Process for the preparation of inorganic compounds from desulphurized gypsum to reduce greenhouse gas emissions

Abstract

The present invention relates to a method for preparing inorganic compounds using desulfurization gypsum to reduce emission of greenhouse gases, in more detail, to a method for preparing inorganic compounds in which desulfurization gypsum, which is an industrial waste as a recycling resource, and a leaching agent, which can be reused after separation, are used as raw materials, thereby preparing anhydrous gypsum and calcium carbonate for various uses such as construction materials, and thus, compared to the existing process, greenhouse gases and process costs can be significantly reduced.

Description

Technical Field

[0001] This invention relates to a method for preparing inorganic compounds using desulfurized gypsum to reduce greenhouse gas emissions. More specifically, it relates to a method for preparing inorganic compounds, wherein desulfurized gypsum, an industrial waste that is a recyclable resource, and a dissolving agent are used as raw materials to prepare anhydrous gypsum and calcium carbonate for various applications such as building materials. The dissolving agent can be reused after separation, thus significantly reducing greenhouse gases and process costs compared to existing processes. Background Technology

[0002] South Korea's greenhouse gas emissions averaged 662 million tons of CO2 equivalent (eq.) annually from 2007 to 2017, with the energy and industrial sectors accounting for over 94% of emissions. Although CO2's global warming potential (GWP) is 1, lower than other greenhouse gases, its production reached 604 million tons of CO2 equivalent, accounting for over 91% of total production, significantly impacting global warming. Furthermore, the 2017 production increased by 23% compared to 2007, highlighting the growing severity of the problem.

[0003] Precipitated calcium carbonate (PCC, CaCO3) is used as an additive and filler to improve quality in the food, paper, rubber, plastics, and coating industries. Existing PCC preparation technology involves removing carbon dioxide from limestone mined from mines at high temperatures to produce quicklime, which is then reacted again with carbon dioxide in the following manner.

[0004] The first reaction is: CaCO3 (limestone) → CaO (lime) + CO2 (≥900℃)

[0005] Second CaO + H₂O → Ca(OH)₂

[0006] The third step is Ca(OH)₂ + CO₂ → CaCO₃(PCC) + H₂O

[0007] However, the existing methods require significant processing costs due to the heat source used to convert limestone into quicklime, and also pose a problem of adverse environmental impacts caused by greenhouse gases such as carbon dioxide generated from the heat source and the dissociation of limestone.

[0008] In addition, anhydrous gypsum (calcium sulfate, CaSO4) is used as a representative building material. Since South Korea does not have mines where anhydrous gypsum can be mined, most of its usage needs to be imported from abroad.

[0009] Therefore, there is still a need for a method that can reduce greenhouse gas emissions and process costs while producing anhydrous gypsum and calcium carbonate for use in various industrial materials. Summary of the Invention Technical problems to be solved

[0010] The purpose of this invention is to provide a method for preparing inorganic compounds that uses desulfurized gypsum, an industrial waste that is a recycled resource, and a dissolving agent as raw materials. This method can prepare anhydrous gypsum and calcium carbonate for various applications such as building materials. The dissolving agent can be reused after separation, thus significantly reducing greenhouse gases and process costs compared to existing processes. Technical solution

[0011] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing inorganic compounds using desulfurized gypsum, comprising: a step of preparing anhydrous gypsum powder, wherein a mixture of desulfurized gypsum, a dissolving agent, and water is filtered to separate a filtrate and an anhydrous gypsum cake, and the separated anhydrous gypsum cake is dried; and a step of preparing calcium carbonate powder, wherein a gas containing carbon dioxide is supplied to the filtrate obtained in the step of preparing anhydrous gypsum powder and filtered to separate a calcium carbonate cake and a dissolving agent solution, and the separated calcium carbonate cake is dried, wherein the dissolving agent solution obtained in the step of preparing calcium carbonate powder is supplied to the step of preparing anhydrous gypsum powder and reused. Beneficial effects

[0012] According to the method for preparing inorganic compounds using desulfurized gypsum of the present invention, since desulfurized gypsum produced in FBC boilers as a recycled resource is used as raw material, the amount of limestone used as a natural resource can be reduced, thereby protecting resources. Since the process of turning limestone into quicklime, which is not required in existing calcium carbonate preparation methods, can reduce the cost of heat source required and greenhouse gases such as carbon dioxide generated in the quicklime preparation process, it is environmentally friendly.

[0013] Furthermore, desulfurized gypsum, an undervalued circular resource, can be used to produce high-value-added hard calcium carbonate and anhydrous gypsum. In particular, the domestic production of anhydrous gypsum, which is heavily reliant on imports, is possible. Moreover, the CaO separated from desulfurized gypsum can significantly contribute to reducing greenhouse gas emissions through its reaction with carbon dioxide. Attached Figure Description

[0014] Figure 1 The process of Example 1, which is a method for preparing the inorganic compound of the present invention, is illustrated schematically.

