Carbon dioxide separation and recovery method and carbon dioxide regeneration method

Abstract

This will realize a simple method to prevent the deterioration or loss of absorber function caused by solid precipitation, a phenomenon unique to phase-separation carbon dioxide absorbents, without making the CO2 separation and capture equipment significantly more complicated than conventional CO2 separation and capture systems. [Solution] A method for separating and recovering carbon dioxide, comprising: a first step of contacting a carbon dioxide absorbent solution 150 containing a phase-separation type carbon dioxide absorbent with a CO2-containing gas containing carbon dioxide using an absorption device 100, causing the carbon dioxide to be absorbed into the carbon dioxide absorbent solution 150 to obtain an absorption solution 160 in a reaction stage A in which solidification is limited; a second step of transferring the absorption solution 160 to a solidification device 200; and a third step of transferring the absorption solution in the solidification device 200 to a reaction stage B in which the carbon dioxide absorbent and the carbon dioxide react to form a reaction solidified product, thereby obtaining a reaction solidified product-containing liquid.

Description

[Technical Field]

[0001] The present invention relates to a method for separating and capturing carbon dioxide and a method for regenerating carbon dioxide. [Background technology]

[0002] Suppressing the rise in global average temperature caused by anthropogenic greenhouse gas emissions is one of the most important challenges facing modern society, and there is a need for the development and early implementation of technologies that will enable the separation, capture, transport, and fixation of CO2 from CO2 emission sources or the atmosphere at low energy costs.

[0003] Conventionally, carbon dioxide absorbents that have been used to remove carbon dioxide from combustion exhaust gases, the atmosphere, etc., such as monoethanolamine solutions, remain in a liquid phase even after absorbing carbon dioxide, making it difficult to separate the absorbent from the liquid solvent after carbon dioxide absorption. Therefore, when the absorbent is heated to be regenerated, the solvent must be heated at the same time, resulting in the problem of consuming excess thermal energy.

[0004] Known carbon dioxide absorbents that can solve this problem are those that combine with carbon dioxide to form a solid precipitate, i.e., phase-separation carbon dioxide absorbents (see Patent Documents 1 and 2). Such phase-separation carbon dioxide absorbents can phase-separate the solid precipitate from the liquid solvent containing the carbon dioxide absorbent, thereby reducing the heating energy required to regenerate the absorbent. Examples of phase-separation carbon dioxide absorbents include monoxylenediamine (MXDA), paraxylenediamine (PXDA), and isophoronediamine (IPDA).

[0005] However, when attempting to put a phase separation-based carbon dioxide separation and capture process into practical use, there are concerns that problems not anticipated in conventional processes may arise, such as pipe clogging and deterioration or loss of absorber performance due to solids being deposited everywhere inside the absorber, for example, on the inner walls, piping, and surfaces of internal structures. Therefore, in order to put a phase separation-based carbon dioxide removal system into practical use, it is necessary to develop an effective method for handling solids in the absorber.

[0006] Therefore, a gas treatment device has been proposed that includes a treatment tower that contains a treatment liquid, has a nozzle at the bottom for injecting the gas to be treated into the treatment liquid, and has a discharge hole at the top for discharging the treated gas to be treated; a regeneration tower that is provided with a heating device and has a recovery hole at the top for recovering the gas to be recovered; and a connecting pipe that connects the bottom of the treatment tower with the bottom of the regeneration tower and slopes downward from the treatment tower side toward the regeneration tower side, and the treatment tower is equipped with a partition plate that vertically divides the interior of the treatment tower into a nozzle area including the nozzle's outlet hole and other areas, and is provided in the treatment tower except for the upper end of the treatment tower (see Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7026938 [Patent Document 2] Patent No. 7441557 [Patent Document 3] Patent No. 7616304 Summary of the Invention [Problem to be solved by the invention]

[0008] When the phase separation-based carbon dioxide capture methods described in Patent Documents 1 and 2 are implemented, there are concerns that solids produced by reaction with carbon dioxide will precipitate everywhere inside the absorber, such as on the inner walls, piping, and surfaces of internal structures, which could lead to problems such as clogged pipes and reduced performance or loss of the absorber. Furthermore, the slurry containing the precipitated microparticles is highly viscous, requiring a large amount of energy to transport, which could result in the entire CO2 capture system becoming larger and more complex. For example, in Patent Document 3, a mechanism not found in conventional CO2 capture systems is added to the absorber to handle the highly viscous slurry produced inside the absorber.

[0009] The objective of the present invention is to realize a simple method for preventing the deterioration or loss of absorber function caused by solid precipitation, a phenomenon unique to phase-separation carbon dioxide absorbents, without making the CO2 separation and capture equipment significantly more complicated than conventional CO2 separation and capture systems. [Means for solving the problem]

[0010] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that the reaction in which a phase-separation type carbon dioxide absorbent absorbs carbon dioxide and precipitates a solid is composed of two reaction stages, namely, reaction stage A in which the carbon dioxide absorbent absorbs carbon dioxide, and reaction stage B in which the liquid phase absorbent that has absorbed carbon dioxide undergoes crystallization and precipitates a solid, thereby realizing the present invention.

