GB2029409A - Production of Carboxylic Acids and Their Esters - Google Patents

Abstract

A process for the preparation of aliphatic carboxylic acids and esters thereof by reacting carbon monoxide with alcohols of the formula ROH and eaters thereof of the formula <IMAGE> R and R' being saturated hydrocarbyl radicals with 1 to 12 carbon atoms. The reaction is carried out at elevated pressure (34 atmospheres or greater) in the presence of a ruthenium catalyst and a halogen-containing promoter (e.g. hydrogen iodide or an alkyl halide). Acetic acid and methyl acetate are obtained from methanol.

Description

SPECIFICATION Production of Carboxylic Acid and their Esters This invention concerns a process for the preparation of carboxylic acids and their ester derivatives by reaction of alcohols and their derivatives with carbon monoxide.

More specifically, the inventive process concerns the selective synthesis of aliphatic carboxylic acids and their esters from aliphatic alcohols by reaction with carbon monoxide in the presence of a ruthenium-containing catalyst component and a halogen-containing promoter. Eq. 1 is illustrative of this process, where R is a linear, branched-chain or cyclic saturated hydrocarbyl radical containing 1 to 12 carbon atoms. Methanol carbonylation to acetic acid is a specific illustration of this general synthesis.

ROH+COoRCOOH (1) A wide variety of aliphatic carboxylic acids of differing carbon numbers and structures are presently important articles of commerce. The production of acetic acid, for example, now exceeds 1 billion Kg per annum in the United States, (see "Trends in Petrochemical Technology" by A. M.

Brownstein (1976), chapters 4 and 5; and "Petrochemicals from Coal" by P. M. Spitz, Chemtech, May 1 977, p. 295); important applications for this acid include the production of cellulose acetate and vinyl acetate. There are several commercially proven routes to acetic acid manufacture, including oxidation of ethylene via acetaldehyde, liquid-phase oxidation of saturated hydrocarbons, n-butene oxidation and methanol carbonylation. To the extent that methanol is currently produced from synthesis gas (a mixture of CO and hydrogen), acetic acid via methanol carbonylation also effectively becomes a 'syngas' chemical. Furthermore, since syngas may be generated from a variety of sources, including heavy oil residuals and coal stocks, (see: "Trends in Petrochemical Technology" by A. M. Brownstein (1976), chapters 4 and 5; and "Petrochemicals from Coal" by P. M. Spitz, Chemtech, May 1977, p.

295), this syngas route to acetic acid will likely become increasingly important in an era of petroieum shortages.

Carbonylation processes for the preparation of carboxylic acid from alcohols are well known in the art, these have been directed especially to the production of acetic acid by the carbonylation of methanol. In particular, a variety of soluble and supported forms of cobalt, nickel, iron, iridium and rhodium have been patented in recent years as catalysts for methanol carbonylation to acetic acid. In the case of carbonylation processes of the prior art, comprising the metal carbonyls or modified metal carbonyls of cobalt, iron and nickel, each are characterised by the need for high partial pressures of carbon monoxide in order that the carbonyls remain stable under the'5;2000C temperatures normally employed, (see: "Carbon Monoxide in Organic Synthesis" by J. Falbe (1967), chapters II and Ill).

Dicobalt octacarbonyl, for example, requires partial pressures of carbon monoxide in the range of 270 to 700 atmospheres (4,000 psi to 10,000 psi). Furthermore, said cobalt, nickel and iron catalysts of the prior art generally display relatively poor selectivities to the desired carboxylic acids due to the substantial formation of undesirable by-products. Said by-products comprise substantial amounts of ethers, aldehydes, higher carboxylic acids, carbon dioxide, methane and water. (N. Von Kutepow et al, Chemie-lng. Techn. 37,383 (1965)).

More recently, a series of very active carbonylation catalyst have been patented (see for example: Belgium Patent 713,296 (1968), U.S. Patent 3,772,380 (1973) and U.S. Patent 3,717,670 (1973) where the active constituents contain a rhodium or iridium component in combination with a halogen promoter. These catalyst combinations are characterised by being effective under relatively mild operating conditions and achieving high selectivity to desired acetic acid in the case of methanol carbonylation. However, both iridium and rhodium are rare, costly metals, and rhodium in particular is predicted to be in increasingly short supply due to expanded uses in petro-chemical catalysis and in catalytic muffler applications. Furthermore, in recent reports, it is noted that much dimethylether is also formed during the rhodium-catalyzed carbonylation of methanol in pure methanol solvent. (T.

Matsumato et al, Bull. Chem. Soc. Japan, 50, 2337 (1977)).

It is the object of this invention to disclose the use of certain classes of ruthenium-containing catalyst which are effective in the selective carbonylation of aliphatic alcohols to the corresponding aliphatic carboxylic acids containing one additional carbon atom per molecule. The process of this invention is primarily directed to the synthesis of acetic acid from methanol. Here the ruthenium-based process is characterised by selectivities to acetic acid exceeding 90 mole %, high liquid yields and the suppression of gaseous by-product formation. In particular, the preferred ruthenium catalysts of this process are those which minimize the formation of carbon dioxide, due to competing water-gas shift, and methane due to methanation (Eq. 2 and 3). Other products, particularly the formation of methyl acetate (Eq. 4), are equilibrium controlled and will ultimately yield acetic acid.

