Method for simultaneously producing alkyl mercaptan and dialkyl disulfide from alcohol

Abstract

A process for the simultaneous production of alkyl mercaptans and dialkyl disulfides comprising the successive steps of: a) reacting C1-C4 alcohols in the presence of hydrogen sulfide (H2S) to produce a stream (M) comprising alkyl mercaptans, water and optionally unreacted hydrogen sulfide. b) purifying stream (M) to obtain stream (N) enriched in alkyl mercaptans. c) recovering a first portion of the stream (N) comprising the purified alkyl mercaptans from step b). d) oxidizing a second portion of the alkyl mercaptan stream (N) with sulfur to produce a stream (O) comprising dialkyl disulfides, hydrogen sulfide and optionally unreacted alkyl mercaptans. e) Purifying stream (O) to separate the rich dialkyl disulfides on the one hand and the hydrogen sulfide and optionally the alkyl mercaptans that have not reacted in step d) on the other hand. f) recycling the hydrogen sulfide and optionally alkyl mercaptans separated in step e) into stream (M) obtained from step a). g) recovering the dialkyl disulfide separated in step e).

Description

Technical Field

[0001] The present invention relates to a method for simultaneously producing alkyl mercaptan and dialkyl disulfide from alcohol.

Background Art

[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 (hereinafter denoted as CH 3 SH 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 in the synthesis of dialkyl disulfides, especially in the synthesis of dimethyl disulfide (hereinafter denoted as DMDS).

[0003] Dialkyl disulfides, especially dimethyl disulfide, are of great industrial interest in themselves and are widely used industrially. For example, but not limited to, they are used as anti-coking additives and anti-CO additives in petroleum raw materials subjected to steam cracking for ethylene production, or as soil fumigants in agriculture, especially as catalyst sulfurization additives in the hydrotreatment of petroleum cuts.

[0004] Compared with other products used in such applications, for example, di-tert-alkyl polysulfides, organic disulfides, and especially DMDS have many advantages. For example, DMDS has a high sulfur content (68%) and non-coking decomposition products (CH 4 , H 2 S). Furthermore, in such applications, DMDS provides generally higher performance quality than other commercially available products commonly used, such as di-tert-alkyl polysulfides.

[0005] At present, methods for producing methyl mercaptan by various synthetic routes are known.

[0006] Methyl mercaptan can be produced from methanol (CH 3 OH) and hydrogen sulfide (H 2 S) by the following reaction (1). CH 3 OH + H 2 S → CH 3 SH + H 2 O (1)

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

[0008] Other methods are described in the literature, formation of CS 2 and H 2 from methane and sulfur by reaction (3): CH 4 + H 2 S + S → CS 2 + 3H 2 (3) hydrogenation of CS 2 produced above using the hydrogen generated by reaction (4): CS 2 + 3H 2 → CH 3 SH + H 2 S (4) combining various reactions such as these.

[0009] Dimethyl disulfide has conventionally been synthesized by oxidation with sulfur by the following reaction (5): 2CH 3 SH + S → CH 3 SSCH 3 + H 2 S (5)

[0010] The oxidation of this alkyl mercaptan by sulfur, catalyzed by a homogeneous or heterogeneous organic or inorganic base agent, in batch or continuous mode, results in the production of hydrogen sulfide and RSxR (sulfur rank x greater than 2) (for example, in the synthesis of DMDS, dimethyl polysulfide CH 3 SxCH 3 ). Further, this synthesis step generally requires a large excess of methyl mercaptan.

[0011] Here, in relation to current ecological considerations, there is actually a need for a method for synthesizing alkyl mercaptan and dialkyl disulfide that is more environmentally friendly while maintaining a high yield at the present time. SUMMARY OF THE INVENTION

[0012] Accordingly, one subject of the present invention is a method for simultaneously producing alkyl mercaptan and dialkyl disulfide, comprising the following successive steps. a) Reacting a C 2 ~C 1 alcohol in the presence of hydrogen sulfide (H 4 S) to produce a stream (M) containing alkyl mercaptan, water, and optionally unreacted hydrogen sulfide. b) Purifying the stream (M) to obtain a stream (N) rich in alkyl mercaptan. c) Recovering a first portion of the stream (N) containing the alkyl mercaptan purified in step b). d) Oxidizing a second portion of the stream (N) of alkyl mercaptan with sulfur to produce a stream (O) containing dialkyl disulfide, hydrogen sulfide, and optionally unreacted alkyl mercaptan. e) Purifying the stream (O) to separate, on the one hand, rich dialkyl disulfide and, on the other hand, hydrogen sulfide and optionally alkyl mercaptan that did not react in step d). f) A step of recycling the hydrogen sulfide separated in step e) and optionally the alkyl mercaptan into the stream (M) obtained from step a). g) A step of recovering the dialkyl disulfide separated in step e).

