Method for drying methyl mercaptan by azeotropic distillation

Abstract

The present invention relates in particular to a method for drying methyl mercaptan by azeotropic distillation, which comprises the steps of: 1) introducing a stream (A) containing methyl mercaptan and water into a distillation column (1); 2) distilling the stream (A) in the distillation column (1); 3) recovering the distillate (B) as a gas, preferably at the top of the distillation column; 4) condensing the distillate (B), preferably in a condenser (2) to obtain a liquid condensate (C); 5) separating the condensate (C), preferably using a decanter (3), to obtain two separate liquid phases: an aqueous phase (D) and an organic phase (E) containing methyl mercaptan; 6) optionally introducing all or part of the organic phase (E) into the distillation column (1) as reflux; and 7) recovering the dried stream (F) containing methyl mercaptan, preferably at the bottom of the distillation column. The present invention also relates to a method for producing methyl mercaptan, which comprises this drying method.

Description

Technical Field

[0001] The present invention particularly relates to a method for drying methyl mercaptan by azeotropic distillation. The present invention also relates to a method for producing methyl mercaptan including the above drying method.

Background Art

[0002] Mercaptans are of great industrial interest and are currently widely used in the chemical industry, particularly as starting materials in the synthesis of more complex organic molecules. For example, methyl mercaptan (CH3SH or MeSH) is used as a starting material in the synthesis of methionine, an essential amino acid for animal nutrition. Methyl mercaptan is also used, among other applications, in the synthesis of dialkyl disulfides, particularly dimethyl disulfide (DMDS), which is a sulfurizing agent for hydrotreating catalysts for petroleum fractions.

[0003] The industrial synthesis of methyl mercaptan is generally carried out by two known routes. The first is what is called the so-called methanol route, in which methyl mercaptan is produced from methanol and hydrogen sulfide by the following reaction (1). CH3OH + H2S → CH3SH + H2O (1) In this method, side reactions occur and dimethyl sulfide is produced by the following reaction (2). CH3OH + CH3SH → CH3SCH3 + H2O (2)

[0004] The second route is what is called the so-called carbon monoxide route, and it enables the production of methyl mercaptan from carbon monoxide, hydrogen, hydrogen sulfide, and / or sulfur, for example, by the following reactions (3) and (4). CO + 2H2 + H2S → CH3SH + H2O (3) CO + S + 3H2 → CH3SH + H2O (4)

[0005] As shown by the aforementioned reaction, the synthesis of methyl mercaptan involves the production of water, regardless of the route used. Therefore, it is necessary to next separate the methyl mercaptan from the water. However, water is slightly soluble in methyl mercaptan. Therefore, some water always remains in the resulting product and it is necessary to remove it as much as possible.

[0006] In fact, there are industrial applications where it is desirable for the residual water content in methyl mercaptan to be very low. For example, in the synthesis of dimethyl disulfide by sulfur oxidation of methyl mercaptan, water can reduce the activity of the catalyst for this reaction.

[0007] In addition, when the residual water content in methyl mercaptan is high (especially on the order of thousands of ppm) and the temperature is less than about 16 °C, some of the water cannot dissolve and can decant, promoting the formation of solid methyl mercaptan hydrate. These solid residues pose a risk of clogging the equipment and cause significant safety issues related to facilities and transportation.

[0008] To avoid such risks, the drying of methyl mercaptan has conventionally been carried out by adsorption of water onto molecular sieves. However, this method has many drawbacks.

[0009] For example, the regeneration of molecular sieves is carried out at high temperatures, resulting in the formation of undesirable by-products such as dimethyl sulfide.

[0010] Furthermore, when methyl mercaptan is produced by the methanol route, if trace amounts of methanol are present in the methyl mercaptan to be dried, it can extremely reduce the water adsorption capacity of the molecular sieve. This requires an increased frequency of regeneration, raises the manufacturing cost, and increases the formation of undesirable by-products.

[0011] Therefore, there is a need for methyl mercaptan with a low water content, preferably as low a water content as possible.

[0012] There is also a need for a method for drying methyl mercaptan that is efficient and that makes it possible to avoid all or some of the drawbacks of known drying methods. SUMMARY OF THE INVENTION

[0013] One object of the present invention is to provide a method for drying methyl mercaptan, wherein the method makes it possible to obtain methyl mercaptan having a low water content, preferably a water content of 1500 ppm or less.

[0014] Another object of the present invention is to provide a method that can completely or partially overcome the drawbacks of drying methods used heretofore, and in particular the drawbacks of drying methods using molecular sieves.

[0015] Another object of the present invention is to provide a method in which the drying method is controlled and / or does not change over time.

[0016] An object of the present invention is to provide a method for preparing methyl mercaptan, wherein the method makes it possible to obtain methyl mercaptan having a low water content, preferably a water content of 1500 ppm or less.

[0017] An object of the present invention is to provide an integrated process for preparing methyl mercaptan that is more environmentally friendly and more economical.

[0018] The present invention satisfies all or some of the above objects.

[0019] Methyl mercaptan and water can form an azeotropic mixture, preferably a heteroazeotropic mixture. The term "azeotropic mixture" specifically refers to a liquid mixture that boils while maintaining a certain composition (the gas phase has the same composition as the liquid phase). Preferably, methyl mercaptan and water form an azeotropic mixture at a pressure of 0.05 bar (absolute pressure) to 75 bar (absolute pressure), preferably 1 bar (absolute pressure) to 30 bar (absolute pressure), and more preferably 5 bar (absolute pressure) to 15 bar (absolute pressure).

