JP7633380B2 - Method for purifying hydrolyzable organic solvents and method for producing resins for purifying hydrolyzable organic solvents - Google Patents

Description

The present invention relates to a method for purifying hydrolyzable organic solvents and a method for producing a resin for purifying hydrolyzable organic solvents.

Semiconductors are manufactured through hundreds of complex processes. The line width of a semiconductor is determined by the photoresist process. The photoresist process includes the steps of applying resist to a silicon wafer, exposing the wafer to short-wavelength light from a light source through a mask, developing the photomask, etching the areas without resist, and removing the resist. The resist applied to the wafer is a solvent in which an acid generator, a resin solution, and additives are dissolved in an organic solvent. The organic solvent used is an ester-based organic solvent such as PGMEA (propylene glycol monomethyl ether acetate) and ethyl lactate, or PGME (propylene glycol monomethyl ether), cyclohexanone, etc., as the main component.

In recent years, the processing dimension requirements for semiconductor line widths have become finer year by year. Refining semiconductor line widths promotes the miniaturization and high performance technology of IT devices. As semiconductor line widths become finer, the light source used in the exposure process has increasingly shifted from g-line and i-line levels to short-wavelength ArF, EUV, and X-rays, and the amount of impurities in the organic solvents used around the resist coating has also been set low. Among the impurities contained in organic solvents, particularly metal elements, if there are a large amount of remaining metal elements, will adhere to the wafer and lead to a decrease in semiconductor performance. For this reason, metal elements are always listed as an item to be reduced.

On the other hand, it is known that ester-based organic solvents such as PGMEA used in semiconductor manufacturing undergo hydrolysis and generate acids when they come into contact with moisture, acid, or alkali. Therefore, in the purification of ester-based organic solvents, methods such as distillation and the use of chelating resins have been proposed as methods for removing metal impurities without generating acid.

Patent Document 1 describes a method for reducing metal ions in a photoresist composition by washing a chelating resin with deionized water, a mineral acid solution, and optionally an ammonium hydroxide solution, washing the resin with an organic solvent, mixing the resin with a photoresist composition, and heating and filtering the mixture. However, this method was insufficient in terms of removing Fe in particular.

Patent Document 2 describes a method in which a resin solution for forming a photoresist film is passed through a filter substrate having ion exchange groups and/or chelating groups fixed to a polyolefin nonwoven fabric at a flow rate (SV value) of 10 h ^-1 or less. However, Patent Document 2 describes only the Na concentration as the impurity concentration, and the inventors' investigations have revealed that the removal of heavy metals such as Fe and Cr is inferior to the case where a chelating resin is used.

Patent Document 3 describes a method for removing metal impurities from a liquid to be treated, such as PGMEA, using a chelating resin in which the amount of metal impurities contained has been reduced by a mineral acid solution. However, further investigation by the inventors revealed that, depending on the liquid to be purified, heavy metals such as Fe and Cr may not be sufficiently removed.

Special Publication No. 2000-501201 JP 2013-061426 A JP 2019-141800 A

Therefore, the present invention aims to provide a method for producing a resin for purifying hydrolyzable organic solvents that can reduce the concentration of metal impurities in a hydrolyzable organic solvent while suppressing the generation of acid, and a method for purifying a hydrolyzable organic solvent using the resin.

In view of the above problems, the inventors conducted extensive research and discovered that by using a cation exchange resin optionally mixed with a chelating resin, it is possible to suppress acid generation from hydrolyzable organic solvents while reducing metals that cannot be removed by the chelating resin alone, thus completing the present invention.

That is, the present invention relates to a method for purifying a hydrolyzable organic solvent , the method comprising a purification step of purifying the hydrolyzable organic solvent by contacting the hydrolyzable organic solvent with a cation exchange resin mixed with a chelating resin, the volume ratio of the cation exchange resin to the total amount of the cation exchange resin and the chelating resin being 10 to 50 % , and the hydrolyzable organic solvent being an ester-based organic solvent or a mixed solvent containing an ester-based organic solvent .

