GB2053915A - Process for the conversion of methanol to other organic compounds - Google Patents

Abstract

Oxygenated organic compounds are produced by catalytically decomposing methanol vapour to synthesis gas and converting the synthesis gas so-produced, or the carbon monoxide remaining after separation of the hydrogen therefrom, by contact with a conversion catalyst and optionally with methanol. The process is particularly applicable to the hydrocarbonylation of methanol to ethanol.

Description

SPECIFICATION Continuous process for the production of an oxygenated organic compound The present invention relates to a continuous process for the production of oxygenated organic compounds, e.g. ethanol, acetic acid and glycols from methanol as the sole feedstock.

Methanol is one of the largest-volume bulk organic chemicals produced in the world today and it has a great potential as a starting material for the production of other chemicals. Conventionally methanol is produced by the catalytic reaction of carbon monoxide with hydrogen at elevated pressures according to the equation: CO + 2H2 CH,OH Until comparatively recently the methanol synthesis reaction was carried out at high pressure (up to 345 bars) and temperatures in the region of 4000C in the presence of a zinc oxide/chromium oxide catalyst. Recent improvements in catalyst performance brought about by promotion with, for example, copper additives have enabled lower temperatures (ca 2600C) and pressures (ca 50 bars) to be used.

The process most commonly used for the production of a mixture consisting for the most part of carbon monoxide and hydrogen and to a lesser extent carbon dioxide is the steam reforming of natural gas and in certain locations where this gas is in surplus (e.g. in the Middle East) the large scale production of methanol is a more attractive method of disposal than simply flaring. Methanol is a non-corrosive liquid under normal conditions and can be transported and stored in conventional ways. Consequently it can be shipped without difficulty over long distances.

This new development is of particular interest to industrialised nations because it creates the possibility of importing relatively cheap methanol in bulk as a chemical feedstock. Furthermore, this new source of carbon will supplement crude oil supplies, thus enabling this dwindling reserve to be conserved. One of the valuable industrial products which can be obtained from methanol is ethanol, by the hydrocarbonylation reaction. In general ethanol is presently manufactured either by the fermentation of natural products (eg molasses) or by the hydration of ethylene in the presence of an acid catalyst such as. phosphoric acid.With the impending scarcity and expense of crude oil, from which ethylene is derived, researchers have been stimulated to investigate other routes to ethanol and in this context methanol hydrocarbonylation in particular has been under increasing scrutiny. The course of this reaction can be represented by the following equation: CH3OH + CO + 2H2 = C2H50H + H20 Generally the reaction is carried out in the presence of a cobalt salt as catalyst and at elevated pressure and temperature. Although the reaction has been known for some time early reports were discouraging because of the lack of selectivity to ethanol.Thus in a paper published in Science 113, 206 (1951) Wender, Friedel and Orchin reported that methanol was reacted with synthesis gas (1 H2:1 CO) in the presence of dicobalt octacarbonyl as catalyst to produce methylformate (2%), methyl acetate (9.0%), ethyl alcohol (38.3%), ethyl acetate (6.3%), propyl alcohol (4.7%), butyl alcohol (0.09%), methane (8.5%), propyl acetate (0.1%) and a small amount of unidentified product, the total conversion of methanol being 76.4%. Our copending applications Nos. 22490/77 (BP Case No 4386), 78300608.3 (European) (BP Case No 4478), 79300174.4 (European) (BP Case No 4516) and 39054/78 (BP Case No 4662) describe methods of suppressing or inhibiting undesirable by-product formation and thereby increasing the total realisable yield and selectively to ethanol.Furthermore we have made improvements in the process for the catalytic decomposition of methanol to synthesis gas, which process was studied in the early part of this century. Most of the early studies were of an academic nature and were mainly concerned with zinc-containing catalysts. A more recent study directed towards a process for the production of synthesis gas from methanol was reported in Industrial and Engineering Chemistry 40, (4), page 583 (1948). In this report methanol is decomposed to carbon monoxide and hydrogen over a Filtros supported mixture of copper and nickel oxides maintained at a temperature in the range 350 to 4000 C. The synthesis gas produced by this method was never more than 97% pure, the by-products being 0.2% carbon dioxide and 2% inerts, including nitrogen and gaseous hydrocarbons.A major disadvantage of this process was the high rate of carbon deposition and because of this the catalyst required frequent regenerations. In our copending applications Nos 31538/77 (BP Case No 4430) and 39565/78 (BP Case No 4663) we describe improved catalysts for the conversion of methanol into synthesis gas.

The improvements made to the synthesis gas production process have stimulated us to develop an improved process for the production of oxygenated organic compounds from methanol as the sole feedstock.