[0020] Therefore, the inventors have discovered that it is possible to dry methyl mercaptan by distillation, preferably azeotropic distillation.

[0021] Surprisingly, the method according to the present invention actually enables efficient drying of methyl mercaptan. In particular, the drying method according to the present invention makes it possible to obtain methyl mercaptan containing 0 ppm to 1500 ppm of water.

[0022] Unlike molecular sieves, the drying method according to the present invention makes it possible to maintain a drying method that does not change over time and can be easily controlled according to operating conditions, particularly temperature and pressure conditions. In particular, it is possible to control and / or select the water content of the methyl mercaptan obtained by the drying method according to the present invention.

[0023] Furthermore, the drying method avoids the regeneration cycle of molecular sieves and thus avoids the further generation of dimethyl sulfide (DMS), which is an undesirable by-product (incinerated as waste in some cases).

[0024] The drying method according to the present invention is easy to implement and can be adapted to any equipment for the production of methyl mercaptan by either the methanol route or the carbon dioxide route. Therefore, it is possible to obtain an integrated process for the production of methyl mercaptan that is more environmentally friendly and more economical.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0026] According to the present invention, the unit ppm (parts per million) represents a mass fraction.

[0027] According to the present invention, the expression "between X and X" includes the recited limit values.

[0028] The term "drying" means the removal of water.

[0029] The term "dried methyl mercaptan" particularly means methyl mercaptan obtained from the drying method according to the present invention. The stream (F) defined below may contain or consist of the dried methyl mercaptan.

[0030] Particularly, the term "dried methyl mercaptan" means methyl mercaptan containing 0 ppm to 1500 ppm, preferably 0 ppm to 1000 ppm, for example 10 ppm to 800 ppm, and more preferably 40 ppm to 800 ppm of water, based on the total weight of methyl mercaptan and water.

[0031] Also, the term "dried methyl mercaptan" may be understood to mean a composition comprising methyl mercaptan and water in an amount of 0 ppm to 1500 ppm, preferably 0 ppm to 1000 ppm, for example 10 ppm to 800 ppm, more preferably 40 ppm to 800 ppm, based on the total weight of methyl mercaptan and water.

[0032] Optionally, the dried methyl mercaptan may contain trace amounts of methanol, H2S and sulfur by-products. The term "traces" of a compound is understood to mean an amount of 0 ppm to 1000 ppm. In particular, the sulfur by-products are dimethyl sulfide and dimethyl disulfide.

[0033] The dried methyl mercaptan may be in liquid or gaseous form, preferably liquid.

[0034] The term "methyl mercaptan purification step" particularly means a step for producing a stream rich in methyl mercaptan. The term "stream rich in methyl mercaptan" particularly means a stream containing a weight percentage of methyl mercaptan greater than the weight percentage of methyl mercaptan in the total weight of the stream before the purification step.

[0035] [Method for Drying Methyl Mercaptan] The present invention relates to a method for drying methyl mercaptan, comprising the following steps. 1) A step of introducing a stream (A) containing methyl mercaptan and water into a distillation column (1) 2) A step of distilling the stream (A) in the distillation column (1) 3) A step of recovering the distillate (B) as a gas, preferably at the top of the distillation column 4) A step of condensing the distillate (B) preferably in a condenser (2) to obtain a liquid condensate (C) 5) Separating the condensate (C), preferably using a decanter (3), to obtain an aqueous phase (D) and an organic phase (E) containing methyl mercaptan, which are two separate liquid phases. 6) Optionally introducing all or part of the organic phase (E) as reflux into the distillation column (1). 7) Recovering a stream (F) containing dried methyl mercaptan, preferably at the bottom of the distillation column (1).

[0036] The stream (F) corresponds to dried methyl mercaptan, especially as defined above. This is preferably recovered from the distillation column at the bottom of the distillation column.

[0037] The distillation in step 2) is carried out at a pressure of 0.05 bar (absolute pressure) to 75 bar (absolute pressure), preferably 1 bar (absolute pressure) to 30 bar (absolute pressure), more preferably 5 bar (absolute pressure) to 15 bar (absolute pressure), for example, about 10 bar (absolute pressure), 11 bar (absolute pressure), 12 bar (absolute pressure), 13 bar (absolute pressure), 14 bar (absolute pressure) or 15 bar (absolute pressure).

[0038] The distillation in step 2) can be carried out at a temperature of 20°C to 200°C, preferably 60°C to 100°C, more preferably 65°C to 95°C, for example, 70°C to 90°C. Preferably, the distillation in step 2) is carried out at a temperature of 40°C to 200°C at the bottom of the distillation column, preferably 80°C to 100°C, and at a temperature of 20°C to 100°C at the top of the distillation column, preferably 60°C to 80°C.

[0039] Particularly preferably, the distillation in step 2) is carried out at a pressure of 5 bar (absolute pressure) to 15 bar (absolute pressure) and a temperature of 60°C to 100°C. In particular, the distillation in step 2) is carried out at a pressure of 5 bar (absolute pressure) to 15 bar (absolute pressure) and a temperature of 70°C to 90°C. In particular, the distillation in step 2) is an azeotropic distillation.

