Oct. 30, 1973
`
`f. E. PAULIK ET AL
`PRODUCTION OF CARBOXYi...IC ACIDS AND ESTERS
`
`3,769,329
`
`Filed March 12, 1970
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`INVENTORS
`FRANK E. PAULIK
`ARNOLD HERSHMAN
`WALTER R. KNOX
`JAMES F. ROTH.
`
`BY
`
`~c:?~
`ATTORNEY
`
`CE Ex. 2037
`Daicel v. Celanese
`IPR2015-00171
`
`001
`
`

`
`United States Patent Office
`
`3,769,329
`Patented Oct. 30, 1973
`
`1
`
`3,769,329
`PRODUCTION OF CARBOXYLIC ACIDS
`AND ESTERS
`Frank E. Paulik and Arnold Hershman, Creve Coeur,
`Walter R. Knox, Town and Country, and James F.
`Roth, S!· Louis, Mo., assignors to Monsanto Company,
`St. LouiS, Mo.
`.
`.
`Continuation-in-part of abandoned application Ser. No.
`628,581, Apr. 5, 1967. This application Mar. 12, 1970,
`Ser. No. 2,413
`Int. Cl. C07c 51/12,67/00
`U.S. Cl. 260-488 K
`
`20 Claims
`
`ABSTRACT OF THE DISCLOSURE
`The present invention relates to a process for the
`preparation of carboxylic acids and esters, specifically _by
`the reaction of alcohols or the ester, ether and halide
`derivatives thereof, with carbon monoxide in the presence
`of catalyst systems containing as active constituents a
`rhodium component and a halogen component. The proc(cid:173)
`ess is also directed to the production of mixtures of
`organic acids and/or organic esters.
`
`BACKGROUND OF THE INVENTION
`This application is a continuation-in-part of application
`Ser. No. 628,581 filed Apr. 5, 1967, now abandoned.
`This application is also a continuation-in-part of co(cid:173)
`pending application Ser. No. 701,637, filed Jan. 30, 1968,
`now abandoned, which was a continuation-in-part of
`application Ser. No. 628,581.
`.
`This invention relates to a process for the preparation
`of carboxylic acids and esters. More particularly, it relates
`to a process for the reaction of alcohols and the ester,
`ether and halide derivatives thereof, with carbon mon(cid:173)
`oxide in the presence of catalyst systems containing as
`active constituents a rhodium component and a halogen
`component to yield carboxylic acids and/or esters selec(cid:173)
`tively and efficiently.
`Carbonylation processes for the preparation of car(cid:173)
`boxylic acids from alcohols are well known in the art
`and have been directed especially to the production of
`acetic acid by the carbonylation of methanol. The prior
`art teaches the use of a number of catalysts for the syn(cid:173)
`thesis of carboxylic acids by reaction of alcohols with
`carbon monoxide at elevated temperatures and pressures
`in both vapor phase reactions and liquid phase reactions.
`Catalysts such as phosphoric acid, phosphates, activated
`carbon, heavy metal salts such as zinc and cuprous chlo(cid:173)
`rides silicates of various metals, and ·boron trifluoride in
`vari~us hydration states have been reported to function
`for the production of acetic acid by reaction of methanol
`and carbon monoxide at elevated temperatures and pres(cid:173)
`sures of the order of 400° C. and 10,000 p.s.Lg., respec(cid:173)
`tively. However, even under such severe conditions the
`yields of acid were poor. Somewhat less severe reaction
`conditions of temperature and/or pressure have been re(cid:173)
`ported employing specific catalyst compositions, e.g., 330°
`C.-340° C. and 2,250 p.s.i.g. using liquid phosphoric acid
`containing copper phosphate; 300° C.-500° C. and 2,000
`p.s.i.g.-4,000 p.s.i.g. using active charcoal impregnated
`with phosphoric acid; and 260° C.-360° C. and 2,800
`p.s.i.g.-15,000 p.s.i.g. using metal carbonyls, such as iron,
`cobalt and nickel, in conjunction with their halides or
`free halogens in the liquid phase. Even using these specific
`catalyst compositions at the less severe reaction condi(cid:173)
`tions, substantially poorer yields of the desired carboxylic
`acid product and substantially slower reaction rates are
`obtained than those achieved in the process of this inven-
`tion.
