Process for the preparation of mercaptans by hydrothiolysis of purified dialkyl sulfides

Abstract

This invention relates to a method for preparing at least one thiol, the method comprising the following steps: A) introducing H2S and at least one alcohol into a first reactor; B) reacting H2S with said at least one alcohol to obtain an effluent stream comprising at least one thiol, at least one dialkyl sulfide, and at least one dialkyl disulfide (DADS), and optionally unreacted H2S; C) separating from said effluent stream of step B) a stream F1 comprising one or more thiols, a stream F2 comprising one or more dialkyl sulfides and one or more DADS, and optionally a stream F3 comprising H2S; D) performing a purification step on stream F2 to separate: a stream F2' comprising one or more dialkyl sulfides; and one or more DADS; E) introducing stream F2' and H2S into a second reactor; F) performing a hydrothiolysis reaction of one or more dialkyl sulfides with H2S to obtain an effluent stream F4 comprising one or more thiols and optionally unreacted H2S; G) optionally, recycling stream F4 obtained from step F) back to step A).

Description

[0001] This invention relates to a method for preparing thiols from at least one alcohol and hydrogen sulfide, including a method for hydrothiolysis of purified dialkyl sulfides.

[0002] Thiols have attracted considerable attention in industry and are currently widely used in the chemical industry, especially as starting materials for the synthesis of more complex organic molecules. For example, methyl mercaptan (CH3SH) is used as a starting material for the synthesis of methionine (an essential amino acid for animal nutrition). Methyl mercaptan is also used in the synthesis of dialkyl disulfides, particularly dimethyl disulfide (DMDS), a sulfidation additive used in hydrogenation catalysts for petroleum fractions, and other applications.

[0003] Thiols, and especially methylthiols, are typically synthesized industrially from alcohols and hydrogen sulfide by known methods at elevated temperatures in the presence of a catalyst, according to the following equation (1):

[0004] Main reaction

[0005] ROH + H₂S → RSH + H₂O (1)

[0006] However, the reaction, according to the following equation (2), leads to the formation of byproducts such as dialkyl sulfides (which are symmetrical in the following case):

[0007] ROH + RSH → RSR + H2O (2)

[0008] Furthermore, when the main reaction is carried out in the presence of several alcohols, asymmetric dialkyl sulfides can also be obtained according to the following equations (3) and (4) (examples are given with two alcohols):

[0009] ROH+R'OH+2H2S->RSH+R'SH+2H2O (3)

[0010] ROH + R'SH → RSR' + H2O (4)

[0011] Symmetrical or asymmetric dialkyl sulfide byproducts are obtained in large quantities industrially and are primarily disposed of. This represents a loss of efficiency in the thiol production process and an increase in the costs associated with their disposal.

[0012] Dialkyl sulfides are sometimes upgraded by means of the following reaction (5) (also known as hydrothiolysis) to obtain the corresponding thiols:

[0013] Hydrogen sulfide reaction

[0014] RSR'+H2S->RSH+R'SH (5)

[0015] In the case of methyl mercaptan, the hydrogenolysis reaction is written according to the following equation (6):

[0016] CH3SCH3 + H2S -> 2 CH3SH (6)

[0017] The hydrothiolysis unit can therefore be integrated into the main unit for producing thiols obtained from at least one alcohol and H2S. However, adding a new unit to an existing industrial unit may cause technical integration problems. In particular, when the hydrothiolysis unit is integrated into the main thiol production unit, the inventors have observed unexpected blockages in the reactor or downstream of the hydrothiolysis unit.

[0018] Therefore, there is a need for a unit for the production of thiols from one or more alcohols and H2S, which incorporates a hydrothiolysis reaction and is industrially feasible, safe and inexpensive.

[0019] One object of the present invention is to provide an integrated method for preparing thiols, particularly from at least one alcohol and H2S, wherein dialkyl sulfide byproducts are treated by hydrosulfolysis in an industrially feasible and safe manner.

[0020] Another object of the present invention is to provide a method for preparing thiols, particularly from at least one alcohol and H2S, which incorporates an easy-to-perform hydrothiolysis method and, in particular, uses simple and inexpensive facilities.