[0011] The first aspect of the present invention resides in a method for separating and recovering carbon dioxide, comprising: a first step of contacting a carbon dioxide absorbent solution containing a phase-separation type carbon dioxide absorbent with a CO2-containing gas containing carbon dioxide using an absorption device, thereby causing the carbon dioxide to be absorbed into the carbon dioxide absorbent solution to obtain an absorbed solution in reaction stage A in which solidification is limited; a second step of transferring the absorbed solution to a solidification device; and a third step of advancing the reaction of the absorbed solution in the solidification device to transition to reaction stage B in which the absorbed solution becomes a reaction solidified product, thereby obtaining a reaction solidified product-containing liquid.

[0012] A second aspect of the present invention is the method for separating and recovering carbon dioxide according to the above aspect, wherein in the first step, the method, contact ratio, and contact temperature of the carbon dioxide absorbent solution and the CO2-containing gas containing carbon dioxide are controlled so that the generation of the reaction solidified product is within a predetermined range.

[0013] A third aspect of the present invention is the method for separating and recovering carbon dioxide according to the above aspect, wherein the absorption apparatus is a bubbling apparatus that injects the CO2-containing gas into the carbon dioxide absorbent solution, a spray-type apparatus that injects the CO2-containing gas into an upper space in which the carbon dioxide absorbent solution is accommodated, a tray tower-type apparatus that brings the CO2-containing gas into contact with the carbon dioxide absorbent solution on a plurality of stacked trays, or a packed tower-type apparatus that brings the carbon dioxide absorbent solution into contact with the CO2-containing gas in a packed tower packed with packing.

[0014] A fourth aspect of the present invention is the method for separating and recovering carbon dioxide according to claim 1, wherein the carbon dioxide absorbent solution contains at least one selected from monoxylenediamine (MXDA), paraxylenediamine (PXDA), and isophoronediamine (IPDA), and a non-polar solvent.

[0015] A fifth aspect of the present invention is a method for regenerating carbon dioxide, which comprises regenerating carbon dioxide from the reaction solidified product-containing liquid obtained by the method for separating and capturing carbon dioxide according to any one of the first to fourth aspects.

[0016] A sixth aspect of the present invention is a method for regenerating carbon dioxide according to the above aspect, which comprises carrying out the carbon dioxide separation and recovery method using a polar solvent as the solvent for the carbon dioxide absorbent solution in the first step, and then treating the obtained reaction solidified product-containing liquid with a nonpolar solvent and removing the polar solvent to obtain a nonpolar reactant which is a nonpolar suspension containing the reaction solidified product and the nonpolar solvent or a slurry obtained therefrom; a step b of heating the nonpolar reactant obtained in the step a under pressure, normal pressure or reduced pressure, and separating and recovering carbon dioxide to regenerate the carbon dioxide absorbent from the nonpolar reactant, thereby obtaining a carbon dioxide absorbent nonpolar solution; and a step c of treating the carbon dioxide absorbent nonpolar solution obtained in the step b with the polar solvent to replace the solvent, thereby obtaining a carbon dioxide absorbent polar solution. [Effects of the Invention]

[0017] According to the present invention, carbon dioxide separation and recovery using a phase-separation type carbon dioxide absorbent can be performed using a simple absorption device and solidification device, and carbon dioxide separation and recovery can be realized without requiring complicated solid precipitation countermeasures such as removing precipitated solids and suppressing solid precipitation. [Brief explanation of the drawings]

[0018] [Figure 1] A diagram showing the process of transporting the absorbent liquid that has absorbed carbon dioxide from the spray-type absorption device and crystallizing it at another location. [Figure 2] A diagram showing the process of transferring the absorbent that has absorbed carbon dioxide from the bubbling type absorption device and crystallizing it at another location. [Figure 3] 4 is a graph showing the change over time in viscosity of a carbon dioxide absorbent solution in Test Example 1. [Figure 4] 3 is a graph showing the change in temperature of the carbon dioxide absorbent solution over time in Test Example 1. [Figure 5] 6 is a graph showing the change over time in viscosity of a carbon dioxide absorbent solution in Test Example 2. [Figure 6] 6 is a graph showing the change in temperature of the carbon dioxide absorbent solution over time in Test Example 2. [Figure 7] 6 is a graph showing the change over time in viscosity and temperature of a carbon dioxide absorbent solution in Test Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will now be described in further detail. The carbon dioxide separation and recovery method of the present invention includes a first step of contacting a carbon dioxide absorbent solution containing a phase-separation type carbon dioxide absorbent with a CO2-containing gas containing carbon dioxide using an absorption device, thereby causing the carbon dioxide absorbent solution to absorb carbon dioxide and obtaining an absorbed solution in reaction stage A in which solidification is limited; a second step of transferring the absorbed solution to a solidification device; and a third step of advancing the reaction in the absorbed solution in the solidification device to transition to reaction stage B in which a reaction solidified product is produced, thereby obtaining a reaction solidified product-containing liquid.

