Hydrazine Raschig process

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 ... 

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). 

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. 

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... 

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. 

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. 

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. 

Raschig process -for hydrazine [HYDRAZINE AND ITS DERIVATIVES] (Vol 13) -for hydrazine [HYDRAZINE AND ITS DERIVATIVES] (Vol 13)... 

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). 

Because the decomposition rates are relatively insensitive to temperature, Eq. (18.3) is operated at 130°C to 150°C and 3.0 MPa132 to speed up the ratedetermining step. Excess ammonia, at a ratio of 40 1, is used to minimize the hydrazine-chlorine decomposition. Synthesis efficiency favors a dilute system although the increase in operating cost due to the low concentration may ultimately become inhibiting. The Raschig process is shown in Figure 18.1132. 

The Raschig process can also be used to react amines with chloramine to make monosubstituted or unsymmetrical disubstituted hydrazines. 

Figure 18.1. Raschig Process for Hydrazine Production. (Reproduced by permission of Wiley-VCH)...

As in the Raschig process, aqueous caustic reacts with chlorine to make sodium hypochlorite solution. The urea solution is prepared by dissolving urea in water with the addition of steam to provide the heat needed for the endothermic dissolution. The temperature is kept at about 5°C for 43 percent urea solution. Glue is added at a ratio of 0.5g/Uter of solution to inhibit side reactions. The urea and hypochlorite solutions are added to the hydrazine reactor at a ratio of 1 4, and the reaction temperature is allowed to rise to 100°C. The crude product contains approximately 35 g N2H4/liter and can be refined in the same steps as used for the Raschig process. 

Raschig/Olin Process. The Raschig/Olin process is used to make anhydrous hydrazine. In this process Reactions (22-67) through (22-69) also occur. However the refining area has a different design from the Raschig process. Additional details are given in Reference 132. 

Fig. 22.26. Raschig process for hydrazine production. (Courtesy of Wiley-VCH. Schirmann, J.P, in Ullmann s Encyclopedia of Industrial Chemistry, Vol. A13, pp. 177-190, Reinhold Publishing, New York, 1996.)...

The primary synthesis of hydrazine is the Raschig process, and the first step in the process leads to chloramine, NH2C1 ... 

Hydrazine is currently prepared via a plethora of methods, the most popular of which is the Raschig process, which involves controlled hypochlorite oxidation leading to hydrazine formation. The Raschig process suffers from the formation of a stoichiometric quantity of sodium chloride by-product. The Bayer Ketazine process employs acetone to trap the hydrazine as dimethyl-ketazine. The acetone is re-cycled but sodium chloride is again formed. 

For a long time, the Raschig process, which was discovered in 1907, was used for the production of hydrazine. Here, ammonia is oxidized with sodium hypochlorite in alkahne solution (pH = 8 11). In the initial rapid reaction, (55) sodium hypochlorite reacts with ammonia, forming chloramine. Chloramine then reacts with ammonia in a slower second reaction. ... 

In anhydrous systems, the low hydrazine concentration is avoided. Chlorine and ammonia can react in the gas phase to form chloramine, which then reacts with ammonia to form hydrazine. As in the Raschig process, the reaction (57) of chloramine with hydrazine limits the yields. Substituted hydrazines can be prepared using this process with the appropriate substituted amines. 

The overall eqnation of the reaction of chloramine with hydrazine is as follows (Raschig process, see Section 5.2.1) ... 

The amination of ammonia with chloramine to form hydrazine is an example of this mechanism (Raschig process) ... 

The formation of azine is not a means of trapping the hydrazine formed in the Raschig process with acetone, the reaction proceeding by way of two distinct intermediates dimethyl oxazirane and acetone hydrazone, as follows ... 

Sodium hypochlorite solution (ca. 1.5 mol/L), ammonia and acetone in a molar ratio of 1 15 to 20 2 are reacted together at 35°C. A solution results consisting of 5 to 7% by weight of acetone azine together with sodium chloride and excess ammonia. This ammonia is distilled off and returned to the reaction. Next, the acetone azine-water-azeotrope (b.p. 95°C) is distilled off leaving the sodium chloride solution. Herein lies the essential difference from the Raschig process in which the hydrazine water mixture has to be separated from solid sodium chloride. 

For most uses, hydrazine is produced as hydrazine hydrate in a formulation with water. The hydrate may be produced commercially by three methods the Raschig process, the ketazine process, and the peroxide process. The Raschig process, the original commercial production process for hydrazine, involves oxidation of ammonia to chloramine with sodium hypochlorite, then further reaction of the chloramine with excess ammonia and sodium hydroxide to produce an aqueous solution of hydrazine with sodium chloride as a by-product. Fractional distillation of the product yields hydrazine hydrate solutions. Currently, most hydrazine is produced by the ketazine process, which is a variation of the Raschig process. Ammonia is oxidized by chlorine or chloramine in the presence of an aliphatic ketone, usually acetone. The resulting ketazine is then hydrolyzed to hydrazine. In the peroxide process, hydrogen peroxide is used to oxidize ammonia in the presence of a ketone. Anhydrous hydrazine is the formulation used in rocket fuels and is produced by dehydration of the hydrate by azeotropic distillation with aniline as an auxiliary fluid (Budavari et al. 1989 lARC 1974 Schmidt 1988 WHO 1987). 

It has now been discovered that the stability of concentrated hydrazine, particularly as prepared by the Raschig process and its corrosiveness to metals are associated with a property most simply explained as its potential acidity which can be neutralised, treating the hydrazine as the dissociating medium or solvent, by the addition of certain substances which are weakly basic and which are non-reactive with hydrazine. 

In the commercial production of hydrazine by the Raschig process, a large excess of ammonium hydroxide and fresh sodium hypochlorite are first reacted to make chloramine. Chloramine is then converted to crude hydrazine by rapid heating. The reactor effluent, containing about 2.5 wt% of hydrazine, is stripped of unreacted ammonia. The hydrazine solution is then concentrated... 

The drawbacks of the Raschig process include a large amount of byproduct chlorides (i.e., six times more than the product hydrazine). Further, both chloramine and hydrazine are unstable at higher concentrations. They decompose to nitrogen and ammonium chloride. 

The reaction between diaziridine and additional ketone produces azine, which is hydrolyzed to form hydrazine with the regeneration of ketone. There are two improvements over the Raschig process, namely, 1) use of ketone as a nitrogen carrier and 2) stabilizing the N-N bond of hydrazine. 

Hydrazine is obtained from the Raschig process as the monohydrate and is used in this form for many purposes. Dehydration is difficult, and direct methods to produce anhydrous N2H4 include reaction 14.33. 

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