WO2005113453A1

WO2005113453A1 - Photocatalytic de-emulsification

Info

Publication number: WO2005113453A1
Application number: PCT/EP2005/052184
Authority: WO
Inventors: Christian Sattler; Karl-Heinz Funken; Christian Jung; Lamark De Oliveira
Original assignee: Deutsches Zentrum für Luft- und Raumfahrt e. V.
Priority date: 2004-05-21
Filing date: 2005-05-12
Publication date: 2005-12-01
Also published as: EP1756011A1; DE102004025007B4; DE102004025007A1

Abstract

The invention relates to a method for photocatalytic de-emulsification with the aid of iron ions. The invention relates to a method for the de-emulsification of aqueous organic emulsions. Said method is characterised by the following steps a) addition of an oxidant and an iron compound containing Fe <2+ >or Fe <3+ >ions to an aqueous organic emulsion with a pH value = 5, b) irradiation of the emulsion with UV and/or VIS Light and c) deposition of the formed organic phase.

Description

Photocatalytic emulsion gap α

The invention relates to a method for photocatalytic emulsion cleavage using iron ions.

Emulsions are used in many areas of technology. Especially for the disposal of used emulsions, they are often broken down into their components.

Emulsions are usually broken down either chemically by quantitative addition of strong electrolytes such as acids or salts, thermally by distillation or evaporation or by membrane technology (ultrafiltration). The use of strong electrolytes in chemical emulsion splitting can lead to high salt loads in the waste water and means a high consumption of these electrolytes.

The Photo-Fenton oxidations have not previously been used for emulsion splitting, but have already been used, for example, in the treatment of waste water in the textile industry. A successful overview of the use of Photo-Fenton oxidation for the treatment of wastewater can be found in Advances in Environmental Research 8 (2004) 553-597. The use of Photo-Fenton Oxidation especially for waste water from the textile industry is described in Water Research 36 (2002) 2703-2710. The treatment of waste water in the prior art aims at a quantitative destruction of the organic Compounds and the associated quantitative use of hydrogen peroxide and possibly also iron salts.

No. 5,266,214 A describes the treatment of waste water with the Photo-Fenton oxidation. In the process described, the organic impurities are quantitatively broken down by the photo-fenton oxidation, the concentration of H ₂ 0 ₂ having to be at least twice as high as that of the organic impurities. Furthermore, an additional step for the production of iron oxalate is necessary in the process described.

DD 48573 A describes a two-stage process for emulsion splitting, in which in a first step the emulsion is broken up by adding a salt and then in a second step separate from it, post-oxidation is necessary.

The publication "Integrated photocatalytic waste water recycling in textile finishing" by Sattler et al. In the conference volume of the "3rd International Conference on Oxidation Technologies for Water and Waste Water Treatment", May 2003, describes the treatment of waste water in the textile industry with the help of the photo -Fenton Reaction: In the described process, the machine oils contaminating the washing water are quantitatively destroyed, the hydrogen peroxide is used quantitatively and the iron is not recycled.

In order to remove organic constituents from emulsions using the Photo-Fenton reaction, the quantitative use of hydrogen peroxide was previously necessary. So far, the iron had to be in one The amount added was sufficient to quantitatively destroy the organic compounds. Iron could only be removed from the emulsion by precipitation with lye, which led to a high salt load and possibly a pH value that was incompatible with the rest of the process, and it was previously not possible to recycle it in a simple way.

Common methods for emulsion splitting are the evaporation of a liquid, the removal of a phase by salting out, mechanical action, addition of electrolyte and discharge at electrodes.

The object of the present invention is therefore a process for the cleavage of aqueous-organic emulsions without the quantitative (stoichiometric) use of cleavage reagents previously required. Another object of the present invention is to purify organically contaminated wastewater not by quantitatively breaking down the total amount of these contaminants but by separating these organic contaminants.