`Certain disadvantages present in the carbonylation
`
`20
`
`2
`processes described in the prior art are catalyst instabil(cid:173)
`ity, lack of product selectivity, and low levels of catal.yst
`reactivity. One particular disadvantage of carbonylatron
`processes of the prior art is their dependence upon the u~e
`of catalysts comprised of such metal carbonyls or modr-
`5 fled metal carbonyls as dicobalt octacarbonyl, iron car(cid:173)
`bonyl and nickel carbonyl, all of which require the use
`of high partial pressures of carbon monoxide to remain
`stable under the necessarily high reaction temperatures
`10 employed. For example, dicobalt octacarbonyl requires
`partial pressures of carbon monoxide as high as 3,000
`p.s.i.g. to 10,000 p.s.i.g. under normal carbonylation con(cid:173)
`ditions of 175° C. to 300° C.
`Still another disadvantage of carbonylation processes
`15 disclosed in the prior art is their relatively low level of
`activity. This low level of activity requires higher cat(cid:173)
`alyst concentrations, longer reaction times, and higher
`temperatures to obtain substantial reaction rates and con(cid:173)
`versions. Consequently larger and costlier processing
`equipment is required.
`Another disadvantage of carbonylation processes dis-
`closed heretofore is their inability to maintain high selec(cid:173)
`tivity to the desired carboxylic acid at temperatures re(cid:173)
`quired for high conversion levels and high reaction rates.
`25 At these higher temperatures, undesirable byproducts
`comprising substantial amounts of ethers, aldehydes,
`higher carboxylic acids, carbon dioxide, methane and
`water are formed, thereby resulting in substantial yield
`losses and necessitating additional product purification
`30 and recycle steps in the processing.
`Another disadvantage of carbonylation processes de(cid:173)
`scribed in the prior art is their dependence on catalyst
`systems which require the use of substantially chemically
`pure carbon monoxide feedstocks to maintain high selec-
`35 tivity and high yield to the desired carboxylic acid prod(cid:173)
`uct. For example, certain cobalt containing catalyst sys(cid:173)
`tems described heretofore when employed with carbon
`monoxide feed streams containing impurities such as hy(cid:173)
`drogen, result in the production of a number of undesir-
`40 able byproducts including methane, carbon dioxide, alde(cid:173)
`hydes, alcohols of the same carbon number as the desired
`carboxylic acid, and carboxylic acids of higher carbon
`number than desired. Consequently, substantial loss in
`selectivity and yield to the desired carboxylic acid occurs.
`45 Catalysts of the prior art cause the formation of trouble(cid:173)
`some gaseous byproducts such as carbon dioxide and
`methane as well as dimethyl ether in the reactor system,
`thereby suppressing the carbon monoxide partial pressure
`and ultimately causing a decrease in the desired carbonyla-
`50 tion reaction rate: Often additional processing steps are
`required to remove these undesirable byproducts, necessi(cid:173)
`tating the use of larger and costlier processing equipment.
`It is, therefore an object of the present invention to
`overcome the ab~ve disadvantages and thus provide an
`55 improved and more economically and commercially feasi(cid:173)
`ble carbonylation process for the production of organic
`acids and their esters.
`Another object of this invention is to provide a more
`reactive and more stable carbonylation catalyst system
`60 than has been heretofore described in the prior art.
`Still another object of the present invention is to pro(cid:173)
`vide a more selective and more reactive carbonylation
`catalyst system for the production of carboxylic acids.
`Another object of the present invention is to provide a
`65 carbonylation catalyst system which results in the produc(cid:173)
`tion of a higher yield of the desired carboxylic acid with
`no substantial formation of ethers, aldehydes, higher car(cid:173)
`boxylic acids, carbon dioxide, methane, water and other
`undesirable byproducts.
`Still another object of the present invention is the pro(cid:173)
`vision of an improved carbonylation process enabling the
`
`70
`
`002
`
`

`
`3,769,329
`
`4
`be taken from the following non-limiting partial list of
`suitable materials.