Accordingly the present invention provides a continuous process for the production of an oxygenated organic compound which process comprises feeding methanol in the vapour phase to a methanol decomposition zone wherein the methanol is contacted with a decomposition catalyst under conditions of elevated temperature and pressure which effect decomposition of methanol to carbon monoxide and hydrogen and passing the carbon monoxide and hydrogen so-produced, with or without adjustment of the molar proportions thereof, or the carbon monoxide after separation of hydrogen therefrom, to a conversion zone wherein it is contacted with a catalyst, and optionally with methanol, under reaction conditions which effect formation of an oxygenated organic compound.

The conversion zone may contain, for example, a catalyst comprising a supported rhodium component or a supported mixture of a rhodium component and a chromium component, which catalyse the conversion of carbon monoxide and hydrogen in the gaseous phase to oxygenated hydrocarbons. The reaction of a mixture of carbon monoxide and hydrogen over a supported mixture of a rhodium component and a chromium component to form a mixture of C1 to C4 oxygenated hydrocarbons, including ethanol and acetic acid, is described in our copending application No 79/14253) (Case 4776). Alternatively the conversion zone may contain a rhodium compound promoted with a halogen, eg an iodide or bromide, which catalyses the reaction of methanol and carbon monoxide in the liquid phase to produce acetic acid. Such a process is now generally known as the Monsanto process.As another alternative methanol may be converted in the conversion zone to glycols. It may be necessary for the purpose of the aforesaid reactions to adjust the molar ratio of the carbon monoxide to hydrogen produced in the decomposition zone to a value more suitable for each individual reaction. This may readily be accomplished by methods well-known in the art. In other reactions embraced within the scope of the present invention it may even be necessary to remove the hydrogen from the mixture before passing to the methanol conversion zone. However since two volumes of hydrogen are produced for every volume of methanol the synthesis gas produced in the methanol decomposition zone is suitable without modification for reaction with methanol in the liquid phase in the presence of a cobaltcontaining catalyst to produce ethanol.

Preferably therefore the invention provides a continuous process for the production of ethanol which comprises passing the carbon monoxide and hydrogen produced in the decomposition zone to a conversion zone where it is contacted in the liquid phase with methanoland a hydrocarbonylation catalyst under conditions of elevated temperature and pressure which effect the formation of ethanol.

Even more preferably the invention provides a continuous process for the production of ethanol from a methanol feedstock which process comprises: A. feeding a part of the methanol feedstock in the vapour phase to a methanol decomposition zone wherein the methanol is contacted with a decomposition catalyst under conditions of elevated temperature and pressure which effect decomposition of methanol to synthesis gas, B. passing the synthesis gas from the methanol decomposition zone, with or without additional hydrogen, to a synthesis gas compression zone wherein the synthesis gas is compressed, C. feeding compressed synthesis gas from the compression zone and the remainder of the methanol feedstock to a hydrocarbonylation zone wherein the synthesis gas and methanol are contacted in the liquid phase with a cobalt-containing catalyst under conditions of elevated temperature and pressure, thereby producing a liquid product containing ethanol and dissolved gas, D. passing the liquid product from the hydrocarbonylation zone to a gas/liquid separation zone wherein the product is separated into a gas phase and a liquid phase containing ethanol, and E. passing the liquid phase containing ethanol to a purification zone wherein substantially pure ethanol is recovered.

The separate zones will now be discussed in turn with particular reference to the process in which methanol is converted in a hydrocarbonylation reaction to ethanol.

The methanol decomposition zone It is preferred to feed anhydrous methanol to the methanol decomposition zone because the presence of water makes the efficient production of a carbon monoxide and hydrogen mixture much more difficult. On the other hand the methanol may be diluted with carbon monoxide, hydrogen or carbon dioxide which may be recycled from, for example, the gas/liquid separation zone. Since the decomposition of methanol is endothermic the use of diluents offers a convenient method for introducing heat into the reaction.

The methanol decomposition catalyst may be any catalyst active for the decomposition of methanol to synthesis gas. A preferred methanol decompositoin catalyst is a supported metal of Group VIII of the Periodic Table either alone or in combination with one or more other metals from Groups I to VIII of the Periodic Table. In the context of the present specification the Periodic Table referred to is that contained in the Handbook of Chemistry and Physiscs, 44th Edition, published by the Chemical Rubber Publishing Company in 1 963. Supports which may suitably be used include silica, alumina and mixtures thereof, titania, zirconia and zeolites both natural and synthetic. A preferred support is silica. It will be appreciated that although the catalyst may be introduced into the reaction zone as a supported metal compound or mixture of metal compounds, under the conditions pertaining during the course of the reaction such compounds may well be chemically reduced. In such circumstances the precise chemical nature of the catalyst at any time during the reaction is not known with any degree of certainty, with the result that the catalyst can only be characterised by reference to the metals it contains. Group VIII metals, which in combination with a support, are found to be particularly effective include for example, rhodium and cobalt, both alone and in combination with other metals. The Group VIII metal may be admixed with one or more other Group VIII metals and/or with metals of Groups I to VII of the Periodic Table, such as iron, copper, chromium, gold and zinc.A preferred catalyst is a mixture of rhodium and copper supported on silica. The catalyst may be prepared by conventional methods such as impregnation from a solution of a compound of the metal or metals, or precipitation. The supported metal catalyst may suitably contain from 0.1 to 20%, preferably from 0.2 to 10% by weight of the metal or metals. Further details of this process may be found in our copending application No 31 538/77.

