Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/10—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction with carbon monoxide
  • C07C51/12—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction with carbon monoxide on an oxygen-containing group in organic compounds, e.g. alcohols
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/54—Preparation of carboxylic acid anhydrides
  • C07C51/56—Preparation of carboxylic acid anhydrides from organic acids, their salts, their esters or their halides, e.g. by carboxylation

Definitions

• the present invention relates in general to a carbonylation process and in particular to a carbonylation process for the production of acetic acid and/or acetic anhydride in the presence of a Group VIII metal carbonylation catalyst, a halogen- containing co-catalyst, and a finite concentration of water.
• a Group VIII metal carbonylation catalyst a halogen-containing co-catalyst
• a finite concentration of water a finite concentration of water.
• acetic acid is produced by the carbonylation in the liquid phase of methanol and/or a reactive derivative thereof in the presence of a rhodium - or an indium - containing carbonylation catalyst, an iodine-containing co-catalyst, a finite concentration of water, and optionally, a promoter are operated on a commercial scale.
• the continuous rhodium-catalysed, homogeneous methanol carbonylation process is said to consist of three basic sections; reaction, purification and off-gas treatment.
• the reaction section comprises a stirred tank reactor, operated at elevated temperature and pressure, and a flash vessel. Liquid reaction composition is withdrawn from the reactor and is passed through a flashing valve to the flash tank where the majority of the lighter components of the liquid reaction composition (methyl iodide, methyl acetate and water) together with product acetic acid are vaporised.
• the vapour fraction is then passed to the purification section whilst the liquid fraction (comprising the rhodium catalyst in acetic acid) is recycled to the reactor (as shown in Figure 2 of Howard et al).
• the purification section is said to comprise a first distillation column (the light ends column), a second distillation column (the drying column) and a third distillation column (the heavy ends column) (as in Figure 3 of Howard et al).
• a first distillation column the light ends column
• the drying column the drying column
• the heavy ends column the heavy ends column
• methyl iodide and methyl acetate are removed overhead along with some water and acetic acid.
• the vapour is condensed and allowed to separate into two phases in a decanter, both phases being returned to the reactor.
• acetic anhydride by carbonylation is known from, for example, GB-A-1468940 which discloses the two-stage production of an anhydride of a monocarboxylic acid by reacting a carboxylate ester satisfying the formula RCOOR or an ether satisfying the formula ROR with an acyl halide satisfying the formula RCOX, formed in situ or in a separate stage, under substantially anhydrous conditions, wherein X is iodide or bromide, the Rs may be the same or different and each R is a monovalent hydrocarbyl radical or a substituted monovalent hydrocarbon radical wherein the or each substituent is inert.
• the acyl halide may be produced by carbonylation of a halide satisfying the formula RX at super atmospheric pressure, R being as hereinbefore defined, and the carbonylation may be effected in the presence as catalyst of a Group VIII noble metal, and optionally a promoter.
• RX a halide satisfying the formula RX at super atmospheric pressure
• R being as hereinbefore defined
• the carbonylation may be effected in the presence as catalyst of a Group VIII noble metal, and optionally a promoter.
• GB-A- 1468940 it is important that the carbonylation reaction should be carried out under substantially anhydrous conditions.
• acetic anhydride can be produced with or without the net co-production of acetic acid.
• EP-A-87870 discloses a process for the production of acetic anhydride with or without the net co- production of acetic acid from methanol and carbon monoxide in a series of esterification, carbonylation and separation steps comprising:- (1) reacting methanol with recycle acetic acid in an esterification step to form an esterification product containing predominantly methyl acetate, water and optionally unreacted methanol,
• the carbonylatable reactant in carbonylation processes for the production of acetic acid there is used methanol and/or a reactive derivative thereof which is, for example, either methyl acetate, dimethyl ether, or methyl iodide.
• methyl acetate is formed in situ by the reaction of methanol with acetic acid present in the liquid reaction composition either by way of solvent for the carbonylation or by way of the product of carbonylation, methyl acetate is a carbonylatable reactant of choice for the production of acetic acid.
• the carbonylation reactant in the production of acetic anhydride by carbonylation there is generally used methyl acetate.
• the present invention provides a process for the production of acetic acid and/or acetic anhydride which process comprises carbonylating with carbon monoxide in a liquid reaction composition in a carbonylation reactor at least one methyl ester of an aliphatic carboxylic acid having a boiling point equal to or greater than the temperature of the carbonylation reaction in the presence of a Group VIII metal carbonylation catalyst, a hydrocarbyl halide co-catalyst and in the presence or absence of water.
