Aqueous amine solution for carbon dioxide fixation, method for absorbing and fixing carbon dioxide using the aqueous amine solution, method for storing carbon dioxide, method for recovering carbon dioxide, and method for recycling the aqueous amine solution.

Abstract

We provide a suite of technologies that enable safe, energy-efficient, and low-cost transportation of carbon dioxide. [Means] An aqueous amine solution for carbon dioxide fixation containing 10 to 50% by mass of an amine compound, wherein the amine compound is one or more selected from the group consisting of 2-amino-2-methyl-1-propanol, 2-amino-2-hydroxymethyl-1,3-propanediol, and 2-amino-2-methyl-1,3-propadiol. Aqueous amine solution for carbon dioxide fixation.

Description

Technical Field

[0001] The present invention relates to an amine aqueous solution for carbon dioxide fixation, a method for absorbing and fixing carbon dioxide using the amine aqueous solution, a method for storing carbon dioxide, a method for recovering carbon dioxide, and a method for recycling the amine aqueous solution.

Background Art

[0002] Carbon dioxide (hereinafter sometimes referred to as CO2) can cause global warming. Therefore, it is desired to reduce its emissions. In addition to technologies that reduce carbon dioxide emissions themselves, such as energy conservation, fuel conversion, and new energy utilization, the need for technologies to fix carbon dioxide contained in exhaust gases is increasing. As one of the technologies for fixing carbon dioxide, a method is known in which carbon dioxide fixed at a carbon dioxide source such as a power plant or an industrial area is isolated in a storage area such as underground or in the sea.

[0003] While carbon dioxide sources are widely distributed worldwide, suitable storage areas are limited to some regions. Therefore, carbon dioxide separated and recovered at the source needs to be transported over a long distance to the storage area. In this case, ships, which are less costly than building pipelines, are considered suitable means of transportation, and it has been proposed to physically liquefy carbon dioxide and transport it by ship (Patent Document 1, Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] However, this method requires liquefying high-purity carbon dioxide under low-temperature and high-pressure conditions of -20°C and 2MPa, and maintaining that liquefied state. This presents safety and energy efficiency problems, such as the possibility of tank explosions if the power supply is interrupted during transport. Therefore, a new method of transporting carbon dioxide that is both safe and energy-efficient is desired.

[0007] Therefore, the objective of the present invention is to provide a series of technologies that enable the safe, energy-saving, and low-cost transportation of carbon dioxide. [Means for solving the problem]

[0008] As a result of diligently investigating the above problems, the inventors of this invention have obtained the following findings. By using a specified amine aqueous solution, carbon dioxide can be absorbed within a specified temperature range, and then the amine aqueous solution that has absorbed carbon dioxide can be solidified at room temperature. • By solidifying the amine aqueous solution that has absorbed carbon dioxide, carbon dioxide can be safely stored and transported without problems such as leakage. By keeping the temperature of the amine aqueous solution during carbon dioxide absorption within a predetermined range, a decrease in the carbon dioxide absorption rate can be prevented. By absorbing carbon dioxide into a predetermined amine aqueous solution under pressurized conditions, the carbon dioxide absorption rate and efficiency can be improved. • The solidified amine aqueous solution, after absorbing carbon dioxide, releases the absorbed carbon dioxide when placed in a heated environment, allowing for carbon dioxide recovery and the recycling of the original amine aqueous solution.

[0009] Based on the above findings, the inventors have completed the following invention. [1] An aqueous amine solution for carbon dioxide fixation containing 10 to 50% by mass of an amine compound, The amine compound is one or more selected from the group consisting of 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, and 2-amino-2-hydroxymethyl-1,3-propanediol. Aqueous amine solution for carbon dioxide fixation.

[0010] [2] The aqueous amine solution for carbon dioxide fixation according to [1], wherein the content of the amine compound is 20 to 45% by mass. [3] A method for absorbing and fixing carbon dioxide, comprising the step of absorbing and fixing carbon dioxide using an aqueous solution of carbon dioxide fixing amine described in [1] or [2] at a temperature of 40°C or higher and 80°C or lower.

