WO2025073665A1

WO2025073665A1 - Closed carbon loop process

Info

Publication number: WO2025073665A1
Application number: PCT/EP2024/077546
Authority: WO
Inventors: Lukas Mayr; Dieter Flick; Jens Peter JOHANNSEN; Andre BADER; Marco Bosch; Stefan Hannemann
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2023-10-06
Filing date: 2024-10-01
Publication date: 2025-04-10
Anticipated expiration: 2026-04-06

Abstract

The present invention relates to a closed carbon loop process comprising: a first step, wherein hydrogen is produced via water electrolysis, a second step, wherein oxygen and/or steam is reacted in a carbon gasification step with solid carbon produced in the fifth step and hydrogen produced in the first step to yield carbon oxides and/or hydrocarbons, wherein the hydrocarbons optionally comprise hetero atoms, a third step, wherein the carbon oxides and/or hydrocarbons produced in step two are converted in a chemical reaction step into carbon-containing products, a fourth step, wherein the carbon-containing products produced in step three are used until they become waste, a fifth step, wherein the waste based on the carbon-containing product produced in step three is converted into solid carbon and a hydrogen-containing product.

Description

Closed Carbon Loop Process

Description

The present invention relates to a closed carbon loop process comprising: a first step, wherein hydrogen and oxygen are produced via water electrolysis, a second step, wherein the oxygen is reacted in a carbon gasification step with solid carbon produced in the fifth step and hydrogen produced in the first step to yield carbon oxides and/or hydrocarbons, wherein the hydrocarbons optionally comprise hetero atoms, a third step, wherein the carbon oxides and/or hydrocarbons produced in step two are converted in a chemical reaction step into carbon-containing products, a fourth step, wherein the carbon-containing products produced in step three are used until they become waste, a fifth step, wherein the waste based on the carbon-containing product produced in step three is converted into solid carbon and a hydrogen-containing product, preferably hydrogen.

Hydrogen (H2) produced with a low product carbon footprint (PCF) is both required as a feedstock for the (petro-)chemical industry and as an alternative fuel in the challenge to reduce emission of greenhouse gases such as CO2. A major route to green H2 is electrolysis of water utilizing electricity from renewable sources such as solar and wind energy.

Unfortunately, the energy demand of water electrolysis is high and therefore only profitable at locations with low-prized renewable electricity. Such locations are especially wind parks near the coast, offshore or regions with high annual solar radiation. The locations of hydrogen demand, like chemical production sites, however, are not necessarily located close to the locations with favorable conditions to produce sufficient amounts of green electricity. The chemical production sites are often located far inland.

In addition, there is often no suitable carbon source available to produce raw materials like synthetic hydrocarbons at locations with low-prized renewable electricity. As a result, energy-intensive "direct air capture" or carbon capture from other CO2 sources are needed.

Thus, geographic decoupling of places with abundant renewable energy, such as from wind and/or solar power, and places of energy demand, such as large industrial sites, will remain and require energy vectors.

Such energy vectors could be hydrocarbons. For the chemical industry hydrocarbon are on the one hand an energy source, on the other hand a material source of hydrogen and carbon. Vectors under consideration, such as hydrogen or ammonia, require new infrastructure, whereas the logistic of hydrocarbon is well developed. Typical hydrocarbons used in the chemical industry are naphtha, natural gas (NG), synthetic natural gas (SNG), methanol, ethylene and/or propylene. For these chemicals even a pipeline infrastructure exists.

Beside the logistic challenges, a large portion of recyclable waste is still just used thermally generating CO2. Waste gasification concepts produce low-hydrogen synthesis gas and circumvent this problem, but create a new problem, as this low-hydrogen synthesis gas can only be used as raw material for the chemical value chain if large quantities of hydrogen is added.

Some kinds of closed carbon loops have already been disclosed:

WO 2021/239831 discloses a circular carbon process including a methanation step, a methane pyrolysis and using the pyrolytic carbon as a reducing agent in a chemical process producing carbon monoxide that is used for the methanation step. These three process steps are preferably conducted on one side as a joint plant set-up. The benefit of WO 2021/239831 is that carbon can still be used as a reducing agent resulting in carbon oxide emissions, but this carbon oxide is not emitted to the atmosphere but converted to methane resulting in a closed carbon cycle.

DE 10 2013 219 681 describes the use of carbon as an energy carrier transporting hydrogen. A carbon cycle is disclosed containing production of methane by soot from methane pyrolysis and hydrogen from water electrolysis, such methane is transported in a pipeline to a production site, where hydrogen is needed for energy generation, therefore, at that production site methane is dissociated into hydrogen and soot, finally that soot is transported to the place of the methanation step.

Task

Thus, the present invention addresses several challenges: transport of hydrogen, availability of carbon as raw material for chemicals or fuels as an alternative to fossil carbon, CO2 emissions of waste recycling.