• the carbonylation product comprises acetic anhydride.
• the carbonlylation product comprises acetic acid.
• Water may be introduced to the carbonylation reactor together with or separately from other components of the reaction composition. Water may be separated from other components of the reaction composition withdrawn from the reactor and may be recycled in controlled amounts to maintain the concentration of water in the liquid reaction composition.
• the water concentration in the liquid reaction composition for the production of acetic acid may be in the range from 0.1 to 15% by weight, preferably below 11% by weight, more preferably below 7% by weight.
• Esters suitable in the process have a boiling point equal to or greater than the carbonylation reaction temperature. Typically the reaction temperature is at least 100°C. Suitable methyl esters having a boiling point higher than methyl acetate may be selected from:-
• R is selected from (i) C 2 to C 3 o aliphatic hydrocarbyl groups and substituted derivatives thereof.
• R may also comprise an aromatic functionality provided the aromatic group and the ester functionality is separated by at least one aliphatic carbon moiety, for example methyl phenylacetate.
• R is an organic group
• X is either S, Se, P or As
• m is 0, 1 or 2
• n is either 1 or 2
• the C 2 to C 3 o hydrocarbyl group (i) may suitably be an alkyl group or an alkenyl group.
• Suitable alkyl groups may be linear or cyclic, branched or unbranched groups.
• the alkyl or alkenyl group may contain from 5 to 20 carbon atoms.
• suitable olefinically unsaturated esters include maleic acid esters, acrylic acid esters, and itaconic acid esters.
• n in the formula (I) is greater than 1, for example 2.
• Suitable esters of formula (I) wherein n is greater than 1 are for example dimethyl adipate, dimethyl succinate and dimethyl glutarate.
• An advantage of employing, for example, dimethyl succinate is that because of its higher density and hence higher moles of methyl per unit volume than methyl acetate it is possible to use less of it, thereby allowing more space in the reactor for acetic acid or acetic anhydride. Additionally an advantage of the esters is their reduced vapour pressure allowing a higher partial pressure of CO in the reactor.
• Suitable aromatic groups include C ⁇ -aryl groups which may be substituted with up to five substituents.
• Suitable substituents of the group R in the formula (I) include alkyl, aryl, alkoxy, aroxy or carboxylate, and hydroxyl groups.
• the preferred ester is where R is C 3 and n is 2, namely dimethyl glutarate. In particular the use of dimethyl glutarate provides the advantage that it does not precipate out of solution.
• R may be independently the same as in the formula (I), including groups of the formula OR' wherein R' is a group as defined aforesaid.
• suitable polymeric materials include polymeric esters having a repeat unit which is: either [CH(CO 2 CH 3 )CH 2 ] m (III)
• m is in the range 50 to 500.
• suitable methyl esters of inorganic oxo-acids include trimethyl phosphate, trimethyl borate, dimethyl carbonate, and dimethyl sulphate.
• Suitable methyl esters having a boiling point equal to or greater than the carbonylation reaction temperature include methyl hexanoate, methyl octanoate, methyl decanoate, methyl-3-hydroxybenzoate, dimethyl adipate, dimethyl succinate and dimethyl glutarate.
• the methyl ester may comprise substantially the whole of the carbonylatable reactant or it may be replaced in part by, for example, one or more of methanol, methyl acetate, and methyl iodide.
• the methyl ester is present at a concentration of from 0.1 to 40 weight percent, preferably from 10 to 30 weight percent.
• the replacement of methyl acetate by a methyl ester having a boiling point equal to or greater than the reaction temperature in the liquid carbonylation reactor composition can offer several advantages. Firstly, reducing the amount of volatile components in product distillation, for example with reference to Howard et al in the flashing section of the reactor section and the first distillation column of the purification section, will simplify the plant and its operation and thereby reduce costs. Secondly, by decreasing the partial pressure of ester reactant in the reaction mixture a higher partial pressure of carbon monoxide can be utilised, thereby giving higher catalyst activity at a given temperature, or a lower total reaction pressure may be employed if desired.
• the carbonylation is accomplished in the presence of a Group VIII metal carbonylation catalyst.
• Suitable metals of Group VIII include for example nickel, cobalt, and the noble metals.
• the carbonylation catalyst is a noble metal of Group VIII of the Periodic Table of the Elements.
• the Group VIII noble metal there may be used iridium, osmium, platinum, palladium, rhodium or ruthenium, preferably rhodium or iridium.
