Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1998-07-09
2001-03-06
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06197997
ABSTRACT:
The present invention relates in general to loaded ion-exchange resins, their preparation, their use in aqueous and non-aqueous solvent applications and, in particular, their use in the purification of acetic acid and/or acetic anhydride prepared by the Group VIII noble metal catalysed, methyl iodide promoted carbonylation of methanol and/or methyl acetate by removal therefrom of iodide derivatives, eg. alkyl iodides and the like.
Ion-exchange resins are well-known commercial products. Typically, they are synthetic insoluble cross-linked polymers carrying acidic or basic side-groups which have high exchange capacity. They have many applications, including water-treatment, extraction, separation, analysis and catalysis. A feature of ion-exchange resins is that to a greater or lesser extent their volume can change with changes in their solvent environment, for example from aqueous to organic and vice-versa. Thus, for example, the ion-exchange gel resin, AMBERLITE IR120™ can shrink by as much as 40% when its environment is changed from aqueous (as purchased) to the silver-exchanged form in acetic acid and can swell correspondingly in the reverse operation. Macroreticular resins too can shrink, albeit less markedly, when their environment is changed from aqueous to non-aqueous. For many of the applications referred to hereinbefore ion-exchange resins are used in loaded form, for example loaded with metals, generally by ion-exchange or impregnation of the swollen resin. It is our experience that when ion-exchange gel resins at least are loaded in the swollen form, their effectiveness in the shrunken form is not that which might be expected from the amount of the loaded moiety present.
The problem to be solved by the present invention is that of providing a loaded ion-exchange resin having improved effectiveness in the shrunken form. We have surprisingly found that a solution to the problem is to load the ion-exchange resin in the shrunken form, as opposed to the swollen form.
Accordingly the present invention provides a loaded ion-exchange resin, which resin has been loaded in its shrunken form.
The ion-exchange resin may be any suitable resin. It may be, for example, an ion-exchange gel resin, a macroreticular ion-exchange resin or indeed any other resin which experiences a volume change upon changing the nature of its solvent environment. The invention is particularly applicable to gel resins because these exhibit a pronounced loss in effectiveness upon changing their environment from aqueous to organic.
The ion-exchange resin may be loaded with H
+
ions, at least one metal and/or a group of atoms which together form a charged moiety. The metal may be in the form of a cation of the metal. The metal may be any metal of Groups I to VIII of the Periodic Table, for example a metal of Groups Ib, IIb, III, Va, VIa, VIla and VIII. The Periodic Table referred to herein is that to be found in Advanced Inorganic Chemistry by Cotton and Wilkinson, Fourth Edition, published in 1980 by John Wiley and Sons. Preferred metals include silver, palladium and mercury. Alternatively, or in addition, the ion-exchange resin may be loaded with a group of atoms which together form a charged moiety. The charged moiety may be anionic or cationic. A typical anionic charged moiety may be a sulphonic acid anion.
It is believed though we do not wish to be bound by any theory that ion-exchange resins loaded in the swollen form may lose their effectiveness in the shrunken form because a high proportion of the loaded moiety becomes trapped within the resin during its collapse consequent upon change of solvent and hence is unavailable for the purpose for which it was loaded.
In another embodiment the present invention provides a process for the production of a loaded ion-exchange resin as hereinbefore described which process comprises loading an ion-exchange resin in its shrunken form.
Suitable ion-exchange resins and loading moieties are as hereinbefore described.
The shrunken form of the resin may suitably be obtained by changing the liquid environment of the resin from a swelling environment to a shrinking environment. Thus, for example, removal of water from a gel resin and replacement with acetic acid provides the resin in its shrunken form. In a preferred mode of operating the process the shrunken form of the resin is thereafter loaded. Loading of the resin in its shrunken form may suitably be accomplished by ion-exchange and/or by impregnation. Loading may be accomplished at ambient or elevated temperature.
The loaded ion-exchange resins of the present invention may be used in any process in which a resin is conventionally employed, particularly in those processes in which the solvent environment would otherwise cause shrinkage of the gel with associated loss in effectiveness.
In another aspect the present invention therefore provides for use of a loaded ion-exchange resin as hereinbefore described in a process in which the solvent environment causes shrinkage of the resin.
Such a process is the removal of iodide compounds from the liquid carboxylic acids and/or carboxylic anhydrides obtained from the Group VIII noble metal catalysed, alkyl iodide co-catalysed carbonylation of alcohols and/or their reactive derivatives. It is known that a problem associated with acetic acid and/or acetic anhydride so-produced is that even after distillation the acetic acid and/or acetic anhydride frequently contains small amounts of iodide impurities. Whilst the exact nature of these compounds is not known for certain, they probably comprise a mixture of methyl iodide and other higher alkyl iodides, HI and iodide salts. Such impurities are particularly troublesome since they can poison many of the catalysts which are employed in subsequent chemical conversions of the acetic acid and/or acetic anhydride. A case in point is the catalysts used to prepare vinyl acetate from ethylene and acetic acid which are extremely sensitive to iodide impurities.
Accordingly in a further embodiment the present invention provides a process for removing iodide compounds from a liquid carboxylic acid and/or carboxylic anhydride obtained from the Group VIII noble metal catalysed, alkyl iodide co-catalysed carbonylation of alcohols and/or their reactive derivatives which process comprises contacting the liquid carboxylic acid and/or carboxylic acid anhydride with a metal loaded ion-exchange resin as hereinbefore described wherein the metal is one or more of the metals silver, palladium or mercury.
Processes for producing a liquid carboxylic acid and/or anhydride by the Group VIII noble metal catalysed, alkyl iodide co-catalysed carbonylation of alcohols and/or their reactive derivatives are well-known in the art.
In a preferred aspect this embodiment provides a process for removing iodide compounds from acetic acid and/or acetic anhydride obtained from the rhodium-catalysed, methyl iodide co-catalysed carbonylation of methanol and/or methyl acetate.
A preferred ion-exchange resin is an ion-exchange gel resin, for example AMBERLITE IR120, and AMBERLITE IR118. The ion-exchange resin is preferably one which is loaded with silver.
The iodide compounds may be C
1
to C
10
alkyl iodides, hydrogen iodide or iodide salts, and in particular methyl iodide and/or C
5
to C
7
iodides.
The process may suitably be carried out by passing liquid acetic acid and/or acetic anhydride contaminated with iodide compounds through a fixed bed of the resin at a predetermined rate. Preferably the resin bed is graded by backflushing before use. The feed rate employed will depend on a number of variables including the amount of iodide impurities in the acetic acid and/or acetic anhydride, the degree of acetic acid and/or acetic anhydride purity required and the particular resin employed. Typical flow rates are in the range 0.5 to 50, preferably 5 to 15 bed volumes per hour. Optimum flow rates will depend upon the temperature of the resin bed and can readily be determined.
The temperature at which the process is carried out must be high enough to prevent acetic acid
Carey John Laurence
Jones Michael David
Poole Andrew David
BP Chemicals Limited
McKane Joseph K.
Murray Joseph
Nixon & Vanderhye
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