A PROCESS FOR THE CONVERSION OF LIGHT ALKANES TO AROMATIC COMPOUNDS WITH IMPROVED SELECTIVITY

Abstract

In a process for the catalytic conversion of lower hydrocarbons to aromatic compounds comprising benzene, toluene and xylenes, a process stream containing lower hydrocarbons is contacted with a zeolitic catalyst having an MFI framework and containing 0.1 to 10 percent by weight of a zinc compound. The process stream further contains one or more sulfur compounds, especially hydrogen sulfide, for improving the selectivity.

Claims

1. A process for the catalytic conversion of gas mixtures, said process comprising: contacting a process stream with a zeolitic catalyst, the zeolitic catalyst having an MFI framework and comprising 0.1 to 10 percent by weight of a zinc compound, and converting at least part of the process stream to aromatic compounds comprising benzene, toluene and xylenes, wherein the process stream comprises lower hydrocarbons and one or more sulfur compounds, wherein the lower hydrocarbons are at least 50% by volume of ethane.

2. The process of claim 1, wherein the content of the one or more sulfur compounds in the process stream is 10-100 ppm.

3. The process of claim 1, further comprising forming a gas stream effluent of unconverted olefins and recycling at least a portion thereof back to the process.

4. The process of claim 1, wherein the zeolite catalyst is ZSM-5.

5. The process of claim 1, wherein the zinc compound is metallic and/or oxidic zinc.

6. The process of claim 1, wherein the zeolite further comprises 1 to 5 percent by weight of a phosphorus compound.

7. The process of claim 1, wherein the zeolite catalyst is embedded in a binder matrix.

8. The process of claim 7, wherein the binder matrix comprises alumina.

9. The process of claim 1, wherein the process stream comprises 90 to 100 percent by volume ethane.

10. The process of claim 1, wherein the sulfur compound is H.sub.2S.

11. The process of claim 1, wherein the temperature is in the range 550-600° C., and the pressure is in the range 3-20 bar abs.

12. The process of claim 1, wherein the process stream is derived from subjecting raw natural gas to a gas processing step selected from compression, refrigeration, absorption, adsorption or combinations thereof, thereby obtaining pure methane and said process stream.

13. The process of claim 1, wherein the one or more sulfur compounds are added to the process stream.

14. The process of claim 1, further comprising combining said aromatic compounds comprising benzene, toluene and xylene, with a pyrolysis gasoline obtained as a by-product in a separate ethylene production through steam cracking, thereby forming a combined stream comprising benzene, toluene and xylene, and optionally subsequently subjecting the combined stream to one or more fractionation steps for producing pure grade benzene, toluene and xylene products.

15. The process of claim 1, wherein the selectivity of methane does not exceed 5%.

16. The process of claim 1, wherein the selectivity of aromatics with nine or more carbon atoms does not exceed 2%.

17. The process of claim 1, wherein the selectivity of ethylene is at least 30%.

18. A process for the catalytic conversion of gas mixtures of lower hydrocarbons, which contain at least 50% by volume of ethane, to aromatic compounds comprising benzene, toluene and xylenes, said process comprising the steps of contacting a process stream containing lower hydrocarbons with a zeolitic catalyst having an MFI framework and containing 0.1 to 10 percent by weight of a copper compound, wherein the process stream further contains one or more sulfur compounds.

19. The process of claim 1, the process comprising adding one or more sulfur compounds to a pre-process stream to obtain the process stream.

20. The process of claim 1, wherein the process stream further comprises a diluent.

21. The process of claim 20, wherein the diluent is N.sub.2.

22. The process of claim 1, wherein the process stream further comprises methane.

23. The process of claim 1, wherein the process stream consists of lower hydrocarbons, one or more sulfur compounds, and, optionally, a diluent.

Description

EXAMPLE

[0058] Catalyst: 5 wt % Zn supported on H-ZSM-5 having a silica to alumina ratio of 40.

[0059] Conditions: 550° C., 3 bar abs., WHSV=3, 10 vol % C.sub.2H.sub.6 in N.sub.2.

[0060] In the figures are shown ethane conversion and product selectivity over time on stream (TOS); closed symbols are results without H.sub.2S, i.e. without H.sub.2S being added; open symbols are results with 60 ppm H.sub.2S in the feed.

[0061] The figures reveal that the conversion over time is essentially the same with and without H.sub.2S in the feed (FIG. 1). In particular, it is noted that the conversion in the presence of H.sub.2S is lower in the beginning, but soon (after about 20 hours) surpasses the conversion of the same catalyst operating under sulfur-free conditions.

[0062] The BTX yield with H.sub.2S in the feed is somewhat lower (FIG. 2), but the selectivity to ethylene (and other light olefins) is significantly higher with H.sub.2S in the feed (FIG. 3). Further it is seen that the methane (FIG. 4) and C.sub.94 (FIG. 5) selectivities are dramatically lower in the presence of H.sub.2S.