Method for processing a composition and method for recycling used hydraulic fluid.

Abstract

To provide a method for efficiently recovering glycol and polyalkylene glycol from used water-glycol-based hydraulic fluid, which have a purity suitable for reuse in the production of water-glycol-based hydraulic fluid. [Solution] A method for processing a composition comprising alkylene glycol, polyalkylene glycol, an organic acid, and water, comprising: (I) adding a basic compound to the composition; (II) after step (I), distilling the composition and recovering at least a portion of the water and alkylene glycol as distilled components; and (III) after step (II), adding water to the residual components of the composition, separating them into an oil phase containing polyalkylene glycol and an aqueous phase containing alkylene glycol and water, and recovering them.

Description

Technical Field

[0001] The present invention relates to a method for treating a composition and a method for recycling a used working fluid.

Background Art

[0002] Regarding a working fluid containing water and glycol (hereinafter sometimes referred to as a water-glycol working fluid), it is known to treat the used water-glycol working fluid. As this type of technology, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2015-147904) describes a water-glycol working fluid that is easy to treat waste liquid by containing a specific polyoxyalkylene glycol. Patent Document 1 describes a method of heating the working fluid to a temperature above the cloud point of the polyoxyalkylene glycol contained in the working fluid, adding a flocculation treatment agent to flocculate the polyoxyalkylene glycol component, filtering off the flocs, and reducing the COD value of the waste liquid.

[0003] Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2001-072991) describes a method for recovering polyalkylene glycol from a used water-glycol working fluid. Patent Document 2 describes subjecting the used liquid of the water-glycol working fluid to a flocculation treatment to remove impurities that can be flocculated, and separating the aqueous solution containing polyalkylene glycol obtained by this treatment into a polyalkylene glycol layer and a water layer by a water washing treatment using the cloud point phenomenon, and recovering the polyalkylene glycol layer.

[0004] Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2013-111509) describes a method for recovering glycols from a used water-glycol working fluid. Patent Document 3 describes adding an inorganic alkali to a used working fluid containing ionic components such as water, glycols, polyalkylene glycol, and fatty acids and then distilling, and electrodialyzing the distillate.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-147904 [Patent Document 2] Japanese Patent Publication No. 2001-072991 [Patent Document 3] Japanese Patent Publication No. 2013-111509 [Overview of the project] [Problems that the invention aims to solve]

[0006] As described above, methods have been proposed for recovering polyalkylene glycols and glycols from used water-glycol-based hydraulic fluids. However, all of the above methods aim to separate either polyalkylene glycols or glycols, and have not considered how to efficiently recover both polyalkylene glycols and glycols. In light of this situation, one of the objectives of the present invention is to provide a method for efficiently recovering glycols and polyalkylene glycols from used water-glycol-based hydraulic fluids that can be reused in the production of water-glycol-based hydraulic fluids. [Means for solving the problem]

[0007] A method for processing a composition comprising alkylene glycol, polyalkylene glycol, organic acid, and water in accordance with this disclosure is: (I) A step of adding a basic compound to the composition, (II) After step (I), the composition is distilled and at least a portion of the water and alkylene glycol is recovered as distilled components, (III) After step (II), water is added to the residual components of the composition, and the oil phase containing polyalkylene glycol and the aqueous phase containing alkylene glycol and water are separated and recovered. [Effects of the Invention]

[0008] According to the processing method described herein, glycol and polyalkylene glycol, which can be reused in the manufacture of water-glycol-based hydraulic fluids, can be efficiently recovered from used water-glycol-based hydraulic fluids. [Modes for carrying out the invention]

[0009] [Summary of the Embodiment] First, embodiments of the processing method relating to this disclosure will be listed and described. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or greater and B or less".

[0010] A method for processing a composition comprising alkylene glycol, polyalkylene glycol, organic acid, and water in accordance with this disclosure is: (I) A step of adding a basic compound to the composition, (II) After step (I), the composition is distilled and at least a portion of the water and alkylene glycol is recovered as distilled components, (III) After step (II), water is added to the residual components of the composition, and the oil phase containing polyalkylene glycol and the aqueous phase containing alkylene glycol and water are separated and recovered.

