Method for producing clean hydrogen

Abstract

The present invention relates to a method for producing clean hydrogen and, more specifically, to a method for producing clean hydrogen, comprising: a methane reforming step of converting a methane-containing gas into a reformed gas containing hydrogen, CO, and CO2 by a reforming reaction using steam; a step of obtaining a mixed gas of hydrogen and carbon dioxide by subjecting the reformed gas to water-gas shift (WGS); a separation step of separating hydrogen and carbon dioxide from the mixed gas; and a step of mixing the separated carbon dioxide with sodium sulfate, ammonia, and water.

Description

Technical Field

[0001] The present disclosure relates to a method for producing clean hydrogen, and more particularly, to a method for producing clean hydrogen that can economically produce clean hydrogen using industrial by-products and can contribute to carbon neutrality by fixing carbon dioxide into carbonates (minerals). Background Art

[0002] Recently, with the establishment of the goal of carbon neutrality related to climate change globally, hydrogen (H 2 ) has received increasing attention. Among them, clean hydrogen refers to hydrogen in which hydrogen is produced using fossil fuels, but the generated carbon dioxide (CO 2 ) is removed in a way that captures or stores it rather than being released into the atmosphere, and it is selected as one of the main means of carbon neutrality. Therefore, in order to produce clean hydrogen, CCUS (Carbon Capture, Utilization, and Storage) technology for capturing and utilizing CO 2 is required.

[0003] Currently, most hydrogen production is carried out by reforming natural gas, which may mainly consist of methane, and such methods can generally be divided into methods using steam or oxygen. Currently, most reforming of methane uses the steam reforming method, and the main reaction formulas are as follows:

[0004] CnHm + nH 2 O → (n + m / 2)H 2 + nCO (endothermic reaction, ΔH = 206 kJ / mol)

[0005] CO + H 2 O → CO 2 + H 2 (exothermic reaction, ΔH = -41 kJ / mol)

[0006] The steam reforming sequence of methane is as follows. Sulfur components contained in natural gas (raw material) can be removed, and reformed gas containing hydrogen and carbon monoxide (CO) can be produced through a reforming reactor using steam. The generated reformed gas can increase the hydrogen yield through a water-gas shift (WGS) reaction. At the same time, when high-purity hydrogen is required, purification methods such as the pressure swing adsorption (PSA) method can be utilized. As can be seen from the reaction, CO 2 may be generated when producing hydrogen through the WGS reaction. Therefore, CO 2 needs to be utilized to produce clean hydrogen.

[0007] Meanwhile, sodium bicarbonate (NaHCO 3 ) can be used in multiple fields such as food, feed, leather, medicine, etc., and can be obtained through one of the representative CCUS technologies that can use CO 2 . The basic technology for producing sodium bicarbonate can be the Solvay process, which can produce sodium bicarbonate as a by-product during the process of producing sodium carbonate and calcium chloride from NaCl contained in seawater. In addition to NaCl, sodium bicarbonate can also be produced using Na 2 CO 3 , NaOH, etc. In addition, sodium sulfate (Na 2 SO 4 ) can be used. Na 2 SO 4 can be produced in large quantities as a by-product of industrial waste.

[0008] Flue gas desulfurization refers to the removal of sulfur (S) components, especially sulfur dioxide (SO 2 ), from the exhaust gases emitted from steel mills, thermal power plants, etc. With the development of industry, harmful gases such as sulfur oxides (SO x ) emitted from various factories, thermal power plants or incinerators cause serious air pollution and various diseases in the human body such as respiratory diseases, asthma, lung cancer, etc. Currently, the desulfurization agents for dry desulfurization can include sodium bicarbonate (NaHCO 3 ), activated carbon, calcium hydroxide (Ca(OH) 2 ), etc. And in the case of desulfurization agents such as sodium bicarbonate, it is known that when sodium bicarbonate is sprayed on high-temperature exhaust gases, it maximizes the specific surface area, thus generating excellent adsorption and reaction efficiency. At this time, sodium sulfate (Na 2 SO 4 ) waste may be generated as a by-product of the desulfurization treatment. The generated Na 2 SO 4 can be landfilled. In addition, recently, with the popularization of electric vehicles expanding, the demand for lithium (a raw material for secondary batteries) has been increasing day by day. The main by-products generated during lithium production can be silica (SiO 2 ) and sodium sulfate (Na 2 SO 4 ). It is expected that with the increasing demand for lithium in the future, the amount of sodium sulfate by-product generated will also increase. Therefore, for the supply of secondary batteries, technologies that can recycle sodium sulfate should be developed in advance, but no suitable methods are provided.

