DE102004025007A1 - Photocatalytic emulsion splitting - Google Patents

Abstract

The invention relates to a process for photocatalytic emulsion cleavage with the aid of iron ions. The invention relates to a process for the cleavage of aqueous-organic emulsions, characterized by the process steps DOLLAR A a) adding an oxidizing agent and an iron compound having Fe.sup.2 + or Fe.sup.3 +.sup. Ions to form an aqueous-organic emulsion a pH of 5, DOLLAR A b) irradiation of the emulsion with UV and / or VIS light and DOLLAR A c) deposition of the organic phase formed.

Description

object The invention is a process for photocatalytic emulsion splitting using iron ions.

emulsions are used in many areas of technology. Especially for disposal of used emulsions they are often in their Components decomposed.

emulsions become common either chemically by quantitative addition of strong electrolytes like acids or salts, thermally by distillation or evaporation or else split by membrane technology (ultrafiltration). The use of strong Electrolytes in the chemical demulsification can lead to high salt load lead in the wastewater and means a high consumption of just these electrolytes.

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

US 5,266,214 A describes the treatment of waste water with the Photo-Fenton oxidation. In the process described, the organic impurities are quantitatively decomposed by the photo-Fenton oxidation, wherein the concentration of H ₂ O ₂ must be at least twice as high as that of the organic impurities. Furthermore, in the process described an additional step for the production of iron oxalate is necessary.

The Publication "Integrated photocatalytic waste water recycling in textile finishing "by Sattler et al. In the proceedings 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 method become the machine water contaminating the washing water quantitatively destroyed. The hydrogen peroxide is used quantitatively and the iron will not be recycled.

Around Organic components from emulsions with the help of Photo-Fenton To remove reaction, so far was the quantitative use necessary for hydrogen peroxide. The iron had so far in one Scope were added, which was sufficient to the organic Quantitatively destroy compounds. Iron could only through precipitation be removed with lye from the emulsion, resulting in high salt load and to one with the rest Process possibly incompatible pH value guided has not yet been recycled in a simple way.

task The present invention thus provides a method for the cleavage of aqueous-organic emulsions without the hitherto necessary quantitative (stoichiometric) use of Cleaving reagents. Another object of the present invention is in that, organically contaminated wastewater not by quantitative Degradation of the total amount of these impurities but by separation of these to clean organic contaminants.

• a) Zufügen eines Oxidationsmittels und einer Fe²⁺ – oder Fe³⁺ – Ionen aufweisenden Eisenverbindung zu der Emulsion mit einem pH – Wert von ≤ 5,
• b) Bestrahlen der Emulsion mit UV- und/oder VIS-Licht, und
• c) Abscheiden der gebildeten organischen Phase.

The above object is achieved in a first embodiment by a process for the cleavage of aqueous-organic emulsions characterized by the process steps

• a) adding an oxidizing agent and an Fe ²⁺ or Fe ³⁺ ion-containing iron compound to the emulsion having a pH of ≤ 5,
• b) irradiating the emulsion with UV and / or VIS light, and
• c) depositing the formed organic phase.

The present invention represents a significant improvement over the previously used methods for emulsion splitting, since the use of photons as an energy source, the use of chemicals can be significantly reduced. The emulsion is mixed with iron ions and the pH is adjusted to ≦ 5, in particular ≦ 4. Under these conditions, rapid cleavage of aqueous and organic phases can be achieved. The phases separate especially at a temperature of more than 50 ° C within a period in the range 1 to 20 min and can be separated via a separator. Upon irradiation of the emulsion 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 has been found that in this treatment emulsifiers or surfactants are preferably attacked and lose their surface-active action. The mainly existing oily impurities are attacked much slower and can be separated as an organic phase. The addition of chemicals in this process is therefore no longer stoichiometrically as flocculants or cleavage aids, but catalytically or sub-stoichiometrically.

When The use of iron compounds has proven particularly advantageous such as iron hydroxide, iron oxide, iron chloride, iron sulfate, iron oxalate, Iron chlorate and / or iron perchlorate exposed. The use ferric sulfate has been found to be particularly advantageous because not, as for example, iron oxalate, the iron salt in one additional step must be made. In this process can be used as raw material both iron (II) and iron (III) are used, since iron (II) in the aforementioned Conditions of the process easily be oxidized to iron (III) can.

Especially The iron compound can be concentrated at up to 5% by weight. the concentration of TOC present in the emulsion (total organic carbon = total organic carbon). Surprisingly was the iron compound in connection with the irradiation and the Peroxide already in a concentration of up to 5 wt .-% in the Able to split the emulsion. This could be due to that the emulsifiers and / or surfactants percentage a higher proportion of C-N and C-O bonds compared to paraffins and oils. These bonds are obviously made easier by the Photo-Fenton Reaction attacked.

Prefers is used as the oxidant peroxide in o.g. Procedure, especially preferably used hydrogen peroxide, as this is particularly easy to handle and readily available is. Alternatively, however, other peroxides such as sodium peroxide or silicon peroxide as well as the usual in detergent technology Perborates, percarbonates and persulfates.

According to one preferred embodiment the emulsion at a temperature in the range of 0 to 100 ° C, in particular in a range of 50 to 100 ° C, and especially split in a range of 80 to 100 ° C. Above 100 ° C you would in the range of a thermal process for emulsion splitting come because this is the boiling point of water. The lower limit from 0 ° C results from the freezing point of water, while the preferred Lower limits 50 or 80 ° C show that at these temperatures on the one hand the Emulsion splits particularly quickly, and on the other hand, the organic Molecules with a small or even no delay or activation period be reduced.

