KR101189075B1 - Carbon dioxide separating method comprising regenerating process of absorption and system using the same - Google Patents

Abstract

The present invention relates to a method for separating carbon dioxide, including a step of regenerating a carbon dioxide absorbent aqueous solution, and a carbon dioxide separation apparatus using the same, in separating carbon dioxide contained in a combustion flue gas, by reacting the exhaust gas with a carbon dioxide absorbent aqueous solution and an acid solution. Generating a first salt and separating carbon dioxide; reacting the strong salt solution with the first salt to produce a second salt; separating and reusing the carbon dioxide absorbent solution; and reacting the strong acid solution with the second salt to form a third salt. It is characterized in that the carbon dioxide is separated, including the step of generating a salt, precipitation of the acid as a crystal, and separation and reuse. The carbon dioxide is reacted with an acid solution when the carbon dioxide is separated, thereby lowering the solubility of the carbon dioxide. Can be removed to save energy. It is possible to maximize the efficiency of the process by reusing the carbon dioxide absorbent aqueous solution and acid solution, and energy-saving continuous commercial absorption separation process is possible.

Description

Carbon dioxide separating method comprising regenerating process of absorption and system using the same}

The present invention relates to a method for separating carbon dioxide contained in an exhaust gas and a separator using the same, and more particularly, to a method for separating carbon dioxide including a process of reusing a carbon dioxide absorbent and a separator using the same.

Global warming due to the recent increase in carbon dioxide in the atmosphere is one of the important environmental problems that humanity must solve. This carbon dioxide is emitted in large quantities during the burning of fossil fuels. Therefore, a technology for separating and removing only carbon dioxide from exhaust gas generated after burning fossil fuel has been developed, and the already developed carbon dioxide separation techniques include absorption, adsorption, deep cooling, and membrane separation.

As a technique commercialized in the absorption method, there is a wet amine method. The wet amine method uses an amine absorbent as a method of recovering carbon dioxide contained in combustion flue gas. The first commercial facility, called Gas Spec FT-1 (Dow Chemical, 1982), uses a mixture of alkanolamine and corrosion inhibitor as an absorbent to reduce degradation of oxygen and increase carbon dioxide absorption. Have. Since then, many wet absorption methods using amines as absorbents have been commercialized.

The wet absorption process using such amines shows a high carbon dioxide recovery efficiency, but there is a problem in that a high operating temperature is required in the reactor, and thus a lot of energy is required.

In addition, since the absorbent liquid used in the wet amine method is expensive, a process of removing and regenerating carbon dioxide is necessary to increase the efficiency of the process. However, in order to remove carbon dioxide back to the absorbent and regenerate the absorbent, unlike physiological absorbers that are regenerated by reducing the pressure, amine-type absorbers, which are chemical absorbents, must break chemical bonds. There is a problem that is required.

On the other hand, in the already developed carbon dioxide separation technology, the adsorption method is a method of separating carbon dioxide contained in the exhaust gas by using a solid adsorbent such as zeolite and activated carbon that selectively adsorbs carbon dioxide from the exhaust gas. When the adsorption is made, the energy consumption required for pressurization is large, and when the adsorption is performed at normal pressure, the productivity is low due to low productivity, and the consumption of power costs due to low pressure desorption has a big problem. There is a problem that is difficult to apply to the same large combustion flue gas.

Therefore, the problem to be solved by the present invention is a carbon dioxide separation method and an acid solution including an absorbent regeneration step of removing the carbon dioxide at a lower temperature by reacting the aqueous solution of the absorbent absorbing carbon dioxide from the exhaust gas in the absorption tower of the absorption process with an acid solution It is to provide a method for separating the aqueous solution with the absorbent.

The second problem to be solved by the present invention is to provide a carbon dioxide separation apparatus using the separation method.