`RhC13
`RhBr3
`Rhl3
`RLCla·3HzO
`RhBr3 ·3H20
`Rh2(C0)4Clz
`Rh2(C0)4Br2
`Rh2(C0)4I2
`Rh2(CO)s
`Rh[(C6Hs)aP]z(CO)I
`Rh[(C6H 5)aP]z(CO)Cl
`Rh metal
`Rh(N03 )a
`RhCI[(C6H5)aP]z(CHalh
`Rh(SnC13 ) [ (CaHs)aP]a
`RhCI(CO) [(CaHs)aAsh
`Rhl(CO) [(C6Hs)aSb]z
`[(n-C4H9 ) 4N][Rh(CO)zXz] where X=Cl-, Br-, I(cid:173)
`[(n-C~9)4As]z[Rhz(CO)zY4] where Y=Br-, I-
`[ (n-C4Hg) 4P] [Rh(CO)I4]
`Rh[(C6H5)aP]z(CO)Br
`Rh[(n-C4H 9 ) 3P]z(CO)Br
`Rh [ ( n-C4H 9 )aP Jz( CO )I
`RhBr[(C6H 5)aP]a
`Rhi[(C6H 5)aP]a
`RhCl[ CCaHs)aPJa
`RhCl[ (C6H5)aP]aHz
`[(CaHs) 3P]aRh(CO)H
`Rh20 3
`[Rh(CzH4)zCl]z
`K4RhzClz(SnCla)4
`35 ~RhzBrz(SnBr3 ) 4
`K4Rhzlz(Snla)4
`With those materials listed above as capable of pro(cid:173)
`viding the rhodium component which do not contain a
`40 halogen component from the group consisting of bro(cid:173)
`mine and iodine, it will be necessary to introduce into
`the reaction zone such a halogen component. For exam(cid:173)
`ple, if the rhodium component introduced is rhodium
`metal or Rh20 3, it will be necessary to also introduce a
`halide component such as methyl iodide, hydrogen iodide,
`45 iodine or the like.
`As noted above, while the halogen component of the
`catalyst system may be in combined form with the
`rhodium, as for instance, as one or more ligands in a
`coordination compound of rhodium, it generally is pre-
`50 ferred to have an excess of halogen present in the cat(cid:173)
`alyst system as a promoting component. By excess is
`meant an amount of halogen greater than 2 atoms of hal(cid:173)
`ogen per atom of rhodium in the catalyst system. This
`promoting component of the catalyst system consists of
`55 a halogen and/or halogen compound such as hydrogen
`halide, alkyl- or aryl halide, metal halide, an1monium
`halide, phosphonium halides, arsonium halide, stibonium
`halide and the like. The halogen of the promoting com(cid:173)
`ponent may be the same or different from that already
`60 present as ligands in the coordination compound of rho(cid:173)
`dium. Generally, the halogen in the promoting compo(cid:173)
`nent is iodine or bromine with iodine being preferred.
`Accordingly, suitable halogen providing or promoting
`components may be selected from the following list of
`halogen and/or halogen-containing compounds.
`
`3
`efficient and selective production of carboxylic acids or
`their esters by reaction of alcohols and alcohol deriva(cid:173)
`tives with carbon monoxide in the presence of an im(cid:173)
`proved and more stable catalyst system, thus enabling
`the use of lower catalyst concentration, lower tempera- 5
`ture, lower pressure, and shorter contact time than has
`been generally possible heretofore and facilitating prod(cid:173)
`uct isolation, catalyst recovery and recycle without sub(cid:173)
`stantial catalyst decomposition and loss.
`These and other objects of the present invention will 10
`become apparent to those skilled in the art from the ac(cid:173)
`companying description and disclosure.
`SUMMARY OF THE INVENTION
`In accordance with the present invention, a feed com- 15
`ponent comprising a saturated hydrocarbyl alcohol or the
`ester, ether or halide derivative thereof or mixtures of
`these are converted to a carboxylic acid or an ester of
`said feed component and said acid or a mixture of said
`acid and ester, by reacting the feed component in the liq- 20
`uid phase with carbon monoxide at temperatures from
`about 50° C. to 300° C. and at partial pressures of car(cid:173)
`bon monoxide from 1 p.s.i.g. to 15,000 p.s.i.g. and higher,
`preferably 5 p.s.i.g. to 3,000 p.s.i.g., and more preferably
`10 p.s.i.g. to 1,000 p.s.i.g., in the presence of a catalyst 25
`system containing as active constituents a rhodium com(cid:173)
`ponent and a halogen component in which the halogen
`is selected from the group consisting of bromine and io(cid:173)
`dine, preferably iodine. The present process is particu(cid:173)
`larly advantageous at lower pressures, although higher 30
`pressures may also be used.