[0040] The distillation in step 2) may be carried out in any known type of distillation column. This may be a tray column (e.g., a distillation column having sieve trays with caps, sieve trays including valves, or perforated sieve trays), or a packed column (e.g., a distillation column having bulk packing or structured packing). The distillation in step 2) may preferably be carried out in a tray column having 5 to 50 trays, more preferably 10 to 40 trays, for example, 25 to 30 trays. The distillation in step 2) may be carried out in a divided wall column (DWC). The dividing wall may be fixed or movable, and may, for example, be provided with structured packing or bulk packing.

[0041] Stream (A) is preferably a liquid or a gas.

[0042] Preferably, stream (A) contains, or consists of, methyl mercaptan, water, and optionally trace amounts of methanol, H2S, and sulfur by-products.

[0043] Stream (A) may contain at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, for example at least 99% by weight of methyl mercaptan, based on the total weight of methyl mercaptan and water.

[0044] Stream (A) may contain at least 0.15% by weight of water, preferably at least strictly more than 0.15% by weight of water, based on the total weight of methyl mercaptan and water. Stream (A) may contain up to 30% by weight, preferably up to 10% by weight of water, based on the total weight of methyl mercaptan and water. Stream (A) may contain from 0.15% by weight, preferably strictly more than 0.15% by weight and up to 30% by weight of water, based on the total weight of methyl mercaptan and water.

[0045] Stream (A) may contain from 0.15% by weight, preferably strictly more than 0.15% by weight and up to 10% by weight of water, based on the total weight of methyl mercaptan and water.

[0046] Preferably, stream (A) contains water in an amount of more than 0.15% by weight, preferably strictly more than 0.15% by weight and up to 5% by weight, based on the total weight of methyl mercaptan and water.

[0047] For example, stream (A) contains water in an amount of more than 0.15% by weight, preferably strictly more than 0.15% by weight and up to 2% by weight, for example from 0.15% to 1.5% by weight or from 0.15% to 1% by weight, based on the total weight of methyl mercaptan and water, the balance being presumably methyl mercaptan.

[0048] After the distillation step 2) of stream (A), a gaseous distillate (B) is obtained. This distillate (B) corresponds, in particular under the pressure and / or temperature conditions of the distillation step 2), to an azeotropic mixture, preferably a heterogeneous azeotropic mixture.

[0049] Thus, the distillation in step 2) makes it possible, in particular, to produce an azeotropic mixture (i.e., azeotropic distillation). Once recovered and condensed as a liquid (condensate (C)), it is obtained in a two-phase state, and these two phases can be easily separated, in particular by decantation.

[0050] The condensation step (4) of the distillate (B) may be carried out by any prior art. The condensation may be carried out in a condenser separate from or incorporated into the distillation column. A liquid condensate (C) is then obtained. The condensate (C) preferably contains two phases, one of which is an aqueous phase and the other is an organic phase (containing methyl mercaptan). During the condensation step (4), the temperature may be from 20°C to 50°C and / or the pressure may be from 5 bar (absolute pressure) to 15 bar (absolute pressure).

[0051] The distillate (B) and the condensate (C) preferably have the same composition.

[0052] In the separation step 5), any known method may be used. Most preferably, decantation is used. During the separation step, the temperature may be 20°C to 50°C and / or the pressure may be 5 bar (absolute pressure) to 15 bar (absolute pressure). At the end of step 5), two separated liquid phases, an aqueous phase (D) and an organic phase (E) containing methyl mercaptan, are obtained. According to one embodiment, the aqueous phase (D) contains water, preferably trace amounts of H2S, optionally preferably trace amounts of methyl mercaptan, and optionally preferably trace amounts of sulfur by-products.

[0053] H2S and, optionally, methyl mercaptan and sulfur by-products can be separated from the aqueous phase. This separation may be carried out using any known means, preferably stripping, which may be thermal stripping or stripping using an inert gas (e.g., stripping using nitrogen, methane or CO2). The gas phase then generates a vent, hereinafter referred to as vent E3.

[0054] According to one embodiment, vent E3 may be incinerated and / or the aqueous phase (D) may be discharged to the wastewater network.

[0055] According to another embodiment, vent E3 can be sent to a methanol absorption column to recover sulfur compounds such as H2S and / or methyl mercaptan contained in vent E3 by gas (vent)-liquid (methanol) extraction.

[0056] According to one embodiment, if the reflux step 6) is not carried out, the organic phase (E) is recovered at the end of step 5).

[0057] According to another embodiment, the organic phase (E) is used in whole or in part as the reflux of the distillation column (1).

[0058] In step 6), the reflux ratio may be 0 to 0.99, preferably 0 to 0.60. The term "reflux ratio" means the mass ratio [organic phase (E) / stream (A)].

[0059] Therefore, the method of the present invention enables the obtaining of dried methyl mercaptan as defined above.

[0060] The method according to the present invention may be carried out in a continuous or batch mode, preferably in a continuous mode.

[0061] During steps 1) to 7) of the method, the pressure may be from 0.05 bar (absolute pressure) to 75 bar (absolute pressure), preferably from 1 bar (absolute pressure) to 30 bar (absolute pressure), more preferably from 5 bar (absolute pressure) to 15 bar (absolute pressure), for example, about 10 bar (absolute pressure), 11 bar (absolute pressure), 12 bar (absolute pressure), 13 bar (absolute pressure), 14 bar (absolute pressure) or 15 bar (absolute pressure).

[0062] Preferably, a trace amount of methanol may be contained in stream (A) and / or distillate (B) and / or condensate (C) and / or aqueous phase (D) and / or stream (F).

[0063] According to one embodiment, stream (A) is connected to an apparatus for producing methyl mercaptan from methanol and hydrogen sulfide.

