Process for continuously preparing methyl mercaptan from carbon compounds, sulfur and hydrogen

Abstract

The invention relates to a process for continuously preparing methyl mercaptan by reacting a mixture comprising carbon compounds with sulfur and hydrogen, wherein the carbon disulfide and hydrogen sulfide compounds which form are subsequently converted to methyl mercaptan.

Claims

1. A process for preparing methyl mercaptan, comprising the steps of a) hydrogenating carbon disulfide and b) reacting the hydrogen sulfide, which is contained in the reaction mixture formed the reactions before, with at least one of the compounds selected from the group consisting of alcohols, ethers, and aldehydes, in the presence of a metal oxide catalyst, wherein hydrogen is only added if required, wherein said process is preceded by the reaction of carbon compounds or hydrocarbons with sulfur to give carbon disulfide and the formation of carbon disulfide is effected in the presence of a catalyst based on a Co—Ni system or an H-ZSM-5-zeolite.

2. The process as claimed in claim 1, wherein the methyl mercaptan is removed from the reaction mixture that is formed in the hydrogenation of the carbon disulfide.

3. The process as claimed in claim 1, wherein the carbon disulfide is converted at a reaction pressure of at least 5 bar and a temperature of at least 200° C.

4. The process as claimed in claim 1, wherein the hydrogen sulfide is reacted with methanol.

5. The process as claimed in claim 1, wherein the molar CS.sub.2/H.sub.2/H.sub.2S ratio after the hydrogenation of the carbon disulfide ranges from 1:1:1 to 1:10:10.

6. The process of claim 5, wherein said molar CS.sub.2/H.sub.2/H.sub.2S ratio ranges from 1:1:1 to 1:5:10.

7. The process as claimed in claim 1, wherein the hydrocarbons or carbon compounds originate from off-gas streams from processes for generating energy or chemical products.

8. The process as claimed in claim 1, wherein the hydrocarbons or carbon compounds originate from the workup of processes for oxidizing hydrocarbons and for synthesizing nitrogen and sulfur compounds.

9. The process as claimed in claim 1, wherein the hydrocarbons or carbon compounds originate from biological metabolism processes.

10. The process as claimed in claim 1, wherein the carbon disulfide is formed in the presence of liquid or gaseous sulfur, in a one-stage or multistage non-catalyzed homogeneous reaction or using a catalyst.

11. The process as claimed in claim 1, wherein, after removal of the methyl mercaptan, unconverted gaseous feed-stocks and by-products are removed and recycled into the process.

12. The process as claimed in claim 1, wherein the total amount of the hydrogen sulfide is adjusted by varying the carbon-hydrogen ratio of the compounds present in the reaction mixture or of the H.sub.2 content in the reaction gas fed to the process, and by varying one or more of the process parameters selected from the group of: residence time, reaction temperature and reaction pressure.

13. The process as claimed in claim 1, wherein reactive distillations, bubble column reactors, fixed bed reactors, trickle bed reactors, staged reactors or tube bundle reactors are used for the catalyzed conversion to methyl mercaptan.

14. The process as claimed in claim 1, wherein the reaction of the hydrocarbons with sulfur and the hydrogenation of the carbon disulfide formed to methyl mercaptan are performed in one reaction apparatus.

15. The process as claimed in claim 1, wherein the reaction mixture which arises in the formation of carbon disulfide is supplied directly with no drop in a second process step tier hydrogenation of the carbon disulfide.

16. The process as claimed in claim 1, wherein the metal oxide catalyst is an alkali metal tungstate, alkali metal molybdate, or alkali metal molybdate comprising transition metal oxides or sulfides as promoters.

17. The process as claimed in claim 16, wherein at least one of the promoters selected from the group of oxides or sulfides of chromium, iron, cobalt, manganese and rhenium is present in the alkali metal tungstates, alkali metal molybdates or halogenated alkali metal tungstates or alkali metal molybdates.

18. The process as claimed in claim 1, wherein the metal oxide catalyst comprises molybdates or tungstates comprising transition metal and alkali metal oxides or sulfides as promoters.

19. The process as claimed in claim 1, wherein the metal oxide catalyst is a supported catalyst, which comprises oxidic molybdenum and potassium compounds, where Mo and K may be present in one compound, and which comprise at least one active oxidic compound of the general formula A.sub.xO.sub.y, A is one or more element from the iron or manganese group and x and y are each integers from 1 to 7.

