JP2013082680A - Method for recovering propylene glycol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering propylene glycol with high purity from a solution containing propylene glycol, an organic acid component and a colored component discharged from a production process of propylene oxide.SOLUTION: The method aims to recover propylene glycol from an absorption liquid containing propylene glycol, an organic acid component and a colored component, discharged from a process of producing propylene oxide by vapor phase catalytic oxidation of propylene with oxygen. The method comprises subjecting the absorption liquid to chromatography using a salt type cation exchange resin as a separation carrier and water as a developer, and recovering at least one fraction having high concentration of propylene glycol from the column effluent.

Description

  The present invention relates to a method for recovering propylene glycol from an aqueous solution containing propylene glycol discharged from a process for producing propylene oxide. More specifically, the present invention relates to a method for recovering propylene glycol from a solution containing propylene glycol, an organic acid component and a coloring component discharged from a process for producing propylene oxide from propylene.

  Propylene glycol is produced on a large scale by hydrating propylene oxide obtained by gas phase catalytic oxidation of propylene with oxygen. In this method, propylene is first converted to propylene oxide by gas phase catalytic oxidation. The reaction gas containing propylene oxide emitted from the reactor is washed with an absorbing solution in an absorption tower. The absorbing solution that has absorbed propylene oxide is then diffused in a stripping tower to release propylene oxide. Propylene oxide is further purified if desired, and then reacted with water to form propylene glycol. On the other hand, the absorbing solution from which propylene oxide has been released is circulated to the absorption tower. The production process of propylene oxide will be described in more detail. The gas phase catalytic oxidation of propylene is performed by circulating a mixed gas containing propylene and oxygen through a fixed bed of the metal catalyst. The mixed gas usually contains an inert gas such as nitrogen or methane, and contains a small amount of an inhibitor that prevents the oxidation reaction such as propylene dichloride from proceeding excessively. In particular, when air is used as an oxygen source, the mixed gas contains a large amount of nitrogen. From the reaction gas containing propylene oxide, the propylene oxide is usually separated through a washing step of about 1 to 3 steps. For example, in the simplest case, the reaction gas is washed with water in one stage to absorb propylene oxide into water, and then the propylene oxide absorbed is released to recover the released propylene oxide. Further, the propylene oxide that has been released can be recovered by washing again with water and absorbing it, and then releasing the propylene oxide by releasing again the water that has absorbed the propylene oxide. . In some cases, a step of washing the reaction gas with water and quenching it may be provided before these washing steps. In the washing step of these reaction gas or crude propylene oxide, the water used for washing is recycled. The reaction gas contains various by-products in addition to propylene oxide, and these are also absorbed into water when the gas is washed. Typical examples are organic acids such as formic acid and oxalic acid, and coloring components. Since caustic soda is usually added to the water used for washing to adjust the pH, these organic acids are present in the washing water as soda salts of organic acids. In addition, propylene glycol in which propylene oxide is hydrated is present in the water used for washing. Since these non-volatile components gradually accumulate in the water as the water is circulated, it is sometimes necessary to withdraw some of them from the system and replenish water. The composition of the extracted aqueous solution varies depending on the reaction conditions and the like, but contains, for example, 3 to 7 g of formic acid and the like and an unidentified coloring component per 100 g of propylene glycol.

  Several methods have been proposed for obtaining ethylene glycol recovered from the discharged crude ethylene glycol aqueous solution in the ethylene oxide production process corresponding to the above-described propylene oxide production process. For example, Patent Document 1 describes a method for recovering high-purity ethylene glycol by distillation and adsorption treatment with activated carbon. Patent Document 2 describes a method in which an aqueous ethylene glycol solution recovered by adsorption treatment with an ion exchange resin and activated carbon is used, and then a hydration reaction liquid containing ethylene glycol is dehydrated in a dehydration distillation column. Patent Documents 3 to 6 describe a method for recovering high-purity ethylene glycol.

Japanese Patent Publication 45-10324 US3904656 JP-A-57-106632 JP-A-57-142930 JP-A-57-142931 JP 58-62124 A

  The subject of this invention is providing the method of collect | recovering high purity propylene glycol from the solution containing the propylene glycol discharged | emitted from the manufacturing process of propylene oxide, an organic acid component, and a coloring component.