[0009] Therefore, when developing a method for economically producing clean hydrogen using such industrial by-products, its wide application in related fields is expected. Summary of the Invention

[0010] Technical Problem

[0011] One aspect of the present disclosure is to provide a method for producing clean hydrogen that can ensure environmental friendliness and economic feasibility, because baking soda and gypsum (CaSO 4 ) are produced by using sodium sulfate generated as an industrial by-product and carbon dioxide generated by steam reforming of methane-containing natural gas, without secondary costs for treating industrial by-products.

[0012] Technical Solution

[0013] According to one aspect of the present disclosure, a method for producing blue hydrogen can be provided, which includes: an operation of removing sulfur as an impurity; a methane reforming operation of converting a methane-containing gas into a reformed gas containing hydrogen, CO, and CO 2 by a reforming reaction using steam; an obtaining operation of performing a water-gas shift (WGS) on the reformed gas to obtain a mixed gas of hydrogen and carbon dioxide; a separating operation of separating hydrogen and carbon dioxide from the mixed gas; and a mixing operation of mixing the separated carbon dioxide, sodium sulfate, ammonia, and water.

[0014] Beneficial Effects

[0015] The present disclosure can produce clean hydrogen by using carbon dioxide generated by the reforming reaction of natural gas, and can also be economically operated by selling baking soda because the cost of treating waste can be reduced by producing baking soda by using a waste product containing sodium sulfate as a by-product. In addition, by stably fixing carbon dioxide as a carbonate (mineral), there may be an effect contributing to carbon neutrality due to carbon dioxide capture, utilization, and storage (CCUS) technology. Description of the Drawings

[0016] Figure 1 An exemplary overall process diagram for producing clean hydrogen using methane is shown.

[0017] Figure 2 The results of XRD analysis of baking soda (left) and gypsum (right) produced by the method proposed by an embodiment of the present disclosure are shown.

[0018] Figure 3 is a graph of the yield of baking soda according to the water / waste weight ratio and the NH 3 / Na + molar ratio.

[0019] Figure 4 is a graph of the purity and yield of baking soda according to the NH 3 / Na + molar ratio. Detailed implementation manners

[0020] In the following, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the embodiments of the present disclosure can be modified in various other forms, and the scope of the present disclosure is not limited to the embodiments described below.

[0021] According to the present disclosure, a method for producing clean hydrogen can be provided, which includes: a methane reforming operation of converting a methane-containing gas into a reformed gas containing hydrogen, CO, and CO 2 by a reforming reaction using steam; an obtaining operation of performing a water-gas shift (WGS) on the reformed gas to obtain a mixed gas of hydrogen and carbon dioxide; a separating operation of separating hydrogen and carbon dioxide from the mixed gas; and a mixing operation of mixing the separated carbon dioxide, sodium sulfate, ammonia, and water.

[0022] The methane reforming operation of converting a methane-containing gas into a reformed gas containing hydrogen, CO, and CO 2 can be carried out by producing a reformed gas containing hydrogen and carbon monoxide (CO) via a reforming reactor using steam.

[0023] The methane-containing gas that can be used in the present disclosure can be methane gas or natural gas having 70% or more of methane by volume, and when using natural gas, before the methane reforming operation, an operation of removing sulfur components contained in the natural gas can be performed.

[0024] The operation of removing sulfur components can be carried out by: a catalytic removal method in which the waste gas is heated and removed using metal oxides such as ZnO, CuO, MoO, etc., in which SO 2 is absorbed into water to generate H 2 SO 4 an exhaust gas absorption method, in which limestone (CaCO 3 ) of Ca 2+ reacts with SO 2 to generate CaSO 4 a lime method, in which baking soda (NaHCO 3 ) is added to generate sodium hydroxide by a natural soda method, etc., but the method of removing sulfur is not particularly limited.

