RU2215729C1 - Method for detoxification of polychlorobiphenyls - Google Patents

Abstract

FIELD: environment protection measures. SUBSTANCE: method is accomplished by catalytic liquid-phase dechlorination of polychlorobiphenyls. Process is carried out under carbon dioxide at 55-70 C and pressure 1-3 atm in aliphatic alcohol (mainly methanol) medium. Utilized are alkali and alkali-earth metal carbonates or hydroxides, or alcoholates in presence of catalytic system containing (i) cobalt carbonyl or alkali or alkali-earth metal salts of cobalt carbonyl and (ii) cocatalyst. The latter is olefin oxide of formula

, where R represents hydrogen or alkyl of formula CnH_2nX, with n=1-5 and X being H or Cl. Catalyst is used with concentration of cobalt in alcohol solution 0.2-5.0% of the weight of polychlorobiphenyl and amount of cocatalyst corresponds to 10-80 mol per 1 mol cobalt. EFFECT: improved economical efficiency of process. 14 ex

Description

 The invention relates to the field of environmental protection, and more specifically to methods of dechlorination of ecotoxicants - polychlorinated aromatic compounds, namely polychlorinated biphenyls (PCBs), which form even more toxic substances, chlorinated dioxins, when stored or burned. PCBs have been accumulated in large quantities in world industry, as Due to their high technical properties, they were actively used as highly heat-resistant and inert dielectrics, hydraulic fluids, etc.

 Low chemical inertness and good oil solubility leads to the accumulation of PCBs in the fatty tissues of humans and animals, and being highly toxic, they suppress immunity and contribute to carcinogenesis and other dangerous diseases. The invention can be most effectively used in the chemical and electrical industries in connection with the need for detoxification of PCBs used as highly thermally stable dielectrics - technical names "SOVOL" and "SOVTOL", abroad called "AROCHLORIES". Known physical and physico-chemical methods of dechlorination of ecotoxicants containing chlorine: electrochemical, radiation, photochemical, thermal. All of them have certain disadvantages. The main ones are high energy intensity and low selectivity.

 Thermal combustion methods are deemed unsuitable because when burning organochlorine raw materials, even more toxic waste is formed: dioxin, chlorine, phosgene.

 The most promising are chemical methods of dechlorination. The task is to dechlorinate raw materials with the conversion of these compounds into non-toxic safe compounds, for example oxygen-containing.

 For ecologically highly hazardous chlorinated compounds with a planar structure, the so-called “dioxin-like”, it is sufficient to partially dechlorinate PCBs, while their toxicity decreases sharply.

 A known method of dechlorination of PCBs with Na-naphthalene with the addition of a fifty-fold excess of metallic sodium in a solution of tetrahydrofuran in an inert atmosphere for 4 hours (US patent 4326090, class C 07 C 1/20, 1982). The disadvantage of this method is the use of sodium metal in large quantities and an organic solvent, which makes the process explosive and low-tech.

 A known method of recovering PCBs with hydrosilanes in the presence of Ni-Raney with a molar ratio of PCB: hydrosilane: Ni-Raney is equal to 1: 20-25: 10-12.5 (Russian patent 2030378, CL 07 15/14, publ. 10.03 1995 g.).

A known method of catalytic reductive dehydro-chlorination carried out using heterogeneous reducing catalysts in a fine dispersed state in a hydrogen atmosphere at temperatures up to 400 ^o C (German patent 19903987. The disadvantages of these methods include the high energy intensity of the process, fairly fast poisoning of the surface of the catalyst and high corrosion activity environment as a result of the release of hydrogen chloride during dehydrohalogenation.

The closest in technical essence to the proposed method is a method of liquid-phase dechlorination of aromatic chlorides using a heterogeneous catalyst containing nickel with a concentration of 1-8 wt. % on a carbon carrier and promoted by palladium with a concentration of 2-10 wt. % with respect to nickel in a hydrogen atmosphere with the addition of a NaBH ₄ reducing agent in an ethanol-containing solvent. In this case, the molar content of the chloroaromatic compound (in C-C): catalyst: NaBH ₄ is 1: (0.03-50): (1-350) (Russian patent 2100338, publ. 12/27/1997 - prototype). The disadvantage of the prototype method is the use of an expensive and scarce catalyst component — palladium and a reducing agent — sodium borohydride.

 For this reason, the prototype method has not found wide application.

