Claims:1. A method for making solid hydroxylamine nitrate comprising,
Reacting an acid salt of hydroxylamine with a metal salts in an organic solvent medium, getting a by-product from the reaction , removing the by-product by method selected from distillation or filtration , recovering the hydroxylamine nitrate salt by method selected from filtration or distillation at a temperature between 25 ° centigrade to 50 ° centigrade,
wherein said hydroxylamine salt is selected from the group consisting of hydrochlorides, sulphates, phosphates, nitrates, borates, nitrites, phosphates, hydrogen phosphates, sulphites,
wherein said metal salt is selected from the group consisting of zinc chloride, zinc nitrate, lead nitrate, lead chloride, lead sulphate, thallium nitrate, thallium chloride, thallium sulphate, silver chloride, silver nitrate, silver sulphate, mercury nitrate, mercury chloride, mercury nitrate, antimony nitrate, antimony fluoride, nickel nitrate, nickel chloride, nickel sulphate ,cadmium nitrate, cadmium chloride, cadmium sulphates chromium nitrate, manganese nitrate, manganese sulphate and manganese chloride, wherein said solvent is selected from ethanol, methanol, dichloromethane, diethyl ether, ethyl acetate, hexane, heptanes, isopropanol, n-butanol, isobutanol , methyl acetate and methyl tertiary butyl ether, wherein the hydroxylamine nitrate obtained has a purity of at least 99.99% and wherein the hydroxylamine nitrate does not contain any species selected from metal ions, ammonium salts and nitric acid.
, Description:FIELD OF THE INVENTION
The invention is related to inorganic synthesis techniques and more particularly to the synthesis of hydroxylamine energetic oxidiser salts at ambient temperature without any metal ion, nitric acid, ammonium nitrate impurity.

