JP2009006275A - Efficient recovering method of carbon dioxide in exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovering method of carbon dioxide of high purity, not only highly efficiently recovering carbon dioxide in gas, but also highly efficiently eliminating carbon dioxide from an aqueous solution having absorbed carbon dioxide. <P>SOLUTION: The recovering method of carbon dioxide from gas containing carbon dioxide comprises (1) a process of absorbing carbon dioxide into an aqueous solution by bringing gas containing carbon dioxide into contact with the aqueous solution containing only isopropyl aminoethanol as an effective component (content of isopropyl aminoethanol in the aqueous solution is 35-50 wt.%), and (2) a process of eliminating and recovering carbon dioxide by heating the aqueous solution having absorbed carbon dioxide obtained in the process (1). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention absorbs carbon dioxide (CO ₂ ) contained in a gas by using an aqueous solution for carbon dioxide recovery, and subsequently recovers by desorbing carbon dioxide from the aqueous solution for carbon dioxide recovery in which carbon dioxide has been absorbed. Regarding the method.

  In recent years, frequent weather fluctuations and disasters that are thought to be caused by global warming have greatly affected agricultural production, living environment, energy consumption, and the like. This global warming is considered to be due to an increase in the atmosphere of greenhouse gases such as carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons, which increase as human activities become active. The most important greenhouse gas is carbon dioxide in the atmosphere. To prevent global warming, the Kyoto Conference on Global Warming Prevention (COP3) was held in December 1997, and the Kyoto Protocol adopted at that conference entered into force on February 16, 2005, reducing CO2 emissions. There is an urgent need to take measures toward this.

  Sources of carbon dioxide include coal, heavy oil, natural gas and other thermal power plants, factory boilers or kilns in cement plants, blast furnace blast furnaces that reduce iron oxide with coke, gasoline, heavy oil, There are transportation equipment such as automobiles, ships, and aircraft that use light oil as fuel. Of these, those other than transportation equipment are fixed facilities, and are expected to be easy to implement measures to reduce carbon dioxide emissions.

  Several methods have been known so far for recovering carbon dioxide in gas. And now, various methods are widely studied.

  For example, after a gas containing carbon dioxide is brought into contact with an alkanolamine aqueous solution in an absorption tower to absorb carbon dioxide, the carbon dioxide recovery aqueous solution is heated to desorb and recover carbon dioxide in the desorption tower. Developed since the 1930s and put into practical use in urea synthesis plant towers. This method is economical and easy to enlarge.

  Here, examples of the alkanolamine include monoethanolamine (hereinafter sometimes referred to as MEA), diethanolamine (hereinafter sometimes referred to as DEA), triethanolamine (hereinafter sometimes referred to as TEA), methyldiethanolamine ( Hereinafter, it may be indicated as MDEA), diisopropanolamine (DIPA), diglycolamine (DGA), etc., but MEA is usually used.

However, when an aqueous solution of these alkanolamines is used as the absorbing solution, the material of the device is highly corrosive, so it is necessary to use expensive corrosion-resistant steel for the device or to reduce the concentration of amine in the absorbing solution. . Further, since the absorbed carbon dioxide is difficult to desorb, it is necessary to desorb and recover by heating the desorption temperature to a high temperature of 120 ° C. In addition, the energy required for desorbing carbon dioxide from the absorbing solution is also high at ₂₀ cal / mol CO ₂ . For example, in order to collect carbon dioxide at a power plant using this method, extra energy equivalent to 20% of the power generation amount is required. In an era where reduction of carbon dioxide generation, energy saving and resource saving are required, this high energy consumption is a major factor that impedes the practical use of carbon dioxide absorption and recovery equipment.

  For example, in Patent Document 1, a so-called hindered amine aqueous solution having a steric hindrance such as an alkyl group around an amino group is brought into contact with combustion exhaust gas under atmospheric pressure, and carbon dioxide is absorbed in the aqueous solution. A method for removing carbon dioxide is described.

  Patent Document 1 describes examples of 2-methylaminoethanol (hereinafter also referred to as MAE) and 2-ethylaminoethanol (hereinafter also referred to as EAE) as hindered amines. MAE and EAE Is described as being preferred for carbon dioxide absorption.