[0011] Used water-glycol-based hydraulic fluids contain not only water, polyalkylene glycol, and glycols, which are the components of the hydraulic fluid, but also organic acids, which are degraded products generated during the use of the hydraulic fluid. It is known that distillation is performed to treat such used hydraulic fluids (Patent Document 3). Patent Document 3 describes that by adding an inorganic alkaline component before distillation, the degraded products can be left as a residue in the boiler along with polyalkylene glycol, which is a high-boiling point component, thereby improving the processability of the degraded products. In the method of Patent Document 3, glycol, which has a relatively low boiling point, can be recovered as a distillate component obtained by distillation. On the other hand, the recovery of polyalkylene glycol has not been considered. On the other hand, Patent Document 1 removes polyalkylene glycol by flocculating it by adding a flocculant to a flame-retardant hydraulic fluid composition in order to reduce the COD in the waste liquid, and the reuse of polyalkylene glycol is not envisioned. If the flocculated polyalkylene glycol were to be reused as a raw material for water-glycol-based hydraulic fluids, further treatment such as removing the flocculant would be necessary. Patent Document 2 describes a method for removing degraded substances from the working fluid by coagulation treatment, followed by recovery of polyalkylene glycol by a water washing treatment utilizing the cloud point phenomenon. However, it does not consider the recovery of glycols contained in the aqueous phase after the water washing treatment.

[0012] In contrast, according to the processing method of this disclosure, at least a portion of the alkylene glycol and water is recovered by distillation after adding a basic compound. Next, water is added to the still residue (residual components), and the aqueous phase containing the remainder of the alkylene glycol and the phase containing the polyalkylene glycol are separated by cloud point separation. In this way, polyalkylene glycol from which degraded products have been removed can be recovered from the residual components after distillation. According to the processing method of this disclosure, water, alkylene glycol, and polyalkylene glycol, which are the main components of a water-glycol-based working fluid, can be recovered from a composition containing alkylene glycol, polyalkylene glycol, an organic acid, and water, while removing the organic acid.

[0013] In the above processing method, step (III) may be repeated multiple times. By repeating step (III) multiple times, polyalkylene glycol with a further reduced organic acid content can be recovered.

[0014] The processing method described above is further carried out after step (III), (IV) The step may include distilling the aqueous phase recovered in step (III) above to recover water and at least a portion of alkylene glycol as distilled components. By performing step (IV), the recovery efficiency of alkylene glycol from the composition being treated can be further improved.

[0015] A method for processing a composition comprising alkylene glycol, polyalkylene glycol, organic acid, and water in accordance with this disclosure is: (a) A step of adding water to the composition and separating it into an oil phase containing polyalkylene glycol and an aqueous phase containing alkylene glycol and water, and recovering them. (b) After step (a), the recovered aqueous phase is distilled to recover water and at least a portion of alkylene glycol as distilled components, The above step (b) is carried out in an alkaline environment.

[0016] According to the processing method described herein, an oil phase containing polyalkylene glycol is separated from the composition to be processed, and then, the aqueous phase is subjected to an alkaline environment to convert the organic acid into a salt, and water and alkylene glycol are recovered by distillation. In this way, water, alkylene glycol, and polyalkylene glycol, which are the main components of a water-glycol-based working fluid, can be recovered from a composition containing alkylene glycol, polyalkylene glycol, organic acid, and water, while removing the organic acid.

[0017] In the above processing method, step (a) may be carried out in an alkaline environment. By carrying out step (a) in an alkaline environment, organic acids can be reliably left in the aqueous phase as salts, and polyalkylene glycol with a lower organic acid content can be recovered.

[0018] In the above treatment method, the step (a) may be repeated multiple times. By repeating the step (a) multiple times, a polyalkylene glycol with a lower organic acid content can be recovered.

[0019] In the above treatment method, the composition may be a used working fluid. According to the treatment method of the present disclosure, organic acids that increase with the use of the working fluid can be removed from the used working fluid, and water, alkylene glycol, and polyalkylene glycol can be efficiently recovered. Each of the recovered components can be reused as a raw material for a water glycol-based working fluid.

[0020] The recycling method of the used working fluid according to the present disclosure is a method including the above treatment method. In the recycling method, the composition may be a used working fluid, and each of the water and alkylene glycol recovered in the step (II), and the oil phase containing the polyalkylene glycol recovered in the step (III) may be reused as part of the raw material of the working fluid. According to the recycling method of the present disclosure, water, alkylene glycol, and polyalkylene glycol can be recovered from the used working fluid with high energy efficiency, working efficiency, and yield, and then reused as raw materials for a water glycol-based working fluid.