[0015] Figure 2The process of a comparative example of the present invention, corresponding to the prior art, is illustrated schematically.

[0016] Figure 3 The X-ray diffraction analysis results of the anhydrous gypsum powder obtained in Examples 1 and 2 are shown.

[0017] Figure 4 The X-ray diffraction analysis results confirming the acquisition of varaterite-type PCCs in Examples 1 and 2 are shown.

[0018] Figure 5 The X-ray diffraction analysis results of the inorganic compounds (anhydrous gypsum powder and PCC) obtained in the comparative examples are shown.

[0019] Figure 6 The SEM analysis results of the PCC obtained in Example 1 are shown.

[0020] Figure 7 The SEM analysis results of the PCC obtained in the comparative example are shown. Detailed Implementation

[0021] The present invention will now be described in more detail.

[0022] The method for preparing inorganic compounds using desulfurized gypsum according to the present invention includes: a step of preparing anhydrous gypsum powder, wherein a mixture of desulfurized gypsum, a dissolving agent, and water is filtered to separate a filtrate and an anhydrous gypsum cake, and the separated anhydrous gypsum cake is dried; and a step of preparing calcium carbonate powder, wherein a gas containing carbon dioxide is supplied to the filtrate obtained in the step of preparing anhydrous gypsum powder and filtered to separate a calcium carbonate cake and a dissolving agent solution, and the separated calcium carbonate cake is dried, wherein the dissolving agent solution obtained in the step of preparing calcium carbonate powder is supplied to the step of preparing anhydrous gypsum powder and reused.

[0023] In this specification, the step of preparing anhydrous gypsum powder may be referred to as the first step, and the step of preparing calcium carbonate powder may be referred to as the second step.

[0024] The method for preparing inorganic compounds using desulfurized gypsum according to the present invention includes the following steps: preparing anhydrous gypsum powder, filtering a mixture of desulfurized gypsum, a dissolving agent and water to separate it into filtrate and anhydrous gypsum cake, and drying the separated anhydrous gypsum cake.

[0025] In desulfurized gypsum (CaO·CaSO4), CaO dissolves in water and separates from CaSO4, but to a lesser extent. Therefore, a dissolving agent that promotes dissolution is added. Various components can be used as the dissolving agent, as described below; in one specific embodiment, NH4Cl can be used. The reaction at this time is as follows.

[0026] CaSO4·CaO (solid) + 2NH4Cl (solution) → CaSO4 (solid) + CaCl2 (solution) + 2NH3 (solution) + H2O (liquid)

[0027] In one specific embodiment of the invention, due to the reaction, the mixture of desulfurized gypsum, dissolving agent and water may contain CaSO4 (solid), CaCl2 (solution), 2NH3 (solution) and H2O (liquid). Since the solubility of CaCl2 in water is higher than that of Ca(OH)2 generated when no dissolving agent is added separately (i.e., when only desulfurized gypsum and water are mixed), a small amount of water can be used to dissolve CaO and separate it from anhydrous gypsum.

[0028] The desulfurization gypsum used in this invention is prepared to remove sulfur oxides generated in a circulating fluidized bed boiler (CFBC boiler). Its raw material is limestone, and the desulfurization reaction pathway in the CFBC boiler is as follows.

[0029] First, CaCO3 → CaO + CO2 (850-900℃)

[0030] The second step is CaO + SO₂ + 1 / 2O₂ → CaSO₄

[0031] The desulfurized gypsum (CaO·CaSO4) used in this invention may contain 40-60% by weight of CaSO4 and 25-45% by weight of CaO. The conversion rate of CaO in the second step of the desulfurization reaction is about 50%. Unreacted CaO present in the desulfurized gypsum is used to prepare precipitated calcium carbonate, and the other components can be used as anhydrous gypsum products.

[0032] The dissolving agent used in the step of preparing anhydrous gypsum powder can be selected from NH4Cl, sodium boride, urea, NH4NO3 and combinations thereof, for example, NH4Cl.

[0033] In the step of preparing anhydrous gypsum powder, the weight ratio of desulfurized gypsum to water can be 1:5 to 1:45, for example, 1:5 to 1:40, 1:6 to 1:30, or 1:8 to 1:20. When the water content relative to desulfurized gypsum is lower than the above ratio, the amount of CaO dissolved in the desulfurized gypsum is negligible, and therefore the quality (purity) of the anhydrous gypsum and the amount of calcium carbonate prepared may decrease. On the other hand, when the water content is higher than the above ratio, it is difficult to obtain further benefits.

