JP2008168227A - Absorbing liquid of carbon dioxide in exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for absorbing and dissociating CO<SB>2</SB>in an exhaust gas to efficiently recover CO<SB>2</SB>of high purity in a low energy consumption state. <P>SOLUTION: This absorbing liquid for separating and recovering carbon dioxide from the exhaust gas containing carbon dioxide contains 2-amino-2-methyl-1-propanol (a), N-ethyl-2-aminoethanol (c) and, if necessary, N-methyldiethanolamine (b). The sum total concentration of the amines (a)-(c) in the absorbing liquid is 20-60 wt.% and the amines (a)-(c) are contained in the absorbing liquid so as to satisfy 0.1≤a<0.6, o≤b≤0.6, 0.2≤c≤0.6 and a+b+c=1 [wherein a, b and c are the respective weight ratios of the amines (a), (b) and (c) with respect to the total amines of (a), (b) and (c)]. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

In the present invention, carbon dioxide (CO ₂ ) contained in a gas is absorbed using a CO ₂ absorbing solution for separating and recovering, and the CO ₂ recovering solution, and then CO ₂ absorption in which CO _{2 is} absorbed. The present invention relates to a method of separating and recovering CO ₂ from a liquid.

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 thought to be due to the increase in the atmosphere of greenhouse gases such as CO ₂ , methane, nitrous oxide, and chlorofluorocarbon, which increase with the increase in human activity. The most important greenhouse gas is atmospheric CO ₂ . To prevent global warming, the Kyoto Conference on Global Warming Prevention (COP3) was held in December 1997, and the Kyoto Protocol adopted at the conference entered into force on February 16, 2005, reducing CO ₂ emissions. There is an urgent need to take measures toward this.

Sources of CO ₂ include coal, heavy oil, natural gas fueled thermal power plants, factory boilers or cement kilns, 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 CO ₂ emissions.

Several methods have been known so far for recovering CO ₂ in gas. And now, various methods are widely studied.

For example, after absorption of CO ₂ by a gas containing CO ₂ is contacted with an aqueous alkanolamine solution in an absorption tower, a method for desorption recovered CO ₂ and the CO ₂ absorbing solution by heating at desorption column, Developed since the 1930s and put into practical use in urea synthesis plant towers. This method is economical and easy to enlarge.

  Here, monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA), diglycolamine (DGA) and the like are known as alkanolamines. However, monoethanolamine is usually used.

However, for example, when an aqueous solution of alkanolamine such as MEA is used as the absorbing solution, although the CO ₂ absorption capacity per unit volume is excellent, the corrosiveness of the material of the device is high, so that expensive corrosion-resistant steel is used for the device. It is necessary to reduce the concentration of amine in the absorbing solution. Further, since it is difficult to desorb absorbed CO ₂ , it is necessary to desorb and recover by heating the desorption temperature to a high temperature of 120 ° C. In addition, there is a disadvantage that the energy required to desorb CO ₂ from the absorbing solution is as high as 20 Cal / mol CO ₂ . For example, in order to collect CO ₂ 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 CO ₂ generation, energy saving and resource saving are required, this high energy consumption is a major factor hindering the practical use of CO ₂ absorption and recovery equipment.

In Patent Document 1, the secondary hindered amine is limited to the removal of CO ₂ from the combustion exhaust gas, and 2-methylaminoethanol (MAE), 2-ethylaminoethanol (EAE), 2-propylaminoethanol (PAE), And 2-isopropylaminoethanol, with EAE and MAE being preferred.

Di-unsubstituted alkylaminopropanol and di-unsubstituted alkylaminobutanol as tertiary amines, i.e. di-unsubstituted alkylaminopropanol and di-unsubstituted alkylaminobutanol substituted with methyl, ethyl, propyl, isopropyl groups 1-diethylamino-2-propanol and 3-diethylamino-1-propanol are exemplified. However it is likely to significantly dissipate the absorbed CO ₂ by mixing other specific amines is not mentioned.

  Patent Document 2 proposes a secondary amino group bonded to a secondary or tertiary carbon or a primary amine bonded to a tertiary carbon, as in the above-mentioned document, by limiting to an aqueous amine solution as an absorbing solution. 2-Amino-2-methyl-1-propanol (AMP) and 2-methylpiperazine have also been proposed.