[0025] The reformed gas can be subjected to a water-gas shift (WGS) to obtain a mixed gas of hydrogen and carbon dioxide. The water-gas shift can be a process in which carbon monoxide reacts with steam to generate hydrogen, and its reaction formula can be as follows.

[0026] <Reaction formula>

[0027]

[0028] When high-purity hydrogen is required, a purification process such as a pressure swing adsorption (PSA) process can be carried out, and in addition, a moisture removal process can be used, such as an adsorbent, to add to the gas that has undergone a water-gas shift reaction.

[0029] Hydrogen can be obtained by separating hydrogen from the mixed gas of hydrogen and carbon dioxide obtained through this process. In this case, the separation of hydrogen and carbon dioxide can be carried out, for example, by the following: selectively introducing a pressure swing adsorption (PSA) process of an adsorbent that reacts with CO 2 or H 2 and produces high-purity hydrogen through a change in operating pressure, a membrane separation process that separates hydrogen from the mixed gas by utilizing the difference in permeability according to the size of gas molecules, and an amine wetting process that separates hydrogen from the mixed gas by introducing an amine that selectively interacts with CO 2 into the reactor, etc.

[0030] Since carbon dioxide should be utilized to identify clean hydrogen, in the present disclosure, sodium sulfate can be used together with the carbon dioxide obtained in this way to produce baking soda.

[0031] More specifically, it can include an operation of mixing the carbon dioxide separated from the mixed gas with sodium sulfate, ammonia, and water to produce baking soda.

[0032] For this purpose, according to the present disclosure, an operation of mixing the separated carbon dioxide with sodium sulfate, ammonia, and water can be carried out, and a mixing operation can be carried out that includes mixing the carbon dioxide in a countercurrent manner into the mixed solution obtained by mixing a sodium sulfate solution and an ammonia water solution.

[0033] The sodium sulfate solution can be a solution obtained by solid-liquid separation of a sodium sulfate-containing material with a sodium sulfate content of 50% by weight or more.

[0034] During this operation, when producing baking soda by reacting carbon dioxide with a sodium sulfate-containing material (waste), the present disclosure can provide a method of removing undissolved impurities to improve the purity of the produced baking soda, and due to the characteristics of the waste, ammonia can be effectively mixed even in a high pH state of the solution to dissolve carbon dioxide and produce baking soda.

[0035] More specifically, the mixing operation can be carried out by including the following: mixing a sodium sulfate solution and an ammonia water solution and mixing carbon dioxide in a countercurrent manner into the mixed solution.

[0036] In this case, the sodium sulfate solution can be obtained by dissolving a sodium sulfate-containing material such as a sodium sulfate-containing material of a desulfurization by-product in an eluent, and can be obtained by using a material having a sodium sulfate content of 50% or more. For example, the sodium sulfate-containing waste can be produced by desulfurizing an exhaust gas containing a sulfur oxide (SO x ) component with baking soda, and can also be waste produced as a by-product of a lithium production plant. For example, it can be produced by desulfurizing the exhaust gas generated by combustion in a thermal power plant, a factory, an incinerator, etc. or the exhaust gas generated by electroplating in a steel mill sintering plant with baking soda. The waste containing sodium sulfate can contain heavy metal components such as lead (Pb), zinc (Zn), etc. that can be dissolved, and can contain a large amount of alkaline components such as sodium (Na), potassium (K), calcium (Ca), etc., and can also have a large amount of chlorine (Cl) component characteristics. Most of the baking soda used as a desulfurizing agent can react with SOx and can be converted into a sodium sulfate component, and some insoluble gangue components contained in the exhaust gas may also be included. Specifically, the main crystal phases constituting the desulfurization waste can be sodium sulfate, sodium chloride, potassium chloride, sodium carbonate, calcium sulfate, calcium carbonate, etc., and can include iron oxide. In the main crystal phase of the desulfurization dust solution, sodium sulfate, sodium chloride, potassium chloride, etc. can be components that are highly soluble in water, and can therefore be dissolved in water to produce an alkaline desulfurization dust solution.

