Process for preparing methyl mercaptan

Abstract

The present invention relates to a process for preparing methyl mercaptan comprising the specific steps a) to h).

Description

Title of the invention: Process for preparing methyl mercaptan technical field

[0001] The present invention relates to a process for preparing methyl mercaptan from at least one carbon oxide. Previous techniques

[0002] Methyl mercaptan is of great industrial interest, particularly as a raw material for the synthesis of methionine, an essential amino acid widely used in animal feed. Methyl mercaptan is also a raw material for many other molecules, notably dimethyl disulfide (DMDS), a sulfidation additive for hydrotreating catalysts of petroleum fractions, among other applications.

[0003] Methyl mercaptan is commonly produced in large quantities industrially, from methanol and H2S, but it can also be produced from at least one carbon oxide, for example from carbon dioxide, carbon monoxide or a mixture of carbon dioxide and carbon monoxide.

[0004] Methyl mercaptan can in particular be produced directly from carbon monoxide, hydrogen and hydrogen sulfide according to the following reaction:

[0005] CO + 2 H2 + H2S -> CH3SH + H2O (1).

[0006] The main by-product of this reaction is carbon dioxide (CO2). Carbon oxysulfide (COS) is considered the reaction intermediate that leads to methyl mercaptan after hydrogenation according to the following reactions:

[0007] CO + H2S -> COS + H2 (2)

[0008] COS + 3 H2 CH3SH + H2O (3).

[0009] As for CO2, it is produced by several side reactions, such as:

[0010] CO + H2O -> CO2 + H2 (4)

[0011] COS + H2O -> CO2 + H2S (5)

[0012] 2 COS -> CO2 + CS2 (6).

[0013] Various processes for preparing methyl mercaptan from carbon monoxide have been described in the literature.

[0014] For example, US patent application 2007 / 213564 describes a process for the continuous production of methyl mercaptan from carbon monoxide, dihydrogen, and hydrogen sulfide, said reaction being catalyzed by a family of silica-supported K2MoO4-based catalysts. According to this process, 70% of the carbon monoxide can be converted.

[0015] Furthermore, US patent application 2010 / 094059 cites a family of TeO2 / K2MoO4-based catalysts supported on a porous support selected from SiO2, Al2O3, TiO2, Al2O3-SiO2, ZrO2, zeolites, carbonaceous materials, and a promoter characterized exclusively by tellurium oxide (TeO2). It is demonstrated that the conversion to carbon monoxide is 59%.

[0016] Methyl mercaptan can also be produced from a mixture of carbon dioxide and carbon monoxide, as described for example in US application 2008 / 293974.

[0017] Methyl mercaptan can also be produced from carbon dioxide, as described for example in applications EP 0 171 312 and US 2008 / 262270.

[0018] Despite all this research work, there is still a need for a methyl mercaptan preparation process leading to very good methyl mercaptan productivity or excellent conversion to carbon monoxide.

[0019] It has been discovered that a specific process makes it possible to obtain improved productivity in methyl mercaptan but also excellent conversion to carbon monoxide. Description of the invention

[0020] The invention therefore relates to a process for preparing methyl mercaptan, comprising at least the following steps:

[0021] a) optionally reaction of at least one carbon oxide, selected from carbon dioxide and a mixture of carbon dioxide and carbon monoxide, and dihydrogen in the presence of at least one CAI catalyst to obtain a mixture comprising carbon monoxide, carbon dioxide, dihydrogen and water;

[0022] b) optionally drying the mixture obtained at the end of step a) to obtain a mixture comprising carbon monoxide, carbon dioxide, and dihydrogen;

[0023] c) reaction of at least one carbon oxide (OC), possibly from step a) or step b), hydrogen sulfide (H2S) and dihydrogen (H2) in the presence of at least one CA2 catalyst, the molar ratio OC / H2 / H2S being 1 / X / Y, with X varying from 0 to 10 and Y varying from 1 to 4, to obtain a flux (M) comprising at least methyl mercaptan, non-condensable products and water;