  In Patent Document 3, claim 1 is a combination of 100 parts by weight of primary alkanolamine and secondary alkanolamine containing tertiary carbon: 1 to 25 parts by weight, and claim 3 is AMP or 1,3-propanediol. A combination of 100 parts by weight of a secondary alkanolamine with 1 to 25 parts by weight is disclosed, examples of which are AMP-MAE, AMP-piperazine (PZ), DEA-MAE, and DEA-PZ. .

Although it is still limited to combustion exhaust gas in Patent Document 4, it is possible to improve the energy required for absorption and recovery by improving the CO ₂ absorption amount and absorption rate using a mixed aqueous solution of secondary amine and tertiary amine. Yes.

Preferred secondary amines include piperazine in addition to alkanolamines such as 2-methylaminoethanol (MAE), 2-ethylaminoethanol (EAE), 2-isopropylaminoethanol (IPAE), 2-n-butylaminoethanol (nBAE) and the like. , 2-methylpiperazine dimethylpiperazine, and cyclic amines of 2-piperidinoethanol are exemplified. Preferred tertiary amines include 2-dimethylaminoethanol (DMAE), 2-diethylaminoethanol (DEAE), 3-dimethylamino-1-propanol (3DMA1P), 4-dimethylamino-1-butanol (4DMA1B), 2-dimethyl. Amino-2-methyl-1-propanol (2DMA2M1P), N-ethyl-N-methylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, Nt-butyldiethanolamine (tBDEA), N-methyldiisopropanolamine ( MDIPA) is shown. However, the concentration of the tertiary alkanolamine is extremely limited to ± 10% by weight of the concentration that absorbs the largest amount of CO ₂ alone.

As described above, many attempts have been made to improve the absorption and desorption recovery of CO ₂ . However, further reduction of the balance between absorption and desorption recovery performance, the reaction heat of CO ₂ absorption, in other words, the heat necessary for CO ₂ desorption is a major issue.
Japanese Patent No. 2871334 U.S. Pat. No. 4,112,052 Japanese Patent No. 2871335 Patent 3197183

In view of the above problems of the prior art, the present invention aims to provide a method for efficiently and apart absorbing and de of CO ₂ in the gas at low energy consumption, to separate and recover high purity CO ₂ And Specifically, CO ₂ is absorbed efficiently by using a CO ₂ absorbing solution having a large amount of CO ₂ absorption and CO ₂ desorption per unit amount and low energy required for CO ₂ desorption. It is another object of the present invention to provide a method for separating and recovering high purity CO ₂ by desorption.

The present inventors have found that in order to solve the above problems, intensive studies and as a result, how do and how absorption rate to dissipate a lot of CO ₂ in the process of dissipation of CO ₂ absorbed than the absorption of CO ₂ Has been found to be an important point for the purpose of efficiently absorbing and desorbing CO ₂ . The 2-amino-2-methyl-1-propanol, N- methyldiethanolamine and high CO ₂ absorption by the three amines be specific composition of N- ethyl-2-aminoethanol, absorption rate, a high CO ₂ It was found that the amount of desorption and the desorption rate were remarkably shown. As a result of further research based on this knowledge, the present invention has been completed.

  That is, the present invention provides the following carbon dioxide absorbing solution and carbon dioxide absorbing method for separating and recovering the following carbon dioxide.

