Clean hydrogen production method

Abstract

The present invention relates to a method for producing clean hydrogen, and more particularly to a method for producing clean hydrogen, including 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 water-gas shift (WGS) of the reformed gas, a separation step of separating the 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 invention relates to a method for producing clean hydrogen, and more specifically, to a method for producing clean hydrogen that can not only economically produce clean hydrogen using industrial by-products but also fix carbon dioxide as carbonate, a mineral, thereby contributing to carbon neutrality. [Background technology]

[0002] In recent years, hydrogen (H2) has been attracting more attention as the goal of carbon neutrality has been established around the world in relation to climate change. Clean hydrogen is produced using fossil fuels, but the carbon dioxide (CO2) produced is captured or stored and removed so that it is not released into the atmosphere. It is considered one of the main methods for achieving carbon neutrality. Therefore, producing clean hydrogen requires CCUS (Carbon Capture, Utilization, and Storage) technology, which captures and utilizes CO2.

[0003] Currently, most hydrogen production is carried out by reforming natural gas, which is primarily composed of methane, and the methods used can be broadly divided into those that use steam or oxygen. Currently, most methane reforming uses the steam reforming method, and the main reaction formula is as follows:

[0004] CnHm + nH2O → (n + m / 2)H2 + nCO (endothermic reaction, ΔH = 206 kJ / mol) CO + H2O → CO2 + H2 (exothermic reaction, ΔH = -41 kJ / mol)

[0005] The process for steam reforming methane is as follows: sulfur components contained in the raw material natural gas are removed, and the gas is passed through a reforming reactor using steam to produce a reformed gas containing hydrogen and carbon monoxide (CO). The hydrogen yield of the produced reformed gas is increased through the Water Gas Shift (WGS) reaction. Meanwhile, if high-purity hydrogen is required, it goes through a purification process such as the Pressure Swing Adsorption (PSA) process. As can be seen from the above reaction, CO2 is generated when hydrogen is produced through the WGS reaction. Therefore, CO2 must be utilized to produce clean hydrogen.

[0006] Meanwhile, sodium bicarbonate (NaHCO3) can be used in a variety of fields, including food, feed, leather, and medicine, and is one of the leading CCUS technologies that can be produced using CO2. The technology that forms the basis of sodium bicarbonate production is the Solvay process, which produces 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 Na2CO3, NaOH, etc. Sodium sulfate (Na2SO4) can also be used. Na2SO4 is generated in large quantities as a by-product of industrial waste.

[0007] Flue gas desulfurization refers to the removal of sulfur (S) components, especially sulfur dioxide (SO2), from exhaust gases emitted from steel mills, thermal power plants, etc. With the development of industry, sulfur oxides (SO2) emitted from various factories, thermal power plants, and incinerators have increased. xHarmful gases such as CO₂ and CO₂ lead to serious air pollution and can cause various illnesses, including respiratory diseases, asthma, and lung cancer. Desulfurization agents currently used in dry desulfurization include sodium bicarbonate (NaHCO₃), activated carbon, and calcium hydroxide (Ca(OH)₂). In particular, sodium bicarbonate, when injected into high-temperature exhaust gas, maximizes its specific surface area, demonstrating excellent adsorption and reaction efficiency. Sodium sulfate (Na₂SO₄) is generated as a by-product of the desulfurization process. This Na₂SO₄ is disposed of by landfilling. Furthermore, the recent expansion of electric vehicles has led to increased demand for lithium, a raw material for secondary batteries. The main by-products generated during lithium production are silica (SiO₂) and sodium sulfate (Na₂SO₄). The amount of sodium sulfate by-product generated is expected to increase in line with the growing demand for lithium. Therefore, the development of technology capable of recycling sodium sulfate is essential for the widespread use of secondary batteries, but a suitable method has yet to be developed.

