EP0617985A1 - Process for the dehalogenation of the aromatic halogenated hydrocarbons - Google Patents

Abstract

A process for the dehalogenation of halogenated aromatic hydrocarbons had to be developed in which in a closed circulation, avoiding a pyrolytic reaction, the halogenated aromatic hydrocarbons are dehalogenated and the residues, without environmentally harmful effect, are fed to expedient reuse or can be stored in a standard landfill. This was achieved by a process which can be carried out on an industrial scale by hydrothermally treating solids containing halogenated aromatic hydrocarbons in aqueous suspensions or solutions at temperatures of 150 to 330@C for 5 to 200 minutes.

Description

The invention relates to a process for the dehalogenation of halogenated aromatic hydrocarbons, in particular of solids loaded with polyhalogenated dibenzodioxins and / or furans.

• 1. Nach EP 92250343 werden die organischen Halogenide mit Toluol und Xylol extrahiert und anschließend einer katalytischen Hydrodehalogenierung unterworfen. Dieses aufwendige Verfahren ist insbesondere für die großtechnische Reinigung von kontaminierten Böden oder Stäuben aus energetischen Gründen nicht sinnvoll einsetzbar.
• 2. Die Dechlorierung organischer Chlorverbindungen mit elementarem Natrium wird in DE 28 13 200 beschrieben. Die Wirtschaftlichkeit dieses Verfahrens ist jedoch durch den hohen Wassergehalt der Filterstäube beeinträchtigt.
• 3. In "Environ. SCI. Technol., 21 (11) 1058-88" ist die direkte thermokatalytische Zerstörung von organischen Chlorverbindungen in Filterstäuben beschrieben. Dieses Verfahren hat den Nachteil, daß die thermokatalytisch behandelten Staub-Rückstände wasserlöslische anorganische Bestandteile enthalten. Die Auslaugbarkeit dieser Rückstände verursacht Entsorgungsschwierigkeiten, da ihre obertägige Deponierung problematisch ist.
• 4. Bei dem Einsatz von Aktivkohle oder Kalk/Aktivkohlegemischen als Adsorptionsmittel wird die Entsorgungsproblematik durch die Brandgefahr von Aktivkohle zusätzlich verstärkt, was erhöhten Sicherheitsaufwand erforderlich macht. Die Entsorgung derartiger Rückstände kann durch thermokatalytische Zerstörung der organischen Chloride bei 400 °C unter Sauerstoffausschluß erfolgen, jedoch ist auch in diesem Fall die obertägige Deponierung wegen den auslaugbaren anorganischen Verbindungen in den Rückständen problematisch.

Halogenated aromatic hydrocarbons are found, for example, as PCBs, PCDDs and PCDFs in waste incineration plants, in metal remelting plants and in soils contaminated with residues from industrial processes. The dehalogenation of such hydrocarbons is difficult because the highly toxic polychlorinated dibenzodioxins and furans are very stable and are only present in traces in the contaminated soils or dusts of the gas cleaning systems. The following methods have been proposed for the disposal of such dusts and contaminated soils:

• 1. According to EP 92250343, the organic halides are extracted with toluene and xylene and then subjected to a catalytic hydrodehalogenation. This complex process cannot be used sensibly, particularly for large-scale cleaning of contaminated floors or dusts for energy reasons.
• 2. The dechlorination of organic chlorine compounds with elemental sodium is described in DE 28 13 200. However, the economy of this process is affected by the high water content of the filter dust.
• 3. "Environ. SCI. Technol., 21 (11) 1058-88" describes the direct thermocatalytic destruction of organic chlorine compounds in filter dusts. This process has the disadvantage that the thermocatalytically treated dust residues contain water-soluble inorganic constituents. The leachability of these residues causes difficulties in disposal since their landfilling is problematic.
• 4. When using activated carbon or lime / activated carbon mixtures as an adsorbent, the disposal problems are exacerbated by the fire risk of activated carbon, which makes increased safety requirements necessary. Such residues can be disposed of by thermocatalytically destroying the organic chlorides at 400 ° C. with the exclusion of oxygen, but in this case as well the surface dumping is problematic because of the leachable inorganic compounds in the residues.

