JP6860147B2 - Absorbents and absorbents for substituted piperazine compounds and acid gases - Google Patents

Description

The present invention relates to a substituted piperazine compound that can be used for treating a gas containing an acid gas, and an absorbent and an absorbent liquid using the substituted piperazine compound.

Facilities such as thermal power plants, steel mills, and boilers use large amounts of fuel such as coal, heavy oil, and super-heavy oil, and sulfur oxides, nitrogen oxides, carbon dioxide, etc. emitted by combustion of fuel are used. From the standpoint of preventing air pollution and preserving the global environment, acidic gas requires quantitative and concentration restrictions on its release. In addition, carbon dioxide is regarded as a problem as a main cause of global warming, and movements to curb emissions are becoming active worldwide. For this reason, gas treatment measures are being promoted to separate or remove acid gases in combustion exhaust gas and process exhaust gas, and various studies are being energetically promoted to enable the recovery and storage of carbon dioxide. There is.

As a method for separating or recovering carbon dioxide, for example, a PSA (pressure swing) method, a membrane separation concentration method, a chemical absorption method utilizing reaction absorption by a basic compound, and the like are known. In the chemical absorption method, an amine absorption method in which an alkanolamine-based basic compound is mainly used as an absorbent is generally used, but such a basic compound is used not only for carbon dioxide but also for other acid gases. Also exhibits absorbency and can be used as an absorbent for various acid gases. In the treatment process by the chemical absorption method, generally, an aqueous liquid containing an absorbent is used as an absorption liquid, carbon dioxide contained in the gas is absorbed by the absorption liquid, and then the absorption liquid is heated to absorb the absorbed carbon dioxide. Regenerate the absorbent by releasing it. The absorbed liquid after regeneration is cooled and reused in the absorption step, and the absorbed liquid is circulated so as to alternately repeat these steps (see, for example, Patent Document 1 below).

Items related to the performance of the absorption liquid include the absorption rate and capacity of carbon dioxide, and the heat of reaction with carbon dioxide, in order to reduce the equipment cost and energy recovery required for the separation and recovery of carbon dioxide. The absorbent used for the absorbent is determined in consideration of these items. Generally, a combination of a plurality of types of amine compounds is used. The reason is that it is practically difficult to find an excellent amine compound in all of the above items, and a large number of absorbent combinations and combinations of absorbents are used so as to combine compounds having different properties to complement each other's properties. Comprehensive investigations and studies have been conducted on the compositions, and various combinations and compositions have been reported (see, for example, Patent Document 2 below).

Japanese Unexamined Patent Publication No. 2009-214089 Japanese Unexamined Patent Publication No. 2008-13400

However, the combination of absorbents proposed by the comprehensive study as described above does not mean that the absorbent solution is totally excellent, and it is necessary to further improve it practically. Further, there is a problem that the composition of the absorbing liquid fluctuates with time due to the volatility of the amine compound, and it is necessary to regularly control and adjust the quality of the absorbing liquid.

An object of the present invention is to provide an absorbent solution that solves the above-mentioned problems, can suppress compositional fluctuations over time when prepared and used as an absorbent solution, and reduces the burden of regular quality control and adjustment. It is to provide a novel compound possible, and an absorbent and an absorbent for acid gas treatment using the compound.

In order to solve the above problems, the present inventors have conducted intensive studies, and as a result, by designing the molecule of the amine compound with reference to the molecular structure and absorption performance of the conventional absorbent, an extremely promising compound can be obtained. It was obtained, and the present invention was completed.

According to one aspect of the present invention, the substituted piperazine compound is represented by the following general formula.

The acid gas absorber and the carbon dioxide absorber contain the above-mentioned substituted piperazine compound as an active ingredient. The absorption liquid for acid gas treatment and the absorption liquid for carbon dioxide treatment may be prepared so as to contain the above-mentioned substituted piperazine compound and water.

According to the present invention, a substituted piperazine compound having low volatility and excellent acid gas absorption performance is provided, and the substituted piperazine compound is used as an acid gas absorber to suppress quality fluctuations over time and to perform regular quality control. Since it is possible to provide an absorbing liquid capable of reducing the burden of adjustment, the work load in gas treatment is reduced, which is economically advantageous.

The graph which shows the absorption performance of carbon dioxide in the absorption liquid which used the substituted piperazine compound (trans-1) as an absorbent. The chart which shows the diffraction intensity in the powder X-ray diffraction of a substituted piperazine compound (trans-1). The chart which shows the diffraction intensity in the powder X-ray diffraction of a substituted piperazine compound (cis-1). The graph which shows the absorption performance of carbon dioxide in the absorption liquid which used the substituted piperazine compound (cis-1) as an absorbent together with the absorption performance of the substituted piperazine compound (trans-1).

Items related to the performance of the absorption liquid used in the recovery of carbon dioxide include the absorption rate and capacity of carbon dioxide, and the heat of reaction during carbon dioxide absorption. In order to reduce the operating cost and energy consumption required for the separation and recovery of carbon dioxide, the absorbent to be used for the absorbent is determined in consideration of these items. At that time, it is common to select a plurality of types of absorbents and combine them so as to complement each other's performance to prepare an absorbent solution. For example, cyclic amino compounds generally have a high rate of carbon dioxide absorption but low water solubility. On the other hand, alkanolamines having a hydroxyl group are water-soluble, but the absorption rate of carbon dioxide is relatively slow. Therefore, by combining these and complementing each other's defects, a good absorption liquid in terms of water solubility and absorption rate can be obtained. However, since the cyclic amino compound has a low boiling point and a relatively high vapor pressure, it is easily vaporized during regeneration of the absorbing liquid. On the other hand, the boiling point of alkanolamines is higher than that of cyclic amino compounds, but the emission from the absorbent is still not negligible. Therefore, by repeating the use / regeneration of the absorbent liquid, the composition fluctuation of the absorbent liquid due to the dissipation of the absorbent liquid becomes remarkable. In order to solve the problem of the composition fluctuation of the absorbent liquid over time, it is important to use an absorbent that is hard to vaporize. That is, it is necessary to find a compound having a larger molecular weight than the conventional one and exhibiting good absorption performance.

The inventors of the present application examined the molecular structure of a compound satisfying the above requirements while considering the relationship between the molecular structure of a conventional absorbent and the absorption performance, and attempted to design the molecule of an absorbent having a large molecular weight. .. At that time, various combinations of conventional absorbents were investigated, and an attempt was made to combine the molecular structures of the two types of absorbents constituting the combination into one molecular structure. As a result, a novel substituted piperazine compound having a molecular structure in which piperazine and N-methyldiethanolamine (hereinafter abbreviated as MDEA) are bound has been realized. Therefore, the present application proposes a novel substituted piperazine compound. This is a compound designed to take advantage of piperazine, which has a high absorption rate of carbon dioxide, to suppress its volatility and improve its water solubility, and has a structure suitable for an absorbent.