[0020] That is, in the present invention, even when a carbon dioxide absorbent solution containing a phase-separation type carbon dioxide absorbent is brought into contact with a CO2-containing gas containing carbon dioxide, if the process is carried out under specified conditions, even if carbon dioxide is absorbed into the carbon dioxide absorbent solution, only a reaction in which the carbon dioxide is absorbed into the carbon dioxide absorbent occurs, and at this point, a state in which solid precipitation has not yet occurred can be maintained, thereby achieving a reaction stage A in which solidification is limited, and even if the absorption solution of this reaction stage A is transported to another device by a pump or the like, solidification does not occur, and precipitation does not occur in the pump or transport pipe, and it can be solidified in a solidification device separate from the absorption device, which is the first point.

[0021] On the other hand, reaction stage B is a stage in which the carbon dioxide absorbed inside the carbon dioxide absorbent undergoes a chemical reaction to crystallize, but in reaction stage B, it is not necessary to further bring the absorption solution of reaction stage A into contact with a CO2-containing gas. In reaction stage B, the carbon dioxide absorbent and carbon dioxide in the absorption solution can be reacted with each other to form a reaction solidified product without further bringing the absorption solution obtained in step 1 into contact with a CO2-containing gas, and this is the second point.

[0022] Here, the reaction mechanisms of reaction step A and reaction step B are not entirely clear. However, in reaction step A, first, the carbon dioxide absorbent and carbon dioxide in the absorption solution react (reaction a), producing a compound derived from the carbon dioxide absorbent and carbon dioxide, but not yet solidifying. Second, the carbon dioxide absorbent and carbon dioxide react to form a reaction solidified product, some or most of which dissolves in the solution and, in some cases, becomes supersaturated with respect to the solution. Third, the reaction solidified product produced by the reaction of the carbon dioxide absorbent and carbon dioxide (reaction a) is ionized, or the reaction intermediates associate and aggregate, dissolving in the solution. Furthermore, it is possible that several of the above states coexist, and it is even possible that carbon dioxide that has not reacted with the reaction solidified product is dissolved in the absorption solution.

[0023] Meanwhile, in reaction stage B, a reaction solidified product is produced in the absorbent solution of reaction stage A. However, the mechanism of reaction in reaction stage B, in which a reaction solidified product is produced and a reaction solidified product-containing liquid in which the reaction solidified product is dispersed, is not clear. Possible states include a first state (reaction b) in which the reaction between the carbon dioxide absorbent and carbon dioxide compound produced in reaction stage A further progresses to produce a reaction solidified product; a second state (reaction b) in which the dissolved or superdissolved carbon dioxide absorbent and carbon dioxide compound produced in reaction stage A solidifies to form a solidified product; a state (reaction b) in which the reaction solidified product is ionized and dissolved in the absorbent solution, or a state in which reaction intermediates associate and aggregate to form a solidified product from an unsolidified state; a state in which carbon dioxide dissolved in the absorbent solution reacts with unreacted carbon dioxide absorbent to form a reaction solidified product; or a combination of these states. While these may include states that cannot be considered reactions, in the present invention, all of these states are referred to as reactions, and the reaction state B is the period up to the completion of this reaction.

[0024] Although the reaction mechanism of a carbon dioxide absorbent, particularly a reaction between isophoronediamine (IPDA) and carbon dioxide is not necessarily clear, the present invention finds that the reaction in which carbon dioxide is absorbed into the carbon dioxide absorbent and the reaction in which an intermediate product resulting from the carbon dioxide absorbent and carbon dioxide further react to form a reaction solidified product differ in reaction mechanism and reaction time, and can be said to utilize the time difference between these reactions. Here, the reaction stage in which carbon dioxide is absorbed into the carbon dioxide absorbent is reaction stage A, and the reaction stage in which an intermediate product resulting from the carbon dioxide absorbent and carbon dioxide further react to form a reaction solidified product is reaction stage B.

[0025] The time difference between these two reactions can be controlled by various factors, such as the concentration of the carbon dioxide absorbent solution, the contact time between the CO2-containing gas (the gas to be treated) and the carbon dioxide absorbent, control of the contact temperature, addition of a liquid, solid, or gas that promotes or inhibits crystallization, selection of a carbon dioxide absorbent or a mixture of different carbon dioxide absorbents, and selection of a solvent.

[0026] In particular, by adjusting the time required to proceed to reaction stage B to be sufficiently longer than the time required for reaction stage A, after obtaining an absorption solution in reaction stage A where carbon dioxide is absorbed, the absorption solution can be transferred to the outside of the absorber by utilizing the time difference and proceed to reaction stage B at a different location. After transferring the absorption solution to a different location, the process may be made more efficient by performing an operation to promote reaction stage B, such as temperature control, addition of a liquid, solid or gaseous additive that promotes reaction stage B, or impact.

[0027] The important condition for preventing the transfer of the absorbent to other equipment or parts within the absorber is whether or not solids are produced by the reaction. This is because solids can adhere to internal structures or clog pipes. In comparison, the increase in viscosity and temperature of the absorbent solution are less important. However, measuring viscosity is useful as a guide to determine whether solids have formed, since continuous measurement of the amount of solids deposited is difficult.

