GB2041924A - Manufacture of Ethyl Esters and of Ethylene from Synthesis Gas - Google Patents

Abstract

A process is provided for the synthesis of carboxylic acid ethyl eaters by reacting a mixture of carbon monoxide and hydrogen (syngas) with a carboxylic acid or anhydride. The reaction is conducted at a temperature between 100 and 350 DEG C. and a pressure of at least 500 psi (3.45 mPa), in the presence of a ruthenium catalyst. The ethyl ester is preferably pyrolyzed to form ethylene.

Description

SPECIFICATION Manufacture of Ethylene from Synthesis Gas This invention concerns a process for the synthesis of carboxylic acid ethyl esters, preferably as part of a two-step process for the preparation of ethylene, from mixtures of carbon monoxide and hydrogen (commonly known as synthesis gas or syngas).

More specifically, the inventive process concerns the selective synthesis of carboxylic acid ethyl esters from synthesis gas by reacting said mixtures of CO/H2 with one or more carboxylic acid coreactants in the presence of one or more ruthenium catalyst complexes to form ethyl esters of said carboxylic acid coreactants. The resulting ethyl ester intermediates can then be pyrolyzed to ethylene.

The process is exemplified by, but not limited to, CO hydrogenation in the presence of an acyclic carboxylic acid (RCOOH where R is an organic radical) to form an ethyl ester of said acid, which upon pyrolysis yields ethylene and regenerates said acid according to stoichiometry of eq (1) and (2).

2CO+4H2+RCOOHoC2H500CR+2H20 (1) C2H5OOCReC2H4+HOOCR (2) Alternatively the ethyl ester may be isolated and used as is, or as an intermediate in the production of ether useful and important chemicals. For example, ethyl esters such as ethyl acetate and ethyl propionate are widely used as solvents, particularly for surface coatings.Alternatively the ethyl ester (RCOOC2H6) may be hydrolyzed to ethanol as illustrated in eq 3, and the ethanol used as a source of other two carbon molecules of commercial importance, and their derivatives, such as acetaldehyde, acetic acid, acetic an hydride, acetaldol, and cellulose acetates RCOOC2H5+H2OoRCOOH+C2H5OH (3) It is one purpose of this invention to provide a new, two-step route to the production of ethylene using mixtures of carbon monoxide and hydrogen as the primary building block, that proceeds via the intermediate formation of ethyl esters of carboxylic acids.

A number of routes have been suggested previously for the production of ethylene from synthesis gas, (c.f. P. H. Spitz, Chemtech, May 1977, p. 295) including: Variations in Fischer-Tropsch technology Methanol homologation to ethanol, followed by dehydration Dimethyl ether cracking Direct synthesis from CO/H2 mixtures To our knowledge, however, the production of ethylene from synthesis gas via the intermediate formation of ethyl esters (eq 1 and 2) has not been proposed previously. This new route to ethylene has several important advantages, most notable, both the initial formation of the ethyl esters from syngas, using the novel class of ruthenium catalysts disclosed here, and the subsequent pyrolysis of said ethyl esters, are selective chemical reactions when carried out in accordance with the examples and specifications disclosed herein.In particular, the use of the ruthenium catalyst disclosed here represent an important advance in the technology for making two-carbon molecules and their derivatives, directly from synthesis gas.

The selective pyrolysis of esters, particularly acyclic esters, to alkenes and the corresponding acids, is well documented in the literature (See: C. H. DePuy and R. W. King, Chemical Reviews, 60, 431(1960)). The reaction may be carried out in either the liquid or vapor phases, it does not require a catalyst and is relatively simple in experimental procedure. Furthermore, yields of alkene elimination product are nearly always excellent and sometimes quantitative. Themolysis of ethyl esters of aliphatic carboxylic acids, for example, has been reported to yield ethylene and the corresponding carboxylic acids in a number of cases (See: G. G. Smith and F. W. Kelly, Progress in Physical Organic Chemistry, Vol. 8, Wiley-lnterscience (1 971)). Specific examples include the pyrolysis of ethyl acetate to ethylene and acetic acid (eq 2) (A. T.Blades, Can. J. Chem., 32, 366 (1954)).