[0024] d) purification of the stream (M) to obtain a liquid stream (Ml) comprising at least methyl mercaptan and water and a gaseous stream (M2) comprising at least said non-condensable products and water;

[0025] e) recycling said stream (M2) from step d) to step c) including at least one drying;

[0026] f) optionally further purification of the stream (Ml) to obtain a stream (P) comprising at least methyl mercaptan;

[0027] g) optionally drying of the methyl mercaptan obtained at the end of step f); and

[0028] h) recovery of the methyl mercaptan.

[0029] The process according to the invention notably allows the continuous synthesis of methyl mercaptan. It also allows for improved methyl mercaptan productivity and excellent conversion to carbon monoxide.

[0030] Furthermore, the process according to the invention makes it possible to recycle impurities from the final product. In particular, step e) makes it possible to recycle non-condensable products, notably carbon dioxide and carbon monoxide, which have not reacted and are thus re-engaged in the synthesis.

[0031] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the following description.

[0032] It is specified that the expressions "from ... to ..." used in this description should be understood as including each of the mentioned limits.

[0033] As previously stated, the process according to the invention includes in particular:

[0034] a) optionally reacting at least one carbon oxide, selected from carbon dioxide and a mixture of carbon dioxide and carbon monoxide, and dihydrogen in the presence of at least one CAI catalyst to obtain a mixture comprising carbon monoxide, carbon dioxide, dihydrogen and water;

[0035] b) optionally drying the mixture obtained at the end of step a) to obtain a mixture comprising carbon monoxide, carbon dioxide, and dihydrogen.

[0036] Thus, steps a) and b) of the process according to the invention are not necessarily implemented.

[0037] In particular, step a) is implemented when the carbon oxide is chosen from carbon dioxide and a mixture of carbon dioxide and carbon monoxide.

[0038] During this step a), the reaction as defined above is carried out in the presence of at least one CAL catalyst. This reaction is known as "Retro water-gas shift" (RWGS).

[0039] The CAI catalyst can be any catalyst known to a person skilled in the art.

[0040] In particular, the CAI catalyst can be selected from:

[0041] - zirconia-supported molybdenum and potassium-based catalysts such as K2MoO4 / ZrO2, as described in document WO 2019 / 122072;

[0042] - Molybdenum and potassium-based catalysts of the Mo-SK and / or Mo-OK type on a hydroxyapatite support such as K2MoS4 / CaiO(PO4)6(OH)2 or K2MoO4 / CaiO(PO4)6(OH)2, as described in document WO 2014 / 154885;

[0043] - the catalysts described in US patent application 2010 / 0286448 composed of a porous support such as SiO2, TiO2, silico-aluminas, zeolites and carbon nanotubes, on which a metal has been electrolytically deposited; K2MoO4, as well as another metal oxide acting as a promoter, are then impregnated on this support;

[0044] - Mo and K-based catalysts (in particular K2MoO4) promoted by TeO2 and supported such as K2MoO4 / TeO2 / SiO2, described in US document 2010 / 094059;

[0045] - several catalysts and in particular a catalyst comprising an active component based on Mo-OK, an active promoter and possibly a support, as described in application WO 2005 / 040082. The exemplified catalysts are K2MoO4 / Fe2O3 / NiO or K2MoO4 / CoO / CeO2 / SiO2, each supported on silica.

[0046] Advantageously, the CAI catalyst is chosen from catalysts comprising at least one active component based on molybdenum, preferably based on molybdenum and potassium, more preferably based on molybdenum, oxygen and potassium of the Mo-OK type, optionally on a support, preferably a metal oxide, more preferably a metal oxide in which the metal(s) are chosen from Al, Si, Mg, Ca, Ti, Zr, Ce, V, Cr, Mn, Zn, Ga, Ge, Sn, Bi, Y, Nb and La and their mixtures, even more preferably chosen from Zr, Al, Ti, Si and their mixtures, better the support is chosen from ZrO2, Al2O3, TiO2 and SiO2, better still the support is chosen from ZrO2 and Al2O3.

