ITMI942660A1 - PROCESS FOR REMOVING POLYCHLOROBIPHENYLS FROM MINERAL OILS - Google Patents

Abstract

In a reactor and temperature between 10 and 150 ° C and at pressure, lower than 5 Atm, the mineral oil contaminated with polychlorinated biphenyls is contacted and reacted with a multiphasic system comprising an alkaline aqueous solution, a hydrogenation catalyst, a catalyst of phase transfer and a source of hydrogen.

Description

The present invention relates to a process for removing polychlorinated biphenyls from mineral oils, in particular from electrical contaminated dielectric oils.

In the following description the polychlorinated biphenyls will be indicated with -PCB- and the process for removing PCBs from mineral oils will be indicated with - decontamination-.

PCBs may be present in the mineral oil of electrical transformers; as PCBs are toxic to animal and plant organisms and are not biodegradable, this mineral oil must be decontaminated.

The problem of decontaminating these mineral oils has been tackled by several parties with different methods; it is understood that only chemical methods can give satisfactory results when it is necessary to decontaminate large quantities of mineral oil.

Numerous decontamination methods are known which employ ultraviolet radiation or treatments with strongly oxidizing substances or with alkali metals or with strong nucleophiles.

According to US patent No. 4,144,152, dioxins are degraded in methanolic solution and in the presence of ultraviolet radiation. After what was revealed by said patent, the decontamination was carried out in the presence of a semiconductor (TiO 2), both in suspension (Chemosphere 1985, 14, 195) and immobilized on membranes (US 4,806,51A); in the latter case the pentaclarophenol was reacted.

Some photochemical methods for PCB reduction use ultraviolet radiation to produce ozone. A pilot plant has been described that operates in this way and is capable of handling 40,000 gallons of contaminated oil per day (35th Annual Purdue Industriai Waste Conferente, May 1990).

It is known that in nature the decomposition of PCBs occurs by Fe <2> + H2 O2 (Environ. Sci Technol. 1991. 25. 1419).

Numerous processes have been known for a long time which use superoxide ion as oxidant, also generated by electrochemical way (Journal of Am. Chem. Soc., 1987, 109, 8081 and Environ. Sci, Techonol., 1988 22, 1182). A portable demonstration plant based on the electrochemical process was developed by Resource Engineering Inc. (Chemical Week, April 1, 1987, 13).

Alkali metals have been used for a long time as a means to decontaminate mineral oils containing PCBs for a long time, as in the processes of Chemical Waste Management and Degussa; more recently the use of metallic sodium supported on sand or on inert support has been reported (Jap. Pat.

74.8. 570 and Can. Pat. 1, 247, 139).

The Sunohio process is well known (IEEE Trans. Power Apparat. Sys., 1983, PAS-102, 3893), called PCBX which uses metallic sodium together with naphthalene; this Process was used in the U.S.A.

Numerous methods, also developed industrially, are based on nucleophilic substitution, such as the Vertac process (US. PAT., 4, 327, 368 and US. PAT., H, J 53, 793).

Other methods, all based on this technology, are still published and implemented (Eur. Pat., 397,310 and US. Pat., 4, 663 027 and US. Pat., 4.748.

292). The latter methods use an alcoholate or potassium hydroxide as nucleophile, in the presence of a solvent (usually PEG) capable of providing anionic activation to the attacking base.

The drawbacks of the known processes are the low reaction rate (ultraviolet radiation and superoxide ion) or the possibility of explosion (alkali metals) or the production of by-products that must in any case be disposed of (drawbacks present in all the processes described, with the exception of ultraviolet reaction).

This reaction (Equation 1)

has been known for a long time, but has not been applied to PCBs in mineral oils so far, because decomposition takes a long time and the necessary catalysts are often very expensive. However, its potential application value is very high, as PCBs would not generate by-products (Rylander, P. H; "Catalytic Hydrogenation in Organic Synthesis"; Academic Press: New York, 1973; PP 235-248 and Klebon, Van Rantwick, in "Hydrogenation in Synthetic Organic Chemistry Delft University Press: Delphi, The Netherlands, 1977).

