FR2543946A1 - Production of methanol by hydrogenolysis of methyl formate in the presence of a supported metal catalyst - Google Patents

Abstract

The subject of the present invention is the production of methanol by hydrogenolysis of methyl formate, under hydrogen pressure, in the presence of a catalyst based on a metal of group VIII and a metal of group IVA deposited on a support. The conversion is carried out, preferably, at a temperature of between 200 and 250 DEG C and under a total pressure of 40 to 70 bars.

Description

Methanol production is currently provided mainly by the conversion of syngas produced by steam reforming, natural gas or naphtha or from heavy residues of oil or coal under pressure in the presence of catalysts based on zinc oxide. The first generation of catalysts, zinc oxides and chromium, required high operating pressures (250 - 350 atm) (see DE 293 787 - FR 540 543).

A second generation of more active catalysts based on copper and zinc oxides made it possible to work, in the late 1960s, under much milder pressure conditions (50,100 atm) (see US 3,326,956). ; however, the very high sensitivity of these catalysts to poisoning necessitates very large sections of purification of the synthesis gas.

Another possibility of producing methanol is the hydrogenolysis of methyl formate under hydrogen pressure in the presence of a catalyst according to the drafting

This is particularly the object of a US patent (US 1 302 011) in which is claimed the use of a copper-based catalyst.

Several other documents describe the conversion of methyl formate to methanol and carbon monoxide (US 3872 210, 4303 630 and 4319 050).

The major disadvantage of the results of the prior art lies in the fact that only one molecule of methanol is obtained per molecule of transformed formate; moreover, in the case of US Pat. No. 4,319,050, a very large production of dimethyl ether is observed, up to a selectivity of 75% relative to the converted methyl formate.

Thus it has been discovered that it is possible to promote the hydrogenolysis of methyl formate to methanol according to reaction (1) by operating in the presence of a supported metal catalyst containing the following elements: the rhodium whose weight percentage is chosen between 0.1 and 5% and preferably between 0.5 and 2% and at least one element selected from the group consisting of Germanium, tin and lead and whose weight percentage is between 0.1 and 10 % and more particularly between 1 and 3%. It is advantageous to use two of the above metals or even three of these metals.

The support may be chosen from the oxides of the elements of groups II,
III, and / or IV of the periodic table of elements such as oxides of barium, calcium and magnesium, titanium, zirconium, thorium, zinc, aluminum and silicide, taken alone or in a mixture with each other such that zinc, magnesium, calcium and barium aluminates, and preferably in the group consisting of carriers whose adsorption heat of ammonia is less than 65 kilojoules per mole.

This ammonia adsorption measurement is determined in the test described in "Journal of catalysis" 2 - 211-222 (1963)
This method consists in heating the support to 6000C under vacuum to obtain a total degassing; then the support is placed in a calorimeter at 320 ° C and an amount of ammonia is introduced such that the final pressure of the system reaches equilibrium 40kPa and the amount of heat released is measured.

The catalyst can be prepared by different impregnation procedures of the support and the invention is not limited to a specific procedure. Impregnation LiopXration consists, for example, in bringing the preformed support into contact with an aqueous or organic solution of a compound of the metal or metals chosen, the volume of solution being in excess with respect to the retention volume of the support or equal to this volume. Rhodium and additional metal can be introduced simultaneously or successively.

After allowing contact between the support and the solution for several hours, the impregnated support is advantageously filtered, washed with distilled water, dried and calcined in air between 110 and 6000 ° C and preferably between 110 and 550 ° C. Before use the catalyst is reduced under hydrogen at 200 ° C. to 6000 ° C. and preferably at 300 ° C. to 5000 ° C., this reduction being able to be carried out immediately after the calcination, or later at the user's.

The element selected from the group consisting of tin, germanium and lead may be introduced onto the support pre-impregnated with the noble metal and optionally calcined or calcined and reduced, in aqueous solution or in hydrocarbon solution, depending on the nature of the precursor uses.

