METHOD AND SYSTEM FOR USING THE CARBON OXIDE ARISING IN THE PRODUCTION OF ALUMINIUM

Abstract

A process can utilize carbon oxides formed in the production of aluminum, by electrolytic reduction of aluminum oxide in a melt using at least one anode made of a carbon-comprising material. A pyrolysis of hydrocarbons, in particular methane or natural gas, is carried out in which pyrolysis carbon and hydrogen are formed. The pyrolysis carbon is used for the production of the at least one anode. The hydrogen formed in the pyrolysis of methane is mixed with carbon dioxide and/or carbon monoxide from the electrolytic production of aluminum, to produce a gas stream which is parsed to a further use. An integrated plant contains an electrolysis apparatus for producing aluminum by melt-electrolytic reduction of aluminum oxide, and also contains at least one reactor in which pyrolysis carbon and hydrogen are produced by pyrolysis of hydrocarbons.

Claims

1: A process for utilizing carbon oxides formed during an electrolytic production of aluminum by electrolytic reduction of aluminum oxide, the process comprising: carrying out a pyrolysis of hydrocarbons, in which pyrolysis carbon and hydrogen are formed, and mixing the hydrogen formed in the pyrolysis of the hydrocarbons with carbon dioxide and/or carbon monoxide from the electrolytic production of aluminum, to produce a gas stream which is passed to a further use, wherein the electrolytic reduction of aluminum oxide is in a melt using at least one anode made of a carbon-comprising material, and wherein the pyrolysis carbon is used to produce the at least one anode.

2: The process according to claim 1, further comprising: feeding a hydrogen-comprising gas stream and a gas stream comprising carbon dioxide and/or carbon monoxide, or a gas stream comprising a mixture of hydrogen and carbon dioxide d/or carbon monoxide, to a reverse water gas shift reaction in which at least part of the carbon dioxide is reacted with hydrogen and reduced to carbon monoxide, to produce a synthesis gas stream.

3: The process according to claim 2, wherein the synthesis has stream is subsequently fed to a chemical or biotechnological plant.

4: The process according to claim 2, wherein the synthesis gas stream is used for producing methanol, methane, at least one alcohol, and/or at least one other chemical of value.

5: The process according to claim 1, wherein a ratio of carbon dioxide and carbon monoxide in a gas stream obtained in the electrolytic production of aluminum is set via selection of an anodic current density in an electrolysis.

6: The process according to claim 1, wherein a ratio of carbon dioxide and carbon monoxide in a gas stream obtained in the electrolytic production of aluminum is set via selection of a temperature of an electrolyte.

7: The process according to claim 1, wherein a ratio of carbon dioxide and carbon monoxide in a gas stream obtained in the electrolytic production of aluminum is set via selection of a reactivity of the pyrolysis carbon of the at least one anode.

8: The process according to claim 1, wherein volatile hydrocarbons formed in the production of the at least one anode are recirculated via a conduit to a reactor for the pyrolysis of hydrocarbons.

9: The process according to claim 1, wherein part of the carbon oxides formed in the electrolytic production of aluminum is recirculated via a conduit to a reactor for the pyrolysis of hydrocarbons.

10: An integrated plant comprising: an electrolysis apparatus for producing aluminum by melt-electrolytic reduction of aluminum oxide, at least one reactor in which pyrolysis carbon and hydrogen are produced by pyrolysis of hydrocarbons, comprises at least one apparatus in which anodes for the electrolysis of aluminum are produced from the pyrolysis carbon or a carbon mixture comprising the pyrolysis carbon, at least one apparatus in which hydrogen from the pyrolysis is mixed with carbon oxides from the electrolysis of aluminum, to obtain a resulting gas mixture, and at least one feed device for passing the resulting gas mixture to a further use.

11: The integrated plant according to claim 10, further comprising at least one device in which a reverse water gas shift reaction is carried out and which is in functional communication with the at least one reactor in which pyrolysis of methane occurs.

12: The integrated plant according to claim 11, further comprising at least one chemical or biotechnological plant which is in functional communication with the at least one reactor or with the at least one device in which a reverse water gas shift reaction is carried out.

