JP7690774B2 - Method for removing organic acids - Google Patents

Description

The present invention relates to a method for removing organic acids.

Dirt such as processing oils, paints, inks, resins, and foreign matter adheres to parts manufactured in various industrial fields such as automobiles, machinery, precision equipment, printing, resin processing, and molding, as well as the manufacturing equipment and associated facilities, buildings, packaging materials, containers, and floors. To remove this dirt, halogen-based solvents, hydrocarbon-based solvents, glycol ether-based solvents, aqueous cleaners, semi-aqueous cleaners, and mixtures of these are used as solvents to remove the dirt.

Cleaning methods include immersing the object to be cleaned in a cleaning tank containing a solvent that removes dirt and cleaning using a combination of ultrasonic waves, jets, and vibrations, or spraying the solvent that removes dirt onto it using a shower or spray. There is also a method in which dirt is removed in the vapor of the solvent that removes dirt or by spraying the vapor onto it. If it is necessary to dry the solvent that removes dirt, methods such as drying by spraying hot air onto the object or drying in a vacuum are also used.

In these cleaning processes, dirt adhering to the object being cleaned dissolves or becomes mixed in as impurities in the solvent used to remove the dirt. If cleaning is performed when a large amount of impurities are dissolved or mixed in, there is a risk that these impurities will re-adhere to the object being cleaned, affecting the cleanliness and performance quality. Therefore, if impurities have accumulated after using the solvent to remove dirt for a while, it is necessary to reduce the impurities and return the object to a clean state.

One way to make the dirt-removing solvent pure is to drain the solvent that has accumulated impurities and replace it with unused solvent, but a method with better running costs is to remove only the impurities from the dirt-removing solvent and reuse it as regenerated liquid.

One method for obtaining regenerated liquid is distillation separation. Generally, the boiling point of the solvent that removes dirt is lower than that of the impurities, so the impurities do not evaporate, and the solvent that removes dirt is heated under temperature and pressure conditions that allow only the solvent to evaporate, and then the liquid is cooled to condense it and recovered as clean regenerated liquid.

However, when the solvent used to remove dirt and dirt are repeatedly heated for a long period of time through repeated regeneration by heated distillation and heated cleaning, they gradually decompose and react, producing small amounts of organic acids. The organic acids produced have a lower boiling point than the original substance, and may be mixed into the regenerated liquid. When cleaning is performed with a regenerated liquid containing organic acids, problems such as stains becoming more likely due to a decrease in cleaning performance and the generation of odors specific to organic acids can occur. For example, when dirt containing cations such as ammonium ions or sodium ions is mixed into a regenerated liquid containing organic acids, it reacts with the organic acids to form solid salts at room temperature, causing stains when drying after cleaning. For this reason, it is necessary to remove the organic acids from the regenerated liquid.

In the field of dry cleaning, a method for removing organic acids from stain-removing solvents has been used in which fatty acids, a type of organic acid, are adsorbed onto adsorbents such as alumina silica gel and activated carbon, known as deoxidizers (see, for example, Patent Documents 1 and 2). However, adsorption alone results in an equilibrium state, and it is difficult to completely remove organic acids, so there is a demand for technology that can remove organic acids to a greater extent by utilizing chemical reactions, etc.

In addition, as a method for removing organic acids from alcohol, there is a method of purifying an alcohol-containing liquid such as alcoholic beverages by contacting it with a strong basic anion exchange resin, a weak basic anion exchange resin, and a strong acid cation exchange resin (see, for example, Patent Document 3). Although organic acids are also described as a target for removal, the main purpose of this method is to remove unpleasant odors such as those of aldehyde compounds, and unpleasant flavors caused by salts such as minerals, and the use of this method is different from that of the present invention.

Although there are methods for removing mineral acids and organic acids from solutions using ion exchange resins (see, for example, Patent Document 4), the actual solution is water (discharge water), anion exchange resins are used in fuel cells, and although there is a description of organic acids, the acids actually removed are mainly mineral acids such as hydrogen fluoride, hydrogen chloride, and sulfuric acid that show higher reactivity with metals than organic acids, i.e., inorganic acids, which are different from the solvents that remove the dirt targeted by this invention, and the type of acid removed is also different, so the application is different from that of this invention.

Special Publication No. 49-027262 Patent No. 3456387 Patent No. 6718309 Special Publication No. 2008-509522

The object of the present invention is to provide an effective method for removing trace amounts of organic acids contained in the regenerating solution of a stain-removing solvent.

As a result of extensive research into solving the above-mentioned problems, the inventors discovered a method for effectively removing organic acids without adversely affecting the solvent used to remove the stains, and thus completed the present invention.

That is, the present invention relates to a method for removing an organic acid by contacting a solution containing a solvent that contains at least 10% by volume of an alcohol or an ether, has a flash point of 41°C or higher or has no flash point, and an organic acid with a weakly basic anion exchange resin.

