Purification method and apparatus for tetraalkylammonium ion-containing liquid to be treated

Abstract

To provide a purification method of a liquid to be treated which can suppress cracks of a resin even if a strongly acidic cation exchange resin is used, and reduces a content of metal impurities in the liquid to be treated containing tetraalkylammonium ions.SOLUTION: A purification method of a liquid to be treated includes an impurity removal step of passing a liquid to be treated containing tetraalkylammonium ions and metal impurities through a container filled with a hydrogen ion type or tetraalkylammonium ion cation exchange resin, and reducing a content of the metal impurities in the liquid to be treated, wherein a degree of crosslinking of the cation exchange resin is 16 to 24%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for purifying a liquid to be treated, which reduces the content of metal impurities in the liquid containing tetraalkylammonium ions and metal impurities.The present invention also relates to a method and apparatus for recovering an aqueous tetraalkylammonium salt solution from the liquid to be treated, which reduces the content of metal impurities in the liquid containing tetraalkylammonium ions and metal impurities. [Background technology]

[0002] In the manufacture of electronic components such as semiconductor devices, liquid crystal displays, and printed circuit boards, a photoresist film is formed on a substrate such as a wafer, irradiated with light or the like through a pattern mask, and then developed by dissolving unnecessary photoresist with a developer. Further processing such as etching is performed, and then the insoluble photoresist film on the substrate is peeled off. Photoresists are classified into positive-type photoresists, in which the exposed portions become soluble, and negative-type photoresists, in which the exposed portions become insoluble. Alkaline developers are primarily used as developers for positive-type photoresists. While organic solvent-based developers are the mainstream for developers of negative-type photoresists, alkaline developers are also sometimes used.

[0003] As the alkaline developer, an aqueous solution of tetraalkylammonium hydroxide (hereinafter also referred to as "TAAH") is usually used. Therefore, the waste liquid discharged in the photoresist development process (hereinafter also referred to as "photoresist development waste liquid") contains not only photoresist but also metal ions (metal impurities) and tetraalkylammonium ions (hereinafter also referred to as "TAA ions").

[0004] Conventionally, the main methods for treating photoresist developer waste have been to concentrate it using evaporation or reverse osmosis, then dispose of it (by incineration or collection by a contractor), or to biodegrade it using activated sludge and then discharge it into the atmosphere. However, from the perspective of reducing the environmental impact, attempts have been made to recover and reuse TAAH from photoresist developer waste.

[0005] Patent Document 1 discloses a method for recovering TAA ions by adsorbing them onto a cation exchange resin and then eluting them as tetraalkylammonium salts (hereinafter also referred to as "TAA salts") using an acid solution. In Patent Document 1, in the process of recovering the TAA salt solution, the pH and / or electrical conductivity of the effluent are measured, and recovery is stopped when these values ​​change by a predetermined amount, thereby obtaining a TAA salt solution with a reduced metal ion concentration. TAAH is then produced using the TAA salt solution as a raw material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2012 / 090699 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the method described in Patent Document 1, the recovered TAA salt solution is finally evaporated and concentrated, and then electrolyzed to obtain TAAH. In this concentration step, metal ions remaining in the TAA salt solution can cause scale formation, which is a problem.

[0008] On the other hand, a commonly used method for reducing the amount of metal impurities is to adsorb metal impurities using a strongly acidic cation exchange resin. However, when a strongly acidic cation exchange resin is converted into the tetraalkylammonium ion form, the resin contains more water than when it is in the hydrogen ion form, causing it to swell. Therefore, repeated conversion between the hydrogen ion form and the tetraalkylammonium ion form causes cracks to form and the resin to break due to the repeated shrinkage and swelling.

[0009] Therefore, an object of the present invention is to provide a method and apparatus for purifying a liquid containing tetraalkylammonium ions, which can suppress cracking of the resin even when a strongly acidic cation exchange resin is used, thereby reducing the content of metal impurities in the liquid.Another object of the present invention is to provide a method and apparatus for recovering an aqueous tetraalkylammonium salt solution from a liquid containing tetraalkylammonium ions, which can suppress cracking of the resin even when a strongly acidic cation exchange resin is used. [Means for solving the problem]

[0010] In view of the above problems, the inventors conducted extensive research and discovered that by using a highly cross-linked, strongly acidic cation exchange resin, it is possible to suppress cracking of the resin and reduce the content of metal impurities in the treated liquid containing tetraalkylammonium ions, thereby completing the present invention.

[0011] That is, the present invention provides: an ion exchange step in which a regenerant containing tetraalkylammonium ions is passed through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; Tetraalkylammonium ion type Strong acidity an impurity removal step in which a liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a vessel filled with a cation exchange resin to reduce the content of the metal impurities in the liquid to be treated; and, A method for purifying a liquid to be treated, comprising the steps of: Strong acidity The cross-linking degree of the cation exchange resin is 16 to 24%. The exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / LR or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant used in the ion exchange step is 2.4 to 25 mass %. The method for purifying a liquid to be treated is characterized by:

[0012] The present invention also provides an ion exchange means for passing a regenerant containing tetraalkylammonium ions through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; Tetraalkylammonium ion type Strong acidity An impurity removal means for reducing the content of metal impurities in a liquid to be treated by passing the liquid to be treated, which contains tetraalkylammonium ions and metal impurities, through a container filled with a cation exchange resin. and, A purification apparatus for a liquid to be treated, comprising: Strong acidity The cross-linking degree of the cation exchange resin is 16 to 24%. The exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / LR or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant in the ion exchange means is 2.4 to 25 mass %. The present invention relates to a purification device for a liquid to be treated, characterized in that:

[0013] Furthermore, the present invention provides an ion exchange step in which a regenerant containing tetraalkylammonium ions is passed through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; Tetraalkylammonium ion type Strong acidity an impurity removal step in which a liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a vessel filled with a cation exchange resin to reduce the content of the metal impurities in the liquid to be treated; and, A method for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated, comprising: Strong acidity The cross-linking degree of the cation exchange resin is 16 to 24%. The exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / LR or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant used in the ion exchange step is 2.4 to 25 mass %. The method for recovering an aqueous solution of a tetraalkylammonium salt from a liquid to be treated is characterized by:

[0014] Furthermore, the present invention provides an ion exchange means for passing a regenerant containing tetraalkylammonium ions through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; Tetraalkylammonium ion type Strong acidity An impurity removal means for reducing the content of metal impurities in a liquid to be treated by passing the liquid to be treated, which contains tetraalkylammonium ions and metal impurities, through a container filled with a cation exchange resin. and, An apparatus for recovering an aqueous solution of a tetraalkylammonium salt from a liquid to be treated, comprising: Strong acidity The cross-linking degree of the cation exchange resin is 16 to 24%. The exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / LR or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant in the ion exchange means is 2.4 to 25 mass %. The apparatus for recovering an aqueous solution of a tetraalkylammonium salt from a liquid to be treated is characterized by: [Effects of the Invention]

[0015] According to the present invention, a method and apparatus for purifying a liquid to be treated, which reduces the content of metal impurities in a liquid containing tetraalkylammonium ions, can be provided by using a highly cross-linked, strongly acidic cation exchange resin, which can suppress cracking of the resin. Furthermore, according to the present invention, a method and apparatus for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated, which can suppress cracking of the resin, can be provided by using a highly cross-linked, strongly acidic cation exchange resin with a small particle size. In addition to the above, when a highly cross-linked, small-particle strongly acidic cation exchange resin is used, a method and apparatus for purifying a liquid to be treated, which exhibits little pH fluctuation at the initial stage of liquid passage, and a method and apparatus for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing the configuration of a purification device according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing the configuration of a purification device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Method for purifying the liquid to be treated> The purification method according to the present invention comprises an impurity removal step of passing a liquid to be treated containing tetraalkylammonium ions and metal impurities through a vessel filled with a cation exchange resin in the hydrogen ion form (hereinafter also referred to as "H form") or the tetraalkylammonium ion form (hereinafter also referred to as "TAA form") to reduce the content of the metal impurities in the liquid to be treated. Furthermore, the purification method according to the present invention is characterized in that the degree of crosslinking of the cation exchange resin is 16 to 24%. The purification method according to the present invention will be described in detail below.

[0018] [Impurity removal process] The impurity removal process is a process in which a liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a container filled with an H-type or TAA-type cation exchange resin to reduce the content of the metal impurities in the liquid to be treated.

[0019] (Liquid to be treated) In the present invention, the liquid to be treated containing tetraalkylammonium ions and metal impurities is not particularly limited as long as it contains at least tetraalkylammonium ions and metal impurities. However, since these components are contained and are generated in large quantities in semiconductor manufacturing processes, liquid crystal display manufacturing processes, and the like, the liquid to be treated is preferably a solution derived from photoresist development wastewater discharged in these processes. Photoresist development wastewater is a wastewater discharged when exposed photoresist is developed with an alkaline developer, and is typically an aqueous solution exhibiting an alkaline pH of 10 to 14. Therefore, in the photoresist development wastewater, the photoresist dissociates its acidic groups, such as carboxyl groups and phenolic hydroxyl groups, and dissolves in the form of a salt with TAA ions derived from TAAH. Therefore, the photoresist development wastewater is a solution primarily containing photoresist, TAA ions, and metal impurities. The liquid to be treated according to the present invention is, for example, a solution obtained by adsorbing TAA ions in the photoresist development waste liquid onto a cation exchange resin, and then eluting the TAA ions with an acid such as hydrochloric acid, thereby recovering the TAA salt.

[0020] Specifically, the photoresist developer waste solution is first passed through a container filled with an H-type cation exchange resin, allowing the TAA ions to be adsorbed onto the cation exchange resin. Since the metal ions contained in the waste solution are also cationic, they are adsorbed onto the cation exchange resin during this process. Even if the metal ions are present, if the metal-containing ionic species themselves become anionic in the waste solution due to chemical equilibrium reactions such as complex formation, they are not adsorbed by the cation exchange resin and are discharged from the container. On the other hand, organic components derived from the photoresist dissolved in the resist developer waste solution are usually in the anionic form and are therefore less likely to be adsorbed by the cation exchange resin, allowing most of them to be removed. Furthermore, even if nonionic components are present, they are not adsorbed by the cation exchange resin at this stage and are discharged (flowed out), allowing most of them to be removed. After the photoresist developer waste solution is passed through the cation exchange resin, any remaining photoresist components and other impurities may be washed away by flushing the resin with ultrapure water or a highly purified TAAH aqueous solution.

[0021] Then, by passing an aqueous solution of a mineral acid (e.g., hydrochloric acid, sulfuric acid, etc.) through a container filled with the cation exchange resin converted to the TAA form, the hydrogen ions contained in the aqueous solution are sequentially replaced with the adsorbed TAA ions, and the TAA ions flow out of the container as the acid salt of the mineral acid used (TAA salt). The resulting solution containing the TAA salt can then be treated with a (highly crosslinked) cation exchange resin (preferably one with a small particle size) to obtain the treated solution of the present invention. The treated solution thus obtained contains tetraalkylammonium ions and metal impurities, and the purification method of the present invention is a purification method for reducing the content of metal impurities in the treated solution.

[0022] The process of recovering TAAH from photoresist development waste solution as a treatment liquid containing TAA salt is publicly known, as described in Patent Document 1, for example. The container, cation exchange resin, type or amount of acid, and acid flow method used in this process can be appropriately selected from known methods. Here, the (highly cross-linked) cation exchange resin used in this process can also be a strongly acidic cation exchange resin with a cross-linking degree of 16% to 24% according to the present invention. In this case, cracking of the resin due to repeated use can be prevented in this process as well. Furthermore, the same resin can be used from the process of recovering the treatment liquid to the ion exchange process and impurity removal process described below, which is preferable from the viewpoint of operability.