13: The integrated plant according to claim 10, wherein the at least one apparatus for producing anodes is connected via a feed device to the at least one reactor, where carbon produced pyrolytically in the at least one reactor is fed via the at least one feed device to the at least one apparatus for producing anodes, and a binder and optionally other carbons are optionally fed via a further feed device to the at least one apparatus for producing anodes.

14: The integrated plant according to claim 12, wherein the integrated plant comprises at least one conduit for hydrogen which leads from the at least one reactor to the at least one chemical or biotechnological plant, and/or wherein the integrated plant comprises at least one conduit for hydrogen which leads from the at least one reactor to the at least one device in which a reverse water gas shift reaction is carried out.

15: The integrated plant according to claim 12, wherein the integrated plant comprises at least one conduit for carbon dioxide and/or carbon monoxide which leads from the electrolysis apparatus to the at least one device in which a reverse water gas shift reaction is carried out or to the at least one chemical or biotechnological plant.

16: The integrated plant according to claim 12, wherein the integrated plant comprises at least one conduit for synthesis gas comprising at least carbon monoxide and hydrogen, wherein the at least one conduit leads from the at least one device in which a reverse water gas shift reaction is carried out to the at least one chemical or biotechnological plant.

17: The process according to claim 1, wherein the hydrocarbons are natural gas or methane.

18: The integrated plant according to claim 10, wherein the hydrocarbons are natural gas or methane.

Description

[0052] The present invention will be illustrated below with the aid of working examples with reference to the accompanying drawings. The drawings show:

[0053] FIGS. 1 and 2 a schematic simplified plant flow diagram of a plant according to the invention for utilizing the carbon oxides formed in the melt-electrolytic production of aluminum.

[0054] In the following, reference will firstly be made to FIGS. 1 and 2 and an illustrative variant of the process of the invention and also an integrated plant which can be used in the process will be explained in more detail with the aid of this schematically simplified depiction. Only the essential plant parts of such an integrated plant are shown by way of example in the drawing. The integrated plant comprises a plant region in which a methane pyrolysis process is carried out, with this plant region comprising, inter alia, a methane pyrolysis reactor 1 in which a pyrolysis of methane or of another hydrocarbon or of natural gas is carried out. For this purpose, methane is fed via a feed conduit 2 to this pyrolysis reactor 1 and energy is supplied to the reactor 1 via a device 5 in order to bring the methane to the temperature of, for example, more than 800° C. required for the pyrolysis. Hydrogen and pyrolysis carbon are formed by the pyrolytic decomposition in the methane pyrolysis reactor 1. The hydrogen is conveyed from the reactor 1 via the conduit 4 into a further reactor 13 in which a reverse water gas shift reaction, which will be explained in more detail later, takes place. The pyrolysis carbon produced in the reactor 1 is fed via a feed device 3 to an apparatus 6 in which anodes for the melt electrolysis are produced from the pyrolysis carbon or a carbon mixture of the abovementioned type. The volatile hydrocarbons formed in the production of the anode are recirculated via a conduit 19 to the methane pyrolysis reactor 1.

[0055] A binder, for example pitch, and optionally further carbon sources such as calcined petroleum coke are fed to this apparatus 6 via a further feed device 7 and the electrodes (anodes) produced in this way in the apparatus 6 are then conveyed via a further feed device 8 from the apparatus 6 to the plant 9 in which the melt flux electrolysis of aluminum oxide takes place. This plant 9 is supplied via various feed devices 10, which are depicted here in schematically simplified form only by a single line, with the further starting materials required for the melt flux electrolysis, namely aluminum oxide, cryolite which is used for lowering the melting point of the solids to be melted and also energy which is necessary to bring this mixture of solids to the melting temperature of the eutectic, which is generally about 950° C. Aluminum is then formed as product in this plant 9 and can be discharged from the plant via the discharge device 11, Furthermore, a gas mixture of carbon dioxide and carbon monoxide in a ratio which depends on various parameters in the electrolysis of the aluminum oxide is formed in the plant 9 by oxidation of the anode carbon. This gas mixture is discharged from the plant 9 via the conduit 12 and fed to a reactor 13 for a reverse water gas shift reaction. Part of this gas mixture can alternatively be discharged from the plant 9 via the conduit 20 and fed to the methane pyrolysis reactor 1.

