Field of the Invention

This invention relates to the method of fabrication of nitric acid.

Background of the Invention

The method of synthesis of nitric acid by a two-stage process is known. As a first step, ammonia NH ₃ is synthesised from a mixture of gaseous nitrogen and hydrogen ammonia in the presence of a catalyst containing platinum, iron, ruthenium, osmium or other precious metals at high temperature and pressure. The synthesis of ammonia is called the Haber-Bosch process from the names of two researchers: Fritz Haber and Carl Bosch, who invented this method and brought it to the stage of mass industrial production for which they received Nobel Prize in chemistry in 1918 and 1931.

Nitrogen dioxide i.e. nitric acid anhydride is obtained by burning ammonia in oxygen. This process was invented by Wilhelm Ostwald and patented in 1902. Nowadays it bears his name. Burning ammonia in oxygen leads to the formation of nitrogen dioxide, which dissolved in water forms nitric acid, which is the basis for the production of nitrate fertilizers and nitroglycerin, the basic substance for obtaining dynamite and other explosives.

Ammonia synthesis is carried out by bringing gaseous nitrogen to contact with the surface containing these metals, which leads to the decomposition of nitrogen molecules into single atoms as a result of dissociative adsorption. Nitrogen atoms react with hydrogen molecules, which leads to the synthesis of ammonia molecules on the surface and their desorption. The result is gaseous ammonia. In order to stabilize the ammonia molecules, high pressure of the component was applied, because the synthesis of ammonia results in a two-fold decrease of the number of gas molecules. In order to overcome relatively high energy barriers, it is also necessary to use high temperatures. The solution to obtain industrial ammonia synthesis was the Haber-Bosch synthesis method. The method used osmium or a mixture of uranium and uranium carbide as a catalyst. The synthesis was carried out at the pressure of 100 MPa at 800°C. Relatively much energy was used in this method, about 78 GJ/ton. The method was invented by Fritz Haber in 1908, who received the Nobel Prize for Chemistry in 1919 for his achievements. In 1908 Fritz Haber signed an agreement with Badische Anilin- und Soda Fabrik (BASF) regarding the implementation of ammonia production. On behalf of BASF, Carl Bosch was responsible for the method and made a significant contribution to the development of the synthesis method, for which he was also awarded the Nobel Prize in 1931. This method is called the Haber-Bosch method.

The synthesis of ammonia is an initial stage to obtain nitrogen and oxygen compounds, in particular to obtain nitric acid anhydride, i.e. nitrogen dioxide N0 _2. Nitrogen dioxide is obtained by combustion of ammonia in oxygen. The process is divided into two stages: the first stage is the combustion of ammonia in oxygen, which leads to the formation of nitric oxide and water. The process is carried out in the presence of a catalyst containing 90% platinum and 10% rhodium. This process is strongly exothermic. In the second stage, nitrogen oxide is oxidized to nitrogen dioxide. The process is carried out by oxidation in the presence of water and is characterized by low exothermicity. The obtained ammonia dioxide is dissolved in water, which leads to obtaining nitric acid. Its reaction with ammonia leads to the formation of ammonium nitrate, the basic component of nitrogen fertilizers. Other reactions of nitric acid with the potassium or calcium base lead to the formation of potassium nitrate or calcium nitrate, bearing commercial names of potassium or calcium nitrate, which are the basic fertilizers containing simultaneously two elements necessary to fertilize plants: nitrogen and potassium or calcium respectively.

Object and Summary of the Invention

The subject matter of the Invention is the process of nitric oxide fabrication using group III metal nitrides, including aluminum, gallium or indium, or mixtures containing these compounds. This leads to the removal of the Haber-Bosch process and the first stage of the Ostwald process from the chain of reactions leading to the production of nitric acid. Nitrides AIN, GaN or InN in contact with molecular gas nitrogen break down nitrogen molecules into atoms and allow the synthesis of ammonia from a mixture of molecular gas nitrogen and molecular gas hydrogen. The process of dissociative adsorption was discovered in the ab initio calculations of molecular nitrogen adsorption on the surface of AlN(OOOl), published in P. Strak et al. J. Appl. Phys. 118 (2015) 095705-1-14.

In addition, ab inito calculations showed that molecular oxygen disintegrates on the surface of A1N(0001) leading to the formation of separate atoms on the surface. This process is an energy barrier-free process.

Other ab initio calculations have shown that a clean AIN(OOO) surface containing separate atoms of nitrogen and oxygen is an energetically stable object. This system can be converted to a system of NO molecules adsorbed on the A1N(0001) surface. However, the energy of the molecular system is 4.37 eV higher. Under these conditions, NO synthesis is therefore not possible and separation into separate atoms takes place. Completely different results were obtained with oxygen adsorption on the surface of AlN(OOOl) in case of its coverage with N atoms. In this case, NO molecules are synthesized and placed in two positions: H3 and T4. In general, both configurations are possible, but the H3 configuration is charge and the T4 configuration is energy preferred. The desorption of the NO molecule is facilitated by the addition of an additional N2 molecule as a pair of atoms saturating the broken Al bonds. At high temperatures and in the presence of nitrogen, the resulting nitric oxide desorbs from the surface of the A1N(0001), resulting in a gaseous nitric oxide. The further stage of nitric acid production is based on the second stage of the Ostwald process.