`DESCRIPTION OF THE DRAWINGS
`The accompanying drawing is a flow scheme illustrat(cid:173)
`ing an embodiment of the present invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`For purposes of the present invention, the catalyst sys(cid:173)
`tem essentially includes a rhodium component and a halo(cid:173)
`gen component in which the halogen is either bromine
`or iodine. Generally, the rhodium component of the cat(cid:173)
`alyst system of the present invention is believed to be
`present in the form of a coordination compound of rho(cid:173)
`dium with a halogen component providing at least one
`of the ligands of such coordination compound. In addi(cid:173)
`tion to the rhodium and halogen, in the process of the
`present invention, these coordination compounds also gen(cid:173)
`erally include carbon monoxide ligands thereby forming
`such compounds or complexes of rhodium as
`[Rh(CO)zBrb [Rh(C0) 2I]a
`and the like. Other moieties may be present if desired.
`Generally, it is preferred that the catalyst system contain
`as a promoting component, an excess of halogen over
`that present as ligands in the rhodium coordination com(cid:173)
`pound. The terms "coordination compound" and "coordi(cid:173)
`nation complex" used throughout this specification means
`a compound or complex formed by combination of one
`or more electronically rich molecules or atoms capable of
`independent existence with one or more electronically
`poor molecules or atoms, each of which may also be ca(cid:173)
`pable of independent existence.
`The essential rhodium and halogen component of the
`catalyst system of the present invention may be provided
`by introducing into the reaction zone a coordination com(cid:173)
`pound of rhodium containing halogen ligands or may be
`provided by introducing into the reaction zone separately
`a rhodium compound and a halogen compound. Among
`the materials which may be charged to the reaction zone
`to provide the rhodium component of the catalyst system
`of the present invention are rhodium metal, rhodium salts
`and oxides, organo rhodium compounds, coordination
`compounds of rhodium, and the like. Specific examples
`of materials capable of providing the rhodium constitu(cid:173)
`ent of the catalyst system of the present invention may 75
`
`65
`
`RX
`
`where R=any alkyl- or aryl-group and X= Br or I,
`70 e.g., CH31, C 6HsBr, CH3CH21, etc.;
`Xz or Xa(cid:173)
`where X=Br or I, e.g., Br2, 12, 13-, etc.;
`HX
`
`003
`
`

`
`3,169,329
`
`5
`
`20
`
`45
`
`5
`where X=Br or I, e.g., HBr, HI;
`RCX
`~
`where R=any alkyl- or aryl-group and X=Br or I, e.g.,
`CHaO I,
`~
`
`etc.;
`
`~MX, R4MX3, or R3MX2
`where R=hydrogen or any alkyl, M=N, P, As, or Sb,
`X=Br or
`1PH3B12,
`I, e.g., NH4I, PH4I3, PH3I2,
`(C6H5)aPI2, and/or combinations of R, M, and X.
`Although any amount of the promoting component of
`the catalyst system of the present invention may be em(cid:173)
`ployed, the amount employed is such as to produce a
`ratio of atoms of halogen to atoms of rhodium in the
`catalyst system of from above 2:1 to 50,000:1 and higher.
`However, the preferred ratio is 5:1 to 5,000:1 halogen
`atoms per rhodium atom. A more preferred ratio of
`halogen atoms to rhodium atoms is 10:1 to 2,500:1.