[0008] Therefore, if a method for economically producing clean hydrogen using such industrial by-products is developed, it is expected to be widely applicable in related fields. Summary of the Invention [Problem to be solved by the invention]

[0009] One aspect of the present invention is to provide an environmentally friendly method for producing clean hydrogen that is economical and does not require secondary costs for processing industrial by-products, by producing sodium bicarbonate and gypsum (CaSO4) from carbon dioxide generated by steam reforming of methane-containing natural gas using sodium sulfate generated as an industrial by-product. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a method for producing blue hydrogen, which includes a step of removing sulfur as an impurity, a step of converting methane-containing gas into a reformed gas containing hydrogen, CO, and CO2 through a reforming reaction using steam, a step of subjecting the reformed gas to water-gas shift (WGS) to obtain a mixed gas of hydrogen and carbon dioxide, a 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. [Effects of the Invention]

[0011] This invention can produce clean hydrogen by using carbon dioxide generated in the natural gas reforming reaction, and can produce sodium bicarbonate using sodium sulfate-containing waste as a by-product, reducing waste disposal costs and enabling economical operation by selling the sodium bicarbonate. Furthermore, it can stably fix carbon dioxide as a mineral carbonate, contributing to carbon neutrality as a carbon capture, utilization, and storage (CCUS) technology. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows an exemplary overall process diagram for producing clean hydrogen using methane. [Figure 2] 1 shows XRD analysis results of baking soda (left) and gypsum (right) produced by a process proposed in accordance with an embodiment of the present invention. [Figure 3] 1 is a graph of the yield of sodium bicarbonate depending on the weight ratio of water / waste and the molar ratio of NH3 / Na+. [Figure 4] 1 is a graph showing the purity and yield of sodium bicarbonate depending on the molar ratio of NH3 / Na+. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor device according to a first embodiment of the present invention; FIG. 2 is a block diagram of a semiconductor device according to a first embodiment of the present invention; FIG. 3 is a block diagram of a semiconductor device according to a first embodiment of the present invention;

[0014] According to the present invention, there is provided a method for producing clean hydrogen, which includes 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 water-gas shift (WGS) of the reformed gas, a separation step of separating the hydrogen and carbon dioxide from the mixed gas, and a step of mixing the separated carbon dioxide with sodium sulfate, ammonia, and water.

[0015] The methane reforming step, in which a methane-containing gas is converted into a reformed gas containing hydrogen, CO, and CO2 through a reforming reaction using steam, can be carried out by producing a reformed gas containing hydrogen and carbon monoxide (CO) through a reforming reactor using steam.

[0016] Meanwhile, the methane-containing gas usable in the present invention may be methane gas or natural gas containing 70% or more by volume of methane. When natural gas is used, a step of removing sulfur components contained in the natural gas may be performed prior to the methane reforming step.

[0017] The sulfur removal process involves catalytic removal, which involves heating the exhaust gas and removing it using metal oxides such as ZnO, CuO, and MoO; flue gas absorption, which involves absorbing SO2 into water to produce H2SO4; and the Ca removal process using limestone (CaCO3). 2+ The method for removing sulfur can be the lime method in which SO2 reacts with HCl to produce CaSO4, or the Trona method in which sodium bicarbonate (NaHCO3) is added to produce Glauber's salt, but there is no particular limitation on the method for removing sulfur.

[0018] The reformed gas is subjected to water-gas shift (WGS) to produce a mixture of hydrogen and carbon dioxide. The water-gas shift is a process in which carbon monoxide reacts with water vapor to produce hydrogen, and the reaction formula is as follows:

[0019] <Reaction formula>

number

[0020] Meanwhile, if high-purity hydrogen is required, a purification process such as a pressure swing adsorption (PSA) process can be performed, and a moisture removal process can be added to the gas that has undergone the water-gas shift reaction using an adsorbent or the like.

[0021] Hydrogen can be obtained by separating it from the mixture of hydrogen and carbon dioxide obtained through this process. Separation of hydrogen and carbon dioxide can be performed using, for example, a pressure swing adsorption (PSA) process, which produces high-purity hydrogen by changing the operating pressure after introducing an adsorbent that selectively reacts with CO2 or H2, a membrane separation process, which separates hydrogen from the mixture by utilizing the difference in permeation speed depending on the size of gas molecules, or an amine wet process, which separates hydrogen from the mixture by introducing an amine that selectively interacts with CO2 into the reactor.

[0022] Since carbon dioxide must be utilized to be recognized as clean hydrogen, the present invention produces sodium bicarbonate using the carbon dioxide thus obtained and sodium sulfate. More specifically, sodium bicarbonate can be produced by mixing the carbon dioxide separated from the mixed gas with sodium sulfate, ammonia, and water.

