FR2587027A1 - Process for the production of carboxylic acid esters by carbonylation of alcohols - Google Patents

Abstract

Process for converting an alcohol having n carbon atoms to a product containing the corresponding acid having n + 1 carbon atoms and/or the ester of this acid with the starting alcohol. The process consists in bringing the alcohol into contact with carbon monoxide in the presence of a catalyst containing at least one cobalt compound in combination with at least one titanium compound. The titanium is preferably introduced in the form of a titanium complex of formula Ti(OR)4-x-y (OR')x Ly in which R and R' are hydrocarbon groups or hydrogen atoms, L is a ligand, and x and y are integers from 0 to 4 such that the sum x + y is less than or equal to 4. The reaction takes place in the presence or in the absence of solvent at a temperature from 50 to 250 DEG C and a carbon monoxide partial pressure from 5 to 40 MPa. The reaction makes it possible in particular to prepare methyl acetate from methanol.

Description

The present invention relates to a process for converting an alcohol containing n carbon atoms (n being an integer from 1 to 20) into a product containing the corresponding organic acid containing n + 1 carbon atom and / or the ester alcohol containing n carbon atom with said organic acid.

This process consists in reacting an alcohol, in the liquid phase, with a gas containing carbon monoxide in the presence of a catalyst containing cobalt or at least one cobalt compound associated with titanium or at least one titanium compound.

The processes for carbonylation of alcohols to acids or their esters are well known; the most used is the carbonylation of methanol into acetic acid and / or methyl acetate. Many catalysts have been proposed to achieve this transformation. They usually use, apart from the acid catalysis processes, catalysts comprising carbonyl complexes of transition metals, the activity of which is most often quite low, despite severe operating conditions. For example, dicobalt octacarbonyl is generally used under a partial pressure of carbon monoxide of up to 65 idPa and at a temperature of the order of 2500C.

The introduction into the catalytic formula of an activator composed by a halogenated derivative, and in particular by an iodized derivative, made it possible to a certain extent, to compensate for the lack of activity of carbonyl metals.

The literature thus mentions a large number of catalytic compositions which can be used in solution and which contain, associated with one or more iodinated derivatives, various complexes of metals, for example of cobalt FR-A-2 440 349, US-A-4 133 963 , DE-A-2 303 271; rhodium
US-A-3,769,329 and US-A-4,102,920; various noble metals: iridium, ruthenium, palladium or platinum FR-A-1,573,130 and US-A-3,772,380; nickel US-A-2,593,440, US-A-2,729,651, US-A-2,739,169, EP-A-18,927, EP-A-39,052, and FR-A-2,540,861.

All these catalysts have a certain number of disadvantages, among which we can cite the instability due in particular to the decomposition of carbonylmetallic compounds or the lack of selectivity due in particular to the severity of the operating conditions necessary for obtaining a reasonable activity, as is the case with metals such as nickel or cobalt.

All the catalytic compositions containing iodine or iodine derivatives also have the disadvantage of generally causing significant corrosion of usual materials and require the use of expensive special alloys (JP-B-7844446).

On the other hand, the risk of pollution of carbonylation products by traces of iodinated compounds generally requires complex purification operations.

 It has now been found, and it is the object of the present invention, that most of the foregoing disadvantages can be largely avoided by using a catalytic composition comprising cobalt or at least one cobalt and titanium compound or at least one titanium compound, for carbonylating an alcohol containing n carbon atoms, into a product comprising the ester of this alcohol with the acid containing n + 1 carbon atoms. It is then easy, if desired, to pass from this ester to the free acid, or to a mixture of the ester with the acid, by well known methods, for example by hydrolysis.

The catalytic composition used in the present invention advantageously comprises a cobalt compound. The cobalt compound used for implementing the process according to the present invention can be introduced into the reaction medium, for example in the form of carbonyl complexes of cobalt or of their salts such as dicobalt octacarbonyl, cobalt hydride tetracarbonyl, salts of the tetracarbonyl cobaltate anion, for example those of formula Co (RaOH) 6 ++ tCo (CO) 4] 2 in which R a OH represents an alcohol, or in the form of cobalt acetate, or of any compound of cobalt generally used in so-called "oxo" reactions, leading to the in situ formation of a carbonyl complex of cobalt under the reaction conditions. Ligands can optionally be used with the cobalt compound, for example amines, phosphines , arsines, stibines or hydrocarbon ligands, either as a mixture or as a complex prepared beforehand.