This invention provides a process for the synthesis of carboxylic acid ethyl esters by reaction of a mixture of carbon monoxide and hydrogen with a liquid medium containing one or more aliphatic carboxylic acids or acid anhydrides containing up to 1 2 carbon atoms, wherein the reaction is carried out in the presence of a ruthenium catalyst at a temperature of between 1000 and 3500C, and at a superatmospheric pressure of at least 500 psi (3.45 mPa). Formation of the ethyl ester can be followed by pyrolysis of the ethyl ester to ethylene.

In order to present the inventive concept in the greatest possible detail as to promote its understanding, the following supplementary disclosure is submitted: Synthesis of Ethyl Esters A. Ruthenium Catalyst Composition-Catalyst precursors that are suitable in the practice of the first stage of this invention, particularly the synthesis of ethyl esters from synthesis, gas, contain ruthenium. The catalytically active species are then believed to comprise ruthenium in complex combination with carbon monoxide and hydrogen, the most effective catalysis is acheived when the ruthenium species are solubilized in the carboxylic acid coreactant employed to satisfy the stoichiometry of eq. 1.

The preferred ruthenium catalyst precursors may take many different forms. For instance, the ruthenium may be added to the reaction mixture in an oxide form, as in the case of, for example, ruthenium(lV) oxide, hydrate, anhydrous ruthenium(lV) dioxide and ruthenium(VIII) tetraoxide.

Alternatively, it may be added as the salt of a mineral acid, as in the case of ruthenium(lll) chloride, hydrate, ruthenium(lll) bromide, anhydrous ruthenium(lll) chloride and ruthenium nitrate, or as the salt of a suitable organic carboxylic acid (see Section B, below), for example, ruthenium(lll) acetate, ruthenium(lil) propionate, ruthenium butyrate, ruthenium(lil) trifluoroacetate, ruthenium octanoate, ruthenium naphthenate, ruthenium valerate and ruthenium(lll) acetylacetonate. The ruthenium may also be added to the reaction zone as a carbonyl or hydrocarbonyl derivative.Here, suitable examples include triruthenium dodecacarbonyl, hydrocarbonyls such as H2Ru4(CO)13 and H4Ru4(CO)l2, and substituted carbonyl species such as the tricarbonylruthenium(ll) chloride dimer, [Ru(CO)3CI2]2.

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, phosphorus, arsenic and antimony. These elements, in their trivalent oxidation states, particularly tertiary phosphorus 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 1 2 carbon atoms, or they may be part of a heterocyclic ring system, or be mixtures thereof.Illustrative examples of suitable ligands thay may be used in this invention include: triphenylphosphine, tri-n-butylphosphine, triphenylphosphite, triethylphosphite, trimethylphosphite, trimethylphosphine, tri-pmethoxyphenylphosphine, triethylphosphine, trimethylarsine, triphenylarsine, tri-p-tolyiphosphine, tricyclohexylphosphine, dimethylphenylphosphine, trioctylphosphine, tri-oZtolylphosphine, 1,2bis(diphenylphosphino)ethane, triphenylstibine, trimethylamine, triethylamine, tripropylamine, tri-noctylamine, pyridine, 2,2'-dipyridyl, 1,1 0-phenanthroline, quinoline, N,N'-dimethylpiperazine, 1,8bis(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 dicarbonylbis(triphenylphosphine)ruthenium(ll) chloride 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, described below.

A further important class of ruthenium catalyst precursor, useful in the conversion of carbon monoxide-hydrogen mixtures to ethyl ester derivatives, consists of one or more suitable ruthenium oxide, salt and/or carbonyl derivative species in combination with a cocatalyst. There are several classes of suitable co-catalysts. One such class which may be added to the reaction mixtures to enhance the activity of the solubilized ruthenium catalysts is the salts of the alkali and alkaline earth metals. Illustrative examples of effective alkali metal salts include the alkali metal halides, for instance, the fluoride, chloride, bromide and iodide salts, together with the alkali and alkaline earth metal salts of suitable carboxylic acids (see Section B, below). The preferred alkali and alkaline earth metal salts are the bromides.These salts may be added over a wide range of concentrations, from about 0.01 to at least 102 moles of alkali or alkaline earth salt per gm atom of ruthenium present in the reaction mixture.