As a result of studying means for solving the above problems, the following inventions have been found.
[1] A method for recovering propylene glycol from an absorption liquid containing propylene glycol, an organic acid component and a coloring component discharged from a propylene oxide production process by vapor phase catalytic oxidation of propylene with oxygen,
A recovery method comprising recovering at least one fraction having a high propylene glycol concentration from a column effluent by subjecting the absorption liquid to chromatography using a salt-type cation exchange resin as a separation carrier and water as a developing agent.
[2] The obtained aqueous solution of propylene glycol contains propylene glycol in an amount of at least 70% by weight of the amount contained in the absorbing solution, and the concentration of propylene glycol in the obtained aqueous solution of propylene glycol is 0 of the concentration in the absorbing solution. The collection method according to [1], which is twice or more.
[3] The obtained aqueous solution of propylene glycol contains propylene glycol in an amount of at least 85% by weight of the amount contained in the absorbing solution, and the concentration of propylene glycol in the obtained aqueous solution of propylene glycol is 0 of the concentration in the absorbing solution. The collection method according to [1], which is twice or more.
[4] Divide the column effluent into at least two fractions, one of which is a propylene glycol fraction containing most of the propylene glycol contained in the absorbent and the other fraction in the absorbent. The recovery method according to any one of [1] to [3], which is a waste liquid fraction containing most of the organic acid component and coloring component that were included.
[5] Any one of [1] to [4], wherein the fraction rich in propylene glycol is treated with a cation exchange resin and an anion exchange resin, and then circulated in a process for producing propylene glycol by hydrolysis of propylene oxide. Or a recovery method as described above.

[6] Divide the column effluent into at least three fractions, the first fraction containing high concentrations of organic acid components and colored components, little propylene glycol, the second fraction being An organic acid component, a coloring component and propylene glycol are contained at a low concentration, and the third fraction contains almost no organic acid component and a coloring component, and contains a high concentration of propylene glycol.
The second fraction is circulated as an absorption liquid in the propylene oxide production process, or mixed with the absorption liquid discharged from the propylene oxide production process and processed by chromatography.
The collection method according to any one of [1] to [3], wherein the third fraction is further processed to recover purified propylene glycol.
[7] Divide the column effluent into at least three fractions, the first fraction containing a high concentration of organic acid components and colored components, little propylene glycol, and the second fraction An organic acid component, a coloring component and propylene glycol are contained at a low concentration, and the third fraction contains almost no organic acid component and a coloring component, and contains a high concentration of propylene glycol.
The second fraction is used as a developing agent in subsequent chromatography,
The collection method according to any one of [1] to [3], wherein the third fraction is further processed to recover purified propylene glycol.

[8] A method for recovering propylene glycol from an absorption liquid containing propylene glycol, an organic acid component and a coloring component discharged from a propylene oxide production process by vapor-phase catalytic oxidation of propylene with oxygen,
The absorption liquid is supplied to a chromatographic column packed with a salt-type cation exchange resin, water is supplied to elute the absorption liquid, and a fraction rich in at least propylene glycol is recovered from the column effluent. The collection method.
[9] The recovery method according to [8], wherein the salt type cation exchange resin is a Na salt type strongly acidic ion exchange resin.
[10] The recovery method according to [8] or [9], wherein the absorbing solution is concentrated until the concentration of propylene glycol becomes 200 g / L or more, and then subjected to chromatography.
[11] The propylene glycol fraction contains propylene glycol in an amount of at least 70% by weight of the amount contained in the absorption liquid, and the concentration of propylene glycol in the obtained aqueous propylene glycol solution is 0 of the concentration in the absorption liquid. The collection method according to any one of [8] to [10], which is twice or more.
[12] The fraction rich in propylene glycol contains propylene glycol in an amount of at least 85% by weight of the amount contained in the absorbent, and the concentration of propylene glycol in the obtained aqueous propylene glycol solution is 0 of the concentration in the absorbent. The collection method according to any one of [8] to [10], which is twice or more.
[13] The recovery method according to any one of [8] to [12], in which a fraction rich in propylene glycol is treated with a cation exchange resin and an anion exchange resin and then distilled to recover the recovered propylene glycol.
[14] The column effluent is divided into at least three fractions, the first fraction containing a large amount of the organic acid component and the colored component contained in the absorbent, and the second fraction in the absorbent. Any one of [8] to [10], containing only a small amount of the organic acid component, coloring component and propylene glycol contained, and the third fraction containing a large amount of propylene glycol contained in the absorbent. The recovery method described.
[15] The third fraction contains propylene glycol in an amount of at least 70% by weight of the amount contained in the absorbent, and the concentration of propylene glycol in the obtained aqueous propylene glycol solution is 0. The collection method according to [14], which is twice or more.
[16] The recovery method according to [14], wherein the chromatography column is supplied with the second fraction following the absorption liquid and then with water.
[17] A method of recovering propylene glycol as substantially described in FIG. 2 and the Examples.

