KR102576171B1 - Method of Manufacturing Metal Carbonate using Electrolysis and Separation of Metal ions - Google Patents

Abstract

The present invention relates to a method for producing metal carbonate from concentrated seawater desalination, comprising the steps of precipitating calcium hydroxide and magnesium hydroxide from concentrated seawater desalination containing calcium ions and magnesium ions to separate metal ions; Generating sodium hydroxide by chloro-alkaline electrolysis of the concentrated water from which metal ions are separated; and a carbonation step of forming calcium carbonate and magnesium carbonate by reacting the calcium hydroxide and magnesium hydroxide produced by the metal ion separation with carbon dioxide. The manufacturing method according to the present invention can produce metal carbonate in an eco-friendly way by utilizing concentrated seawater desalination and carbon dioxide, and is excellent in terms of process stability, yield, and economy.

Description

Manufacturing method of metal carbonate using electrolysis and separation of metal ions {Method of Manufacturing Metal Carbonate using Electrolysis and Separation of Metal ions}

The present invention relates to a method for preparing a metal carbonate using electrolysis and metal ion separation.

Various greenhouse gases that cause global warming include carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons, among which carbon dioxide accounts for the largest volume. Carbon dioxide has the lowest global warming potential, but continues to burn fossil fuels in industrial processes and accounts for 65% of global greenhouse gas emissions.

Accordingly, carbon dioxide capture and storage technologies are being studied, and carbon dioxide capture and utilization (CCU) is proposed as a promising CO ₂ treatment technology due to its versatility compared to other CO ₂ mitigation methods such as carbon dioxide capture and storage (CCS). there is. Since carbon dioxide in CCU is captured and converted into organic and inorganic compounds by various methods such as wet absorption and adsorption, CCU is classified into organic and inorganic CCU.

Compared to organic CCUs, inorganic CCUs can handle large amounts of CO ₂ and energy savings are possible because no catalyst is required for metal carbonate formation. Inorganic CCUs can capture carbon dioxide by converting it into inorganic compounds such as magnesium carbonate, calcium carbonate, and sodium bicarbonate.

On the other hand, in the seawater desalination process, which is a process of removing salt from seawater to make it into water, in order to facilitate the supply of drinking water and industrial water, concentrated seawater desalination is generated. . Accordingly, the development of technology for capturing carbon dioxide using concentrated seawater desalination has been continuously conducted.

Existing carbon dioxide capture technology using concentrated seawater desalination directly reacts carbon dioxide without separating metal ions from concentrated seawater desalination or separates metal ions from concentrated seawater desalination using electrolysis, but in this case, the desired metal There was a problem in that the ions were not separated and the yield was low and the economic feasibility was lowered.

An object of the present invention is to provide a method for producing a metal carbonate salt for capturing carbon dioxide using concentrated seawater desalination.

In addition, it is intended to provide a manufacturing method that can separate metal ions in concentrated seawater desalination to provide a desired metal carbonate and is excellent in terms of process stability, economy and efficiency.

In order to achieve the above object, the present inventors have completed the present invention by combining a metal ion separation step, an electrolysis step and a carbonation step.

In the present invention, "seawater desalination concentrated water" is abundantly dissolved in metal ions, and the metal ions that account for the largest portion are calcium, magnesium, and sodium, and other, although the concentration is not high, potassium, lithium, barium, etc. are dissolved.

The present invention provides a method for precipitating and separating sodium, magnesium, and calcium, which account for the largest proportion of metal ions in concentrated seawater desalination, in solid form.

The present invention includes the steps of separating metal ions by precipitating calcium hydroxide and magnesium hydroxide from concentrated seawater desalination containing calcium ions and magnesium ions; Generating sodium hydroxide by chloro-alkaline electrolysis of the concentrated water from which metal ions are separated; and a carbonation step of forming calcium carbonate and magnesium carbonate by reacting the calcium hydroxide and magnesium hydroxide generated by the metal ion separation with carbon dioxide.