The present invention to achieve the first object,

In the carbon dioxide separation method included in the exhaust gas using a carbon dioxide absorbent aqueous solution, (A) the exhaust gas is reacted with a carbon dioxide absorbent aqueous solution to absorb the carbon dioxide contained in the exhaust gas, and then the carbon dioxide absorbent solution absorbing the carbon dioxide; Reacting the acid solution to produce a first salt and separating carbon dioxide; (B) reacting the strong salt solution with the first salt to produce a second salt and separating the absorbent aqueous solution; and (C) the agent It provides a carbon dioxide separation method comprising the step of reacting the two salts with a strong acid solution to form a third salt, precipitate the acid as a crystal, separate and reuse.

According to an embodiment of the present invention, the carbon dioxide absorbent in step (A) is monoethanolamine (MEA), methyl diethanolamine (MDEA), diethanolamine (DEA), triethanolamine (TEA) and 2- It may be any one selected from amino-2-methyl-1-propanol (AMP). Preferably, it may be monoethanolamine (MEA) having excellent solubility in water at room temperature and excellent reaction rate.

According to another embodiment of the present invention, in the step (A), the acid solution is a solution using an acid capable of crystallization, preferably a benzoic acid solution or an oxalic acid solution.

According to another embodiment of the present invention, in the step (A), the absorbent is 10 to 40% by weight, the acid solution is 5 to 10% by weight, and the remainder is based on the total weight of the aqueous solution of the carbon dioxide-containing absorbent and the acid solution reactant. It consists of water.

According to another embodiment of the present invention, the solubility of carbon dioxide in the mixed solution of the acid solution and the carbon dioxide-containing absorbent aqueous solution when reacting the carbon dioxide-containing absorbent aqueous solution and the acid solution in the step (A) is 0.4 ~ 0.7 CO ₂ mol / MEA mol.

According to another embodiment according to the present invention, in step (B), the strong base solution may be sodium hydroxide or calcium hydroxide, and preferably sodium hydroxide.

According to another embodiment of the present invention, the strong acid solution in step (C) may be hydrochloric acid, sulfuric acid or nitric acid.

According to another embodiment according to the present invention, the reaction temperature in the (A), (B) and (C) step may be 40 ~ 60 ℃.

According to another embodiment of the present invention, the carbon dioxide separation method of the present invention may further include the step of reusing the absorbent aqueous solution by transferring the aqueous solution of the absorbent separated in the step (B) to the step (A).

According to another embodiment according to the present invention, the carbon dioxide separation method of the present invention further comprises the step of transporting the separated acid precipitated as a crystal in the step (C) to the step (A) to reuse as an acid solution. Can be.

According to another aspect of the present invention,

A carbon dioxide separation apparatus included in an exhaust gas by using an aqueous solution of carbon dioxide absorbent, wherein the aqueous carbon dioxide absorbent solution reacts to absorb carbon dioxide in the exhaust gas, and an absorbent aqueous solution containing carbon dioxide reacts with an acid solution. 1, a stripper for generating a salt and separating carbon dioxide, a first separator reacting with a strong base solution to produce a second salt, and a first separator for separating an aqueous absorbent solution and the second salt with a strong acid to react the third salt. It provides a carbon dioxide separator comprising a second separator for producing and precipitating and separating the acid into crystals.

According to the present invention, by reducing the solubility of carbon dioxide by reacting with the acid solution during the separation of carbon dioxide from the exhaust gas (exhaust gas) it is possible to remove the carbon dioxide at a lower temperature than the conventional process, energy saving, carbon dioxide absorbent and acid solution, etc. Can be reused to maximize process efficiency and enable energy-saving continuous commercial absorption separation processes.

1 is a conceptual diagram showing a method for separating carbon dioxide including a process of regenerating an aqueous solution of carbon dioxide absorbent according to the present invention.
2 is a graph showing the carbon dioxide solubility in the MEA aqueous solution compared with the case where no benzoic acid solution is added by varying the weight of the monoethanolamine (MEA) and the benzoic acid solution at a reaction temperature of 40 ° C.
(X axis is CO ₂ solubility, Y axis is CO ₂ partial pressure.)
(● is the first experimental value of solubility of carbon dioxide in 10% by weight of MEA, 5% by weight of benzoic acid solution; ○ is the second experimental value of solubility of carbon dioxide in 14% by weight of MEA, 1% by weight of benzoic acid solution; ▼ is 13% by weight of MEA, benzoic acid solution) 3rd experimental value of solubility of carbon dioxide at 2% by weight; solid line is 10% by weight of MEA, carbon dioxide solubility when not added to benzoic acid solution)

Hereinafter, the present invention will be described in detail.

