EP0039354A1 - Production of carboxylic acids and their esters - Google Patents

Abstract

Production of carboxylic acids and their esters by reaction of alcohols and their derivatives with carbon monoxide in the presence of one or more compositions of ruthenium catalysts and an activator containing a halogen.

Description

Production of Carboxylic Acids 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 supported ruthenium-containing catalyst component and a halogen-containing promoter. Eq. 1 is illustrative of this process, where R is a linear, branchedchain 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 + CO → RCOOH (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 2 billion lbs. per annum in the United States*; 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 acetaldhyde, liquid-phase oxidation of saturated hydro-carbons, n-butene oxidation and methanol carbonylation. To the extent that methanol is currently produced from

*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. 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*, this syngas route to acetic a cid will likely become increasingly important in an era of petroleum shortages.

Carbonylation processes for the preparation of carboxylic acids 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 characterized by the need for high partial pressures of carbon monoxide in order that the carbonyls remain stable under the 200°C temperatures normally employes.** Dicobalt octacarbonyl, for example, requires partial pressures of carbon monoxide in the 4,000 psi to 10,000 psi (275.79 to 689.5 bar) range. 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.

*See: "Trends in Petrochemical Technology" by A. M. Brownsteian (1976), Chapters 4 and 5; and "Petrochemicals from Coal" by P. M. Spitz, Chemtech, May 1977, p.295.

**See: "Carbon Monoxide in Organic Synthesis" by J. Falbe (1976), Chapters II and III. Said by-products comprise substantial amounts of ethers, aldehydes, higher carboxylic acids, carbon dioxide, methane and water.*

More recently, a series of very active carbonylation catalysts have been patented** where the active constituents contain a rhodium or iridium component in combination with a halogen promoter. These catalyst combinations are characterized 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 petrochemical catalysis and in catalytic muffler applications. Furthermore, in recent reports, it is noted that much dimethylether is also formed during the rhodium-catalyzed carbonyl ation of methanol in pure methanol solvent. ***

It is the object of this invention to disclose the use of certain classes of novel supported ruthenium-containing catalysts 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 characterized by selectivities to acetic acid exceeding

*N. Von Kutepow et al, Chemie-Ing. Techn. 37,383 (1965 ).

**See for exa mple: Belgium Patent 713,296 (1968) , U. S. Patent 3, 772,380 (1973 ) and U. S. Patent 3,717, 670 (1973 ).

***T. Matsumato et al. Bull. Chem. Soc. Japan, 50, 2337 (1977) . 90 mole %, high liquid yields and the suppressing 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 (Eqs. 2 and 3). Other products, particularly the formation of methyl acetate (Eq. 4), are equilibrium controlled and will ultimately yield acetic acid. CO+H₂O → C0₂+H₂ (2) CO+3H₂ → CH₄+H₂O (3)

CH₃COOH+ CH₃OH → CH₃COO CH₃ +H₂O (4)

To achieve the desired 90% acetic acid selectivities and yields via the ruthenium-catalyzed carbonylation process, it has been found necessary to add an iodide or bromide-containing promoter to the reaction mixture, prior to carbonylation.

The preferred structural compositions of these catalyst components are more fully disclosed infra.

PROCESS EMBODIMENTS

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 supported ruthenium catalyst precursors and a halgen-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 12 carbon atoms by a process comprising the following steps: a) Contacting said aliphatic alcohol with at least a catalytic quantity of a supported ruthenium-containing catalyst component in the presence of a halogen-containing promoter in which the halogen is either bromide or iodine. b) Heating said reaction mixture under superatmospheric pressures of 500 psi (34.47 bar) 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.