In fact, the hydrodechlorination of PCB with hydrogen or with one of its precursors leads to biphenyl as the only reaction product (Equation 2):

The latter compound can be considered to all intents and purposes a component of mineral oil.

Note that so far the hydrodhalogenation of PCBs in mineral oil has not been reported however.

Recently it has been known that a multiphase system consisting of a highly alkaline aqueous solution and a hydrogenation catalysts are capable of hydrodhalogenating aromatic polyhalides, present in an organic solvent, if a phase transfer catalyst is also present (Journal Chem, Soc ., Perkin Trans. 1, 1993, page 529) in which, however, reactions on PCBs are not reported nor mineral oil is used as a solvent.

Now we have found that, surprisingly, PCB-contaminated mineral oils are decontaminated quickly if the hydrodhalogenation reaction is carried out in the presence of: an aqueous alkaline solution, a hydrogenation catalyst, preferably Palladium supported on Nickel-Raney carbon, or a hydrogenation catalyst based on Ruthenium or Rhodium, using molecular hydrogen, or sodium hypophosphite or hydrazine as the source of hydrogen and if the reactions are carried out in the presence of a phase transfer catalyst, preferably in the presence of Aliquat 336 (Tricaprilil Methyl Ammonium Chloride).

It is known that the phase transfer catalysts are insoluble in the two phases, oil and aqueous solution, or are absorbed on the surface of the hydrogenation catalyst.

The reaction is very fast, so much so that, as described in Example 2, operating only at 50 ° C, the contamination of the mineral oil dropped from the initial 550 ppm to 23 ppm after only 2.0 hours of reaction.

Similarly, starting from 5,000 ppm, according to Example 1, the concentration dropped to 100 ppm by operating at 50 ° C for 8 hours.

It should be noted that, if one operates without Aliquat 336 as described in the process exemplified in Example 2, no reaction takes place.

The main advantages of the invention are given: a) by the possibility of operating on mineral oil without preventive treatments and at low temperatures, b) by the absence of harmful by-products of the process, c) by the high reaction rate. Other advantages are: the treated mineral oil still has high dielectric characteristics and, after removing the humidity and gases present, it can still be used in an electrical transformer; the process is versatile in that molecular hydrogen or its precursor can be used as a source of hydrogen the hydrogenation catalysts can be recycled either using a batch decontamination process or by setting up a continuous system, such as a CSTR (continuous stirred tank reactor).

Some examples are given below to describe the hydrodea logenation of PCBs in mineral oil.

The PCB formulations used in the examples described here were Aroclor 125A, Apirollo 1A88 and Aroclor 1260.

The initial concentration of PCBs in the oils was between 5,000 ppm and 105 ppm.

The phase transfer catalyst was generally Aliquat 336, although hexaldecyltributylphosphonium chloride, tribenzylethylammonium chloride, phenyltributylammonium chloride and tetraethylammonium chloride gave good results.

The temperature was between 50 ° C and 80 ° C, in all the examples described here.

Were used:

- Different hydrogenation catalysts, but it was found that the best result from the point of view of effectiveness was obtained with the use of Palladium catalysts supported on carbon, Nickel-Raney, based on Ruthenium, based on Rhodium.

Different hydrogen sources, such as molecular hydrogen, ammonium formate or sodium hypophosphite or hydrazine;

- Bases such as NaOH, KOH or K2 CO3;

- Various dielectric oils containing PCBs.

EXAMPLES

Example no

7 ml of oil contaminated with 5000 ppm of Aroclor 1260, 5 ml of KOH 50% (w / v), 50 mg of Pd / C 5%, 100 mg of Aliquat 336 with hydrogen at atmospheric pressure. After 8 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 98%. 100 ppm of mono, di and trichlorobiphenyls remained in the oil Example 1a

Operating under the same conditions as example 1 except for the reducing agent (2.65 g of sodium hypophosphite dihydrate instead of hydrogen gas) and of the phase transfer agent (0.49 g of hexadecyltributylphosphonium chloride instead of aliquat 336) after 30 hours a low decontamination yield (35%) was observed even if the qualitative profile showed a decrease in the high chlorinated congeners.

