Absorption solution for absorbing acidic compound from gaseous emission

Abstract

To provide an absorption solution for absorbing acidic compounds such as carbon dioxide from gaseous emissions, wherein the absorption solution offers a high absorption rate and facilitates wastewater treatment after regeneration.SOLUTION: The present invention provides an absorption solution for absorbing acidic compounds from gaseous emissions, which contain the acidic compounds. The absorption solution contains a component (a): water, a component (b): N,N,N',N'-tetramethyl hexamethylene diamine, and a component (c): a first or second amine with a solubility in water at 20°C of less than 3 g / L.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an absorption solution for absorbing acid compounds from a gaseous effluent containing said compounds. [Background technology]

[0002] In recent years, there has been a demand for more efficient technology for recovering acidic compounds such as carbon dioxide from gas fields, thermal power plants, steel mills, cement plants, waste incineration facilities, and biomass-related facilities.

[0003] For example, Patent Document 1 discloses an absorption solution which is an aqueous solution containing N,N,N',N'-tetramethylhexane-1,6-diamine and a specific primary or secondary amine, and which prevents phase separation of the resulting salt when absorbing acidic compounds in a gaseous effluent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2011-528993 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not mention wastewater treatment of the water-enriched fraction after regeneration. Furthermore, it has been found that when carbon dioxide is absorbed using the absorption solution shown in the document, there are problems such as a slow absorption rate and difficulty in wastewater treatment after regeneration.

[0006] The present invention therefore relates to an absorbent solution for absorbing acidic compounds, such as carbon dioxide, from gaseous effluents, which has a fast absorption rate and which, after regeneration, allows for easy wastewater treatment. [Means for solving the problem]

[0007] As a result of intensive research by the present inventors to solve such problems, it was found that an aqueous solution containing N,N,N',N'-tetramethylhexamethylenediamine and a specific primary amine or secondary amine having low solubility in water has a high absorption rate for acidic compounds, and that after absorption and further separation of the acidic compounds, the absorbent solution after regeneration, is rich in water and the fraction can be easily treated as wastewater. Based on this finding, the present inventors have completed the present invention.

[0008] The present invention relates to the following [1] and [2]. [1] An absorption solution for absorbing acidic compounds from a gaseous effluent containing the acidic compounds, the absorption solution comprising the following components (a) to (c): (a) Water (b) N,N,N',N'-Tetramethylhexamethylenediamine (c) a primary or secondary amine having a solubility in water of less than 3 g / L at 20°C [2] A method for absorbing an acidic compound, comprising an absorption step of contacting a gaseous effluent containing an acidic compound with the absorption solution described in [1] above to absorb the acidic compound into the absorption solution. Effect of the Invention

[0009] According to the present invention, it is possible to provide an absorption solution which has a high absorption rate for absorbing acidic compounds such as carbon dioxide from a gaseous effluent, and which facilitates wastewater treatment of the water-enriched fraction of the absorption solution after the absorption and separation of the acidic compounds. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an overview of an apparatus for evaluating an absorbing solution of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The absorbing solution of the present invention is an absorbing solution for absorbing acidic compounds from a gaseous effluent containing the acidic compounds, and contains the following components (a) to (c): (a) Water (b) N,N,N',N'-Tetramethylhexamethylenediamine (c) a primary or secondary amine having a solubility in water of less than 3 g / L at 20°C

[0012] The mechanism by which the above-mentioned effects can be achieved by using such components is presumed to be as follows. A wide variety of amines are known for absorbing acidic compounds. A primary amine or a secondary amine having a solubility in water of less than 3 g / L cannot achieve a sufficient absorption rate of an acidic compound due to its low solubility in water. In addition, when N,N,N',N'-tetramethylhexamethylenediamine is used alone as the active ingredient of the absorption solution, the water-enriched fraction is easy to be disposed of in the wastewater, but the absorption rate is insufficient.