[0037] In this way, the sodium sulfate-containing material of the present disclosure can be a desulfurization by-product.

[0038] The eluent is not particularly limited as long as it is a material that can elute sodium ions when it encounters a sodium sulfate-containing material, but can be at least one selected from water and an aqueous ammonia solution, and can be, for example, water.

[0039] More specifically, in this case, in order to recover sodium sulfate from the sodium sulfate-containing waste in the form of a sodium sulfate solution containing sodium ions, the ratio of the sodium sulfate-containing waste and the ratio of the eluent may be important, and when the ratio of the eluent is too low, the sodium sulfate waste may not be completely dissolved, resulting in a large amount of residue, which reduces the recovery rate of sodium.

[0040] The ratio of the eluent that does not lose sodium sulfate as a residue can be 1.2 parts by weight or more of the eluent per 1 part by weight of the sodium sulfate waste. Preferably, 1.4 parts by weight to 3 parts by weight, for example, 2 parts by weight to 3 parts by weight of the eluent can be mixed with 1 part by weight of the sodium sulfate waste, and when the eluent may be included in an excessive amount exceeding this range, even when carbon dioxide is dissolved in the subsequent sodium-containing solution, baking soda may not precipitate as baking soda, and therefore, the amount of baking soda flowing out in a dissolved state in the solution may increase, thereby reducing the recovery rate of baking soda.

[0041] Reference Figure 3 , the recovery rate of sodium bicarbonate can be adjusted by adjusting the mass ratio between the sodium sulfate-containing material and water (eluent). In order for the recovery rate of sodium bicarbonate to be 50% or higher (based on Na + moles), the mass ratio between the sodium sulfate-containing material and the eluent can be from 1:1.4 to 1:3. When the mass ratio of the eluent to the sodium sulfate-containing material is less than this range, sodium sulfate may not dissolve and may thus be lost as a residue, which may tend to reduce the recovery rate of sodium ions. When the mass ratio of the eluent to the sodium sulfate-containing material exceeds 3, the recovery rate of sodium ions may increase, but the concentration of sodium ions may be low, so the reaction may not be possible, and there may be a problem that the amount of sodium ions flowing out into the waste liquid increases, thereby reducing the production amount of sodium bicarbonate.

[0042] When the sodium sulfate solution obtained from a certain ratio of sodium sulfate-containing waste and a certain ratio of eluent is applied to the method for producing sodium bicarbonate of the present disclosure, the sodium in the sodium sulfate-containing waste can be recovered as 60% or more of sodium bicarbonate.

[0043] Since the pH range of the most generated bicarbonate ions is from pH 7 to 10, for example, from 7.5 to 9, and more preferably from pH 8 to 9, it is thus desirable to maintain the pH at 8 to 9 to improve the efficiency of sodium bicarbonate production. In addition, when the pH exceeds 10, alkaline ammonia may not dissolve sufficiently, and when the pH decreases, bicarbonate ions (HCO 3 - ) may be converted into carbonic acid (H 2 CO 3 ), which may reduce the productivity of sodium bicarbonate.

[0044] Carbon dioxide is an acidic gas and can dissolve well in the sodium sulfate solution, but when producing sodium bicarbonate using only carbon dioxide and the sodium sulfate solution, the pH will continuously decrease, which will reduce the yield of sodium bicarbonate production. Therefore, in the present disclosure, the yield of sodium bicarbonate can be increased by mixing ammonia that can act as a pH buffer with sodium sulfate, for example, by mixing ammonia with the sodium sulfate solution as an aqueous ammonia solution.

[0045] Generally, in order to dissolve ammonia in a solution such as water, etc., gaseous ammonia can be introduced into the aqueous solution. However, there may be such a characteristic: when ammonia is introduced into the aqueous solution, the pH may further increase, and in an aqueous solution in an alkaline state, ammonia exists in the form of NH 3 rather than NH 4 +The state exists, making it easy to dissociate from water. Therefore, generally, to produce high-concentration ammonia water, the pressure of the device for dissolving ammonia gas can be operated at a high level, or the reaction surface area can be increased to dissolve ammonia in the solution.

