Ammonia gas production method

Abstract

The present invention provides a method for producing ammonia gas that contains a high concentration of ammonia from a liquid containing ammonia. [Solution] A method for producing ammonia gas, comprising: step A, contacting a liquid containing ammonia with MgHPO4 to bond the ammonia to MgHPO4 and obtain MgNH4PO4·6H2O; step B, physically dehydrating the MgNH4PO4·6H2O obtained in step A; and step C, heating the MgNH4PO4·6H2O after physical dehydration to recover ammonia gas.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing ammonia gas. [Background Art]

[0002] Generally, ammonia is contained in wastewater from food factories, livestock wastewater and the like, and efficient and effective removal of ammonia is desired. In addition, when the concentration of ammonia increases in a methane fermentation tank using methanogenic bacteria operated in a biogas plant, the efficiency of methane fermentation decreases. Therefore, conventionally, there are examples where separation and recovery have been performed using a stripping technique. Further, as an apparatus for separating ammonia from the effluent discharged from a methane fermentation tank, an apparatus provided with a reticulated fiber disk in an ammonia removal tank has been proposed (see Patent Document 1). [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent No. 7518581 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, the ammonia concentration in the gas recovered by the stripping technique is only a few percent. For use as an energy source such as biogas, for example, a concentration of at least 50% or more of ammonia is required. A gas containing ammonia at a high concentration is useful as a fuel, and when separated into hydrogen gas and nitrogen gas by a catalyst, application to fuel cells and the like can also be expected. In addition, it is merely described that ammonia separated by the ammonia separation apparatus described in Patent Document 1 is subjected to solid-liquid separation and used as nitrogen-containing liquid fertilizer. It is also possible to neutralize the dilute ammonia aqueous solution obtained by any of the above methods to obtain an ammonium salt. Although ammonium salts are useful, for example, as nitrogen-containing fertilizers, their uses are limited, and surplus nitrogen-containing fertilizers or surplus ammonium salts are difficult to dispose of directly due to concerns about soil contamination.

[0005] One embodiment of this disclosure aims to solve the problem of a method for producing ammonia gas in which ammonia gas containing a high concentration of ammonia can be obtained from a liquid containing ammonia. [Means for solving the problem]

[0006] The following embodiments are included as specific means for solving the above problems. <1> Step A involves contacting a liquid containing ammonia with MgHPO4 to bond the ammonia to MgHPO4 and obtain MgNH4PO4·6H2O, Step B involves physically dehydrating the MgNH4PO4·6H2O obtained in step A, Step C involves heating the MgNH4PO4·6H2O after physical dehydration to recover ammonia gas, A method for producing ammonia gas, including the gas itself.

[0007] <2> The aforementioned step C includes a first heating step of heating under reduced pressure at a temperature of 100°C to 150°C, and a second heating step of heating at atmospheric pressure at a temperature higher than that of the first heating step. <1> A method for producing ammonia gas as described above. <3> Step B includes filling a container through which gas flows with MgNH4PO4·6H2O and removing free water by passing air through the container. <1> or <2> A method for producing ammonia gas as described above.

[0008] " <4> The aforementioned MgHPO4 is a thermal decomposition product of magnesium ammonium phosphate, obtained by heating and dehydrating magnesium ammonium phosphate (MgNH4PO4·6H2O), resulting in MgNH4PO4·nH2O (where n is 0-1), and then further heating to remove ammonia gas. <1> ~ <3> A method for producing ammonia gas as described in any one of the following. <5> Step A involves contacting the MgHPO4 remaining after recovering ammonia in step C with the wastewater. <1> ~ <4> A method for producing ammonia gas as described in any one of the following. <6> Using the MgHPO4 obtained by recovering ammonia through the execution of step C, the operations of steps A, B, and C are performed two or more times. <1> ~ <5> A method for producing ammonia gas as described in any one of the following. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, a method for producing ammonia gas is provided that allows ammonia gas containing a high concentration of ammonia to be obtained from a liquid containing ammonia. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram showing one aspect of the flow of each step in the method for producing ammonia gas according to this disclosure. [Figure 2] Figure 2 is a graph showing the results of measuring the water content of struvite particles after physical dehydration by varying the flow rate of air passing through them, for struvite particles with an average particle diameter of more than 88 μm and struvite particles with an average particle diameter of less than 32 μm immersed in water. [Figure 3] Figure 3 is a graph showing the results of calculating the energy required to remove free water in the experiment shown in Figure 2. [Figure 4] Figure 4 is a graph showing the relationship between the maximum heating temperature conditions in the first heating stage and the measured results of ammonia release and ammonia gas concentration in the second heating stage. [MODES FOR CARRYING OUT THE INVENTION]

