Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF AMMONIA"

Abstract

An improved process for the preparation of ammonia by reducing electrochemically inorganic nitrate and/or nitrite laden waters/waste waters of neutral or basic pH in an electrochemical cell having stainless steel as cathode and an expanded precious triple metal oxide coated titanium as anode separated by a conventional cation-exchange membrane at -1.1 to -1.2 V placed in two compartment cell at a distance of 5mm from the cathode and the anode, allowing the solutions containing 1 to 30% (w/v) of sodium nitrate and sodium nitrite independently through the cathode compartment and deionized water through the anode compartment to flow under gravity at the rate of 5 to 10 ml/min; at temperature 10 to 50 °C; at current density 1 to 80 mA/cm2 for 1 to 6 h with a potential drop of 2 to 5 V across the two electrodes to obtain ammonia in aqueous solution form.

Full Text

The present invention relates to an improved process for the prepation ammonia. This is a simple technique for the electrolytic reduction of both inorganic nitrates and nitrites in industrial effluents and nitrate contaminated waters to ammonia using a two compartment membrane cell. Nitrate and nitrite are the two high valent compounds of fixed nitrogen which are biologically less important but carcinogens. Industries which are producing nitro compounds discharge the end liquor possessing with considerable amounts of inorganic nitrates and nitrites in to rivers and the sea as there is no alternative to it. Selective reduction of these oxides gives not only an important product ammonia which is an essential raw material for agriculture and chemical industry but it saves the fixed nitrogen from being lost to the universe. Moreover, the enrichment of these inorganic oxides in rivers and sea may slowly lead to the contamination of ground waters or water reservoirs which ultimately becomes a threat to the environment. Thus, the reduction of nitrate and nitrite ion levels in waters has of ut most industrial and biological importance. Nitrate ion is reduced physiologically in nature by dissimilatory method involving nitrate reductases. This method produces only ammonia with no free intermediates rather than nitrogen or nitrogen oxides (T. Brittain, R. Blackmore, C. Greenwood, A. J. Thomson, Eur. J. Biochem. 1992, 209, 793-802). The limitation of this natural methods is that it is a slow and leaky process. Nitrite ion is also reduced physiologically in nature by assimilatory method involving nitrite reductases. This method produces only ammonia with no free intermediates rather than nitrogen or nitrogen oxides (T. Brittain, R. Blackmore. C. Greenwood, A. J. Thomson, Eur. J. Biochem. 1992, 209, 793-802). However, this method is a slow and leaky process. Both, nitrate and nitrite are also converted physiologically in nature to nitrogen by denitrification or degradation method involving microorganisms. Nitric oxide (NO) and nitrogen oxide N2O are also produced in this method (W. J. Payne, Denitrification, John Wiley & Sons: New York, 1981; R. Knowies, Microbiol. Rev. 1982, 46, 43-70). The limitation of this methods is that it is very slow and leaky. Moreover, it releases N2O which is a greenhouse gas implicated in atmospheric ozone depletion, and cause about 30% loss in the total fixed nitrogen in a year. A. P. Murphy has reported (Nature, 1991, 350, 223-225) a chemical method for the reduction of trace quantities of nitrate ion in ground waters with aluminium powder in the pH range of 9.0 to 10.5. About 60 to 95% of ammonia was reported to be the principal product followed by nitrogen gas and nitrite depending on the experimental conditions. The main drawback of this method is that it requires an additional step to remove the dissolved aluminium and the alkali that is used to maintain the pH from the purified water. R. M. Carlsen (Anal. Chem. 1986, 58, 1590-91) has suggested a continuous flow method of reduction of nitrate ion to ammonia in an alkaline environment by activated granular zinc bed. The drawback of this method is that the nitrate containing water has to be made alkaline before the treatment is given. Moreover, the treated water requires an additional step to remove the zinc dissolved in and the alkali added to it. R. B. Mellon J. Ronnenberg, W. H. Campbell and S. Diekmann (Nature. 