FIELD OF THE INVENTION

The present invention relates to an improved method for production of concentrated aqueous solutions of hydrazine hydrate using recyclable solid activator for ketazine formation and catalyst free ketazine hydrolysis.

BACKGROUND OF THE INVENTION

Hydrazine hydrate (N2H4.H2O), a colorless liquid having an ammonical odor, is the simplest diamine and unique in its class because of the N—N bond. It was first prepared in 1887 by Curtius from diazo acetic ester. In 1893 Thiele suggested that the oxidation of ammonia with hypochlorite should yield hydrazine hydrate and in 1906 Raschig demonstrated this process, variations of which constitute the chief commercial methods of manufacture in the 1990's. It is a mild base that is miscible in polar solvents such as water, ammonia, amines and alcohols.

During the past fifty years hydrazine hydrate has emerged from an interesting curiosity to a chemical manufactured in tons. Hydrazine hydrate has been known since 1863, and in 1875 Emil Fischer prepared and characterized the aryl compounds of hydrazine hydrate. It was in 1887 Curtius succeeded in isolating hydrazine hydrate itself by the action of alkali on diazo acetic ester.

Raschig, following a suggestion by Thiele, showed that hydrazine hydrate could be produced by the action of sodium hypochlorite on aqueous ammonia, the yield being greater in presence of excess ammonia. Raschig found that 60-70% yields of hydrazine hydrate could be obtained in the presence of glue or gelatin and attributed this effect to the increased viscosity of the solution. Joyner showed that increasing the ammonia:hypochlorite ratio increased the yield of hydrazine hydrate and the yield was proportional to the amount of glue added when this was present in small amounts. The manufacture of hydrazine hydrate by a similar procedure from urea instead of ammonia was patented about this time, yields reported being 70%.

The discovery that hydrazine hydrate containing 15% methanol could be employed as a rocket fuel when mixed with oxidizing agents such as nitric acid, hydrogen peroxide or oxygen, stimulated the expansion of production of hydrazine hydrate in Germany during the Second World War.

The direct fixation of nitrogen and hydrogen to hydrazine is thermodynamically unfavorable. Instead the commercially feasible process involves partial oxidation of ammonia (or urea) using hypochlorite or hydrogen peroxide. Bayer first commercialized such a process, using acetone and hypochlorite as oxidant. Another process developed by Produits Chimiques Ugine Kuhlmann (PCUK) and practiced by Atofina (France) and Mitsubishi Gas (Japan) involves the oxidation of ammonia by hydrogen peroxide in presence of butanone and another component that apparently functions as an oxygen-transfer agent. Oxidation of Benzophenone imine also received much attention, but is not commercially used.

The first large scale use of hydrazine hydrate was as a fuel for powering the rocket, a German ME-163 fighter plane during the World War II. Production in the United States began in 1953 at the Lake Charles, La. plant of the Olin Corporation (now Arch Chemicals) a facility then having a capacity of 2040 metric tons. In 2004, world capacity is approximately 462100 metric tons, reported as N2H4. Most of this is in the form of hydrazine hydrate. Hydrazine hydrate and its simple methyl and dimethyl derivatives have endothermic heats of formation and high heats of combustion. Hence, these compounds are used as rocket fuels. Other derivatives are used as gas generators and explosives. Hydrazine, a base slightly weaker than ammonia forms a series of useful salts. As a strong reducing agent, Hydrazine hydrate is used for corrosion control in boilers and hot water heating system; also for metal plating, reduction of noble-metals catalysts, and hydrogenation of unsaturated bonds in organic compounds.

Hydrazine hydrate is also an oxidizing agent under suitable conditions. Having two active nucleophilic nitrogen and four replaceable hydrogen, hydrazine is the starting material for many derivatives. Some among them are, as a foaming agent for plastics application, in manufacture of antioxidants, polymers, polymer cross-linkers and chain extenders, as well as in fungicides, herbicides, plant growth regulators and pharmaceuticals. Hydrazine hydrate is also a good ligand; numerous complexes have been studied. Many heterocyclics are based on hydrazine, where the rings contain from one to four nitrogen atoms as well as other heteroatoms. The many advantageous properties of hydrazine hydrate continued its commercial utility. Hydrazine is produced commercially, primarily as an aqueous solution (which is known as hydrazine hydrate) typically in varying % by weight of hydrazine hydrate. The following references serve as the prior-art for the preparation of hydrazine hydrate by various approaches.