[0021] The recycling method of the used working fluid according to the present disclosure is a method including the above treatment method. In the recycling method, the composition may be a used working fluid, and each of the oil phase containing the polyalkylene glycol recovered in the step (a), and the water and alkylene glycol recovered in the step (b) may be reused as part of the raw material of the working fluid. According to the recycling method of the present disclosure, water, alkylene glycol, and polyalkylene glycol can be recovered from the used working fluid with high energy efficiency, working efficiency, and yield, and then reused as raw materials for a water glycol-based working fluid.

[0022] [Specific Examples of Embodiments] The following describes in more detail the processing method for the composition relating to this disclosure and the recycling method for used working fluid.

[0023] (Composition to be processed) The method for processing compositions according to this disclosure is a method for processing compositions comprising alkylene glycol, polyalkylene glycol, organic acid, and water. The compositions to be processed may be, for example, used flame-retardant hydraulic fluids, water-soluble grinding and cutting oils, water-soluble heat transfer oils, coolants (refrigerants for circulating equipment and facilities), and other industrial water-based compositions. More specifically, used water-glycol-based hydraulic fluids.

[0024] Examples of alkylene glycols (hereinafter sometimes abbreviated as AG) included in the composition to be treated include glycols having 2 to 12 carbon atoms, such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, and tetrapropylene glycol, and may contain one or more of these. In addition, glycerin may be included as a glycol other than alkylene glycol.

[0025] The polyalkylene glycol (hereinafter sometimes abbreviated as PAG) contained in the composition to be treated includes copolymers of ethylene oxide (EO) and propylene oxide (PO), polyethylene glycol polymerized from EO alone, and polypropylene glycol polymerized from PO alone, and may contain one or more of these. The PAG may also include polyalkylene glycol to which organic functional groups such as OH groups, methyl groups, and ethyl groups have been further added. The molecular weight of the PAG is not particularly limited, but may be around 200 to 30,000.

[0026] Examples of organic acids included in the composition to be treated are formic acid, acetic acid, propionic acid, butyric acid, glycolic acid, lactic acid, etc., and one or more of these may be included. These organic acids are produced as degraded products when AG and PAG contained as components of the working fluid are subjected to shear, heat, and oxidation during use. The organic acids may also include saturated fatty acids with 8 to 20 carbon atoms, unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid, dibasic acids such as dimer acid, and tribasic acids such as trimer acid. The organic acids may also be included in the composition as active ingredients of the working fluid.

[0027] The composition to be processed may contain other components in addition to those listed above. Examples of other components include heterocyclic nitrogen compounds such as benzotriazole to impart corrosion protection to the working fluid, amine compounds such as alkanolamines, dialkylalkanolamines, and trialkylalkanolamines, silicones added as defoaming agents, and colorants.

[0028] The proportion of each component in the composition to be treated is not particularly limited, but for example, the initial composition of the treatment method according to this disclosure may contain approximately 20-80% water, 5-80% AG, 5-50% PAG, 0-10% organic acid, and 0-20% other components. More specifically, it may contain approximately 30-50% water, 20-60% AG, 10-40% PAG, 0-5% organic acid, and 0-5% other components. Generally, the composition of a water-glycol-based working fluid is approximately 40% water, 40% AG, 15% PAG, and 5% additives, but the proportion of degraded products such as organic acids increases with use of the working fluid.

[0029] (Processing method) [First Processing Method] A first processing method, which is one aspect of the processing method relating to this disclosure, is: (I) A step of adding a basic compound to the composition to be treated (hereinafter sometimes referred to as the alkali addition step), (II) After step (I) above, a step of distilling the composition and recovering at least a portion of water and alkylene glycol as distilled components (hereinafter sometimes referred to as the first distillation step), (III) After step (II), water is added to the residual components of the composition, and the oil phase containing polyalkylene glycol and the aqueous phase containing alkylene glycol and water are separated and recovered (hereinafter sometimes referred to as the cloud point separation step).