[0021] Specifically, it has been observed that the preparation of one or more thiols from at least one alcohol and H2S can lead to the formation of dialkyl disulfide impurities (recorded as DADS and of type RSSR). Unbound by theory, these DADS can be formed according to the following balanced equation (7) (an example starting with methanol):

[0022] 2CH3SH+CH3OH→CH3-SS-CH3+CH4+H2O (7)

[0023] The inventors have determined that these DADS are ultimately obtained together with one or more dialkyl sulfides and then in a reactor in which hydrolysis of sulfides is performed. Over time, they can lead to pressure losses on the catalyst and / or blockage of the reactor or further downstream of the process. This phenomenon can be explained by coking of the catalyst due to parasitic or secondary reactions resulting from the hydrolysis of DADS. Sulfur products or impurities formed by such reactions can accumulate and cause blockages in industrial facilities, leading to obvious safety and production problems. This can be further problematic when the effluent stream from the hydrolysis reactor is recycled to the main mercaptan production unit.

[0024] In particular, when methyl mercaptan is formed from methanol and H2S, dimethyl disulfide (DMDS) may be formed secondarily. When this DMDS is present during the hydrolysis reaction, facilities (inside the reactor and downstream of the hydrolysis reactor) have been observed to be clogged by sulfur impurities.

[0025] The inventors have surprisingly discovered that when dialkyl sulfides previously separated from DADS are subjected to hydrosulfide hydrolysis, these pressure losses and / or blockages are no longer observed.

[0026] Therefore, the present invention relates to a method for the preferred continuous preparation of at least one thiol, the method comprising the following steps:

[0027] A) Introduce H2S and at least one alcohol into the first reactor;

[0028] B) React H2S with at least one alcohol to obtain an outlet stream comprising at least one thiol, at least one dialkyl sulfide and at least one dialkyl disulfide (DADS) and possibly unreacted H2S;

[0029] C) Separate the outlet stream obtained from step B) as follows:

[0030] - Stream F1 containing one or more thiols

[0031] - Stream F2 containing one or more dialkyl sulfides and one or more DADS, and

[0032] - Optional material flow F3 containing H2S;

[0033] D) Perform a purification step on feed stream F2 to separate:

[0034] - A feed stream F2' containing one or more dialkyl sulfides; and

[0035] -One or more DADS;

[0036] E) Introduce the feed stream F2' and H2S into the second reactor;

[0037] F) Perform a hydrothiolysis reaction of one or more dialkyl sulfides with H2S to obtain an outlet stream F4 containing one or more thiols and possibly unreacted H2S.

[0038] G) Optionally, the material flow F4 obtained from step F) is recycled back to step A).

[0039] Sulfides, disulfides and thiols

[0040] The term "thioether (sulfide)" specifically refers to any organic compound containing the -CSC- functional group.

[0041] The term "disulfide" specifically refers to any organic compound containing the -CSSC- functional group.

[0042] The term "dialkyl sulfide" specifically refers to compounds of the following general formula (I):

[0043] RS-R' (I)

[0044] R and R', which may be the same or different, are independently saturated straight-chain, branched, or cyclic, optionally substituted hydrocarbon groups.

[0045] Preferably, R and R', which may be the same or different, are independent of each other straight-chain, branched or cyclic alkyl groups containing between 1 and 18 carbon atoms, preferably between 1 and 12 carbon atoms.

[0046] The same or different R and R' can be independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl (and their positional isomers). Preferably, the same or different R and R' can be independently selected from methyl, ethyl, octyl, and dodecyl.

[0047] Preferably, R and R' are the same (which corresponds to a symmetrical dialkyl sulfide).

[0048] Symmetrical dialkyl sulfides particularly have the following general formula (II):

[0049] RSR (II)

[0050] R is defined as above.

