METHOD FOR PREPARING HYDROGEN FROM AMMONIA BY USING PRESSURE SWING ADSORPTION

Abstract

A method for preparing hydrogen from ammonia by using pressure swing adsorption (PSA) is provided. The method for preparing hydrogen from ammonia, of the present invention, comprises the steps of: generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction by using a catalyst; performing purification by selectively adsorbing unreacted ammonia gas from a gas containing unreacted ammonia and low-purity hydrogen and nitrogen, which are supplied through the high-temperature reaction and cooled; and performing purification by separating high-purity hydrogen from the gas consisting of low-purity hydrogen and nitrogen, wherein purification is carried out by using a carbon molecular sieve (CMS) adsorbent so as to desorb the unreacted ammonia gas through PSA.

Claims

1. In a method for manufacturing hydrogen from ammonia, the method comprising steps of: generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction by using a catalyst; performing purification by selectively adsorbing undecomposed ammonia gas from a gas containing undecomposed ammonia and low-purity hydrogen and nitrogen, which are supplied through the high-temperature reaction and cooled; and performing purification by separating high-purity hydrogen from the gas consisting of low-purity hydrogen and nitrogen, wherein purification is carried out by using a carbon molecular sieve (CMS) adsorbent so as to desorb the undecomposed ammonia gas through PSA.

2. The method for manufacturing hydrogen from ammonia of claim 1, wherein CMS loaded with metal halide is used as the adsorbent.

3. The method for manufacturing hydrogen from ammonia of claim 2, wherein the metal halide is one or more selected from MgCl.sub.2, CaCl.sub.2, SrCl.sub.2, MgBr.sub.2, CaBr.sub.2, and SrBr.sub.2.

4. The method for manufacturing hydrogen from ammonia of claim 1, wherein the adsorbent is applied to undecomposed ammonia having an ammonia decomposition rate of 80 to 99%, a concentration of undecomposed ammonia of 0.5 to 11%, pressure of 3 barg to 9 barg, and a temperature of 20 to 50? C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a process diagram schematically illustrating a manufacturing process for producing hydrogen from ammonia according to an embodiment of the present disclosure.

[0021] FIG. 2 is a cross-sectional schematic diagram of an ammonia adsorption/desorption test device configured to adsorb, desorb, and remove undecomposed ammonia gas using an adsorbent in an embodiment of the present disclosure.

[0022] FIG. 3 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 5% was adsorbed at 7 bar pressure using CMS as an adsorbent in an embodiment of the present disclosure.

[0023] FIG. 4 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 2% was adsorbed at 7 bar pressure using CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

[0024] FIG. 5 is diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 5% was adsorbed at 7 bar pressure using CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

[0025] FIG. 6 is diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 2% was adsorbed at 5 bar pressure using CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

[0026] FIG. 7 is diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 5% was adsorbed at 5 bar pressure using CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

BEST MODE FOR INVENTION

[0027] Hereinafter, the present disclosure will be described.

[0028] An aspect of the present disclosure is to provide an adsorbent that can be applied to the method of undecomposed ammonia adsorption/desorption process using a PSA method to supplant the existing TSA, in a process of extracting hydrogen from ammonia through a high temperature and high pressure reaction using a catalyst. Specifically, in the present disclosure, undecomposed ammonia is removed by a PSA method by using carbon molecular sieve (CMS) as the adsorbent, and furthermore, an aspect of the present disclosure is to provide a method of manufacturing hydrogen from ammonia that can improve the adsorption performance of undecomposed ammonia by a PSA method by using CMS loaded with metal chloride such as MgCl.sub.2 as the adsorbent.

[0029] In a method for manufacturing hydrogen from ammonia by using pressure swing adsorption (PSA), the method including steps of: generating hydrogen and nitrogen from ammonia gas through a high-temperature reaction by using a catalyst; performing purification by selectively adsorbing undecomposed ammonia gas from a gas containing undecomposed ammonia and low-purity hydrogen and nitrogen, which are supplied through the high-temperature reaction and cooled; and performing purification by separating high-purity hydrogen from the gas consisting of low-purity hydrogen and nitrogen, wherein purification is carried out by using a carbon molecular sieve (CMS) adsorbent so as to desorb the undecomposed ammonia gas through PSA.

[0030] FIG. 1 is a process diagram schematically illustrating a manufacturing process for manufacturing hydrogen from ammonia according to an embodiment of the present disclosure.

[0031] As illustrated in FIG. 1, generally, a method of extracting hydrogen from ammonia first includes a process of generating hydrogen and nitrogen from ammonia gas through a high temperature reaction using a catalyst.