An equally preferred catalyst is the amorphous aluminosilicate produced by mixing, under reaction conditions which effect formation of the aluminosilicate, a source of silica, a source of alumina, a source of alkali metal, water and one or more polyamines other than an alkylene diamine. Suitable sources of silica include, for example, sodium silicate, silica hydrosol, silica gel, silica sol and silicic acid. The preferred source of silica is an aqueous colloidal dispersion of silica particles. A suitable commercially available source of silica is LUDOX Colloidal Silica marketed by du Pont (LUDOX is a Registered Trade Mark). Suitable sources of alumina include; for example, sodium aluminate, aluminium sulphate and alumina. The preferred source of alumina is sodium aluminate prepared by dissolving alumina particles in e;xcess sodium hydroxide solution.Suitable sources of alkali metal include alkali metal hydroxides and alkali metal oxides. Preferably, the alkali metal is sodium. It will of course be appreciated that each source of silica, alumina and alkali metal can be supplied by one or more initial reactants and then mixed together in any order. For example sodium silicate is a source of both sodium and silica. A suitable polyamine is a polyethylene polyamine having the formula:

wherein x is an integer greater than 1 and R1 is hydrogen or an organic radicai such as, for example, an alkyl group containing from 1 to 6 carbon atoms, a cycloaliphatic group or an aromatic group. Examples of suitable polyethylene polyamines are diethylene triamine, triethylene tetramine, tetraethylene pentamine and pentaethylene hexamine. Mixtures of the aforesaid polyethylene polyamines may also be used.Alternatively the branched isomers of the amines having the formula (I) and mixed or higher polyamines, eg 1-amino-3-(2'-amino-ethylamino) propane and bis [1 ,2-(3'-aminipropylamino)jethane may be used. Conditions which effect formation of the aluminosilicate may be, for example, a temperature in the range from 80 to 21 00C, preferably from 135 to 1 900C, and a pressure in the range from 70 to 400 psig, preferably from 100 to 250 psig. The mixture may suitably be held under these conditions for a time not less than 4 hours and preferably from 20 to 100 hours.

The sources of silica, alumina and alkali metal, water and the polyamine may be mixed in quite wide proportions. Thus the ratio of the silica source to the alumina source may be in the range from 10:1 to 150:1, preferably from 1 5:1 to 100:1 based on the equivalent moles of silica and alumina in the respective sources. The alkali metal source may be present in an amount from 50 to 0.02, preferably from 10 to 0.1 moles of alkali metal per mole equivalent of total silica and alumina in the respective sources. The polyamine or mixture thereof may suitably be present in an amount from 50 to 0.02, preferably from 10 to 0.1 moles per mole equivalent of total silica and alumina in the respective sources. The amount of water is not critical provided sufficient is present to carry out the reaction.The reaction is suitably carried out in a closed vessel capable of withstanding the elevated pressures employed. Furthermore the reaction mixture is preferably agitated during formation of the aluminosilicate. The solid aluminosilicate so-prepared may be filtered off and washed with water at a temperature in the range, for example, from 1 5 to 950C. Aluminosilicates prepared as hereinbefore described are amorphous and are characterised by a relatively high silica to alumina ratio, ie SiO2Al2O3 > 10. The aluminosilicate may be used as the sole methanol decomposition catalyst or may be used as a support for the metals hereinbefore outlined. In either case it is preferred to activate the catalyst before- use.This may suitably be achieved by heating in air at a temperature in the range 400 to 7000C for a period of from 2 to 8 hours. Further details of this catalyst and its method of preparation may be found in our copending application No 39565/78.

Suitable conditions of temperature and pressure which effect decomposition of methanol to synthesis gas are a temperature in the range 200 to 6000 C, preferably 300 to 4500C and a pressure up to 100 atmospheres, preferably from 1 to 50 atmospheres. Since the decomposition of methanol is equilibrium limited it is preferred to employ high temperatures in combination with elevated pressure.

The methanol decomposition zone may suitably comprise a vapouriser and preheater wherein liquid methanol is converted to methanol vapour and raised to the reaction temperature, a reactor containing the methanol decomposition catalyst and a condenser wherein product from the reactor is cooled. The catalyst may be present in the reactor in the form of either a fixed bed or a fluidised bed. The reactor may be of any type conventionally employed in this type of reaction, eg a tubular reactor.