`Generally, it is preferred that the process of the pres(cid:173)
`ent invention be carried out in an acidic reaction me(cid:173)
`dium. For purposes of the present invention, an acidic
`reaction medium is defined as one in which an alkyl
`halide is present or will be formed. The alkyl halide is
`one in which the alkyl radical corresponds to an alkyl
`radical of the feed alcohol, ester, ether or halide. For
`example, if the alcohol is methanol, the alkyl halide will
`be the methyl halide. Such alkyl halide may be added
`to the reaction medium as such or may be formed in
`situ within the reaction medium from the feed acohol,
`ester, ether or halide and the halide present in the cat(cid:173)
`alyst system. The reaction medium is considered acidic
`when under reaction conditions as herein set forth, at
`least 0.1% of the total halogen atoms in the system is
`present as the alkyl halide. It is preferred, however, that
`at least 1.0% of the total haolgen atoms in the system is
`present as the alkyl halide.
`The liquid reaction medium employed may include
`any solvent compatible with the catalyst system and may
`include pure alcohols, or mixtures of the alcohol feed(cid:173)
`stock and/or the desired carboxylic acid and/or esters
`of these two compounds. However, the preferred solvent
`and liquid reaction medium for the process of this inven(cid:173)
`tion is the desired carboxylic acid itself. Water may also
`be added to the reaction mixture to exert a beneficial
`effect upon the reaction rate.
`Suitable feedstocks are saturated hydrocarbyl alcohols
`although these alcohols may be charged together with
`an acid or ester as discussed below. The term ''saturated
`hydrocarbyl," as used herein, is meant to include not
`only the saturated acyclics, i.e., alkyls, but also the sat(cid:173)
`urated alicyclics, i.e., cycloalkyls, and the alicyclicacy(cid:173)
`clics. These feedstocks also include the alkyl saturated
`hydrocarbyl halides, esters and ether derivatives of the
`desired alcohol feedstock.
`Examples of useful feedstocks employed for the car(cid:173)
`bonylation reaction of the present invention include the
`following compounds:
`ROH wherein R is a saturated hydrocarbyl radical of
`1 to 20 carbon atoms,
`R' -O_JR' wherein R' is a saturated hydrocarbyl radical
`of 1 to 19 carbon atoms and wherein the total number
`of carbon atoms in the compound does not exceed 20,
`0
`R-~-0-R'
`wherein R' is a saturated hydrocarbyl radical of 1
`to 19 carbon atoms and wherein the total number of
`carbon atoms in the compound does not exceed 20,
`R-X wherein R is a saturated hydrocarbyl radical of
`1 to 20 carbon atoms and X is a halogen which is
`chlorine, bromine or iodine.
`
`6
`The saturated hydrocarbyl radicals in the above com(cid:173)
`pounds include straight-chain, branched-chain and cyclic
`saturated radicals and generally contain one carbon atom
`less than that of the desired acid. Included within these
`feed materials are such specific compounds as methanol,
`ethanol, propanol and isopropanol, the butanols, penta-
`nols, hexanols, cyclohexanols, cyclopentanols, and also
`the higher alcohols such as the decanols, dodecanols, hex(cid:173)
`adecanols, nonadecanols and including isomeric forms,
`10 methyl ether, ethyl ether, n-propyl ,ether, isopropyl ether,
`n-butyl ether, methyl acetate, ethyl acetate, pentyl acetate,
`methyl chloride, propyl bromide, heptyl iodide, and the
`like.
`Polyhydric saturated hydrocarbyl alcohols may also
`15 be employed as starting materials for the production of
`polybasic acids, for example, 1,4-butanediol, which when
`subjected to reaction with carbon monoxide under the
`conditions described herein with the catalyst of the in(cid:173)
`vention, yields adipic acid.
`The most useful feedstocks are the alkanols of 1 to 20
`carbon atoms and the ester, ether and halide derivatives
`thereof. Particularly useful as feedstocks are the alkanols
`of 1 to 10 carbon atoms and the ester, ether and halide
`derivatives thereof. Alkanols of 1 to 5 carbon atoms and
`25 the ester, ether and halide derivatives thereof are pre(cid:173)
`ferred feeds. Methanol is the paticularly preferred feed.
`It is to be understood that the feed may include a mixture
`of the above defined alcohols, esters, ethers or halides.
