JP2016043285A - Method of treating triethanolamine-containing waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce COD of triethanolamine-containing waste liquid.SOLUTION: An oxidizing agent is added to triethanolamine-containing waste liquid, the pH of the waste liquid is controlled to fall in an alkaline region, and when decrease of oxidation reduction potential stops, the pH of the waste liquid is controlled to fall in an acidic area.SELECTED DRAWING: None

Description

  The present invention relates to a method for treating a triethanolamine-containing waste liquid that decomposes triethanolamine contained in the waste liquid and reduces the chemical oxygen demand of the waste liquid.

  A paste material obtained by kneading a fine metal powder such as nickel or copper and an organic material is used as a material for electronic parts such as capacitors and chip resistors.

  The metal fine powder is often produced using a dry reduction method or a wet reduction method. Specifically, when producing a metal fine powder by a wet reduction method, a reducing agent or an additive is added to an aqueous solution containing a salt that is a raw material for the metal, and a reduction reaction is performed in the aqueous solution. Getting is generally done.

  An amine may be used as the reducing agent or additive. For this reason, the salt concentration of the waste liquid generated when the metal powder is produced may increase, resulting in a waste liquid having a high COD (chemical oxygen demand). Since such waste liquid causes pollution such as eutrophication, it cannot be discharged into public water areas without being treated. Therefore, treatment is required when draining the waste liquid.

  Japan's environmental standards for organic matter in public water bodies are based on BOD (biological oxygen demand) for rivers and COD for lakes and seas. According to the Water Pollution Control Law, COD and BOD are defined as the allowable limits of 160 mg / l and daily average of 120 mg / l as uniform drainage standards. That is, the waste liquid cannot be drained unless the COD is reduced to approximately 0.1 g / l, and it is preferable that the waste liquid be as low as possible.

  Furthermore, in some prefectures, there are cases where stricter standards for addition are stipulated by regulations. In order to ensure water quality environmental standards in closed waters where there is significant pollution, water quality regulations are imposed to reduce the total amount of organic pollutants discharged to the sea area to below the standard value, rather than concentration regulations. . Thus, in order to prevent pollution such as water pollution, it is necessary to treat the waste liquid containing amine as described above to reduce COD.

  Various methods have been proposed for the decomposition of organic substances for reducing COD. When applying biological treatment such as that shown in Non-Patent Document 1 using activated sludge and biological membranes that have been known for a long time, there is a risk that organisms will die in a high salt concentration solution such as the above-mentioned waste liquid. Therefore, it is difficult to apply biological treatment as it is. For this reason, the method using biological treatment needs to be diluted to a concentration at which living organisms can survive, and the scale of equipment required to increase the liquid volume due to dilution increases the cost of investment and running. There is.

  For this reason, Patent Document 1 also proposes a method of removing organic substances from the liquid by solidifying by evaporation to dryness without decomposing the organic substances. However, the method of Patent Document 1 has a demerit that the energy cost required for heating is large. Moreover, in the method of patent document 1, since the solidified collection | recovery has adhesiveness, the problem of handling property, such as it becoming difficult to adhere to an evaporation kiln and to remove, is also big.

  As a method for decomposing organic substances, for example, a method shown in Patent Document 2 is known in which, in addition to biodegradation, chemical oxidative decomposition is performed using an oxidizing agent such as sodium hypochlorite. Sodium hypochlorite is a strong oxidant and is an easy-to-use oxidant widely used for sterilization of tap water and food.

  This sodium hypochlorite self-decomposes and becomes chlorine gas at a pH of 5 or lower, and dissipates. Therefore, the effective chlorine concentration in the aqueous solution decreases and the oxidation ability decreases. For this reason, usually sodium hypochlorite is often added in an alkaline pH region.