CO+H2O=CO2+H2 (2) CO+3H2CH4+H20 (3) CH3CooH+CH3oH=CH3COOCH3+H2O (4) To achieve the desired > 90% acetic acid selectivities and yields via the ruthenium-catalyzed carbonylation process, it has been found preferable to operate all methanol carbonylations in a manner such that the ruthenium catalyst/methanol/acetic acid reaction mixtures do not come in contact with iron- or steel-containing walls and fitting commonly used in constructing pressure reactors. For this reason, illustrative embodiments, described infra, are carried out for the most part in glass-lined or silver-lined equipment.

Finally, it has been found necessary in this ruthenium catalysis to add an iodide or bromidecontaining promoter to the reaction mixture, prior to carbonylation, in order to achieve the desired rapid and selective formation of acetic acid. The preferred structural compositions of these catalyst components are more fully disclosed infra.

In the broadest aspect of this invention, carboxylic acids and their ester derivatives, are prepared from alcohol reactants and their ester derivatives by contacting said reactants with carbon monoxide in the presence of one or more ruthenium catalyst precursors and a halogen-containing promoter, and heating said reaction mixture under superatmospheric pressures until the desired acid products are formed.

In the narrower practice of this invention, aliphatic carboxylic acids and their ester derivatives containing 2 or more carbon atoms are prepared from aliphatic alcohol reactants containing 1 to 1 2 carbon atoms or esters thereof by a process comprising the following steps: a) Contacting said aliphatic alcohol or ester with at least a catalytic quantity of a rutheniumcontaining catalyst component in the presence of a halogen-containing promoter in which the halogen is either bromine or iodine.

b) Heating said reaction mixture under superatmospheric pressures of 34 atmospheres (500 psi) or greater with sufficient carbon monoxide to satisfy the stoichiometry of the desired aliphatic acid or ester product, until substantial formation of the desired acids and their esters has been achieved, and c) Isolating said acids and their ester derivatives contained therein.

In order to present the inventive concept in the greatest possible detail as to promote its understanding, the following supplementary disclosure is submitted.

A. Catalyst Composition The catalyst precursors that are suitable in the practice of this invention essentially include a ruthenium component and a halogen component in which the halogen is either bromine or iodine. A wide range of ruthenium catalyst compositions may be employed. Generally it is believed, without limiting the invention thereby, that the catalytically active ruthenium species of this invention, present during alcohol carbonylation is in the form of a coordination complex of ruthenium and a halogen species.These coordination compounds also generally include carbon monoxide ligands, and thereby ruthenium complexes such as Ru(CO)312 have been isolated from typical product mixtures (see Examples 14-1 5). Other moieties may also be present, as desired, and the ruthenium may be introduced into the reaction zone as a coordination complex of ruthenium containing halogen ligands or it may be introduced as separate components, the ruthenium compound and a halogen compound.

Specific examples of ruthenium compounds suitable for the practice of this invention include iodide-containing ruthenium salts such as ruthenium(lil) triodide, ruthenium(ll) diiodide, and tricarbonylruthenium(II) diiodide. Alternatively, carbonylation of typical n-alcohols may be effected by adding the ruthenium to the reaction mixture in an oxide form, as in the case of, for example, ruthenium(lV) dioxide, hydrate, anhydrous ruthenium(lV) dioxide and ruthenium(Vlll) tetraoxide. It may be introduced into the reaction zone also as the salt of a mineral acid, as in the case of ruthenium(lll) chloride, hydrate, ruthenium(lll) bromide, anhydrous ruthenium(lil) chloride and ruthenium nitrate, or as the salt of a suitable organic carboxylic acid.Here examples include ruthenium(lil) acetate, ruthenium(lll) propionate, ruthenium hexafluoroacetylacetonate, ruthenium( I I I) trifluoroacetate, ruthenium octanoate, ruthenium naphthenate, ruthenium valerate and ruthenium(lll) acetylacetonate.

The ruthenium may also be further added to the reaction zone as a carbonyl or hydrocarbonyl derivative. Suitable examples in this case include triruthenium dodecarbonyl, hydrocarbonyls such as H2Ru4(CO),3 and H4Ru4(CO)12, and substituted carbonyl species such as tricarbonylruthenium(ll) chloride dimer, [Ru(CO)3C12].

Another important class of catalyst precursor is where the ruthenium is added to the reaction zone as one or more oxide, salt or carbonyl derivative species in combination with one or more Group VB tertiary donor ligands. The key elements of the Group VB ligands include nitrogen, phosphorous, arsenic and antimony. These elements, in their trivalent oxidation states particularly tertiary phosphorous and nitrogen, may be bonded to one or more alkyl, cycloalkyl, aryl, substituted aryl, aryloxide, alkoxide and mixed alkaryl radicals, each containing from 1 to 12 carbon atoms, or they may be part of a heterocyclic ring system, or be mixtures thereof. Illustrative examples of suitable ligands that may be used in this invention include: triphenylphosphine, tri-n-butylphosphine, triphenylphosphite, triethylphosphite, trimethylphosphite, trimethylphosphine, tri-p methoxyphenylphosphine, triethylphosphine, trimethylarsine, triphenylarsine, tri-p-tolylphosphine, tricyclohexylphosphine, dimethylphenylphosphine, trioctylphosphine, tri-o-tolylphosphone, 1,2bis(diphenylphosphine)ethane, triphenylstibine, trimethylamine, triethylamine, tripropylamine, tri-noctylamine, pyridine, 2,2'-dipyridyl, 1,1 0-phenanthroline, quinoline, N,N'-dimethylpiperazine, 1,8 bis(dimethylamino)naphthalene and N,N-dimethylaniline.

