Method for producing hydrogen from ammonia using pressure swing adsorption

Abstract

A method for producing hydrogen from ammonia using pressure swing adsorption is provided. The hydrogen production method of the present invention is a method for producing hydrogen from ammonia, comprising: a step of generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction using a catalyst; a step of selectively adsorbing and purifying undecomposed ammonia gas from a gas containing low-purity hydrogen and nitrogen and undecomposed ammonia that has been supplied and cooled through the high-temperature reaction step; and a step of separating and purifying high-purity hydrogen from the gas composed of the low-purity hydrogen and nitrogen. The method is characterized in that the undecomposed ammonia gas is desorbed and purified by pressure cycling adsorption (PSA) using a CMS (Carbon Molecular Sieve) adsorbent.

Description

Technical Field

[0001] The present invention relates to a method for producing hydrogen from ammonia, and more particularly, to a method for producing hydrogen from ammonia, which can remove undecomposed ammonia by a pressure swing adsorption method using an adsorbent CMS (Carbon Molecular Sieve).

Background Art

[0002] Conventional ammonia removal processes have been mainly used for an ammonia recovery process to improve the performance of the Haber-Bosch method and an ammonia removal process to prevent discharge into the atmosphere.

[0003] In the hydrogen production process using ammonia, ammonia is decomposed into nitrogen and hydrogen by a catalyst under high-temperature conditions as shown in the following Reaction Formula 1, and undecomposed ammonia is contained in the decomposition gas (N 2 , H 2 ) according to the decomposition rate, and high-purity hydrogen is produced through a process of removing this. [Reaction Formula 1] 2NH 3 →N 2 +3H 2

[0004] For this purpose, as a conventionally applied process, a temperature swing adsorption method (TSA, Temperature Swing Adsorption) in which ammonia is adsorbed and removed using an adsorbent, and then the temperature of the adsorbent after adsorption is raised for desorption / regeneration has been mainly used. In this method, problems such as maintaining the temperature inside the adsorption tower uniformly during desorption and then cooling the inside of the adsorption tower to prepare for the adsorption process have occurred, and there have been various problems to be solved for use in an actual process.

[0005] Therefore, recently, an ammonia adsorption / regeneration process using the pressure swing adsorption (PSA) method has been proposed, and research has been conducted on a laboratory scale to confirm its potential at a low concentration level of several thousand ppm. There have been laboratory studies on removing low-concentration ammonia, but recently, an ammonia decomposition hydrogen production process has been proposed to produce clean hydrogen. There is no adsorbent for the ammonia adsorption / desorption process of the PSA method and no case presenting such a process for removing undecomposed ammonia that may occur in this process.

[0006] Normally, the decomposition reaction of ammonia for hydrogen production proceeds at normal pressure to 9 bar_g, and there are many studies attempting to carry out the decomposition under pressure for the effective operation of the subsequent hydrogen purification process. When the decomposition proceeds under such pressurized conditions, the ammonia removal process located after the decomposition process and the process for purifying hydrogen can be realized by the PSA method, which has the advantage of a simple process configuration. However, when ammonia is decomposed under a pressurized state, as the decomposition rate of ammonia decreases, undecomposed ammonia remains at the % concentration level. If this is not removed, the load on the hydrogen purification equipment increases, and there is a high possibility that the finally produced hydrogen contains ammonia, which may cause problems such as not being able to meet the quality of hydrogen.

[0007] For this reason, conventional research has used various adsorbents to remove ammonia. As an example, zeolite, alumina, silica gel, and activated carbon are mainly used (AIChE Journal, 2000, 46(8)), or metal halides (MgCl 2 , CaCl 2 , SrCl 2 , MgBr 2 , CaBr 2 , SrBr 2 ) etc. have been used in research (ACS Sustainable Chem. Eng, 2018.6(5)).

