CA1119204A - Manufacture of ethylene from synthesis gas - Google Patents

Abstract

MANUFACTURE OF ETHYLENE FROM SYNTHESIS GAS
(D#75,673-F) ABSTRACT OF THE DISCLOSURE
This invention concerns a two-step process for the preparation of ethylene from mixtures of carbon monoxide and hydrogen (commonly known as synthesis gas) by reaction of said carbon monoxide/hydrogen mixtures with a carboxylic acid in the presence of one or more ruthenium catalyst complexes to form an ethyl ester of said carboxylic acid coreactant, followed by pyrolysis of said ethyl ester intermediate to ethylene.

-I-

Description

SUMMARY AND BACKGROUND OF INVENTION
This invention concerns 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 ethylene from synthesis gas by reacting said mixtures of CO/~2 with one or more carboxylic acid coreactant in the presence of one or more ruthenium catalyst complexes to form ethyl esters of said carboxylic acid coreactants, and then pyrolyzing said ethyl ester intermediates 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 (l) and (2) 2CO + 4H2 ~ RCOOH ~ C2H5OOCR + 2H2O (l) : C2~5OOCR ~ C2H4 + 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 (RCOOC2H5) 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 anhydride, acetaldol, and cellulose acetates RCOOC2H5 + H2O ~ RCOOH + C2H5OH (3).

l~lg204 It is the 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*, including:
Variations in Fischer-Tropsh 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 notably, both the initial formation of the ethyl esters from syngas, using the novel class of rutheniùm catalysts : 20 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 catalysts 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 *P. ~. Spitz, Chemtech, May 1977, p. 295.

lll9Z04 well documented in the literature**. 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, fox example, has been reported to yield ethylene and the corresponding carboxylic acids in a number of cases***.
Specific examples include the pyrolysis of ethyl acetate to ethylene and acetic acid**** ~eq 23.
PROCESS EMBODIMENTS
In the broadest aspect of this invention, ethylene i6 prepared from mixtures of carbon monoxide and hydrogen (synthesis gas) by first reacting said mixtures with a carboxylic acid coreactant in the presence of one or more ruthenium catalyst complexes to form an ethyl ester of said carboxylic acid coreactant, followed by pyrolysis of said ethyl ester intermediate to ethylene.
In the narrower practice of this invention, ethylene is prepared from a synthesis gas mixture of carbon monoxide and hydrogen by a process comprising the ollowing:
)Contacting said mixture of carbon monoxide and hydrogen with a li~uid medium containing one or more ali-phatic carboxylic acids or acid anhydrides and a ruthenium catalyst precursor _ _ _ **See: C. H. DePuy and R. W. King, Chemical Reviews, 60, 431(1960).
***See: G. G. Smith and F. W. Kelly, Progress in Physical Organic Chemistry, Vol. 8, Wiley-Interscience (lg71) ****A. T. Blades, Can. J. Chem., 32, 366(1954).

bHeating said reaction mixture to temperatures of between about 100~ and 350C, at superatmospheric pressures of 500 psi or greater with sufficient carbon monoxide and hydrogen to satisfy the stoichiometry of the desired ester synthesis, until substantial formation of the desired ethyl esters has been achieved.
C)Isolating said ethyl esters contained therein, and pyrolyzing said esters under an inert atmosphere to yield the desired ethylene and regenerating the coreactant carboxylic acid.
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 Com~osition - 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 i effective catalysis is achieved when the ruthenium species are solubilized in the carboxylic acid coreactant employed to satisfy the stoichiometry of eq. l.
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(IV) oxide, hydrate, anhydrous ruthenium(IV) dioxide and ruthenium(VIII~ tetraoxide.
Alternatively, it may be added as the salt of a mineral acid, as in the case of ruthenium(III) chloride, hydrate, - lll9Z04 .