[0023] To achieve this, according to the present invention, a step of mixing the separated carbon dioxide with sodium sulfate, ammonia, and water is carried out, and the mixing step may include a step of countercurrently mixing carbon dioxide with a mixed solution obtained by mixing a sodium sulfate solution with an aqueous ammonia solution.

[0024] On the other hand, the sodium sulfate solution may be a solution obtained by solid-liquid separation of a sodium sulfate-containing substance having a sodium sulfate content of 50% by weight or more.

[0025] The present invention provides a method for producing sodium bicarbonate by reacting carbon dioxide with a sodium sulfate-containing substance (waste) at this stage, which can remove undissolved impurities to increase the purity of the produced sodium bicarbonate, and can efficiently mix ammonia to dissolve carbon dioxide and produce sodium bicarbonate even in a high pH state of the solution due to the characteristics of the waste.

[0026] More specifically, the mixing step may include mixing a sodium sulfate solution with an aqueous ammonia solution, and countercurrently mixing carbon dioxide into the mixed solution.

[0027] The sodium sulfate solution may be obtained by dissolving a sodium sulfate-containing material, such as a desulfurization by-product, in an eluent, or may be obtained using a material with a sodium sulfate content of 50% or more. For example, the sodium sulfate-containing waste may be produced by desulfurizing exhaust gas containing sulfur oxides (SOx) with sodium bicarbonate, or by-product waste from a lithium production plant. For example, the sodium sulfate-containing waste may be produced by desulfurizing exhaust gas generated by combustion at thermal power plants, factories, incinerators, etc., or exhaust gas generated in a sintering plant of a steel mill after electrostatic precipitator treatment with sodium bicarbonate. The sodium sulfate-containing waste may contain eluted heavy metals such as lead (Pb) and zinc (Zn), and is characterized by a high content of alkalis such as sodium (Na), potassium (K), and calcium (Ca), as well as a high content of chlorine (Cl). Most of the sodium bicarbonate used as a desulfurization agent reacts with SOx and is converted to sodium sulfate, and some insoluble gangue components contained in the exhaust gas are also present. Specifically, the main crystalline phases constituting the desulfurization waste are sodium sulfate, sodium chloride, potassium chloride, sodium carbonate, calcium sulfate, calcium carbonate, etc., and also contain iron oxides. Of the main crystalline phases in the desulfurization dust aqueous solution, sodium sulfate, sodium chloride, potassium chloride, etc. are highly soluble in water, and therefore can be dissolved in water to produce an alkaline desulfurization dust aqueous solution.

[0028] Thus, the sodium sulfate-containing material of the present invention can be a desulfurization by-product.

[0029] The eluent is not particularly limited as long as it is a substance that can elute sodium ions upon contact with the sodium sulfate-containing substance, and may be, for example, one or more selected from water and an aqueous ammonia solution, such as water.

[0030] More specifically, in such a 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 to the eluent is important. If the ratio of the eluent is too low, the sodium sulfate waste will not be completely dissolved, and a large amount of residue will be generated, resulting in a reduced recovery rate of sodium.

[0031] The ratio of the eluent that does not cause sodium sulfate to be lost as a residue is 1.2 parts by weight or more per 1 part by weight of the sodium sulfate waste. Preferably, 1.4 to 3, for example, 2 to 3 parts by weight of the eluent is mixed per 1 part by weight of the sodium sulfate waste. If the eluent is contained in excess of this range, even if carbon dioxide is subsequently dissolved in the sodium-containing solution, it will not precipitate as sodium bicarbonate. Therefore, the content of sodium bicarbonate dissolved in the solution and effluent will increase, resulting in a lower recovery rate of sodium bicarbonate.