U.S. Pat. Nos. 4,189,411; 3,972,878; 3,972,876; 4,093,656; 3,948,902; 6,562,311; 6,482,383; 6,605,265; 5,986,134; EP70155; CN100526237; U.S. Pat. Nos. 4,724,133; 4,725,421; GB1164460; FR1315348; GB1174050; GB1211547; U.S. Pat. No. 3,607,041; FR1506943; and Kirk Othmer, 3rdedition, 12, 734-755; Journal of American Chemical Society, 1929, 51, 3394-3409; Ullmann's encyclopedia of industrial chemistry, 1989, A13, 182-183.

Though, several of these methods are practical at laboratory level, only some of them are useful at industrial production. Most of these reported methods are difficult to be practiced at the industrial production due to one or more of the following factors: (a) stringent monitoring of the working solutions; (b) catalyst solutions with varied ranges; (c) low reaction yield due to difficulties in impurity removal; (d) operationally difficult reaction conditions/parameters; (e) catalytic hydrolysis of ketazine to give hydrazine hydrate; (f) high energy requirements.

Objective of the Invention

In view of the limitations in the prior art, the main objective of the present invention is to provide an efficient process for the production of concentrated aqueous solutions of hydrazine hydrate.

Another objective of the present invention is to provide a process for production of hydrazine hydrate, using solid acetamide as the recoverable catalyst for ketazine formation and catalyst free hydrolysis of ketazine to give aqueous solutions of hydrazine hydrate.

Another objective of the present invention is to provide a process which involves catalyst free hydrolysis of ketazine to give hydrazine hydrate with lower volume ratio of water to ketazine (1:1.5), unlike the known methods, where a catalyst and higher water volume ratio is required for hydrolysis.

Yet another objective of the present invention is to provide a method for hydrazine hydrate production, where all unreacted and excess substrates are recoverable and reusable making it a highly energy efficient, clean and eco-friendly process.

SUMMARY OF THE INVENTION

Aiming at the defects and limitations in the prior-art, we have developed a new and highly effective, industrially simple and economically viable process for the production of hydrazine hydrate. Briefly, the present invention features improved process for production of concentrated aqueous solutions of hydrazine hydrates, comprising:

(a) reacting hydrogen peroxide, ammonia, and ketone to form an azine in presence of an activator;

(b) separating the resulting mixture from step (a) into a ketazine layer and a aqueous solution layer;

(c) concentration of ketazine and recovery of methyl ethyl ketone by evaporation;

(d) purification of ketazine by vacuum distillation;

(e) recovery of acetamide from aqueous layer by dehydration;

(f) then returning the recovered methyl ethyl ketone and acetamide to step (a);

(g) hydrolysis of the ketazine to obtain hydrazine hydrate and regenerating the methyl ethyl ketone;

(h) and recycling the methyl ethyl ketone to the stage (a),

(i) concentration of hydrazine hydrate obtained in stage (g) to obtain 40-80% of hydrazine hydrate.

In an embodiment of the present invention, the activator used for ketazine formation stage (a) is acetamide and ammonium acetate.

In another embodiment of the present invention, the acetamide used in stage (a) is a crystalline solid.

In another embodiment of the present invention, the acetamide recovered from dehydration stage (e) is further purified by centrifugation or filtration under vacuum to get crystalline solid.

In an embodiment of the present invention, the hydrogen peroxide is a 50 to 70 weight % H2O2solution.

In another embodiment of the present invention, the molar ratio of hydrogen peroxide:methyl ethyl ketone:and ammonia is 1:4:3.

In another embodiment of the present invention, the stage (a) is carried out at temperatures ranging of 0 to 60° C.

In another embodiment of the present invention, the stage (c) evaporation is carried out at temperatures ranging from 85 to 110° C.

In another embodiment of the present invention, the stage (d) vacuum distillation is carried out at temperatures ranging from 75 to 100° C., preferably between 80-90° C.

In another embodiment of the present invention, the volume ratio of ketazine:water in hydrolysis stage (g) is 18:12.

In another embodiment of the present invention, the hydrolysis stage (g) is carried out under a pressure ranging from 2 to 20 bars, preferably between 8 to 12 bars, and temperature ranging from 150 to 200° C., preferably between 175 to 200° C.

In another embodiment of the present invention, the stage (i) purification and concentration is carried out in one cycle.

The present process can be performed easily and is a very economic strategy which is most viable for industrial scale.

