PROCESS AND PLANT FOR PRODUCING METHANOL AND CARBON MONOXIDE

Abstract

The present invention specifies a process and a plant for simultaneous production of methanol and pure carbon monoxide which includes synthesis gas production by partial oxidation of an input stream containing hydrocarbons and subsequent methanol synthesis. According to the invention carbon dioxide is separated from the raw synthesis gas using a sorption apparatus and at least partially introduced into the input gas for the methanol synthesis reactor.

Claims

1. A process for producing methanol and pure carbon monoxide from an input stream containing hydrocarbons, comprising: (a) providing an input stream containing hydrocarbons, (b) supplying the input stream containing hydrocarbons to a partial oxidation stage, (c) at least partially reacting the input stream containing hydrocarbons in the partial oxidation stage with a stream of an oxygen-containing oxidant under partial oxidation to afford a raw synthesis gas stream containing hydrogen, carbon monoxide, carbon dioxide and methane, (d) discharging the raw synthesis gas stream from the synthesis gas production plant and dividing the raw synthesis gas stream into a first raw synthesis gas substream and into a second raw synthesis gas substream, (e) introducing at least a portion of the first raw synthesis gas substream into a methanol synthesis reactor, at least partially converting the first raw synthesis gas substream in the methanol synthesis reactor under methanol synthesis conditions, (f) discharging a methanol-containing first reactor product stream from the methanol synthesis reactor, cooling the first reactor product stream to below its dew point and separating the cooled first reactor product stream in a phase separation apparatus into a first liquid product stream and a first residual gas stream containing unconverted synthesis gas constituents and inert components, discharging the first liquid product stream from the process as a raw methanol product stream, (g) dividing the first residual gas stream into a methanol synthesis purge stream and into a recycle stream which is recycled to the methanol synthesis reactor, (h) introducing at least a portion of the second raw synthesis gas substream into a sorption apparatus for removal of carbon dioxide using a physical or chemical sorption process, discharging a carbon dioxide-depleted synthesis gas stream and a carbon dioxide-enriched gas stream from the sorption apparatus, (j) introducing at least a portion of the carbon dioxide-depleted synthesis gas stream into a cryogenic gas fractionation stage, separating the carbon dioxide-depleted synthesis gas stream in the cryogenic gas fractionation stage into the following substreams: (j1) a carbon monoxide-rich gas stream which is discharged from the process as a carbon monoxide product stream, (j2) a hydrogen-rich gas stream, (j3) an offgas stream containing methane, hydrogen and carbon monoxide which is at least partially supplied to a burner of a heating apparatus as a first heating gas, wherein the carbon dioxide-enriched gas stream is at least partially introduced into the methanol synthesis reactor.

2. The process according to claim 1, wherein the hydrogen-rich gas stream is at least partially introduced into the methanol synthesis reactor.

3. The process according to claim 2, wherein a proportion of the hydrogen-rich gas stream such that the stoichiometry number which relates to the entirety of all material streams introduced into the methanol synthesis reactor at the reactor inlet of the methanol synthesis reactor is between 1.8 and 2.4 is introduced into the methanol synthesis reactor.

4. The process according to claim 1, wherein the hydrogen-rich gas stream is at least partially supplied to the burner of the heating apparatus as a second heating gas.

5. The process according to claim 1, wherein a portion of the input stream containing hydrocarbons is supplied to the burner of the heating apparatus as a third heating gas.

6. The process according to claim 1, wherein at least a portion of the methanol synthesis purge stream is supplied to the burner of the heating apparatus as a fourth heating gas.

7. The process according to claim 1, wherein the heating apparatus is used for steam production, wherein the steam produced is at least partially used as a moderator in the partial oxidation stage.

8. The process according to claim 1, wherein the heating apparatus is used for steam production, wherein the steam produced is at least partially provided to external consumers.

9. The process according to claim 1, wherein a carbon dioxide-containing gas stream deriving from a process-external source is additionally introduced into the methanol synthesis reactor.

10. The process according to claim 1, wherein the heating apparatus is used for preheating the input stream containing hydrocarbons and/or the stream of the oxygen-containing oxidant.

11. The process according to claim 1, wherein the methanol synthesis purge stream is separated using a separation apparatus into a first purge stream enriched in hydrogen and into a second purge stream depleted in hydrogen and enriched in carbon oxides and methane, wherein at least a portion of the first purge stream enriched in hydrogen is supplied to the burner of the heating apparatus as a fourth heating gas and wherein at least a portion of the second purge stream enriched in carbon oxides and methane is passed to the partial oxidation stage.

