METHOD FOR PREPARING METHYL MERCAPTAN

Abstract

The present invention relates to a method for preparing methyl mercaptan, in batches or continuously, preferably continuously, said method including at least the following steps: a) reacting at least one hydrocarbon feedstock in the presence of hydrogen sulphide (H.sub.2S) and optionally sulphur (S) such as to form carbon disulphide (CS.sub.2) and hydrogen (H.sub.2); b) reacting said carbon disulphide (CS.sub.2) by hydrogenation in the presence of said hydrogen (H.sub.2) obtained in step a) such as to form methyl mercaptan (CH.sub.3SH), hydrogen sulphide (H.sub.2S) and possibly hydrogen (H2); c) optionally recirculating said hydrogen sulphide (H.sub.2S) formed during step b) to step a); and d) recovering the methyl mercaptan.

Claims

1. A process for preparing methyl mercaptan, batchwise or continuously, said process comprising at least the following steps: a) reacting at least one hydrocarbon charge in the presence of hydrogen sulphide (H.sub.2S) and optionally of sulphur (S) to form carbon disulphide (CS.sub.2) and hydrogen (H.sub.2), b) carrying out a hydrogenation reaction of said carbon disulphide (CS.sub.2) in the presence of said hydrogen (H.sub.2), both obtained in step a), to form methyl mercaptan (CH.sub.3SH), hydrogen sulphide (H.sub.2S) and optionally hydrogen (H.sub.2), c) optionally, recycling said hydrogen sulphide (H.sub.2S) formed in step b) to step a), and d) recovering the methyl mercaptan.

2. The process according to claim 1, wherein the hydrocarbon charge is a hydrocarbon charge in gaseous, liquid or solid form and comprises at least one hydrocarbon having a hydrocarbon chain in saturated or unsaturated linear, branched or cyclic form.

3. The process according to claim 1, wherein the hydrocarbon charge comprises at least one alkane.

4. The process according to claim 1, wherein the hydrocarbon charge is methane.

5. The process according to claim 1, wherein the hydrogen sulphide formed in step b) is recycled into step a).

6. The process according to claim 1, wherein hydrogen is formed in step b) and is reacted with sulphur to form hydrogen sulphide.

7. The process according to claim 1, wherein the molar H.sub.2S/hydrocarbon charge ratio is between 0.5 and 10, endpoints included.

8. The process according to claim 1, wherein step a) is carried out at a reaction temperature between 500 C. and 1300 C.

9. The process according to claim 1, wherein step b) is carried out at a reaction temperature between 100 C. and 400 C.

10. The process according to claim 1, wherein the methyl mercaptan is reacted with sulphur to form dimethyl disulphide.

11. The process according to claim 1, wherein the process is performed continuously.

12. The process according to claim 1, wherein the hydrocarbon charge is in gaseous form.

13. The process according to claim 1, wherein the hydrocarbon charge comprises at least one alkane selected from the group consisting of methane, ethane, propane and butane.

14. The process according to claim 1, wherein the molar H.sub.2S/hydrocarbon charge ratio is between 1 and 3, endpoints included.

15. The process according to claim 1, wherein step a) is carried out at a reaction temperature between 700 C. and 1100 C.

16. The process according to claim 1, wherein step a) is carried out at a reaction temperature between 800 C. and 1000 C.

17. The process according to claim 1, wherein step b) is carried out at a reaction temperature between 200 C. and 300 C.

Description

EXAMPLES

[0101] For each of the examples, the reaction products and the products which have not reacted are vaporized and analysed by gas chromatography with a capillary column equipped with a detector (microGC, screen/PPU column in series with a PoraPLOT column from Agilent Technologies, pTCD detector).

[0102] In the examples below, the degrees of conversion and selectivity are determined as follows:

[0103] Degree of molar conversion of CH.sub.4 (% C.sub.CH4):

% C.sub.CH4=[(n.sub.0CH4n.sub.CH4 residual)/n.sub.0CH4]*100

where n.sub.0CH4 is the initial number of moles of CH.sub.4 and n.sub.CH4 residual is the number of moles of unreacted CH.sub.4.

[0104] Degree of molar conversion of CS.sub.2 (% C.sub.CS2):

% C.sub.CS2=[(n.sub.0CS2n.sub.CS2 residual)/n.sub.0CS2]*100

where n.sub.0CS2 is the initial number of moles of CS.sub.2 and n.sub.CS2 residual is the number of moles of unreacted CS.sub.2.

[0105] Molar selectivity for CH.sub.3SH (% SCH.sub.3SH):

% S.sub.CH3SH=[n.sub.CH3SH/(n.sub.0CS2n.sub.CS2 residual)]*100

where n.sub.CH3SH is the number of moles of CH.sub.3SH produced during the process according to the invention.

[0106] Molar selectivity for CS.sub.2:

% S.sub.CS2=[n.sub.CS2/(n.sub.0CH4n.sub.CH4 residual)]*100

where n.sub.CS2 is the number of moles of CS.sub.2 produced in the process of the invention.

Example 1

[0107] An Incoloy 800 HT reactor containing 12 grams of catalyst containing 0.5% by weight of platinum on alumina, sold by STREM is placed in an oven. The catalyst is intercalated between two layers of carborundum.

[0108] The reactor is supplied with 20 NL.Math.h.sup.1 (or 893 mmol.Math.h.sup.1) of hydrogen sulphide (H.sub.2S) and 10 NL.Math.h.sup.1 (or 446 mmol.Math.h.sup.1) of methane (CH.sub.4). These two gases are preheated independently to 500 C. before entering the reactor. The reactor is brought to a temperature of 900 C. by means of the oven, and the pressure at the outlet of the reactor is regulated at 3 bar absolute. The flow rate of the exiting gases, taken under the standard conditions of temperature and pressure, in other words 0 C. and 1 atmosphere (101325 Pa), is 37.5 NL.Math.h.sup.1.