The concentration of the cobalt compound in the reaction medium can vary widely, it is advantageously such that the molar ratio number of moles of alcohol to the number of cobalt atoms (alcohol / Co) is from 10: 1 to 50,000: 1 and preferably from 50: 1 to 5000: 1 and most preferably from 50: 1 to 500: 1.

The catalytic composition of the present invention comprises titanium which can be introduced in the form of a compound which is soluble or insoluble in the reaction medium. Titanium can also be deposited on a support.

The titanium compound which can be used according to the present invention can be introduced into the reaction medium, for example in the form of a titanium complex of general formula
Ti (OR) (OR ') L
4-xy xy in which R and R ′ represent, independently of one another, a hydrogen atom or a hydrocarbyl radical having, for example, from 1 to 30 carbon atoms. example: alkyl groups having from 1 to 20 carbon atoms, cycloalkyl groups having from 3 to 12 carbon atoms, aryl groups having from 6 to 20 carbon atoms, and aralkyl groups having from 7 to 20 carbon atoms ,
L represents a ligand coordinated to titanium by a heteroatom for example an oxygen or halogen atom, or a hydrocarbon ligand, such as for example a cyclopentadienyl or substituted cyclopentadienyl anion, x and y are integers from O to 4 such that the sum x + y is less than or equal to 4.

Mention may be made, as example of ligand L, of halides, acetylacetonate, substituted acetylacetonates and carboxylates.

Mention may be made, as an example of a titanium compound, and without the list being exhaustive: tetraalkyltitanates having for example from 4 to 80 carbon atoms such as tetramethyl titanate, tetraisopropyl titanate, tetra n-butyl titanate, acetylacetonatoalkoxytitanes for example, his (acetylacetonato) diisopropoxytitane, titanium hydroxide preferably obtained by hydrolysis of titanium tetrachloride in an ammoniacal medium. The titanium compound can either be soluble or insoluble in the reaction medium. It can for example be used on an organic or inorganic support, such as crosslinked polystyrene, silica, alumina, activated carbon. When a support is used, the titanium is generally deposited by any method well known to those skilled in the art, for example by impregnation or by chemical grafting. The concentration of the titanium compound in the reaction medium can vary widely, it is advantageously such that the molar number of moles of alcohol to the number of titanium atoms is from 5: 1 to 5000: 1 and preferably 10: 1 at 500: 1 and most preferably from 15: 1 to 100: 1.

The carbonylation reaction medium generally consists of the reaction alcohol or its mixture with the ester produced.

The reaction can be carried out in the absence of solvent or in the presence of a solvent. Any solvent having properties of chemical inertness and stability under the reaction conditions can be used. It is possible, for example, to employ an aliphatic or aromatic hydrocarbon, an ether, an amide.

Examples of solvents that may be mentioned include: toluene, hexane, heptane, diethyl ether, dioxane, tetrahydrofuran and acetamide.

The alcohols which are used are chosen from the group formed by alcohols having from 1 to 20 carbon atoms in their molecule and one or more hydroxyl groups.

Among the alcohols, saturated aliphatic alcohols are preferably used having preferably from 1 to 10 carbon atoms, cycloaliphatic alcohols preferably having from 3 to 15 carbon atoms, aromatic alcohols preferably having from 6 to 14 carbon atoms or araliphatic alcohols having for example from 7 to 15 carbon atoms and preferably from 7 to 12 carbon atoms. Preferably saturated aliphatic monohydric alcohols are used.

As specific examples of alcohols, mention may be made of methanol and ethanol.

The use of the catalytic system of the present invention containing cobalt and titanium makes it possible to obtain esters with acceptable yields in the absence of iodine or of iodized compound. It is however possible to carry out the reaction in the presence of iodine or an inorganic or organic iodine compound.