One or more of these ruthenium-tertiary Group VB donor ligand combinations may be preformed, prior to addition to the reaction zone, as in the case, for example, of tris(triphenylphosphine)ruthenium(ll) chloride and tricarbonylbis(triphenylphosphine)ruthenium or alternatively, said complexes may be formed in situ.

The performances of each of these classes of ruthenium catalyst precursor are illustrated by the accompanying examples, (Eg. Examples 1-11).

As previously noted, while the halogen component of the catalyst system may be in combined form with the ruthenium, as for instance in ruthenium(lll) iodide and Ru(CO)312, it generally is preferred to have an excess of halogen present in the catalyst system as a promoting agent. By excess is meant an amount of halogen greater than three atoms of halogen per atom of ruthenium in the catalyst system. This promoting component of the catalyst system may consist of a halogen, and/or a halogen compound. Suitable halogen compounds include hydrogen halides, such as hydrogen iodide and aqueous hydriodic acid, alkyl and aryl halides containing 1 to 12 carbon atoms such as methyl iodide, ethyl iodide, 1-iodopropane, 2-iodobutane, 1-iodobutane, ethyl bromide, iodobenzene and benzyl iodide as well as acyl iodides such as acetyl iodide.Also suitable as halogen coreactants are the alkali and alkalene earth halides, ammonium and phosphonium halides. Suitable examples include sodium iodide, cesium iodide, potassium iodide, tetramethylammonium iodide, tetrabutylphosphonium iodide and potassium bromide. Iodide-containing promoters are the preferred coreactants for the ruthenium catalyzed carbonylation reaction of this invention, particularly those alkyl iodide containing 1 to 1 2 carbon atoms wherein the alkyl radical corresponds in carbon number and structure tu the alkyl radical of the aliphatic alcohol reactant.

B. Alcohol Composition Suitable alcohol reactants for the ruthenium-catalyzed carbonylations of this invention include saturated, aliphatic, hydrocarbyl alcohols, ROH, and their ester derivatives. The saturated hydrocarbyl radicals (R) may include straight-chain, branched-chain and cyclic saturated radicals containing 1 to 12 carbon atoms. Generally these radicals contain one carbon less than that of the desired acid.

Examples of alcohols that may be readily carbonylated to the corresponding aliphatic carboxylic acids by the process of this invention include methanol, ethanol, n-propanol, iso-propanol, the butanols, pentanols, heptanols, including n-heptanol, the decanols, dodecanols, as well as the cyclohexanol and cyclopentanols.

Also suitable as reactants for the carbonylation process of this invention are the corresponding aliphatic carboxylic acid esters of the alcohol classes defined supra. These esters will have the general formula

where R and R' are saturated hydrocarbyl radicals that may be straight-chain, branched-chain or cyclic, and contain 1 to 12 carbon atoms. Suitable examples of these esters include methyl acetate, ethyl acetate, propyl acetate, propyl propionate, ethyl propionate, pentyl acetate and the like.

The alcohol reactants may also be mixtures of one or more aliphatic alcohol reactant in combination with one or more aliphatic carboxylic acid ester. This is exemplified in Example 27, described infra, for a mixture of methanol and methyl acetate. The preferred feedstocks for this carbonylation process are alkanols of 1 to 12 carbon atoms. Methanol is d particularly preferred feed.

C. Solvent Composition As described supra, carbonylation to produce desired carboxylic acids is generally carried out by contacting the above defined reactant component, preferably an alcohol with gaseous carbon monoxide, in a liquid-phase containing a catalyst system which includes the rutheniumcontaining component and a halogen-containing promoter, such as methyl iodide. Generally thereby, the liquid phase, prior to carbonylation, consists substantially of the alcohol feed component, and a preferred embodiment is where the ruthenium-iodide catalyst combinations are substantially solubilized in the alcohol reactant alone, prior to carbonylation. Following carbonylation, the ruthenium catalyst combinations are then primarily solubilized in the aliphatic carboxylic acid products. Examples 1 to 3 illustrate this embodiment for the case of methanol carbonylation to acetic acid.

A second embodiment of this process is where the liquid-phase components, containing the ruthenium catalyst, include, prior to carbonylation, substantial quantities of carboxylic acid ester, carboxylic acid product, aqueous coproduct and/or inert diluent. The initial addition of various proportions of alcohol, acid, acid ester and water can substantially alter and control the final product distribution. Illustrative examples include those cases where the liquid feed comprises mixtures of an aliphatic alcohol, an acid having one carbon atom more than the alcohol, and the ester of said acid and said alcohol. Example 27 provides exemplification for this embodiment, where the liquid feed comprises methanol, methyl acetate and methyl iodide and acetic acid as the major product fraction.

Similarly, Example 28 illustrates the case when the liquid feed comprises methanol, water and acetic acid.

Ruthenium-catalyzed alcohol carbonylation may also be conducted in the presence of one of more inert diluents. Preferably these diluents should have boiling points higher than that of the product acids and/or esters. Suitable inert diluents that may aid in solubilization of the rutheniumiodide catalysts and aid in the desired carbonylation process include aromatic hydrocarbons of from 6 to 20 carbon atoms, higher-boiling organic carboxylic acids and the esters composed of the aforementioned acids in combination with the feedstocks undergoing carbonylation. Examples 26 and 29 illustrate cases where xylene and toluene are added as inert diluents during methanol carbonylation to acetic acid. Quaternary ammonium and phosphonium salts are also suitable inert diluents for this process, particularly low-melting salts such as tetrabutylphosphonium acetate.