Item 1. An absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide,
The absorbent is
(I) containing 2-amino-2-methyl-1-propanol (a), N-methyldiethanolamine (b) and N-ethyl-2-aminoethanol (c);
The total concentration of the amines (a) to (c) in the absorbing solution is 20 to 60% by weight, and the amines (a) to (c) are 0.1 ≦ a ≦ 0.6. , 0 <b ≦ 0.6, 0.2 ≦ c ≦ 0.6 and a + b + c = 1,
[Where a represents the weight ratio of the amine of (a) to the total amines of (a) to (c);
b represents the weight ratio of the amine of (b) to the total amines of (a) to (c);
c represents the weight ratio of the amine of (c) to the total amines of (a) to (c)]
Or the absorbent is
(Ii) containing 2-amino-2-methyl-1-propanol (a) and N-ethyl-2-aminoethanol (c) and not containing N-methyldiethanolamine (b);
The total concentration of the amines (a) and (c) in the absorbing solution is 20 to 60% by weight, and the amines (a) and (c) are 0.4 ≦ a ≦ 0.6. , 0.4 ≦ c ≦ 0.6 and a + c = 1.
[Where a represents the weight ratio of the amine of (a) to the total amine of (a) and (c);
c represents the weight ratio of the amine of (c) to the total amines of (a) and (c)]
Absorbing liquid.

Item 2. (1) a step of bringing a gas containing carbon dioxide into contact with the absorbing liquid according to item 1 at a temperature of 60 ° C. or lower; and (2) an absorbing liquid in which carbon dioxide obtained in step (1) is absorbed is 70. A method for separating and recovering carbon dioxide, comprising a step of desorbing and recovering carbon dioxide by heating at a temperature of at least ° C.

The method for separating and recovering carbon dioxide using the carbon dioxide-absorbing liquid of the present invention can absorb and desorb CO ₂ in gas with an efficient and low energy consumption, and recover high-purity CO _2. . As a result, the CO ₂ absorption tower, the CO ₂ 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.

The method for separating and recovering carbon dioxide using the carbon dioxide absorbing liquid of the present invention also has a feature that the reaction heat of CO ₂ absorption is small. Since the reaction heat of CO ₂ absorption corresponds to the heat necessary for CO ₂ desorption, the energy consumption necessary for desorbing CO ₂ can be kept low.

In addition, alkanolamines such as MEA used for CO ₂ absorption generally show high corrosiveness to metal materials such as carbon steel, but the aqueous solution of mixed amine used in the present invention has a markedly reduced corrosiveness, This 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.

(1) Carbon dioxide absorbent The carbon dioxide absorbent of the present invention contains 2-amino-2-methyl-1-propanol (a) and N-ethyl-2-aminoethanol (c).

  In one embodiment, the carbon dioxide absorbing liquid of the present invention comprises 2-amino-2-methyl-1-propanol (a), N-methyldiethanolamine (b), and N-ethyl-2-aminoethanol (c). contains.

  In the embodiment, the total concentration of the amines (a) to (c) in the absorbing solution is usually 20 to 60% by weight, preferably about 25 to 50% by weight.

  Here, the weight ratio of the amine of (a) to the total amine of (a) to (c) is a, the weight ratio of the amine of (b) to the total amine of (a) to (c) is b, When the weight ratio of the amine of (c) to the total amines of a) to (c) is c, the absorbent according to the present invention contains the amines of (a) to (c) with 0.1 ≦ a ≦ 0.6. 0 <b ≦ 0.6, 0.2 ≦ c ≦ 0.6, and a + b + c = 1 (preferably 0.15 ≦ a ≦ 0.5, 0.1 ≦ b ≦ 0.55, 0.2 ≦ c ≦ 0.55 and a + b + c = 1, more preferably 0.20 ≦ a ≦ 0.45, 0.2 ≦ b ≦ 0.5, 0.2 ≦ c ≦ 0.5, and a + b + c = 1 ) To satisfy.

  In another embodiment of the present invention, the carbon dioxide absorbing liquid does not contain N-methyldiethanolamine (b), and 2-amino-2-methyl-1-propanol (a) and N-ethyl-2-aminoethanol ( c).

  In the embodiment, the total concentration of the amines (a) and (c) in the absorbing solution is usually 20 to 60% by weight, preferably about 25 to 50% by weight.

  Here, when the weight ratio of the amine of (a) to the total amine of (a) and (c) is a, and the weight ratio of the amine of (c) to the total amine of (a) and (c) is c, The absorbing liquid of the present invention comprises the amines (a) and (c), 0.4 ≦ a ≦ 0.6, 0.4 ≦ c ≦ 0.6, and a + c = 1 (preferably 0.45 ≦ a ≦ 0.5, 0.5 ≦ c ≦ 0.55, and a + c = 1, more preferably 0.5 ≦ a ≦ 0.45, 0.55 ≦ c ≦ 0.5, and a + c = 1) Includes to satisfy.