As shown by the following general formula, the proposed substituted piperazine compound (1) has a molecular structure in which the molecular weight is increased by introducing a substituent into the heterocyclic skeleton of piperazine as a base, and the substituent has a substituent. Is an N-di (2-hydroxyethyl) aminomethyl group. That is, the substituted piperazine compound (1) is a complex amine compound having a structure in which one molecule of piperazine and two molecules of MDEA are bonded. Since the substituent has a hydroxyl group, the water solubility of the substituted piperazine compound (1) is improved as compared with piperazine.

Substituents having the structure of MDEA have been adopted in consideration of the unique reaction linkage and effectiveness in the absorption liquid of the mixed system of piperazine and MDEA. In a mixed system of piperazine and MDEA, the acceptance of hydrogen by MDEA shifts the equilibrium of the carbamate formation reaction between carbon dioxide and piperazine, and promotes the increase of bicarbonate ion and the uptake of new carbon dioxide. .. That is, the design is intended to realize such reaction linkage within one molecule. In the substituted piperazine compound (1), two substituents are introduced into the heterocyclic skeleton. This is based on the fact that carbon dioxide absorption is most efficient when the number of amino groups in MDEA relative to the amino groups in piperazine in the mixture is equivalent. That is, the substituted piperazine compound (1) is designed so that hydrogen acceptance by the amino group of the substituent and carbamate formation by the amino group of the heterocycle proceed efficiently in the molecule, and high absorption performance is expected. ..

In the molecular design of the substituted piperazine compound (1), a prediction model (EPI suite: The Estimations Programs Interface for Windows, available from URL) that predicts and calculates the physical properties of new substances. Http://www.epa.gov/ opptintr / exposure / rubs / episuitedl.htm) is used to predict the volatility of the designed molecule and use it to evaluate the molecular structure. According to the prediction model, the estimated values of the boiling point and vapor pressure (25 ° C.) of the substituted piperazine compound (1) are 523.6 ° C. and 3.19 × 10 ^-12 Pa. Estimated values of boiling point and vapor pressure (25 ° C) based on the prediction model of piperazine (boiling point: 146 ° C, vapor pressure (25 ° C): 21.3 Pa) are 163.75 ° C and 94.9 Pa, and MDEA (boiling point: 247 ° C). , Vapor pressure (25 ° C.): 0.0267 Pa) Since the estimated values are 233.46 ° C. and 0.327 Pa, the reliance on the estimated values by the prediction model is valid. Therefore, according to the estimated value of the substituted piperazine compound (1), it can be considered that the substituted piperazine compound (1) actually has satisfactory properties for solving the problem of time-dependent fluctuation in the absorption liquid. ..

The substituted piperazine compound (1) can be prepared by a known synthetic method according to the following synthetic route using 2,5-dimethylpyrazine (2) as a starting material. Alternatively, the 2,5-pyrazinedicarboxylic acid (3) produced by the oxidation of 2,5-dimethylpyrazine (2) in this synthetic route is available as a commercially available product, and may be used as a starting material. According to the synthetic route, 2,5-pyrazinedicarboxylic acid (3) is converted to piperazinedicarboxylic acid (4) by catalytic reduction with hydrogen. The piperazine dicarboxylic acid (4) is converted into an ester compound (5) in which a carboxy group is esterified, and a condensation reaction with diethanolamine (6) is carried out to obtain a diamide compound (7). When the amide group of this compound is reduced to convert the carbonyl group to a methylene group, the substituent attached to the piperazine ring becomes a di (2-hydroxyethyl) aminomethyl group. In order to proceed with this reduction reaction, the hydroxyl group of the diamide compound (7) is protected in advance and converted into the protected amide compound (8), and then the carbonyl group is reduced. Since the protected amine compound (9) thus obtained is a substituted piperazine compound (1) having a protected hydroxyl group, the substituted piperazine compound (1) can be obtained by deprotecting the protected amine compound (9). The hydroxyl group of the diamide compound (7) is suitably protected by benzylation with benzyl bromide, at which time the amino group of the piperazine ring is also benzylated. Deprotection proceeds favorably by a hydrogenation reaction using a Pd / C catalyst, and protection of both the hydroxyl group and the amino group of the piperazine ring is removed. The reaction conditions of each reaction step in the synthetic route will be described in Examples described later.

The intermediate compound from 2,5-piperazindicarboxylic acid (4) to the protected amine compound (9) and the substituted piperazine compound (1), which is the final product, in the above-mentioned synthetic route each have a substituent for the heterocycle. There are cis and trans isomers with respect to the binding of, and each of the cis and trans substituted piperazine compounds (cis-1, trans-1) is a cis and trans type 2,5-piperazindicarboxylic acid. It can be synthesized from each of the acids (cis-4, trans-4) while retaining the steric isomerism. In the above synthetic route, it is described that a trans-type substituted piperazine compound (trans-1) is produced from a trans-type 2,5-piperazine dicarboxylic acid (trans-4), but a cis-type substituted piperazine compound is produced. (Cis-1) is also obtained from the cis-type 2,5-piperazindicarboxylic acid (cis-4) in the same manner.

The 2,5-piperazindicarboxylic acid (4) obtained by the catalytic reduction reaction is a 1: 1 mixture of cis-type and trans-type isomers, and the cis-type is obtained by isomer separation or isomerization of this mixture. Alternatively, a trans-type 2,5-piperazindicarboxylic acid (cis-4 or trans-4) can be obtained as a single substance.

Regarding the isomerization of 2,5-piperazine dicarboxylic acid (4), the cis-type 2,5-piperazine dicarboxylic acid (cis-4) can be isomerized to the trans-type by heating in an aqueous potassium hydroxide solution. Is. Therefore, by subjecting the cis-type and trans-type mixtures of 2,5-piperazindicarboxylic acid (4) produced by catalytic reduction to isomerization treatment, trans-2,5-piperazindicarboxylic acid (trans-4) can be obtained. can get.

Regarding the isomer separation of 2,5-piperazindicarboxylic acid (4), the isomer mixture can be separated into each isomer by precipitating one isomer by utilizing the difference in solubility between the isomers. Specifically, by adjusting the reaction solution after the catalytic reduction reaction (basic aqueous solution of 2,5-piperazindicarboxylic acid (4)) to about pH 6.3, trans-type 2,5-piperazindicarboxylic acid (2,5-piperazindicarboxylic acid (4)) trans-4) precipitates from the aqueous solution. By filtering this, pure trans-2,5-piperazindicarboxylic acid (trans-4) can be obtained. In the filtrate, precipitation of both isomers occurs due to irritation during filtration or the like, so the pH is once lowered to about 3.0 or less to dissolve the precipitate. As a result, a solution rich in cis-2,5-piperazindicarboxylic acid (cis-4) was obtained, and by adjusting this solution to about pH 4.3, cis-2,5-piperazindicarboxylic acid (cis-) was obtained. 4) precipitates. By filtering this, pure cis-2,5-piperazindicarboxylic acid (cis-4) is obtained. After that, if the recovered filtrate is adjusted to be basic (about pH 13) and the precipitate of the filtrate is dissolved, trans-2,5-piperazindicarboxylic acid (trans-4) and cis can be obtained by repeating the above operation. -2,5-Piperazine dicarboxylic acid (cis-4) can be alternately precipitated and filtered.