[0047] Preferably, the active component is K2MoO4.

[0048] Preferably, the CAI catalyst comprises a support, preferably chosen between ZrO2 and Al2O3.

[0049] In a particularly preferred manner, the CAI catalyst is chosen from K^oOV ZrO2 and K2MoO4 / A12O3.

[0050] The reaction temperature can vary over wide ranges, for example between 250 and 900°C, depending on the target CO2 conversion rate and the catalyst used. The pressure can also vary from atmospheric pressure to 100 bar, although pressures of 20 bar or less are preferred.

[0051] Step b) can be implemented.

[0052] Preferably, the mixture obtained at the end of step a) is dried. In other words, according to this embodiment, step b) is carried out, i.e., it is not optional.

[0053] Steps a) and b) are generally not carried out when the carbon dioxide is carbon monoxide. In other words, steps a) and b) are not carried out when carbon monoxide is the only carbon dioxide initially involved in the process according to the invention. Indeed, the objective of step a) is to increase the CO / CO2 ratio when carbon dioxide is present.

[0054] As previously stated, the method according to the invention comprises:

[0055] c) reaction of at least one carbon oxide (OC), possibly from step a) or step b), hydrogen sulfide (H2S) and dihydrogen (H2) in the presence of at least one CA2 catalyst, the molar ratio OC / H2 / H2S being 1 / X / Y, with X varying from 0 to 10 and Y varying from 1 to 4, to obtain a stream (M) comprising at least methyl mercaptan, non-condensable products and water.

[0056] Thus, carbon oxide (CO) can be carbon monoxide alone, or carbon oxide (CO) can be carbon dioxide or a mixture of carbon dioxide and carbon monoxide.

[0057] When carbon oxide (CO) is carbon dioxide or a mixture of carbon dioxide and carbon monoxide, then it can be from step a) or step b).

[0058] Carbon monoxide, hydrogen sulfide, and dihydrogen are advantageously supplied continuously to the reactor(s) in which the process according to the invention is implemented. Advantageously, the carbon monoxide, hydrogen sulfide, and dihydrogen are in liquid, solid, or gaseous form, preferably in gaseous form.

[0059] The CA2 catalyst can be any catalyst known to a person skilled in the art.

[0060] In particular, the CA2 catalyst can be chosen from those as described above.

[0061] Advantageously, the CA2 catalyst is chosen from catalysts comprising at least one active component based on molybdenum, preferably based on molybdenum and potassium, more preferably based on molybdenum, oxygen and potassium of the Mo-OK type, optionally on a support, preferably a metal oxide, more preferably a metal oxide in which the metal(s) are chosen from Al, Si, Mg, Ca, Ti, Zr, Ce, V, Cr, Mn, Zn, Ga, Ge, Sn, Bi, Y, Nb and La and mixtures thereof, even more preferably chosen from Zr, Al, Ti, Si and mixtures thereof, better the support is chosen from ZrO2, Al2O3, TiO2 and SiO2, better still the support is chosen from ZrO2 and Al2O3.

[0062] Preferably, the active component is K2MoO4.

[0063] Preferably, the CA2 catalyst comprises a support, preferably chosen between ZrO2 and Al2O3.

[0064] In a particularly preferred manner, the CA2 catalyst is chosen from among IQMoOV ZrO2 and K2MOO4 / AI2O3.

[0065] According to a particular embodiment, when steps a) and b) are implemented, then the CA2 catalyst is the CAI catalyst used in step a).

[0066] During step c), the molar ratio OC / H2 / H2S is 1 / X / Y, with X varying from 0 to 10 and Y varying from 1 to 4.