[0028] The present invention utilizes the above-mentioned matters to maintain, for as long as possible, the state of reaction stage A, in which carbon dioxide and a carbon dioxide absorbent react to result in an absorption solution that is substantially free of solidified matter, and to delay the timing of reaction stage B, in which the reaction of solidifying a reaction intermediate between carbon dioxide and a carbon dioxide absorbent progresses and solidified matter begins to be substantially generated throughout the absorption solution until the reaction is completed to form a completely solidified matter, thereby carrying out the carbon dioxide absorption reaction in a reaction absorption apparatus, and transferring the absorption solution from the absorber while it is in reaction stage A, in which carbon dioxide has been absorbed but solid precipitation has not yet begun, or in which only a small amount of solid precipitation that does not significantly affect the viscosity has occurred, and causing the absorption solution to enter reaction state B in a location other than the absorber, such as a storage device or a regeneration device, and allowing the solidification reaction, which may cause a functional failure of the absorber, to proceed.

[0029] The present invention has the effect of solving process problems such as the formation of a high viscosity slurry in an absorber, and the clogging of pipes and loss of absorber function due to solid precipitation.

[0030] In other words, the present invention makes it possible to convert an absorption apparatus used in an existing carbon dioxide removal process that uses monoethanolamine, N-methyldiethanolamine, potassium hydroxide, sodium hydroxide, or the like as a carbon dioxide absorbing liquid into a carbon dioxide absorbent of a phase separation type without the need for adding or modifying a complex mechanism. The structures of existing absorption devices include, for example, bubbling type, spray type, tray type, packed tower type, etc., but are of course not limited to these.

[0031] The carbon dioxide separation and recovery method of the present invention will be specifically described below with reference to the drawings.

[0032] Figure 1 is a schematic diagram showing an example of a CO2 separation and capture apparatus that realizes the carbon dioxide separation and capture method of the present invention. The gas treatment apparatus shown in Figure 1 comprises an absorption apparatus 100, a solidification apparatus 200 which is a storage apparatus or a regeneration apparatus, and a communication pipe 300 that connects the two.

[0033] The absorber 100 has an inlet 110 for CO2-containing gas, which is air or exhaust gas to be treated, and an outlet 120 for gas after carbon dioxide has been absorbed and removed from the CO2-containing gas. The absorber 100 is connected to the solidification device 200 by a communication pipe 300, and a liquid pump 310 is installed in the communication pipe 300.

[0034] The absorber 100 has a spray nozzle 130 inside, and the carbon dioxide absorbent solution 150 sprayed by the liquid feed pump 140 and the spray nozzle 130 adsorbs carbon dioxide within the absorber 100 and accumulates in a liquid phase state within the absorber 100. The absorbent solution 160 containing the carbon dioxide absorbent that has absorbed the carbon dioxide is sent to the solidification device 200, which is a storage device or a regeneration device, by the communicating pipe 300 and the liquid feed pump 310 before the solidification reaction proceeds.

[0035] Inside the solidification device 200, which is a storage device or a regeneration device, a solidification reaction of the liquid-phase absorbing solution 210 containing the carbon dioxide absorbent sent from the absorption device 100 proceeds, and a solid phase 220 gradually appears.

[0036] 2 is a schematic diagram showing another example of a CO2 separation and capture apparatus of the present invention, in which a bubbling method is used as a method for contacting the gas to be treated with the carbon dioxide absorbent. That is, the absorption device 100A stores an absorption liquid introduced via a liquid supply pump 140A, and is equipped with a pipe 110A for bubbling the CO2-containing gas, which is the gas to be treated, into the absorption solution. The absorption solution becomes an absorption solution 160A containing a carbon dioxide absorbent that has absorbed carbon dioxide, and the gas after carbon dioxide has been absorbed from the CO2-containing gas is discharged from an outlet 120A.

[0037] The absorption device 100A is connected to a solidification device 200A, which is a storage device or a regeneration device, via a communication pipe 300A and a liquid feed pump 310A. The absorption solution 160A, which contains a carbon dioxide absorbent that has absorbed carbon dioxide, is fed to the solidification device 200A, which is a storage device or a regeneration device, via the communication pipe 300A and the liquid feed pump 310A before the solidification reaction proceeds.

[0038] Inside the solidification device 200A, which is a storage device or a regeneration device, a solidification reaction of the liquid-phase absorbing solution 210A containing the carbon dioxide absorbent sent from the absorption device 100A progresses, and a solid phase 220A gradually appears.

[0039] The present invention is carried out using the apparatus shown in FIG. 1 or FIG. 2 as described above. In the first step, a carbon dioxide absorbent solution is brought into contact with carbon dioxide in an absorption device, and the carbon dioxide is absorbed into the carbon dioxide absorbent solution to obtain an absorbent solution in reaction stage A in which solidification is limited.

[0040] That is, the method includes the following steps: a first step of absorbing carbon dioxide into a solution containing a carbon dioxide absorbent, which is a compound that absorbs carbon dioxide and precipitates a solid, and a solvent, to obtain an absorbed solution in a liquid state in which carbon dioxide has been absorbed, or in a liquid state containing a very small amount of solid precipitation that does not significantly affect the viscosity of the solution (this state is called reaction state A); a second step of removing the absorbed solution obtained in the first step from the absorption device in a state in which there is almost no solid precipitation, or in a state in which even if there is a small amount of solid precipitation, it is so small that it does not cause a significant change in viscosity, and transferring it to a solidification device that is a storage device or a regeneration device; and a third step of precipitating a solid from the absorbed solution obtained in the second step in a solidification device that is a storage device or a regeneration device.