[0046] To recover 50 mol% of baking soda based on + molar concentration, a sodium sulfate solution and an ammonia water solution can be mixed so that the ammonia (NH 3 ) / sodium (Na + ) molar ratio can be 0.8 to 1.5, preferably greater than 0.6 and 1.3 or less, such as 0.7 or greater and 1.2 or less. The reason why ammonia is necessary in the process of producing baking soda by injecting carbon dioxide into waste containing sodium sulfate can also be understood based on the following thermodynamic information. When the ammonia (NH 3 ) / sodium (Na + ) molar ratio is less than 0.8, the recovery rate of baking soda may decrease, and when the molar ratio increases, the recovery rate of baking soda may increase, but the purity of baking soda may decrease.

[0047] Referring to Figure 3 and Figure 4 , when the ratio of ammonia (NH 3 ) / sodium (Na + ) is 0.6 or less, the yield of baking soda may decrease because it may be below the optimal pH range for producing baking soda, and when the pH is 1.5 or higher, the yield may be high, but a large amount of impurities such as (NH 4 ) 2 SO 4 etc. may be produced, thus reducing the purity of baking soda. The preferred ratio of ammonia (NH 3 ) / sodium (Na + ) is 1.25 to 1.35.

[0048] The reaction for producing baking soda can be as follows.

[0049] Baking soda production reaction using sodium sulfate (Reaction A):

[0050] Na 2 SO 4 +2CO 2 +2H 2 O→NaHCO 3 +H 2 SO 4

[0051] Baking soda production reaction using sodium sulfate and ammonia (Reaction B):

[0052] Na 2 SO 4 +2NH3 + 2CO 2 + 2H 2 O → 2NaHCO 3 +(NH 4 ) 2 SO 4

[0053] The free energy of reaction A (ΔG, 298K) can be 160.653 kJ / mol, and the free energy of reaction B (ΔG, 298K) can be 42.702 kJ / mol.

[0054] In this way, reaction A using only sodium sulfate and carbon dioxide has a positive value and may not be a spontaneous reaction as a result. When ammonia is added, it has a negative value, thus determining it to be a spontaneous reaction. Therefore, it can be determined that ammonia acting as a pH buffer is necessary when producing bicarbonate using sodium sulfate.

[0055] The operation of obtaining a mixed solution by mixing a sodium sulfate solution and an ammonia water solution can be carried out at a temperature of 25°C or higher and lower than 100°C. When exceeding this temperature range, the solubility of sodium sulfate tends to decrease, which may reduce the yield.

[0056] The ammonia that can be used in the present disclosure can be ammonia, or a mixed solution, mixed gas or solid containing ammonia, and can be, for example, an ammonia water solution.

[0057] In addition, for the production of baking soda, carbon dioxide should be dissolved in an elution solution containing sodium ions. Therefore, after the operation of obtaining a mixed solution by mixing a sodium sulfate solution and an ammonia water solution, the present disclosure can perform a mixing operation of mixing a gas containing carbon dioxide with the mixed solution in a countercurrent manner.

[0058] According to the present disclosure, when mixing in a countercurrent manner, the contact area between the sodium sulfate solution and carbon dioxide can be maximized, thereby increasing the dissolution of carbon dioxide and thus baking soda can be effectively produced. In this case, when carbon dioxide is injected into the ammonia-containing solution, baking soda can be generated by the reaction of sodium ions with bicarbonate ions (HCO 3 - ) generated by carbon dioxide in the solution.

[0059] The carbon dioxide used in this case can be pure carbon dioxide or a nitrogen mixed gas containing 10 vol% to 30 vol% of carbon dioxide, and for example, can be at least one selected from the following: FINEX off gas (FOG), FINEX tail gas (FTG), blast furnace gas (BFG), electric converter gas, coal-fired power plant exhaust gas, gas-fired power plant exhaust gas, incinerator exhaust gas, glass melting exhaust gas, thermal facility exhaust gas, petrochemical process exhaust gas, petrochemical process gas, pre-combustion exhaust gas, and gasifier exhaust gas. In addition, carbon dioxide can be concentrated and used by using wet amine method, membrane method, dry pressure swing adsorption / desorption method, etc. to increase the concentration of carbon dioxide.