The present invention also relates to a method for producing a resin for purifying a hydrolyzable organic solvent, the method comprising the step of mixing a chelating resin with a cation exchange resin, the volume ratio of the cation exchange resin to the total amount of the cation exchange resin and the chelating resin being 10 to 50 % , and the hydrolyzable organic solvent being an ester-based organic solvent or a mixed solvent containing an ester-based organic solvent .

According to the present invention, it is possible to provide a method for producing a resin for purifying a hydrolyzable organic solvent, which can reduce the concentration of metal impurities in a hydrolyzable organic solvent while suppressing the generation of acid, and a method for purifying a hydrolyzable organic solvent using the resin.

The method for producing a resin for purifying a hydrolyzable organic solvent according to the present invention includes a step of mixing a chelating resin with a cation exchange resin. When a chelating resin is not used and only a cation exchange resin is used, this step can also be said to be a step of preparing a cation exchange resin. The method for purifying a hydrolyzable organic solvent according to the present invention includes a purification step of contacting a hydrolyzable organic solvent with a cation exchange resin optionally mixed with a chelating resin to purify the hydrolyzable organic solvent. The volume ratio of the cation exchange resin to the total amount of the cation exchange resin and the optional chelating resin is 10 to 100%.

(Hydrolyzable organic solvent)
The hydrolyzable organic solvent, which is the liquid to be purified in the present invention, is an ester-based organic solvent that generates an acid by hydrolysis. The liquid to be purified in the present invention may be a mixed solvent of two or more organic solvents including at least an ester-based organic solvent. The liquid to be purified is not particularly limited, but examples thereof include ester-based organic solvents such as PGMEA (propylene glycol monomethyl ether acetate), ethylene glycol monoethyl ether acetate, ethyl-3-ethoxypropyl acetate, ethyl lactate, butyl lactate, butyl acetate, and isopentyl acetate, and mixed solvents of these ester-based organic solvents with PGME (propylene glycol monomethyl ether), cyclohexanone, and the like. Among these, PGMEA or a mixed solvent of PGMEA/PGME is preferred. The ratio of PGMEA in the mixed solvent of PGMEA/PGME is not particularly limited, and can be appropriately adjusted according to the purpose.

The water concentration of the hydrolyzable organic solvent (before purification) used in the present invention is preferably 20 to 10,000 mg/L from the viewpoint of suppressing hydrolysis and stabilizing metal purification performance. The upper limit of the water concentration is preferably low, more preferably 5,000 mg/L, and even more preferably 1,000 mg/L. The water concentration can be measured by the Karl Fischer method using, for example, a Karl Fischer volumetric moisture meter (product name: Aquacounter AQ-2200, manufactured by Hiranuma Sangyo Co., Ltd.).

(Cation exchange resin)
The ion exchange resin is obtained by introducing functional groups into a copolymer having a three-dimensional network structure obtained by copolymerizing, for example, styrene and divinylbenzene (DVB) in the presence of a catalyst and a dispersant. Examples of the cation exchange resin used in the present invention include a strongly acidic cation exchange resin having a sulfonic acid group (-SO ₃ H) and a weakly acidic cation exchange resin having a carboxylic acid group (-COOH). The cation exchange resin may be either a transparent gel type having a small pore diameter, or a macrolitericular type (MR type) or a macroporous type (also called a porous type or high-porous type) having macropores having a large pore diameter. In the present invention, a strongly acidic cation exchange resin is preferably used from the viewpoint of removing metals. Among them, an MR type strongly acidic cation exchange resin is preferable from the viewpoint of the balance between the inhibition of acid generation and the metal removal performance. Moreover, a highly crosslinked gel type strongly acidic cation exchange resin is preferable from the viewpoint of more effectively inhibiting acid generation. The highly cross-linked gel-type strongly acidic cation exchange resin specifically refers to a gel-type strongly acidic cation exchange resin having a cross-linking degree of 16% to 24%.