[0041] In the first step, the contact method, contact ratio, and contact temperature between the carbon dioxide absorbent solution and the CO2-containing gas containing carbon dioxide are controlled to keep the generation of the reaction solidified product within a predetermined range, i.e., a state where, even if minute solid precipitation occurs, the amount is so small that it does not cause a significant change in viscosity.

[0042] In order to maintain this state, the method of contacting the carbon dioxide absorbent solution with the CO2-containing gas, for example, the contact method such as bubbling or spraying, the contact ratio, the contact temperature, the contact pressure, etc., are appropriately controlled so that the absorbent solution can be transferred to the solidification device without adversely affecting the absorption device, and solid precipitation is carried out in the solidification device.

[0043] The suspension or slurry containing the reaction solidified material in the solidification device may be treated by a conventional method.

[0044] The carbon dioxide absorbent that can be used in the present invention is not particularly limited as long as it is a phase-separation type carbon dioxide adsorbent, and examples thereof include isophoronediamine (IPDA), monoxylenediamine (MXDA), paraxylenediamine (PXDA), etc. Also, an amine compound mixture containing these may be used.

[0045] The carbon dioxide absorbent is dissolved in a solvent to form an absorption solution. The solvent is not limited as long as it is compatible with the amine compound. For example, at least one polar solvent selected from water, methanol, ethanol, acetone, acetic acid, ammonia, dimethyl sulfoxide (DMSO), sulfuric acid, etc. may be used, and in some cases, a non-polar solvent may be mixed.

[0046] In any case, the type of solvent, the concentration of the carbon dioxide absorbent, etc. are selected so that the reaction state A is maintained for as long as possible, as described above. The concentration of the carbon dioxide absorbent is selected from the range of, for example, 0.05 to 10 M, or preferably 0.08 to 3 M. The concentration unit "M" represents "mol / L."

[0047] As described above, the temperature of the absorption solution is also selected so that the reaction state A is maintained for as long as possible, and is selected from the range of, for example, 0 to 90°C, preferably 5 to 60°C. Furthermore, the pressure inside the absorber is also one of the conditions selected so that reaction state A is maintained as long as possible.

[0048] As described above, the carbon dioxide separation and recovery method of the present invention can be carried out using simple absorption equipment and solidification equipment that have been conventionally used, and has the effect of enabling carbon dioxide separation and recovery to be achieved without the need for complicated solid precipitation countermeasures such as removing precipitated solids and suppressing solid precipitation.

[0049] Furthermore, the method for regenerating carbon dioxide from the reaction solidified product-containing liquid obtained by the carbon dioxide separation and recovery method of the present invention is not particularly limited, but an example will be described below.

[0050] The carbon dioxide regeneration method of the present invention comprises: Polar solvents After carrying out the carbon dioxide separation and recovery method as described above, the following steps are carried out: step a) treating the obtained reaction solidified product-containing liquid with a nonpolar solvent and removing the polar solvent to obtain a nonpolar reactant, which is a nonpolar suspension containing the reaction solidified product and the nonpolar solvent or a slurry obtained therefrom; step b) heating the nonpolar reactant obtained in step a under pressure, normal pressure or reduced pressure to separate and recover carbon dioxide and regenerate the carbon dioxide absorbent from the nonpolar reactant to obtain a carbon dioxide reactant nonpolar solution; and step c) treating the carbon dioxide nonpolar solution obtained in step b with a polar solvent to replace the solvent and obtain a carbon dioxide reactant polar solution.

[0051] The reaction solidified product-containing liquid obtained by the separation and recovery method is obtained as a suspension or slurry in a polar solvent, but if this is first treated with a nonpolar solvent, the reaction solidified product will move into the nonpolar solvent and the polar solvent can be separated and removed. This makes it possible to obtain a nonpolar reaction product, which is a nonpolar suspension containing the reaction solidified product and the nonpolar solvent or a slurry obtained therefrom.

[0052] Furthermore, when the non-polar reactant thus obtained is heated under increased pressure, normal pressure, or reduced pressure, carbon dioxide can be separated and recovered, and the carbon dioxide absorbent can be regenerated from the non-polar reactant, thereby obtaining a carbon dioxide reactant non-polar solution.

[0053] Here, the non-polar solvent may be at least one of hexane, octane, nonane, decane, benzene, toluene, xylene, diethyl ether, cyclohexane, and the like.

[0054] Then, by treating the carbon dioxide non-polar solution thus obtained with a polar solvent, solvent substitution can be performed, and a carbon dioxide reactant polar solution can be obtained, which can be reused as the reactant solution used in the separation and recovery method of the present invention. By using this carbon dioxide regeneration method, the amount of energy input can be reduced by lowering the regeneration temperature when regenerating CO2 from the reactants that absorbed CO2. In addition, even if the reactants are regenerated without being separated, the amount of energy input can be sufficiently reduced. [Example]

[0055] The present invention will be described in more detail below with reference to specific test examples and examples, but the present invention is not limited to the examples shown below. In the test examples, the degree of crystallization was evaluated by measuring the solution viscosity in real time. A&D's SV-10A tuning fork vibro viscometer was used for real-time viscosity and temperature measurements. Vaisala's GMP251 CO2 probes (CO2 concentration 0-20%) and GMP252 (CO2 concentration 0-10,000 ppm) were used to measure CO2 concentration.

