KR101316543B1 - Method For Absorbing CO₂Continuously To Minimize The Rgenerating Energy - Google Patents

Abstract

The present invention relates to a carbon dioxide absorption method, to minimize the production of salt in the carbon dioxide absorption process, and to a carbon dioxide absorption process that can minimize the renewable energy by effectively removing the generated salt. The carbon dioxide absorption process of the present invention includes a gas contact step of contacting a gas containing carbon dioxide to a carbon dioxide absorbent having sterically hindered cyclic amine added to an alkali carbonate; A carbon dioxide absorption step of absorbing carbon dioxide from the gas; Separating a salt from the absorbent in which the carbon dioxide is absorbed; Regenerating the absorbent from which the salt has been separated.

Description

Method For Absorbing CO₂Continuously To Minimize The Rgenerating Energy}

The present invention relates to a process capable of minimizing the renewable energy of the carbon dioxide absorbent, and to a carbon dioxide absorption method capable of minimizing the renewable energy by minimizing the generation of salt in the carbon dioxide absorption process, and effectively separating the generated salt.

Carbon dioxide is one of the greenhouse gases that cause global warming, and it is an acid gas with high generation and fixed sources. Various methods of separating and removing carbon dioxide emitted from the energy industry process have been studied. In particular, many studies on liquid absorption method having the best economic efficiency have been conducted.

Among the liquid absorption methods, the most commonly used method is alkanolamine method using monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and Benfield using potassium carbonate. Law.

Alkanolamine method is a method to make a 20-30wt% solution by mixing various alkanolamine absorbing carbon dioxide with water, which has been commercialized since the 1970s because of its fast carbon dioxide absorption ability.

However, this method consumes excessive energy of 4.0 ~ 4.2 GJ / ton CO ₂ (in case of MEA) during the regeneration process. In addition, there is a problem that the oxidation reaction occurs by the pollutants (O ₂ , SO ₂ , NO _x ) present in the combustion exhaust gas, corroding the facility made of carbon steel.

In order to lower the high regeneration heat, absorbers have been developed to reduce carbamate binding ability by attaching methyl or ethyl groups around nitrogen atoms that remove carbon dioxide by directly carbamate-bonding carbon dioxide in alkanolamines to cause steric hindrance. AMP (2-amino-2-methyl-1-propanol).

This absorbent is not as fast as MEA in terms of CO2 absorption, but has the advantage of significantly lower renewable energy. For the KS-1 absorbent of Mitsubishi Heavy Industries known to use a similar sterically hindered amine as a main material it can be seen that renewable energy is very low as _{2.8 ~ 3.2 GJ / ton CO 2} . However, most of these amines are alkanol amines with hindered groups around the primary amine.

As a high sterically hindered amine technology, Japanese Patent Application Laid-Open No. 08-103630 discloses a system using a mixture of an aqueous solution and a steric resistance piperazine derivative as an absorbent having a large amount of CO ₂ absorption per unit mole of adsorbent and a unit volume and a high absorption rate and low renewable energy. It is starting. At this time, the mixing ratio of the steric resistance piperazine derivative was limited to 15 to 65% by weight in an aqueous solution.

However, when used at 20wt% or more, solubility problem occurs. To dissolve piperazine derivatives, it is necessary to mix substances such as alcohol, and because they are simply mixed with water, alkaline carbonates with bicarbonate promotion are not mixed. In the case of the CO ₂ absorption reaction, the bicarbonate formation reaction is not superior to the carbamate formation reaction.

As a method of capturing carbon dioxide, which is an acid gas, using a liquid alkaline substance such as sodium hydroxide, sodium carbonate, potassium carbonate, potassium hydroxide, etc., a representative process is a Benfield process or a catacarb process. The Benfield process is a method in which some alkanolamine is added to improve the disadvantage of slow carbon dioxide reaction rate. The catacarb process uses potassium carbonate as a main substance and uses organic or inorganic substances that are not known as reaction rate improving agents.

However, in the catacarb process, since salts of potassium bicarbonate are generated in the absorption process, in order to solve this problem, the absorption tower and the stripping column are operated at 120 ° C. or higher, thus requiring high energy and operating at inlet gas pressure of 10 atm or higher. It has a disadvantage.

An object of the present invention is to provide a composition of an absorbent capable of minimizing salt generation in a carbon dioxide absorption process using an alkali carbonate material. It is also an object of the present invention to provide a process that can effectively remove and remove salts generated in the carbon dioxide absorption process to minimize the renewable energy.