The carbonylation reaction is carried out in the presence of a liquid phase, preferably under substantially anhydrous conditions in the start-up phase. The residual water content in the initial reaction mixture will generally be less than about 5% by weight and preferably less than 1: d by weight. Generally the reaction is initiated in the presence of very low water content at the start, which may require the prior drying of the compounds involved and possibly the solvent.

The temperature and pressure conditions, although variable depending on the alcohol involved, the catalytic system and the other constituents of the reaction medium are chosen to ensure a reasonable reaction rate in the following zones - temperature of about 50 at about 2500C and preferably about
120 to approximately 220 ° C., partial pressure of carbon monoxide from approximately 5 to approximately 40
megapascals (MPa) and preferably around 5 to 30 MPa and a
particularly preferably from about 8 to about 20 MPa.

The gas containing carbon monoxide is preferably essentially pure carbon monoxide, as it is available commercially. However, the presence of impurities such as for example carbon dioxide, nitrogen or methane even in relatively large amounts is not harmful. It is preferable that the gas used does not contain hydrogen, however a tiny amount of hydrogen can be tolerated.

The following examples illustrate the invention without limiting its scope.

In the examples, the alcohol conversion is expressed in mol% and the yield of products is in mole percent. The gas used is essentially pure carbon monoxide.

EXAMPLE 1
Into a stainless steel autoclave with a useful volume of 300 ml, equipped with a temperature control with electric heating and a stirring with magnetic drive, 1.3 g of Co2 (C) 8 (7.6 milliatomes ( mat.) of Co), 10 g of commercial bis (acetylacetonato) diisopropoxytitanium (ie 20.6 mat. of Ti) and 40.5 g of methanol. The autoclave is closed and purged with essentially pure carbon monoxide, then a carbon monoxide pressure equal to 12 MPa is established.

The temperature is then brought to 1650C for 16 hours. The maximum pressure observed is 18.2 MPa. After cooling, the autoclave is degassed and the reaction products are analyzed by vapor phase chromatography (CPV). The methanol conversion is 36.5%. The yield of methyl acetate is 27.4%.

EXAMPLE 2
In the same apparatus as in Example 1, 0.6 g of Co2 (CO) 8 (3.5 mat. Of Co), 36, ex of bis (acetylacetonato) diisopropoxytitane (ie 76 mat. Of Ti) is introduced. and 41.4 g of methanol. The carbon monoxide pressure is cold set to 11 MPa. The temperature is raised to 1500C for 14 hours. The methanol conversion is 50.40 / 0: The yield of methyl acetate is 49.8%.

EXAMPLE 3 (comparative)
This example is not part of the invention and is intended to show the beneficial effect of the titanium compound.

In the same apparatus as in Example 1, 0.6 g of
Co2 (CO) 8 (3.5 mat. Of Co) and 41.4 g of methanol. The carbon monoxide pressure is cold set at 11 MPa, The temperature is brought to 1500C for 14 hours. The conversion of methanol is 10.2%. The yield of methyl acetate is 7.8%.

EXAMPLE 4
In the same apparatus as in Example 1, 7.9 g of bis (acetylacetonato) diisopropoxytitanium, (16.27 mat. Of Ti), and then 7 mat are introduced. of cobalt in the form of Co (CH30H) 6 Co (CO) 4J 2 in solution in 4C, 1 g of methanol. The carbon monoxide pressure is set cold at 8 XPa and the temperature is then brought to 160 C for 7 hours. The methanol conversion is 30.9%. The yield of methyl acetate is 23.2.

EXAMPLE 5
In the same apparatus as in Example 1, 1.2 g of Co2 (C) 8 (7.0 mat. Of Co) are introduced and then 20 mat. of titanium in the form of titanium hydroxide, freshly prepared by hydrolysis of Ti Cl4 in an aqueous ammonia medium, suspended in 48.2 g of methanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 14 hours. The methanol conversion is 24%. The yield of methyl acetate is 17.8%.