[0011] [4] The method for absorbing and fixing carbon dioxide according to [3], wherein the temperature of the amine aqueous solution for carbon dioxide fixation is 40°C or higher and 60°C or lower. [5] The method for absorbing and fixing carbon dioxide according to [3] or [4], wherein carbon dioxide is absorbed and fixed under pressurized conditions.

[0012] [6] A process of absorbing and fixing carbon dioxide by any of the methods in [3] to [5], A step of solidifying the amine aqueous solution containing the absorbed and fixed carbon dioxide, A method for storing carbon dioxide, which includes [a specific feature / feature]. The method described in [7] [6] includes the step of heating the solidified amine aqueous solution containing carbon dioxide, which has been stored by the method described in [6], to 80°C or higher. Methods for capturing carbon dioxide.

[0013] [8] [7] The carbon dioxide is removed by the carbon dioxide recovery method described above, and the carbon dioxide fixing amine aqueous solution is restored and recovered. A method for recycling amine aqueous solutions used for carbon dioxide fixation.

Advantages of the Invention

[0014] According to the aqueous amine solution for carbon dioxide fixation of the present invention, it is possible to transport carbon dioxide safely, energy - savingly, and at low cost.

Brief Description of the Drawings

[0015] [Figure 1] Figure 1 is a schematic diagram showing the state of the carbon dioxide absorption experiment using the aqueous amine solution of the present invention. [Figure 2] Figure 2(a) is a graph showing the change in the absorption and fixation amount of carbon dioxide with respect to time, and Figure 2(b) is a table showing the absorption and fixation rate of carbon dioxide in the aqueous amine solution of each concentration. [Figure 3] Figure 3 shows the results of measuring the viscosity (cp) of the AMP aqueous solution after passing gas through the 30% by mass and 35% by mass AMP aqueous solutions for 120 minutes and then leaving them at room temperature (25°C) for 60 minutes. [Figure 4] Figure 4 is a graph showing the relationship between the elapsed time (minutes) and temperature (°C) when left at room temperature (25°C) after introducing carbon dioxide into the 35% by mass AMP aqueous solution shown in Figure 3. [Figure 5] Figure 5 is a conceptual diagram showing the state of the carbon dioxide fixation experiment under pressurized conditions. [Figure 6] Figure 6 is the result of plotting the absorption and fixation amount with respect to the contact time with carbon dioxide in the AMP aqueous solution of each concentration under the carbon dioxide pressurization condition of 0.1 MPa. [Figure 7] Figure 7 is a flowchart showing the procedure for evaluating the stability of the solidified aqueous amine solution. [Figure 8] Figure 8 is a table showing the results of measuring the amount of carbon dioxide released during the standing period by gas chromatography after separating 50 g of the 35% by mass AMP aqueous solution fixed with carbon dioxide and leaving it at 25°C for 3 days.

Modes for Carrying Out the Invention

[0016] <Amine aqueous solution for carbon dioxide fixation> The carbon dioxide fixation amine aqueous solution of the present invention is a carbon dioxide fixation amine aqueous solution containing 10 to 50% by mass of an amine compound, wherein the amine compound is one or more selected from the group consisting of 2-amino-2-methyl-1-propanol (hereinafter sometimes referred to as AMP), 2-amino-2-methyl-1,3-propanediol (hereinafter sometimes referred to as AMPD), and 2-amino-2-hydroxymethyl-1,3-propanediol (hereinafter sometimes referred to as AHPD).

[0017] (AMP, AMPD, AHPD) The amine compound contained in the amine aqueous solution for carbon dioxide fixation of the present invention is one or more selected from the group consisting of AMP, AMPD, and AHPD. The amine aqueous solution for carbon dioxide fixation of the present invention may contain multiple types of the above-mentioned amines, or it may contain only one type of amine. In particular, from the viewpoint of carbon dioxide absorption and storage properties, it is preferable that the amine contained is AMP.

[0018] In the carbon dioxide recovery method of the present invention described below, heating is required when desorbing carbon dioxide. However, in order to reduce the energy required, other amines may be mixed with the above-mentioned AMP, AHPD, and AMPD. Examples of other amines include 3-aminomethyl-3,5,5-trimethylcyclohexylamine (hereinafter sometimes referred to as IPDA). An aqueous solution of IPDA is known to be able to fix carbon dioxide, and it is known that a portion of it solidifies upon fixation.

