CH686571A5 - Fast catalytic photo-oxidn. of organic cpds. in industrial waste liquor - Google Patents

Abstract

Catalytic photo-oxidn. of industrial waste liquor contaminated with organic cpds. (I) with H2O2 in the presence of Fe-III cpds. uses the Fe-III cpd. in the form of a solid Fe2O3 catalyst deposited on a support and is carried out in visible light at temps. up to 70 deg C. Also claimed is a catalyst of finely divided Fe2O3 immobilised on bentonite.

Description

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CH 686 571 A5

description

The invention relates to a process for the catalyzed photooxidation of at least partially soluble or emulsifiable organic impurities in waste water by means of immobilized iron (IIi) compounds.

It particularly concerns the complete mineralization of industrial organic contaminants to CO2 by hydrogen peroxide in the presence of Fe203 on bentonite and visible light, the Fe203 solid catalyst and its use in this oxidation process.

An extensive state of the art is known about the oxidation of contaminated water with iron (II) catalysts. For example, DE 2 703 267, DE 2 927 911, DE 3 840 823 and CH 613 917 describe soluble iron salts as catalysts for the oxidation of the contaminants, which takes place without exposure to light and not to total decomposition to CO2.

DE 2 729 760 protects in particular titanium oxide, zinc oxide and silicon dioxide as solid catalysts for the oxidative treatment of impurities with oxygen-containing gases and UV light. DE 4 026 831 claims soluble iron-III salts alone or together with TÌO2 as a catalyst for waste water oxidation.

The most important disadvantage of the known methods lies in the contamination of the at least partially purified wastewater with residues of the soluble iron salts or their flocculation products or with only partially degraded or oxidation products of the organic impurities. This is particularly demonstrated for phenolic impurities in US 4,861,484 and applies in particular to pollutant loads in industrial waste water which are well above 100 ppm total organic carbon.

The task was therefore to improve the catalyzed oxidative purification of industrial waste water with a pollutant content of substantially more than 100 ppm TOC and to provide a cheap, non-toxic and reusable catalyst.

This object is achieved by the method according to claim 1, the catalyst according to claim 9 and the use of the catalyst according to claims 10 and 11.

It is solved in particular by a process with a heterogeneous iron catalyst made from finely divided iron III oxide, which is immobilized on a support, which is preferably a bentonite.

The particular advantage of this process lies in the complete degradation of the carbon content of the pollutants to CO2 at temperatures below 70 ° C in visible light in less than 2 hours, preferably less than 30 minutes, even for substituted phenolic impurities such as nitrophenol and chlorophenol that are difficult to degrade.

Another advantage is the reusability of the catalyst.

The solid catalyst used according to the invention advantageously has an iron content of 0.1 to 5 mmol, preferably 0.3 to 3 mmol and particularly preferably 1 to 2 mmol of iron per gram of catalyst and is used in amounts of 10 to 1000 g, preferably 50 to 500 g and particularly preferably 150 up to 350 g per mole of impurity.

1 to 50 moles of hydrogen peroxide per mole of organic impurities were advantageously used for the process according to the invention, 1 to 30 moles being preferred and 10 to 25 moles being particularly preferred.

Unexpectedly, degradation begins in the light at 20 ° C, but not in the dark. The process according to the invention is used at a maximum of 70 ° C., preferably between 25 and 60 ° C., for industrial applications with loads significantly above 2000 ppm TOC, a synergistic effect occurring under the simultaneous action of visible light.

The catalyst according to the invention is therefore an extremely finely divided iron-II-oxide deposited on bentonite. The iron content of the catalyst is between 0.1 and 5 mmol Fe / g catalyst, preferably 0.3 to 3 mmol iron and particularly preferably 1 to 2 mmol iron per gram catalyst.

The use of iron III oxide on bentonite as a catalyst in the photo-oxidative degradation by hydrogen peroxide enables complete mineralization even of difficult-to-decompose organic contaminants in industrial wastewater at temperatures after a maximum of 70 ° C under the influence of visible light, whereby the combination of Catalyst and visible light leads to a synergistic effect.