The known methods can therefore not provide a satisfactory remedy for the increasingly pressing disposal problems in the field of halogenated hydrocarbons.

It is therefore an object of the present invention to provide a process which can be carried out on an industrial scale, in which the halogenated aromatic hydrocarbons are dehalogenated in a closed circuit while avoiding a pyrolytic reaction and the residues can be recycled sensibly without an environmentally harmful effect or can be stored in a normal landfill.

A special object of the present invention is to destroy the organic halogen compounds which occur in the filter dusts of remelting plants in the non-ferrous metal industry and adhere to the filter aids and to make the lime dusts used as filter aids usable again for exhaust gas purification after the organic chlorides have been destroyed, the calcium chloride crystallize from the solutions, activate them and use them as drying agents, for example.

This object is achieved in that the halogenated aromatic hydrocarbons bound to solids, which contain polyhalogenated dibenzodioxins and / or furans, are treated hydrothermally in aqueous suspensions or in solutions, the temperatures between 150-330 ° C. and the residence times between 5 and 200 minutes lie.

Surprisingly, it was found that with such a hydrothermal treatment in alkaline media, preferably at temperatures of 230-330 ° C. and residence times of less than 30 minutes, more than 90% of the organic halides are broken down when the decomposition liquid contains additions of aluminum, copper, zinc, Nickel, chromium or iron in amounts of 0.01 - 10 g per liter can be added.

The polyhalogenated dibenzodioxins and furans are hydrolytically dehalogenated with a particularly high effect at temperatures of 250 - 330 ° C if the pH is greater than 7.

The halides split off go into solution and are separated off by crystallization in a subsequent step.

The method is also applicable to filter dusts from waste or special waste incineration plants as well as on contaminated soils.

The process is preferably carried out in continuously operating tubular reactors in which the aqueous suspension of contaminated dusts (30-300g / l solids content) is heated to 250-330 ° C in a few minutes with turbulent flow and after a residence time of 10-15 minutes Temperature is cooled to below the boiling point.

This information relates to both coal and lime-containing solids, with lime-containing solids according to the invention being filtered off after the hydrothermal treatment, dried and returned to the exhaust gas purification as calcium hydroxide. In a special process variant, calcium chloride is crystallized out of the filtrate and, after filtration and drying, used as a drying agent.

The recycled filter dusts can be returned to the filter system after they have been broken down by more than 90%.

The process conditions according to the invention have a temperature range of 150-330 ° C. with a residence time of 5-200 minutes. Above the specified temperature limit, the reaction temperature approaches the critical temperature, while at temperatures below 150 ° C the reaction times are too long for an industrial process to achieve a reasonable space / time yield. Basically, the process according to the invention is a hydrolytic dehalogenation which can take place under reducing and oxidizing conditions in a hydrogen or oxygen atmosphere.

The additives according to the invention must be metered in such a way that the lower explosion limit of oxyhydrogen is reliably avoided by hydrogen being released.

Fig. 1

Prinzipieller Ablaufplan eines Verfahrens zur Dehalogenierung von Filterstäuben,

Fig. 2

Prinzipieller Verfahrensablauf bei der Dehalogenierung von Lösungen

Fig. 3

Analyse eines typischen kalkhaltigen Filterstaubes (Metallumschmelzanlage)

Fig. 4

Analyse einer typischen Flugasche (Müllverbrennungsanlage)

Fig. 5

Analyse eines mit 1.2.3.4. TCDD dotierten Einsatzkalks

Fig. 6

Analyse eines typischen kokshaltigen Filterstaubs (Müllverbrennungsanlage)

Fig. 7

Abbaugrade von polyhalogenierten Dibenzodioxinen/Furanen.