1992. 355. 717-719) have suggested a rapid and efficient method for the removal of nitrate and nitrite ions in potable waters catalyzed by immobilized enzymes in an electro-bioreactor. The reaction was driven by an electrical current of voltage > 1.28 V and resulted in the complete conversion of inorganic nitrates and nitrites to nitrogen without residues. This method works only in the presence of immobilized enzyme as catalyst over the electrode surface. J. H. Wang, B. C. Baltzis and G. A. Lewandowski (Biotechnol. Bioeng. 1995, 46, 159-171) have reduced the nitrate in laden water to nitrogen by biochemical methods using immobilized nitrate, nitrite and nitrous oxide reductase enzymes. This method is useful to treat dilute solutions of nitrate ion but slow as it is enzyme controlled catalytic reaction. K. Ogura and H. Ishikawa have electrolytically reduced the nitrite in the presence of nitrito complexes of iron chelates as catalysts (J. Chem. Soc. Faraday Trans. I. 1984, 80, 2243). Hydroxyl amine was obtained as the major product at low coulombic efficiency with low turnovers of the complex. The limitations of this method are that it has low coulombic efficiency and requires a catalyst. T. J. Meyer et. al. (J. Am. Chem. Soc., 1986, 108, 5876; Inorg. Chem. 1987, 26, 1746; J. Chem. Soc. Chem. Commun. 1985, 507) have electrolytically reduced the nitrite ion in small volumes with the help of a costly nitrito complexes of iron porphyrins. In this method, hydroxyl amine is produced as the major or one of the significant side products in a series of one-electron steps at low coulombic efficiency. The limitations of this method are that it requires a specially designed catalyst and a supporting electrolyte. Further, the coulombic efficiencies are very low. I. Taniguchi, N. Nakashima, K. Matsushita and K. Yasukouchi have used nickel and cobalt cyclams (J. Electroanal. Chem. 1987, 224, 199-209) as catalysts and reduced the nitrite electrolytically to hydroxyl amine as one of the major product. The major limitation of this method is that it is useful to treat small volumes of nitrite solutions. Moreover, the catalyst is costly and the coulombic efficiency of the system is low. Additionally, this method requires a supporting electrolyte to be added to large volumes of nitrite solution, and this makes the separation of the catalyst difficult. H. L. Li, W. C. Anderson, J. Q. Chambers and D. T David (Inorg. Chem. 1989, 28, 863-868) have electrolytically reduced the nitrate and the nitrite ions in concentrated sodium hydroxide solutions having low valent cobalt-cyclam species as catalysts. A mixture of hydroxyl amine and ammonia in the presence are reported to be obtained. The limitations of this method is that it requires cobalt-cyclam complex to catalyze the reaction and sodium hydroxide as electrolyte which later on complicates the separation of them from water. T. Taniguchi, N. Naka Shima and K. Yasukouchi (J. Chem. Soc. Chem. Commn. 1986, 1815-1815) have also reported the reduction of nitrate ion at a mercury electrode in alkaline solutions using cobalt(III) and Nickel(II)-cyclam complexes as catalysts. The limitations of this method are that it requires a metal complex to catalyze the reaction and an alkali as supporting electrolyte. Further it uses mercury as the cathode material which is generally not advisable as it is carcinogenic. J. E. Torn and F. C. Anson (J. Am. Chem. Soc. 1989, 111, 2444-2451) have claimed the conversion of nitrite ion and nitric oxide in an alkaline medium at Hg-pool (-0.9 V) cathode. 