Salts of quaternary ammonium and phosphonium cations are also effective as cocatalysts in the process of this invention. Suitable quaternary phosphonium salts are those which are substantially inert under the CO-hydrogenation conditions and which have the formula:

where1, R2, R3 and R4 are organic radicals bonded to the phosphorous atom by a saturated aliphatic carbon atom, and X is an anionic species, preferably a halogen ion such as bromide. The organic radicals useful in this instance include alkyl, aryl, alkylaryl and cycloalkyl radicals having, where possible, 1 to 20 carbon atoms. The alkyl radicals may contain both branched and linear chains and include the methyl, ethyl, n-butyl, iso-butyl, heptyl, 2-ethylhexyl, and dodecyl radicals. Suitable aryl and alkylaryl radicals include, but are not limited to, phenyl, p-methacrylphenyl, benzyl, p-tolyl, palkylphenyl, o-tolyl and m-tolyl. Suitable quaternary phosphonium salts useful in the practice of this invention include tetramethylphosphonium bromide, tetrabutylphosphonium chloride, tetrabutylphosphonium iodide, tetrabutylphosphonlum bromide, tetraphenyiphosphonium bromide, heptyl(triphenyl)phosphonium bromide and methyl(triphenyl)phosphonium bromide. The corresponding quaternary phosphonium hydroxides, nitrates and carboxylic acid salts may also be useful in this instance, as well as the corresponding quaternary ammonium salts such as tetramethylammonium bromide and tetra-n-propylammonium bromide, and the corresponding iminium salts such as bis(triphenylphosphine)iminium nitrate.Examples 1-8 provide evidence for the effectiveness of the ruthenium oxide-quaternary phosphonium and ammonium couples.

B. Carboxylic Acids-Carboxylic acids useful in the process of this invention form the acid moiety of the desired ethyl ester intermediate. Preferably, said acids are also useful as solvents for the ruthenium catalyst combinations. Suitable carboxylic acids include aliphatic acids, alicyclic monocarboxylic acids, heterocyclic acids and aromatic acids, both substituted and non-substituted. For example, this invention contemplates the use of lower mono aliphatic acids of 1 to 1 2 carbon atoms such as formic acid, acetic, propionic, butyric, isobutyric, valeric, caprioic, capric, periargonic and lauric acids, together with dialiphatic acids of 2 to 6 carbons, such as oxalic, malonic, succinic and adipic acids.The invention further contemplates the use of substituted monoaliphatic acids containing one or more functional substituents, such as the lower alkoxy, chloro, fluoro, cyano, alkylthio, and amino functional groups, examples of which include acetoacetic acid, dichloroacetic and trifluoroacetic acid, chloropropionic acid, trichloroacetic acid, monofluoroacetic acid and the like. Among the suitable aromatic acids contemplated are benzoic acid, naphthoic acids, toluic acids, chlorobenzoic acids, aminobenzoic acids and phenylacetic acid, The alicyclic monocarboxylic acids may contain from 3 to 6 carbons in the ring, both substituted and unsubstituted, and may contain one or more carboxyl groups, such as cyclopentanecarboxylic acid and hexahydrobenzoic acids.The heterocyclic acids may contain 1 to 3 fused rings both substituted and unsubstituted together with one or more carboxylic groups, examples include quinolinic, furoic and picolinic acids, Mixtures of said classes of carboxylic acids, in any ratio, may also be used in the inventive process. The preferred carboxylic acids are the lower aliphatic acids such as acetic acid, propionic acid and butyric acid, together with substituted aliphatic acids such as trifluoroacetic acid.

Also suitable in the practice of this invention are the acid anhydrides of said carboxylic acids.

These acid anhydrides may be used both as useful solvents for the ruthenium catalyst and as coreactants which provide the acid moiety of the desired ethyl ester intermediate. Particularly useful 'are the anhydride of lower aliphatic carboxylic acids containing 3 to 1 2 carbon atoms such as acetic anhydride, propionic anhydride and n-butyric anhydride. Here reduction to practice includes Example 21.