In order to solve the above problems, according to a preferred embodiment of the present invention, a gas contact step of contacting a gas containing carbon dioxide to a carbon dioxide absorbent added sterically hindered cyclic amine to the alkali carbonate; A carbon dioxide absorption step of absorbing carbon dioxide from the gas; Separating a salt from the absorbent in which the carbon dioxide is absorbed; It provides a method for removing carbon dioxide comprising the step of regenerating the absorbent separated from the salt.

According to another suitable embodiment of the present invention, the salt separation process is characterized by using a decanter separator.

According to another suitable embodiment of the present invention, the alkali carbonate is potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), potassium bicarbonate (KHCO ₃ ) And sodium bicarbonate (NaHCO ₃ ) It is characterized in that at least one selected from the group consisting of.

According to another suitable embodiment of the invention, the hindered cyclic amine is 1-amino-4methyl piperazine, 1- (2-aminoethyl) -4methyl piperazine, 1- (2-hydroxyethyl) -4methyl piperazine, 1- (2-aminoethyl) -piperazine, 1- (2-hydroxyethyl) -piperazine, 2-aminoethyl-piperazine, 1-ethyl-piperazine, 2,5- Dimethyl-piperazine, cis 2,6-dimethyl-piperazine, 1,4-dimethyl-piperazine, trans 2,5-dimethyl-piperazine, 1-methyl piperazine, 2-methyl piperazine, 1-ethyl piper It is characterized in that it is at least one member selected from the group consisting of azine, 2-peperidin ethanol, 3-peperidin ethanol, 4-peperidin ethanol, 2-aminoethyl-1-piperidine and homopiperidine.

According to another suitable embodiment of the present invention, a gas contact step of contacting a gas containing carbon dioxide to a carbon dioxide absorbent to which 20wt% or less potassium carbonate is added 10wt% or less 2-methylpiperazine; A carbon dioxide absorption step of absorbing carbon dioxide from the gas; Separating a salt from the absorbent in which the carbon dioxide is absorbed; It provides a method for removing carbon dioxide comprising the step of regenerating the absorbent separated from the salt.

According to the carbon dioxide absorption process according to the present invention, it is possible to provide a composition of the carbon dioxide absorbent that can minimize the generation of salt, and to effectively treat the salt generated in the carbon dioxide absorption process.

1 schematically shows a carbon dioxide absorption process according to the present invention.
Figure 2 schematically shows a process of separating the salt produced using the decanter separator in the carbon dioxide separation process according to the present invention.

The present invention provides a method of improving the absorption rate, significantly lowering the salt production rate, and effectively separating the salts, by using an absorbent in the form of a hindered cyclic amine added to the alkali carbonate material.

Carbon dioxide absorbent of the present invention is 20wt% or less alkali carbonate; And 10 wt% or less of sterically hindered cyclic amines, wherein salts do not occur most in the composition. However, when the above composition is used to enhance the ability to absorb carbon dioxide, salt generation is increased. The salt is generated by separating the solution from the salt.

The absorbent of the present invention is characterized by using not more than 20wt% of alkali carbonate as the main substance. The alkali carbonate was limited to sodium and potassium, which are Group 11 metal elements, and carbonate was used as a mixture of bicarbonate and carbonate.

As the hindered cyclic amine, a material in which an alkyl group is variously bonded is used to give a hindered effect around a nitrogen atom to which carbon dioxide directly reacts. In general, when the nitrogen atom of the amine reacts with carbon dioxide, carbon dioxide is absorbed in the form of carbamate. The hindered cyclic amine additive added to the aqueous solution of potassium carbonate is a secondary amine, which is a type of steric hindrance mixed, so it is mainly used rather than carbamate. Absorbed in carbonate form.

Also, when used in combination with alkali carbonate and additives, some additives absorb carbon dioxide in the form of carbamate, as shown in Equation 1 below.

Thereafter, as shown in Equation 2, the alkali cation of the alkali carbonate acts as a coulomb force on some of the additives absorbed in the form of carbamate, thereby promoting the presence of bicarbonate rather than carbamate. This suppresses salt formation compared to the prior art and as a result can significantly reduce the renewable energy.

In other words, when only the hindered cyclic amine is present, Equation 2 does not proceed, so the reduction of renewable energy is small. However, when present with Alkali carbonate, Equation 2 proceeds, so the renewable energy is greatly reduced.

