Methods for the removal of CO2 from atmospheric air or other CO2-containing gas in order to achieve CO2 emissions reductions or negative CO2 emissions

Abstract

A process for the production of at least one of amorphous carbon or graphite, preferably of carbon black, from atmospheric air, biogas or flue gas CO2 is given, including at least the following steps: a) isolation of concentrated CO2 of a concentration of at least 50% v/v from atmospheric air, green house air or flue gas preferably by means of a cyclic adsorption/desorption process on amine-functionalized adsorbents; b) conversion of said captured CO2 into a gaseous or liquid saturated or unsaturated hydrocarbon by hydrogenation: c) cracking of said saturated or unsaturated hydrocarbon to at least one of amorphous carbon or graphite, preferably carbon black, wherein the H2 resulting from step c) is at least partially used in the hydrogenation of step b).

Claims

1. A method for the production of at least one of amorphous carbon or graphite from atmospheric air CO2 comprising at least the following steps: a) isolation of concentrated CO2 of a concentration of at least 50% v/v from atmospheric air performed by means of a cyclic adsorption/desorption process on solid support amine-functionalized adsorbents selected from the group consisting of (i) a weak ion exchange resin, (ii) an amine-functionalized cellulose, (iii) an amine-functionalized silica, and (iv) an amine-functionalized carbon, wherein the amine functions on the solid support amine-functionalized adsorbent are incorporated through covalent bonds, and wherein desorption of CO2 is performed by heating of the adsorbent to above 80° C.; b) conversion of said concentrated CO2 into a gaseous or liquid saturated or unsaturated hydrocarbon by hydrogenation; and c) cracking of said saturated or unsaturated hydrocarbon to yield H2 and at least one of amorphous carbon or graphite and sequestering the produced at least one of amorphous carbon or graphite underground, wherein the H2 resulting from step c) is at least partially used in the hydrogenation of step b), and wherein either one or a combination of the following is used to supply heat for CO2 desorption in step a): heat stored in the produced carbon and/or hydrogen in step c), and heat released from step b).

2. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected from the group consisting of: linear, branched or cyclic alkanes, linear, branched or cyclic alkenes, alkynes, or a mixture thereof.

3. The method according to claim 1, wherein further H2 required for step b) is provided via splitting of H2O.

4. The method according to claim 1, wherein further H2 required for step b) is provided via cracking of saturated or unsaturated hydrocarbon from fossil or biogenic sources in a step according to step c).

5. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected to be methane, and wherein the further two moles H2 per mole CO2 required for step b) is provided via splitting of H2O.

6. The method according to claim 1, wherein heat release from step b), in the form of methanation reaction, is used to supply heat for the CO2 desorption step of the CO2 capture device.

7. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected to be methane, and wherein cracking of methane in step c) is performed thermally above a temperature of 800° C.

8. The method according to claim 7, wherein methane cracking in step c) is performed in an electrically heated reactor.

9. The method according to claim 1, where at least one of steps a)-c) is performed continuously and/or cyclically.

10. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected to be methane, and wherein methane cracking is step c) is performed in a liquid metal reactor.

11. The method according to claim 1, wherein atmospheric CO2 is provided in step a) by an adsorption/desorption process using an amine-functionalized adsorbent where desorption of CO2 is performed by heating of the adsorbent to above 90° C., without or in combination with reducing the pressure to below 500 mbar (abs).

12. The method according to claim 1, wherein the heat stored in the produced carbon and/or hydrogen in step c) is used to preheat methane, entering the reactor of step c) and/or is used to provide heat for the CO2 desorption step of the CO2 capture device in step a).

13. The method according to claim 1, wherein parts of the hydrogen needed for step b), is provided by recycling product hydrogen from the saturated or unsaturated hydrocarbon cracking reaction in step c), and a remainder of needed hydrogen is supplied by electrolysis of water using electricity, where electrolysis is performed by either alkali, polymer electrolyte membrane or solid oxide electrolyzers, and/or wherein the remainder hydrogen is supplied by cracking according to step c), of saturated or unsaturated hydrocarbon, from fossil or biogenic sources.

14. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected to be methane, and wherein methane cracking is step c) is performed in a liquid metal reactor, using liquid tin.

15. The method according to claim 1, where the produced at least one of amorphous carbon or graphite is used in metallurgy as carburizer for tungsten carbide or silicon carbide, as reducing agent for solar grad silicon, as rubber filler, as addition for refractory bricks, as black pigment in plastics or concrete, as high temperature insulation, as asphalt or concrete binder or as construction aggregate or it is safely sequestered above or underground.