[0064] According to one embodiment, stream (A) is connected to an apparatus for producing methyl mercaptan from at least one of carbon monoxide, hydrogen and hydrogen sulfide and / or sulfur.

[0065] The present invention also relates to the use of azeotropic distillation for drying methyl mercaptan. In particular, said azeotropic distillation corresponds to the distillation described in step 2) of the drying method according to the present invention.

[0066] The present invention also relates to the dried methyl mercaptan as defined above.

[0067] [Method for preparing methyl mercaptan via the methanol route] The present invention relates to a method for producing methyl mercaptan, comprising the following steps. a) Reacting methanol with hydrogen sulfide to produce a preferably gaseous stream (M) containing methyl mercaptan, water, optionally unreacted H2S and sulfur by-products b) Optionally, condensing the stream (M) c) Optionally, performing at least one step of purifying the stream (M) to obtain a stream rich in methyl mercaptan d) Drying the stream obtained in step a), step b) or step c) by the above drying method

[0068] Preferably, in step c), the at least one purification step preferably corresponds to at least one phase separation step by decantation and / or at least one distillation step.

[0069] Step c) may in particular correspond to one or more phase separation steps (e.g., one or two decantation steps) and / or one or more distillation steps (e.g., one or two distillation steps).

[0070] In particular, after step c), a stream rich in methyl mercaptan and containing water is obtained.

[0071] Preferably, step c) makes it possible to remove H2S, sulfur by-products and most of the water from the stream (M) via one or more purification steps. Preferably, by step c), at least 50% by weight of water, for example at least 70% by weight or at least 90% by weight of water, is removed from the stream (M). H2S and sulfur by-products may remain in trace amounts at the end of step c).

[0072] Therefore, the method may include the following steps. a) Reacting methanol with hydrogen sulfide to produce a stream (M) containing methyl mercaptan, water, unreacted H2S and sulfur by-products b) Optionally, a step of condensing the stream (M) c1) A step of separating a gas stream (N) containing unreacted hydrogen sulfide, an aqueous stream (O), and a stream (P) containing methyl mercaptan, water, unreacted hydrogen sulfide, and sulfur by-products from the stream (M), preferably by decantation c2) A step of distilling the stream (P) to obtain a stream (R) containing hydrogen sulfide preferably at the top of the distillation column and a stream (S) containing methyl mercaptan, water, and sulfur by-products preferably at the bottom of the distillation column c3) A step of distilling the stream (S) to obtain a stream (T) containing methyl mercaptan and water preferably at the top of the distillation column and a stream (U) containing sulfur by-products preferably at the bottom of the distillation column c4) Optionally, a step of separating the methyl mercaptan in the stream (T) from water, preferably by decantation, to obtain a stream (V) containing methyl mercaptan and water and a stream (W) containing water d) A step of drying the stream (T) or the stream (V) by the drying method according to the present invention

[0073] Therefore, steps c1 to c4 are purification steps for obtaining a stream in which methyl mercaptan is gradually concentrated

[0074] The stream (M) and / or the stream (P) and / or the stream (T) and / or the stream (V) may preferably contain a trace amount of unreacted methanol in some cases

[0075] <Step a) - Reaction> In step a), methanol is reacted with hydrogen sulfide to produce a stream (M) containing methyl mercaptan, water, optionally unreacted H2S, and optionally sulfur by-products

[0076] Before step a), a gas stream of an H2S reagent and a methanol reagent may be prepared as follows

[0077] Liquid methanol is injected into gaseous H2S. This injection enables the methanol to vaporize partially or entirely. Subsequently, the mixture of H2S and methanol can be completely vaporized as necessary to obtain a total gas stream.

[0078] Therefore, preferably, a gas stream of H2S and methanol prepared as described above, or separate gaseous methanol and H2S are introduced into the reactor.

[0079] The reactor may be isothermal or adiabatic, and may be one equipped with trays, multi-tubular, or one equipped with a fixed bed. Preferably, an adiabatic reactor is selected.

[0080] The reaction temperature may be 200°C to 500°C, preferably 200°C to 400°C. Preferably, the reaction temperature is 200°C to 360°C. Exceeding this temperature may physically damage the catalyst (especially due to sintering and coking).

[0081] The pressure may be 1 bar (absolute pressure) to 40 bar (absolute pressure).

[0082] The molar ratio of H2S / methanol may be 1 to 50, preferably 1 to 25. H2S is preferably in excess relative to methanol. The reactor may preferably contain a catalyst for the methyl mercaptan production reaction in the gas phase. Among the catalysts that can be used, the following catalysts can be mentioned. - Alumina-based catalysts - Thorium dioxide ThO2 preferably deposited on a silicate carrier - Cadmium sulfide-based catalysts preferably on an alumina carrier - Catalysts based on oxides (MgO, ZrO2, rutile (R) and anatase (A) TiO2, CeO2, and γ-Al2O3) - A catalyst based on a metal oxide, preferably doped with an alkali metal (Li, Na, K, Rb, Cs) and optionally supported on SiO2, Al2O3 or Nb2O5 - A catalyst based on an alkali metal carbonate - A catalyst based on an alkali metal salt of a specific acid of a transition metal (Cr, Mo, W, Ni) impregnated on γ-alumina or other metal oxides - Potassium tungstate on alumina K2WO4 / Al2O3

[0083] Thus, a stream (M) containing alkyl mercaptan, water, optionally unreacted H2S and sulfur by-products is obtained.

