypochlorite  

NaOCl + NaCl + H2O - NH2Cl + NaOH N2H4 + NaCI + H2O 

Sodium hypochlorite is obtained as a ca. 4.7 mol/L solution by mixing chlorine and sodium hydroxide with cooling in a molar ratio of 1 2 (see Fig, 1.4.-3). This is diluted to ca. 1 mol/L and reacted with an aqueous ammonia solution (ca. 15%) at temperatures around 0°C (with cooling) forming chloramine and sodium hydroxide. The yield is almost quantitative. 

The alkaline chloramine solution is then reacted, at ca. 130°C under pressure, with a 20- to 30-fold molar excess of anhydrous ammonia. The excess ammonia then separated from the reaction mixture, is recycled. Water and the hydrazine-water azeotrope (b.p. 120.5°C) are distilled off leaving solid sodium chloride. The aqueous hydrazine solution obtained is finally concentrated by distillation. Ca. 70% of the theoretical yield is obtained. Important side reactions are  

This reaction is particularly catalyzed by copper. A large excess of ammonia and the addition of complexing agents such as ethylenediaminetetra-acetic acid (EDTA) are used as countermeasures. 

Commercial production of hydrazine from its elements has not been successful. However three processes are available for the commercial production of hydrazine 1) The Raschig Process, 2) The Raschig/Olin Process, 3) The Hoffmann (urea) Process, 4) Bayer Ketazine Process, and 5) the Peroxide process from Produits Chimiques Ugine Kuhlmann (of France). 

The Raschig process was discovered in 1907 and then modified into the Olin process. The chemical reactions take place in the liquid phase and involve three steps  

Hydrazine is produced in the hydrated form with one mole of water added. Although a significant fraction of hydrazine is used as the hydrate, numerous applications (such as rocket propulsion) require anhydrous hydrazine. Because of the azeotrope at 68% hydrazine, reactive distillation or extractive distillation must be used to produce pure hydrazine. 

sodium hypochlorite is produced by feeding chlorine into a 30% aqueous caustic solution in a circulating reactor/cooler system. To avoid sodium chlorate formation, the reaction temperature is kept below 30°C and NaOH concentration is kept below 1 g/liter. Typical reaction temperature is 5 °C132. 

the reaction rate for chloramine (NH2CI ) formation is rapid relative to the formation of hydrazine in Eq. (18.3). In this step dilute ammonia solution (5% to 15%) is added to the NaOCl at a ratio of 3 1. Use of NaOCl is estimated to be 3.5 pounds per pound of hydrazine. 

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Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Raschig process See hydrazine, rasorite See kernite, borax. 

In a variation of the Raschig process for making hydrazine, amines rather than ammonia ate reacted with chloramine to give the corresponding alkyl hydrazine ... 

In the iadustrial synthesis of phenyUiydraziae [100-63-0] the reduciag agent is sodium bisulfite. It is also possible to react aniline with chloramine as ia the Raschig process (79) ... 

Raschig Process. The Raschig process (92) is based on the oxidation of ammonia with hypochlorite according to the following overall... 

MMHa.nd UDMH. MonomethyUiydrazine and yyz -dimethylhydrazine are manufactured by Olin Corp. using the same Raschig process and equipment employed for anhydrous hydrazine. Chloramine, prepared as described above, reacts with methylamine or dimethylamine instead of with... 

Urea Process. In a further modification of the fundamental Raschig process, urea (qv) can be used in place of ammonia as the nitrogen source (114—116). This process has been operated commercially. Its principal advantage is low investment because the equipment is relatively simple. For low production levels, this process could be the most economical one. With the rapid growth in hydrazine production and increasing plant size, the urea process has lost importance, although it is reportedly being used, for example, in the People s RepubHc of China (PRC). 

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. 

The estimated world production capacity for hydrazine solutions is 44,100 t on a N2H4 basis (Table 6). About 60% is made by the hypochlorite—ketazine process, 25% by the peroxide—ketazine route, and the remainder by the Raschig and urea processes. In addition there is anhydrous hydrazine capacity for propellant appHcations. In the United States, one plant dedicated to fuels production (Olin Corp., Raschig process), has a nominal capacity of 3200 t. This facihty also produces the two other hydrazine fuels, monomethyUiydrazine and unsymmetrical dimethyUiydrazine. Other hydrazine fuels capacity includes AH in the PRC, Japan, and Russia MMH in France and Japan and UDMH in France, Russia, and the PRC. 

The most widely used process for the production of phenol is the cumene process developed and Hcensed in the United States by AHiedSignal (formerly AHied Chemical Corp.). Benzene is alkylated with propylene to produce cumene (isopropylbenzene), which is oxidized by air over a catalyst to produce cumene hydroperoxide (CHP). With acid catalysis, CHP undergoes controUed decomposition to produce phenol and acetone a-methylstyrene and acetophenone are the by-products (12) (see Cumene Phenol). Other commercial processes for making phenol include the Raschig process, using chlorobenzene as the starting material, and the toluene process, via a benzoic acid intermediate. In the United States, 35-40% of the phenol produced is used for phenoHc resins. 

An additional mole of ammonium sulfate per mole of final lactam is generated duting the manufacture of hydroxylamine sulfate [10039-54-0] via the Raschig process, which converts ammonia, air, water, carbon dioxide, and sulfur dioxide to the hydroxylamine salt. Thus, a minimum of two moles of ammonium sulfate is produced per mole of lactam, but commercial processes can approach twice that amount. The DSM/Stamicarbon HPO process, which uses hydroxylamine phosphate [19098-16-9] ia a recycled phosphate buffer, can reduce the amount to less than two moles per mole of lactam. Ammonium sulfate is sold as a fertilizer. However, because H2SO4 is released and acidifies the soil as the salt decomposes, it is alow grade fertilizer, and contributes only marginally to the economics of the process (145,146) (see Caprolactam). 