Only with 2-amino-2-methyl-1-propanol, although there is a certain amount of CO ₂ desorption, the CO ₂ absorption rate is also low. The only N- methyldiethanolamine CO ₂ absorption amount is small, CO ₂ absorption rate is low. Further, only with N-ethyl-2-aminoethanol, the amount of CO ₂ absorption is not particularly large, but the CO ₂ absorption rate is high. However, the CO ₂ desorption amount is small and the CO ₂ desorption rate is low.

The present inventor has CO 2 _- as well as predicting the substantial CO ₂ recovery amount in the liquid circulation cycle of the absorption tower and stripping tower of absorption and dissipation processes from vapor-liquid equilibrium data of CO ₂ aqueous amine solution, screening of the absorbent The conditions under which this substantial CO ₂ recovery amount can be estimated almost correctly were found, and the CO ₂ absorption amount, absorption rate, CO ₂ desorption amount and desorption rate of aqueous solutions of many amines and their mixtures were measured.

Specifically, after absorbing CO ₂ at 40 ° C. from a gas stream containing 20% CO ₂ , the temperature and temperature are increased to 70 ° C. under the same gas stream, and the amount and rate of CO ₂ released are measured. It was found that the CO ₂ emission obtained here was in a clean proportional relationship with the value of the vapor-liquid equilibrium data.

Surprisingly, 2-amino-2-methyl-1-propanol and N-ethyl-2-aminoethanol, and optionally N-methyldiethanolamine in an aqueous solution with a specific composition, these amines alone It was found that an extremely high CO ₂ emission amount that could not be obtained with the aqueous solution containing 1 was obtained.

In an aqueous solution containing 2-amino-2-methyl-1-propanol and N-ethyl-2-aminoethanol and, if necessary, N-methyldiethanolamine in the above proportion, CO ₂ absorption, CO ₂ absorption rate, CO ₂ Both the desorption amount and the CO ₂ desorption rate showed high values. That is, an extremely large synergistic effect is obtained with an aqueous solution containing these amines in the above proportions. This This synergistic effect in the range other than the composition less CO ₂ desorption amount and CO ₂ desorption rate can only be obtained a low value.

In general, the higher the concentration of the amine component, the greater the amount of CO ₂ absorbed, the rate of absorption, the amount of desorption and the rate of desorption per unit liquid volume, which is desirable from the viewpoint of energy consumption and the size and efficiency of plant equipment. When the weight concentration exceeds 70%, the amount of CO ₂ absorbed decreases because the effect of water as an activator decreases. The amine component is not uniformly mixed with water, the viscosity is increased, and the pH of the liquid to absorb CO ₂ is sometimes arise problems such as would foaming and emulsification conditions when the drops.

  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. Etc. may be added.

  The carbon dioxide absorbing liquid of the present invention uses water as a solvent.

(1) Method for separating and recovering carbon dioxide The present invention includes (1) a step of bringing a gas containing carbon dioxide into contact with the above-mentioned carbon dioxide absorption liquid at a temperature of 60 ° C. or less, and (2) the step (1). Provided is a method for separating and recovering carbon dioxide, comprising a step of heating the obtained absorption liquid in which carbon dioxide has been absorbed at a temperature of 70 ° C. or higher to desorb and recover carbon dioxide.

The gas containing CO ₂ includes, for example, a thermal power plant fueled with heavy oil, natural gas, etc., a boiler in a factory or a kiln in a cement factory, a blast furnace in a steelworks that reduces iron oxide with coke, and carbon in pig iron Exhaust gas from the converter of the same steel mill that burns steel to produce steel, and the CO ₂ concentration in the gas is usually about 5 to 30% by volume, particularly about 10 to 20. In such a CO ₂ concentration range, the effects of the present invention are suitably exhibited. Incidentally, when using CO ₂ absorbing solution comprising a mixed aqueous amine solution in the present invention, the oxygen as a gas to co-exist in the gas containing CO _2, carbon monoxide (CO) or hydrogen, water vapor in addition to CO _2, such as CO Even if gas is contained, there is no influence on the absorption and emission performance of CO ₂ . Nitrogen oxides such as nitrogen monoxide (NO) and sulfur oxides such as sulfur dioxide (SO ₂ ) also have no effect on the absorption and emission performance of CO ₂ at about 100 ppm.