16. The method according to claim 1 for the production of carbon black, from atmospheric air, including at least the following steps: a) isolation of concentrated CO2 of a concentration of at least 50% v/v from atmospheric air; b) conversion of said captured CO2 into a gaseous or liquid saturated or unsaturated hydrocarbon by hydrogenation; c) cracking of said saturated or unsaturated hydrocarbon to yield H2 and carbon black, wherein the H2 resulting from step c) is at least partially used in the hydrogenation of step b).

17. The method according to claim 16, where the produced carbon black is used in metallurgy as carburizer for tungsten carbide or silicon carbide, as reducing agent for solar grad silicon, as rubber filler, as addition for refractory bricks, as black pigment in plastics or concrete, as high temperature insulation, as asphalt or concrete binder or as construction aggregate or it is safely sequestered above or underground.

18. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected from the group consisting of: methane, ethane, propane, butane, ethylene, propene, butylene, or a mixture thereof.

19. The method according to claim 1, wherein further H2 required for step b) is provided via splitting of H2O, wherein the splitting of H2O is a photocatalytic splitting, a photolectrochemical splitting, a radiolysis, a photobiological splitting, (thermal) plasma splitting or an electrolysis, or a combination thereof.

20. The method according to claim 1, wherein further H2 required for step b) is provided via thermal cracking of saturated or unsaturated hydrocarbon in a step according to step c), said saturated or unsaturated hydrocarbon stemming from fossil or biogenic sources, wherein the produced carbon is further used in metallurgy as carburizer for tungsten carbide or silicon carbide, as reducing agent for solar grad silicon, as rubber filler, as addition for refractory bricks, as black pigment in plastics or concrete, as high temperature insulation, as asphalt or concrete binder or as construction aggregate or it is safely sequestered above or underground.

21. The method according to claim 1, wherein further H2 required for step b) is provided via thermal cracking of methane from fossil or biogenic sources, in a step according to step c).

22. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected to be methane, and wherein the further two moles H2 per mole CO2 required for step b) is provided via splitting of H2O, wherein the splitting of H2O is a photocatalytic splitting, a photolectrochemical splitting, a radiolysis, a photobiological splitting, (thermal) plasma splitting or an electrolysis, or a combination thereof.

23. The method according to claim 1, where isolation of concentrated CO2 of a concentration of at least 50% v/v from atmospheric air in step a) is performed by means of a cyclic adsorption/desorption process on amine-functionalized adsorbents, wherein the concentration of the concentrated CO2 provided in step a) is in the range of 50-100% v/v, or in the range of 90-100% v/v.

24. The method according to claim 1, wherein the saturated or unsaturated hydrocarbon is selected to be methane, and wherein cracking of methane in step c) is performed thermally above 900° C., or in a range of 1100° C.-1600° C.

25. The method according to claim 1, wherein the step c) in the form of methane cracking is carried out continuously.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

(2) FIG. 1 shows in a) the most general conversion scheme involving DAC and subsequent conversion via a hydrocarbon to elementary carbon and in b) the situation where the hydrocarbon is alkene so as to have a closed stoichiometry:

(3) FIG. 2 a material flow diagram of the method for the production of carbon from atmospheric CO2 via methanation;

(4) FIG. 3 shows the energy consumption of the process steps of the method for the production of carbon from atmospheric CO2, wherein all enthalpy of formation values are considered at standard states of 25° C. and 101 kPa.

DESCRIPTION OF PREFERRED EMBODIMENTS

(5) FIG. 1a shows the most general conversion scheme for the sequence DAC (or capturing from other CO2-containing gases such as biogas or flue gases).fwdarw.hydrocarbon.fwdarw.elementary carbon in the form of at least one of amorphous carbon or graphite, in particular of carbon black. The first step is the step of direct air capture, either directly from the atmosphere with a CO2 content in the range of above 350 ppm v/v or from flue gas with a CO2 content in the range of 2-20% v/v, or 5-15% v/v, or from biogas with a CO2 content in the range of 30-70% v/v, or 40-55% v/v. The isolated CO2, in liquid or gaseous form, is the subjected to a step of hydrogenation to a hydrocarbon. Depending on the type of reaction of the hydrogenation a further supply of H2 beyond the ½ nH2 indicated may be required. In the following step the hydrocarbon is cracked to at least one of amorphous carbon or graphite, preferably carbon black.

(6) FIG. 1b) shows one possible implementation of such a process where the hydrocarbon into which the captured CO2 is converted is alkene.

(7) In both cases of FIGS. 1 a) and b) the elementary oxygen resulting from the hydrogenation process is either obtained directly or indirectly. In case where the oxygen is obtained indirectly this usually means that first water results from the hydrogenation which water is subsequently split into hydrogen and oxygen, and the hydrogen of that splitting is used again in the hydrogenation process as illustrated in FIG. 2. It is also possible that the water resulting from the hydrogenation process is removed from the system and the additional hydrogen required in the hydrogenation process in this case where water is generated is provided by a different source, e.g. by cracking of additional hydrocarbon from a different source.