[0032] Referring to FIG. 3, the recovery rate of sodium bicarbonate can be adjusted by adjusting the mass ratio of the sodium sulfate-containing material and the eluent water. + In order to achieve a concentration (molar basis) or more, the mass ratio of the sodium sulfate-containing substance to the eluent introduced can be 1:1.4 to 1:3. If the mass ratio of the eluent to the sodium sulfate-containing substance is below this range, the sodium sulfate will not dissolve and will be lost as a residue, tending to reduce the recovery rate of sodium ions. If the mass ratio of the eluent to the sodium sulfate-containing substance exceeds 3, the recovery rate of sodium ions will increase, but the concentration of sodium ions will be low, preventing the reaction from proceeding, increasing the content of sodium ions discharged as waste liquid, and potentially resulting in a reduced production rate of sodium bicarbonate.

[0033] When a sodium sulfate solution obtained with such a ratio of sodium sulfate-containing waste to eluent is applied to the method for producing sodium bicarbonate of the present invention, 60% or more of the sodium in the sodium sulfate-containing waste can be recovered as sodium bicarbonate.

[0034] On the other hand, the pH range in which bicarbonate ions are most abundantly produced is between pH 7 and 10, for example, between pH 7.5 and 9, and more preferably between pH 8 and 9. Therefore, in order to increase the efficiency of producing sodium bicarbonate, it is preferable to maintain the pH between 8 and 9. Furthermore, if the pH exceeds 10, basic ammonia may not dissolve sufficiently, and if the pH is lower than this, bicarbonate ions (HCO3 - ) may be converted to carbonic acid (H2CO3), reducing the rate of sodium bicarbonate production.

[0035] Carbon dioxide is an acidic gas and therefore easily dissolves in sodium sulfate solution. However, if sodium bicarbonate is produced using only carbon dioxide and sodium sulfate solution, the pH will decrease continuously, resulting in a decrease in the yield of sodium bicarbonate. Therefore, in the present invention, the yield of sodium bicarbonate can be improved by mixing ammonia, which can act as a pH buffer, with sodium sulfate. For example, an aqueous ammonia solution is mixed with the sodium sulfate solution.

[0036] Generally, to dissolve ammonia in a solution such as water, gaseous ammonia is bubbled into the solution. However, when ammonia is bubbled into the solution, the pH further increases, and in the basic solution, ammonia dissolves as NH4 + It exists in the form of NH3 rather than NH4, and has the characteristic of easily dissociating from water. Therefore, in order to produce highly concentrated ammonia water, it is generally necessary to operate the device that dissolves ammonia gas at high pressure or to increase the reaction surface area to dissolve ammonia in the solution.

[0037] On the other hand, Na + In order to recover 50 mol% of sodium bicarbonate based on the molar concentration of sodium bicarbonate, the sodium sulfate solution and the ammonia aqueous solution are mixed in a ratio of ammonia (NH3) / sodium (Na +The ammonia (NH3) / sodium (Na) molar ratio is 0.8 to 1.5, preferably more than 0.6 and 1.3 or less, for example, 0.7 or more and 1.2 or less. The reason why ammonia is essential in the process of producing sodium bicarbonate by injecting carbon dioxide from sodium sulfate-containing waste can also be understood from the following thermodynamic information. + If the molar ratio of ) is less than 0.8, the recovery rate of sodium bicarbonate will decrease, and if the molar ratio increases, the recovery rate of sodium bicarbonate will increase, but the purity of sodium bicarbonate may decrease.

[0038] Meanwhile, referring to FIGS. 3 and 4, the ammonia (NH3) / sodium (Na + If the ratio of ammonia (NH3) / sodium (Na) is less than 0.6, it is below the optimized pH range for producing sodium bicarbonate, and the yield of sodium bicarbonate may decrease. If the pH is more than 1.5, the yield is high, but a large amount of impurities such as (NH4)2SO4 is produced, and the purity of sodium bicarbonate may decrease. + ) ratio is 1.25 to 1.35.

[0039] The reaction to produce sodium bicarbonate is as follows:

[0040] Sodium bicarbonate reaction using sodium sulfate (Reaction A): Na2SO4+2CO2+2H2O→NaHCO3+H2SO4 Reaction B: Sodium bicarbonate formation using sodium sulfate and ammonia: Na2SO4+2NH3+2CO2+2H2O→2NaHCO3+(NH4)2SO4

[0041] The free energy of reaction A (△G, 298K) is 160.653kJ / mol, and the free energy of reaction B (△G, 298K) is 42.702kJ / mol.