[0023] (Tetraalkylammonium ion) As described above, the liquid to be treated used in the present invention is a solution obtained by eluting TAA ions (TAAH) as TAA salts from photoresist developer waste liquid and recovering them. Specific examples of the TAA ions in the liquid to be treated include ions derived from tetraalkylammonium hydroxides, such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethyl(2-hydroxyethyl)ammonium hydroxide, triethyl(2-hydroxyethyl)ammonium hydroxide, dimethyldi(2-hydroxyethyl)ammonium hydroxide, diethyldi(2-hydroxyethyl)ammonium hydroxide, methyltri(2-hydroxyethyl)ammonium hydroxide, ethyltri(2-hydroxyethyl)ammonium hydroxide, and tetra(2-hydroxyethyl)ammonium hydroxide, which are alkalis used in photoresist developers. Among these, the most commonly used tetramethylammonium ions and tetrabutylammonium ions derived from tetramethylammonium hydroxide and tetrabutylammonium hydroxide are preferred for use in the present invention, with tetramethylammonium ions derived from tetramethylammonium hydroxide being particularly preferred. The liquid to be treated used in the present invention is a solution in which the above-mentioned tetraalkylammonium ions have been recovered, for example, as chloride salts, and is preferably an aqueous solution of a tetraalkylammonium chloride such as tetramethylammonium chloride or tetrabutylammonium chloride, and more preferably an aqueous solution of tetramethylammonium chloride. That is, the tetraalkylammonium ions contained in the liquid to be treated according to the present invention are preferably tetraalkylammonium ions derived from tetraalkylammonium chlorides such as tetramethylammonium chloride or tetrabutylammonium chloride, and more preferably tetraalkylammonium ions derived from tetramethylammonium chloride.

[0024] Here, we will explain typical photoresist development wastewater discharged from the development process in semiconductor and liquid crystal display manufacturing. The development process typically involves the use of a single-wafer automatic developing machine. In this machine, the process using a developer containing TAAH and the subsequent rinsing (substrate cleaning) with pure water are performed in the same tank. The rinsing process uses pure water in an amount 5 to 1000 times the amount of the developer. Therefore, the developer used in the development process is typically diluted 5 to 10 times. As a result, the photoresist development wastewater discharged from this development process contains approximately 0.001 to 2.5 mass% TAAH, approximately 10 to 100 ppm resist, and 0 to several tens of ppm surfactant. Furthermore, wastewater from other processes may be mixed in, and the TAAH concentration may be lower than the above range. The TAA ion concentration of the liquid to be treated obtained from a photoresist development waste liquid having a TAAH concentration of, for example, 0.001 to 2.5 mass % is 0.001 to 2.5 mass %. The liquid to be treated obtained from a photoresist development waste liquid may be used after adjusting the TAA ion concentration by, for example, concentration.

[0025] (metal impurities) Photoresist developer waste liquid contains multiple metal ions as metal impurities, and therefore the liquid to be treated also contains these metal ions. Examples of metal ions include monovalent ions such as sodium and potassium, divalent ions such as magnesium, calcium, and zinc, and polyvalent ions such as aluminum, nickel, copper, chromium, and iron. These metal ions are typically contained in the photoresist developer waste liquid (liquid to be treated) at approximately 0.1 to 1,000 ppb. The counter ions of the tetraalkylammonium ions in the photoresist developer waste liquid are typically hydroxide ions. However, depending on the factory, or after neutralization, at least a portion of the counter ions of the tetraalkylammonium ions is typically at least one selected from inorganic anions such as fluoride ions, chloride ions, bromide ions, carbonate ions, bicarbonate ions, sulfate ions, hydrogen sulfate ions, nitrate ions, phosphate ions, hydrogen phosphate ions, and dihydrogen phosphate ions, and organic anions such as formate ions, acetate ions, and oxalate ions. However, since most of these anions are removed in the stage of preparing the liquid to be treated from the photoresist development waste liquid, it is believed that almost none of these anions are contained in the liquid to be treated.

[0026] (cation exchange resin) In the present invention, a strongly acidic cation exchange resin with a crosslinking degree of 16% to 24% is used as the H-type or TAA-type cation exchange resin. Highly crosslinked resins with a crosslinking degree within the above range have high strength due to the densely packed crosslinked structure present within the resin. When a cation exchange resin with a crosslinking degree of less than 16% is used, the strength of the resin becomes insufficient, increasing the possibility of cracking of the resin during purification. Furthermore, when a cation exchange resin with a crosslinking degree of more than 24% is used, the ion exchange rate and the resin regeneration rate become slow. Thus, in the present invention, it has been found that by using a strongly acidic cation exchange resin with a high crosslinking degree of 16% to 24%, cracking of the resin during purification can be suppressed. Furthermore, highly crosslinked cation exchange resins are also preferred in that they have a large exchange capacity and can be introduced with many functional groups.

[0027] Any resin with a crosslinking degree of 16% to 24% can be used as the H-type cation exchange resin. Examples of such H-type cation exchange resins include Amberjet (registered trademark) 1060H and 1600H (trade names, manufactured by Organo Corporation), AMBERLITE (registered trademark) IRN99H, 200C, and 200CT (trade names, manufactured by DuPont), AMBEREX 210 (trade name, manufactured by DuPont), Diaion (registered trademark) SK116 (trade name, manufactured by Mitsubishi Chemical Corporation), and Purolite (registered trademark) C100X16MBH (trade name, manufactured by Purolite Co., Ltd.).

[0028] The TAA-type cation exchange resin may be a resin obtained by previously ion-exchanging one of the resins exemplified as the H-type cation exchange resins into the TAA-type. That is, when the liquid to be treated is purified using a TAA-type cation exchange resin in the impurity removal step, the purification method according to the present invention may include the following ion exchange step prior to the impurity removal step. An ion exchange process in which a regenerant containing tetraalkylammonium ions is passed through a vessel filled with a hydrogen ion-form cation exchange resin to convert the hydrogen ion-form cation exchange resin into a tetraalkylammonium ion-form cation exchange resin. The TAA-type cation exchange resin obtained in the ion exchange step can be used in the impurity removal step, which will be described later.

[0029] The particle size of the cation exchange resin is preferably 200 μm to 720 μm. A particle size of 720 μm or less is within the particle size range of common ion exchange resins, making it easy to repurpose and operate existing facilities. Furthermore, a cation exchange resin with a particle size of 200 μm or more has a common surface area and can sufficiently remove metal impurities. Furthermore, a cation exchange resin with a particle size of 200 μm or more can suppress an increase in the differential pressure between the resin outlet and the resin inlet. Furthermore, the particle size of the cation exchange resin is more preferably 500 μm to 560 μm in the H-form. Small particle size cation exchange resins with particle sizes within this range have a large surface area and are easy to convert from the H-form to the TAA-form. Therefore, when converting the resin to the TAA-form, less H-form resin remains, further suppressing the initial pH fluctuation when the liquid to be treated is passed through the resin. Furthermore, small particle size cation exchange resins have a large surface area and therefore excellent metal impurity removal performance. In the present invention, particle size refers to the harmonic mean diameter.