(8) FIG. 2 schematically shows the situation where the conversion takes place via methane as the hydrocarbon. In this case per mole C two additional moles H2 are required for the methanation, which are made available via a step of cracking H2O, again offering the benefit of having a closed system and, as in case of the scheme according to FIG. 1b, a total overall reaction equation of
CO2.fwdarw.C+O2

(9) FIG. 3 finally shows the scheme according to FIG. 2 with the thermodynamic considerations showing the unexpected economic feasibility of the process using the methanation route. Given with solid arrows are the material transport pathways, dashed arrows indicate possible heat transport pathways allowing for an overall optimized thermal structuring of the process for optimum energy use, as will also be detailed further below.

Example 1. Heat Recovery from Produced Carbon and Hydrogen

(10) The carbon produced by cracking of methane is leaving the cracking reactor as either hot carbon aerosol or hot carbon particles, which roughly have the same temperature as the methane cracking reactor temperature. The carbon product particles or carbon product aerosol have to be cooled before final collection e.g. through water sprays. The heat transferred from the hot particles or hot aerosol to the water can be collected as steam or hot water, which can then be subsequently used to e.g. supply heat for the operation of the DAC plant. The heat capacity of carbon is 8.5 J/mol/K. Assuming the methane cracking reactor is operated at 1550° C., which is also roughly the temperature of the carbon product, and the carbon product is subsequently cooled to 100° C., the heat which can be recovered from cooling the carbon product is (8.5 J/mol carbon/K*1450K)=12.3 kJ/mol carbon.

(11) Similarly to the carbon product the hydrogen leaving the cracking reactor is cooled together with carbon product. It is possible to cool the hydrogen to a final temperature of 150-300° C., which is a possible operation temperature range of the methanation reactor, so that heating of at least parts of the methane is avoided. Different final cooling temperatures of carbon and hydrogen can be achieved by separation of hydrogen and carbon, e.g. through a cyclone. The isobaric heat capacity of hydrogen is 28.8 J/mol/K. Assuming the methane cracking reactor is operated at 1550° C. and the hydrogen product is cooled to 250° C., the heat which can be recovered from cooling the hydrogen product is (28.8 J/mol H2/K*1300 K*2 mol H2/mol carbon)=74.9 kJ/mol carbon.

(12) The heat recovered from cooling the carbon and hydrogen product can be used to supply heat for the DAC plant, which requires heat at around 80-120° C. for the CO2 desorption process, as further described in WO2016/005226. The total amount of heat which can be supplied from cooling the carbon and hydrogen product is 12.3 kJ/mol carbon+74.9 kJ/mol carbon=87.2 kJ/mol carbon, which can supply a significant part of the thermal energy requirement of the DAC process. Alternatively a part of the heat from the carbon and hydrogen product can be used to pre-heat the methane input into the methane cracking reactor, however, this process layout is technically more challenging (possibility of carbon black deposits in the heat exchanger, slow indirect gas to gas heat exchange process).

Example 2. Heat Recovery from Methanation

(13) Methanation proceeds according to the following reaction scheme:
CO2+4H2.fwdarw.2H2O+CH4

(14) Methanation is an exothermic reaction providing 165 kJ of heat per mole of CH4 produced. Depending on the type of methanation used, the heat is released at different temperatures, e.g. if chemical methanation system is used the reaction occurs at a temperature of 150-300° C. and if biological methanation system is used the reaction occurs at a temperature of 50-100° C. Chemical methanation systems are especially interesting since heat release is at a temperature sufficiently high, so that the supplied heat can be used to provide heat for the DAC plant, as described in Example 1.

Example 3. Recycling of Hydrogen from Methane Cracking to Methanation Reactor

(15) The methane cracking reaction, e.g. according to the process as proposed by Geissler et al in Chemical Engineering Journal 299 (2016) 192-200, yields two moles of hydrogen per one mole of carbon produced, according to the following reaction scheme:
CH4.fwdarw.C+2H2

(16) State of the art carbon black processes combust the produced hydrogen to provide heat for the methane cracking reaction as well as other process heat. In order to reduce electricity consumption for the electrolysis of water, it is favorable to separate the product hydrogen from the product carbon and feed the hydrogen back to the methanation reactor, which works according to the reaction scheme provided in Example 2. If two moles of hydrogen from methane cracking are fed back to the methanation reactor, two moles of hydrogen have to be supplied from electrolysis instead of 4 moles of hydrogen which would be necessary if no hydrogen recycling was implemented. Due to the relatively high energy demand for the electrolysis of water (286 kJ/mol H2O), recycling of hydrogen from methane cracking to methanation reactor is energetically highly favorable.

(17) If product hydrogen from methane cracking contains remainders of methane, such methane can also be fed back to the methanation reactor, keeping system complexity for the hydrogen recycling step low.