In the case of the conventional amine absorption process, in order to separate carbon dioxide by removing the carbon dioxide bound to the absorbent in the stripping process and to reuse the absorbent, a large amount of energy was required because it uses the principle of removing carbon dioxide by raising the temperature of the carbon dioxide absorbed solution. .

In addition, because the absorbent aqueous solution is expensive, it is necessary to remove and regenerate carbon dioxide in order to increase the efficiency of the process, but in order to remove carbon dioxide and regenerate the absorbent again, the amine-type absorbent, which is a chemical absorbent, must break chemical bonds. Furnace heating required a lot of energy.

According to one embodiment of the present invention, a method of separating carbon dioxide from an exhaust gas after combustion and regenerating an aqueous solution of a carbon dioxide absorbent is as follows.

(A) reacting the exhaust gas with an aqueous solution of carbon dioxide absorbent to absorb carbon dioxide contained in the exhaust gas, and then reacting the carbon dioxide absorbent solution absorbing the carbon dioxide with an acid solution to generate a first salt and separating carbon dioxide. (B) reacting the first salt with a strong base solution to form a second salt and separating the absorbent aqueous solution; and (C) reacting the second salt with a strong acid solution to produce a third salt and acid. It is characterized in that it comprises the step of precipitating and separating into crystals.

A method of separating carbon dioxide from an exhaust gas after combustion and regenerating an aqueous solution of a carbon dioxide absorbent according to an exemplary embodiment of the present invention will be described in detail with reference to FIG. 1.

First, after combustion, exhaust gas is reacted with an aqueous solution of carbon dioxide absorbent in an absorber to form an absorbent containing carbon dioxide, the exhaust gas from which carbon dioxide is removed is discharged into the atmosphere, and the aqueous absorbent solution containing carbon dioxide is acidified in a stripper. The solution may be reacted with the solution to produce a first salt and the carbon dioxide may be separated and stored separately.

Next, the first salt may be reacted with a strong base solution in a first separator to produce a second salt, and an aqueous solution of carbon dioxide absorbent may be separated and reused in the absorber.

The second salt may then be reacted with a strong acid solution in a second separator to form a third salt and stored separately, and the acid precipitated as crystals may be separated and reused in the stripper.

According to a preferred embodiment of the present invention, in order to separate the carbon dioxide from the aqueous solution of the absorbent containing carbon dioxide by reacting the acid solution in the stripper to reduce the carbon dioxide solubility in the aqueous solution of the absorbent, carbon dioxide can be separated and removed with less energy. It is done.

The aqueous solution of the amine-based absorbent containing carbon dioxide reacts with the acid solution to change the pH and lower the carbon dioxide solubility to remove carbon dioxide at a temperature lower than the conventional process temperature.After that, the first salt is an aqueous solution of a strong base using an aqueous strong base solution. Recovered and reused, the second salt is produced by reacting with a strong acid aqueous solution to recover and reuse the acid precipitated as a crystal and discard or reuse the third salt produced here is a problem of the conventional amine-based absorption process Can be solved.

According to another preferred embodiment of the present invention, the absorbent in step (A) is selected from monoethanolamine, methyl diethanolamine, diethanolamine, triethanolamine and 2-amino-2-methyl-1-propanol It may be one, and preferably monoethanolamine (MEA) having excellent solubility in water at room temperature and excellent reaction rate.

According to another preferred embodiment of the present invention, in the step (A) by the following [Scheme 1] is characterized in that the carbon dioxide absorbent aqueous solution is absorbed in the exhaust gas (exhaust gas).

[Reaction Scheme 1]

R-NH ₂ + H ₂ O + CO ₂ → R-NH ₃ HCO ₃

Where

R-NH ₂ is monoethanolamine and the reaction temperature is 40 to 60 ° C.