[0056] [Test Example 1]: Control of crystallization time by IPDA concentration IPDA is used as a phase-separation carbon dioxide absorbent, and water is used as the solvent. 40 g of IPDA aqueous solution containing 10 wt%, 50 wt%, or 90 wt% IPDA is prepared in a beaker, and this is used as the absorbent solution. In this example, we demonstrate that the time lag between CO2 absorption and crystallization can be controlled by changing the concentration of the IPDA solution.

[0057] A mixed gas consisting of 90% nitrogen and 10% carbon dioxide was blown into each of the CO2 absorbing solutions with three different IPDA concentrations at 500 mL / min for 5 minutes, and CO2 was absorbed into the solution by bubbling.

[0058] After 5 minutes of bubbling, the bubbling of the mixed gas is stopped, which ends reaction a between IPDA and CO2, and the solution is allowed to stand. In this state, reaction state A is maintained. Next, without contact with the mixed gas containing carbon dioxide, reaction b, which causes crystallization (solidification) within the solution, progresses, and the solution transitions to reaction state B.

[0059] The progress of crystallization can be evaluated by measuring the viscosity of the solution in real time. Figures 3 and 4 show the results of real-time measurements of the solution's viscosity and temperature, respectively. Measurement of the solution's viscosity and temperature began at elapsed time t = 0 (unit: minutes), and the solution was left to stand for one minute from t = 0 to t = 1 without any further action. From t = 1 to t = 6, a mixed gas consisting of 90% nitrogen and 10% carbon dioxide was blown into the solution at 500 mL / min for five minutes while stirring with a stirrer. After that, the blowing of the mixed gas and stirring were stopped, and the solution was left to stand for approximately two to four hours.

[0060] Figure 3 shows that, for all IPDA concentrations, there is a time lag between the time CO2 injection is stopped (t = 6) and the onset of a rapid increase in viscosity of the solution, i.e., the onset of crystallization. The 50 wt% IPDA solution exhibited the earliest rapid viscosity increase, with an inflection point at approximately t = 50. That is, the time lag Δt (units: minutes) from the cessation of CO2 injection to the onset of a rapid viscosity increase is Δt = 50 - 6 = 44. The 10 wt% IPDA solution exhibited Δt = 60 - 6 = 54, and the 90 wt% IPDA solution exhibited the greatest time lag, Δt = 120 - 6 = 114. Therefore, there is a time lag between CO2 absorption and the onset of crystallization, and this time lag can be controlled by adjusting the IPDA concentration. In particular, the crystallization time can be delayed by adjusting the IPDA concentration above or below 40%-60%, avoiding the range.

[0061] [Test Example 2]: Control of crystallization time by flow time of gas to be treated IPDA is used as a phase-separation carbon dioxide absorbent, and water is used as the solvent. 40 g of an IPDA aqueous solution containing 90 wt% IPDA is prepared in a beaker, and this is used as the absorbent solution. In this test example, we demonstrate that the time difference between CO2 absorption and the progress of crystallization can be controlled by changing the injection time of the CO2-containing mixed gas.

[0062] A mixed gas consisting of 90% nitrogen and 10% carbon dioxide was bubbled into the IPDA solution at 500 mL / min for 5 or 10 minutes, allowing the CO2 to be absorbed into the solution. After 5 or 10 minutes of bubble-in, reaction A was terminated by stopping the gas bubble-in, and the solution was allowed to stand. Reaction B allowed crystallization to proceed within the solution without contact with the carbon dioxide-containing gas.

[0063] Figures 5 and 6 show the results of real-time measurements of the viscosity and temperature of the solution, respectively. Measurements of the solution's viscosity and temperature began at elapsed time t = 0 (unit: minutes), and the solution was left to stand for one minute, from t = 0 to t = 1. A mixed gas consisting of 90% nitrogen and 10% carbon dioxide was blown into the solution at 500 mL / min while stirring with a stirrer, for five minutes, from t = 1 to t = 6, in the case of a 5-minute blowing time, and for ten minutes, from t = 1 to t = 11, in the case of a 10-minute blowing time. After that, the blowing of the mixed gas and stirring were stopped, and the solution was left to stand for approximately 2 to 4 hours.

[0064] Figure 5 shows that when the mixed gas injection time is 5 minutes, there is a time lag of Δt = 120 - 6 = 114 from the cessation of injection to the start of rapid crystallization, whereas when the injection time is 10 minutes, a rapid increase in viscosity due to crystallization occurs within 10 minutes of the cessation of injection. Therefore, by changing the mixed gas injection time, it is possible to control the time lag between CO2 absorption and the progress of crystallization.