B. Ruthenium Catalyst Component. In the catalysts of this invention, the ruthenium component is dispersed on one or more solid carriers or supports. Suitable supports for the ruthenium may include, but are not limited to, activated and inactivated carbons, alumina, silica-alumina, zeolites, as well as zeolite molecular sieves, magnesia, diatomaceous earth, bauxite, titania, zirconia, clays, lime, magnesium silicate, silicon carbide, as well as various organic polymers. The supports may be in the form of powders, pellets, spheres, shapes and extrudates. They should also be of suitable porosity such that they may be employed in fixed or fluidized bed ratios. The ruthenium component to be dispersed upon the solid support phase, may be added to said supports in the form of a ruthenium oxide, as in the case of, for example, ruthenium( IV) dioxide, hydrate, anhydrous ruthenium(IV) dioxide and ruthenium(VIII) tetraoxide, or as the salt of a mineral acid, as in the case of ruthenium(II) chloride, hydrate, ruthenium(III) bromide, anhydrous ruthenium(II) chloride and ruthenium nitrate. Alternatively, the ruthenium may be added as the salt of a suitable organic carboxylic acid. Here examples include ruthenium(III) acetate, ruthenium(III) propionate, ruthenium hexafluoroacetylacetonate, ruthenium(III) trifluoroacetate, ruthenium octanoate, ruthenium naphthenate, ruthenium valerate and ruthenium(III) acetylacetonate. This invention also contemplates the use of iodide-containing ruthenium salts such as ruthenium(III) triiodide, ruthenium(II) dioxide and tricarbonylruthenium(II) dioxide, as well as ruthenium carbonyl or hydrocarbonyl derivatives such as triruthenium dodecacarbonyl, H₂Ru₄(CO)₁₃ and H₄Ru₄ (CO)₁₂, and substituted carbonyl species such as the tricarbonylruthenium(II) dimer, [Ru(CO)₃C¹ ₂].

Generally, the solid phase of said ruthenium-containing catalyst system is prepared by first dissolving or slurrying the selected ruthenium oxide, salt etc, eg

RnCI₃3H₂O, with a suitable solvent system and subsequently impregnating the selected inert support or carrier with said ruthenium-containing mixture. These solutions or slurries may be poured onto the carrier, or the solid carrier may be immersed in excess of the liquid solution or slurries, with the excess being subsequently removed.

The impregnated support is then maintained at a temperature sufficient to volatize the solvent component, eg. at a temperature between 150°C and 325°C, to permit drying of the composite solid catalyst. A vacuum may also be applied to the catalyst in order to volatalize the solvent, although use of vacuum is not essential. During this stage of the process, the volatile solvent evaporates from the solid catalytic product, and the ruthenium component remains on the support. Optionally this ruthenium impregnated solid then may be treated with hydrogen or carbon monoxide/hydrogen mixtures at elevated temperatures in order to cause at least partial reduction of the ruthenium component to ruthenium metal or a low valency form of ruthenium such as ruthenium(1).

The solvent which may be used to dissolve the ruthenium oxide or salt compound prior to impregnation onto the support should be a liquid of relatively low boiling point ( 150°C). A preferrable group of solvents include mineral acid solutions such as hydrochloric acid and nitric acid, carboxylic acids such as acetic acid, propionic acid, and halogenated solvents like chloroform and carbon tetrachloride, ketones such as acetone and methyl isobutyl ketone, alcohols such as methanol, isopropanol and tert-butanol, aromatics such as benzene, tolune and xylene, as well as certain heterocyclic solvents like pyridine and N-methylpyrrolidone. The choice of solvent is dependent optionally upon the nature of the ruthenium oxide or salt to be used for impregnation.

Generally it is believed, without limiting the invention thereby, that the catalytically active ruthenium species of this invention, during the alcohol carbonylation is in the form of a coordination complex of ruthenium and an iodide or bromide-containing halogen component that may or may not, contain carbon monoxide ligands. 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 these halogen ligands, as for example, when the halogen is impregnated onto the catalyst. Alternatively, the ruthenium compound and the halogen component may be introduced separately into the reaction zone.