Another method is to knead the wet support powder with catalyst precursors and then form and dry.

Examples of metal precursors that can be used in the preparation of the catalyst are the following:
For rhodium, it is possible to use compounds such as chlorides, nitrates or soluble organic acid salts in the impregnating solvent, for example rhodium chloride, rhodium nitrate, soluble salts of organic acids such as rhodium acetate, but also chlorides or nitrate of rhodium hexamine.

It is also possible to use organometallic rhodium compounds in solution in a hydrocarbon, for example in a saturated paraffinic hydrocarbon whose hydrocarbonaceous chain contains from 6 to 12 carbon atoms, in a naphthenic hydrocarbon which contains from 6 to 12 carbon atoms. or in an aromatic hydrocarbon containing from 6 to 11 carbon atoms; rhodium acetylacetonate is preferably used.

The element selected from the group consisting of tin, germanium and lead may be introduced via compounds such as tin chlorides, bromides and nitrate, halides, nitrate, acetate and carbonate. germanium chloride and oxalate in aqueous solution or preferably by means of alkyl, cycloalkyl or aryl-tin, germanium and lead metals such as for example: tetrabutyltin, tetramethyltin, tetrapropyl-germanium, tetraethyl-lead, diphenyl étai n, diphenyl-germanium or tetraphenyl-lead in hydrocarbon solution.

The support can be of varied nature, as already mentioned above. A particularly suitable support has specific characteristics such that a specific surface area, determined by the BET method, of between 10 and 500 square meters per gram and a total pore volume of between 20 and 130 cm 3 per 100 grams of support and preferably comprised between 50 and 110 cm3 per 100 grams of support.

Once the catalytic metals are fixed on the support, the catalyst advantageously undergoes a high temperature activation treatment under hydrogen, for example 300 - 500 ° C., in order to obtain an active metal phase. for example, a slow rise in the temperature under hydrogen flow up to the maximum reduction temperature, for example between 300 and 5000 ° C. and preferably between 350 and 45 ° C., followed by holding for 1 to 6 hours at this temperature. temperature.

The reaction between hydrogen and methyl formate can be carried out in a continuous or batch reactor, under a total pressure of between 10 and 100 bar and preferably between 40 and 70 bar, although it is possible to operate without inconvenience. for example, up to 300 bar, at a temperature between 180 and 3000C and preferably between 200 and 2500C and with a molar ratio of hydrogen to methyl formate of between 2 and 10 and more preferably between 2 and 5.

The following nonlimiting examples illustrate the invention
Example 1
This example, for comparison purposes, uses a support whose heat of neutralization of ammonia does not meet the requirements of the invention.

The catalyst used comprises rhodium and tin deposited on an alumina whose specific surface area is equal to 200 m 2 per gram, the total pore volume equal to 60 cm 3 per 100 g of alumina and the heat of adsorption of ammonia at 105 kJ / mole.

The preparation of the catalyst is done in two stages
- Rhodium fixation by impregnation of rhodium trichloride in aqueous solution, followed by filtration, drying at 1100C, calcination in air at 450 ° C and a reduction in hydrogen at 450 ° C.

 - Fixing the tin on the support pre-impregnated with rhodium, calcined and reduced1 in the form of tetrabutyltin in solution in normal heptane. After leaving the catalyst and the tetrabutyltin solution under reflux for heptane for 4 hours, the catalyst is washed with heptane and then dried.

The catalyst is then loaded into a tubular reactor and then reduced for 4 hours in a stream of hydrogen.

The operating conditions for the hydrogenolysis of methyl formate are as follows:
- VVH = 4.5 l / l / hour
- Molar ratio, H2 / methyl formate = 5
The pressure was varied between 30 and 50 bar and the temperature between 220 and 2500C.

The catalyst has the following composition: Rh 1% weight, Sn 2.5% weight on alumina.

