Process for co-producing methyl mercaptan and dimethyl disulfide from carbon oxides

Abstract

Process for the co-production of methyl mercaptan and dimethyl disulfide from carbon oxides. The present invention relates to a process for the co-production of methyl mercaptan and dimethyl disulfide, comprising the following successive steps: a) reacting at least one carbon oxide in the presence of hydrogen sulfide (HS) and hydrogen to form a stream (M) comprising methyl mercaptan, water, and optionally unreacted hydrogen sulfide; b) purifying said stream (M) to obtain a methyl mercaptan-enriched stream (N) and a stream containing non-condensable compounds (M uncond ) to obtain c) Optionally, the stream of non-condensable compounds obtained from step b) (M uncond recycling to step a); d) recovering a first portion of the purified methyl mercaptan-containing stream (N) from step b); e) oxidizing a second portion of said methyl mercaptan stream (N) with sulfur to form a stream (O) comprising dimethyl disulfide, hydrogen sulfide, and optionally unreacted methyl mercaptan; f) purifying said stream (O) to separate, on the one hand, the enriched dimethyl disulfide and, on the other hand, the hydrogen sulfide and optionally the methyl mercaptan not reacted in step e); g) recycling the hydrogen sulfide and optionally the methyl mercaptan isolated in step f) to the stream (M) obtained from step a); h) recovering the dimethyl disulfide isolated in step f). The present invention relates to a method comprising the steps of:

Description

[Technical field]

[0001] The present invention relates to a process for the co-production of methyl mercaptan and dimethyl disulfide from carbon oxides. [Background technology]

[0002] Mercaptans are of great industrial interest and are currently widely used in the chemical industry, especially as starting materials in the synthesis of more complex organic molecules. For example, methyl mercaptan (CH 3 Methyl mercaptan is used as a starting material in the synthesis of methionine, an essential amino acid for animal nutrition. Methyl mercaptan is also used in the synthesis of dimethyl disulfide (DMDS).

[0003] Dimethyl disulfide is of great industrial interest and is very widely used in industry, for example, but not limited to, as a catalytic sulfurizing additive, especially in the hydrorefining of petroleum fractions, as an anti-coking and anti-CO additive in petroleum feedstocks subjected to steam cracking for ethylene production, or as a soil fumigant in agriculture.

[0004] Compared to other products used in these applications, such as di-tert-alkyl polysulfides, DMDS has many advantages. For example, DMDS has a high sulfur content (68%) and no coking cracking products (CH 4 , H 2 Moreover, in these applications, DMDS provides higher overall performance qualities than other commonly used commercial products such as di-tert-alkyl polysulfides.

[0005] Currently, methods for producing methyl mercaptan via various synthetic routes are known.

[0006] Methyl mercaptan is converted to methanol (CH) according to the following reaction (1): 3OH) and hydrogen sulfide (H 2 S). CH 3 OH + H 2 S → CH 3 SH + H 2 O (1)

[0007] It is also possible to produce methyl mercaptan from carbon monoxide (CO) according to the following reaction (2). CO + 2H 2 + H 2 S → CH 3 SH + H 2 O (2)

[0008] Other processes have been described in the literature and involve combinations of various reactions such as: - According to reaction (3), methane, H 2 S and CS from sulfur 2 and H 2 Formation: CH 4 + S + H 2 S → CS 2 + 3H 2 (3) - CS with the hydrogen formed above according to reaction (4) 2 Hydrogenation of: CS 2 + 3H 2 → CH 3 SH + H 2 S (4)

[0009] The process for the synthesis of dimethyl disulfide is conventionally carried out by oxidation with sulfur according to the following reaction (5). 2CH 3 SH + S → CH 3 SSCH 3 + H 2 S (5)

[0010] This oxidation of methyl mercaptan with sulfur, in batch or continuous mode and catalyzed by homogeneous or heterogeneous organic or inorganic basic agents, is accompanied by the formation of hydrogen sulfide and also the formation of dimethyl polysulfides, described as MeSxMe, with a sulfur rank x greater than 2. Moreover, this synthesis process generally requires a large excess of methyl mercaptan.

