Hydrazine urea process

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. 

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). 

Hoffman A process for making hydrazine by reacting urea and sodium hypochlorite in water ... 

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. 

Although the earlier processes for the commercial production of hydrazine used urea as a raw material, modem processes employ direct ammonia oxidation. In one such process, reactions occur in two steps ... 

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. 

Hydrazine is formed in a multitude of chemical reactions. Only a few processes have acquired commercial importance. These all oxidize ammonia or urea, an ammonia derivative, to hydrazine. Sodium hypochlorite or hydrogen peroxide is used as the oxidizing agent. Certain processes (Bayer-, H202-processes) operate in the presence of ketones. 

In this process a mixture of urea, sodium hypochlorite and sodium hydroxide is converted into hydrazine, sodium chloride and sodium carbonate. 

Preparation of t-butykmine. t-Butylurea, obtained from Eastman or Fisher or prepared from t-butanol, urea, and coned, sulfuric acid, is heated with phthalic anhydride to produce t-butylphthalimide, which is cleaved by refluxing with aqueous-alcoholic hydrazine to phthalhydrazidc and t-butylamine. After cooling, the mixture is made acid (HCI) and the heterocyclic product removed by filtration. Suitable processing of the filtrate affords pure t-butylamine hydrochloride. 

Derivation The preferred method is a two-step process (1) reaction of sodium hypochlorite and ammonia to yield chloramine (Nfi,Cl) and sodium hydroxide (2) reaction of chloramine, ammonia, and sodium hydroxide to yield hydrazine, sodium chloride, and water. Noteworthy is the need to carry out the reactions in the presence of such colloidal materials as gelatin, glue, or starch to prevent unwanted side reactions that would reduce the yield of hydrazine. An older method utilized the reaction of sodium hypochlorite or calcium hypochlorite with urea. 

Fig. 69. Schematic of the processes in an amperometric urea electrode based on the pH dependence of the anodic oxidation of hydrazine.

Thioacetamide, which is well established for the precipitation of ZnS in solutions, can be also used [68] in which case the films have been deposited from acidic solutions. The addition of urea has a beneficial effect on the adherence [68], Some attempts have been made to deposit ZnS by using thiosulfate-based solutions [16], As compared to CdS and PbS it appears that the deposition of ZnS films is not yet optimized and in addition presents some differences in the growth mechanism. This is illustrated by the lower activation energy values ( 20 kJ.rnol" ) which has been determined in the ammonia-thiourea-hydrazine process, which is more likely characteristic of a diffusion limited growth [69]. The deposition of indium sulfide has been also reported in acidic solutions using TA [52], along with a detailed study of the influence of the deposition conditions on the structural and optical properties of the films. 

Liquid explosives have different volatilities, which varied the combustion processes. The important characteristic is the variation of reaction phase in the combustion reactions. Generally, because alkyl nitrates and some of alkene nitrates are highly volatile, their combustion reactions proceed in gas state. In contrast, the combustion reactions of nitroglycerine, azide nitrate ether, and aqueous hydrazine proceed in both gas and solid phases. The reactions of mercury fulminate and urea perchlorate mainly proceed in solid state. 

At temperatures below 1100 K the process fails, because the formation of the active NH2 radicals becomes too slow. At temperatures above 1400 K, NH3 is consumed without destroying a comparable amount of NO. The addition of H2 or H2O2 shifts the effective temperature window to lower temperatures due to a more efficient NH2 production at low temperatures, but at high temperatures the NH3 destruction is accelerated, thus the width of the temperature window is not changed significantly [33]. Also, other NH2 precursor molecules like urea, (NH2)2C0, or hydrazine, N2H4, can be injected [42]. 

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