  On the other hand, organic substances may go through various intermediates when decomposed into carbon dioxide. In order to decompose this organic substance-derived intermediate, alkalinity is often not optimal. Therefore, in an alkaline environment in which the oxidizing agent exhibits oxidation ability, the intermediate derived from the organic matter cannot be sufficiently decomposed, and the COD of the waste liquid cannot be effectively reduced.

  Among organic substances, amines, especially triethanolamine, which is one of them, are simply alkaline and cannot be effectively decomposed when treated with hypochlorous acid. Addition of sodium hypochlorite and a long treatment time are required.

JP 2009-220047 A JP 2000-220088 A

Yoroku Wada, “Basics and Mechanism of Newest Water Treatment Technology Understandable” [Second Edition], Hidekazu System, Inc., July 10, 2012, p145-174 Mitsuaki Uragaki et al. Bulletin 37 of Yokohama City Environmental Science Research Institute (2013) "Oxidative decomposition of triethanolamine by ozone" Takaya Akimaru et al. Abstracts of the 75th Annual Meeting of the Chemical Society of Japan (I306) (2010) “Decomposition of ethylene glycol using ultrasonic reaction field”

  Therefore, an effective method for decomposing triethanolamine using sodium hypochlorite is desired in the treatment of waste liquid containing triethanolamine.

  Therefore, the present invention has been proposed in view of such circumstances, and it is possible to effectively decompose triethanolamine and efficiently reduce chemical oxygen demand (COD). It aims at providing the processing method of an ethanolamine containing waste liquid.

  The method for treating a triethanolamine-containing waste liquid according to the present invention that achieves the above-described object is to add an oxidizing agent to the waste liquid containing triethanolamine, adjust the pH of the waste liquid to an alkaline region, and reduce the oxidation-reduction potential. The pH of the waste liquid is adjusted to an acidic region when it is no longer used.

  In the present invention, triethanolamine can be effectively decomposed and chemical oxygen demand (COD) can be efficiently reduced. Thereby, in this invention, even if it is a waste liquid which contains triethanolamine in high concentration and has a high COD, the COD can be effectively reduced to the drainage regulation value.

  Below, the processing method of the triethanolamine containing waste liquid to which this invention is applied is demonstrated in detail. Note that the present invention is not limited to the following detailed description unless otherwise specified.

  The treatment method of the triethanolamine-containing waste liquid effectively performs the triethanolamine decomposition reaction by adjusting the pH of the waste liquid in two stages when the triethanolamine decomposition reaction is performed by adding an oxidizing agent. Like that. Thus, in this method for treating a triethanolamine-containing waste liquid, even if triethanolamine is contained, the chemical oxygen demand (hereinafter referred to as COD) can be efficiently reduced with a small amount of oxidizing agent. .

  The treatment method of this triethanolamine-containing waste liquid can be applied in any form as long as it is a waste liquid containing triethanolamine.

  The decomposition reaction of triethanolamine will be described. When triethanolamine is oxidized and decomposed by an oxidizing agent, it is finally mineralized through various intermediates. When an oxidizing agent is added to a waste liquid containing triethanolamine, an oxide of triethanolamine is formed in the presence of the oxidizing agent as shown in the following reaction formula 1. As shown in Reaction Scheme 1, triethanolamine becomes ethylene oxide after passing through hydroxylamine. This is reported, for example, in Non-Patent Document 2. The oxidizing agent here is ozone, but it is not limited to ozone, and general oxidizing agents such as oxygen and hydrogen peroxide can be used.

  Next, it is generally known that ethylene oxide becomes ethylene glycol when it reacts with water as shown in the following reaction formula 2. Therefore, the ethylene oxide produced | generated by Reaction formula 1 reacts with the water in a waste liquid, and becomes ethylene glycol.

  Next, ethylene glycol is further oxidized and decomposed as shown in the following reaction formula 3. For example, Non-Patent Document 3 reports that such a reaction occurs.

