KR100554656B1 - Method for the removal of carbon dioxide from gas mixture - Google Patents

Abstract

The present invention is to provide a tertiary amine-based absorbent among alkanolamines used to absorb acid gases such as carbon dioxide (CO ₂ ), H ₂ S and the like.

In the present invention, an aqueous amine solution used to absorb acid gas, especially carbon dioxide, is triisopropanolamine (TIPA), and monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), which is a conventional commercial absorbent. And N-methyldiethanolamine (MDEA).

Absorbent of the present invention exhibits a higher or similar absorption capacity than the existing amine absorbent at a temperature near room temperature, and has the effect of absorbing carbon dioxide at an appropriate level of absorption rate in the mixed gas.

Description

Method for the removal of carbon dioxide from gas mixture

1 is a schematic diagram of a device for measuring carbon dioxide absorption rate using a wet wall tube.

Figure 2 is a graph showing the absorption capacity of the absorbent with respect to carbon dioxide according to the pressure change.

Explanation of symbols on main parts of drawing

1 gas inlet 2 mass flow regulator

3: water vapor saturation device 4: tubular wet wall tower

5 gas flow meter 6 gas outlet

7: absorbent inlet 8: pump

9: absorbent outlet 10: air thermostat

The present invention relates to a method for separating carbon dioxide from a mixed gas, and in particular, an aqueous amine solution used to absorb carbon dioxide is triisopropanolamine (TIPA), and has an absorption capacity higher or similar to that of a conventional amine absorbent at a temperature near room temperature. In addition, the present invention relates to a method for separating carbon dioxide from a mixed gas by using a tertiary amine-based absorbent of alkanolamine which can absorb carbon dioxide in a mixed gas at an appropriate level of absorption rate.

Since the early 19th century, when industrialization began, the concentration of acid gases such as carbon dioxide (CO ₂ ), CH ₄ , H ₂ S, and COS increased rapidly in the mid-20th century. As global warming is accelerating due to this increase in acid gas, regulations on emissions and treatments are becoming more stringent.

The United Nations Conference on Environment and Development in Rio, Brazil, in June 1992, has led to increasing international interest in global warming, and developed countries, including the United States and Japan, have reduced global greenhouse gas emissions by 5.2% in 2010 compared to 1990. International agreements on reducing acid gas have been made.

In particular, the separation of carbon dioxide, which accounts for about 50% of the acid gases causing global warming, has become a more important problem. Therefore, there is an urgent need for advance technology development.

Techniques for suppressing the increase in acid gas include energy-saving technology for reducing emissions, separation and recovery of released acid gas, technology for using or immobilizing acid gas, and alternative energy technologies that do not emit acid gas. .

As the acid gas separation technology studied so far, absorption method, adsorption method, membrane separation method, deep cooling method, etc. have been proposed as a realistic alternative. In particular, the absorption method is easy to process a large amount of gas and is suitable for low concentration gas separation, so it is easy to be applied to most industries and power plants, and the monoethanolamine (MEA) manufactured by ABB Iummus Crest is used as an absorbent. The process is operating in Trona (CA, USA) and Shady Point (Oklahoma, USA).

However, the above absorption process using MEA consumes a large amount of energy for acid gas separation, a large amount of absorbent is used, and there is a problem of corrosion of the separation facility by the absorbent. Therefore, development of new additives and absorbents to solve this problem is difficult. There is an urgent need.

Many researchers have studied how to separate and recover acid gases such as carbon dioxide (CO ₂ ), H ₂ S, and COS from mixed gases emitted from smelting and thermal power plants using chemical reactions with aqueous alkanolamine solutions. come.

Alkanolamines widely used in the past include primary, secondary and tertiary series of MEA, diethanolamine (DEA), triethanolamine (TEA), and N-methyldiethanolamine (MDEA). In particular, although MEA and DEA have been used a lot because of the advantages of having a high reaction rate, it is known that there are many difficulties due to problems such as high corrosiveness, high renewable energy and deterioration. In addition, MDEA has a low absorption rate while low corrosion and regeneration heat. Therefore, the development of new absorbents is urgently required.