The energy dependence of the nitrogen molecule along with the stages of decomposition is shown in the figure Fig. 1, which shows the energy and configuration of the N ₂ molecule during adsorption at the surface of AlN(OOOl). It shows that the adsorption process takes place without an energy barrier and the adsorption energy on a clean surface of A1N(0001) is 6.05 eV/molecule N _2. It is a huge energy gain, leading to a spontaneous reaction. As also shown, the nitrogen adsorption process has a similar amount of energy to cover 0.25 of the monolayer. This is illustrated in the figure where Fig. 2 shows the dependence of the adsorption energy of molecular nitrogen (N ₂ ) on the surface of A1N(0001) as a function of nitrogen coverage. On the surface covered with atomic nitrogen adsorption of molecular hydrogen takes place, which causes the formation of ammonia molecules and their desorption. This leads to a significant improvement in the efficiency of the process. If the surface is covered to 0.27 monolayer during adsorption, the nitrogen molecule is broken down into atoms, leading to a high adsorption energy of 6 eV. For higher coverage, the decomposition does not occur, the nitrogen molecule is adsorbed at the surface with an adsorption energy of 1 eV. This means that coverage up to 0.27 monolayer is easy to achieve and higher coatings are unavailable at technically achievable nitrogen pressures. This way of ammonia synthesis process is characterized by a quality that allows for highly desirable, mentioned above industrial applications of this reaction.

Further results are related to the adsorption of oxygen on the surface of AlN(OOOl). Oxygen molecules are adsorbed without an energy barrier and break down into individual atoms, which are also placed in H3 nodes. This is illustrated in the figure where Fig. 4 shows the energy dependence of the 0 ₂ molecule on the surface during adsorption on the surface of AlN(OOOl).

The last stage is the reaction of nitrogen oxide molecule formation by combining N and O atoms adsorbed on the surface of AlN(OOOl). This is illustrated in the Fig. 5 that shows the configuration of atoms during the formation of nitric oxide (NO) molecules. The synthesis of nitrogen fertilizers is of great importance for the nutrition of the growing world population. According to estimates of the World Food and Agriculture Organization (FAO), currently nitrogen fertilizers provide 40% of the world's food production. Currently, about 50% of nitrogen in human organisms comes from the chemical synthesis of ammonia, the remaining amount is obtained through the natural synthesis of nitrogen compounds in plants. In the period since the invention of the Ostwald and Haber-Bosch methods to the present day, the population of the Earth has grown 4.2 times from 1.7 billion to more than 7 billion. During this time, food production has increased 7.8 times, protecting humanity from hunger and ensuring the survival of 50% of the world's population. This was achieved only through the use of nitrogen fertilizers, which are made from artificially synthesized ammonia. A significant cost of producing ammonia is the need to use molecular hydrogen. This is the dominant part of the production costs. Hydrogen is currently obtained from the combustion of methane which leads to the production of carbon dioxide, which leads to the deepening of the greenhouse effect, which is harmful on a global scale. It is estimated that 20% of the world's methane is used in the production of hydrogen and then ammonia. There is therefore a need to find other methods of obtaining nitric acid without using hydrogen. Hydrogen occurs in the intermediate stage, the initial state is oxygen and nitrogen, and the final state is nitrogen dioxide. It is therefore possible to remove hydrogen from the nitric acid production chain, which would bring enormous material and environmental benefits.

Brief description of the figures.

The invention has been explained in Figure 1 to 5.

Figure 1 demonstrates the molecular nitrogen (N2) reaction path during adsorption on the surface of A1N(0001) for dissociative nitrogen adsorption. On the vertical axis, the energy of the system is presented, calculated in relation to energy level of a molecule located far from the surface. In the graph we denote: 1 - nitrogen atoms in molecule N ₂ , 2 - aluminium atoms, 3 - nitrogen atoms in the AIN crystal. The subsequent stages of the reaction are shown in the diagrams, for which arrows 4 indicate the amount of energy of a given configuration.

Figure 2 presents the nitrogen adsorption energy dependence on the nitrogen coverage of AlN(OOOl) surface. Molecular hydrogen adsorption takes place on the surface covered with atomic nitrogen, which leads to the formation of ammonia molecules and their desorption.

Figure 3 presents the energy dependence of N and O atoms, adsorbed on clean AlN(OOOl) surface in function of their distance. The energy of the pair of atoms is the lowest at a long distance. On the clean surface of A1N(0001) there is no synthesis of nitric oxide NO.