[0051] Specifically, the dialkyl sulfide according to the present invention is selected from dimethyl sulfide, diethyl sulfide, dioctyl sulfide, didodecyl sulfide, and methyl ethyl sulfide. The dialkyl sulfide according to the present invention may be selected from dimethyl sulfide, di-n-propyl sulfide, diisopropyl sulfide, di-n-butyl sulfide, di-sec-butyl sulfide, and diisobutyl sulfide. Most particularly preferably, the dialkyl sulfide is dimethyl sulfide (DMS).

[0052] The thiols according to the invention are particularly those corresponding to the hydrogenolysis of dialkyl sulfides as defined above. The term "thiols" specifically refers to alkyl thiols.

[0053] Specifically, the term "alkylthiol" refers to compounds of the following general formula (III) or (IV):

[0054] R-SH(III) or R'SH(IV),

[0055] Where R and R' are defined for the above general formula (I).

[0056] Particularly preferred is methyl mercaptan.

[0057] Specifically, the term "dialkyl disulfide" (hereinafter also referred to as DADS) means a compound of the following general formula (V):

[0058] RSS-R' (V),

[0059] Where R and R' are defined for the above general formula (I).

[0060] Specifically, the dialkyl disulfide according to the invention is selected from dimethyl disulfide, diethyl disulfide, dioctyl disulfide, didodecyl disulfide, and methyl ethyl disulfide. The dialkyl disulfide according to the invention may be selected from dimethyl disulfide, diethyl disulfide, dioctyl disulfide, and didodecyl disulfide. Most particularly preferably, the dialkyl disulfide is dimethyl disulfide (DMDS).

[0061] For steps A) through E), it should be understood that when the two reagents are introduced into the reactor, they can be introduced into the reactor separately or they can be combined before being introduced into the reactor. The introduction is performed routinely.

[0062] Fresh H2S and / or recycled H2S can be fed into one or more reactors in which the main reaction and / or hydrolysis of sulfur occur. The recycled H2S can be unreacted H2S collected at the end of one or more of steps B), C), D) and / or F), preferably at the end of steps C) and / or F).

[0063] Step B) – The reaction of at least one alcohol with H2S to form a thiol

[0064] The reaction between alcohols and H₂S to form thiols and water is a known reaction, for example, as described in patents US 2820062, US 7645906 B2, and US2820831. For example, the reaction can be carried out at temperatures from 200°C to 450°C and / or at pressures ranging from reduced pressure to 100 bar. Generally, a catalyst is present, such as alumina promoted by alkali metals and / or alkaline earth metals. H₂S may be present in excess.

[0065] In these reagents, at least one alcohol may be used, preferably one or two alcohols. Preferably, only one alcohol is used. One or more alcohols may be selected, in particular, from (C1-C2)... 18 ) or even (C1-C 12 Alkyl alcohols, and mixtures thereof. In particular, the alcohol may be selected from methanol, ethanol, octanol, dodecyl alcohol, and mixtures thereof. Preferably, the alcohol used is methanol.

[0066] At the end of this step, an effluent stream is collected, in particular, containing at least one thiol, at least one dialkyl sulfide (as a byproduct), and at least one dialkyl disulfide (DADS) (as a byproduct or impurity), and possibly H2S. The effluent stream may also contain water.

[0067] Step C) – One or more thiols are separated from one or more dialkyl sulfides on the one hand and on the other hand from… DADS separation

[0068] Prior to step C), the effluent stream from step B) may undergo one or more purification steps, for example, to remove any water and / or H2S that may be present. These purification steps may be performed by routine separation and / or decantation and / or distillation.

[0069] In step C), the outlet stream obtained from step B) is separated as follows:

[0070] - Stream F1 containing one or more thiols

[0071] - Stream F2 containing one or more dialkyl sulfides and one or more DADS, and

[0072] - Optional material flow F3 containing H2S.

[0073] Separation step C) can be performed by conventional methods, preferably by distillation (especially under reduced pressure). During distillation, the pressure can be between 1 and 40 bar absolute pressure, and / or the temperature at the top of the column can be between 20°C and 100°C, and the temperature at the bottom of the column can be between 40°C and 200°C. For example, distillation can be carried out at pressures between 0.1 bar and 10 bar absolute pressure, especially between 1 and 10 bar absolute pressure.