[0030] Basic compounds added in the alkali addition step include KOH, K2CO3, KHCO3, NaOH, Na2CO3, NaHCO3, CsOH, Cs2CO3, CsHCO3, LiOH, Li2CO3, etc. Basic compounds may also be added as aqueous solutions prepared in advance. For example, a 10-50% aqueous KOH solution can be added to the composition to be treated. The amount of basic compound to be added should be adjusted according to the amount of organic acids contained in the composition to be treated, but it is preferable to add an amount greater than or equal to the amount necessary for all organic acids to form salts. Basic compounds can be added in an amount of 0.1-5% by weight, preferably 0.1-2% by weight, relative to the composition to be treated. By adding basic compounds, the organic acids contained in the composition to be treated can be converted into high-boiling point salts.

[0031] The temperature of the alkali addition step is not particularly limited. A basic compound (which may be an aqueous solution) is added to the composition to be treated at approximately 10-40°C and stirred until homogeneous. Heating may also be performed along with stirring. If heating is performed, the temperature can be approximately 40-90°C.

[0032] Following the alkali addition step, step (II) (first distillation step) is performed to distill the composition to which the basic compound has been added, and to recover at least a portion of the water and alkylene glycol contained in the composition as fractions by distillation. Distillation is preferably carried out by simple distillation under reduced pressure, but is not limited to this. Preferably, in order to prevent bumping of water, the distillation conditions for water are first set to 7 to 20 kPa and 40 to 60°C. Subsequently, if the Ag is ethylene glycol, it is preferable to distill under the conditions of 1 to 10 kPa and 90 to 130°C; if it is propylene glycol, it is preferable to distill under the conditions of 1 to 10 kPa and 90 to 130°C; if it is dipropylene glycol, it is preferable to distill under the conditions of 1 to 10 kPa and 120 to 210°C; and if it is glycerin, it is preferable to distill under the conditions of 1 to 10 kPa and 180 to 240°C.

[0033] In the first distillation step, it is preferable to distill off a portion of the water and alkylene glycol contained in the composition before distillation. In the first distillation step, 95% or more, preferably 98% or more, of the water contained in the composition before distillation can be distilled off, and about 50-90%, preferably about 60-90%, of the alkylene glycol contained in the composition before distillation can be distilled off. The water and alkylene glycol may be recovered separately by utilizing the temperature difference of their boiling points, or they may be recovered together. The first distillation step is terminated when the fraction (recovered amount) relative to the input amount reaches a target value (for example, 60%) or more. From the viewpoint of ease of handling of the residue in the pot, the target value for fraction recovery is usually 50-80%.

[0034] The organic acid content in the mixed liquid of water and alkylene glycol recovered in the first distillation step is preferably 20 ppm or less, and more preferably 10 ppm or less. The residue (residual components) in the first distillation step mainly contains alkylene glycol residue, polyalkylene glycol, and organic acid salts.

[0035] Following the first distillation step, step (III) (cloud point separation step) is performed, in which water is added to the residual components to separate them into an oil phase containing polyalkylene glycol and an aqueous phase containing alkylene glycol and water, and then recover them. This step is a cloud point separation step that utilizes the cloud point of PAG. Water may be added and heated as needed to adjust the temperature to be above the cloud point of PAG, and cloud point separation may be performed under heating. By heating the mixture obtained in step (II) with added water to a temperature above the cloud point of PAG, the mixture is separated into a phase containing polyalkylene glycol (oil phase) and an aqueous phase containing alkylene glycol, water, and a water-soluble organic acid salt.

[0036] The cloud point separation process may be carried out by batch processing using static separation, or by continuous processing using a countercurrent separation apparatus or the like. When cloud point separation is performed by batch processing, it is also preferable to repeat the cloud point separation process multiple times. That is, water may be added to the oil phase obtained by cloud point separation, and cloud point separation may be performed again. There is no limit to the number of repetitions, but from the viewpoint of balancing impurity separation efficiency, extraction efficiency and reduction of energy consumption for processing, it is preferable to repeat it about 2 to 4 times. In the case of continuous processing, cloud point separation can be carried out while continuously adding water to the residual components of the first distillation process. The amount of water added to the residual components is not particularly limited as long as PAG can be separated, but for example, a total of 2 to 3 times the amount of water as the residual components can be added.