The contact time, which is defined as: the volume of catalyst in litres the total volume of gas in litres/second at NTP may suitably be in the range from 0.01 to 30, preferably from 1 to 5 seconds.

It is preferred to separate any unreacted methanol and feed this to the methanol hydrocarbonylation zone. The decomposition of methanol produces 2 volumes of hydrogen for every volume of carbon monoxide.

The synthesis gas compression zone In this zone the synthesis gas produced in the methanol decomposition zone is compressed to the pressure at which the methanol hydrocarbonylation reaction is to be carried out. Various gaseous recycle streams, such as unreacted synthesis gas from the hydrocarbonylation zone, may be fed to the synthesis gas compression zone and hydrogen may also be fed to balance the hydrogen to carbon monoxide ratio of the synthesis gas under compresison. The zone may suitably comprise a compressor capable of compressing gases to the pressures prevailing in the hydrocarbonylation zone.

The methanol hydrocarbonylation zone Whilst it is preferred that the methanol feed to this zone be substantially pure the presence of small amounts of certain impurities eg water can be tolerated. Preferably the methanol feed to this zone is taken from the same source as the methanol feed to the decomposition zone.

The cobalt forming one of the catalyst components may be added in the form of dicobalt octacarbonyl which may be prepared by heating an anhydrous cobalt compound in a non-aqueous solvent at a temperature greater than 100C and in a superatmosphere of carbon monoxide.

Alternatively the cobalt may be added in any form which will react under the prevailing reaction conditions to form a cobalt carbonyl or cobalt carbonyl/hydride complex, which is believed to be a requisite for the formation of an active catalyst. Cobalt is preferably added in the ionic form but the use of cobalt metal to react in situ to form ionic cobalt which then further reacts to form the desired cobalt complex is a possible alternative. Typical sources of cobalt are, for example, compounds such as cobalt acetate, cobalt formate, cobalt propionate and the like, which under the reaction conditions form carbonyl or carbonyl hydride complexes. The amount of cobalt present may suitably be sufficient to provide a cobalt to methanol molar ratio in the range from 1:10 to 1:1000, preferably from 1:40 to 1:800.

In addition to the catalyst one or more catalyst promoters are preferably incorporated in the reaction mixture. Suitable promoters include iodine, bromine and certain organo-phosphorus and/or nitrogen compounds. Preferably the cobalt catalyst is promoted with iodine, even more preferably with a combination of both iodine or bromine, preferably iodine, and an organo phosphorus or organonitrogen compound. The iodine or bromine may be added either in ionic form, eg as cobalt iodide or cobalt bromide, or as molecular iodine (12) or bromine (Br2). Furthermore the iodide or bromide may be added as an alkyl or aryl iodide or bromide, preferably methyl iodide. However the iodide or bromide may also be added in ionic form utilising cations which are inert with regard to the hydrocarbonylation reaction.Typical of the inert form is potassium iodide or bromide, sodium iodide or bromide and lithium iodide or bromie. The molar ratio of cobalt to iodine or bromine may suitably be in the range 1:3 to 10:1, preferably 1:1 to 5:1. Suitable organo-phosphorus and organo-nitrogen compounds are compounds having the formula:

wherein X is nitrogen or phosphorus and A, B and C are individually monovalent organic radicals, or X is phosphorus and any two of A, B and C together form an organic divalent cyclic ring system bonded to the X atom, or X is nitrogen and all of A, B and C together form an organic trivalent cyclic ring system bonded to the X atom. Such compounds are described more fully in our copending application No 78300608.3 (European) (BP Case No 4478).Preferred compounds having the formula (II) are triethylphosphine, tri-n-butylphosphine, tricyclohexylphosphine, tri-t-butylphosphine and triphenylphosphine. Suitable organo-nitrogen compounds of formula (II) include pyridine, diphenylamine and triphenylamine. Alternatively the promoter may be a compound containing two or more atoms, which atoms are either identical or combinations of dissimilar atoms of the elements nitrogen and phosphorus, with the proviso that no two of the atoms are directly bonded to each other. Such compounds are generally referred to as polydentate ligands and are described in more detail in our copending application No 39054/78 (BP Case No 4662) which is incorporated herein by reference.

Suitable polydentate ligands include (C8H5)2P(CH2)P(C6H5)2, (C6H2P(CH2)4P(C6H5)2 and (C6H5)2P(CH2)6P(C6H5)2.