The volume ratio of the cation exchange resin to the total amount of the cation exchange resin and any chelating resin described later is 10 to 100%, preferably 20 to 100%. Here, 100% means that only the cation exchange resin is used. According to the purification method of the present invention, even when only the cation exchange resin is used, it is possible to reduce metal impurities in the purification target liquid while suppressing acid generation. From the viewpoint of more effectively suppressing acid generation, it is preferable to use the cation exchange resin and the chelating resin in a mixed bed or multiple beds. In that case, the volume ratio of the cation exchange resin to the total amount of the cation exchange resin and the chelating resin is preferably 10% to 50%, more preferably 10% to 33%.

Examples of the cation exchange resin used in the present invention include, but are not limited to, AMBERLITE (registered trademark) IRN99H (gel-type strongly acidic cation exchange resin, product name, manufactured by DuPont), AMBERLITE (registered trademark) CR99 K/350, TAPTEC (registered trademark) HCRS Na (all gel-type strongly acidic cation exchange resins, product names, manufactured by DuPont), AMBERJET (registered trademark) 1060H (gel-type strongly acidic cation exchange resin, product name, manufactured by Organo Corporation), ORLITE (registered trademark) DS-1 (gel-type strongly acidic cation exchange resin, product name, manufactured by Organo Corporation), ORLITE (registered trademark) DS-4 (MR-type strongly acidic cation exchange resin, product name, manufactured by Organo Corporation), etc. As the ion form of the cation exchange resin, the hydrogen ion form (H form) is preferable from the viewpoint of metal removal. When a resin having another ion form (for example, a sodium ion form, a potassium ion form, etc.) is used, it is preferable to convert the resin to an H-type in advance by a known method.

(chelating resin)
In the present invention, the cation exchange resin can be mixed with a chelating resin as desired. When a chelating resin is mixed, the cation exchange resin and the chelating resin may be mixed or multiple beds. In either case, the effect of the present invention can be obtained. The chelating resin is a resin having a functional group (chelating group) capable of forming a chelate (complex) with a metal ion. The functional group is not particularly limited as long as it is a functional group capable of forming a chelate (complex) with a metal ion. Examples of the functional group include an aminomethyl phosphate group, an iminodiacetic acid group, a thiol group, and a polyamine group. From the viewpoint of selectivity for a plurality of metal species, the chelating resin preferably has an aminomethyl phosphate group or an iminodiacetic acid group as a functional group.

It is preferable that the ionic form of the chelating resin is H-form. Examples of chelating resins include, but are not limited to, AMBERSEP (registered trademark) IRC747UPS (trade name, manufactured by DuPont, chelating group: aminomethyl phosphate group), AMBERSEP (registered trademark) IRC748 (trade name, manufactured by DuPont, chelating group: iminodiacetic acid group), ORLITE (registered trademark) DS-21 (trade name, manufactured by Organo Corporation, chelating group: aminomethyl phosphate group), ORLITE (registered trademark) DS-22 (trade name, manufactured by Organo Corporation, chelating group: iminodiacetic acid group), DIAION (registered trademark) CR11 (trade name, manufactured by Mitsubishi Chemical Corporation, chelating group: iminodiacetic acid group), S930 (trade name, manufactured by Purolite Co., Ltd., chelating group: iminodiacetic acid group), and S950 (trade name, manufactured by Purolite Co., Ltd., chelating group: aminophosphate group). When the ion form of the resin is the sodium ion form (Na form), the ion form can be converted from the Na form to the H form by a known method before use.