BACKGROUND OF THE INVENTION
Hydroxylamine nitrate is a salt of hydroxylamine which is used as a reducing agent, in the recovery of spent nuclear fuel, as a reagent for preparing various industrial, speciality and pharmaceutical chemicals, in photographic applications, gas generators, composite propellants etc. Currently hydroxylamine nitrate is explored as monopropellant in space applications which has a potential to replace hydrazine. HAN required for space applications should be highly concentrated, pure without any impurities like metal ion, nitric acid and ammonium nitrate.
Commercially available solution of HAN is very dilute, oftentimes being shipped in inert containers at a maximum concentration of 24%.
Various methods for preparing HAN have been proposed over the years .These processes suffers from various drawback from a commercial safety and /or technical perspective.
Hydroxylamine nitrate were traditionally made by the reaction of free hydroxylamine base with nitric acid in the presence of a noble metal catalyst in an acidic medium . US PATENTS (2827363, 2823101, 3406011, 3649170, 3767758, 3856924) are related to methods that involve the use of NOX compounds which are difficult to handle especially since the reaction is carried out in an acidic medium, HAN prepared by this method was contaminated with excess nitric acid which is known to affect thermal stability of HAN. Also ammonium nitrate was produced as a side product. All these methods produces HAN which are dilute aqueous solutions and require further distillation to get the concentrated product. The water from such an aqueous solutions of HAN becomes more difficult to remove as the HAN concentration increases and becomes dangerous. This requires ever increasing vacuum and temperature conditions to complete the extraction process. These operating conditions makes any processing plant vulnerable to an accident .Also, the process is difficult, expensive and dangerous.
US 4066736 and US 5182092 deal with a methods of preparing hydroxylamine nitrate and involve the reaction between aqueous metal nitrate salt mainly sodium, potassium, ammonium, calcium or barium nitrate salts with aqueous hydroxylamine sulphate salt. These methods also produce very dilute solutions of HAN which require further time and energy consuming hazardous distillation process. Also, the water soluble impurities like metal ions can interfere with the thermal stability of hydroxylamine nitrate.
OBJECT OF THE INVENTION
It is an objective of the present invention to provide a safe process for the synthesis of solid HAN.
It is another objective of the present invention to provide a process for the synthesis of solid HAN at room temperature without involving any heating and expensive cooling systems.
It is also an objective of the present invention to provide a process which does not involve high temperature distillation.
It is a further objective of the present invention that does not involve the use of expensive cooling systems.
It is another objective of the present invention to produce HAN without any metal ion destabilizers.
It is further an objective of the present invention to produce HAN free of nitric acid impurity.
Another aspect of the present invention is to produce HAN without ammonium nitrate impurity.
In another feature, the present invention produces HAN without any metal ion, nitric acid, or ammonium nitrate impurity.
Another feature of the present invention is a method for the room temperature synthesis of solid HAN.
STATEMENT OF INVENTION
According to this invention there is provided a process for making solid hydroxylamine nitrate by the reaction between a hydroxylamine salt selected from hydrochlorides, sulphates, phosphates, nitrates, borates, nitrites, phosphates, hydrogen phosphates, sulphites and the like is reacted with a solvent solution of a metal salt selected from zinc chloride, zinc nitrate, lead nitrate, lead chloride, lead sulphate, thallium nitrate, thallium chloride, thallium sulphate, silver chloride, silver nitrate, silver sulphate, mercury nitrate, mercury chloride, mercury nitrate, antimony nitrate, antimony fluoride, nickel nitrate, nickel chloride , nickel sulphate ,cadmium nitrate, cadmium chloride, cadmium sulphates chromium nitrate, manganese nitrate, manganese sulphate and manganese chloride and the like. The reaction takes place in an organic medium at room temperature without any heating and cooling procedures involved. The by-product formed is separated by process selected from filtration or distillation. Solid hydroxylamine nitrate is recovered by process selected from filtration and distillation. The reaction can also be carried out in aqueous media and in mixtures of aqueous and solvent systems.
SUMMARY OF THE INVENTION