Table 1

<tb><SEP> YIELDS <SEP> (% <SEP> wt)
<tb> Tempera- <SEP> Pressure <SEP> Conver
<tb> ture <SEP> (C) <SEP> (bars) <SEP><SEP> (% wt) <SEP> CH30H <SEP> (CH3) 2 <SEP> CH4 <SEP> CO <SEP> C02
<tb> 220 <SEP> 50 <SEP> 60 <SEP> 13.40 <SEP> 25.00 <SEP> --- <SEP> 11.2 <SEP> 10,
<tb> 250 <SEP> 50 <SEP> 99.7 <SEP> 15.5 <SEP> 38.5 <SEP> 0.9 <SEP> 25.7 <SEP> 18.9 <SEP>
<tb> 250 <SEP> 30 <SEP> 99.0 <SEP> 20, <SEP> 28.9 <SEP>0> 6 <SEP><SEP> 24.2 <SEP> 25 3 <SEP>
<Tb>
The results, shown in Table 1, show that
the use of a support, whose heat of adsorption of ammonia is equal to 105 kilojoules per mole, makes it possible to obtain high conversions. However, one notes the important formation of dimethyl ether (of the order of 40% of converted methyl formate), carbon monoxide and carbon dioxide.

The rise in temperature promotes the formation of carbon oxides: the selectivity to (CO + CO 2) increases from 36% at 220 ° C. to 45% at 250 ° C.
- the pressure increase to a minor effect. The production selectivity of (CO + CO 2) at 250 ° C is 50% at 30 bar and 45% at 50 bar.

The cumulative selectivities of CH 3 OH + CO are equal to 41% at 220 ° C. and 50 bar, 41.3% at 2500 ° C. and 50 bar and 44.6% at 250 ° C. and 30 bar.

Example 2
The procedure is as in Example 19 except that silica is used as a support whose specific surface area, measured by the BET method, is equal to 450 m 2 per gram and the total pore volume to 80 cm 3 per 100 grams .

The heat of adsorption of ammonia on this support is equal to 63 kilojoules per mole.

The results are grouped in Table 2
Table 2.

<Tb>

<SEP> YIELDS <SEP> (% <SEP> weight)
<tb> Tempera- <SEP> Pressure <SEP> Conversion
<tb> ture <SEP> (C) <SEP> (bars) <SEP> (% <SEP> Weight) <SEP> CH3OH <SEP> (CH3) 20 <SEP> CH4 <SEP> CO <SEP> CO2 <September>
<tb> 220 <SEP> 50 <SEP> 30 <SEP> 24.00 <SEP> 0.08 <SEP> 0.07 <SEP> 5.80 <SEP> 0.05 <SEP>
<tb> 250 <SEP> 50 <SEP> 58 <SEP> 43.5 <SEP> 0.15 <SEP> 0.21 <SEP> 12.8 <SEP> 1.3
<tb> 250 <SEP> 30 <SEP> 55 <SEP> 39.3 <SEP> 0.15 <SEP> 0.20 <SEP> 13.8 <SEP> 1.50
<Tb>
The cumulative selectivities CH30H + CO are equal to
2200 C: 99.3%
2500 C: 96.5% at P = 30 atm
97.1% at P = 50 atm
Example 3
The operation is carried out under the same conditions as those of Example 1 except that the volume space velocity is equal to 1.5 liter of methyl formate per liter of catalyst per hour. The catalyst used is of the same type as that used in Example 1 except that the support is composed of a mixture of thorium oxide for 56% by weight and silica for 33% by weight, the specific surface area of which is equal to 100 m 2 per gram and the total pore volume at 30 cm3 per 100 grams. The adsorption heat of ammonia for this support is equal to 58 kilojoules per mole.