Here, the sodium hydroxide generated by the electrolysis may be recycled and added to the metal ion separation step.

In one aspect of the present invention, the metal ion separation step may be separation by a pH swing method. The pH swing method is to obtain calcium hydroxide and magnesium hydroxide by treating concentrated seawater desalination with an alkaline solution and adjusting the pH.

Specifically, when an alkali solution is added to concentrated seawater desalination, the pH increases accordingly, and the pH at which magnesium hydroxide and calcium hydroxide precipitate are different from each other, so that magnesium hydroxide and calcium hydroxide can be precipitated and separated according to the pH.

More specifically, the metal ion separation step is the step of precipitating and separating magnesium hydroxide by adjusting the pH of concentrated seawater desalination to 7 to 11, and the pH of concentrated water from which magnesium hydroxide is separated is adjusted to 11 to 11. 13 to precipitate and separate calcium hydroxide.

That is, when the pH of the concentrated seawater desalination water is 7 to 11, magnesium hydroxide precipitates first and calcium ions still exist in the aqueous solution in an ionic state. After that, the pH of the concentrated seawater desalination water is increased to 11 to 13 to obtain calcium hydroxide. It can precipitate. Magnesium hydroxide and calcium hydroxide in solid form can be filtered through filter paper.

The alkali solution used to increase the pH may be sodium hydroxide, and this sodium hydroxide may be obtained from chloro-alkali electrolysis described later.

Since the carbonation process is performed after separating calcium ions and magnesium ions through the metal ion separation step, each of the prepared calcium carbonate and magnesium carbonate can be used separately according to its purpose. In addition, since it is not easy to separate calcium carbonate and magnesium carbonate per se, metal carbonate can be obtained with high purity by carbonation after metal ion separation.

On the other hand, in the present invention, "chloro-alkali electrolysis" is a process of discharging chlorine gas on the anode side when electrolyzing seawater desalination concentrated water, and discharging a mixture containing sodium hydroxide aqueous solution and hydrogen gas on the cathode side. means A schematic diagram of a specific “chloro-alkali electrolysis” process is shown in FIG. 3 .

In the present invention, seawater desalination concentrated water separates and removes calcium ions and magnesium ions through a metal ion separation process, and then is put into a “chloro-alkali electrolysis” process.

When calcium and magnesium ions, which are divalent metals present in concentrated water, are introduced into the electrolysis process as they are, they are precipitated in the electrolysis device and cause membrane fouling, resulting in a problem of lowering yield and economic feasibility of the process. . Accordingly, in the present invention, the concentrated water that has undergone the metal ion separation process is introduced into the “chloro-alkali electrolysis” process.

The electrolysis step may use an electrolysis device including an anode chamber and a cathode chamber separated by a sodium ion exchange membrane, and concentrated water may be added to the anode chamber. In addition, the prepared sodium hydroxide aqueous solution can be obtained through a cathode chamber.

The sodium ion exchange membrane is permeable only to sodium ions, so it can generate chlorine gas in the anode chamber and hydrogen gas and sodium hydroxide in the cathode chamber. Here diluted sodium hydroxide can be added to the anode chamber. Sodium hydroxide can be added to increase the sodium hydroxide production rate.

As described above, the produced sodium hydroxide may be recycled to the metal ion separation step and used as a pH adjusting agent.

In the electrolysis step, the electrolysis time may be 500 seconds or more, 1000 seconds or more, or 1400 seconds or more, and specifically may be 500 seconds to 3000 seconds. Preferably, it may be 1000 to 3000 seconds, 1000 to 2500 seconds, or 1000 to 2000 seconds.

In the electrolysis step, the current density of the electrolysis may be 1.5 to 4 kA/m ² . Preferably, it may be 2 to 4, 2.5 to 4, or 2.5 to 3.5 kA/m ² , and most preferably 3 kA/m ² .

Magnesium hydroxide and calcium hydroxide prepared in the metal ion separation step and the electrolysis step may form magnesium carbonate and calcium carbonate through a carbonation step.