`In accordance with the present invention the carbonyla-
`30 tion reaction may be carried out by intimately contacting
`the above defined feed components, preferably an alcohol,
`which depending on the carbon number and operating
`conditions may either be in the vapor or liquid phase, with
`gaseous carbon monoxide in a liquid reaction medium con-
`35 taining a catalyst system such as [Rh (CO) 3112 and a
`halogen-containing promoting component, such as meth(cid:173)
`yl iodide, under conditions of temperature and pressure
`suitable as described above to form the carbonylation
`product. The particular conditions selected are the same
`40 whether the feed component is charged as vapor or liquid.
`The temperature will be in the range of 50° C. to 300°
`C. with the preferred range being 100° C. to 240° C.
`Partial pressures of carbon monoxide of the order of 1
`p.s.i.g. to 15,000 p.s.i.g. may be employed, however, 5
`p.s.i.g. to 3,000 p.s.i.g. carbon monoxide partial pressure
`is generally preferred, a more preferred range is from 10
`p.s.i.g. to 1,000 p.s.i.g. Higher pressures may be used if
`desired under proper conditions.
`Alternatively, carboxylic acids may be produced if de(cid:173)
`sired via reaction of the feed components and carbon
`50 monoxide in the vapor phase over the rhodium contain(cid:173)
`ing catalyst systems described above, dispersed upon inert
`supports. Such as catalyst system may be operated as a
`conventional fixed bed catalystic reactor. For example,
`methyl alcohol, methyl iodide, and carbon monoxide may
`55 be passed over a catalyst system consisting, for example,
`of [Rh(COhih dispersed on an inert support material
`such as alundum, activated carbon, clays, alumina, silica(cid:173)
`alumina, and ceramics, etc., in a fixed bed reactor main(cid:173)
`tained at elevated temperature and pressure, as described
`60 above, to produce acetic acid in high yields. However, use
`of a liquid reaction medium as above described is pre(cid:173)
`ferred in the process of this invention.
`While any amount of carbon monoxide may be em(cid:173)
`ployed, a typical carbonylation reaction selective to car-
`65 boxylic acid requires at least one mole of carbon mon(cid:173)
`oxide per hydrocarbyl radical (molar basis). Excess of
`carbon monoxide over
`the aforesaid stoichiometric
`amount, however, may be present. Carbon monoxide
`70 streams containing inert impurities such as hydrogen, .car(cid:173)
`bon dioxide, methane, nitrogen, noble gases, water and
`paraffinic hydrocarbons having from 1 to 4 carbon atoms,
`may be employed, if desired, for example, from an avail(cid:173)
`able plant gas stream, with no adverse effect; however, in
`75 such cases total reactor pressure will have to be increased
`
`004
`
`

`
`7
`to maintain a desired carbon monoxide partial pressure.
`The concentration of carbon monoxide in the feed gas
`mixture is from 1 vol. percent to 100 vol. percent, a pre(cid:173)
`ferred range being from 10 vol. percent to 99.9 vol. per(cid:173)
`cent.
`The reaction rate is dependent upon catalyst concentra(cid:173)
`tion and temperature. Concentrations of the rhodium
`containing component of the catalyst system in the liquid
`phase between 10-s moles/liter and I0-1 moles/liter, are
`normally employed, with the preferred range being 10-4
`moles/liter to IQ-2 moles/liter. Higher concentrations
`even to the extent of 1 mole/liter may, however, be used
`if desired. Higher temperatures also favor higher reaction
`rates.
`The active rhodium containing catalytic system is pref(cid:173)
`erably supplied as a catalyst solution. The solution can
`also include liquid reactants, products and mixtures there(cid:173)
`of which function as solvents or reaction media. It has
`been found that the nature of the products obtained in the
`present carbonylation process can be controlled by the use
`of various proportions of alcohol, ester and acid as the
`solvent for such a catalyst solution. A preferred group of
`solvents is discussed below for use when reacting the
`aforementioned preferred saturated hydrocarbyl alcohols
`having 1 to 20 carbon atoms. This preferred group of sol(cid:173)
`vents is comprised of the alcohol in the feed, an acid hav(cid:173)
`ing 1 carbon atom more than such alcohol, the ester of the
`said acid and the said alcohol, the diether of the said al(cid:173)
`cohol, a halide of the said alcohol and mixtures thereof. A
`still more preferred group of solvents is comprised of the
`aforesaid alcohol, the acid, and the ester of the said acid
`and said alcohol.