It is an object of the present invention to demonstrate a closed carbon loop with low CO2 emissions. It is a further object of the present invention to demonstrate a closed carbon loop without any need of transporting hydrogen. It is a further object of the present invention to demonstrate a closed carbon loop with an alternative for fossil carbon as raw material and thus, avoiding high transformation cost in chemical industry by providing a drop-in solution. It is a further object of the present invention to demonstrate a closed carbon loop to increase energy efficiency of synthetic raw material production. It is a further object of the present invention to demonstrate a closed carbon loop meeting recycling quota and avoiding CO2 emissions from waste treatments.

Invention

This task is solved by the present invention relating to a closed carbon loop process comprising: a first step, wherein hydrogen and oxygen are produced via water electrolysis, a second step, wherein the oxygen, preferably produced in the first step, and/or steam is reacted in a carbon gasification step with solid carbon produced in the fifth step to carbon oxide and wherein hydrogen produced in the first step is reacted with that carbon oxides to hydrocarbons, wherein the carbon oxides and/or hydrocarbons optionally comprise hetero atoms, preferably O, S, P, N, Si, Zn, a third step, wherein the hydrocarbons produced in step two are converted in a chemical reaction step into carbon-containing products, a fourth step, wherein the carbon-containing products produced in step three are used until they become waste, a fifth step, wherein the waste based on the carbon-containing product produced in step three is converted into solid carbon and at least one hydrogen-containing product, preferably hydrogen.

General comments

The present invention provides a solution for all three challenges: waste streams are not converted into carbon oxide or low-hydrogen synthesis gas, but (i) pyrolyzed to solid carbon and hydrogen or (ii) pyrolyzed to solid carbon, especially recovered carbon black, gaseous hydrocarbons, liquid hydrocarbons and/or carbon oxides, wherein the hydrocarbons may comprise hetero atoms, preferably O, S, P, N, Si, Zn.

The hydrocarbon can be used materially as a drop-in solution and thus be a low-cost alternative to fossil hydrocarbon.

The present invention discloses to recycle waste on a large-scale basis without CO2 emissions and thus without the purchase of CO2 certificates. In addition, the product has a recycled content of 100 %. The present invention also helps meeting recycling quotas and reducing overall CO2 emissions.

At the site of hydrocarbon production, significantly more products can be produced with the same energy input than in comparable processes with a "carbon capture" step. In addition, the needed amount of hydrogen is at least halved in view of the CO2-route. The closed carbon loop described can be realized by a variety of technologies, both with already established processes and with new technologies further increasing energy efficiency.

First Step

In the first step hydrogen and oxygen are produced via water electrolysis. The water electrolysis of step one can be done with different technologies like alkaline, polymer electrolyte membrane (PEM) or as solid oxide electrolysis cell (SOEC). Typical parameters are described, e.g., in (Final Report BMBF funded project: „Studie uber die Planung einer Demonstrationsanlage zur Wasserstoff-Kraftstoffgewinnung durch Elektrolyse mit Zwischenspeicherung in Salzkavernen unter Druck PlanDelyKaD". DLR et al., Christoph Noack et al, Stuttgart 5.2.2015).

The water electrolysis is preferably processed by using regenerative energy, e.g., energy from wind parks, solar, geothermal energy, hydropower and/or nuclear power.

The water electrolysis is preferably conducted at a site with low electricity cost, preferably with electricity costs below 50 ELIR/MW. Depending on the actual price of the electricity, the water electrolysis can also preferably be operated discontinuously.

The water electrolysis production site is preferably close to the site of the generation of regenerative energy. Preferably, the water electrolysis and the generation of regenerative energy are conducted at the same production site.

Second step

In the second step the oxygen, preferably produced in the first step, and/or steam, preferably oxygen and optionally steam, is reacted in a carbon gasification step with solid carbon produced in the fifth step and the hydrogen produced in the first step to hydrocarbons. Optionally, the carbon gasification is conducted in a two-step process: reaction of oxygen and carbon to carbon oxide and reaction of these carbon oxide with hydrogen to hydrocarbons. The produced hydrocarbons, optionally comprising hetero atoms, are preferably liquid hydrocarbons, preferably naphtha (Fischer-Tropsch products) and derived naphtha-like-fractions, methanol, ethanol, methane, olefines, especially ethylene and propylene, saturated and aromatic hydrocarbons like benzene, toluene or xylene, more preferably naphtha and/or methanol.

The carbon gasification reaction is well known in the state of the art. Depending on the ratio of hydrogen and carbon monoxide contained in the gas mixture, various products can be produced from syngas, for example liquid fuels using the Fischer-Tropsch process at a preferred ratio of hydrogen to carbon monoxide of 1 - 2 : 1 , alcohols such as methanol or ethanol at a preferred ratio of about 2 : 1 , or methane or synthetic natural gas (SNG) by methanation reaction at a preferred ratio of about 3 : 1.