ruthenium(III) bromide, anhydrous ruthenium(III) chloride and ruthenium nitrate, or as the salt of a suitable organic carboxylic acid (see Section B, below), for example, ruthenium(III) acetate, ruthenium(III) propionate, ruthenium butyrate, ruthenium(III) trifluoroacetate, ruthenium octanoate, ruthenium napththenate, ruthenium valerate and ruthenium(III~ 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)12, and substituted carbonyl species such as the tricarbonylruthenium(II) chloride dimer, [Ru(CO)3C12]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 combi-nation with one or more Group ~ tertiary donor ligands. The key elements of the Group ~Y~ ligands include nitrogen, phosphorous, arsenic and antimony. These elements, in their trivalent oxidation states, particularly tertiary phospho-rous 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: tri-phenylphosphine, tri-n-butylphosphine, triphenylphosphite, triethylphosphite, trimethylphosphite, trimethylphosphine, tri-p-methoxyphenylphosphine, triethylphosphine, trimethyl-arsine, triphenylarsine, tri-p-tolylphosphine, tricyclo-hexylphosphine, dimethylphenylphosphine, trioctylphosphine, lll~Z(34 tri-o-tolylphosphine, 1,2-bis(diphenylphosphino)ethane, tri-phenylstibine, trimethylamine, triethylamine, tri-propylamine, tri-_-octylamine, pyridine, 2,2'-dipyridyl, l,10-phenanthrolinel 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(II) chloride and dicar-bonylbis(triphenylphosphine)ruthenium(II) chloride or alter-natively, said complexes may be formed in situ.
The performances of each of these classes of ruthenium catalyst precursor are illustrated by the ac-companying 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 ll~9Z04 alkali or alkaline earth salt per gm atom of ruthenium present in the reaction mixture.
Salts of guaternary ammonium and phosphonium cations are also effective as cocatalysts in the process of this invention. Suitable guaternary phosphonium salts are those which are substantially inert under the CO-hydrogenation conditions and which have the formula:

Rl R2 ~ P - R3 X
_ R4 _ where Rl, 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, p-alkylphenyl, o-tolyl and m-tolyl. Suitable quaternary phosphonium salts useful in the practice of this invention include tetramethylphosphonium bromide, tetrabutylphosphonium chloride, tetrabutylphosphonium iodide, tetrabutylphosphonium bromide, tetraphenylphosphonium bromide, heptyl~txiphenyl)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 quatexnary ammonium lll9Z04 salts such as tetramethylammonium bromide and tetra-_-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 12 carbon atoms such as formic acid, acetic, propionic, butyric, isobutyric, valeric, caprioic, capric, perlargonic 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 trifluroacetic 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 lll9Z04 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 12 carbon atoms such as acetic anhydride, propionic anhydride and n-butyric anhydride. ~ere 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 10 6 weight percent, and even lesser amounts, of ruthenium, ex-pressed 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 carboxylic 11192~4 acid diluent/ reactant. A ruthenium catalyst concentration of from about 1 x 10 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. O~eratinq Temperature - The temperature range which can usefully be employed in these ester syntheses 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 t~,ings. Again using ruthenium as the active metal, the range of operability is from about 100 to 350C when super-atmospheric pressures of syngas are employed. A narrower range of 180-260C 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 procecs of this invention. A preferred operating range for solutions of ruthenium(IV) oxide in acetic acid is 20 from 2000 psi to 7500 psi, although pressures above 7500 psi 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 the~e examples.
F. Gas Com~sition - The relative amounts of carbon monoxide and hydrogen which may be initially present in the syngas mixture are variable, and these amounts may be varied over a wide range. In general, the mole ratio of C0-to-~2 is in the ~ , ~ .. . . . . . .

