Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2000-03-24
2001-07-03
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S149000, C502S024000, C502S028000
Reexamination Certificate
active
06255510
ABSTRACT:
This invention relates to the production of aromatic carboxylic acids such as terephthalic acid and isophthalic acid.
Terephthalic acid for example is produced commercially by oxidising p-xylene with oxygen in a liquid phase which comprises a lower aliphatic carboxylic acid solvent, such as acetic acid, and a dissolved heavy metal catalyst system (usually cobalt and manganese and a bromine promoter). A slurry of terephthalic acid in the solvent is withdrawn from the reactor and is subjected to a solids-liquid separation process resulting in crude terephthalic acid crystals which may be subsequently processed further and a mother liquor filtrate which, in addition to catalyst and promoter used in the oxidation reaction, contains dissolved terephthalic acid and various by-products and impurities. These by-products and impurities arise from various sources such as minor impurities in the p-xylene feed stock to the reaction, incomplete oxidation of p-xylene resulting in partially oxidised products and by-products arising from the competing side reactions in the oxidation of p-xylene to terephthalic acid.
It is common practice to recycle a large proportion of the recovered mother liquor to the oxidation reaction in order to return catalyst and promoter to the oxidation reaction while purging a smaller proportion to a solvent recovery system so as to maintain the level of impurities and by-products in the reaction within tolerable limits. In the solvent recovery system, the mother liquor purge is subjected to evaporation to remove a substantial proportion of the aliphatic acid solvent and water present (which can be returned to the oxidation reaction) leaving a concentrate containing terephthalic acid and impurities/by-products together with some of the heavy metal catalyst present in the original mother liquor filtrate. The concentrate (the residues) may then be disposed of or, if economically justifiable, treated in order to recover valuable components for recycling, e.g. catalyst metals. Typical downstream treatments of the residues include catalyst recovery, pyrolytic decomposition to eliminate substantially all of the organic content of the residues (e.g. by incineration in a high temperature furnace) and anaerobic/aerobic biological treatment to reduce chemical oxygen demand (COD).
The present invention is concerned with catalyst metal recovery via pyrolysis of the residues where the catalyst metals are present to a significant extent in their (III) and/or (IV) states as oxides thereof and as such are insoluble in water and only very sparingly soluble in acids.
U.S. Pat. No. 3,341,470 discloses incinerating the residues to oxide ash and dissolving the ash with sulphuric acid containing chloride. The manganese and cobalt components are recovered by treatment of the solution with sodium carbonate to precipitate cobalt and manganese as their carbonates. The recovered carbonates are then treated with acetic acid to produce acetates for recycle to the oxidation reaction.
U.S. Pat. No. 4,786,621 discloses recovery of cobalt and manganese, and other metals, in the form of their acetate salts directly from mixed metal oxides present in incinerator ash comprising fly ash and clinkers. The process recovers these metals by use of acetic acid at about the boiling point or reflux temperature and atmospheric pressure in conjunction with use of cobalt metal or hydrazine as reducing agent.
U.S. Pat. No. 4,546,202 discloses recovery of cobalt and manganese from solid aromatic acid incinerator ash by combining the ash with glacial acetic acid, or mixtures of acetic acid and water and heating the mixture under pressure in a stirred reactor. Although it is acknowledged that hydrobromic acid will react with cobalt and manganese oxides, the described reaction is conducted in the absence of bromide.
According to the present invention there is provided a process for the recovery of cobalt and/or manganese from ash containing cobalt and/or manganese as oxides thereof, comprising contacting the ash with an organic acid or an organic acid anhydride with or without bromide ions and recovering the cobalt and/or manganese.
Preferably the cobalt and/or manganese is recovered as acetic acid soluble salts thereof.
The invention is particularly applicable to the treatment of catalyst metal-containing residues obtained by treatment of the mother liquor purge in the course of the production of aromatic carboxylic acids by the liquid phase oxidation of a hydrocarbon precursor of the aromatic carboxylic acid in a monocarboxylic acid solvent containing a catalyst system comprising cobalt and/or manganese and a promoter such as bromine.
We have found that recovery of cobalt and/or manganese can be secured using acetic acid or acetic anhydride without introducing bromide ions to the recovery process; however, recovery can be significantly enhanced without employing high temperature and pressure conditions if bromide ions are present in the reaction.
The present invention is based on the recognition that dissolution of the otherwise difficult to dissolve cobalt and/or manganese oxides obtained following pyrolysis, e.g. incineration, can be readily achieved using an aliphatic acid or aliphatic acid anhydride such as acetic anhydride, preferably in conjunction with a bromide.
The bromide ions may be introduced initially so that the reaction between the anhydride and the ash takes place in the presence of bromide ions. Alternatively, the bromide ions may be introduced after the reaction between the acid or anhydride and the ash has been initiated. Conveniently the amount of bromide employed comprises from 0.5 to 2.0 moles (preferably less than 2 moles, between 0.5 and about 1.5 to 1.8 moles) of bromide for each mole of cobalt or manganese.
In practising the process of the invention, the amount of bromide employed need only be approximately the molar equivalent of the cobalt and/or manganese content of the ash. The use of an amount of bromide which is less than the molar equivalent of the cobalt and/or manganese content of the ash will result in lower recovery of the metals. However, this may be advantageous since operation in a bromide lean regime allows greater flexibility for adjustment of final bromide to metals ratio and may reduce or eliminate the need to treat bromine-containing offgas. Also, in this event, the cobalt/manganese containing residue remaining after treatment can be recycled for further treatment by the process of the invention.
Preferably the bromide is present in the form of hydrogen bromide although we do not exclude the possibility of using other bromides such as acetyl bromide. Thus, according to a preferred aspect of the invention approximately one mole of hydrogen bromide is employed for each mole of metal present in the ash. Thus, for example, where the ash contains both cobalt and manganese oxides, the hydrogen bromide employed corresponds to about one mole per mole of each metal. However, we do not exclude the possibility of greater amounts of bromide being used although, in this event, bromine evolution during the course of the reaction may give rise to increased problems in terms of treating and disposing of bromine-containing gases. Nevertheless as referred to below, greater amounts of bromide may be advantageous in terms of controlling the bromide to metals ratio of the catalyst/promoter system supplied to an oxidation reaction for the production of aromatic carboxylic acids.
Where bromide ions are employed, preferably the bromide is introduced in a liquid phase vehicle; for example dissolved in an aliphatic acid such as acetic acid, or in water.
The organic acid anhydride employed is conveniently acetic anhydride. The organic acid is conveniently acetic acid. A mixture of an organic acid and an organic acid anhydride may also be used and has been found to be effective. Preferably such a mixture should comprise an organic acid and the corresponding acid anhydride, for example a mixture of acetic acid and acetic anhydride is suitable for use in the reaction. If water is present in the rea
Bartlett Julie Ann
Fairhurst Roger Gaskell
Royall David John
E. I. Du Pont de Nemours and Company
Krukiel Charles E.
Nazario-Gonzalez Porfirio
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