As hereinbefore indicated we have found that the formation of undesirable by-products can be suppressed or inhibited by the addition of certain compounds. It is therefore preferred to employ the methanol hydrocarbonylation processes described in our copending applications Nos 22490/77 (BP Case No 4386), 78300608.3 (European) (BP Case No 4478) and 79300174.4 (European) (BP Case No 4516) which are hereby incorporated by reference into this specification. In application No 22490/77 the added compound has the formula:

wherein the substituent R is a hydrocarbyl group or an oxygen-containing hydrocarbyl group and the substituent X is the group -OR1 in which R1 is independently a hydrogen atom, a hydrocarbyl group or an oxygen-containing hydrocarbyl group.Examples of suitable compounds having the formula (III) are acetic acid, acetic anhydride, methyl acetate, propionic acid, phenylacetic acid, decanoic acid, benzoic acid and butyl acetate. In application No. 78300608.3 the additive is an inert liquid. Such compounds include aryl halides, thiophenes, long-chain acids, and silicone oils. Specific examples of inert liquids are chlorobenzene, decanoic acid, polydimethylsiloxane fluids and methyl phenyl silicone fluids. In application No. 79300174.4 the additive is an oxygen-containing organic compound comprising an aldehyde, a ketone, an alcohol or an ether or a mixture of two or more such compounds. Examples of such compounds include n-propanol, n-butanol, acetone, acetaldehyde, 1 ,4-dioxane, tetrahydrofuran, di-n-propyl ether and diphenyl ether.

The conditions of elevated temperature and pressure may suitably be a temperature in the range from 1 50 to 25O0C preferably from 1 80 to 2300C and a pressure greater than 100 bars, preferably in the range from 140 to 300 bars.

The methanol hydrocarbonylation zone may suitably comprise any conventional design of gas/liquid reactor capable of withstanding elevated pressure and having inlets for the introduction of gas and liquid feeds and outlets for the removal of gas (including unreacted feed gases) and liquid products.

The unreacted synthesis gas is preferably withdrawn from the reactor and recycled to the synthesis gas compression zone.

The gas/liquid separation zone The product contianing ethanol and dissolved gas from the hydrocarbonylation zone is passed to a gas/liquid separation zone wherein the product is separated into a gas phase and a liquid phase containing ethanol. Preferably the gas phase is recycled to the synthesis gas compression zone.

The purifiction zone The liquid phase from the gas/liquid separation zone is passed to a purification zone wherein substantially pure ethanol is recovered. Suitably the purifiction zone may comprise four distillation columns. In the first column the liquid phase may be separated into an overhead fraction separable into a gaseous component and a liquid component containing compounds having a lower boiling point than ethanol eg acetaldehyde, a side-stream fraction containing the bulk of the ethanol and a base fraction containing compounds having a boiling-point higher than ethanol, eg higher alcohols, together with the catalyst. Preferably the first distillation column is operated at superatmospheric pressure. Suitably the gaseous component of the overhead fraction may be separated from the liquid component and recycled to the synthesis gas compression zone.The liquid component of the overhead fraction may be fed to the second distillation column, also suitably operated at superatmospheric pressure, and separated into an overhead fraction containing compounds having a iower boiling point than methanol eg dimethyl ether and a base fraction containing unconverted methanol and compounds boiling higher than methanol. Preferably the base fraction from the second distillation column is recycled to the hydrocarbonylation zone. The base fraction from the first distillation column may be fed to a third distillation column wherein there is removed overhead a fraction containing higher alcohols and there is removed from the base a residue containing the catalyst, which fraction is preferably recycled to the hydrocarbonylation zone.The side-stream fraction from the first distillation column may be fed to the fourth distillation column from which there is removed overhead a fraction containing methanol and from the base substantially pure ethanol, which may thereafter be purified by means wellknown in the art.

A preferred embodiment of the invention will now be described by reference to the following Example and the accompanying Drawing which takes the form of a flow sheet.

EXAMPLE Referring to the Drawing substantially anhydrous methanol was fed from the feed tank 1 via line 2 to the vaporiser and preheater 3 where it was converted into a-gas at ca 3000C and 50 bars pressure.

The hot gas was passed via line 4 to the methanol decomposition reactor 5 wherein it was contacted with an amorphous aluminosilicate catalyst prepared in the manner described in our copending application No 39565/78, the reactor being maintained at 4000C and 50 bars pressure and the nominal contact time being 0.1 seconds. The gaseous product which contained 86.96% w/w carbon monoxide, 12.45% w/w hydrogen and 0.59% w/w methane was.removed from the reactor through line 6 and passed to the condenser 7. The wet methanol recovered from the condenser was passed via line 8 to the liquid inlet of the methanol homologation reactor 1 3. The liquid-free synthesis gas mixture was fed via line 9 to the synthesis gas compression zone.The methanol conversion was 85% and the molar yields of carbon monoxide and methane on the methanol fed were 84% and 1% respectively, where: % molar yield on methanol fed = moles of methanol converted to a particular product x 100 moles of methanol fed The molar ratio of hydrogen to carbon monoxide in the synthesis gas mixture was 1.98:1. In the synthesis gas compression zone, the synthesis gas recycle stream 22, a small stream of make-up hydrogen 23 and the gaseous product from the methanol decomposition zone (stream 9) were combined and compressed to 200 bars in a five-stage centrifugal compressor with inter-stage cooling and knock-out of condensed liquid. The composite compressed gas at 200 bars left the synthesis gas compression zone via line 14 and was fed to the base of the hydrocarbonylation reactor 13.