[0011] Now, in the context of current environmental considerations, there is currently a real need for a method for synthesizing methyl mercaptan and dimethyl disulfide that is more environmentally friendly while at the same time maintaining high yields. Summary of the Invention

[0012] Thus, one object of the present invention is a process for the co-production of methyl mercaptan and dimethyl disulfide, comprising the following successive steps: a) Hydrogen sulfide (H 2 reacting at least one oxide of carbon in the presence of (S) and hydrogen to form a stream (M) comprising methyl mercaptan, water, and optionally unreacted hydrogen sulfide; b) purifying said stream (M) to obtain a methyl mercaptan-enriched stream (N) and a stream containing non-condensable compounds (M uncond ) to obtain c) Optionally, the stream of non-condensable compounds obtained from step b) (M uncond recycling to step a); d) recovering a first portion of the purified methyl mercaptan-containing stream (N) from step b); e) oxidizing a second portion of said methyl mercaptan stream (N) with sulfur to form a stream (O) comprising dimethyl disulfide, hydrogen sulfide, and optionally unreacted methyl mercaptan; f) purifying said stream (O) to separate, on the one hand, the enriched dimethyl disulfide and, on the other hand, the hydrogen sulfide and optionally the methyl mercaptan that has not reacted in step e); g) recycling the hydrogen sulfide and optionally the methyl mercaptan isolated in step f) to the stream (M) obtained from step a); h) recovering the dimethyl disulfide isolated in step f). The method includes:

[0013] This method allows the continuous synthesis of methyl mercaptan and dimethyl disulfide. This co-production of products allows the energy cost of said synthesis to be reduced. This energy saving is the primary environmental benefit.

[0014] It also makes it possible to adjust the production of each product according to demand. For example, the synthesis of methyl mercaptan may be preferred to that of dimethyl disulfide. This flexibility of the process is also an advantage. It is also possible to produce only methyl mercaptan if required, i.e. to stop the process at step d). Likewise, all of stream (N) may be involved in the oxidation step e) if required. This flexibility of the process is a great advantage. It makes it possible to vary the production of products as required within one and the same facility.

[0015] This co-production then allows for the recycling of impurities in the final product. Methyl mercaptan that did not react during the sulfur oxidation reaction, and hydrogen sulfide produced during this oxidation step, are recycled to the methyl mercaptan synthesis. These impurities are usually incinerated, and the sulfur oxides (SO 3 ), which are a potential cause of acid rain, are recycled to the methyl mercaptan synthesis. 2 ) which currently leads to the formation of sulphur dioxide. These emissions are no longer permitted. Therefore, by recycling all of these light impurities, their incineration is avoided. The recycling step g) according to the invention thus makes it possible to recycle hydrogen sulphide in a closed facility. Since hydrogen sulphide is a toxic gas, a closed recycling allows limited handling of this gas and therefore limits accidents.

[0016] It would be possible to separate hydrogen sulfide from methyl mercaptan to economically utilize these impurities. However, this separation is very difficult and requires a distillation system with a very long column. As a result, this separation is very energy intensive. Therefore, recycling these two impurities into the same stream (i.e., without separation) and incorporating them into the existing purification steps of the synthesis process is a simple and very energy advantageous solution. Moreover, the oxidation step with sulfur generally requires a very large excess of methyl mercaptan.

[0017] This recycling is integrated into the purification steps that are essential to the synthesis process, and is therefore easy to implement and cheap in terms of energy. It does not require any additional steps in the synthesis process.

[0018] Finally, these impurities, compounds from the first synthesis step, namely reagents for hydrogen sulfide and products for methyl mercaptan, are concentrated in this first step of the process, reducing the consumption of starting materials.

[0019] Regarding reactions, the claimed method encompasses the following two reactions: Carbon monoxide: CO + 2H 2 + H 2 S → CH 3 SH + H 2 O Carbon dioxide: CO 2 + 3H 2 + H 2 S → CH 3 SH + 2H 2 O, and subsequently, 2CH 3 SH + S → CH 3 SSCH 3 + H 2 S

[0020] These reactions can be simplified if hydrogen sulfide is recycled to the first step as follows: 2CO + 4H 2 + H 2 S + S → CH 3 SSCH 3 + 2H 2 O, or 2CO 2 + 6H 2 + H 2 S + S → CH 3 SSCH 3 + 4H 2 O [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram of an apparatus for carrying out the claimed methods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Other characteristics, aspects, objects and advantages of the present invention will become more clearly apparent upon reading the following description.