The chelating resin used in the present invention is preferably in the hydrogen ion form, and the total amount of metal impurities eluted when 25 volumes of hydrochloric acid having a concentration of 3% by mass are passed through the chelating resin is preferably 5 μg/mL-R or less. Such a commercially available product can also be used as the chelating resin. Here, "25 volumes" means that 25 volumes of hydrochloric acid are passed through the chelating resin. The unit "/mL-R" means "per mL of the volume of the chelating resin in the saturated equilibrium state." The saturated equilibrium state refers to a state in which the chelating resin is saturated by contacting the chelating resin with the atmosphere at 25° C. and 100% relative humidity for 30 minutes or more. "Passing through hydrochloric acid" includes not only passing hydrochloric acid through the chelating resin, but also immersing the chelating resin in hydrochloric acid. The total amount of metal impurities per mL of chelating resin (μg/mL-R) can be calculated from the amount of each eluted metal impurity (μg/L), the volume of the eluent used for elution (L), and the volume of the chelating resin (mL) using the following formula.
Total amount of metal impurities (μg/mL-R)=(amount of each metal impurity (μg/L)×volume of eluent (L))/volume of chelating resin (mL)

The chelating resin having a total metal impurity content of 5 μg/mL-R or less can be obtained, for example, by the method described in Patent Document 3. That is, the method is a purification method in which a mineral acid solution containing 1 mg/L or less of metal impurities and having a concentration of 5 mass% or more is brought into contact with the chelating resin. This reduces the total amount of metal impurities (particularly the amount of eluted metals such as Na, Ca, Mg, and Fe) eluted when 25 times the volume of hydrochloric acid having a concentration of 3 mass% is passed through the chelating resin to 5 μg/mL-R or less. By purifying a hydrolyzable organic solvent using such a chelating resin having a reduced amount of metal impurities, a high-purity hydrolyzable organic solvent containing less metal impurities can be obtained. As the mineral acid solution, hydrochloric acid, sulfuric acid, nitric acid, etc. can be used. When the above purification is performed using a Na-type chelating resin, the ionic form is converted to the H-type by performing the above purification.

(Anion exchange resin)
As described above, in the present invention, a cation exchange resin and an optional chelating resin are mixed and used, but an anion exchange resin can also be used in combination. By using an anion exchange resin, acid generation can be reliably suppressed. Therefore, even when only a cation exchange resin is used or when other acid generation is a concern, it is possible to perform purification with acid generation further suppressed by using an anion exchange resin in combination. When an anion exchange resin is used, the amount of the anion exchange resin used can be, for example, 0.1 to 100% by volume based on the total amount of the cation exchange resin and the optional chelating resin.

Examples of anion exchange resins include strongly basic anion exchange resins having quaternary ammonium bases and weakly basic anion exchange resins having primary to tertiary amino groups. Examples of anion exchange resins include, but are not limited to, ORLITE (registered trademark) DS-2 (gel-type strongly basic anion exchange resin, product name, manufactured by Organo Corporation), DS-5 (MR-type strongly basic anion exchange resin, product name, manufactured by Organo Corporation), and DS-6 (MR-type weakly basic anion exchange resin, product name, manufactured by Organo Corporation). Among these, MR-type anion exchange resins are preferred.

The cation exchange resin, any chelating resin, and any anion exchange resin (hereinafter collectively referred to as "ion exchange resins") may be pretreated, as necessary, before being used in the purification of the hydrolyzable organic solvent to suppress water elution from the resin. That is, the purification method according to the present invention may have a pretreatment step in which, before the purification step, the cation exchange resin, any chelating resin, and any anion exchange resin are pretreated to suppress water elution from the resin.