[0074] Preferably, material flows F1 and F2 are liquids, and / or material flow F3 is a gas. Material flow F3 may be wholly or partially:

[0075] -Recycle back to step A), and / or

[0076] -Recycle back to step E), and / or

[0077] - Combined with material flow F1 or F2.

[0078] Step D) – Purification of dialkyl sulfides

[0079] In step D), in particular, a purification step is performed on feed stream F2 to obtain:

[0080] - A feed stream F2' containing one or more dialkyl sulfides; and

[0081] - One or more DADS or a flow containing one or more DADS F5.

[0082] Step D) is particularly the step of separating one or more dialkyl sulfides on one side and one or more DADS on the other side, and optionally separating heavy impurities present in stream F2. Step D) is more particularly the step of separating dimethyl sulfides from DMDS present in stream F2.

[0083] In particular, a feed stream F2' rich in one or more dialkyl sulfides was obtained. DADS or F5 feed streams can be collected and optionally purified. The term "feed stream F2' rich in one or more dialkyl sulfides" specifically means a feed stream in which the weight percentage of one or more dialkyl sulfides contained (relative to the total weight of said feed stream F2') is greater than the weight percentage of one or more dialkyl sulfides relative to the total weight of said feed stream (i.e., feed stream F2) prior to said purification step.

[0084] Stream F2 may contain at least 80% by weight, preferably at least 95% by weight, of one or more dialkyl sulfides relative to the total weight of stream F2. For example, stream F2 contains one or more dialkyl sulfides between 95% by weight and 99.9% by weight relative to the total weight of stream F2.

[0085] The material flow F2 may contain between 0.1% and 20% by weight, preferably between 0.1% and 5% by weight, relative to the total weight of the material flow F2.

[0086] The purification step may correspond to at least one distillation step, or at least one step of adsorbing one or more DADS onto a porous support (e.g., activated carbon), or at least one step of selectively extracting one or more DADS using a solvent (e.g., water) that is immiscible with one or more dialkyl sulfides and miscible with one or more DADS. These various techniques may be combined.

[0087] Ideally, the purification step corresponds to at least one distillation step, preferably a single distillation step. According to one embodiment, the purification step consists of a single distillation step.

[0088] The pressure during distillation can be between 0.05 and 75 bar absolute pressure, preferably between 1 and 30 bar absolute pressure, and more particularly between 5 and 15 bar absolute pressure, for example, about 10, 11, 12, 13, 14 or 15 bar absolute pressure.

[0089] The distillation temperature can be between 20°C and 250°C, preferably between 60°C and 200°C, and even more preferably between 100°C and 180°C.

[0090] The temperature at the top of the column can be between 20°C and 250°C, preferably between 60°C and 200°C, and even more preferably between 100°C and 180°C. In particular, the top of the column is at a temperature between 100°C and 180°C and a pressure between 5 and 15 bar absolute pressure.

[0091] The temperature at the bottom of the column can be between 50°C and 300°C, preferably between 100°C and 250°C. In particular, the temperature at the bottom of the column is higher than the temperature at the top of the column.

[0092] A portion of feed stream F2' can be returned to the distillation column as reflux (hereinafter feed stream F6). The mass reflux ratio (F6 / F2') in the column can be between 0 and 0.99, preferably between 0 and 0.70.

[0093] Preferably, flow F2' is collected at the top of the tower and DADS (or flow F5) is collected at the bottom.

[0094] As indicated above, stream F3 can be combined with stream F2, in which case it can undergo purification step D). In the case of distillation, H2S is finally obtained at the top along with stream F2' and can be sent together to the hydrogen sulfide decomposition reactor.

[0095] Distillation can be performed in any known type of distillation column. It can be a column with trays (e.g., trays with caps, trays with valves, or trays with sieves) or with packing (e.g., with monolithic (bulk) packing or structured packing). Distillation can be performed in tray columns (plate columns) that preferably contain between 5 and 50 trays, more preferably between 10 and 40 trays, such as between 10 and 30 trays. Distillation can also be performed in separation columns (distribution columns, "DWC" or partition wall columns). Separation plates can be fixed or movable, for example, using structured or monolithic packing.