[0065] [Test Example 3]: Controlling crystallization time by selecting absorbent MXDA is used as a phase-separation type carbon dioxide absorbent, and water is used as the solvent. 40 g of an MXDA aqueous solution containing 10 wt% MXDA is prepared in a beaker, and this is used as the absorbent solution. This test example demonstrates that even when the CO2 absorbent is MXDA, the time difference between absorption and crystallization can be controlled.

[0066] A mixed gas consisting of 90% nitrogen and 10% carbon dioxide was bubbled into the MXDA solution at 500 mL / min for 10 or 15 minutes, allowing the CO2 to be absorbed into the solution by bubbling. After 10 or 15 minutes of bubble-flow, reaction a was terminated by stopping the gas bubble-flow, and the solution was allowed to stand. Reaction b allowed crystallization to proceed within the solution without contact with the carbon dioxide-containing gas.

[0067] Figure 7 shows the real-time measurement results of the viscosity and temperature of the solution over a 15-minute injection period. Measurement of the solution's viscosity and temperature began at elapsed time t = 0 (unit: minutes). The solution was left undisturbed for one minute from t = 0 to t = 1. For the 15-minute injection period, a mixed gas consisting of 90% nitrogen and 10% carbon dioxide was injected at 500 mL / min while stirring the solution with a stirrer from t = 1 to t = 16. The gas injection and stirring were then stopped, and the solution was left undisturbed for at least eight hours. After the gas injection was stopped, the solution remained colorless and transparent for at least two hours. However, after three hours, the entire solution became cloudy and solid precipitation progressed. Between nine and sixteen hours after the injection was stopped, further crystallization progressed, and the sensor part of the viscometer, i.e., the two tuning forks immersed in the solution, merged together due to the growth of transparent plate-like crystals, making it impossible to continue measuring the viscosity using the tuning-fork vibration viscometer.

[0068] On the other hand, when the mixed gas injection time was 10 minutes, the solution began to become cloudy within 10 minutes after the injection was stopped. Therefore, even when MXDA was used as the CO2 absorbent, it was found that the time difference between CO2 absorption and crystallization could be controlled by changing the mixed gas injection time. Furthermore, these results showed that even though they are both phase-separation type CO2 absorbents, IPDA and MXDA have different time differences between CO2 absorption and crystallization. In other words, it is possible to control the time difference between CO2 absorption and crystallization by mixing two or more different phase-separation type CO2 absorbents, such as IPDA and MXDA.

[0069] [Test Example 4]: Control of crystallization time by CO2 concentration in the gas to be treated IPDA is used as a phase-separation carbon dioxide absorbent, and water is used as the solvent. 700 g of an IPDA aqueous solution containing 10 wt% IPDA is prepared in a beaker, and this is used as the absorbent solution. In this test example, it is shown that the time lag between CO2 absorption and crystallization can be controlled by the concentration of CO2 injected.

[0070] Compressed air, i.e., atmospheric air containing approximately 400 ppm carbon dioxide, was blown into the CO2 absorption solution at a flow rate of 3 L / min. The solution remained colorless and transparent for approximately 20 hours, but gradually began to become cloudy between 20 and 22 hours after blowing. 10 mL of the solution was placed in a vial after 20, 22, and 24 hours of blowing and then allowed to stand with the cap on. Samples taken after 22 and 24 hours showed slight cloudiness at the time of collection, but after more than 20 hours of standing, the amount of white solid precipitate clearly increased several-fold. This indicates that even when the blown-in carbon dioxide concentration was at atmospheric levels of approximately 400 ppm, there was a time lag between CO2 absorption and crystallization, and that this time lag could be adjusted by adjusting the carbon dioxide concentration of the gas being treated.

[0071] [Example 1] IPDA is used as a phase-separation carbon dioxide absorbent, and water is used as the solvent. 10 kg of an IPDA aqueous solution containing 10 wt% IPDA is prepared and placed inside the absorption tower as the absorbent solution. A mixed gas consisting of 90% nitrogen and 10% carbon dioxide is blown into the liquid at 125 L / min for 5 minutes. Test Example 1 shows that there is almost no change in viscosity within 60 minutes after the blowing is stopped, meaning that solid precipitation hardly progresses. Therefore, it is preferable to transfer the absorbent solution to the solidification device using a liquid pump within this time period to prevent solid precipitation within the absorption device.

[0072] However, since solid precipitation begins to increase when the viscosity of the liquid phase exceeds 1.5 times the initial viscosity before carbon dioxide absorption as a rough guide, if slight solid precipitation is acceptable, it is sufficient to transfer the material within the time when the viscosity becomes 1.5 times the initial viscosity, that is, within 100 minutes from the stop of blowing. Similarly, in the case of a continuous process, solid precipitation in the absorber can be avoided by transferring the material to the solidification device while the residence time in the absorber is preferably within 60 minutes, and at most within 100 minutes.

[0073] When the concentration of the IPDA aqueous solution is 50 wt% and 90 wt%, the time for the viscosity to reach 1.5 times the initial viscosity is 60 minutes and 80 minutes, respectively, after the stop of blowing, as shown in Test Example 1. Therefore, in this case, it is sufficient to limit the residence time in the absorber to no more than 60 minutes and 80 minutes, respectively.