20. The process of claim 19, wherein A is one or more elements selected from the group consisting of Co, Mn, and Re.

21. The process as claimed in claim 1, wherein molybdate- or tungstate-containing catalysts are used, which comprise transition metal and alkali metal oxides or sulfide as promoters.

22. The process as claimed in claim 1, wherein the hydrogenation of carbon disulfide is effected in the presence of a catalyst.

23. The process as claimed in claim 22, wherein the catalyst is an alkali metal molybdate or alkali metal tungstate.

24. The process of claim 1, wherein the at least one of the compounds reacted with the hydrogen sulfide is selected from the group consisting of methanol, dimethyl ether, and formaldehyde.

25. The process of claim 1, which results in the formation of methyl mercaptan with a selectivity of up to 98 percent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates a process of an embodiment of the invention.

(2) FIG. 2a shows the formation of carbon disulfide by the reaction of sulfur with methane at 525° C. with subsequent hydrogenation to methyl mercaptan over a catalyst which comprises 2.9 m % CoO and 28 m % K.sub.2MoO.sub.4 on an SiO.sub.2 support.

(3) FIG. 2b shows the product selectivities and the CS.sub.2 conversion for the hydrogenation step which follows the CS.sub.2 formation.

(4) FIG. 1 serves to further explain the process, wherein “Route a” denotes, in an illustrative manner, the reaction of methane with sulfur, hydrogen and methanol or CO/CO.sub.2 to give methyl mercaptan and “Route b” the direct hydrogenation of carbon disulfide to methyl mercaptan with simultaneous reaction of hydrogen sulfide with methanol or CO/CO.sub.2. What is important for the economic viability of the process is the possibility of using a multitude of solid, liquid and/or gaseous, carbon- and hydrogen-containing starting materials, which are reacted with sulfur in the process, and the fact that this stream need not be purified and desulfurized in a complicated manner. Moreover, all by-products which are removed after the reaction can be recycled into the process. Advantageously, if a sequential process regime is selected, all reactions proceed within the same pressure range, such that it is possible to dispense with a costly compression of the gases between the individual reaction steps. The reactions are effected at the starting pressure of the gases, under which they leave the first process step. Advantageously, this pressure is set to 5 to 50 bar, especially 8 to 40 bar. Gases which are inert for the purposes of the process are discharged continuously or discontinuously from the process via a purge gas stream.

EXAMPLES

(5) The process presented here comprises two stages.

(6) In the first stage, methane was converted in liquid sulfur at a pressure of 15-50 bar and a temperature of 500-550° C. to carbon disulfide and hydrogen sulfide. This involved bubbling the methane through the liquid sulfur phase and cooling the product gas, immediately after it leaves the liquid phase, to approx. 150° C. by means of a cooler placed atop the reactor.

(7) Hydrogen was added to the reaction product of the first stage, with the aid of which the carbon disulfide formed in the first stage was hydrogenated in the second stage at 15-50 bar and temperatures of 150-450° C. to methyl mercaptan. The reactants were provided in two ways: 1. H.sub.2S and CS.sub.2 were prepared in a preliminary reactor from methane and sulfur. (Example 1) 2. H.sub.2S was prepared in a preliminary reactor from H.sub.2 and sulfur, and CS.sub.2 was added to the preliminary reactor by means of an HPLC pump. (Example 2)

(8) The catalytic activity was determined for a single pass through the reactor.

Example 1

(9) Sulfur was heated to 500° C. under a pressure of 15 bar, and a mixture of methane and nitrogen (1:1) was introduced. This procedure led to a methane conversion of 48.4% under steady-state conditions and hence to a product gas mixture consisting of 16.3% CS.sub.2, 17.4% CH.sub.4, 33.7% N.sub.2 and 32.6% H.sub.2S. Carbon-containing by-products were not observed (selectivity for CS.sub.2=100%). Percentages in the case of gas mixtures should be interpreted as % by volume.

(10) H.sub.2 was added to this product mixture which was fed to the second stage. Thus, for the second stage, the reactant composition was 9% CS.sub.2, 9.6% CH.sub.4, 18.7% N.sub.2, 18.2% H.sub.2S and 44.5% H.sub.2. For the K.sub.2MoO.sub.4/SiO.sub.2 catalyst, the conversions, yields and selectivities of this hydrogenation are reported as a function of temperature in Table 1 (reaction pressure p=15 bar).

