Process and plant for producing olefins

Abstract

A method (100) for producing olefins is proposed, wherein a first gas mixture (b) is produced by means of a steam cracking process (1) and a second gas mixture (s) is produced by means of an oxygenate-to-olefin process (2), the first gas mixture (b) and the second gas mixture (s) each containing at least hydrocarbons with one to four carbon atoms. It is proposed that from the first gas mixture (b) a first fraction (h) is formed which contains at least the great majority of the hydrocarbons with four carbon atoms previously contained in the first gas mixture (b), from the second gas mixture (s) a second fraction (y) is formed which contains at least the great majority of the hydrocarbons with four carbon atoms previously contained in the second gas mixture (s), and that the hydrocarbons contained in the second fraction (y) and previously in the second gas mixture (s) are predominantly subjected in the steam cracking process (1) to cracking conditions under which any n-butane present is reacted by less than 92%. The invention further relates to an apparatus for this purpose.

Claims

1. Method (100) for obtaining olefins, wherein a first gas mixture (b) is produced by means of a steam cracking process (1) and a second gas mixture (s) is produced by means of an oxygenate-to-olefin process (2), the first gas mixture (b) and the second gas mixture (s) containing at least hydrocarbons with one to four carbon atoms, characterised in that from the first gas mixture (b) a first fraction (h) is formed which contains at least the great majority of the hydrocarbons with four carbon atoms previously contained in the first gas mixture (b), from the second gas mixture (s) a second fraction (y) is formed which contains at least the great majority of the hydrocarbons with four carbon atoms previously contained in the second gas mixture (s), and the hydrocarbons contained in the second fraction (y) and previously in the second gas mixture (s) are predominantly subjected in the steam cracking process (1) to cracking conditions under which any n-butane present is reacted by less than 92%.

2. Method (100) according to claim 1, wherein under the cracking conditions to which the hydrocarbons contained in the second fraction (y) and, before that, in the second gas mixture (s) are subjected in the steam cracking process (1), less than 91%, 90%, 89%, 88%, 87%, 85%, 80% or 75% and more than 50% or 60% of the n-butane present is reacted.

3. Method (100) according to claim 1 or 2, wherein any hydrocarbons which are present in the first fraction (h) or formed therefrom are also at least partly subjected to the steam cracking process (1).

4. Method (100) according to one of the preceding claims, wherein oxygenates contained in the second gas mixture (s) or formed therefrom are at least partially subjected to the oxygenate-to-olefin process (1).

5. Method (100) according to one of the preceding claims, wherein hydrocarbons previously contained in the second gas mixture (s) but not in the second fraction (y), or formed therefrom, are at least partially subjected to the steam cracking process (1).

6. Method (100) according to one of the preceding claims, wherein the steam cracking process is carried out using at least two cracking furnaces (1a-1c) operated under different cracking conditions.

7. Method (100) according to one of the preceding claims, wherein the oxygenate-to-olefin process (2) is partially or exclusively carried out using at least one olefin which is, in particular, not present in the first and/or second gas mixture (b, s).

8. Method (100) according to claim 7, wherein the oxygenate-to-olefin process (2) is carried out using at least two reactors which are operated under different conditions.

9. Method (100) according to one of the preceding claims, wherein the second fraction (y) is formed from the second gas mixture (b) such that it is poor in hydrocarbons having one to three carbon atoms.

10. Method (100) according to claim 9, wherein the second fraction (y) is formed from the second gas mixture (s) by separation of at least the great majority of the hydrocarbons with at most three carbon atoms that were previously contained in the second gas mixture (s).

11. Method (100) according to claim 10, wherein hydrocarbons having one, two and/or three carbon atoms, separated from the second gas mixture (s), are combined at least partially with the first gas mixture (b) and/or with at least one fraction formed from the first gas mixture (b) to form at least one combined stream.

12. Method according to claim 11, wherein at least two further fractions are formed from the combined stream.

13. Method according to one of the preceding claims, wherein only hydrocarbons contained in the first gas mixture (b) and/or in the second gas mixture (s) or formed therefrom are subjected to the steam cracking process (1).