The process according to the invention is exemplified by 4-nitrophenol and 4-chlorophenol. The total degradation of the carbon of this compound to CO2, the so-called mineralization, is represented by reaction equations I and II.

For the technical application of the method according to the invention, the total amount of organic contamination can be roughly determined by an analytical quick determination.

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CH 686 571 A5

+ 7 02

6 CO2 + HNO3 + 2 H2O

+ 6.5 O2

6 CO2 + HCl + 2 H2O

II

Examples

Iron oxide bentonite catalyst

250 ml of a 0.2 M NaOH solution are heated to 80 ° C. and added to 100 ml of a 0.01 M FeCs solution with vigorous stirring. After 20 minutes, the brown mixture is added very slowly, with intensive stirring, to a 0.05% suspension of Na bentonite in water, stirred for a further 24 hours, then left to stand for 2 to 3 days, decanted and the sediment then centrifuged.

For cleaning, wash twice with 0.02N H2SO4 or HCl and three times with water. The water is removed by rinsing twice with absolute ethanol, the catalyst is dried at room temperature, and then calcined, e.g. calcined step by step for 3 hours at 120 ° C., 3 hours at 300 ° C. and 5 hours at 500 ° C.

The analysis shows about 1.4 mmol Fe / g catalyst.

Mineralization of 4-nitrophenol or 4-chlorohenol

20 ml of a 0.01 M solution of the organic impurity with 0.6 ml of H2O2 (0.23 M) and 0.05 g of catalyst or unloaded bentonite are used in a closed vessel. The evolution of C02 is followed by gas chromatography on 500 jil samples from the gas volume of the reaction vessel (GOW MAC, Parapak column)

20 ml of 0.01 M solution contain about 1.4% nitrophenol or about 1.3% chorphenol.

30 ml CO2 corresponds to a complete mineralization of the impurity.

Fig. 1: Photooxidation of 4-nitrophenol Fig. 2: Oxidation of 4-nitrophenol in the dark Fig. 3: Photooxidation of 4-chlorophenol Fig. 4: Oxidation of 4-chlorophenol in the dark

1 contains 4 examples:

1. 10 ~ 2 M 4-nitrophenol, 0.24 M H2O2, 0.05 g Fe bentonite catalyst (dried at 120 ° C), T = 28 ° C

2. 10 "2 M 4-nitrophenol, 0.24 M H2O2, 0.05 g Fe bentonite catalyst (dried at 120 ° C), T = 60 ° C

3. IO "2 M 4-nitrophenol, 0.23 M H2O2, 0.05 g recycled Fe-bentonite catalyst (dried at 130 ° C), T = 65 ° C

4. 10 "2 M 4-nitrophenol, 0.24 M H2O2, 0.05 g bentonite catalyst not loaded with Fe (dried at 120 ° C), T = 28 ° C

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2 contains 2 examples:

1. IO "2 M 4-nitrophenol, 0.24 M H2O2, 0.05 g Fe bentonite catalyst (dried at 120 ° C), T = 65 ° C

2. 10 ~ 2 M 4-nitrophenol, 0.24 M H2O2, 0.05 g non-Fe loaded bentonite catalyst (dried at 120 ° C), T = 65 ° C

3 contains 3 examples:

1. 10 "2 M 4-chlorophenol, 0.23 M H2O2, 0.05 g Fe bentonite catalyst (dried at 500 ° C), T = 26 ° C

2. 10 ~ 2 M 4-chlorophenol, 0.23 M H2O2, 0.05 g Fe bentonite catalyst (dried at 130 ° C), T = 65 ° C

3. 10_2 M 4-chlorophenol, 0.23 M H2O2, 0.05 g bentonite catalyst not loaded with Fe (dried at 500 ° C), T = 26 ° C

4 contains 2 examples:

1. 10 "2 M 4-chlorophenol, 0.23 M H2O2, 0.05 g Fe bentonite catalyst (dried at 500 ° C), T = 65 ° C

2. 10 ~ 2 M 4-chlorophenol, 0.23 M H2O2, 0.05 g bentonite catalyst not loaded with Fe (dried at 500 ° C), T = 65 ° C

Table 1:

pollution

Nitrophenol

Chlorophenol

Kataly

reaction

temperature

% Reduction

100% degradation in the light

° C

in min.