[0030] (When using H-type cation exchange resin) When a liquid to be treated containing TAA ions and metal impurities is passed through a vessel filled with H-form cation exchange resin, hydrogen ions in the resin exchange with TAA ions in the liquid to be treated, converting the H-form cation exchange resin to TAA-form cation exchange resin. Furthermore, the cationic metal impurities in the liquid to be treated are also adsorbed by the cation exchange resin, thereby reducing the content of metal impurities in the liquid to be treated. That is, when using H-form cation exchange resin, the cation exchange resin can be converted from H-form to TAA-form using the liquid to be purified without performing a separate ion exchange process described below to convert the cation exchange resin from H-form to TAA-form. The cation exchange resin converted to TAA-form in this way can be subsequently used in the impurity removal process. After this process, the cation exchange resin will contain a mixture of TAA-form and metal ion-form cations. If unreacted exchange groups remain, hydrogen ion-form cation exchange resin will also be present.

[0031] When using an H-form cation exchange resin, the content of metal impurities in the liquid to be treated can be reduced by passing the liquid through it once. However, to improve purification efficiency, the liquid to be treated may be passed through the cation exchange resin that has been converted to the TAA form (and metal ion form) by passing the liquid through it once again. That is, the impurity removal process may be repeated multiple times. When the liquid to be treated is passed through the cation exchange resin that has been converted to the TAA form (and metal ion form) again, the TAA ions adsorbed on the resin exchange with the metal ions remaining in the liquid to be treated, and the metal ions are adsorbed on the resin, thereby further reducing the content of metal impurities in the liquid to be treated.

[0032] Furthermore, when the liquid to be treated is passed through an H-type cation exchange resin, the pH of the effluent flowing out of the vessel becomes strongly acidic due to the influence of hydrogen ions eluted from the cation exchange resin. Therefore, in this case, the purification method according to the present invention may include a neutralization step for neutralizing the effluent obtained in the impurity removal step. When the impurity removal step is repeated multiple times, for example, after the first impurity removal step, a neutralization step for the effluent flowing out can be performed, and the pH-adjusted liquid after the neutralization step can be used to perform the second impurity removal step. The neutralization step can be performed using a known method. Specifically, for example, the effluent can be collected in a container such as a storage tank and the pH can be adjusted using an alkali such as TAAH. Note that only the liquid to be treated that flows out in the early stage of the liquid passage, when the pH fluctuates significantly, can be collected in a separate container such as a storage tank, and the pH can be adjusted, and then mixed with the remaining liquid to be treated that flows out later. Alternatively, the liquid to be treated that flows out in the early stage of the liquid passage, when the pH fluctuates significantly, can be discarded. Examples of alkalis used for neutralization include tetramethylammonium hydroxide and ammonium hydroxide.

[0033] (When using TAA type cation exchange resin) When a liquid to be treated containing TAA ions and metal impurities is passed through a vessel filled with a TAA-type cation exchange resin, the TAA ions in the resin exchange with the metal ions in the liquid, resulting in the metal ions being adsorbed onto the resin. This reduces the content of metal impurities in the liquid. If unreacted exchange groups (hydrogen ions) remain in the cation exchange resin during the ion exchange process, these hydrogen ions are also exchanged with metal ions in the liquid to be treated during this process. By using a cation exchange resin that has been converted from the H-type to the TAA-type in advance, the metal ions in the liquid to be treated are exchanged with the TAA ions adsorbed on the resin, rather than with hydrogen ions, when the liquid to be treated is passed through the resin. This reduces fluctuations in the TAA ion concentration and pH in the liquid to be treated at the initial stage of passage. Thus, the use of a TAA-type cation exchange resin in the impurity removal process is preferable from the perspective of suppressing pH fluctuations at the initial stage of passage and improving metal impurity removal efficiency.

[0034] (Passing of liquid to be treated) As a method for passing the liquid to be treated through a container filled with a cation exchange resin, conventionally known methods can be appropriately adopted depending on the type and shape of the cation exchange resin. In the present invention, the term "container" refers to any "tower" or "tank" such as an adsorption tower that can be filled with an ion exchange resin and that can purify the liquid to be treated (whether by water flow or batchwise). This term is not limited to this. Specific examples include a column method in which the cation exchange resin is packed into a column having an inlet at the top and an outlet at the bottom, and the liquid to be treated is continuously passed through using a pump. Another example is a batch method in which the liquid to be treated is passed through a container filled with the cation exchange resin, allowed to contact the resin for a suitable period of time, and the supernatant liquid is removed. When using the column method, the size of the column can be appropriately determined depending on the performance of the cation exchange resin. From the viewpoint of efficient purification, it is preferable that the ratio (L / D) of the column height (L) to the diameter (D) is 0.5 to 30, and the space velocity (SV) of the liquid to be treated is 1 (1 / hr) or more and 150 (1 / hr) or less.

[0035] (Recovery of effluent) When the liquid is passed through the column, the liquid containing tetraalkylammonium ions and metal impurities flows through the container, resulting in an effluent with a reduced content of metal impurities. The effluent is then collected in a storage tank or the like. The purified liquid is an aqueous solution of tetraalkylammonium salts. The metal impurity content can be measured, for example, using an Agilent 8900 triple quadrupole ICP-MS (trade name, manufactured by Agilent Technologies, Inc.).

[0036] [Ion exchange process] The ion exchange process is a process for converting an H-form cation exchange resin into a TAA-form cation exchange resin prior to the impurity removal process described above. That is, it is a process for preparing a TAA-form cation exchange resin to be used in the impurity removal process. The ion exchange process is performed by passing a regenerant containing TAA ions through a container filled with an H-form cation exchange resin. The H-form cation exchange resin is as described above. When the regenerant containing TAA ions is passed through the H-form cation exchange resin, ion exchange occurs between the hydrogen ions of the cation exchange resin and the TAA ions contained in the regenerant, and the TAA ions are adsorbed onto the cation exchange resin. As a result, the H-form cation exchange resin is converted into a TAA-form cation exchange resin.