[0013] Therefore, the present inventors have examined various amines and found that the three components of the primary or secondary amine, N,N,N',N'-tetramethylhexamethylenediamine, and water are compatible with each other. In such an aqueous solution, the primary or secondary amine is dissolved in water, and therefore a sufficient reaction rate can be obtained. Furthermore, since the aqueous solution after absorbing and then desorbing an acidic compound has a cloud point, it is separated into a layer rich in N,N,N',N'-tetramethylhexamethylenediamine and a layer rich in water by placing the aqueous solution under a temperature condition exceeding the cloud point temperature. By separating the two, the interaction between the primary or secondary amine and water disappears, and most of the primary or secondary amine is present in the layer rich in N,N,N',N'-tetramethylhexamethylenediamine. As a result, the concentration of the amine component in the water-rich layer is reduced, making it easier to treat the layer as wastewater. The present invention will be described in detail below.

[0014] 1. Acidic compounds and gaseous effluents Examples of acidic compounds in the present invention include carbon oxides such as carbon dioxide, sulfur oxides such as sulfur monoxide, sulfur dioxide and sulfur trioxide, nitrogen oxides such as nitrogen monoxide, nitrogen dioxide, nitrogen trioxide, nitrous oxide, dinitrogen trioxide, dinitrogen tetroxide and dinitrogen pentoxide, and sulfur compounds such as hydrogen sulfide.

[0015] The gaseous effluent in the present invention refers to a gas containing an acidic compound, such as exhaust gas from a thermal power plant using petroleum, coal, natural gas, or the like as fuel, exhaust gas from a kiln in a cement factory, exhaust gas from a blast furnace or converter in an ironworks, exhaust gas from a waste incineration facility, and biomass exhaust gas discharged by putrefaction or fermentation. The present invention is particularly suitable for use in treating exhaust gases that contain moisture, and is particularly suitable for use in treating low-rank coal that has a high moisture concentration in the exhaust gas, exhaust gases from thermal power plants that use natural gas as fuel, exhaust gases from waste incineration facilities, and biomass-based exhaust gases.

[0016] 2. The absorbing solution of the present invention [Component (a)] The component (a) in the present invention is water. Water serves as a medium for the components (b) and prevents the absorption solution from thickening after contact with an acidic compound, i.e., after neutralization.

[0017] [Component (b)] Component (b) in the present invention is N,N,N',N'-tetramethylhexamethylenediamine represented by the following chemical formula. It has been found that component (b) not only acts to absorb acidic compounds in the absorbing solution, but also unexpectedly acts as a dissolving aid in water for amines with low solubility in water. That is, by using component (b), even an amine that is almost insoluble in water, such as the amine of component (c), can be dissolved in a larger amount in the absorbing solution of the present invention. Thus, the use of component (b) in the absorbing solution of the present invention is one of the features of the present invention.

[0018] [ka]

[0019] [Component (c)] The component (c) in the present invention is a primary or secondary amine having a solubility in water at 20° C. of less than 3 g / L. From the viewpoint of reducing the burden of wastewater treatment and from the viewpoint of efficient reuse of component (c), it is preferable that component (c) has a lower solubility in water. For example, the solubility of component (c) in water at 20° C. is preferably 3 g / L or less, more preferably 1 g / L or less.

[0020] The structure of component (c) is preferably a monoamine having an alkyl group, more preferably a primary monoamine having an alkyl group, from the viewpoints of low foaming and quality stability during repeated use. The number of carbon atoms in the alkyl group is preferably 5 or more, more preferably 6 or more, and is preferably 10 or less, more preferably 8 or less. The alkyl group may be linear or branched, but is preferably branched from the viewpoint of low foaming.

[0021] Specific preferred examples of the amine component (c) include 2-ethylhexylamine (solubility in water at 20° C.: 0.3 g / L) and n-octylamine (solubility in water at 20° C.: 0.2 g / L). Only one type of component (c) may be used, or two or more types of components may be used in combination.

[0022] [Other ingredients] Furthermore, the absorbing solution of the present invention may contain components such as an oxidation stabilizer and a corrosion inhibitor, if necessary.

[0023] Properties of the Absorbent Solution of the Present Invention The amount of component (a) in the absorbing solution of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of reducing the viscosity increase during the absorption of acidic compounds and preventing the precipitation of salts. On the other hand, from the viewpoint of reducing the energy required for the separation of amine components and the recovery of acidic compounds, the amount of component (a) is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0024] The amount of component (b) in the absorbing solution of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoints of the saturated absorption capacity of acidic compounds and the solubility of component (c) in water. On the other hand, from the viewpoint of preventing thickening during absorption of acidic compounds, the amount of component (b) is preferably 58% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0025] The amount of component (c) in the absorbing solution of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of the absorption rate of the acidic compound. On the other hand, from the viewpoint of the solubility in components (a) and (b), the amount of component (c) is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less.