  Patent Document 2 describes a carbon dioxide removal method including a step of bringing an aqueous amine solution into contact with a mixed gas to absorb carbon dioxide and a step of desorbing carbon dioxide from the aqueous solution.

  Patent Document 2 discloses a compound containing a secondary amino group bonded to a secondary or tertiary carbon or a primary amine bonded to a tertiary carbon, for example, 2-methylpiperazine (hereinafter referred to as 2MPZ) as an aqueous amine solution. 2), 2-amino-2-methyl-1-propanol (hereinafter sometimes referred to as AMP), and the like.

  In Patent Document 3, (A) the molecule has one alcoholic hydroxyl group and a primary amino group, and the primary amino group is a tertiary carbon atom having two unsubstituted alkyl groups. 100 parts by weight of an amine compound selected from the group consisting of a compound that is bound and (C) diethanolamine: and (D) piperazine, (E) piperidine, (F) morpholine, (G) glycine, (H) 2 -Piperidinoethanol and (I) a group having one alcoholic hydroxyl group and a secondary amino group in the molecule, wherein the second amino group is a group having a chain of 2 or more carbon atoms including a bonding carbon atom. Contacting a mixed aqueous solution of 1 to 25 parts by weight of an amine compound selected from the group consisting of a compound having a bonded N atom and an unsubstituted alkyl group having 3 or less carbon atoms with combustion exhaust gas at atmospheric pressure. Features and Method of removing carbon dioxide in combustion exhaust gas is described that. Patent Document 3 describes that ethylaminoethanol and 2-methylaminoethanol are preferable as the amine compound represented by (I).

  In Patent Document 4, a combustion exhaust gas under atmospheric pressure is brought into contact with an amine mixed aqueous solution in which each concentration of secondary amine and tertiary amine is in the range of 10 to 45% by weight, and the CO 2 in the combustion exhaust gas is contacted. A method for removing carbon is described. As a reference example, there is also shown an experimental example of 2-isopropylaminoethanol (hereinafter sometimes referred to as IPAE) and other 30% liquid.

  The carbon dioxide recovery method comprises the removal of carbon dioxide from the combustion exhaust gas, that is, the absorption process of carbon dioxide into the aqueous solution, and the desorption process of carbon dioxide from the aqueous solution that has absorbed carbon dioxide. In order to recover carbon, not only the absorption process is performed with high efficiency, but also the desorption process needs to be performed with high efficiency.

  As described above, in the past, many attempts have been made to improve the efficiency of the process of absorbing carbon dioxide into an aqueous solution, but the efficiency of desorption of carbon dioxide has not been studied or has been studied. There was only a method with an insufficient amount and rate of desorption. Therefore, the conventional carbon dioxide recovery method has a problem that the balance between absorption and desorption of carbon dioxide is poor and the efficiency of carbon dioxide recovery is poor.

In addition, it is a big problem to reduce the heat of reaction for carbon dioxide absorption, in other words, the heat required for carbon dioxide desorption.
Japanese Patent No. 2871334 US Pat. No. 4,112,052 Japanese Patent No. 2871335 Patent 3197183

  In view of the above problems of the prior art, the present invention not only absorbs carbon dioxide in a gas with high efficiency, but also efficiently desorbs carbon dioxide from an aqueous solution that has absorbed carbon dioxide. It aims at providing the method of collect | recovering high purity carbon dioxide with energy consumption. Specifically, carbon dioxide is efficiently absorbed using an aqueous solution for carbon dioxide recovery that has a large amount of carbon dioxide absorption and carbon dioxide desorption per unit and low energy required for carbon dioxide desorption. It is another object of the present invention to provide a method for recovering high purity carbon dioxide by desorption.

  In addition to absorption of carbon dioxide into an aqueous solution containing alkanolamine, the present inventors have also intensively studied the elimination of carbon dioxide from an aqueous amine solution that has absorbed carbon dioxide. As a result, when using an aqueous solution containing 35 to 50% by weight of isopropylaminoethanol (hereinafter sometimes referred to as IPAE) among various alkanolamines, not only shows high carbon dioxide absorption and absorption rate. The present inventors have found that carbon dioxide can be recovered with extremely high efficiency by remarkably showing a high carbon dioxide desorption amount and desorption rate. As a result of further research based on this knowledge, the present invention has been completed.