The substituted piperazine compound (1) exerts a function as an absorbent for acid gases such as carbon dioxide, sulfur oxides, nitrogen oxides and hydrogen chloride by means of four amino groups. Its molecular structure is designed to imitate the combination of piperazine and MDEA, which exhibit excellent performance in absorbing carbon dioxide, and thus is expected to have particularly high absorption performance in carbon dioxide. The absorption / emission performance of carbon dioxide in the absorption liquid using the substituted piperazine compound (1) as an absorbent is understood from FIG. FIG. 1 shows the results of measuring the loading of carbon dioxide (the number of moles of carbon dioxide absorbed per mole of the absorbent) in the absorbent liquid using the trans-type substituted piperazine compound (trans-1) as the absorbent, and shows the results for comparison. Therefore, the measurement results of the piperazine / MDEA (molar ratio = 1: 2) in the absorption solution are also described (in FIG. 1, “PZ” is piperazine and “TEDAPz” is the substituted piperazine compound (1). ) Is shown).

As can be seen from the measurement results shown in FIG. 1, the absorbent solution of the substituted piperazine compound (1) absorbs carbon dioxide at a temperature of 50 ° C. (from the start to 60 minutes) and at a temperature of 80 ° C. (after 60 minutes). Releases carbon dioxide. Therefore, the substituted piperazine compound (1) functions as an absorbent for carbon dioxide, and can be used as an active ingredient to form an absorbent for carbon dioxide treatment. Compared with the mixed absorption liquid of piperazine / MDEA, the absorption rate of carbon dioxide in the absorption liquid of the trans-type substituted piperazine compound (trans-1) is small, but the emission of the absorbent is suppressed during the heating and regeneration of the absorption liquid. By optimizing the temperature conditions by taking advantage of this, more carbon dioxide can be loaded. It is clear from the results of FIG. 4 described later that the absorption liquid used as the absorbent also exhibits good absorption performance for the cis-type substituted piperazine compound (cis-1). The cis-type substituted piperazine compound (cis-1) exhibits an absorption behavior closer to that of the piperazine / MDEA mixed absorption solution than the trans-type compound. As described above, the substituted piperazine compound (1) is useful as an absorbent in both the cis type and the trans type. Therefore, the substituted piperazine compound (1) can also be used as an absorbent in a mixed state of cis type and trans type.

When preparing an absorption liquid using the substituted piperazine compound (1) as an absorbent, it is possible to improve the absorption / dissipation performance of the absorption liquid by adding an auxiliary agent or adjusting the solvent composition. As the auxiliary agent, a compound that plays a role of MDEA in the combination of piperazine and MDEA, that is, a compound that can act as a hydrogen ion receptor that receives hydrogen ions from the substituted piperazine compound (1) can be used. Therefore, it can be selected from various compounds having an active methylene group, and examples thereof include MDEA and 2- (isopropylamino) ethanol (IPAE), but it is not necessary to limit the compound to amino compounds. However, a water-soluble compound having an affinity with the substituted piperazine compound (1) is suitable from the viewpoint of dissolution stability of the substituted piperazine compound (1) in the absorbing solution. When the compound has a higher acid dissociation constant pKa than the substituted piperazine compound (1), it easily acts as a hydrogen ion receptor in the coexistence state. The pKa value of the compound varies depending on the measurement conditions, but can be easily selected by comparison using the pKa values under the same measurement conditions. For example, oxocarboxylic acid esters such as ethyl acetoacetate and dimethyl malonate and malonic acid diesters have active hydrogen and have a high pKa value (ethyl acetoacetate: 11, dimethyl malonate: 13). The contained water-soluble compound can be used as an auxiliary agent. In addition, cyano compounds such as malononitrile and ethyl cyanoacetate and meldrum's acid also have an active methylene group.

Amino compounds other than MDEA and IPAE that can be used as auxiliaries include, for example, monoethanolamine (MEA), 2-amino-2-methylpropanol, diethanolamine, 2- (methylamino) ethanol (MAE), 2- (Ethylamino) ethanol (EAE), 2- (propylamino) ethanol (PAE), N-ethyl-2-amino-2-methylpropanol, 1-dimethylamino-2-propanol, 2-amino-2-methylpropanol , Diisopropanolamine, triethanolamine and other chain aminoalkanols. Practically, from the viewpoint of water solubility, chain aliphatic amino alcohols having 10 or less carbon atoms, preferably 5 or less carbon atoms are preferable. In terms of high pKa value, it is preferable that the chain aliphatic amino alcohol has a sum of the number of amino groups and the number of hydroxyl groups of 3 or less, and generally, the pKa value is preferably about 8.5 or more.

As an absorbent, another amino compound may be used in combination with the substituted piperazine compound (1). However, since the substituted piperazine compound (1) is a compound designed as an absorbent that is hard to vaporize during heat regeneration, it is desirable to select an absorbent that is equally hard to vaporize in order to use it in combination with the absorbent. Therefore, an amino compound having a large molecular weight is preferable, and examples thereof include amino polyols such as diglycolamine.

In general, the absorbent concentration of the absorbing liquid can be appropriately set according to the amount of acid gas such as carbon dioxide contained in the gas to be treated, the treatment speed, and the like, and the fluidity and consumption loss of the absorbing liquid can be set appropriately. A concentration of about 10 to 50% by mass is applied in consideration of suppression and the like. For example, an absorbing liquid having a concentration of about 30% by mass is preferably used for treating a gas having a carbon dioxide content of about 20%. Also in the present invention, the concentration of the absorbent can be appropriately set according to the acid gas content of the gas to be treated, the treatment speed, and the like, and the concentration of the absorbent is about 10 to 50% by mass of the absorbent. preferable. When a hydrogen ion-accepting compound is added as an auxiliary agent, a concentration of about 10 to 50% by mass is applied as the total amount of the absorbent and the auxiliary agent. The concentration of the auxiliary agent may be set so as to correspond to about 0.5 to 1.2 times the molar equivalent with respect to the heteronitrogen (amino group of the piperidine ring) of the absorbent. By combining the absorbent and the auxiliary agent, the carbon dioxide absorption rate of the absorbing liquid is increased, and the absorption amount per contact time, that is, the absorption performance is improved.