[18] A reaction gas containing propylene oxide obtained by vapor-phase catalytic oxidation of propylene with oxygen is washed with an absorbing solution to absorb propylene oxide into the absorbing solution, and then propylene oxide is released from the absorbing solution. After the release, the absorbing solution containing propylene glycol, the organic acid component and the coloring component discharged from the process of producing propylene oxide used for washing the reaction gas again is concentrated as necessary, and then the cation exchange resin is used. By separating it by chromatography using water as a developing agent as a separation carrier,
A method for recovering propylene glycol, comprising obtaining an aqueous propylene glycol solution in which the concentrations of an organic acid component and a coloring component are relatively reduced.

[19] An aqueous solution containing propylene glycol, an organic acid component, and a coloring component discharged from a process for producing propylene oxide including a step of washing a reaction gas containing propylene oxide obtained by vapor-phase catalytic oxidation of propylene with oxygen with water Is optionally concentrated, if desired, by chromatographic separation using a cation exchange resin as a separation carrier and water as a developing agent,
A first fraction containing an organic acid component and a coloring component and substantially free of propylene glycol; an organic acid component; a second fraction containing a coloring component and propylene glycol at a low concentration; and an organic acid component and a coloring component. Split into at least three fractions of a third fraction that contains little propylene glycol and a high concentration of propylene glycol;
A method for recovering propylene glycol, wherein the second fraction is circulated to the above-mentioned propylene oxide production process or circulated to the chromatographic separation step, and the third fraction is recovered as an aqueous propylene glycol solution. .
[20] The recovery method according to [19], wherein the second fraction is circulated to the propylene oxide production process.

[21] A process for producing propylene oxide comprising a step of washing a reaction gas containing propylene oxide obtained by vapor-phase catalytic oxidation of propylene with oxygen with water, and reacting propylene oxide obtained from this production process with water. In the method for producing propylene glycol, which comprises a step of preparing a reaction liquid containing propylene glycol, and a step of waiting for propylene glycol after removing water by dehydration distillation,
By appropriately concentrating an aqueous solution containing propylene glycol, organic acid component, and coloring component discharged from the propylene oxide production process, if desired, and then chromatographically separating the cation exchange resin as a separation carrier and water as a developing agent, A method for recovering propylene glycol, comprising obtaining an aqueous propylene glycol solution having reduced concentrations of an organic acid component and a colored component, and supplying the aqueous solution to a stage prior to dehydration distillation in a propylene glycol production process.
[22] The propylene glycol aqueous solution obtained by chromatograph separation is further treated with a cation exchange resin and an anion exchange resin, and then supplied to the stage before the dehydration distillation of the propylene glycol production process, [21] ] The collection method of description.

[23] Propylene glycol discharged from a process for producing propylene oxide, including a step of washing a reaction gas containing propylene oxide obtained by vapor-phase catalytic oxidation of propylene with oxygen with water, a crude product containing an organic acid component and a coloring component In a method for recovering propylene glycol, an aqueous solution of propylene glycol is appropriately concentrated as desired, then supplied to a chromatographic column packed with a cation exchange resin and developed with water, and the column effluent is divided and acquired according to its composition. ,
From the column effluent, a waste liquid portion containing a high concentration of organic acid components and coloring components but almost no propylene glycol and a propylene glycol portion containing propylene glycol at a high concentration were separated and removed from the system. A recovery method, wherein a circulating portion containing propylene glycol at a low concentration is collected and circulated to the above-described chromatographic step, and the crude propylene glycol aqueous solution is subsequently supplied to the column.
[24] The recovery method according to [23], wherein the circulating portion is a portion following the propylene glycol portion.
[25] The recovery method according to [23], wherein the circulation part is a part located between the waste liquid part and the propylene glycol part.
[26] The circulation part is composed of both a part located between the waste liquid part and the propylene glycol part and a part subsequent to the propylene glycol part, which are mixed and supplied to the column. [23] The recovery method according to [23].
[27] The circulation part consists of both a part located between the waste liquid part and the propylene glycol part and a part subsequent to the propylene glycol part, and supplies the former to the column following the crude propylene glycol aqueous solution, Then, the latter is supplied to a column, The collection method of [23] characterized by the above-mentioned.
[28] The recovery method according to any one of [1] to [27], wherein the gas phase catalytic oxidation is performed in the presence of a metal catalyst.
[29] The recovery method according to [28], wherein the metal catalyst is a catalyst containing (a) copper oxide and (b) ruthenium oxide.