The above object is achieved in a first embodiment by a process for the cleavage of aqueous-organic emulsions characterized by process steps a) adding an oxidizing agent and an iron compound containing Fe ²⁺ or Fe ³⁺ ions to the emulsion with a pH value of <5, b) irradiating the emulsion with UV and / or VIS light, and c) separating the organic phase formed. The present invention represents a significant improvement over the previously used methods for emulsion splitting, since the use of chemicals can be significantly reduced by using photons as an energy source. The selective destruction of the surface-active substances by a Photo-Fento reaction is thus the core of the present invention. Iron ions are added to the emulsion and the pH is adjusted to <5, in particular <4. Under these conditions, the aqueous and organic phases can be rapidly split. The phases separate in particular at a temperature of more than 50 ° C. within a period in the range from 1 to 20 minutes and can be separated using a separator. When the emulsion is irradiated with light, the organic substances in the water are oxidized by the hydroxyl radicals formed in situ and / or the photochemical cleavage of iron complexes and / or the formation of other / further reactive intermediates. Surprisingly, it was found that emulsifiers or surfactants are preferably attacked in this treatment and lose their surface-active effect. The main oily contaminants are attacked much more slowly and can separate out as an organic phase. In this process, chemicals are no longer added stoichiometrically as flocculants or cracking aids, but rather catalytically or sub-stoichiometrically.

The present invention thus differs from the prior art primarily in that essentially no constituents in the aqueous solution, such as toluene or benzene, are destroyed, but rather emulsions are split where the oil-containing component is dispersed in a dispersed oil-containing phase Dispersant water is present. Furthermore, it was not obvious to a person skilled in the art to split an emulsion by means of a photochemical reaction, since emulsions have a different refractive index and higher turbidity (they usually appear milky white) than aqueous solutions contaminated with organic substances due to the oil droplets present.

The use of iron compounds such as iron hydroxide, iron oxide, iron chloride, iron sulfate, iron oxalate, iron chlorate and / or iron perchlorate has proven to be particularly advantageous. The use of iron sulfate has proven to be particularly advantageous since, as in the case of iron oxalate, for example, the iron salt does not have to be produced in an additional step. Both iron (II) and iron (III) can be used as raw material in this process, since iron (II) can easily be oxidized to iron (III) under the aforementioned conditions of the process.

In contrast to the cited prior art, significantly fewer iron ions and peroxide are required in the present invention.

In particular, the iron compound can be used at a concentration of up to 5% by weight of the concentration of the TOC (total organic carbon) present in the emulsion. Surprisingly, the iron compound in connection with the radiation and the peroxide was able to split the emulsion at a concentration of up to 5% by weight. This could be due to the fact that the emulsifiers and / or surfactants have a higher percentage of CN and C-0 bonds in the Compared to paraffins and oils. These bonds are obviously more easily attacked by the Photo-Fenton reaction.

A peroxide in the abovementioned is preferred as the oxidizing agent. Process, particularly preferably hydrogen peroxide, because this is particularly easy to handle and is readily available. Alternatively, however, other peroxides such as sodium peroxide or silicon peroxide can also be used, as can the perborates, percarbonates and persulfates customary in detergent technology.

According to a preferred embodiment, the emulsion is split at a temperature in the range from 0 to 100 ° C., in particular in a range from 50 to 100 ° C., and very particularly in a range from 80 to 100 ° C. Above 100 ° C one would reach the range of a thermal emulsion splitting process, since this is the boiling point of water. The lower limit of 0 ° C results from the freezing point of water, while the preferred lower limits 50 and 80 ° C result from the fact that, at these temperatures, the emulsion splits particularly quickly on the one hand, and the organic molecules with a on the other short or even no delay or activation period.

The irradiation is preferably carried out with a UV-VIS light source which is selected from the group discharge lamp, incandescent lamp, sun, in particular a medium-pressure mercury lamp. This has proven to be particularly effective in known Photo-Fenton processes due to the special spectrum and the intensity of the lighting. The process is particularly advantageously characterized in that the iron compound which accumulates in the organic phase is withdrawn from the aqueous phase and then removed from the organic phase, and then optionally fed back to the partially or completely untreated emulsion. During the experiments preceding this invention it was surprisingly found that, despite their polar nature, the iron compounds accumulate primarily in the organic phase. As a result of this, the iron can be removed from the aqueous phase relatively easily by separating the organic phase in the last step of the process. On the one hand, this has the advantage that the otherwise usual high salt load in the wastewater is avoided by precipitation of the iron compound as hydroxide, and on the other hand that the iron can be recycled by removing it from the organic phase and then feeding it back into the emulsion ,

In order to make the separation of the iron compound from the aqueous phase particularly simple, it has surprisingly turned out to be particularly advantageous that an oil, in particular about 1 g / l, is added to the untreated emulsion to separate the iron compound. Preference is given to using oils that are particularly difficult to degrade due to the Photo-Fenton process. This can guarantee a minimum amount of organic substances in the emulsion and thus transport of the iron compound. Design example:

The process was tested on wastewater from curtain production. These contained preparation oils and non-ionic surfactants as emulsifiers. To make it easier to check reproducibility, model wastewater with the same composition was also treated in the laboratory.