`It has been found that a preferred range of molar ratios
`of the said alcohol to the said ester when employing these
`two components in the liquid reaction medium is from
`0.001 to 10,000. However, within this range, there are
`subranges of ratios of alcohol to ester which are condu(cid:173)
`cive to the formation of particular product distributions.
`The use of an alcohol-ester containing liquid reaction
`medium in which the alcohol to ester molar ratio is less
`than 2: 1, preferably 0.001: 1 to 2: 1 (and including pure
`ester as the feed to the reaction) yields a product with a
`high proportion of acid, e.g., reaching substantially 100%
`organic acid. Alternatively, the use of such a ratio of
`alcohol to ester in which the ratio is greater than 10:1,
`preferably 10:1 to 10,000:1 (including a pure alcohol as
`the feed) may yield a product with a very high proportion
`of the ester, e.g., reaching substantiaily 100% ester.
`Within this latter alcohol/ester 11atio range of 10:1 to
`10,000: 1 there exist two alternative embodiments of the
`invention. In the first such embodiment the product con(cid:173)
`sists essentially of 100% ester at alcohol conversion levels
`up to about 90 mole percent. The second such embodi(cid:173)
`ment exists when the alcohol conversion level exceeds
`about 90 mole percent in which instance the product is
`substatially completely the acid. Within the alcohol to
`ester ratio range of 2:1 to 10:1 within the reaction me(cid:173)
`dium, the relative proportions of acid and ester in the
`product may be controlled. As the ester concentration
`goes down, the ester production goes up subject to the
`conversion level as above indicated.
`The above cases are summarized below.
`
`Major product
`Acid.
`Mixed acid and ester.
`
`Alcohol/ester ratio in
`reaction medium:
`0.00:1 to 2:1 ----------
`2:1 to 10:1 ------------
`10:1 to 10,000:1-
`(a) To about 90% al(cid:173)
`cohol conv. -----(cid:173)
`(b) Above about 90%
`alcohol conv. -----
`The desired acid of one acrbon atoms more than that of
`the hydrocarbyl radical of the feed component may be
`present in the reaction mixture, e.g., as solvent. This acid 75
`
`Ester.
`
`Acid.
`
`3,769,329
`
`5
`
`15
`
`8
`will readily esterify, and the control of the product distri(cid:173)
`bution taught above is applicable, with the ratio of alco(cid:173)
`hol to ester being the controlling factor.
`The preferred ratio range for high ester production is
`an alcohol/ester ratio in the reaction medium of 10:1 to
`10,000:1. The preferred ratio range for high 'acid produc(cid:173)
`tion is an alcohol/ester ratio of 0.001:1 to 2:1.
`In the carrying out of the above described embodiment
`for the production of high proportion of acid, e.g., acetic
`10 acid, as the desired product, the charge to the reactor in(cid:173)
`cludes a relatively low proportion of the alcohol. Thus,
`in the production of acetic acid as the major product, the
`ratio generally is no more than 2 moles of methanol per
`mole of methyl acetate. Consequently the purification sys-
`tern employs a distillation train to recover the acetic acid
`product by distillation, while the remaining lower boiling
`components consisting principally of methyl iodide, on(cid:173)
`reacted methanol, and methyl acetate are recycled.
`In the absence of other compounds as solvents having a
`20 higher boiling point than acetic acid (discussed below), a
`portion of the acetic acid product containing the rhodium
`and halogen catalyst system is recycled to the reactor to
`return the said catalyst system to the reaction zone.
`In carrying out a second embodiment, described above,
`25 for the production of high proportion of ester, e.g., meth(cid:173)
`yl acetate, as the desired product, the charge to the reac(cid:173)
`tor includes a relatively high proportion of alcohol, e.g.,
`greater than 10 moles of methanol per mole of methyl
`acetate. Consequently the purification system employs a
`30 distillation train to recover the methyl acetate by distilla(cid:173)
`tion, while the remaining components consisting princi(cid:173)
`pally of the rhodium containing component, methyl iodide
`(or other halide promoters) methanol and acetic acid are
`recycled. The methyl acetate is hydrolyzed for example
`35 by contacting with steam, as described herein, thus isolat(cid:173)
`ing the acetic acid with the recovery of methanol, which
`may be recycled. However, the ester product is often used,
`per se for example, as a solvent in chemical processing or
`for the formulation of coating compositions. In this em-
`40 bodiment, the process is operated under conditions such
`as to maintain alcohol conversion below 90%.
