KR102190874B1 - liquid absorbent of carbon dioxide, preparation method thereof and removal method of carbon dioxide using the same - Google Patents

Abstract

The present invention relates to a carbon dioxide absorbing liquid, a method of manufacturing the same, and a method of removing carbon dioxide using the same. The carbon dioxide absorbing liquid according to the present invention is a carbon dioxide absorbent, which can chemically absorb carbon dioxide in an aqueous solution and provides an amine group (-NH ₂ ) that can be regenerated by heating, an amino acid mimetic containing an amine group and a carboxyl group, or an alkali thereof Metal salts; And an aqueous solution containing a transition metal oxide that provides an acid point and contains a transition metal that does not coordinate with a carbon dioxide absorbent as a carbon dioxide absorption catalyst.

Description

[Liquid absorbent of carbon dioxide, preparation method thereof and removal method of carbon dioxide using the same}

The present invention relates to a carbon dioxide absorbing liquid, a method of manufacturing the same, and a method of removing carbon dioxide using the same.

Recently, the amount of CO ₂ emitted into the atmosphere has increased exponentially, and global climate change is attracting great attention. In particular, the burning of fossil fuels produces the largest amount of greenhouse gases. It will take considerable time to establish an alternative to fossil fuel sources, green energy sources, on an industrial scale, and until then, it may be difficult for fossil fuels to be replaced by these alternative energy sources.

Although the use of fossil fuels is inevitable in terms of energy demand, the largest anthropogenic source is fossil fuel-burning power plants, accounting for one-third of total carbon dioxide emissions. Therefore, various approaches have been proposed to remove or capture carbon dioxide from flue gas on a large scale. Because of its retro-fit nature, the post-combustion capture method is best suited for capturing carbon dioxide and can be easily retrofitted. In the case of the collection method after combustion, various methods such as absorption method, adsorption method, and cryogenic method may be used. Among these, an absorption process using alkanolamine as a liquid absorbent is well established. In addition, among the technologies for controlling high concentration carbon dioxide emitted from industrial processes, an absorption method using an alkali absorbent such as alkanol amines is widely applied in post-combustion. Compared to other separation methods, the absorption method has advantages of commercialization, high technology reliability, and large processing capacity. Alkanolamines commonly used are primary, secondary, tertiary amines or mixtures thereof.

Until now, the role and effect of liquid alkanolamine absorbents such as mono ethanol amine (MEA), diethanol amine (DEA), methyldiethanol amine (MDEA), triethanolamine (TEA), or mixtures thereof have been extensively studied. Primary amines show a fast reaction rate with CO ₂ , but due to their strong binding force with carbon dioxide, a lot of energy is required during regeneration, which makes regeneration very difficult and increases the overall cost of the process. On the other hand, secondary and tertiary amines have slow CO ₂ absorption, which suggests that secondary and tertiary alkanolamines cannot be used in industrial processes. Along with this, another disadvantage of alkanol amines that makes the use of alkanol amine absorbents difficult in practical industrial processes is their high degree of corrosiveness, which leads to corrosion of the device by toxicity, high volatility and strong alkalinity.

Therefore, amino acid salt solutions are of interest as a substitute for carbon dioxide absorbents. Amino acids have similar functional groups such as alkanolamines. It is also expected to behave like alkanol amines for CO ₂ . However, amino acids do not decompose in the presence of oxygen.

Several amino acid salt solutions have been reported for CO ₂ absorption. For CO ₂ absorption, amino acid salts of glycine, alanine, proline, lysine, histidine and sarcosine have been previously screened. Among the reported amino acid salts, proline and sarcosine have higher rates of CO ₂ absorption than other amino acid salts. Interestingly, the lysine amino acid salt has the highest CO ₂ absorption capacity due to the additional presence of amino functional groups. However, the rate of CO ₂ absorption is slow compared to other amino acids for lysine.

Use of the invention improves the high CO ₂ gajina the absorption capacity of CO ₂ with a slow rate of absorption amino acid salt of CO ₂ absorption rate by using the approach of adding the metal oxide by, for removing high concentrations of carbon dioxide discharged to the amino acid salt in an industrial process I want to.

A first aspect of the present invention is to use an amino acid mimetic containing an amino acid, an amine group and a carboxyl group, or an alkali metal salt thereof, which can chemically absorb carbon dioxide in an aqueous solution and provide an amine group (-NH ₂ ) that can be regenerated by heating. Step a to select; a step b of selecting a transition metal oxide containing a transition metal that does not coordinate with the carbon dioxide absorbent selected in step a and provides an acid point as a carbon dioxide absorption catalyst under the condition of an aqueous solution containing the carbon dioxide absorbent selected in step a; And step c of preparing a carbon dioxide absorbing liquid by adding the carbon dioxide absorbent selected in step a and the carbon dioxide absorbing catalyst selected in step b to water.