The present invention relates to a process for the production of hydroxyl ammonium nitrate. More particularly, the present invention relates to an improved process for the production of hydroxyl ammonium nitrate by combining the reactants in the presence of an organic solvent. Accordingly the present invention provides an improved method for the production of hydroxyl ammonium nitrate. In this process a hydroxyl ammonium salt is reacted with a solvent solution of a metal salt selected from zinc chloride, zinc nitrate, lead nitrate, lead chloride, lead sulphate, thallium nitrate, thallium chloride, thallium sulphate, silver chloride, silver nitrate, silver sulphate, mercury nitrate, mercury chloride, mercury nitrate, antimony nitrate, antimony fluoride, nickel nitrate, nickel chloride, nickel sulphate, cadmium nitrate, cadmium chloride, cadmium sulphates, chromium nitrate, manganese nitrate, manganese sulphate and manganese chloride and the like. Thus the invention is related to a method for making solid hydroxylamine nitrate and comprises reacting an acid salt of hydroxylamine with a metal salts in an organic solvent medium getting a by-product from the reaction, removing the by-product by a method selected from filtration and distillation, recovering the hydroxylamine nitrate salt by a method selected from distillation, filtration and counter current extraction at a temperature between about 25 °C and about 50 ° C.
Solvents used in the method maybe selected from ethanol, methanol, dichloromethane, diethyl ether, ethyl acetate, hexane, heptanes, isopropanol, n-butanol, isobutanol, methyl acetate and methyl tertiary butyl ether, Butanol, ether, diethyl ether, lower ethers, lower alcohols and mixture thereof, are example of more organic solvents. Butanol refers to n-butyl alcohol, sec-butyl alcohol, and isobutyl alcohol. The reaction can also be carried out in aqueous media and in mixtures of water and solvent systems. Examples of mixtures of solvent-water systems are alcohol water systems. Other co solvent systems may be used.
The hydroxylamine nitrate is recovered from the organic solvent medium by an appropriate method like distillation, filtration or counter current extraction .Any organic soluble impurities from the raw materials can be removed by treatment with activated carbon.
The hydroxylamine nitrate obtained has a purity of at least 99.99% and does not contain any species selected from metal ions, ammonium salts and nitric acid. The method is safe and does not lead to exothermic or explosive reactions. The reaction may be carried out at a temperature between 25 – 35 ° Celsius temperature, more preferably between 20ºC to 30 ºC.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1. Shows the FTIR spectrum of hydroxylammonium nitrate. The accessory used for FTIR analysis is ATR peak.
Fig 2. Shows the Raman spectrum of hydroxylamine nitrate.
Fig 3. Shows the DSC trace of hydroxylamine nitrate.
Fig4a. Shows the DTA trace of 90% HAN prepared by neutralisation method and 90% HAN prepared by proposed method by double decomposition reaction in an organic solvent.
Fig4b Shows the TGA curves of 90% HAN prepared by neutralisation method and 90% HAN prepared by proposed method by double decomposition reaction in an organic solvent.
Fig.5 Shows the schematic of a batch reactor.
Fig 6a. Shows the dP (extent of reaction) and dP/dT (rate of reaction) values of the 90% hydroxylamine nitrate at 100 degree centigrade in a batch reactor (simulation of space thruster) prepared from neutralisation of 50% hydroxylamine with 70% nitric acid at low temperature.
Fig 6b. Shows the dP (extent of reaction) and dP/dT (rate of reaction) values of the 80% hydroxylamine nitrate at 100 degree centigrade in a batch reactor (simulation of space thruster) prepared from our proposed method by double decomposition reaction in an organic solvent.
The IR and Raman spectra of the samples are shown in Fig. 1 & 2 respectively. The spectral bands observed in FTIR and RAMAN are in agreement with the reported literature values. The peaks- 1300, 1400, 727, 830, 1050cm-1 corresponds to nitrate ion concentration and the bands-1179, 1512, 2720, 2955, 3150, 1007cm-1 corresponds to hydroxylammonium ion concentration. Peaks corresponding to water content of the HAN samples are 3000-3750, 1655 cm-1.The band corresponding to frequencies 1300 cm-1 and 1179 cm-1 are concentration dependant whereas the bands corresponding to frequencies 1050 cm-1 and 1007 cm-1 are found independent of HAN concentration. In Raman spectra nitrate ion band at 1048cm-1 is prominent when compared to FTIR peak, also the hydroxylammonium cation band at 1007cm-1 weak in FTIR is detected in Raman.
DSC (fig. 3) The heat of fusion of the material is in agreement with the reported literature value.
Monopropellant Decomposition Studies -The monopropellant decomposition was followed using thermal analyzer and constant volume batch reactor. Thermal analysis studies were carried out using Perkin Elmer STA 6000 thermal analyzer. 10 mg of sample is heated at a rate of 10oC/min in flowing nitrogen atmosphere. DTA-TGA analysis gives information on onset temperature of decomposition, % weight loss, rate of decomposition and energy released during decomposition. (Fig 4a and 4b)