D. catalyst Concentration The quantity of ruthenium catalyst employed in the instance invention is not critical and may vary over a wide range. In general, the carbonylation process is desirably conducted in the presence of a catalytically effective quantity of the active ruthenium species which gives the desired acid and/or ester products in reasonable yields. Reaction preceeds when employing as little as about 1 x 1 0-6 weight percent, and even lesser amounts, of ruthenium, basis the total weight of the reaction mixture.The upper concentration is dictated by a variety of factors including catalyst cost, partial pressure of carbon monoxide, operating temperature and choice of diluent, reactant. A ruthenium catalyst concentration of from about 1 x 10-5 to about 1 0 weight percent ruthenium, based on the total weight of reaction mixture, is generally desirable in the practice of this invention.

E. Operating Temperature The temperature range which can usefully be employed in these ester syntheses is a variabie dependent upon other experimental factors including the choice of alcohol reactant, the pressure, and the concentration and particular choice of catalyst among other things. Again using ruthenium as the active metal, the range of operability is from about 300 to 3500C when superatmospheric pressures of syngas are employed. A narrower range of 1 70-2400C represents the preferred temperature range when the major products are aliphatic carboxylic acids and their ester derivatives. Table II is evidence of how the narrower range is derived.

F. Pressure Superatmospheric pressures of 34 atmospheres (500 psi) or greater lead to substantial yields of desirable carboxylic acids and their esters by the process of this invention. A preferred operating range for solutions of ruthenium(lll) acetylacetonate in methanol is from 34 to 340 atmospheres (500 psi to 5000 psi), although pressures above 340 atmospheres (5000 psi) also provide useful yields of desired ester. Table II is evidence of this preferred, narrower range of operating pressures. The pressures referred to here represent the total pressure generated by all the reactants, although they are substantially due to the carbon monoxide fraction in these examples.

G. Gas Composition Insofar as can be determined, the best selectivities and yields of carboxylic acid/esters can be obtained within a reasonable reaction period by using a substantially carbon monoxide gaseous atmosphere. In all syntheses, the amount of carbon monoxide present in the reaction mixture is a variable, but sufficient should be present to satisfy the stoichiometry of Eq. 1.

Particularly in continuous operations, but also in batch experiments, the carbon monoxide may also be used in conjunction with up to 50% by volume of one or more other gases. These other gases may include one or more inert gases such as nitrogen, argon, neon and the like, or they may include gases that may, or may not, undergo reaction under CO carbonylation conditions such as carbon dioxide, hydrogen, hydrocarbons such as methane, ethane, propane and the like, ether such as dimethyl ether, methylethyl ether and diethyl ether, alkanols, such as methanol and acid esters such as methyl acetate.

H. Production Distribution As far as can be determined, without limiting the invention thereby, the ruthenium catayst, onestep carbonylation process disclosed herein leads to the formation of two classes of primary products.

The first class of primary products is carboxylic acids, preferably aliphatic carboxylic acids containing two (2) or more carbon atoms. The second class of primary products are ester derivatives of these carboxylic acids. In the case where methanol is the alcoholic reactant the principal products are acetic acid and methyl acetate. Minor by-products detected in the liquid product fraction include small amounts of water, ethyl acetate, propyl acetate, ethanol and dimethyl ether. Carbon dioxide, methane and dimethyl ether may be detected in the off-gas together with unreacted carbon monoxide.

I. Mode of Operation The process of this invention can be conducted in a batch, semi-continuous or continuous fashion. During carbonylations of typical alcohol reactants it is desirable to minimize the formation of gaseous by-products, particularly the formation of CO2 and methane, due to competing water-gas shift and methanation reactions (Eq. 2 and 3). We have found in this work with ruthenium catalysts, that gaseous by-product formation can be held to a minimum by avoiding contact between the rutheniumcontaining liquid reaction mix and any iron or steel-containing metal surfaces during the carbonylation step. Of particular concern here are the metal surfaces, such as 31 6 stainless steel surfaces, commonly used in the construction of high-pressure reactors.One means by which this contact can be minimized is by running the alcohol carbonylation reaction in a glass-lined reactor. A second, alternative, method is to have the carbonylation reactor lined with some other inert materials, such as using a silver-lined reactor, prior to effecting the alcohol carbonylation. Further alternatives include the use of titaniumlined pressure reactors, tantalum-lined reactors, and reactors having Hastelloy (Registered Trade Mark) alloy or copper-nickel alloy surfaces. Example 32 is illustrative of the need to use lined pressure reactors during the ruthenium-catalyzed acetic acid synthesis. The ruthenium catalyst of this invention may be initially introduced into the reaction zone batchwise, or it may be continuously or intermittently introduced into such a zone during the course of the synthesis reaction.Operating conditions can be adjusted to optimize the formation of the desired acid and/or ester product, and said material may be recovered by methods well known in the art, such as distillation, fractionation, extraction and the like. A fraction rich in ruthenium catalyst components may then be recycled to the reaction zone, if desired, and additional acid and/or ester products generated by CO carbonylation. Example 31 illustrates the usefulness of the recycle technique.