[0067] Thus, the molar ratio OC / H2 / H2S varies from 1 / 0 / 1 to 1 / 10 / 4.

[0068] Advantageously, X varies from 0 to 3, preferably from 0.1 to 3, more preferably from 1 to 3.

[0069] Advantageously, Y varies from 1 to 2, preferably Y is equal to 1.

[0070] Thus, according to a preferred embodiment, the OC / H2 / H2S molar ratio varies from 1 / 0 / 1 to 1 / 3 / 3, preferably from 1 / 0.1 / 1 to 1 / 3 / 2, more preferably from 1 / 1 / 1 to 1 / 3 / 1.

[0071] According to a particular embodiment, when the carbon oxide is carbon monoxide alone, then X can be equal to 0. In this particular embodiment, the molar ratio OC / H2 / H2S can then vary from 1 / 0 / 1 to 1 / 0 / 10, preferably from 1 / 0 / 1 to 1 / 0 / 2, more preferably it is equal to 1 / 0 / 1.

[0072] The reaction temperature in step c) advantageously ranges from 200 to 500°C, preferably from 250 to 400°C, and more preferably from 300 to 350°C. For reasons of conversion for the lower limit and material strength for the upper limit, a range of 250 to 400°C, preferably from 300 to 350°C, is preferred.

[0073] The reaction in step c) can be carried out indifferently at atmospheric pressure, under pressure, or even under vacuum, the person skilled in the art knowing how to adapt the reaction pressure conditions according to the nature of the reactants used, the reaction temperatures chosen, the flow rates and the conversion rates and yields targeted.

[0074] Advantageously, the pressure during step c) ranges from 0.1 to 5 MPa, preferably from 0.7 to 2 MPa, more preferably from 0.8 to 1.5 MPa, even more preferably from 0.9 to 1.1 MPa.

[0075] Preferably, the reaction of step a) and / or step c) can take place in fixed-bed, multitubular, microchannel, catalytic wall or fluidized bed, isothermal or adiabatic tubular reactors.

[0076] As previously stated, the method according to the invention comprises:

[0077] d) purification of the stream (M) to obtain a liquid stream (Ml) comprising at methyl mercaptan and water and a gaseous stream (M2) comprising at least said non-condensable products and water.

[0078] This purification step allows the stream (M) to be separated into two streams, the liquid stream (M1), comprising at least methyl mercaptan and water, and the gaseous stream (M2) comprising at least said non-condensable products and water.

[0079] The stream (M1) includes, in particular, the majority of the water (i.e., more than 50%, preferably more than 90% of the total quantity of water in the stream (M)). The stream (M2) includes, in particular, less than 10%, preferably less than 5%, of the total quantity of water in the stream (M) (this may be residual or trace water).

[0080] The flux (Ml) may include, in addition to methyl mercaptan and water, dimethyl sulfide (DMS).

[0081] The purification step may include one or more condensation steps, optionally followed by one or more decantation steps, optionally followed by one or more distillation steps. Preferably, said purification step (d) includes at least one condensation step (in particular as described below) and optionally one distillation step (in particular as described below).

[0082] Preferably, the flux (M) is condensed.

[0083] Any type of condenser can be used for this operation, such as plate or shell and tube heat exchangers. Preferably, the condenser is a separate-fluid type, meaning there is no contact between the gases to be condensed and the refrigerant. The refrigerant can be a liquid or a gas, such as air, water, glycols, brine, ammonia, Freons, or oils.

[0084] The condensation temperature can range from 20°C to 70°C, preferably from 30°C to 60°C. The pressure can range from 1 bar absolute to 100 bar absolute. The objective is to condense a maximum amount of methyl mercaptan and water relative to the non-condensable compounds, which will allow for easy separation of the liquid and gaseous phases.

[0085] Non-condensable products (or compounds) include, in particular, compounds remaining in a gaseous state at the temperatures and pressures of said production process, especially after the condensation step.