[0042] Thus, in the case of Reaction A using only sodium sulfate and carbon dioxide, the reaction is not spontaneous because the pH is positive, but when ammonia is added, the reaction is spontaneous because the pH is negative. Therefore, when producing sodium bicarbonate using sodium sulfate, ammonia is required to act as a pH buffer.

[0043] On the other hand, the mixing step of mixing the sodium sulfate solution and the aqueous ammonia solution to obtain a mixed solution may be performed at a temperature of 25° C. or higher and lower than 100° C. If the temperature is outside this range, the solubility of sodium sulfate tends to decrease, which may result in a decrease in yield.

[0044] The ammonia that can be used in the present invention may be ammonia itself, a mixed solution containing ammonia, a mixed gas, or a solid, and may be, for example, an aqueous ammonia solution.

[0045] Furthermore, to produce sodium bicarbonate, carbon dioxide must be dissolved in the eluate solution containing sodium ions. Therefore, the present invention performs a mixing step of countercurrently mixing a gas containing carbon dioxide into the mixed solution after the step of mixing a sodium sulfate solution with an aqueous ammonia solution to obtain a mixed solution.

[0046] In the countercurrent mixing method according to the present invention, the contact area between the sodium sulfate solution and carbon dioxide is maximized, increasing the dissolution rate of carbon dioxide and enabling the efficient production of sodium bicarbonate. In this case, when carbon dioxide is injected into the ammonia-containing solution, sodium ions in the solution and bicarbonate ions (HCO3 - ) can produce sodium bicarbonate.

[0047] The carbon dioxide used in this case may be pure carbon dioxide or a nitrogen-mixed gas containing 10 to 30 volume % carbon dioxide, and may be, for example, one or more selected from the group consisting of FINEX off-gas (FOG), FINEX tail gas (FTG), blast furnace gas (BFG), converter gas, exhaust gas from a coal-fired power plant, exhaust gas from a gas power plant, exhaust gas from an incinerator, exhaust gas from a glass melting plant, exhaust gas from a thermal facility, exhaust gas from a petrochemical process, process gas from a petrochemical process, pre-combustion exhaust gas, and exhaust gas from a gasifier. Furthermore, in order to increase the concentration of carbon dioxide, the carbon dioxide can be concentrated using a wet amine method, a separation membrane method, a dry pressure swing adsorption / desorption method, or the like.

[0048] Meanwhile, the reaction pressure of the sodium bicarbonate production reactor where the carbonation reaction occurs can be 1 to 10 atm, and the reaction temperature can be 50°C or less. If 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 is high, reducing the economic viability of the final product, sodium bicarbonate. The carbonation reaction time can vary depending on the method of carbon dioxide injection. When carbon dioxide is injected in gas form, the reaction time varies depending on whether or not aeration is performed. If aeration is performed, the reaction time can be 4 hours or less. However, the optimized pressure and reaction time can vary depending on the size, space, and conditions of the reactor.

[0049] On the other hand, when carbon dioxide dissolves in a (water) solution, it forms carbonic acid (H2CO3) and bicarbonate ions (HCO3 - ), carbonate ions (CO3 2- ) and the chemical formula of baking soda is NaHCO3, so only when the amount of bicarbonate ions in the solution increases will they bond with sodium ions and increase the production of baking soda, which precipitates as a solid due to its low solubility.

[0050] The sodium sulfate solution of the present invention may also be a solution obtained by solid-liquid separation of a liquid-phase sodium sulfate-containing substance having a sodium sulfate content of 30% by weight or more, i.e., by separating the solid from the liquid. In this case, the solid-liquid separation device is not particularly limited, and any device capable of separating the solid and liquid phases can be used.

[0051] On the other hand, the filtrate after the carbonation reaction contains sulfate ions (SO4 2- ) is contained in large amounts. Therefore, a calcium-containing substance can be added to the filtrate to produce gypsum (CaSO4). In this case, the calcium-containing substance can be one or more selected from the group consisting of waste cement, waste concrete, coal material, fly ash, steel slag, low- or high-level quicklime (CaO), calcium chloride (CaCl2), wollastonite, limestone, olivine, serpentine, asbestos, and deinking ash. Furthermore, if the purity of the gypsum is low, the purity can be increased by recovering ammonia and adding sulfuric acid and gypsum to the remaining filtrate.