[0096] At the end of step D), the feed stream F2' contains, in particular, less than 1000 ppm (by mass), preferably less than 500 ppm, more preferably less than 100 ppm or even less than 10 ppm of DADS. In particular, the feed stream F2' contains strictly less than 1000 ppm (by mass).

[0097] One or more thiols may be collected from stream F1 and / or stream F4, preferably collected from stream F1.

[0098] Step F) – Hydrogen sulfide reaction of one or more dialkyl sulfides with H2S

[0099] The feed streams F2' and H2S are introduced into the second reactor.

[0100] Under the reaction temperature and pressure conditions, the hydrogen sulfide hydrolysis reagent can be in gaseous (gas state), liquid (liquid state) or solid (solid state) form, preferably in gaseous or liquid form.

[0101] The temperature for the hydrolysis of sulfur can be between 100°C and 500°C, preferably between 200°C and 400°C, more preferably between 200°C and 380°C, and even more preferably between 250°C and 380°C.

[0102] The hydrolysis reaction can be carried out at pressures between 50 mbar and 100 bar absolute pressure, preferably between atmospheric pressure (about 1 bar) and 50 bar absolute pressure, and advantageously between 5 and 20 bar absolute pressure.

[0103] The H2S / dialkyl sulfide molar ratio can be between 0.1 / 1 and 50 / 1, preferably between 2 / 1 and 20 / 1. Preferably, the ratio is between 2 / 1 and 15 / 1, more preferably between 2 / 1 and 8 / 1, for example between 2 / 1 and 6 / 1, such as 4 / 1.

[0104] The flow rate (velocity) of dialkyl sulfides entering the reactor in which hydrothiolysis of sulfur occurs can be gradual.

[0105] The reaction is advantageously carried out in the presence of a catalyst. The reagents (one or more dialkyl sulfides and H₂S) can be controlled with a specific contact time with the catalyst. This parameter is expressed by the space-time velocity equation:

[0106] (HSV) = (Total CNTP gas flow rate, based on the volume of dialkyl sulfide + H2S entering) / (Volume of catalyst in reactor).

[0107] HSV can be used at 100 and 1200h -1 between

[0108] GHSV (Gaseous Hourly Space Velocity) can be measured at 1 and 100,000 h. -1 Between 100 and 10,000 h -1 Between 100 and 3000 hours, priority is given to [the specific timeframe]. -1 between.

[0109] The hydrogen sulfide reaction can be carried out in any type of reactor, such as a fixed-bed tubular reactor, a multi-tube reactor with microchannels, a catalyst wall, or a fluidized bed, preferably a fixed-bed tubular reactor.

[0110] The amount of each reagent supplied to the reactor can vary depending on the reaction conditions (e.g., temperature, space velocity, etc.) and is determined based on common sense. Hydrogen sulfide can be present in excess.

[0111] Therefore, any type of catalyst that allows the catalytic hydrolysis reaction can be used.

[0112] Particularly noteworthy are catalysts (whether promoted or non-promoted) based on zeolites, alumina (Al2O3), silica (SiO2), titanium dioxide (TiO2), aluminosilicates, bentonite, or zirconium oxide (ZrO2). These catalysts comprise or may consist of zeolites, alumina (Al2O3), silica (SiO2), titanium dioxide (TiO2), aluminosilicates, bentonite, or zirconium oxide (ZrO2), and optionally one or more promoters.

[0113] The term "promoter" (also known as "dopant") specifically refers to a chemical substance or composition of chemical substances that can alter and, in particular, improve the catalytic activity of a catalyst. For example, the term "promoter" refers to a chemical substance or composition of chemical substances used, relative to a single catalyst, to improve the conversion and / or selectivity of a catalytic reaction. Such substances are known, for example, alkali metals, nickel (Ni), molybdenum (Mo), cobalt (Co), tungsten (W), or combinations thereof (e.g., a combination of NiMo and CoMo). It should be understood that these promoters may be in the form of their oxides or sulfides (e.g., sodium may be in the oxidized form of Na₂O). Preferably, the promoter is selected from alkali metal oxides, particularly Na₂O.