10 to 36% ammonia is obtained with low coulombic efficiency. Iron-substituted hetero polytungastates are used to catalyze the reaction. The limitation of these methods are that it requires a catalyst and a supporting electrolyte. The yield of ammonia and the coulombic (21 to 50) efficiency are low. Further it uses mercury as the cathode material which is generally not advisable as it is carcinogen. T. J. Meyer et. al. (J. Am. Chem. Soc. 1982, 104, 5817-5819; 1986, 108, 5876-5885; fnorg. Chem. 1986, 25, 1041-1053; 1988, 27, 4772; 1991, 30, 629; 1987, 26, 1746-1750; 1992, 31, 3280-3285; J. Chem. Soc. Chem. Commun., 1985, 507) have reported the electrochemical reduction of nitrite ion to ammonia in the presence of a supporting electrolyte. Monomeric or thin polymeric films of ruthenium, osmium or iron based complexes are used to catalyze this reaction. The drawbacks of these methods are that they require special skills to develop polymeric film electrodes containing costly catalytic species. Moreover, the life of such polymeric film-electrodes is limited. Besides, this method releases toxic oxides as byproducts and is not feasible if supporting electrolyte is not added to the nitrite containing waters. E. S. Sera'yanor, M. N. Ter-Akopyan, D. I. Leikis, R. K. Karatskheliya and T. Sh. Machavariani (Electrokhimiya 1983, 19, 1248-52) have reduced both nitrate and nitrite ions on polycrystalline silver electrodes in basic solutions. Ammonia is obtained as the principle product. The limitation of this method is that the reduction processes occur only when a supporting electrolyte is added to the nitrite and nitrite containing solutions. H. L. Li, J. Q. Chambers and D. T. Hobbs (./. Appl. Electrochem. 1988, 18, 454-458), have reduced both nitrate and nitrite ions at lead, zinc, nickel, iron and phthalocyanine modified electrodes in sodium hydroxide solutions. Ammonia is obtained as the principle product. The limitation of this method is that all the contaminated solutions have to be alkalized before the treatment is given. Moreover, the cathode has to be modified with lead, zinc, nickel, iron and phthalocyanine films to perform the proposed reductions. H. L. Li, D. H. Robertson, J. Q. Chambers and D. T. Hobbs (J. Electrochem. Soc. 1988, 135, 1154-1158) have also reduced the nitrate and nitrite ion solutions in 0.25 M sodium carbonate at 80 °C at platinum and nickel electrodes. The formation of nitrogen at low current densities and ammonia at high current densities was observed. The limitation of this method is that it requires costly electrodes. Moreover, the addition of supporting electrolyte to the contaminated solutions is necessary. R. Terms, K. Patel, K. Hashimoto and A, Fujishima have used B-doped diamond electrode (J. Eleciroanal Chem. 1993, 347, 409-415) as efficient and stable electrodes for ammonia production from nitrate solutions. The drawbacks of this method are that the electrode materials are co'stly and it requires sodium hydroxide to be added to the substrate solution. S. Catlarin (J. Appl. Electrochem. 1992, 22, 1077-1081) have reduced the nitrate ion to ammonia using silver-copper and copper-indium-selenide electrodes in sodium hydroxide solutions. The drawbacks of this method are that the electrode materials are costly and it needs sodium hydroxide to be add as the supporting electrolyte in the substrate solution. K. Tanaka, N. Komeda and T. Matsui (Inorg. Chem. 1991, 30, 3282-3288) have performed the assimilatory and dissimilatoiy reductions of nitrate and nitrite ions to ammonia through the formation of free nitric oxide at a (Bu4N)4[MoFe3S4(SPh)3(O2C6Cl4)]2 modified glassy carbon electrode under controlled potential electrolysis at -1.25 V vs saturated calomel electrode (SCE) in water at pH 10. The drawback of this method is that it needs the costly cathode which in turn to be modified with a costly MoFe cluster. It requires an alkali to be added to the substrate to adjust the pH to 10. F. V. Pedres, R. T. Agisti and J. A. A. Enguidanos has patented an electrochemical process (Span. ES 2,065,807, Cl. COI Cl/02 April 10, 1992) for the electrolytic reduction of trace quantities of both nitrate and nitrite ions in industrial waters to ammonia using galvanized steel tubes as cathodes. This method is developed to treat only contaminated waters to protect the carbon-steel-water distribution and waste-water pipes against corrosion. J. J. Kaczur, D. W. Cawlfield and K. E. Jr. Woodard (US 