[0086] Non-condensable compounds may include, in particular, unreacted carbon oxide(s), i.e., carbon monoxide and / or carbon dioxide, unreacted dihydrogen, unreacted hydrogen sulfide, possibly carbon oxysulfide (COS), and any other inert non-condensable compound produced or introduced during said process. Preferably, non-condensable compounds are understood to mean unreacted carbon oxide(s), unreacted dihydrogen, unreacted hydrogen sulfide, and possibly carbon oxysulfide (COS).

[0087] According to step e), the stream (M2) from step d) is then recycled to step c), the recycling including at least one drying step. The stream (M2) may be recycled in whole or in part, preferably the entire stream (M2) is recycled.

[0088] This drying step is particularly important in the process according to the invention because it allows for improved productivity in methyl mercaptan.

[0089] Drying during this recycling allows almost all of the water from the stream (M2) to be eliminated.

[0090] Preferably, the recycling further includes a purge to remove the methane that may be produced during the reaction in step c).

[0091] As previously stated, the method according to the invention comprises:

[0092] f) optionally further purification of said stream (Ml) to obtain a stream (P) comprising at least methyl mercaptan.

[0093] This step f) allows obtaining a stream (P) comprising enriched methyl mercaptan.

[0094] Preferably, the additional purification of said stream (Ml) is carried out. In other words, according to this embodiment, step f) is implemented, i.e., it is not optional.

[0095] Advantageously, this additional purification can be carried out by decantation and / or distillation. In particular, it allows the removal of water and / or dimethyl sulfide that may be present in the stream (Ml). It can be done by decantation, for example to remove water (an aqueous phase and an organic phase including methyl mercaptan are obtained), and / or by distillation, for example to remove water and / or dimethyl sulfide.

[0096] During distillation, the pressure can range from 0.05 to 40 absolute bars, preferably from 1 to 25 absolute bars and / or the temperature can range from -60°C to +60°C, preferably from 10 to 50°C, at the top of the column; and from +20°C to +200°C, preferably from 20°C to 100°C, at the bottom of the column.

[0097] Preferably, the additional purification includes at least one decantation step and at least one distillation step.

[0098] The process according to the invention may further include: g) optionally drying the methyl mercaptan obtained at the end of step f).

[0099] Advantageously, the methyl mercaptan obtained at the end of step f) is dried.

[0100] At the end of the process, the methyl mercaptan is recovered, according to step h).

[0101] The drying steps b), e), and g) according to the invention can be carried out identically or differently from one another. In particular, reactive and consumable desiccants (e.g., sulfuric acid, calcium chloride, phosphoric anhydride), or regenerable moisture adsorbents (e.g., activated alumina, activated clay, molecular sieves, silica gel), or regenerable absorbent liquids (e.g., glycols (TEG, DEG), propylene carbonate), or condensers, or membranes can be used. Azeotropic distillation, in particular as described in WO 2022 / 129801, can also be used.

[0102] Activated alumina generally refers to a moisture adsorbent made of highly porous aluminum oxide with a very large specific surface area. It is highly resistant to mechanical and thermal shocks as well as abrasion. It is supplied in beads of uniform diameters, which limits preferential flow paths in a bed.

[0103] It can be used to dry all types of gases. It is frequently used in pressure cycle dryers (PSA).

[0104] On compressed air, it makes it possible to produce air with a dew point below -70°C.

[0105] Activated clay generally refers to natural clay that has been dried to give it a moisture-absorbing property. It has good adsorption capacity at room temperature, does not degrade when wet, and is easily regenerated by heating. It is inert, has no impact on health or the environment, and is generally inexpensive.

[0106] Molecular sieves generally refer to synthetic crystalline zeolites, the arrangement of atoms of which defines cavities of uniform dimensions. They only allow the passage of molecules smaller than or the same size as these cavities.