The method for bringing the gas containing CO ₂ into contact with the carbon dioxide absorbent of the present invention is not particularly limited. For example, a method of bubbling and absorbing a gas containing CO _{2 in the} aqueous solution, a method of dropping the aqueous solution into a gas stream containing CO ₂ (spraying or spraying method), or a magnet or metal mesh This is performed by a method in which a gas containing CO ₂ and the aqueous solution are brought into countercurrent contact with each other in an absorption tower containing a filler. The absorbed CO ₂ is considered to form carbamate anions and bicarbonate ions in the aqueous solution.

The liquid temperature when the gas containing CO ₂ is absorbed by the absorption liquid 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 at the time of CO ₂ 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, when an aqueous solution having a total concentration of amine components (a) to (c) of 30 to 60% by weight is used, the CO ₂ saturated absorption amount at the time of CO ₂ absorption (40 ° C.) is 4 to 4%. 9 g / 50 ml approximately, in particular 5~8g / 50ml about saturated CO ₂ absorption rate of the time that has absorbed CO ₂ 3/4 of absorption is 0.05~0.30g / 50ml / min approximately, in particular 0 0.07 to 0.20 g / 50 ml / min. The CO ₂ saturated 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 CO ₂ absorption rate is 3/4 of the saturated absorption of CO _2. is a value measured using a infrared CO ₂ meter at the time that has absorbed. When the amine component concentration above 30 wt%, the value of the above-mentioned CO ₂ saturation absorption and CO ₂ absorption rate decreases after taking the highest value with an amine concentration of 40 to 50 wt%.

Further, the aqueous solution used in the present invention has a feature that the reaction heat of CO ₂ absorption is small. Since the reaction heat of CO ₂ absorption corresponds to the heat necessary for CO ₂ desorption, the energy consumption necessary for desorbing CO ₂ can be kept low. As a specific example, it can be easily understood by referring to Example 9 and Comparative Examples 4 and 5.

CO ₂ The CO ₂ from the absorbed solution desorbed as a method for recovering pure or high concentrations of CO _2, a method of leaving it bubbled kettle was similarly heated aqueous solution and distilled, plate column, 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. Thus, CO ₂ is released to release the carbamate anions and bicarbonate ions.

The liquid temperature during CO ₂ desorption is usually 70 ° C. or higher, preferably 80 ° C. or higher, and 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 at the time of desorption of CO ₂ 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.

In the method of the present invention, when an absorbing solution in which the total concentration of the amine components (a) to (c) is 30 to 60% by weight is used, the CO ₂ desorption amount at the time of CO ₂ desorption (70 ° C.) Is about 0.8 to 3.0 g / 50 ml, particularly about 1.0 to 2.5 g / 50 ml, and the average CO ₂ desorption rate from the start of temperature increase to 10 minutes is 0.12 to 0.25 g / It is about 50 ml / min, especially about 0.15 to 0.20 g / 50 ml / min. The CO ₂ desorption amount is a value measured with a total organic carbon meter, and the CO ₂ desorption rate is a value measured with an infrared CO ₂ meter. When the amine component concentration is 30% by weight or more, the CO ₂ desorption amount and the average CO ₂ desorption rate are substantially proportional to the concentration.

Thus, even when the temperature during CO ₂ desorption is relatively low at 70 ° C., a good CO ₂ desorption amount and CO ₂ desorption rate can be achieved from the aqueous amine solution. Of course, when the temperature at the time of CO ₂ desorption exceeds 70 ° C., for example, as the temperature increases to 80 ° C., 90 ° C., 100 ° C., 110 ° C., 120 ° C., the CO ₂ desorption amount and the CO ₂ desorption rate further increase. improves.