[0037] (Regenerant containing tetraalkylammonium ions) The regenerant containing TAA ions is not particularly limited as long as it is an aqueous solution containing TAA ions. Specific examples of regenerants containing TAA ions include aqueous solutions of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethyl(2-hydroxyethyl)ammonium hydroxide, triethyl(2-hydroxyethyl)ammonium hydroxide, dimethyldi(2-hydroxyethyl)ammonium hydroxide, diethyldi(2-hydroxyethyl)ammonium hydroxide, methyltri(2-hydroxyethyl)ammonium hydroxide, ethyltri(2-hydroxyethyl)ammonium hydroxide, and tetra(2-hydroxyethyl)ammonium hydroxide. Among these, the most commonly used aqueous solutions of tetramethylammonium hydroxide and tetrabutylammonium hydroxide are preferred for use in the present invention, with tetramethylammonium hydroxide being particularly preferred.

[0038] The content of TAA ions in the regenerant can be, for example, 0.1% by mass to 25% by mass.

[0039] (Passing of regenerant) The method for passing the regenerant containing TAA ions through a container filled with a cation exchange resin can be suitably selected from conventional methods depending on the type and shape of the cation exchange resin. Specifically, for example, a column containing the cation exchange resin is filled with the resin, and a solution containing tetraalkylammonium ions is continuously passed through the column using a pump (column method). Alternatively, a batch method is used in which the solution is passed through a container filled with the cation exchange resin, and the resin is allowed to contact the resin for a suitable period of time, followed by removal of the supernatant. When using a column method, the size of the column can be determined appropriately depending on the performance of the cation exchange resin. For example, for a solution containing 0.1 to 25% by mass of TAA ions, the ratio of the column height (L) to the diameter (D) (L / D) is preferably 0.5 to 30, and the space velocity (SV) of the solution is preferably 1 (1 / hr) or more but 150 (1 / hr) or less.

[0040] The amount of regenerant passed through the vessel can be determined appropriately, taking into account the exchange capacity of the cation exchange resin filled in the vessel. When a solution containing cations exceeding the exchange capacity of the cation exchange resin is passed through, whether or not TAA ions are escaping (breakthrough) without being adsorbed can be confirmed by analyzing the TAA ion concentration in the liquid flowing out of the vessel using ion chromatography. A simpler method is to measure the height of the cation exchange resin in the vessel. When the counterion of the cation exchange resin changes from hydrogen ions to TAA ions, the volume of the resin increases, depending on the type of cation exchange resin. Therefore, adsorption of TAA ions can be confirmed by measuring the volume of the cation exchange resin. Furthermore, if the pH of the regenerant passed through the vessel is alkaline (i.e., 10 or higher), the pH of the liquid passing through the vessel becomes alkaline, allowing this to be confirmed using a pH meter. Furthermore, when TAA ions are present in the liquid flowing out of the vessel, the electrical conductivity of the liquid increases, allowing this to be confirmed using a conductivity meter.

[0041] (Recovery of effluent) When the column method is used, hydrogen ions that have been ion-exchanged with TAA ions flow out of one end of the container as a regenerant containing tetraalkylammonium ions is passed through, and the counter ions are anions corresponding to the regenerant (salt) used. The effluent is then collected in a storage tank or the like.

[0042] [Cation exchange resin regeneration process] The purification method of the present invention may also include a regeneration step of regenerating the cation exchange resin that contacted the liquid to be treated in the impurity removal step. Resin regeneration can be achieved by contacting the resin with an acid using a known method, thereby removing impurities such as metal ions and converting the resin from the TAA ion form to the H form. The resulting H form cation exchange resin can be reused in the impurity removal step. The acid used in the regeneration step is not particularly limited as long as it generates hydrogen ions in an aqueous solution, and examples include aqueous mineral acid solutions such as hydrochloric acid and sulfuric acid. Among these, hydrochloric acid is preferred because it is industrially available at low cost and its concentration can be easily adjusted. The concentration and amount of hydrochloric acid used are not particularly limited, as long as they are sufficient to convert the resin to the H form and remove impurities such as metal ions. Typically, the resin can be converted from the TAA ion form to the H form by contacting the cation exchange resin with 1 to 10% by mass of hydrochloric acid at a rate of 3 to 20 (L / L resin). In the regeneration step, in addition to washing with the mineral acid, washing with ultrapure water or pure water may also be performed as appropriate.

[0043] <Refining equipment for treated liquid> The purification apparatus according to the present invention includes an impurity removal means for reducing the content of metal impurities in a liquid to be treated, the liquid containing tetraalkylammonium ions and metal impurities, by passing the liquid through a vessel filled with a cation exchange resin in the hydrogen ion or tetraalkylammonium ion form. The purification apparatus according to the present invention is further characterized in that the degree of cross-linking of the cation exchange resin is 16 to 24%. Details of the impurity removal means are the same as those described above for the impurity removal step in the purification method according to the present invention.

[0044] When a TAA type cation exchange resin is used, the purification device according to the invention may comprise the following ion exchange means: An ion exchange means for converting a hydrogen ion-form cation exchange resin into a tetraalkylammonium ion-form cation exchange resin by passing a regenerant containing tetraalkylammonium ions through a vessel filled with the hydrogen ion-form cation exchange resin. The TAA-type cation exchange resin obtained by the ion exchange means can be used as the cation exchange resin in the impurity removal means. Details of the ion exchange means are the same as those described above for the ion exchange step in the purification method according to the present invention.

[0045] When an H-type cation exchange resin is used, the purification apparatus according to the present invention may further include a neutralization means for neutralizing the effluent obtained in the impurity removal means. Details of the neutralization means are the same as those described above for the neutralization step in the purification method according to the present invention.

[0046] The purification apparatus according to the present invention may further comprise a regeneration means for regenerating the cation exchange resin that has come into contact with the liquid to be treated in the impurity removal means. Details of the regeneration means are the same as those described above for the regeneration step in the purification method according to the present invention.

[0047] FIG. 1 is a schematic diagram showing an example of a purification apparatus for purifying a liquid to be treated using a cation exchange resin adjusted to the TAA form with a TAAH aqueous solution. While FIG. 1 shows an example in which an adsorption tower is used as the container for packing the cation exchange resin, the container is not limited to an adsorption tower. First, a regenerant containing TAA ions (e.g., a TAAH aqueous solution) is passed from a storage tank 3 through adsorption tower 1, which is filled with an H-form cation exchange resin as an ion exchange means, and the effluent is recovered through a waste liquid line 10. Then, as an impurity removal means, a liquid to be treated containing TAA ions and metal impurities is passed from storage tank 2 through adsorption tower 1, and the effluent, in which the content of metal impurities in the liquid to be treated has been reduced, is recovered in storage tank 5. Here, the solutions in storage tanks 2, 3, and 4 may be individually pumped to adsorption tower 1 by pump 6, as shown in FIG. 1, or a single pump may be used to pump the liquid to adsorption tower 1 by switching valves.