[0023] It is pointed out that the expressions "from to" and "between" as used herein should be understood as including each of the limit values ​​mentioned.

[0024] The process according to the invention comprises the eight consecutive steps mentioned above, namely steps a) to h), which may also include intermediate purification steps.

[0025] <Step a)-Reaction> In step a), at least one carbon oxide, hydrogen and hydrogen sulfide, preferably in gaseous form, are reacted, optionally in the presence of at least one catalyst, thereby forming a stream (M), preferably in gaseous form, comprising methyl mercaptan, water and optionally unreacted hydrogen sulfide. Depending on the degree of conversion of the reaction, stream (M) may comprise hydrogen, unreacted hydrogen sulfide, carbonyl sulfide (COS) and optionally at least one unreacted carbon oxide.

[0026] This synthesis step requires hydrogen sulfide, which can participate in the reaction as it is mentioned in the previous paragraph or as shown in the reaction scheme above, or it can be generated in situ from sulfur and hydrogen. According to this variant, the reagents of the reaction are carbon oxide(s), sulfur, and hydrogen.

[0027] The carbon oxides may be carbon monoxide, carbon dioxide, or a mixture thereof.

[0028] In particular, step a) is carried out at a temperature between 200° C. and 500° C., preferably between 200° C. and 400° C. In particular, step a) is carried out at a pressure between 1 and 100 bar, preferably between 3 and 30 bar absolute.

[0029] Preferably, in step a), carbon oxides / S / H 2 S / H 2 The molar ratio is 1 / 0 / 0.05 / 0.05 to 1 / 20 / 40 / 100. Preferably, it is 1 / 0 / 0.5 / 1 to 1 / 0 / 10 / 20. In particular, it is 1 / 0 / 1 / 2.

[0030] Preferably, in step a), in the absence of sulfur, CO / H 2 / H 2 The S ratio is between 1 / 0.05 / 0.05 and 1 / 40 / 100. Preferably, it is between 1 / 0.5 / 1 and 1 / 10 / 20. In particular, it is 1 / 2 / 1.

[0031] Step a) may be carried out in one or more catalyst beds, preferably fixed beds. It may also be carried out in a reactor with one or more reaction zones, where the reagent(s) are optionally fed between the individual zones. Thus, the reagents, preferably H 2 and / or H 2 S may be introduced separately into each catalyst bed or reaction zone.

[0032] The at least one catalyst used in step a) is known and may in particular be chosen from: - Catalysts based on molybdenum and potassium supported on zirconia, such as those described in WO 2019 / 122072, e.g. K 2 MoO 4 / ZrO 2 These catalysts are capable of reacting with CO / H in a ratio of 1 / 2 / 1 at a temperature of 320°C and a pressure of 10 bar. 2 / H 2 It is tested using the S ratio. - catalysts based on molybdenum and potassium of the Mo-SK and / or Mo-OK type on a hydroxyapatite support, such as those described in WO 2014 / 154885, e.g. K 2 MoS 4 / Ca 10 (PO 4 ) 6 (OH) 2 Or K 2 MoO 4 / Ca 10 (PO 4 ) 6 (OH) 2 These catalysts are capable of reacting with CO / H in a ratio of 1 / 2 / 1 at a temperature of 280°C and a pressure of 10 bar. 2 / H 2 It is tested using the S ratio. - a catalyst as described in US Patent Application Publication No. 2010 / 0286448, comprising SiO on which metals are electrolytically deposited 2 , TiO 2 Catalysts composed of porous supports such as silica-alumina, zeolites, and carbon nanotubes. 2 MoO 4 , and additionally another metal oxide acting as a promoter, is subsequently impregnated onto the support. - TeO, as described in U.S. Patent Application Publication No. 2010 / 094059 2 Mo and K (especially K) supported by the promoter 2 MoO 4 )-based catalysts, e.g. 2 MoO 4 / TeO 2 / SiO 2 etc. Catalyst K 2 MoO 4 / TeO 2 / SiO 2 is a 1 / 1 / 2 ratio CO / H at 300°C and 2 bar pressure. 2 / H 2 S ratio and 2000 hours -1 The gas is tested using a space velocity of 0.01 to 0.15. WO 2005 / 040082 describes several catalysts, in particular those with an active component based on Mo-OK, an active promoter and optionally a support. The catalysts shown are 2 MoO 4 / Fe 2 O 3 / NiO or K 2 MoO 4 / CoO / CeO 2 / SiO 2 These catalysts were run at a temperature of 320°C and a pressure of 7 bar on a 1 / 1 / 2 ratio of CO / H 2 / H 2 S ratio and 3000 hours -1 The gas is tested using a space velocity of 0.01 to 0.15.