The development and research of additives to improve the reaction rate of the absorbent is being actively conducted. The method is divided into a method of mixing two absorbents and a method of using a surfactant and a catalyst as a reaction rate improving additive. MEA with high reaction rate but low absorption capacity and absorbent such as MDEA and 2-amine-2-methyl-1-propanol (AMP) with low reaction rate but high absorption capacity are used in the middle of two characteristics. Complementary effect The method of using additives utilizes the properties of the existing aqueous amine solution with a large absorption capacity and the rapid reaction characteristics of the additive.

These studies improve the reaction characteristics by using additives that increase the reaction rate to the basic absorption of tertiary amines and stericly hindered amines with high absorption capacity. In other words, the development of amines with high absorption capacity occupies a very important position with the development of additives to improve the reaction rate.

 Primary and secondary amines generally follow the following mechanism,

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

For tertiary amines such as MDEA and steric hindered amines

_{CO 2 + RNH 2 + H 2} O → RNH 3 + + HCO 3 -

Therefore, theoretically, two amines are required to absorb one carbon dioxide for primary and secondary amines, whereas two and three amine absorption capacity is required for tertiary and steric amines because carbon dioxide and amines react 1: 1. Can be seen.

The gas selectivity of these tertiary amines is a very important requirement in today's stringent environmental regulations, and the regeneration characteristics reduce the energy savings and the total operating costs of the acid gas treatment process. The reaction rate is generally lower than that of the primary and secondary amines such as MEA and DEA, but the absorption capacity is high.

An example of absorbing acid gas using an aqueous absorbing solution is as follows.

US Pat. No. 4,405,581 describes tritertarybutylaminoethanol, 2- (tertarybutylamino) -1-propanol, 2- (isopropylamino) -1-propanol, and the like. A method of selectively absorbing H ₂ S and carbon dioxide in a mixed gas using large steric amines of butylaminoethoxy) -ethane (BTEE) and ethoxyethoxyethanol-tertiarybutylamine (EEETB) , U.S. Patent No. 4,112,051, mentions the removal of carbon dioxide in acid gas using absorbents such as the steric hindered amine family 2-piperadinmethanol, 2-piperadinethanol and 2-amino-2-methyl-1-butanol Doing.

In addition, US Pat. No. 6,051,161 describes 2-aminopropionamide, 2-amino-2-methylpropionamide, 2-amino-2-methyl-N-methylpropionamide, and the like. Amine aqueous solutions of amide, 2-dimethylamino-N, N-dimethylacetamide and 2- (t-butylamino) acetamide are described in US Pat. Nos. 6,280,503 and 5,390,667, such as magnesium oxide, magnesium hydroxide or magnesium hydroxide. A method of absorbing carbon dioxide using a magnesium compound is proposed.

However, the prior arts have the disadvantage that the absorption capacity can be increased when the amine with high steric hindrance for absorption of acid gas is high, but the absorption rate is very low. There is a problem that must be done.

The present invention is to solve the problems of the prior art, absorbing the carbon dioxide in an appropriate level in the mixed gas by using an absorbent showing an absorption capacity and absorption rate higher or similar to the amine absorbent such as MDEA at a temperature near room temperature The purpose is to provide a way to do it.

In the method for separating carbon dioxide from the mixed gas, the carbon dioxide is contacted with an aqueous amine solution containing a tertiary amine-based absorbent in the alkanolamine in the absorption tower.

In the present invention, the tertiary amine-based absorbent is selected to use triisopropanolamine (TIPA), the aqueous amine solution further contains 30% by weight or more of water.