C. Catalyst Concentration-The quantity of ruthenium catalyst employed in the instant invention is not critical and may vary over a wide range. In general, the novel process is desirably conducted in the presence of a catalytically effective quantity of the active ruthenium species which gives the desired 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, expressed as Ru basis the total weight of the reaction mixture. The upper concentration is dictated by a variety of factors including catalyst cost, partial pressures of carbon monoxide and hydrogen, operating temperature and choice of carboxyic acid diluent/reactant.A ruthenium catalyst concentration of from about 1 x10-5 to about 10 weight percent ruthenium, based on the total weight of reaction mixture, is generally desirable in the practice of this invention.

D. Operating Temperature-The temperature range which can usefully be employed in these ester synthesis is a variable dependent upon other experimental factors including the choice of carboxylic acid co-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 1000 to 3500C when superatmospheric pressures of syngas are employed. A narrower range of 1 80-2600C represents the preferred temperature range when the major products are methyl and ethyl acetates.

Table 2 is evidency of how the narrower range is derived.

E. Pressure--Superatmospheric pressures of 500 psi or greater lead to substantial yield of desirable alkanol ester by the process of this invention, A preferred operating range for solutions of ruthenium(lV) oxide in acetic acid is from 2000 psi to 7500 psi (13.8 to 51.7 mPa), although pressures above 7500 psi (51.7 mPa) also provide useful yields of desired ester. Table 2 is evidency 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 and hydrogen fractions in these examples.

F. Gas Composition-The relative amounts of carbon monoxide and hydrogen which may be initially present in the syngas mixture are available, and these amounts may be varied over a wide range. In general, the mole ratio of CO-to-H2 is in the range from about 20:1 up to about 1:20, preferably from about 5:1 to 1:5, although ratios outside these ranges may also be employed. Particularly in continuous operations, but also in batch experiments, the carbon monoxide-hydrogen gaseous mixtures 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 hydrogenation conditions such as carbon dioxide, 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.

In all syntheses, the amount of carbon monoxide and hydrogen present in the reaction mixture should be sufficient to satisfy the stoichiometry of eq (1).

G. Product Distribution-As far as can be determined, without limiting the invention thereby, the ruthenium-catalyst one-step CO-hydrogenation process disclosed herein leads to the formation three classes of primary products, namely the methanol, ethanol and n-propanol ester derivatives of the corresponding co-reactant carboxylic acid. In the case then where propionic acid is the co-reactant, the principal products are methyl propionate, ethyl propionate and n-propyl propionate. Minor by-products detected in the liquid product fraction include small amounts of water, glycol dipropionate and n-butyl propionate. Carbon dioxide and methane may be detected in the off-gas together with unreacted carbon monoxide and hydrogen.Where > 90% of the carboxylic acid charge has been converted to ester derivatives, the liquid product may also contain substantial quantities of methanol, ethanol and npropanol.

H. Mode of Operation-The novel process of this invention can be conducted in a batch, semicontinuous or continuous fashion. The catalyst 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 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 ester products generated by CO hydrogenation.

I. Identification Procedures-The products of CO-hydrogenation have been identified in this work by one or more of the following analytical procedures, viz, gas-liquid phase chromatography (gic), 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).

Pyrolysis of Ethyl Esters The pyrolytic elimination of esters may be carried out in either the liquid or the vapor phase by simply heating the ester in a metal bath, or with a free flame if its boiling point is sufficiently high, or by passing the compound through a heated tube. The ester pyrolysis reaction is relatively simple in experimental procedure, it does not require a catalyst, and yields are nearly always excellent, sometimes quantitative. Where the pyrolysis of an ester is carried out in the vapor phase, the ester is normally added dropwise to the top of a vertically-mounted quartz tube packed with glass helices or beads, the products are swept from the reaction chamber by a slow stream of inert gas and collected in suitable cold traps.

For preparative purposes the pyrolysis of aliphatic esters, particularly acyclic esters, to alkene and the corresponding acid is best carried out at temperatures ranging from 200 to 6009C. This temperature range is effective, for example, for the pyrolysis of ethyl esters of aliphatic carboxylic acids, where the desired products are ethylene and recovered carboxylic acid. Examples include the selective pyrolysis of ethyl propionate to ethylene and propionic acid, as well as the generation of ethylene plus acetic acid from ethyl acetate (eq 2).

Generally, these pyrolyses are most conveniently carried out at atmospheric or near-atmospheric pressures, in the presence of one or more inert gases used to sweep the product from the reaction zone. Suitable inert gases include helium, argon, neon, nitrogen and the like.