EXAMPLE 6
In the same apparatus as in Example 1, 1.2 g of Co2 (CO) 8 (7 mat. Of Co), 2.6 g of bis (benzoylacetonato) dimethoxytitanium (20 mat. Of Ti) and 40.4 g are introduced. methanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 7 hours. The methanol conversion is 22.7%. The yield of methyl acetate is 15.6%.

EXAMPLE 7
In the same apparatus as in Example 1, 0.6 g of C 2 (CO) 8 (3.5 m of Co) is introduced, 34 g of tetra n-butyletitanate (100 m of
Ti) and 41.1 g of methanol. The carbon monoxide pressure is cold set to 12 MPa and the temperature is then brought to 1700C for 7 hours. The methanol conversion is 33.6%. The yield of methyl acetate is 33.6%.

EXAMPLE 8
In the same apparatus as in Example 1, 1.2 g of C 2 (CO) 8 (7 mat. Of Co), 6.1 g of titanium lactate (prepared according to the method described in US-A-2) are introduced. 870,181) and 39.3g of methanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 14 hours. The methanol conversion is 30.4% and the yield of methyl acetate is 19%.

EXAMPLE 9
In the same apparatus as in Example 1, 3.6 g of Co2 (C) 8 (21 mat. Of Co), 21.2 g of methanol and 10.3 g of tetramethyl titanate (60 mat. Of Ti) are introduced. in suspension. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 7 hours. After cooling, and without opening the reactor, 93.3 g of liquid product are withdrawn. This contains 20 ppm by weight of titanium. The yield of methyl acetate is 15.2%.

On the reaction mixture which remains in the reactor, a second charge is introduced consisting of 136.2 g of methanol and 4.1 g of Co2 (C) 8 (23.8 mat. Of Co). The carbonylation is carried out under the same conditions as for the first charge (12 MPa of cold CO, 16O0C for 7 hours). 136.4 g of liquid product are drawn off. The yield of methyl acetate is 9.1%.

A third charge of 89.5 g of methanol and 3.4 g of Co2 (CO) 8 (20 mat. Of Co) is then introduced. Carbonylation is carried out under the same conditions as for the first charge. 97.7 g of liquid product are drawn off. The yield of methyl acetate is 9.9X.

A fourth charge is introduced. 106g of methanol and 3.4g of Co2 (C) 8 (20 mat. of Co). Carbonylation is carried out under the same conditions as for the first charge. 110.7 g of liquid product are drawn off. The yield of methyl acetate is 8.9%.

A fifth charge of 83.3 g of methanol and 3.3 g of Co2 (CO) 8 (19.6 mat. Of Co) is introduced. Carbonylation is carried out under the same conditions as for the first charge. The reactor is then opened and a total of 137.4 g of liquid product containing suspended solid is collected. The yield of methyl acetate is 10.4%.

This example shows that it is possible to reuse several times a titanate insoluble in the reaction medium, such as methyl titanate, and that the activity remains constant during successive charges.

EXAMPLE 10
In the same apparatus as in Example 1, 1.2 g of C 2 (CO) 8 (7 mat. Of Co), 0.56 ml of pyridine (7 mmol), 3.44 g of tetramethyl titanate (20 Ti) and 43.5 g of methanol. The carbon monoxide pressure is set cold to 11.6 MPa and the temperature is then brought to 1600C for 7 hours. The methanol conversion is 25.1% and the yield of methyl acetate is 15.2%.

EXAMPLE 11
In the same apparatus as in Example 1, 1.2 g of C 2 (CO) 8 (7 mat. Of Co), 1.42 g of tri-n-butylphosphine (7 mmol), 3.44 g of tetramethyl are introduced. titanate (20 mat. of Ti) and 42.7 g of methanol.

The carbon monoxide pressure is cold set to 12 MPa and the temperature is then brought to 16O0C for 7 hours. The methanol conversion is 30.2% and the yield of methyl acetate is 20%.

EXAMPLE 12
In the same apparatus as in Example 1, 1.2 g of Co2 (CO) 8 (7 mat. Of Co), 3.44 g of tetramethyl titanate (20 mat. Of
Ti), 34.2 g of toluene as solvent and 13.5 g of methanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 7 hours. The conversion of methanol is 29% and the yield of methyl acetate is 16%.