By putting the same mixture of Example 1 to react, with the exception of aliquat 336, the reaction was very slow, so much so that after 6 days the yield was 14%, with a decrease of a few high-chlorinated congeners.

Example 2

In a 25 ml two-necked flask thermostated at 50 ° C and under magnetic stirring, 7 ml of contaminated oil were reacted with 550 ppm of Aroclor 1254.5 ml of KOH 50% (w / v) 50 mg of Pd / C 5%, 50 mg of Pd / C 5%, 100 mg of Aliquat 336 with hydrogen at atmospheric pressure. After 2 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 96%. 23 ppm of mono, di and tri chlorobiphenyls remained in the oil.

Example 2a

Under the same conditions of Example 2 but in the absence of aliquat 336 and at 80 ° C, after 6 hours of reaction no decontamination yield was found, the addition of 0.1 g of hexadecyltributylphosphonium chloride resulted instead after 4 hours of reaction at 80 ° C a yield of 94% with a concentration of low-chlorinated PCBs equal to 34 ppm.

The substitution of the base (NaOH at the place of the KOH) allowed the achievement of 96% yield in just 1 hour of reaction with a low-chlorinated RCB concentration of 22 ppm.

The use of 0.1 ml of 98% hydrazine hydrazine instead of hydrogen gave a degradation yield of 92% in 2 hours, with a PCB residue of 42 ppm.

Example 3

20 ml of contaminated oil with 550 ppm of Aroclor 1254.5 ml of KOH 50% (w / v), 50 mg of Pd / C

5%, 100 mg of Aliquat 336 with hydrogen at atmospheric pressure After 2 hours the decontamination yield was 80%, while after 4 hours it was reached 96%, with a concentration of low-chlorinated PCBs of 22 ppm.

Example No. 4

10 ml of oil contaminated with 465 ppm of Aroclor 1260.5 ml of KOH 50% (w / v), 50 mg of Pd / C 5%, 100 mg of Aliquat 336 with 0.1 ml of 98% hydrazine. After 4 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 90%. 46 ppm of mono, di and trichlorobiphenyls remained in the oil.

Example 5

In a 50 ml two-necked flask thermostated at 60 ° C and under magnetic stirring, 20 ml of contaminated oil were reacted with 580 ppm of Apirolio 1488 T, 10 ml of KOH 50% (w / v); 50 mg of 5% Pd / C, 100 mg of Aliquat 336 with 0.2 ml of 98% hydrazine. After 4 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 82%. 102 ppm of PCB remained in the oil which after a further 4 hours of reaction dropped to 35 ppm of mono and dichlorobiphenyls (94% yield).

Example 6

In a 50 ml two-necked flask thermostated at 60 ° C and under magnetic stirring, 25 ml of contaminated oil were reacted with 648 ppm of Apirolio 1488 T, 10 ml of KOH 50% (w / v), 75 mg of Pd / C 5%, 178 mg of Aliquat 336 with hydrogen at atmospheric pressure. After 4 hours of reaction, gas chromatography analysis with ECD detector showed a degradation yield of 90% while after 4 hours 26 ppm of low chlorinated PCBs (96%) remained.

Example 7

In a 50 ml two-necked flask thermostated at 60 ° C and under magnetic stirring, 20 ml of contaminated oil were reacted with 105 ppm of Apirolio 1488 T, 10 ml of KOH 50% (w / v), 73 mg of Pd / C 5%, 174 mg of Alìquat 33 6 with hydrogen at atmospheric pressure. After 2 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 90%. 10 ppm of mono and dichlorobiphenyls remained in the oil.