5,376,240, Cl. 204-128; C25 Bl/100, December 27, 1994) have patented the removal of oxynitrogen species from aqueous solutions. In this method, an aqueous solution containing inorganic oxynitrogen species was electrochemically reduced in a cathode compartment having a large surface area. Nitrogen or ammonia and purified water were the end products. The drawback of this method is that it requires an electrolyte in absence of which the electrolysis does not take place easily. The main objective of the present invention is to provide an improved method for the reduction of nitrate and nitrite ions to ammonia which obviates the drawbacks as detailed above. Another objective of the present invention is to use cation-exchange membrane as a solid polymer electrolyte to conduct electrolysis in the absence of supporting electrolyte and to keep the catholyte and anolyte solutions separately Still another objective of the present invention is to use stainless steel as the cheapest cathode for the reduction of both nitrate and nitrite ions each separately to ammonia. Still another objective of the present invention is to use membrane cells for the reduction of both inorganic nitrates and nitrites present in industrial effluents to an useful product, ammonia. In the drawing (Sheet No. 1) accompanying this specification describes a view of the electrolytic membrane cell. The capacity of each of the electrode compartments of the cell was about 75 ml. The surface area of stainless steel cathode plate (1) was around 150 cm2. The titanium anode (2) having an effective total surface area of around 60 to 65 cm" was an expanded titanium sheet with a precious triple metal oxide coating. Both these electrodes were separately fitted inside the electrode chambers made of perspex (4). They were separated by about 0.5 cm by a thin pre-conditioned cation-exchange membrane (3) between them. About 250 ml each of distilled water and sodium nitrate (or sodium nitrite) solutions were used as anolyte and catholyte, respectively. They were circulated through the electrode compartments at the rate of 5 to 10 ml/min, under gravity with the aid of inlets (5) and outlets (6) provided for them to the cell. A luggin type saturated calomel electrode which is not shown in the figure in Sheet No. 1 was placed behind the cathode for measuring the electrode (1) potential. Accordingly the present invention provides an improved process for the preparation of ammonia, which comprises reducing electrochemically inorganic nitrate and/or nitrite laden waters/waste waters of neutral or basic pH in an electrochemical cell having stainless steel as cathode and an expanded precious triple metal oxide coated titanium as anode separated by a conventional cation-exchange membrane at -1.1 to -1.2 V placed in two compartment cell at a distance of 5mm from the cathode and the anode, allowing the solutions containing 1 to 30% (w/v) of sodium nitrate and sodium nitrite independently through the cathode compartment and deionized water through the anode compartment to flow under gravity at the rate of 5 to 10 ml/min; at temperature 10 to 50 °C; at current density 1 to 80 mA/cm2 for 1 to 6 h with a potential drop of 2 to 5 V across the two electrodes to obtain ammonia in aqueous solution form. In an embodiment of the present invention,the salts sodium nitrate and sodium nitrite of analytical grade were used to provide the required inorganic nitrate and nitrite ions in solution, respectively. In another embodiment of the present invention, the concentration of sodium nitrate or sodium nitrite was varied in the range of 10 to 20% (w/v). In yet another embodiment of the present invention, the potential at the cathode was in the range of-1.1 to -1.2 V vs saturated calomel electrode. In yet another embodiment of the present invention, the catholyte and the anolyte solutions were set to flow through the respective electrode compartments at the rate 5 to 10 ml/min under garvity. In yet another embodiment of the present invention, the nitrate and the nitrite ions were reduced to ammonia at the constant current density25 to 40 mA/cm2. In yet another