A second aspect of the present invention is a carbon dioxide absorbent, which can chemically absorb carbon dioxide in an aqueous solution and provides an amine group (-NH ₂ ) that can be regenerated by heating, an amino acid mimetic containing an amine group and a carboxyl group, or an alkali thereof. Metal salts; And as a carbon dioxide absorption catalyst, it provides a composition for absorbing carbon dioxide containing a transition metal that does not coordinate with the carbon dioxide absorbent and a transition metal oxide providing an acid point.

A third aspect of the present invention provides an amine group (-NH ₂ ) capable of chemically absorbing carbon dioxide and regenerating by heating in a method of removing carbon dioxide from a carbon dioxide-containing gas through gas-liquid contact with a carbon dioxide absorbing liquid. Amino acid, amine group and carboxyl group-containing amino acid mimetics or alkali metal salts thereof; And a first step of preparing a water-based carbon dioxide absorbing liquid containing a transition metal oxide that provides an acid point and contains a transition metal that is not coordinated therewith. And a second step of removing carbon dioxide from the carbon dioxide-containing gas through gas-liquid contact with the carbon dioxide absorbing liquid of the first step.

Hereinafter, the present invention will be described in detail.

Amino acid refers to a molecule having both an amine group (-NH ₂ ) and a carboxy (-COOH) group, and in general, an alpha-amino acid (HOOC-CH(R)-NH ₂ ) in which two functional groups are attached to one carbon. It is called.

Amino acid salts (eg, hydrochloride, metal salt) as well as amino acid mimetics containing amine and carboxyl groups (eg, sarcosine) belong to the homogeneous category of amino acids applied in the present invention.

Amino acids have amino groups that can react with acidic gases like alkanol amines, so carbon dioxide can be selectively absorbed and removed by amino groups. However, the aqueous amino acid solution exists in the form of Zwitterion, which has amphoteric properties that can act as acids or alkalis at pH 5-6. That is, since amino acids are protonated by providing hydrogen ions contained in acidic carboxyl groups in aqueous solutions to basic amino groups, they cannot react directly with carbon dioxide.

For example, glycine (HOOC-CH ₂ -NH ₂₎ of the case, while providing H ⁺ ions of the carboxyl group (-COOH) to the amino group (NH ₂₎ in an aqueous solution carboxylate (COO ^-) present in ionic form, and the amino group By adding H ⁺ ions, it has the properties of'-'and'+' in the form of ammonium ion, NH ₃ ⁺ . Therefore, the glycine aqueous solution itself cannot induce a direct chemical reaction with carbon dioxide because amino groups involved in carbon dioxide absorption are converted into ammonium ions. However, when an alkali metal hydroxide (MOH) is impregnated with an amphoteric glycine as shown in Formula (1) in an equimolar amount, the carboxyl group in the conjugate base form is substituted with metal ions including Na ⁺ , and OH ^- is an ammonium ion in the conjugate acid form. By donating a proton (H ⁺ ) from and being dehydrogenated, the amino group is converted into an activated glycine salt (MOOC-CH ₂ -NH ₂ ). Glycine salt carbon dioxide absorbing mechanism is the same as the well-known alkanolamine, and formula (2) is an active group such as a carbamate by reaction with CO ₂ (-RNHCOO ^-) is generated and the glycidyl nephritis ion (RNH ₃ ^+).

_{^{- OOC-CH 2 -NH 3 +}} + MOH → MOOC-CH 2 -NH 2 + H 2 O

[M=Na, Li, K] (1)

_{2 RNH 2 + CO 2 → RNHCOO} - + RNH 3 +

[R=CH ₂ COOM] (2)

When an alkali metal is added to the amino acid-containing aqueous solution, the alkali metal is substituted with the carboxyl group from which a proton is lost, and the OH ⁻ of the alkali metal and H ⁺ of the ammonium ion are bonded to each other, thereby generating an amino functional group involved in carbon dioxide absorption. It is possible to activate -NH ₃ ⁺ to -NH ₂ from an alkali cation supply regardless of the type of alkali metal. Accordingly, non-limiting examples of alkali metal hydroxide (MOH) capable of activating -NH ₃ ⁺ into -NH ₂ in an amino acid or amino acid mimic in an aqueous solution include NaOH, LiOH, KOH, and the like.