[0011] Hereinafter, the method for producing ammonia gas according to the present disclosure will be described in detail. The description of the requirements set forth below may be made based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments, and modifications can be appropriately made and carried out within the scope of the object of the present disclosure.

[0012] In the present disclosure, a numerical range indicated using "~" means a range that includes the numerical values described before and after "~" as the lower limit and upper limit, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of a numerical range described in another stepwise description. Further, in the numerical ranges described in the present disclosure, the upper limit or lower limit described in a certain numerical range may be replaced with the values shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, "normal temperature" or "room temperature" refers to the atmospheric temperature in an uncontrolled temperature state, which is usually in the range of 20°C to 35°C. In experimental conditions, "normal temperature" or "room temperature" refers to 25°C unless otherwise specified.

[0013] In the present disclosure, the term "step" includes not only an independent step, but also a case that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved. Components indicated by the same reference numerals in each drawing mean the same components. Descriptions of overlapping components and reference numerals in each drawing may be omitted. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

[0014] [Method for Producing Ammonia Gas] The method for producing ammonia gas according to the present disclosure (hereinafter also referred to as "the production method according to the present disclosure") comprises: Step A of bringing an ammonia-containing liquid into contact with MgHPO₄ and binding ammonia to MgHPO₄ to obtain MgNH₄PO₄·6H₂O; Step B of physically dehydrating the MgNH₄PO₄·6H₂O obtained in Step A; and Step C of heating the MgNH₄PO₄·6H₂O after the physical dehydration and recovering ammonia gas.

[0015] One aspect of the flow of each step of the production method of the present disclosure is shown in Figure 1. In the present disclosure, hereinafter, "MgHPO₄" may be referred to as "dehydrated newberyite", "MgNH₄PO₄" as "dehydrated dittmarite", "MgNH₄PO₄·6H₂O" as "struvite (hexahydrate)", and "MgNH₄PO₄·H₂O" as "dittmarite", respectively. As is clear from the above composition, dehydrated newberyite represents the anhydride of newberyite. In the present disclosure, "dehydrated newberyite" may be simply referred to as "newberyite". As is clear from the flow shown in Figure 1 above, struvite (MgNH₄PO₄·6H₂O) exists as a hexahydrate, is dehydrated by, for example, vacuum heating treatment to form dittmarite (MgNH₄PO₄·H₂O), and is further deammoniated by heating treatment or the like to form dehydrated newberyite (MgHPO₄). Dehydrated newberyite (MgHPO₄) reacts with an ammonia-containing aqueous solution (i.e., NH 4+ , OH - by coming into contact therewith, adsorbs ammonia and water to form struvite (MgNH₄PO₄·6H₂O). The ammonia-containing aqueous solution includes the ammonia-containing liquid that is the target of the production method of the present disclosure, and in one aspect, for example, ammonia-containing effluent discharged from food factories and the like is also included. In the present disclosure, high-concentration ammonia gas is produced by utilizing deammoniation and ammonia absorption in each of these steps. Each step in the present disclosure is described below.

[0016] (Step A) Step A in this disclosure is a step in which a liquid containing ammonia is brought into contact with dehydrated Newbergite, i.e., MgHPO4, to bond the ammonia to MgHPO4 and obtain MgNH4PO4·6H2O.