  According to the present invention, high-purity propylene glycol can be recovered from a solution containing propylene glycol, an organic acid component, and a coloring component discharged from the production process of propylene oxide.

It is a schematic diagram which shows the outflow situation of propylene glycol, an organic acid component, and a coloring component in the chromatography of an absorption liquid. It is a conceptual diagram which shows an example of an apparatus suitable for implementation of the method of this invention.

Examples of the method for producing propylene oxide to which the present invention can be applied include a production method in which propylene and oxygen are reacted in the presence of a metal catalyst containing a metal oxide or the like. For the production method of reacting propylene and oxygen in the presence of such a metal catalyst, for example, WO2011 / 075458, WO2011 / 0754559, WO2012 / 005822, WO2012 / 005823, WO2012 / 005824, WO2012 / 005825, WO2012 / 005831, WO2012 / 005832, WO2012 / 005835, WO2012 / 005837, WO2012 / 009054, WO2012 / 009059, WO2012 / 009058, WO2012 / 009053, WO2012 / 009057, WO2012 / 009055, WO2012 / 009055, WO2012 / 009055 and the like. As the catalyst used in the production method, the following (a), (b), (c), (d), (e), (f), (g), (h), (i), (j), ( and a catalyst containing at least two selected from the group consisting of k), (l), (m), (n), (o), (p) and (q).
(A) copper oxide (b) ruthenium oxide (c) manganese oxide (d) nickel oxide (e) osmium oxide (f) germanium oxide (g) chromium oxide (h) thallium oxide (i ) Tin oxide (j) bismuth oxide (k) antimony oxide (l) rhenium oxide (m) cobalt oxide (n) osmium oxide (o) lanthanoid oxide (p) tungsten oxide (q) alkali Metal component or alkaline earth metal component, preferably a catalyst containing (a) copper oxide and (b) ruthenium oxide, more preferably (a) copper oxide, (b) ruthenium oxide and (q) A catalyst containing an alkali metal component or an alkaline earth metal component.

  In the gas mixture containing propylene oxide obtained by the above production method, usually 0.5% to 5% propylene oxide, unreacted propylene, unreacted oxygen, diluent gas (nitrogen, helium, argon, methane, Ethane, etc.), acrolein, propionaldehyde, acetaldehyde, acetone, produced water, carbon dioxide, carbon monoxide, organic acids and the like. This gas mixture is guided to a propylene oxide absorption tower and brought into countercurrent contact with water or an absorption liquid containing water as a main component to obtain an aqueous propylene oxide solution. Subsequently, this aqueous propylene oxide solution is guided to a diffusion tower to dissipate and discharge propylene oxide, while the absorbing liquid is recovered. In this circulating water, propylene oxide reacts with a small amount of water in the above-described absorption operation and emission operation to produce propylene glycol or a polymer thereof, and these compounds accumulate by repeating absorption and emission. Is done. The present invention is directed to an absorbing solution in which such propylene glycol or a polymer thereof is accumulated.

  The absorption liquid containing propylene glycol, organic acid component and coloring component discharged from the process of recovering propylene oxide from the reaction gas containing propylene oxide by vapor phase catalytic oxidation of propylene with oxygen is concentrated as necessary Then, it is subjected to chromatography using a salt type cation exchange resin as a separation carrier and water as a developing agent. Thereby, from the column effluent, an aqueous propylene glycol fraction containing most of the propylene glycol contained in the absorption liquid and having reduced concentrations of the organic acid component and the coloring component is obtained.

  In a first embodiment of the invention, the effluent from the column is divided into at least two fractions. One of the fractions is a propylene glycol aqueous solution fraction containing most of the propylene glycol contained in the absorption liquid, and the other fraction is a waste liquid containing most of the organic acid components and coloring components contained in the absorption liquid. It is a fraction. This aqueous propylene glycol fraction is distilled to obtain propylene glycol. For example, in the same manner as described in US Pat. No. 3,904,656, this aqueous propylene glycol fraction is purified with an ion exchange resin or purified with an ion exchange resin and activated carbon, and then subjected to a conversion step from propylene oxide to propylene glycol. In addition, distill.