Important features of amino acid salts are fast reaction rates, highly achievable cyclic loading, good stability to oxygen to avoid formation of highly toxic nitrogen oxides, and advantageous binding energy. In addition, the presence of carboxylate functional groups in the amino acid adds the possibility of a salt function with potassium hydroxide or lithium hydroxide and ensures the non-volatility of the amino acid salt when a liquid absorbent is used in a stripper.

A method of removing carbon dioxide from carbon dioxide-containing gas through gas-liquid contact with a carbon dioxide absorbing liquid. Among the high-concentration carbon dioxide control technologies emitted from industrial processes, in order to be used for post-combustion, it absorbs carbon dioxide as well as carbon dioxide absorption capacity. Speed is also important.

Accordingly, the present invention is characterized by using a transition metal oxide as a catalyst to improve the CO ₂ absorption rate of the amino acid salt in an aqueous solution in order to use the amino acid salt to remove high concentration carbon dioxide discharged from an industrial process.

Metal oxides have not been used to improve the rate of CO ₂ absorption of amino acid salts.

Lysine (Chemical Formula 1) has two amine groups, and has superior CO ₂ absorption capacity compared to other amino acids, but has a slow CO ₂ absorption rate.

An amino acid having one amine group does not have a stoichiometric number of moles of CO ₂ that can be absorbed per unit mole when reacting with a carbon dioxide molecule as shown in Formula (2) above. However, when lysine has two amine groups and reacts with carbon dioxide in an aqueous solution, there are many more functional groups that can react than other amino acids in which one amine group is present, so the stoichiometric amount of CO ₂ that can be absorbed per unit mole The reaction may proceed with a theoretical mole number of 0.5 or more. As a result, lysine has superior carbon dioxide absorption capacity compared to other amino acids in which one amine group is present. Therefore, when a composition for absorbing lysine carbon dioxide is used, it can be economical by preventing the consumption of a large amount of an expensive absorbent.

Using VLE (Vapour-Liquid Equilibrium) experiments, the present inventors discovered that the oxide of the first row (cycle 4) transition metal plays a catalytic role in terms of the CO ₂ absorption rate of the lysine potassium salt in the aqueous solution. The highest efficiency was observed with CuO and its recyclability was confirmed by XRD and FT-IR spectroscopy.

In addition, a possible functional pathway based on NMR studies on metal oxides in CO ₂ absorption efficiency can be proposed as shown in Scheme 1 below.

[Scheme 1]

The catalytic activity of the transition metal oxide in the first row (cycle 4) of the periodic table depends on the defect sites on the metal oxide surface. When the surface of the metal oxide is exposed to water, a metal hydroxide is produced that can act as a Bronsted acid after the reaction. Due to the additional presence of Lewis acidity derived from the unsaturated coordination environment of the metal oxide, the metal oxide may be suitable for improving the rate of CO ₂ absorption in the amino acid salt absorption liquid.

Therefore, the composition for absorbing carbon dioxide according to the present invention

As a carbon dioxide absorbent, an amino acid, an amine group and a carboxyl group-containing amino acid mimetic or an alkali metal salt thereof providing an amine group (-NH ₂ ) that can chemically absorb carbon dioxide in an aqueous solution and can be regenerated by heating; And

As a carbon dioxide absorption catalyst, a transition metal oxide that contains a transition metal that does not coordinate with a carbon dioxide absorbent and provides an acid point

Contains.

The composition for absorbing carbon dioxide according to the present invention may further include an alkali metal hydroxide (MOH) capable of activating -NH ₃ ⁺ of an amino acid or amino acid mimic with -NH ₂ in an aqueous solution. Therefore, the carbon dioxide absorbing liquid according to the present invention may be a strong basic aqueous solution having a pH of 10 or more. When the carbon dioxide absorbing liquid according to the present invention is a basic aqueous solution, the absorption efficiency of CO _{2 in} water can be improved by a chemical absorption method during gas-liquid contact.

In order to increase the CO ₂ absorption capacity, the amino acid or amino acid mimetic may be one having two or more amine groups, such as lysine. Accordingly, the composition for absorbing carbon dioxide according to the present invention may contain lysine or an alkyl li metal salt thereof as a carbon dioxide absorbent and CuO as a carbon dioxide absorption catalyst. Since CuO has a higher Lewis acid point index than other metal oxides, the reaction rate between the carbon dioxide absorbent and the carbon dioxide can be significantly increased. Through the experiment, the best carbon dioxide absorption rate compared to other metal oxides was observed in CuO (FIG. 3).

