Method and apparatus for producing hydrocarbons

Abstract

A method for producing hydrocarbons is proposed, in which a product stream containing hydrocarbons is produced from a methane-rich feed stream and from an oxygen-rich feed stream in a reaction unit which is configured for implementing a method for oxidative coupling of methane, the product stream or at least a stream formed therefrom being treated cryogenically in at least one separation unit using at least one liquid, methane-rich stream. It is provided that in the at least one separation unit (10) a recycle stream is formed from methane contained in product stream (c) and from methane contained in the at least one liquid, methane-rich stream (e, v), the recycle stream being fed to the reaction unit (1) as the methane-rich feed stream (a), and in that the liquid, methane-rich stream (e, v) is provided as makeup.

Claims

1. A method for producing hydrocarbons by oxidative coupling of methane comprising: contacting a methane-rich feed stream and an oxygen-rich feed stream in a reaction unit configured for oxidative coupling of methane to produce a product stream comprising hydrocarbons and unreacted methane; cryogenically separating the product stream in at least one separation unit using at least one liquid, methane-rich stream to form a recycle stream comprising unreacted methane and at least a portion of methane contained in the at least one liquid, methane-rich stream; and feeding the recycle stream to the reaction unit, wherein the methane-rich feed stream consists of the recycle stream and the methane-rich feed stream is the only methane feed to the reaction unit; wherein the at least one liquid, methane-rich stream is produced using a pressurised, methane-containing gas mixture that is provided separately from the product stream and wherein the liquid, methane-rich stream is used in an amount that is greater than or equal to the amount of methane which is converted in the reaction unit and which is lost by separation losses.

2. The method according to claim 1, wherein the cryogenic separation comprises a cooling procedure in at least one heat exchanger which is operated with the at least one liquid, methane-rich stream as refrigerant.

3. The method according to claim 1, wherein the cryogenic separation comprises a separation procedure in a cryogenic separation device in which the at least one liquid, methane-rich stream is charged as reflux.

4. The method according to claim 3, wherein an absorption column and/or a distillation column is used as the cryogenic separation device.

5. The method according to claim 1, wherein natural gas is used as the pressurised, methane-containing gas mixture.

6. The method according to claim 1, wherein the liquid, methane-rich stream is produced at least in part from a liquid stream which is formed from the pressurised, methane-containing gas mixture using a distillation process.

7. The method according to claim 6, wherein the pressurised, methane-containing gas mixture is at least partly rid of impurities before the distillation process is carried out.

8. The method according to claim 7, wherein sulphur compounds, carbon dioxide and/or mercury are at least partly removed from the pressurised, methane-containing gas mixture.

9. The method according to claim 6, wherein the pressurised, methane-containing gas mixture is depleted in nitrogen, hydrogen and/or helium in the distillation process.

10. The method according to claim 9, wherein a dividing wall column is used to deplete the pressurised, methane-containing gas mixture in nitrogen, hydrogen and/or helium in the distillation process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of an apparatus for producing hydrocarbons according to an embodiment of the invention.

(2) FIG. 2 is a schematic view of an apparatus for producing hydrocarbons according to an embodiment of the invention.

(3) FIG. 3 is a schematic partial view of an apparatus for producing hydrocarbons according to an embodiment of the invention.

(4) FIG. 4 is a schematic partial view of an apparatus for producing hydrocarbons according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) In the figures, identical elements have been shown with the same reference numerals. For the sake of clarity, a repeated description of identical elements is not provided.

(6) FIG. 1 shows an apparatus for producing hydrocarbons using a method for oxidative coupling of methane according to an embodiment of the invention. The apparatus is denoted overall by reference numeral 100. In the illustrated example, the apparatus 100 comprises a reaction unit 1 which is configured for implementing a method for oxidative coupling of methane and comprises for example one or more heated reactors, configured in a manner known per se, having suitable catalysts. The reaction unit 1 can also comprise, for example reaction devices arranged downstream, for example reaction devices for subsequent steam cracking.

(7) Fed to the reaction unit 1 is a methane-rich feed stream a and an oxygen-rich feed stream b, and a product stream c is removed which can have the composition mentioned at the outset (more than 60% methane, less than 10% hydrocarbons having two or more carbon atoms and 10 to 20% of other components such as nitrogen, argon, hydrogen, carbon monoxide and/or carbon dioxide). This product stream undergoes one or more processing steps, for example a water wash, amine scrubbing, an adsorptive purification, one or more drying steps, condensation, cooling etc. Corresponding steps are summarised here by block 2. Further steps, as shown here by suspension marks, can be provided.

(8) A correspondingly processed stream which is freed in particular from water and carbon dioxide and is now denoted by d is fed to a separation unit, collectively denoted by 10 and is cooled therein in a heat exchanger 3 and is fed into an absorption column 4. Charged onto the absorption column 4 is a liquid, methane-rich stream e as reflux. The absorption column 4 is operated such that in the bottom thereof, a mixture predominantly or exclusively containing hydrocarbons having two or more carbon atoms is separated which can be removed as stream f. A mixture which is free or almost free from hydrocarbons having two or more carbon atoms or also pure or almost pure methane is removed as stream a at the top of the absorption column 4.