[0084] <Step b) - Condensation> The stream (M) obtained at the end of step a) may optionally be condensed by any prior art, preferably using one or more condensers or economizers. During condensation, the stream (M) is cooled to the lowest possible temperature to maximize the removal of water, but must be maintained strictly above 16 °C to avoid the formation of solid hydrates of methyl mercaptan. Preferably, the stream (M) is condensed at a temperature of 20 °C to 70 °C, for example, 30 °C to 60 °C.

[0085] <Step c) - Purification> Preferably, in step c), the at least one purification step preferably corresponds to at least one phase separation step by decantation and / or at least one distillation step. Step c) may in particular correspond to one or more phase separation steps (e.g., one or two decantation steps) and / or one or more distillation steps (e.g., one or two distillation steps).

[0086] Preferably, step c) enables the removal of unreacted H2S and / or sulfur by-products and / or water from the stream (M) via one or more purification steps. In particular, after step c), a stream rich in methyl mercaptan is obtained.

[0087] Purification step c) may be carried out according to any prior art, particularly according to the following steps c1) to c4).

[0088] <Step c1 - Separation> In the separation step c1), preferably by decantation, a gas stream (N) containing unreacted hydrogen sulfide, an aqueous stream (O), and a stream (P) containing methyl mercaptan, water, unreacted hydrogen sulfide, and sulfur by - products are obtained.

[0089] Preferably, stream (M) is separated at a temperature of 20 °C to 70 °C, preferably 30 °C to 60 °C. The pressure may be from 1 bar (absolute pressure) to 40 bar (absolute pressure).

[0090] The obtained stream (P) may particularly be a gas or a liquid. When stream (P) is a gas, stream (N) and stream (P) may be mixed.

[0091] Particularly, preferably the liquid aqueous stream (O) contains at least 50 wt%, preferably at least 70 wt%, more preferably at least 90 wt% water relative to the total weight of water present in stream (M). Thus, the aqueous stream (O) may be sent to a degassing device. Subsequently, the degassed aqueous stream may be sent to wastewater treatment.

[0092] The gas stream (N) may be recycled to the reactor feed of step a). In this case, a purge of this stream (N) is carried out to avoid the accumulation of inert substances and / or impurities in this recycle loop. Examples of inert substances and / or impurities include methane, CO, CO2, H2, and N2. The gas stream obtained from this purge is called vent E1. When stream (N) and stream (P) are mixed, the same type of purge may be carried out to obtain a gas stream called vent E1'.

[0093] According to one embodiment, the vent E1 or vent E1' is sent for incineration.

[0094] According to another embodiment, the vent E1 or vent E1' may be sent to a methanol absorption column to recover sulfur compounds such as H2S and / or methyl mercaptan contained in the vent E1 or vent E1' by gas (vent)-liquid (methanol) extraction.

[0095] <Step c2 - Removal of H2S by distillation> Next, the stream (P) is distilled, and preferably a stream (R) containing hydrogen sulfide is obtained at the top of the distillation column, and preferably a stream (S) containing methyl mercaptan, water and sulfur by-products is obtained at the bottom of the distillation column. During distillation, the pressure may be from 1 bar (absolute pressure) to 40 bar (absolute pressure), and / or the temperature may be from -60°C to +60°C at the top of the distillation column and from +20°C to +200°C at the bottom of the distillation column.

[0096] The stream (R) containing H2S is recovered at the top of the distillation column and may optionally be recycled to the reactor feed for step a).

[0097] In particular, the distillation in step c2) makes it possible to remove the H2S remaining in the stream (P) (it is understood that a trace amount of H2S may remain in the stream (S)).

[0098] <Step c3 - Removal of sulfur by-products by distillation> The stream (S) is distilled, and preferably a stream (T) containing methyl mercaptan and water is obtained at the top of the distillation column, and preferably a stream (U) containing sulfur by-products is obtained at the bottom of the distillation column.

[0099] During distillation, the pressure may be from 1 bar (absolute pressure) to 40 bar (absolute pressure), and / or the temperature may be from +20°C to +100°C at the top of the distillation column and from +40°C to +200°C at the bottom of the distillation column.

[0100] In particular, the distillation in step c3) makes it possible to remove sulfur by-products remaining in the stream (S) (it is understood that a small amount of sulfur by-products may remain in the stream (T)).

[0101] <Separation of 4-methyl mercaptan and water in step c4> Before step c4), the stream (T) is cooled to as low a temperature as possible to maximize the removal of water, but must be kept strictly above 16 °C to avoid the formation of solid hydrates of methyl mercaptan. Preferably, the stream (T) is cooled to a temperature of 20 °C to 70 °C, for example 30 °C to 60 °C.

[0102] This cooling makes it possible to maximize the separation of water during step c4) while maintaining the temperature strictly above 16 °C to avoid the formation of solid hydrates of methyl mercaptan. Then, the separation of methyl mercaptan and the remaining water is preferably carried out by decantation, preferably obtaining a stream (V) containing liquid methyl mercaptan and water and a stream (W) containing preferably liquid water.

[0103] In particular, in step c4), the stream (W) contains at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight of the water present in the stream (T) with respect to the total weight of the water.

[0104] The stream (T) or the stream (V) corresponds to the stream (A) defined above.

[0105] Then, the obtained stream (V) or stream (T) can be dried according to the drying method of the present invention.

[0106] In the separation step c4), it is possible to recover the gas phase thus separated from both the stream (W) and the stream (V), both of which are liquids. This gas stream is referred to as vent E2.

