METHOD FOR PREPARING MERCAPTANS WITH SULFHYDROLYSIS OF PURIFIED DIALKYL SULFIDES

Abstract

The present invention relates to a process for preparing at least one mercaptan, comprising the following steps: A) H.sub.2S and at least one alcohol are introduced into a first reactor; B) the H.sub.2S and said at least one alcohol are reacted to obtain an outlet stream comprising at least one mercaptan, at least one dialkyl sulfide and at least one dialkyl disulfide (DADS) and possibly unreacted H.sub.2S; C) said outlet stream obtained from step B) is separated into: a stream F1 comprising the mercaptan(s), a stream F2 comprising the dialkyl sulfide(s) and the DADS(s), and optionally a stream F3 comprising H.sub.2S; D) a purification step is performed on stream F2 in order to separate: a stream F2 comprising the dialkyl sulfide(s); and the DADS(s); E) stream F2 is introduced with H.sub.2S into a second reactor; F) a sulfhydrolysis reaction of the dialkyl sulfide(s) with H.sub.2S is performed to obtain an outlet stream F4 comprising said mercaptan(s), and possibly unreacted H.sub.2S; G) optionally, stream F4 obtained from step F) is recycled into step A).

Claims

1. A process for preparing at least one mercaptan, comprising the following steps: A) H.sub.2S and at least one alcohol are introduced into a first reactor; B) the H.sub.2S and said at least one alcohol are reacted to obtain an outlet stream comprising at least one mercaptan, at least one dialkyl sulfide and at least one dialkyl disulfide (DADS) and possibly unreacted H.sub.2S; C) said outlet stream obtained from step B) is separated into: a stream F1 comprising the mercaptan(s), a stream F2 comprising the dialkyl sulfide(s) and the DADS(s), and optionally a stream F3 comprising H.sub.2S; D) a purification step is performed on stream F2 in order to separate: a stream F2 comprising the dialkyl sulfide(s); and the DADS(s); E) stream F2 is introduced with H.sub.2S into a second reactor; F) a sulfhydrolysis reaction of the dialkyl sulfide(s) with H.sub.2S is performed to obtain an outlet stream F4 comprising said mercaptan(s), and possibly unreacted H.sub.2S; G) optionally, stream F4 obtained from step F) is recycled into step A).

2. The preparation process according to claim 1, in which said step D) corresponds to at least one distillation step, or to at least one step of adsorption of the DADS(s) on a porous support, or to at least one step of selective extraction of the DADS(s) using a solvent that is immiscible with said dialkyl sulfide(s) and miscible with said DADS(s).

3. The preparation process according to claim 1, in which said step D) corresponds to at least one distillation step, preferentially to a single distillation step.

4. The preparation process according to claim 3, in which, in the distillation step D), the pressure is between 0.05 and 75 bar absolute, preferably between 1 and 30 bar absolute, more particularly between 5 and 15 bar absolute.

5. The preparation process according to claim 3, in which, in the distillation step D), part of stream F2 may be returned to the distillation column as reflux.

6. The preparation process according to claim 3, in which, in the distillation step D): the column head temperature is between 20? C. and 250? C., preferably between 60? C. and 200? C., more preferentially between 100? ? C. and 180? C.; and the column bottom temperature is between 50? C. and 300? C., preferably between 100? C. and 250? ? C.

7. The preparation process according to claim 1, in which step F) is performed in the presence of a catalyst chosen from promoted or non-promoted catalysts based on zeolites, alumina (Al.sub.2O.sub.3), silica (SiO.sub.2), titanium dioxide (TiO.sub.2), aluminosilicate, bentonite or zirconia (ZrO.sub.2); preferably, the catalyst is a zeolite.

8. The preparation process according to claim 1, in which, in step F), the H.sub.2S/dialkyl sulfide mole ratio is between 0.1/1 and 50/1, preferably between 2/1 and 20/1, more preferentially between 2/1 and 8/1.

9. The preparation process according to claim 1, in which, in step G), all of the stream F4 is recycled into step A).

10. The preparation process according to claim 1, in which the alcohol of step A) is methanol.

Description

DESCRIPTION OF THE FIGURES

[0117] FIG. 1 schematically shows a methyl mercaptan production unit incorporating a process for the sulfhydrolysis of a purified dimethyl sulfide (DMS).

[0118] In step A), H.sub.2S and methanol are placed in the reactor in which step B) takes place, to form a stream comprising methyl mercaptan, DMS and DMDS. This stream undergoes separation in step C) to obtain: [0119] a stream F1 comprising methyl mercaptan, [0120] a stream F2 comprising the DMS and the DMDS, and [0121] an optional stream F3 comprising H.sub.2S; [0122] Stream F2 is distilled to separate the DMS from the DMDS impurity and to obtain a stream F2 at the top of the column comprising purified DMS. A stream F5 comprising the DMDS is obtained at the bottom of the column. A stream F6, part of F2, is returned to the distillation column. Stream F2 is introduced with a stream of H.sub.2S, into a reactor to perform the sulfhydrolysis reaction (step F)). An outlet stream F4 comprising methyl mercaptan and H.sub.2S is obtained. Stream F4 is fully recycled into step A).

[0123] The examples below are given for illustrative purposes and do not limit the present invention.

EXAMPLES

Example 1: Separation of the DMDS Impurity Prior to the Sulfhydrolysis Reaction

Test A:

[0124] A dimethyl sulfide (DMS) sulfhydrolysis reaction is performed in the presence or absence of DMDS, as follows.

[0125] DMS comprising the following (relative to the total weight DMS+DMDS) is introduced into a reactor: [0126] either 0.02% by weight of DMDS; [0127] or 14% by weight of DMDS.

[0128] The sulfhydrolysis reaction is performed under the following conditions.

[0129] The catalyst used is TCC101? from Axens (catalyst in 1/8 extruded form with an internal radius of 7.7 mm).

[0130] It is a Y-type zeolite with a lattice parameter of between 24.30 and 24.70 ?, an Si/Al ratio of between 2.5 and 15 and comprising less than 10% by weight of Na.sub.2O.

[0131] The reaction temperature is 340? C. and the pressure is 25 barg.

[0132] The H.sub.2S/DMS mole ratio is 30.0.

[0133] Result: With DMS comprising 14% by weight of DMDS, clogging was observed in the reactor after a few hours, whereas with DMS comprising 0.02% by weight of DMDS, no clogging was observed after 1000 hours.

[0134] This test demonstrates the role of the DMDS impurity in the clogging phenomena.

Test B:

[0135] Before performing the sulfhydrolysis reaction as described in test A, the introduced DMS is first separated or not from the DMDS impurity by distillation.

[0136] The distillation conditions are as follows:

[0137] A column with a number of trays of between 10 and 20 is used.

[0138] The column head pressure is between 5 and 15 barg.

[0139] The column head temperature is between 130? ? C. and 140? C.

[0140] The column bottom temperature is between 135? ? C. and 150? C.

[0141] The reflux flow rate is between 900 kg/h and 1200 kg/h.

Composition of the Entering Stream:

[0142]

TABLE-US-00001 TABLE 1 Mass composition of the Without With stream introduced into distillation Distillation the sulfhydrolysis reactor (F2) (F2) % DMS 98.8% 99.3% % MeSH 0.07% 0.08% % H.sub.2O 0.60% 0.60% % DMDS 0.53% 0.02%

[0143] Without prior distillation, clogging occurs after 100 h of running the sulfhydrolysis. With prior distillation, no clogging is observed after 1000 h.