• Rhodium is the catalyst of choice for the production of acetic anhydride under anhydrous conditions, whereas both rhodium and iridium are preferred for the production of acetic acid in the presence of water.
• the catalyst may comprise any metal compound which is soluble in the liquid reaction composition.
• the catalyst may be added to the liquid reaction composition in any suitable form which dissolves in the liquid reaction composition or is convertible to a soluble form.
• suitable rhodium-containing compounds which may be added to the liquid reaction composition include [Rh(CO) 2 Cl] 2 , [Rh(CO) 2 I] 2 , [Rh(Cod)Cl] 2 , Rh(III) chloride, Rh(III) chloride trihydrate, Rh(III) bromide, Rh(III) iodide, Rh(III) acetate, Rh dicarbonlylacetylacetonate, RhCl 3 (PPh 3 ) 3 and RhCl(CO)(PPh 3 ) 2 .
• the rhodium catalyst concentration in the liquid reaction composition is in the range from 50 to 5000 ppm by weight of rhodium, preferably from 100 to 1500 ppm.
• green iridium acetate which may be used in an acetic acid or aqueous acetic acid solution.
• the iridium catalyst is present in the liquid reaction composition at a concentration in the range from 400 to 5000 ppm by weight of iridium, preferably from 700 to 3000ppm.
• the catalyst may be attached to a suitable carrier, for example by complexing with a suitable ligand.
• promoters for the carbonylation catalysts in the process of the invention.
• the choice of promoter will depend to some extent on the particular noble metal used as catalyst.
• the promoter is suitably selected from the group consisting of iodide salts of alkali and alkaline earth metals of which lithium iodide is preferred, quaternary ammonium iodides, quaternary phosphonium iodides, and phosphine oxides.
• the promoter may be present up to its limit of solubility.
• ruthenium and/or osmium may be used as promoters as described, for example, in EP-A-0728727.
• the promoter is suitably a metal selected from ruthenium, osmium, tungsten, rhenium, zinc, cadmium, indium, aluminium, gallium and mercury, and is preferably selected from ruthenium and osmium. Ruthenium is the more preferred promoter for iridium catalysts.
• the promoter is present in an effective amount up to the limit of its solubility in the liquid reaction composition.
• the promoter is suitably present in the liquid reaction composition at a molar ratio of promoter: iridium of [0.5 to 15]: 1.
• a suitable promoter concentration is 400 to 5000 ppm by weight of promoter metal.
• Suitable hydrocarbyl halide co-catalysts include alkyl halides.
• the alkyl halide is an iodide.
• the hydrocarbyl halide is methyl iodide.
• the concentration of methyl iodide in the liquid reaction composition is in the range from 1 to 30% by weight, for example from 5 to 20% by weight.
• the carbon monoxide reactant may be essentially pure or may contain inert impurities such as carbon dioxide, methane, nitrogen, noble gases, water and Ci to C 4 paraffinic hydrocarbons.
• the presence of hydrogen in the carbon monoxide feed and generated in situ by the water gas shift reaction is preferably kept low in the production of acetic acid as its presence may result in the formation of hydrogenation products.
• the amount of hydrogen in the carbon monoxide reactant is preferably less than 1 mol %, more preferably less than 0.5 mol % and yet more preferably less than 0.3 mol % and/or the partial pressure of hydrogen in the carbonylation reactor is preferably less than 1 bar partial pressure, more preferably less than 0.5 bar and yet more preferably less than 0.3 bar.
• the presence of hydrogen may, on the other hand, be beneficial in the production of acetic anhydride.
• the partial pressure of carbon monoxide in the reactor is in the range greater than 0 to 40 bar, typically from 4 to 30 bar.
• the total pressure of the carbonylation reaction is suitably in the range 10 to 200 barg, preferably 15 to 100 barg, more preferably 15 to 50 barg.
• the temperature of the carbonylation reaction is suitably in the range 100 to 300°C, preferably in the range 150 to 220°C.
• the process of the present invention may be performed as a batch or a continuous process, preferably as a continuous process.
• Acetic acid product may be recovered for example from the liquid reaction composition by withdrawing vapour and/or liquid from the carbonylation reactor and recovering acetic acid from the withdrawn material.
• acetic acid is recovered from the liquid reaction composition by continuously withdrawing liquid reaction composition from the carbonylation reactor and recovering acetic acid from the withdrawn liquid reaction composition by one or more flash and/or fractional distillation stages in which the acetic acid, is separated from the other components of the liquid reaction composition such as rhodium or iridium catalyst,
• Acetic anhydride may be recovered in similar manner except for the non- participation of water in the recovery process.