Examples of pretreatment methods include contacting the hydrolyzable organic solvent to be purified with an ion exchange resin, or contacting the ion exchange resin with a pretreatment organic solvent having a higher dielectric constant at 25°C than the hydrolyzable organic solvent to be purified. Specifically, a method is used in which the hydrolyzable organic solvent to be purified is passed through a column packed with ion exchange resin before use in purification, and the passing of the solvent is continued until the water concentration in the solvent at the inlet and outlet of the column is approximately the same. Another method is to pass a pretreatment organic solvent having a higher dielectric constant at 25°C than the hydrolyzable organic solvent to be purified through a column packed with ion exchange resin before use in purification, and the passing of the solvent is continued until the water concentration in the solvent at the inlet and outlet of the column is approximately the same. In this case, after passing the pretreatment organic solvent, the hydrolyzable organic solvent to be purified may be passed through the column until the water concentration in the solvent at the inlet and outlet of the column is approximately the same. As the pretreatment organic solvent, an alcohol such as methanol or ethanol having a dielectric constant of 20 or more at 25°C is preferably used.

Another pretreatment method for suppressing water elution from the resin is to place a heat-resistant container filled with ion exchange resin inside a dryer and heat (dry) for several hours. The drying conditions can be set to an appropriate temperature and time from 50°C to 120°C for 1 hour to 24 hours depending on the type of ion exchange resin. By carrying out this treatment, the water content in the ion exchange resin can be reduced to 10% by mass or less. The drying method can be any of normal pressure, reduced pressure, and vacuum drying, but reduced pressure or vacuum drying is preferred because of the short drying time and high efficiency. The water content of the ion exchange resin can be calculated using the following formula.
Moisture content (mass%)=((mass (g) of resin heated using a dryer−mass (g) of resin completely dried using a heat-drying moisture meter)/mass (g) of resin heated using a dryer)×100

Here, in the above formula, the resin heated by the dryer is obtained by heating the resin as described above (moisture content is 10% by mass or less). The resin heated by the dryer is then stored and moved to avoid contamination with moisture from the air until it is measured by the heat-drying moisture meter. The resin is then placed on a heat-drying moisture meter and further dried completely at 105°C for several minutes to several tens of minutes, thereby obtaining a resin that has been completely dried by the heat-drying moisture meter. As the heat-drying moisture meter, for example, the MX-50 (product name) manufactured by A&D can be used. Note that, in order to increase the accuracy of the measurement, 5 g or more of the resin before drying is sampled and measured.

The method for contacting the hydrolyzable organic solvent with the ion exchange resin is not particularly limited, but examples include a batch processing method and a continuous liquid passing processing method using a column. Of these, the continuous liquid passing processing method is preferred from the standpoint of operability and efficiency.

In the continuous liquid passing treatment method, the ion exchange resin is packed in a purification tower such as a column. The height of the resin-packed bed of the purification tower is not particularly limited, and can be, for example, 100 to 1500 mm. Next, the hydrolyzable organic solvent is passed through at, for example, 2 to 100 BV at SV (space velocity, h ⁻¹ ) 2 to 20. Here, BV (Bed volume) represents the flow rate multiple of the solvent to be passed through relative to the amount of resin. From the viewpoint of removing metals, the passing of the hydrolyzable organic solvent is preferably performed at SV 2 to 20, more preferably SV 5 to 10. The direction of the passing may be either downward flow or upward flow. By passing the liquid in this way, metal impurities in the hydrolyzable organic solvent are adsorbed by the ion exchange resin and removed.

Next, the batch processing method will be described. First, the ion exchange resin is filled into a reaction tank equipped with a stirrer. Next, the hydrolyzable organic solvent is filled into the reaction tank. The volume ratio is not particularly limited, but a ratio of 2 to 200 parts organic solvent per 1 part resin is suitable. Then, the mixture is left for, for example, 0.5 to 24 hours. After leaving the mixture, the stirrer is operated to mix the resin and organic solvent uniformly. The stirring speed and stirring time may be appropriately determined depending on the size of the reaction tank, the processing amount, etc. After stirring is completed, filtration or the like is performed to separate the resin and the hydrolyzable organic solvent, thereby removing metal impurities and obtaining a purified hydrolyzable organic solvent.

In addition, when the ion exchange resin is subjected to a pretreatment to suppress the elution of water from the resin before being used for the purification of the hydrolyzable organic solvent, the container such as a column used for the pretreatment can be used as it is to carry out the purification process in which the hydrolyzable organic solvent is brought into contact with the ion exchange resin.