[0017] In step A of Figure 1, the aqueous solution containing ammonia (NH3) and water (H2O) can be any ammonia-containing liquid that is to be treated in the manufacturing method of the present disclosure. Specifically, any liquid containing ammonia and water, such as wastewater from a food processing plant or livestock farming, can be treated without any particular limitations. Furthermore, ammonium salt aqueous solutions containing low concentrations of ammonia obtained in each step of the manufacturing method of the present disclosure can also be treated in step A.

[0018] The dehydrated Newbergite used in step A is obtained by thermally decomposing and dehydrating magnesium ammonium phosphate (MAP: MgNH4PO4·6H2O), a crystal precipitated by the reaction of magnesium, ammonia, and phosphorus. MAP may be obtained using commercially available reagents, or MAP may be recovered from sewage sludge, etc. For example, the desired dehydrated Newbergite can be obtained by performing the MAP process three times, with a heating rate of 70°C / min and a final temperature of 325°C. Alternatively, dehydrated Newbergite can be obtained by heating the MAP at a heating rate of 5°C / min and maintaining a temperature of 180°C for 3 hours. Furthermore, dehydrated Newbergite can be obtained not only from the thermal decomposition products of MAP described above, but also by dehydrating commercially available dismagnesium phosphate (MgHPO4·3H2O). An example of commercially available dismagnesium phosphate is the dismagnesium phosphate manufactured by Taihei Chemical Industry Co., Ltd. As shown in the above composition, commercially available dismagnesium phosphate is the trihydrate of Newbergite.

[0019] The average particle size of Newbergite can be 10 μm to 100 μm. Smaller particles are preferable from the viewpoint of contact efficiency with wastewater containing ammonia, while larger particles are preferable from the viewpoint of dewatering efficiency. Therefore, the average particle size of Newbergite throughout the entire process is preferably 40 μm to 80 μm. Newbergite can be processed by sieving the obtained Newbergite using a sieve with a predetermined mesh size to obtain particles of a desired particle size. In this disclosure, as an example of one embodiment, small-particle Newbergite is used, which consists of particles that have passed through a sieve with a mesh size of 32 μm, and large-particle Newbergite is used, which consists of particles that remain on a sieve with a mesh size of 88 μm.

[0020] In step A, from the viewpoint of binding the ammonia-containing liquid to Newbergite and adsorbing the ammonia sufficiently, the contact time between the wastewater and Newbergite depends on the ammonia content in the wastewater. Generally, however, it is preferable to maintain the temperature of the ammonia-containing liquid in step A at room temperature (25°C) to 100°C, and more preferably at 80°C to 90°C. From the viewpoint of sufficient ammonia adsorption, the contact time is preferably 30 minutes or more, and more preferably 1 hour or more. There is no particular upper limit to the contact time, but once the ammonia absorption reaction is complete, the ammonia adsorption reaction will not proceed even if the contact is extended further, so from the viewpoint of reaction efficiency, it can be 3 hours or less, and preferably 2 hours or less. When a liquid containing ammonia reacts with Newbergite, struvite (MgNH4PO4·6H2O) is obtained. The reaction between Newbergite and wastewater containing ammonia in step A is represented by the following equation.

[0021] [ka]

[0022] The struvite (hexahydrate) obtained in step A is then subjected to the next step, step B. The struvite (hexahydrate) obtained here can also be sieved to obtain the desired particles, similar to the Newbergite described earlier.

[0023] (Process B) Step B in this disclosure is a step of physically dehydrating the MgNH4PO4·6H2O (i.e., struvite) obtained in Step A described above. In step A, the struvite obtained by immersing in wastewater containing ammonia contains a large amount of water. In step B, the water contained in the struvite is physically dehydrated. There are no particular restrictions on the physical dewatering method; any known method that can physically dewater the water adhering to the struvite particles can be applied as appropriate. Physical dewatering methods include arranging struvite on a moisture-permeable sheet such as filter paper to filter out the moisture, storing struvite in a container and circulating gas such as air through it, and separating solids and liquids by centrifugal separation.

