Aniline azeotropes

A key feature of the Halcon process is the use of low pressure distillation (less than 80 kPa = 12 psi) to break the phenol-aniline azeotrope and allow economical separation of aniline from phenol (67). 

A mixture of cyclohexane bp 80.8 "C) and benzene hp 80.1 "C) can, for example, be separated by distillation after adding aniline, since the interaction between benzene and aniline is greater than that between cyclohexane and aniline. Azeotropic mixtures can be separated similarly by extractive distillation (e.g.. water-ethanol by adding glycerol). Hydrocarbons with similar boiling points can be separated by extractive distillation in the presence of polar liquids (nitrobenzene, phenol, furfurol). 

Anhydrous hydrazine, required for propellant appHcations and some chemical syntheses, is made by breaking the hydrazine—water azeotrope with aniline. The bottom stream from the hydrate column (Fig. 4) is fed along with aniline to the azeotrope column. The overhead aniline—water vapor condenses and phase separates. The lower aniline layer returns to the column as reflux. The water layer, contaminated with a small amount of aniline and hydrazine, flows to a biological treatment pond. The bottoms from the azeotrope column consist of aniline and hydrazine. These are separated in the final hydrazine column to give an anhydrous overhead the aniline from the bottom is recycled to the azeotrope column. 

Acetone-methanol Minimum-hoiling azeotrope Water, aniline, ethylene glycol ... 

Although less common, azeotropic mixtures are known which have higher boiling points than their components. These include water with most of the mineral acids (hydrofluoric, hydrochloric, hydrobromic, perchloric, nitric and sulfuric) and formic acid. Other examples are acetic acid-pyridine, acetone-chloroform, aniline-phenol, and chloroform-methyl acetate. 

In the manufacture of aniline from nitrobenzene the reactor products are condensed and separated into an aqueous and organic phases in a decanter. The organic phase is fed to a striping column to recover the aniline. Aniline and water form an azeotrope, composition 0.96 mol fraction aniline. For the feed composition given below, make a mass balance round the column and determine the stream compositions and flow-rates. Take as the basis for the balance 100 kg/h feed and a 99.9 percentage recovery of the aniline in the overhead product. Assume that the nitrobenzene leaves with the water stream from the base of the column. 

The refining area has five steps 1) ammonia removal, 2) NaCl concentration and removal, 3) hydrazine-water distillation to reach azeotropic concentration, 4) extractive distillation with aniline to break the azeotrope and 5) distillation to separate hydrazine from aniline. Sometimes 50% caustic replaces aniline in the extractive distillation. If ultra pure hydrazine is needed, freeze crystallization is used to remove the supernatant fluid. Assays between 99.5% and 99.99% have been achieved. 

Reaction step I is conveniently carried out in a stainless steel reactor using a hydrocarbon solvent to expel water of the reaction as an azeotrope. Completion of the reaction can be determined by measuring the water of reaction or through disappearance of both the 2-ethyl-6-methyl aniline and methoxyacetone by gas chromatography (GC) or high performance liquid chromatography (HPLC). 

Benzene-cyclohexane Minimum-boiling azeotrope Aniline ... 

Heptane isomers-toluene Close-boiling and minimumboiling azeotropes Aniline, phenol ... 

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). 

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