[0048] The resin in the adsorption tower 1 after use in purification can be reused by washing and regenerating it as follows. After passing ultrapure water (or pure water) through the ultrapure water (or pure water) line 7 to wash the resin in the adsorption tower 1, an acid such as hydrochloric acid is passed through the storage tank 4 to remove metal impurities and TAA ions adsorbed on the resin, converting the resin to the H-type. Next, a regenerant containing TAA ions (e.g., a TAAH aqueous solution) is passed through the storage tank 3 (corresponding to the ion exchange means) to regenerate the resin as a TAA-type cation exchange resin. The regenerated TAA-type cation exchange resin can be reused as a TAA-type cation exchange resin to be used in the impurity removal means. Alternatively, the resin in the adsorption tower 1 after use in purification can be washed by passing ultrapure water (or pure water) through the ultrapure water (or pure water) line 7, and then reused as a TAA-type cation exchange resin to be used in the impurity removal means. However, if the resin is reused as an impurity removal means without passing hydrochloric acid through it, as in the latter case, metal impurities that cannot be completely eluted by TAAH will remain in the resin. Therefore, it is preferable to periodically combine the former regeneration method, in which hydrochloric acid is passed through it. The waste liquid used for washing is discharged by type according to the values ​​of the pH meter 8 and the electrical conductivity meter 9.

[0049] FIG. 2 is a schematic diagram showing an example of a purification apparatus for purifying a liquid to be treated using an H-type cation exchange resin. While FIG. 2 shows an example in which an adsorption tower is used as a container for packing the cation exchange resin, the container is not limited to an adsorption tower. First, a liquid to be treated containing TAA ions and metal impurities is passed from a storage tank 12 through an adsorption tower 11 packed with an H-type cation exchange resin as an impurity removal means, and the effluent is collected in a storage tank 14. Because the resulting effluent is strongly acidic, it may be neutralized as necessary. Specifically, an aqueous solution containing an alkali (e.g., TAAH) is passed from a storage tank 13 to the storage tank 14 for neutralization. Here, in the initial stage of passing the liquid to be treated in the impurity removal step, hydrogen ions in the H-type cation exchange resin are exchanged with TAA ions and metal ions, causing a rapid drop in the pH of the effluent. Therefore, it is not preferable to mix the strongly acidic solution that flows out at the beginning of the liquid passage with the effluent that flows out later in storage tank 14, because this increases the amount of alkali required for neutralization. Therefore, it is preferable to check the pH of the effluent that flows out at the beginning of the liquid passage using a pH meter 17 installed upstream of waste liquid line 19, and to discharge the strongly acidic effluent from waste liquid line 19 upstream of storage tank 14. Furthermore, a pH meter 17 is also installed in storage tank 14 to adjust the pH of the final effluent to be treated. When the impurity removal step is repeated, the effluent to be treated (neutralized as necessary) that flows out is then passed from storage tank 14 to adsorption tower 11, and the effluent is again recovered in storage tank 14.

[0050] The resin in the adsorption tower 11 after use in purification can be reused by cleaning and regenerating it as follows. After passing ultrapure water (or pure water) through the ultrapure water (or pure water) line 16 to wash the resin in the adsorption tower 11, the effluent collected in the storage tank 14 is passed through the adsorption tower 11, whereby the resin is regenerated as a TAA-type cation exchange resin. Alternatively, after passing ultrapure water (or pure water) through the ultrapure water (or pure water) line 16 to wash the resin in the adsorption tower 11, the TAAH aqueous solution from the storage tank 13 is passed through the adsorption tower 11, whereby the resin is regenerated as a TAA-type cation exchange resin. The regenerated TAA-type cation exchange resin can be reused as a TAA-type cation exchange resin for use in the impurity removal means. While the former method can reduce the amount of chemical solution used, it is inefficient in converting the resin to the TAA-type, considering the pH of the effluent. Therefore, the latter method is preferred from the viewpoint of the efficiency of converting the resin to the TAA-type. Furthermore, since metal impurities that cannot be completely eluted by TAAH remain in the resin, it is preferable to periodically combine it with a regeneration method in which hydrochloric acid (not shown) is passed through, as explained with respect to the purification apparatus shown in FIG. 1.

[0051] The purification apparatus according to the present invention can also be used in combination with an anion exchange resin and a particulate removal filter. When these are combined, a container filled with an anion exchange resin can be placed before or after a container filled with a cation exchange resin, or both ion exchange resins can be mixed and filled in the same container. Furthermore, the container filled with an anion exchange resin is preferably placed upstream of the storage tank 5 or 14. Furthermore, the particulate removal filter is preferably provided between the container filled with the cation exchange resin and / or the anion exchange resin and the storage tank 5 or 14. Note that, although known anion exchange resins and particulate removal filters can be appropriately selected and used, it is preferable that the anion exchange resin be converted to the Cl form.

[0052] <Method for recovering aqueous tetraalkylammonium salt solution> As described above, the purification method of the present invention is a method for purifying a liquid containing tetraalkylammonium ions and metal impurities, thereby reducing the content of metal impurities in the liquid. However, the present invention can also be described as a method for recovering a purified aqueous tetraalkylammonium salt solution from the liquid containing tetraalkylammonium ions and metal impurities by reducing the content of metal impurities in the liquid. In other words, the liquid purified by the purification method of the present invention is a recovered aqueous tetraalkylammonium salt solution. A highly pure TAAH solution can then be obtained by contacting the aqueous tetraalkylammonium salt solution with an anion exchange resin or by electrolysis, for example.

[0053] The method for recovering an aqueous tetraalkylammonium salt solution according to the present invention comprises an impurity removal step of passing a liquid containing tetraalkylammonium ions and metal impurities through a vessel filled with a cation exchange resin in the hydrogen ion or tetraalkylammonium ion form to reduce the content of the metal impurities in the liquid, and is characterized in that the degree of crosslinking of the cation exchange resin is 16 to 24%. Details of the method for recovering an aqueous tetraalkylammonium salt solution according to the present invention are the same as those described above for the purification method according to the present invention, and therefore further description will be omitted.