C. Halogen Component - While the halogen component of said catalyst system may be in combined form with the ruthenium, as for instance in ruthenium(III) iodide and Ru(CO)₃I₂, it is generally 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, that may be introduced into the reaction zone in a gaseous or liquid- form, or saturated in a suitable solvent or reactant. Satisfactory halogen promoters include hydrogen halides, such as hydrogen iodide and gaseous hydriodic acid, alkyl and aryl halides containing 1 to 2 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 alkaline earth halides, and ammonium and phosphonium halides. Suitable examples include sodium iodide, cesium iodide, potassium iodide, tetramethyl-ammonium 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 12 carbon atoms wherein the alkyl radical corresponds in carbon number and structure to the alkyl radical of the aliphatic alcohol reactant. D. 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 hydrocarbylradicals (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:

O II R-C-OR',

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 preferred feedstocks for this carboxylation process are alcohols of 1 to 12 carbon atoms. Methanol is a particularly preferred feed, but where it is desirable to produce high proportions of carboxylic acid product, the liquid charge may also include by-products or co-products which are recycled along with the aliphatic alcohol. A further embodiment of the process then, is when the liquid phase components, prior to carbonylation, consist of mixtures of the aforementioned aliphatic alcohols together with the corresponding ethers, alkyl halides and carbonylic acid ester. For example, where acetic acid is the desired product, the feedstock may consist of methanol in combination with derivatives thereof, such as dimethyl ether, methyl acetate and methyl iodide. Likewise, the alcohol reactants may be mixtures of one or more aliphatic alcohol reactancts, and these may be in combination with one or more aliphatic ethers, or aliphatic carboxylic acid esters. Example 24, described infra, illustrates this embodiment, when the liquid charge is a mixture of methanol, methyl acetate and methyl iodide, and acetic acid is the major product fraction.

A further class of suitable feedstocks for this process are liquid-phase components which contain substantial quantities of carboxylic acid product, aqueous coproduct and/or inert diluent. The initial addition of various proportions of alcohol, acid and 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 a carbon atom more than the alcohol, and the ester of said acid and said alcohol. Example 25 provides exemplifi cation of this embodiment. Here the liquid feed comprises methanol, methyl acetate, methyl iodide and acetic acid. A similar case is where the liquid feed comprises methanol, water and acetic acid.

Ruthenium-catalyzed alcohol carbonylation may also be conducted in the presence of one or 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 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.

E. Ruthenium Concentration - The quantity of ruthenium catalyst employed in the instant 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. The reaction proceeds when employing concentrations of ruthenium on the support of between 0.01 wt. % and 10 wt. %. This is the range normally employed, with the preferred range being 0.1 wt. % to 5 wt. %. Higher concentrations of ruthenium may be used to the extent of 20 wt. %.

F. Operating Temperature - The temperature range which can usefully be employed in these acid/ester syntheses is a variable, 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 30° to at least 400°C, when superatmospheric pressures of syngas are employed. A narrower range of 180° - 350°C represents the preferred temperature range when the major products are aliphatic carboxylic acids and their ester derivatives. Table I is evidency of how the narrower range is derived.

G. Pressure - Superatmospheric pressures of 500 psi (34.47 bar) 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 (III) acetylacetonate in methanol is from 500 psi (34.47 bar) to 4000 psi (275.79 bar), although pressures above 4000 psi (274.79 bar) also provide useful yields of desired ester. Table I 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. H. 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, ethers such as dimethyl ether, methylethyl ether and diethyl ether, alkanols such as methanol and acid esters such as methyl acetate.

I. Product Distribution - As far as can be determined, without limiting the invention thereby, the ruthenium catalyst, one-step 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 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 and dimethyl ether. Carbon dioxide, methane and dimethyl ether may be detected in the off-gas together with unreacted carbon monoxide.

J. Mode of Operation - The process of this invention can be conducted in a batch, semi-continuous or continuous fashion. The solid catalyst may be employed as a fixed or fluid bed; the reactor may consist of a series of catalyst beds or the catalyst may be placed in tubes with a heat exchange medium around the tubes. So as to provide certain operating advantages, the metal content of the catalyst may be varied through the reactor bed, and the reactants may be passed up-flow or down-flow through the reactor.