[0026] The total amount of components (b) and (c) in the absorbing solution of the present invention is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of achieving both the saturated absorption amount and the absorption speed of the acidic compound. On the other hand, from the viewpoint of preventing thickening, the total amount is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. If the total amount of components (b) and (c) in the absorbing solution is too large, the absorbing solution may thicken and gel when it absorbs an acidic compound, so the total amount is preferably 60% by mass or less.

[0027] The mass ratio ((b) / (c)) of component (b) to component (c) in the absorbing solution of the present invention is, from the viewpoint of maintaining the dissolved state of component (c) in water, preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. On the other hand, from the viewpoint of the absorption rate of carbon dioxide, the mass ratio is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less.

[0028] The viscosity of the absorbing solution of the present invention is preferably as low as possible from the viewpoint of improving the fluidity in the equipment. Specifically, the viscosity is preferably 50 mPa s or less, more preferably 25 mPa s or less, and even more preferably 15 mPa s or less. The viscosity here is a value measured using a Brookfield viscometer (for example, TVB-10 manufactured by Toki Sangyo Co., Ltd.) at 30° C. and a rotation speed of 60 rpm.

[0029] [Method of preparing the absorbing solution] The absorbing solution of the present invention can be prepared by mixing the above-mentioned components (a), (b) and (c), and further optional components, if necessary, by known means.

[0030] 3. The method for absorbing acidic compounds according to the present invention The method for absorbing an acidic compound of the present invention includes the following absorption steps.

[0031] [Absorption process] In the absorption step, the gaseous effluent containing the acidic compounds is contacted with the above-mentioned absorbing solution of the present invention to absorb the acidic compounds into the absorbing solution. The method of contacting the gaseous effluent with the absorbing solution of the present invention is not particularly limited. For example, there may be mentioned a method of bubbling a gaseous effluent into an absorbing solution, a method of spraying an absorbing solution into a stream of a gaseous effluent, or a method of countercurrently contacting an absorbing solution with a gaseous effluent in an absorption tower.

[0032] The temperature in the absorption step is preferably 10°C or higher, more preferably 20°C or higher, while it is preferably 55°C or lower, more preferably 50°C or lower. The pressure in the absorbing step may be about normal pressure, but may be increased in order to increase the absorption rate.

[0033] [Desorption step] The absorbing solution that has absorbed the acidic compounds in the absorption step is treated in the desorption step to desorb the acidic compounds from the absorbing solution. Meanwhile, the absorbing solution is regenerated by the desorption of the acidic compounds. Specific methods for the desorption step include a method in which the absorption solution is heated in a container different from that used in the absorption step to desorb the acidic compounds, and a method in which the absorption solution is introduced into a desorption tower and heated while expanding the liquid interface in the desorption tower. By such methods, the acidic compounds that have reacted with the amine are liberated and released from the absorption solution. The liberated acidic compounds can be recovered by known means.

[0034] The temperature in the desorption step is preferably 70° C. or higher, more preferably 80° C. or higher, and is preferably 120° C. or lower, more preferably 100° C. or lower, and further preferably 90° C. or lower. The pressure in the desorption step may be about normal pressure, but may be increased in order to increase the efficiency of the desorption step.

[0035] [Separation process] In the separation step, the absorbent solution regenerated through the desorption step is preferably continuously introduced into a specific container (e.g., a separation tank), and the regenerated absorbent solution is separated into a layer rich in water and a layer rich in component (b) by maintaining the heated state in the desorption step or by heating the absorbent solution again.

[0036] One of the features of the present invention is that, from among various amines capable of absorbing acidic compounds, the specific amines component (b) and component (c) are employed as active ingredients in the absorbing solution. Since an aqueous solution containing components (b) and (c) has a cloud point, the aqueous solution can be separated into a water-rich layer and a layer rich in (b) and (c) by heating the aqueous solution to a temperature above the cloud point. In the separation step, a higher temperature is preferable within a range not exceeding the boiling point of water, i.e., 100°C at normal pressure, since this reduces the amine concentration in the water-rich layer. On the other hand, from the viewpoint of reducing the energy required for separation, it is preferable to supply the absorption solution to the separation step while maintaining the heating state during the acidic compound desorption step. Therefore, the specific temperature range of the absorption solution in the separation step is preferably 60°C or higher, more preferably 70°C or higher, while it is preferably 99°C or lower, more preferably 90°C or lower, so that the solution can be separated into a water-rich layer and a component (b)-rich layer. The pressure in the separation step may be about normal pressure, but may be increased or decreased in order to increase the separation efficiency.