[0107] According to one embodiment, the vent E2 is incinerated.

[0108] According to another embodiment, the vent E2 may be sent to a methanol absorption column to recover sulfur compounds such as H2S and / or methyl mercaptan contained in the vent E2 by gas (vent)-liquid (methanol) extraction.

[0109] [Method for preparing methyl mercaptan via a carbon monoxide route] The method for producing methyl mercaptan via a carbon monoxide route is carried out using at least one carbon monoxide, hydrogen, and hydrogen sulfide and / or sulfur. The carbon monoxide is selected from carbon monoxide (CO) and carbon dioxide (CO2). Preferably, the carbon monoxide is carbon monoxide (CO).

[0110] Therefore, the method is preferably carried out using a mixture of carbon monoxide, hydrogen, and hydrogen sulfide. The main by-product of this synthesis is carbon dioxide (CO2).

[0111] Carbonyl sulfide (COS) is considered to be a reaction intermediate that produces methyl mercaptan after hydrogenation according to the following reaction. CO + H2S → COS + H2 COS + 3H2 → CH3SH + H2O CO2 itself is the result of several side reactions as follows. CO + H2O → CO2 + H2 COS + H2O → CO2 + H2S 2COS → CO2 + CS2

[0112] The obtained carbon dioxide can optionally be recycled to produce methyl mercaptan according to the following formula. CO2 + 3H2 + H2S → CH3SH + 2H2O

[0113] Such a method for producing methyl mercaptan is widely described, for example, in European Patent Application Publication No. 0171312 or International Publication No. 08 / 125452.

[0114] Therefore, the present invention relates to a method for producing methyl mercaptan including the following steps. a-ox) Reacting at least one carbon monoxide, H2, H2S and / or sulfur in the presence of at least one catalyst, preferably in gaseous form, to produce a stream (J) preferably in gaseous form, containing methyl mercaptan, water and optionally said at least one carbon monoxide, H2, unreacted H2S and carbonyl sulfide (COS). b-ox) Optionally, condensing the stream (J). c-ox) Optionally, performing at least one purification step on the stream (J) to obtain a stream rich in methyl mercaptan. d-ox) Drying the stream obtained in step a-ox), step b-ox) or step c-ox) by the above drying method.

[0115] When the carbon monoxide is CO, the stream (J) may contain unreacted CO and CO2 generated during step a-ox).

[0116] In particular, the method for producing methyl mercaptan includes the following steps. a-ox) Reacting at least one carbon monoxide, H2, H2S and / or sulfur in the presence of at least one catalyst, preferably in gaseous form, to produce a stream (J) preferably in gaseous form, containing methyl mercaptan, water and optionally said at least one carbon monoxide, H2, unreacted H2S and carbonyl sulfide (COS). b-ox) Condensing the stream (J). c1-ox) Separating, preferably by decantation, from the liquid stream (J), a liquid organic phase (K) containing methyl mercaptan and water, and a liquid aqueous phase (L). c2-ox) Optionally, preferably a step of separating compounds that cannot be condensed to obtain a gas stream (J') (said separation can be carried out simultaneously with step b-ox) or step c1-ox)) d-ox) A step of drying the stream (K) by the drying method defined above e-ox) Optionally, a step of recycling the stream (J') to step a-ox)

[0117] Therefore, steps c1-ox) and c2-ox) are, in particular, purification steps for obtaining a stream in which methyl mercaptan is gradually concentrated.

[0118] According to one embodiment, the stream (J) or the stream (K) corresponds to the stream (A) according to the present invention.

[0119] <Step a-ox) - Reaction> Reaction step a) is a well-known step. In particular, step a-ox) is carried out at a temperature of 200°C to 500°C, preferably 200°C to 400°C. In particular, step a-ox) is carried out at a pressure of 1 bar (absolute pressure) to 100 bar (absolute pressure), preferably 3 bar (absolute pressure) to 30 bar (absolute pressure).

[0120] Preferably, in step a-ox), the molar ratio of carbon dioxide / S / H2S / H2 is 1 / 0 / 0.05 / 0.05 to 1 / 20 / 40 / 100. This molar ratio is preferably 1 / 0 / 0.5 / 1 to 1 / 0 / 10 / 20. In particular, this molar ratio is 1 / 0 / 1 / 2.

[0121] Preferably, in step a-ox), in the absence of sulfur, the ratio of CO / H2 / H2S is 1 / 0.05 / 0.05 to 1 / 40 / 100. This ratio is preferably 1 / 0.5 / 1 to 1 / 10 / 20. In particular, this ratio is 1 / 2 / 1.