[0052] 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 is preferably injected at a flow rate of 2.5 to 5 L / min. If the flow rate is less than the above range, the residence time of the solution becomes too long, causing stagnation of the solution and making it difficult to obtain a sufficient reaction surface area. If the flow rate exceeds this range, the residence time of the solution becomes too short, causing an insufficient reaction.

[0053] The carbon dioxide-containing gas is preferably injected at a flow rate of 2.5 to 5 L / min. If the flow rate is less than the above range, the discharge pressure is low, which causes a problem that the gas is not smoothly transported to the end of the reactor. If the flow rate is more than this range, the residence time of the gas is too short, which causes a problem that the reaction does not occur sufficiently.

[0054] The present invention will be described in more detail below with reference to specific examples. The following examples are merely illustrative examples to aid in understanding the present invention, and the scope of the present invention is not limited thereto. [Example]

[0055] Example 1. Hydrogen production As an example of the present invention, a hydrogen production experiment was carried out according to the process diagram shown in Figure 1. The composition of the methane-containing gas used is shown in Table 1 below, and the XRD analysis result of the finally produced sodium bicarbonate is shown in Figure 2. Also, Figure 3 is a graph showing the yield of sodium bicarbonate produced using carbon dioxide remaining after hydrogen was separated from the mixed gas generated by reforming methane. During the synthesis of sodium bicarbonate, Na dissolved from ammonia and sodium sulfate-containing waste was used. + It can be seen that the recovery rate of the produced sodium bicarbonate changes depending on the molar ratio of sodium sulfate-containing waste and the ratio of water.

[0056] [Table 1]

[0057] First, the methane gas is heated to approximately 320°C through a preheater, and then the desulfurization process is carried out. The desulfurization reactor is filled with catalysts such as ZnO, CuO, and MoO, which convert unsaturated hydrocarbons into hydrogen compounds and absorb unreacted sulfur components as hydrogen sulfide. The desulfurized methane gas is mixed with steam and heated to 520°C before passing through the reformer. Here, the following reactions basically occur:

[0058] CnHm + nH2O → (n + m / 2)H2 + nCO (endothermic reaction, ΔH = 206 kJ / mol) CO + H2O → CO2 + H2 (exothermic reaction, ΔH = -41 kJ / mol)

[0059] The total heat balance is an endothermic reaction, and reformed gas is produced after passing through the reformer at a temperature of approximately 830°C. The reformed gas then passes through the WGS (Water Gas Shift) reactor. The change in gas composition before and after passing through the WGS reactor is shown in Table 2 below. CO reacts with water vapor in the reformed gas to produce hydrogen and CO2.

[0060] CO+H2O=CO2+H2

[0061] The above reaction is exothermic, and the temperature of the converted gas becomes approximately 420°C.

[0062] [Table 2]

[0063] A pressure cycling process (PSA) is performed to separate hydrogen and carbon dioxide from the produced mixed gas. The pressure cycling process is carried out in the order of adsorption, regeneration, discharge, and pressurization, producing high-purity hydrogen (99.999%). The separated carbon dioxide is also concentrated to over 90% through the pressure cycling process. Meanwhile, in order for the produced hydrogen to be recognized as clean hydrogen, carbon dioxide must be utilized. Therefore, in the present invention, sodium bicarbonate is produced using the carbon dioxide obtained in this process and sodium sulfate.

[0064] The sodium sulfate-containing waste used in this example was a desulfurization by-product having the composition shown in Table 3 below.

[0065] [Table 3]

[0066] Sodium sulfate-containing waste, a desulfurization by-product, contains inorganic substances as shown in Table 3 above, and exhibits a pH of 9 or higher when dissolved in water. In a carbonation reactor such as that shown in Figure 1, ammonia, water, and sodium sulfate are mixed, and carbon dioxide may be further mixed therewith. The ammonia, water, and sodium sulfate may be added individually or in a mixed state.

[0067] The filtrate from the carbonation reactor after the carbonation reaction contains sulfate ions (SO4 2- Therefore, it is possible to produce gypsum (CaSO4) by adding a calcium-containing substance to the filtrate.