[0114] The term "alkali metal" specifically refers to lithium, sodium, potassium, rubidium, and cesium, with sodium being preferred.

[0115] Specifically, the catalyst comprises less than 10% by weight of an accelerator relative to the total weight of the catalyst, more preferably less than 2% by weight of an accelerator. The catalyst may comprise an accelerator between 0% and 10% by weight relative to the total weight of the catalyst, preferably between 0% and 2% by weight, for example between 0.01% and 2% by weight of an accelerator.

[0116] Therefore, the following catalysts can be used:

[0117] - Promoted or non-promoted zeolite; preferably X, Y or L type zeolite, more preferably Y type zeolite;

[0118] -Alumina-based catalysts, whether promoting or not;

[0119] Catalysts based on alumina, catalysts based on NiMo (nickel / molybdenum) and / or CoMo (cobalt / molybdenum) supported on alumina, catalysts based on cadmium sulfide supported on alumina, catalysts based on tungsten trisulfide supported on alumina, catalysts based on alumina promoted by at least 1% by weight of alkali metal oxide, or catalysts based on non-promoted alumina (e.g., γ-alumina) (such catalysts are particularly described in patent applications WO 2018 / 035316, WO 2017 / 210070 and US2008 / 0200730);

[0120] -Promoted or non-promoted silica (SiO2) catalysts;

[0121] -Promoted or non-promoted titanium dioxide (TiO2) catalysts (especially as described in patent application FR3101631);

[0122] -Promoting or non-promoting aluminosilicate-based catalysts;

[0123] - Promoted or unpromoted bentonite-based catalysts, for example, promoted with at least 1% by weight of an alkali metal oxide, as described in US2008 / 0200730; and

[0124] -Promoted or non-promoted zirconium oxide-based catalysts (especially as described in patent application FR 3101631).

[0125] Preferably, the catalyst according to the invention is a promoted or non-promoted X, Y or L type zeolite, more preferably Y type zeolite.

[0126] Zeolites are crystals formed by aluminosilicate microporous frameworks or supports, with their interconnected pore spaces initially occupied by cations and water molecules.

[0127] The zeolite according to the invention particularly has a content of 24.30 and The lattice parameters and / or Si / Al ratio between 2.5 and 15. Therefore, it can be mentioned that Axens Corporation, under the name... Zeolite for sale.

[0128] Specifically, the zeolite contains less than 10% by weight of alkali metal oxide relative to the total weight of the zeolite, more preferably less than 2% by weight of alkali metal oxide. Specifically, the alkali metal oxide is sodium oxide (Na₂O).

[0129] Most particularly preferably, the catalyst is a Y-type zeolite containing between 0% and 10% by weight, preferably between 0.01% and 10% by weight, and more preferably between 0.01% and 2% by weight relative to the total weight of the zeolite.

[0130] The initial zeolite cation (e.g., sodium) can be completely or partially replaced by at least one other cation, such as those selected from (in addition to the cations to be replaced in the following list): H, Li, Na, K, Mg, Ca, Cs, Ba, La, Zr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Cu, Zn, Ag, Sn, and Ga.

[0131] These cation exchanges can be performed using conventional techniques.

[0132] For example, zeolite can be treated in ammonium form. This involves calcination in the presence of steam. Then, the ammonium form (NH4) is removed by heating. + ) zeolite is converted into proton form (H + Steam treatment hydrolyzes the Si-O-Al bonds. Aluminum migrates into the micropore volumes in the form of aluminum fragments. During the formation of these aluminum or aluminum-silicon materials, partial lattice collapse occurs, creating mesopores. Silicon in these portions of the lattice is then transported to the vacancies via steam. This technique is explained in particular in the publication by Christine EAKirschhock, Eddy J.P. Feijen, Pierre A. Jacobs, and Johan A. Martens: March 15, 2008, https: / / doi.org / 10.1002 / 9783527610044.hetcat0010 (Part 2. Preparation of Solid Catalysts; 2.3. Bulk Catalysts and Supports; 2.3.5 Hydrothermal Zeolite Synthesis).