The present invention will be described in more detail below.

The alcohol and ether described in this invention are components that make up the solvent for removing dirt. When used as a solvent for removing dirt, it is used in a cleaning tank or the like, so a certain amount is required to be stored, but when alcohol or ether is included as an ingredient, it often has a flash point, so if it is stored in an amount greater than the specified amount, it is subject to regulations under the Fire Service Act. However, if the mixed solvent has a flash point of 21°C or higher, it is classified as Class 4, Class 2 petroleum or higher under the Fire Service Act, but even if it is stored in an amount less than the specified amount, it can be stored in a sufficient amount as a solvent for removing dirt, and if the flash point is 41°C or higher, it does not reach the flash point even under cleaning conditions of 40°C, which is often adopted to improve the cleaning effect, so it is relatively safe and is commonly used. Furthermore, if the mixed solvent does not have a flash point, it can be stored in a sufficient amount without being regulated by the Fire Service Act.

The flash point in this invention is for a solvent that contains at least 10% by volume of alcohol or ether. If both alcohol and ether are less than 10% by volume, the solvent will be on the safe side in terms of ignition, but will be inferior in terms of cleaning properties against dirt.

The alcohols and ethers described in the present invention are not particularly limited as long as they are liquid at room temperature and exhibit good cleaning properties against dirt, but in order to facilitate drying of the objects to be cleaned after cleaning, those with a boiling point of 230°C or less are preferred. Examples of suitable alcohols include alcohols having 6 or more carbon atoms, such as hexanol, heptanol, octanol, nonanol, decanol, undecanol, 4-methyl-2-pentanol, and 2-ethyl-1-butanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, and diethylene glycol monoisobutyl ether. Examples include glycol ethers such as diethylene glycol isopropyl methyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, and dipropylene glycol monoethyl ether; glycols such as ethylene glycol, diethylene glycol, propylene glycol, hexylene glycol, and isoprene glycol; methoxybutanols such as 3-methoxy-1-butanol and 3-methyl-3-methoxy-1-butanol; lactate esters such as methyl lactate and ethyl lactate; and cyclic ether alcohols such as tetrahydrofurfuryl alcohol and furfuryl alcohol.

There are no particular restrictions on the conditions for heating and distilling the solvent, so long as the pressure and temperature conditions are such that the dirt does not evaporate as a liquid or solid and the solvent evaporates, but generally temperature conditions between 80°C and 250°C are used.

There are no particular limitations on the means for heating the solvent, but it is preferable to use something that will not pose a risk of ignition when it comes into contact with the solvent. Methods that can be used include circulating heat transfer oil or steam through the pipes, or using electric heating wires.

The organic acid to be removed is not particularly limited as long as it is generated by decomposition or reaction due to heating of ethanol or ether, but since the purpose is to remove organic acids that are mixed into the regenerated liquid by heating and distillation and have a boiling point lower than that of the solvent used to remove dirt, examples of organic acids that have a boiling point of 230°C or less include carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, 3-hydroxypropionic acid, isobutyric acid, pivalic acid, 2-hydroxypropionic acid, 2,2-bis(hydroxymethyl)propionic acid, pyruvic acid, methacrylic acid, t-butylacetic acid, glyceric acid, 2,2-dimethylbutyric acid, 2-methylbutyric acid, isovaleric acid, 2-ethylbutyric acid, 2-hydroxyisobutyric acid, acrylic acid, 2-methyl-3-butenoic acid, glycolic acid, pentenoic acid, 3-ethoxypropionic acid, 2-methylvaleric acid, 3-methylvaleric acid, and 4-methylvaleric acid.

There are no particular limitations on the type of anion exchange resin, and it can be used according to the application, but the solvent used to remove dirt must be neutral, so it must remain neutral even when the anion exchange resin is added. For this reason, a weakly basic anion exchange resin is particularly preferred.

The mechanism by which the anion exchange resin removes the organic acid is not particularly limited, but in order to maintain the liquid neutrality without reducing the cleaning quality of the solvent that removes dirt, it is preferable that the organic acid is converted into water by an ion exchange reaction between hydroxide ions derived from the anion exchange resin and anions dissociated from the organic acid, and at the same time, the hydroxide ions react with protons dissociated from the organic acid to form water.

There are no particular limitations on the temperature when the stain-removing solvent is brought into contact with the anion exchange resin, but since the stain-removing solvent may contain water, it is desirable to use a temperature above the temperature at which the stain does not solidify. Also, since the stain-removing solvent may have a flash point, it is preferable to use a temperature below the flash point. Therefore, a temperature range of 0°C to 80°C is preferable.

There are no particular limitations on the flow rate when the dirt-removing solvent is brought into contact with the anion exchange resin, but since the dirt-removing solvent may be a hazardous material with a flash point, a flow rate of 1 m/sec or less is preferable.