The purification method according to the present invention is mainly for the purification of hydrolyzable organic solvents by continuous operation, that is, after the purification (passing of liquid) of the hydrolyzable organic solvent to be purified is started in the purification step, the passing of liquid is continuously performed without stopping midway until the purification is completed. However, the purification of hydrolyzable organic solvents can also be performed by intermittent operation. When the purification of hydrolyzable organic solvents is performed by intermittent operation, the hydrolysis of the organic solvent may proceed due to external moisture or functional groups derived from the resin inside the test system, and moisture or acid may be generated. Therefore, when performing the purification by intermittent operation, it is preferable that the purification method according to the present invention has a blowing step in which, after the start of the purification step, the hydrolyzable organic solvent eluted from the outlet of the purification tower filled with a cation exchange resin, an optional chelating resin, and an optional anion exchange resin is discharged outside a storage tank for storing the hydrolyzable organic solvent after purification for a certain period of time. For example, when the passage of the hydrolyzable organic solvent is stopped for 30 minutes or more after the start of the purification step, the hydrolyzable organic solvent eluted from the outlet of the purification column is discharged outside the storage tank at 0.5 BV or more relative to the amount of ion exchange resin (cation exchange resin, any chelating resin, and any anion exchange resin) as a blowing step, and then the purification step is resumed. By providing the blowing step, it is possible to reduce the moisture and acid generated during the operation stop. The blow amount in the blowing step (the amount of the hydrolyzable organic solvent discharged outside the system) can be set in advance based on the operation stop time, the moisture amount in the hydrolyzable organic solvent at the outlet of the purification column, the acid concentration, and the resistivity value. Alternatively, it is possible to set by online monitoring that automatically stops the blowing step and switches to the purification step when the resistivity value set in advance is reached. Note that even when the purification of the hydrolyzable organic solvent is performed by continuous operation, the above blowing step can be performed as necessary.

According to the purification method of the present invention, the generation of acid from the hydrolyzable organic solvent is suppressed, so that the pH of the hydrolyzable organic solvent after the purification step can be kept close to neutral. Specifically, the pH of the hydrolyzable organic solvent after the purification step can be set to 5 to 7. However, depending on the type of hydrolyzable organic solvent, the pH may be, for example, 4 or less.

According to the purification method of the present invention, the concentration of each metal in the hydrolyzable organic solvent can be reduced by 70% by mass or more, preferably 80% by mass or more in the purification step. Examples of metal impurities contained in the hydrolyzable organic solvent include Li, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Sr, Ag, Cd, Sn, Ba, and Pb.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition, "Example 5" should be read as "Reference Example 5".

The methods for measuring metal concentration, acetic acid concentration and moisture concentration are as follows:

(Metal Concentration)
Metal concentrations (ng/L) were measured using an Agilent 8900 triple quadrupole ICP-MS (trade name, manufactured by Agilent Technologies, Inc.).

(Acetic acid concentration)
The acetic acid concentration (ppm by mass) was measured using a capillary electrophoresis system (product name: Agilent 7100, manufactured by Otsuka Electronics Co., Ltd.).

(Water concentration)
The water concentration was measured by the Karl Fischer method using a Karl Fischer volumetric moisture meter (product name: Aquacounter AQ-2200, manufactured by Hiranuma Sangyo Co., Ltd.).