(9) Instead of a single absorption column 4, it is also possible to use any other suitable unit capable of recovering a mixture which predominantly or exclusively contains hydrocarbons having two or more carbon atoms which can be removed as stream f and is capable of recovering a mixture which is free or almost free from hydrocarbons having two or more carbon atoms or pure or almost pure methane which can be removed as stream a. For example, combined units consisting of a part operating by absorption and a part operating by distillation, configured as a double column, or two separate columns can be used. The configuration and implementation in terms of apparatus depend on the contents of the individual components of stream d. It is crucial that the mixture of stream a or the pure or almost pure methane of this stream a is free or almost free from hydrocarbons having two or more carbon atoms. The mixture of stream f can contain certain amounts of methane. Due to the use of absorption column 4 or of an appropriate other unit, the components which are later contained in stream a do not have to be condensed in order to form a corresponding stream a. Therefore, corresponding components can be returned directly to the reaction unit 1. The absorption column 4 or a corresponding unit can be operated at pressures of less than 30 bars, for example at 13 to 17 bars, more generally at pressures which result in a temperature of the top of the absorption column 4 or of a corresponding unit of below 97 C. In this way, stream a no longer contains any or contains almost no hydrocarbons having two or more carbon atoms.

(10) According to the embodiment of the invention shown here, stream e is formed using a pressurised, methane-containing gas mixture, denoted here by g. Stream g is provided, for example via a natural gas supply 5, in particular by a pipeline. The pressurised, methane-containing gas mixture of stream g is for example in a natural gas pipeline at a pressure of 40 to 60 bars and is thus capable of liquefaction, if appropriate after previous expansion.

(11) Some of the pressurised, methane-containing gas mixture of stream g can be expanded, for example as stream h, by a valve (not shown) to a pressure of less than 9 bars and can then be used as fuel gas. The remainder is delivered to a preparation procedure which operates for example at a pressure of 10 to 50 bars, for example at 20 to 45 bars or at 30 to 40 bars. In any case, the pressure is below the critical pressure of methane.

(12) Appropriate gas mixtures from pipelines, such as the pressurised, methane-containing gas mixture of stream g, still typically contain traces of impurities such as sulphur compounds, carbon dioxide and mercury. Impurities of this type can be removed in an adsorptive purification device 6 in which for example streams n and o, which are described below, can also be used for regeneration.

(13) A correspondingly purified stream i can undergo any desired further processing steps 7, for example the removal of carbon dioxide or drying. The further processed stream, now denoted by k, is then cooled in a heat exchanger 8 and transferred to a distillation column 9 at a suitable height. The distillation column 9 is used to recover a methane-rich top stream from the methane-containing, pressurised gas mixture of streams f and k. If stream k already has an adequate purity, i.e. in particular if it already has an adequate methane content, pure liquefaction without the use of a distillation column 9 is also possible.

(14) A gaseous top stream can be drawn off from the distillation column 9, liquefied through the condensation chamber of a head condenser 91 which is operated with a suitable refrigerant stream l and is recharged at least in part as stream m at the top of the distillation column 9. Methane which is not liquefied in the head condenser 91 of the distillation column 9 can be drawn off as stream n and for example can be used, as mentioned, for regeneration purposes. Stream e, which has already been described and which substantially consists of liquid methane, can be removed at the top of the distillation column 9 by a suitable liquid removal device (not shown) or can be drawn off from the head condenser 91 or from a corresponding container. It is understood that the invention can be used employing different types of head condensers, for example external head condensers comprising distinct separator containers.

(15) A liquid fraction which can consist predominantly of hydrocarbons having two or more carbon atoms separates in the bottom of the distillation column 9. However, it is also possible to operate the distillation column 9 such that a gas mixture also containing further components to be separated separates in the bottom of the column. The bottom of the distillation column 9 can also still contain a considerable amount of methane. It is important that a fraction which allows the above-described use and which only has corresponding components is formed at the top of the distillation column 9.

(16) A stream o which is removed from the bottom of the distillation column 9 and is not evaporated in a sump evaporator 92 of the distillation column 9 can also be used as fuel gas, and therefore the composition thereof is less critical compared to stream m. As shown, the heat exchanger 8 can also be operated with a stream removed from the bottom of the distillation column 9. It is also possible, if appropriate, to dispense with a sump evaporator 92.

(17) The distillation column 9 can be operated under differing conditions which can also depend on the specific gas composition which is present. For example, pressures of from 13 to 36 bars or from 28 to 36 bars can be used.

(18) Drawn off from the top of the absorption column is a stream a which preferably contains the predominant proportion of the methane contained in product stream c and in the liquid, methane-rich stream e. This stream is used as the methane-rich feed stream a. Thus, in the illustrated example, it is provided to only use stream e, which has been mentioned several times, to make up the methane. Stream e originates from the separately provided, methane-containing gas mixture of stream g which is processed appropriately.