12. A plant for producing methanol and pure carbon monoxide from an input stream containing hydrocarbons, comprising the following constituents in fluid connection with one another: (a) a means for providing the input stream containing hydrocarbons, (b) a means for supplying the input stream containing hydrocarbons to a partial oxidation stage, (c) a partial oxidation stage, a means for supplying a stream of an oxygen-containing oxidant to the partial oxidation stage, a means for discharging a raw synthesis gas stream containing hydrogen, carbon monoxide, carbon dioxide and methane from the partial oxidation stage, (d) a means for dividing the raw synthesis gas stream into a first raw synthesis gas substream and into a second raw synthesis gas substream, (e) a methanol synthesis reactor, a means for introducing at least a portion of the first raw synthesis gas substream into the methanol synthesis reactor, (f) a means for discharging a methanol-containing first reactor product stream from the methanol synthesis reactor, a means for cooling the first reactor product stream to below its dew point, a phase separation apparatus for separating the cooled first reactor product stream into a first liquid product stream and a first residual gas stream containing unconverted synthesis gas constituents and inert components, a means for discharging the first liquid product stream from the process as a raw methanol product stream, (g) a means for dividing the first residual gas stream into a methanol synthesis purge stream and into a recycle stream which is recycled to the methanol synthesis reactor, (h) a sorption apparatus for removal of carbon dioxide using a physical or chemical sorption process, a heating apparatus having at least one burner, a means for introducing at least a portion of the second raw synthesis gas substream into the sorption apparatus, a means for discharging a carbon dioxide-depleted synthesis gas stream and a carbon dioxide-enriched gas stream from the sorption apparatus, (j) a cryogenic gas fractionation stage suitable for separation of the carbon dioxide-depleted synthesis gas stream in the cryogenic gas fractionation stage into the following substreams: (j1) a carbon monoxide-rich gas stream which is dischargeable from the process as a carbon monoxide product stream, (j2) a hydrogen-rich gas stream, (j3) an offgas stream containing methane, hydrogen and carbon monoxide which is at least partially introduceable to the at least one burner of the heating apparatus as a first heating gas, means for introducing at least a portion of the carbon dioxide-depleted synthesis gas stream into the cryogenic gas decomposition stage, further comprising a means which allow the carbon dioxide-enriched gas stream to be at least partially introduced into the methanol synthesis reactor.

13. The plant according to claim 12, further comprising a means which allow the hydrogen-rich gas stream to be at least partially supplied to the burner of the heating apparatus as a second heating gas.

14. The plant according to claim 12, further comprising a means which allow a portion of the input stream containing hydrocarbons to be supplied to the burner of the heating apparatus as a third heating gas.

15. The plant according to claim 12, further comprising a means which allow at least a portion of the methanol synthesis purge stream to be supplied to the burner of the heating apparatus as a fourth heating gas.

16. The plant according to claim 12, further comprising a means which allow the heating apparatus to be used for steam production, wherein the steam produced is at least partially usable as a moderator in the partial oxidation stage.

17. The plant according to claim 12, further comprising a means which allow the heating apparatus to be used for steam production, wherein the steam produced is at least partially providable to external consumers.

18. The plant according to claim 12, further comprising a means which allow a carbon dioxide-containing gas stream deriving from a process-external source to be additionally introducible into the methanol synthesis reactor.

19. The plant according to claim 12, further comprising a means which allow the heating apparatus to be usable for preheating the input stream containing hydrocarbons and/or the stream of the oxygen-containing oxidant.

20. A plant according claim 12, further comprising a means which allow the methanol synthesis purge stream to be separable using a separation apparatus, preferably a membrane separation apparatus, into a first purge stream enriched in hydrogen and into a second purge stream depleted in hydrogen and enriched in carbon oxides and methane, at least a portion of the first purge stream enriched in hydrogen to be suppliable to the burner of the heating apparatus as a fourth heating gas, at least a portion of the second purge stream enriched in carbon oxides and methane to be suppliable to the partial oxidation stage.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0062] Developments, advantages and possible applications of the invention are also apparent from the following description of working and numerical examples and the drawings. The invention is formed by all of the features described and/or depicted, either on their own or in any combination, irrespective of the way they are combined in the claims or the dependency references therein.