An Enviolet ^® reactor from ack aqua concept GmbH was used. The emulsion cleavage is carried out as follows. FeS0 ₄ heptahydrate was added as a catalyst in a concentration of 50 to 100 mg / l of the emulsion. After adding 0.01 g / l to 0.1 g / l H ₂ O ₂ , the solution was irradiated with a commercially available mercury vapor lamp. Medium pressure mercury lamps with an output of 125W - 12000 W and an emission maximum of 254 nm were used as the light source. The heat radiation from the light source is used to heat the emulsion. After a treatment time of a few minutes, the phases separated and could be separated using a conventional oil separator. Different biodegradable fats and oils of different chain lengths (C10 - C40) were examined as model substances. The emulsions were kept stable by using conventional surfactants. Sample volumes of 0.8 I - 3000 I with a TOC content of> 1000 mg / 1 were irradiated. The volume-related output of the lamps was 4 - 200 W / 1. Fig. 1 shows that no decrease in TOC in the aqueous phase can be observed at neutral pH (points). The emulsion does not separate. Even raising the temperature without using a Catalyst did not result in segregation, and even lowering the pH without using the photocatalyst does not result in segregation. This could only be observed at pH values ≤ 5, especially at pH 3 and the presence of the photocatalyst / oxidizing agent system and under radiation (squares).

During the treatment, the iron ions were simultaneously enriched in the organic phase. This effect could be followed spectroscopically. This enabled the separation to be checked and the process to be easily regulated.

The speed and the course of the emulsion cleavage depended strongly on the reaction temperature apart from the pH value. In contrast, the catalyst concentration could be varied within a wide range without the degradation rate being changed in a relevant manner. FIG. 2 shows that at a temperature of 30 ° C. after 25 min, a spontaneous drop in the TOC was observed both at a catalyst concentration of 50 mg / l and at 200 mg / l. This was because the aqueous and organic phases separated. When the reaction temperature increased, the emulsion cleavage split earlier. So you could observe the cleavage after 10 min at 60 ° C. The cleavage started spontaneously at 90 ° C. However, when the reaction temperature was increased, it was observed that the TOC did not drop as quickly as at low temperatures. This is because the water solubility of the organic substances is better at higher temperatures. The effects of emulsion cleavage and photocatalytic oxidation were therefore superimposed here. A reduction in TOC of 70- 80% can be observed after 30 min as long as the pH remained adjusted as described above.

Claims

claims

1. Process for the cleavage of aqueous-organic emulsions characterized by the process steps a) adding an oxidizing agent and an iron compound containing Fe ²⁺ or Fe ³⁺ ions to the emulsion with a pH of <5, b) irradiating the Emulsion with UV and / or VIS light, and c) separating the organic phase formed.

2. The method according to claim 1, characterized in that iron hydroxide, iron oxide, iron chloride, iron sulfate, iron oxalate, iron chlorate and / or iron perchlorate is used as the iron compound.

3. The method according to claim 1 or 2, characterized in that the iron compound is used in a concentration of up to 5% by weight based on the concentration of the TOC (total organic carbon) present in the emulsion.

4. The method according to any one of claims 1 to 3, characterized in that a peroxide, in particular hydrogen peroxide, is used as the oxidizing agent.

5. The method according to any one of claims 1 to 4, characterized in that the emulsion is split at a temperature in the range from 0 to 100 ° C.

6. The method according to any one of claims 1 to 5, characterized in that the irradiation with a UV light source carries out, which is selected from the group discharge lamp, incandescent lamp, sun, in particular medium pressure mercury lamps.

7. The method according to any one of claims 1 to 6, characterized in that the iron compound accumulating in the organic phase is removed from the aqueous phase and then removed from the organic phase, then optionally fed back to the partially or completely untreated emulsion.

8. The method according to any one of claims 1 to 7, characterized in that an oil, in particular about 1 g / l, is added to separate the iron compound from the aqueous phase.