[Formula 1]

2R-NH _{2 (amine) + CO 2 ⇔ [R-} NH-CO 2 -] [R-NH 3 +]

[Formula 2]

^{_{[R-NH-CO 2 -}} ] [R-NH 3 +] + H 2 O + M + ⇔ [R-NH 3 +] [HCO 3 -] + R-NH 2 + M +

In the present invention, a secondary amine in the form of two carbon bonds around a nitrogen atom is used as the hindered cyclic amine. On the other hand generally the higher the reaction mechanism for the absorption of carbon dioxide is the water supply of the amine is less the number of the hydrogen combines with the nitrogen atom a prerequisite for forming carbamates are formed in the form of bicarbonate renewable energy is being lowered CO ₂ Absorption Rate Tends to slow down. Since the hindered cyclic amine used in the present invention has a hindered group around the nitrogen atom, the bicarbonate is formed more, and once the carbamate is formed, the carbamate becomes bicarbonate when the alkali ions of the alkali carbonate are acted on. Formed and less heat is absorbed. The lower heat of absorption reaction means less energy is used in the later regeneration reaction.

The hindered cyclic amine used in the present invention has a boiling point higher than 110 ° C. to 120 ° C., which is a temperature at which the carbamate or bicarbonate is removed and regenerated at 1 atmosphere, so that the amount of evaporation loss of the amine absorbent is small. It has merit. On the other hand, the type of hindered cyclic amine used in the present invention was limited to a substance in which 500 g or more was dissolved based on solubility in 1 liter of water at 25 ° C.

Preferred sterically hindered cyclic amines used in the present invention include 1-amino-4methyl piperazine, 1- (2-aminoethyl) -4methyl piperazine, 1- (2-hydroxyethyl) -4methyl piperazine, 1- (2-aminoethyl) -piperazine, 1- (2-hydroxyethyl) -piperazine, 2-aminoethyl-piperazine, 1-ethyl-piperazine, 2,5-dimethyl-piperazine, cis 2,6-dimethyl-piperazine, 1,4-dimethyl-piperazine, trans 2,5-dimethyl-piperazine, 1-methyl piperazine, 2-methyl piperazine, 1-ethyl piperazine, 2-peperidine Preference is given to one or more substances selected from ethanol, 3-peperidinethanol, 4-peperidinethanol, 2-aminoethyl-1-piperidine and homopiperidine.

Potassium carbonate in alkali carbonate materials has limited solubility and potassium bicarbonate precipitates when used alone. In addition, potassium carbonate can remove carbon dioxide when used as an alkali carbonate, but the removal speed is considerably slow. When potassium carbonate is used as an alkali carbonate and mixed with an sterically hindered cyclic amine aqueous solution at 80 ° C. or less, it is preferable to use only a composition of 20 wt% or less. This is because if the content of potassium carbonate exceeds 20wt%, a problem of excessive salt generation may occur.

The hindered cyclic amines used as additives absorb carbon dioxide in a mixture of carbamate and bicarbonate. At this time, the hindered cyclic amine is preferably used in the composition of 10wt% or less. If the content of sterically hindered cyclic amine exceeds 10 wt%, the problem of excessive salt formation may occur as well.

The present invention provides a process for effectively removing the salt generated during the carbon dioxide absorption process while suppressing the generation of excessive salts.

Hereinafter, with reference to the accompanying drawings will be described in detail the carbon dioxide absorption process and salt removal process of the present invention.

Figure 1 schematically illustrates the carbon dioxide absorption process of the present invention.

Carbon dioxide absorption process of the present invention, the carbon dioxide absorption process using the absorbent includes a gas contact step (S110), carbon dioxide absorption step (S120), salt separation step (S130), absorbent regeneration step (S140).

The gas contacting step (S110) is to contact the gas containing carbon dioxide to the carbon dioxide absorbent to which the hindered cyclic amine is added to the alkali carbonate. In this case, it is preferable to use an aqueous solution containing 20 wt% or less of alkali carbonate and 10 wt% or less of sterically hindered cyclic amine. Meanwhile, the carbon dioxide absorbent may further include a corrosion inhibitor, a coagulant aid, an oxygen inhibitor, an antifoaming agent, or a mixture thereof.

The alkali carbonate includes at least one selected from potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), potassium bicarbonate (KHCO ₃ ), and sodium bicarbonate (NaHCO ₃ ). It is preferable to use one material.