[0063] FIG. 1 a schematic representation of the process/the plant according to one embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0064] In the configuration of a process/a plant according to the invention shown in FIG. 1 conduit 11 supplies an input stream containing hydrocarbons, for example natural gas, in a preferred example natural gas having a methane content of at least 80% by volume, to a noncatalytic partial oxidation stage (POX) 10. The oxygen required as an oxidant for the partial oxidation is supplied to the partial oxidation stage via conduit 13. The noncatalytic partial oxidation stage is operated under partial oxidation conditions known per se. As an additional operating medium the POX stage is optionally supplied with steam and/or carbon dioxide as moderator.

[0065] In a further example (not shown) the partial oxidation stage may be in the form of an autothermal reformer (ATR) which in one example is operated at a pressure of 60 bara. As an additional operating medium the ATR is optionally supplied with steam and/carbon monoxide as moderator.

[0066] The partial oxidation stage 10 carries out an at least partial conversion of the input stream containing hydrocarbons under synthesis gas production conditions to afford a raw synthesis gas stream containing hydrogen (H.sub.2), carbon monoxide (CO) and components inert in the context of methanol synthesis such as methane (CH.sub.4) which is discharged from the partial oxidation stage and divided into a first raw synthesis gas substream (conduit 14) and into a second raw synthesis gas substream (conduit 16).

[0067] Via conduit 14 the first raw synthesis gas substream is supplied to a methanol synthesis reactor 20, in which there follows an at least partial conversion of the first raw synthesis gas substream under methanol synthesis conditions. The resulting raw methanol product is via conduit 18 discharged from the methanol synthesis reactor 20 and sent for further processing, workup, storage or to a consumer.

[0068] For the purposes of the present description the term “methanol synthesis reactor” and the reference numeral 20 are to be understood as meaning that they comprise not only the catalytic reactor(s) for methanol synthesis but also further customary constituents of a methanol synthesis unit familiar to those skilled in the art (not shown): [0069] conduits and at least one compressor for construction of a circuit for unconverted synthesis gas, [0070] coolers for cooling the reactor product stream of the methanol synthesis reactor, [0071] a phase separation apparatus for separating the cooled reactor product stream of the methanol synthesis reactor into a first liquid product stream and a first residual gas stream containing unconverted synthesis gas constituents and inert components, [0072] an apparatus for dividing the first residual gas stream into a methanol synthesis purge stream and into a recycle stream which is recycled to the methanol synthesis reactor.

[0073] The methanol synthesis purge stream is discharged from the methanol synthesis reactor via conduit 22.

[0074] The second raw synthesis gas substream is introduced into a sorption apparatus 30 for removal of carbon dioxide via conduit 16. In one example the sorption apparatus operates according to a physical sorption process and cryogenic methanol is used as the absorbent/scrubbing medium (Rectisol process). Details of this process are known to those skilled in the art. This results in further synergistic advantages since in one example a portion of the methanol produced in the methanol synthesis reactor 20 may be used as scrubbing medium. In one example portions of the apparatuses for workup of the raw methanol product discharged from the methanol synthesis reactor 20 via conduit 18 may also be used for regenerating the scrubbing medium laden with carbon dioxide. In one example waste heat from the apparatuses for workup of the raw methanol product may be used for heating or preheating of the scrubbing medium laden with carbon dioxide, for example for the purposes of regeneration.

[0075] For the purposes of the present description the term “sorption apparatus” and the reference numeral 30 are to be understood as meaning that they comprise not only the actual removal/separation of carbon dioxide but also the regeneration of the employed sorption medium and the production of a carbon dioxide-enriched gas stream. The carbon dioxide-enriched gas stream is compressed to methanol synthesis pressure in a compressor 32 arranged in the conduit path of the conduit 34 and according to the invention supplied to the methanol synthesis reactor 20 via conduit 34. In one example conduit 34 opens into conduit 14, by means of which the first raw synthesis gas substream is introduced into the methanol synthesis reactor. In one example conduit 34 opens directly into the methanol synthesis reactor.

[0076] A carbon dioxide-depleted synthesis gas stream is discharged from the sorption apparatus 30 via conduit 36, passed to a cryogenic gas fractionation stage 40 and introduced thereto. The cryogenic gas fractionation stage separates the carbon dioxide-depleted synthesis gas stream into the following substreams:

[0077] (1) A carbon monoxide-rich gas stream. This stream is discharged from the process as a carbon monoxide product stream via conduit 42.

[0078] (2) A hydrogen-rich gas stream. This is supplied via conduit 44 to the methanol synthesis reactor 20 and used therein to establish the desired stoichiometry number for the methanol synthesis. In one example the stoichiometry number thus established is between 1.8 and 2.4, preferably between 2.0 and 2.2. In one example the stoichiometry number thus established is 2.1.