[0033] <Step b)-Purification> At least one step of the purification of stream (M) is to produce a stream enriched in methyl mercaptan (N) and a stream containing non-condensable compounds (M uncond ) is obtained. Preferably, the purification step is 2 It becomes possible to separate S from the stream (M).

[0034] The purification step b) may comprise one or more condensation steps and optionally one or more subsequent decantation steps and optionally one or more subsequent distillation steps. Preferably, the purification step b) comprises at least one condensation step (in particular as described below) and optionally a distillation step (in particular as described below).

[0035] <Condensation> Preferably, the stream (M) is condensed.

[0036] For this operation, any type of condenser may be used, such as a tubular or plate exchanger. Preferably, the condenser has separate fluids, i.e. there is no contact between the gas to be condensed and the coolant fluid. The coolant fluid may be liquid or gas, such as air, water, glycol, brine, ammonia, freon, or oil.

[0037] The condensation temperature can be between 20° C. and 70° C., preferably between 30° C. and 60° C. The pressure can be between 1 bar and 100 bar absolute. The objective is to condense maximum amounts of methyl mercaptan and water relative to non-condensable compounds, which allows easy separation of the liquid and gas phases.

[0038] The term "non-condensable compounds" refers in particular to compounds that remain in gaseous form at the temperature and pressure of the production process, in particular after the condensation step. Non-condensable compounds that may be mentioned in particular include unreacted carbon oxide(s), i.e. carbon monoxide and / or carbon dioxide, hydrogen, unreacted hydrogen sulfide, optionally carbonyl sulfide (COS), and any other non-condensable inert compounds generated or introduced during the course of the process. Preferably, the term "non-condensable compounds" refers to unreacted carbon oxide(s), unreacted hydrogen, unreacted hydrogen sulfide, and optionally carbonyl sulfide (COS).

[0039] These non-condensable compounds are separated and transported to stream M uncond Construct the condensed stream (M Cond ) may then be subjected to the following purification step(s).

[0040] <Water separation> The water separation step may be carried out by any conventional technique, in particular by decantation. Cond ) is in liquid form. Thus, the following is preferably decanted into the stream (M Cond ) is separated from - an organic phase (M org ), and -Aqueous phase (M aq ).

[0041] In particular, in the water separation step, the aqueous phase (M aq ) comprises at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight of water based on the total weight of water present in stream (M).

[0042] <H 2 Distillation of S> The organic phase containing methyl mercaptan (M org ) may also be subjected to a distillation step to remove traces of hydrogen sulfide that may still be present in this stream.

[0043] During the distillation, the pressure may be 0.05 to 40 bar, preferably 1 to 25 bar absolute, and / or the temperature may be −60° C. to +60° C., preferably 10 to 50° C. at the top of the column, and +20° C. to +200° C., preferably 20° C. to 100° C. at the bottom of the column.

[0044] Depending on the purification step of step b), stream (N) may be converted into stream (M cond ), Stream(M org ), or the methyl mercaptan stream obtained from the distillation process described above.

[0045] <Additional drying step for stream (N)> Stream (N) is a zeolite mixture of MgSO over molecular sieves. 4 Above, H 2 SO 4 Using CaCl 2 The mixture may be dried over low-temperature or by azeotropic distillation.

[0046] The stream recovered after completion of step b) is designated (N).

[0047] According to a preferred embodiment, the purification step b) comprises one or more condensation steps followed by one or more decantation steps and optionally one or more distillation steps.