[0013] This method enables the continuous synthesis of alkyl mercaptan and dialkyl disulfide. The simultaneous production of this product makes it possible to reduce the energy cost of synthesis. This energy saving is the first ecological advantage.

[0014] This method also makes it possible to adjust the production of each product according to demand. For example, the synthesis of alkyl mercaptan may be preferred over the synthesis of dialkyl disulfide. This flexibility in this method is also an advantage. If necessary, it is also possible to produce only alkyl mercaptan, that is, to stop the method in step c). Similarly, if necessary, all of the stream (N) can participate in the oxidation step d). This flexibility in this method is a significant advantage. This method makes it possible to adapt the production of products as needed in one and the same facility.

[0015] Next, this simultaneous production makes it possible for the impurities of the final product to be recycled. The alkyl mercaptan that did not react during the oxidation reaction with sulfur and the hydrogen sulfide generated during this oxidation step are recycled to the alkyl mercaptan synthesis. These impurities are usually incinerated, resulting in the generation of sulfur oxides (SO 2 ) which can cause acid rain. At present, these emissions are no longer allowed. Here, by recycling all of these light impurities, these incinerations can be avoided. Therefore, the recycling step f) according to the present invention enables the recycling of hydrogen sulfide in a closed facility. Since hydrogen sulfide is a toxic gas, the closed recycling makes it possible to limit the handling of this gas and thereby limit accidents.

[0016] It would also be possible to separate hydrogen sulfide from alkyl mercaptan in order to economically utilize these impurities. However, this separation is very difficult and requires a distillation apparatus equipped with a very tall column. As a result, this separation consumes extremely large amounts of energy. Therefore, recycling (i.e., not separating) these two impurities into the same stream, which is incorporated into the existing purification process of the synthesis method, is a simple and very energy - advantageous solution; furthermore, the oxidation process with sulfur generally requires a very large excess of alkyl mercaptan.

[0017] This recycling is incorporated into the purification process that is essential for the synthesis method. Therefore, this recycling is easy to implement and is energy - inexpensive. This recycling does not require additional steps in the synthesis method.

[0018] And these impurities, which are compounds from the first synthesis step: reagents for hydrogen sulfide and products for alkyl mercaptan, enhance the first step of this method and result in a reduction in the consumption of starting materials.

[0019] Regarding the reaction, the claimed method includes the following two reactions: ROH + H 2 S → RSH + H 2 O 2RSH + S → RSSR + H 2 S

[0020] When recycling hydrogen sulfide within the first step, these reactions can be simplified as follows: 2ROH + H 2 S + S → RSSR + 2H 2 O

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

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

[0023] As used herein, the expression “... to...” should be understood to include each of the recited lower and upper limits.

[0024] The method according to the present invention includes the following seven consecutive steps: steps a) to g). This method may include an intermediate purification step.

[0025] Step a) Reaction:

[0026] In step a), C 1 to C 4 alcohol is reacted with hydrogen sulfide to produce a stream (M) containing C 1 to C 4 alkyl mercaptan, water, optionally unreacted hydrogen sulfide and optionally sulfur-based by-products.

[0027] The C 1 to C 4 alcohol according to the present invention is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol and tert-butanol. Preferably, the alcohol is methanol, ethanol, n-propanol or n-butanol, preferably methanol.

[0028] The alcohol and hydrogen sulfide may be introduced separately into the reactor. It is also possible to prepare a premix of these reagents.

[0029] Prior to step a), the gas streams of the hydrogen sulfide reagent and the alcohol reagent may be prepared as follows. Liquid alcohol is injected into gaseous hydrogen sulfide. This injection allows the alcohol to partially or completely evaporate. Then, if necessary, the mixture of hydrogen sulfide and alcohol can be completely evaporated to obtain a complete gas stream.

[0030] Therefore, preferably, a gas stream of a mixture of hydrogen sulfide and alcohol prepared as described above is introduced into the reactor. It is also possible to introduce gaseous alcohol and hydrogen sulfide into the reactor separately.

[0031] The reactor can be a plate type, multitubular type or fixed bed type isothermal reactor or adiabatic reactor. Preferably, an adiabatic reactor is selected.

[0032] The reaction temperature can be 200°C to 500°C, preferably 200°C to 400°C. Preferably, the reaction temperature is 200°C to 360°C. Above this temperature, the catalyst may be physically damaged (especially by sintering and coking).