The invention is explained in more detail below with the aid of several exemplary embodiments. Show it:

Fig. 1

Basic flow chart of a process for the dehalogenation of filter dusts,

Fig. 2

Basic procedure for the dehalogenation of solutions

Fig. 3

Analysis of a typical calcareous filter dust (metal remelting plant)

Fig. 4

Analysis of a typical fly ash (waste incineration plant)

Fig. 5

Analysis of one with 1.2.3.4. TCDD-doped lime

Fig. 6

Analysis of a typical coke-containing filter dust (waste incineration plant)

Fig. 7

Degradation levels of polyhalogenated dibenzodioxins / furans.

1, filter dust is mixed with water with addition of the additives according to the invention, heated and, after the reaction temperature has been reached, subjected to a residence time in accordance with the conditions specified in the process claims.

After the suspension has cooled, the filtration is carried out with subsequent drying of the solid.

Calcium chloride is crystallized out of the filtrate and the residual water is circulated.

The basic process sequence for the dehalogenation of solutions can be seen in FIG. 2.

Several test procedures for the method according to the invention are described below. In the experiments, filter dusts are used in accordance with the analyzes given in FIGS. 3 to 6. The results can be summarized as follows:

example 1

A suspension of filter dust (analysis in FIG. 3) and water with a solids content of 300 g per liter was produced. 3 g / l of metallic aluminum were added to the suspension. The mixture was then heated in an autoclave under an air atmosphere to 270 ° C. in 50 minutes. After a dwell time of 20 minutes, the mixture was cooled to 50 ° C. As can be seen in FIG. 7, column 1, it can be seen that a degree of degradation of 90% can be achieved.

Example 2

Filter dust (Fig. 3) was treated as in Example 1, but additionally covered with oxygen. The analysis result (Fig. 7, column 2) shows that additional oxygen has no positive influence on the breakdown of the polyhalogenated dibenzodioxins and furans.

Example 3

A suspension was prepared as in the previous examples and heated to 270 ° C. in an autoclave in a hydrogen atmosphere in 50 minutes. The analysis results of the residue show, according to FIG. 7, column 3, that additional hydrogen does not bring any improvement for the decomposition of the organic chlorides.

Example 4

A suspension of filter dust and water with a solids content of 300 g / l was heated to 270 ° C. in an air atmosphere in 50 minutes without the additional addition of aluminum. After a residence time of 20 minutes, the suspension was cooled to 50 ° C. and the residue was filtered off. The analysis of the residue shows that although the organic chlorides are degraded, the degradation rate (FIG. 7, column 4) is, however, significantly lower than in example 1.

Example 5

A suspension of filter dust (analysis in FIG. 3) and water with a solids content of 100 g / l and a copper sulfate addition of 1.5 g / l was heated to 270 ° C. in an oxygen atmosphere in 50 minutes. After a residence time of 20 minutes, the mixture was cooled to 50 ° C. and the residue was filtered off. The analysis of the residue (Fig. 7, column 5) shows that the addition of copper sulfate and oxygen causes an increase in the degradation rate compared to Example 4.

Example 6

Filter dust was treated as described in Example 5, but an additional 150 g / l sodium aluminate was added to the suspension. Analysis of the residue (Fig. 7, column 6) shows that the addition of sodium aluminate causes a further increase in the rate of degradation.

Example 7

Filter dust (Fig. 3) was treated as in Example 1, but not heated to 270 ° C but to 300 ° C in about 55 minutes. After a dwell time of 20 minutes, the mixture was cooled to 50 ° C. The degree of degradation of 94%, shown in Fig. 7, column 7, shows the positive influence of elevated temperature.

Example 8

5 from calcium chloride, which was doped with 300 ug / l 1.2.3.4-TCDD, was mixed with water and the solution obtained was heated to 300 ° C. in air in 55 minutes. After a dwell time of about 20 minutes, the mixture was cooled to 50 ° C. The degree of degradation of the 1.2.3.4 TCDD (Fig. 7, column 8) was 88%.

Example 9

Filter dust (analysis in Fig. 4) was stirred with water and 3 g / l aluminum was added. The solids content of the suspension was 300 g / l (pH> 7). The suspension was heated to 300 ° C. in 55 minutes, held at this temperature for 20 minutes and then cooled to 50 ° C. The degree of degradation (FIG. 7, column 9) of the contents of polyhalogenated dibenzodioxins / furans was 93%.