где R - водород или алкил формулы С_nН_2nX при n=1-5, X=Н, Сl.In order to reduce the cost and simplify the technology of neutralization, it is proposed that the liquid phase dechlorination of ethoxicants, in particular PCBs, be carried out in an atmosphere of carbon monoxide in the environment of lower aliphatic alcohols (mainly methanol) using carbonates or hydroxides or alcoholates of alkali or alkaline earth metals in the presence of a catalytic system based on cobalt or carbonyls salts of an alkaline or alkaline earth metal of cobalt carbonyl and cocatalyst - olefin oxide of the formula

where R is hydrogen or alkyl of the formula C _n H _2n X at n = 1-5, X = H, Cl.

The process is carried out at a temperature of 55-70 ^o C and a pressure of carbon monoxide 1-3 ATM. The catalyst is taken with a concentration of cobalt in an alcohol solution of 0.2-5.0% per halide. The amount of cocatalyst is 10-80 mol per 1 mol of cobalt.

где R - водород или алкил формулы С_nН_2nX, при n=1-5, X=Н, Сl.Salient features of the proposed method are:
- the process of dehydrochlorination of polychlorinated biphenyls in a medium of carbon monoxide,
the use of a catalytic system based on cobalt carbonyls or a salt of an alkaline or alkaline earth metal cobalt carbonyl and cocatalyst - olefin oxide of the formula

where R is hydrogen or alkyl of the formula C _n H _2n X, when n = 1-5, X = H, Cl.

- carrying out the process at a temperature of 55-70 ^o With a pressure of carbon monoxide up to 3 ATM. in the environment of lower aliphatic alcohol (mainly methanol) using carbonates or hydroxides or alkoxides of alkali or alkaline earth metals,
- the concentration of cobalt in an alcohol solution of 0.2-5.0 wt.% per polychlorobiphenyl, the amount of olefin oxide 10-80 moles per mole of cobalt.

The choice of optimal values of the process conditions is explained by the following: at temperatures above 70 ^o C and pressure above 3 atm. just as with a cobalt concentration in an alcohol solution below 0.2 wt.%, the activity and stability of the catalytic system decreases, and an increase in the cobalt concentration of more than 5 wt.% does not lead to a change in the process indicators, but causes only unnecessary waste of expensive cobalt.

 The proposed method is carried out as follows: in a reaction flask or autoclave, previously purged with carbon monoxide, a cobalt carbonyl catalyst or its salt with a cobalt concentration of 0.2-5.0 wt.% Calculated on polychlorobiphenyl, solvent, base and cocatalyst is added in an amount (not less than necessary for the reaction): 10 mol of olefin oxide per 1 mol of catalyst. The process is carried out under given conditions with vigorous stirring and a constant supply of carbon monoxide. At the end of the reaction, the conversion of the initial chloride (or a mixture thereof) is determined by GLC. As a result, environmentally hazardous chloride or a technical mixture of aromatic chlorides is converted into non-toxic carboxyl compounds (acids or esters) with a low chlorine content.

 The industrial applicability of the invention is confirmed by examples. Experimental data on the conditions and results of the examples are shown in the table. All experiments were carried out until a high chloride conversion of above 80% was achieved.

 Example 1

 Methanol, 20 ml, is charged into a thermostated, carbon monoxide purged flask with a volume of 100 ml; potassium carbonate - 1 g (7 mmol); cobalt carbonyl - 0.1 g (0.3 mmol); 2,4,4'-trichlorobiphenyl -1 g (6 mmol); propylene oxide - 0.35 g.

The concentration of cobalt on chloride is 3%. weight ratio of propylene oxide: cobalt carbonyl = 20: 1. The reaction is carried out at atmospheric pressure of carbon monoxide at a temperature of 60 ^° C. Chloride conversion is 99%. Chlorine conversion is 40%.

Claims (1)

A method of neutralizing polychlorobiphenyls by catalytic liquid phase dechlorination at an elevated temperature in a gas atmosphere, characterized in that the process is carried out in an atmosphere of carbon monoxide under a pressure of 1-3 atm at 55-70 ^o C in an environment of lower aliphatic alcohols, mainly methanol, using carbonates, or hydroxides or alcoholates of alkali or alkaline earth metals in the presence of a catalytic system containing cobalt carbonyl or a salt of an alkali or alkaline earth metal of cobalt carbonyl and the catalyst is an olefin oxide of the formula

where R is hydrogen or alkyl of the formula C _n H _2n X at n = 1-5, X = H, C1,
while the catalyst is taken with a concentration of cobalt in an alcohol solution of 0.2-5.0 wt. % per polychlorobiphenyl, and cocatalyst in the amount of 10-80 mol per 1 mol of cobalt.

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