(Ion exchange resin)
Details of each ion exchange resin used in the following examples are as follows.
ORLITE (registered trademark) DS-21 (trade name, manufactured by Organo Corporation): chelating resin, chelating group: aminomethyl phosphate group ORLITE (registered trademark) DS-4 (trade name, manufactured by Organo Corporation): MR type strongly acidic cation exchange resin, ion exchange group: sulfonic acid group ORLITE (registered trademark) DS-1 (trade name, manufactured by Organo Corporation): gel type strongly acidic cation exchange resin, ion exchange group: sulfonic acid group, degree of crosslinking: standard AMBERLITE (registered trademark) CR99 K/350 (trade name, manufactured by DuPont): gel type strongly acidic cation exchange resin, degree of crosslinking: low AMBERLITE (registered trademark) IRN99H (trade name, manufactured by DuPont): gel type strongly acidic cation exchange resin, degree of crosslinking: high ORLITE (registered trademark) DS-6 (trade name, manufactured by Organo Corporation): MR type weakly basic anion exchange resin

[Comparative Example 1 and Examples 1 to 5: Comparison of Mixed Bed Ratios]
(Purification of PGMEA)
A PFA resin column (inner diameter: 16 mm, height: 300 mm) was packed with ORLITE (registered trademark) DS-21, a chelating resin, and ORLITE (registered trademark) DS-4, an MR type strongly acidic cation exchange resin, in a mixed bed ratio (volume ratio) of the cation exchange resins shown in Table 1, so that the total volume was 36 mL. It was confirmed that the total amount of metal impurities eluted when 3% by mass of hydrochloric acid was passed through the chelating resin at a volume ratio of 25 times was 5 μg/mL-R or less. As a pretreatment, PGMEA (trade name: PM Thinner, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was passed through the column at SV5 until the water concentration in the PGMEA at the column inlet and the column outlet reached the same level, thereby removing the water in the resin. It has also been confirmed that in the above pretreatment, water can also be removed from the resin by passing, instead of PGMEA, a liquid having a larger relative dielectric constant at 25° C. than PGMEA, such as methanol.
Next, 20 BV of PGMEA was passed through the resin after the pretreatment at SV5, and a purification process was performed. PGMEA (stock solution) before purification and PGMEA at the column outlet after purification were collected, and the Cr concentration, acetic acid concentration, and water concentration were measured. The results are shown in Table 1. It should be noted that the generated acetic acid was within the measurement error range up to 5 mg/L (absolute value), that is, it can be considered that there was almost no generation of acetic acid. In addition, the Cr and acetic acid concentrations in the stock solution differ in each example, but this is due to differences in the lots of the stock solution.

As shown in Table 1, in Examples 1 to 5, in which the mixed bed ratio of cation exchange resin was 10% to 100%, the Cr concentration in the purified PGMEA was less than 15 ng/L, and metals could be removed efficiently while suppressing the production of acetic acid. In particular, in Examples 1 to 4, in which a mixed bed of chelating resin and cation exchange resin was used, the production of acetic acid was almost completely suppressed. On the other hand, in Comparative Example 1, in which the mixed bed ratio of cation exchange resin was 0%, i.e., only chelating resin was used, the Cr removal rate in the purified PGMEA was 55%, indicating that metals were not sufficiently removed.

[Examples 6 to 7: Comparison of Cr removal performance depending on the type of strongly acidic cation exchange resin]
PGMEA was purified in the same manner as in Example 3, except that ORLITE (registered trademark) DS-1 (gel-type strongly acidic cation exchange resin, degree of crosslinking: standard) and AMBERLITE (registered trademark) CR99 K/350 (gel-type strongly acidic cation exchange resin, degree of crosslinking: low, K-type converted to H-type) were used as the strongly acidic cation exchange resin to be mixed with the chelating resin (mixed bed ratio: 25% by volume). PGMEA (raw solution) before purification and PGMEA at the outlet of the column after purification were sampled, and the Cr concentration and water concentration were measured. The results are shown in Table 2 together with those of Example 3.

As shown in Table 2, DS-4, an MR-type strongly acidic cation exchange resin, was found to have particularly superior metal removal performance compared to DS-1, a gel-type strongly acidic cation exchange resin, and CR99 K/350, a gel-type small particle strongly acidic cation exchange resin.