According to another preferred embodiment of the present invention, the acid solution reacting with the absorbent containing carbon dioxide in the step (A) is not limited in the present invention as long as it is a solution using a crystallizable acid, more preferably a benzoic acid solution or Oxalic acid solution.

According to another preferred embodiment of the present invention, in the step (A), the absorbent is 10 to 40% by weight, the acid solution is 5 to 10% by weight based on the total weight of the aqueous solution of the carbon dioxide-containing absorbent and the acid solution reactant. The carbon dioxide-containing absorbent aqueous solution may be water, and the solubility of carbon dioxide may be 0.4 to 0.7 CO ₂ mol / MEA mol in a mixed solution of the acid solution and the carbon dioxide-containing absorbent aqueous solution when the stripper reacts with the acid solution.

The solubility of carbon dioxide in 10% by weight of monoethanolamine (MEA) not added with benzoic acid solution was measured by varying the reaction temperature, and the solid line is shown in FIG. 2. It can be seen that the solubility of carbon dioxide decreases when reacting at a high temperature relative to the same partial pressure of carbon dioxide.

In addition, carbon dioxide solubility was measured at a reaction temperature of 40 ° C. in an aqueous solution in which 5% by weight of benzoic acid was added to 10% by weight of MEA. When benzoic acid was added in comparison with the partial pressure of the same carbon dioxide, it can be seen that the same carbon dioxide solubility reduction effect as the reaction at a high temperature of 80 to 100 ° C. or higher without the addition of benzoic acid even at a lower temperature of 40 ° C.

Carbon dioxide separation method according to a preferred embodiment of the present invention is characterized in that it is possible to separate the carbon dioxide from the absorbent (MEA) without heating to a high temperature to reduce the energy required for the carbon dioxide separation and MEA aqueous solution recovery and regeneration process. .

According to another preferred embodiment of the present invention, in step (B), the acid solution and the carbon dioxide is removed, the sodium hydroxide or calcium hydroxide is reacted with an aqueous solution of the absorbent, preferably sodium hydroxide to react to form a second salt to absorb the absorbent The aqueous solution can be separated.

According to another preferred embodiment of the present invention, the strong acid solution in step (C) is not limited in the present invention as long as it can be well dissociated in an aqueous solution, preferably hydrochloric acid, sulfuric acid, or nitric acid solution.

Specific reactions in the steps (A), (B) and (C) are the same as in the following [Scheme 2].

^{_{2H 2 O ↔ H 3 O +}} + OH - ( Equation 1)

_{CO 2 + 2H 2 O ↔ HCO} 3 - + H 3 O + ( Equation 2)

^{_{HCO 3 - + H2O ↔ CO 3}} -2 + H 3 O + ( Equation 3)

R-NH ₃ ⁺ + H ₂ O ↔ R-NH ₂ + H ₃ O ⁺ (Equation 4)

_{^{R-NHCOO - + H 2 O}} ↔ R-NH 2 + HCO 3 - ( formula 5)

R-NH ₃ ⁺ + acid (benzoic acid) ↔ salts (Mea-benzoate) (s) + H ₂ O (Equation 6)

salts (first salt, MEA-benzoate) (s) + Base (Ca (OH) ₂ ) (aq) ↔ salts (second salt, calcium benzoate) (s) + H ₂ O (Equation 7)

salts (second salt, calcium benzoate) (s) + Acid (HCl) (aq) ↔ salts (third salt, CaCl ₂ ) (aq) + acid (benzoic acid) (s) (Expression 8)

According to a preferred embodiment of the present invention, the reaction temperature in the steps (A), (B) and (C) may be 40 ~ 60 ℃, the absorbent aqueous solution separated in the step (B) the (A) The method may further include reusing the absorbent aqueous solution by transferring to the step, and may further include reusing the acid separated by the crystal in the step (C) into the step (A) to reuse the acid solution.

The method for separating carbon dioxide according to the present invention is characterized by separating the carbon dioxide even at a lower reaction temperature by reducing the solubility of carbon dioxide in the aqueous solution by adding the benzoic acid solution to the aqueous solution of the absorbent containing carbon dioxide.