  That is, the present invention provides a novel method for efficiently recovering the following carbon dioxide.

Item 1. A method for recovering carbon dioxide from a gas containing carbon dioxide,
(1) As an active ingredient, the formula [I]:

A step of bringing a gas containing carbon dioxide into contact with an aqueous solution containing only isopropylaminoethanol represented by formula (2), and absorbing the carbon dioxide into the aqueous solution; and (2) carbon dioxide obtained in the step (1) is absorbed. Heating the aqueous solution to desorb and recover carbon dioxide,
A method for recovering carbon dioxide containing
The content of isopropylaminoethanol in the aqueous solution is 35 to 50% by weight,
Carbon dioxide recovery method.

  Item 2. In the step (1), a gas containing carbon dioxide is brought into contact with the aqueous solution at a temperature of 60 ° C. or lower, and the aqueous solution in which carbon dioxide is absorbed in the step (2) is heated at a temperature of 70 ° C. or higher to produce carbon dioxide. Item 2. The carbon dioxide recovery method according to Item 1, wherein carbon is desorbed.

  The method for separating and recovering carbon dioxide using the carbon dioxide absorbing liquid of the present invention not only has a high carbon dioxide absorption rate, but also easily desorbs absorbed carbon dioxide as compared with known aqueous solutions for carbon dioxide recovery. Thus, an extremely high carbon dioxide recovery amount per cycle of the absorption / desorption process can be obtained. Further, the heat of reaction for absorption of carbon dioxide is low, and carbon dioxide in the gas can be absorbed and desorbed with an efficient and low energy consumption, so that high purity carbon dioxide can be recovered. As a result, the carbon dioxide absorption tower, the carbon dioxide desorption tower, and the devices associated therewith can be miniaturized, the amount of liquid circulation can be reduced, energy loss can be reduced, and construction costs can be reduced.

  In addition, alkanolamines such as monoethanolamine used for carbon dioxide absorption are generally highly corrosive to metal materials such as carbon steel, but the aqueous solution of the mixed amine used in the present invention is also significantly reduced in corrosivity. However, it is advantageous in that it is not necessary to use expensive high-grade corrosion resistant steel in plant construction.

The present invention is described in detail below.
The method of the present invention comprises:
(1) As an active ingredient, the formula [I]:

A step of bringing a gas containing carbon dioxide into contact with an aqueous solution containing only isopropylaminoethanol represented by (hereinafter also referred to as an aqueous solution for carbon dioxide recovery), and allowing the aqueous solution to absorb carbon dioxide, and (2 ) Heating the aqueous solution in which the carbon dioxide obtained in the above step (1) is absorbed, and desorbing and collecting the carbon dioxide;
And the content of isopropylaminoethanol in the aqueous solution is 35 to 50% by weight.

Carbon dioxide recovery aqueous solution The concentration of isopropylaminoethanol in the carbon dioxide recovery aqueous solution in the present invention is 35 to 50% by weight, preferably 37 to 48% by weight, and more preferably 38 to 45% by weight.

  In general, the higher the concentration of the amine component, the greater the amount of carbon dioxide absorbed, the absorption rate, the desorption amount, and the desorption rate per unit liquid volume, which are desirable from the viewpoint of energy consumption and the size and efficiency of plant equipment. Is too high, water may not sufficiently function as an activator for absorbing carbon dioxide, and causes problems such as an increase in viscosity. However, when the isopropylaminoethanol concentration of the present application is 35 to 50% by weight, There is no significant performance degradation.

  When the aqueous solution containing isopropylaminoethanol in the above concentration range is used as an aqueous solution for carbon dioxide recovery, not only the carbon dioxide absorption amount and carbon dioxide absorption rate, but also the carbon dioxide desorption amount and carbon dioxide desorption rate are high. This is advantageous for efficient carbon dioxide recovery.

  In addition, anticorrosives such as phosphoric acid are used in the aqueous solution to prevent corrosion of equipment, antifoaming agents such as silicone are used to prevent foaming, and antioxidants are used to prevent deterioration of the absorbent. A small amount may be added.