[0048] According to a preferred embodiment, the purification step b) comprises a condensation step and a subsequent decantation step and optionally a distillation step.

[0049] Step c) - Optional recirculation Stream M in gaseous form which is recovered in the course of purification step b) and which may contain unreacted carbon monoxide and / or carbon dioxide, unreacted hydrogen sulfide, unreacted hydrogen and any carbonyl sulfide that may be present. uncond may be recycled prior to step a) for resubmission in the reaction. A purge may be provided to adjust the amount of the recycled stream.

[0050] <Step d)-Recovery of Methyl Mercaptan>

[0051] The process according to the invention then comprises a step of recovering methyl mercaptan. A part of stream (N), designated (N1), is recovered, optionally for participation in another process. A second part of stream (N), designated (N2), is itself involved in the next step of the process according to the invention, namely step e).

[0052] <Step e)-Oxidation> In step e), a portion of the methyl mercaptan (N2) obtained after completion of step d) is reacted by oxidation with sulfur to form a stream (O) comprising dimethyl disulfide, hydrogen sulfide, optionally unreacted methyl mercaptan and optionally dimethyl polysulfides.

[0053] This step is described, for example, in EP 0 976 726. For example, step e) may be carried out at elevated temperature and pressure, for example at temperatures between 20° C. and 200° C., preferably between 20° C. and 100° C., and at pressures between 2 and 30 bar, preferably between 2 and 15 bar absolute, typically at about 70° C. and under about 6 bar, for example in the case of the oxidation of methyl mercaptan with sulfur.

[0054] The oxidation reaction e) is carried out in a reactor which may contain a catalyst. A basic catalyst is preferably used. This basic catalyst may be homogeneous, biphasic or heterogeneous (solid). If the catalyst is homogeneous, i.e. soluble in mercaptans, amines, amidines and guanidines are preferred. If the basic catalyst forms a biphasic aqueous phase, all water-soluble bases such as sodium hydroxide, potassium hydroxide and hydroxides of alkali metals, alkaline earth metals or ammonium are preferred. If the base envisaged is a solid, any solid with basic properties may be envisaged, such as MgO, CaO, alumina or any other support (silica, zirconia, titanium oxide, hydrotalcite, hydroxyapatite, etc.) optionally doped with alkali metal oxides or alkaline earth metal oxides, or zeolites, optionally doped. Preferably, the heterogeneous catalyst is a basic ion exchange resin, more preferably the heterogeneous catalyst is Amberlyst® A21 resin sold by DuPont.

[0055] The methyl mercaptan / sulfur molar ratio in the oxidation step e) may be from 0.1 to 100, preferably from 1 to 50, more preferably from 1 to 20.

[0056] This oxidation step may make it possible to form a gas stream (O12) containing hydrogen sulfide and possibly unreacted methyl mercaptan, and a liquid stream (O11) containing dimethyl disulfide and residual dimethyl polysulfides.

[0057] <Additional degassing process> Stream (O) or liquid stream (O11) may then be treated in a degasser to remove residual gases such as hydrogen sulfide or possible methyl mercaptan from the liquid stream to form stream (O22). The degassed liquid stream is referred to as (O21).

[0058] <Polysulfide additional retrogradation process> The liquid stream (O21) obtained from the additional degassing step or the stream (O11) obtained from the oxidation step may be subjected to a step of retrogradation to convert the residual polysulfides to dimethyl disulfide by converting the high sulfur rank polysulfides to lower sulfur rank polysulfides, ideally to disulfides. The reactor used in this retrogradation step is known as the finisher. It contains an inlet for methyl mercaptan, which is introduced in excess to increase the conversion of the reaction. This finishing step may make it possible to form a gas stream (O32) containing hydrogen sulfide and possibly unreacted methyl mercaptan, as well as a liquid stream (O31) containing dimethyl disulfide.

[0059] <Additional degassing process> The liquid stream (O31) may be subjected to an additional degassing step. The liquid stream (O31) may be treated in a degasser to remove residual gases such as hydrogen sulfide and possibly unreacted methyl mercaptan to form stream (O42). The degassed liquid stream is referred to as (O41).

