Liquid purification or separation – Processes – Chemical treatment
Patent
1995-09-22
1997-07-01
McCarthy, Neil
Liquid purification or separation
Processes
Chemical treatment
210908, 210909, C02F 170
Patent
active
056434650
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for reducing the content of halogen-containing organic compounds in aqueous systems by reduction with hydrogen in the presence of a metal catalyst.
RELATED ART
AOX is the abbreviation for organic halogen compounds which are capable of being adsorbed onto active carbon (adsorbable organic (X) halogen compounds; X=fluorine, chlorine, bromine, iodine). The AOX value is determined in accordance with DIN 38409 (Part 14). Typical examples of AOX compounds are methylene chloride, trichloroethylene, perchloroethylene, chloroform, carbon tetrachloride and also PCB, HCH, DDT and chloroparaffins.
As a result of increasing environmental awareness, wastewater treatment is also acquiring increasing significance. AOX are undesirable in wastewaters on account of their chronic toxicity to human beings. In addition, AOX compounds are persistent and bioaccumulatable which leads to their accumulation in the environment. Accordingly, the AOX content of wastewaters in Germany is limited by legislative measures (cf. E. Oswald, "Metalloberflache" 1990, 44, 186-190).
In a fairly recent synoptic article, E. Oswald (cf. "Metalloberflache" 1990, 44, 186-190) names three particularly important processes for the chemical treatment of AOX-containing wastewaters, namely: oxidative processes has been described by J. K. Beattie. In this variant, organochlorine compounds are degraded with ruthenium tetroxide in aqueous medium to form carbonate and chloride (cf. Pure & Appl. Chem. 1990, 62, 1145-1146).
According to R. A. Miller, organic compounds, such as 1,3,5-trichlorobenzene, can be oxidized in aqueous medium at an acidic pH value which should be no more than 4 (cf. U.S. Pat. No. 4,212,735). Air, for example, may be used as the oxidizing agent. Miller proposes a ternary combination of nitrate ions, bromide and/or iodide ions and also transition metal ions of at least one transition metal with two or more oxidation numbers as a characteristic co-catalyst system. The preferred pH range is below 1 while the preferred temperature is above 150.degree. C.
In addition, reducing processes have also been described in the literature. According to K. H. Sweeny, persistent organic compounds, such as halogenated pesticides, can be removed from aqueous systems by allowing the solutions to flow through a column containing a reducing metal catalyst, such as Fe-Cu, at or in the vicinity of the neutral point.
E. G. Baker and L. J. Sealock describe the catalytic decomposition of chlorinated organic compounds in aqueous solution (cf. Report PNL-6491-2; Order No. DE88-009535; April 1988; the document is available through NTIS--National Technical Information Service; United States Department of Commerce; cf. also the abstract in Chem. Abstr. 110[12]:101110f). The Baker/Sealock process comprises treating the wastewaters with transition metal catalysts at temperatures of 300.degree. to 400.degree. C. and under high pressures. Unfortunately, it is attended by the disadvantage that it requires very drastic conditions in regard to temperature and pressure. In addition, the authors describe reduced nickel as the only effective catalyst so that the general usefulness of other transition metal catalysts appears highly questionable.
In a review, G. Dehoust, C. Ewen and R. Gensicke describe organohalogen-containing waste as problematical waste in waste management (cf. "Mull und Abfall" 1991, 23, 283-294). They mention hydrogenation as one method of treating waste containing organohalogen compounds. This method is based on the principle of reacting the chlorine formed during the hydrogenation of organo-halogen-containing waste to form hydrogen chloride. Bromine-, flourine- or iodine-containing waste behaves in the same way. The reaction may be schematized as follows: represents hydrogen, HCl represents hydrogen chloride and R--H represents a hydrocarbon.
There are essentially two variants of the hydrogenation process. Thermal hydrogenation, also known as thermocracking, is carried out at temperatures of 700.d
REFERENCES:
patent: 4212735 (1980-07-01), Miller
patent: 4351978 (1982-09-01), Hatano et al.
patent: 4618686 (1986-10-01), Boyer
patent: 4747937 (1988-05-01), Hilfman et al.
patent: 4758346 (1988-07-01), Johnson
patent: 4775475 (1988-10-01), Johnson
patent: 4909947 (1990-03-01), Johnson et al.
patent: 5051030 (1991-09-01), Saka et al.
patent: 5352335 (1994-10-01), Beaver
Din 38 409 (Part 14).
Metalloberflache 1990, 44 186-190, E. Oswald.
Pure & Appl. Chem. 1990, 62, 1145-1146.
Report PNL-6491-2; Order No. DE88-009535; April 1988: the document is available through NTIS -National Technical Information Service; United States Department of Commerce (document not enclosed).
Chem. Abstr. 110[12]: 101110f.
"Mull und Abfall" 1991, 23, 283-294.
Chem. Abstr. 110:81873b.
AIChE Journal 1992, 38 (No. 7), 1003-1012.
Chem. Abstr. 107 [20]: 182791s.
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
McCarthy Neil
Ortiz Daniel S.
Szoke Ernest G.
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