[0033] The pressure can be 1 to 40 bar absolute.

[0034] The hydrogen sulfide / alcohol molar ratio can be 0.1 to 100, preferably 1 to 50, and even more preferably 1 to 20. Hydrogen sulfide is preferably in excess relative to the alcohol.

[0035] The reactor may preferably contain a catalyst for the alkyl mercaptan formation reaction in the gas phase. Among the catalysts that may be used, alumina-based catalysts; preferably thorium dioxide ThO deposited on a silicate support 2 ; preferably cadmium sulfide-based catalysts on an alumina support; the following oxides: MgO, ZrO 2 , TiO 2 rutile (R) and TiO 2 anatase (A), CeO 2 , and γ-Al 2 O 3 -based catalysts; preferably catalysts doped with alkali metals (Li, Na, K, Rb, Cs) and optionally SiO 2 , Al2 O 3 or Nb 2 O 5 a catalyst based on a metal oxide supported thereon; 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 another metal oxide; potassium tungstate K on alumina 2 WO 4 / Al 2 O 3 , may be mentioned.

[0036] Preferably, the catalyst is an alkali metal oxide impregnated on alumina, and even more preferably, sodium oxide or potassium oxide on γ-type alumina.

[0037] Thus, a stream (M) containing alkyl mercaptan, water, optionally unreacted hydrogen sulfide and sulfur-based by-products is obtained.

[0038] Additional condensation step: The method according to the invention may include at least one step of condensing the stream (M).

[0039] Preferably, the stream (M) obtained from step a) may be condensed by any prior art using one or more condensers or economizers. Preferably, the stream (M) is condensed at a temperature of 20°C to 70°C, for example, 30°C to 60°C.

[0040] Step b) Purification: The method according to the invention includes at least one purification step of the stream (M).

[0041] Preferably, in step b), the at least one purification step preferably corresponds to at least one phase separation step by decantation and / or at least one distillation step. In particular, step b) may correspond to one or more phase separation steps, for example one or two decantation steps, and / or one or more distillation steps, for example one or two distillation steps.

[0042] Preferably, step b) enables the removal of by-products based on water, unreacted hydrogen sulfide and / or sulfur that may be present in stream (M) by means of one or more purification steps. Specifically, after step b), a stream rich in alkyl mercaptan is obtained.

[0043] Preferably, step b) includes a step of removing at least one H 2 S, preferably by distillation. Preferably, step b) includes at least one decantation step and at least one distillation step, and these two steps enable the separation of H 2 S from stream (M). The decantation step and / or distillation step may be carried out under the following conditions for steps b1) and b2). The purification step b) may be carried out by any prior art, and in particular by steps b1) and / or b2), preferably steps b1)-b4) in series as described below.

[0044] Step b1 - Separation: The separation step b1) preferably produces, by decantation, a gas stream (M1) containing unreacted hydrogen sulfide; an organic stream (M2) containing alkyl mercaptan, optionally water, optionally unreacted hydrogen sulfide and optionally by-products based on sulfur; an aqueous stream (M3); and

[0045] Preferably, the stream (M) is separated at a temperature of 20°C to 70°C, preferably 30°C to 60°C. The pressure may be 1 to 40 bar absolute.

[0046] In particular, the obtained stream (M2) may be a gas or a liquid. When the stream (M2) is a gas, the streams (M1) and (M2) may be combined.

[0047] Specifically, the preferably liquid aqueous stream (M3) contains at least 50% by weight of water, preferably at least 70% by weight of water, more preferably at least 90% by weight of water, based on the total weight of the water present in the stream (M). Therefore, the aqueous stream (M3) may be sent to a degassing device. Subsequently, the degassed aqueous stream may be sent to wastewater treatment.

[0048] The gas stream (M1) may be recycled into the reactor feed for step a). In this case, the purge of this stream (M1) may be carried out so as to avoid the accumulation of inert substances and / or impurities in this recycle loop. Examples of inert substances and / or impurities that may be mentioned are: gaseous alkanes, CO, CO 2 , H 2 and N 2 . The gas stream obtained from this purge is called E1. When combining the streams (M1) and (M2), the same type of purge may be carried out to obtain a gas stream called E2.

[0049] According to one embodiment, the gas stream E1 or the gas stream E2 is sent for incineration.

[0050] According to another embodiment, for recovering sulfur-based compounds such as hydrogen sulfide and / or alkyl mercaptans contained by gas-liquid (alcohol) absorption, the gas stream E1 or the gas stream E2 may be sent to an alcohol absorption column, and the alcohol is selected as a reagent.