Preferably, the conversion of solid carbon of step two is conducted at locations of low-prized available renewable energy, preferably with electricity costs below 50 ELIR/MW. Preferably, step one and step two are conducted at the same production site, the hydrocarbon production site. Preferably, the hydrogen produced in step one and used in step two has neither to be compressed nor transported nor stored. Whereas - in time when the water electrolysis is conducted discontinuously - the produced hydrocarbons, preferably liquid hydrocarbons, can easily be stored at the site of the hydrocarbon production and/or at the site of the chemical production.

The produced hydrocarbon of step two can be used as raw material in the chemical industry. It can be transported to chemical production sites via established transport routes like pipelines. Thus, an additional step is preferably the transport of the raw material produced in step two to the chemical production site conducting the chemical conversion of step three, preferably in existing pipeline or via shipping.

Third step

In the third step the hydrocarbons produced in step two are converted in a chemical reaction step into carbon-containing products. Beside the hydrocarbons of step two, optionally, hydrocarbons produced in step five are converted in a chemical reaction step into carbon-containing products in the third step.

This conversion is preferably conducted continuously. Typically, this conversion is conducted at a chemical production site located far inland. Typically, the electricity costs are above 50 ELIR/MW at these chemical production site that were built up a long time ago.

Hydrocarbons, optionally comprising hetero atoms, like naphtha, methanol, olefins, and methane, among others, have a direct entry point into well-established chemical value chains and can be used directly as a “drop-in” solution. These hydrocarbons are needed to produce a variety of different carbon-containing end-products.

For example, methanol serves as a raw material in the production of olefines, formaldehyde, acetaldehyde, acetic acid, methyl acetate, acetic anhydride and vinyl acetate. Naphtha or pyrolysis oil serves as raw material for olefines such as for example ethylene and propylene, particularly in a steam cracker. Important intermediates are ethylenoxide, ethylbenzole, ethanolamines and propylenoxide, acrylic acid, aldehydes and butanols. Methane or pyrolysis gas serves as a feed for the synthesis gas production, particularly via partial oxidation.

Preferred carbon-containing end-products are styrene (e.g., Styropor, Neopor, Styrodur), ten- sides (e.g. Lutensol, Pluriol) and co-polymeres (e.g. Sokalan).

Typically, the carbon-containing products are transported by a suitable transport means, e.g., via ship or truck, to the customers.

Beside the carbon-containing product, carbon-containing waste streams might result from the production of said carbon-containing products.

Fourth step

In the fourth step the carbon-containing products produced in step three are used by custom- ers/consumers until end of life of these products and/or until the carbon-containing products become waste.

Typically, the carbon-containing products becoming waste are collected and sorted according to the respective waste management system. This system seeks to address the four most relevant different types of waste, including MSW, food waste, mixed plastics waste (often from packaging), tires, C&l waste, and C&D waste. MSW, also known as municipal solid waste, refers to the waste generated by households and other institutions within a community. Food waste, on the other hand, is waste generated from food production, processing, and consumption. C&l waste is waste generated by commercial and industrial activities, while C&D waste is waste generated from construction and demolition activities.

Preferably, the sorted carbon-containing products are transported by a suitable transport means, e.g., via ship or truck, to the production site conducting the process of step five.

Fifth step

In the fifth step the waste based on the carbon-containing products produced in step three is converted, especially pyrolyzed, into solid carbon and hydrogen, or converted, especially pyrolyzed, into solid carbon, especially recovered carbon black, gaseous hydrocarbons and liquid hydrocarbons, wherein the hydrocarbons may comprise hetero atoms. The compositions of hydrocarbons (condensable and not condensable) and recovered carbon black are known in the state of the art: They are described, e.g., in EP 0713906 A1, WO 95/03375 A1 and Jorg Woidasky, Ullmanns Encyclopedia of Industrial Chemistry, chapter 5.2.1 “Pyrolysis”, pages 15- 17, 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim (DOI:

10.1002/14356007. a21_057.pub2).

In addition, in the fifth step, the carbon-containing waste streams resulting from the production of said carbon-containing products in step three are converted, especially pyrolyzed, into solid carbon and hydrogen, or converted, especially pyrolyzed, into solid carbon, especially recovered carbon black, gaseous hydrocarbons and liquid hydrocarbons.

In addition, in the fifth step, carbon-containing products produced by any method externally from the closed carbon loop can be added to said carbon-containing products and/or carbon-containing waste stream and converted, especially pyrolyzed, into solid carbon and hydrogen or converted, especially pyrolyzed, into solid carbon, especially recovered carbon black, gaseous hydrocarbons and liquid hydrocarbons in the fifth step.

Preferably, the conversion into solid carbon and hydrogen can either be conducted directly via waste pyrolysis or via the combined processes of waste gasification, hydrating gasification, e.g., methanation, and methane pyrolysis. Preferably, the conversion into solid carbon, especially recovered carbon black, gaseous hydrocarbons and liquid hydrocarbons be conducted directly via waste pyrolysis.