[0060] In the sodium bicarbonate production reactor where the carbonation reaction occurs, the reaction pressure can be 1 atm to 10 atm, and the reaction temperature can be 50 °C or lower. When the pressure of the carbonation reactor exceeds 10 atm, a sufficient amount of carbon dioxide can be dissolved, but the energy required for the carbonation reactor may be high, which reduces the economic feasibility of sodium bicarbonate that may be the final product. The time period of the carbonation reaction can vary depending on the method of injecting carbon dioxide. When carbon dioxide is injected as a gas, the time period can vary depending on whether aeration is performed, and when aeration is performed, a time period of 4 hours or shorter can be spent. However, the optimized pressure and reaction time can vary depending on the size / space / conditions of the reactor.

[0061] When carbon dioxide is dissolved in an (aqueous) solution, depending on the pH, carbon dioxide can exist in the form of carbonic acid (H 2 CO 3 ), bicarbonate ion (HCO 3 - ), or carbonate ion (CO 3 2- ), and since the chemical formula of sodium bicarbonate is NaHCO 3 , the amount of bicarbonate ions in the solution should be large, so that the combination with sodium ions increases and the production of sodium bicarbonate increases, and sodium bicarbonate can precipitate as a solid due to its low solubility.

[0062] The sodium sulfate solution of the present disclosure can be a solution obtained by separating a liquid sodium sulfate-containing material having a sodium sulfate content of 30 wt% or more via solid-liquid separation (i.e., separating solids and liquids). In this case, the solid-liquid separation device is not particularly limited, and any device capable of separating the solid phase and the liquid phase can be used.

[0063] The filtrate obtained after the carbonation reaction can contain a large amount of sulfate ions (SO 42- )。Therefore, a calcium-containing material can be added to the filtrate to produce gypsum (CaSO 4 ). In this case, the calcium-containing material can be at least one selected from the following: waste cement, waste concrete, coal ash, fly ash, iron slag, low-grade or high-grade quicklime (CaO), calcium chloride (CaCl 2 ), wollastonite, limestone, olivine, serpentine, asbestos, and deinking ash. In addition, when the purity of the gypsum is low, the purity of the gypsum can be increased by recovering ammonia and adding sulfuric acid and gypsum to the remaining filtrate.

[0064] The aqueous ammonia solution injected into the mixing reactor in which the aqueous ammonia solution and the sodium sulfate solution are mixed to obtain a mixed solution can preferably be injected at a flow rate of 2.5 L / min to 5 L / min. When the flow rate is less than this range, the residence time of the solution may be too long, resulting in stagnation of the solution, making it difficult to obtain a sufficient reaction surface area. When it exceeds this range, the residence time of the solution may be too short, causing the problem that sufficient reaction cannot occur.

[0065] The carbon dioxide-containing gas can preferably be injected at a flow rate of 2.5 L / min to 5 L / min. When the flow rate is less than this range, there may be problems such as a low outlet pressure and the gas may not be smoothly transported to one end of the reactor. When the flow rate exceeds this range, the residence time of the gas may be too short and its reaction may not occur sufficiently.

[0066] Hereinafter, the present disclosure will be described in more detail through specific examples. The following examples may be only examples to help understand the present disclosure, and the scope of the present disclosure is not limited thereto.

[0067] Embodiments of the Invention

[0068] Examples

[0069] 1. Production of Hydrogen

[0070] As an embodiment of the present disclosure, a hydrogen production experiment is carried out according to the Figure 1 flow chart. The composition of the methane-containing gas used in this case is shown in Table 1 below, and the XRD analysis results of the finally produced baking soda are shown in Figure 2 . In addition, Figure 3 shows the results of baking soda produced by using the carbon dioxide remaining after separating hydrogen from the mixed gas generated by methane reforming. It can be seen that according to the molar ratio of Na + extracted from ammonia and the waste material containing sodium sulfate, as well as the ratio of the waste material containing sodium sulfate and the ratio of water, during the synthesis of baking soda, the recovery rate of the produced baking soda changes.