[0107] For water adsorption, the following molecular sieves are generally used:

[0108] - 3A: drying of unsaturated hydrocarbons

[0109] - 4A: drying of closed circuits

[0110] - 13X: drying of gases in general and of natural gas in particular.

[0111] Silica gel is generally obtained by precipitation of silica from a sodium silicate solution, using sulfuric acid. This leads to a very porous product, capable of adsorbing approximately 30% of its weight in water at room temperature.

[0112] Silica gel is normally colorless, but by incorporating approximately 1% cobalt chloride, it turns blue when dry and pink when wet, i.e., close to saturation. This color indication is very useful for indicating when to replace or regenerate the desiccant.

[0113] Silica gel can be regenerated by heating, but this causes it to disintegrate and limits its future adsorption capacity. The regeneration temperature must always remain below 120°C.

[0114] Calcium chloride is generally capable of absorbing up to 4 to 5 times its weight in water. It becomes deliquescent and dissolves in the absorbed water. Under these conditions, it is then not regenerable.

[0115] Calcium chloride was long used to dehydrate oil drilling gases before being replaced by glycol processes. It remains recommended for small units.

[0116] Glycols are liquids generally used to dehydrate gases in large-capacity units. These units are easy to operate and readily automated. The process is continuous, with an absorption section where the gas is dehydrated and a regeneration section where the glycol is freed of the absorbed water.

[0117] The glycols used are mainly DEG (diethylene glycol), TEG (triethylene glycol) and TREG (tetraethylene glycol).

[0118] Molecular sieves are particularly preferred for carrying out the drying according to the invention.

[0119] According to a first preferred embodiment, the process for preparing methyl mercaptan according to the invention comprises at least the following steps:

[0120] a) reaction of at least one carbon oxide, selected from carbon dioxide and a mixture of carbon dioxide and carbon monoxide, and dihydrogen in the presence of at least one CAI catalyst to obtain a mixture comprising carbon monoxide, carbon dioxide, dihydrogen and water;

[0121] b) optionally drying the mixture obtained at the end of step a) to obtain a mixture comprising carbon monoxide, carbon dioxide, and dihydrogen;

[0122] c) reaction of at least one carbon oxide (OC), possibly from step a) or step b), hydrogen sulfide (H2S) and dihydrogen (H2) in the presence of at least one CA2 catalyst, the molar ratio OC / H2 / H2S being 1 / X / Y, with X varying from 0 to 10 and Y varying from 1 to 4, to obtain a flux (M) comprising at least methyl mercaptan, non-condensable products and water;

[0123] d) purification of the stream (M) to obtain a liquid stream (Ml) comprising at least methyl mercaptan and water and a gaseous stream (M2) comprising at least said non-condensable products and water;

[0124] e) recycling said stream (M2) from step d) to step c) including at least one drying;

[0125] f) optionally further purification of said stream (Ml) to obtain a stream (P) comprising at least methyl mercaptan;

[0126] g) optionally drying of the methyl mercaptan obtained at the end of step f);

[0127] h) recovery of methyl mercaptan.

[0128] According to a second preferred embodiment, the process for preparing methyl mercaptan according to the invention comprises at least the following steps:

[0129] c) reaction of at least one carbon oxide (CO), possibly from step a) or step b), hydrogen sulfide (H2S) and dihydrogen (H2) in the presence of at least one CA2 catalyst, the molar ratio OC / H2 / H2S being 1 / X / Y, with X varying from 0 to 10 and Y varying from 1 to 4, to obtain a flux (M) comprising at least methyl mercaptan, non-condensable products and water;

[0130] d) purification of the stream (M) to obtain a liquid stream (Ml) comprising at least methyl mercaptan and water and a gaseous stream (M2) comprising at least said non-condensable products and water;

[0131] e) recycling said stream (M2) from step d) to step c) including at least one drying;

[0132] f) optionally further purification of said stream (Ml) to obtain a stream (P) comprising at least methyl mercaptan;

[0133] g) optionally drying of the methyl mercaptan obtained at the end of step f);

[0134] h) recovery of the methyl mercaptan.