Preferably, the density of the produced solid carbon is in the range of 1 to 3.5 g/cm³ (real density in xylene, ISO 8004), preferably 1.5 to 2.5 g/cm³.

Preferably, the bulk density of the produced solid carbon is in the range of 0.5 to 2.5 g/cm³, more preferably in the range of 0.75 to 1 .5 g/cm³.

The solid carbon produced in the fifth step is preferably transported by a suitable transport means, e.g., via ship or truck, to the hydrocarbon production site of step one and/or two. Due to favorable transport costs, especially in deep-sea vessels, intercontinental transport is also economically and technically feasible.

Optionally, the solid carbon is stored either on the carbon production site of step five or on the hydrocarbon production site of step one and/or two. Thus, the conversion of step five can be conducted discontinuously.

Solid carbon obtained via pyrolysis of tires is typically ground and pelletized before storage or transport. The produced hydrogen produced by the waste pyrolysis or by methane pyrolysis can either be used energetically or materially. Preferably, the pyrolytic hydrogen is used locally, e.g., in industries, for hydrogen filling stations located close to the carbon production site or for heating. Alternatively, the hydrogen is used in the chemical production site of step three converting hydrocarbon into carbon containing products. For example, hydrogen is used for heating cracking furnaces to blend GUD fuels, to heat endothermic reactions or rectification columns or to produce NH3, Syngas, downstream products like aromats, ketons (e.g., cyclododecanon), aldehydes (e.g hexanal), cyclic hydrocarbons (e.g. cyclohexan), amins (e.g., butylamine, propylamine), alcohols (e.g. butanol, heptanol, butandiol, menthol).

The carbon production site can on the one hand be located close to the chemical conduction site; on the other hand, the carbon production can be conducted decentral.

Therefore, the present invention optionally comprises an additional step of reacting hydrogen from the fifth step to (i) NH3, (iv) Syngas, (v) downstream products like aromats, ketons (e.g. cyclododecanon), aldehydes (e.g hexanal), cyclic hydrocarbons (e.g. cyclohexan), amins (e.g. butylamine, propylamine) and/or alcohols (e.g. butanol, heptanol, butandiol, menthol).

Therefore, the present invention optionally comprises an additional step of converting hydrocarbons from the fifth step in the chemical reaction step of step three into carbon-containing products.

Conversion into solid carbon and hydrogen via waste pyrolysis

Optionally, in the fifth step the waste based on the carbon-containing products produced in step three is pyrolyzed into solid carbon and hydrogen by waste pyrolysis or into solid carbon, especially recovered carbon black, gaseous hydrocarbons and liquid hydrocarbons.

In the context of the present invention, the term “waste pyrolysis” relates to a thermal decomposition or degradation of a feedstock such as end-of life-carbon-containing materials like plastic waste under inert conditions and results in a gas, a liquid, and a solid carbon (char) fraction. Optionally, the waste based on the carbon-containing products is pre-treated before entering a pyrolysis reactor. During the pyrolysis, the feedstock is converted in a pyrolysis unit into a great variety of chemicals including gases such as H₂, CO, Ci- to C4-alkanes, C₂- to C4-alkenes, ethyne, propyne, 1-butyne, pyrolysis oil such as C5+ hydrocarbons, mainly C11 to C21 hydrocarbons, having a boiling range of 25 °C to 500 °C, preferably 80 to 250°C, and char. In addition, water can be formed during the pyrolysis. The term “pyrolysis” includes slow pyrolysis, fast pyrolysis, flash catalysis and catalytic pyrolysis. These pyrolysis types differ regarding process temperature, heating rate, residence time, feed materials feed particle size, etc. resulting in different product quality. The pyrolysis unit may be operated adiabatically, isothermally, nonadi- abatically, non-isothermally, or combinations thereof. The pyrolysis reactions may be carried out in a single stage or in multiple stages.

To obtain the hydrogen and solid carbon according to the present invention, the feedstock is preferably inserted into a pyrolysis reactor using a dosing unit such as for example a screw or an extruder or a rotary valve or a pneumatic conveyor or a liquid injector. The feedstock is optionally pre-heated in e.g., a heat exchanger prior to insertion into the pyrolysis reactor and/or subjected to a pre-pyrolysis at a temperature in the range of, for example, from about 200 °C to about 360 °C. Next, the feedstock is heated in the pyrolysis reactor to a temperature in the range of from about 350 °C to about 900 °C, more preferably in the range of from 400 °C to about 550 °C, and a pressure in the range of from about 0.5 bar to about 2 bar(abs), more preferably in the range of from 0.9 bar to about 1.5 bar(abs). The pyrolysis reactor is preferably selected from the group comprising fluidized bed reactors, moving bed reactors,, screw reactors, Auger reactors, extruders, stirred tank reactors, rotary kiln reactor, reactors making use of hydrothermal treatment and/or energy input by mechanical or infrared devices and combinations thereof. Preferably, the pyrolysis is performed in the pyrolysis reactor under an inert atmosphere exempt of oxygen or air. Pyrolysis processes as such are known. They are described, e.g., in EP 0713906 A1 and WO 95/03375 A1.