[0068] Ammonia is expensive, so it is preferable to recover ammonia for economical process operation. The filtrate from the carbonation reactor has a pH between 7 and 8, and most of the ammonia is in the form of ammonium ions (NH4 + ) in the solution. To recover this, the pH must be increased to 10 or higher to recover the ammonia in gas form, or in steam form using steam. Therefore, quicklime (CaO), a calcium-containing substance, is added to raise the pH. In addition to quicklime, slaked lime, which can also raise the pH, can be used. More than 90% of the ammonia in the solution can be recovered, and the recovered ammonia is reused in the carbonation reactor.

[0069] When ammonia is recovered, the only ions remaining in the solution are calcium (Ca 2+ ) and sulfate (SO4 2- ) is present. If the pH is higher than 6, residual carbonate (CO3 2- ) ions to produce lime (CaCO3) and hydrated lime (Ca(OH)2) as impurities, so it is necessary to reduce the pH to below 6. To reduce the pH, an acid must be added, such as sulfuric acid (H2SO4) or hydrochloric acid (HCl). The wastewater from the gypsum extraction reactor is treated in a wastewater treatment process.

[0070] 2. Water:waste ratio and ammonia (NH3):sodium (Na + ) yield and purity of sodium bicarbonate When a sodium sulfate solution is obtained by performing solid-liquid separation from a desulfurization by-product, which is a sodium sulfate-containing substance, using an eluent, in order to confirm the yield and purity of sodium bicarbonate depending on the ratio of water (eluent):waste (desulfurization by-product), water:waste ratios of 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 were prepared and stirred in a first reactor.

[0071] After stirring, each eluate was diluted with ammonia (NH3) / sodium (Na + ) were changed to 0.6, 0.8, 1.0, 1.3, and 1.5, and the mixture was stirred in the second reactor, and then carbon dioxide was added to the third reactor to start the reaction.

[0072] As can be seen from Figures 3 and 4, if the water / waste ratio is too low, the waste does not dissolve, resulting in a decrease in the amount of eluate and a decrease in the recovery rate of sodium bicarbonate. + It can be seen that the concentration is low and the recovery rate of sodium bicarbonate is low. + When the ratio of ammonia (NH3) / sodium (Na) is less than 0.6, the pH is low and the recovery rate of sodium bicarbonate decreases. + When the ratio of (NH4)2SO4 is high, such as 1.5 or more, the yield of sodium bicarbonate increases, but impurities such as (NH4)2SO4 are produced, and it can be seen that the purity of sodium bicarbonate decreases.

[0073] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those skilled in the art that various modifications and variations are possible within the scope that does not deviate from the technical idea of ​​the present invention described in the claims.

Claims

1. The methane-containing gas is converted into hydrogen, CO, and CO by a reforming reaction using steam. ２ a methane reforming stage for converting the methane into a reformed gas comprising obtaining a mixed gas of hydrogen and carbon dioxide by performing a water-gas shift (WGS) of the reformed gas; a separation step of separating hydrogen and carbon dioxide from the mixed gas; and mixing the separated carbon dioxide with sodium sulfate, ammonia, and water.

2. 2. The method of claim 1, wherein the mixing step comprises mixing carbon dioxide in a countercurrent manner with a mixed solution obtained by mixing a sodium sulfate solution and an aqueous ammonia solution.

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

4. 3. The method for producing clean hydrogen according to claim 2, wherein the sodium sulfate solution is obtained by performing solid-liquid separation from a sodium sulfate-containing substance using an eluent.

5. The method for producing clean hydrogen according to claim 4, wherein the mass ratio of the sodium sulfate-containing material to the eluting agent is 1:1.2 to 1:

3.

6. The sodium sulfate solution and ammonia are mixed to form ammonia (NH ３ ) / Sodium (Na ＋ 3. The method for producing clean hydrogen according to claim 2, wherein the ratio of the above is 0.8 to 1.

5.

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

8. The method for producing clean hydrogen according to claim 2 , wherein the ammonia is a mixed solution, mixed gas, or solid containing ammonia.

9. 2. The method for producing clean hydrogen according to claim 1, further comprising the step of removing sulfur as an impurity from the methane-containing gas prior to the methane reforming step.

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