[0135] Between the two embodiments above, the first embodiment is preferred.

[0136] The following examples illustrate the invention without however limiting its scope as defined by the claims annexed to the description of the present invention. Examples

[0137] Example 1: preparation of the K2MoO4 catalyst supported on alumina: K2MoO4 / Al2Q3

[0138] The catalyst was prepared by the dry impregnation method. For this, a quantity of potassium molybdate (K2MoO4) was dissolved in water, then this solution was impregnated onto alumina, followed by maturation for 2.5 hours, drying at 100°C in an oven for 15 hours, and then calcination at 500°C under a stream of air for 4 hours. The concentration of the impregnation solution was chosen so that the final molybdenum content in the catalyst was 8% by mass.

[0139] Example 2: preparation of the K₂MoO₄ catalyst supported on zirconia: K₂MoO₄ / ZrO₂

[0140] The catalyst was prepared by the dry impregnation method. For this purpose, a quantity of potassium molybdate (K2MoO4) was dissolved in water, and this solution was then impregnated onto zirconia, followed by a maturation period of 2.5 hours, drying at 100°C in an oven for 15 hours, and then calcination at 500°C under a stream of air for 4 hours. The concentration of the impregnation solution was chosen so that the final molybdenum content in the catalyst was 8% by mass. Example 3#: Catalytic Test 1

[0141] The catalyst used is that of example 1: K2MoO4 / A12O3.

[0142] Before testing, the catalyst was activated in situ with a procedure consisting of a first drying step with nitrogen sweeping at 250°C, followed by a sulfidation with H2S at the same temperature for 1 hour and ending with a reduction / sulfurization step with H2 / H2S at 350°C for 1 hour.

[0143] The performance of the catalyst was then evaluated for the production reaction of methyl mercaptan in a fixed-bed reactor with a catalyst volume of 3 mL, a temperature of 320°C, under a pressure of 10 bar (1 MPa), with different volumetric compositions of feed gas CO2 / H2 / H2S and a GHSV (Gas Hourly Space Velocity) of 1166 h1. The reactants and products were analyzed online by gas chromatography.

[0144] Three different CO2 / H2 / H2S feed gas volume compositions were implemented: 1 / 3 / 1, 1 / 2 / 1, and 1 / 1 / 1. During testing, a Trockenperlen-type silica gel was used when a drying step was included. In this case, the stream to be dried passes through a dedicated vessel containing the Trockenperlen-type silica gel to carry out the drying step.

[0145] Three processes for the production of methyl mercaptan have been implemented:

[0146] - a comparative IP process not including step e) of recycling with drying;

[0147] - a comparative process P2, comprising the same steps as those of process PI, with, in addition, a recycling stage but without drying, and

[0148] - a P3 process according to the invention, comprising the same steps as those of the PI process and further comprising a recycling step including drying (step e)).

[0149] The results have been summarized in the following Table 1:

[0150] [Tables 1] CO2 / H2 / H2S feed composition (molar ratio) Productivity in M ​​eSH (gh 1 .Lcat 1 ) for process P 1 (comp) Productivity in M ​​eSH (gh 1 .Lcat 1 ) for process P 2 (comp) Productivity in M ​​eSH (gh 1 .Lcat 1 ) for process P 3 (inv) 1 / 3 / 17 31 51 1 / 2 / 19 40 64 1 / 1 / 18 54 91

[0151] The results presented in Table 1 above show that the process according to the invention makes it possible to obtain a significantly improved methylmercaptan productivity compared to the comparative process, with different molar ratios. Example 4#: Catalytic Test 2

[0152] The catalyst used is that of example 2: K2MoO4 / ZrO2

[0153] Before testing, the catalyst was activated in situ with a procedure consisting of a first drying step with nitrogen sweeping at 250°C, followed by a sulfidation with H2S at the same temperature for 1 hour and ending with a reduction / sulfurization step with H2 / H2S at 350 °C for 1 hour.