Further, since alcohol-based solvents such as alcohols and polyols are effective in enhancing the dissolution stability of the substituted piperazine compound (1), an aqueous solution containing such a solvent is used as a solvent to prepare an absorbent solution. May be prepared. The addition of a solvent can stabilize the expression of function as an absorbent. When an alcohol-based solvent is added, it is preferable to set the solvent concentration of the aqueous solution in consideration of the solubility of acid gas and the like. Further, if necessary, various other conventionally used additives may be added to the absorption liquid.

An aqueous liquid containing the substituted piperazine compound (1) as an absorbent is prepared, and this is used as the absorbent to bring the gas and the absorbent into gas-liquid contact, whereby the acid gas contained in the gas becomes the absorbent. Be absorbed. Therefore, it can be used as an absorption liquid for acid gas treatment for removing acid gas such as sulfur oxide, nitrogen oxide, carbon dioxide, hydrogen sulfide, and hydrogen halide, and can be applied to gas treatment such as combustion exhaust gas. If necessary, the treatment can be carried out by appropriately selecting from various treatment forms such as scrubber cleaning by blowing gas and a form in which a filler is passed. Since the acid gas absorbed by the absorption liquid can be dissipated according to thermal equilibrium, the absorption liquid is regenerated by heating and can be used again. In general, the heating temperature of the absorbent during regeneration can be set near the boiling point. The heating temperature can be appropriately adjusted by adjusting the pressure of the regeneration atmosphere as needed.

[Synthesis of Substituted Piperazine Compound (1) 1]
According to the above-mentioned synthesis route, the substituted piperazine compound (1) was synthesized by the following procedure. In the synthesis below, a trans-type substituted piperazine compound (trans-1) was obtained.

<2,5-Pyrazinedicarboxylic acid (3)>
To 840 ml of a mixture of pyridine and water (mixed mass ratio: 20/1), 54 g (498 mmol) of 2,5-dimethylpyrazine (manufactured by Tokyo Kasei Co., Ltd.) and 224 g (2.02 mol) of selenium dioxide were added. The mixture was stirred and the mixture was heated to reflux for 48 hours. The reaction solution is cooled to room temperature and filtered, the filtration residue is washed with a mixed solution of pyridine and water (mixed mass ratio: 20/1), the filtrate and the washing solution are combined, and the liquid is distilled off to obtain a solid substance. It was.

The obtained solid was dispersed in a 2M dimethylamine aqueous solution used as an extraction solvent, and the residual solid was removed from the extract by filtration. By distilling off the solvent from the extract, 71 g (yield 85%) of 2,5-pyrazinedicarboxylic acid (3) was obtained.

<2,5-Piperazine dicarboxylic acid (4)>
9.35 g (167 mmol) of potassium hydroxide and 11 g (65 mmol) of 2,5-pyrazinedicarboxylic acid (3) were dissolved in water (200 ml). A 5% Pd / C catalyst was added to this solution at a ratio of 5 mol% with respect to the reaction substrate, hydrogen (1 MPa) was supplied while heating at 50 ° C., and the hydrogenation reaction was carried out for 18 hours. It was confirmed by gas chromatography that the raw material was consumed and the reaction was proceeding quantitatively. The reaction solution was filtered to remove the catalyst to obtain an aqueous solution of the product. For this product, ^{the measurement result obtained by 1} H NMR measurement is the reference (Witiak, DT; Nair, RV; Schmid, FA, "Synthesis and antimetastatic properties of stereoisomeric tricyclic bis (dioxopiperazines) in the Lewis lung carcinoma model". By agreeing with the chemical shift value described in ", J. Med. Chem. 1985, 28, 1228-1234), it was confirmed that it was 2,5-piperazin dicarboxylic acid (4).

<Isomer separation of 2,5-piperazindicarboxylic acid (4)>
When the pH was adjusted to 6.3 by adding a 3M HCl aqueous solution to the aqueous solution of 2,5-piperazindicarboxylic acid (4) obtained as the aqueous solution of the product described above, a white solid substance was precipitated from the aqueous solution. The solid matter was separated by filtration of the aqueous solution and dried to obtain 7 g of the solid matter. ^{From the 1} H NMR measurement result of the obtained solid matter, it was confirmed by the above-mentioned reference that this solid matter was a trans-type 2,5-piperazindicarboxylic acid (trans-4) (yield 63%).

On the other hand, a 3M HCl aqueous solution was added to the filtrate obtained by the above filtration to adjust the pH to 3.0, and the precipitate after filtration was dissolved in the filtrate. When a 2MKOH aqueous solution was added to this aqueous solution to adjust the pH to 4.3, a white solid substance was precipitated from the aqueous solution. The solid matter was separated by filtration of this aqueous solution and dried to obtain 4 g of the solid matter. ^{From the 1} H NMR measurement results, it was confirmed by the above-mentioned reference that this solid substance was a cis-type 2,5-piperazindicarboxylic acid (cis-4) (yield 37%).

<Isomerization of 2,5-piperazindicarboxylic acid (4)>
An aqueous solution of 2,5-piperazindicarboxylic acid (4), which is a cis: trans mixture (1: 1), obtained by the above-mentioned hydrogenation reaction was put into an autoclave and heated at 200 ° C. for 16 hours. The product contained in the obtained aqueous solution was a trans-type 2,5-piperazindicarboxylic acid, and it was ^{confirmed by 1 1 1} H NMR measurement that the isomerization from the cis-type to the trans-type proceeded.

<Trans-ester compound (trans-5): trans-2,5-piperazindicarboxylic acid dimethyl ester>
The dehydration reaction was carried out by dissolving 14 g (78 mmol) of trans-2,5-piperazindicarboxylic acid (trans-4) in methanol (800 ml), adding concentrated sulfuric acid (80 g, 10 eq) as a catalyst, and heating under reflux for 18 hours. I made it progress. After the reaction, saturated aqueous sodium carbonate solution and methylene chloride were added to adjust the pH of the aqueous phase to 9.0, and the organic phase and the aqueous phase were separated. The organic phase was taken out, methylene chloride and excess methanol were distilled off and concentrated, and hexane was added to the residue to form a precipitate from hexane. The precipitate was separated by filtration and dried to give 10.5 g of product. ¹ H NMR measurement of the obtained product was carried out, and it was confirmed that the product was a trans-2,5-piperazindicarboxylic acid dimethyl ester by agreement with the measured values in the above references (yield). 69%).

<Trans-diamide compound (trans-7): trans-2,5-piperazine dicarboxylic acid di (2-hydroxyethyl) amide>
A mixture of 1.3 g (6.3 mmol) of the trans-ester compound (trans-5) and 1.3 g (13 mmol) of diethanolamine (6) was heated at 80 ° C. for 2 hours to allow the condensation reaction to proceed. The reaction mixture was solidified, and the solidified product was washed with methanol to remove residual diethanolamine from the solidified product and decanted to obtain 2.3 g of the solidified product as a crude product. ¹ H NMR measurement of the obtained solidified product confirmed that the two carboxy groups of trans-2,5-piperazindicarboxylic acid were trans-diamide compounds (trans-7) amidated with diethanolamine (trans-7). Yield 96%).