Pyrolysis gases, oils and solid carbon are optionally subjected to one or more purification methods prior to the utilization as a feedstock to produce syngas or for cracking processes to produce olefins and aromatics. Suitable purification methods comprise filtration, extraction, dehalogenation, distillation, adsorption, and hydrotreatment. Such methods are for example disclosed in W02023/061834 A1 , WO 2023/061798 A1 , WO 2023/072644 A1 , WO 2023/073059 A1 , WO 2021/224287 A1, EP3997032 and EP 0713906 A1.

Conversion into solid carbon and hydrogen via a combination of waste gasification, methane synthesis and methane pyrolysis

Optionally, in the fifth step the waste based on the carbon-containing products produced in step three is converted into solid carbon and hydrogen by a combination of gasifying the waste, synthesizing the produced syngas to methane and pyrolyzing methane to hydrogen. Waste Gasification

Optionally, the waste based on the carbon-containing products is pre-treated before entering a gasifier. A suitable pre-treatment method or combination of pre-treatment methods in a pretreatment unit should provide a sufficiently homogeneous carbon-based feedstock to the waste gasification reaction and likewise enable the continuous production of syngas by waste gasification.

The pre-treatment method is preferably selected from the group comprising drying, comminution, classification, sorting, agglomeration, thermochemical methods, and biological methods.

Suitable gasifiers comprise counter-current fixed bed reactors, co-current-fixed bed reactors, bubbling fluidized bed reactors, circulation fluidized bed reactors, and downdraft or updraft entrained flow reactors. The selection of size and reactor type depends on several parameters, including the composition of the (carbonaceous) feedstock, demand of products, moisture content and availability of the (carbonaceous) feedstock. Preferably, the gasifier is an „oxygen blown" gasifier, i.e. , oxygen is preferably used as the oxidant in suitable gasifiers listed above.

The waste gasification reaction in a gasifier is typically carried out at a temperature > 700 °C in the presence of a sub-stoichiometric amount of an oxidant such as oxygen, air, steam, supercritical water, CO2, or a mixture of the aforementioned. Oxygen is the most common oxidant used for waste gasification because of its easy availability and low cost. If steam acts as oxidant, the syngas has a higher first molar ratio H2 : CO than in case if air is used as oxidant. For example, a typical molar ratio “air : combined feedstock” ranges from 0.3 to < 1.

The conversion of a feedstock in the gasifier produces a syngas which consists primarily of H2, CO, CO2, methane, other hydrocarbons, and impurities. Said syngas has a dedicated molar ratio H2 : CO when leaving the gasifier which ranges from about 0.1 : 1 to about 3 : 1 and depends on the type of solid and/or liquid feedstocks used, the oxidant and other reaction conditions applied such as temperature and/or residence time of the reactants in the gasifier.

Typical impurities in the raw syngas produced from the waste gasification reaction in a gasifier comprise chlorides, sulfur-containing organic compounds such as sulfur dioxide, trace heavy metals (e.g., as respective salts) and particulate residues. Various chemical and/or physical methods for removal of such impurities from said raw syngas such as filtration, scrubbing, hydrotreatment and ab-/adsorption are known and can be chosen and adapted according to the type and respective concentration of the impurities in said raw syngas and the tolerance to such impurities in the successive process steps.

Bulk particulate impurities can be removed from the raw syngas by a cyclone and/or filters, fine particles, and chlorides by wet scrubbing, trace heavy metals, catalytic hydrolysis for converting sulfur-containing organic compounds to H2S and acid gas removal for extracting sulfur- containing gases such as H2S. Bulky and fine particles in the syngas may also be removed with a quench in a soot water washing unit.

A waste gasification reaction usually results in further reaction products such as solid and/or highly viscous carbonaceous residues (e.g., char and/or tar) which can be further treated in separate steps.

Hydrating gasification I methane synthesis I methanation

Next, the produced syngas most preferably having a molar ratio H2 : CO of about 3 to about 1 is subjected to a hydrating gasification, preferably methanation, reaction in a hydrating gasification unit resulting in a gaseous product stream comprising methane. The hydrating gasification unit is downstream of and fluidically connected to the at least one syngas producing (waste gasification) unit and/or the at least one syngas purification unit of the waste gasification unit.

The methanation reaction is described by chemical reaction schemes (1) and (2):

The methanation reaction and suitable methanation units are for example described in S. Rbnsch, J. Schneider, S. Matthischke, M. Schluter, M. Gbtz, J. Lefebvre, P. Prabhakaran, S. Bajohr: Review on methanation - From fundamentals to current projects; Fuel 166 (2016) 276- 296 and can be selected and adapted by the skilled person.