  Conventionally, alkanolamines such as MEA used for carbon dioxide absorption are generally highly corrosive to metal materials such as carbon steel, but the mixed amine aqueous solution used in the present invention is also extremely corrosive. This is advantageous in that it is not necessary to use expensive high-grade corrosion-resistant steel in plant construction.

Carbon dioxide absorption step As described above, the method of the present invention includes the step of bringing a carbon dioxide-containing gas into contact with an aqueous solution for carbon dioxide recovery and causing the aqueous solution to absorb carbon dioxide.

  There is no particular limitation on the method of bringing the gas containing carbon dioxide into contact with the aqueous solution containing isopropylaminoethanol. For example, a method of bubbling and absorbing a gas containing carbon dioxide in the aqueous solution, a method of dropping the aqueous solution into a gas stream containing carbon dioxide (a spraying or spraying method), or a magnetic or metal mesh This is performed by a method in which a gas containing carbon dioxide and the aqueous solution are brought into countercurrent contact in an absorption tower containing a filler.

In general, carbon dioxide absorbed by an organic amine aqueous solution is considered to form carbamate anions and bicarbonate ions in the aqueous solution, but according to the inventors' ¹³ C-NMR measurement, 2-aminoethanol, which is a typical primary alkanolamine, has a large amount of carbamate anions that exhibit a high heat of absorption reaction, and produces less bicarbonate ions that exhibit a low heat of reaction. Even in the secondary alkanolamine, 2-ethylaminoethanol (EAE) has a large amount of carbamate anion that exhibits a high heat of absorption reaction like MEA, and produces less bicarbonate ion that exhibits a low heat of reaction. On the other hand, in the isopropylaminoethanol of the present invention, it was found that the carbamate anion exhibiting a high absorption reaction heat is trace, and that most of the bicarbonate ion exhibiting a low absorption reaction heat is generated. Even in the same secondary alkanolamine, isopropylaminoethanol has an alkyl group that is a methyl group or an ethyl group (hereinafter also referred to as MAE) and 2-ethylaminoethanol (hereinafter also referred to as EAE). Was found to behave quite differently. The reason why isopropylaminoethanol is remarkably excellent in carbon dioxide desorption is considered to be due to such a reason.

  The liquid temperature when the gas containing carbon dioxide is absorbed in the aqueous solution is usually from room temperature to 60 ° C. or less, preferably 50 ° C. or less, more preferably about 20 to 45 ° C. The amount of absorption increases as the temperature decreases, but the extent to which the temperature is lowered is determined by the gas temperature in the process, the heat recovery target, and the like. The pressure during carbon dioxide absorption is usually about atmospheric pressure. Although it is possible to pressurize to a higher pressure in order to enhance the absorption performance, it is preferable to carry out under atmospheric pressure in order to suppress energy consumption required for compression.

  In the method of the present invention, the saturated carbon dioxide absorption at the time of carbon dioxide absorption (40 ° C.) of an aqueous solution containing 35 to 50% by weight of isopropylaminoethanol is about 100 to 140 g / L, particularly about 110 to 130 g / L. The carbon dioxide absorption rate at the time of absorbing 3/4 of the saturated absorption amount is about 1.5 to 4.0 g / L / min, particularly about 2.0 to 3.0 g / L / min.

  Here, the saturated carbon dioxide absorption is a value obtained by measuring the amount of inorganic carbon in the aqueous solution with a gas chromatographic total organic carbon meter, and the carbon dioxide absorption rate is 3/4 of the saturated absorption. It is a value measured using an infrared carbon dioxide meter when carbon is absorbed.

  Further, the aqueous solution used in the present invention has a feature that the reaction heat of carbon dioxide absorption is small. Since the reaction heat for carbon dioxide absorption corresponds to the heat required for desorption of carbon dioxide, the energy consumption necessary for desorbing carbon dioxide can be kept low.

Carbon dioxide desorption step The method of the present invention includes a step of heating and recovering the carbon dioxide by heating the aqueous solution obtained by the carbon dioxide absorption step.

  As a method of desorbing carbon dioxide from an aqueous solution that has absorbed carbon dioxide and recovering pure or high-concentration carbon dioxide, a method of heating the aqueous solution and defoaming with a kettle as in distillation, a plate tower, a spray Examples include a method of heating by expanding the liquid interface in a tower, a desorption tower containing a magnetic or metal mesh filler. Thereby, carbon dioxide is liberated and released from the carbamate anion and bicarbonate ion.