[0133] The catalyst according to the invention may contain stabilizers and / or binders. Stabilizers and binders are those conventionally used in the field of catalysts. The catalyst may be pre-activated or pretreated.

[0134] Step G) – Optional Recirculation

[0135] The effluent stream F4 from the second reactor in step F) can be partially or completely recycled back to the first reactor in step A). ​​Therefore, the H2S contained in stream F4 can be fully or partially recycled. A particular advantage of this recycling is that the entire mercaptan production process has only one H2S inlet, for example, at the inlet of the hydrolysis reactor.

[0136] Therefore, the method for hydrothiolysis of purified dialkyl sulfides according to the invention, integrated into an industrial facility for the production of thiols, allows for the efficient reprocessing of dialkyl sulfide byproducts as products of interest, and advantageously recycles H2S while preventing any blockages and / or pressure losses, enabling safe and continuous operation.

[0137] The resulting thiols are a result of the main reaction and the hydrogen thiolysis reaction, which increases productivity.

[0138] Furthermore, thiols derived from hydrogen thiolysis and unreacted H2S can be directly (especially without intermediate purification steps) reintroduced into the main reactor without affecting the reaction between one or more alcohols and H2S.

[0139] The thiols produced by the two reactions (the main reaction and the hydrothiolysis reaction) can then be purified and / or collected at a single location, such as at the outlet of the main reactor.

[0140] Therefore, according to the present invention, a simple and efficient method for upgrading dialkyl sulfides can be obtained, which is fully integrated into the industrial mercaptan production chain. The apparatus is particularly easy to implement: it can be easily connected to the main unit and requires only minimal modifications.

[0141] The present invention also relates to purifying DADS impurities from a feed stream containing dialkyl sulfides using at least one distillation prior to performing hydrothiolysis of dialkyl sulfides with H2S, particularly as described above.

[0142] Unless otherwise stated, the phrase "between X and X" includes the boundary mentioned. Attached Figure Description

[0143] Figure 1 :

[0144] Figure 1 The diagram schematically shows a methyl mercaptan production unit that incorporates a process for the hydrolysis of purified dimethyl sulfide (DMS).

[0145] In step A), H2S and methanol are placed in the reactor in which step B) is carried out to form a feed stream containing methyl mercaptan, DMS, and DMDS. This feed stream undergoes separation in step C) to obtain:

[0146] - Flow F1 containing methyl mercaptan

[0147] -Including DMS and DMDS material flow F2, and

[0148] -Optional material flow F3 containing H2S;

[0149] Distillation stream F2 is used to separate DMS from DMDS impurities, and stream F2' containing purified DMS is obtained at the top of the column. Stream F5 containing DMDS is obtained at the bottom of the column. Stream F6 (a portion of F2') is returned to the distillation column. Stream F2' and H2S stream are introduced into the reactor to perform hydrosulfide reaction (step F). An outlet stream F4 containing methyl mercaptan and H2S is obtained. Stream F4 is completely recycled to step A).

[0150] The following examples are given for illustrative purposes and are not intended to limit the invention. Example

[0151] Example 1: Separation of DMDS impurities before hydrogen sulfide hydrolysis reaction

[0152] Test A :

[0153] The dimethyl sulfide (DMS) hydrogenolysis reaction is carried out as follows, with or without DMDS.

[0154] DMS containing the following (by weight relative to the total weight of DMS+DMDS) is introduced into the reactor:

[0155] -0.02% by weight of DMDS; or

[0156] -14% by weight of DMDS.

[0157] The hydrogenolysis reaction is carried out under the following conditions.

[0158] The catalyst used was obtained from Axens. (1 / 8 extruded catalyst with an inner radius of 7.7 mm).

[0159] It is a Y-type zeolite with lattice parameters between 24 and 30. Between 2.5 and 15, the Si / Al ratio is between 2.5 and 15, and it contains less than 10% by weight of Na2O.

[0160] The reaction temperature was 340℃ and the pressure was 25 barg.

[0161] The H2S / DMS molar ratio is 30.0.