Preferably the irradiation is carried out with a UV-VIS light source, the selected is from the group discharge lamp, light bulb, sun, in particular is a medium pressure mercury radiator. This one has become known Photo-Fenton processes due to the special spectrum and intensity of illumination proved to be particularly effective.

Especially Advantageously, the method is characterized in that the iron compound which accumulates in the organic phase the aqueous Phase withdraws and then removed from the organic phase, then optionally the partial or completely feeds untreated emulsion again. During the this invention Previous experiments were surprisingly found that The iron compounds, despite their polar nature, especially in enrich the organic phase. This circumstance can do that Iron relatively easy by the deposition of the organic phase be removed in the last step of the process of the aqueous phase. On the one hand, this has the advantage that the otherwise high salt load in the wastewater by precipitation the iron compound is avoided as a hydroxide, on the other hand that The iron can be recycled by making it organic Phase is removed and then fed back to the emulsion can.

Around the separation of the iron compound from the aqueous phase particularly simple it has surprisingly been shaped turned out to be particularly advantageous that one for the separation the iron compound from the aqueous Phase of the untreated emulsion an oil, in particular about 1 g / l, added. This is particularly preferred by the Photo-Fenton process hardly degradable oils used. This allows a minimum amount of organic matter in the emulsion and thus a transport of iron compound are guaranteed.

Embodiment:

The Procedure was on wastewater tested out of the curtain production. These contained preparation oils as well nonionic surfactants as emulsifiers. For easier verification of Reproducibility were also model effluent in the laboratory with the same Composition treated.

An Enviolet ^® reactor from ack aqua concept GmbH was used. The emulsion splitting is carried out as follows. As catalyst FeSO ₄ heptahydrate was added in a concentration of 50 to 100 mg / l of the emulsion. After addition of 0.01 g / l to 0.1 g / l H ₂ O ₂ , the solution was irradiated with a commercial mercury vapor lamp. The light source was mercury medium pressure lamps with a power of 125 W 12000 W and an emission maximum of 254 nm used. The heat radiation of the light source is used to heat the emulsion. After a treatment time of a few minutes, the phases separated and could be separated via a conventional oil separator. Different biodegradable fats and oils of different chain lengths (C10 - C40) were investigated as model substances. The emulsions were kept stable by the use of conventional surfactants. Sample volumes of 0.8 l to 3000 l were irradiated with a TOC content of> 1000 mg / l. The volume-related power of the lamps was 4-200 W / l. 1 shows that at neutral pH no decrease of the TOC in the aqueous phase is observed (dots). The emulsion does not separate. Also, raising the temperature without using a catalyst did not cause segregation and lowering the pH without using the photocatalyst does not lead to segregation. This could only be observed at pH values ≦ 5, in particular at pH 3 and the presence of the photocatalyst / oxidant system and under irradiation (squares).

at At the same time the iron ions were treated in the organic Enriched phase. This effect could be followed spectroscopically become. This allowed the separation to be controlled and one allow easy control of the process.

The speed and the course of the emulsion splitting depended strongly on the reaction temperature, apart from the pH value. By contrast, the catalyst concentration could be varied within a wide range without the rate of degradation being changed significantly. 2 shows that at a temperature of 30 ° C after 25 min both at a catalyst concentration of 50 mg / l and at 200 mg / l a spontaneous drop in TOC was observed. This was because the aqueous and organic phases separated. As the reaction temperature increased, the splitting of the emulsion split sooner. So it was possible to observe the cleavage after 10 min at 60 ° C. At 90 ° C, the cleavage started spontaneously. However, as the reaction temperature was raised, it was observed that the TOC did not decrease as rapidly as at low temperatures. This is because, at higher temperatures, the water solubility of the organic substances is better. Thus, the effects of emulsion cleavage with photocatalytic oxidation were superimposed here. At all reaction conditions a reduction of the TOC by 70-80% after 30 min was observed, as long as the pH value was adjusted as described above.

Claims (8)

A process for the cleavage of aqueous-organic emulsions characterized by the process steps a) adding an oxidizing agent and an iron compound having Fe ²⁺ or Fe ³⁺ ions to the emulsion having a pH of ≤ 5, b) irradiating the emulsion with UV and / or VIS light, and c) depositing the organic phase formed. Method according to claim 1, characterized in that as iron compound iron hydroxide, Iron oxide, iron chloride, iron sulfate, iron oxalate, iron chlorate and / or iron perchlorate. Method according to claim 1 or 2, characterized in that the iron compound in a Concentration of up to 5 wt .-% based on the concentration the TOC present in the emulsion (total organic carbon = total Organic carbon). Method according to one the claims 1 to 3, characterized in that as an oxidizing agent Peroxide, in particular hydrogen peroxide used. Method according to one the claims 1 to 4, characterized in that the emulsion in a Temperature in the range of 0 to 100 ° C splits. Method according to one the claims 1 to 5, characterized in that the irradiation with a UV light source, which is selected from the group discharge lamp, light bulb, sun, in particular Medium pressure mercury lamp. Method according to one the claims 1 to 6, characterized in that in the organic Extracting phase-enriching iron compound of the aqueous phase and subsequently removed from the organic phase, then optionally the partial or completely feeds untreated emulsion again. Method according to one the claims 1 to 7, characterized in that one for the separation of the iron compound from the watery Phase of the emulsion an oil, in particular about 1 g / l, added.