• the autoclave was pressure tested to 40 barg with nitrogen and then flushed three times with carbon monoxide up to 10 barg.
• An initial charge consisting of an ester (approx. 50. Og), acetic acid (approx. 58. Og), methyl iodide (approx. 9.8g) and water (approx. 10. Og), was placed into the autoclave, which was then re-purged with carbon monoxide to 4 barg and vented slowly so as not to lose any volatiles. Then carbon monoxide (approx.
• Example 2 Experiment A was repeated except that the charge consisted of methyl octanoate (49.06g, 310mmol), acetic acid (58. lg, 967mmoI), water (10.65g, 591mmol) and methyl iodide (9.89g, 69.6mmol).
• the iridium catalyst solution consisted of H 2 IrCi 6 solution (1.368g), water (5.0g, 278mmol) and acetic acid (6.1g, lOlmmol).
• the initial reaction rate, based on carbon monoxide uptake was 8.9mol/l/hr.
• Acetic acid was the major liquid product detected (>99%). This demonstrates an example of a linear g methyl ester as a substitute for methyl acetate.
• Example 3 This demonstrates an example of a linear g methyl ester as a substitute for methyl acetate.
• a baseline experiment was performed using rhodium catalyst instead of an iridium based catalyst as per examples 1-17.
• the experiment was performed in an autoclave charged with methyl acetate (47.77g, 645 mmol), acetic acid ( 57.5g, 958mmol), water(14.24g, 791 mmol) and methyl iodide (25.52g, 180 mmol).
• 15 rhodium catalyst solution comprised of [RhCl(CO) 2 ] 2 (0.1525g, 0.39 mmol) with acetic acid (15g, 250 mmol).
• Example 18 Experiment C was repeated except that the charge consisted of dimethyl glutarate ( 50.5g, 315 mmol), acetic acid (63.2g, 1053mmol), water (14.25g, 792 mmol) and methyl iodide (25.76g, 181 mmol).
• the rhodium catalyst solution comprised of [RhCl(CO) 2 ] 2 (0.15g, 0.385 mmol) with acetic acid (15g, 250 mmol). The rate of the reaction, based on carbon monoxide uptake started at the rate of 10.0 mol/l/h and slowly declined until virtually all the methyl acetate had been consumed. Acetic acid was the major liquid product detected ( >99%).
• the experiment was performed in an autoclave charged with methyl acetate (32.5g, 645 mmol), acetic acid (74.5g, 1242mmol), water (14.0g, 777 mmol), methyl iodide (25.04g, 176 mmol)and [Ru(CO) 4 I 2 ] (1.82g, 3.9 mmol).
• the rhodium catalyst solution comprised of [RhCl(CO) 2 ] 2 (0.1524g, 0.39 mmol) with acetic acid (15g, 250 mmol).
• Example 23 Experiment 22 was repeated except the charge consisted of dimethyl glutarate (34.0g, 212 mmol), acetic acid (78.02g, 1300mmol), water (14.01g, 777 mmol), methyl iodide (27.01g, 190 mmol) and [Ru(CO) 4 I 2 ] (3.60g, 7.6 mmol).
• the rhodium catalyst solution comprised of [RhCl(CO) 2 ] 2 (0.15g, 0.386 mmol) with acetic acid (15.01g, 250 mmol). The rate of the reaction, based on carbon monoxide uptake started at the rate of 21.5 mol/l/h and slowly declined until virtually all the methyl acetate had been consumed. Acetic acid was the major liquid product detected ( >99%).
• a baseline experiment was performed using rhodium catalyst supported on a quarternised Purolite 4-VP resin.
• the experiment was performed in an autoclave charged with methyl acetate (25.045g, 338 mmol), acetic acid (31.45g, 524mmol), water (8.506g, 472 mmol), methyl iodide (10.355g, 73mmol).
• the rhodium catalyst comprised of [RhCl(CO) 2 ] 2 (0.064g, 0.16 mmol) supported on 13.906g of methyl iodide quarternised Purolite 4-VP resin (dry weight before quarternisation: 7.758g).
• the rhodium catalyst comprised of [RhCl(CO) 2 ] 2
• Total propionic acid analyses of less than 30ppm are below the detection limit for the combined propionic acid precursors e.g. ethyl iodide, ethyl acetate, acetaldehyde, diethylglutarate and mono-ethylglutarate.
• propionic acid precursors e.g. ethyl iodide, ethyl acetate, acetaldehyde, diethylglutarate and mono-ethylglutarate.

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