[0071] [Table 1]

[0072] Composition of methane-containing gas

[0073] Composition <![CDATA[Methane (CH 4 )]]> <![CDATA[Ethane (C 2 H 6 )]]> <![CDATA[Propane (C 3 H 8 )]]> <![CDATA[Butane (C 4 H 10 )]]> Component (volume%) 90.09 6.0 2.5 1.1 Composition <![CDATA[Carbon dioxide (CO 2 )]]> <![CDATA[Nitrogen (N 2 )]]> <![CDATA[Oxygen (O 2 )]]> Sulfur Component (volume%) 0.1 0.2 0～2 0.01

[0074] First, the methane gas is heated to about 320 °C by a preheater and then undergoes a desulfurization process. The desulfurization reactor is filled with catalysts such as ZnO, CuO, MoO, etc. The unsaturated hydrocarbons are converted into hydrogen compounds and the unreacted sulfur components are converted into hydrogen compounds of hydrogen sulfide and are absorbed. The desulfurized methane gas is mixed with steam to raise the temperature to 520 °C and then passes through the internal space of the reformer. In this case, the following reactions mainly occur:

[0075] C n H m +nH 2 O→(n+m / 2)H 2 +nCO (endothermic reaction, ΔH = 206 kJ / mol)

[0076] CO + H 2 O→CO 2 +H 2 (exothermic reaction, ΔH = -41 kJ / mol)

[0077] The total heat balance is an endothermic reaction and passes through the reformer at a temperature of about 830 °C. The reformed gas passes through a water-gas shift (WGS) reactor. The changes in the gas composition before and after passing through the WGS reactor are shown in Table 2. CO reacts with the steam in the reformed gas to produce hydrogen and CO 2 .

[0078] CO + H 2 O = CO 2 +H 2

[0079] This reaction is an exothermic reaction and the temperature of the converted gas is about 420 °C.

[0080] [Table 2]

[0081] Changes in gas composition before / after passing through the WGS reactor

[0082] Composition Before the WGS reaction After the WGS reaction <![CDATA[H 2 > 49％ 55％ CO 9％ 3％ <![CDATA[CO 2 > 5％ 12％ <![CDATA[CH 4 > 3％ 3％ <![CDATA[H 2 O]]> 34％ 27％

[0083] To separate hydrogen and carbon dioxide from the produced mixed gas, the produced mixed gas is passed through a pressure cycle process (PSA). The pressure cycle process proceeds through an adsorption process - regeneration process - discharge process - pressurization process and produces high-purity hydrogen (99.999%). The separated carbon dioxide is also concentrated to over 90% through the pressure cycle process. In order for the produced hydrogen to be recognized as clean hydrogen, the carbon dioxide should be utilized. In the present disclosure, sodium sulfate and the carbon dioxide obtained in this way are used to produce baking soda.

[0084] The waste material containing sodium sulfate used in this embodiment uses a desulfurization by-product having the composition shown in Table 3 below.

[0085] [Table 3]

[0086] Composition of waste material containing sodium sulfate (desulfurization by-product)

[0087]

[0088] The waste material containing sodium sulfate as the desulfurization by-product contains inorganic materials as shown in Table 3 above, and thus exhibits the property of having a pH of 9 or higher when dissolved in water. In a carbonation reactor such as Figure 1 the carbonation reactor shown, ammonia, water, and sodium sulfate are mixed, and carbon dioxide is additionally mixed therein. Ammonia, water, and sodium sulfate are introduced separately or in a mixed state.

[0089] The filtrate from the carbonation reaction in the carbonation reactor contains a large amount of sulfate ions (SO 4 2- ). Therefore, a calcium-containing material is added to the filtrate to produce gypsum (CaSO 4 ).

[0090] Since ammonia has a high unit price, in order to operate the process economically, it is desirable to recover ammonia. The pH of the filtrate from the carbonation reactor is 7 to 8, and most of the ammonia exists in the form of ammonium ions (NH 4 + ). In order to recover ammonia, the pH should be increased to 10 or higher, and steam should be used to recover ammonia in the form of gas or in the form of steam. Therefore, quicklime (CaO, a calcium-containing material) is introduced to increase the pH. In addition to quicklime, slaked lime that can increase the pH can also be used. More than 90% of the ammonia in the solution can be recovered, and the recovered ammonia can be reused in the carbonation reactor.