Methanol was fed also from feed tank 1 via line 10 and combined with the liquid recycle stream 11 from the purification zone and the wet methanol stream 8 (96.39% w/w methanol, 3.61% w/w water) from the condenser 7 forming part of the methanol decomposition zone. The combined liquid stream was introudced via the inlet 12 into the methanol hydrocarbonyiation reactor 13, wherein the methanol-containing liquid phase containing the cobalt-based catalyst was contacted with the synthesis gas stream 14 from the synthesis gas compression zone. Cobalt was introduced into the reactor 1 3 as cobalt acetate tetrahydrate [Co(OAc)2.4H2O] and the molar ratio of methanol to cobalt in the reaction mixture was maintained in the region of 160:1.In addition iodine and triphenylphosphine were present in the reaction mixture and the atomic ratio of cobalt to iodine to phosphorus was maintained at about 1:1:2. The reactor pressure was maintained constant at 200 bars and the temperature of the reaction mixture was controlled at 1950C.The residence time of the liquid phase in the reactor was 1 hour, residence time being defined as follows: Residence time (hrs) = Volume of reactor occupied by the liquid phase at STP (litres) Total flow of liquid into the reactor (litres/hour at STP) Under these reaction conditions the molar conversions of methanol and carbon monoxide were 31.19/0 and 35.8% respectively.The molar yield and selectively to realisable ethanol were 25.1% and 80.8% respectively while the molar yield and selectivity to realisable acetic acid were 0.3% and 1.0% respectively. A small amount of methane was also produced in the reactor and the molar yield based on the carbon monoxide fed was 3.1%.

In this context the total realisable yield of ethanol is defined as the yield of free ethanol plus the yield of ethanol realisable by the hydrolysis of ethanol-yielding esters (eg ethyl acetate). In the same way the total methanol fed is defined as the free methanol in the feed plus the methanol realisable by the hydrolysis of methanol-yielding esters (eg methyl acetate).

Thus, the % molar yield of realisable ethanol = Moles of methanol converted into realisable ethanol x 100 Total moles of methanol fed and the % molar selectivity to realisable ethanol = Moles of methanol converted into realisable ethanol x 100 Total moles of methanol converted The yield of realisable acetic acid is defined as the yield of free acetic- acid plus the yield of acetic acid realisable by the hydrolysis of acetic acid-yielding esters (eg methyl acetate).

Thus the % molar yield of realisable acetic acid = Moles of methanol converted into realisable acetic acid x 100 Total moles of methanol fed The liquid phase from the hydrocarbonylation reactor 13 was withdrawn via line 1 6 at a rate sufficient to maintain a constant level in the reactor and fed to the gas/liquid separation zone where the pressure was reduced from 200 bars to ca 10 bars by multistage flash separation. The dissolved gases which were flashed off were withdrawn via line 1 7 and combined with the vent gas stream 1 5 which exits from the vapour space above the liquid surface in the hydrocarbonylation reactor 13. This combined gas stream was fed via line 1 9 and was added to the gaseous product vented from the top of column 1 (Product Topping Column) via line 20.A small offgas purge was-withdrawn from the combined stream from lines 1 9 and 20 via line 21 to ensure that the inert gases such as methane did not build up to high concentrations in the gaseous feed. The residual gaseous product which forms the synthesis gas recycle stream was fed via line 22 to the synthesis gas compression zone.

The degassed crude liquid product at ca 10 bars pressure was taken from the gas/liquid separation zone via line 1 8 to column 1 (Product Topping Column) of the purification zone. This column was operated at about 10 bars pressure and taken from the colum were three fractions as follows: (a) an overhead fraction which separated into a gasous component and a liquid component containing materials boiling below ethanol. The gaseous component was recycled to the synthesis gas compression zone via line 20, (b) a side-stream fraction containingt the bulk of the ethanol and (c) a base product containing materials having a higher boiling point than ethanol.

The low-boilers in the overhead fraction taken from column 1 were fed via line 24 to column 2 (the Lights Column) which was operated at a pressure of about 10 bars. The low-boiling compounds (mainly dimethyl ether) were removed overhead and despatched to waste via line 27. The base product which consisted mainly of unreacted methanol was passed to the recycle liquid stream 11 via line 28.

The base product from column 1 was fed to column 3 (the Catalyst Recovery Column) which was operated at a pressure of about 1 bar. An overhead fraction containing higher alcohols and other high boiling organic compounds was removed via line 29. The base product containing the cobalt catalyst, promoters etc was combined with the liquid recycle stream 11 via line 30.

