JP7780281B2 - Separation structure and separation method - Google Patents

Description

The present invention relates to a separation method.

2. Description of the Related Art A technology (DAC: Direct Air Capture) has been developed that directly removes carbon dioxide (CO ₂ ), which is considered to be one of the causes of global warming, from gases (such as air) that contain CO 2 .

For example, Patent Document 1 mentions a DAC that uses an aqueous amine solution as a carbon dioxide absorption liquid. When carbon dioxide is dissolved in an aqueous amine solution, the neutral amine and carbon dioxide react to produce carbamate ions and protonated amine, thereby absorbing the carbon dioxide. On the other hand, when the carbamate ions and protonated amine are heated, neutral amine and carbon dioxide are produced, allowing the carbon dioxide to be recovered.

Special Publication No. 2020-521625

However, DAC, which uses an aqueous amine solution as the carbon dioxide absorption liquid, is complicated because it requires heating all of the absorption liquid that has absorbed the carbon dioxide.

The objective of the present invention is to provide a separation method that can easily capture carbon dioxide.

The separation method according to the present invention comprises a precipitation step and a separation step. In the precipitation step, carbon dioxide is supplied to an absorption liquid containing a solvent and an amine dissolved in the solvent, thereby producing a mixture in which a product formed by carbon dioxide combining with the amine is precipitated in the solvent. In the separation step, the solvent and the product contained in the mixture produced in the precipitation step are separated.

The present invention provides a separation method that can efficiently capture carbon dioxide.

FIG. 1 is a flow chart illustrating a separation method according to an embodiment of the present invention. Schematic diagram for explaining the preparation process Schematic diagram for explaining the deposition process Schematic diagram for explaining a first separation step Schematic diagram for explaining a first heating step Schematic diagram for explaining the second separation step Schematic diagram for explaining a second heating step

The separation method according to this embodiment is used to capture carbon dioxide. Figure 1 is a flow diagram illustrating the separation method according to this embodiment. Figures 2 to 7 are schematic diagrams illustrating the separation method according to this embodiment.

As shown in FIG. 1, the separation method according to this embodiment includes a preparation step, a precipitation step, a first separation step, a first heating step, a second separation step, and a second heating step. The steps from the precipitation step to the second heating step can be repeatedly performed.

1. Preparation Step As shown in FIG. 2, a solvent 10 and an amine A are mixed to prepare an absorbing solution 10A containing the solvent 10 and the amine A dissolved in the solvent 10.

Examples of solvents that can be used as the solvent 10 include dimethyl sulfoxide (DMSO), ether, acetone, and alcohol. DMSO is particularly suitable due to its low vapor pressure and low environmental impact.

When amine A combines with carbon dioxide, it produces product B, which has a lower solubility in solvent 10 than amine A. Examples of amine A that can be used include orthophenylenediamine (o-phenylenediamine), cyclohexylamine, ethylenediamine, and styrene oxide. o-Phenylenediamine is particularly suitable because it is easily soluble in a wide range of solvents, including alcohols and ethers. Cyclohexylamine forms 1,3-dicyclohexylurea, which has a long molecular chain conformation, upon absorbing _CO2 , and is therefore easily separated as a solid in the first and second separation steps. Similarly, ethylenediamine forms ammonium carbamate, which has a long molecular chain conformation, upon absorbing _CO2 , and is therefore easily separated as a solid in the first and second separation steps.

The content of solvent 10 in absorption liquid 10A can be 70 wt% or more and 95 wt% or less. The content of amine A in absorption liquid 10A can be 5 wt% or more and 30 wt% or less.

3, carbon dioxide is supplied to the prepared absorption solution 10A, whereby carbon dioxide combines with amine A to produce product B, which is then precipitated in the solvent 10. Since the solubility of product B in solvent 10 is lower than the solubility of amine A in solvent 10, product B becomes a solid and precipitates in solvent 10. As a result, a mixture 10B of solvent 10 and product B is produced.

For example, when solvent 10 is DSMO and amine A is o-phenylenediamine, carbon dioxide combines with the o-phenylenediamine to produce 1,3-Dihydro-2H-benzimidazol-2-one (2-benzimidazolone). Because the solubility of 2-benzimidazolone in DSMO is lower than that of o-phenylenediamine, the 2-benzimidazolone solidifies and precipitates in the DSMO. In this case, carbon dioxide can be recovered at a high recovery rate of over 95%.