Meanwhile, the hindered cyclic amines include 1-amino-4methyl piperazine, 1- (2-aminoethyl) -4methyl piperazine, 1- (2-hydroxyethyl) -4methyl piperazine, 1- (2 -Aminoethyl) -piperazine, 1- (2-hydroxyethyl) -piperazine, 2-aminoethyl-piperazine, 1-ethyl-piperazine, 2,5-dimethyl-piperazine, cis 2,6- Dimethyl-piperazine, 1,4-dimethyl-piperazine, trans 2,5-dimethyl-piperazine, 1-methyl piperazine, 2-methyl piperazine, 1-ethyl piperazine, 2-peperidinethanol, 3- It is preferred that it is at least one substance selected from peperidinethanol, 4-peperidinethanol, 2-aminoethyl-1-piperidine and homopiperidine.

In the carbon dioxide absorption step (S120), carbon dioxide is absorbed from the gas containing the carbon dioxide. At this time, the absorption step is preferably to proceed at a pressure range of 1 to 30 atm and 20 ℃ to 90 ℃, it is more preferable to proceed at 40 ℃ to 60 ℃.

The salt separation step (S130) is a step in which the absorbent reacted with carbon dioxide in the carbon dioxide absorption step is separated into a salt layer and a liquid layer by passing through a decanter. The gradient separator may be a gravity gradient separator, a gradient gradient separator, a centrifugal gradient separator, a gradient centrifuge, or the like.

Figure 2 schematically shows the gradient centrifuge and salt separation process used in the present invention. The inclined centrifuge 20 has a rotating outer cylinder 21, a rotating inner cylinder 22 in the form of a screw conveyor, an inlet 23 for supplying an absorbent solution in which carbon dioxide is absorbed, and a first outlet through which solid salt is discharged. (24), a second outlet 25 through which the absorbent solution from which the salt has been removed is discharged. When the absorbent liquid 21 in which the carbon dioxide absorption process is completed is injected into the inlet 23, the salt in the form of solid content sinks to the lower layer while the screw conveyor inner cylinder 22 in the inclined centrifuge 20 rotates. The layer will be located at the top. The upper liquid layer is supplied to the carbon dioxide absorption process through the first outlet 24 again, and the salt of the lower part is discharged through the second outlet 25 and supplied to the absorbent regeneration process. After the salt is heated to 80 ~ 120 ℃ dissolved can be used in the process for preparing the absorbent again.

In the regeneration step (S140) to regenerate the absorbent absorbed the carbon dioxide. At this time, the regeneration process is preferably carried out in a temperature range of 1 to 10 atm, 105 ℃ to 120 ℃.

Hereinafter, the absorbent capacity of the carbon dioxide absorbent was measured using the absorbent aqueous solution of the present invention and a known absorbent aqueous solution. The measurement method was a gas chromatography (GC) to measure the concentration of the gas discharged without being absorbed in the injected gas (30% CO ₂ + 70% N ₂ ), when saturation is 10 minutes average concentration difference It measured and prescribed | regulated when it is 0.01%. The measurement results are shown in Table 1 below. Referring to Table 1 below, it can be seen that the carbon dioxide absorbing capacity (Capacity, mol CO ₂ / mol absorbent) of the carbon dioxide absorbent is generally high when the sterically hindered cyclic amine and potassium carbonate are mixed at a predetermined ratio.

In Table 1 below, PZ is piperazine, 2-methyl PZ is 2-methyl piperazine, homoPZ is homopiperazine, MEA is monoethanolamine, DEA is diethanolamine, TEA is triethanolamine, and AMP is 2- Amino-2-methyl-1-propanol.

Composition (wt%) Absorption
Temperature (℃) t _B
(min) t _B
(min) Capacity
(mol CO ₂ / mol absorbent) Example 1 K ₂ CO ₃ 15wt% /
PZ 10wt% 40 100 180 0.828 60 88 160 0.742 80 72 149 0.641 Example 2 K ₂ CO ₃ 15wt% /
2-methyl PZ 10wt% 40 82 185 0.864 60 74 171 0.761 80 58 157 0.627 Example 3 K ₂ CO ₃ 15wt% /
homo PZ 10wt% 40 81 192 0.786 60 84 156 0.738 80 75 137 0.662 Comparative Example 1 MEA 30wt% 60 153 230 0.537 Comparative Example 2 DEA 30wt% 60 54 182 0.478 Comparative Example 3 TEA 30wt% 60 2 75 0.144 Comparative Example 4 AMO 30wt% 60 64 266 0.601

The heat of absorption reaction was measured when the carbon dioxide absorption reaction was performed on the same amount of absorbent using SETARAM's heat absorption measurement equipment. The measurement results are shown in Table 2 below. In Table 2 below, KS 1 is a carbon dioxide absorbent manufactured by Mitsubishi Heavy Industries.