[0122] Step a-ox) may be carried out on one or more catalyst beds, preferably on a fixed bed. Step a-ox) may be carried out in a reactor comprising one or more reaction zones, and the reagent(s) may optionally be fed between the various zones. Thus, the reagent, preferably H2 and / or H2S, may be introduced separately onto the various catalyst beds or reaction zones. The at least one catalyst used in step a-ox) is known and may in particular be selected from the following catalysts. · Catalysts based on molybdenum and potassium supported on zirconia such as K2MoO4 / ZrO2 described in International Publication No. WO 2019 / 122072. These catalysts are tested at a temperature of 320 °C and a pressure of 10 bar using a CO / H2 / H2S ratio of 1 / 2 / 1. · K2MoS4 / Ca described in International Publication No. WO 2014 / 154885 10 (PO4)6(OH)2 or K2MoO4 / Ca 10 · Mo-S-K and / or Mo-O-K type catalysts based on molybdenum and potassium on a hydroxyapatite support such as K2MoO4 / Ca(PO4)6(OH)2. These catalysts are tested at a temperature of 280 °C and a pressure of 10 bar using a CO / H2 / H2S ratio of 1 / 2 / 1. · Catalysts consisting of a porous support such as SiO2, TiO2, silica-alumina, zeolite and carbon nanotubes described in US Patent Application Publication No. 2010 / 0286448, on which a metal is electrodeposited. Then, this support is impregnated with K2MoO4 and another metal oxide acting as a promoter. · Catalysts based on Mo and K (in particular K2MoO4) promoted and supported by TeO2 such as K2MoO4 / TeO2 / SiO2 described in US Patent Application Publication No. 2010 / 094059. The catalyst K2MoO4 / TeO2 / SiO2 is tested at a temperature of 300 °C and a pressure of 2 bar with a CO / H2 / H2S ratio of 1 / 1 / 2 and a space velocity per hour of 2000 / h. ·International Publication No. 2005 / 040082 describes several catalysts, in particular catalysts comprising an active ingredient based on Mo - O - K, an activity promoter, and optionally a carrier. The exemplified catalysts are K2MoO4 / Fe2O3 / NiO or K2MoO4 / CoO / CeO2 / SiO2, each supported on silica. These catalysts are tested at a temperature of 320 °C and a pressure of 7 bar, with a CO / H2 / H2S ratio of 1 / 1 / 2 and a space velocity of 3000 / h.

[0123] <Step b - ox) - condensation> For this operation, any type of condenser can be used, such as a tube heat exchanger or a plate heat exchanger. Preferably, the condenser has a separated fluid, i.e., the gas to be condensed and the refrigerant fluid do not come into contact. The refrigerant fluid may be a liquid or a gas such as air, water, brine, ammonia, freon, oil, or others.

[0124] The condensation temperature may be 20 °C to 70 °C, preferably 30 °C to 60 °C. The pressure may be 1 bar (absolute pressure) to 100 bar (absolute pressure). The purpose is to condense the maximum amount of methyl mercaptan and water for non - condensable compounds (such as CO / COS / CO2 / H2 / H2S), thereby enabling easy separation of the liquid phase and the gas phase.

[0125] <Step c - ox) - purification> (Step c1 - ox) - water separation) The separation step c1 - ox) may be carried out via any prior art, in particular decantation. Preferably, the stream (J) is liquid. Thus, preferably by decantation, an organic phase (K) containing methyl mercaptan and water and an aqueous phase (L) are separated from the stream (J).

[0126] In particular, in step c1 - ox), the aqueous phase (L) contains at least 50% by weight, preferably at least 70% by weight, and more preferably at least 90% by weight of water relative to the total weight of water present in the stream (J).

[0127] (Separation of compounds that cannot be condensed in process c2-ox) The term "compounds that cannot be condensed" particularly means compounds that remain gaseous at the temperature and pressure of the manufacturing method, especially after the condensation step (b-ox). Examples of compounds that cannot be condensed include, in particular, carbon oxides (CO and / or CO2), H2, H2S, carbonyl sulfide (COS), methane, and any other inert non-condensable compounds produced or introduced during the method.

[0128] The separation may be carried out by any conventional technique. The stream (J’) is obtained as a gas containing, in particular, non-condensable compounds such as carbon oxides (CO and / or CO2), H2, H2S, carbonyl sulfide (COS), methane, and any other inert non-condensable compounds produced or introduced during the method.

[0129] According to one embodiment, the stream (J’) may preferably be recycled directly (without an intermediate purification step) to process a-ox). According to another embodiment, the stream (J’) may be partially purged. If not recycled, the stream (J’) may be sent to an incinerator or any other gas treatment device.

[0130] In particular, regardless of whether the method for producing methyl mercaptan is via the methanol route or the carbon oxide route, each of these routes may include at least one purification step as defined above, which is preferably a step of separating water and methyl mercaptan by decantation before drying (for example, steps c1), and / or c4) and c1-ox), respectively).

[0131] In particular, such a process enables the separation of water from methyl mercaptan, obtaining methyl mercaptan having a residual moisture content, that is, methyl mercaptan having a moisture content that depends on the solubility of water in methyl mercaptan at the separation temperature. Generally, this moisture content is 0.15% by weight, preferably strictly more than 0.15% by weight to 30% by weight, for example, 0.15% by weight to 10% by weight, based on the total weight of methyl mercaptan and water. Preferably, this moisture content is 0.15% by weight, preferably strictly more than 0.15% by weight to 5% by weight, based on the total weight of methyl mercaptan and water. For example, this moisture content is 0.15% by weight, preferably strictly more than 0.15% by weight to 2% by weight, for example, 0.15% by weight to 1.5% by weight or 0.15% by weight to 1% by weight, based on the total weight of methyl mercaptan and water.

[0132] After this step, the above-described method for drying methyl mercaptan can be carried out more efficiently and economically, and the amount of water before drying is reduced to a minimum.

Examples

[0133] The following examples illustrate the invention but are in no way limiting.

[0134] (Example 1: Comparative test using molecular sieve) Continuous drying by molecular sieve requires at least two dryers arranged in parallel (when the first one is in adsorption, the second one is in regeneration).

[0135] An adsorption tower (dryer) containing 1 kg of Siliporite (registered trademark) RA molecular sieve (particle size 1 / 8 inch) was used. The flow rate of methyl mercaptan to be dried was 1 kg / hour. The compositions at the inlet and outlet of this dryer are as follows.