[0019] ·Can be solidified Conventionally, aqueous solutions containing monoethanolamine (MEA), known to be capable of fixing carbon dioxide, do not solidify at room temperature. However, aqueous solutions containing the specified amine compound described above solidify at room temperature even after absorbing carbon dioxide. Therefore, since there is no problem of leakage, it is suitable for the stable storage of carbon dioxide for long periods of time and is useful in applications involving the long-distance transport of carbon dioxide. In this specification, "room temperature" preferably means 18°C ​​to 30°C, and more preferably 18°C ​​to 27°C.

[0020] • Carbon dioxide absorption efficiency MEA is known to be able to absorb and fix carbon dioxide, as shown by the following equation.

[0021] [ka]

[0022] (R 1 (represents an amine residue)

[0023] In the amine compounds AMP, AMPD, and AHPD contained in the amine aqueous solution for carbon dioxide fixation of the present invention, the following reactions occur in addition to the reaction of formula (1) above during the absorption and fixation of carbon dioxide.

[0024] [ka]

[0025] In other words, when using MEA, two molecules of amine are used to convert one molecule of carbon dioxide into R 1 NHCOO - In contrast to the method of fixation described above, in AMP, AMPD, and AHPD used in the present invention, one molecule of amine is recovered as shown in formula (2) above, so one molecule of carbon dioxide is converted to HCO3 by one molecule of amine. -Since it fixes carbon dioxide in this manner, it is theoretically expected to have twice the absorption efficiency compared to MEA, and can contribute as an efficient carbon dioxide absorbent and fixative.

[0026] (Concentration of amine compounds) The amine aqueous solution for carbon dioxide fixation of the present invention contains an amine compound at a concentration of 10% by mass or more and 50% by mass or less, based on the entire aqueous solution (100% by mass). By setting the concentration of the amine compound above the lower limit mentioned above, the amount of carbon dioxide absorbed is increased, and when solidifying the amine aqueous solution after absorption, excessive evaporation of water is not required, resulting in good overall energy efficiency.

[0027] Furthermore, by keeping the concentration of the amine compound below the above upper limit, it is possible to prevent the solidification of the amine aqueous solution during carbon dioxide absorption, thereby preventing a decrease in the amount of amine absorbed and a decrease in the absorption rate.

[0028] The concentration of the amine compound in the aqueous amine solution of the present invention is preferably 20% by mass or more and 45% by mass or less, with a lower limit of 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 32% by mass or more. Furthermore, the upper limit is more preferably 42% by mass or less, even more preferably 40% by mass or less, and particularly preferably 38% by mass or less.

[0029] Figure 1 shows an experiment in which carbon dioxide was absorbed using the amine aqueous solution of the present invention. Industrially, a method is employed in which an amine aqueous solution is sprayed from the top of an absorption tower and carbon dioxide is absorbed by droplets of the amine aqueous solution. However, for this basic experiment, the following simplified method is used. As an amine aqueous solution, 100 mL of a 10-50% by mass AMP aqueous solution was placed in a two-necked flask. A mixed gas (CO2:N2 (volume ratio) = 14.9:85.1) simulating exhaust gas from a coal-fired power plant was introduced into the aqueous solution as shown in Figure 1. The gas passed through a condenser and was collected in a gas bag. The amount of carbon dioxide gas emitted was determined by measuring the carbon dioxide gas concentration using a gas chromatograph. The amount of carbon dioxide absorbed and fixed by the amine aqueous solution (g / L) was calculated from the amount of carbon dioxide gas introduced and emitted, and the results of measuring this amount over time are shown in Figure 2(a).

[0030] The gas introduction rate was set to 700 mL / min, the introduction time to 120 minutes, and the two-necked flask was kept warm at 40°C using a water bath. As shown in Figure 2(a), when the AMP concentration was 10% by mass, the amount of carbon dioxide absorbed and fixed was low due to the low AMP concentration. Also, when the AMP concentration was 50% by mass, solids were generated immediately after the gas introduction began, suppressing gas diffusion, which also resulted in a low amount of carbon dioxide absorbed and fixed. When the AMP concentration was between 20% by mass and 40% by mass, a carbon dioxide absorption and fixation amount of 60 g / L or more was obtained.