[0091] When ammonia is recovered, the remaining ions in the solution are calcium (Ca 2+ ) and sulfate (SO 4 2-)。When the pH is 6 or higher, due to the reaction of the remaining carbonate (CO 3 2- ) ions in the solution to produce lime (CaCO 3 ) and slaked lime (Ca(OH) 2 ) as impurities, it is necessary to lower the pH to 6 or lower. To lower the pH, an acid such as sulfuric acid (H 2 SO 4 ), hydrochloric acid (HCl), etc. should be added. The wastewater from the gypsum extraction reactor is treated through a wastewater treatment process.

[0092] 2. Yield and purity of sodium bicarbonate according to the water: waste ratio and ammonia (NH 3 ): sodium (Na + ) ratio

[0093] To determine the yield and purity of sodium bicarbonate according to the water (eluate): waste (desulfurization by - product) ratio, when obtaining a sodium sulfate solution by solid - liquid separation from the desulfurization by - product containing sodium sulfate through the eluate, the water: waste ratio is prepared as 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 and stirred in the first reactor.

[0094] In a state where the ammonia (NH 3 ) / sodium (Na + ) ratio is 0.6, 0.8, 1.0, 1.3, and 1.5, after stirring each eluate solution that has ended stirring in the second reactor, then carbon dioxide is added in the third reactor to start the reaction.

[0095] As can be seen in Figure 3 and Figure 4 , it can be confirmed that when the water / waste ratio is too low, since the waste may not dissolve, reducing the amount of the eluate solution, which reduces the recovery rate of sodium bicarbonate, and when the amount of water is too high, the concentration of Na + in the solution may be low, which reduces the recovery rate of sodium bicarbonate. In addition, when the ammonia (NH 3 ) / sodium (Na + ) ratio is 0.6 or lower, the pH may be low, which reduces the recovery rate of sodium bicarbonate. When the ammonia (NH 3 ) / sodium (Na + ) ratio is 1.5 or higher, the yield of sodium bicarbonate may increase, but impurities such as (NH 4 ) 2 SO 4 may be generated, which reduces the purity of sodium bicarbonate.

[0096] Although the embodiments of the present disclosure have been described in detail above, the scope of the present disclosure may not be limited thereto, and it will be apparent to those skilled in the art that various modifications and variations may be possible within the scope of the technical concept of the present disclosure described in the claims.

Claims

1. A method for producing clean hydrogen, comprising: A methane reforming operation that converts a methane-containing gas into a reformed gas containing hydrogen, carbon monoxide (CO), and carbon dioxide (CO 2 ) by a reforming reaction using steam; an obtaining operation of performing water-gas shift (WGS) on the reformed gas to obtain a mixed gas of hydrogen and carbon dioxide; a separating operation of separating hydrogen and carbon dioxide from the mixed gas; and a mixing operation of mixing the separated carbon dioxide, sodium sulfate, ammonia, and water.

2. The method according to claim 1, wherein the mixing operation comprises mixing carbon dioxide into a mixed solution obtained by mixing a sodium sulfate solution and an ammonia water solution in a countercurrent manner.

3. The method according to claim 2, wherein the sodium sulfate solution is obtained by solid-liquid separation of a sodium sulfate-containing material having a sodium sulfate content of 30 wt% or more.

4. The method according to claim 2, wherein the sodium sulfate solution is obtained by solid-liquid separation of a sodium sulfate-containing material using an eluent.

5. The method according to claim 4, wherein the mass ratio of the sodium sulfate-containing material to the eluent is 1:1.2 to 1:

3.

6. The method according to claim 2, wherein the sodium sulfate solution and the ammonia are mixed such that the ratio of ammonia (NH 3 ) / sodium (Na + ) is from 0.8 to 1.

5.

7. The method according to claim 2, wherein the mixing operation is performed under conditions of a temperature of 25°C or higher and lower than 100°C and a pH of 7 to 10.

8. The method according to claim 2, wherein the ammonia is an ammonia-containing mixed solution, mixed gas, or solid.

9. The method according to claim 1, further comprising an operation of removing sulfur as an impurity from the methane-containing gas before the methane reforming operation.

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