[0037] In the cloud point separation step, it is preferable to recover approximately 80-95% of the PAG contained in the composition before cloud point separation as PAG contained in the oil phase. The oil phase usually contains water. In addition, the oil phase may contain some AG. For example, the oil phase may contain approximately 40-60% PAG, 0-10% AG, and 40-60% water. It is preferable that the amount of organic acid contained in the oil phase is 100 ppm or less. The aqueous phase obtained in the cloud point separation step contains water, AG, organic acid salts, additives, etc., and contains almost no PAG.

[0038] By performing the alkali addition step, the first distillation step, and the cloud point separation step described above in this order, AG is recovered by the first distillation step, PAG is recovered by the cloud point separation step, and the degraded organic acids are separated into the aqueous phase obtained in the cloud point separation step. The processing method according to the present invention may end with the above steps. The AG and water recovered in the first distillation step and the PAG separated in the cloud point separation step all have a low content of degraded products and can be recycled as part of the raw materials for newly produced water-glycol-based working fluid. The aqueous phase containing degraded products can be discarded.

[0039] Furthermore, the aqueous phase obtained in the cloud point separation step may be distilled. That is, in the processing method according to the present disclosure, after step (III), a step (IV) may be performed in which the aqueous phase recovered in step (III) is distilled to recover water and at least a portion of alkylene glycol as distilled components (hereinafter sometimes referred to as the second distillation step).

[0040] The distillation in the second distillation step may be carried out under the same conditions as in the first distillation step. Since the distillation conditions are redundant, their description is omitted.

[0041] The alkylene glycol obtained as a fraction in the second distillation step may be about 20-40%, preferably about 30-40%, of the alkylene glycol contained in the aqueous phase before distillation. The completion of the second distillation step may be determined when no fraction is obtained. The organic acid content in the mixed liquid of water and alkylene glycol recovered in the second distillation step is preferably 10 ppm or less. The alkylene glycol obtained as a fraction in the second distillation step can be recycled as is, or mixed with the alkylene glycol obtained in the first distillation step, as a raw material for a new aqueous glycol working fluid.

[0042] The still residue (residual components) from the second distillation process mainly contains residual AG, PAG, and salts of organic acids. This still residue can be disposed of as waste.

[0043] The recovery rate of PAG and AG recovered by the above-described processing method is not particularly limited, but it is possible to recover 80% or more, preferably 90% or more, of the PAG contained in the composition to be processed. In addition, it is possible to recover 70% or more, preferably 80% or more, of the AG contained in the composition to be processed.

[0044] [Second Processing Method] A second processing method, which is one aspect of the processing method relating to this disclosure, is a method for processing the above-mentioned composition to be processed, (a) A step of adding water to the composition, separating it into an oil phase containing polyalkylene glycol and an aqueous phase containing alkylene glycol and water, and recovering them. (b) After step (a), the recovered aqueous phase is distilled to recover water and at least a portion of alkylene glycol as distilled components, The above step (b) is carried out in an alkaline environment.

[0045] The difference between the first and second processing methods is that in the first processing method, cloud point separation is performed after the first distillation step, whereas in the second processing method, the distillation step is performed after the cloud point separation. In both the first and second processing methods, the distillation step is carried out in an alkaline environment. In the second processing method, the cloud point separation in step (a) may be carried out in an alkaline environment, or a basic compound may be added after step (a) and before step (b).

[0046] A basic compound is added to carry out step (b), or steps (a) and (b), in an alkaline environment. The basic compound can be the same as that described in the alkali addition step above, and the addition of the basic compound can be carried out in the same manner.

[0047] Step (a) is a cloud point separation step, and the same methods and conditions as in the cloud point separation step in the first processing method can be used. However, the composition to be processed in the cloud point separation step in the second processing method tends to have a high AG content because it has not undergone distillation. For this reason, the amount of water added for cloud point separation tends to be greater than the amount of water used for the cloud point separation step in the first processing method. When cloud point separation is repeated multiple times by batch processing, there is no particular limit to the number of repetitions, but it can be 2 to 4 times.

[0048] In step (a), PAG is recovered as an oil phase. It is preferable to recover about 80-95% of the PAG contained in the composition to be treated as an oil phase. The oil phase may contain water. It may also contain a portion of AG. For example, the oil phase may contain about 40-60% PAG, about 0-10% AG, and about 40-60% water. It is preferable that the amount of organic acid contained in the oil phase is 100 ppm or less. The aqueous phase obtained in the cloud point separation step contains water, AG, and organic acid salts.