[0008] The AIChE Journal has conducted research on various adsorbents, but only the adsorption data (isothermal adsorption curves) of ammonia can be utilized, and there is no additional data regarding whether it is applicable to the process of removing the adsorbed ammonia (regenerating the adsorbent), making it difficult to determine whether it is applicable as PSA. In particular, in the case of adsorbents, hysteresis, where the profiles of the adsorption curve and the desorption curve are different, is also observed, so it is difficult to determine the applicability of PSA based only on the isothermal adsorption curve. Also, in ACS Sustainable Chem. Eng, it was operated at a high temperature (150 °C), applied for the TSA (temperature swing adsorption) process, and a different operation method from the PSA method was also applied.

[0009] On the other hand, recently, there have been some studies on adsorbents for the application of pressure swing adsorption (PSA) and the improvement of adsorbents, but they are only restrictively applicable only in the relatively low ammonia concentration range (<1000 ppm), and the application of the PSA method in the undecomposed ammonia concentration range (% concentration level) that can be produced in the ammonia decomposition hydrogen production process for the undecomposed ammonia removal process has not been carried out. Also, the portion that can be utilized as the working capacity by the ammonia adsorption / desorption cycle is low, and it is difficult to determine whether the conventional research was research targeting PSA.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] In view of various requirements arising for hydrogen production and hydrogen transportation in realizing a hydrogen society, the present invention focuses on ammonia as a recently attracting means of hydrogen transportation and production, and attempts to remove undissociated ammonia in the process of decomposing ammonia to produce hydrogen. Specifically, the present invention aims to provide a method for producing hydrogen from ammonia, which can remove the undissociated ammonia by the PSA (pressure swing adsorption) method in the steps of decomposing ammonia, removing undissociated ammonia, and separating / purifying hydrogen, which are the main steps of the ammonia decomposition hydrogen extraction process using a catalyst.

[0012] Further, the technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those having ordinary knowledge in the technical field to which the present invention belongs from the following description.

Means for Solving the Problems

[0013] Therefore, one aspect of the present invention is a step of generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction using a catalyst; a step of selectively adsorbing and purifying undissociated ammonia gas from the gas containing low-purity hydrogen, nitrogen, and undissociated ammonia that is supplied and cooled through the high-temperature reaction step; and a step of separating and purifying high-purity hydrogen from the gas composed of the low-purity hydrogen and nitrogen, which is a method for producing hydrogen from ammonia, characterized in that the undissociated ammonia gas is desorbed and purified by a pressure swing adsorption method (PSA) using a CMS (Carbon Molecular Sieve) adsorbent, and relates to a method for producing hydrogen from ammonia.

[0014] In the present invention, CMS loaded with metal halide can be used as the adsorbent.

[0015] The metal halide is MgCl 2 、CaCl 2 、SrCl2 , MgBr 2 , CaBr 2 and SrBr 2 One or more selected from can be used.

Advantages of the Invention

[0016] According to the present invention as described above, by removing undecomposed ammonia by pressure swing adsorption (PSA) using a CMS (Carbon Molecular Sieve) adsorbent, the ammonia adsorption amount is improved, and at the same time, the desorption performance is ensured, so that undecomposed ammonia (0.5 - 11% concentration) generated in the process for ammonia decomposition hydrogen production can be removed, which has a useful effect.

[0017] In addition, compared with the conventional TSA and Scrubbing methods, it has less energy consumption, a simple structure, and can be applied to the ammonia decomposition hydrogen production process. Furthermore, in the process of producing hydrogen from ammonia, the undecomposed ammonia gas can be effectively desorbed and removed and used as a heat source for the ammonia decomposition hydrogen production process, thereby improving the efficiency of the overall hydrogen production manufacturing process.

Brief Description of the Drawings

[0018]

Figure 1

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Figure 7

Mode for Carrying Out the Invention

[0019] The present invention will be described below.

[0020] The present invention is characterized by presenting an adsorbent applicable in a PSA method for the undecomposed ammonia absorption / desorption process of the conventional TSA method in the process of extracting hydrogen from ammonia through a high-temperature and high-pressure reaction using a catalyst. Specifically, the present invention uses CMS (Carbon Molecular Sieve) as the above adsorbent for removing undecomposed ammonia in a PSA method, and further, by using CMS loaded with metal chlorides such as MgCl 2 etc. as an adsorbent, it is possible to improve the adsorption performance of undecomposed ammonia in a PSA method, and provides a method for producing hydrogen from ammonia.