Hereinafter, when solubility of the monoethanolamine (MEA) as an aqueous absorbent and the acid solution as benzoic acid was added to the MEA aqueous solution, the solubility of carbon dioxide was measured by the following experimental procedure.

Basic gas-liquid phase equilibrium experiments include a MEA reservoir to store a benzoic acid solution and an MEA solution, and a CO ₂ to store carbon dioxide. It was measured using an experimental device consisting of an equilibrium reactor in which a reservoir, carbon dioxide and an aqueous solution form a gas-liquid phase equilibrium.

The solubility of carbon dioxide was measured by measuring the volume and pressure before and after equilibration at a constant temperature.

First, the equilibrium reactor and CO ₂ Make the reservoir close to vacuum and CO ₂ Fill the reservoir with pure carbon dioxide gas and equilibrate the reactor with a certain amount of benzoic acid solution and MEA solution of known density. At this time, the temperature is kept constant, the volume of CO ₂ by measuring the pressure in the reservoir CO ₂ using a program called Allprops The density of carbon dioxide gas in the reservoir was calculated. This allowed us to calculate the amount of carbon dioxide for the first time.

Next, the equilibrium reactor and CO ₂ The valves between the reservoirs were opened to wait for phase equilibrium, and then the pressure of the gas phase was measured when equilibrium was reached. Allprops can also be used to calculate the density and the amount of carbon dioxide not dissolved in the aqueous solution after equilibrium. CO ₂ The volume of carbon dioxide is equal to the volume of the reservoir and the equilibrium reactor and the volume of the liquid minus.

Then, the pressure of the gaseous phase corrected in consideration of water vapor evaporation at the pressure measured after equilibrium is the partial pressure of carbon dioxide, and CO ₂ is determined through the difference between the amount of first carbon dioxide and the amount of later carbon dioxide. The loading was measured.

In addition, as a comparative experiment with carbon dioxide solubility in the aqueous solution of the absorbent according to the present invention, Experimental Example 1 and except that the experiment was carried out after filling a certain amount of the MEA aqueous solution without adding the benzoic acid solution to the equilibrium reactor in Experimental Example 1 The same procedure was followed.

2 shows the solubility value of carbon dioxide measured in the present invention. In FIG. 1, the X axis represents CO ₂ solubility, and the Y axis represents partial pressure. The solubility unit of carbon dioxide is expressed as CO ₂ mol / MEA mol.

First, carbon dioxide solubility was measured in an aqueous solution of 10% by weight of monoethanolamine (MEA) by varying the reaction temperature (40, 80, 100, 120 ° C), and the result is shown by the solid line of FIG. 2.

Next, the solubility of carbon dioxide was measured by varying the weight of monoethanolamine (MEA) and benzoic acid at the reaction temperature of 40 ℃. 1 is the first experimental value of solubility of carbon dioxide in an aqueous solution of 14% by weight of monoethanolamine and 1% by weight of benzoic acid, and ● is a second experimental value of solubility of carbon dioxide in an aqueous solution of 10% by weight of monoethanolamine and 5% by weight of benzoic acid, Are the third experimental values of solubility of carbon dioxide in an aqueous solution of 13% by weight of monoethanolamine and 2% by weight of benzoic acid.

The solubility of carbon dioxide in 10 wt% monoethanolamine and 5 wt% aqueous solution of benzoic acid according to the present invention is the same as that of carbon dioxide at 80-100 ° C. when no benzoic acid is added. According to the present invention it can be seen that even at a lower temperature solubility of carbon dioxide is reduced to separate the carbon dioxide, the energy saving effect in reusing the absorbent aqueous solution.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the carbon dioxide separation apparatus according to the present invention.

1 is a conceptual diagram illustrating a carbon dioxide separation apparatus including a process of regenerating a carbon dioxide absorbent according to the present invention.

The carbon dioxide separation apparatus including the process of regenerating the carbon dioxide absorbent according to the present invention comprises an absorption reactor, a stripper, a first separator, and a second separator.