[0024] In particular, from the viewpoint of good dewatering efficiency and not affecting struvite particles, it is preferable that step B includes filling the struvite into a container through which gas flows and removing free water by circulating gas in the container. Examples of containers through which gas flows include hollow containers equipped with a gas inlet and a gas outlet. The gas circulating in the container is not particularly limited. In one embodiment, an inert gas or air is preferred, as it does not affect the struvite particles and is easy to handle. From the viewpoint of efficiently removing free water, it is preferable to circulate compressed air within the container. Compressed air can be supplied into the container using a compressor, blower, or the like, thereby circulating within the container.

[0025] There are no particular restrictions on the container through which the gas flows, as long as the gas can flow efficiently. Examples of containers through which gas flows include hollow columnar containers such as cylinders and prisms with open ends, gas-impermeable containers having two openings through which gas can flow, containers like sieves having a gas-impermeable frame and a bottom made of a material through which gas can flow, and empty cases for water purification. A columnar container through which gas flows with open ends may be hollow with a gas-impermeable outer wall, and the openings at both ends may have a gas-permeable mesh or the like that allows for gas inflow and exhaust.

[0026] There are no restrictions on the gas that passes through the container for the purpose of removing free water, but for the sake of ease of the process, air may be used as the gas. The gas passing through the container may be at room temperature, or it may be heated to, for example, 30°C to 50°C to further improve the efficiency of free water removal. Since energy is required to heat the gas, the gas in step B is preferably at room temperature, and even if heated, it is preferable that the temperature does not exceed 50°C.

[0027] According to the inventors' research, as the pressure of the supplied gas increases, the time required to remove free water decreases. To investigate the relationship between particle size and the free water removal effect, we will prepare struvite particles with different particle sizes and conduct an investigation. First, the particles will be sieved using a sieve with a mesh size of 88 μm, and the particles remaining on the sieve will be designated as a sample of struvite particles with an average particle size greater than 88 μm. Furthermore, the particles will be sieved using a sieve with a mesh size of 32 μm, and the particles that pass through the sieve will be designated as a sample of struvite particles with an average particle size less than 32 μm. Figure 2 is a graph showing the results of measuring the water content when struvite particles with an average particle size exceeding 88 μm and struvite particles with an average particle size less than 32 μm were packed into a column with an inner diameter of 4 mm at a rate of 0.2 g each, and the flow rate of air passing through the column was varied. According to Figure 2, for struvite particles with an average particle size of 88 μm or more, free water was removed in about 800 seconds when air was circulated at 6.63 m / s, and even when air was circulated at 1.33 m / s, free water was removed in about 1100 seconds. On the other hand, for struvite particles with an average particle size of less than 32 μm, free water was removed in about 950 seconds when air was circulated at 6.63 m / s, and in about 1600 seconds when air was circulated at 1.33 m / s. Figure 3 is a graph showing the results of calculating the energy required to remove free water in the experiment shown in Figure 2. The energy was calculated by determining the work J using the pressure on the struvite in the column measured using a data logger, the column cross-sectional area, the empty air velocity, and the time taken for dehydration. From this work and the mass (g) of the dehydrated free water, the work J / g required to dehydrate 1g was calculated. As shown in Figure 3, for struvite particles with an average particle diameter of 88 μm or more, the best removal efficiency was obtained when air was circulated at a speed of 1.33 m / s. It was also found that this condition yielded the best removal efficiency among the six conditions tested in the experiment. On the other hand, it was found that even for struvite particles with an average particle diameter of less than 32 μm, the best removal efficiency was achieved when air was circulated at a speed of 1.33 m / s. However, the removal efficiency under these conditions was found to be lower than the removal efficiency for struvite particles with an average particle diameter of more than 88 μm, as described above, when air was circulated at a speed of 1.33 m / s. Thus, the removal of free water varies depending on the particle size of the struvite and the flow rate of the supplied gas, with a smaller average particle size tending to result in lower free water removal efficiency.

[0028] (Process C) Step C is a process in which the dehydrated MgNH4PO4·6H2O obtained through step B described above is heated to recover ammonia gas. In step B, the free water that is to be heated is removed, meaning that the struvite is partially dried and is in the hexahydrate form. By removing the free water in step B, the loss of thermal energy from heating, which is used to evaporate the free water remaining in the struvite, is reduced, and ammonia gas can be recovered more efficiently. Step C can be carried out by heating struvite. Struvite is the hexahydrate of MAP, and by applying heat from an external source, NH3 and H2O are separated to form dehydrated Newbergite. This reaction is represented by the following equation.