[0021] Such a method for producing hydrogen from ammonia according to the present invention includes a step of generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction using a catalyst; a step of selectively adsorbing and purifying undecomposed ammonia gas from the gas containing low-purity hydrogen, nitrogen, and undecomposed ammonia that has been supplied and cooled through the high-temperature reaction step; and a step of separating and purifying high-purity hydrogen from the gas composed of the low-purity hydrogen and nitrogen. In the method for producing hydrogen from ammonia, the undecomposed ammonia gas is desorbed and purified by a pressure swing adsorption (PSA) method using a CMS (Carbon Molecular Sieve) adsorbent.

[0022] Figure 1 is a process diagram schematically showing the manufacturing process for producing hydrogen from ammonia according to an embodiment of the present invention.

[0023] As shown in Figure 1, generally, a method for extracting hydrogen from ammonia first includes a step of generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction using a catalyst.

[0024] Generally, ammonia is decomposed into nitrogen and hydrogen through a high-temperature reaction, and the concentration of undecomposed ammonia varies depending on the decomposition conditions. Table 1 below shows the concentration of undecomposed ammonia according to the decomposition rate of ammonia, the pressure for ammonia decomposition, and the temperature for removing undecomposed ammonia.

[0025] As shown in Table 1 below, it can be seen that when ammonia is typically decomposed at the 90% level, about 5.3% (53,000 ppm) level of ammonia remains. Therefore, in the present invention, considering the conversion rate level that can be used in the ammonia decomposition hydrogen extraction step, an adsorbent applicable to a pressure swing adsorption (PSA) process under the conditions of an undecomposed ammonia residue condition of 0.5 to 11.1%, 40°C, and 3 to 9 bar_g, and a method for producing hydrogen using the adsorbent are to be provided.

[0026]

Table 1

[0027] Next, in the present invention, the undecomposed ammonia gas is selectively adsorbed and purified from the gas containing low-purity hydrogen and nitrogen and undecomposed ammonia that has been supplied and cooled through the high-temperature reaction process.

[0028] In this case, the present invention is a technology for removing undecomposed ammonia generated in the ammonia decomposition hydrogen production process, and is characterized by removing undecomposed ammonia by a PSA (pressure swing adsorption) method using an adsorbent CMS (carbon molecular sieve). By using such CMS as an ammonia adsorption / desorption adsorbent, it is possible to ensure a higher level of adsorption / desorption working capacity of undecomposed ammonia compared to the conventional PSA process.

[0029] In the process conditions for adsorbing and removing undecomposed ammonia using the CMS of the present invention, it is preferable to use undecomposed ammonia gas having an ammonia decomposition rate of 80 to 99%, an undecomposed ammonia concentration of 0.5 to 11%, a pressure of 3 bar_g to 9 bar_g, and a temperature of 20 to 50°C.

[0030] It is also preferable to use CMS carrying a metal halide as an adsorbent, which can provide better adsorption performance than CMS not carrying a metal chloride.

[0031] More preferably, the metal chloride is MgCl 2 , CaCl 2 , SrCl 2 , MgBr 2 , CaBr 2 and SrBr 2 The present invention relates to the use of one or more types selected from the above.

[0032] On the one hand, the operating capacity of the ammonia adsorption / removal process using conventional activated carbon as the adsorbent varies depending on the temperature and pressure conditions. When applied in the TSA method, if it is not pretreated with metal halide, it is 0.6 mmol / g, and when treated with MgCl 2 it is known to have an operating capacity of up to 2.1 mmol / g. However, for large-capacity gas treatment, this process has low economic efficiency due to the time required for heating and cooling and the additional energy consumption, making it difficult to handle large-capacity treatment and increasing the generation of greenhouse gases due to additional energy use. Also, when applying the adsorption / desorption process of undecomposed ammonia in the PSA method using conventional activated carbon as the adsorbent, for activated carbon not pretreated with metal chloride, it is at the level of 0.77 mmol / g, and when treated with MgCl 2 it is also known to have an operating capacity of 1.57 mmol / g under the condition of 9 bar_g [Research on the Adsorption and Desorption Characteristics of Metal-Impregnated Activated Carbon with Metal Precursors for Ammonia Regeneration and Concentration (Clean Technol. 26(2) 2020, 137-144)].