[0109] Gas-chromatographic analysis of the exiting gases indicates the presence of four gases: unconverted CH.sub.4 and H.sub.2S, and also CS.sub.2 and H.sub.2, which have been produced with a molar H.sub.2/CS.sub.2 ratio of 4. Under these conditions, the molar conversion of CH.sub.4 is 32%, with a selectivity for CS.sub.2 of 100%.

[0110] These exiting gases, after cooling to a regulated temperature of 250 C., are introduced into a second reactor, containing 50 mL of NiMo/alumina catalyst (HR448, sold by Axens), doped with 11.6% of K.sub.2O (according to the Cata 3 preparation described in patent application WO2010/046607). The pressure is 3 bar (0.3 MPa) absolute in the oven, at 250 C. Gas-chromatographic analysis of the exiting gases shows that the CS.sub.2 has been completely converted (100%) with a selectivity of 100% for methyl mercaptan, in other words each molecule of carbon disulphide has been converted to methyl mercaptan in accordance with reaction (4). The reaction mixture also comprises hydrogen sulphide, hydrogen, and the unreacted methane. The entirety of these compounds may be recycled into step a).

Example 2

[0111] Example 1 was repeated, this time adding 5.7 g.Math.h.sup.1 of sulphur (or 178 mmol.Math.h.sup.1) to the 10 NL.Math.h.sup.1 of methane (or 446 mmol.Math.h.sup.1) and with a reduction in the 20 NL.Math.h.sup.1 of H.sub.2S to 10 NL.Math.h.sup.1 (446 mmol.Math.h.sup.1). The sulphur is introduced in liquid form at 130 C. with the other reactants, at the top of the reactor, the internal reactor temperature being maintained at 900 C. and the internal pressure at 3 bar (310.sup.5 Pa) absolute. The flow rate of the exiting gases, taken under standard conditions of temperature and pressure, is 28 NL.Math.h.sup.1.

[0112] Gas-chromatographic analysis of the exiting gases indicates the following molar composition: CH.sub.4: 21% (or 262 mmol.Math.h.sup.1), H.sub.2S: 22% (or 275 mmol.Math.h.sup.1), CS.sub.2: 14% (or 175 mmol.Math.h.sup.1) and H.sub.2: 43% (or 537 mmol.Math.h.sup.1).

[0113] The mass balance realized with these analyses indicates that sulphur has been converted to 100%, that methane has been converted to 39% to carbon disulphide (CS.sub.2), and that CS.sub.2 and hydrogen (H.sub.2) have been produced with a molar H.sub.2/CS.sub.2 ratio of 3.07.

[0114] In the same way as in example 1, the exiting gases, after cooling to a regulated temperature of 250 C., are introduced into the second reactor, which contains 50 mL of NiMo/alumina catalyst (HR448 from Axens) doped with 11.6% of K.sub.2O. The pressure is 3 bar absolute.

[0115] Gas-chromatographic analysis of the exiting gases indicates that CS.sub.2 has been converted to 100% with a 100% selectivity for methyl mercaptan (or 175 mmol.Math.h.sup.1). Moreover, the amount of H.sub.2S recovered at the end of this second step corresponds, within the margins of measurement error, to the amount required for the first step (or approximately 450 mmol.Math.h.sup.1). The process according to the invention is an autonomous system which advantageously allows the recycling of the residual compounds to step 1), for example H.sub.2S. CS.sub.2 and hydrogen were unquantifiable.

[0116] This example shows that it is entirely possible to envisage a process for synthesis of methyl mercaptan in which the entirety of the H.sub.2S produced could be recycled, and there would be no need for it to be synthesized for the purposes of said process for synthesis of methyl mercaptan.

[0117] The examples below further illustrate the process of the present invention as indicated in example 1 above, but with the first step reproduced with different catalysts.

Example 3

[0118] The catalyst of the first step from example 1 was replaced by 30 mL of a catalyst containing 2% by weight of palladium on alumina (Engelhard). The reaction was subsequently carried out at 700 C., 800 C. and 900 C. The results are collated in Table 1.

Example 4

[0119] The catalyst from the first step in example 1 was replaced by 60 cm of platinum wire with a diameter of 0.4 mm. The reaction was subsequently carried out at 900 C. The results are collated in Table 1.

Example 5

[0120] The catalyst from the first step in example 1 was replaced by 20 superposed sheets (thickness of one sheet=0.152 mm, volume of 20 sheets=0.611 mL) made of platinum and rhodium and sold by Umicore. The reaction was subsequently carried out at 900 C., 1000 C. and 1100 C. The results are collated in Table 1.

Example 6

[0121] The catalyst in the first step in example 1 is replaced by 30 mL of catalyst containing 19% by weight of chromium oxide (Cr.sub.2O.sub.3) on alumina (T2777, sold by Sd-Chemie). The catalyst underwent a prior sulphurizing treatment with a stream of H.sub.2S (20 NL.Math.h.sup.1) for four hours at 900 C., so as to convert the Cr.sub.2O.sub.3 into Cr.sub.2S.sub.3 and to prevent the formation of oxygenous products during the main reaction of the methane with the H.sub.2S. These oxygenous products might interfere in the steps of subsequent recovery of the methyl mercaptan. The reaction was subsequently carried out at 900 C. The results are collated in Table 1 below:

TABLE-US-00001 TABLE 1 Example N Temperature ( C.) CH.sub.4 conversion % CS.sub.2 selectivity % 3 700 9 100 3 800 12 100 3 900 18 100 4 900 11 100 5 900 30 100 5 1000 57 100 5 1100 85 100 6 900 28 100