[0029] [ka]

[0030] Heating can be done in one step, but ammonia has a lower boiling point than water, at about -33°C, but it is highly soluble in water; for example, its solubility in water at 0°C is 89.9 g / 100 cm³. 3 Therefore, it is preferable to first remove water from the hydrate and then recover the ammonia gas.

[0031] From the viewpoint of ammonia gas production efficiency, it is preferable that process C includes a first heating step of heating under reduced pressure at a temperature of 100°C to 150°C, and a second heating step of heating under atmospheric pressure at a temperature higher than that of the first heating step. The reactions in the first and second heating stages can be represented, for example, by the following equation, where n is between 0 and 1.

[0032] [ka]

[0033] The first heating step is preferably a step in which heating is performed under reduced pressure and at a temperature of 100°C to 150°C. The decompression conditions can be any pressure lower than atmospheric pressure, for example, 0.3 to 0.9 atmospheres, preferably 0.4 to 0.8 atmospheres, and more preferably 0.5 to 0.7 atmospheres. The temperature can be between 100°C and 150°C, with 120°C to 140°C being preferred.

[0034] It is thought that the first heating step removes water from the struvite, generating dehydrated ditomalite (i.e., MgNH4PO4) as an intermediate. Subsequently, a second heating step is performed. The second heating step is carried out at atmospheric pressure, and it is preferable that the temperature conditions are higher than the heating temperature in the first heating step. The temperature conditions are preferably at least 50°C higher than the heating temperature in the first heating step. For example, a temperature of 250°C or higher is more preferable, and 300°C to 330°C is even more preferable. There are no particular upper limits on the temperature conditions in the second heating stage. From the viewpoint of energy consumption, productivity, and maintaining the stability of the compound being processed, the temperature conditions in the second heating stage can be 450°C or lower, preferably 400°C or lower, and more preferably 330°C or lower. If the heating temperature in the second heating stage exceeds 330°C, chemical decomposition of the compound may proceed, which is undesirable.

[0035] For example, in the second heating stage, heating at atmospheric pressure at a higher temperature than in the first heating stage generates ammonia gas from the dehydrated ditomalite, and the dehydrated ditomalite becomes dehydrated newbergite. For example, by heating to 300°C in the second heating step, a high concentration of ammonia gas can be obtained.

[0036] Furthermore, the MgHPO4 used in step A, which is the thermal decomposition product of magnesium ammonium phosphate, may also be obtained by heating MgNH4PO4·6H2O, dehydrating it to obtain MgNH4PO4·nH2O (where n is 0-1), and then further heating it to remove ammonia gas. In other words, when ammonia gas is produced in step C, the struvite is ultimately converted into dehydrated Newbergite, and the resulting dehydrated Newbergite can be used in step A of the manufacturing method of this disclosure to adsorb ammonia in wastewater containing ammonia.

[0037] That is, step A in the manufacturing method of the present disclosure may be a step of contacting the MgHPO4 obtained after recovering ammonia by carrying out step C with the wastewater. The dehydrated Newbergite obtained after recovering the high-concentration ammonia gas produced in process C can be used for the treatment of liquids containing ammonia, i.e., for the adsorption of ammonia from liquids containing ammonia.

[0038] Therefore, in the manufacturing method of the present disclosure, the operations of steps A, B, and C can be performed two or more times using the MgHPO4 obtained by recovering ammonia through the execution of step C. In this way, by performing each of the steps A → B → C two or more times, high-concentration ammonia gas can be produced from ammonia-containing wastewater more cost-effectively and efficiently.