[0074] On the other hand, as shown in Test Example 2, when the concentration of the IPDA aqueous solution is 90 wt % and the bubbling time is 10 minutes, the viscosity is already 1.5 times or more of the initial value immediately after the blowing is stopped, and solid precipitation progresses rapidly, making it difficult to transport the absorption solution in the liquid phase to the solidification device.

[0075] [Example 2] MXDA was used as a phase-separation carbon dioxide absorbent, with water as the solvent. 10 kg of an MXDA aqueous solution containing 10 wt% MXDA was prepared and placed inside the absorption tower as the absorbent solution. A mixed gas consisting of 90% nitrogen and 10% carbon dioxide was blown into the liquid at 125 L / min for 5 minutes. Test Example 3 showed that the viscosity change was very small within 120 minutes after the blowing was stopped, but after 160 minutes, the viscosity increased to 1.5 times the initial viscosity. Therefore, by limiting the residence time in the solidification device to preferably 120 minutes or less, or at most 160 minutes, and then transferring the liquid to the precipitation device, it is possible to avoid the problem of solid precipitation in the absorption device.

[0076] [Example 3] IPDA is used as a phase-separation carbon dioxide absorbent, with water as the solvent. 7 kg of an IPDA aqueous solution containing 10 wt% IPDA is prepared in an absorber. According to Test Example 4, when air containing approximately 400 ppm of carbon dioxide is blown into this CO2-absorbing solution at a flow rate of 30 L / min, the solution remains colorless and transparent for approximately 20 hours. However, after 20 to 22 hours of blowing, the solution gradually becomes cloudy due to solid precipitation. By transferring the solution into a solidification device within one hour, just before the clouding begins or after 20 to 24 hours, just after slight solid precipitation begins, it is possible to avoid the problem of solid precipitation in the absorber. [Industrial Applicability]

[0077] The present invention can be used in the fields of CO2 fixation, CO2 capture, and CO2 transportation in general. [Explanation of symbols]

[0078] 100, 100A: Absorber 110: Air or exhaust gas inlet 110A: Piping 120, 120A: Gas outlet 130: Nozzle 140, 140A: Liquid delivery pump 150: Carbon dioxide absorbent solution 160, 160A: CO2 absorbent solution 200, 200A: Solidification device 210, 210A: CO2 absorbed solution 220, 220A: Solid phase 300, 300A: Communication pipe 310, 310A: Liquid delivery pump

Claims

1. A carbon dioxide absorbent solution is prepared, the carbon dioxide absorbent solution containing a phase-separation type carbon dioxide absorbent containing at least one selected from monoxylenediamine (MXDA), paraxylenediamine (PXDA), and isophoronediamine (IPDA), and a polar solvent; The carbon dioxide absorbent solution and the carbon dioxide-containing CO ２ The method comprises: a first step of contacting the carbon dioxide absorbent solution with a gas containing the reactant and absorbing the carbon dioxide into the carbon dioxide absorbent solution to obtain a reactant, the time for absorbing the carbon dioxide is set within a predetermined time to generate the reactant, and obtaining an absorbed solution containing the reactant of reaction stage A that has not been solidified; a second step of transferring the absorbed solution containing the reactant of reaction stage A to a solidification device; and a third step of transferring the reactant to reaction stage B, where the reactant becomes a reaction solidified product, without performing any solidification treatment of the reactant other than allowing time to pass in the solidification device, and obtaining a reaction solidified product-containing liquid. A method for separating and recovering carbon dioxide, wherein the predetermined time for maintaining the first step is equal to or less than the time required for the viscosity of the absorption solution to become 1.5 times its initial viscosity.

2. The absorber contains the carbon dioxide absorbent solution. ２ a bubbling device for blowing in a gas containing carbon dioxide; ２ a spray-type device for blowing in a gas containing CO; ２ a tray tower type apparatus in which the contained gas is brought into contact with the carbon dioxide absorbent solution on a plurality of stacked trays; and a packed tower in which the carbon dioxide absorbent solution and the CO ２ 2. The method for separating and recovering carbon dioxide according to claim 1, wherein the method is any one selected from the group of packed column type devices that contact the carbon dioxide-containing gas.

3. A method for regenerating carbon dioxide, comprising regenerating carbon dioxide from the reaction solidified product-containing liquid obtained by the method for separating and recovering carbon dioxide according to claim 1 or 2.

4. A method for regenerating carbon dioxide as set forth in claim 3, comprising the steps of: after carrying out the carbon dioxide separation and recovery method, treating the obtained reaction solidified product-containing liquid with a nonpolar solvent and removing the polar solvent to obtain a nonpolar reactant which is a nonpolar suspension containing the reaction solidified product and the nonpolar solvent or a slurry obtained therefrom; heating the nonpolar reactant obtained in step a under pressure, normal pressure or reduced pressure, and separating and recovering carbon dioxide to regenerate the carbon dioxide absorbent from the nonpolar reactant to obtain a carbon dioxide absorbent nonpolar solution; and treating the carbon dioxide absorbent nonpolar solution obtained in step b with the polar solvent to replace the solvent, thereby obtaining a carbon dioxide absorbent polar solution.

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