[0056] The reverse water gas shift reaction which is carried out in the reactor 13 and proceeds according to the reaction equation (3) above serves to lower the proportion of carbon dioxide in the gas mixture and increase the proportion of carbon monoxide in the gas mixture. For this purpose, the reactor 13 is supplied via the conduit 4 with hydrogen which reacts with the gas mixture from the plant 9 for the melt electrolysis, with energy also being supplied to the reactor 13 via the feed device 14 in order to bring the gas mixture to the appropriately higher temperatures as are necessary to shift the equilibrium of the reverse water gas shift reaction according to reaction equation (3) in the direction of the products carbon monoxide and water. In this way, a synthesis gas which comprises hydrogen, carbon monoxide and optionally a proportion of carbon dioxide is produced in the reactor 13 and this can subsequently be discharged from the reactor 13 via the conduit 15 and fed to a chemical or biotechnological plant 16. Further hydrogen originating from the pyrolysis of methane 1 can optionally be fed to this plant 16 via the conduit 17 drawn in as a broken line in order to increase, for example, the content of hydrogen in the gas mixture.

[0057] In principle, the reactor 13 in which the reverse water gas shift reaction takes place can, in a variant of the invention, also be omitted and a gas mixture which is discharged from the melt flux electrolysis via the conduit 12 can be fed directly via a continuous conduit to the plant 16, since this gas mixture from the conduit 12 already comprises carbon monoxide and the required hydrogen can be fed directly via the conduit 17 to the chemical or biotechnological plant 16, so that a mixture of carbon monoxide, optionally carbon dioxide and hydrogen from the methane pyrolysis is ultimately provided in the plant 16 and this gas mixture is a synthesis gas which can then be reacted in the plant 16 to give a further product such as methanol or another alcohol. This product is then discharged from the chemical or biotechnological plant 16 via the conduit 18.

[0058] According to the present invention, a gas stream 15, which can be passed to a further use, is thus in the simplest case produced by mixing a hydrogen-comprising gas stream 4 with a gas stream 12 comprising at least carbon monoxide from the melt flux electrolysis 9. The reactor 13 for the reverse water gas shift reaction can be omitted, so that the two gas streams 4 and 12 can be combined upstream of the chemical or biotechnological plant 16 and then fed via a conduit 15 to the plant. However, when the reactor 13 is omitted, it is likewise possible to feed hydrogen 4 and carbon monoxide and/or carbon dioxide 12 as separate gases to the plant 16, so that mixing of these gas streams in principle takes place only in the plant 16. This variant is likewise encompassed by the scope of protection of the present invention.

LIST OF REFERENCE NUMERALS

[0059] 1 Methane pyrolysis process comprising methane pyrolysis reactor [0060] 2 Feed conduit for methane or other hydrocarbons [0061] 3 Feed device for pyrolysis carbon [0062] 4 Conduit for hydrogen [0063] 5 Device for the supply of energy [0064] 6 Apparatus for anode production [0065] 7 Feed device for binder and optionally petroleum coke or other carbons [0066] 8 Feed device for anodes [0067] 9 Plant for the melt flux electrolysis [0068] 10 Feed devices for energy, aluminum oxide and cryolite [0069] 11 Discharge device for aluminum [0070] 12 Conduit for gas mixture [0071] 13 Reactor for reverse water gas shift reaction [0072] 14 Feed device for energy [0073] 15 Conduit for synthesis gas [0074] 16 Chemical or biotechnological plant [0075] 17 Conduit for hydrogen [0076] 18 Discharge device for chemical products [0077] 19 Conduit for volatile hydrocarbons [0078] 20 Conduit for gas mixture [0079] 21 Conduit for methane from the methanation plant