20 min.

50 min

100 min

+

+

60

75

-

-

<50

recycled.

+

65

100

-

-

20th

+

+

28

5

20th

40

> 200 *

-

+

28

0

<1

<1

-

+

-

65

42

65 *

78 *

> 200 *

-

-

65

<1

8th

25th

> 400 *

+

+

65

100

-

-

20th

+

+

26

<2

3rd

6

> 500 *

-

+

26

0

<1

<1

-

+

-

65

40

60

70 *

<200 *

-

-

65

<1

<1

4th

-

* = estimated

Table 1 summarizes the results of the examples. The results demonstrate the effectiveness of the bentonite loaded with one-Ill-oxide and the reaction temperature in the range 60/65 ° C compared to room temperature.

The catalyst has a very long lifespan and can be used for at least days or weeks, depending on the amount of contaminants in the wastewater. With relatively strongly acidic wastewater, which causes a gradual dissolution of Fe2C> 3, the lifespan naturally suffers from this effect.

The catalyst can be regenerated by washing, if no appreciable loss of iron has occurred, as described in the cleaning step of the catalyst preparation, first with acid and then with water and then, as described there with ethanol, removing the water, predrying the catalyst at room temperature and then calcined, e.g. gradually, as indicated there at 120 ° C, 300-C and 500 ° C.

If wastewater has been treated with relatively little contamination, the washing stages can often be saved and it is sufficient to dry and calcine the catalyst, as indicated in the cleaning stage of the catalyst production.

However, if there has been a noticeable loss of iron, especially if the iron content has dropped below 1 or even below 0.3 mmol of iron per gram of catalyst, the catalyst suspended in water is reacted with the reaction product of NaOH and FeCb as described in the first stage of the catalyst preparation treated and then further treated as described in the example for the production of the iron oxide bentonite catalyst, including the calcination.

The recycled catalyst shows practically unchanged effectiveness if the iron content is approximately the same as before.

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CH 686 571 A5

Claims (11)

Claims 1. A process for the catalytic photooxidation of industrial wastewater contaminated by organic compounds with hydrogen peroxide in the presence of iron-Ill compounds, characterized in that the iron-Ill compound is used in the form of an Fe2C> 3 solid catalyst deposited on a support and the Oxidation is carried out at temperatures up to 70 "C in visible light. 2. The method according to claim 1, characterized in that the carrier is a bentonite. 3. The method according to claim 1, characterized in that the solid catalyst has an iron content of 0.1 to 5 mmol Fe / g catalyst. 4. The method according to claim 1 or 2, characterized in that the solid catalyst is used in an amount of 50 to 500 g / mol total amount of the organic impurities. 5. The method according to any one of the preceding claims, characterized in that the hydrogen peroxide is used in a concentration of 1 to 50 mol / mol total amount of the organic impurities. 6. The method according to any one of the preceding claims, characterized in that the oxidation is carried out at temperatures from 20 to 70 ° C. 7. The method according to any one of the preceding claims, characterized in that the oxidation is carried out at temperatures of 25 to 65 ° C. 8. The method according to any one of the preceding claims, characterized in that the photooxidation leads to complete mineralization. 9. A catalyst for carrying out the process according to claim 1 for mineralizing organic compounds in industrial waste water by photooxidation with hydrogen peroxide consisting of finely divided iron III oxide immobilized on bentonite. 10. A catalyst according to claim 9, characterized in that its iron content is between 0.1 and 5 mmol Fe / g catalyst. 11. Use of iron III oxide on bentonite as a catalyst in the process according to claim 1. 5