JP2005058974A - Method for detoxifying dioxins in incineration ash - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently detoxifying dioxins in incineration ash in a calm condition. <P>SOLUTION: In this method for detoxifying dioxins in the incineration ash, the ash containing dioxins is subjected to acidic treatment, and then allowed to react with 2-propanol in the presence of a hydrogen activating catalyst and an alkaline substance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for detoxifying dioxins in incineration ash.

  Dioxins discharged into the environment from municipal waste incineration facilities have become a social problem, and in recent years their emission regulations have been strengthened. Dioxins are extremely toxic, are chemical substances that affect the human body even in very small amounts, and are chemically very stable, so once they enter the environment, they may remain and accumulate for a long time. . In particular, the incineration ash discharged from incineration facilities contains a large amount of dioxins, and therefore, the development of the treatment technology is energetically advanced. As main treatment methods for dioxins in incinerated ash, a melt treatment method, a supercritical water method, a catalyst treatment method, and the like have been proposed so far. The melt treatment method is a method that decomposes dioxins contained in the incineration ash by heating the incineration ash under a high temperature condition of 1200 ° C or higher. However, in order to create a high temperature condition, a large amount of energy must be input. Processing costs will increase. The supercritical water method is a method of hydrolyzing dioxins in the incinerated ash by setting water to a supercritical state of 374 ° C. and 218 atm or more, but it requires a high temperature and a high pressure, so there is a problem in safety. Another disadvantage is that it is difficult to increase the size of the apparatus. The catalyst treatment method is a method in which incinerated ash is heated to about 400 ° C. to gasify dioxins to expel them into the gas phase, and the gasified dioxins are brought into contact with the catalyst to oxidize and decompose. Since it is necessary to heat to about ˜400 ° C., development of a catalyst that operates at a lower temperature is desired.

According to Japanese Patent Application Laid-Open No. 2001-340488 (Patent Document 1), in order to detoxify dioxins, the dioxins are reacted with a secondary alcohol in the presence of a hydrogen activation catalyst such as palladium and an alkaline substance. A method of reacting has been proposed.
According to this method, dioxins can be dechlorinated by dechlorinating the chlorine contained in them under mild conditions, but as a detoxification treatment method for dioxins contained in incinerated ash, It was still not satisfactory.

JP 2001-340488 A

  An object of the present invention is to provide a method for efficiently detoxifying dioxins in incineration ash under mild conditions.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted an acid treatment on incinerated ash containing dioxins and then reacting with 2-propanol in the presence of a hydrogen activation catalyst and an alkaline substance. The present inventors have found that dioxins in the incinerated ash can be easily dechlorinated and rendered harmless, thereby completing the present invention.

  That is, according to the present invention, the incineration ash containing dioxins is acid-treated and then reacted with 2-propanol in the presence of a hydrogen activation catalyst and an alkaline substance. A method is provided.

  According to the present invention, dioxins contained in incineration ash can be made harmless efficiently under mild conditions.

  Incinerated ash containing dioxins, which are the detoxified substances of the present invention, includes both fly ash and furnace ash. The dioxins in this case include various conventionally known ones such as chlorinated dibenzo-para-dioxins (PCDDs), chlorinated dibenzofurans (PCDFs), coplanar-PCBs (Co-PCBs), and the like.

  Various conventionally known catalysts can be used as the hydrogen-activated metal catalyst used in the present invention. Such include transition metals, particularly Group 8 metals of the Periodic Table, preferably platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), nickel and the like. The hydrogen activated metal is used in the form of a metal compound such as an oxide in addition to a metal.

The hydrogen-activated metal catalyst used in the present invention can be preferably used as a supported catalyst supported on a carrier. As the carrier, conventionally known various porous materials such as silica gel (silica), alumina, silica-alumina, magnesia, titania, zirconia, zeolite, sepiolite, clay, activated carbon and the like are used. In the present invention, it is particularly preferable to use silica gel, alumina, activated carbon or the like.
In a supported catalyst in which a hydrogen-activated metal is supported on a carrier, the amount of the supported metal is 0.1 to 20% by weight, preferably 0.5 to 10% by weight, based on the total catalyst.

  As the alkaline substance used in the present invention, any substance can be used as long as it can neutralize hydrogen chloride. Such things include lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, calcium hydroxide, magnesium hydroxide and the like. In the present invention, sodium hydroxide or potassium hydroxide that is inexpensive and has high solubility in 2-propanol is particularly preferable. The alkaline substance is used in the form of powder or 2-propanol solution, but is preferably used in the form of 2-propanol solution. In this case, in the 2-propanol solution, the concentration of the alkaline substance is 0.05 to 5% by weight, preferably 0.1 to 2% by weight.

  The acid treatment of incineration ash containing dioxins can be carried out by bringing the incineration ash into contact with an acidic aqueous solution. In this case, as the acid, in addition to inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, organic acids such as formic acid, acetic acid, citric acid, and organic sulfonic acid can be used.