In addition, the carbon dioxide absorbing liquid manufacturing method according to the present invention

A step of selecting an amino acid that can chemically absorb carbon dioxide in an aqueous solution and provides an amine group (-NH ₂ ) that can be regenerated by heating, an amino acid mimetic containing the amine group and carboxyl group, or an alkali metal salt thereof as a carbon dioxide absorbent;

a step b of selecting a transition metal oxide containing a transition metal that does not coordinate with the carbon dioxide absorbent selected in step a and provides an acid point as a carbon dioxide absorption catalyst under the condition of an aqueous solution containing the carbon dioxide absorbent selected in step a; And

a carbon dioxide absorbent selected in step a; And step c of preparing a carbon dioxide absorption liquid by adding the carbon dioxide absorption catalyst selected in step b to water.

At this time, step b may select a carbon dioxide absorption catalyst by screening from oxides of transition metals in period 4 of the periodic table.

In addition, step b may select a carbon dioxide absorption catalyst from the group consisting of CuO, Fe ₂ O ₃ , NiO and MnO ₂ .

Further, the carbon dioxide absorbing solution manufacturing method according to the present invention further adds a step b-1 of selecting the concentration of the transition metal oxide selected in step b by measuring the carbon dioxide absorption rate of the carbon dioxide absorbing solution according to the concentration of the transition metal oxide selected in step b. can do.

Alternatively, the method for preparing a carbon dioxide absorbing solution according to the present invention further adds a step b-2 of selecting the concentration of the transition metal oxide selected in step b by measuring the change in viscosity of the carbon dioxide absorbing solution according to the concentration of the transition metal oxide selected in step b. I can.

The carbon dioxide absorbing liquid according to the present invention includes a carbon dioxide absorbing agent of 0.5 to 2M; And it may be an aqueous solution containing a carbon dioxide absorption catalyst of 0.05 to 0.5M.

In the carbon dioxide absorbing liquid according to the present invention, the carbon dioxide absorbent may be specifically 0.7 to 1.5 M, and more specifically 0.8 to 1.2 M. If the concentration of the carbon dioxide absorbent in the aqueous solution is less than 0.5 M, the concentration of the amino acid is too low, so there may be a problem that the carbon dioxide absorption rate and capacity decrease. If it exceeds 2 M, the viscosity of the aqueous solution is excessively increased and the carbon dioxide diffuses and reacts with the absorbent. You may have difficulty doing it. In the experiment, as the concentration of lysine increased to 1.0 M, the carbon dioxide absorption rate increased, but when it exceeded 1.0 M, it was confirmed that the absorption rate decreased. When the lysine concentration was 1.0 M, the absorption rate of about 2.3 kPa/s was increased in the absence of CuO. It was confirmed that the carbon dioxide absorption rate of 0.32 kPa/s appeared when 0.3 M of CuO was added (FIGS. 2 and 4).

In the composition for absorbing carbon dioxide of the present invention, the concentration of the metal oxide catalyst may be 0.05 to 0.5 M. Specifically, it may be 0.1 to 0.5 M, and more specifically, it may be 0.2 to 0.4 M. If the concentration of the metal oxide catalyst is less than 0.05 M, the role of the metal oxide may be insignificant and the increase in the carbon dioxide absorption rate may not be large. If the concentration of the metal oxide catalyst exceeds 0.5 M, the viscosity of the absorbent is excessively increased, so that carbon dioxide is added to the active site of the metal oxide. It can be difficult to diffuse to reach, which can reduce the rate of carbon dioxide absorption. In the experiment, as the CuO concentration increased to 0.3 M, the carbon dioxide absorption rate increased, but when it exceeded 0.3 M, it was confirmed that the absorption rate decreased. When 1.0 M lysine and 0.3 M CuO were added, the absorption rate reached 0.32 kPa/s. The carbon dioxide absorption rate was confirmed (FIG. 4).

Furthermore, according to the present invention, a method of removing carbon dioxide from a carbon dioxide-containing gas through gas-liquid contact with a carbon dioxide absorbing liquid,

An amino acid that can chemically absorb carbon dioxide and provides an amine group (-NH ₂ ) that can be regenerated by heating, an amino acid mimetic containing an amine group and a carboxyl group, or an alkali metal salt thereof; And a first step of preparing a water-based carbon dioxide absorbing liquid containing a transition metal oxide that provides an acid point and contains a transition metal that is not coordinated therewith. And

And a second step of removing carbon dioxide from the carbon dioxide-containing gas through gas-liquid contact with the carbon dioxide absorbing liquid in the first step.