EXAMPLE 13
In the same apparatus as in Example 1, 1.2 g of
Co2 (CO) 8 (7 mat. Of Co), 3.44 g of tetramethyl titanate (20 mat. Of
Ti), 33.9 g of tetrahydrofuran as solvent and 14.5 g of methanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 7 hours. The methanol conversion is 38% and the yield of methyl acetate is 27%.

EXAMPLE 14 15g of silica (S = 300 m / g) are washed with nitric acid, calcined in air at 450ut, then cooled under nitrogen. 70 ml of distilled and deaerated heptane are added thereto, then 34 g (100 mmol) of tetra-n-butyl titanate.

The azeotrope "heptane-l butanol" is distilled at 930C. The solid is then collected by filtration, then washed twice with 30 ml of pentane, then dried under vacuum at 400C.

In the same apparatus as in Example 1, 2.4 g of
Co2 (CO) 8 (14 mat. Of Co), the titanate supported on silica prepared above and 79.2 g of methanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 16O0C for 14 hours. The yield of methyl acetate is 13.6%. The conversion of methanol is 20%.

EXAMPLE 15
In the same apparatus as in Example 1, 1.2 g of
Co2 (CO) 8 (7 mat. Of Co), 10 g of bis (acetyl-acetonato) diisopropoxytitane (20.5 mat. Of Ti), and 43.5 g of ethanol. The carbon monoxide pressure is cold set at 12 MPa and the temperature is then brought to 1600C for 7 hours. The yield of ethyl propionate is 5.5%. The methanol conversion is 18%.

Claims (9)

1.- Process for carbonylation of an alcohol containing n carbon atoms with a view to forming a product comprising the ester of this alcohol with the acid containing n + 1 carbon atoms, which consists in reacting, in the liquid phase, said alcohol with a gas containing carbon monoxide in the presence of a catalyst containing cobalt or at least one cobalt compound, characterized in that the reaction is carried out in the presence of titanium or at least one titanium compound. 2. A process according to claim 1 in which a saturated monohydroxylated aliphatic alcohol having from 1 to 10 carbon atoms is used. 3.- Method according to claim 1 or 2 wherein the alcohol used is methanol or ethanol. 4.- Method according to one of claims 1 to 3 wherein one uses a cobalt compound selected from the group formed by cobalt compounds leading to the in situ formation of a carbonyl complex of cobalt, the carbonyl complexes of cobalt and the salts of the carbonyl complexes of cobalt. 5.- Method according to one of claims 1 to 4 wherein one uses a cobalt compound selected from the group formed by dicobalt octacarbonyl, cobalt hydride tetracarbonyl and the salts of the tetracarbonyl anion cobaltate. 6.- Method according to one of claims 1 to 5 wherein one employs a titanium compound chosen from the group formed by the titanium compounds of general formula Ti (OR) 4 (OR ') L in 4-xy x- y which R and R 'represent, independently of one another, a hydrogen atom or a hydrocarbyl radical having from 1 to 30 carbon atoms, x and y are whole numbers from O to 4 such that the sum x + y is less than or equal to 4 and L is a ligand chosen from among  ligands coordinated to titanium by a heteroatom and the ligands  hydrocarbons.  7.- Method according to one of claims 1 to 6 wherein  employs a titanium compound selected from the group consisting of tetraalkyltitanes, acetyletaetonatoalkoxytitanes, and hydroxide  titanium.  8.- Method according to one of claims 1 to 7 wherein the  cobalt concentration is such that the alcohol / Co molar ratio is  from 10: 1 to 50,000: 1 and the concentration of titanium is such that the  alcohol / Ti molar ratio is from 5: 1 to 5000: 1.  9.- Method according to one of claims 1 to 8 wherein the  reaction temperature is about 50 to about 2500C, the pressure  partial carbon monoxide is about 5 to about 40 MPa, and  the gas containing carbon monoxide is preferably monoxide  essentially pure carbon.