embodiment of the present invention, the cell potential was in the range of 2 to 5 V. In yet another embodiment of the present invention, the temperature of the anolyte and catholyte solutions was maintained in the temperature range of 25 to 3 5 °C. In yet another embodiment of the present invention, a cation exchange membrane was placed in the two compartmental cell at a distance of 5 mm from the cathode and the anode. According to the present invention, the nitrate ion reduces to ammonia by accepting eight electrons per nitrogen atom from the cathode in a single or closely separated steps with the association of suitable number of water molecules. Similarly, the nitrite ion converts to ammonia by accepting six electrons from the electrode as shown below. NO3 + 8e~ + 6H2O → NH3 + 9OH-NO2- + 6e~ + 5H20 → NH3 + 7OH- These reactions were conducted separately on a laboratory scale using a rectangular (18x15 cm2) perspex membrane cell consisting of a thin stainless steel cathode (150 cm2) and a special triple metal oxide coated titanium anode, one on either side of the membrane. Solutions of known concentrations of sodium nitrate as the source for nitrate ion and sodium nitrite as the source for nitrite ion prepared separately were used as catholyte solutions. Distilled water was used as a common anolyte in all the experiments. A cation exchange membrane of about 80 to 85 cm2 exposed area was used in the cell to keep the electrode chambers separate. The temperature of the catholyte and the anolyte solutions during the cell operation was controlled externally by circulating water through the outer jacket of the respective reservoirs and placing the receivers at the cell outlets in a water bath regulated at at the temperature between 10 to 50 °C. The anolyte and catholyte solutions were allowed to flow through the respective electrode chambers at the rate of 5 to 10 ml/min under gravitational force. A constant current ranging between 1 to 12 A was applied for a period of 1 to 6 h. The cathode potentials were measured during the electrolysis, against saturated calomel electrode while the cell potential was constant at 2 to 5 V. In these experiments, the substrate, sodium nitrate and sodium nitrite concentrations were varied from 1 to 30% (w/v). It was found to be advantageous to work with a concentrated solution preferably between 5 to 20% (w/v) to that of the salt. It is generally preferable to maintain the molar ratio between water and the substrate (nitrate and/or nitrite) to be equal to 20 or in the range between 2 to 90, while the water serves as the cheapest source for the required hydrogen. The process according to the present invention was carried out at different temepratures ranging between 10 to 50 °C. It was found that the inorganic oxides were reduced at all temperatures at the cathode to ammonia at the same efficiency with excellent yields with out any appreciable loss of ammonia. However, at high temperatures an accountable loss of ammonia was found due to evaporation. The above process was done at different current densities varying from 1 to 80 mA/cm2. It was found to be advantageous to work at low current densities preferably between 10 to 40 mA/cm2. A rise in the solution temperature at the cell outlet was noted while working at high current densities (> 50 mA/cnr). While carrying out the processes with 20 to 30% of both the sodium nitrate and sodium nitrite salts, the ammonia formed in the cathode compartment was found to be transported to anode compartment by about 0.1 to 0.14 g (nearly one-tenth of the ammonia formed in the cathode compartment) in 6 h as ammonium ion by ion-exchange process. After the electrolysis, the catholyte and anolyte solutions were collected. The pH of the catholyte was initially at 7 and it increased to nearly 12, while that of the anolyte it was about 1.3 to 1.5, in all the cases, at the end of the experiment. Ammonia was estimated in 30 ml of each of the solutions by Orion Ion Analyzer model 940 coupled with ammonia sensing electrode. Two ml of the Ionic Strength Adjuster (ISA) specified for ammonia estimation was commonly added