In the carbonation step, carbon dioxide is not reactive, but can be converted into ionic carbon dioxide forms such as bicarbonate (HCO ₃ ^- ) and carbonate (CO ₃ ^{2 -} ) if there is sodium hydroxide that is easily ionized in water. Accordingly, carbon dioxide and sodium hydroxide directly react to form sodium bicarbonate, bicarbonate, and carbonate.

That is, in the present invention, carbon dioxide may react with sodium hydroxide generated by the electrolysis before reacting with calcium hydroxide and magnesium hydroxide to exist as ionic carbon dioxide of carbonate and/or bicarbonate. Carbon dioxide exists as carbonate (CO ₃ ^2- ) and/or bicarbonate (HCO ₃ ^- ) and can readily react with metal ions.

In the carbonation step of calcium, ionic carbon dioxide and calcium hydroxide may directly react to produce calcium carbonate. The properties of calcium carbonate can be controlled by adjusting the reaction temperature, reaction time, or pH value of the carbonation step.

Meanwhile, the step of carbonating magnesium may further include reacting magnesium hydroxide with an acid prior to reacting with ionic carbon dioxide. This is a step of extracting magnesium ions from magnesium hydroxide, and since magnesium hydroxide is insoluble in water, it is difficult to convert to magnesium carbonate, and in order to carbonate magnesium hydroxide itself, high temperature and high pressure are required. It is preferable to further include a step of extracting magnesium ions in this way prior to the carbonation step of magnesium. The acid may be hydrochloric acid.

The magnesium carbonate produced in the carbonation step of magnesium in the carbonation step may have a nesquehonite property. However, the properties of magnesium carbonate can be controlled by adjusting the reaction temperature, reaction time, or pH value of the carbonation step.

Through the method for producing metal carbonate according to the present invention, it was possible to separate and obtain calcium carbonate and magnesium carbonate from concentrated seawater desalination and carbon dioxide, respectively, and could be appropriately used according to each purpose.

The present invention may also provide calcium carbonate and magnesium carbonate prepared through the method for preparing a metal carbonate of the present invention.

According to the present invention, it is possible to provide a method for producing a metal carbonate salt capable of capturing and removing a large amount of carbon dioxide, which is a greenhouse gas. After separating metal ions from seawater desalination concentrated water, carbon dioxide can be captured to provide the desired metal carbonate, and products of each process can be produced in high yield, and the process stability, efficiency, and economy are also excellent.

1 is a schematic diagram of the entire process of the present invention.
Figure 2 is a schematic diagram showing the entire process of the present invention by Aspen simulation.
3 is a schematic diagram showing an electrolysis process according to Example 2;
Figure 4 shows the sodium concentration with time during the electrolysis of Example 2.
5 shows the OH ^- concentration over time during electrolysis in Example 2, where i ₁ is 0.5 kA/m ² , i ₂ is 1.5 kA/m ² , and i ₃ is current density of 3.0 kA/m ^{2 .} it indicated the time
6 shows Cl ⁻ concentration over time during electrolysis in Example 2, where i ₁ is 0.5 kA/m ² , i ₂ is 1.5 kA/m ² , and i ₃ is current density of 3.0 kA/m ² . it indicated the time

Hereinafter, preferred embodiments and experimental examples are presented to aid understanding of the present invention. However, the following Examples and Experimental Examples are only provided to more easily understand the present invention, and the content of the present invention is not limited by the following Examples and Experimental Examples.

[Example]

The metal ion separation and carbonation processes were simulated with Aspen Plus V.10.0, and the electrolysis process was simulated with Mathworks' dynamic simulation program MATLAB® version R2020b, and the results were entered into the Aspen model for further simulation. Figure 2 shows the process according to the Aspen simulation. The ambient temperature was 298 K and the pressure was 101.325 kPa.

Example 1. Metal ion separation process

The metal ion separation process was performed in a continuous stirred tank reactor (CSTR).