  In a second embodiment of the invention, the effluent from the column is divided into at least three fractions. The first fraction is a fraction containing an organic acid component and a coloring component at a high concentration but hardly containing propylene glycol. The second fraction is a fraction containing an organic acid component, a coloring component and propylene glycol at a low concentration. The third fraction is a fraction containing almost no organic acid component and coloring component but containing propylene glycol at a high concentration. The first fraction is sent to a waste liquid treatment facility. The second fraction is circulated as an absorption liquid in the propylene oxide production process, or is mixed with the absorption liquid discharged from the propylene oxide production process and supplied to the chromatography. The third fraction is recovered as an aqueous propylene glycol solution. In this embodiment, propylene glycol contained in the absorption liquid discharged from the absorption process is recovered in the third fraction in high yield.

  In yet another embodiment, the second fraction is fed to the column followed by the absorbent and then water. That is, the absorption liquid supplied to the column is continuously discharged with the second fraction and water. In this embodiment, the concentration of propylene glycol in the third fraction can be increased.

  The crude aqueous propylene glycol solution discharged from the propylene oxide production process can be used as it is for chromatography by the method of the present invention, but it is only necessary to concentrate it appropriately and then supply it to the chromatography with a small chromatographic apparatus. In addition, a small amount of water as a developing agent is also preferable. Usually, after concentrating until the density | concentration of propylene glycol becomes 200 g / L or more, it supplies to the chromatography by this invention method.

  A cation exchange resin is used as a packing material for the chromatography column. As the cation exchange resin, a carboxylic acid type such as a weakly acidic or moderately acidic one can be used, but usually a strong acid, particularly a styrene-based strong acid cation exchange which is a sulfonated product of a styrene-divinylbenzene crosslinked copolymer. Resin is used. This type of cation exchange resin is commercially available under various trademarks including Diaion (registered trademark). The cation exchange resin is preferably preloaded with a cation in an aqueous solution used for chromatography. In particular, in the case of a resin having no neutral salt resolving power, it is used as a preload type. However, in some cases, a free alkali may be present in a crude propylene glycol aqueous solution, and the load type may be used during use.

  The chromatid separation operation can be performed according to a conventional method. In the simplest case, after filling the column with the cation exchange resin, water is drained to the surface of the resin bed, and then a predetermined amount of an aqueous solution containing propylene glycol is supplied to the top of the resin bed as a solution to be treated. While draining water from the bottom of the column, the liquid to be treated is lowered in the resin bed, and when the surface of the liquid to be treated reaches the surface of the resin bed, developing water is supplied to the upper part of the resin bed. The liquid to be treated is developed with water while draining water from the bottom of the column. The solution flowing out from the bottom of the column is collected according to its composition. For example, by continuously measuring the concentration of propylene glycol in the effluent with a refractometer and the concentration of organic acid salt with an electric conductivity meter, the effluent fraction of the desired composition can be fractionated as a propylene glycol aqueous solution. .

  In FIG. 1, the schematic diagram which shows the outflow situation of propylene glycol, an organic acid component, and a coloring component in the chromatography of the column effluent obtained by said operation is shown. In such an outflow situation, in the present invention, each embodiment is divided into two fractions, three fractions, four fractions, five fractions, and the like.

  In the first embodiment of the invention, the effluent is divided into two fractions. Fraction I contains most of the organic acid component and coloring component contained in the absorbent and is discarded as waste. Fraction II contains most of the propylene glycol contained in the absorbent and is recovered as an aqueous propylene glycol solution. Moreover, the amount of impurities relative to propylene glycol in the recovered propylene glycol aqueous solution is much lower than that in the absorbing solution. The recovered aqueous propylene glycol solution is further purified to produce commercial grade propylene glycol. For example, an aqueous propylene glycol solution is treated with an ion exchange resin to remove ionic materials and coloring components, and then distilled to give commercial grade propylene glycol. In other embodiments, after purifying with an ion exchange resin or purifying with an ion exchange resin and activated carbon, the aqueous propylene glycol solution is added to the process of converting propylene oxide to propylene glycol in the same manner as described in US Pat. No. 3,904,656. . The advantage of this method is that no special distillation equipment is required. This is because the propylene glycol recovered from the absorbing solution by chromatography is processed together with the production process of propylene glycol by the hydrolysis reaction of propylene oxide. As described above, since the propylene glycol recovered from the absorbing solution by chromatography usually contains a small amount of an organic acid component and a coloring component, in order to obtain pure propylene glycol, the propylene glycol aqueous solution must be distilled. In addition, these impurities are preferably removed. In order to remove these impurities, the aqueous propylene glycol solution is treated with a cation exchange resin and an anion exchange resin that adsorb these impurities. The cation exchange resin is usually a strongly acidic cation exchange resin based on a styrene-divinylbenzene crosslinked copolymer. As the anion exchange resin, a strongly basic anion exchange resin in which a quaternary ammonium group is introduced as a functional group into a styrene-divinylbenzene crosslinked copolymer is usually used. Weakly basic anion exchange resins having a primary to tertiary amino group as a functional group can also be used. These ion exchange resins may be used separately or in combination. The regeneration of the ion exchange resin used for the purification of the aqueous propylene glycol solution can be performed by a conventional method using an acid such as hydrochloric acid or sulfuric acid, or an alkali such as caustic soda.