The carbon dioxide absorbing liquid in the first step may be prepared by the method for preparing the carbon dioxide absorbing liquid according to the present invention described above, and may be a composition for absorbing carbon dioxide according to the present invention.

The method of removing carbon dioxide from the carbon dioxide-containing gas through gas-liquid contact with the carbon dioxide absorbing liquid according to the present invention may be performed in a carbon dioxide removal apparatus such as a scrubber having a gas-liquid contact module as shown in the schematic diagram of FIG. In addition, through gas-liquid contact, carbon dioxide can be chemically absorbed from the exhaust gas into the absorption liquid.

The method of removing carbon dioxide from a carbon dioxide-containing gas through gas-liquid contact with a carbon dioxide absorbing liquid according to the present invention is in which carbon dioxide is removed through heating from the carbon dioxide absorbing liquid that has absorbed carbon dioxide through chemical absorption in the second step to regenerate the carbon dioxide absorbing liquid. The third step may be further included, and the recycled carbon dioxide absorbing liquid may be reused in the second step.

Existing carbon dioxide absorbents are very difficult to regenerate because they require a lot of energy during regeneration due to their strong binding force with carbon dioxide, but the catalyst improves not only the reaction speed in the forward direction but also the reaction speed in the reverse direction. When heated by the absorption catalyst (MO _x ), the carbon dioxide removal rate can also be improved.

For example, in the method of removing carbon dioxide from a carbon dioxide-containing gas through gas-liquid contact with a carbon dioxide absorbing liquid according to the present invention, a carbon dioxide absorbing liquid and a carbon dioxide-containing exhaust gas are respectively supplied to an absorption tower, and carbon dioxide in the carbon dioxide-containing exhaust gas is supplied as an absorbent in the gas-liquid contact module. Absorbing and discharging the carbon dioxide-containing absorbent liquid and the exhaust gas from which the carbon dioxide has been removed, respectively; The carbon dioxide-containing absorbent liquid discharged from the absorption tower is heated in a regeneration tower to evaporate carbon dioxide, and the gaseous carbon dioxide and the absorbent liquid are respectively discharged to regenerate the absorbent liquid.

Furthermore, the metal oxide catalyst itself can also be reused. In the carbon dioxide absorption liquid according to the present invention in which the carbon dioxide absorption reaction has been performed, the transition metal oxide can be filtered through a filter and then reused by applying heat of 60 to 80°C under vacuum (FIG. 5).

In the carbon dioxide absorbing liquid of the present invention, amino acids are non-toxic and environmentally friendly, and since the vapor pressure is relatively lower than that of alkanolamine absorbents, the volatility is low, so that the loss of the absorbent can be reduced in the stripping reaction that requires a high temperature when applied to industrial facilities. In addition, since the carbon dioxide absorption rate can be increased due to the metal oxide catalyst, carbon dioxide can be removed with high efficiency. In particular, in the present invention, when the amino acid is lysine, carbon dioxide can be absorbed at a high dose, thereby providing an economy that can reduce the amount of expensive amino acid absorbent used.

1 is a graph showing VLE experimental data of alanine, proline, and lysine on carbon dioxide absorption rate.
2 is a graph showing VLE data of lysine with different concentrations for carbon dioxide absorption rate.
Figure 3 is a metal versus carbon dioxide absorption rate It is a graph showing VLE experimental data according to oxide.
4 is a graph showing carbon dioxide absorption rates for various concentrations of CuO.
5 is a graph showing a comparison of the XRD pattern of CuO that is not used and CuO recovered after the reaction.
6 is a graph showing a comparison of FT-IR spectra of unused CuO and CuO recovered after reaction.
FIG. 7 is a graph showing NMR spectra of a lysine salt, a lysine salt dissolved in potassium hydroxide, a lysine potassium salt solution absorbing carbon dioxide, and a metal oxide having a lysine potassium salt.
8 is a schematic diagram showing that the scrubber chemically absorbs carbon dioxide from the exhaust gas into the absorbing liquid through gas-liquid contact.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

Materials and measurements

All purchased compounds were of analytical grade and were used without further purification. Metal oxides and amino acids (alanine, proline, and lysine) were purchased from Aldrich, and lysine monohydrochloride salt was purchased from a local company. All purchased chemicals were used without purification.

FT-IR spectra were recorded using the ATR method using a Varian 640-IR FT-IR spectrometer. ¹ H NMR and ¹³ C NMR were recorded on Varian 300 MHz and Varian 125 MHz instruments, respectively.

pH measurement : pH was measured for all samples before and after CO ₂ absorption at room temperature.