[0032] Generally, ammonia is decomposed into nitrogen and hydrogen through a high-temperature reaction, and a concentration of undecomposed ammonia varies depending on decomposition conditions. Table 1 below illustrates the concentration of undecomposed ammonia according to a decomposition rate of ammonia, a pressure for decomposing ammonia, and a temperature for removing undecomposed ammonia.

[0033] As illustrated in Table 1 below, when ammonia is typically decomposed to a 90% level, it can be seen that a level of about 5.3% (53,000 ppm) of ammonia remains. Accordingly, in the present disclosure, considering a level of a conversion rate that can be used in an ammonia decomposition hydrogen extraction process, an adsorbent that can be applied to a pressure swing adsorption (PSA) process under conditions of 0.5 to 11.1% residual ammonia, 40? C., 3 to 9 bar_g, and a method for manufacturing hydrogen using the adsorbent are provided.

TABLE-US-00001 TABLE 1 Conversion Temperature rate NH.sub.3 N.sub.2 H.sub.2 after (%) (%) (%) (%) cooling(? C.) Pressure 80 11.1 22.2 66.7 40 3~9 bar_g 90 5.3 23.7 71.1 40 3~9 bar_g 95 2.6 24.4 73.1 40 3~9 bar_g 99 0.5 24.9 74.6 40 3~9 bar_g

[0034] Subsequently, in the present disclosure, purification is performed by selectively adsorbing undecomposed ammonia gas among a gas containing undecomposed ammonia and low-purity hydrogen and nitrogen, which are supplied through the high-temperature reaction process and cooled.

[0035] In this case, in the present disclosure, undecomposed ammonia is removed by a PSA (pressure swing adsorption) method using an adsorbent carbon molecular sieve (CMS) as a technology for removing undecomposed ammonia generated in an ammonia decomposition hydrogen production process. By using the CMS as an ammonia adsorption/desorption adsorbent, working capacity for adsorption/desorption of undecomposed ammonia may be secured at a higher level than that of the conventional PSA process.

[0036] As process conditions for adsorption and removal of undecomposed ammonia using the CMS of the present disclosure, it is preferable to use undecomposed ammonia gas having an ammonia decomposition rate of 80 to 99%, a concentration of undecomposed ammonia of 0.5 to 11%, pressure of 3 barg to 9 barg, and a temperature of 20 to 50? C.

[0037] In addition, preferably, CMS loaded with metal chloride is used as an adsorbent. As a result, better adsorption performance, compared to when CMS, not loaded with metal chloride, is used as an adsorbent, may be shown.

[0038] More preferably, at least one selected from MgCl.sub.2, CaCl.sub.2, SrCl.sub.2, MgBr.sub.2, CaBr.sub.2, and SrBr.sub.2 is used as the metal chloride.

[0039] Meanwhile, in a working capacity of the ammonia adsorption/removal process using existing activated carbon as an adsorbent, an adsorption amount varies depending on temperature and pressure conditions, but when applied by a TSA method, it is known to have a working capacity of up to 0.6 mmol/g when not pretreated with metal halide and 2.1 mmol/g when treated with MgCl.sub.2. However, this process has a problem of making it difficult to process large volumes of gas due to low economic feasibility due to a time required for heating and cooling and a use of additional energy, and increasing greenhouse gas generation due to the use of additional energy. In addition, even when the adsorption/desorption process of undecomposed ammonia was applied using the PSA method using existing activated carbon as an adsorbent, it is known to have a working capacity of up to 0.77 mmol/g in activated carbon when not pretreated with metal halide and 1.57 mmol/g under 9 bar_g conditions when treated with MgCl.sub.2 [Study on the adsorption and desorption characteristics of metal-impregnated activated carbon according to metal precursors for regeneration and concentration of ammonia (Clean Technol. 26(2) 2020, 137-144)].

[0040] As described above, it can be seen that when the conventional activated carbon is used as an adsorbent, an adsorption capacity is lowered compared to when CMS of the present invention or CMS loaded with metal chloride, which will be described later, is used as an adsorbent.

[0041] Subsequently, in the present disclosure, high-purity hydrogen may be produced by separating and purifying high-purity hydrogen from the gas composed of the low-purity hydrogen and nitrogen. Although various methods have been proposed for purifying such high-purity hydrogen, the present invention is not limited to specific process conditions, and various processes may be used without limitations.

MODE FOR INVENTION

[0042] Hereinafter, the present invention will be described in detail through examples.

Example

[0043] An ammonia adsorption/desorption test was performed using carbon molecular sieve (CMS) in a process for removing undecomposed ammonia. For comparison, an adsorption/desorption test was also performed on CMS loaded with MgCl.sub.2 with A to remove undecomposed ammonia. Here, loading of MgCl.sub.2 was performed, wherein distilled water containing MgCl.sub.2 and CMS are mixed to a level of 4 wt % compared to CMS, and CMS was completely loaded in an MgCl.sub.2 solution and then mixed and dried, and subsequently, dried in a nitrogen atmosphere at 200? C. for 1 hour to completely remove residual moisture, additionally, which was used in an ammonia adsorption/desorption experiment.