Figure 4 presents the dependence of the energy of an oxygen molecule on its distance from the surface of A1N(0001) covered by nitrogen atoms. The energy of the pair of oxygen atoms is decreased for distance increase. In the graph the three positions of oxygen are marked: 5 - far from the surface - the oxygen atoms form the 0 ₂ molecule, 6 - the molecule dissociated and two NO molecules have formed at T4 positions, 7 - one of the NO molecules was moved to H3 position. These positions are illustrated in Fig 5. Figure 5 presents the configurations of the oxygen atoms in the molecule when approaching a nitrogen coated A1N(0001) surface: 5 - 0 ₂ molecule is far from the surface, 6 - NO molecules are formed, and located in positions T4, 7 - one of the NO molecules has been moved to position H3. The top row shows a top view, the bottom row a side view. Nitrogen atoms are marked with grey small balls, aluminium atoms with large balls, oxygen atoms with black small balls, and hydrogen pseudoatoms with very small balls. These results prove that it is possible to synthesize nitric oxide on the surface of A1N(0001) in conditions rich in nitrogen.

The subject of the Invention is demonstrated on the examples of applications.

Example

Synthesis of nitric acid on the surface of AIN (0001) single crystal.

The AIN single crystal was cut to expose the aluminum surface, i.e. the A1N(0001) surface. This surface is washed in hexane, royal water and deionized water. It is then located in a reaction chamber in which the ammonia flow, at a pressure of 10 kPa, is activated. The temperature in the chamber is raised to 800°C and the A1N(0001) surface is heated under these conditions for 10 minutes to remove oxygen. The nitrogen oxide synthesis process is carried out by injecting a 100: 1 molecular nitrogen/oxygen mixture into the reaction chamber, maintaining temperature and raising the gas pressure to lOMPa. The process is carried out continuously with the flow of the nitrogen/oxygen mixture. Nitrogen oxide is collected from the gas mixture flowing out, which in the next reactor is oxidized to nitrogen dioxide. Nitrogen dioxide is dissolved in water to obtain nitric acid.

Example

Synthesis of nitric acid on the surface of AIN (0001) layer deposited on sapphire substrate.

The AI ₂ O ₃ single crystal sapphire substrate was cut to expose the aluminum surface. This surface is washed in hexane, royal water and deionized water. It is then located in an epitaxy chamber of organometallic compounds from the gaseous phase (MOVPE) in which the surface is nitrided by the ammonia flow. The AIN layer is deposited when the flow of the A1 carrier and the flow of NEE is switched on. This structure is transferred to a reaction chamber in which the ammonia flow is activated at a pressure of 10 kPa to remove the adsorbed oxygen. The process of nitric oxide synthesis is carried out by injecting a 100:1 molecular mixture of nitrogen and oxygen into the reaction chamber, maintaining temperature and raising the gas pressure to lOMPa. The process is carried out continuously with the flow of the nitrogen/oxygen mixture. Nitrogen oxide is collected from the gas mixture flowing out, which in the next reactor is oxidized to nitrogen dioxide. Nitrogen dioxide is dissolved in water to obtain nitric acid.

Example TTT

Synthesis of nitric acid on the surface of the AIN (0001) layer obtained by nitriding the sapphire substrate.

The AI ₂ O ₃ monocrystalline sapphire substrate was cut to expose the aluminum surface. This surface is washed in hexane, royal water and deionized water. It is then located in a reaction chamber in which the ammonia flow, at a pressure of 10 kPa, is activated. The temperature in the chamber is raised to 800°C and the surface of AI ₂ O ₃ is nitrided for 30 minutes to form an AIN layer. The nitrogen oxide synthesis process is carried out by injecting a 100:1 molecular nitrogen/oxygen mixture into the reaction chamber, maintaining temperature and raising the gas pressure to lOMPa. The process is carried out continuously with the flow of the nitrogen/oxygen mixture. Nitrogen oxide is collected from the gas mixture flowing out, which in the next reactor is oxidized to nitrogen dioxide. Nitrogen dioxide is dissolved in water to obtain nitric acid.

Example IV

Synthesis of nitric acid on the surface of AIN (0001) layer obtained by sintering AIN powder.

AIN ceramics is obtained by sintering the AIN powder in a nitrogen atmosphere at a temperature of 1500°C. It is then located in an epitaxy chamber of the gaseous phase organometallic compounds (MOVPE) in which the surface is purified by the flow of ammonia. The process of nitric oxide synthesis is carried out by injecting a 100: 1 molecular nitrogen/oxygen mixture into the reaction chamber, maintaining temperature and increasing gas pressure to lOMPa. The process is carried out continuously with the flow of the nitrogen/oxygen mixture. Nitrogen oxide is collected from the gas mixture flowing out, which in the next reactor is oxidized to nitrogen dioxide. Nitrogen dioxide is dissolved in water to obtain nitric acid

Application

The method can be applied in the mass production of nitrogen fertilizers, explosives and plastics.