Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2000-06-05
2001-09-04
Lambkin, Deborah C. (Department: 1626)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000
Reexamination Certificate
active
06284940
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method for decomposing a halogenated organic compound, and more particularly, to a method for decomposing a halogenated organic compound contained in soil such as polychlorodibenzo-p-dioxins (PCDD), polychlorodibenzofurans (PCDF), and coplanar polychlorobiphenyl (PCB) (These materials are hereinafter generally referred to as “dioxins”.) with good operation property and high efficiency.
In incineration plants such as those for municipal waste, dioxins precursors (precursors for the dioxins) including organic compounds such as phenols, benzene and acetylene, chlorinated aromatic compounds such as chlorophenols and chlorobenzenes, and chlorinated alkyl compounds are formed during incineration. When flyash coexists with the dioxins precursors, the precursors change to the dioxins under the catalytic action of the flyash, and the generated dioxins exist in incineration ash. Also, the generated dioxins sometimes contaminate the incineration plant and ambient soil therearound.
Conventional technologies for decomposing dioxins in soil include a method using supercritical state water, a method using ozone or ultraviolet rays, a method by heating, a method utilizing special fungi such as “Maitake” or “Enokidake” or wood-rotting bacteria, and a method using a catalyst.
Conventional methods for decomposing dioxins contained in flyash are as follows;
(1) To keep dioxins-containing flyash for 1-2 hours at a temperature between 320 and 400° C. under a reductive atmosphere such as nitrogen (for instance, 2 hours at 320° C. or 1-1.5 hours at 340° C.) (Hagenmaier process, “ORGANOHALOGEN COMPOUNDS Vol. 27 (1996)” p.147-152);
(2) Heating dioxins-containing flyash at 300-500 ° C. under the existence of a dioxins formation inhibitor (JPA 4-241880).
However, all of the above-mentioned methods for decomposing dioxins contained in soil have problems in decomposition efficiency or treating operation. Especially, the method using ultraviolet rays offers a low decomposition efficiency as the rays are effective only at the irradiated surface. Also, the method using catalysts has difficulties in treating operation. The method by heating has problems of recombination and evaporation of dioxins, and the method using bacteria has low decomposition efficiency.
The methods described in the above items (1) and (2) for decomposing dioxins contained in flyash have a drawback that their high treatment temperature and long treatment time require much energy and high cost. Especially, in the above mentioned method (1), it is required to carry out the treatment under a reductive atmosphere such as nitrogen gas, bringing about complexity and a high cost.
OBJECT AND SUMMARY OF THE INVENTION
A first object of the present invention is to provide a method for decomposing a halogenated organic compound which can effectively decompose the dioxins in soil.
A first aspect of the method for decomposing a halogenated organic compound is for achieving the first object. According to the method, halogenated organic compound reacts under heating with one or more amino acid compounds selected from a group of amino acids, polyamino acids, amino acid salts, and polyamino acid salts.
In the first aspect method, dehalogenation occurs by the reaction of the amino acid compound with halogens such as chlorine in dioxins, thus achieving the decomposition of dioxins.
As the amino acid compound does not vaporize under a reaction temperature effective for decomposition of dioxins, it can be added and mixed of in liquid or solution form, with object to be treated such as soil, and can be easily heated and brought into reaction.
A second object of the present invention is to provide a method for decomposing a halogenated organic compound, in which soil or other media containing halogenated organic compounds are treated with amino acids, salts thereof, polyamino acids, or salts thereof to effect the decomposition of the halogenated organic compounds while preventing the lumping and deposition of treated materials, thus enabling an effective decomposition of halogenated organic compounds with favorable operation properties.
A second aspect of the method for decomposing a halogenated organic compound is for achieving the second object.
According to the method, one or more amino acid compounds selected from a group consisting of amino acids, polyamino acids, and amino acid salts are added to and mixed with materials containing halogenated organic compounds, followed by addition and mixing of a water-absorbing agent and subsequent heating of the resultant mixture.
While the material such as soil easily forms lump or deposit, the water-absorbing agent added and mixed prior to the heating step absorbs water, so that the material assumes a fine granule form with non-sticking and free flowing nature.
Thus, lumping and deposition of the material are prevented, whereby the material is mixed and, handled easily with giving a high heating efficiency and a high decomposition efficiency of the halogenated organic compounds.
The method according to the second aspect is especially effective for the treatment of soil contaminated with dioxins which is particularly easy to form lump and deposit. As the water-absorbing agent, quicklime (calcium oxide) is particularly suitable.
A third object of the present invention is to improve a process for decomposing a halogenated organic compound in which at least one of the amino acid compounds is added to and mixed with solid material, such as soil contaminated with halogenated organic compounds, and if desired followed by adding and mixing of a water-absorbing agent, and subsequent heating of the resultant mixture to decompose the halogenated organic compounds. The third object is to provide a method which enables an effective mixing of the decomposing agent with solid material, and an effective mixing of the water-absorbing agent with the mixture of solid material and the decomposing agent, thus providing a decrease of water content during the mixing of the decomposing agent, an improvement of handling properties of the mixture, and a decrease of requirements for decomposing agent or water-absorbing agent by an improvement of addition effect thereof, thus in overall enabling an effective decomposition of halogenated organic compounds.
Third and fourth aspects of the method for decomposing a halogenated organic compound are for achieving the third object.
The method of the third aspect comprises a mixing step in which the amino acid compound is added to and mixed with solid material contaminated with halogenated organic compounds, and a heating step in which the mixture from the mixing step is subjected to a heating treatment to decompose halogenated organic compounds. The mixing step uses a mixing apparatus comprising a mixing media such as plurality of cylindrical rods contained in a drum which vibrates while rotating around a horizontal axis, achieving a homogeneous mixing as a result of mutual collision between the solid material and the rods induced by the vibration.
The method of the fourth aspect comprises a first mixing step in which the amino acid compound is added to and mixed with solid material contaminated with halogenated organic compounds, a second mixing step in which a water-absorbing agent is added to and mixed with the mixture from said first mixing step, and a heating step in which the mixture from said second mixing step is subjected to a heating treatment to decompose halogenated organic compounds. The first mixing step uses a mixing apparatus comprising a mixing media such as plurality of cylindrical rods contained in a drum which vibrates while rotating around a horizontal axis, achieving a homogeneous mixing as a result of mutual collision between the solid material and the rods induced by the vibration.
When the amino acid compound is added to the solid material to be treated such as soil and mixed according to the method of the third and fourth aspects, the solid material and the amino acid compound are mixed
Hashimoto Masanori
Suzuki Katsuaki
Kanesaka & Takeuchi
Kurita Water Industries Ltd.
Lambkin Deborah C.
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