[0037] The amine concentration in the water-rich layer obtained through the separation step is sufficiently low, so that the water-rich layer can be discharged as wastewater as is or after minor treatment by known means. Furthermore, a part of the water-rich layer can be reused for adjusting the moisture content of the component (b)-rich layer. On the other hand, the component (b)-rich layer obtained through the separation step contains a high concentration of component (c). Therefore, the component (b)-rich layer can be reused as an absorption solution. EXAMPLES

[0038] The present invention will be specifically described below with reference to examples. Note that the following examples are merely illustrative of the present invention and do not imply any limitation. Note that "normal pressure" refers to 101.3 kPa, and "normal temperature" refers to 25°C.

[0039] Examples 1 to 3 and Comparative Examples 1 to 2 Aqueous solutions having the compositions shown in Table 1 were prepared as the absorbing solutions of Examples 1 to 3 or Comparative Examples 1 and 2. One hour after preparation, the appearance of each absorbing solution at room temperature was uniform and transparent.

[0040] Test Example 1 An apparatus for evaluating the saturated carbon dioxide absorption capacity of each absorbing solution was constructed as follows. The outline of the apparatus is shown in Figure 2. The carbon dioxide cylinder 21 and drying tube 22 (manufactured by Kartell, material: PE, total length (mm): 270, size (diameter Φ x height H) (mm): 20 x 200, desiccant: silica gel) were connected with a pressure-resistant hose. As a container C for the absorption solution, 25 g of any of the absorption solutions shown in Table 1 was placed in a 080100-02 bubbler (manufactured by Shibata Scientific Co., Ltd., capacity: 30 mL, size (diameter Φ×height H) (mm): 28×149, accessory: glass filter P160). This was connected to a drying tube 22. Two more drying tubes were prepared and connected in series to vessel C (drying tube A and drying tube B). Container D was prepared by placing 50 g of 85% by weight phosphoric acid aqueous solution in a reagent bottle with a filter unit (manufactured by SHIBATA, capacity: 100 mL, manufacturer's part number 016060-100) and connecting it to drying tube A. Container D containing the phosphoric acid aqueous solution was intended to capture the amine as a salt in case it volatilized when measuring the total mass change.

[0041] The total mass of A, B, C and D before the supply of carbon dioxide was defined as the initial mass. The initial liquid temperature and the experimental atmosphere were kept at 20°C ± 1°C, and carbon dioxide was bubbled at 0.5 L / min. The temperature in container C and the changes in the total mass of A, B, C, and D were recorded over time.

[0042] In addition, the temperature rise of the container C was observed, and the highest temperature reached was recorded and used as an index of the energy required to separate the acidic compounds and regenerate the absorbing solution. As a result of the experiment, the temperatures of the absorbing solutions of Examples 1 to 3 and Comparative Examples 1 and 2 were all below 40°C, and it was determined that the amount of energy required to regenerate the absorbing solution was small for practical use.

[0043] Test Example 2 In the above Test Example 1, the total mass was recorded when the change in the total mass became less than 0.1 g after 5 minutes of bubbling. The difference between this total mass and the initial mass was calculated, and the saturated absorption capacity was determined by converting it into the increase in mass per liter of the absorbing solution. The higher the saturated absorption capacity, the better the absorbing solution was.

[0044] Test Example 3 In the above Test Example 2, the behavior up to 70% of the saturated absorption capacity was linearly approximated, and the slope was defined as the absorption rate. The absorption rate was calculated as the increase in mass per liter of the absorbing solution per minute. The higher the absorption rate, the better the absorbing solution was considered to be.