[0060] <Step f)-Purification> The process according to the invention comprises at least one purification step of the liquid stream obtained from the oxidation step e). This liquid stream may be the stream (O) obtained directly from the oxidation reaction e) or, depending on the presence of additional degassing or retrogradation steps, stream (O11), stream (O21), stream (O31) or stream (O41). This step makes it possible to separate, on the one hand, the enriched dimethyl disulfide and, on the other hand, the hydrogen sulfide and possibly the methyl mercaptan that has not reacted in step e). Such a step may in particular make it possible to separate: -Dimethyl disulfide in high concentrations, hydrogen sulfide and possibly unreacted methyl mercaptan, and Impurities such as heavy products, volatile compounds, hydromethyl disulfide, or mercaptomethyl methyl sulfide.

[0061] This purification step f) may comprise successive distillation steps to isolate dimethyl disulfide. In particular, purification step f) may comprise one or more distillation steps and, optionally, one or more base catalysis steps.

[0062] According to a first embodiment, the purification step f) may be carried out by any conventional technique, in particular by steps f1) to f4) as described below. In particular, the purification step corresponds to step f1) or step f6) as described below.

[0063] <Step f1) - H formed 2 Removal of S> The purification step f1), preferably by distillation, produces: a gas stream (P12) comprising hydrogen sulfide and possibly unreacted methyl mercaptan, and - A liquid stream containing mainly dimethyl disulfide (P11).

[0064] During the distillation, the pressure may be between 0.05 and 15 bar, preferably between 1 and 10 bar absolute. The temperature at the bottom of the column may be between 50 and 300° C., preferably between 50 and 200° C. At the top of the column, the temperature may be between 30 and 200° C., preferably between 30 and 120° C.

[0065] <Step f2) - Removal of heavy products> A second distillation of stream (P11) may follow, thereby obtaining: a stream (P22) constituting the column head and containing mainly dimethyl disulfide and traces of residual volatile impurities, and - A stream (P21) constituting the column tail and containing a mixture of heavy impurities.

[0066] The heavy distillate impurities stream (P21) may be recycled to the dimethyl disulfide synthesis process defined above, in particular to step e) or step f1), and in order to avoid the accumulation of impurities during this process, it is possible to provide a recycle pipe with a purge.

[0067] <Step f3)-Removal of hydromethyl disulfide by basic reaction> The stream resulting from step e) or stream (P11) and / or stream (P22) can be reacted in a reactor containing a basic catalyst to convert hydromethyl disulfide to dimethyl trisulfide according to the following reaction: MeSSH + MeSSMe → MeSH + MeSSMe

[0068] The basic catalyst may be of any type known to those skilled in the art. The basic catalyst is preferably heterogeneous with respect to the reaction medium so as to facilitate subsequent separation. The basic catalyst may therefore be selected, for example, from anion exchange resins such as Amberlyst® A21 from DuPont, basic catalysts in free amine form, alumina doped with sodium oxide and / or potassium oxide, magnesium oxide (MgO) and basic zeolites. It is also possible to use the catalysts listed above for the oxidation reaction e). Preferably, the basic catalyst is an anion exchange resin.

[0069] <Step f4 - Removal of trace volatile compounds> A third distillation of the stream resulting from step f3) may finally be carried out, thereby obtaining: - a top stream (P31) containing traces of methyl mercaptan formed in step f3), and - A stream (P32) which constitutes the tower tail and contains dimethyl disulfide.

[0070] According to a second embodiment, purification step f) may be carried out in steps f5) and f6) described below. <Step f5-Removal of Undesirable Impurities by Basic Reaction> The liquid stream (O) obtained directly from the oxidation reaction e) or, depending on the presence of an additional degassing or retrogradation step, stream (O11), stream (O21), stream (O31) or stream (O41) may be subjected to a basic catalysis reaction. These streams may therefore be fed into a reactor containing a basic catalyst so that undesired impurities are removed. The catalyst used may be a catalyst as disclosed for step f3) defined above.

[0071] <Step f6 - Removal of trace volatile compounds and heavy impurities> A distillation of the stream resulting from step f5) may then be carried out, thereby obtaining: a stream at the top of the column comprising hydrogen sulfide and traces of methyl mercaptan; a stream removed from the side comprising dimethyl disulfide, and - A stream that constitutes the tower tail and contains a mixture of heavy impurities.