[0051] Process b2 - Removal of hydrogen sulfide by distillation Stream (M) or stream (M2) is Preferably at the top of the column, with a stream (M4) containing hydrogen sulfide; Preferably at the bottom of the column, with a stream (M5) containing alkyl mercaptans and optionally by-products based on water and optionally sulfur, and may be subjected to distillation to obtain.

[0052] During distillation, the pressure may be 0.05 - 40 bar absolute, preferably 1 - 25 bar absolute, and / or the temperature may be -60 °C to +60 °C at the top of the column, preferably 10 °C to 50 °C, and +20 °C to +200 °C at the bottom of the column, preferably 20 °C to 100 °C.

[0053] The stream (M4) containing hydrogen sulfide may be recovered at the top of the column and optionally recycled into the reactor feed for step a).

[0054] Specifically, the distillation step b2) enables the removal of hydrogen sulfide from stream (M) or stream (M2) (trace amounts of hydrogen sulfide may still be present in stream (M5)).

[0055] Process b3 - Optional removal of sulfur-based by-products by distillation: The distillation of stream (M2) or stream (M5) is Preferably at the top of the column, with a stream (M6) containing alkyl mercaptans and optionally water; Preferably at the bottom of the column, with a stream (M7) which may contain sulfur-based by-products, and may be carried out to obtain.

[0056] During distillation, the pressure may be 1 - 40 bar absolute, and / or the temperature may be +20 °C to +100 °C at the top of the column and +40 °C to +200 °C at the bottom of the column.

[0057] Specifically, the distillation step b3), if present, enables the removal of by-products based on sulfur remaining in stream (M2) or stream (M5) (trace sulfur-based by-products may still be present in stream (M6)).

[0058] Step b4 - Optional separation of alkyl mercaptan and trace water: Stream (M2) or stream (M5) or stream (M6) may undergo an additional purification step aimed at removing residual water. Prior to this step b4), stream (M2) or stream (M5) or stream (M6) may be cooled to as low a temperature as possible to maximize water removal. Preferably, stream (M2) or stream (M5) or stream (M6) is cooled to a temperature of 20°C to 70°C, for example, 30°C to 60°C.

[0059] This cooling enables maximizing the separation of water that may still be present in the stream during step b4). When the alkyl mercaptan is methyl mercaptan, a temperature strictly higher than 16°C is maintained to prevent the formation of solid methyl mercaptan hydrate.

[0060] Then, the separation of alkyl mercaptan and residual water is preferably a liquid, stream (M8) containing alkyl mercaptan; preferably a liquid, stream (M9) containing water, and can preferably be carried out by decantation to obtain.

[0061] Specifically, in step b4), stream (M9) contains at least 50% by weight of water, 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 (N).

[0062] In the separation step b4), it is possible to recover the thus-separated gas phase from the streams (M8) and (M9), both of which are liquids. This gas stream is referred to as E3.

[0063] According to one embodiment, the gas stream E3 is incinerated.

[0064] According to another embodiment, the gas stream E3 may be sent to an alcohol absorption column to recover sulfur-based compounds such as hydrogen sulfide and / or alkyl mercaptans contained therein by gas-liquid extraction, and the alcohol corresponds to the alcohol used as a reagent.

[0065] Additional step of drying the stream Subsequently, the resulting stream (M2) or stream (M5) or stream (M6) or stream (M8) may be dried.

[0066] Molecular sieves, MgSO 4 , H 2 SO 4 , CaCl 2 Or drying may be performed by azeotropic distillation, which is only possible when the alcohol used as a reagent is methanol.

[0067] The stream recovered as a result of step b) is denoted as (N).

[0068] Step c) Recovery of alkyl mercaptan: Subsequently, the method according to the invention includes a step of recovering alkyl mercaptan. A portion of the stream (N) denoted as (N1) is recovered, optionally, for subjecting to another method. A second portion of the stream (N) denoted as (N2) is itself subjected to the next step of the method according to the invention: step d).

[0069] Step d) Oxidation: In step d), a portion (N2) of the alkyl mercaptan obtained as a result of step c) is reacted by oxidation with sulfur to produce a stream (O) containing dialkyl disulfide, hydrogen sulfide, optionally unreacted alkyl mercaptan, and optionally dialkyl polysulfide.

[0070] This step is described, for example, in European Patent Application Publication No. 0976726. For example, step d) may be carried out at a high temperature of, for example, 20 °C to 200 °C, preferably 20 °C to 100 °C, and under a pressure of 2 to 30 bar absolute, preferably 2 to 15 bar absolute. Typically, for example, in the case of the oxidation of methyl mercaptan with sulfur, it may be carried out at about 70 °C and about 6 bar.

