Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Combined
Reexamination Certificate
2002-06-03
2004-07-13
Raymond, Richard L. (Department: 1624)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Combined
C562S412000, C562S414000
Reexamination Certificate
active
06761860
ABSTRACT:
The present invention relates to a novel process for the production of monocarboxylic and polycarboxylic aromatic acids by the catalytic oxidation in homogeneous phase of aromatic compounds carrying at least one oxidizable substituent group attached directly to the carbon atom of the corresponding aromatic nucleus.
FIELD OF THE INVENTION
Processes for the production of monocarboxylic and polycarboxylic aromatic acids are well known in the literature. They are normally carried out in liquid phase, operating either continuously or discontinuously and using as substrates aromatic compounds carrying at least one oxidisable substituent group attached directly to the carbon atom of the corresponding aromatic nucleus, where the expression “oxidisable substituent group” is intended to indicate any substituent in which a carbon atom is bonded directly to the aromatic nucleus and which, as a result of oxidation, is converted into a carboxylic group.
The oxidizing agent is generally gaseous molecular oxygen, preferably diluted with an inert gas; for obvious reasons of practicality, air (optionally enriched with molecular oxygen) is the gaseous mixture most commonly used for this purpose. The oxidation reaction is normally carried out using as solvent an aqueous organic acid, preferably acetic acid, normally with a water content of from 2 to 5%.
Those reactions are carried out in the presence of a catalytic complex generally composed of one or more metals, normally in the form of salts soluble in the reaction solvent, and a suitable activator. The metal performs the function of catalyzing the actual oxidation reaction while the activator is used to return the metal (which undergoes a reduction in its oxidation number during catalysis) to its original valency, thus enabling it to regain and exert its catalytic activity. The activator may itself be a metal, in which case it also will preferably be present in the form of a salt soluble in the reaction medium; alternatively, it is possible to use organic compounds having carbonyl functions, such as ketones or aliphatic aldehydes, preferably acetaldehyde, or molecular bromine.
DE-1147571 discloses a method for the synthesis of phtalic acids by catalytic oxidation of the corresponding alkave precursors in liquid phase, the precursors are not dissolved in a suitable solvent but are used as the solvent themselves.
British patent GB-1063964 describes a process for the production of monocarboxylic and polycarboxylic aromatic acids at temperatures of preferably from 80 to 130° C. and pressures of from 1 to 60 kg/cm
2
by means of a catalytic complex substantially based on zirconium and cobalt.
U.S. Pat. No. 5,112,992 describes the production of aromatic acids at temperatures of from 100 to 275° C., using metals from groups IIIA and IVA of the periodic table of elements (groups IIIB and IVB according to the new notation adopted, for example, by Perry, Chemical Engineers' Handbook, VI edition, 1984), in particular zirconium and hafnium, in order to increase the kinetics of oxidation reactions that use catalytic complexes based on cobalt and manganese in the presence of bromine as the activator.
European patent application EP-475926 describes a process for the production of polycarboxylic aromatic acids which uses a catalytic complex based on manganese and cobalt and which operates at temperatures of from 100 to 220° C. and at pressures of 100 kilopascals or higher.
International patent application WO 98/29378 describes a catalytic complex, operating in absence of bromine, which comprises:
1. at least one metal having a valency higher than 2 which belongs to group VIIIA of the periodic table of elements, preferably ruthenium, iridium, palladium, platinum; and/or at least one metal from group VIIA, preferably rhenium; and/or cerium; and
2. at least one metal from group IVA of the periodic table of elements, preferably zirconium and/or hafnium;
where the catalytic pair cerium-zirconium constitutes the preferred complex for implementing the invention.
N. B. groups VIIIA, VIIA and IVA indicated above correspond, respectively, to groups VIII, VIIB and IVB according to the new notation adopted, for example, by Perry, Chemical Engineers' Handbook, VI edition.
The catalytic complex described in WO 98/29378 is used for the production of monocarboxylic and polycarboxylic aromatic acids, preferably from meta- and para-xylene, operating at temperatures of from 90 to 150° C., preferably from 105 to 115° C., and at pressures of from 1 to 20 barg, preferably from 2 to 5 barg.
Finally, U.S. Pat. No. 5,527,957, WO 93/24440, WO 97/30963 and WO 92/18454 disclose processes for the manufacture of polycarboxylic acids by catalytic oxidation in liquid phase of the corresponding precursors wherein the stage of filtering the end product is carried out at high pressures and temperatures whereas WO 96/111899 discloses a process for the manufacture of polycarboxylic acids in which the major portion of the mother liquors resulting from the filtration stage is recycled into the oxidation reactor.
The above listed five documents relate however to oxidation processes carried out in presence of bromine as the activator, whose activating action takes place at temperatures of about 150 to 250° C. and at pressures of at least 20-25 barg; given the high operating conditions, the corresponding plants have to be construed with particularly resistant materials, such as titanium or its alloys, with an evident increase in costs; a process for the manufacture of monocarboxylic and polycarboxylic aromatic acids in absence of bromine is thus preferable.
DESCRIPTION OF THE INVENTION
Monocarboxylic and polycarboxylic aromatic acids have a very low solubility in the solvents conventionally used in oxidation reactions of the type described above; therefore, they can be readily isolated from the reaction medium by simple filtration.
The catalytic complex used in the production of monocarboxylic and polycarboxylic acids is normally obtained by mixing into the reaction solvent at least one metal having catalytic action, generally in the form of a soluble salt, and an activator. The formation of the complex in its catalytically active state is not generally immediate but, depending on the case concerned, requires a time ranging from 30 to 90 minutes; this phenomenon is readily detectable with the naked eye because it is accompanied by a clear change in colour in the reaction solution.
The catalytic complex so formed is, however, a relatively unstable system; in fact, if it is not used within a short period, it undergoes a process of degradation which leads to a reduction in the valency of the metal which, in turn, loses its catalytic power; in this case too, the degradation of the catalytic complex is readily detectable with the naked eye because the solution containing it gradually returns to its original colour. In the mother liquors resulting from the production of monocarboxylic and polycarboxylic acids, this degradation process begins almost immediately after filtration and is generally complete within a few hours. It will be appreciated that the degradation of the catalytic complex is a phenomenon which is hardly desirable because it involves not only a reduction in its oxidizing capacity (and therefore a drop in yield of the entire production cycle) but, much more seriously, a substantial reduction in its selectivity, with the consequent formation of mixtures of various products.
The object of the present invention is therefore to provide a novel process for the continuous production of monocarboxylic and/or polycarboxylic acids, such as, for example, benzoic acid, terephthalic acid, isophthalic acid, trimesic acid and N2,6-naphthalenedicarboxylic acid, by the oxidation in liquid phase of the corresponding alkyl aromatic hydrocarbons in absence of bromine, which process does not have the disadvantages specified above; in particular, it relates to a process operating at temperature and pressure conditions lower than those of standard bromine-based processes and in which most of the catal
Codignola Franco
Moro Antonio
Dykas Frank J.
Nipper Stephen M.
Shaver Robert L.
Tucker Zachary C.
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