The organic acid removal method of the present invention can efficiently remove organic acids from solvents used to remove stains such as processing oils, paints, inks, resins, and foreign matter adhering to parts manufactured in industrial fields such as automobiles, machinery, precision equipment, printing, resin processing, and molding, as well as the manufacturing equipment and associated facilities for these, buildings, packaging materials, containers, floors, etc.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

Example 1, Comparative Example 1
<Effects on solvents used to remove stains from ion exchange resin>
A basic anion exchange resin was added at 1.0% by weight to 10 ml of Sample 1 (flash point: none) shown in Table 1, and the mixture was allowed to stand for two days. After standing, the basic anion exchange resin was removed, and 0.3 ml of BTB indicator was added dropwise to observe the change in the color of the liquid.

The BTB indicator shows a yellow color at pH 6 or less, and a blue color at pH 7.6 or more. When a BTB indicator is added to a solvent for removing stains in which no organic acid has been generated, the liquid color turns yellow. Therefore, even when a basic anion exchange resin is added to a solvent for removing stains in which organic acid has been generated, it is desirable for the color to turn yellow when the BTB indicator is added; if the color turns blue, this is undesirable because the basic anion exchange resin added is too basic. Therefore, evaluation was performed according to the following evaluation criteria. The results are shown in Table 2.

Evaluation criteria: ◯: The liquid color is yellow when BTB indicator is added
×: The color of the solution when the BTB indicator was added was blue. Examples 2 to 3, Comparative Examples 2 to 4
<Effect of ion exchange resin>
An acid remover such as an ion exchange resin was added to 10 ml of Sample 1 shown in Table 1, and the mixture was allowed to stand for 7 days. After standing, the acid remover was removed, 0.3 ml of BTB indicator was added, and neutralization titration was performed with 0.02 N sodium hydroxide/methanol solution to measure the acid concentration.

The acid concentration before the heat distillation when no organic acid was generated was set to 0%, and the acid concentration after the heat distillation when organic acid was generated (day 0) was set to 100%, and the degree to which the acid concentration had decreased after 7 days was measured and evaluated according to the following evaluation criteria. The results are shown in Table 3.

Evaluation criteria: ◎: Acid concentration after 7 days is 0-10%
◯: Acid concentration after 7 days is 11-50%
△: Acid concentration after 7 days is 51-75%
×: Acid concentration after 7 days is 76-100%
The meanings of the abbreviations in Table 1 are as follows:

DPM: Dipropylene glycol monomethyl ether DGDE: Diethylene glycol diethyl ether

Examples 4 to 12
<Acid removal effect of weakly basic ion exchange resin in various solvents>
Each sample shown in Table 4 was placed in a sample bottle, to which 1% by weight of a weakly basic ion exchange resin was added, and the sample bottle was rotated at 100 rpm for 3 hours for stirring, and then allowed to stand for 20 hours. After standing, the weakly basic ion exchange resin was removed, 0.3 ml of a BTB indicator was added, and neutralization titration was performed with a 0.02 N sodium hydroxide/methanol solution to measure the acid concentration.

The acid concentration was compared before and after the addition of the weakly basic ion exchange resin to evaluate how much acid was removed. The results are shown in Table 5.

Comparative Examples 5 to 13
<Acid removal effect of alumina silica gel in various solvents>
The acid removal effect of alumina silica gel was evaluated in the same manner as in Examples 4 to 12, except that alumina silica gel was added instead of the weakly basic ion exchange resin. The results are shown in Table 5.

The meanings of the abbreviations in Table 4 are as follows:

MMB: 3-methyl-3-methoxy-1-butanol DPM: dipropylene glycol monomethyl ether PNP: propylene glycol monopropyl ether DGDE: diethylene glycol diethyl ether HPN: heptanol DGIB: diethylene glycol monoisobutyl ether IPDM: diethylene glycol isopropyl methyl ether

Claims (4)

A method for removing an organic acid, comprising contacting a weakly basic anion exchange resin with a solution containing one or more cleaning solvents selected from the group consisting of water, n-decane, n-dodecane, alcohols having 6 or more carbon atoms, glycol ethers, glycols, methoxybutanols, and cyclic ether alcohols, the solvent containing 10% by volume or more of at least one of an alcohol and an ether and having a flash point of 41° C. or higher or no flash point, and an organic acid. A method for removing organic acids, characterized in that the alcohol and ether described in claim 1 are at least one selected from diethylene glycol monoisobutyl ether, diethylene glycol isopropyl methyl ether, 3-methyl-3-methoxy-1-butanol, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, heptanol, and diethylene glycol diethyl ether. A method for removing an organic acid, characterized in that the alcohol and ether described in claim 1 are at least one selected from diethylene glycol diethyl ether and dipropylene glycol monomethyl ether. A method for removing an organic acid, characterized in that the solvent according to claim 1 is a cleaning solution.