J. Identification Procedure The products of carbonylation have been identified in this work by one or more of the following anelytical procedures, viz. gas-liquid phase chromatography (glc), infrared (ir), mass spectrometry, nuclear magnetic resonance (nmr) and elemental analyses, or a combination of these techniques.

Analyses have, for the most part, been parts by weight, all temperatures are in degrees centrigrade and all pressures in atmospheres, and pounds per square inch gauge (psi).

Having described the inventive process in general terms, the following examples are submitted to supply specific and illustrative embodiments.

Example 1 To a Flushed sample of methanol (25 gm, 0.78 mole) and methyl iodide (5.0 gm, 35 mmole) in a glass-lined reactor equipped for pressuring, heating, cooling and means of agitation is added 0.954 gm of ruthenium dioxide, hydrate (5 mmole). The mixture is stirred to dissolve most of the solids, yielding a dark, almost black, liquid. The reactor is sealed, flushed with CO, pressured to 136 atmospheres (2000 psi) with CO, and then heated to 2200C with rocking for 3 hours. Maximum pressure is 292.5 atmospheres (4300 psi), gas uptake 102 atmospheres (1500 psi). On cooling, an offgas sample is taken during depressuring of the reactor, and 45 gm of clear, deep-red liquid product is recovered. Liquid samples are analyzed by gic and by Karl Fischer titration.

Typical analytical data for the liquid product, by glc using a 1 82.9x0.3 17 cm (6 ft.x 1/8") column of 60/80 mesh Poropak-OS, 1 40-2800C, are as follows: Methanol conversion > 98% Acetic acid conc. 96.9 wt % Methyl acetate conc. 0.8 wt % Water 2.1 wt% Miscellaneous 0.2 wt % Gas samples are analyzed using a 10 ft.x 1/8" column of 5A molecular sieve (25-990C) in combination with a 1 82.9x0.31 7 cm (6 ft.x 1/8") column of Porapak-Q (70-2400C).

Typical off-gas analyses show: CO=96.6%, CO2=0.5%, CH4=1.1%.

The acetic acid and methyl acetate fractions may be recovered from the crude liquid product by fractional distillation at atmospheric pressure. The residual ruthenium catalyst may be recycled for additional carbonylation duty using fresh methanol charge.

Example 2 To a N2-flushed sample of methanol (20 gm. 0.63 mole) and methyl iodide (3.97 gm, 28 mmole) in a glass-lined reactor is added 0.608 gm of ruthenium iodide. The mixture is stirred to dissolve most of the solids, yielding a dark, almost black, liquid. The reactor is sealed, flushed with CO, pressured to 136 atmospheres (2000 psi) with CO, and then heated to 2200C with rocking for 1 8 hours. Maximum pressure is 253.5 atmospheres (3725 psi), gas uptake 100.4 atmospheres (1475 psi). On cooling, an off-gas sample is taken during depressuring of the reactor, and 35.1 gm of ciear, deep-red liquid product is recovered. Samples are analyzed by glc and by Karl Fischer titration.

Typical data for the liquid product by glc are as follows: Methanol conversion > 98% Acetic acid conc. 97.3 wt % Methyl acetate conc. 1.4 wt % Ethyl acetate conc. 0.7 wt % Water 0.2 wt % Miscellaneous 0.5 wt % Typical off-gas analyses show: CO=93.2%, CO2=5.5%, CH4=1.3% The acetic acid and methyl acetate fractions may be secured from the iodide liquid product by fractional distillation at atmospheric pressure. The residual ruthenium catalyst may be recycled for additional carbonylation duty using fresn methanol charge.

Example 3 To a Flushed sample of methanol (25 gm, 0.78 mole) and methyl iodide (5.0 gm, 35 mmole) in a glass-lined reactor is added 0.477 gm of ruthenium(lV) dioxide, hydrate (2.5 mmole). The mixture is stirred to dissolve most of the solids, the reactor sealed, flushed with CO and pressured to 34 atmospheres (500 psi) with CO. The mixture is heated to 2200C with rocking, and at temperature the pressure raised to 272 atmospheres (4000 psi) with additional CO. The pressure is maintained at 272 atmospheres (4000 psi) by a pressure regulator hooked to a CO surge tank. After 5 hours, the reactor is rapidiy cooled, an off-gas sample taken during depressuring of the reactor, and 39.1 gm of clear yellow liquid recovered. There is no evidence of any solid fraction at this stage. Liquid samples are analyzed by glc and Karl Fischer titration.

Typical data for the liquid product are as follows: Methanol conc. 0.3 wt % Acetic acid conc. 73.4 wt % Methyl acetate conc. 16.4 wt 9/0 Ethyl acetate conc. 2.3 wt % Water conc. 3.7 wt % A similar product distribution is achieved where the above experiment is repeated using 3.8 gm of ethyl bromide (35 mmole) instead of methyl iodide, as the halogen promoter, and 23 gm of ethanol as the alcohol reactant. Following the carbonylation step, the liquid product is recovered and analyzed to contain 25% propionic acid plus propionate esters.

Table I Max.

