OXYDATION DES COMPOSES HALOGENES ORGANIQUES DANS LES EAUX USEES

OXIDATION OF ORGANIC HALOGEN COMPOUNDS IN WASTEWATERS

Abrégé anglais

Wastewaters containing organic halogen compounds are oxidized by reacting the
wastewaters with nitric acid at from 100 to 350°C under from 5 to 190 bar.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for oxidizing wastewaters containing organic halogen
compounds, which comprises reacting the wastewaters with nitric acid at from 100 to
350°C under from 5 to 190 bar.
2. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the organic halogen compounds are
dissolved in the wastewaters.
3. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the reaction is carried out at from 180 to
320°C.
4. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the reaction is carried out under from 30 to
150 bar.
5. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the reaction is carried out at from 250 to
300°C.
6. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the reaction is carried out under from 70 to
130 bar.
7. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the concentration of nitric acid in thewastewater is from 1 to 30% by weight.
8. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the oxidation is carried out at a pH 6.

9. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the reaction is carried out continuously.
10. A process for oxidizing wastewaters containing organic halogen
compounds as claimed in claim 1, wherein the reaction is carried out in a tubular
reactor.

Description

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I
The Oxidation of Organic Halogen Cr , - ' in Wastewaters
The present invention relates to a process for oxidizing v~t~vva.~ containing
organic halogen compounds at elevated ~ la~ucS and under elevated pressures withrlitric acid.
The removal of organically bound halogen from vva~ represents a
problem, especially when the organic halogen compounds are readily soluble in water.
These cnmro.m~ are very often removed from the water by adsorption onto active
carbon before the wastewater is subjected to a biological treatment. In this case,
disposal of the resulting active carbon is likewise a problem because inainrr~tinn
thereof must be carried out in such a way that no dioxin compounds can form, or a safe
landfill is necessary for the active carbon. These types of disposal of the active carbon
are very costly.
It is an object of the present invention to remedy the above-mentioned
a~lvall~.
We have found that this object is achieved by a novel and improved procesi for
oxidizing ~va~t~vva~ containing organic halogen ~nmr~lmfie which comprises reacting
the ~va.~t~vv..",l~ with nitric acid at from 100 to 350 C under from S to 190 bar.
The present process cam be carried out in the following way:
It is possible to add the amount of nitric acid necessary for breaking down
organic halogen cnmro~n~le in particular adsorbable organic halogen compounds
(AOX), of from I to 30% by weight, preferably from I to 20% by weight, p,~ .ulally
preferably from I to 10% by weight, to the wastewater to be treated in pressurized
containers at from l00 to 350 C, particularly preferably from 250 to 300 C, under from
5 to 190 bar, preferably from 30 to 150 bar, ~a ~h,ulally preferably from 70 to 130 bar.
The nitric acid which can be used is ~....,. ~.,~,. '..1 preferably from l0 to 70/0 by
weight aqueous nitric acid, IJa~ ,ulally preferably from 30 to 70% by weight technical
aqueous nitric acid.
The nitric acid may also already be present, owing to the synthesis, in sufficient
amounts in the wastewater and thus need not be metered in. It is also possible to use
impure waste acid.
Examples of suitable pressurized containers are tubular reactors or autoclaves

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connected in a cascade.
In a preferred ~lubvdil~ lL, the wastewater is conveyed by a pump through a
heat exchanger in which it is preheated to 220 C. SulJa~ u~ ly, the preheated
vva~t~ is heated, by directly feeding in 100 bar of stearn or by indirect heating, to
250-C. After the nitric acid has been adjusted to the c.-n~ rnt-~ti.-n necessary for AOX
breakdown in the wastewater at 250 C, the latter is conveyed through a reactor without
back-rnixing (eg. tubular reactor which has fittings and is lined with tantalurn or
zirconium). After a holdup time of 5 to 30 min, the reaction solution is subjected to
uuuut~ ,ull~llL cooling with the feed, and is d~,vlllu~ v.
For the continuous rmh~' ' of the process, it is possible and preferred to use
tubular reactors in which the flow of the liquid is adjusted so that there is no back-
mixing.
Examples
Example I
A wastewater which, besides other impurities, contained p~ lu~lllu~v~ul~onic
acid and vil~;LIuulllùlu acid and had a nitric acid content of 16 g/l was subjected to
oxidative treatment in a continuous system under the following conditions:
reaction L~ ,IaLul~ = 250~C, pressure = 75 bar, holdup time = 15 min
Analytical results for the oxidative treat~nent
Sample TOC AOX COD NCS DNCS
[ppm] [ppm] [ppm] [ppm] [ppm]
Feed 1690 6~0 1720 140 2400
Discharge 86 0.5 260 < I 12
Breakdown [%] 94.9 > 99 84.8 > 99 99.5
. .

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AOX = adsorbable organic halogen compounds,
COD = chemical oxygen demand,
NCS = p-nitrochlorosulfonic acid,
DNCS = 2,4-dinitrochloro acid
Example 2
A ~a~ which, besides other impurities, contained 1-amino-2-cbloro-4-
1,ydlu~~ 1"~ nl~n~ was subjected to oxidative treatment in a continuous system with
5% by weight HNO3 at 250 or 265 C urlder 75 bar with a holdup time of 15 min.
Analytical results for the oxidative treatment
Test TOC COD AOX
[ppm] [ppm] [ppm]
I
Feed 7400 19600 640
Discharge 1560 3840 110
Breakdown [%] 78.9 80.4 82.8
Feed 7800 18400 720
Discharge 1170 2270 130
Breakdown [%] 85 87.7 81.9
Test conditions 1: T = 250~C, p = 75 bar, holdup time = 15 min, 5% by weight
HNO3
Test conditions 2: T = 265 C, p = 75 bar, holdup time = 15 min, 5% by weight
HNO3

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Example 3
A wastewater from production of a color pigment, which, besides other impurities,
contained t~ a~lllulupllLllalic acid and tetrachloroph~h~ acid in solution as sodium
salts was treated with 5% by weight HN03 in a continuous system at 260 C under 80
bar.
Analytical results for the oxidative treatment
Sample TOC TCPA TCAM AOX
[ppm] [ppm] [ppm] [ppm]
Feed 2860 1070 5770 3200
Discharge 270 < 5 < 5 120
Breakdown [%] 90.6 > 99 > 99 96.3
TCPA = t~LIà~,lllulu~ dlic, acid
TCAM = tetrachlu,~,~,l,ll,,.l,..";i acid
Example 4
A wastewater which was loaded with the volatile llyl~u~bulls chloroform,
tetrachlu,ul~ , dichloroethane, trichloroethane and tetrachloroethane was mixed
with 5% by weight nitric acid and passed through a coiled tube under the conditions of
265 C and 80 bar with a holdup time of 15 minutes, preventing back-mixing by a
suitable flow }ate.

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AOX TOC C I
Feed mg/1 2465 615
Discharge mg/1 12 6 2400
Breakdown % 99.9 98.9
The example shows that the volatile aliphatic chlorohydrocarbons are virtually
Luall~iL~Li~ly eliminated and chlorine is recovered after the treatment as chloride,
within the accuracy of the ~ ,~c~ lL.