(19) FIG. 2 shows an apparatus for producing hydrocarbons using a method for oxidative coupling of methane according to a further embodiment of the invention. The reaction unit 1 has not been shown here, only streams a and d corresponding to FIG. 1 are shown.

(20) The separation unit 10 of the apparatus shown in FIG. 2 corresponds to a demethanizer of a steam cracking process. The separation unit 10 is shown in a greatly simplified form. A plurality of streams, valves, heat exchangers, containers etc., have not been shown. The separation unit comprises four (counterflow) heat exchangers 31 to 34, but it can also have more or fewer corresponding heat exchangers and further heat exchangers. The heat exchangers 31 to 34 can be cooled in particular using suitable refrigerant streams, shown here in dashed lines, in addition to the streams described in the following.

(21) Stream d is guided through the heat exchanger 31, is cooled therein and is then fed into a liquid separator 11. Here, fluid which remains as gas is guided through the heat exchanger 32, is cooled and fed into a liquid separator 12. Here as well, fluid remaining as gas is guided through the heat exchanger 33, is further cooled and transferred to an absorption column 4 at for example approximately 35 bars abs. and at approximately 100 C.

(22) Here as well, a liquid methane-rich stream e is charged at the head of the absorption column 4 and washes out hydrocarbons having two or more carbon atoms into the bottom of the absorption column. However, in the illustrated example, the absorption column 4 is operated such that separated in the bottom of the column is a mixture which still contains considerable amounts of methane in addition to hydrocarbons having two or more carbon atoms. This mixture is removed as stream p and is expanded in a distillation column 13. In typical methods for processing streams from steam cracking processes, condensates from the separator containers 11 and 12 are also expanded in said distillation column. This can also be the case in methods for oxidative coupling of methane, but is not necessarily provided here.

(23) Drawn off from the top of the absorption column 4 is a stream q substantially consisting of methane and hydrogen. This stream is cooled in the heat exchanger 34 to a temperature below the boiling temperature of methane at the used pressure and is transferred to a hydrogen separator 14 in which substantially pure methane is separated as liquid. This alone is used as the methane-rich feed stream a, whereas hydrogen as stream r is used elsewhere, for example for hydrogenation purposes.

(24) The distillation column 13 is operated in such a way that a methane-rich top gas, preferably substantially pure methane accumulates at the top of the column. This is drawn off, passed through a condensation chamber of a head condenser 131 which is operated using a suitable refrigerant stream in the evaporation chamber thereof and is charged onto the distillation column 13 in the form of stream s as liquid reflux. Some of the liquefied stream s can be drawn off, brought to the pressure of the absorption column 4 by a pump 15 and used as reflux in the form of the mentioned stream e. It is stressed explicitly that streams s and e can also be recovered in a different manner, for example by means of external separator containers and/or external head condensers.

(25) It is possible to remove from the bottom of the distillation column 13 a low-methane stream t which contains the predominant proportion of the hydrocarbons, contained in stream d, having two or more carbon atoms. Part of stream t can be evaporated in a sump evaporator 132 of the distillation column 13 and reintroduced into said column, a further part is removed as stream u and can be directed out of the apparatus after any desired optional intermediate steps.

(26) Thus, in the embodiment shown in FIG. 2, stream e is not necessarily provided directly externally, it can also initially at least be partly formed from methane from the distillation column 13 or from the head condenser 131 thereof. Nevertheless, here as well methane is provided externally, namely as stream v. Stream v is obtained in the same manner as stream e which was described with regard to FIG. 1. Therefore, reference is made to the above details. A partial stream w of stream v can also be used for cooling purposes. However, stream v can also be guided in its entirety in the same manner as illustrated stream w.

(27) A dividing wall column can also be used instead of the single distillation column 9. The use of a dividing wall column takes into account the fact that for example natural gas, which is provided as the pressurised, methane-containing gas mixture of stream g, typically contains considerable amounts of nitrogen. To prevent said nitrogen from passing into stream e or v, nitrogen is depleted in the dividing wall column. Otherwise, said nitrogen could contaminate products of a corresponding apparatus. Nitrogen could also be fed into the circulation, which circulation has been described several times, and could accumulate in the circulation if it is not converted in the reaction unit 1.

(28) FIG. 3 shows a detail of an apparatus according to the invention in which a corresponding dividing wall column is denoted by 9 in the same manner as the standard distillation column 9 in FIGS. 1 and 2. Incorporation emerges from the denotation of the respective streams. In the example shown, the dividing wall column 9 comprises a head condenser 91 and a sump evaporator 92. After being cooled in the heat exchanger 8, the gas stream k which still contains nitrogen is fed into a region of the dividing wall column 9, shown here on the left. In a region of the dividing wall column 9, shown on the right, nitrogen-depleted methane can be removed and used as stream e (corresponding to FIG. 1) or as stream v (corresponding to FIG. 2).

(29) FIG. 4 shows a particularly simple variant. Here, stream e or v is merely obtained through liquefaction of an appropriately purified stream k or i. This variant is suitable for cases in which the gas mixture of stream g already has a composition conforming to specifications. If stream g is already free from other disruptive impurities, it is also possible to dispense with the purifying device 6.