Ethylene glycol _(HOCH 2 _CH 2 OH) is passed through the glycolaldehyde _(HOCH 2 -CHO), via a glyoxal (OHC-CHO) or glycolic acid _(HOCH 2 -COOH), glyoxylic acid (OHC-COOH), and Formic acid (HCOOH) is finally mineralized.

  Triethanolamine is mineralized through various intermediates as shown in Reaction Schemes 1-3. Therefore, in the decomposition reaction of triethanolamine, it is necessary to make the pH during the reaction suitable for the decomposition according to the intermediate. In the decomposition reaction of triethanolamine, triethanolamine can be effectively decomposed by adjusting the pH appropriately.

  First, in the reaction of the reaction formula 1, if the amine is acidified, an amine salt is formed and the decomposition reaction is difficult, so it is necessary to make it alkaline. Therefore, the waste liquid containing triethanolamine is made alkaline. Since the base dissociation constant pKb of triethanolamine is about 6.3, it is desirable that the pH is higher than this value.

  Then, when the reaction of Reaction Formula 3 is considered through the reaction of Reaction Formula 2, ethylene glycol is divided into two pathways from glycol aldehyde to become glyoxal or glycolic acid. At this time, since glycolic acid has a slower reaction rate than glyoxal, it is necessary to induce the reaction to glyoxal. Glycolic acid, which is an acid, is likely to be produced when the pH is high. Therefore, acidic acid is preferable for inducing glyoxal.

  Therefore, in the method of treating a triethanolamine-containing waste liquid, in order to convert triethanolamine into a free amine form capable of reacting and to derive from glycolaldehyde to glyoxal, a weakly alkaline pH that is an intermediate pH between acidic and alkaline is used. It is desirable to do. A suitable pH range is pH 8 to 10, preferably pH 8.5 to 9.5.

  And after passing through glyoxal, it is mineralized through glyoxylic acid and formic acid, but glyoxal, glyoxylic acid and formic acid are more easily decomposed when acidic. However, if the pH is too low, hypochlorous acid added as an oxidizing agent is decomposed into chlorine, so that the oxidation ability is significantly reduced.

Generally, the state in which the oxidizing power of the sodium hypochlorite aqueous solution is high is about pH 5 where the abundance ratio of hypochlorous acid (HOCl) is the highest. When the pH is less than 5, self-decomposition tends to increase the generation of chlorine gas, and the oxidizing power tends to decrease. On the other hand, when the pH is higher than 5, the abundance ratio of hypochlorite ions (OCl ⁻ ) increases and the oxidizing power tends to decrease. This hypochlorite ion is known to have lower oxidizing power than hypochlorous acid.

  Therefore, for the decomposition of glyoxal, glyoxylic acid and formic acid, it is suitable that the pH of the waste liquid is in the range of pH 4 to 6, preferably pH 4.5 to 5.5.

  In the method for treating a triethanolamine-containing waste liquid, in order to smoothly proceed and effectively decompose the decomposition reaction of triethanolamine, after adding an oxidant, it is divided into two stages in accordance with the decomposition reaction of the produced intermediate. Adjust the pH.

  Specifically, as shown in Reaction Formula 1, when an oxidizing agent is added to the waste liquid to oxidize triethanolamine to decompose it into ethylene oxide, weak alkalinity is preferable, so that the pH is 8 to 10, preferably pH 8. Adjust to the range of 5 to 9.5 (first stage). And, in order to further promote the decomposition reaction from ethylene oxide, suppress the formation of glycolic acid, and induce the reaction to glyoxal, the acid is preferable, so the pH is pH 4-6, preferably pH 4.5-5. Adjust to a range of 5 (second stage).

  The timing for switching the pH from the first stage to the second stage is preferably after the triethanolamine has completely reacted in the decomposition reaction from triethanolamine to ethylene oxide shown in Reaction Formula 1. When the pH is switched to acidic with the triethanolamine remaining, the triethanolamine becomes an amine salt, which makes it difficult to decompose and makes it difficult to reduce COD.