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

Synthesis of Ethyl Esters Example 1 To an 850 ml glass-lined autoclave reactor equipped for pressuring, heating, cooling and means of agitation is charged 0.764 gm of ruthenium(lV) oxide, hydrate (4.0mmole), 17.64 gm of heptyl(triphenyl)phosphonium bromide (40mmole) and propionic acid (50 gm). Upon stirring under a nitrogen atmosphere most of the solids dissolve to give a deep-red solution. The reactor is then sealed, flushed with CO/H2, pressured to 2000 psi with synthesis gas (a 1:1 mixture of hydrogen and carbon monoxide) and heated to 2200C with agitation. At temperature, the pressure within the reactor is raised to 6300 psi (43.44 mPa) with CO/H2 mix, and the pressure held constant throughout the 1 8 hour run by automatic addition of more synthesis gas from a large surge tank.Upon cooling, the excess gases are sampled and vented, and the deep-yellow liquid product (73.8 gm) removed for analysis.

There is no solid product fraction.

Analysis of the liquid fraction by gas-liquid chromatography (gic) shows the presence of: 38.2 wt % ethyl propionate 1 6.5 wt % methyl propionate 8.4 wt % n-propyl propionate 0.8 wt % n-butyl propionate 0.9 wt % glycol dipropionate 2.7 wt % water 27.8 wt % unreacted propionic acid.

The ethyl propionate, together with the corresponding methyl, propyl and butyl propionates were isolated from a portion of the crude liquid product (58.8 gm) by stripping under reduced pressure (0.8 cm Hg). The residual liquid 'bottoms' (32.1 gm) contained the solubilized ruthenium catalyst, the clear distillate fraction (26. 1 gm) contained: 58.3 wt % ethyl propionate 22.9 wt % methyl propionate 10.5 wt % propyl propionate 0.4 wt % butyl propionate This distillate liquid was further purified by fractional distillation.

Example 2 To an 850 ml glass-lined autoclave equipped for pressurizing, heating, and means of agitation is charged 0.764 gm of ruthenium (IV) oxide, hydrate (4.0 mmole), 13.58 gm of tetrabutylphosphonium bromide (40 mmole), and 50 gm of propionic acid. The mixture is stirred to dissolve most of the solids, the reactor sealed, flushed with CO/H2 pressured to 2000 psi (13.8 mPa) with synthesis gas (1:1, CO/H2) and heated to 2200C with agitation. At temperature, the pressure within the reactor is raised to 6300 psi with CO/H2 and the pressure held constant throughout the 1 8 hour run by automatic addition of more synthesis gas from a large surge tank. Upon cooling, the excess gases are sampled and vented, and the deep-red liquid product (87.8 gm) removed for analysis. There is no solid product fraction.

Analysis of the liquid fraction by gas-liquid chromatography (glc) shows the presence of: 31.8 wt % ethyl propionate 29.9 wt % methyl propionate 3.4 wt % n-propyl propionate 2.0 wt % n-butyl propionate 1.9 wt % propionic acid 14.3 wt % ethanol 7.5 wt % methanol 1.5 wt n-propanol The ethyl propionate and ethanol, together with the corresponding C, and C3-C4 alkyl propionates, were isolated from the crude liquid product (50.3 gm) by fractional distillation under reduced pressure (0.4 cm Hg). The residual liquid 'bottoms' (12.5 gm) contained the solubilized ruthenium catalyst.

Example 3 To an 850 ml glass-lined autoclave equipped for pressurizing, heating and means of agitation is charged 0.764 gm of ruthenium (IV) oxide, hydrate (4.0 mmole), 14.29 gm of methyl(triphenyl)phosphonium bromide (40 mmole) and propionic acid (50 gm). The mixture is stirred to dissolve most of the solids, the reactor sealed, flushed with CO/H2 and pressured to 2000 psi (13.8 mPa) with synthesis gas (1:1, CO/H2). Over a period of 45-60 minutes the autoclave is heated, with agitation, to 220cC. At temperature the reactor pressure is raised to 6300 psi with CO/H2 and the pressure held constant overnight by automatic addition of more synthesis gas from a large surge tank.