Gas-liquid equilibrium studies (Vapour-Liquid Equilibrium studies): VLE system consists of a gas reservoir, reactor, temperature sensors, pressure gauges, pumps, and real-time recorder. The total reactor volume was 300 mL. 100 mL of an amine acid solution and a catalyst were added to the reactor, and magnetically stirred at 300 rpm to perform a reaction between the absorbent and CO ₂ . Before introducing the CO ₂ into the reactor, the reaction mixture was evacuated using a vacuum pump at room temperature. The reaction mixture was preheated and a water bath was formed to carry out the reaction at the desired temperature, 40°C. The absorption test was performed while opening the connection valve between the reservoir and the reactor and injecting carbon dioxide at a constant pressure. During the course of the reaction, the pressure in the reactor decreased as a function of CO ₂ absorption.

Example 1: amino acids and CO ₂ reaction

First, 0.2 M amino acid salts of alanine, proline and lysine were screened in VLE. Amino acid absorption liquid was prepared from KOH and each amino acid. Amino acids and KOH were dissolved in water at room temperature and mixed together to prepare an appropriate aqueous solution. In VLE experiments, after injecting CO ₂ at a constant pressure and calculated the CO ₂ absorption rate (absorption rate) in 40 ℃. The change in CO ₂ pressure depends on the absorbent liquid. The initial CO ₂ absorption rate was calculated from the linear fit equation. The absorption rate for the amino acid potassium salt 1.0M is shown in Figure 1. The order of the carbon dioxide absorption rate is proline>alanine> lysine, and this order is similar to the value of previous literature. Figure 1 shows that the absorption rate of proline and alanine is higher than that of lysine.

Next, the lysine potassium salt was screened at different concentrations. The change in CO ₂ absorption rate is shown in FIG. 2. When the concentration exceeded 1.0M, the absorption performance was smaller than that of 0.5M and 1.0M. The high concentration of lysine may be the result of changing the viscosity of the solution. Also, when the amino acid concentration is higher, amino acids are precipitated. Therefore, 1.0M lysine salt solution was selected for further study. For use on an industrial scale, a solution of lysine monohydrochloride, which is cheaper than lysine, was used instead of lysine. The CO ₂ absorption performance of lysine hydrochloride is almost similar to that of lysine.

Example 2: role of metal oxide

To 1.0 M of lysine salt, 0.2 M of transition metal oxide of the first row (cycle 4) was added, and their absorption enhancing performance was screened at 40°C. The initial absorption rate was calculated using a linear fit equation from the left view of FIG. 3, which is a result measured for 500 seconds. The calculated CO ₂ absorption rate for the screened metal oxide is shown in Figure 3 (right view). 1.0 M lysine potassium salt solution has a CO ₂ absorption rate of 0.199 kPa/s. As a result of adding MnO ₂ (0.2M) to the lysine solution, CO ₂ absorption was improved from 0.199 kPa / s to 0.230 kPa / s. This result clearly shows that the addition of a heterogeneous catalyst can improve CO ₂ absorption even in a high concentration amino acid salt solution. In addition, by improving the absorption kinetics of the lysine potassium salt, it is suggested that the lysine salt absorption liquid combined with the metal oxide can be successfully used in industrial processes. Next, in terms of enhancing CO ₂ absorption, another 4-cycle transition metal oxide was screened and the results are shown in FIG. 3 (right view). The effect of Fe ₂ O ₃ and NiO is similar to that of MnO ₂ , but this metal oxide efficiency is superior to that of MnO ₂ . The best carbon dioxide absorption rate in the 1.0 M lysine absorbent was observed in CuO (right view in FIG. 3). Among the screened metal oxides, Cr ₂ O ₃ exhibits negative absorption effects that may occur due to amino acids binding to metal centers. This is supported by the dissolution of Cr ₂ O ₃ in the absorbent solution because the color of the absorbent solution changes from brown to dark brown. The change in the CO ₂ absorption efficiency for metal oxides comes from the Lewis and Bronsted acid sites of each oxide. The acid point of the metal oxide was calculated using pyridine FT-IR. Metal oxides with the highest active sites, such as CuO, provided the highest CO ₂ absorption efficiency.

By choosing the best catalyst CuO, the effect of catalyst concentration and CO ₂ pressure on the CO ₂ absorption rate was further studied. While changing the CuO concentration from 0.1M to 0.5M, the total change of the CO ₂ pressure according to each catalyst concentration and the calculated CO ₂ absorption rate therefrom are shown in FIG. 4. While the concentration of CuO increased from 0.1 M to 0.3 M, the CO ₂ absorption rate steadily increased. However, increasing the concentration above 0.3 M decreases the efficiency. This can occur due to the high viscosity nature of the lysine absorbent liquid when a higher concentration of catalyst is added. When the viscosity of the absorbent liquid increases, it can be very difficult for the CO ₂ to diffuse and reach the active site of the metal oxide.