lllgZ04 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 C0 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 (l~.
G. Product Distribution - As far as can be determined, without limiting the invention thereby, the ruthenium-catalyst one-step C0-hydrogenation process disclosed herein leads to the formation of 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 _-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 11~92~4 derivatives, the liquid product may also contain substantial quantities of methanol, ethanol and n-propanol.
H. Mode of ODeration - The novel process of this invention can be conducted in a batch, semi-continuous or continuous fashion. The catalyst may be initially introduced into the reaction zone batchwise, or it may be continuously or inter-mittently 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 (glc), infrared (ir), mass spectrometry, nuclear magnetic resonance (nmr) and elemental analyses, or a ; 20 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 liguid or the vapor phase by simply heating the ester in a metal bath, or with a free flame if its boiling point is suf~ici~ntly high, or by passing the compound through a heated tube. The ester pyrolysis reaction is relatively simple in experimental procedure, it does not 111~20~

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 600C. 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 prese~ce 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 speci-fic and illustrative embodiments.

111~204 SYNTHES I S OF ET~IYL ESTERS
E X A M P L E
-To an 850 ml glass-lined autoclave reactor equipped for pressuring, heating, cooling and means of agitation is charged 0.764 gm of ruthenium(IV) 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 220C with agitation. At temperature, the pressure within the reactor is raised to 6300 psi with CO/H2 mix, 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-yellow liquid product (73.8 gm) removed for analysis. There is no solid product fraction.
Analysis of the liquid fraction by gas-liquid chromatography (glc) shows the presence of:
38.2 wt % ethyl propionate 16.5 wt % methyl propionate 8.4 wt % n-propyl propionate 0.8 wt % _-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) 1119;~04 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.

lll9Z04 .
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 with synthesis gas (1:1, CO/H2) and heated to 220C with agitation. At temperature, the pressure within the reactor is raised to 6300 psi with 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 liguid 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, toge~her with the corresponding Cl 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.

2~

To an 850 ml glass-lined autoclave equipped for pressurizing, heating and means of agitation is charged 0.76 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 with synthesis gas (1:1, CO/H2).
Over a period of 45-60 minutes the autoclave is heated, with agitation, to 220C. 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 glc shows the presence o:
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.

~119~)4 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 (15.7 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.

lll9Z~4 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 S ruthenium(IV) oxide, hydrate (4.0 mmole) or ruthenium(IV) chloride, hydrate in combination with various quaternary alkyl and aryl ammonium 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.

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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/~2, pressured to 2000 psi with CO/H2 (l:l) and heated to 220 with agitation.
At temperature, the pressure within the reactor is raised to 10 6300 psi with CO/H2 and the pressure held constant throughout the 18 hour run by automatic addition of more synthesis gas from a large surge tank. ~pon 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 % _-propyl acetate 3.2 wt % water 32.3 wt % unreacted acetic acid 1~92~)4 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 i6 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 with synthesis gas (CO~H2, 1:1). Over a period of 60-75 minutes, the autoclave is heated, with agitation, to 220C, and held at temperature overnight. Total gas uptake is 1150 psi. 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.

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(III) chloride, hydrate and ruthenium(III) acetylacetonate in combination with tertiary group VB donar ligands such as triphenylphosphine and tri-n-butylphosphine, aæ well as of preformed ruthenium complexessuch as dicarbonylbis(triphenylphosphine)ruthenium(II) chloride.

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lll9Z~4 PYROLYSIS OF ETHXL ESTER
E X A_M P L E 2 8 A 3.5 cm diameter quartz tube, 43 cm in length, is packed with glass helices, set in a vertical plane and heated to 450-460~C. 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 liguid (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.

~1192~)4 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.

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:

~119Zl)4 E X A M _ L E 3 0 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 450-460C. 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 nitroqen-n-propanol slush bath (trap 3). After 30 minutes of operation, an analysis of the water-white 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 lS 6.2 wt % propyl propionate The liquid collected in trap 3 showed the presence of:
54% ethylene 6% ethane.

1~9Z~)4 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 S 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 preceeding specification.