[0039] As described above, according to the manufacturing method of this disclosure, ammonia can be adsorbed from a liquid containing ammonia using MgHPO4 obtained after producing a high concentration of ammonia gas, thus the material that adsorbs ammonia is recycled. Therefore, it becomes possible to produce ammonia gas with efficiency proportional to the amount of wastewater when processing various liquids containing ammonia. Furthermore, the manufacturing method disclosed herein enables efficient production of ammonia gas using only a heating device and a vacuum device. Since the resulting ammonia gas has a high concentration exceeding 50% by volume, it can be used as a fuel, such as biogas, and solves the problem of wastewater such as low-concentration ammonia water, thus having a wide range of applications. [Examples]

[0040] The manufacturing method of this disclosure will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing procedures, etc., shown in the following examples can be modified as appropriate, as long as they do not deviate from the spirit of this disclosure. Therefore, the method for producing ammonia gas according to this disclosure should not be interpreted restrictively by the specific examples shown below. Unless otherwise specified, "%" and "ppm" below refer to mass-based percentages.

[0041] The method for producing ammonia gas related to this disclosure will be explained in more detail below.

[0042] [Preparation of Newbergite (MgHPO4) particles] For Newbergite, a sieving method was used to separate the particles using a sieve with a mesh size of 88 μm. The particles remaining on the 88 μm sieve were used as a sample of Newbergite particles with an average particle size greater than 88 μm. The remaining particles were then separated using a sieve with a mesh size of 32 μm. The particles that passed through the 32 μm sieve were prepared as a sample of Newbergite particles with an average particle size less than 32 μm.

[0043] [Study on the recovery rate of ammonia water] (Process A-1) First, Newbergite particles with an average particle size of less than 32 μm were immersed in a 3000 ppm ammonia solution (at room temperature), which was prepared as a model for a liquid containing ammonia. Subsequently, the process of heating the material to a final temperature of 325°C at a heating rate of 70°C / min was repeated three times to convert Newbergite into struvite. Subsequently, the concentration of the ammonia solution was measured one hour after immersion, and the ammonia recovery rate after immersion was calculated to be approximately 20%. The ammonia concentration was similarly measured after immersion in ammonia water for 2 hours, and the calculated ammonia recovery rate was approximately 28%. When the pH of the ammonia solution was measured with a pH meter, it was found to be above 11, indicating that it was alkaline.

[0044] (Process A-2) Using the same Newbergite particles with an average particle size of less than 32 μm as in process A-1, the immersion and heating were carried out in the same manner as in process A-1, except that the immersion temperature in ammonia water was maintained at 80°C to 90°C by a water bath. The ammonia recovery rate was calculated in the same manner as in process A-1, and the recovery rate after 1 hour of immersion in ammonia water was approximately 39%, and the recovery rate after 2 hours of immersion was also approximately 39%. The pH of the ammonia solution was above 11, indicating it was alkaline. This indicates that heating during immersion in ammonia water improves the ammonia recovery rate of Newbergite particles.

[0045] (Process A-3) Using the same Newbergite particles with an average particle size of less than 32 μm as in process A-1, the immersion temperature in ammonia water was maintained at 80°C to 90°C by a water bath, in the same manner as in process A-2. Subsequently, the temperature was increased at a rate of 5°C / min to a final temperature of 180°C, and maintained at this temperature for 3 hours to convert Newbergite into struvite. When the ammonia recovery rate was calculated in the same manner as in process A-1, the recovery rate after 1 hour of immersion in ammonia water was approximately 40%, and the recovery rate after 2 hours of immersion was approximately 50%. The pH of the ammonia solution was above 11, indicating it was alkaline.

[0046] (Process A-4) First, hydrochloric acid was added to the ammonia solution as a pH adjuster to adjust the pH to 9.83. Subsequently, using the same Newbergite particles with an average particle size of less than 32 μm as in step A-1, the immersion temperature in ammonia water was maintained at 80°C to 90°C by a water bath, in the same manner as in step A-2. Subsequently, the temperature was increased at a rate of 5°C / min to a final temperature of 180°C, and maintained at this temperature for 3 hours to convert Newbergite into struvite. When the ammonia recovery rate was calculated in the same manner as in process A-1, the recovery rate after 1 hour of immersion in ammonia water was approximately 59%, and the recovery rate after 2 hours of immersion was also approximately 59%.