Pres. Conc. (Wt%) In Liquid [Ru] Temp. atmos Product Example Catalyst Solventa (wt%) ( C) (psi)b water HOAc MeOAc MeOH 4 Ru(acac)3c-Mel MeOH 0.41 220 277.3 3.48 82.1 10.9 (4075) 5 RuCl3-Mel MeOH 0.42 220 282.4 4.12 75.7 13.3 (4150) 6 RuO2-Mel MeOH 0.42 220 246.6 1.54 86.5 9.0 (3625) 7 Ru3(CO)12-Mel MeOH 0.42 220 270.5 4.67 68.1 21.4 0.5 (3975) 8 RuCl2(PPh3)3-Mel MeOH 0.40 220 292.6 15.1 15.2 33.7 9.3 (4300) 9 Ru(acac-Fe6)3d-Mel MeOH 0.41 220 284.0 3.15 72.0 19.7 0.3 (4175) 10 [Ru(CO)3Cl2]2-Mel MeOH 0.42 220 302.8 1.80 81.1 12.9 0.1 (4450) 11 Rul3-Mel MeOH 0.39 220 262.0 #0.1 97.3 1.4 (3850) aCharging 50 g of methanol (1.56 mole), 10 g of methyl iodide (71 mmole) and 2.5 mmole ruthenium.

bInitial pressure 136 atmospheres (2000 psi).

cRuthenium(III) acetylacetonate.

dRuthenium(III) hexafluoroacetylacetonate.

Examples 4 to 11 In these preparations, the carbonylation of methanol to acetic acid is carried out in accordance with the procedure of Example 2 using various soluble ruthenium catalyst compositions but under similar conditions of temperature, pressure and initial methanol-to-ruthenium mole ratio. As can be seen from the data summarized in Table I, which follows, a variety of ruthenium oxides, salts and complexes, in combination with Group VB tertiary donor ligands are effective for methanol conversion to acetic acid and/or methyl acetate. Here, the water concentrations in the liquid product has been estimated by Karl-Fischer titration while other components are basis glc analyses.

Table II Charge Mixture Conc. (wt%) in Liquid Ru Mel MeOH Time Product Example Precursor (mmole) (mmole) (mole) (hr) H2O HOAc MeOAc MeOH 12 RuCl3xH2O 1.25 71 1.56 6 7.6 43.8 36.3 0.9 13 RuCl3xH2O 5.0 71 1.56 6 3.8 70.8 20.2 0.9 14 RuCl3xH2O 10.0 71 1.56 6 3.5 79.1 13.4 1.3 15 RuO2xH2O 10.0 35 0.78 1.5 8.0 47.4 30.0 0.7 16 Ru(acac)3 1.25 71 0.78 6 12.5 24.8 43.0 2.6 17 Ru(acac)3 1.25 4.4 0.78 6 13.5 1.0 28.7 46.8 Examples 12-23 In these examples using the techniques and procedure of Example 1, the effect of varying the operating temperatures, pressures and mole ratio has been examined. Methanol carbonylation to acetic acid and methyl acetate are the standard reactions; ruthenium dioxide, ruthenium(lil) chloride and ruthenium(lil) acetylacetonate are the catalyst precursors.The results are summarized in Tables II and III. It is evident from the data that methanol carbonylation to acetic acid may be achieved via a wide range of conditions, e.g.: 1) Initial mole ratios of methanol to ruthenium up to at least 103 or greater (2) Operating temperatures of 30 to 2400C 3 Superatmospheric pressures of 34 atmospheres (500 psi) or greater.

Upon allowing the crude product solutions from typical carbonylation runs, such as Examples 14 and 15, to stand for a period of one or more days, significant quantities (0.1It1.2 gm) of yellow crystalline solids were observed to precipitate. These solids were recovered by filtration, washed with diethyl ether and dried in vacuo. The materials were identified by spectroscopic observations and elemental analyses as tricarbonylruthenium(ll) iodide, Ru(CO)312. Calc. for Rul2C303; Ru, 23.0%; C, 8.20%; I, 57.8%. Found: Ru, 23.8%; C, 7.198%; 1, 56.7%.

Spectra of the crude liquid products show the presence of this and similar ruthenium carbonyl species.

Table Ill Preys. Conc. (wt /O) In Liquid Temp atmos Product Example Precursor (00C) (psi) H20 HOAc MeOAc MeOH 1 8 Ru(acac)3a 240 285.8 4.6 86.0 4.8 (4200) 19 Ru(acac)3a 170 251.7 8.7 12.9 33.1 5.6 (3700) 20 Ru(acac)3a 30 204.1 0.2 4.7 95.0 (3000)C 21 RuCI3xH20b 220 336.8 2.5 83.2 9.5 (4950) 22 RuCI3xH2Ob 220 173.5 39.6 5.0 1 5.5 1 7.9 (2550) 23 RuCI3xH2Ob 150 34.0 19.8 < 5.0 28.8 11.6 (500)C aCharging 50 g of methanol (1.56 mole), 10 g of methyl iodide (71 mmole) and 2.5 mmole ruthenium(lil) acetylacetonate.

bCharging 10.0 mmole ruthenium(lil) chloride, hydrate.

CRun at constant pressure.

Example 24 Following the procedures of Example 1, 0.702 g of ruthenium chloride, hydrate (2.5 mmole), methanol (50 gm) and 18.0 gm of hydriodic acid (50% aqueous solution) are charged to the glass-lined reactor. The reactor is flushed with CO, pressure to 1 36 atmospheres (2000 psi) with carbon monoxide and heated to 2200C for 6 hours. After cooling, the clear, yellow liquid product (79 gm) is recovered and analyzed as follows: Acetic acid conc. 54.1 wt % Methyl acetate conc. 16.0 wt % Water conc. 11.5 wt % Methanol conc. 0.5 wt % Example 25 To a N2-flushed sample of methanol (50 mg) is added 0.702 mg of ruthenium chloride hydrate.