[0034] In the step of preparing anhydrous gypsum powder, the weight ratio of desulfurized gypsum to dissolving agent can be from 1:0.7 to 1:2, for example, from 1:0.75 to 1:1.8 or from 1:0.8 to 1:1.5. When the content of dissolving agent relative to desulfurized gypsum is lower than the above ratio, the amount of CaO dissolved in the desulfurized gypsum is negligible, and therefore the quality (purity) of anhydrous gypsum and the amount of calcium carbonate prepared may decrease. On the other hand, when the content of dissolving agent is higher than the above ratio, it is difficult to obtain further benefits.

[0035] In the step of preparing anhydrous gypsum powder, the separated anhydrous gypsum cake can be dried to prepare anhydrous gypsum powder. The prepared anhydrous gypsum can be used as building material, fertilizer, etc. after washing and drying processes.

[0036] The preparation of anhydrous gypsum powder can be carried out at 20-30°C, for example, at room temperature for 2-10 hours, or for example, for 2-8 hours or 2-6 hours.

[0037] The method for preparing inorganic compounds using desulfurized gypsum according to the present invention includes: a step of preparing calcium carbonate powder; supplying a gas containing carbon dioxide to the filtrate obtained in the step of preparing anhydrous gypsum powder and filtering to separate calcium carbonate cake and a dissolving agent solution; and drying the separated calcium carbonate cake.

[0038] Due to the reaction between CaO separated from desulfurized gypsum and the dissolving agent, the filtrate obtained in the step of preparing anhydrous gypsum powder may contain CaCl2 and NH3. In one specific embodiment, when a gas containing carbon dioxide is supplied to the filtrate from which CaO is dissolved (calcium is dissolved in the form of CaCl2) to impart carbon dioxide, CaCl2 precipitates as CaCO3 (PCC), and NH3 (in solution) reacts with Cl... - It combines to form NH4Cl.

[0039] CaCl2 (solution) + 2NH3 (solution) + 2H2O (liquid) + CO2 (gas) → CaCO3 (solid) + 2NH4Cl (solution) + H2O (liquid)

[0040] In the step of preparing calcium carbonate powder, the mixture can be separated into calcium carbonate cake and a dissolving agent solution. The separated dissolving agent solution can be supplied to the step of preparing anhydrous gypsum and reused. In one specific embodiment, the dissolving agent can be NH4Cl, which can be supplied again to the step of preparing anhydrous gypsum powder for the dissolution of CaO in desulfurized gypsum, thus reducing the process cost associated with using the dissolving agent.

[0041] There are no particular restrictions on the carbon dioxide-containing gas used in the preparation of calcium carbonate powder; for example, exhaust gas from a circulating fluidized bed combustion boiler or 100% carbon dioxide gas can be used. Although there are no particular restrictions, the carbon dioxide-containing gas can be supplied at a rate of 100-500 ml / min.

[0042] In the step of preparing calcium carbonate powder, after separating the calcium carbonate cake and the dissolving agent solution, the dissolving agent is supplied to the step of preparing anhydrous gypsum powder, and the calcium carbonate powder can be prepared by drying the separated calcium carbonate cake. The prepared calcium carbonate can be precipitated calcium carbonate (PCC), which, unlike limestone, has high whiteness and small particle size, and is therefore used as a functional agent in various industries.

[0043] The preparation of calcium carbonate powder can be carried out at 20-30°C, for example, at room temperature for 1-5 hours, or for example, for 1-4 hours or 1-3 hours.

[0044] The present invention will now be described in more detail through examples and comparative examples. However, the scope of the present invention is not limited thereto.

[0045] [Example]

[0046] Example 1, Example 2 and Comparative Example

[0047] The method for preparing inorganic compounds using desulfurized gypsum according to the present invention is carried out based on the composition shown in Table 1 below. (Step 1: Step for preparing anhydrous gypsum powder; Step 2: Step for preparing calcium carbonate powder)

[0048] Example 1 uses a dissolving agent for the first time, Example 2 uses the dissolving solution separated from the reaction in step 2 of Example 1, and the comparative example uses only desulfurized gypsum and water, without using a dissolving agent alone.

[0049] Figure 1 and Figure 2 The process of Example 1 and the process of the comparative example, which are methods for preparing inorganic compounds of the present invention, are illustrated schematically, respectively.

[0050] [Table 1]

[0051] Figure 3 and Figure 4 The X-ray diffraction analysis results of the inorganic compounds (anhydrous gypsum powder and calcium carbonate (PCC)) obtained in Examples 1 and 2 are shown in Figure 2, respectively.