The aqueous solution from which CO ₂ has been desorbed is sent again to the CO ₂ absorption step and recycled (recycled). In addition, the heat generated during CO ₂ 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 CO ₂ recovered in this manner is usually as high as about 95 to 99% by volume. This pure CO ₂ or high-concentration CO ₂ is used as a chemical, a synthetic raw material for polymer substances, a cooling agent for freezing foods, and the like. In addition, it is also possible to sequester and store the recovered CO ₂ in the underground or the like where technology is currently being developed.

  Next, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.

Example 1
A glass gas cleaning bottle was immersed in a constant temperature water bath set to a temperature of 40 ° C., and 50 ml of an aqueous solution containing 15% by weight of AMP, 15% by weight of MDEA and 15% by weight of EAE was filled therein. A mixed gas containing 20% by volume of CO ₂ and 80% by volume of N ₂ is dispersed in a foam state through this glass filter having a coarseness of 100 μm and a diameter of 13 mm at atmospheric pressure and 0.7 liter / min. Absorbed.

The CO ₂ 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 CO ₂ meter, and the CO ₂ absorption was measured from the difference in the CO ₂ flow rate between the inlet and the 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 CO ₂ meter. Saturated absorption amount was the amount of time at which the CO ₂ concentration in the absorbing solution outlet matches the CO ₂ concentration of the inlet. The rate of absorption at the time of absorbing the half of absorption are absorbed most of CO ₂ gas, is equal to the CO ₂ feed rate, comparing the absorption rate at the time of absorbing the 3/4 of the absorption It was. Absorption rate at saturation absorption 3/4 absorbed CO ₂ saturated absorption 5.55g was 0.12 g / min. The CO ₂ absorption measured with a total organic carbon meter was 5.58 g, 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 CO ₂ 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 CO ₂ desorption amount was 2.06 g and the desorption rate was 0.16 g / min.

Example 2
Using the same apparatus as in Example 1, except that oxygen is contained 10% by volume in the same conditions, the saturated absorption amount of CO ₂ with the same absorbent solution as employed in Example 1, the same speed and CO ₂ desorption Volume and speed measurements were taken. The saturated absorption of CO _{2 at} 40 ° C. was 5.65 g, and the absorption rate at the absorption of 3/4 of the saturated absorption was 0.12 g / min. The amount of CO ₂ desorbed at 70 ° C. was 2.20 g, and the desorption rate was 0.15 g / min.

Examples 3-7
Using the same apparatus as in Example 1, AMP in the composition described in Table 1 under the same conditions, MDEA, and saturated absorption amount of CO ₂ with an amine aqueous solution containing EAE, the speed and CO ₂ desorption amount and same speed Was measured. The obtained results are shown in Table 1.

Example 8
A stainless steel pressure-resistant container having a capacity of 1.5 liters equipped with a stirring blade was filled with 700 ml of an absorbent having the same composition as in Example 1. By varying the pressure of 0.1-0.6 atm total pressure of _CO 2 -N ₂ mixed gas containing CO ₂ into the vessel, CO ₂ partial pressure of saturation between 0.2MP from 0.003MP Absorption was measured. The container was heated by an electric heater wound around the outer wall of the container, and gas-liquid equilibrium curves at 40 ° C, 70 ° C, 100 ° C and 120 ° C were measured.

The result is shown in FIG. 40 shows a ℃, wide CO ₂ high equilibrium solution in partial pressure CO ₂ concentration (0.54molCO ₂ / mol amine 0.02MP), in a low equilibrium solution in a wide CO ₂ partial pressure reversed at 120 ° C. CO ₂ The concentration (0.02 MP at 0.06 mol CO ₂ / mol amine) was shown, and it became clear that efficient CO ₂ recovery was possible by absorption at low temperature and desorption operation at high temperature.

Example 9
A thermos with an internal volume of 300 ml containing a magnetic stirrer, thermocouple, and electrothermal pipe heater was filled with 200 ml of an absorption liquid having the same composition as in Example 1, and then CO ₂ gas was blown at 200 ml / min, and the liquid temperature was The rise was continuously recorded with a temperature recorder until CO ₂ absorption was completed. Next, once again add the same amount of liquid of the same composition to this device, and control the current amount of the heater so that the temperature of the liquid rises at the same rate as the temperature rise at the previous CO ₂ injection with a pipe heater. Then, the amount of electric power was measured. As a result, the reaction heat of CO ₂ absorption was 17.6kcal / molCO _2.