The side-stream from column 1 was fed to column 4 (the Ethanol Topping Column) which was operated at atmospheric pressure. A fraction consisting mainly of unconverted methanol (97.94% w/w methanol, 2.06% w/w methyl acetate) was taken from the top of the column and transferred via line 31 to the liquid recycle stream 11. The base product 74.79% w/w ethanol, 21.2% w/w water,1.72% w/w ethylacetate, 1.46% w/w methanol and 0.82% w/w other impurities was withdrawn from the column via line 32 and the ethanol so obtained was further purified by known procedures including hydroextractive distillation to yield pure ethanol.

The composition of the various streams is given in the accompanying Table. In addition to the components listed in the Table small amounts of other by-products such as acetaldehyde, 1,1- dimethoxyethane, methyl ethyl ether, diethyl ether, propanol and 3-hydroxybutanol were formed. Since the amount of each of these compounds is small the low-boiling compounds are included in the Table with dimethyl ether and the high-boiling compounds are included with butanol.

TABLE Stream compositions

Steam No. 2 8 9 10 11 14 - Wet Inlet Total MeOH to MeOH to Syngas MeOH to Liquid Gas to Input to Stream Decomp n Homulog n to Homolog n Recycle Homolog n Homolog n Reaction Description Rector Reactor Compressr Reactor. Stream Reactor Reactor. Product Steam Cmpositions % w/w Carbon Monoxide - - 86.96 - - 72.67 34.21 21.95 Hydrogen - - 12.45 - - 10.76 5.06 3.24 Methane - - 0.59 - - 9.60 4.52 5.12 Dimethyl Ether - - - - 0.03 1.90 0.91 1.30 Methyl Acetate - - - - 1.54 0.20 0.66 0.68 Methanol 100 96.39 - 100 81.91 4.87 48.42 33.27 Ethyl Acetate - - - - 0.06 - 0.02 0.42 Ethanol - - - - 5.23 - 1.93 19.31 Water - 3.61 - - 9.77 - 3.73 12.64 Butanols - - - - 1.46 - 0.54 2.07 Stream Totals (pbw) 195.34 30.40 164.94 119.50 346.93 441.92 938.75 938.75 TABLE Stream compositions continued

Steam No. 18 19 20 21 22 23 24 Liquid ex Gas ex Column 1 Column 2 Stream Separatn Separatn Overhead Recycled Make-up Feed Description Zone Zone Gas Gas Purge Syngas Hydrogen (Lights) Steam Compositions % w/w Carbon Monoxide - 72.42 - 64.33 64.33 - Hydrogen - 10.67 - 9.49 9.49 100 Methane - 16.89 - 15.01 15.01 - Dimethyl Ether 1.86 - 27.27 3.05 3.05 - 0.95 Methyl Acetate 0.98 - 2.87 0.32 0.32 - 1.59 Methanol 47.74 - 69.86 7.80 7.80 - 87.07 Ethyl Acetate 0.60 - - - - - Ethanol 27.71 - - - - - Water 18.14 - - - - - 9.65 Butanols 2.97 - - - - - 0.74 Stream Totals (pbw) 654.21 284.54 35.76 44.10 276.20 0.78 258.21 TABLE Stream compositions continued

Steam No. 25 26 27 28 29 30 31 32 Column 4 Column 3 Column 3 Column 4 Feed Feed Column 2 Column 2 Overheads Column 3 Overheads Column 4 Stream (Ethanol (Catalyst Overheads Base (Catalyst Base (Ethanol Base Description Topping) Rec'y) (Lights) Product Rec'y) Product Topping) Product.

Steam Compositions % w/w Carbon Monoxide - - - - - - - Hydrogen - - - - - - - Methane - - - - - - - Dimethyl Ether - - 100 0.05 - - - Methyl Acetate 0.45 - - 1.60 - - 2.06 0.01 Methanol 22.43 - - 87.86 - - 97.94 1.46 Ethyl Acetate 1.34 0.24 - - - 0.65 - 1.72 Ethanol 58.54 22.23 - - - 59.51 - 74.79 Water 16.60 58.22 - 9.74 75.33 29.52 - 21.21 Butanols 0.64 19.31 - 0.75 24.67 10.32 - 0.81 Stream Totals (pbw) 278.71 81.53 2.32 255.89 51.07 30.46 60.58 218.13

Claims (19)

1. A continuous process for the production of an oxygenated organic compound which process comprises feeding methanol in the vapour phase to a methanol decomposition zone wherein the methanol is contacted with a decomposition catalyst under conditions of elevated temperature and pressure which effect decomposition of methanol to carbon monoxide and hydrogen and passing the carbon monoxide and hydrogen so-produced, with or without adjustment of the molar proportions thereof, or the carbon monoxide after separation of hydrogen therefrom, to a conversion zone wherein it is contacted with a catalyst, and optionally with methanol, under reaction conditions which effect formation of an oxygenated organic compound.