Composition (wt%), 25 ° C △ H
(GJ / ton CO ₂ ) Example 1 K ₂ CO ₃ 15wt% /
PZ 10wt% 1.45 Example 2 K ₂ CO ₃ 15wt% /
2-methyl PZ 10wt% 1.36 Example 3 K ₂ CO ₃ 15wt% /
homo PZ 10wt% 1.42 Comparative Example 1 MEA 30wt% 1.93 Comparative Example 5 KS 1 1.55

Generally, the heat of regeneration is composed of the sum of heat of absorption reaction, latent heat of solvent and sensible heat. In the case of chemical absorbents, heat of absorption reaction accounts for at least 50% of the total renewable energy. On the other hand, in the case of the absorbent having the heat of absorption about twice as high as the latent heat of the solvent, water, the regenerated heat is composed of 50% of heat of absorption, 35% of latent heat and 15% of sensible heat. In other words, the heat of chemical reaction is very high in the heat of regeneration of the chemical absorbent. From Table 2, it can be seen that the heat of absorption reaction of the alkali carbonate carbon dioxide absorbent to which the hindered cyclic amine is added is the lowest. This means that the renewable energy of the carbon dioxide absorbent of the present invention is also the lowest.

Composition (wt%), 25 ° C Salt production rate (wt%) Removal rate (%) Example 1 K ₂ CO ₃ 15wt% /
PZ 10wt% 0 - Example 2 K ₂ CO ₃ 15wt% /
2-methyl PZ 10wt% 0 - Example 3 K ₂ CO ₃ 15wt% /
homo PZ 10wt% 0 - Example 4 K ₂ CO ₃ 20wt% /
PZ 10wt% 6 100 Example 5 K ₂ CO ₃ 20wt% /
2-methyl PZ 10wt% 2 100 Example 6 K ₂ CO ₃ 20wt% /
homo PZ 10wt% 15 100 Comparative Example 1 MEA 30wt% 0 - Comparative Example 5 KS 1 0 -

As mentioned above, although the technical idea of this invention was described with attached drawing, this was demonstrated as an example of a preferable embodiment, and does not limit this invention. In addition, any person having ordinary knowledge in the technical field to which the present invention belongs may be modified in various ways without departing from the scope of the technical idea of the present invention.

Claims (6)

A gas contact step of contacting a gas containing carbon dioxide to a carbon dioxide absorbent to which an hindered cyclic amine is added to the alkali carbonate;
A carbon dioxide absorption step of absorbing carbon dioxide from the gas;
Separating a salt from the absorbent in which the carbon dioxide is absorbed;
And regenerating the absorbent from which the salt is separated, wherein the carbon dioxide absorbent comprises 20 wt% or less of alkali carbonate, 10 wt% or less of sterically hindered cyclic amine, and a residual amount of water. The method of claim 1, wherein the salt separation process is performed using a decanter separator. delete The method of claim 1, wherein the alkali carbonate is potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), potassium bicarbonate (KHCO ₃ ) and sodium bicarbonate (NaHCO ₃ Carbon dioxide removal method characterized in that at least one selected from the group consisting of. The method of claim 1, wherein the hindered cyclic amine is 1-amino-4methyl piperazine, 1- (2-aminoethyl) -4methyl piperazine, 1- (2-hydroxyethyl) -4methyl piperazine, 1- (2-aminoethyl) -piperazine, 1- (2-hydroxyethyl) -piperazine, 2-aminoethyl-piperazine, 1-ethyl-piperazine, 2,5-dimethyl-piperazine, cis 2,6-dimethyl-piperazine, 1,4-dimethyl-piperazine, trans 2,5-dimethyl-piperazine, 1-methyl piperazine, 2-methyl piperazine, 1-ethyl piperazine, 2-peperidine Carbon dioxide removal method characterized in that at least one selected from the group consisting of ethanol, 3-ferridine ethanol, 4-ferridine ethanol, 2-aminoethyl-1- piperidine and homo piperidine. A gas contact step of contacting a gas containing carbon dioxide to a carbon dioxide absorbent containing 20 wt% or less potassium carbonate, 10 wt% or less 2-methylpiperazine, and a residual amount of water;
A carbon dioxide absorption step of absorbing carbon dioxide from the gas;
Separating a salt from the absorbent in which the carbon dioxide is absorbed;
Regenerating the absorbent from which the salt is separated.

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