The onset of decomposition of 90% HAN prepared by neutralization method is 149°C and the onset of decomposition of 90% HAN prepared by proposed method is 147°C which is almost similar for two different HAN prepared by different methods. (Fig 4a) .Also the slope of weight loss curve is more or less similar for HAN prepared by neutralization method and HAN prepared by proposed method. (Fig 4b).

In a constant volume batch reactor [8] 200 micro liters of HAN solution was injected through a syringe infusion pump into a chamber preheated to fixed temperature. The pressure and the temperature rise inside the chamber are recorded against time. A schematic of the batch reactor is shown in Fig. 5.

Batch reactor analysis gives information on rate of decomposition by following the rate of pressure rise when HAN is injected into a preheated chamber. This isothermal decomposition simulates a realistic condition and isolates the thermal history of the sample unlike in a conventional thermal analysis technique
Solid HAN was diluted to 80%. In a constant volume batch reactor 200 micro litre of HAN solution was injected through a syringe infusion pump to the reactor chamber which was preheated to 100 degree centigrade .The pressure and the temperature on decomposition was recorded as a function of time .Batch reactor studies gives information on extent of decomposition (?P) and rate of decomposition (?P/?T) which shows the performance of the monopropellant.
Fig 6a represents the ?P and ?P/?T values of 90% HAN at 100°C prepared by neutralisation method ( titration of 50% free hydroxylamine base with 70 % nitric acid at sub ambient temperature) and Fig 6b represents the ?P and ?P/?T values of 80% HAN at 100°C prepared by proposed method (double decomposition between a stable salt of hydroxylamine and organic solution of a metal nitrate salt at room temperature).It is evident from the data that the performance of 80% HAN prepared by proposed method is far more better(higher ?P and higher ?P/?T values) than 90% HAN prepared by neutralisation method at the same temperature in a batch reactor.
EXAMPLES
The present invention is illustrated with the help of the following examples, which are not intended to limit the scope of the invention and any modifications falls within the scope of this invention.
1. 25 g of zinc nitrate is dissolved in 100 ml 7:3 ethanol/methanol mixture in a round bottom flask equipped with nitrogen, thermometer and dropping funnel. The reaction mass is stirred for 1 hour to ensure complete dissolution of zinc nitrate. 18.3486 g of hydroxylamine hydrochloride is dissolved in 100 ml methanol , this solution is added to the solution of zinc nitrate through a dropping funnel .The reaction between zinc nitrate and hydroxylamine hydrochloride is instantaneous at room temperature and the reaction goes to completion within few minutes. HAN precipitate formed is easily separated by centrifugation followed by filtration .Then the filtrate is distilled at room temperature to retrieve solvent which can be reused for the next batch.

2. 25 g of silver nitrate is dissolved in 500 ml ether in a round bottom flask equipped with nitrogen, thermometer and dropping funnel. The reaction mass is stirred for 3 hour to ensure complete dissolution of silver nitrate. 12.078 g of hydroxylamine sulphate is dissolved in 100 ml ether , this solution is added to the solution of silver nitrate through a dropping funnel .The reaction between silver nitrate and hydroxylamine sulphate is instantaneous at room temperature and the reaction goes to completion within few minutes. HAN precipitate formed is easily separated by centrifugation followed by filtration .Then the filtrate is distilled at room temperature to retrieve solvent. Etherate distillate can be reused for the next batch.

3. 25 g of lead nitrate is dissolved in 500 ml ether in a round bottom flask equipped with nitrogen, thermometer and dropping funnel. The reaction mass is stirred for 2 hour to ensure complete dissolution of lead nitrate. 10.4906 g of hydroxylamine hydrochloride is dissolved in 100 ml ether , this solution is added to the solution of lead nitrate through a dropping funnel .The reaction between lead nitrate and hydroxylamine hydrochloride is instantaneous at room temperature and the reaction goes to completion within few minutes. Lead chloride precipitate formed is easily separated by centrifugation followed by filtration .Then the filtrate is distilled at room temperature to retrieve solid HAN. Etherate distillate can be reused for the next batch.

4. 25 g of chromium nitrate is dissolved in 100 ml methanol in a round bottom flask equipped with nitrogen, thermometer and dropping funnel. The reaction mass is stirred for 1 hour to ensure complete dissolution of chromium nitrate. 15.38 g of hydroxylamine sulphate is dissolved in 100 ml methanol , this solution is added to the solution of chromium nitrate through a dropping funnel .The reaction between chromium nitrate and hydroxylamine sulphate is instantaneous at room temperature and the reaction goes to completion within few minutes. HAN precipitate formed is easily separated by centrifugation followed by filtration .Then the filtrate is distilled at room temperature to retrieve solvent which can be reused for the next batch.