Example 3: CuO Regeneration characteristics

After the CO ₂ absorption experiment according to Example 1, the metal oxide was filtered through a filter and dried under high vacuum. Prior to the reusability test, the recovered catalyst was dried at 70° C. for 12 hours. XRD patterns were compared for the recovered CuO and the new CuO catalyst (FIG. 5). The XRD pattern of the recovered CuO after the new CuO and CO ₂ absorption experiment suggests that the recovered CuO did not change from the initial active form. The recovered CuO can be utilized in a carbon dioxide absorption process, and according to the results obtained in FIG. 5, a CuO catalyst can be used in many cycles.

In addition, the FT-IT spectrum of the recovered CuO is shown in FIG. 6. New CuO shows an absorption band at 1400 cm ^-1 corresponding to the Cu-O frequency in the metal oxide. In the recovered catalyst, an added peak along with a clear peak of CuO indicates that a minimal amount of lysine is present in the recovered CuO. However, the presence of residual amino acids by the CuO catalyst did not affect the CO ₂ absorption efficiency.

Example 4: Lysine and NMR study of metal oxide

To understand the mechanism of improving the CO ₂ absorption efficiency of metal oxides, NMR spectra of lysine salt, lysine salt with KOH (potassium salt of lysine), lysine potassium salt solution in which CO ₂ is absorbed, and metal oxide with lysine potassium salt Were recorded at D ₂ O. ¹ H NMR and ¹³ C NMR are shown in FIG. 7. The peaks at 2.61 and 3.24 ppm are the actual peaks of the lysine salt in D ₂ O. After the addition of KOH, a chemical shift in lysine was observed from 2.61 ppm to 3.00 ppm and from 3.24 ppm to 3.84 ppm. In other words, due to the influence of chemical bonds such as cation exchange, the electronic state around the atomic nucleus is changed, and the inherent properties occurring in the atom or atomic nucleus are deviated, and the energy level of the internal electrons slightly changes, resulting in a difference in resonance frequency (ppm). Is done. For alkali metals in the same group, the electronegativity decreases as the atomic number increases, and the chemical shift increases as the electronegativity of the substituent increases. Therefore, the electronegativity increases in the order of Li>Na> K according to the atomic number of the three alkali metals. Accordingly, the ¹ H-NMR spectrum can confirm the difference in chemical shift according to the type of the substituted metal, and through this chemical shift, it can be confirmed that the absorbent is chlorinated by substitution of the metal cation. ^{In the 13} C-NMR spectrum, the movement of carbon atoms is 15-20 times greater than that of protons, and absorption occurs in a lower magnetic field than hydrogen.

When purging CO ₂ into the lysine potassium salt solution, the peaks generated at 161 and 170 ppm in ¹³ C NMR suggest that bicarbonate and carbamate species are produced. More interestingly, the addition of metal oxides to the lysine potassium salt solution did not produce peaks of additional impurity levels. This indicates that the addition of metal oxide only improves the CO ₂ absorption efficiency without side reactions.

Example 5: pH study

The pH was calculated before and after the CO ₂ absorption study. The pH decreased after absorption, and the captured CO ₂ can be calculated based on the production of bicarbonate in the solution as confirmed by ¹³ C NMR spectroscopy.

conclusion

In the aqueous potassium salt solution of lysine, the effect of metal oxide on CO ₂ absorption efficiency was confirmed. It has been demonstrated that the addition of metal oxides to the aqueous solution of lysine potassium salt increases the CO ₂ absorption efficiency. Among the screened metal oxides, the best CO ₂ absorption efficiency was obtained for CuO. The recycling properties of metal oxides were tested for up to 3 cycles, confirming that CuO can be used successfully in concentrated amino acid potassium salt solutions. A mechanism for enhancing the absorption of CO _{2 with} the aid of metal oxides has been proposed based on NMR spectroscopy studies. Experimental results of lysine amino acid salts to improve CO ₂ absorption efficiency suggest that this could be an attractive method for trapping CO ₂ in the flue gas. Based on this experimental study, the lysine salt solution could be an interesting alternative to the conventional amine-based solution for trapping CO ₂ in the flue gas.

From the above description, those skilled in the art to which the present invention pertains will be able to understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. In this regard, it should be understood that the embodiments described above are illustrative in all respects and not limiting. The scope of the present invention should be construed that all changes or modifications derived from the meaning and scope of the claims to be described later rather than the above detailed description and equivalent concepts are included in the scope of the present invention.