Upon cooling, the excess gases are sampled and vented, and the deep-red liquid product (70.4 gm) removed for analysis. There is no solid product fraction.

Analysis of the liquid fraction by gic shows the presence of: 33.8 wt % ethyl propionate 32.6 wt % methyl propionate 7.2 wt % n-propyl propionate 0.7 wt % n-butyl propionate 0.99 wt % water 16.0 wt % unreacted propionic acid An analysis of a typical off-gas sample revealed the presence of: 38.8 % hydrogen 38.2 % carbon monoxide 12.8 % carbon dioxide 6.2 % methane Stripping of a sample of crude liquid product (59.0 gm) under reduced pressure (0.4 cm Hg) yielded a water-white distillate fraction (42.5 gm) and a red viscous liquid bottoms (1 5.7 gm) containing the active ruthenium catalyst. The distillate fraction showed the presence of: 35.2 wt % ethyl propionate 32.4 wt % methyl propionate 7.5 wt % propyl propionate Ethyl propionate may be isolated from this product distillate by fractional distillation.

Examples 1 11 Following the procedures of Example 1, in these examples synthesis gas conversion to ethyl propionate is carried out in the presence of a constant weight of ruthenium (IV) oxide, hydrate (4.0 mmole) or ruthenium (IV) chloride, hydrate in combination with various quaternary alkyl and aryl ammmonium and phosphonium halides, alkali-metal halides and iminium salts. A summary of the yield data for each of these ruthinium catalyst combinations is given in Table 1.

Table 1 Synthesis of Esters of Propionic Acid from Syngasa Liquid Product Composition (wt %)b Ruthenium Catalyst Propionete Esters Unreacted Example Composition Methyl Ethyl Propyl Butyl H20 Propionic Acid 4 RuO2-1OPh4PBr 14.7 14.8 17.0 1.3 0.58 49.1 5 RuO2-1OPh4PCl 43.0 2.1 16.1 0.6 0.53 34.2 6 Ru02-10Bu4PCI 44.6 5.1 13.9 1.1 3.99 12.9 7 RuO2-10Bu4Pl 2.7 3.8 5.2 1.2 0.64 83.4 8 RuO2-10Bu4NBr 12.9 4.2 13.6 23.9 1.78 36.7 9 RuO2-1OCsBr 5.1 0.2 1.0 0.8 14.8 66.0 10 RuO21 OCsl 9.6 1.9 4.1 5.47 61.5 11 RuCl3-5(Ph3P)2NNO3 48.2 14.2 9.6 1.8 2.87 3.7 Experimental Conditions: : Ru02xH20, 4.0 mmole; C2H6COOH, 50 gm; Temp., 220 ; Pressure, 6000- 6300 psi (41.37-43.44 mPa).

bEstimated by gas-liquid chromatography, water by Karl-Fischer titration.

Examples 12-19 Following the procedure of Example 1, in these cases synthesis gas conversion to ethyl propionate is catalyzed by solutions of ruthenium (IV) oxide, hydrate and heptyl(triphenyl)phosphonium bromide solubilized in propionic acid over a range of operating temperatures, pressures, ruthenium concentrations and quaternary phosphonium/Ru molar ratios. The yield data for each of these experimental ranges is summarized in Table 2.

Table 2 Synthesis of Esters of Propionic Acid from Syngasa Liquid Product Composition Ruthenium Catalyst Reaction: Propionate Esters Unreacted Example Composition Temp( C) Pressure (psi/mPa) Methyl Ethyl Propyl H2O Propionic Acid 12 RuO2-10HpPh3PBr 260 6300 43.44 72.0 2.7 7.5 1.2 3.3 13 RuO2-10HpPh3PBr 220 6300 43.44 16.5 38.2 8.4 1.2 27.8 14 RuO2-10HpPh3PBr 180 6300 43.44 16.4 3.3 2.4 0.15 75.5 15 RuO2-10HpPh3PBr 220 4000 27.58 12.2 12.4 17.5 0.59 54.0 16 RuO2-10HpPh3PBr 220 2000 13.8 4.3 0.5 25.2 0.50 66.6 17 RuO2-4HpPh3PBr 220 6300 43.44 21.1 32.5 9.4 1.10 29.3 18 RuO2-HpPh3PBr 220 6300 43.44 51.2 16.0 6.0 0.99 20.1 19 RuO2-10HpPh3PBrc 220 6300 43.44 24.8 24.6 10.0 0.76 36.3 aExperimental conditions: RuO2XH2O, 4.0 mmole, C2H5COOH, 50 gm.

bEstimated by gas-liquid chromatography, water by Karl-Fischer titration.

cCharging 2.0 mmole RuO2XH2O.

