EP3911627A1 - Process for preparing a compound of formula rsh by hydrosulfurization - Google Patents

Abstract

The invention relates to a process for preparing a compound of formula RSH in which R represents an alkyl group, by gas-phase catalytic reaction of hydrogen sulfide with a compound of formula ROH in the presence of a solid catalyst; in this process, the reaction is carried out in the presence of a catalyst comprising or consisting of one or more pure or mixed rare earth oxides, one or more pure or mixed rare earth sulfides, or one or more pure or mixed rare earth oxysulfides, provided that, when the rare earth is lanthanum, said catalyst is a mixed oxide of lanthanum and at least one metal selected from rare earths or otherwise, and, when the rare earth is cerium, said catalyst is supported on an alumina.

Description

DESCRIPTION

TITLE: PROCESS FOR PREPARING A COMPOUND OF FORMULA RSH BY HYDROSULFURATION

The invention relates to a process for the catalytic gas phase hydrosulfurization of a corresponding thiol alcohol. It is more particularly described for the manufacture of methanethiol from methanol and from hydrogen sulphide, without its scope being restricted therein.

The hydrosulfurization reaction of methanol to methanethiol by catalytic route in the gas phase is known. Usually, this is carried out in the presence of a catalyst based on tungsten oxide and an alkali metal supported on an alumina, as described for example in patent WO2013092129A1.

However, some research on alternative catalysts exists in the literature. Thus, the work of Plaisance and Dooley (Catalysis Letters, 2009, 128, 449-458) describe the use of catalysts based on different metal oxides such as tungsten (WO3), lanthanum (La2O ₃ ) or titanium. (T1O2) supported on various solids. Of all, tungsten oxide is the most active. This work shows that the activity of each of the catalysts tested depends on different parameters and that it is difficult to determine the optimal conditions common to several catalysts. In addition, with the catalyst based on lanthanum oxide supported on alumina (La ₂ O ₃ / Al ₂ O ₃ ), a high conversion of methanol is obtained, but this is accompanied by a very low selectivity in methanethiol, which makes this catalyst incompatible with application on an industrial scale.

Furthermore, Ziolek et al. (Journal of Molecular Catalysis A: Chemical, 1997, 97, 49-55) describe the influence of the adsorption of hydrogen sulphide during the hydrosulphurization reaction of methanol in the presence of different catalysts based on oxides magnesium (MgO), titanium (T1O2), zirconium (ZrÜ2), cerium (CeÜ2) and aluminum (Al ₂ O ₃ ). The authors observed in particular the strongest adsorption of hydrogen sulphide on ceria and correlated this phenomenon with increased selectivities for methanethiol and dimethylsulphide. However, at medium conversion of methanol, this catalyst generates a large quantity of methane, to the detriment of the selectivity for methanethiol, to such an extent that methane becomes the majority product of the reaction under certain conditions.

It appears that to date, the need still exists to develop the conditions for a catalytic hydrosulfurization reaction of methanol in the gas phase, both in terms of the catalyst and of the process parameters, which has both a of high conversion of methanol, high selectivity to methanethiol and which reduces the production of non-recoverable by-products such as light compounds.

The invention provides a method which satisfies these requirements.

This process makes it possible to prepare a compound of formula RSH where R represents an alkyl group, by gas phase catalytic reaction of hydrogen sulphide with a compound of formula ROH, in the presence of a solid catalyst, this catalyst comprising or consisting of a or pure or mixed rare earth (s) oxides, pure or mixed rare earth (s) sulphide (s) or pure rare earth (s) oxy-sulphide (s) or mixed, provided that when the rare earth is lanthanum, said catalyst is a mixed oxide of lanthanum and at least one metal selected from rare earths and when the rare earth is cerium, said catalyst is supported.

It has been observed that by using such a catalyst, the selectivity was improved significantly compared to the catalysts described in the prior art, in particular by a decrease which can reach an order of magnitude of at least 40% in non-products. recoverable products such as carbon monoxide, carbon dioxide, methane, hydrogen and dimethyl ether. Thus, the main product is methanethiol, and dimethylsulfide constitutes the majority secondary product. The latter can be skillfully recycled to be converted to methanethiol, thus increasing the overall yield of the methanethiol process. In addition, by virtue of this process, the reaction can be carried out over a wider and generally lower temperature range than those of known processes. More generally, this process has the advantage of being flexible and depending on the operating conditions such as the temperature, the selectivity can be oriented towards one product or another.