According to a preferred embodiment of the present invention, the absorption reactor is a carbon dioxide absorbent aqueous solution reacts to absorb the carbon dioxide of the exhaust gas (exhaust gas), the stripper reacts the aqueous solution of the absorbent containing carbon dioxide and the acid solution to produce a first salt Separating and discharging carbon dioxide, the first separator reacting the first salt with a strong base to produce a second salt, and separating the absorbent aqueous solution, and the second separator reacting the second salt with a strong acid to form a third salt. Is formed and the acid is precipitated into crystals and separated.

The aqueous solution of the absorbent may be monoethanolamine, the reaction temperature in the absorption reactor may be 40 ~ 60 ℃ by a heater additionally provided in the absorption reactor, the incoming flue gas and the absorbent reacts in the absorption reactor to exhaust gas It is characterized by absorbing carbon dioxide.

In the stripper, the absorbent containing carbon dioxide made in the absorption reactor may react with the acid solution supplied from the acid solution reservoir additionally provided to the stripper to generate a first salt and remove the carbon dioxide from the absorbent, which is then added to the stripper. The reaction temperature in the stripper by the heater provided as characterized in that 40 ~ 60 ℃.

In the first separator, the first salt reacts with the strong base solution supplied from the strong base solution reservoir additionally provided in the first separator to generate a second salt, and the separated absorbent may be transported and used again in the absorption reactor. It features.

In the second separator, the second salt generated in the first separator reacts with the strong acid solution supplied from the strong acid solution reservoir additionally provided in the second separator to form and separate the acid by crystallization while generating a third salt. The acid may be transferred and reused as an acid solution in the stripper.

Claims (12)

In the method for separating carbon dioxide contained in the exhaust gas using an aqueous solution of carbon dioxide absorbent,
(A) reacting the exhaust gas with an aqueous solution of carbon dioxide absorbent to absorb carbon dioxide contained in the exhaust gas, and then reacting the carbon dioxide absorbent solution and an acid solution absorbing the carbon dioxide to produce a first salt and separating carbon dioxide. ;
(B) reacting the first salt with a strong base solution to produce a second salt and separating the absorbent aqueous solution; And
(C) reacting the second salt with a strong acid solution to produce a third salt, and depositing and separating the acid into crystals. The method of claim 1,
The carbon dioxide absorbent in step (A) is a carbon dioxide separation method, characterized in that the monoethanolamine, methyl diethanolamine, diethanolamine, triethanolamine or 2-amino-2-methyl-1-propanol. The method of claim 1,
In the step (A), the acid solution is a carbon dioxide separation method, characterized in that the benzoic acid solution or oxalic acid solution that can be precipitated as a crystal. delete delete The method of claim 1,
The strong base solution in step (B) is carbon dioxide separation method, characterized in that the sodium hydroxide or calcium hydroxide. The method of claim 1,
The strong acid solution in step (C) is carbon dioxide separation method, characterized in that hydrochloric acid, sulfuric acid or nitric acid. The method of claim 1,
Reaction temperature in the step (A), (B) and (C) is a carbon dioxide separation method, characterized in that 40 ~ 60 ℃. The method of claim 1,
Carbon dioxide separation method further comprising the step of transferring the aqueous solution of the absorbent separated in the step (B) to the step (A) to reuse the aqueous solution of the absorbent. The method of claim 1,
The carbon dioxide separation method further comprising the step of transferring the acid precipitated as a crystal in the step (C) to the step (A) and reused as an acid solution. In the carbon dioxide separation apparatus included in the exhaust gas using a carbon dioxide absorbent aqueous solution,
An absorption reactor for reacting the aqueous solution of carbon dioxide absorber to absorb carbon dioxide contained in exhaust gas;
A stripper for reacting the absorbent aqueous solution having absorbed carbon dioxide with an acid solution to form a first salt and separating carbon dioxide;
A first separator for reacting the first salt with a strong base aqueous solution to produce a second salt, and separating the absorbent aqueous solution; And
And a second separator for reacting the second salt with a strong acid solution to produce a third salt and depositing and separating the acid into crystals. The method of claim 11,
And absorbing the aqueous solution of the absorbent separated in the first separator to the absorption reactor for reuse, and transferring the acid precipitated and separated from the crystal in the second separator to the stripper for reuse as an acid solution.

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