[0071] The oxidation reaction d) is carried out in a reactor, which may contain a catalyst. Preferably, a basic catalyst is used. This basic catalyst can be homogeneous, two-phase, or heterogeneous (solid). When the catalyst is homogeneous, i.e., soluble in the mercaptan, amines, amidines, and guanidines are preferred. When the basic catalyst forms a two-phase aqueous phase, all water-soluble bases such as sodium hydroxide, potassium hydroxide, and alkali metal hydroxides, alkaline earth metal hydroxides, or ammonium hydroxide are preferred. When the assumed base is solid, any solid having basic properties can be assumed, for example, MgO, CaO, alumina, or any other support (silica, zirconia, titanium oxide, hydrotalcite, hydroxyapatite, etc.) optionally doped with an alkali metal oxide or alkaline earth metal oxide, or an optionally doped zeolite. Preferably, the heterogeneous basic catalyst is a basic ion exchange resin; more preferably, the heterogeneous catalyst is the Amberlyst® A21 resin sold by DuPont.

[0072] The alkyl mercaptan / sulfur molar ratio in the oxidation step d) may be 0.1 to 100, preferably 1 to 50, more preferably 1 to 20.

[0073] This oxidation step may be capable of producing a gas stream (O12) containing hydrogen sulfide and optionally unreacted alkyl mercaptan, and a liquid stream (O11) containing dialkyl disulfide and optionally residual dialkyl polysulfide.

[0074] Additional degassing step: Next, the stream (O) or the liquid stream (O11) may be processed in a degassing device to remove residual gases such as hydrogen sulfide or alkyl mercaptan that may be present from the liquid stream to produce a stream (O22). The degassed liquid stream is referred to as (O21).

[0075] Additional step for retrogradation of polysulfide The liquid stream (O21) obtained from the previous additional degassing step or the stream (O11) obtained from the oxidation step may undergo a retrogradation process of polysulfide with a higher sulfur rank to a polysulfide with a lower sulfur rank, preferably to disulfide, in order to convert residual polysulfide to dialkyl disulfide. The reactor used for this retrogradation step is known as a finishing device. The finishing device is equipped with an inlet for the alkyl mercaptan introduced in excess to increase the reaction conversion. This finishing step may be capable of producing a gas stream (O32) containing hydrogen sulfide and optionally unreacted alkyl mercaptan, and a liquid stream (O31) containing dialkyl disulfide and residual dialkyl polysulfide.

[0076] Additional degassing step: The liquid stream (O31) may undergo an additional degassing step. The liquid stream (O31) may be processed in a degassing device to remove residual gases such as hydrogen sulfide and optionally unreacted alkyl mercaptan to produce a stream (O42). The degassed liquid stream is referred to as (O41).

[0077] Step e) Purification The method according to the invention comprises at least one purification step of the liquid stream obtained from the oxidation step d). This liquid stream can be the stream (O) or the stream (O11), stream (O21), stream (O31) or stream (O41) directly obtained from the oxidation reaction d), depending on the presence of an additional degassing step or retrogradation step. This step makes it possible to separate, on the one hand, the rich dialkyldisulfide and, on the other hand, hydrogen sulfide and optionally the alkyl mercaptan that did not react in step d). In particular, such a step rich dialkyldisulfide, hydrogen sulfide, optionally with unreacted alkyl mercaptan, and impurities such as heavy products, volatile compounds, hydroalkyldisulfides or mercaptoalkylalkylsulfides, can be separated.

[0078] This purification step e) may include one or more distillation steps for separating the dialkyldisulfide. Specifically, the purification step e) may include one or more distillation steps and optionally one or more basic catalyst steps. Specifically, the purification step corresponds to the following step e1) or step e6).

[0079] According to a first embodiment, the purification step e) may be carried out by any prior art and in particular in one or a series of steps e1) to e4) as described hereinafter.

[0080] Step e1) Removal of the generated H 2 S The purification step e1) is preferably by distillation, a gas stream (P12) containing hydrogen sulfide and optionally unreacted alkyl mercaptan and optionally volatile impurities; and a liquid stream (P11) mainly containing dialkyldisulfide, is produced.

[0081] In distillation, the pressure may be from 0.05 to 15 bar absolute, preferably from 1 to 10 bar absolute. The temperature at the bottom of the column may be from 50°C to 300°C, preferably from 50°C to 200°C. At the top of the column, the temperature may be from 30°C to 200°C, preferably from 30°C to 120°C.