The hydrating gasification reaction is for example a catalytic reaction using nickel on alumina catalysts, preferably a honeycomb shape catalyst, at 1 to 70 bar and 200 to 700 °C, preferably 5 to 60 bar, more preferably 10 to 45 bar and preferably 200 to 550 °C, more preferably 10 to 45 bar.

Methane pyrolysis/decomposition

Optionally the methane produced in the hydrating gasification step is purified and conditioned. In the methane pyrolysis step, also named methane decomposition, methane is pyrolyzed/de- composed into solid carbon and hydrogen. The process of methane decomposition is also referred to as methane pyrolysis since no oxygen is involved. The decomposition can be conducted in different ways known to the persons skilled in the art: catalytically or thermally, and with heat input via plasma, resistance heating, liquid metal processes or autothermal (see for example N. Muradov and T. Veziroglu: “Green” path from fossil-based to hydrogen economy: An overview of carbon-neutral technologies", International Journal Hydrogen Energy 33 (2008) 6804-6839, H.F. Abbas and W.M.A. Wan Daud: Hydrogen production by methane decomposition: A review, International Journal Hydrogen Energy 35 (2010) 1160-1190), R. Dagle et al.: An Overview of Natural Gas Conversion Technologies for Co-Production of Hydrogen and Value- Added Solid Carbon Products, Report by Argonne National Laboratory and Pacific Northwest National Laboratory (ANL-17/11, PNNL-26726) November 2017). In another variant of the invention parts of the pyrolysis gas from waste pyrolysis can be co-fed with methane, e.g., CO. Hydrogen in the pyrolysis gas can be utilized too.

Thus, the generic term methane pyrolysis covers a wide range of processes. The best known and most advanced of these are: Plasma pyrolysis, Inductive pyrolysis, Metal melting/ Metal salt melting, Moving bed process and Fluidized and fixed bed catalytic process and Partial combustion. These processes differ in the form of the energy used (thermal, electrical, etc.), the process conditions (temperature, pressure, etc.), the catalysts and/or auxiliary materials used, the process flow etc.

The solid carbon type generated in the methane decomposition depends on the reaction conditions, reactor, and heating technology. Examples are carbon black from plasma processes carbon powder from liquid metal processes granular carbon from thermal decomposition in fixed, moving, or fluidized bed reactors.

The separation of solid carbon depends on the chosen pyrolysis technology and is known by the skilled person in the art. For example, in a plasma pyrolysis the solid carbon in the form of carbon black is discharged from the reactor with the gas and then separated, e.g. by a cyclone. The solid carbon might be post-treated, e.g. agglomerated. Depending on the process and the metals used in molten metal pyrolysis, the carbon floats on the melt and is skimmed off or leaves the reactor together with the gas stream and is then separated, e.g. filter/cyclone. In addition, a purification step to remove residual metal from the carbon could be required e.g. washing, evaporation. In the catalytic pyrolysis technology and in the fixed and moving bed technology, the solid carbon is deposited on the surface of the catalyst and/or support and taken off the reactor via the catalyst and/or support.

The methane pyrolysis unit is downstream of and fluidically connected to the hydrating gasification unit and/or a purification unit of the hydrating gasification unit.

Plasma Pyrolysis

For plasma pyrolysis, a plasma with >3000 °C is generated and mixed with natural gas, which is pyrolyzed (see for example WO2015116797, WO2015116800). The gas mixture leaves the reactor at temperatures between 1500 - 2000 °C. The reaction produces solid carbon in the form of carbon black which is discharged from the reactor with the gas and then separated. Various technologies such as arc, microwave and gas plasma technologies can be used for this purpose.

Partial Combustion process or pulsed reaction process

For a partial or pulsed combustion process, the heat for the thermal pyrolysis reaction is supplied by pulsed combustion (see for example W02020118417 and US20220185664). Before a feedstock (containing hydrocarbon), is split into hydrogen and solid carbon in a combustion chamber, a combustible gas (containing hydrocarbons and oxidants) is pre-mixed in a mixing chamber. The reaction in the combustion chamber takes place when the gas mixture is heated up to 1350K and a pressure of over 20 bar is reached. Products leaving the reactor will be separated into gas and solid carbon for further processing.

Molten metal I molten metal salt

The pyrolysis processes using molten metals or molten metal salts (see for example W02020161192, WO2021183959) use the heat from the melt for pyrolysis. In addition, metals can be selected that have a catalytic effect, so that pyrolysis can take place at relatively low temperatures of about 800 - 1200 °C. Methane is fed into the molten metal; the bubbles formed in the process rise upwards in the reactor, whereby the hydrocarbons, preferably methane, decomposes and forms hydrogen and solid carbon. Depending on the process and the metals used, the carbon floats on the melt and is skimmed off or leaves the reactor together with the gas stream and is then separated. In both cases, the carbon is characterized by a very small particle size and bulk density. Due to adhesion of the melt to the carbon particles, purification of the carbon might be necessary for some processes and applications.