The method of the invention is described below in more detail with characteristics which can be considered alone or in combination (s) regardless of the combination (s), and preferred variants of implementation are provided.

Before this more detailed description, certain terms used in the text are defined.

By rare earths, we mean the 15 lanthanides (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium), as well as scandium and yttrium.

According to the invention, the catalyst may be present in the form of an oxide (or oxyhydroxide), sulphide and any intermediate form containing S and O which is called oxysulphide. In the formulas defining the compounds obtained or used, the term “alkyl” denotes a linear or branched monovalent hydrocarbon radical having from 1 to 20 carbon atoms, advantageously from 1 to 6 carbon atoms, such as methyl or ethyl , propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, n-hexyl or a cyclic monovalent hydrocarbon radical having from 3 to 20 carbon atoms, advantageously from 3 to 6 carbon atoms, such as cyclopropyl, cyclohexyl, but not limited to these radicals.

According to a process of the invention, the catalyst is chosen from rare earth oxides, hydroxides or even rare earth oxyhydroxides and at least one other metal which is not a rare earth. The catalyst can also be chosen from mixed oxides (hydroxides or oxyhydroxides) of rare earths and of at least one other metal which is not a rare earth. The term “mixed oxides” is understood to mean an oxide based on several rare earths. The catalyst can also be chosen from mixed sulphides of several rare earths, mixed sulphides of one or more rare earths and at least one other metal which is not a rare earth, oxy-sulphides of several rare earths. , mixed oxidesulfides of one or more rare earths and at least one other metal which is not a rare earth, and mixtures of said mixed oxides, mixed sulfides and mixed oxidesulfides. Said metal which is not a rare earth is preferably zirconium.

The catalyst may also comprise, in addition to the aforementioned oxides, sulphides and / or oxysulphides, one or more oxides of different rare earth metals.

In a variant of the invention, the catalyst is supported, advantageously on alumina, pretreated or not, which makes it possible to circumvent the problems of blockages which can potentially be observed in the presence of materials based on rare earths in powder form.

As indicated above, the process of the invention is particularly advantageous for the preparation of methanethiol by catalytic hydrosulfurization of methanol, but it may be suitable for obtaining any RSH compound, where R is an alkyl as defined above.

Among the catalysts suitable according to the invention, certain combinations are selected because of their efficiency. Thus, advantageously, the catalyst comprises or consists of mixed oxides of lanthanum, cerium, neodymium and zirconium; in this combination, the proportions of zirconium oxide and cerium are in the majority relative to those of the oxides of lanthanum and of neodymium.

According to the invention, a support has also been developed which makes it possible to increase the performance of the catalysts used. This support can be an alumina modified with potassium, with a potassium content of between 0.1% and 20% (m / m), preferably between 0.5% and 10%, and more preferably between 0.5% and 5%. In a variant of the invention, the use of ceria supported on an alumina thus modified is reported, in a range of supported cerium oxide contents of between 0.1% and 50% (m / m), preferably between 0.5% and 30% (m / m). This makes it possible to remarkably increase the methanethiol productivity of certain catalysts used according to the invention, and in particular ceria, which, in the pure state, has a high selectivity for methane, which has drawbacks in the production of methanethiol. on an industrial scale.

In the process of the invention, the ratio of hydrogen sulphide to the ROH compound preferably ranges from 0.5 to 20, preferably from 1 to 15, and more preferably from 1 to 10.

It was previously indicated that one of the interests of the invention was to be able to widen the range of reaction temperatures. Thus, it can be carried out at a temperature of 200 ° C to 450 ° C, preferably from 250 ° C to 420 ° C, and more preferably from 275 ° C to 400 ° C, advantageously under a pressure of between 2 and 20 bar , preferably from 5 to 15 bar, and even more preferably from 7 to 14 bar and for a contact time of the ROH compound with the catalyst ranging from 0.1 seconds to 60 seconds.