Allied-Signal Process. Cyclohexanone [108-94-1] is produced in 98% yield at 95% conversion by liquid-phase catal57tic hydrogenation of phenol. Hydroxylamine sulfate is produced in aqueous solution by the conventional Raschig process, wherein NO from the catalytic air oxidation of ammonia is absorbed in ammonium carbonate solution as ammonium nitrite (eq. 1). The latter is reduced with sulfur dioxide to hydroxylamine disulfonate (eq. 2), which is hydrolyzed to acidic hydroxylamine sulfate solution (eq. 3). 

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

In the 1930s, the Raschig Co. in Germany developed a different chlorobenzene-phenol process in which steam with a calcium phosphate catalyst was used to hydrolyze chlorobenzene to produce phenol (qv) and HCl (6). The recovered HCl reacts with air and benzene over a copper catalyst (Deacon Catalyst) to produce chlorobenzene and water (7,8). In the United States, a similar process was developed by the BakeHte Division of Union Carbide Corp., which operated for many years. The Durez Co. Hcensed the Raschig process and built a plant in the United States which was later taken over by the Hooker Chemical Corp. who made significant process improvements. 

At one time the requirement for phenol (melting point 41°C), eould be met by distillation of eoal tar and subsequent treatment of the middle oil with eaustic soda to extraet the phenols. Such tar acid distillation products, sometimes containing up to 20% o-cresol, are still used in resin manufacture but the bulk of phenol available today is obtained synthetically from benzene or other chemicals by such processes as the sulphonation process, the Raschig process and the cumene process. Synthetic phenol is a purer product and thus has the advantage of giving rise to less variability in the condensation reactions. 

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

The economics of this process are to some extent dependent on the value of the acetone which is formed with the phenol. The process is, however, generally considered to be competitive with the modified Raschig process in which there is no by-product of reaction. In all of the above processes benzene is an essential starting ingredient. At one time this was obtained exclusively by distillation of coal tar but today it is commonly produced from petroleum. 

Industrial preparation of hydrazine is based on this reaction of ammonia with an alkaline solution of sodium hypochlorite, known as the Raschig process introduced in 1907. 

Hydrazine is prepared by the Raschig process, the first step of which involves the production of chloramine, NH2C1. The process can be summarized by the equations... 

Architectural coatings, 18 55-56 economic aspects of, 18 73-74 Architectural fabrics, 13 394 Architectural paints, 18 72 Archives, preservation of, 11 414 Arch Raschig process flow sheet, 13 578 Arc melting techniques, 25 522-523 ARCO process, 23 342 Arc-resistance furnace, 12 304 Arc resistance testing, 19 587 Arctic polar stratospheric clouds, effect on ozone depletion, 17 789-790 Arc vaporization, 24 738 Arc welding, copper wrought alloys,... 

Peroxide cure systems, in rubber compounding, 22 793-794 Peroxide decomposers, 3 111-114 Peroxide decomposition, 24 279-280 Peroxide formation, by VDC, 25 694. See also Hydrogen peroxide Peroxide initiators, 23 379-380 worldwide producers of, 24 303 Peroxide-ketazine process, 23 582-583 flow sheet for, 23 582 versus Raschig process, 23 583 Peroxide linkages, in VDC polymer degradation, 25 713... 

Rare-metal thermocouples, 24 461 RAR receptors, 25 787-789 Raschig process, 13 571, 576, 577-579 flow sheet for, 13 578 versus hypochlorite-ketazine processes, 13 581... 

Hydrazine may he produced by several methods. The most common commercial process is the Raschig process, involving partial oxidation of ammonia or urea with hypochlorite. Other oxidizing agents, such as chlorine or hydrogen peroxide may he used instead of hypochlorite. The reaction steps are as follows. 

The above reaction is catalyzed by copper and other trace metal impurities and can be prevented by adding a suitable complexing agent. In a modification of the Raschig process, what is known as Olin-Raschig process, liquid chlorine feed is continuously absorbed in dilute NaOH solution forming sodium hypochlorite which, similar to the Raschig process, is made to react with... 

In the Raschig process (prior to 1924), NaOH, chlorine and ammonia react in aq soln to form dil soln of hydrazine, with Na chloride as a by-product also by oxidation of urea by Na hypochlorite. For its purification can be used fractional distillation, flash distillation or conversion to the slightly sol sulfate, followed by treatment of the latter with coned NaOH soln. 

Until the late 1890s, coumarin was obtained commercially only from natural sources by extraction from tonka beans. Synthetic methods of preparation and industrial manufacturing processes were developed starting principally from ortho-creso (Raschig process), phenol (Pechmann reaction) and salicylaldehyde (Perkin reaction). Various methods can be used to obtain coumarin from each of these starting materials. In order to be suitable for perfumery uses, synthetic coumarin must be highly pure (Bauer et al., 1988 Boisde Meuly, 1993). 

In the modified Raschig process , used by Bayer A.G. and by Mobay Chem. Co. for large scale production of hydrazine, the intermediacy of an oxaziridine could be clearly evidenced (81MI50800). In this process ammonia and hypochlorite are reacted in the presence of acetone to form ketazine (302). Nitrogen-nitrogen bond formation is faster by a factor of about 1000 in the presence of acetone than in its absence. Thus acetone does not merely trap hydrazine after formation, but participates in the N—N bond forming reaction. Very fast formation of oxaziridine (301), which is isolable, is followed by its likewise fast reaction with ammonia. 

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