  In a second embodiment of the invention, the effluent is divided into three fractions: a waste fraction, a circulating fraction and an aqueous propylene glycol fraction. In the second embodiment, the portion rich in the colored component and organic acid component that flows out first and containing almost no propylene glycol is collected as the first fraction. This first fraction is treated as a waste liquid. Next, a portion containing a small amount of each of the coloring component, organic acid component, and propylene glycol that flows out following the first fraction is fractionated as a second fraction. This second fraction is recycled to the propylene oxide production process or to the chromatographic separation process. The second fraction circulated in the production of propylene oxide is used for gas scrubbing in the same process, and then discharged again from the same process and supplied to the chromatograph separation process. In this way, the second fraction is directly or indirectly supplied again to the chromatographic separation step, and propylene glycol therein is recovered as a third fraction described later. Usually, the second fraction is advantageously recycled to the propylene oxide production process as long as the water balance allows.

Finally, a portion rich in propylene glycol that flows out following the second fraction and containing almost no organic acid component and coloring component is fractionated as a third fraction. This third fraction is further purified by distillation to recover propylene glycol. Prior to distillation purification, if necessary, an adsorption treatment may be performed with a cation exchange resin, an anion exchange resin, or even activated carbon. Further, at the end of the third fractionation, when the concentration of propylene glycol in the effluent is lowered and the solution to be treated and water as a developing agent are alternately supplied to the column, the subsequent treatment is performed. Coloring components and organic acid components derived from the aqueous solution may be mixed.
Therefore, it is preferable that the portion where the propylene glycol concentration is reduced is separated from the third fraction and mixed with the previously obtained second fraction. According to the method of the second embodiment, propylene glycol is obtained in a high yield, and the concentration of impurities in the recovered propylene glycol aqueous solution is lower than in the case of the first embodiment.

  In other embodiments of the invention, the fraction of low propylene glycol concentration obtained from the column effluent is fed to the column following the absorption and subsequent feed of water to the column. These procedures are preferred in that a fraction of an aqueous propylene glycol solution having a high concentration of propylene glycol can be recovered from the column effluent. This is because the absorption liquid supplied to the column is first discharged by the circulating fraction containing propylene glycol at a low concentration.

  The third embodiment of the present invention is a method of separating the effluent using the circulating fraction recovered from the previous effluent as part of the effluent. For example, the effluent is divided into four fractions. Fraction I contains an organic acid component and a colored component at high concentrations, but contains little propylene glycol. Fraction II contains high concentrations of propylene glycol. Fraction III contains propylene glycol at a low concentration. Fraction IV contains propylene glycol at a lower concentration. Since fraction I contains a large amount of impurities, it is discarded as waste liquid. Fraction II contains most of the propylene glycol contained in the absorbent and is recovered as an aqueous propylene glycol solution. Fraction II is further purified to recover propylene glycol as before. Fraction III is a circulating fraction and is fed to the column following the absorbent. Even if the absorption liquid, the circulation fraction and the water are supplied in this order, the outflow location and the outflow curve of the organic acid component and the coloring component are not changed as compared with the case where the absorption liquid and the water are supplied in this order. However, in the outflow of propylene glycol, although the outflow location is almost the same, the maximum value of the outflow curve becomes larger. Therefore, the concentration of propylene glycol in the aqueous propylene glycol fraction is increased by supplying the circulating fraction to the column following the absorption liquid. Fraction IV is discarded or returned to the propylene oxide production process for use as an absorbent. Fraction IV may be mixed with the circulating fraction and used as the effluent, but is not preferred because the propylene oxide concentration in the circulating fraction is reduced.