  The liquid temperature at the time of desorption of carbon dioxide is usually 70 ° C. or higher, preferably 80 ° C. or higher, more preferably about 90 to 120 ° C. The higher the temperature, the greater the amount of absorption, but the higher the temperature, the greater the energy required to heat the absorbent, so the temperature is determined by the process gas temperature, heat recovery target, etc. The pressure during carbon dioxide desorption is usually about atmospheric pressure. Although the pressure can be reduced to a lower pressure in order to enhance the desorption performance, it is preferably performed under atmospheric pressure in order to suppress energy consumption required for the pressure reduction.

  The amount of carbon dioxide desorbed at the time of carbon dioxide desorption (70 ° C.) of an aqueous solution containing 35 to 50% by weight of isopropylaminoethanol of the present invention is about 35.0 to 60.0 g / L, particularly 40.0 to 55. The average carbon dioxide desorption rate from the start of temperature increase to 10 minutes is about 1.5 to 3.5 g / L / minute, particularly about 2.0 to 3.0 g / L / minute. .

  The carbon dioxide desorption amount is a value measured with a total organic carbon meter, and the carbon dioxide desorption rate is a value measured with an infrared carbon dioxide meter. When the amine component concentration is 20% by weight or more, the carbon dioxide desorption amount and the average carbon dioxide desorption rate are substantially proportional to the concentration.

  Thus, even when the temperature during carbon dioxide desorption is relatively low at 70 ° C., a good carbon dioxide desorption amount and carbon dioxide desorption rate can be achieved from the aqueous amine solution. Of course, when the temperature at the time of carbon dioxide desorption exceeds 70 ° C., for example, as the temperature increases to 80 ° C., 90 ° C., 100 ° C., 110 ° C., 120 ° C., the carbon dioxide desorption amount and the carbon dioxide desorption rate further increase. improves.

  The aqueous solution from which carbon dioxide has been desorbed is sent again to the carbon dioxide absorption step and recycled (recycled). In addition, the heat generated during carbon dioxide absorption is generally cooled by heat exchange in a heat exchanger in order to preheat the aqueous solution injected into the desorption tower in the aqueous solution recycling process.

  The purity of the carbon dioxide recovered in this manner is usually as high as about 95 to 99% by volume. This pure carbon dioxide or high-concentration carbon dioxide is used as a chemical, a synthetic raw material for a polymer substance, a cooling agent for freezing foods, or the like. In addition, it is possible to sequester and store the recovered carbon dioxide in the underground, where technology is currently being developed.

  The carbon dioxide desorption performance is the carbon dioxide absorption conditions assumed in an actual plant, for example, a temperature of 40 ° C., a carbon dioxide partial pressure of 20 kPa and a carbon dioxide desorption condition, for example, a temperature of 120 ° C. and a carbon dioxide partial pressure of 100 kPa. This is manifested by comparing carbon concentration (loading) differences with vapor-liquid equilibrium test data.

  Next, although an Example, a comparative example, and a reference example are demonstrated in detail about this invention, this invention is not limited to this Example. In the present specification, unless otherwise specified, “%” means “% by weight”.

Example 1
A glass gas cleaning bottle was immersed in a constant temperature water bath set so that the temperature of the liquid was 40 ° C., and this was filled with 50 ml of an aqueous solution containing 35% by weight of isopropylaminoethanol. In this liquid, a mixed gas containing 20% by volume of carbon dioxide and 80% by volume of N ₂ is dispersed in the form of foam through a glass filter having a coarseness of 100 μm and a diameter of 13 mm at atmospheric pressure and 0.7 liter / min. Absorbed.

  The carbon dioxide concentration in the gas before the absorbing liquid and in the gas at the outlet of the absorbing liquid was continuously measured with an infrared carbon dioxide meter, and the amount of carbon dioxide absorbed was measured from the difference in the carbon dioxide flow rate at the inlet and outlet. If necessary, the amount of inorganic carbon in the absorbing solution was measured with a gas chromatographic total organic carbon meter and compared with a value calculated from an infrared carbon dioxide meter. The saturated absorption amount was the amount at the time when the carbon dioxide concentration at the outlet of the absorbing liquid coincided with the carbon dioxide concentration at the inlet. Since the absorption rate is almost equal to the carbon dioxide supply rate when 1/2 of the absorption amount is absorbed, it is compared with the absorption rate when 3/4 of the absorption amount is absorbed. It was. The absorption rate at the time of absorption of carbon dioxide saturated absorption 112.3 g / L and saturated absorption 3/4 was 2.64 g / L / min. The carbon dioxide absorption measured with a total organic carbon meter was 113 g / L, which agreed well with the value obtained by gas analysis.