The mixture is charged to the glass-lined reactor, frozen down with dry-ice and 9.0 gm of hydrogen iodide injected in from a side ampule. The reactor is pressured to 136 atmospheres (2000 psi) with CO and heated to 2200C with rocking for 6 hours. Maximum pressure is 285.8 atmospheres (4200 psi), gas uptake is 102 atmospheres (1 500 psi). On cooling and depressuring of the reactor, 82.5 gm of clear yellow liquid product is recovered. There is no evidence for any solid precipitate.Typical analytical data for the liquid product by glc and Karl Fischer titration are as follows: Acetic acid conc. 60.2 wt % Methyl acetate conc. 24.7 wt % Water conc. 4.8 wt % Methanol conc. 1.0 wt % Example 26 In this preparation methanol carbonylation is carried out as described in Example 1, except that the charge mixture consists of 1.25 mg of ruthenium chloride, hydrate (4.5 mmole), methanol (24 gm), xylene (56 gm) and 10.56 gm of sodium iodide (71 mmole). The reactor is pressured with CO and heated to 2200C with rocking for 6 hours. Analysis of the product liquid shows the presence of significant quantities of methyl acetate and acetic acid.

Example 27 In this preparation, following the procedures of Example 1, the glass-lined reactor is charged with 1.25 mg of ruthenium chloride, hydrate (4.5 mmole), methanol (24 gm), methyl iodide (10 gm) and 56 gm of methyl acetate (0.76 mole). The reactor is pressured with CO, and heated to 2200C with rocking.

Analyses of the liquid product (95 gm) by glc shows near quantitative conversion of the methyl acetate and methanol fractions to acetic acid. Acetic acid concentration in the crude product is > 90 wt %.

Typical off-gas analyses are as follows: CO=96.7%, Cm2=1.2%, CH4=1.2%.

Example 28 In this preparation, following the procedure of Example 1, the glass-lined reactor is charged with 1.25 gm of ruthenium chloride, hydrate (4.5 mmole), methanol (24 gm), methyl iodide (10 gm), together with 12.9 gm of water and 43.1 gm of acetic acid (0.72 mole). The reactor is sealed, flushed with CO and pressured to 136 atmospheres (2000 psi) with carbon monoxide. The mixture is heated to 2200C with rocking, and held at 2200C for 6 hours.Analyses of the liquid product by glc and Karl Fischer titration show: Acetic acid conc. 72.9 wt % Methyl acetate conc. 5.0 wt % Water conc. 1 6.2 wt % Methanol 0.3 wt % Example 29 Following the procedure of Example 1, 1.25 gm of ruthenium chloride, hydrate (4.5 mmole), methanol (24 gm), methyl iodide (5 gm) and 61 gm of toluene are charged to the glass-lined reactor.

The reactor is flushed with CO, pressured to 1 36 atmospheres (2000 psi) with carbon monoxide and heated to 2200C for 6 hours. Gas uptake is 56.1 atmospheres (825 psi). Upon cooling, an off-gas sample is taken during depressuring of the reactor, and 101 gm of clear liquid product is secured.

There is no solids fraction. Liquid samples analyzed by glc and Karl Fischer show the presence of: 40.7% acetic acid 7.1% methyl acetate 2.1% water 0.3% methanol 48.7% toluene solvent.

Off-gas analyses show: 95.1% CO, 2.0% CO2 and 2.0% CH4.

Example 30 In this example, n-heptanol carbonylation is carried out by the procedure of Example 1. The charge mixture consists of 0.351 gm of ruthenium chloride, hydrate (1.27 mmole), methyl iodide (5 gm) and 90.6 gm of n-heptanol (0.78) mole). The glass-lined reactor is sealed, flushed with CO and pressured with carbon monoxide. The reactor is heated to 2200C with rocking, gas uptake is 51 atmospheres (750 psi). Upon cooling and depressuring the reactor, the recovered, clear, yellow liquid product is shown by glc analyses to contain 66.3% n-octanoic acid.

Example 31 To the glass-lined pressure reaction of Example 1, equipped with pressurizing, heating, cooling and means of agitation is added 2.77 gm of ruthenium chloride hydrate (10 mmole) methanol (50 grin) 1.56 mole) and methyl iodide (10 gm). The reactor is sealed, flushed with CO, pressured with carbon monoxide to 136 atmospheres (2000 psi) and heated to 2200C for 3 hours. Gas uptake is Ca 68 atmospheres (1000 psi). On cooling and depressuring the reactor, 86.5 gm of clear yellow liquid product is recovered. There is no evidence of solid residue or precipitate at this stage. Both the methyl acetate and acetic acid product fractions are recovered as clear, water-white liquids by fractional distillation of the crude liquid product at 1 atm pressure.The residual bottoms fraction (12.1 gm) is recharged to the reactor with additional methanol (50 gm) and methyl iodide (10 gm), and carbonylation effected as described supra. After again fractionally distilling the liquid product to recover methyl acetate and acetic acid fractions, carbonylation of a third sample of methanol (50 gm) is carried out likewise using the residual ruthenium catalyst (12 gm). Samples of liquid products from the three ruthenium catalyst cycles are analyzed by Karl Fischer and glc techniques. Data are summarized in Table IV.