[0031] Even at an AMP concentration of 50% by mass, the amount of carbon dioxide absorbed and fixed can be improved by employing methods such as absorbing the gas while applying ultrasound, so as not to suppress gas diffusion. Furthermore, even when using an absorption tower, an industrial method, gas diffusion is not easily suppressed, so it is possible to achieve sufficient carbon dioxide absorption and fixation even at high AMP concentrations.

[0032] Figure 2(b) shows the absorption and fixation rates of carbon dioxide in amine aqueous solutions of various concentrations. "Liquid" represents the absorption and fixation rate before solid formation, while "Solid" represents the absorption and fixation rate after solid formation in the aqueous solution. In the case of an AMP concentration of 50% by mass, a large amount of solid was formed, resulting in a low absorption and fixation rate after solid formation.

[0033] <Methods for absorbing and fixing carbon dioxide> The present invention provides a method for absorbing and fixing carbon dioxide, comprising the step of absorbing and fixing carbon dioxide by raising the temperature of the above-mentioned amine aqueous solution for carbon dioxide fixation to 40°C or higher and 80°C or lower.

[0034] (Temperature of amine aqueous solution during absorption and fixation process) In this invention, carbon dioxide is fixed in an amine aqueous solution at a temperature higher than room temperature. Typically, exhaust gas from a thermal power plant, factory, etc., is introduced into the amine aqueous solution of this invention, and the temperature of this exhaust gas heats the amine aqueous solution to the predetermined temperature. If heating is insufficient, a separate heating means may be provided to raise the temperature of the amine aqueous solution. Also, if the temperature of the exhaust gas is too high, a separate cooling means may be provided to cool the exhaust gas to a desired temperature range.

[0035] The temperature of the amine aqueous solution in the absorption and fixation process is preferably 70°C or lower, and more preferably 60°C or lower. By keeping the temperature of the amine aqueous solution above the lower limit mentioned above, solidification of the amine aqueous solution can be prevented, and a decrease in carbon dioxide absorption can be prevented. Furthermore, by keeping the temperature of the amine aqueous solution below the upper limit mentioned above, a decrease in carbon dioxide absorption due to excessively high temperatures can be prevented, and a decrease in the absorption rate can also be suppressed, thereby reducing energy consumption.

[0036] As described above, in the carbon dioxide absorption and fixation process, it is preferable that the amine aqueous solution be in liquid form in order to prevent a decrease in the absorption and fixation rate and the amount of carbon dioxide absorbed and fixed. As described above, if the amine concentration of the amine aqueous solution is high, solids tend to form easily, but in that case, the decrease in the absorption and fixation rate and the amount of carbon dioxide absorbed and fixed can be prevented by raising the temperature of the amine aqueous solution to prevent the formation of solids.

[0037] In addition to the gas bubbling into the amine aqueous solution shown in Figure 1, the absorption and fixation process can also be industrially performed by spraying the amine aqueous solution from the top of an absorption tower, allowing the carbon dioxide to be absorbed by droplets of the amine aqueous solution.

[0038] <Methods for storing carbon dioxide> The present invention provides a method for storing carbon dioxide, comprising the steps of absorbing and fixing carbon dioxide by the method described above, and solidifying an aqueous amine solution containing the absorbed and fixed carbon dioxide.

[0039] An aqueous amine solution containing a predetermined amine that has absorbed and fixed carbon dioxide at a temperature higher than room temperature, between 40°C and 80°C, can be solidified by lowering its temperature to room temperature.

[0040] MEA, which was known to be capable of absorbing and fixing carbon dioxide, remained liquid even when the aqueous solution was brought to room temperature after absorbing and fixing carbon dioxide, and did not solidify. Being liquid makes it difficult to handle, as leakage can occur during long-term transport. In the method of the present invention, the amine aqueous solution containing a predetermined amine that has absorbed and fixed carbon dioxide solidifies at room temperature, significantly improving handling during transport.