[0079] In one example (not shown) the hydrogen-rich gas stream is at least partially supplied to a burner of a heating apparatus 50 as heating gas. In one example (not shown) the entire hydrogen-rich gas stream is supplied to the burner of the heating apparatus 50 as heating gas and in one example (not shown) the proportion of the hydrogen-rich gas stream not required for establishing the desired stoichiometry number for the methanol synthesis is supplied to the burner of the heating apparatus 50 as heating gas.

[0080] In one example conduit 44 opens into conduit 14, by means of which the first raw synthesis gas substream is introduced into the methanol synthesis reactor. In one example conduit 44 opens directly into the methanol synthesis reactor.

[0081] (3) An offgas stream containing inert components, methane, hydrogen and carbon monoxide. This stream is at least partially supplied as heating gas to a burner of a heating apparatus 50 via conduit 46. The burner of the heating apparatus 50 is further supplied via conduit 56 with an input stream containing hydrocarbons, for example natural gas, as fuel gas. In one example the burner of the heating apparatus 50 is further supplied via conduit 22 with at least a portion of the methanol synthesis purge stream from the methanol synthesis reactor as fuel gas.

[0082] In one example the heating apparatus 50 is used for steam production. To this end boiler feed water is introduced into the heating apparatus 50 via conduit 52 and evaporated therein. The steam produced is discharged from the heating apparatus 50 via conduit 54. In one example a portion of the steam produced is used as moderator in the partial oxidation stage 10. In one example at least a portion of the steam produced is provided to external consumers (export steam).

[0083] Further advantages and an even more flexible process mode result from the following examples which are combinable with the basic process according to the invention:

[0084] In one example carbon dioxide from a process-external CO.sub.2 source is additionally introduced into the partial oxidation stage. This is especially advantageous when the process-external CO.sub.2 stream is available at elevated pressure so that compression before introduction into the partial oxidation stage is minimized or even completely avoided.

[0085] In one example carbon dioxide from a process-external CO.sub.2 source is additionally introduced into the methanol synthesis reactor.

[0086] In one example hydrogen from a process-external hydrogen source is used to adjust the desired stoichiometry number for the methanol synthesis.

Numerical Example

[0087] The following table shows a comparison of calculated parameters of the invention with a process scheme according to the prior art (DE 10214003 B34) for a predetermined production amount of CO and methanol.

TABLE-US-00001 TABLE Comparison of calculated parameters of the invention with a process scheme according to the prior art (DE 10214003 B4) for a predetermined production amount of CO and methanol. Comparative Invention CO production kg/h 14560 14558 MeOH production kg/h 34296 34308 Natural gas feed kg/h 27914 27999 Oxygen feed kg/h 35860 35621 Kg of syngas/kg of 2.071 2.015 Synthesis gas to kg/h 25949 2582 Synthesis gas to kg/h 31861 30585 CO2 recycling kg/h 2181 1938 Compressor power kW 160 130 Compressor cooling kW 140 117 MeOH feed stream kg/h 36856 3764 Stoichiometry 2.085 2.086 CO2 to MeOH mol % 1.76% 2.74% CO to MeOH mol % 29.74% 28.43% H2 to MeOH mol % 67.43% 67.75% CO/CO2 to MeOH 16.9 10.4 Superheated steam kg/h 127431 124781

[0088] The invention achieves the following advantages over the prior art: [0089] provision of a gas having a higher CO.sub.2 content which is more suitable for methanol synthesis results in a higher efficiency of the methanol synthesis. [0090] Less CO.sub.2 requires compression to a lower pressure. The saving in terms of compressor power and coaling power is about 15% to 20%. [0091] The oxygen demand falls by about 0.5% to 0.8%. [0092] An excess steam production which is about 2% lower may be advantageous when no external utilization of steam and thus no steam export is desired.

LIST OF REFERENCE SYMBOLS

[0093] [10] Partial oxidation stage [0094] [11] Conduit [0095] [13] Conduit [0096] [14] Conduit [0097] [16] Conduit [0098] [18] Conduit [0099] [20] Methanol synthesis reactor [0100] [22] Conduit [0101] [30] Sorption apparatus [0102] [32] Compressor [0103] [34] Conduit [0104] [36] Conduit [0105] [40] Cryogenic gas fractionation stage [0106] [42] Conduit [0107] [44] Conduit [0108] [46] Conduit [0109] [50] Heating apparatus [0110] [52] Conduit [0111] [54] Conduit [0112] [56] Conduit

[0113] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.