[0162] Results: In the case of DMS containing 14 wt% DMDS, clogging was observed in the reactor after several hours, while in the case of DMS containing 0.02 wt% DMDS, no clogging was observed after 1000 hours.

[0163] This test demonstrates the role of DMDS impurities in the clogging phenomenon.

[0164] Test B:

[0165] Before performing the hydrogen sulfide hydrolysis reaction as described in Test A, the introduced DMS is first separated from the DMDS impurities by distillation, with or without.

[0166] The distillation conditions are as follows:

[0167] Use a tower with between 10 and 20 trays.

[0168] The pressure at the tower head is between 5 and 15 barg.

[0169] The tower head temperature is between 130℃ and 140℃.

[0170] The temperature at the bottom of the tower is between 135℃ and 150℃.

[0171] The reflux velocity is between 900 kg / h and 1200 kg / h.

[0172] Composition of the incoming material flow:

[0173] [Table 1]

[0174]

[0175] Without pre-distillation, clogging occurred after 100 hours of hydrolysis. With pre-distillation, no clogging was observed after 1000 hours.

Claims

1. A method for preparing at least one thiol, comprising the following steps: A) Introduce H2S and at least one alcohol into the first reactor; B) React H2S with at least one alcohol to obtain an outlet stream comprising at least one thiol, at least one dialkyl sulfide and at least one dialkyl disulfide (DADS) and possibly unreacted H2S; C) Separate the outlet stream obtained from step B) as follows: - Flow F1 containing one or more thiols - A feed stream F2 containing one or more dialkyl sulfides and one or more DADS, and - Optional material flow F3 containing H2S; D) Perform a purification step on feed stream F2 to separate: - A feed stream F2' containing one or more dialkyl sulfides; and - One or more DADS; E) Introduce the feed streams F2' and H2S into the second reactor; F) Perform a hydrothiolysis reaction of one or more dialkyl sulfides with H2S to obtain an outlet stream F4 containing one or more thiols and possibly unreacted H2S. G) Optionally, the material flow F4 obtained from step F) is recycled back to step A).

2. The preparation method according to claim 1, wherein step D) corresponds to at least one distillation step, or at least one step of adsorbing one or more DADS onto a porous support, or at least one step of selectively extracting one or more DADS using a solvent that is immiscible with one or more dialkyl sulfides and miscible with one or more DADS.

3. The preparation method according to claim 1 or 2, wherein step D) corresponds to at least one distillation step.

4. The preparation method according to claim 3, wherein step D) corresponds to a single distillation step.

5. The preparation method according to claim 3, wherein in the distillation step D), the pressure is between 0.05 and 75 bar absolute pressure.

6. The preparation method according to claim 3, wherein in the distillation step D), the pressure is between 5 and 15 bar absolute pressure.

7. The preparation method according to claim 3, wherein in the distillation step D), a portion of the feed stream F2' is returned to the distillation column as reflux.

8. The preparation method according to claim 3, wherein in the distillation step D): - The tower head temperature is between 20℃ and 250℃; and - The temperature at the bottom of the tower is between 50°C and 300°C.

9. The preparation method according to claim 3, wherein in the distillation step D): - The tower head temperature is between 100℃ and 180℃; and - The temperature at the bottom of the tower is between 100°C and 250°C.

10. The preparation method according to claim 1 or 2, wherein step F) is performed in the presence of a catalyst selected from promoting or non-promoting catalysts based on zeolite, alumina (Al2O3), silica (SiO2), titanium dioxide (TiO2), aluminosilicate, bentonite or zirconium oxide (ZrO2).

11. The preparation method according to claim 1 or 2, wherein in step F), the molar ratio of H2S / dialkyl sulfide is between 0.1 / 1 and 50 / 1.

12. The preparation method according to claim 1 or 2, wherein in step F), the molar ratio of H2S / dialkyl sulfide is between 2 / 1 and 8 / 1.

13. The preparation method according to claim 1 or 2, wherein in step G), all of the material flow F4 is recycled to step A).

14. The preparation method according to claim 1 or 2, wherein the alcohol in step A) is methanol.

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