Sodium hydroxide obtained through electrolysis according to Example 2 was used as a buffer solution, the pH of seawater desalination concentrated water was adjusted to approximately 10 to precipitate solid magnesium hydroxide, and sodium hydroxide was further added to approximately pH At 12, calcium hydroxide was precipitated. The production mechanism of calcium hydroxide and magnesium hydroxide is as follows.

<Calcium hydroxide and magnesium hydroxide production mechanism>

Ca ²⁺ + 2OH ^- ↔ Ca(OH) ₂

Mg ²⁺ + 2OH ^- ↔ Mg(OH) ₂

Example 2. Electrolysis of desalinated fresh water

The process of Example 2 is as described in the schematic diagram of FIG. 3 . The ionic behaviors of Na ⁺ , Cl ^- , OH ^- , and water molecules were simulated in both the anode and cathode chambers.

When saturated NaCl in seawater desalination concentrated water is supplied to the electrolysis chamber and electrolyzed, Cl ^- ions are oxidized at the anode to form Cl ₂ gas, and Na ⁺ ions flow through the ion permeable membrane to the cathode chamber, or NaCl It can be released in the form of an aqueous solution. At the cathode, water molecules were reduced to produce H ₂ gas and OH ^- ions, and OH ^- ions reacted with Na ⁺ in the cathode chamber and hydroxylated by the ion-permeable membrane, which allowed only Na ⁺ to pass through but not OH ^- ions. sodium was produced. In addition, diluted sodium hydroxide was additionally added to the cathode chamber to increase the concentration of sodium hydroxide, thereby promoting the reaction between Na ⁺ and OH ^- ions, thereby improving the NaOH production rate. The anode, cathode and overall electrolysis mechanism are as follows.

<Oxidation Electrode Cell Reaction Mechanism>

2Na ⁺ + 2Cl ^- →Cl ₂ + 2Na ⁺ + 2e ^-

2Cl ^- →Cl ₂ + 2e ^-

<Reduction Electrode Cell Reaction Mechanism>

2H ₂ O + 2e ^- →H ₂ + 2OH ^-

Na ⁺ + OH ^- → NaOH

<Overall Electrolysis Mechanism>

2H ₂ O + 2NaCl→H ₂ + Cl ₂ + 2NaOH (aq)

Example 3. Carbon dioxide absorption process

The robust design of Aspen's velocity-based Radfrac block was simulated by designing an absorption tower. The inner column was designed in 20 stages using MELLAPAK SULZER 250Y absorbent packing. In this system, exhaust gas flows in from the bottom of the absorption tower and flows to the top, and NaOH flows in from the top of the absorption tower and flows to the bottom, maximizing the contact surface between the two. Carbon dioxide was absorbed into the aqueous solution during contact. Table 1 below summarizes the parameters of the Aspen design performed in Example 3.

parameter data carbon dioxide source combustion gas metal ion source desalinated seawater Carbon dioxide flow rate (kmol/h) 0.1 NaOH flow rate (kmol/h) 0.16 Absorbent column type Rate-Based Calculation Model (Radfrac) number of steps 20 Packing type in absorbent Mellapak Packed 250Y Packing details Sulzer/Standard Total length of packing in absorbent 3.89m absorbent internal diameter 0.1m Top pressure 0.998atm

NaOH has high solubility in an aqueous solution and can be dissociated into Na ⁺ and OH ^- ions to form a basic aqueous solution. Accordingly, by reacting non-reactive carbon dioxide with sodium hydroxide, ionic forms of carbon dioxide such as bicarbonates and carbonates can be produced. Thus, sodium hydroxide introduced from the top of the absorption tower and carbon dioxide introduced from the bottom of the absorption tower reacted in the absorption tower to form sodium bicarbonate.