[0047] (Process A-5) Except for using Newberg particles with an average particle size of 88 μm or more instead of Newberg particles with an average particle size of less than 32 μm, the samples were immersed in 3000 ppm ammonia water (at room temperature), which was prepared as a model of a liquid containing ammonia, under the same conditions as in process A-1, and the temperature was increased under the same conditions as in process A-1. Subsequently, the ammonia recovery rate was calculated in the same manner as in process A-1, and the recovery rate after 1 hour of immersion in ammonia water was approximately 10%, and the recovery rate after 2 hours of immersion was approximately 19%.

[0048] From the above evaluation, it was found that smaller Newbergite particles yield a higher ammonia recovery rate, and that the ammonia recovery rate for converting Newbergite to struvite can be controlled by the immersion and subsequent heating conditions.

[0049] [Consideration of physical dehydration] In the study of process B, the effect of removing free water was investigated using struvite particles that were experimentally immersed in water. Figure 2 is a graph showing the results of measuring the water content when 0.2 g each of struvite particles with an average particle size exceeding 88 μm and struvite particles with an average particle size less than 32 μm, immersed in water, were packed into a column with an inner diameter of 4 mm, and the flow rate of air passing through was varied. According to Figure 2, for struvite particles with an average particle size of 88 μm or more, free water was removed in about 800 seconds when air was circulated at 6.63 m / s, and even when air was circulated at 1.33 m / s, free water was removed in about 1100 seconds. On the other hand, for struvite particles with an average particle size of less than 32 μm, free water was removed in about 950 seconds when air was circulated at 6.63 m / s, and in about 1600 seconds when air was circulated at 1.33 m / s.

[0050] From this, it was confirmed that in step B, which involves the physical dehydration of MgNH4PO4·6H2O, larger struvite particle sizes result in better dehydration efficiency. As previously mentioned, it was confirmed that a smaller average particle size of struvite improves the particle surface area, resulting in better ammonia adsorption efficiency. Therefore, it is considered preferable to appropriately select the Newbergite particles used as raw materials, the particle size of the struvite particles converted from the Newbergite particles, and the amount of gas permeated in step B, according to the purpose.

[0051] <Example 1> (Process A) Under the conditions of the above-mentioned process (A-4), which showed the highest ammonia recovery rate in process A, Newbergite particles were treated to adsorb ammonia and obtain struvite particles. (Process B) For struvite particles with an average particle size of less than 32 μm that had undergone the above process (A-4), the free water was removed by circulating air at 6.63 m / s for 1000 seconds, as the above study showed that this method provided a good removal rate of free water. The air circulation was performed at room temperature.

[0052] Next, process C was performed under different conditions. (Process C-1) The struvite particles from which free water was removed in process A-4 and process B above were subjected to process (C-1) under the following conditions. As the first heating step, the temperature was raised from room temperature to 105°C to 150°C at a rate of 15°C / min under reduced pressure of 0.6 atmospheres, and held for 10 minutes. Next, as the second heating step, the mixture was heated to 300°C at atmospheric pressure to obtain dehydrated Newbergite. This was used as the manufacturing method for Example 1.

[0053] <Example 2> (Process C-2) The struvite particles from which free water was removed in process A-4 and process B above were subjected to process (C-2) under the following conditions. As the first heating step, the temperature was raised from room temperature to 120°C at a rate of 15°C / min under reduced pressure of 0.6 atmospheres, and held for 10 minutes. Next, as the second heating step, the mixture was heated to 300°C at atmospheric pressure to obtain dehydrated Newbergite. This was used as the manufacturing method for Example 2.

[0054] <Example 3> (Process C-3) The struvite particles from which free water was removed in process A-4 and process B above were subjected to process (C-3) under the following conditions. As the first heating step, the temperature was raised from room temperature to 135°C at a rate of 15°C / min under reduced pressure of 0.6 atmospheres, and held for 10 minutes. Next, as the second heating step, the mixture was heated to 300°C at atmospheric pressure to obtain dehydrated Newbergite. This was used as the manufacturing method for Example 3.