To ensure maximum yields of desirable carboxylic acid products, contact between the liquid reaction mix and any iron-rich metal surfaces should be limited wherever possible during the carbonylation step. One means by which this contact can be minimized is by carrying out 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 by using a silver-lined reactor, prior to effecting the alcohol carbonylation. Further alternatives include the use of titanium-lined pressure reactors, tantalum-lined reactors, and reactors having Hastelloy alloy or copper-nickel alloy surfaces.

Generally, operating conditions, can be adjusted to optimize the formation of any desired acid and/or ester product, and said materials may be recovered by methods well known in the art, such as distillation, fractionation, extraction and the like. By-product alkyl ethers, alkyl halides and carboxylic acid esters may then be recycled to the reaction zone, if desired, and additional acid and/or ester products generated by CO carbonylation. K. Identification Procedure - The products of carbonylation have been identified in this work by one or more of the following analytical 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 by parts by weight; all temperatures are in degrees centigrade and all pressures in 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

This example illustrates a method of preparation of a solid catalyst, comprising 1% of ruthenium dispersed upon a carbon-containing support.

A sample of Columbia grade SXZ activated carbon material is first pretreated to remove metal impurities in the following manner: 900cc of carbon support is heated to 55°C overnight in 2700cc of 10% nitric acid. The acid is decanted and the support is washed with distilled water to approximately a pH of 4. Drying is accomplished in a vacuum oven at 100°C overnight. To prepare a 1% ruthenium on carbon catalyst, 1.28g of ruthenium chloride hydrate (36.5%Ru) is first dissolved in 5cc HCl and 5cc HNO₃ with heating. This solution is diluted to 30cc with water and added to 50g of the pretreated carbon support material. The volume of the ruthenium solution is adjusted to bring the support to incipient wetness.

The ruthenium-treated carbon is then prereduced by flowing the sample in a quartz tube and purging with hydrogen for 30 minutes at a H₂ flow of 12 P/hr. The sample is then heated to 315°C for 1 hour and at 490°C for 2.5 hr. under the same H₂ flow conditions, upon cooling to 70°C it is purged with nitrogen until reaching ambient temperature and stored under N₂.

Example 2

This example illustrates the utility of a typical supported ruthenium catalyst for the production of acetic acid from methanol.

To a 25 ml capacity continuous, reactor of Hastelloy-C construction is charged a sample of 1% ruthenium-on-carbon, prepared by the procedure of Example 1. The temperature of the reactor and preheater is raised to 250°C and the process is conducted at a feed rate of methanol (0.13 mole/hr.), methyl iodide (0.01 mole/hr.) and carbon monoxide (0.16 mole/hr). The pressure within the reactor is held at 3000 psi (206.84). under steady state conditions, a typical composition of the liquid product effluent (determined by glc) is detailed below; acetic acid : 92.2wt% methyl iodide/methyl acetate : 4.6wt% methanol : 0.1wt% water : 2.8wt% As can be seen from this data the conversion of the methanol feed is 99% per pass and the majority of the product is acetic acid. In particular, chromatographic analysis of this liquid product indicates no substantial production of by-products such as aldehydes, higher boiling carboxylic acids and/or alcohols.

Carbon balance across the reactor (basis both liquid and gaseous effluent components) is 98.8%. Production of acetic acid under the steady state conditions is 75 gm HOAc/g Ru/hr.

Example 3-17

In these examples, samples of the standard, 1% ruthenium-on-carbon catalyst, prepared by the procedure in Example 1, have been evaluated for the carbonyation of methanol to acetic acid over a range of operating temperatures and pressures. The operating procedures are those illustrated in Example 2; the feed rates are methanol (0.13 mole/hr.), methyl iodide (0.01 mole/hr.) and carbon monoxide (0.13 mole/hr.). Typical components of the liquid product effluents under steady state conditions are shown in Table 1.