  In order to confirm the state in which the total amount of triethanolamine has been reacted, it is possible to measure the oxidation-reduction potential (ORP) in the waste liquid. In the state where triethanolamine, which is a reducing substance, is present, ORP decreases, and ORP does not increase even when an oxidizing agent such as sodium hypochlorite is added. Even if ORP increases temporarily at the time of addition, ORP falls immediately because sodium hypochlorite is consumed by reaction. If the decomposition reaction proceeds and triethanolamine disappears, the reaction after glyoxal becomes difficult to proceed in an alkaline state, so that an oxidizing agent such as sodium hypochlorite is not consumed and ORP does not decrease. That is, the point in time when the oxidation state can be maintained without adding an oxidizing agent such as sodium hypochlorite becomes the timing for switching the pH from the first stage to the second stage. The ORP that can be confirmed to be in an oxidized state varies depending on the pH, but in the alkaline state, the potential is 730 to 800 mV, preferably 750 to 780 mV, with a silver-silver chloride electrode as a reference electrode.

  As described above, in the method for treating a triethanolamine-containing waste liquid, the decomposition reaction is not simply performed in an alkaline environment, but an oxidation agent is added to start the decomposition reaction of triethanolamine and then mineralize. In the meantime, the pH of the waste liquid is adjusted stepwise according to the decomposition reaction. In the method for treating a triethanolamine-containing waste liquid, when an oxidizing agent is added to the waste liquid to decompose triethanolamine into ethylene oxide, the production of amine salt is suppressed and the decomposition reaction is promoted as weakly alkaline. And in the processing method of a triethanolamine containing waste liquid, since it induces to the reaction to glyoxal through ethylene glycol and glycol aldehyde from ethylene oxide, the reaction rate of decomposition | disassembly can be made quick by acidifying a waste liquid. Therefore, in this treatment method for triethanolamine-containing waste liquid, by appropriately adjusting the pH stepwise, the decomposition reaction of triethanolamine into ethylene oxide is promoted, and the reaction rate proceeds to glyoxal with a high reaction rate. Therefore, the decomposition reaction can be performed effectively. Thereby, in the processing method of a triethanolamine containing waste liquid, even if triethanolamine is contained, COD of a waste liquid can be reduced efficiently. Further, in this treatment method, even when high concentration of triethanolamine is contained and COD is high, COD can be efficiently reduced to the drainage regulation value.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

Example 1
In Example 1, 300 ml of an aqueous solution containing 6 g / l of triethanolamine heated to 50 ° C. was prepared and used as an original solution. The COD of this original solution was 5.2 g / l.

  Next, a 12% by weight sodium hypochlorite aqueous solution was added to the original solution. When adding sodium hypochlorite, the pH of the first stage was adjusted using a 4 mol / l sodium hydroxide solution so that the pH during the reaction was 9. The sodium hypochlorite aqueous solution was continuously added until the ORP using a silver-silver chloride electrode as a reference electrode was 750 mV.

  And after ORP reaches 750 mV, only when ORP decreases when the addition of sodium hypochlorite is stopped, sodium hypochlorite is added intermittently, and the ORP decreases even when the addition is stopped. The addition was continued until no more was seen. Finally, the added sodium hypochlorite aqueous solution was 78 ml. The COD at this stage could be considerably reduced to 0.8 g / l.

  Next, as the second stage pH adjustment, while maintaining the solution to which sodium hypochlorite was added at 50 ° C., sulfuric acid having a concentration of 16% by weight was added to adjust the pH to 5, and after stabilization, Stirring was continued for 30 minutes. Then, the solution was fractionated and COD was analyzed. The COD of this solution was 0.1 g / l, and it was confirmed that the triethanolamine contained could be almost completely decomposed.