  Subsequently, the liquid temperature was raised to 70 ° C. in several minutes in the same gas stream, and the amount of carbon dioxide desorbed from the liquid and the desorption rate were measured. The desorption rate used for comparison was the average desorption rate from the start of temperature increase to 10 minutes. The carbon dioxide desorption amount was 44.25 g / L and the desorption rate was 2.08 g / L / min.

Examples 2 and 3
As Examples 2 and 3, an aqueous solution containing isopropylaminoethanol with the composition shown in Table 1 was prepared, and using the same apparatus as in Example 1, under the same conditions, the saturated absorption amount of carbon dioxide, the same rate, and carbon dioxide desorption. The amount of separation and the same speed were measured. Table 1 also shows the saturated absorption amount of carbon dioxide at 40 ° C., the saturated absorption amount, the absorption rate at 3/4 absorption, and the carbon dioxide desorption amount at 70 ° C.

Comparative Examples 1-7
An aqueous solution containing IPAE, 2-methylpiperazine (2MPZ), 2-ethylaminoethanol (EAE), and dimethylaminoethanol (DMAE) at the concentrations shown in Table 2 under the same conditions using the same apparatus as in Example 1. The saturated absorption amount of carbon dioxide, the absorption rate, the carbon dioxide desorption amount, and the same rate were measured. The obtained results are shown in Table 2.

  As shown in Table 1 above, the methods of Examples 1 to 3 using an aqueous solution in which the concentration of IPAE is in the range of 35 to 50% by weight are the saturated absorption amount of carbon dioxide, carbon dioxide absorption rate, carbon dioxide desorption. Separation amount and carbon dioxide desorption rate were high, and carbon dioxide could be efficiently recovered.

  On the other hand, as shown in Table 2, the method of Comparative Example 1 using an aqueous solution having an IPAE concentration of 30% by weight is higher in saturated carbon dioxide absorption, carbon dioxide desorption than in Examples 1-3. Both the separation amount and the carbon dioxide desorption rate were low, and the efficiency of carbon dioxide recovery was poor.

  Further, the method of Comparative Example 2 using an aqueous solution having an IPAE concentration of 60% by weight, compared with the methods of Examples 1 to 3, was a saturated absorption amount of carbon dioxide, a carbon dioxide absorption rate, a carbon dioxide desorption amount, and All the carbon dioxide desorption rates were low, and the efficiency of carbon dioxide recovery was poor.

  As shown in Table 2, the aqueous solutions of Comparative Examples 3 to 5 containing 2MPZ, EAE or MDEA at 45% by weight as in Example 1 of the present application had particularly low carbon dioxide desorption amount and desorption rate.

  As is clear from these, the method of the present invention using an aqueous solution containing 35 to 50% by weight of IPAE is compared with a method using an aqueous solution having an IPAE concentration outside the above range, and an aqueous solution containing only amines other than IPAE. In particular, since the carbon dioxide desorption amount and desorption rate are excellent and the balance between absorption and desorption of carbon dioxide is good, carbon dioxide can be efficiently recovered.

Example 5
A stainless steel pressure-resistant vessel having a capacity of 1.5 liters equipped with a stirring blade was filled with 700 ml of an absorbing solution consisting of the same 45 wt% isopropylaminoethanol aqueous solution as in Example 3. By changing the pressure of the carbon dioxide-N ₂ mixed gas containing carbon dioxide to 0.1-0.6 atm in total pressure in this container, the carbon dioxide partial pressure is saturated between 0.003MP and 0.2MP. Absorption was measured. The container was heated by an electric heater wound around the outer wall of the container, and a gas-liquid equilibrium curve at 40 ° C. and a gas-liquid equilibrium curve at 120 ° C. were measured.