The concentration of the tertiary amine is 5 to 70% by weight, preferably 10 to 40% by weight, the temperature of the absorption tower in the absorption step for separating carbon dioxide from the mixed gas is 20 to 60 ℃, preferably Is 30 to 50 ° C., and the pressure of carbon dioxide is preferably set to 0.05 to 30 atmospheres, preferably 0.1 to 10 atmospheres.

Figure 1 of the accompanying drawings schematically shows a device for measuring the carbon dioxide absorption rate using a wet wall tube used in the present invention.

In the device of Figure 1, reference numeral 1 is a gas inlet, 2 is a mass flow regulator, 3 is a water vapor saturator, 4 is a tubular wet wall column, 5 is a gas flow meter, 6 is a gas outlet, 7 is an absorbent inlet, 8 is a pump, 9 represents an absorbent outlet and 10 represents an air thermostat.

First, the mixed gas flowing through the gas inlet 1 passes through the mass flow regulator 2, and then comes into contact with water in the steam saturation device 3 and is then sent to the tubular wet wall tower 4. In the tubular wet wall tower 5 the mixed gas flows upward, and the absorbents having a constant concentration introduced by the operation of the pump 8 of the absorbent inlet 7 are sprayed downwards so that they come into contact with each other at the central part. In this process, the carbon dioxide of the mixed gas is removed while absorbed by the absorbent. The absorbent absorbing carbon dioxide is collected in the lower part of the wall column 4 and discharged to the outside through the absorbent outlet 9. If necessary, the absorbent absorbing carbon dioxide can be reused after removing carbon dioxide by heating. The mixed gas from which carbon dioxide has been removed is discharged through the gas flow meter 5 and the gas outlet 6 positioned above the wall tower 4. Since the tubular wet wall tower 4 is surrounded by an air thermostat having a constant temperature as shown in FIG. 1, it is possible to maintain a constant temperature when removing carbon dioxide from the mixed gas.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

A amine aqueous solution of 30 wt% TIPA was prepared as an absorbent by mixing TIPA and tertiary distilled water having a purity of 98% or more. This aqueous amine solution was used for contact with a mixed gas in an absorption tower at 60 ° C. to measure the absorption ability for carbon dioxide.

The number of moles of carbon dioxide absorbed per mole of amine was measured and compared at various pressures.

The equilibrium cell used for the measurement of absorbency was manufactured by injecting about 250 ml of absorbent into 316 stainless steel. A magnetic bar was placed inside the cell and rotated so that the phase equilibrium reached quickly between the absorbent and carbon dioxide.

The pressure gauge to measure the pressure inside the cell used a HEISE pressure gauge having an accuracy of ± 0.1% and a pressure measuring range of 0 to 750 psi. The temperature inside the cell was measured with a K-type thermocouple with an accuracy of ± 0.1 ° C. In the absorption equilibrium experiment where the partial pressure of carbon dioxide was lower than atmospheric pressure, nitrogen was used to control the pressure. The temperature of the water in the thermostat was controlled using a Zeotech RBC-20 cold circulation tank.

Hewlett-Packard, 5890 Series gas chromatography was used for the analysis of gas phase components. The gas chromatograph sensor is a thermal conductivity (TCD) sensor, and the separation column is PORAPAKQ mesh.

Comparative Example 1

Example 1 was the same as in Example 1 except that the absorbent of the aqueous amine solution was prepared using MEA instead of TIPA.

The results are shown in FIG.

Comparative Example 2

Except for using the AMP instead of TIPA in Example 1 to prepare an absorbent of the aqueous amine solution was the same as in Example 1.

The results are shown in FIG.

Comparative Example 3

Example 1 was the same as in Example 1 except for preparing the absorbent of the aqueous amine solution using MDEA instead of TIPA.

The results are shown in FIG.

According to Figure 2, when compared to the conventional commercial absorbent MEA shown in Comparative Example 1 of the TIPA aqueous solution according to Example 1 of the present invention at the same temperature, pressure and composition conditions, the carbon dioxide absorption capacity of about 144% or more at atmospheric pressure or more It showed a good absorption capacity of 118% or more than the AMP and MDEA of Comparative Examples 2 and 3.