Comparative Example 1
Using the same apparatus as in Example 1, was measured saturation absorption of CO _2, the speed and CO ₂ desorption amount and the same speed with an aqueous solution containing AMP 45 wt% under the same conditions. The saturated absorption of CO _{2 at} 40 ° C. was 5.43 g, and the absorption rate at the absorption of 3/4 of the saturated absorption was 0.05 g / min. The amount of CO ₂ desorbed at 70 ° C. was 2.52 g, and the desorption rate was 0.17 g / min. It was found that all of the CO ₂ absorption amount, the CO ₂ absorption rate, the CO ₂ desorption amount, and the CO ₂ desorption rate were low.

Comparative Examples 2-3
Using the same apparatus as in Example 1, MDEA described in Table 2 under the same conditions, and the EAE using an aqueous solution at a concentration shown in Table 2, the saturated absorption amount of CO _2, the speed and CO ₂ desorption amount And the same speed was measured. The obtained results are shown in Table 2.

In Comparative Examples 2 to 3, MDEA had a relatively large amount of CO ₂ desorption at 70 ° C., but the CO ₂ absorption rate at 40 ° C. was low, and saturation did not reach saturation at 60 minutes. Although EAE has a high CO ₂ absorption rate at 40 ° C., the amount of CO ₂ desorption at 70 ° C. is small.

Comparative Example 4
Measurement of the heat of reaction CO ₂ absorption AMP30 wt% aqueous solution using the same apparatus as in Example 9, the reaction heat of CO ₂ absorption was 19.0kcal / molCO _2.

Comparative Example 5
Measurement of the heat of reaction CO ₂ absorption EAE30 wt% aqueous solution using the same apparatus as in Example 9, the reaction heat of CO ₂ absorption was 18.0kcal / molCO _2. From a comparison between Example 9 and Comparative Examples 4 and 5, it can be seen that the absorbent used in the present invention has a characteristic that the reaction heat of CO ₂ absorption is small.

From these results, according to the method of the embodiment, CO ₂ in the gas can be absorbed and desorbed and recovered with efficient and low energy consumption.

The gas-liquid parallel curve of 40 degreeC, 70 degreeC, 100 degreeC, and 120 degreeC in Example 8 is shown.

Claims (2)

An absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide,
The absorbent is
(I) containing 2-amino-2-methyl-1-propanol (a), N-methyldiethanolamine (b) and N-ethyl-2-aminoethanol (c);
The total concentration of the amines (a) to (c) in the absorbing solution is 20 to 60% by weight, and the amines (a) to (c) are 0.1 ≦ a ≦ 0.6. , 0 <b ≦ 0.6, 0.2 ≦ c ≦ 0.6 and a + b + c = 1,
[Where a represents the weight ratio of the amine of (a) to the total amines of (a) to (c);
b represents the weight ratio of the amine of (b) to the total amines of (a) to (c);
c represents the weight ratio of the amine of (c) to the total amines of (a) to (c)]
Or the absorbent is
(Ii) containing 2-amino-2-methyl-1-propanol (a) and N-ethyl-2-aminoethanol (c) and not containing N-methyldiethanolamine (b);
The total concentration of the amines (a) and (c) in the absorbing solution is 20 to 60% by weight, and the amines (a) and (c) are 0.4 ≦ a ≦ 0.6. , 0.4 ≦ c ≦ 0.6 and a + c = 1.
[Where a represents the weight ratio of the amine of (a) to the total amine of (a) and (c);
c represents the weight ratio of the amine of (c) to the total amines of (a) and (c)]
Absorbing liquid. (1) a step of bringing a gas containing carbon dioxide into contact with the absorbent according to claim 1 at a temperature of 60 ° C. or lower; and (2) an absorbent in which carbon dioxide obtained in the step (1) is absorbed. A method for separating and recovering carbon dioxide, comprising a step of desorbing and recovering carbon dioxide by heating at a temperature of 70 ° C. or higher.

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