(Measurement result)
trans-diamide compound (trans-7): white solid, mp 102.5-13.8 ° C (from AcOEt / Et ₂ O)
^{1 1} H NMR (399.78MHz, D ₂ O): δ = 3.76 (dd, J = 11.0, 3.0Hz, 2H), 3.66-3.38 (m, 14H), 3.27 (dt, J = 13.6, 6.0Hz, 2H) , 3.04 (dd, J = 13.4, 3.0Hz, 2H), 2.52 (dd, J = 13.4, 11.0Hz, 2H), 6H (-NH, -OH) was not observed
¹³ C NMR (100.53 MHz, D ₂ O): δ = 173.85 (2C), 59.39 (2C), 59.37 (2C), 54.98 (2C), 50.84 (2C), 48.66 (2C), 46.61 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₁₄ H ₂₉ N ₄ O ₆ [M + H] ⁺ 349.2082, found 349.2082

<Hydroxy group protection of trans-diamide compound (trans-7)>
5.0 g (13 mmol) of the trans-diamide compound (7) obtained by the above-mentioned production method is dissolved in N, N-dimethylformamide (15 ml), cooled to 0 ° C., and 2.2 g (7eq) of hydrogen. Sodium hydride was added. After adding 1.6 g (7 eq) of benzyl bromide to this, the reaction was allowed to proceed with stirring for 3 hours. Then, water was added to the reaction solution and stirred to stop the reaction, and the solvent was distilled off under reduced pressure to obtain a residue. Ethyl acetate was added to the residue to prepare an organic phase, and the organic phase was washed successively with water and brine. The organic phase after washing was taken out, dried with a desiccant, and the solvent was distilled off at source pressure to concentrate. Crystallization of this concentrate with ether gave 10.7 g of a white solid. ¹ H NMR measurement of the obtained white solid was performed. The results are as follows, and the product is a protected amide compound (trans-8) in which hydrogen is replaced with a benzyl group at the four hydroxyl groups and two cyclic amino groups of the trans-diamide compound (7). It was confirmed (yield 88%).

(Measurement result)
^{1 1} H NMR (399.78 MHz, CDCl ₃ ): δ = 7.33-7.17 (m, 30H), 4.38 (s, 4H), 4.17 (dd, J = 16.0, 12.0Hz, 4H), 3.78-3.38 (m, 20H) ), 3.08 (d, J = 12.8Hz, 2H), 2.84 (d, J = 11.2Hz, 2H), 2.50 (t, J = 11.2Hz, 2H)

<Reduction of protected amide compound (trans-8)>
9.5 g (10 mmol) of the protected amide compound (trans-8) obtained by the above-mentioned production method was added to dehydrated THF (100 ml) and dissolved to prepare a protected amide compound solution. A 0.8 g (2 eq) _{THF solution of LiAlH 4} was prepared, and the protected amide compound solution was gradually added dropwise and mixed while stirring the mixture, and the mixture was heated under reflux for 14 hours to allow the reaction to proceed. Then, the reaction solution was cooled to room temperature, and water (0.8 ml), a 15% aqueous sodium hydroxide solution (0.8 ml) and water (2.4 ml) were slowly added dropwise to the reaction solution while stirring. The reaction solution was suction-filtered using Celite to remove the precipitate from the reaction solution, and the filtration residue was thoroughly washed with THF. The filtrate and washing solution were combined and THF was distilled off to obtain 7.7 g of a colorless oily product.

The obtained oily product was subjected to ¹ H NMR measurement, ¹³ C NMR measurement, and molecular weight measurement by a high resolution mass spectrometer (HRMS). The results are as follows, and it was confirmed that the product is a protected amine compound (trans-9) in which the hydrogen of the hydroxyl group and amino group of the substituted piperazine compound (trans-1) is substituted with a benzyl group. (Yield 89%).

(Measurement result)
^{1 1} H NMR (399.78 MHz, CDCl ₃ ): δ = 7.25-7.15 (m, 30H), 4.32 (s, 8H), 4.09 (d, J = 13.6Hz, 2H), 3.33 (m, 8H), 3.09 ( d, J = 13.6Hz, 2H), 2.80 (dd, J = 14.4, 12.4Hz, 4H), 2.57 (t, J = 6.2Hz, 8H), 2.37 (m, 4H), 2.00 (m, 2H)
¹³ C NMR (600.13 MHz, CDCl ₃ ): δ = 139.4 (2C), 138.5 (4C), 128.9 (4C), 128.3 (8C), 128.1 (4C), 127.6 (8C), 127.4 (4C), 126.6 ( 2C), 73.0 (8C), 68.9 (4C), 58.2 (2C), 58.1 (2C), 55.0 (4C)
HRMS (ESI ⁺ ) m / z: calcd for C ₅₆ H ₆₉ N ₄ O ₄ [M + H] ⁺ 861.5313, found 861.5307

<Substituted piperazine compound (trans-1): trans-2,5-di (N-di (2-hydroxyethyl) aminomethyl) piperazine>
1.35 g (1.6 mmol) of the protected amine compound (trans-9) obtained by the above-mentioned production method was added to 99% ethanol (30 ml) to dissolve it, and the solution was dissolved in this solution at a ratio of 5 mol% to the reaction substrate. A 5% Pd / C catalyst was added, and hydrogen (1 MPa) was supplied at room temperature with stirring, and the hydrogenation reaction was carried out for 24 hours. The hydrogenation reaction was carried out for 24 hours by continuing to supply hydrogen while heating the reaction solution to 80 ° C. in an autoclave. By gas chromatography, it was confirmed that the raw materials were consumed and the reaction was proceeding quantitatively.

Ethanol was distilled off under reduced pressure from the filtrate obtained by filtering the reaction solution to remove the catalyst, and the obtained solid substance was dissolved by adding an aqueous HCl solution and benzene, and then separated to take out the aqueous phase. This aqueous phase was adjusted to be basic with an aqueous NaOH solution, then separated with ethyl acetate, and the organic phase was taken out and ethyl acetate was distilled off to obtain 0.5 g of a white solid product. Obtained. It was purified by recrystallization in ethanol.

The purified product was subjected to ¹ H NMR measurement and ¹³ C NMR measurement, molecular weight measurement by a high resolution mass spectrometer (HRMS), elemental analysis, and powder X-ray diffraction. The measurement results are as follows (DSS: 3- (trimethylsilyl) -1-sodium propanesulfonate), and a chart showing the diffraction intensity in powder X-ray diffraction is shown in FIG. From this result, it was confirmed that the product was trans-2,5-di (N-di (2-hydroxyethyl) aminomethyl) piperazine (the purified product is its dihydrate) (yield). 99%, melting point 112.2-114.0 ° C. (from EtOH)).