  In the acidic aqueous solution used for acid-treating the incineration ash, the concentration of the acid contained in the solution is 0.1 to 10 mol / L, preferably 1 to 5 mol / L. Examples of the contact method between the incinerated ash and the acidic aqueous solution include a spray method and a dipping method. Although this contact time changes with kinds of incineration ash and the kind of acidic aqueous solution, it is 1 to 24 hours normally, Preferably it is 2 to 12 hours. Moreover, the contact temperature is about normal temperature-about 50 degreeC. By this acid treatment, dioxins contained in the incineration ash are easily dissolved in 2-propanol.

  The usage ratio of the acidic aqueous solution is usually 100 to 2000 parts by weight, preferably 200 to 1000 parts by weight, per 100 parts by weight of incinerated ash.

The method of the present invention is performed by adding acid-treated incineration ash, a catalyst and an alkaline substance to 2-propanol and stirring. The proportion of the incinerated ash per 100 parts by weight of 2-propanol is 0.1 to 50 parts by weight, preferably 1 to 20 parts by weight, and the proportion of the catalyst is 0.01 to 10 parts by weight, preferably 0. 0.1-5 parts by weight, and the proportion of the alkaline substance is 0.05-5 parts by weight, preferably 0.1-2 parts by weight.
The reaction temperature is from room temperature to 82 ° C (the boiling point of 2-propanol), preferably from 30 to 50 ° C.
The reaction atmosphere may be air, but it is desirable to carry out in an inert gas atmosphere such as nitrogen in consideration of safety.

The operation in the present invention will be described below. Dioxins contained in the incinerated ash are extracted into 2-propanol during stirring, and at the same time, react with 2-propanol by the action of a catalyst. Extraction of dioxins into 2-propanol is facilitated by pretreating the incinerated ash with an acid such as hydrochloric acid. This is because the carbonate present in the incineration ash is removed from the incineration ash by converting the carbonate to CO ₂ , the sulfide to H ₂ S, and the metal cation to a soluble chloride. This is thought to be because the extraction efficiency is improved. The decomposition of dioxins in the present invention is considered to proceed according to the reaction formula shown below. Here, as an example, dioxins are dibenzo-para-dioxin monochloride (MCDD) and the alkali compound is sodium hydroxide.

One molecule of 2-propanol and two active hydrogen species (H ^* ) are produced from one molecule of 2-propanol on the catalyst. Further, on the catalyst, chlorine in the dioxins undergoes a substitution reaction with the active hydrogen species, and the dioxins are dechlorinated to produce dibenzo-para-dioxin (DD) and hydrogen chloride. Hydrogen chloride is neutralized with sodium hydroxide to produce sodium chloride and water. In the case of dioxins containing a plurality of chlorines, the dechlorination reaction proceeds sequentially, and finally all chlorine is replaced with hydrogen and rendered harmless.
As described above, the method for detoxifying diiocins in incineration ash according to the present invention simultaneously performs solvent extraction with 2-propanol and detoxification by reaction with 2-propanol.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Comparative Example 1
Add 2.0 g of incineration fly ash containing dioxins obtained from a garbage incineration facility to 2-propanol (60 ml) in which sodium hydroxide (0.24 g) is dissolved, and further support 5% by weight of palladium on alumina. The catalyst (Pd / Al ₂ O ₃ ) 0.20 g was added, and the mixture was allowed to react at 82 ° C. for 8 hours while stirring with a stirrer in a flask equipped with a condenser tube at the top. The concentration of dioxins (4 to 8 chlorides of PCDDs and PCDFs and Co-PCBs) in the incineration fly ash before and after the reaction was analyzed with a high resolution gas chromatograph-mass spectrometer. The total concentration of dioxins in the incineration fly ash was 2000 ng / g before the reaction, but decreased to 1400 ng / g after the reaction. Dioxins were not detected in the solution after the reaction.

Example 1
2.0 g of incineration fly ash containing dioxins obtained from a waste incineration facility was immersed in 2 mol / L hydrochloric acid for 3 hours, washed thoroughly with water, and dried at 110 ° C. for 3 hours. This incinerated fly ash was added to 2-propanol (60 ml) in which sodium hydroxide (0.24 g) was dissolved, and further, 0.20 g of a catalyst (Pd / Al ₂ O ₃ ) on which 5% by weight of palladium was supported on alumina. Was added, and the mixture was reacted at 82 ° C. for 8 hours while stirring with a stir bar in a flask having a condenser tube at the top. The concentration of dioxins (4 to 8 chlorides of PCDDs and PCDFs and Co-PCBs) in the incineration fly ash before and after the reaction was analyzed with a high resolution gas chromatograph-mass spectrometer. The total concentration of dioxins in the incineration fly ash was 2000 ng / g before the reaction, but decreased to 500 ng / g after the reaction. Dioxins were not detected in the solution after the reaction.
From this experimental result, it is clear that detoxification of dioxins can be greatly promoted by acid treatment of incinerated ash.

Claims (1)

  A method for detoxifying dioxins in incineration ash, comprising treating the incineration ash containing dioxins with acid and then reacting with 2-propanol in the presence of a hydrogen activation catalyst and an alkaline substance.