Example 2

The absorption rate of carbon dioxide in a TIPA aqueous solution of 1, 1.5, 2, 2.5 kmol / m 3 at a temperature of 30 ° C. was measured under atmospheric pressure. The molar flow rate of carbon dioxide absorbed according to the concentration of the amine aqueous solution was converted to the gas-liquid contact time and the absorption rate (kmol / m 3 · sec) divided by the surface area.

Comparative Example 4

Example 2 was carried out in the same manner as in Example 2, except that the absorption rate of carbon dioxide was measured using MDEA, a commercial absorbent of a tertiary amine instead of TIPA. The results are shown in Table 1 below.

Concentration of absorbent (kmol / ㎥) Absorption rate × 10 ⁶ (kmol / ㎥ ∙ sec) Comparative Example 4 Example 2 One 2.08 6.87 1.5 3.71 7.92 2 3.82 8.19 2.5 3.97 8.52

According to Table 1, the absorption rate of carbon dioxide of the aqueous TIPA solution of Example 1 showed more than three times better absorption rate in all concentration ranges than MDEA of Comparative Example 4.

Example 3

The absorption rate of carbon dioxide in the mixed gas for 1 kmol / m 3 of TIPA aqueous solution at a temperature of 30 ° C. was measured under partial pressure of different carbon dioxides by adjusting the amount of nitrogen. Table 2 shows the results of converting the molar flow rate of carbon dioxide absorbed into gas-liquid contact time and surface absorption rate (kmol / m 3 · sec).

Comparative Example 5

Except for measuring the absorption rate (kmol / m 3 · sec) of carbon dioxide using a commercial absorbent AMP instead of TIPA in Example 3 was carried out in the same manner as in Example 3. The results are shown in Table 2 below.

CO2 partial pressure (kPa) Absorption rate × 10 ⁶ (kmol / ㎥ ∙ sec) Comparative Example 5 Example 3 5 1.56 0.33 7 2.15 0.47 10 3.09 0.72 15 4.62 1.12

According to Table 2, although the carbon dioxide absorption rate of the TIPA aqueous solution of Example 3 of the present invention is lower than the AMP of Comparative Example 5, as a result it can be seen that the TIPA aqueous solution can also absorb it at a low carbon dioxide partial pressure in the mixed gas. .

The absorbent of the present invention exhibits a higher or similar absorption capacity than the existing amine absorbent at a temperature near room temperature, and has an effect of absorbing carbon dioxide at an appropriate level of absorption rate even in a mixed gas.

Accordingly, the absorbent of the present invention can be used in place of the conventional commercially available absorbent monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP) and N-methyldiethanolamine (MDEA).

Claims (7)

In the method for separating carbon dioxide from the mixed gas, The method of separating the carbon dioxide in the mixed gas, characterized in that the carbon dioxide is contacted with an aqueous amine solution containing a tertiary amine-based absorbent of alkanolamine in the absorption tower. The method of claim 1, wherein the tertiary amine-based absorbent is selected from triisopropanolamine (TIPA) and used. The method of claim 1 or 2, wherein the aqueous amine solution further contains 30% by weight or more of water. The method according to claim 1 or 2, wherein the concentration of the tertiary amine is 5 to 70% by weight. The method of claim 4, wherein the concentration of the tertiary amine is 10 to 40% by weight. The method of claim 1, wherein the temperature of the absorption tower in the absorption step for separating the carbon dioxide from the mixed gas to set the temperature of the carbon dioxide in the mixed gas, characterized in that the pressure of the carbon dioxide is set to 0.05 to 30 atm. Way. The method of claim 6, wherein the temperature of the absorption tower in the absorption step for separating the carbon dioxide from the mixed gas is set to 30 to 50 ℃, the pressure of the carbon dioxide is set to 0.1 to 10 atm to separate the carbon dioxide from the mixed gas Way.

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