The results are shown in Table 3
Table 3

<tb><SEP> YIELDS <SEP> (% <SEP> weight)
<tb> Tempera- <SEP> Pressure <SEP> Conversion
<tb> ture <SEP> (C) <SEP> (bars) <SEP> (% <SEP> weight) <SEP> CH3OH <SEP> (CH3) 20 <SEP> CH4 <SEP> CO <SEP> CO2
<tb><SEP> 220 <SEP> 30 <SEP> 38 <SEP> 22.9 <SEP> 0.1 <SEP> 0.1 <SEP> 14.4 <SEP> 0.5
<tb><SEP> 220 <SEP> 50 <SEP> 46 <SEP> 38.6 <SEP> 0.1 <SEP> 0.1 <SEP> 7.0 <SEP> 0.1
<tb><SEP> 250 <SEP> 30 <SEP> 67 <SEP> 47.8 <SEP> 0.3 <SEP> 0.3 <SEP> 16.7 <SEP> 1.8
<tb><SEP> 250 <SEP> 50 <SEP> 72 <SEP> 54.1 <SEP> 0.2 <SEP> 0.3 <SEP> 15.8 <SE> 1.6
<Tb>
The cumulative selectivities of CH 3 OH and CD are equal to 99.1% at 220 ° C. and 50 bar at 98.2% at 220 ° C. and 30 bar at 97.1% at 250 ° C. and 50 bar and at 96.3% at 250 C and 30 bar.

Example 4
The procedure is the same as in Example 3. The catalyst used is identical to that described in Example 3 except that lletain was replaced by Germanium and lead successively.

The temperature is 250 C and the total pressure is set at 50 atmospheres.

Germanium and lead are impregnated in hydrocarbon solution (n - C7) respectively in the form of tetraethylgermanium and tetraethylplomb.

Table 4

<tb><SEP> YIELDS <SEP> (% <SEP> weight)
<tb> 2nd <SEP> metal <SEP> Conversion
<tb> (% <SEP> weight) <SEP> (% <SEP> weight) <SEP> CH3OH <SEP> (CH3) 20 <SEP> CH4 <SEP> CO <SEP> CO2 <SEP>
<tb> sn <SEP>: <SEP> 2.5 <SEP> 72 <SEP> 54.1 <SEP> 0.2 <SEP> 0.3 <SEP> 15.8 <SEP> 1.6
<tb> Ge <SEP>: <SEP> 2.4 <SEP> 74 <SEP> 55.5 <SEP> 0.2 <SEP> 0.2 <SEP> 16.4 <SEP> 1.7
<tb> pb <SEP>: - <SEP> 2.6 <SEP> 71 <SEP> 54.0 <SEP> 0.2 <SEP> 0.1 <SEP> 15.6 <SEP> 1.1
<Tb>
The cumulative selectivities in methanol and carbon monoxide are equal to:
- 97.1% for the catalyst containing tin
- 97.2% for the catalyst containing germanium
- 98.0% for the catalyst containing lead tin can be replaced by germanium or lead without altering the catalytic properties.

Claims (8)

1) Process for producing methanol in which methyl formate  is treated with hydrogen in the presence of a catalyst, at a temperature  from 180 to 3000C, characterized in that the catalyst contains a support,  rhodium and at least one second element selected from the group constitutes  of tin, germanium and lead, the support being characterized, in the ammonia adsorption test, by heat of adsorption  ammonia less than 65 kilojoules per mole. The process according to claim 1, wherein the rhodium content is  from 0.1 to 5% by weight and the second element content from 0.1 to 10%  in weight. The process according to claim 1, wherein the rhodium content is  from 0.5 to 2% by weight and the second element content from 1 to 3% by weight  weight. 4) Method according to one of claims 1 to 3, wherein the catalyst  result of the incorporation, in a carrier, of at least one compound of  rhodium and at least one compound selected from the group consisting of  alkyl, cycloalkyl and aryl-tin, germanium and lead. 5) Method according to one of claims 1 to 3, wherein the support  has an area of 50 to 500 m2 / g and a pore volume of 0.5 to  1.1 cm3 / g. 6) Method according to one of claims 1 to 5, wherein the support  is silica. 7) Method according to one of claims 1 to 7, wherein the pressure  is 40 to 70 bar and the temperature is 200 to 250 ° C. 8) Method according to one of claims 1 to 8, wherein the report  Hydrogen / ester molar is 2: 1 to 10: 1