[0054] <Recovery device for tetraalkylammonium salt aqueous solution> As described above, the purification apparatus of the present invention is a purification apparatus for a liquid to be treated that reduces the content of metal impurities in the liquid to be treated, which contains tetraalkylammonium ions and metal impurities. However, the present invention can also be described as an apparatus for recovering a purified aqueous tetraalkylammonium salt solution from the liquid to be treated by reducing the content of metal impurities in the liquid to be treated. In other words, the liquid to be treated purified by the purification apparatus of the present invention is a recovered aqueous tetraalkylammonium salt solution. Then, by contacting the aqueous tetraalkylammonium salt solution with an anion exchange resin or electrolyzing it as described above, a highly pure TAAH solution can be obtained.

[0055] The apparatus for recovering an aqueous tetraalkylammonium salt solution according to the present invention comprises an impurity removal means for reducing the content of metal impurities in a liquid to be treated by passing the liquid containing tetraalkylammonium ions and metal impurities through a vessel filled with a cation exchange resin in the hydrogen ion or tetraalkylammonium ion form, and the cation exchange resin has a cross-linking degree of 16 to 24%. Details of the apparatus for recovering an aqueous tetraalkylammonium salt solution according to the present invention are the same as those described above for the purification apparatus according to the present invention, and therefore will not be described here.

[0056] The present invention will be specifically described below with reference to examples. [Example]

[0057] Metal impurities, such as Na, Mg, K, and Ca, were added to 1000 ml of a 10% by mass aqueous solution of tetramethylammonium chloride (TMAC), and an appropriate amount of a 25% by mass aqueous solution of tetramethylammonium hydroxide (TMAH), was then added to prepare a solution to be treated with a pH of 8 to 10. The amount of each metal impurity added was set to be approximately the same as the amount of metal impurities contained in actual photoresist development wastewater.

[0058] [Example 1] (Ion exchange process) This example was tested using a batch method. 10 ml of AMBERJET® 1060H (trade name, manufactured by Organo Corporation, degree of crosslinking: 16%), an H-type strongly acidic cation exchange resin, was placed in a 200 ml PFA beaker. 100 ml of a 2.4 wt. % TMAH aqueous solution was added as a regenerant containing tetraalkylammonium ions. The beaker was swirled and stirred every 15 minutes. The resin was immersed for a total of 1 hour, and the supernatant was removed until the resin no longer leaked. This procedure was repeated twice, followed by the addition of 100 ml of ultrapure water (UPW), gentle stirring, and removal of the supernatant. This procedure was repeated three times, and the remaining TMAH was removed by washing.

[0059] (Impurity removal process) After removing the ultrapure water used for cleaning in the ion exchange process up to the very edge of the resin surface, 100 ml of the liquid to be treated prepared above was added, and the resin was immersed for a total of 30 minutes while stirring by rotating the beaker once every 15 minutes.

[0060] (Metal concentration and pH measurement) The supernatant liquid after immersion was collected and its pH and metal concentration were measured. The pH was measured using a portable multi-purpose water quality meter (product name: MM42-DP, manufactured by Toa DKK Corporation). The metal concentration was measured using an Agilent 8900 triple quadrupole ICP-MS (product name, manufactured by Agilent Technologies). Table 1 shows the percentage reduction in the concentration of each metal impurity in the purified liquid compared to the concentration of each metal impurity in the purified liquid before purification, as well as the pH value of the purified liquid. The characteristic values ​​of the cation exchange resin in Table 1 are values ​​from the manufacturer's catalog.

[0061] [Example 2] Except for using AMBERLITE (registered trademark) IRN99H (trade name, manufactured by DuPont, degree of crosslinking: 16%) as the H-type strongly acidic cation exchange resin, the ion exchange step and impurity removal step were carried out in the same manner as in Example 1, and the pH and metal concentration were measured in the same manner as in Example 1. The results are shown in Table 1.

[0062] [Table 1]

[0063] In Examples 1 and 2, the same volumes of cation exchange resins with the same degree of crosslinking were used and the same amount of regenerant was used. However, as shown in Table 1, the pH of the purified treated liquid was strongly acidic (1) in Example 1 and weakly acidic (4) in Example 2. This is because the AMBERLITE IRN99H used in Example 2 has a smaller particle size and a larger surface area than the AMBERJET 1060H used in Example 1. Specifically, the former is more easily converted to the TMA form in the ion exchange step, resulting in less H-form resin remaining. As a result, pH fluctuations during the initial phase of the impurity removal step due to hydrogen ion efflux were suppressed. Furthermore, it was found that Example 2, which used a resin with a smaller particle size, had better metal impurity removal performance than Example 1.

[0064] [Example 3] In this example, a test was performed using the column method (see Figure 1). 36 ml of H-form strongly acidic cation exchange resin, AMBERLITE® IRN99H (trade name, manufactured by DuPont, degree of crosslinking: 16%), was placed in an adsorption tower (a PFA column with a diameter of 19 mm and a length of 300 mm), and the resin was converted to the TMA form using a 2.5% by mass aqueous solution of TMAH (ion exchange step). Subsequently, 30 BV of the liquid to be treated used in Example 1 was passed through the resin converted to the TMA form at a rate of 5 times the resin volume per hour (impurity removal step). Note that BV (Bed volume) represents the flow rate multiple of the liquid passed relative to the resin volume. The pH and metal concentration of the resulting effluent were measured in the same manner as in Example 1. The results are shown in Table 2.

[0065] [Example 4] In this example, a test was carried out using the column method (see Figure 2). As in Example 3, AMBERLITE (registered trademark) IRN99H (trade name, manufactured by DuPont, degree of crosslinking: 16%) was used as the H-form strongly acidic cation exchange resin. 36 ml of the H-form resin that had not been converted to the TMA form was placed in an adsorption tower similar to that in Example 3, and 30 BV of the liquid to be treated used in Example 1 was passed through at a rate of 5 times the resin volume per hour (impurity removal step). The pH and metal concentration of the resulting effluent were measured in the same manner as in Example 1. The results are shown in Table 2.

[0066] [Table 2]

[0067] As shown in Table 2, in both Example 3, in which a TMA-type cation exchange resin was used as the cation exchange resin in the impurity removal step, and Example 4, in which an H-type cation exchange resin was used, the content of metal impurities was significantly reduced. In particular, in Example 3, in which the resin was converted to the TMA-type beforehand in the ion exchange step and the liquid to be treated was passed through, there was little pH fluctuation because the metal impurities and TMA were ion-exchanged in the impurity removal step. Furthermore, Example 3 showed better results in terms of Na removal performance than Example 4. Comparing the results of Examples 1 and 2 with those of Examples 3 and 4, the latter showed higher metal impurity removal performance and smaller pH fluctuations. This is because the column method generally has higher purification efficiency than the batch method.