2. A process according to claim 1 wherein a mixture of C, to C4 oxygenated hydrocarbons is produced by contacting in the conversion zone hydrogen and carbon monoxide produced in the methanol decomposition zone with a catalyst comprising a supported rhodium component or a supported mixture of a rhodium component and a chromium component.

3. A process according to claim 1 wherein acetic acid is produced by contacting in the conversion zone carbon monoxide, separated from the carbon monoxide and hydrogen produced in the methanol decomposition zone, with methanol and a catalyst comprising a rhodium compound and a halogen in the liquid phase.

4. A process according to claim 1 wherein ethanol is produced by contacting in the conversion zone carbon monoxide and hydrogen, produced in the methanol decomposition zone, with methanol and a hydrocarbonylation catalyst in the liquid phase.

5. A process according to claim 4 wherein ethanol is produced by A. feeding a part of the methanol feedstock in the vapour phase to a methanol decomposition zone wherein the methanol is contacted with a decomposition catalyst under conditions of elevated temperature and pressure which effect decomposition of methanol to synthesis gas.

B. passing the synthesis gas from the methanol decomposition zone, with or without additional hydrogen, to a synthesis gas compression zone wherein the synthesis gas is compressed.

C. feeding compressed synthesis gas from the compression zone and the remainder of the methanol feedstock to a hydrocarbonylation zone wherein the synthesis gas and methanol are contacted in the liquid phase with a cobalt-containing catalyst under conditions of elevated temperature and pressure, thereby producing a liquid product containing ethanol and dissolved gas, D. passing the liquid product from the hydrocarbonylation zone to a gas/liquid separation zone wherein the product is separated into a gas phase and a liquid phase containing ethanol, and E. passing the liquid phase containing ethanol to a purification zone wherein substantially pure ethanol is recovered.

6. A process according to claim 5 wherein the methanol fed to the methanol decomposition zone is anhydrous.

7. A process according to either claim 5 or claim 6 wherein the methanol decomposition catalyst is a supported metal of Group VIII of the Periodic Table either alone or in combination with one or more other metals of Groups I to VIII of the Periodic Table.

8. A process according to claim 7 wherein the decomposition catalyst is a mixture of rhodium and copper supported on silica.

9. A process according to claim 7 wherein the decomposition catalyst is the amorphous aluminosilicate produced by mixing, under reaction conditions which effect formation of the aluminosilicate, a source of silica, a source of alumina, a source of alkali metal, water and one or more polyamines other than an alkylene diamine.

10. A process according to any one of claims 5 to 9 wherein methanol decompssition is effected at a temperature in the range 200 to 6000 C, a pressure of up to 100 atmospheres and a contact time in the range 0.01 to 30 seconds.

11. A process according to any one of claims 5 to 10 wherein the cobalt-containing catalyst is promoted with iodine or bromine.

12. A process according to claims 5 to 11 wherein the cobalt-containing catalyst is promoted with a compound having the formula:

wherein X is nitrogen or phosphorus and A, B and C are individually monovalent organic radicals, or X is phosphorus and any two of A, B and C together form an organic divalent cyclic ring system bonded to the X atom, or X is nitrogen and all of A, B and C together form an organic trivalent cyclic ring system bonded to the X atom.

1 3. A process acording to any one of claims 5 to 11 wherein the cobalt-containing catalyst is promoted with a compound contianing two or more atoms, which atoms are either identical or combinations of dissimilar atoms of the elements nitrogen and phosphorus, with the proviso that no two of the atoms are directly bonded to each other.

14. A process according to any one of claims 5 to 1 3 wherein there is added to the hydrocarbonylation zone a compound haivng the formula:

wherein the substituent R is a hydrocarbyl group or an oxygen-containing hydrocarbyl group and the substituent X is the group -OR1 in which R1 is independently a hydrogen atom, a hydrocarbyl group or an oxygen-containing hydrocarbyl group.

1 5. A process according to any of claims 5 to 14 wherein there is added to the hydrocarbonylation zone an inert liquid comprising an aryl halide, a thiophene, a long-chain acid or a silicone oil.

1 6. A process according to any one of claims 5 to 1 5 wherein there is added to the hydrocarbonylation zone an oxygen-containing organic compound comprising an aldehyde, a ketone, an alcohol or an ether or a mixture of two or more such compounds.

1 7. A process according to any one of claims 5 to 1 6 wherein the hydrocarbonylation zone is maintained at a temperature in the range from 1 50 to 2500C and a pressure in the range 140 to 300 bars.

1 8. A process according to claim 5 substantially as hereinbefore described in the Example and with reference to the accompanying drawing.

19. Oxygenated organic compounds whenever produced by the process as claimed in any one of the preceding claims.