Liquid purification or separation – Processes – Chemical treatment
Patent
1995-09-05
1997-10-14
McCarthy, Neil
Liquid purification or separation
Processes
Chemical treatment
210908, 210909, C02F 170
Patent
active
056768451
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a catalytic treatment process for effluents, which contain particularly halogen-organic and optionally inorganic compounds, with the use of a noble metal catalyst on a support.
The known catalytic treatment processes for effluents, which contain halogen-organic, particularly chloro-organic compounds (AOX), use, for example, alkaline or alkaline earth metals or noble metals or noble metal compounds as a catalyst. Thus, it is known that the decomposition of the chloro-organic compounds contained in the effluent is very successful in the presence of platinum, palladium or rhodium, palladium having the highest activity. Further investigations have shown that the selection of the support material for the catalyst activity should not be underestimated. Thus, it is known that palladium on aluminum oxide as a support has a lower activity than palladium on carbon as a support.
It is an object of the invention to develop a treatment process for effluents with the use of a noble metal catalyst on a support which has an improved activity.
According to the invention, the object is achieved in that the effluent is treated in the presence of hydrogen on a noble metal catalyst on a support whose support material contains inorganic oxide and carbon. According to the invention, inorganic oxides are preferably oxides of aluminum, magnesium, zirconium, silicon, titanium, alone or combinations thereof. The catalyst support preferably contains silicon dioxide as the oxidic constituent. In a preferred variant, the oxide faction of the support amounts to at least 50% in weight, preferably 55 to 85% in weight.
The catalyst contains metals of the eighth subgroup of the Periodic Table of Elements, such as platinum, palladium iridium or rhodium, preferably palladium, alone or in combinations thereof, as the active constituent.
The effluent, particularly an effluent from the epichlorohydrin production, with a pH-value of 3 to 10, preferably 4 to 6, is introduced into at least one reactor in which the noble metal catalyst is situated on a support, and is treated with hydrogen at 5.degree. to 80.degree. C., preferably 10.degree. to 30.degree. C., and 1 to 10 bar.
The adjustment of the pH-value takes place in a manner known per se.
Thus, for example, before the treatment of an effluent from the epichlorohydrin production which normally has a pH-value of from 11 to 13, the pH-value of the effluent is adjusted to a value of .gtoreq.3 or .ltoreq.10 by the addition of an acid, preferably hydrochloric acid.
It was found to be expedient to carry out the treatment in an amount of hydrogen which corresponds at least to the stoichiometrically calculated amount of the AOX-content to be removed.
At a normal pressure and at temperatures between 10.degree. C. and 25.degree. C., the solubility of the hydrogen gas is below 1.7 mg/l and rises proportionally to the working pressure.
The decomposition output may vary according to the starting concentration of the chemical nature of the halogen-organic compounds, the pH-value, the hydrogen gas concentration or gasification rate and the temperature.
By means of a palladium support catalyst with 0.5 or 1% palladium, decomposition outputs of, for example, 0.5 to 4 mg AOX are achieved per hour and gram of catalyst.
The hydrogen may be charged into the effluent either by means of a direct introduction of hydrogen gas or by means of a membrane module.
Membranes of an integral-symmetrical construction and particularly compact membranes are particularly suitable. These membranes have a porous water-resistant support structure and at least one layer of a water-resistant non-porous polymer, the effluent to be gasified being guided past this layer. This non-porous layers consists, for example, of a silicone polymer.
Other methods, for example, by way of gas saturators, are also suitable for the charging of hydrogen.
The charging of hydrogen may take place either when the effluent comes in contact with the catalyst or it may take place separately. In a preferred variant, the charging of the hy
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Bretz Karl-Heinz
Derleth Helmut
Neuenfeldt Gerhard
Ottmann Alfred
Schindler Hubert
McCarthy Neil
Solvay Deutschland GmbH
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