Catalytic processes

Catalysts can also be used to reduce the high reaction temperatures (see for example WO2011029144, WO2016154666). For hydrocarbon, preferably methane, pyrolysis, a very cost-effective alternative is the use of iron oxide catalysts. Reaction temperatures of about 700 to 1000°C can be realized. To achieve the best possible heat and mass transfer, the reactions take place, for example, in the fluidized bed, with the catalyst as the fluidized material.

Moving or fixed bed processes, preferably electric heated moving bed

The methane decomposition can either be realized as fixed bed, preferably in a cyclical operation mode, as described for example in WO 2018/083002, or in a moving bed as described for example in US 2982622, WO 2019/145279 and WO 2020/200522. The methane pyrolysis is preferably conducted in an electrically heated moving or fixed bed reactor, wherein the bed contains as substrates preferably carbon materials, metals, ceramics, and a mixture thereof, preferably at temperatures ranging from 800 to 2000°C and at pressures ranging from 1 to 100 bar.

The solid carbon formed in the pyrolysis is deposited on the substrates. The carbon from the reactor is discharged, optionally processed, or partially recycled into the reactor. Preferably, the hydrogen is purified, and the exhaust gas from the purification process is further processed.

Preferably, the solid carbon is transported or stored as produced from the pyrolysis directly, e.g., without any conditioning process steps like agglomerating, cooling and/or drying.

Preferably the reactor is filled with substrates moving from the top to the bottom of the reactor enabling a rapid heat transfer. The methane is fed into the reactor at the bottom. The mass flows are adjusted in such a way that the heat capacity flows of gas and substrates are almost the same and thus the substrates are heated by the product gas moving to the top of the reactor and the methane is heated by the heated substrates moving to the bottom of the reactor.

The decomposition process is heated electrically, preferred by resistive heating (Joule heating) of the substrate as described for example in US 2982622, WO 2019/145279 and WO 2020/200522.

Figure

Fig 1: Schematic presentation of the present invention

Fig 2: Schematic presentation of the present invention regarding recovered carbon black

Example 1 (Syngas - Fischer-Tropsch-Synthesis):

Green electricity is produced by off-shore wind. The electricity is used to produce hydrogen by on-shore PEM electrolysis at a close-by site. At the same site pyrolytic carbon is converted in the presence of water vapor and oxygen to CO and hydrogen in an entrained gasifier. Instead of shifting CO to CO2 to achieve the required H₂:CO ratio, hydrogen from the PEM electrolysis is added. A syngas with a H₂:CO ratio of 2:1 is then converted via a Fischer-Tropsch-Synthesis by an appropriate catalyst to various carbohydrates. Synthetic naphtha is isolated and transported via pipeline to a chemical site. At the chemical site, the synthetic naphtha is converted to olefines, preferably ethylene and propylene, by a hydrogen-fired steam cracker. These chemical building blocks are used to produce a huge variety of chemical products including polymers. At the end-of-life, polymers are converted by waste pyrolysis technology to carbon and hydrogen. Hydrogen is used locally, and carbon is transported back to the site close to the off-shore wind park.

Benefits

Energetic benefits:

At the site close to the off-shore wind park significantly more Fischer-Tropsch products can be produced per MWh electricity compared to an alternative route via direct air capture (DAC) and reverse water gas shift reaction( rWGS) (as described for example in (i) “CO2 from direct air capture as carbon feedstock for Fischer-Tropsch chemicals and fuels: Energy and economic analysis”, M. Marchese et al., Journal of 002 Utilization 46 (2021) 101487 or in (ii) “Energy performance of Power-to- Liquid applications integrating biogas upgrading, reverse water gas shift, solid oxide electrolysis and Fischer-Tropsch technologies", M. Marchese, Energy Conversion and Management: X 6 (2020) 100041 or in (iii) “Nutzung von CO2 aus Luft als Rohstoff fur syn- thetische", Studie im Auftrag des Ministeriums fur Verkehr Baden-Wurttemberg Kraftstoffe und Chemikalien, Dezember 2020, Dominik HeB, Michael Klumpp, Roland Dittmeyer, Institut fur Mikroverfahrenstechnik (IMVT) am KIT).

Comparison of these routes for an energy comparison for 1 mol syngas H2:CO=2:1 assuming an energy consumption electrolysis: 52 MWh/t H2:

theoretic value

The alternative route consumes approximately three times more energy than the proposed route. Example 2 (Syngas - Methanol):

Green electricity is produced by off-shore wind. The electricity is used to produce hydrogen by on-shore PEM electrolysis at a close-by site. At the same site pyrolytic carbon is converted in the presence of water vapor and oxygen to CO and hydrogen in an entrained gasifier. Instead of shifting CO to CO2 to achieve the required H2:CO ratio, hydrogen from the PEM electrolysis is added. A syngas with a H2:CO ratio of 2:1 is then converted by an appropriate catalyst to methanol. Methanol is isolated and transported via pipeline to a chemical site. At the chemical site, methanol is used as a building block to produce a huge variety of chemical products including polymers. At the end-of-life, polymers are converted by waste pyrolysis technology to carbon and hydrogen. Hydrogen is used locally, and carbon is transported back to the site close to the off-shore wind park.