(Measurement result)
^{1 1} H NMR (399.78 MHz, D ₂ O, internal standard: DSS): δ = 3.63 (m, 8H), 2.98 (dd, J = 16.0, 2.8 Hz, 2H), 2.68 (m, 10H), 2.51 (dd) , J = 16.0, 4.4Hz, 2H), 2.43 (dd, J = 12.4, 8,4Hz, 2H), 2.36 (t, J = 11.6Hz, 2H)
¹³ C NMR (600.13 MHz, D ₂ O, internal standard: DSS): δ = 61.7 (4C), 60.3 (2C), 59.0 (4C), 55.4 (2C), 51.2 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₁₄ H ₃₃ N ₄ O ₄ [M + H] ⁺ 321.24946, found 321.2497
Elemental _{analysis: calcd for C 14 H 32 N} 4 O 4 · 2H 2 O: C, 47.17; H, 10.18; N, 15.72, found: C, 47.42; H, 10.16; N, 15.58

[Synthesis of Substituted Piperazine Compound (1) 2]
In the synthesis below, a cis-type substituted piperazine compound (cis-1) was obtained.
<Cis-ester compound (cis-5)>
175 mg (1 mmol) of cis-2,5-piperazindicarboxylic acid (cis-4) obtained by the above-mentioned production method is dissolved in 10 ml of methanol, concentrated sulfuric acid (0.46 ml) is added as a catalyst, and the mixture is heated under reflux for 18 hours. This allowed the dehydration reaction to proceed. After the reaction, saturated aqueous sodium carbonate solution and methylene chloride were added to adjust the pH of the aqueous phase to 9.0, and the organic phase and the aqueous phase were separated. The organic phase was taken out, methylene chloride and excess methanol were distilled off and concentrated, and hexane was added to the residue to form a precipitate from hexane. The precipitate was separated by filtration and dried to give 123 mg of product. ^{By 1} H NMR measurement of the obtained product, it was confirmed that the product was cis-2,5-piperazindicarboxylic acid dimethyl ester, in agreement with the measured values in the above references (yield 61%). ).

<Cis-diamide compound (cis-7) and its hydroxyl group protection>
A mixture of 1.1 g (5.2 mmol) of cis-ester compound (cis-5) and 1.1 g (10 mmol) of diethanolamine was heated at 80 ° C. for 24 hours to allow the condensation reaction to proceed. The reaction solution was cooled to room temperature, and the obtained solidified product was washed with acetone and the acetone was removed by decantation to obtain a solid crude product of the cis-diamide compound (cis-7). The following operation was performed using the obtained solid crude product as it was.

The crude product of the above-mentioned cis-diamide compound (cis-7) was dissolved in N, N-dimethylformamide (30 ml), cooled to 0 ° C., and sodium hydride (2.3 g, 10 eq) was added. Benzyl bromide (6.2 ml, 7eq) was added dropwise thereto, and the mixture was stirred for 3 hours to allow the reaction to proceed. Then, water was added to the reaction solution and stirred to stop the reaction, and the solvent was distilled off under reduced pressure to obtain a residue. Ethyl acetate was added to the residue to prepare an organic phase, and the organic phase was washed successively with water and brine. The organic phase after washing was taken out, dried with a desiccant, and then the solvent was distilled off under reduced pressure and concentrated to obtain a colorless oil. The obtained oil was subjected to ¹ H NMR measurement, ¹³ C NMR measurement, and molecular weight measurement by a high resolution mass spectrometer (HRMS). The results are as follows, and the product is a protected amide compound (cis-8) in which hydrogen is replaced with a benzyl group at the four hydroxyl groups and two cyclic amino groups of the cis-diamide compound (cis-7). (3.14 g, yield from cis-ester compound (cis-5): 68%).

(Measurement result)
^{1 1} H NMR (399.78 MHz, CDCl ₃ ): δ = 7.33-7.17 (m, 30H), 4.38 (s, 4H), 4.17 (dd, J = 16.0, 12.0Hz, 4H), 3.78-3.38 (m, 20H) ), 3.08 (d, J = 12.8Hz, 2H), 2.84 (d, J = 11.2Hz, 2H), 2.50 (t, J = 11.2Hz, 2H)
¹³ C NMR (100.53 MHz, CDCl ₃ ): δ = 171.2 (2C), 138.4 (2C), 138.2 (2C), 137.9 (2C), 128.7 (4C), 128.3 (4C), 128.3 (4C), 128.2 ( 4C), 127.6 (2C), 127.5 (4C), 127.5 (2C), 127.5 (4C), 126.9 (2C), 73.1 (2C), 73.0 (2C), 73.0 (2C), 68.3 (2C), 58.7 ( 2C), 47.7 (2C), 47.7 (2C), 47.7 (2C), 46.2 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₅₆ H ₆₅ N ₄ O ₆ [M + H] ⁺ 889.4899, found 889.4894

<Reduction of protected amide compound (cis-8)>
307 mg (0.345 mmol) of the protected amide compound (cis-8) obtained by the above-mentioned production method was added to dehydrated THF (30 ml) and dissolved to prepare a protected amide compound solution. LiAlH ₄ (59 mg, 4eq) was added, and the mixture was heated under reflux for 18 hours. The disappearance of the raw materials was confirmed, and the reaction solution was cooled to room temperature, and water (60 μl), a 15% aqueous sodium hydroxide solution (210 μl) and water (60 μl) were slowly added dropwise to the reaction solution while stirring. The reaction solution was suction-filtered using Celite to remove the precipitate from the reaction solution, and the filtration residue was thoroughly washed with THF. The filtrate and washing solution were combined and THF was distilled off to obtain a colorless oily product (238 mg).

The obtained oily product was subjected to ¹ H NMR measurement, ¹³ C NMR measurement, and molecular weight measurement by a high resolution mass spectrometer (HRMS). The results are as follows, and the product is a protection in which the hydroxyl group of cis-2,5-di (N-di (2-hydroxyethyl) aminomethyl) piperazine and the hydrogen of the amino group are replaced with a benzyl group. It was confirmed that it was an amine compound (cis-9) (yield 80%).