to all the test solutions. The extent of unreacted nitrate and nitrite ions in the treated solutions were estimated by spectrophotometric methods (Standard Methods for the Examination of Water and Waste Water edited by L. S. Clesceri, A. E. Greenberg and R. R. Trussell, 17th edn., American Public Health Association, American Water Works Association and American Pollution Controlled Federation, Washington, 1989, 7.132-133, 7.129-131) and found that the reacted nitrate/nitrite was equivalent to the amount of ammonia produced at the cathode. Further, 0.2 to 0.5 ml of the electrolyzed solution was added to 10 ml of 1 M NaOH and its differential pulse polarographic responses at -0.43 V vs saturated calomel electrode (L. Meites Polarographic Techniques, 2nd edn. Interscience, New York, 1963) were run to estimate the hydroxyl amine if any, produced during the reductions of both the nitrate and nitrite ions to ammonia. The results showed no formation of hydroxyl amine in the electrolyzed solutions. It was further confirmed by conducting an independent experiment, wherein, a solution of hydroxyl amine of known concentration was circulated through the cathode chamber. The data confirmed the reduction of hydroxyl amine to ammonia at the cathode. Appreciable quantity of ammonia was observed to be transported to the other compartment and some escaped on evaporation during electrolysis when conducted at high current (> 40 mA/cm2) densities and/or with concentrated (> 30%) solutions of both the nitrate and nitrite salts. In the present invention, the reduction of both nitrate and nitrite ions are independently conducted electrochemically in aqueous solutions in an ion-exchange membrane cell. In both cases, ammonia is obtained with high yields at maximum coulombic efficiency. The present method does not require any additional reactant. supporting electrolyte or a catalyst to carry out the multi-electron reduction of these ions under ambient conditions. The byproducts such as hydroxyl amine, nitrogen or the toxic gases are not produced. The cathode at which the reduction processes occurs, is the cheap stainless steel which neither corrodes, decomposes nor participates in the electrochemical or chemical reactions. The anode used here is an expanded triple metal oxide coated titanium electrode. The membrane used in this process is an interpolymer of polyethylene and styrene-divinyl benzene copolymer having fixed sulfonic acid groups which is found to be durable, stable and does not get fouled or reacts with the components of either the reactants or the products. Further, in the present invention, the, membrane does not add any impurity to the product or take part in the chemical/electrochemical reactions occurring in the cell by its virtue of its high ionic conductivity, reduces the cell resistance. As a result, this method does not require any other supporting electrolyte in the anolyte solutions. In the present invention, the solution temperature (10 to 50 °C), the cell potential (2 to 5 V) and the cathode potential (-1.1 to -1.2 V vs a saturated calomel electrode) remained constant throughout the experiment. The following examples are given by way of illustrations of the present invention and should not be construed to limit the scope of the present invention. EXAMPLE 1: The preparation of ammonia was effected by electrolysis of a solution composed of 12.5 g of sodium nitrate and 250 ml of water at the cathode. The solution was electrolyzed for six hours at a current density 13.3 mA/cm2. The cathode potential was -1.20 V vs a saturated calomel electrode, while the solution temperature was maintained at 35 °C and the flow rate at 10 ml/min. The cell potential was maintained at 5 V. The passage of charge equivalent to 4.32 x 104 coulombs i.e. 38% of theoretical current converted 5.98 g of sodium nitrate into 1.195 g of ammonia with 76% coulombic efficiency. EXAMPLE 2 A solution having the composition, 25 g sodium nitrate, 250 ml water was electrolyzed at the cathode at a current density of 13.3 mA/cm2. The cathode potential was -1.20 V vs a saturated calomel electrode, while the cell