[0055] (Process C-4) The struvite particles from which free water was removed in process A-4 and process B above were subjected to process (C-4) under the following conditions. As the first heating step, the temperature was raised from room temperature to 150°C at a rate of 15°C / min under reduced pressure of 0.6 atmospheres, and held for 10 minutes. Next, as the second heating step, the mixture was heated to 300°C at atmospheric pressure to obtain dehydrated Newbergite. This was used as the manufacturing method for Example 4.

[0056] In step C, where dehydrated Newbergite is obtained by the manufacturing methods of Examples 1 to 4, the maximum heating temperature conditions of the first heating step and the amount of ammonia released and the concentration of ammonia gas obtained in the second heating step were measured by the following method. The results are shown in Figure 4.

[0057] The generated ammonia and water were dissolved in an ethanol solution using a scrubber in the subsequent stage, and the ammonia and water in the solution were quantified using a gas chromatograph (manufactured by Shimadzu Corporation) equipped with a BID (Dielectric-Barrier Discharge Ionization Detector). The ammonia concentration and ammonia recovery rate were calculated from the masses of ammonia and water obtained.

[0058] Figure 4 is a graph showing the relationship between the temperature in the first heating stage, the recovery rate of the ammonia gas obtained, and the concentration of the ammonia gas. As is clear from Figure 4, in the manufacturing method of Example 1, even under temperature conditions where the maximum temperature reached in the first heating step is 105°C, more than 50% by volume of ammonia gas can be recovered. Note that in Figure 4, "maximum temperature reached in the first heating step" is written as "temperature reached in the first step". In Figure 4, the temperatures reached in the first heating stage are 105°C for Example 1, 120°C for Example 2, 135°C for Example 3, and 150°C for Example 4. In the manufacturing methods of Examples 2 to 4, when the maximum heating temperature in the first heating step was set to 135°C or higher, the ammonia recovery rate tended to be lower than in Example 1. However, the ammonia gas concentration was approximately 100% by volume. This confirmed that high-concentration ammonia gas can be produced using the manufacturing methods of Examples 1 to 4. Ammonia gas with a concentration of 50% by volume or higher can be used for various purposes, including as fuel.

[0059] Furthermore, since the dehydrated Newbergite (MgHPO4) recovered in step C was entirely derived from MAP, it was confirmed that it could be applied again to step A for ammonia adsorption in ammonia-containing liquids.

Claims

1. A liquid containing ammonia, MgHPO ４ Bring ammonia into contact with MgHPO ４ Bind to MgNH ４ PO ４ 6H ２ Step A to obtain O, MgNH obtained in step A above ４ PO ４ 6H ２ Step B involves physically dehydrating O, Said MgNH after said physical dewatering ４ PO ４ ·6H ２ O heating step C of recovering ammonia gas, A method for producing ammonia gas, including the gas itself.

2. The method for producing ammonia gas according to claim 1, wherein step C includes a first heating step of heating under reduced pressure at a temperature of 100°C to 150°C, and a second heating step of heating at atmospheric pressure at a temperature higher than that of the first heating step.

3. The above step B is MgNH ４ PO ４ 6H ２ A method for producing ammonia gas according to claim 1 or claim 2, comprising filling a container through which a gas flows with O, and removing free water by circulating the gas in the container.

4. The aforementioned MgHPO ４ is magnesium ammonium phosphate (MgNH ４ PO ４ 6H ２ MgNH obtained by heating and dehydrating O) ４ PO ４ nH ２ A method for producing ammonia gas according to claim 1 or claim 2, wherein the ammonia gas is obtained by further heating O (n is 0 to 1) to remove the ammonia gas, and the ammonia gas is a thermal decomposition product of magnesium ammonium phosphate.

5. Step A is the process of recovering ammonia by performing step C and then MgHPO ４ A method for producing ammonia gas according to claim 1 or claim 2, comprising contacting the above-mentioned liquid containing ammonia with the above-mentioned liquid.

6. As a result of carrying out step C, ammonia is recovered and MgHPO is obtained. ４ A method for producing ammonia gas according to claim 1 or 2, wherein the operations of step A, step B, and step C are performed two or more times using [a specific method].

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