Although the reaction is highly selective for methanethiol, dimethylsulfide can also be formed. A reaction of catalytic conversion of said dimethylsulfide into methanethiol can then be carried out in addition, according to techniques well known to those skilled in the art, in order to further improve the yield of the process in methanethiol.

The invention and its advantages are hereinafter illustrated in examples.

Example 1 Manufacture of methanethiol from methanol, in the presence of a catalyst based on mixed oxides, according to the invention

Preparation of the Catl catalyst of LaCeNdZr composition (2 / 21.3 / 5.1 / 71.6):

The catalyst was prepared by synthetic routes of mild chemistry. For example, it can be obtained according to the method described in patent FR2907445A1 or patent FR2859470A1. The specific surface of this catalyst is 75 m ² .g ^_1 . The composition by weight of oxides is 2.0% La2O ₃ , 21.3% CeO2, 5.1% Nd2O ₃ and 71.6% ZrO ₂ . Manufacture of methanethiol by hydrosulphurization of methanol in the presence of the above catalyst:

A catalytic bed of 2 ml of catalyst diluted in carborundum with a particle size of between 0.400 and 0.500 nm is placed in a reactor with an internal diameter of 1.26 cm. The reactor inlet gases consist of a mixture of methanol and hydrogen sulfide.

Different operating conditions are tested and described below:

1) H ₂ S / MeOH molar ratio = 0.5 / temperature = 330 ° C / contact time = 10 s

2) H ₂ S / MeOH molar ratio = 4 / temperature = 375 ° C / contact time = 20 s

3) H ₂ S / MeOH molar ratio = 1.7 / temperature = 400 ° C / contact time = 4 s. The pressure in the reactor is 10 bar.

In order to compare the performance of a process of the invention with a process of the prior art, the same reaction is carried out under the same conditions in the presence of a catalyst consisting of cerium oxide (with a specific surface area of 99 m ² .g ^_1 ) similar to that described in the state of the art.

The results are shown in Table 1 below:

It is observed that, whatever the conditions, the process of the invention exhibits both a higher conversion of methanol and a higher selectivity to methanethiol, while producing very small quantities of light gases in favor of a greater selectivity to dimethylsulfide. These results demonstrate the performance of a catalyst used in a process according to the invention with respect to ceria. They further demonstrate that in order to achieve optimum production of methanethiol, it is advantageous for the process of the invention to include an additional step in which the dimethylsulfide produced is converted into methanethiol, in the presence of a catalyst known to those in the art, such as alumina.

Example 2: Manufacture of methanethiol from methanol, in the presence of a catalyst based on mixed oxides, according to the invention

Preparation of the Cat2 catalyst of LaCeNdZr composition (1.75 / 30.3 / 5.35 / 62.6):

Cat2 catalyst is prepared using the same technique as Cat1 catalyst above. The specific surface of this catalyst is 59 m ² .g ^_1 . The composition by weight of oxides is 1.75% of La2O ₃ , 30.3% of Ced, 5.35% of Nd2O ₃ and 62.6% of Zr0 ₂ .

Manufacture of methanethiol by hydrosulphurization of methanol in the presence of the above catalyst:

The catalytic performances of this catalyst were determined in the same experimental system as Example 1, with an H2S / MeOH molar ratio = 1.7, a temperature of 375 ° C. and a pressure in the reactor of 10 bar.

The performances of the catalysts were compared over a wide range of methanol conversions by varying the mass of catalyst introduced and the flow rate of the various reactants.

The results are shown in Table 2 below:

Example 3: Manufacture of methanethiol from methanol. in the presence of a catalyst based on cerium oxide, supported on modified alumina, according to the invention

Preparation of CatS3 catalyst supported on alumina modified with potassium:

The supported CatS3 catalyst is synthesized by successive impregnations and calcinations (450 ° C in air) of 100 g of commercial alumina with a specific surface area of 171 m ² .g ¹ with a solution of potassium hydroxide (38 g / L), then with a solution of cerium (III) nitrate (1151 g / L). The potassium content is 1.5% by mass, that of cerium oxide 3.5% by mass. The specific surface of the catalyst is 167 m ² .g 1

Manufacture of methanethiol by hydrosulphurization of methanol in the presence of the above catalyst:

The catalytic performances of these catalysts were determined under experimental conditions identical to Example 2.