[0154] The performance of the catalyst was then evaluated for the production reaction of methyl mercaptan in a fixed-bed reactor with a catalyst volume of 3 mL, a temperature of 320°C, under a pressure of 10 bar (1 MPa), with a feed gas volume composition of CO / H2 / H2S in the molar ratio 1 / 0 / 1 and a GHSV (Gas Hourly Space Velocity) of 1000 h1. The reactants and products were analyzed online by gas chromatography.

[0155] The process for the production of methyl mercaptan which has been implemented does not include steps a) and b). It includes steps c) to h) as defined above in the description.

[0156] The results have been summarized in the following table 2:

[0157] [Tables2] Molar conversion to CO (%) Molar selectivity to MeSH (%) Molar selectivity to COS (%) Molar selectivity to CO2 (%) 90 30 36 29

[0158] The results presented in Table 2 above show that the process according to the invention achieves excellent molar conversion to carbon monoxide, significantly improved compared to the molar conversions mentioned in the prior art, which are generally around 60 to 70%. Furthermore, the molar selectivities for MeSH, COS, and CO2 are good, given the absence of hydrogen as an initial reagent.

Claims

Demands

1. A process for preparing methyl mercaptan, comprising at least the following steps: a) optionally reacting at least one carbon oxide, selected from carbon dioxide and a mixture of carbon dioxide and carbon monoxide, and dihydrogen in the presence of at least one CAI catalyst to obtain a mixture comprising carbon monoxide, carbon dioxide, dihydrogen and water; b) optionally drying the mixture obtained at the end of step a) to obtain a mixture comprising carbon monoxide, carbon dioxide, and dihydrogen; c) reaction of at least one carbon oxide (CO), possibly from step a) or step b), hydrogen sulfide (H2S) and dihydrogen (H2) in the presence of at least one CA2 catalyst, the molar ratio CO / H2 / H2S being 1 / X / Y, with X varying from 0 to 10 and Y varying from 1 to 4, to obtain a flux (M) comprising at least methyl mercaptan, non-condensable products and water;d) purification of the stream (M) to obtain a liquid stream (Ml) comprising at least methyl mercaptan and water and a gaseous stream (M2) comprising at least said non-condensable products and water; e) recycling of said stream (M2) from step d) to step c) including at least one drying; f) optionally further purification of said stream (Ml) to obtain a stream (P) comprising at least methyl mercaptan; g) optionally drying of the methyl mercaptan obtained at the end of step f); h) recovery of the methyl mercaptan.

2. A process according to claim 1, characterized in that the mixture obtained at the end of step a) is dried.

3. A process according to claim 1 or 2, characterized in that the CA2 catalyst is selected from catalysts comprising at least one active component based on molybdenum.

4. A method according to any one of the preceding claims, characterized in that when steps a) and b) are carried out, So the CA2 catalyst is the CAI catalyst used in step n A

5. aj. Method according to any one of the preceding claims, characterized in that X varies from 0 to 3, preferably from 0.1 to 3, more preferably from 1 to 3.

6. A method according to any one of the preceding claims, characterized in that Y varies from 1 to 2, preferably Y is equal to 1.

7. A process according to any one of the preceding claims, characterized in that the reaction temperature in step c) ranges from 200 to 500°C, preferably from 250 to 400°C, more preferably from 300 to 350°C.

8. A method according to any one of the preceding claims, characterized in that the pressure during step c) ranges from 0.1 to 5 MPa, preferably from 0.7 to 2 MPa, more preferably from 0.8 to 1.5 MPa, even more preferably from 0.9 to 1.1 MPa.

9. A process according to any one of the preceding claims, characterized in that the additional purification is carried out by distillation and / or decantation.

10. A process according to any one of the preceding claims, characterized in that the methyl mercaptan obtained at the end of step f) is dried.