It is evident from the data that methanol carbonylation to acetic acid may be achieved over a wide range of conditions using the supported ruthenium catalysts of this invention. In particular it may be noted that acetic acid production has been demonstrated at:

1) Operating temperatures of 180° to 350°C

2) Superatmospheric pressures of 500 psi (34.47 bar) to 4000 psi (275.79 bar).

Example 18

This example illustrates the use of different reactant feed rates upon the performance of a typical 1% ruthenium-on- carbon catalyst prepared by the method of Example 1.

To the 23 ml capacity continuous reactor of Example 2 filled with 1% ruthenium-on-carbon catalyst is fed a mixture of methanol (0.13 mole/hr), methyl iodide (0.005 mole/hr.) and carbon monoxide (0.16 mole/hr.). The reactor temperature is maintained at 250°C, the pressure within the reactor is 3000 psi(206.84 bar). Under steady state conditions, a typical composition of the liquid product effluent (determined by glc) is as follows: acetic acid : 67.2 st% methyl iodide/methyl acetate : 17.7 wt% methanol : 1.9 wt% water : 12..5 wt%

Again the conversion of the methanol feed is 98% per pass and acetic acid is the major product fraction.

Example 19

This example illustrates a method of catalyst preparation using ruthenium (IV) oxide, hydrate (Ru0₂ x H₂O as the souce of ruthenium.

A sample of activated carbon material (50 g) which has been pretreated with nitric acid according to the procedure of Example 1, is stirred with a solution of ruthenium (IV) oxide (0.88 g) in 10cc of nitric acid and 200 cc of water, and the volume of the ruthenium solution adjusted to bring the support to insipient wetness. The ruthenium-treated carbon is then placed in a quartz tube and purged with hydrogen for 30 minutes at a H₂ flow rate of 12 1/hr. The sample is next heated to 315°C. for 1 hr and 480°C for 2.5 hr under the same H₂ flow conditions. After cooling to 70°C it is purged with nitrogen before reaching ambient temperature.

Example 20-23

In these syntheses, the carbonylation of methanol to acetic acid is carried out in accordance with the procedure of Example 2 using various supported ruthenium catalyst compositions but under otherwise similar conditions of temperature, pressure and initial methanol-to-methyl iodide mole ratio. As can be seen from the data summarized in Table 2, which follows, a variety of supported ruthenium compositions are effective for methanol conversion to acetic acid and/or methyl acetate. In particular, it may be noted that acetic acid production has been demonstrated using:

1) Supported ruthenium-on-carbon catalysts having a wide range of ruthenium-metal loadings, from 0.5 up to 5 wt% (see Examples 20-22). Here the catalysts were prepared from ruthenium(III) chloride and activated carbon in accordance with the procedure of Example 1.

2) A supported ruthenium-on-carbon catalyst prepared from ruthenium(IV) oxide and activated carbon according to the procedure of Example 19 (see Example 23). a Methanol carbonylations carried out under the conditions of Example 2. b Prepared from ruthenium(III) chloride and activated carbon according to the procedure of Example 1. c Prepared from ruthenium( IV) oxide and activated carbon according to the procedure of Example 19.

Example 24

This example illustrates the use of a liquid feedstock comprising a mixture of methanol, methyl acetate and methyl iodide. Following the procedures of Example 2 wherein the reactor is filled with a typical 1% ruthenium- on-carbon catalyst prepared by the method of Example 1, the carbonylation process is conducted by feeding to said reactor a mixture of methanol (.10 mole/hr), methyl acetate (.03 mole/hr), methyl iodide (.01 mole/hr) and carbon monoxide (.16 mole/hr). The pressure within the reactor is held at 3000 psi (206.84 bar) and the temperature is 250°C. under steady state conditions, the composition of the liquid effluent is as follows: acetic acid : 34.5 wt% methyl iodide/methyl acetate : 35..6 wt% methanol : 8.5 wt% water : 21.4 wt%