[0136]

Table 1

[0137] When a molecular sieve is used, it is found that the amount of dimethyl sulfide (DMS) triples after drying, and the amount of methanol decreases to almost one-tenth. In fact, methanol is adsorbed by the molecular sieve, as a result of which the moisture drying capacity of the molecular sieve is significantly reduced, thereby increasing the frequency of the adsorption / regeneration cycle.

[0138] (Example 2: Drying method according to the present invention) The drying method corresponds to that described with respect to FIG. 1.

[0139] A stream of MeSH to be dried, containing 99.77 wt% MeSH (1000 kg / h) and 0.23 wt% water (2.3 kg / h) with respect to the total weight of MeSH and water, is introduced into a distillation column.

[0140] The azeotropic distillation column has 28 trays and satisfies the following conditions. - The distillation pressure is 13 bar (absolute pressure). - The temperature profile is 90 °C at the bottom of the distillation column and 70 °C at the top of the distillation column. - The reflux ratio is 47%.

[0141] The distillate is recovered as a gas at the top of the distillation column. The distillate contains 98.88 wt% MeSH (467.4 kg / h) and 1.12 wt% water (5.3 kg / h) with respect to the total weight of MeSH and water (472.7 kg / h). The temperature of the distillate is about 72 °C for a pressure of about 12 bar (absolute pressure).

[0142] Next, the distillate is condensed in a condenser. Its composition remains the same and it is recovered as a two-phase liquid at a temperature of about 40 °C for a pressure of about 12 bar (absolute pressure). Next, the condensate is allowed to settle in a decanter, and the following are obtained. The temperature is about 40 °C for a pressure of about 12 bar (absolute pressure) of the two phases. - An aqueous phase containing 98.26 wt% (2.26 kg / h) water and 1.74 wt% MeSH (0.04 kg / h) with respect to the total weight of the aqueous phase (2.3 kg / h), and -An organic phase containing 99.36 wt% MeSH (467.5 kg / h) and 0.64 wt% water (3 kg / h) with respect to the total weight of MeSH and water (470.5 kg / h)

[0143] The dried MeSH is recovered at the bottom of the distillation column and contains less than 10 weight ppm of water with respect to the total weight of methyl mercaptan and water.

[0144] The amounts of methanol and dimethyl sulfide are the same as those of the dried methyl mercaptan at the inlet of stream (A) (about 0.04 kg / h and 0.1 kg / h, respectively).

[0145] As a result, the method of the present invention enables efficient drying of methyl mercaptan while not increasing the amount of DMS by-products. Furthermore, this drying method is not affected by trace amounts of methanol and can be continuously carried out without impairing its performance.

Claims

1. A method for drying methyl mercaptan, comprising: 1) introducing a stream (A) containing methyl mercaptan and water into a distillation column (1); 2) distilling the stream (A) in the distillation column (1); 3) recovering the distillate (B) as a gas at the top of the distillation column; 4) condensing the distillate (B) to obtain a liquid condensate (C); 5) separating the condensate (C) to obtain two separate liquid phases, an aqueous phase (D) and an organic phase (E) containing methyl mercaptan; 6) optionally introducing all or part of the organic phase (E) into the distillation column (1) as reflux; 7) recovering a stream (F) containing dried methyl mercaptan at the bottom of the distillation column. A drying method comprising the above steps.

2. The drying method according to claim 1, wherein the distillation in step 2) is carried out at a pressure of 0.05 bar (absolute pressure) to 75 bar (absolute pressure).

3. The drying method according to claim 1 or claim 2, wherein the distillation in step 2) is carried out at a temperature of 20°C to 200°C.

4. The drying method according to any one of claims 1 to 3, wherein an azeotropic mixture of methyl mercaptan and water is recovered by the distillation in step 2).

5. The drying method according to any one of claims 1 to 4, wherein the stream (A) contains at least 90% by weight or at least 99% by weight of methyl mercaptan based on the total weight of methyl mercaptan and water.

6. The amount of water in the stream (F) is 0 ppm to 1500 ppm or 40 ppm to 800 ppm based on the total weight of methyl mercaptan and water. The drying method according to any one of claims 1 to 5.

7. When step 6) is carried out, the ratio of the mass of the organic phase (E) refluxed to the distillation column (1) to the mass of the stream (A) is 0 to 0.

99. The drying method according to any one of claims 1 to 6.

8. The drying method according to any one of claims 1 to 7, wherein the stream (A) is connected to a device for producing methyl mercaptan from methanol and hydrogen sulfide. Stream (A) is connected to an apparatus for producing methyl mercaptan from carbon dioxide, hydrogen (H ２ ), hydrogen sulfide (H ２ S) and / or sulfur (S), and is the drying method according to any one of claims 1 to 8.

9. A method for producing methyl mercaptan, comprising: a) Reacting methanol with hydrogen sulfide to produce a stream (M) containing methyl mercaptan, water, and optionally unreacted H ２ S and sulfur by-products; b) optionally condensing the stream (M). c) performing at least one step of purifying the stream (M) to obtain a stream rich in methyl mercaptan; d) drying the stream obtained in step c) by the drying method according to any one of claims 1 to 7; A method for producing methyl mercaptan, comprising: **Claim 11** Use of distillation of an azeotropic mixture of methyl mercaptan and water for drying methyl mercaptan by the drying method according to any one of claims 1 to 9.

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