Energetic benefits:

At the close to the off-shore wind park site, significantly more methanol can be produced per MWh electricity compared to an alternative route via DAC and methanol synthesis (as described for example in (i) “Wind power to methanol: Renewable methanol production using electricity, electrolysis of water and CO2 air capture”, M.J. Bos et al., Applied Energy 264 (2020) 114672) or in (ii) https://hifglobal.com/de/process/).

Comparison of these routes for an energy comparison for 1 mol methanol assuming an energy consumption electrolysis: 52 MWh/t H2:

theoretic value

Non-idealities exist for both, carbon gasification and methanol synthesis and impact therefore presumably both routes similarly.

The alternative route consumes approximately 3.5 times more energy than the proposed route. Additional Benefits for both inventive examples:

Transportation benefits:

Instead of transporting compressed hydrogen via new infrastructure (pipelines) or compression vessels, liquids products such as naphtha, methanol or other hydrocarbons can be transported without additional energy effort for compression in existing infrastructure (pipeline, ships). This is more cost efficient, even when considering the costs for carbon back-transport. Carbon as a dense solid can easily be transported by train or in ships by state-of-the art. (Examples today: Coal transport, CPC transport). Shipping cost vary due to local conditions but will also for very long distances be well below 100 €/t, whereas the transportation of hydrogen in hydrogen pipe- lines are estimated to be 150-300 €/t incl. CAPEX depreciation (Nationaler Wasserstoffrat, Was- serstofftransport, Executive Summary, Figure 1).

Emission benefits:

The waste treatment plant avoids CO₂-certificate costs.

Claims

1. Closed carbon loop process comprising: a first step, wherein hydrogen is produced via water electrolysis, a second step, wherein oxygen and/or steam is reacted in a carbon gasification step with solid carbon produced in the fifth step and hydrogen produced in the first step to yield carbon oxides and/or hydrocarbons, wherein the hydrocarbons optionally comprise hetero atoms, a third step, wherein the carbon oxides and/or hydrocarbons produced in step two are converted in a chemical reaction step into carbon-containing products, a fourth step, wherein the carbon-containing products produced in step three are used until they become waste, a fifth step, wherein the waste based on the carbon-containing product produced in step three is converted into solid carbon and a hydrogen-containing product.

2. Process according to claim 1, wherein in the second step, the oxygen and/or steam is reacted in a carbon gasification step with solid carbon produced in the fifth step to carbon oxide and wherein hydrogen produced in the first step is reacted with said carbon oxides to hydrocarbons, wherein the hydrocarbons optionally comprise hetero atoms.

3. Process according to claim 1 or 2, wherein in the fifth step, waste based on the carbon- containing product produced in step three is converted into solid carbon and hydrogen.

4. Process according to any one of claims 1 to 3, wherein the solid carbon is transported from the carbon production site of step five to the hydrocarbon production site of step two by ship or truck.

5. Process according to any one of claims 1 to 4, wherein the hydrocarbons produced in step two are transported from the hydrocarbon production site to the chemical production site of step three in pipelines or via shipping.

6. Process according to any one of claims 1 to 5, wherein the electrolysis and the carbon gasification takes place on the same industrial site, the hydrocarbon production site.

7. Process according to any one of claims 1 to 6, wherein the conversion of the waste to solid carbon to done by pyrolysis.

8. Process according to any one of claims 1 to 7, wherein the hydrocarbons produced in step two are methane, naphtha and/or methanol.

9. Process according to any one of claims 1 to 8, wherein the water electrolysis is processed by using regenerative energy and the generation of regenerative energy and the water electrolysis are conducted at the same production site.

10. Process according to any one of claims 1 to 9, wherein step one, the water electrolysis, is operated discontinuously depending on the actual price of the electricity.

11. Process according to any one of claims 1 to 10, wherein the solid carbon produced in step five has a bulk density in the range of 0.5 to 2.5 g/cc.

12. Process according to any one of claims 1 to 11 , wherein the solid carbon produced in step five is stored at the carbon production site and/or at the hydrocarbon production site.

13. Process according to any one of claims 1 to 12, wherein the hydrocarbons produced in step two are stored at the hydrocarbon production site and/or at the chemical production site.

14. Process according to any one of claims 1 to 13, wherein in step five, carbon-containing waste streams resulting from the production of said carbon-containing products in step three are additionally to said waste based on the carbon-containing product converted into solid carbon and hydrogen.

15. Process according to any one of claims 1 to 14, wherein in step five, carbon-containing products produced by any method externally from said closed carbon loop process are additionally converted into solid carbon and hydrogen.