In order to compare the performance of a process of the invention with a process of the prior art, the same reaction is carried out under the same conditions in the presence of the same pure alumina used as a support for CatS3 and of a catalyst (KS ) consisting of potassium and supported by the same aforementioned alumina, synthesized according to the method described for the CatS3 catalyst. The performances of the catalysts were compared over a wide range of methanol conversions by varying the mass of catalyst introduced and the flow rate of the various reactants.

The results are shown in Table 3 below:

These results demonstrate the effectiveness of ceria supported on a modified alumina, in particular impregnated beforehand with potassium.

Claims

1. Process for preparing a compound of formula RSH where R represents an alkyl group, by gas phase catalytic reaction of hydrogen sulfide with a compound of formula ROH, in the presence of a solid catalyst, characterized in that ' the reaction is carried out in the presence of a catalyst which comprises or consists of one or more pure or mixed rare earth oxide (s), one or more pure or mixed rare earth sulphide (s), or one or more pure or mixed rare earth (s) oxysulfides, provided that when the rare earth is lanthanum, said catalyst is a mixed oxide of lanthanum and of at least one metal chosen from rare earths or not and when the rare earth is cerium, said catalyst is supported. 2. Method according to claim 1, characterized in that the catalyst is chosen from one or more mixed oxides of several rare earths, one or more mixed oxides of one or more rare earths and at least one other metal which is not is not a rare earth, one or more mixed sulphides of several rare earths, one or more mixed sulphides of one or more rare earths and at least one other metal which is not a rare earth, one or more oxy- sulphides of several rare earths, one or more mixed oxy-sulphides of one or more rare earths and of at least one other metal which is not a rare earth, and mixtures of said mixed oxides, mixed sulphides and oxy-sulphides mixed. 3. Method according to claim 1 or 2, characterized in that said metal which is not a rare earth is zirconium. 4. Method according to any one of claims 1 to 3, characterized in that the catalyst comprises one or more oxides of different rare earth metals. 5. Method according to any one of claims 1 to 4, characterized in that the catalyst is supported. 6. Method according to any one of claims 1 to 5, characterized in that the catalyst is supported on alumina, pretreated or not. 7. Process according to any one of claims 1 to 6, characterized in that the methanethiol is prepared by catalytic hydrosulphurization of methanol in the gas phase by reaction with hydrogen sulphide. 8. Method according to any one of claims 1 to 7, characterized in that the catalyst comprises or consists of mixed oxides of lanthanum, cerium, neodymium and zirconium, the proportions of zirconium oxide and of cerium being majority. 9. Process according to any one of claims 1 to 7, characterized in that the catalyst comprises or consists of cerium oxide and is supported in ranges between 0.1% and 50% (m / m), preferably between 0.5% and 30%, on an alumina impregnated with potassium the content of which is between 0.1% and 20% (m / m ), preferably between 0.5% and 10%, and more preferably between 0.5% and 5%. 10. Method according to any one of claims 1 to 9, characterized in that the molar ratio between the hydrogen sulphide and the ROH compound is between 0.5 and 20, preferably from 1 to 15, and even more preferably from 1 to 10. 11. Method according to any one of claims 1 to 10, characterized in that the reaction is carried out at a temperature between 200 ° C and 450 ° C, preferably from 250 ° C to 420 ° C, and even more preferably from 275 ° C to 400 ° C, advantageously under a pressure between 2 and 20 bar, preferably from 5 to 15 bar, and more preferably from 7 to 14 bar, and that the contact time of the ROH compound with respect to the catalyst is included between 0.1 second and 60 seconds. 12. Method according to any one of claims 1 to 11, characterized in that the reaction produces dimethylsulfide and in that a further reaction is carried out for the catalytic conversion of said dimethylsulfide to methanethiol.