Example 20 To a 450 ml glass-lined autoclave equipped for pressuring, heating and means of agitation is charged 0.382 gm of ruthenium (IV) oxide, hydrate (2.0 mmole), 7.15 gm of methyl(triphenyl)phosphonium bromide (20 mmole) and 25 gm of acetic acid. The mixture is stirred to dissolve most of the solids, the reactor sealed, flushed with CO/H2, pressured to 2000 psi (13.8 mPa) with CO/H2(1:1) and heated to 220 with agitation. At temperature, the pressure within the reactor is raised to 6300 psi (43.44 mPa) CO/H2 and the pressure held constant throughout the 18 hour run by automatic addition of more synthesis gas from a large surge tank. Upon cooling, the excess gases are sampled and vented, and the deep-red liquid product (33.5 gm) removed for analysis. There is no solid fraction.

Analysis of the liquid fraction by gas-liquid chromatography shows the presence of: 36.3 wt % ethyl acetate 21.9 wt % methyl acetate 2.5 wt % n-propyl acetate 3.2 wt % water 32.3 wt % unreacted acetic acid Example 21 To a 300 ml glass-lined autoclave equipped for pressuring, heating and means of agitation is charged 0.40 gm of ruthenium (III) acetylacetonate (1.0 mmole), and 50 ml of acetic anhydride. The mixture is stirred under a nitrogen atmosphere to give a clear, deep-red solution. The reactor is then sealed, flushed with CO/H2 (1:1) and pressured to 2700 psi (18.62 mPa) with synthesis gas (CO/H2, 1:1). Over a period of 60-75 minutes, the autoclave is heated, with agitation, to 2200C, and held at temperature overnight. Total gas uptake is 11 50 psi (7.93 mPa).After cooling, the excess gases are vented and the deep-red liquid product (49 ml) removed for analysis. There is no solid fraction.

Analysis of this liquid product by glc shows the presence of: 30.1 % ethyl acetate 0.5 % methyl acetate and 1.6% water.

Examples 22-27 Following the procedures of Example 21, in these cases synthesis gas conversion to ethyl acetate is carried out in the presence of a constant weight of ruthenium salt or complex (1-2 mmole) solubilized in acetic acid (50 ml). The yield data in Table 3 are illustrative of the use of ruthenium salts, such as ruthenium (Ill) chloride, hydrate and ruthenium(lll) acetylacetonate in combination with tertiary group VB donar ligands such as triphenylphosphine and tri-n-butylphosphine, as well as of preformed ruthenium complexes such as dicarbonylbis(triphenylphosphine)ruthenium (II) chloride.

Table 3 Synthesis of Esters of Acetic Acid from Syngasa Liquid Product Composition (%)bc Ruthenium Catalyst Acetate Esters Unreacted Example Composition Methyl Ethyl Propyl H20 AceticAcid 22 RuCI2(PPh3)3 0.5 3.8 1.8 92.6 23 RuCI2(CO)2(PPh3)2 0.4 4.1 1.6 93.5 24 Ru(acac)s-2P8u3 3.6 6.4 1.3 87.6 25 RuCI,--3 PBu3 0.2 6.7 3.2 89.5 26 RuCI33P(OPh)3 4.4 19.5 4.0 65.7 27 RuCI33AsMe3 0.6 8.4 4.0 83.3 8Experimental conditions bEstimated by gas-liquid chromatography, water by Karl-Fischer titration Clncludes some ethyl acetate generated via acetic acid reduction Pyrolysis of Ether Ester Example 28 A 3.5 cm diameter quartz tube 43 cm in length, is packed with glass helices, set in a vertical plane and heated to 450-4600C. Helium is passed slow through the tube at a rate of 60 ml/min, and ethyl propionate is added dropwise to the top of the packed bed at a rate of 1-2 ml/min. The effluent gases pass first through an air trap and then through two further traps cooled in dry-ice-acetone (trap 2) and a liquid nitrogen-n-propanol slush bath (trap 3). After one hour of operation, an analysis of the water-white liquid (48.8 gm) in trap 1 showed the presence of: 34.9% propionic acid 64.1% ethyl propionate 0.1% methyl propionate The liquid collected in trap 3 showed the presence of: 92% ethylene 4% ethane.