14. Apparatus for obtaining olefins, which comprises means that are designed to produce a first gas mixture (b) by means of a steam cracking process (1) and a second gas mixture (s) by means of an oxygenate-to-olefin process (2), so that the first gas mixture (b) and the second gas mixture (s) at least contain hydrocarbons with one to four carbon atoms, characterised by means which are designed to form, from the first gas mixture (b), a first fraction (h) which contains at least the great majority of the hydrocarbons with four carbon atoms previously contained in the first gas mixture (b), to form, from the second gas mixture (s), a second fraction (y) which contains at least the great majority of the hydrocarbons with four carbon atoms previously contained in the second gas mixture (s), and in the steam cracking process, to subject the hydrocarbons contained in the second fraction (y) and, previously, in the second gas mixture (s) predominantly to cracking conditions under which any n-butane present is reacted by less than 92%.

15. Apparatus according to claim 14, which comprises means designed to perform a process according to one of claims 1 to 13.

16. Apparatus according to claim 14 or 15, which comprises at least two cracking furnaces (1a-1c) which are designed for operation under different cracking conditions.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0060] FIG. 1 shows steps of a method for producing olefins according to one embodiment of the invention.

EMBODIMENT OF THE INVENTION

[0061] FIG. 1 shows a method according to one embodiment of the invention schematically in the form of a flow chart. The method as a whole is designated 100.

[0062] The method 100 comprises carrying out a steam cracking process 1 and an oxygenate-to-olefin process 2 in parallel. An apparatus in which the method 100 is implemented comprises corresponding means, i.e. in this case a plurality of cracking furnaces and at least one oxygenate-to-olefin reactor.

[0063] In the embodiment shown, the steam cracking process 1 operates using a plurality of feed streams which can be supplied to a plurality of cracking furnaces operated under different cracking conditions:

[0064] In the embodiment shown, three cracking furnaces 1a, 1b and 1c are shown. For example, the cracking furnace 1a is operated under severe or normal cracking conditions and a stream a, for example a fresh feedstock and/or a recycle stream is fed into this furnace. The stream illustrated as a may be formed from a plurality of streams. As already explained, the method according to the invention may also comprise the exclusive use of recycle streams in the steam cracking process 1. Recycle streams may be, for example, ethane and/or propane streams and/or streams of hydrocarbons with four to eight carbon atoms (olefinic and paraffinic). Fresh feedstocks may be supplied in gaseous and/or liquid form, for example in the form of natural gas and/or naphtha.

[0065] In the embodiment shown, the cracking furnace 1b is operated under mild cracking conditions and supplied with at least one stream y. The stream y is produced as a fraction of a gas mixture s (designated here as the second fraction or second gas mixture) formed by means of the oxygenate-to-olefin process 2. The stream y contains at least the hydrocarbons with four carbon atoms contained in the second gas mixture s, and optionally also longer-chained hydrocarbons (see below). The core of the present invention is the recycling of these and preferably only these hydrocarbons for mild cracking in the cracking furnace 1b.

[0066] Moreover, in the embodiment shown, another cracking furnace 1c is shown which is referred to as a so-called gas cracker and can be supplied with suitable feedstock streams such as ethane C2H6, as shown here. Other gaseous feeds are also suitable. The cracking furnace 1c can be operated under again different cracking conditions as compared to the cracking furnaces 1a and 1b.

[0067] Using the steam cracking process 1, over all a gas mixture b is obtained which is referred to here as the first gas mixture and which can be subjected to one or more preparation steps. In the embodiment shown, for example, an oil fractionation and/or a quenching are carried out in a step 3. Process steam may be produced which can be recycled into the steam cracking process 1 (not shown).

[0068] A gas stream c obtained in step 3 is subjected for example to compression, pre-cooling and drying in a step 4. Such a step 4 may also be supplemented by the elimination 5 of sour gas, with the formation of corresponding streams d. In the sour gas elimination 5 a gas stream is diverted off from step 4 between two compression stages into the sour gas elimination 5, for example, and fed back in later.

[0069] In the step 4, for example, a C3minus stream e which is formed from a corresponding second gas mixture s of an oxygenate-to-olefin process 2 can be used, as explained hereinafter. The result of the joint use of the stream c and the C3minus stream e from the oxygenate-to-olefin process 2 is that a corresponding pre-treatment only has to be carried out once and does not have to be done again separately for the comparatively small amounts of C3minus hydrocarbons from an oxygenate-to-olefin process 2. However, this is optional.

[0070] In the embodiment shown a stream f obtained from step 4, particularly one which has been compressed and partially liquefied and dried, is subjected, as a separation feedstock, to a deethanizer step 6 in which a C2minus fraction g and a C3plus fraction h is obtained. The further processing of the C3plus fraction h is explained hereinafter. The C2minus fraction g is subjected for example to a hydrogenation step 7 in which acetylene is hydrogenated to form ethylene, in particular.