(Measurement result)
^{1 1} H NMR (399.78 MHz, CDCl ₃ ): δ = 7.25-7.15 (m, 30H), 4.30 (s, 8H), 3.92 (d, J = 13.6Hz, 2H), 3.33 (m, 8H), 2.71- 2.40 (m, 20H)
¹³ C NMR (600.13 MHz, CDCl ₃ ): δ = 139.9 (2C), 138.5 (4C), 128.7 (4C), 128.3 (8C), 128.0 (4C), 127.5 (8C), 127.4 (4C), 126.6 ( 2C), 73.7 (4C), 73.0 (4C), 68.8 (4C), 58.5 (2C), 57.0 (2C), 54.9 (2C), 53.1 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₅₆ H ₆₉ N ₄ O ₄ [M + H] ⁺ 861.5313, found 861.5314

<Substituted piperazine compound (cis-1): cis-2,5-di (N-di (2-hydroxyethyl) aminomethyl) piperazine>
231 mg (0.269 mmol) of the protected amine compound (cis-9) obtained by the above-mentioned production method was added to 99% ethanol (15 ml) to dissolve it, and the solution was dissolved in this solution at a ratio of 5 mol% with respect to the reaction substrate. A% Pd (OH) ₂ / C catalyst was added, hydrogen (1 MPa) was supplied at room temperature with stirring, and the hydrogenation reaction was carried out for 24 hours. The hydrogenation reaction was carried out for 24 hours by continuing to supply hydrogen while heating the reaction solution to 80 ° C. in an autoclave. By gas chromatography, it was confirmed that the raw materials were consumed and the reaction was proceeding quantitatively.

Ethanol was distilled off under reduced pressure from the filtrate obtained by filtering the reaction solution to remove the catalyst, and an aqueous HCl solution and benzene were added to the obtained concentrate to dissolve it, and then the mixture was separated to take out the aqueous phase. This aqueous phase is adjusted to be basic with an aqueous NaOH solution, then separated with ethyl acetate, the organic phase is taken out and ethyl acetate is distilled off to obtain a solid product (77 mg). (Yield 89%).

[Synthesis of Substituted Piperazine Compound (1) 3]
The cis-type substituted piperazine compound (cis-1) was obtained by the following synthesis.
<Cis-diamide compound (cis-7) and its hydroxyl group protection>
A mixture of 3.0 g (15 mmol) of cis-ester compound (cis-5) and 3.3 g (32 mmol) of diethanolamine was heated at 80 ° C. for 24 hours to allow the condensation reaction to proceed. The reaction solution was cooled to room temperature, and the obtained solidified product was washed with acetone and the acetone was removed by decantation to obtain a solid crude product of the cis-diamide compound (cis-7). The following operation was performed using the obtained solid crude product as it was.

The crude product of the above-mentioned cis-diamide compound (cis-7) was dissolved in N, N-dimethylformamide (50 ml), cooled to 0 ° C., and sodium hydride (5.0 g, 10 eq) was added. Benzyl bromide (18 ml, 10 eq) was added dropwise thereto, and the mixture was stirred for 4 hours to allow the reaction to proceed. Then, water was added to the reaction solution and stirred to stop the reaction, and the solvent was distilled off under reduced pressure to obtain a residue. Ethyl acetate was added to the residue to prepare an organic phase, and the organic phase was washed successively with water and brine. The organic phase after washing was taken out, dried with a desiccant, and then the solvent was distilled off under reduced pressure and concentrated to obtain a colorless oil. The obtained oil was subjected to ¹ H NMR measurement, ¹³ C NMR measurement, and molecular weight measurement by a high resolution mass spectrometer (HRMS). The results are as follows, and the product is a protected amide compound (cis-8) in which hydrogen is replaced with a benzyl group at the four hydroxyl groups and two cyclic amino groups of the cis-diamide compound (cis-7). (8.07 g, yield from cis-ester compound (cis-5): 60%).

(Measurement result)
^{1 1} H NMR (399.78MHz, CDCl ₃ ): δ = 7.28-7.17 (m, 30H), 4.40 (s, 4H), 4.31 (s, 4H), 3.87 (d, J = 14.0Hz, 2H), 3.75- 3.37 (m, 22H), 2.50-2.48 (m, 2H)
¹³ C NMR (100.53 MHz, CDCl ₃ ): δ = 171.2 (2C), 138.4 (2C), 138.2 (2C), 137.9 (2C), 128.7 (4C), 128.3 (4C), 128.3 (4C), 128.2 ( 4C), 127.6 (2C), 127.5 (4C), 127.5 (2C), 127.5 (4C), 126.9 (2C), 73.1 (2C), 73.0 (2C), 73.0 (2C), 68.3 (2C), 58.7 ( 2C), 47.7 (2C), 47.7 (2C), 47.7 (2C), 46.2 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₅₆ H ₆₅ N ₄ O ₆ [M + H] ⁺ 889.4899, found 889.4894

<Reduction of protected amide compound (cis-8)>
307 mg (0.345 mmol) of the protected amide compound (cis-8) obtained by the above-mentioned production method was added to dehydrated THF (30 ml) and dissolved to prepare a protected amide compound solution. LiAlH ₄ (59 mg, 4eq) was added, and the mixture was heated under reflux for 18 hours. The disappearance of the raw materials was confirmed, and the reaction solution was cooled to room temperature, and water (60 μl), a 15% aqueous sodium hydroxide solution (210 μl) and water (60 μl) were slowly added dropwise to the reaction solution while stirring. The reaction solution was suction-filtered using Celite to remove the precipitate from the reaction solution, and the filtration residue was thoroughly washed with THF. The filtrate and washing solution were combined and THF was distilled off to obtain a colorless oily product (238 mg).

The obtained oily product was subjected to ¹ H NMR measurement, ¹³ C NMR measurement, and molecular weight measurement by a high resolution mass spectrometer (HRMS). The results are as follows, and the product is a protection in which the hydroxyl group of cis-2,5-di (N-di (2-hydroxyethyl) aminomethyl) piperazine and the hydrogen of the amino group are replaced with a benzyl group. It was confirmed that it was an amine compound (cis-9) (yield 80%).

(Measurement result)
^{1 1} H NMR (399.78 MHz, CDCl ₃ ): δ = 7.25-7.15 (m, 30H), 4.30 (s, 8H), 3.92 (d, J = 13.6Hz, 2H), 3.30 (m, 8H), 2.71- 2.40 (m, 20H)
¹³ C NMR (600.13 MHz, CDCl ₃ ): δ = 139.9 (2C), 138.5 (4C), 128.7 (4C), 128.3 (8C), 128.0 (4C), 127.5 (8C), 127.4 (4C), 126.6 ( 2C), 73.7 (4C), 73.0 (4C), 68.8 (4C), 58.5 (2C), 57.0 (2C), 54.9 (2C), 53.1 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₅₆ H ₆₉ N ₄ O ₄ [M + H] ⁺ 861.5313, found 861.5314

<Substituted piperazine compound (cis-1): cis-2,5-di (N-di (2-hydroxyethyl) aminomethyl) piperazine>
1.04 g (1.20 mmol) of the protected amine compound (cis-9) obtained by the above-mentioned production method was added to 99% ethanol (50 ml) to dissolve it, and the ratio of 20 mol% to the reaction substrate was added to this solution. A 20% Pd (OH) ₂ / C catalyst was added, and hydrogen (1 MPa) was supplied at room temperature with stirring, and the hydrogenation reaction was carried out for 24 hours. The hydrogenation reaction was carried out for 24 hours by continuing to supply hydrogen while heating the reaction solution to 80 ° C. in an autoclave. By gas chromatography, it was confirmed that the raw materials were consumed and the reaction was proceeding quantitatively.