[0049] Following step (a), step (b) is performed in which the aqueous phase recovered in step (a) is distilled to recover water and at least a portion of alkylene glycol as distilled components. Step (b) is a distillation step, and the same methods and conditions as the first distillation step in the first treatment method can be used. However, the aqueous phase subjected to step (b) contains a large amount of water and therefore has a large volume of liquid, and contains AG and organic acid salts along with water. For this reason, the distillation time for removing water tends to be longer than in the first treatment method, and energy consumption also tends to be higher. On the other hand, in the second treatment method, AG is recovered in a single distillation step, so the number of steps can be reduced.

[0050] Step (b) yields alkylene glycol and water as fractions, while the degraded organic acid salts are discarded as kettle residue. The obtained alkylene glycol and water fractions can be recycled as raw materials for a new water-glycol-based working fluid.

[0051] [Recycling Methods] The PAG, AG, and water recovered by the first and second treatment methods have reduced organic acid content and can be recycled as raw materials for water-glycol-based working fluids. In the oil phase containing the recovered PAG, the organic acid content is preferably 100 ppm or less. In the fraction containing the recovered AG, the organic acid content is preferably 10 ppm or less. After confirming the PAG content in the obtained oil phase and the water and AG content in the obtained fraction by measurement, recycling can be carried out by adding them as part of the raw materials for water-glycol-based working fluids.

[0052] [Examples] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0053] [Measurement method] In the following method, the content of each component in the liquid was as follows: The content of propylene glycol (hereinafter referred to as PG) and PAG was quantified using a calibration curve by GPC. The water content was measured using a Karl Fischer moisture meter. The content of other components (additives, etc.) was calculated by subtracting the amounts of PG, PAG, and water from the total mass. Formic acid and acetic acid were quantified by capillary electrophoresis, and their sum was considered the content of degraded products containing organic acids.

[0054] [Example 1] The used water-glycol-based hydraulic fluid was treated according to the following procedure. The used hydraulic fluid to be treated had the composition shown as "Composition to be treated" in Table 1. 6 g of 48% potassium hydroxide aqueous solution was added to 300 g of the working fluid to be treated. After stirring and confirming that the liquid to be treated was homogenized, the pressure was reduced to 3 kPa and heated to 120°C, and distillation was performed. The completion of distillation was determined when the fraction reached approximately 65% ​​of the input volume. 203 g of liquid was obtained as the fraction and 103 g as the residue. The fraction had the composition shown as "Fraction 1" in Table 1. Next, deionized water was added to the residue, and cloud point treatment was performed four times by static separation while adjusting the temperature to 90°C to separate the oil phase (PAG phase) and the aqueous phase. The total amount of deionized water added was 250 g. 78 g of the oil phase and 275 g of the aqueous phase were recovered. The PAG phase had the composition shown as "PAG phase" in Table 1. Furthermore, the aqueous phase was reduced to 3 kPa and heated to 120°C, and distillation was performed. 229 g of liquid was obtained as a fraction, and 36 g of liquid remained in the still. The fraction had the composition shown as "Fraction 2" in Table 1. In the second distillation, approximately 10 g of water was lost without being recovered as a fraction.

[0055] Table 1 shows the recovered amount and recovery rate of PAG and PG obtained by the above method as "Results". The total recovery rate (the ratio of the total amount of recovered PAG and PG to the total amount of PAG and PG contained in the used hydraulic fluid to be treated) was 84.3%. Furthermore, the impurity content in the recovered fractions 1 and 2 was less than 10 ppm, which is at a level that allows for reuse as a raw material for water-glycol-based hydraulic fluid. The impurity content in the recovered oil phase was also less than 100 ppm, which is at a level that allows for reuse as a raw material for water-glycol-based hydraulic fluid.

[0056] [Table 1]

[0057] [Comparative Example 1] The same used aqueous glycol-based working fluid as in Example 1 was used for the treatment. 300 g of the working fluid to be treated was subjected to distillation under reduced pressure of 3 kPa to 120°C and heated without adding potassium hydroxide aqueous solution. The completion of distillation was determined when the fraction reached approximately 65% ​​of the input volume. 200 g of liquid was obtained as the fraction, and 100 g of liquid remained in the pot. The composition of the fraction was PG 45 wt%, water 54 wt%, and impurities 7500 ppm. The fraction contained a high amount of impurities, and was deemed unsuitable as a raw material for water-glycol-based working fluids.