Table IV Composition of Liquid Product (Conc. wt /OJ Cyc/e Composition H20 HOAc MeOAc EtOAc MeOH I RuCl3xH2O-MeI 3.47 79-.1 1 13.4 0.7 1.3 II Recycle 7.5 61.9 24.1 1.3 0.8 Ill Recycle 1.73 76.2 16.4 3.0 0.1 Example 32 To the glass-lined reactor of Example 1, equipped with means of pressurizing, heating, cooling and means of agitation is charged 0.996 gm of ruthenium(lll) acetylacetonate (2.5 mmole), 10 gm of methyl iodide (71 mmole) and 50 gm of methanol (1.55 mole). The mixture is stirred to dissolve all solids yielding a deep-red-liquid. The reactor is sealed, flushed with CO, pressured to 1 36 atmospheres (2000 psi) with CO, and then heated to 2200C with rocking overnight.Maximum gas pressure is 272 atmospheres (4000 psi), gas uptake 54.4 atmospheres (800 psi). On cooling and depressuring the reactor 78 gm of clear yellow liquid product is recovered. There is no solid fraction, and analyses of the liquid show: 82.1 wt % acetic acid 10.9 wt % methyl acetate 3.4 wt % water 98% methanol conversion.

In a side-by-side comparison of this typical run data using the glass-lined reactor, a second experiment is conducted charging the same Ru(acac)3/MeOH/Mel mix to a 31 6 stainless steel reactor not having a glass-liner. Again the reactor is pressured to 1 36 atmospheres (2000 psi) with carbon monoxide and heated to 2200 C. Upon cooling and depressuring, however, the reactor yielded only 15.3 gm of a greenish-coloured suspension. Analysis of the liquid by Karl Fischer and glc techniques showed water to be the major product fraction, viz: 8.7 wt % acetic acid 28.0 wt % methyl acetate 33.9 wt % water, and 1 8.5 wt % unreacted methanol.

Furthermore, an off-gas sample confirmed the presence of large quantities of carbon dioxide and methane, as follows: 40.8% CO2; 14.2% CH4; 3.7% CO; 4.6% H2; 9.6% Me20.

As the examples and preceding discussion have documented, numerous advantages accrue from the practice of this invention both in its compositional and process aspects. For example, a relatively large group of ruthenium catalyst combinations are disclosed herein which are useful for the one-step conversion of methanol to acetic acid and its ester derivatives. Furthermore, ruthenium catalyzed methanol carbonylation has been demonstrated over a wide range of temperatures, pressures and initial catalyst/reactant mole ratios.

Claims (13)

Claims

1. A process whereby aliphatic carboxylic acids and their ester derivatives containing 2 or more carbon atoms are prepared from aliphatic alcohol and/or ester reactants having the formulae ROH and

where R and R' are saturated hydrocarbyl radicals containing 1 to 12 carbon atoms, by a procedure comprising:: a) contacting said aliphatic alcohols and/or esters with at least a catalytic quantity of a rutheniumcontaining compound in-the presence of a halogen-containing promoter in which the halogen is either bromine or iodine, b) heating said reaction mixture under superatmospheric pressures of 34 atmospheres (500 psi) or greater with sufficient carbon monoxide to satisfy the stoichiometry of the desired aliphatic acid product, until substantial formation of the desired acids and their esters has been achieved, and c) isolating said acids and their esters contained therein.

2. A process as claimed in claim 1, wherein the ruthenium-containing compound is selected from one or more ruthenium iodide salts, oxides of ruthenium, ruthenium salts of a mineral acid, ruthenium salts of an organic carboxylic acid and ruthenium carbonyl or hydrocarbonyl derivatives.

3. A process as claimed in claim 2, wherein the ruthenium-containing compound is selected from ruthenium(lll) triodide, tricarbonylruthenium(Il) iodide, ruthenium(lV) dioxide, hydrate, anhydrous ruthenium(lV) chloride, ruthenium(VIIl) tetraoxide, ruthenium(lll) chloride, hydrate, ruthenium acetate, ruthenium propionate, ruthenium(lil) hexafluoroacetylacetonate, ruthenium(lll) acetylacetonate, triruthenium dodecacarbonyl and tricarbonylruthenium(ll) chloride.

4. A process as claimed in any preceding claim, wherein the halogen-containing promoter is hydrogen iodide.

5. A process as claimed in any of claims 1 to 3, wherein the halogen-containing promoter is an alkyl halide containing 1 to 12 carbon atoms.

6. A process as claimed in claim 5, wherein the alkyl halide promoter is selected from methyl iodide, ethyl iodide and ethyl bromide.

7. A process as claimed in any preceding claim, wherein the aliphatic alcohol reactant is methanol.

8. A process as claimed in claim 5, wherein the alkyl halide promoter contains an alkyl radical having the same carbon number and structure as the alkyl radical of the aliphatic alcohol reactant.

9. A process as claimed in any preceding claim, wherein the aliphatic carboxylic acids are prepared in the presence of water.

10. A process as claimed in any preceding claim, wherein the alcohol reactant is carbonylated in the presence of one or more aliphatic carboxylic acids.

1 A process as claimed in any prsceding claim, wherein the alcohol and/or ester reactant is carbonylated in the presence of an inert organic diluent.

12. A process as claimed in claim 1 wherein the inert diluent is an aromatic hydrocarbon.

13. A process for preparing aliphatic carboxylic acids and their ester derivatives as claimed in claim 1 and substantially as hereinbefore described with reference to any of the Examples.