`When an ester, ether, or halide is present in the feed(cid:173)
`stock, it is normally charged with equimolar amounts of
`water, although more or less water may be used. The
`45 reference to the ester in the above ratios, is on the basis
`that molar quantity of water is present equivalent to the
`number of moles of ester present.
`It has been found that water may exert a beneficial
`effect on the rate of reaction. An amount of water in
`50 excess of the equimolar quantity of water to ester, e.g.,
`an excess equal to 50% to 300% of such equimolar quan(cid:173)
`tity, already present with such ester, as discussed above,
`promotes the production of the carboxylic acid. On the
`other hand smaller quantities of water, e.g., 50% to 100%
`55 of the equimolar proportions discussed above favor the
`production of ester.
`The above catalyst solutions essentially comprised of:
`(1) the reactant feed component-product acid medium,
`(2) a rhoidum component, and (3) a halogen component,
`60 generally in excess of the rhodium as hereinabove set
`forth, may be further modified by the addition of a high
`boiling, inert solvent as a further component. Such an
`inert solvent must have a boiling point at least 25° C.
`higher (STP) than the product acid and/or ester. Inert
`65 solvents within the present category include paraffin hy(cid:173)
`drocarbons of from 10 to 30 carbon atoms, aromatic hy(cid:173)
`drocarbons of from 12 to 40 carbon atoms, organic acids
`of from 3 to 20 carbon atoms, and esters composed of
`the aforesaid acids in combination with the feedstocks
`70 undergoing carbonylation, and also orthophosphorus and
`orthosilicon alkoxy esters in which the alkoxy group has
`the same number of carbon atoms as the feedstock under(cid:173)
`going carbonylation, as well as the chlorine, bromine, and
`iodine containing derivatives of all of the above said sol(cid:173)
`vents. The followng list exemplifies such solvents: dodec-
`
`005
`
`

`
`3,769,329
`
`9
`ane, hexadecane, naphthalene, biphenyl, propionic acid,
`octanoic acid, phthalic acid, benzoic acid, dioctyl phthal(cid:173)
`ate, dimethyl phthalate, ethyl benzoate, didecyl phthalate,
`dimethyl adipate, triphenyl phosphate, tricresyl phosphate, .
`dibutylphenyl phosphate, tetramethyl orthosilicate, tetra- 5
`butyl orthosilicate, chloronaphthalene, chlorinated biphen(cid:173)
`yls, etc.
`The inert solvents, as described above, refer to the actu-
`al molecular species which are present in the carbonyla(cid:173)
`tion reaction mixture. Consequently, modified derivatives 10
`may be charged initially, for example, an ester having a
`number of carbon atoms which is greater or less than the
`aforesaid ranges by one, two or more carbon atoms.
`Under reaction conditions in the presence of an alcohol
`feedstock, such esters undergo ester interchange to equi- 15
`librium species which are within the above ranges.
`Another embodiment of the process utilizes a high(cid:173)
`boiling, inert solvent such as dimethyl phthalate as de(cid:173)
`scribed above, with the relatively high proportion of an
`alcohol to ester, as above described, together with an 20
`active rhodium component, i.e., a coordination compound
`of rhodium having halogen ligands, and a halogen con(cid:173)
`taining promoter. In this embodiment, patricularly suitable
`for use with a gas-sparged reactor system, the feed is a
`liquid such as methanol with the carbon monoxide intro- 25
`duced in gaseous form. The product stream is then re(cid:173)
`moved as a vapor containing methyl acetate as the prin(cid:173)
`cipal component. In this embodiment of the invention no
`liquid is withdrawn, so that a distinct advantage exists be(cid:173)
`cause of the elimination of catalyst handling; and, conse- 30
`quently a minimization of catalyst losses. The vapor stream
`leaving the reactor is then condensed; it contains the meth-
`yl acetate which is recovered from the liquid condensate
`by