[0045] Test Example 4 The ease of wastewater treatment of the absorbent solution after absorbing carbon dioxide and then desorbing the carbon dioxide was tested as follows. 60 g of each of the absorbing solutions shown in Table 1 was placed in a Maruemu No. 8 screw tube and sealed. Since each absorbing solution here was assumed to be an absorbing solution after absorbing carbon dioxide and then desorbing the carbon dioxide, no carbon dioxide bubbling was performed. As an operation simulating a separation process, each screw tube was left in an oven adjusted to 70°C for one day. After that, the presence or absence of layer separation was visually observed. In addition, samples of the upper and lower layers were taken, and the moisture (mass%), total amine value (KOHmg / g), and tertiary amine value (KOHmg / g) were measured, and the composition was calculated.

[0046] Since component (b) has a cloud point, when the above composition is heated to 70° C., it separates into a layer rich in component (b) (upper layer) and a layer rich in water (lower layer). The lower the amount of amine in the lower layer, the higher the efficiency of reusing the amine in the upper layer and the lower the cost of treating the lower layer as wastewater. In this test, it was determined that the higher the water concentration in the water-rich layer (lower layer) and the lower the amine concentration, the easier the wastewater treatment.

[0047] [Table 1]

[0048] The compositions in the above table are in mass %.

[0049] The absorbing solutions of Examples 1 to 3 and Comparative Examples 1 and 2 were left at 70°C, and as a result, all of the absorbing solutions were separated into an upper layer and a lower layer. With regard to the carbon dioxide absorption rate, the absorbing solutions of Examples 1 to 3 and Comparative Example 1 had a practically sufficient absorption rate, but the absorbing solution of Comparative Example 2 was clearly inferior. From the above experimental results, it was found that the absorbing solutions having the compositions of the present invention (Examples 1 to 3) have properties that allow both a high absorption rate and ease of wastewater treatment. On the other hand, some of the absorbent solutions with the compositions of the comparative examples (Comparative Example 1) were excellent in saturated absorption capacity and absorption speed, but in all cases, the amine concentration in the water-rich layer (lower layer) was found to be high. This suggests that a further step of lowering the amine concentration is necessary to treat the water-rich layer (lower layer) as wastewater. Furthermore, it was found that 60% of n-butylamine was present in the lower layer in Comparative Example 1, and 30% of N-methylbenzylamine was present in the lower layer in Comparative Example 2. This suggests that when the layer (upper layer) rich in component (b) is circulated and reused as an absorption solution, it is necessary to add a considerable amount of n-butylamine or N-methylbenzylamine. In this case, the migration of component (b) to the water-rich layer is also promoted, suggesting that it is necessary to add a larger amount of component (b). In this way, when two or more amines are added in a situation where an amine needs to be added, it becomes necessary to check the ratio of the lost amines each time regeneration is performed, which makes the analysis and addition of each amine very cumbersome. However, when the absorption solution of the embodiment is used, the addition of the "amine used in combination" in the water-rich layer (lower layer) can be handled by adding only a small amount of component (b). This means that the analysis and addition of each amine are simplified or unnecessary, which can be said to be a great advantage in practical use. [Industrial Applicability]

[0050] The absorption solution of the present invention can be used in the field of recovering carbon dioxide from various exhaust gases. [Explanation of symbols]

[0051] 21 Carbon Dioxide Cylinder 22 Drying tube A Drying tube B Drying tube C Container containing absorbing solution D Container containing phosphoric acid solution

Claims

1. An absorption solution for absorbing an acidic compound from a gaseous effluent containing the acidic compound, the absorption solution containing the following components (a) to (c). (a) Water (b) N,N,N',N'-tetramethylhexamethylenediamine (c) A primary or secondary amine having a solubility in water at 20 °C of less than 3 g / L

2. The absorption solution according to Claim 1, wherein the amine of component (c) is a primary monoamine having an alkyl group.

3. The absorption solution according to Claim 2, wherein the amine of component (c) is one or more selected from the group consisting of 2-ethylhexylamine and n-octylamine.

4. The absorption solution according to any one of Claims 1 to 3, wherein the total amount of component (b) and component (c) is 20% by mass or more and 60% by mass or less.

5. The absorption solution according to any one of Claims 1 to 3, wherein the mass ratio ((b) / (c)) of component (b) to component (c) is 1 or more and 30 or less.

6. An absorption method of an acidic compound, comprising an absorption step of bringing a gaseous effluent containing the acidic compound into contact with the absorption solution according to any one of Claims 1 to 3 to absorb the acidic compound in the absorption solution.

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