[0033] Thus, it can be seen that when using ordinary activated carbon as the adsorbent, the adsorption capacity is reduced compared to when using the CMS of the present invention or the CMS supported with metal chloride described below as the adsorbent.

[0034] Subsequently, in the present invention, high-purity hydrogen can be produced by separating and purifying high-purity hydrogen from the gas composed of the above low-purity hydrogen and nitrogen. Although various methods have been proposed as such methods for purifying high-purity hydrogen, the present invention is not limited to specific process conditions and can utilize various processes without limitation. Modes for Carrying Out the Invention

[0035] Hereinafter, the present invention will be described in detail by examples.

[0036] (Example) Ammonia adsorption / desorption tests were carried out using a carbon molecular sieve (CMS) in a process for removing undecomposed ammonia. 2 The CMS loaded with MgCl was also subjected to an adsorption / desorption test for removing undecomposed ammonia. 2 The loading of MgCl was 4 wt% on CMS. 2 Mix CMS with distilled water containing MgCl 2 After the solution was completely loaded onto the CMS, it was dried with mixing, and then further dried at 200°C for 1 hour in a nitrogen atmosphere to completely remove residual moisture, and then used in an ammonia adsorption / desorption experiment.

[0037] FIG. 2 is a schematic cross-sectional view of an ammonia adsorption / desorption test device configured to adsorb and desorb unreacted ammonia gas using an adsorbent in one embodiment of the present invention. As shown in FIG. 2, the pressure in the reactor containing the adsorbent was adjusted using a back pressure regulator so that ammonia adsorption occurred continuously at the target pressure, and the ammonia concentration in the gas to which ammonia was adsorbed was continuously analyzed using an ammonia analyzer. When the adsorption was completed, the valve of the conventional gas line was closed, and the N 2 After opening the flushing line to release the pressure, 2 After desorption was completed, the experimental equipment was configured to supply ammonia-containing gas again to perform adsorption, and the adsorption / desorption performance of the adsorbent was evaluated when the PSA (pressure swing adsorption) process was applied.

[0038] On the one hand, at this time, ammonia adsorption / desorption tests were carried out under various conditions corresponding to the temperature, pressure, and ammonia concentration applicable to the ammonia decomposition hydrogen production process, and the specific conditions are shown in Table 2 below. In this experiment, adsorption was carried out under the temperature and pressure conditions in Table 2 below, and desorption was carried out under the same operating conditions or conditions slightly higher than the adsorption temperature, and the adsorbed ammonia was desorbed while flowing nitrogen under normal pressure conditions. After that, after the ammonia was completely desorbed, the process of adsorbing / desorbing ammonia under the temperature and pressure conditions in Table 2 below was repeated 3 times. And the results of the ammonia adsorption / desorption tests under such various conditions are also shown in Table 2 below.

[0039] In addition, the ammonia adsorption breakthrough curves for each cycle when the undecomposed ammonia (NH 3 ) gas was adsorbed under each condition are shown in Figs. 3 to 7.

[0040] Fig. 3 is a diagram showing the ammonia adsorption breakthrough curves for each cycle when the undecomposed ammonia (NH 3 ) gas with a concentration of 5% was adsorbed at a pressure of 7 bar using CMS as the adsorbent in the examples of the present invention.

[0041] Fig. 4 is a diagram showing the ammonia adsorption breakthrough curves for each cycle when the undecomposed ammonia (NH 2 ) gas with a concentration of 2% was adsorbed at a pressure of 7 bar using CMS supported with 4 wt% of MgCl 3 as the adsorbent in the examples of the present invention.