[0068] [Examples 5 to 6, Comparative Examples 1 to 2] (Measurement of sphericity) Five milliliters of each of the H-form cation exchange resins shown in Table 3 was placed in a 200-ml PFA beaker. 50 ml of a 25% by mass TMAH aqueous solution, serving as a regenerant containing tetraalkylammonium ions, was added, mixed, and the resin was immersed for two hours. The supernatant was then removed, and the resin in the beaker was washed three times with ultrapure water (a total of 150 ml). This process corresponds to the ion exchange process of the present invention and was carried out under conditions in which the TMAH concentration was higher than usual, with the aim of checking for cracks in the resin. The sphericity of the resulting resin was measured using the following method. Using a microscope (trade name: Digital Microscope, manufactured by Keyence Corporation), 500 resin particles were observed, and the ratio of perfectly spherical solids to all observed solids (perfect sphericity) was calculated using the following formula. Perfect sphericity rate (%) = ((500 - number of solids with cracks or chips) / 500) x 100

[0069] The results, together with the degree of crosslinking, are shown in Table 3. In Table 3, AMBERLYST (registered trademark) 16WET (product name) used in Comparative Example 1 and AMBERLITE (registered trademark) IRN97H (product name) used in Comparative Example 2 are both manufactured by DuPont.

[0070] [Table 3]

[0071] As shown in Table 3, Examples 5 and 6, which used highly cross-linked, strongly acidic cation exchange resins, exhibited a high degree of perfect sphericity. This indicates that these resins are less likely to develop cracks or fissures even in a TMAH aqueous solution with a high TMA ion concentration, and are less likely to crack even when repeatedly used in ion exchange processes, impurity removal processes, etc. On the other hand, in Comparative Examples 1 and 2, which used resins with a crosslinking degree lower than the range specified in the present invention, the sphericity was 91 to 98%. It was found that these resins were more likely to crack and the ion exchange resin matrix was more likely to be damaged by repeated use than the resins used in the Examples. [Explanation of symbols]

[0072] 1: Adsorption tower 2: Storage tank (liquid to be treated) 3: Storage tank (TAAH) 4: Reservoir (acid) 5: Reservoir (effluent) 6: Pump 7: Ultrapure water line 8:pH meter 9: Electrical conductivity meter 10: Waste liquid line 11:Adsorption tower 12: Storage tank (liquid to be treated) 13: Storage tank (TAAH) 14: Reservoir (effluent) 15: Pump 16: Ultrapure water line 17:pH meter 18: Electrical conductivity meter 19: Waste liquid line

Claims

1. an ion exchange step in which a regenerant containing tetraalkylammonium ions is passed through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; an impurity removal step in which a liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a vessel filled with the strongly acidic cation exchange resin in the tetraalkylammonium ion form obtained in the ion exchange step, thereby reducing the content of the metal impurities in the liquid to be treated; A method for purifying a liquid to be treated, comprising: A method for purifying a liquid to be treated, characterized in that the degree of crosslinking of the strongly acidic cation exchange resin is 16 to 24%, the exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / L-R or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant used in the ion exchange step is 2.4 to 25 mass%.

2. 2. The method for purifying a liquid to be treated according to claim 1, wherein the particle size (harmonic mean diameter) of the strongly acidic cation exchange resin in the hydrogen ion form is 500 to 560 μm.

3. 3. The method for purifying a liquid to be treated according to claim 1, further comprising a regeneration step of regenerating the strongly acidic cation exchange resin that has come into contact with the liquid to be treated in the impurity removal step.

4. 4. The method for purifying a liquid to be treated according to claim 1, wherein the liquid to be treated is a solution derived from a waste liquid discharged in a photoresist development process.

5. an ion exchange means for passing a regenerant containing tetraalkylammonium ions through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; an impurity removal means for passing a liquid to be treated containing tetraalkylammonium ions and metal impurities through a container filled with the obtained strongly acidic cation exchange resin in the tetraalkylammonium ion form, thereby reducing the content of the metal impurities in the liquid to be treated; A purification apparatus for a liquid to be treated, comprising: A purification apparatus for a liquid to be treated, characterized in that the degree of crosslinking of the strongly acidic cation exchange resin is 16 to 24%, the exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / L-R or more in hydrogen ion form, and the concentration of tetraalkylammonium ions in the regenerant in the ion exchange means is 2.4 to 25 mass%.

6. 6. The apparatus for purifying a liquid to be treated according to claim 5, wherein the particle size (harmonic mean diameter) of the strongly acidic cation exchange resin in the hydrogen ion form is 500 to 560 μm.

7. an ion exchange step in which a regenerant containing tetraalkylammonium ions is passed through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; an impurity removal step in which a liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a vessel filled with the strongly acidic cation exchange resin in the tetraalkylammonium ion form obtained in the ion exchange step, thereby reducing the content of the metal impurities in the liquid to be treated; A method for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated, comprising: A method for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated, characterized in that the degree of crosslinking of the strongly acidic cation exchange resin is 16 to 24%, the exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / L-R or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant used in the ion exchange step is 2.4 to 25 mass%.

8. an ion exchange means for passing a regenerant containing tetraalkylammonium ions through a vessel filled with a strongly acidic cation exchange resin in the hydrogen ion form to convert the strongly acidic cation exchange resin in the hydrogen ion form into a strongly acidic cation exchange resin in the tetraalkylammonium ion form; an impurity removal means for passing a liquid to be treated containing tetraalkylammonium ions and metal impurities through a container filled with the obtained strongly acidic cation exchange resin in the tetraalkylammonium ion form, thereby reducing the content of the metal impurities in the liquid to be treated; An apparatus for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated, comprising: An apparatus for recovering an aqueous tetraalkylammonium salt solution from a liquid to be treated, characterized in that the degree of crosslinking of the strongly acidic cation exchange resin is 16 to 24%, the exchange capacity of the strongly acidic cation exchange resin is 2.4 eq / L-R or more in hydrogen ion form, and the tetraalkylammonium ion concentration of the regenerant in the ion exchange means is 2.4 to 25 mass%.

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