Example 10

Filter dust from the following analysis (FIG. 5) was stirred with 1N sodium hydroxide solution, heated to 270 ° C. in an air atmosphere in 50 minutes and after a dwell time of 20 minutes at pH approx. 14, the mixture was cooled to 50 ° C. The degree of degradation at 1.2.3.4-TCDD (Fig. 7, column 10) was 98%.

Example 11

Filter dust (FIG. 5) was mixed with water and, after addition of 1.5 g / l copper sulfate in an autoclave, heated to 300 ° C. under oxygen in 55 minutes. After a dwell from 20 minutes was cooled to 50 ° C. The degree of degradation at 1.2.3.4-TCDD (Fig. 7, column 11) was 98%.

Example 12

Coke-containing filter dust (analysis in Fig. 6) was mixed with water and 3 g / l aluminum was added. The solids content of the suspension was 300 g / l (pH> 7). The suspension was heated to 300 ° C. in 55 minutes, held at this temperature for 20 minutes and then cooled to 50 ° C. The degree of degradation of the contents of polyhalogenated dibenzodioxins / furans (FIG. 7, column 12) was 85%.

Example 13

A suspension of filter dust (analysis in FIG. 3) and water with a solids content of 100 g / l and a copper sulfate addition of 1.5 g / l and an additional 150 g / l sodium aluminate was heated to 330 ° C. in 60 minutes without additional oxygen . After a dwell time of 20 minutes, the mixture was cooled to 50 ° C. The degradation rate could be improved compared to Example 6 by increasing the temperature to 99%.

For the explanation of FIG. 1, it is pointed out that a partial flow of the filtrate is circulated and enriched in the process. This is indicated by the dashed arrow.

Claims (15)

Process for the dehalogenation of halogenated aromatic hydrocarbons,
characterized,
that halogenated aromatic hydrocarbon-containing solids are treated hydrothermally in aqueous suspensions or solutions at temperatures of 150-330 ° C. for five to 200 minutes. Method according to claim 1,
characterized,
that the hydrothermal treatment is carried out in solutions or suspensions at a pH> 7. Method according to claim 1,
characterized,
that the hydrothermal treatment is carried out in dilute solutions or suspensions with the addition of metallic aluminum and / or compounds of Cu, Ni, Cr, Fe. Method according to claim 1,
characterized,
that the hydrothermal treatment is carried out in dilute sodium aluminate. Method according to claim 1,
characterized,
that the hydrothermal treatment is carried out with the addition of metallic aluminum in the range of 0.3-6 g / l. Method according to claim 5,
characterized,
that copper, zinc, nickel, iron, chromium or their compounds are added, the total amount being 0.01-10 g / l. Method according to one of the preceding claims,
characterized,
that the hydrothermal treatment is carried out in the temperature range of 230-300 ° C. Method according to one of the preceding claims,
characterized,
that the hydrothermal treatment is carried out with a residence time between 5 and 30 minutes. Method according to one of the preceding claims,
characterized,
that the process in a continuously operating tubular reactor under turbulent conditions with a residence time of 10-15 min. is carried out at temperatures of 250 - 330 ° C and then cooled to a temperature below the boiling point. Method according to one of the preceding claims,
characterized,
that the solids content is adjusted to 30-300 g / l. Method according to one of the preceding claims,
characterized,
that filter dusts or filter aids from remelting plants of the non-ferrous metal industry are used as solids. Method according to one of the preceding claims,
characterized,
that filter dusts or filter aids from waste incineration plants are used as solids. Method according to one of the preceding claims,
characterized,
that lime dusts with adhering organic halogen compounds are used as filter dusts. Method according to one of the preceding claims,
characterized,
that coke-containing filter dusts are used. Method according to one of the preceding claims,
characterized,
that the filter aids are returned to the exhaust gas cleaning system after a breakdown of more than 90% of the adhering organic compounds.

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