Ethanol was distilled off under reduced pressure from the filtrate obtained by filtering the reaction solution to remove the catalyst, and ether was added to the obtained concentrate to precipitate a white solid. The solid was collected by filtration to give a solid product (331 mg).

The obtained product was ^{subjected to 1} H NMR measurement and ¹³ C NMR measurement, molecular weight measurement by a high resolution mass spectrometer (HRMS), elemental analysis, and powder X-ray diffraction. The measurement results are as follows, and a chart showing the diffraction intensity in powder X-ray diffraction is shown in FIG. From this result, it was confirmed that the product was a substituted piperazine compound (cis-1) (yield 86%, melting point 98.4-99.6 ° C.).

(Measurement result)
^{1 1} H NMR (399.78 MHz, D ₂ O, internal standard: DSS): δ = 3.65 (m, 8H), 2.89 (m, 4H), 2.70 (m, 12H), 2.50 (dd, J = 13.2, 4.4Hz) , 2H)
¹³ C NMR (600.13 MHz, D ₂ O, internal standard: DSS): δ = 61.7 (4C), 58.8 (4C), 58.3 (2C), 53.2 (2C), 47.1 (2C)
HRMS (ESI ⁺ ) m / z: calcd for C ₁₄ H ₃₃ N ₄ O ₄ [M + H] ⁺ 321.24946, found 321.2495
Elemental analysis: calculated for C ₁₄ H ₃₂ N ₄ O ₄ : C, 52.48; H, 10.07; N, 17.49, found: C, 52.43; H, 9.68; N, 16. 72

[Absorption / emission performance of substituted piperazine compound (trans-1) against carbon dioxide]
Dissolve 6.4 g (20 mmol) of the substituted piperazine compound (trans-1) in water as an absorbent to prepare 50 ml of an aqueous solution having a concentration of 0.4 mol / L, and use this as an absorbent solution for carbon dioxide dioxide as follows. The absorption / emission performance for carbon was measured. Further, 1.7 g of piperazine (20 mmol) and 4.8 g of MDEA (40 mmol) were dissolved in water to prepare 50 ml of an aqueous solution having a piperazine concentration of 0.4 mol / L and an MDEA concentration of 0.8 mol / L. Using this as an absorbent for comparison, the absorption / dissipation performance was measured in the same manner.

Carbon dioxide was blown into 50 mL of the absorption liquid at a rate of 140 mL / min, and the gas-liquid contact time with carbon dioxide was set to 90 minutes to perform the carbon dioxide absorption treatment. During this period, the temperature of the absorbing solution was maintained at 50 ° C. for 0 to 60 minutes, the temperature was raised to 80 ° C. after 60 minutes, and carbon dioxide contained in the absorbing solution was measured by measuring ^{the 13 C-NMR spectrum of the absorbing solution.} The change over time in the amount of carbon was investigated. The obtained result is shown in FIG. 1 as a change in carbon dioxide loading (carbon dioxide absorption amount per amine [mol-CO _{2 / mol-amine]).} As can be seen from FIG. 1, in any of the absorbing liquids, the absorbing liquid absorbs carbon dioxide from 0 to 60 minutes when the temperature is 50 ° C., and carbon dioxide after 60 minutes when the temperature rises to 80 ° C. It is clear that it can be used as an absorbent solution.

In the comparative piperazine / MDEA absorbent, piperazine (PZ) is converted to PZ-dicarbamate via PZ-monocarbamate as it absorbs carbon dioxide, and the dissolution of carbon dioxide through these is the proton of MDEA. It is promoted by its action as a receptor. Given that these properties cause the loading of carbon dioxide in the comparative absorbent to increase rapidly and then approach a certain level, the substituted piperazine compound (trans-1) absorber increases relatively slowly. Shows a continuous loading curve because the division of roles between the amino group of the piperazine ring and the amino group on the substituent side is not so clear, and it is considered that they remain independent of each other in terms of cooperation. .. It is considered that this point can be improved by the solvent composition of the absorbing solution and the coexistence of other components.

[Absorption / emission performance of substituted piperazine compound (cis-1) against carbon dioxide]
The absorption / emission performance of the cis-substituted piperazine compound (cis-1) was measured under the same conditions as the measurement of the absorption / emission performance of the trans-type substituted piperazine compound (trans-1) described above. The measurement results are shown in the graph of FIG. 4 as a time-dependent change in the amount of carbon dioxide absorbed (carbon dioxide absorption amount [g / L] per volume of the absorbing liquid), that is, a time-dependent change in the carbon dioxide concentration of the absorbing liquid. In FIG. 4, the above-mentioned results by the trans-type substituted piperazine compound (trans-1) are also described.

According to FIG. 4, the amount of carbon dioxide absorbed by the cis-type substituted piperazine compound (cis-1) increased rapidly and then gradually approached a certain level, and the cis-type substituted piperazine compound (cis-1) was more absorbed. It exhibits an absorption behavior closer to that of the piperazine / MDEA absorption solution than that of the trans type. From this, in the cis-type substituted piperazine compound (cis-1), the roles are divided between the amino group of the piperazine ring and the amino group on the substituent side, and the amino group on the substituent side is MDEA. It is thought to act as a similar proton receptor. Therefore, it can be said that the cis-type substituted piperazine compound (cis-1) is a compound exhibiting the performance expected from the molecular design based on the piperazine / MDEA mixed system, and it is preferable to use this as an absorbent to form an absorbent solution. It can absorb carbon dioxide at the absorption rate.

INDUSTRIAL APPLICABILITY The present invention can be suitably used in the treatment of exhaust gas containing acid gas such as carbon dioxide emitted from facilities such as thermal power plants, steel mills, and boilers by preparing an absorption liquid for acid gas treatment. It is useful for reducing the amount of carbon dioxide emitted and the impact of acid gas on the environment. As an absorbent for carbon dioxide treatment, it is useful for improving treatment performance and adaptability to target gases, and can contribute to environmental protection.

Claims (5)

A substituted piperazine compound represented by the following general formula.

An acid gas absorber containing the substituted piperazine compound according to claim 1 as an active ingredient. A carbon dioxide absorbent containing the substituted piperazine compound according to claim 1 as an active ingredient. An absorption liquid for acid gas treatment, which contains the substituted piperazine compound according to claim 1 and water. An absorbent solution for carbon dioxide treatment containing the substituted piperazine compound according to claim 1 and water.

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