[0041] Figure 3 shows the results of measuring the viscosity (cp) of AMP aqueous solutions after passing gas through 30% by mass and 35% by mass aqueous solutions for 120 minutes under the conditions shown in Figure 1, and then letting them stand at room temperature (25°C) for 60 minutes. In a 30% by mass AMP aqueous solution, no increase in viscosity was observed, and it remained liquid (2.8 cp). However, in a 35% by mass AMP aqueous solution, the viscosity increased to 84.7 cp, indicating solidification.

[0042] If an aqueous AMP solution with fixed carbon dioxide does not solidify, the AMP concentration can be increased while maintaining the state of carbon dioxide absorption and fixation. Examples of methods for increasing the AMP concentration include vacuum distillation and freeze-drying. Furthermore, in some cases, such as during transport to cold regions, the amine aqueous solution after carbon dioxide absorption and fixation may be solidified by lowering the temperature below room temperature.

[0043] Figure 4 shows the relationship between elapsed time (minutes) and temperature (°C) when carbon dioxide (a mixed gas (CO2:N2 (volume ratio) = 14.9:85.1)) was introduced into a 35% by mass AMP aqueous solution shown in Figure 3 and left at room temperature (25°C). It was found that solid formation began after 10 minutes, and after 30 minutes, when the temperature reached 31.8°C, the entire amine aqueous solution solidified.

[0044] <Methods for capturing carbon dioxide> The carbon dioxide recovery method of the present invention includes the step of heating a solidified amine aqueous solution containing absorbed and fixed carbon dioxide, which has been stored by the carbon dioxide storage method described above, to 80°C or higher. As described above, carbon dioxide is absorbed and fixed in an amine aqueous solution in the carbon dioxide generation area, and the resulting amine aqueous solution is transported to a suitable storage site in a solid state. At the storage site, the fixed carbon dioxide is separated and recovered from the solidified amine aqueous solution. The separated and recovered carbon dioxide is isolated and stored underground, in the sea, or other locations using a prescribed method.

[0045] A solidified amine aqueous solution containing absorbed and fixed carbon dioxide releases the absorbed and fixed carbon dioxide when heated to a predetermined temperature. From the viewpoint of rapidly promoting the desorption of carbon dioxide, the heating temperature is preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. From the viewpoint of energy efficiency, it is preferably 140°C or lower, and more preferably 120°C or lower.

[0046] Industrially, a method for capturing carbon dioxide can be employed in which an amine aqueous solution is sprayed from the top of an absorption tower, and the droplet-like amine aqueous solution is heated to a predetermined temperature to remove carbon dioxide.

[0047] <Recycling method for amine aqueous solutions used for carbon dioxide fixation> The present invention provides a method for recycling amine aqueous solutions for carbon dioxide fixation, in which the solidified amine aqueous solution is heated by the carbon dioxide recovery method described above to remove carbon dioxide, thereby recovering an amine aqueous solution for carbon dioxide fixation containing a predetermined amine compound.

[0048] After heating the solidified amine aqueous solution to release the absorbed and fixed carbon dioxide, the amine compounds in the amine aqueous solution return to their original state before carbon dioxide absorption and fixation. In this way, the recycled amine aqueous solution at the storage site is returned to each carbon dioxide generating area and can be reused again as amine aqueous solution for carbon dioxide fixation.

[0049] <Absorption and fixation of carbon dioxide under pressurized conditions> The carbon dioxide fixation methods described above include bubbling a gas containing carbon dioxide into an amine aqueous solution at atmospheric pressure, and spraying an amine aqueous solution from the top of an absorption tower to absorb carbon dioxide. However, carbon dioxide absorption and fixation can also be performed by bringing a gas containing carbon dioxide into contact with an amine aqueous solution under pressurized conditions.

[0050] The pressurization conditions are preferably 0.01 MPa or higher, more preferably 0.05 MPa or higher, and even more preferably 0.1 MPa or higher, in terms of gauge pressure. There is no particular upper limit, but since the pressurization effect saturates, it is preferably 1 MPa or lower, and even more preferably 0.5 MPa or lower. Furthermore, if the pressure becomes too high, in addition to the amine fixing carbon dioxide, carbon dioxide gas may dissolve in the solvent water. In this case, the solidification of the amine aqueous solution with fixed carbon dioxide may be inhibited. However, even in this case, after releasing the pressure, the amine aqueous solution can be mechanically stirred or ultrasonically stirred to release the carbon dioxide dissolved in the solvent water, and then the entire amine aqueous solution can be solidified.