[0052] from Figure 3It can be confirmed that the anhydrous gypsum after step 1 of Example 1 can be prepared in a form in which CaO and Ca(OH)2 components are removed compared to the raw desulfurized gypsum. Furthermore, in Example 2, it can be confirmed that the reused dissolving agent causes the CaO and Ca(OH)2 components in the raw desulfurized gypsum to dissolve in the same manner as in Example 1. This demonstrates the effectiveness of the reuse of the dissolving agent in the method for preparing inorganic compounds using desulfurized gypsum of the present invention.

[0053] also, Figure 4 The X-ray diffraction analysis results confirming the acquisition of aragonite-type calcium carbonate (PCC) in Examples 1 and 2 are shown. It confirms that aragonite-type PCC was synthesized by adding carbon dioxide to the filtrate in step 2 of Example 1, and that the same type (aragonite) of PCC was also synthesized in Example 2, which reused the dissolving agent from Example 1. This also demonstrates the effectiveness of reusing the dissolving agent in the method for preparing inorganic compounds using desulfurized gypsum of the present invention.

[0054] in addition, Figure 5 The X-ray diffraction analysis results of the inorganic compounds (anhydrous gypsum powder and PCC) obtained in the comparative examples are shown. In the comparative examples, in order to dissolve CaO in desulfurized gypsum, a larger amount of water (solvent) was used in step 1 compared to the examples, and sufficient reaction time was given, but it was confirmed that CaO remained in a hydrated form in the anhydrous gypsum. Furthermore, it was confirmed that PCC in the form of calcite was synthesized in step 2, unlike in the examples.

[0055] Figure 6 The SEM analysis results of the PCC obtained in Example 1 are shown. Figure 7 The SEM analysis results of the PCC obtained in the comparative example are shown, confirming that the PCC obtained in Example 1 is aragonite grains, while the PCC obtained in the comparative example is calcite grains. From Figure 6 As can be seen, unlike calcite particles, spheroidal aragonite particles are spherical in shape. When used as a rubber additive, they have the advantages of maintaining the flexibility of rubber while increasing strength and improving economy. On the other hand, from... Figure 7 As can be seen from this, calcite particles are mainly hexagonal in shape and have angles, thus exhibiting less flexibility compared to aragonite particles.

Claims

1. A method for preparing inorganic compounds using desulfurized gypsum, comprising the method of preparing anhydrous gypsum powder and aragonite-type calcium carbonate powder from desulfurized gypsum, the method comprising: The steps for preparing anhydrous gypsum powder involve filtering a mixture of desulfurized gypsum, a dissolving agent, and water prepared in a CFBC boiler to separate a filtrate and an anhydrous gypsum cake free of quicklime, and then drying the separated anhydrous gypsum cake; and The step of preparing calcium carbonate powder involves supplying a carbon dioxide-containing gas, which is the exhaust gas of a circulating fluidized bed combustion boiler, to the filtrate obtained in the step of preparing anhydrous gypsum powder, and filtering it to separate it into aragonite-type calcium carbonate cake and a dissolving agent solution. The separated calcium carbonate cake is then dried. The desulfurized gypsum mentioned above is a desulfurized gypsum containing quicklime, CaO·CaSO4. The desulfurized gypsum contains 40-60% by weight of CaSO4 and 25-45% by weight of CaO. The anhydrous gypsum mentioned is anhydrous gypsum CaSO4 that does not contain quicklime. The dissolving agent is NH4Cl. The filtrate contains CaCl2 and NH3 generated by the reaction of CaO in the desulfurized gypsum with the dissolving agent, and the anhydrous gypsum cake is CaSO4 from which CaO in the desulfurized gypsum CaO·CaSO4 has been dissolved and removed. In the step of preparing calcium carbonate powder, CaCl2 in the filtrate precipitates as CaCO3, and NH3 reacts with Cl... - The NH4Cl dissolving agent is supplied to the step of preparing anhydrous gypsum powder and reused to dissolve CaO from the desulfurized gypsum.

2. The method for preparing inorganic compounds using desulfurized gypsum according to claim 1, wherein, In the step of preparing anhydrous gypsum powder, the weight ratio of desulfurized gypsum to water is 1:5 to 1:

45.

3. The method for preparing inorganic compounds using desulfurized gypsum according to claim 1, wherein, In the step of preparing anhydrous gypsum powder, the weight ratio of desulfurized gypsum to dissolving agent is 1:0.7 to 1:

2.

4. The method for preparing inorganic compounds using desulfurized gypsum according to claim 1, wherein, The step of preparing anhydrous gypsum powder is carried out at 20-30°C for 2-10 hours.

5. The method for preparing inorganic compounds using desulfurized gypsum according to claim 1, wherein, The step of preparing calcium carbonate powder is carried out at 20-30°C for 1-5 hours.

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