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the synthesis of ethylene from mixtures of carbon monoxide and hydrogen which comprises the following steps:
aContacting said mixtures 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, and a ruthenium catalyst precursor.
b~eating said reaction mixture to temperatures of between about 100° and 350°C, at superatmospheric pressures of 500 psi or greater with sufficient carbon monoxide and hydrogen to satisfy the stoichiometry of the desired ester synthesis, until substantial formation of the desired ethyl esters of said aliphatic carboxylic acids has been achieved.
CIsolating said ethyl ester contained therein, and pyrolyzing said ester under an inert atmosphere to yield the desired ethylene and regenerating the coreactant carboxylic acid.

2. The process of Claim 1 wherein the ruthenium catalyst precursor is a ruthenium oxide.

3. The process of Claim 2 wherein the ruthenium oxide is selected from the group consisting of ruthenium(IV) dioxide, ruthenium(IV)dioxide, hydrate and ruthenium(VIII) tetraoxide.

4. The process of Claim 1 wherein the ruthenium catalyst precursor is the salt of a carboxylic acid derivative.

5. The process of Claim 4 wherein the ruthenium salt is selected from the group consiting of ruthenium acetate, ruthenium propionate, ruthenium butyrate, ruthenium trifluoroacetate, and ruthenium acetylacetonate.

6. The process of Claim 1 wherein the ruthenium catalyst precursor is the salt of a mineral acid.

7. The process of Claim 6 wherein the ruthenium salt is selected from the group consisting of ruthenium chloride, hydrate, ruthenium bromide and anhydrous ruthenium chloride.

8. The process of Claim 1 wherein the ruthenium catalyst precursor contains one or more Group VA tertiary donor ligands.

9. The process of Claim 8 wherein the Group VA
tertiary donor ligands are selected from the group consisting of triphenylphosphine, tri-n-butylphosphine, triphenyl-phosphite, triethylphosphite, trimethylphosphine, triphenyl-arsine and trimethylarsine.

10. The process of Claim 1 when the ruthenium catalyst precursor is employed in the presence of a cocatalyst.

11. The process of Claim 10 wherein the cocatalyst is an alkali metal salt,

12. The process of Claim 11 wherein the alkali metal salt is selected from the group consisting of cesium bromide, cesium iodide and cesium acetate.

13. The process of Claim 10 wherein the cocatalyst is a quaternary ammonium or phosphonium salt.

14. The process of Claim 13 wherein the quaternary phosphonium cocatalyst is a guaternary phosphonium salt of a mineral acid.

15. The process of Claim 14 wherein the quaternary phosphonium salt is selected from the group consisting of heptyl(triphenyl)phosphonium bromide, tetrabutylphosphonium bromide, methyl(triphenyl)phosphonium bromide, tetraphenyl-phosphonium bromide, tetrabutylphosphonium chloride, and tetrabutylphosphonium iodide.

16. The process of Claim 10 wherein the cocatalyst is an iminium salt.

17. The process of Claim 16 wherein the iminium salt cocatalyst is selected from the group consisting of bis(triphenylphosphine)iminium acetate and bis(triphenyl-phosphine)iminium nitrate.

18. The process of Claim 13 wherein the quaternary ammonium cocatalyst is a quaternary ammonium salt of a mineral acid.

19. The process of Claim 18 wherein the quaternary ammonium salt is selected from the group consisting of tetra-methylammonium bromide and tetrabutylammonium bromide.

20. The process of Claim 1 wherein the carboxylic acid coreactant is an aliphatic carboxylic acid of 1 to 12 carbon atoms.

21. The process of Claim 20 wherein the aliphatic carboxylic acid is selected from the group consisting of acetic acid, propionic acid and n-butyric acid.

22. The process of Claim 1 wherein the carboxylic acid anhydride coreactant is an aliphatic carboxylic acid anhydride of 3 to 12 carbon atoms.

23. The process of Claim 22 wherein the carboxylic acid anhydride is selected from the group consisting of acetic anhydride, propionic anhydride and n-butyric anhydride.