[0051] Furthermore, when the amine concentration in the amine aqueous solution is low, if the above pressure becomes too high, the amine aqueous solution may separate into two layers due to the dissolution of carbon dioxide in the solvent water. Even in this case, it is possible to solidify the entire solution while resolving the two-layer separation by stirring the separated amine aqueous solution to release the dissolved carbon dioxide. However, to prevent such two-layer separation, the upper limit of the above pressure is preferably 0.08 MPa or less, and more preferably 0.07 MPa or less.

[0052] Figure 5 shows a conceptual diagram illustrating a carbon dioxide fixation experiment under pressurized conditions. Using an aqueous solution of AMP with a concentration of 10-100% by mass, carbon dioxide gas was brought into contact with the aqueous solution under a gauge pressure of 0.1 MPa. Figure 6 shows the results of plotting the amount of carbon dioxide absorbed and fixed against the contact time with carbon dioxide. The highest fixed volume result was obtained with a 50% by mass AMP aqueous solution. The next highest was 30% by mass, and the lowest was obtained with 10% by mass.

[0053] <Evaluation of the stability of solidified amine aqueous solutions> Figure 7 shows the procedure for evaluating the stability of the solidified amine aqueous solution. To 100 mL of a 35% by mass AMP aqueous solution, a gas at 40°C with a predetermined carbon dioxide concentration (14.9 to 99.5% by volume, the remainder being nitrogen gas) was introduced at a flow rate of 100 to 700 mL / min for 30 to 120 minutes, as shown in Figure 1, to obtain an amine aqueous solution in which carbon dioxide was absorbed and fixed, and the amount of carbon dioxide fixed was measured.

[0054] 50 g of a 35% by mass aqueous solution of AMP with fixed carbon dioxide was taken and left at 25°C for 3 days. The amount of carbon dioxide emitted during the standing period was measured by gas chromatography. The results are shown in Figure 8. As shown in Figure 8, carbon dioxide emission was suppressed to a small extent in all solidified amine aqueous solutions with varying carbon dioxide fixation ratios. While the carbon dioxide emission may appear somewhat higher in the case of a carbon dioxide fixation ratio of 0.93, this is because carbon dioxide was fixed near saturation, and the emission was still relatively low.

Claims

1. An aqueous amine solution for carbon dioxide fixation containing 10 to 50% by mass of an amine compound, The amine compound is one or more selected from the group consisting of 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, and 2-amino-2-hydroxymethyl-1,3-propanediol. Aqueous amine solution for carbon dioxide fixation.

2. The aqueous amine solution for carbon dioxide fixation according to claim 1, wherein the content of the amine compound is 20 to 45% by mass.

3. A method for absorbing and fixing carbon dioxide, comprising the step of absorbing and fixing carbon dioxide using an aqueous solution of carbon dioxide fixing amine described in claim 1, which is heated to 40°C or higher and 80°C or lower.

4. The method for absorbing and fixing carbon dioxide according to claim 3, wherein the temperature of the amine aqueous solution for carbon dioxide fixation is 40°C or higher and 60°C or lower.

5. The method for absorbing and fixing carbon dioxide according to claim 3, wherein carbon dioxide is absorbed and fixed under pressurized conditions.

6. A step of absorbing and fixing carbon dioxide by the method of claim 3, A step of solidifying the amine aqueous solution containing the absorbed and fixed carbon dioxide, A method for storing carbon dioxide, which includes [a specific feature / feature].

7. The method described in claim 6 includes the step of heating the solidified amine aqueous solution containing carbon dioxide, which has been stored by the method described in claim 6, to 80°C or higher. Methods for capturing carbon dioxide.

8. The carbon dioxide recovery method described in claim 7 is used to remove carbon dioxide and restore and recover the carbon dioxide fixing amine aqueous solution. A method for recycling amine aqueous solutions used for carbon dioxide fixation.

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