[0072] The distillation column used to carry out this process may be a side draw column or a partition column.

[0073] When a distributor column is used, the column conditions may be as follows: The column top temperature may be 0°C to 150°C, preferably 10°C to 100°C; The column middle temperature may be 30°C to 200°C, preferably 50°C to 150°C; The column tail temperature may be 50°C to 250°C, preferably 80°C to 180°C; The column internal pressure may be 0.05 bar to 30 bar, preferably 0.1 to 5 bar absolute pressure; The reflux ratio, defined as the mass ratio between the liquid reinjected into the column top and the distillate containing light impurities at the column top, is 0 (no reflux) to 100, preferably 0 to 10.

[0074] According to a third embodiment, it is possible to incorporate a distillation column before steps f5) and f6) to remove volatile impurities before the basic catalysis step.

[0075] <Recirculation process g)> The recycling step g) directs the recycled stream prior to a purification step b) which in particular removes hydrogen sulfide from the purified stream (M) preferably by condensation, optionally followed by decantation and / or distillation.

[0076] The hydrogen sulfide and possibly methyl mercaptan recovered in the course of these steps e) and / or f) and optional additional steps are recycled to stream (M) obtained from step a), i.e. injected into stream (M) to be subjected to purification step b). For example, it may be injected before the condensation step or before the separation step or before the distillation step, preferably before the condensation step. Thus, streams (O12), (O22), (O32), (O42), (P12) and (P31) may be pooled as a single stream and reinjected into stream (M).

[0077] Part or all of the streams may be reinjected into stream (M). If part of the streams is reinjected, the recycle pipe has a purge to control the proportion of the streams that are recycled. Preferably, all of the hydrogen sulfide and optionally methyl mercaptan streams recovered in step e) and / or step f) are recycled to stream (M) obtained from step a).

[0078] <Recovery process h)> Dimethyl disulfide is finally recovered.

[0079] Figure 1:

[0080] FIG. 1 shows one embodiment of steps a) to h) of the method according to the present invention.

[0081] The reaction step a) is carried out in reactor A with at least one carbon oxide, hydrogen sulfide and hydrogen.

[0082] Streams of carbon oxide(s), hydrogen sulfide, and hydrogen enter reactor A via pipe 1. Stream M exits reactor A via pipe 3 and contains methyl mercaptan, water, unreacted hydrogen sulfide, unconverted carbon oxide(s), unconverted hydrogen, and possibly sulfur-based by-products.

[0083] The purification step b) is carried out in an apparatus B, such as a separation apparatus. A stream M of non-condensable compounds, such as unreacted carbon oxide(s), i.e. carbon monoxide and / or carbon dioxide, hydrogen, unreacted hydrogen sulfide, possibly carbonyl sulfide (COS), and any other non-condensable inert compounds produced or introduced during the process, is then fed to the apparatus B. uncond is separated and removed via pipe 4, and the aqueous stream M aq is removed via pipe 6 and stream N containing methyl mercaptan and possibly sulfur-based by-products leaves unit B via pipe 5.

[0084] Pipe 4 is connected to reactor A. Pipe 4 may contain a purge.

[0085] Pipe 5 is divided into pipe 7 and pipe 8. Pipe 8 allows the recovery of methyl mercaptan (step d) of the process above) and pipe 7 conveys the remainder of stream N to reactor D.

[0086] The oxidation step e) is carried out in reactor D. Sulfur is introduced into reactor D via pipe 9. Stream O leaving reactor D via pipe 10 contains dimethyl disulfide, hydrogen sulfide, unreacted methyl mercaptan and possibly sulfur-based by-products.

[0087] The purification step f) is carried out in an apparatus E, such as a distillation column. A stream of hydrogen sulfide and unreacted methyl mercaptan is removed at the top of the column via pipe 11, and the column tails portion is recycled to the reactor D via pipe 13. Pipes 11 and 13 may contain purges. The mid-column portion containing dimethyl disulfide is recovered via pipe 12.