[0042] Fig. 5 is a diagram showing the ammonia adsorption breakthrough curves for each cycle when the undecomposed ammonia (NH 2 ) gas with a concentration of 5% was adsorbed at a pressure of 7 bar using CMS supported with 4 wt% of MgCl 3 as the adsorbent in the examples of the present invention.

[0043] Fig. 6 is a diagram showing the undecomposed ammonia (NH 2 ) gas with a concentration of 2% was adsorbed at a pressure of 5 bar using CMS supported with 4 wt% of MgCl as the adsorbent in the examples of the present invention.3 ) It is a diagram showing the ammonia adsorption breakthrough curves for different numbers of cycles (cycles) when the gas is adsorbed.

[0044] Figure 7 shows CMS loaded with 4 wt% MgCl 2 as the adsorbent in an example of the present invention, and ammonia adsorption breakthrough curves for different numbers of cycles (cycles) when adsorbing a 5% concentration of undecomposed ammonia (NH 3 ) gas at a pressure of 5 bar.

[0045]

Table 2

[0046] As shown in Table 2 and Figures 3 to 7 above, as a result of measuring the ammonia concentration in the gas passing through the adsorption column during the adsorption experiment, it can be seen that when the ammonia adsorption is carried out well, almost no ammonia is measured in the exhaust gas.

[0047] Normally, when MgCl 2 is supported on conventional activated carbon, the adsorption / desorption operation capacity is shown at the level of 1.4 mmol / g under the condition of 7 bar_g. However, when using CMS, which is the adsorbent of the present invention, even without the support of MgCl 2 , it can show an adsorption capacity similar to that of the activated carbon-MgCl 2 adsorbent. Furthermore, when MgCl 2 is supported on CMS, it can be seen that the operation capacity is improved epoch-makingly by about twice, which is a result at a higher level than the highest level of operation capacity seen in the conventional activated carbon-MgCl 2 adsorbent.

[0048] On the other hand, when examining the adsorption curve, it can be seen that the highest level of adsorption amount is shown in the first adsorption cycle, but the adsorption amount decreases slightly in the second and third cycles. This means that the entire amount adsorbed on the adsorbent does not desorb and continues to remain on the adsorbent.

[0049] In this case, in order to completely remove the adsorbed ammonia, it is possible to apply the TSA method. However, due to the problems that may occur when applying TSA as described above, it is appropriate to apply PSA. In particular, by operating with the PSA method, it is possible to effectively use it for removing the undissociated ammonia in the gas produced in the ammonia decomposition hydrogen production process while minimizing the required amount of additional energy.

[0050] As described above, in the detailed description of the present invention, the preferred embodiments of the present invention have been described. However, it goes without saying that those having ordinary knowledge in the technical field to which the present invention pertains can make various modifications without departing from the scope of the present invention. Therefore, the scope of the rights of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the claims described below, but also by those equivalent thereto.

Claims

**Claim 1** A process for producing hydrogen and nitrogen from ammonia gas through a high-temperature reaction using a catalyst; a process for selectively adsorbing and purifying undecomposed ammonia gas from the gas containing low-purity hydrogen, nitrogen, and undecomposed ammonia that has been supplied and cooled through the high-temperature reaction process; and a process for separating and purifying high-purity hydrogen from the gas composed of the low-purity hydrogen and nitrogen; A method for producing hydrogen from ammonia, comprising: A method for producing hydrogen from ammonia, wherein the undecomposed ammonia gas is desorbed and purified by a pressure swing adsorption (PSA) method using a CMS (Carbon Molecular Sieve) adsorbent supported with a metal halide. **Claim 2** The metal chloride is MgCl ２ , CaCl ２ , SrCl ２ , MgBr ２ , CaBr ２ and SrBr ２ The method for producing hydrogen from ammonia according to claim 1, which is one or more selected from **Claim 3** The method for producing hydrogen from ammonia according to claim 1, wherein the adsorbent is applied to undecomposed ammonia having an ammonia decomposition rate of 80 to 99%, an undecomposed ammonia concentration of 0.5 to 11%, a pressure of 3 bar_g to 9 bar_g, and a temperature of 20 to 50°C.

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