potential was 3 V. The cell temperature during the operation was maintained at 35 °C at 10 ml/min flow rate. After the passage of 19% theoretical current (4.32 x 104 coulombs), the total sodium nitrate converted to ammonia was 6.33 g corresponding to 82% coulombic efficiency. Ammonia estimated at the end of 6 h electrolysis was 1.27 g. EXAMPLE 3: A solution having 12.5 g of sodium nitrate and 250 ml of water was electrolyzed in the cell at a current density of 20 mA/cm2. The cathode potential was -1.20 V vs a saturated calomel electrode and the temperature during the experiment was maintained at 35 °C. The cell potential was 5 V. 7.44 g of sodium nitrate was converted to give 1.49 g of ammonia after the passage of 6.48 x 104 C (i. e. 57% of theoretical current). The coulombic efficiency was 88%. EXAMPLE 4: The solution containing 12.5 g of sodium nitrate and 250 ml of water was electrolyzed in the electrolytic cell at the current density 26.7 mA/cm2. The cathode potential was -1.20 V vs a saturated calomel electrode, while the cell potential was 3 V. During the electrolysis, the temperature was maintained at 35 °C. After the passage of 76% of the theoretical current i. e. 8.64 x 104 C, the total quantity of sodium nitrate reacted was 8.12 g. It gave only 1.48 g of ammonia after a loss of about 0.14 g on account of evaporation. The coulombic efficiency was 96%. EXAMPLE 5: The solution containing 50 g of sodium nitrate in 250 ml water was reduced at the cathode at the current density of 13.3 mA/cm2. The potential at the cathode was -1.20 V vs a saturated calomel electrode. The temperature of the cell solutions was maintained at 35 °C and the cell potential at 5 V. After the passage of 4.32 x 104 C, (i. e. 9.5% of theoretical current required for the complete conversion), the cell yielded a total of 1.41 g of ammonia by the reduction of 7.07 g sodium nitrate with a coulombic efficiency of 89%. EXAMPLE 6: A solution containing 75 g sodium nitrate in 2,50 ml water was electrolyzed at the cathode at a current density of 13.3 mA/cm2. The cathode potential was found to be -1.20 V vs a saturated calomel electrode. The cell potential was 3 V. The cell temperature during the operation was maintained at 35 °C at 10 ml/min flow rate. After the passage of 6.3% theoretical current (4.32 x 104 coulombs), the sodium nitrate reacted was 7.66 g corresponding to 95% coulombic efficiency. At the end of 6 h electrolysis the amount of ammonia was found to be 1.53 g. EXAMPLE 7: The solution containing 25 g of sodium nitrate and 250 ml of water was electrolyzed in the electrolytic cell at the current density 13.3 mA/cm2. The cathode potential was -1.20 V v.s a saturated calomel electrode, while the cell potential was 3 V. During the electrolysis, the temperature was maintained at 20 °C. After the passage of 19% of the theoretical current i. e. 4.32 x 10 C' the to total duantity of sodium nitrate reacted was 4'42 5 corresponding to 93% of coulombic efficiency. Ammonia estimated at the end of 6 h electrolysis was 0.88 g. EXAMPLE 8: The solution containing 25 g of sodium nitrate and 250 ml of water was electrolyzed in the electrolytic cell at the current density 13.3 mA/cm2. The cathode potential was -1.20 V vs a saturated calomel electrode, while the cell potential was 3 V. During the electrolysis, the temperature was maintained at 50 °C. After the passage of 19% of the theoretical current i. e. 4.32 x 104 C, the total quantity of sodium nitrate reacted was 4.33 g corresponding to 93% of coulombic efficiency. Ammonia estimated at the end of 6 h electrolysis was 0.58 g only. EXAMPLE 9: A solution having 50 g of sodium nitrate and 250 ml of water was electrolyzed in the cell at a current density of 1 mA/cm2. The cathode potential was -1.20 V v.v a saturated calomel electrode and the temperature during the experiment was maintained at 35 °C. The cell potential was 3 V. 0.339 g of sodium nitrate was converted to give 0.068 g of ammonia after the passage of 3.24 x 103 C (i. e. 0.71% of theoretical current). The coulombic efficiency was 95%. EXAMPLE 10: The solution containing 50 g of sodium nitrate and 250 