<Mechanism of Sodium Bicarbonate Formation>

2NaOH + CO ₂ →Na ₂ CO ₃ + H ₂ O

Na ₂ CO ₃ + H ₂ O + CO ₂ → 2NaHCO ₃

Example 4. Carbonation Process of Calcium and Magnesium Ions

Example 4-1. Carbonation process of calcium ions

Calcium hydroxide produced according to Example 1 can readily react with carbonate and/or bicarbonate in the form of ionic carbon dioxide produced according to Example 3 to precipitate as calcium carbonate. This is a reaction that occurs spontaneously at room temperature, and the carbonation process of calcium ions was also simulated as a continuous production process using CSTR as in Example 1. The carbonation mechanism of calcium ions is as follows.

<Calcium Carbonation Mechanism>

Ca ²⁺ + CO ₃ ^2- → CaCO ₃

Ca2+ + HCO ₃ ^- → CaCO ₃ + H ⁺

CaCO ₃ → Ca ²⁺ + CO ₃ ^2-

CaCO ₃ + H ⁺ → Ca ²⁺ + HCO ₃ ^-

Example 4-2. Carbonation process of magnesium ion

The magnesium hydroxide prepared according to Example 1 is difficult to convert to magnesium carbonate because it is insoluble in water. Thus, first, hydrochloric acid was mixed to extract magnesium ions in an aqueous solution. Magnesium carbonate was produced by reacting the extracted magnesium ions with carbonate and/or bicarbonate in the form of ionic carbon dioxide. The magnesium carbonate production reaction was carried out at room temperature.

The hydrophilic nature of magnesium ions induces an aqueous barrier around the ions to form hydrated structures or can attach to water ligands, which can cause distortion of the crystallization of the formed magnesium carbonate. As a result of this simulation, the properties of magnesium carbonate are nesquehonite, and the properties of magnesium carbonate can be easily changed depending on conditions. The carbonation process of magnesium ions was also simulated as a continuous production process using CSTR as in Example 1, and the mechanism of magnesium ion extraction and carbonation of magnesium is as follows.

<Mg ion extraction mechanism>

Mg(OH) ₂ + 2HCl→MgCl ₂ (aq) + 2H ₂ O

<Mechanism of carbonation of magnesium>

Mg ²⁺ + CO3 ^2- → MgCO ₃

Mg ²⁺ + HCO ₃ ^- → MgCO ₃ + H ⁺

MgCO ₃ → Mg ²⁺ + CO ₃ ^2-

MgCO ₃ + H ⁺ → Mg ²⁺ + HCO ₃ ^-

Mg ²⁺ + CO ₃ ^2- + 3H ₂ O→MgCO ₃ 3H ₂ O (nesquehonite)

Experimental Example 1. Electrolysis simulation results

When starting the electrolysis simulation, it is assumed that there is no initial source in the cell, which means that the cell starts with zero ion concentration and the production stabilizes when the concentration reaches its maximum value. Accordingly, the concentrations of Na ⁺ , Cl ^- , OH ^- were calculated for 3000 seconds, and the simulation results of the electrolysis process according to Example 2 are shown in FIGS. 4 to 6.

Figure 4 shows the sodium concentration as a function of time, reaching a maximum value of 0.1081 kmol/m ³ at approximately 1475 seconds. FIG. 5 shows the OH ⁻ concentration over time, i ₁ is 0.5 kA/m ² , i ₂ is 1.5 kA/m ² , and i ₃ is 3.0 kA/m ² . In addition, FIG. 6 shows the Cl ⁻ concentration over time, i1 is 0.5 kA/m ² , i2 is 1.5 kA/m ² , and i3 is 3.0 kA/m ² When the current density is.

As shown in FIG. 5, when applying current densities of 0.5, 1 and 3 kA/m ² , the maximum concentration of OH ⁻ was achieved at 3 kA/m ² and a constant concentration of 0.1518 kmol/m ³ at 1475 seconds. showed up

Experimental Example 2. Aspen Simulation Data

Simulations were performed using Aspen, and specifically, Aspen data were measured with a thermodynamic model using carbon dioxide solubility in alkanolamine absorbents. In Tables 2 and 3, the In value is an arbitrarily set value, and the Out value is a value calculated through Aspen simulation, and the yield was obtained through the ratio of the In value and the Out value.