Example 25

This example illustrates the recycle of a liquid product effluent to the carbonylation reactor wherein said liquid product comprises a mixture of unreacted methanol, methyl acetate and acetic acid. Following the procedure of Example 2, and using a typical 1% ruthenium-on-carbon catalyst prepared by the method of Example 1, the carbonylation process is conducted by feeding to said reactor the liquid product from Example 2 (0.05 mole/hr), methanol (0.13 mole/hr), methyl iodide (0.01 mole/hr) and carbon monoxide (0.16 mole/hr). The pressure within the reactor is held at 3000 psi (206.84 bar), and the temperature is 250°C. Under steady state conditions the majority of the product is acetic acid.

Example 26

This example illustrates another method of catalyst preparation using an organic solvent to solubilize the ruthenium(III) chloride prior to loading onto the carbon support.

A sample of ruthenium(III) chloride hydrate (1.28 g) is dissolved in a minimal amount of acetone (30 ml). Thissolution is added dropwise to the carbon support, and pretreated according to the procedure of Example 1, until insipient wetness. Excess acetone is removed under vacuo, and solution addition repeated until all the ruthenium has been added to the carbon support. The ruthenium-treated carbon is then prereduced under a flow of hydrogen according to the procedure of Example 1, and stored under a nitrogen atmosphere.

Example 27-30

In these syntheses, the carbonylation of methanol to acetic acid is carried out in accordance with the procedure of Example 2 using various supported ruthenium catalyst compositions but under otherwise similar conditions of temperature, pressure and initial methanol-to-methyl iodide mole ratio. As can be seen from the data summarized in Table 3, which follows, a variety of supported ruthenium catalysts are effective for methanol conversion to acetic acid. In particular, it may be noted that acetic acid production has been demonstrated using:

1) Ruthenium catalysts where the ruthenium is bonded to silica, carbonate, and zeolitic solid supports.

2) A catalyst prepared from a carbon support treated with a solution of .ruthenium chloride hydrate in an organic solvent (acetone). Example 26 is illustrative of this catalyst preparative technique.

^aMethanol carbonylations carried out in accordance with the procedure and conditions of Example 2. bPrepared from ruthenium(III) chloride and activated carbon according to the procedure of Example 26. cPrepared from ruthenium(III) chloride and silica according to a procedure similar to that of Example 1. Methanol carbonylation is carried out at 3500 psi pressure. dPrepared from ruthenium(III) chloride and Linde LZ-752 1/16" extrudates according to a. procedure similar to that of Example 1.

Example 31

In this example a sample of 1% ruthenium-on-carbon catalyst, prepared by the procedure of Example 1, has been evaluated for the carbonylation of methanol to acetic acid under the following process conditions:

Methanol feed rate - 0.13 mole/hr Methyl iodide feed rate - 0.01 mole/hr Carbon monoxide feed rate - 0.16 mole/hr Operating pressure - 3000 psi (206.84 bar)

Operating temperature - 350°C

The operating procedure is similar to that described in Example 2. Under steady state conditions, a typical composition of the liquid product effluent is as follows: acetic acid : 86.5 wt% methyl iodide/methyl acetate : 4.6 wt% methanol : 0.2 wt% water : 8.5 wt%

As can be seen from the data the conversion of the methanol feed is 99% per pass and the majority of the product is acetic acid. In particular, analyses of the liquid product indicates no substantial production of by-products such as aldehydes, higher boiling carboxylic acids and alcohols. Furthermore the same liquid effluents show F2 ppm dissolved ruthenium.