[0082] Step e2) Removal of heavy products Next, the second distillation of the stream obtained from step d) or stream (P11) may be carried out to obtain a stream (P22) that constitutes the top of the column and mainly contains dialkyldisulfide and residual trace amounts of volatile impurities; and a stream (P21) that constitutes the bottom of the column and contains a mixture of heavy impurities. This may be done to obtain.

[0083] The stream (P21) of heavy distillation impurities may be recycled into the dialkyldisulfide synthesis process, particularly into step d) or e1) as defined above. To avoid the accumulation of impurities in the process, it is possible to equip the recycle pipe with a purge.

[0084] Step e3) Removal of hydroalkyldisulfide by basic reaction: The stream obtained from step d) or stream (P11) and / or stream (P22) may be reacted in a reactor containing a basic catalyst so that hydroalkyldisulfide is converted to dialkyltrisulfide by the following reaction: RSSH + RSSR → RSH + RSSSR

[0085] The basic catalyst may be of any type known to those skilled in the art. Preferably, the basic catalyst is heterogeneous with respect to the reaction medium in order to facilitate subsequent separation. Thus, the basic catalyst may 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 above catalyst for the oxidation reaction d). Preferably, the basic catalyst is an anion exchange resin.

[0086] Step e4) Removal of trace volatile compounds: Then, the third distillation of the stream obtained from step e3) is a stream (P31) containing trace amounts of alkyl mercaptans that may be produced in step e3) at the top of the column, and a stream (P32) constituting the bottom of the column and containing dialkyldisulfide, which may be carried out to obtain.

[0087] According to the second embodiment, the purification step e) may be carried out in steps e5) and e6) as follows. Step e5) Removal of undesirable impurities by basic reaction: Depending on the presence of an additional degassing step or retrogradation step, the liquid stream (O) or stream (O11), stream (O21), stream (O31) or stream (O41) directly obtained from the oxidation reaction d) may undergo a basic catalyst reaction. Thus, these streams may enter a reactor containing a basic catalyst to remove undesirable impurities. The catalyst used may be the one disclosed for step e3) as defined above.

[0088] Step e6) Removal of trace volatile compounds and heavy impurities: Then, the distillation of the stream obtained from step e5) is a stream containing hydrogen sulfide and trace amounts of alkyl mercaptans at the top of the column, A stream containing dialkyldisulfide removed on the side, and A stream that constitutes the bottom of the column and contains a mixture of heavy impurities, May be carried out to obtain.

[0089] The distillation column used to carry out this step may be a column with a side draw section or a dividing wall column.

[0090] When a dividing wall 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 bottom temperature may be 50 °C to 250 °C, preferably 80 °C to 180 °C. The pressure inside the column may be 0.05 to 30 bar absolute, preferably 0.1 to 5 bar absolute. The reflux ratio, defined as the mass ratio of the liquid reinjected to the top of the column to the distillate containing light impurities at the top of the column, may be 0 (no reflux) to 100, preferably 0 to 10.

[0091] According to the third embodiment, it is possible to incorporate a distillation column before steps e5) and e6) in order to remove volatile impurities before the basic catalyst step.

[0092] Recycling step f) Recycling step f) recycles the stream before purification step b), and purification step b) removes hydrogen sulfide from the stream (M) to be purified, preferably by distillation.

[0093] Specifically, hydrogen sulfide and optionally alkyl mercaptan recovered during these steps d) and / or e) and optionally additional steps are recycled into the stream (M) obtained from step a), i.e., injected into the stream (M) such that it passes through a purification step b) in which hydrogen sulfide is removed from the stream (M), which is preferably purified by distillation. Preferably, the recycled stream is reinjected into the medium before step b1) and / or step b2). Thus, the streams (O12), (O22), (O32), (O42), (P12) and (P31) may be pooled as a single stream and reinjected into the stream (M).

[0094] Some or all of the stream may be reinjected into the stream (M). When a portion of the stream is reinjected, the recycle pipe is provided with a purge to adjust the proportion of the recycled stream. Preferably, all of the stream of hydrogen sulfide and optionally alkyl mercaptan that did not react in step d) is recycled into the stream (M) obtained from step a).

[0095] Recovery step g And dialkyldisulfide is recovered.

[0096] Figure 1:

[0097] Figure 1 shows one embodiment of steps a) to g) of the method according to the invention.

[0098] Reaction step a) is carried out in reactor A using alcohol and hydrogen sulfide.

[0099] The alcohol stream enters reactor A via pipe 1. The hydrogen sulfide stream enters reactor A via pipe 2. The stream M exiting reactor A via pipe 3 contains alkyl mercaptan, water, unreacted hydrogen sulfide and optionally sulfur-based by-products.