The result is shown in FIG. At 40 ° C., the carbon dioxide concentration (loading) in the equilibrium liquid is high at a wide carbon dioxide partial pressure (0.69 mol CO ₂ / mol amine at 20 kPa), while at 120 ° C., the carbon dioxide concentration in the equilibrium liquid is low at a wide carbon dioxide partial pressure. Carbon concentration (0.13 at 100 kPa molCO ₂ / mol amine), and the loading difference therebetween was 0.55 molCO ₂ / mol amine. It has become clear that efficient carbon dioxide recovery is possible by absorption at low temperature and desorption operation at high temperature.

Example 6
It consists of the same 45 weight% concentration isopropylaminoethanol aqueous solution as Example 3 using the differential thermal reaction calorimeter (SETARAM, DRC) which consists of the glass reaction tank of the same shape installed in the thermostat, and a reference tank. The heat of reaction of carbon dioxide absorption into the absorbing solution was measured. Each of the reaction tank and the reference tank is filled with 150 mL of the absorption liquid of Example 1, and constant temperature water at 40 ° C. is circulated through the jacket portion of the tank. In this state, 100% carbon dioxide was blown into the absorption liquid in the reaction tank at 200 ml / min, and the temperature rise of the liquid was continuously recorded with a temperature recorder until the carbon dioxide absorption was completed, and measured in advance. The reaction heat was calculated using the overall heat transfer coefficient between the reaction tank and the jacket water. As a result, the heat of reaction for carbon dioxide absorption was 15.8 kcal / mol-CO ₂ .

Reference example 1
It is a ¹³ C-NMR spectrum of an aqueous solution containing 30% by weight of isopropyl ethanol and carbon dioxide absorbed in this solution. Absorption of carbon dioxide was carried out under the same conditions as in Example 1, that is, the temperature of the liquid was 40 ° C., 50 ml of an aqueous solution containing 45% by weight of isopropylaminoethanol, 20 vol% carbon dioxide at atmospheric pressure and 0.7 liter / min, and A mixed gas containing 80% by volume of N ₂ was dispersed in the form of foam and distributed for 60 minutes. Absorption of carbon dioxide was _0.701mol-CO 2 / mol- amine. In the case of absorbing carbon dioxide, a peak of bicarbonate anion is seen at a shift value of 162.09 ppm, but a peak derived from carbamate anion is hardly seen.

Reference example 2
A ¹³ C-NMR spectrum of a 30% by weight aqueous solution of 2-ethylaminoethanol (EAE) was measured under the same conditions as in Reference Example 1, and the carbon dioxide was absorbed in the liquid. Absorption of carbon dioxide was _0.665mol-CO 2 / mol- amine. In the case where carbon dioxide was absorbed, a daimyo peak derived from the carbamate anion was observed at a shift value of 162.31 ppm, and the peak of the bicarbonate anion at 163.48 ppm was only half that amount.

It is a vapor-liquid equilibrium data with the carbon dioxide of 45% isopropylaminoethanol aqueous solution of Example 5. It is a ¹³ C-NMR spectrum of a 30% isopropylaminoethanol aqueous solution that absorbed carbon dioxide of Reference Example 1. 4 is a ¹³ C-NMR spectrum of a 30% EAE aqueous solution that absorbed carbon dioxide of Reference Example 2.

Claims (2)

A method for recovering carbon dioxide from a gas containing carbon dioxide,
(1) As an active ingredient, the formula [I]:

A step of bringing a gas containing carbon dioxide into contact with an aqueous solution containing only isopropylaminoethanol represented by formula (2), and absorbing the carbon dioxide into the aqueous solution; and (2) carbon dioxide obtained in the step (1) is absorbed. Heating the aqueous solution to desorb and recover carbon dioxide,
A method for recovering carbon dioxide containing
The content of isopropylaminoethanol in the aqueous solution is 35 to 50% by weight,
Carbon dioxide recovery method. In the step (1), a gas containing carbon dioxide is brought into contact with the aqueous solution at a temperature of 60 ° C. or lower, and the aqueous solution in which carbon dioxide is absorbed in the step (2) is heated at a temperature of 70 ° C. or higher to produce carbon dioxide. The carbon dioxide recovery method according to claim 1, wherein carbon is desorbed.

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