In this way, product B is produced from carbon dioxide and amine A, and carbon dioxide appears to be absorbed into absorption liquid 10A. This process can be carried out at room temperature (e.g., 20°C or higher and 25°C or lower) and under normal pressure.

3. First Separation Step Product B is collected by performing solid-liquid separation of the liquid solvent 10 and the solid product B contained in the mixture 10B produced in the precipitation step.

For solid-liquid separation of solvent 10 and product B, a PF (particulate filter) in which a first space and a second space are separated by a partition wall can be used. The PF preferably has a so-called honeycomb structure. Examples of PFs with a honeycomb structure include GPFs (gasoline particulate filters) and DPFs (diesel particulate filters). Details of these are disclosed, for example, in JP 2014-193782 A, JP 4136319 A, and WO 2011/043434.

In this embodiment, the PF20 shown in Figure 4 is used for solid-liquid separation. The PF20 has a first space 21, a second space 22, and a partition wall 23. The first space 21 and the second space 22 are separated by the partition wall 23. The partition wall 23 has pores that are small enough to allow the liquid solvent 10 to pass through but not the solid product B. The partition wall 23 can be made of, for example, a ceramic material. The partition wall 23 has a first surface S1 on the first space 21 side and a second surface S2 on the second space 22 side.

As shown in Figure 4, when mixture 10B is supplied to first space 21, solvent 10 passes through partition 23, while product B adheres to the first surface S1 of partition 23.

As such, according to this embodiment, product B is precipitated in solvent 10 in the precipitation step, and therefore product B can be easily separated from solvent 10 in this step using a well-known solid-liquid separation method.

Here, when product B adheres to the first surface S1 of the partition wall 23, the pressure loss of the fluid gradually increases. If the amount of adhered product B exceeds a predetermined threshold, the supply of mixture 10B to the first space 21 is stopped, and the process proceeds to the next first heating step. The amount of adhered product B can be estimated based on the pressure loss value of the fluid.

4. First Heating Step: Amine and carbon dioxide are produced by heating product B, which has been separated in the first separation step and is attached to first surface S1 of partition wall 23. As a result, carbon dioxide is liberated from product B, and solid amine A is produced (regenerated), as shown in Fig. 5. Amine A remains attached to first surface S1 of partition wall 23.

For example, if product B is 2-benzimidazole, heating to a temperature of 50°C or higher and 60°C or lower under atmospheric pressure will cause the 2-benzimidazole to dissociate into o-phenylenediamine and carbon dioxide.

In this way, in this embodiment, it is only necessary to heat the solid product B separated from the liquid solvent 10, making it possible to easily recover carbon dioxide.

In this process, product B may be heated by externally heating PF20, or by supplying warm air to product B. Figure 5 illustrates the case where warm air is supplied from the first space 21 side.

5. Second Separation Step In this step, similarly to the first separation step, solvent 10 and product B contained in mixture 10B are subjected to solid-liquid separation, while amine A produced in the first heating step is dissolved in the separated solvent 10. In this way, in this step, collection of product B and removal (recovery) of amine A proceed simultaneously.

In this embodiment, as shown in FIG. 6, the mixture 10B produced in the precipitation step is supplied to the second space 22. Then, the solvent 10 passes through the partition wall 23, while the product B adheres to the second surface S2 of the partition wall 23. Furthermore, the amine A remaining on the first surface S1 of the partition wall 23 in the first heating step dissolves in the solvent 10 that passes through the partition wall 23 and flows into the first space 21. The dissolution of the amine A in the solvent 10 results in the preparation of a new absorption liquid 10A'. The newly prepared absorption liquid 10A' is recovered from the first space 21 to the outside and subjected to the precipitation step.

In this way, by using solvent 10 contained in mixture 10B, amine A produced in the first heating step can be easily removed. In particular, in this embodiment, mixture 10B is supplied to second space 22, allowing amine A to be smoothly backwashed by solvent 10 passing through partition 23.