  The fourth embodiment of the present invention is another method for separating the effluent using the circulating fraction recovered from the previous effluent as part of the effluent. For example, the effluent is divided into five fractions. Fraction I is discarded as waste liquid. Fraction III is a fraction of an aqueous propylene glycol solution that is further purified to recover propylene glycol. Fractions II and IV are circulating fractions that are fed to the column following the absorbent. Fractions II and IV may be supplied separately to the column or mixed. When supplying separately, an absorption liquid, the fraction II, the fraction IV, and water are supplied in this order. Fraction V contains little propylene glycol and is therefore discarded or returned to the propylene oxide production process for use as an absorbent, similar to fraction IV in the third embodiment. When the absorption liquid and the effluent are alternately supplied to the column, since the fraction V and the fraction I in the next operation flow out successively, they may be combined into one fraction.

  It is preferable to collect as much fraction as possible of the aqueous propylene glycol solution containing propylene glycol. Usually, at least 70% by weight, preferably 85% by weight or more of the propylene glycol contained in the absorbing solution is recovered in the fraction of the aqueous propylene glycol solution. Furthermore, the concentration of propylene glycol in the fraction of the recovered aqueous propylene glycol solution is preferably kept at least 0.2 times, in particular 0.3 times the concentration of propylene glycol in the absorbent.

In order to describe the present invention in more detail, a specific embodiment will be described with reference to FIG. However, this embodiment does not limit the scope of the present invention.
In FIG. 2, 1 is a chromatography column in which a resin bed 2 is accommodated. There is a sufficient space above the resin bed 2, and a water supply pipe 3 is opened above the space. Near the surface of the resin bed 2, a crude propylene glycol aqueous solution distributor 4 and a circulating liquid distributor 5 are installed, to which a crude propylene glycol aqueous solution supply pipe 6 and a circulating liquid supply pipe 7 are connected, respectively. First, water is supplied from the water supply pipe 3 to fill the upper part of the column. Next, the supply of water is stopped, and the crude propylene glycol aqueous solution is supplied from the crude propylene glycol aqueous solution supply pipe 6 via the distributor 4, and at the same time, the liquid is allowed to flow out from the bottom of the column at a rate almost the same as the supply rate. In this way, since the crude propylene glycol aqueous solution has a specific gravity greater than that of water, water and the crude propylene glycol aqueous solution are not mixed with each other, and a clear interface is formed near the surface of the resin bed. When a predetermined amount of the crude propylene glycol aqueous solution is supplied, the supply is stopped, and instead, the circulating portion is supplied from the supply pipe 7 through the distributor 5 at the same speed. The supply amount is usually the same as the amount of the circulation portion to be sorted in one cycle. When the supply from the supply pipe 7 is stopped after the supply of the predetermined amount is completed, the water is then supplied from the water supply pipe 3. In this way, there is little mixing of the crude propylene glycol aqueous solution, the circulating part, and water in the upper part of the resin bed, so that the separation efficiency can be increased. On the other hand, the effluent flowing out from the bottom of the column during this time is divided into portions by continuously measuring the concentrations of propylene glycol, organic acid component and coloring component. The concentration of propylene glycol can be easily measured with a refractometer, the concentration of organic acid salt with an electric conductivity meter, and the concentration of coloring components with an absorptiometer.

  According to the present invention, it is possible to provide a method for recovering high-purity propylene glycol from a solution containing propylene glycol, an organic acid component and a coloring component discharged from the production process of propylene oxide.

A Outflow of organic acid component and coloring component B Outflow of propylene glycol 1 Column 2 Ion exchange resin bed 3 Water supply pipe 4 Crude propylene glycol aqueous solution distributor 5 Circulating partial distributor 6 Crude propylene glycol aqueous solution supply pipe 7 Circulating partial supply pipe

Claims (18)