[0071] A stream i further treated in this way is then subjected, for example, to a demethanizer step 8 in which methane CH4 and hydrogen H2 are separated off. A stream k thus freed from methane and hydrogen, which essentially still contains hydrocarbons with two carbon atoms, is subjected to a C2 separating step 9 (for example in a so-called C2 splitter) in which essentially ethylene C2H4 and ethane C2H6 are formed. The ethylene C2H4 is removed from the method 100 as a product, and the ethane C2H6 can be recycled into the steam cracking process 1, for example (see gas cracker 1c). If the process is designed accordingly, a method 100 according to the invention can also operate solely with recycled streams in the steam cracking process 1.

[0072] The C3plus stream h from the deethanizer step 6 is subjected to a depropanizer step 10. In the depropanizer step 10, a C3 fraction m is formed which can be worked up in one or more further process steps. For example, the C3 fraction m is subjected to a hydrogenation step 11 so that any methyl acetylene present as well as propadiene is reacted to form propylene. The stream thus processed, now designated n, is subjected for example to a C3 separating step 12 in which essentially propylene C3H6 and propane C3H8 are formed. The propylene C3H6, in turn, may be removed as product from a corresponding method 100 and the propane C3H8 may be recycled into the steam cracking process 1, for example into the gas cracker 1c.

[0073] A C4plus fraction o also formed in the depropanizer step 10 is subjected for example to full or partial hydrogenation in a hydrogenation step 13. A stream p obtained is fed into a deoctanizer step 14 in which essentially a C4 to C8 stream and a C9plus stream (without abbreviated names) are formed. If a corresponding stream is produced, a C5plus stream q which is produced from the second gas mixture formed in the oxygenate-to-olefin process 2, may also be fed into the deoctanizer step 14. The C9plus stream is removed from the process 100, whereas the C4 to C8 stream can be recycled back into the steam cracking process 1.

[0074] The oxygenate-to-olefin process 2 is particularly designed for reacting dimethyl ether, but methanol and other oxygenates, for example, and even partially or exclusively olefinic hydrocarbons may also be reacted. Corresponding oxygenates are supplied as stream r to one or more reactors and reacted to form a gas mixture s containing olefins, which is referred to here as the second gas mixture. The second gas mixture s, which contains at least or predominantly hydrocarbons with one to five carbon atoms, is subjected to an after-treatment step 15, for example water quenching and the elimination of oxygenates. Water obtained accordingly is drawn off as the stream t, and a stream u freed from oxygenates is fed into a step 16, which will be explained hereinafter. Any oxygenates recovered may be recycled as stream v into the oxygenate-to-olefin process 2.

[0075] In step 16, which has already been mentioned, the stream u is compressed and optionally pre-cooled. As already explained above, condensable components of the stream u are condensed. Any condensate obtained is optionally dried and subjected as a liquid stream w to a depropanizer step 17 in which a C3minus fraction x and a C4plus fraction y are formed from the stream w. The C4plus fraction y contains comparatively small amounts of hydrocarbons with five or more carbon atoms, for example, when corresponding catalysts are used (see above) in the oxygenate-to-olefin process 2. However, if necessary, a separating step 18 may be provided for the purpose of separating off corresponding longer-chained hydrocarbons as the stream q mentioned above. The latter can be further treated as mentioned above. The stream y, which is a C4plus or C4 stream, is recycled into the steam cracking process 1, as also mentioned previously, and cracked under mild conditions in the cracking furnace 1b.

[0076] Whereas the embodiment of the method according to the invention illustrated in FIG. 1 operates using a depropanizer 17, the invention may also be carried out in the same way using a separating sequence with a deethanizer. What matters is that a C4plus or C4 stream is formed from the second gas mixture or the stream s, recycled into the steam cracking process 1 and cracked under mild conditions therein.

[0077] The C3minus stream x may be combined with a stream z which consists of components that cannot be condensed in the condensation step 16, and subjected to an oxygenate removal step 19. An oxygenate stream (not shown) separated off in the oxygenate removal step 19 may be combined with the stream v and re-subjected to the oxygenate-to-olefin process 2. A C3minus stream freed from oxygenates, the stream e mentioned previously, may subsequently be subjected to the process step 4 described previously. However, this is optional.