[0100] Purification step b) is carried out in equipment B such as a separator. The hydrogen sulfide stream is separated and removed via pipe 4, water is removed via pipe 6, and the stream N containing alkyl mercaptan and optionally sulfur-based by-products exits equipment B via pipe 5.

[0101] Pipe 4 is connected to pipe 2 that transports hydrogen sulfide to reactor A.

[0102] Pipe 5 is divided into pipe 7 and pipe 8. Pipe 8 enables the recovery of alkyl mercaptan in the process (step c), and pipe 7 transports the remainder of stream N to reactor D.

[0103] Oxidation step d) is carried out in reactor D. Sulfur is introduced into reactor D via pipe 9. Stream O exiting reactor D via pipe 10 contains dialkyldisulfide, hydrogen sulfide, unreacted alkyl mercaptan, and optionally sulfur-based by-products.

[0104] Purification step e) is carried out in equipment E such as a distillation column. The stream of hydrogen sulfide and unreacted alkyl mercaptan is removed at the top of the column via pipe 11, and the bottom of the column is recycled into reactor D via pipe 13. Pipes 11 and 13 may be provided with a purge. The middle part of the column containing dialkyldisulfide is recovered via pipe 12.

[0105] Pipe 11 recycles the overhead of the column containing hydrogen sulfide and unreacted alkyl mercaptan into pipe 3 and sends stream M to the purification equipment B. The following examples illustrate the invention but are in no way limiting.

Examples

[0106] 1. Removal of sulfur-based waste

[0107] Two units for the production of DMDS and MeSH were compared. One unit does not include step f) of recycling the stream after step a). The other unit is the unit according to the present invention and includes this recycling step f). The production is 50,000 tons / year of MeSH and 50,000 tons / year of DMDS, that is, for each of the two products, a production of 151.5 tons / day (based on 330 days / year), or a production of 6.3 tons / hour (based on 24 hours / day). Under these conditions, stream 11 in Figure 1 contains 2.2 tons / hour of H 2 S and 2.3 tons / hour of MeSH.

Table 1

[0108] This comparison shows two advantages of the method according to the present invention. The first advantage is to avoid the incineration of sulfur-based products and the release of sulfur oxides, which are factors causing air pollution, into the environment. The second advantage is to improve the production yield of MeSH. The present disclosure includes the following embodiments. <1> A method for simultaneously producing an alkyl mercaptan and a dialkyl disulfide, comprising the following consecutive steps. a) Reacting a C 2 alcohol in the presence of hydrogen sulfide (H 1 ~C 4 S) to produce a stream (M) containing an alkyl mercaptan, water, and optionally unreacted hydrogen sulfide. b) Purifying the stream (M) to obtain a stream (N) rich in alkyl mercaptan. c) Recovering a first portion of the stream (N) containing the alkyl mercaptan purified in step b). d) Oxidizing a second portion of the stream (N) of the alkyl mercaptan with sulfur to produce a stream (O) containing a dialkyl disulfide, hydrogen sulfide, and optionally unreacted alkyl mercaptan. e) Purifying the stream (O) to separate, on the one hand, a rich dialkyl disulfide and, on the other hand, hydrogen sulfide and optionally the alkyl mercaptan that did not react in step d). f) Recycling the hydrogen sulfide and optionally the alkyl mercaptan separated in step e) into the stream (M) obtained from step a). g) Recovering the dialkyl disulfide separated in step e). <2> The method according to <1> above, wherein the recycling step f) recycles the stream before the purification step b), and the purification step b) removes hydrogen sulfide from the stream (M) to be purified, preferably by distillation. <3> The method according to <1> or <2> above, characterized in that all of the stream containing hydrogen sulfide and optionally the alkyl mercaptan that did not react in step d) is recycled into the stream (M) obtained from step a). <4> The C 1 ~C 4 alcohol is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, and tert-butanol, and preferably, the alcohol is methanol. The method according to any one of <1> to <3> above. <5> The method according to any one of <1> to <4> above, characterized in that the hydrogen sulfide / alcohol molar ratio in step a) is 0.1 to 100, preferably 1 to 50, and even more preferably 1 to 20. <6> The reaction of step a) is carried out in the presence of a catalyst, and the catalyst is an alumina-based catalyst, preferably thorium dioxide ThO deposited on a silicate support 2, preferably a cadmium sulfide-based catalyst on an alumina support, the following oxides: MgO, ZrO 2 , TiO 2 rutile (R) and TiO 2 anatase (A), CeO 2 , and a catalyst based on γ-Al 2 O 3 , preferably a catalyst based on a metal oxide supported on SiO 2 、Al 2 O 3 or Nb 2 O 5 doped with an alkali metal and optionally, a catalyst based on an alkali metal carbonate, a catalyst based on an alkali metal salt of a specific transition metal acid impregnated on γ-alumina, potassium tungstate K 2 WO 4 / Al 2 O 3 The method according to any one of <1> to <5> above, characterized in that it is selected from <7> The alkyl mercaptan / sulfur molar ratio in the oxidation step d) is 0.1 to 100, preferably 1 to 50, and even more preferably 1 to 20, The method according to any one of <1> to <6> above, characterized in that <8> The reaction temperature in the oxidation step d) is 20°C to 200°C, and the pressure is 2 to 30 bar absolute, The method according to any one of <1> to <7> above, characterized in that <9> The reaction in the oxidation step d) is carried out in the presence of a basic catalyst selected from a homogeneous catalyst, a two-phase catalyst or a heterogeneous catalyst; preferably, the catalyst is a heterogeneous basic catalyst; more preferably, the catalyst is a basic ion exchange resin, The method according to any one of <1> to <8> above, characterized in that <10> The purification step e) includes one or more distillation steps and optionally one or more basic catalyst steps, The method according to any one of <1> to <9> above, characterized in that