Example 8

1 850 ml of contaminated oil with 750-ppm of Apirolio 1488 T, 350 ml of KOH 50% (w / v) were reacted in a 5-liter 5-neck reactor, thermostatically at 60 ° C and under mechanical stirring. , 2.8 g of Pd / C 5%, 7.4 g of Aliqua t 336 with hydrogen at atmospheric pressure. After 8 hours of reaction the graphical gas chromate analysis with ECD detector showed a degradation yield of 70%. After 4 hours of reaction, 30 ppm of mono and dichlorobiphenyls (96%) remained in the oil.

Example 9

1900 ml of contaminated oil with 750 ppm of Apirolio 1488 T, 360 ml of KOH 50% (w / v), g 2, of 5% Pd / C, 7 g, of Aliquat 336 with 10 ml of hydrazine hydrated by 98%. After 8 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 58%. After a further 12 hours of reaction in the oil 145 ppm of mono and declorobiphenyls (81%) remained.

Example 10

54 l of oil contaminated with 500 ppm of Apirolio 1488 T, 8 l of KOH 50% (w / v) g 100 of Pd / C 5%, 250 g of Aliquat 336 with hydrogen at atmospheric pressure. After 16 hours of reaction, gas chromatography analysis with ECD detector showed a degradation yield of 72%. After a further 12 hours of process 85% yield was reached and 75 ppm of mono, di and trichlorobiphenyls remained in the oil.

Example n. 11

In a 150 l reactor, thermostated at 70 ° C and under mechanical stirring, 51 l of contaminated oil were reacted with 740 ppm of Apirolio 1488 T, 26.5 l of KOH 50% (w / v), 100 g of Pd / C 5%, 520 g of Aliquat 336 with hydrogen at atherosphere pressure. After 20 hours of reaction gas chromatography analysis with ECD detector showed a degradation yield of 97% equal to an oil contamination of 22.5 ppm (mono and dichlorobiphenyls).

Example 12

In a 150 l reactor, thermostatically controlled at 70 ° C and under mechanical stirring, 48 l of oil contaminated with 185 ppm of Apirolio 1488 T, 33.5l of KOH 50% (w / v), 100 g of Pd were reacted / C 5%, 480 g of Aliquat 336 with hydrogen at atmospheric pressure After 8 hours of reaction the gas chromatographic analysis with ECD detector showed a degradation yield of 92% of yield the oil was contaminated by only 16.7 ppm of mono and dichlorobiphenyls.

Claims (11)

CLAIMS 1. Process to remove polychlorinated biphenyls from mineral ols by means of the hydrodhalogenation reaction in a multiphase system characterized by that it is carried out in a reactor at a temperature between 10 150 ° C and at a pressure below 5 Atm in which the mineral oil containing the polychlorinated biphenyls is contacted and reacted with a multiphase system comprising an aqueous alkaline solution, a hydrogenation catalyst, a phase transfer catalyst and a hydrogen source. 2 Process according to claim 1 characterized in that the base used to form said aqueous alkaline solution is potassium hydroxide or sodium hydroxide or an alkali metal carbonate or calcium hydroxide or magnesium hydroxide. 3. Process according to claim characterized in that the hydrogenation catalyst is Palladium supported on carbon or Nickel-Raney or a hydrogenation catalyst based on Ruthenium or based on Rhodium. 4. Process according to claims 1, 2, 3 characterized in that the phase transfer catalyst is tricaprylyl methyl ammonium chloride. 5. Process according to claims 1, 2, 3 characterized by that the phase transfer catalyst is hexadecyltributylphosphonium chloride. 6. Process according to claims 1, 2 characterized in that the phase transfer catalyst is tribenzylethylammonium chloride. 7. Process according to claims 1, 2, 3 characterized in that the phase transfer catalyst is phenyltributylammonium chloride. 8. Process according to claims 1, 2, 3 characterized in that the phase transfer catalyst is tetraethylammonium chloride. 9. Process according to claim 1 characterized in that the source of hydrogen is molecular hydrogen or hydrazine or sodium hypophosphite. 10. Process according to claim 1 characterized in that it is applied to mineral oils containing polychlorinated biphenyls in a concentration comprised between 50,000 ppm and 5 ppm. 11. Process according to claim 1c characterized by what it is carried out in a bath or CSTR reactor.