Here, as in the first separation step, as product B adheres to the second surface S2 of the partition wall 23, the pressure loss of the fluid gradually increases. When the amount of product B adhered exceeds a predetermined threshold, the supply of mixture 10B to the second space 22 is stopped, and the process proceeds to the next second heating step.

6. Second Heating Step: Product B separated in the second separation step and attached to the second surface S2 of the partition wall 23 is heated to produce an amine and carbon dioxide. As a result, carbon dioxide is liberated from product B, and solid amine A is produced (regenerated), as shown in Fig. 7. The amine A remains attached to the second surface S2 of the partition wall 23.

In this process, product B may be heated by externally heating PF20, or by supplying warm air to product B. Figure 7 illustrates the case where warm air is supplied from the second space 22 side.

After the second heating step, the process returns to the first separation step. That is, by supplying the mixture 10B to the first space 21, the mixture 10B is separated into the solvent 10 and the product B.

However, in the first separation step from the second time onwards, the solvent 10 and product B contained in mixture 10B undergo solid-liquid separation, while the amine A produced in the second heating step dissolves in the separated solvent 10. In this way, in the first separation step from the second time onwards, the collection of product B and the removal (recovery) of amine A proceed simultaneously, as described in the second separation step.

(Modification of the embodiment)
Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[Modification 1]
In the above embodiment, the separation method includes the preparation step, the precipitation step, the first separation step, the first heating step, the second separation step, and the second heating step, but the preparation step, the first heating step, the second separation step, and the second heating step are optional steps. The separation method may include at least the precipitation step and the first separation step.

[Modification 2]
In the above embodiment, in the second separation step, the mixture 10B is supplied to the second space 22, but the mixture 10B may be supplied to the first space 21.

In this case, product B adheres to the first surface S1 of the partition wall 23, while amine A adhering to the first surface S1 dissolves in the solvent 10 and passes through the partition wall 23. In this way, even if mixture 10B is supplied to the first space 21 in the second separation step, collection of product B and removal of amine A can proceed simultaneously.

However, if amine A dissolves in solvent 10, the viscosity may increase, making it difficult for the amine A to pass through partition 23. Therefore, it is preferable to backwash amine A as in the above embodiment rather than forward wash amine A as in this modified example.

When mixture 10B is supplied to first space 21 in the second separation step, amine A remains on first surface S1 of partition wall 23 in the second heating step, and in the second and subsequent first separation steps, product B adheres to first surface S1 of partition wall 23, while amine A adhering to first surface S1 dissolves in solvent 10 and passes through partition wall 23.

A Amine B Product 10 Solvent 10A Absorption liquid 10B Mixture 20 PF (Particulate filter)
21 First space 22 Second space 23 Partition wall S1 First surface S2 Second surface

Claims (4)

a precipitating step of supplying carbon dioxide to an absorption liquid containing a solvent and an amine dissolved in the solvent, thereby producing a mixture in which a product in which carbon dioxide is bound to the amine is precipitated in the solvent;
a first separation step of separating the solvent and the product contained in the mixture produced in the precipitation step;
a first heating step, after the first separation step, of heating the product separated in the first separation step to produce an amine and carbon dioxide;
a second separation step, after the first heating step, of separating the solvent and the product contained in the mixture produced in the precipitating step, and dissolving the amine produced in the first heating step in the separated solvent;
A separation method comprising: In the first and second separation steps, a particulate filter in which a first space and a second space are separated by a partition wall is used,
In the first separation step, the mixture is supplied to the first space,
In the second separation step, the mixture is supplied to the second space.
The separation method according to claim 1 . After the second separation step, a second heating step is further provided in which the product separated in the second separation step is heated to produce an amine and carbon dioxide.
The separation method according to claim 1 or 2. a precipitating step of supplying carbon dioxide to an absorption liquid containing a solvent and an amine dissolved in the solvent, thereby producing a mixture in which a product in which carbon dioxide is bound to the amine is precipitated in the solvent;
a first separation step of separating the solvent and the product contained in the mixture produced in the precipitation step;
Equipped with
the solvent is dimethyl sulfoxide,
the amine is orthophenylenediamine,
The product is 2-benzimidazolone.
Separation method.