Example 32

In this example a sample of 1% ruthenium-on-carbon catalyst, prepared by the procedure of Example 1, has been evaluated for the carbonylation of methanol to acetic acid under the following process conditions: Methanol feed rate - 0.13 mole/hr

Methyl iodide feed rate - 0.01 mole/hr Carbon monoxide feed rate - 0.16 mole/hr Operating pressure - 3000 psi (206.84 bar) Operating temperature - 300°C

The operating procedure is similar to that outlined in Example 2. Under steady state conditions, a typical composition of the liquid product effluent is as follows: acetic acid 90.2 wt% methyl iodide/methyl acetate 3.8 wt% methanol 0.1 wt% water 5.8 wt%

The composition of the off-gas under these same steady state conditions is as follows: carbon monoxide : 72.0% carbon dioxide : 10.4% methane : 8.1% methyl iodide : 5.8% methyl acetate : 0.8%

As can be seen from this data, once again the conversion of methanol feed is 99% and the majority of the product is acetic acid. As the examples and preceeding 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-stop 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. Finally, the invention is advantageous in that numerous substitutions, modifications and changes can be made without departing from the inventive concept. However, the scope of the invention may best be understood by examining the claims, which follow, read in conjunction with the preceeding specification.

Claims

WHAT IS CLAIMED IS:

1. A process whereby aliphatic carboxylic acids and their ester derivatives containing 2 or more carbon atoms are prepared from aliphatic alcohol reactants having the formulae ROH, where R is a saturated hydrocarbyl radical containing 1 to 12 carbon atoms, by a procedure comprising: a) Contacting said aliphatic alcohols with at least a catalytic quantity of a supported ruthenium-containing compound in the presence of a halogen-containing promoter in which the halogen is either bromine or iodine. b) Heating said reaction mixture under super-atmospheric pressures of 500 psi (34.47 bar) 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

3) Isolating said acids and their esters contained therein.

2. The process of Claim 1 wherein the supported rutheniumcontaining component is prepared from the group of ruthenium compounds consisting of 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. The process of Claim 2 wherein the ruthenium-containing compound is selected from the group consisting of ruthenium (III) triodide, tricarbonylruthenium (II) iodide, ruthenium (IV) dioxide, hydrate, anhydrous ruthenium (IV) chloride, ruthenium (VIII) tetraoxide, ruthenium (III) chloride, hydrate, ru thenium acetate, ruthenium propionate, ruthenium(III) hexafluoroacetylacetonate, ruthenium (III) acetylacetonate, triruthenium dodecarbonyl and tricarbonylruthenium (II) chloride.

4. The process of Claim 1 wherein the ruthenium-containing compound is supported on activated carbon.

5. The process of Claim 1 wherein the ruthenium-containing compound is supported on silica.

6. The process of Claim 1 wherein the ruthenium-containing component is supported on a zeolite.

7. The process of Claim 1 wherein the halogen-containing promoter is hydrogen iodide.

8. The process of Claim 1 wherein the halogen-containing promoter is an alkyl halide containing 1 to 12 carbon atoms.

9. The process of Claim 8 wherein the alkyl halide promoter is selected from the group consisting of methyl iodide, ethyl iodide and ethyl bromide.

10. The process of Claim 9 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.

11. The process of Claim 1 wherein the aliphatic alcohol reactant is methanol, the halogen-containing promoter is methyl iodide and the aliphatic carboxylic acid product is acetic acid.

12. The process of Claim 1 whereby aliphatic carboxylic acids are prepared from mixtures of reactants consisting of one or more aliphatic alcohol reactant having 1 to 12 carbon atoms in combination with one or more aliphatic carboxylic acid ester derivative having the formulae: wherein R and R' are saturated hydrocarbyl radicals containing 1 to 12 carbon atoms.

13. The process of Claim 12 wherein the reactants are a mixture of methanol and methyl acetate.

14. The process of Claim 12 where the aliphatic carboxylic acids are prepared in the presence of an aqueous component.

15. The process of Claim 12 wherein the alcohol reactant is carbonylated in the presence of one or more aliphatic carboxylic acids.

16. The process of Claim 15 wherein methanol is carbonylated in the presence of acetic acid.