(Comparative Example 1)
In Comparative Example 1, the same operation as in Example 1 was performed except that the pH was adjusted to 5 in the first stage and oxidation was performed until the ORP reached 1000 mV. In Comparative Example 1, the second-stage pH adjustment was not performed. The added sodium hypochlorite was 40 ml. The COD was 3.5 g / l, which was higher than the result of the first stage of Example 1.

(Comparative Example 2)
In Comparative Example 2, the same operation as in Example 1 was performed except that the pH was adjusted to 6 in the first stage and oxidation was performed until the ORP reached 900 mV. In Comparative Example 2, the second stage pH adjustment was not performed. The added sodium hypochlorite was 30 ml. The COD was 3.0 g / l, which was higher than the result of the first stage of Example 1.

(Comparative Example 3)
In Comparative Example 3, the same operation as in Example 1 was performed except that the pH of the first stage was adjusted to 7 and oxidation was performed until the ORP reached 850 mV. The second stage pH adjustment was not performed. The added sodium hypochlorite was 38 ml. The COD was 2.7 g / l, which was higher than the result of the first stage of Example 1.

(Comparative Example 4)
In Comparative Example 4, the same operation as in Example 1 was performed except that the pH of the first stage was adjusted to 8 and oxidation was performed until the ORP reached 800 mV. The second stage pH adjustment was not performed. The added sodium hypochlorite was 73.5 ml. The COD was 1.2 g / l, which was higher than the result of the first stage of Example 1.

(Comparative Example 5)
In Comparative Example 5, the same operation as in Example 1 was performed except that the pH of the first stage was adjusted to 10.6 and oxidation was performed until the ORP reached 700 mV. The second stage pH adjustment was not performed. The added sodium hypochlorite was 89 ml. The COD was 2.7 g / l, which was higher than the result of the first stage of Example 1.

(Comparative Example 6)
In Comparative Example 6, a solution in which the pH of the first step was adjusted under the same conditions as in Example 1 was heated to 50 ° C., 16 wt% sulfuric acid was added, and the pH was adjusted to 3.5. The pH of the eye was adjusted and mixed for 30 minutes with stirring. The COD was 0.5 g / l but could not be reduced to a level where it could still be discharged directly.

(Comparative Example 7)
In Comparative Example 7, the first-stage pH-adjusted liquid was heated to 50 ° C. under the same conditions as in Example 1, and 16% strength sulfuric acid was added to adjust the pH to 6.5. The eyes were adjusted for pH and stirred for 30 minutes to mix. The COD was 0.6 g / l but could not be reduced to a level where it could still be discharged directly.

  From the above results, it was confirmed that triethanolamine can be effectively decomposed by adjusting the pH in two stages. As described above, the pH of the first stage is adjusted to 8 to 10, preferably 8.5 to 9.5, and the pH of the second stage is 4 to 6, preferably 4.5 to 5. It was confirmed that the adjustment in the range of .5 was good.

  In particular, the pH adjustment at the first stage shows that pH 9 is optimal when comparing the results of Example 1 and Comparative Examples 1-5. In addition, it was confirmed that the pH adjustment at the second stage was optimum when compared with the results of Example 1 and Comparative Examples 6-7.

Claims (4)

  An oxidant is added to a waste solution containing triethanolamine, the pH of the waste solution is adjusted to the alkaline region, and the pH of the waste solution is adjusted to the acidic region when the oxidation-reduction potential does not decrease. Treatment method for ethanolamine-containing waste liquid.   The said alkali area | region is the range of pH8-10, The processing method of the triethanolamine containing waste liquid of Claim 1 characterized by the above-mentioned.   The said acidic area | region is the range of pH 4-6, The processing method of the triethanolamine containing waste liquid of Claim 1 or Claim 2 characterized by the above-mentioned.   The adjustment from the alkaline region to the acidic region is that when the silver-silver chloride electrode is used as a reference electrode, the redox potential does not decrease from any potential within the range of 730 to 800 mV. The processing method of the triethanolamine containing waste liquid of any one of Claims 1 thru | or 3 characterized by the above-mentioned.