Dehydration of hydrazine by azeotropic distillation

Abstract

A process was developed for dehydrating aqueous solutions of hydrazine by azeotropic distillation with aniline as an entrainer. The ternary system hydrazinewater-aniline, which contains the minimum-boiling aniline-water azeotrope and the maximum-boiling hydrazine-water azeotrope, was studied by fractionation analysis to determine the position of the ridge or distillation barrier in the vapor and liquid surface. The studies showed that the position and curvature of this ridge were favorable for the production, by rectification, of a solution richer in hydrazine than the azeotropic proportions. The process comprised three operations. Approximately 70% of the hydrazine charged to the system was dehydrated.Entrainers that form binary minimum-boiling azeotropes with both hydrazine and water are discussed. Ternary systems with these entrainers have saddlepoint azeotropes that boil intermediate with respect to the other invariant components in the system.Hydrazine is currently being produced by modifications of the German Raschig process, in which it is obtained in a low-concentration ( 1 to 3 % ) aqueous solution (1). Because of the maximum-boiling hydrazine-water azeotrope, sometimes called hydrazine hydrate, conventional distillation methods cannot be used to concentrate this solution to more than about 70 wt. % hydrazine and 30% water. ( 6 ) . In the past, anhydrous hydrazine has been produced chemically through ithe formation of inorganic or organic derivatives which must be subjected to further treatment to yield the dehydrated product ( 2 ) . Since these methods are costly, exploratory work was undertaken t o determine whether an aqueous hydrazine solution could be dehydrated by distilling the solution in the presence of a third component that formed a minimumboiling azeotrope with water. Of t h e numerous materials tested initially, aniline was the first to show real promise as an effective entrainer, and the process described is based on its use. THE HYDRAZINE-WATER-ANILINE SYSTEMThe ternary system hydrazinewater-aniline was studied by fractionation analysis t o determine the principal features of the vaporliquid equilibrium surfaces. The basic principle of this method is t h a t when an invariant component, i.e., a pure compound or azeotrope, is distilled from a mixture, the composition of the remaining solution moves rectilinearly in the opposite direction from the invariant component. This method was used by Ewe11 and Welch ( 3 ) for studying ternary systems with binary azeotropes, and by Lecat(4) for determining the composition of azeotropes in binary systems. The Todd precise fractionation assembly was used for the present analysis.The Todd fractionating column consisted of a 1/2-in. glass column packed %-in. high with 1116411. glass helices. The pot had an opening for a standard-taper thermometer and one for the entrance of nitrogen. All the vapors were condensed in the column head and the reffux was varied by adjusting a valve on the take-off line. Rubber tubing connecting the receiver vent to a bubbler ...

From the dilute solution to the pure compound: Extraction strategy based on a multi-stage process of phase separation

“…Detailed investigations of the vapour pressurecomposition measurements in aqueous hydrazine solutions have been published [21][22][23][24][25]. At atmospheric pressure, this system shows the specific existence of an azeotropic mixture containing around 70 w% of N 2 H 4 , and its boiling point is near 120 °C, higher than those of water and hydrazine [13,15].…”

“…Concentration beyond 70 w% of hydrazine can be achieved by azeotropic distillation with an auxiliary compound that forms an azeotrope with water which boils at a temperature different from that of hydrazine. Aniline and toluene are well suited for this purpose, and several processes have been described [23]. However, depending on the distillation conditions, up to 1% of organic compounds may remain in the hydrazine produced and corrupt the catalytic decomposition of the propellant.…”

“…Liquid-vapour equilibria of the water-hydrazine binary system under atmospheric pressure (composition expressed in molar fraction of N 2 H 4 ; ◇□, experimental data[21][22][23][24][25] ; -, calculated curves).…”

Entrainer Selection and Systematic Design of Heterogeneous Azeotropic Distillation Flowsheets

“…Therefore, the main task becomes SN1−SN2 and boundary crossing becomes necessary. Nevertheless, if a sufficiently curved boundary is found, feasible distillation flowsheets can be devised, as shown by Wilson et al., who used aniline as entrainer to split a mixture of hydrazine + water.

3 Catalog of the location of the main separation task in different RCM topologies.

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Role of aniline in destructing the 1-propanol + toluene azeotrope

“…To achieve the separation and required degree of purity, many techniques such as extractive distillation and azeotropic distillations are widely used in which the systems are often multi component mixtures. In this respect aniline is the popular and desirable extractive solvent used in many instances [1,2]. The value of relative volatility almost equals to one and/or the degree of dissimilarity in the component molecules is normally considered for the chances of azeotropic formation [3].…”