Claims

1. A method for the simultaneous production of alkyl mercaptans and dialkyl disulfides, comprising the following consecutive steps. a) Hydrogen sulfide (H ２ S) in the presence of C １ ~C ４ reacting the alcohol to produce a stream (M) comprising alkyl mercaptans, water, and optionally unreacted hydrogen sulfide. b) A step of purifying stream (M) to obtain a stream (N) rich in alkyl mercaptans. c) A step of recovering a first portion of the stream (N) containing the alkyl mercaptan purified in step b). d) A step of oxidizing a second portion of the stream (N) of alkyl mercaptan with sulfur to produce a stream (O) containing dialkyl disulfide, hydrogen sulfide, and optionally unreacted alkyl mercaptan. e) A step of purifying stream (O) to separate, on the one hand, rich dialkyl disulfide and, on the other hand, hydrogen sulfide and optionally alkyl mercaptan not reacted in step d). f) A step of recycling the hydrogen sulfide and optionally alkyl mercaptan separated in step e) into the stream (M) obtained from step a). g) A step of recovering the dialkyl disulfide separated in step e).

2. The recycling step f) recycles the stream before the purification step b), and the purification step b) removes hydrogen sulfide from the stream (M) to be purified, preferably by distillation. The method according to claim 1.

3. The method according to claim 1 or claim 2, characterized in that all of the stream containing hydrogen sulfide and optionally alkyl mercaptan not reacted in step d) is recycled into the stream (M) obtained from step a).

4. Said C １ -C ４ The alcohol is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol and tert-butanol, and preferably, the alcohol is methanol. The method according to claim 1 or claim 2.

5. The method according to claim 1 or claim 2, characterized in that the hydrogen sulfide / alcohol molar ratio in step a) is 0.1 to 100, preferably 1 to 50, and even more preferably 1 to 20.

6. The reaction of step a) is carried out in the presence of a catalyst, said catalyst being an alumina-based catalyst, preferably thorium dioxide ThO deposited on a silicate support ２ , preferably a cadmium sulfide-based catalyst on an alumina support, the following oxides: MgO, ZrO ２ , TiO ２ rutile (R) and TiO ２ anatase (A), CeO ２ , and a catalyst based on γ-Al ２ O ３ , preferably a metal oxide-based catalyst supported on SiO ２ , Al ２ O ３ or Nb ２ O ５ , an alkali metal carbonate-based catalyst, a catalyst based on an alkali metal salt of a specific transition metal acid impregnated on γ-alumina, potassium tungstate K ２ WO ４ / Al ２ O ３ The method according to claim 1 or claim 2, characterized in that it is selected from

7. The method according to claim 1 or claim 2, characterized in that the alkyl mercaptan / sulfur molar ratio in the oxidation step d) is 0.1 to 100, preferably 1 to 50, and even more preferably 1 to 20.

8. The method according to claim 1 or claim 2, characterized in that the reaction temperature in the oxidation step d) is 20 ° C to 200 ° C and the pressure is 2 to 30 bar absolute.

9. The reaction in the acidification step d) is carried out in the presence of a basic catalyst selected from a homogeneous catalyst, a two-phase catalyst or a heterogeneous catalyst; preferably, the catalyst is a heterogeneous basic catalyst; more preferably, the catalyst is a basic ion exchange resin, the method according to claim 1 or claim 2.

10. The purification step e) comprises one or more distillation steps and optionally one or more basic catalyst steps, the method according to claim 1 or claim 2.

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