Table 2 shows the conversion yields of carbonate and bicarbonate, and Table 3 shows the results of the carbonation process. Metal ions were isolated in the form of metal hydroxides, and calcium hydroxide and magnesium hydroxide were precipitated in yields of 98.9% and 89.1%, respectively. The precipitated calcium hydroxide spontaneously reacted with ionic carbon dioxide to form calcium carbonate. The yield of calcium carbonate was as high as 99.6%.

On the other hand, in the case of magnesium ion, the reactivity was reduced, so it was extracted in an ionic state, and magnesium hydroxide was obtained with a yield of 89.1% according to the metal ion separation step, and then reacted with hydrochloric acid to obtain a salt state, followed by carbonation As progressed, the yield of magnesium carbonate was 61.4%.

reaction formula In Out yield CO ₂ →HCO ₃ ^- 0.0893 kmol 0.00481 kmol 5.39% CO ₂ → CO ₃ ^2- 0.0893 kmol 0.07670 kmol 85.9% CO ₂ →HCO ₃ ^- , CO ₃ ^2- 0.0893 kmol 0.0815 kmol 91.3%

reaction formula In Out yield Ca ²⁺ → Ca(OH) ₂ 0.0276 kmol Ca ²⁺ 0.0273 kmol Ca(OH) ₂ 98.9% Ca(OH) ₂ → CaCO ₃ 0.0273 kmol Ca(OH) ₂ 0.0272 kmol CaCO ₃ 99.6% Mg ²⁺ → Mg(OH) ₂ 0.0448 kmol Mg ²⁺ 0.0399 kmol Mg(OH) ₂ 89.1% Mg(OH) ₂ → Mg ²⁺ 0.0399 kmol Mg(OH) ₂ 0.0398 kmol Mg ²⁺ 99.9% Mg ²⁺ → MgCO ₃ 0.0398 kmol Mg(OH) ₂ 0.0245 kmol MgCO ₃ 61.4%

Claims (11)

Separating metal ions by precipitating calcium hydroxide and magnesium hydroxide from concentrated seawater desalination containing calcium ions and magnesium ions;
Generating sodium hydroxide by chloro-alkaline electrolysis of the concentrated water from which metal ions are separated; and
A carbonation step of reacting the calcium hydroxide and magnesium hydroxide generated by the metal ion separation with carbon dioxide to form calcium carbonate and magnesium carbonate; includes,
Sodium hydroxide generated by the electrolysis is recycled and added to the metal ion separation step, and calcium hydroxide and magnesium hydroxide are separated by a pH swing method using the added sodium hydroxide,
In the carbonation step, carbon dioxide reacts with sodium hydroxide generated by the electrolysis to exist as carbonate and / or bicarbonate, and reacts with calcium hydroxide and magnesium hydroxide to form calcium carbonate and magnesium carbonate. Method for producing a metal carbonate. delete delete According to claim 1,
The metal ion separation step is the step of precipitating and separating magnesium hydroxide by adjusting the pH of concentrated seawater desalination to 7 to 11 and adjusting the pH of concentrated water from which magnesium hydroxide is separated to 11 to 13 to precipitate and separate calcium hydroxide Method for producing a metal carbonate comprising the step. delete According to claim 1,
The electrolysis step is a method for producing a metal carbonate, characterized in that using an electrolysis device comprising an anode chamber and a cathode chamber separated by a sodium ion exchange membrane, and adding concentrated water to the anode chamber. According to claim 1,
Electrolysis time in the electrolysis step is a method for producing a metal carbonate of 500 seconds to 3000 seconds. According to claim 1,
In the electrolysis step, the current density of electrolysis is 1.5 to 4 kA / m ² Method for producing a metal carbonate. delete According to claim 1,
The carbonation step of magnesium in the carbonation step further comprises the step of reacting magnesium hydroxide with an acid before reacting with carbon dioxide. According to claim 1,
The method of producing a metal carbonate in which the magnesium carbonate produced in the carbonation step of magnesium during the carbonation step has a nesquehonite property.