[Examples 8 to 10: Comparison of acetic acid generation due to differences in crosslinking degree]
PGMEA was purified in the same manner as in Example 3, except that AMBERLITE (registered trademark) IRN99H (high cross-linking degree), ORLITE (registered trademark) DS-1 (standard cross-linking degree) and AMBERLITE (registered trademark) CR99 K/350 (low cross-linking degree, K-form converted to H-form) were used as gel-type strongly acidic cation exchange resins to be mixed with the chelating resin (mixed bed ratio: 25% by volume). PGMEA before purification (raw solution) and PGMEA at the outlet of the column after purification were sampled, and the acetic acid concentration and water concentration were measured. The results are shown in Table 3.

As shown in Table 3, it was found that the generation of acetic acid was reliably suppressed when using highly cross-linked resins among gel-type strongly acidic cation exchange resins.

[Reference Example 1: Reduction of acetic acid by anion exchange resin]
PGMEA was purified in the same manner as in Example 3, except that only ORLITE (registered trademark) DS-6, an MR type weakly basic anion exchange resin, was used as the resin. PGMEA (stock solution) before purification and PGMEA at the outlet of the column after purification were sampled, and the acetic acid concentration was measured. The results are shown in Table 4.

As shown in Table 4, it was found that the acetic acid contained in the raw solution can be removed by using an anion exchange resin. Therefore, it was revealed that the hydrolyzable organic solvent can be purified while reliably suppressing the generation of acetic acid by using an anion exchange resin in combination with the cation exchange resin and any chelating resin according to the present invention.

Claims (10)

A method for purifying a hydrolyzable organic solvent , comprising a purification step of purifying the hydrolyzable organic solvent by contacting the hydrolyzable organic solvent with a cation exchange resin mixed with a chelating resin, wherein the volume ratio of the cation exchange resin to the total amount of the cation exchange resin and the chelating resin is 10 to 50 % , and the hydrolyzable organic solvent is an ester-based organic solvent or a mixed solvent containing an ester-based organic solvent . The purification method according to claim 1, wherein the water concentration in the hydrolyzable organic solvent before purification is 20 to 10,000 mg/L. 3. The purification method according to claim 1, further comprising a pretreatment step of performing a pretreatment on the cation exchange resin and the chelating resin before the purification step to suppress water elution from the resin, the pretreatment being a method of contacting the cation exchange resin and the chelating resin with a pretreatment organic solvent having a higher relative dielectric constant at 25°C than that of the hydrolyzable organic solvent, or a method of reducing the water content of the cation exchange resin and the chelating resin to 10 mass% or less using a dryer. The purification method according to any one of claims 1 to 3, wherein an anion exchange resin is further used in combination with the cation exchange resin and the chelating resin. The purification method according to any one of claims 1 to 4, wherein the cation exchange resin is a strongly acidic cation exchange resin. The purification method according to claim 5, wherein the strongly acidic cation exchange resin is an MR type strongly acidic cation exchange resin. The purification method according to claim 5, wherein the strongly acidic cation exchange resin is a gel-type strongly acidic cation exchange resin having a cross-linking degree of 16% to 24%. The purification method according to any one of claims 1 to 7, wherein the concentration of each metal in the hydrolyzable organic solvent is reduced by 80 mass% or more in the purification step. The purification method according to any one of claims 1 to 8, further comprising a blowing step of discharging, after initiation of the purification step, the hydrolyzable organic solvent eluted from an outlet of a purification column packed with the cation exchange resin , the chelating resin and any anion exchange resin, outside a storage tank for storing the purified hydrolyzable organic solvent for a certain period of time. A method for producing a resin for purifying a hydrolyzable organic solvent, comprising the step of mixing a chelating resin with a cation exchange resin, wherein a volume ratio of the cation exchange resin to a total amount of the cation exchange resin and the chelating resin is 10 to 50 % , and the hydrolyzable organic solvent is an ester-based organic solvent or a mixed solvent containing an ester-based organic solvent .