Claims (15)

A step of selecting an amino acid mimetic containing an amino acid, an amine group and a carboxyl group, or an alkali metal salt thereof, which can chemically absorb carbon dioxide in an aqueous solution and provide an amine group (-NH ₂ ) that can be regenerated by heating, as a carbon dioxide absorber;
a step b of selecting a transition metal oxide containing a transition metal that does not coordinate with the carbon dioxide absorbent selected in step a and provides an acid point as a carbon dioxide absorption catalyst under the condition of an aqueous solution containing the carbon dioxide absorbent selected in step a; And
a carbon dioxide absorbent selected in step a; And a step c of preparing a carbon dioxide absorption liquid by adding the carbon dioxide absorption catalyst selected in step b to water,
The transition metal includes at least one selected from the group consisting of Cu, Fe, Ni, and Mn. The method of claim 1, wherein in step b, a carbon dioxide absorption catalyst is selected by screening from oxides of transition metals in period 4 of the periodic table. The method of claim 1, wherein step b is characterized in that the carbon dioxide absorption catalyst is selected from the group consisting of CuO, Fe ₂ O ₃ , NiO and MnO ₂ . The carbon dioxide according to claim 1, further comprising step b-1 of selecting the concentration of the transition metal oxide selected in step b by measuring the carbon dioxide absorption rate of the carbon dioxide absorbing liquid according to the concentration of the transition metal oxide selected in step b. Absorbent liquid preparation method. The carbon dioxide absorbing liquid of claim 1, further comprising step b-2 of selecting the concentration of the transition metal oxide selected in step b by measuring the change in viscosity of the carbon dioxide absorbing liquid according to the concentration of the transition metal oxide selected in step b. Manufacturing method. As a carbon dioxide absorbent, an amino acid, an amine group and a carboxyl group-containing amino acid mimetic or an alkali metal salt thereof providing an amine group (-NH ₂ ) that can chemically absorb carbon dioxide in an aqueous solution and can be regenerated by heating; And
As a carbon dioxide absorption catalyst, it contains a transition metal that is not coordinated with a carbon dioxide absorbent and contains a transition metal oxide that provides an acid point,
The transition metal comprises at least one selected from the group consisting of Cu, Fe, Ni, Mn, carbon dioxide absorption composition. The composition for absorbing carbon dioxide according to claim 6, further comprising an alkali metal hydroxide (MOH) capable of activating -NH ₃ ⁺ of an amino acid or amino acid mimic with -NH ₂ in an aqueous solution. The composition for absorbing carbon dioxide according to claim 6, wherein the amino acid or amino acid mimetic has two or more amine groups. The composition for absorbing carbon dioxide according to claim 6, wherein the carbon dioxide absorbing composition contains lysine or an alkyl lithium metal salt thereof as a carbon dioxide absorbent and CuO as a carbon dioxide absorbing catalyst. According to claim 6, 0.5 to 2M carbon dioxide absorbent; And an aqueous solution containing a carbon dioxide absorption catalyst of 0.05 to 0.5M. The composition for absorbing carbon dioxide according to claim 6, which is a strong basic aqueous solution having a pH of 10 or more. In the method of removing carbon dioxide from a carbon dioxide-containing gas through gas-liquid contact with a carbon dioxide absorbing liquid,
An amino acid that can chemically absorb carbon dioxide and provides an amine group (-NH ₂ ) that can be regenerated by heating, an amino acid mimetic containing an amine group and a carboxyl group, or an alkali metal salt thereof; And a first step of preparing a water-based carbon dioxide absorbing liquid containing a transition metal oxide that provides an acid point and contains a transition metal that is not coordinated therewith. And
A second step of removing carbon dioxide from the carbon dioxide-containing gas through gas-liquid contact with the carbon dioxide absorbing liquid of the first step,
The transition metal includes at least one selected from the group consisting of Cu, Fe, Ni, and Mn. The method of claim 12, further comprising a third step of regenerating the carbon dioxide absorbing liquid by removing carbon dioxide through heating from the carbon dioxide absorbing liquid absorbing carbon dioxide through chemical absorption in the second step, and regenerating the carbon dioxide absorbing liquid in the second step. Carbon dioxide removal method characterized by reuse. The method of claim 12, wherein the first step is performed by the method according to any one of claims 1 to 5. The carbon dioxide removal method according to claim 12, wherein the carbon dioxide absorbing liquid in the first step is the composition for absorbing carbon dioxide according to any one of claims 6 to 11.

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