[0088] Pipe 11 recycles the overhead portion containing hydrogen sulfide and unreacted methyl mercaptan to pipe 3 which carries stream M to purification unit B. The following examples are illustrative of the invention but in no way limiting. EXAMPLES

[0089] Removal of sulfur-based waste

[0090] Two units for the production of DMDS and MeSH were compared: one without step g) of recycling the stream after step a), and the other a unit according to the invention, which includes this recycling step g). 50,000 t / year of MeSH and 50,000 t / year of DMDS are produced, i.e. 151.5 t / day (based on 330 days / year) or 6.3 t / hour (based on 24 hours / day) for each of these two products. Under these conditions, stream 11 in FIG. 1 produces 2.2 t / hour of H 2 Contains MeSH S and 2.3t / hr. [Table 1]

[0091] The comparison shows two advantages of the method according to the present invention: the first advantage is that combustion of sulfur-based products and emission of sulfur oxides into the environment, which cause air pollution, is avoided, and the second advantage is that the yield of MeSH production is improved.

Claims

1. 1. A process for co-producing methyl mercaptan and dimethyl disulfide comprising the following successive steps: a) Hydrogen sulfide (H ２ reacting at least one carbon oxide in the presence of (S) and hydrogen to form a stream (M) comprising methyl mercaptan, water, and optionally unreacted hydrogen sulfide; b) purifying said stream (M) to obtain a methyl mercaptan-enriched stream (N) and a stream containing non-condensable compounds (M ｕｎｃｏｎｄ ) to obtain c) optionally, the stream of non-condensable compounds obtained from step b) (M ｕｎｃｏｎｄ recycling to step a); d) recovering a first portion of the methyl mercaptan-containing stream (N) purified in step b); e) oxidizing a second portion of said methyl mercaptan stream (N) with sulfur to form a stream (O) comprising dimethyl disulfide, hydrogen sulfide, and optionally unreacted methyl mercaptan; f) purifying said stream (O) to separate, on the one hand, the enriched dimethyl disulfide and, on the other hand, the hydrogen sulfide and optionally the methyl mercaptan that has not reacted in step e); g) recycling the hydrogen sulfide and optionally the methyl mercaptan isolated in step f) to the stream (M) obtained from step a); h) recovering the dimethyl disulfide isolated in step f); A method comprising:

2. 2. The process according to claim 1, characterized in that the recycling step g) directs the recycled stream before the purification step b) of removing the hydrogen sulfide from the stream (M) to be purified.

3. 2. The process according to claim 1, characterized in that all of the stream comprising hydrogen sulfide and optionally the methyl mercaptan not reacted in step e) is recycled to the stream (M) obtained in step a).

4. 2. The method according to claim 1, characterized in that in step a) the carbon oxides are carbon monoxide, carbon dioxide or a mixture thereof.

5. 2. The method according to claim 1, characterized in that in step a) the hydrogen sulfide is generated in situ by adding sulfur and hydrogen.

6. Carbon oxides / S / H ２ S / H ２ The molar ratio is from 1 / 0 / 0.05 / 0.05 to 1 / 20 / 40 / 100, or in the absence of sulfur, CO / H ２ / H ２ 2. The method according to claim 1, characterized in that the S ratio is between 1 / 0.05 / 0.05 and 1 / 40 / 100.

7. 2. The process according to claim 1, characterized in that the reaction temperature of step a) is between 200° C. and 500° C., the pressure is between 1 and 100 bar absolute, and said reaction of step a) is carried out in the presence of a catalyst selected from molybdenum and potassium based catalysts of the Mo-S-K and / or Mo-O-K type on a support.

8. 2. The process according to claim 1, characterized in that the methyl mercaptan / sulfur molar ratio in the oxidation step e) is between 0.1 and 100.

9. 2. The process according to claim 1, characterized in that the reaction temperature of the oxidation step e) is between 20° C. and 200° C., the pressure is between 2 and 30 bar absolute, and the reaction of the oxidation step e) is carried out in the presence of a basic catalyst selected from a homogeneous catalyst, a biphasic catalyst, or a heterogeneous catalyst.

10. 2. The process according to claim 1, characterized in that the purification step b) comprises one or more condensations and subsequent one or more decantations and optionally one or more distillations.

11. 11. The process according to any one of claims 1 to 10, characterized in that the purification step f) comprises one or more distillation steps and optionally one or more basic catalysis steps.

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