ml of water was electrolyzed in the electrolytic cell at the current density 80 mA/cm2. The cathode potential was -1.20 V vs a saturated calomel electrode, while the cell potential was 5 V. During the electrolysis, the temperature was maintained at 35 °C. After the passage of 57% of the theoretical current i. e. 25.92 x 104 C, the total quantity of sodium nitrate reacted was 27.11 g. It gave only 4.61 g of ammonia after a loss of about 0.81 g on account of evaporation. The coulombic efficiency was 95%. EXAMPLE 11: Ammonia was also prepared by the electrolysis of a solution of 12.5 g of sodium nitrite in 250 ml of water at the cathode. The solution was electrolyzed for six hours at a current density 13.3 mA/cm2. The cathode potential was -1.10 V vs a saturated calomel electrode, while the solution temperature was maintained constant at 35 °C while the solution flew at 10 ml/min. The cell potential was constant at 3 V. The passage of charge equivalent to 4.32 x 104 coulombs i. e. 41.2% of theoretical current, converted 5.34 g of sodium nitrite into 1.76 g of ammonia with about 83% coulombic efficiency. The experimental data revealed that both the high valent nitrogen oxides, nitrate and nitrite ions can be easily, effectively and economically converted to ammonia by electrolysis in a two compartment membrane cell with high coulombic efficiencies. This method is useful to recover the fixed nitrogen from the carcinogenic nitrate and nitrite salts in effluent discharges or contaminated waters. The main advantages of this method are that 1.It does not require any supporting electrolyte, catalyst, special solvent and special or costly cathode. 2.This method is useful to treat solutions containing both inorganic nitrate, nitrite and their mixture. 3.The present method does not release or involve any toxic gases or any unwanted products released in to the water. 4. The electrolytic cell is compact and can be made with inexpensive and easily moldable plastic materials, inexpensive cathode and a durable anode. 5.The membrane is stable towards the nitrate, nitrite, alkali and ammonia, hence the life of the cell is more. 6. The cell design can be altered with ease depending on the product requirement and the size of the membrane. We Claim: 1 . An improved process for the preparation of ammonia, which comprises reducing electrochemically inorganic nitrate and/or nitrite laden waters/waste waters of neutral or basic pH in an electrochemical cell having stainless steel as cathode and an expanded precious triple metal oxide coated titanium as anode separated by a conventional cation-exchange membrane at -1.1 to -1.2 V placed in two compartment cell at a distance of 5mm from the cathode and the anode, allowing the solutions containing 1 to 30% (w/v) of sodium nitrate and sodium nitrite independently through the cathode compartment and deionized water through the anode compartment to flow under gravity at the rate of 5 to 10 ml/min; at temperature 10 to 50 °C; at current density 1 to 80 mA/cm2 for 1 to 6 h with a potential drop of 2 to 5 V across the two electrodes to obtain ammonia in aqueous solution form. 2. An improved method as claimed in claim 1 wherein the concentration of the inorganic nitrate or nitrite ion is varied from 10 to 20% (w/v). 3. An improved method as claimed in claims 1 to 2 wherein the cathode potential is -1.1 to -1.2 V vs saturated calomel electrode. 4. An improved method as claimed in claims 1 to 3 wherein the constant current is 25 to 40 mA/cm2. 5. An improved method as claimed in claims 1 to 4 wherein the temperature of the anolyte and catholyte solutions is maintained in the temperature range of 25 to 35°C. 6. An improved process for the preparation of ammonia substantially as herein described with reference to the examples and drawing accompanying the specification.

Documents:

42-del-2001-abstract.pdf

42-del-2001-claims.pdf

42-del-2001-correspondence-others.pdf

42-del-2001-correspondence-po.pdf

42-del-2001-description (complete).pdf

42-del-2001-drawings.pdf

42-del-2001-form-1.pdf

42-del-2001-form-19.pdf

42-del-2001-form-2.pdf

42-del-2001-form-3.pdf