[0044] FIG. 2 is a cross-sectional schematic diagram of an ammonia adsorption/desorption test device configured to adsorb, desorb and remove unreacted ammonia gas using an adsorbent in an embodiment of the present disclosure. As illustrated in FIG. 2, pressure in a reactor containing an adsorbent was controlled through a back pressure regulator to ensure that ammonia was continuously adsorbed to a target pressure, and an ammonia concentration in the gas to which ammonia was adsorbed was continuously analyzed using an ammonia analyzer. When adsorption was completed, a valve of an existing gas line was closed, an N.sub.2 flushing line in a lower portion was opened to lower a pressure, and then N.sub.2 was supplied to an upper portion to perform a desorption process.

[0045] When desorption was completed, experimental equipment was configured to supply a gas containing ammonia again to perform adsorption, and the adsorption/desorption performance of the adsorbent when applying the PSA (pressure swing adsorption) process was evaluated.

[0046] Meanwhile, in this case, ammonia adsorption/desorption tests were performed under various conditions depending on a temperature, pressure, and ammonia concentration, that may be applied to an ammonia decomposition hydrogen production process, and specific conditions thereof were illustrated in Table 2 below. In this experiment, adsorption was performed under the temperature and pressure conditions illustrated in Table 2 below, and desorption was performed under the same operating conditions or slightly higher than the adsorption temperature, and the adsorbed ammonia was desorbed while flowing nitrogen at normal pressure conditions. Thereafter, after ammonia was completely desorbed, the process of adsorbing/desorbing ammonia was repeated three times under the temperature and pressure conditions illustrated in Table 2 below. The results of the ammonia adsorption/desorption test under these various conditions were also illustrated in Table 2 below.

[0047] In addition, FIGS. 3 to 7 illustrate an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas was adsorbed under each condition.

[0048] FIG. 3 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 5% was adsorbed at 7 bar pressure using a CMS as an adsorbent in an embodiment of the present disclosure.

[0049] FIG. 4 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 2% was adsorbed at 7 bar pressure using a CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

[0050] FIG. 5 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 5% was adsorbed at 7 bar pressure using a CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

[0051] FIG. 6 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 2% was adsorbed at 5 bar pressure using a CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

[0052] FIG. 7 is a diagram illustrating an ammonia adsorption breakthrough curve by cycle when undecomposed ammonia (NH.sub.3) gas having a concentration of 5% was adsorbed at 5 bar pressure using a CMS loaded with 4 wt % MgCl.sub.2 as an adsorbent in an embodiment of the present disclosure.

TABLE-US-00002 TABLE 2 Adsorbent Virgin CMS CMS loaded with 4 wt % MgCl.sub.2 Adsorption pressure 0.7 MPa 0.7 MPa 0.5 MPa Temperature 40? C. Ammonia concentration 5% 2% 5% 2% 5% Adsorption Capacity 1.13 3.17 2.42 2.51 2.60 (mmol/g)

[0053] As illustrated in Table 2 and FIGS. 3 to 7, as a result of measuring an ammonia concentration in a gas having passed through an adsorption column during an adsorption experiment, when ammonia is well adsorbed, it can be seen that almost no ammonia is measured in an exhaust gas.

[0054] Typically, when MgCl.sub.2 is loaded in existing activated carbon, an adsorption/desorption working capacity was lustrated at a level of 1.4 mmol/g under 7 bar_g conditions, but when CMS, an adsorbent of the present disclosure is used, an adsorption capacity, similar to that of the activated carbon-MgCl.sub.2 adsorbent even without loading of MgCl.sub.2 could be illustrated. Moreover, when MgCl.sub.2 was loaded in CMS, the working capacity was dramatically improved by about 2 times, which was a result, higher than the highest working capacity seen in the existing activated carbon-MgCl.sub.2 adsorbent.

[0055] Meanwhile, looking at an adsorption curve, it can be seen that the highest level of adsorption amount was illustrated in a first adsorption cycle and the adsorption amount was somewhat decreased in a second, and a third adsorption cycle. This means that an entire amount, adsorbed on an absorbent continues to remain in the adsorbent without being desorbed.

[0056] In this case, it is possible to completely remove the adsorbed ammonia when a TSA method is applied, but as described above, it is reasonable to apply a PSA method due to problems that may occur when applying the TSA method. In particular, by operating in the PSA method, it can be effectively used to remove undecomposed ammonia from the gas produced in an ammonia decomposition hydrogen production process while minimizing additional energy consumption.

[0057] While example embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present disclosure as defined by the appended claims.