[0058] [Example 2] 300g of used water-glycol-based working fluid was used as the composition to be treated, and the following procedure was followed. The composition to be treated contained PG 36wt%, PAG 14wt%, water 40wt%, other (additives, etc.) 10wt%, and impurities (degraded products) 3200ppm. First, 6 g of 48% potassium hydroxide aqueous solution was added to 300 g of the working fluid to be treated. After stirring and confirming that the liquid to be treated was homogenized, deionized water was added, and the cloud point separation process was performed four times by static separation while adjusting the temperature to 90°C to separate the oil phase (PAG phase) and the aqueous phase. 81 g of the oil phase and 825 g of the aqueous phase were recovered. The total amount of deionized water added was 600 g. The obtained aqueous phase was subjected to reduced pressure at 3 kPa and heated to 120°C, followed by distillation. 773 g of liquid was obtained as a fraction, and 52 g of liquid remained in the still. The composition of the fraction was PG 11 wt%, PAG 0 wt%, water 89 wt%, and impurities less than 10 ppm. The resulting oil phase consisted of PG 1 wt%, PAG 52 wt%, water 46 wt%, and impurities less than 100 ppm.

[0059] [Comparative Example 2] The same used aqueous glycol-based working fluid as in Example 2 was subjected to the same treatment as in Example 2, but without adding potassium hydroxide aqueous solution. 600g of deionized water was added to 300g of the working fluid to be treated, without adding potassium hydroxide aqueous solution, and the oil phase (PAG phase) and aqueous phase were separated using a countercurrent separation apparatus (manufactured in-house) while adjusting the temperature to 90°C. The oil phase and aqueous phase were recovered separately. The resulting oil phase consisted of 52 wt% PAG, 1 wt% PG, 46 wt% water, and impurities of less than 100 ppm. On the other hand, because basic compounds were not added before distillation, the aqueous phase contained impurities, which could not be removed by distillation, and thus reusable PG could not be obtained.

[0060] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the present invention is defined by the claims and is intended to include all modifications in the sense and scope equivalent to the claims.

Claims

1. A method for processing a composition comprising alkylene glycol, polyalkylene glycol, an organic acid, and water, (I) A step of adding a basic compound to the composition, (II) After step (I), the composition is distilled and at least a portion of the water and alkylene glycol is recovered as distilled components, (III) After step (II), water is added to the residual components of the composition, and the oil phase containing polyalkylene glycol and the aqueous phase containing alkylene glycol and water are separated and recovered. A method for processing a composition.

2. Repeat the above step (III) multiple times. A method for processing the composition described in claim 1.

3. After the above step (III), further, (IV) A step of distilling the aqueous phase recovered in step (III) above, and recovering water and at least a portion of alkylene glycol as distillation components, A method for processing the composition according to claim 1 or claim 2.

4. A method for processing a composition comprising alkylene glycol, polyalkylene glycol, an organic acid, and water, (a) A step of adding water to the composition and separating it into an oil phase containing polyalkylene glycol and an aqueous phase containing alkylene glycol and water, and recovering them, (b) After step (a), the recovered aqueous phase is distilled to recover water and at least a portion of alkylene glycol as distilled components, The above step (b) is carried out in an alkaline environment. A method for processing a composition.

5. The above step (a) is carried out in an alkaline environment. A method for processing the composition described in claim 4.

6. Repeat the above step (a) multiple times. A method for processing the composition according to claim 4 or claim 5.

7. A method for processing the composition according to claim 1 or claim 4, wherein the composition is a used working fluid.

8. A method comprising the processing method described in claim 1, The composition is a used working fluid, The alkylene glycol recovered in step (II) and the oil phase containing polyalkylene glycol recovered in step (III) are reused as part of the raw materials for the working fluid. Recycling methods for used hydraulic fluid.

9. A method comprising the processing method described in claim 4, The composition is a used working fluid, The oil phase containing polyalkylene glycol recovered in step (a) and the alkylene glycol recovered in step (b) are reused as part of the raw materials for the working fluid. Recycling methods for used hydraulic fluid.

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