A method for recovering propylene glycol from an absorption liquid containing propylene glycol, an organic acid component and a coloring component discharged from a propylene oxide production process by subjecting propylene to gas phase catalytic oxidation with oxygen,
A recovery method comprising recovering at least one fraction having a high propylene glycol concentration from a column effluent by subjecting the absorption liquid to chromatography using a salt-type cation exchange resin as a separation carrier and water as a developing agent.   The obtained aqueous solution of propylene glycol contains propylene glycol in an amount of at least 70% by weight of the amount contained in the absorbent, and the concentration of propylene glycol in the obtained aqueous solution of propylene glycol is 0.2 times the concentration in the absorbent. The recovery method according to claim 1, which is as described above.   The obtained aqueous solution of propylene glycol contains propylene glycol in an amount of at least 85% by weight of the amount contained in the absorbing solution, and the concentration of propylene glycol in the obtained aqueous solution of propylene glycol is 0.2 times the concentration in the absorbing solution. The recovery method according to claim 1, which is as described above.   Divide the column effluent into at least two fractions, one fraction being the propylene glycol fraction containing most of the propylene glycol contained in the absorbent and the other fraction being contained in the absorbent. The recovery method according to any one of claims 1 to 3, which is a waste liquid fraction containing most of the organic acid component and the coloring component.   The recovery method according to any one of claims 1 to 4, wherein a fraction rich in propylene glycol is treated with a cation exchange resin and an anion exchange resin, and then circulated in a process for producing propylene glycol by a hydrolysis reaction of propylene oxide. . The column effluent is divided into at least three fractions, the first fraction containing a high concentration of organic acid components and coloring components, little propylene glycol, and the second fraction containing organic acid components. , Containing a coloring component and propylene glycol at a low concentration, and the third fraction contains almost no organic acid component and coloring component, and contains a high concentration of propylene glycol,
The second fraction is circulated as an absorption liquid in the propylene oxide production process, or mixed with the absorption liquid discharged from the propylene oxide production process and processed by chromatography.
The recovery method according to any one of claims 1 to 3, wherein the third fraction is further processed to recover purified propylene glycol. The column effluent is divided into at least three fractions, the first fraction containing a high concentration of organic acid components and coloring components, little propylene glycol, and the second fraction containing organic acid components. , Containing a coloring component and propylene glycol at a low concentration, and the third fraction contains almost no organic acid component and coloring component, and contains a high concentration of propylene glycol,
The second fraction is used as a developing agent in subsequent chromatography,
The recovery method according to any one of claims 1 to 3, wherein the third fraction is further processed to recover purified propylene glycol. A method for recovering propylene glycol from an absorption liquid containing propylene glycol, an organic acid component and a coloring component discharged from a propylene oxide production process by subjecting propylene to gas phase catalytic oxidation with oxygen,
The absorption liquid is supplied to a chromatographic column packed with a salt-type cation exchange resin, water is supplied to elute the absorption liquid, and a fraction rich in at least propylene glycol is recovered from the column effluent. The collection method.   The recovery method according to claim 8, wherein the salt type cation exchange resin is a Na salt type strongly acidic ion exchange resin.   The recovery method according to claim 8 or 9, wherein the absorption liquid is concentrated until the concentration of propylene glycol becomes 200 g / L or more, and then subjected to chromatography.   The fraction rich in propylene glycol contains propylene glycol in an amount of at least 70% by weight of the amount contained in the absorbent, and the concentration of propylene glycol in the obtained aqueous propylene glycol solution is 0.2 times the concentration in the absorbent. It is the above, The collection | recovery method in any one of Claims 8-10.   The fraction rich in propylene glycol contains propylene glycol in an amount of at least 85% by weight of the amount contained in the absorbent, and the concentration of propylene glycol in the obtained aqueous propylene glycol solution is 0.2 times the concentration in the absorbent. It is the above, The collection | recovery method in any one of Claims 8-10.   The recovery method according to any one of claims 8 to 12, wherein a fraction rich in propylene glycol is treated with a cation exchange resin and an anion exchange resin and distilled to recover purified propylene glycol.   The column effluent is divided into at least three fractions, the first fraction containing a large amount of the organic acid component and the coloring component contained in the absorbent, and the second fraction contained in the absorbent. The recovery method according to any one of claims 8 to 10, wherein the organic acid component, the coloring component and propylene glycol are contained in a small amount, and the third fraction contains a large amount of propylene glycol contained in the absorbing solution.   The third fraction contains propylene glycol in an amount of at least 70% by weight of the amount contained in the absorbing solution, and the concentration of propylene glycol in the obtained aqueous propylene glycol solution is 0.2 times or more the concentration in the absorbing solution. The recovery method according to claim 14, wherein   The recovery method according to claim 14, wherein the chromatography column is supplied with the second fraction following the absorption liquid and then with water.   The recovery method according to any one of claims 1 to 16, wherein the gas phase catalytic oxidation is carried out in the presence of a metal catalyst.   The recovery method according to claim 17, wherein the metal catalyst is a catalyst containing (a) copper oxide and (b) ruthenium oxide.

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