Example 29 Using the quartz tube and procedures of Example 28, ethyl acetate is added dropwise to the top of the helix bed at a rate of 1-2 ml/min. After 90 minutes, an analysis of the water-white liquid (58 ml) in trap 1 showed the presence of: 54.1% acetic acid 43.3% ethyl acetate 1.7% water.

The liquid collected in trap 3 showed the presence of: 71% ethylene 6% methyl acetate 21% ethyl acetate.

Example 30 Using the apparatus and pyrolysis procedures of Example 28, a sample (20.6 gm) of the clear, distillate liquid product from Example 1 is added dropwise to the top of the helix bed of the pyrolysis reactor at a rate of 1-2 ml/min. The bed temperature is 450-4600C. The effluent gases are passed first through the air trap and then through two further traps cooled in dry-ice-acetone (trap 2) and a liquid nitrogen-n-propanoi slush bath (trap 3). After 30 minutes of operation, an analysis of the waterwhite liquid (15.5 gm) in trap 1 showed the presence of: 33.9 wt % propionic acid 24.9 wt % methyl propionate 27.2 wt % ethyl propionate 6.2 wt % propyl propionate The liquid collected in trap 3 showed the presence of: 54 , ethylene 6% ethane.

As the examples and preceeding discussion have documented, numerous advantages accrue from the practice of this invention both in its composition 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 synthesis gas to ethyl ester derivatives of carboxylic acids. Furthermore, it is disclosed that the activity of the ruthenium catalysts is significantly improved through the addition of ,certain classes of coordinating ligands and cocatalyst species, particularly the presence of large cationic species. In the presence of said classes of ruthenium catalyst, selective syntheses of desired products has been demonstrated.

Furthermore, in this invention is disclosed a relatively simply, but novel, two-step synthesis of ethylene from synthesis gas employing said classes of ruthenium catalyst for the selective synthesis of said ethyl esters of carboxylic acids, which are then isolated and pyrolyzed to yield the desired ethylene product and regenerate the starting carboxylic acid.

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 subject invention may best be understood by examining the claims, which follow; read in conjunction with the preceding specification.

Claims (12)

Claims

1. A process for the synthesis of carboxylic acid ethyl esters by reaction of a mixture of carbon monoxide and hydrogen with a liquid medium containing one or more aliphatic carboxylic acids or acid anhydrides containing up to 12 carbon atoms, wherein the reaction is carried out in the presence of a ruthenium catalyst at a temperature of between 1000 and 3500C, and at a superatmospheric pressure of at least 500 psi (3.45 mPa).

2. A process as claimed in Claim 1 wherein the ruthenium catalyst is derived from a ruthenium oxide.

3. A process as claimed in Claim 1 wherein the ruthenium catalyst precursor is derived from a salt of a carboxylic acid or mineral acid.

4. A process as claimed in any of the preceding Claims wherein the ruthenium catalyst comprises one or more Group VB tertiary donor ligands.

5. A process as claimed in any of the preceding Claims wherein the ruthenium catalyst is employed in the presence of a cocatalyst.

6. A process as claimed in Claim 5 wherein the cocatalyst is an alkali metal salt, a quaternary ammonium or phosphonium salt or an iminium salt.

7. A process as claimed in any of the preceding Claims wherein the ruthenium catalyst is employed in an amount from 1 x 10-6 to 10 weight % ruthenium, based on the total weight of reaction mixture.

8. A process as claimed in any of the preceding Claims wherein the temperature is from 1 80 to 2600C.

9. A process as claimed in any of the preceding Claims wherein the pressure is from 2000 to 7500 psi (13.8 to 51.7 mPa).

10. A process as claimed in Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 27.

11. Carboxylic acid ethyl esters when synthesized by a process as claimed in any of the preceding Claims.

12. A method for the production of ethylene which comprises pyrolysing a carboxylic acid ethyl ester according to Claim 11.