(11) TABLE-US-00001 TABLE 1 Temp CS.sub.2 Selectivity [%] Yield [%] [° C.] conversion CH.sub.4 MC DMS CH.sub.4 MC DMS 250 17.16 0.00 93.37 0.26 0.00 16.02 0.04 300 66.97 0.00 90.18 0.29 0.00 60.39 0.19 325 95.65 0.00 83.15 0.33 0.00 79.53 0.31 350 99.97 0.00 83.07 0.40 0.00 83.04 0.40 375 99.97 3.23 79.12 0.39 3.23 79.09 0.39 400 99.97 10.09 71.57 0.45 10.09 71.55 0.45

(12) The product selectivities and yields which result for the overall process, based on the CH.sub.4 used, are shown in Table 2.

(13) TABLE-US-00002 TABLE 2 Temp CH.sub.4 Selectivity [%] Yield [%] [° C.] conversion CS.sub.2 MC DMS CS.sub.2 MC DMS 250 49.67 79.30 15.34 0.09 39.39 7.62 0.04 300 49.67 31.62 57.81 0.37 15.71 28.72 0.18 325 49.67 4.16 76.14 0.60 2.07 37.82 0.30 350 49.67 0.03 79.50 0.76 0.01 39.49 0.38 375 48.13 0.03 78.13 0.76 0.01 37.61 0.37 400 44.87 0.03 75.82 0.95 0.01 34.02 0.42

Example 2

(14) The procedure was according to the above-described Option 2 (separate feeding of carbon disulfide). The conditions in the preliminary stage were selected such that, before the hydrogenation stage, a gas mixture of 12.7% N.sub.2, 9.9% CS.sub.2, 12.6% H.sub.2S and 64.8% H.sub.2 was established. At 20 bar and a total flow rate of 18.6 ml/min, the following conversions, yields and selectivities for the hydrogenation were achieved for the catalyst (28% K.sub.2MoO.sub.4/SiO.sub.2) as a function of the main reactor temperature (Table 3).

(15) TABLE-US-00003 TABLE 3 T CS.sub.2 Selectivity [%] Yield [%] [° C.] conversion [%] MC DMS CH.sub.4 MC DMS CH.sub.4 150 1.14 100 0 0 1.14 0 0 165 0.03 100 0 0 0.03 0 0 180 0 100 0 0 0 0 0 195 0.8 100 0 0 0.8 0 0 210 6.84 100 0 0 6.84 0 0 225 10.39 100 0 0 10.39 0 0 240 26.32 100 0 0 26.32 0 0 255 53.91 98.02 1.5 0.48 52.84 0.81 0.26 270 90.07 97.8 1.13 1.07 88.08 1.02 0.96 285 99.94 97.92 0.92 1.15 97.87 0.92 1.15 300 100 97.54 0.87 1.6 97.54 0.87 1.6 315 100 96.7 0.87 2.42 96.7 0.87 2.42 330 100 94.96 0.83 4.22 94.96 0.83 4.22 345 100 92 0.85 7.15 92 0.85 7.15 360 100 87.34 1.09 11.58 87.34 1.09 11.58 375 100 79.81 1.24 18.95 79.81 1.24 18.95 390 100 69.24 1.44 29.32 69.24 1.44 29.32 400 100 61.27 1.53 37.19 61.27 1.53 37.19

Example 3

(16) FIG. 2a shows the formation of carbon disulfide by the reaction of sulfur with methane at 525° C. with subsequent hydrogenation to methyl mercaptan over a catalyst which comprises 2.9 m % CoO and 28 m % K.sub.2MoO.sub.4 on an SiO.sub.2 support. FIG. 2b shows the product selectivities and the CS.sub.2 conversion for the hydrogenation step which follows the CS.sub.2 formation.

Example 4

(17) When carbon disulfide is formed from methane and sulfur (Example 1), hydrogen sulfide is obtained as a coproduct (CS.sub.2:H.sub.2S=1:2). In the subsequent hydrogenation step to give methyl mercaptan (see Example 2), H.sub.2S is likewise formed as a coproduct. At a temperature of 325° C. and a reaction pressure of 15 bar (i) methanol, (ii) CO or (iii) CO.sub.2, individually or together, at least in a total ratio of 1.1:1 (MeOH+CO+CO.sub.2):H.sub.2S was supplied to the resulting product gas mixture in the presence of the hydrogen required. For all three reactants, an H.sub.2S conversion of >95% was observed with simultaneously increased methyl mercaptan yields. By increasing the methanol/CO or CO.sub.2 content and recycling unconverted reactants (after removal of methyl mercaptan), it was possible to achieve full conversion of hydrogen sulfide.