ChemCarb

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The cement industry is one of the largest CO2 emitters and a new and highly innovative strategy would be a direct CO2 decomposition to carbon and oxygen by means of a liquid metal process. In this process, the CO2-rich exhaust gas is fed into a reactor containing a liquid metal alloy. Due to the close contact with the metal alloy, the CO2 is decomposed in carbon and O2. The solid carbon collects on the surface and can be separated and deposited or alternatively used as activated carbon in water treatment. BackgroundThe worldwide increase in population in combination with a steady growth in prosperity leads to a high level of construction activity around the globe as well as in Switzerland, for which large quantities of cement are needed. The cement industry meets this demand and is thus one of the largest CO2 emitters (in Switzerland: 2.5 Mt/yr CO2), whereby the emissions can be divided into 40% from fossil fuels for the thermal calcination process (e.g. CH4 - Eq. 1) and 60% from unavoidable geogenic sources by means of raw materials (CaCO3 - Eq. 2).CH4 + O2 <---> CO2 + 2 H2OCaCO3 <---> CaO + CO2While the use of fossil, carbon-based fuels and their CO2 emissions could already be reduced, the geogenic CO2 emissions from the calcination process of CaCO3 cannot be reduced any further. However, in order to counteract and even further reduce CO2 emissions - while always meeting environmental, energy and economic interests - novel and above all, innovative approaches are required.Issues with "conventional" solutionCurrently, approaches such as Power-to-X concepts (PtX) and synthetic fuels are discussed and developed in which methane, methanol, diesel or kerosine can be synthesised from CO2 emissions in order to prevent direct emission. These processes can be summarised under the term Carbon Capture Utilisation (CCU). In this process, CO2 emissions are catalytically converted by means of electrolyser-based renewable hydrogen, according to Eq. 3: 3. CO2 + 4 H2 <---> CH4 + 2 H2OWith respect to the price level of the aimed "clinker" product in cement industry, this is an economically and energetically highly unattractive path. On the one hand, the investment costs (CAPEX) and on the other hand operation costs (OPEX) of electrolysers are expensive. While their energetic efficiency is about 60%, another additional 50% of the expensive H2 produced, is converted into "useless" water according to Eq. 3. On the other hand, only 25% of a cement waste gas consists of CO2 and - even when purified with common exhaust gas treatment technologies - it still contains particles that can quickly degrade catalytic converters. Both measures together are therefore very costly and make the price of CO2 methanation or the production of synfuels from such CO2 emission even more expensive. In contrast to that, an economically more attractive alternative is provided by so-called "carbon capture storage" technology (CCS), in which the CO2 is only removed from the stream. However, afterwards the CO2 is not put to any use, but it is "stored" underground or maritime as liquid CO2. This process may be feasible for some industries and regions, but it is not a long-term solution to the CO2 problem and may be critically questioned, because of the long transport routes from Switzerland to e.g. Norway. For captured CO2, whether liquid or gaseous, Switzerland cannot offer storage capacities and a CO2 pipeline through neighbouring countries is highly unlikely, so the dilemma is clear. In this sense, new and innovative approaches are needed for the challenging problem at hand. New Innovative Approaches from UMTEC at OSTThe project team consisting of Samuel Hecht (Process Engineer) and Dr Stefanie Mizuno (Chemical Engineer) under supervision of Prof. Dr Andre Heel (head of the R&D group Advanced Materials & Processes) at UMTEC (Institute of Environmental and Process Engineering). The R&D group “Advanced Materials & Processes” (AMP) has extensive expertise in the CO2 processing (PtG, PtX, synfuels, catalysis and innovative material conversion processes) and developed several innovative high-efficiency processes. Two of these - a high-efficiency CO2 methanation and a plasma process for alternative fuels from CO2 - have already been awarded with the FUTUR Foundation's Innovation Prize for Technology Transfer. In the last two years over 12 students completed their bachelor's theses on these two projects and thus contributed to their success. Project description and solution Climate-effective CO2 is a chemically very stable molecule that can conventionally only be split using very high thermal energies or catalytically converted using expensive hydrogen. In order to clearly emphasise the innovative content and originality of the project, the very harsh or expensive conditions under which CO2 can be converted have to be mentioned. In principle, the following processes and conditions are conceivable:1. Thermal (>3000 K) CO2 <---> CO + ½ O22. Kinetic (3 times supersonic) CO2 <---> C + O23. Electrolysis + Catalysis CO2 + 4 H2 <---> CH4 + 2 H2OProcesses 1 (thermal) and 2 (kinetic) are practically mutually exclusive because either high temperatures of >3000 K are required, or typical cement exhaust gas flows of some 100000 m3/h would have to be accelerated to supersonic speed. Process 3 (electrolysis/catalysis) involves, as discussed above, an expensive, complex plant for hydrogen production and additionally catalysis at 300 - 700°C. However, the CO2 would at least be assigned to a use. Overall, this corresponds to a Power-to-Gas (PtG) technology and - at current CO2 prices and as long as no surplus electricity is available - is not economically viable.The aim of this study is therefore to evaluate a new and highly innovative strategy for its applicability to combustion intensive industry, such as the cement and incineration plants. In an almost revolutionary new approach, a direct CO2 decomposition to carbon (C) and oxygen (O2) is to be investigated by means of a liquid metal based carbonisation process (LMC):4. CO2 <---> C (solid) + O2For this purpose, the CO2-rich exhaust gas is simply passed through a thermally activated bubble reactor with a so-called monophasic liquid metal. A liquid metall is typically a monophasic metal alloy of post transition elements such as Ga, In, Tl, Sn, Al or Bi. While the CO2-rich gas flows through the liquid metal from the bottom to the top, the CO2 stays in close contact with the metal alloy surface, causing it’s “catalytic” decomposition to carbon and O2. Since carbon is practically insoluble in most liquid metals, carbon is accumulated on the bubble surfaces or floats due to its lower density (rC,hex= 2.25 g/cm3 vs. rGa-In= 6.44 g/cm3) and the resulting buoyancy effect to the surface (Fig. 1, Attachment Files).In comparison to a conventional heterogenous catalytic process with a solid catalyst, the carbon would be deposited as solid on the surface of the catalytic element and it would be deactivate within a very short time. This is one of the reasons why CO2 splitting by hetrogeneous catalysis is not pursued.This process is intended to convert gaseous climate-impacting CO2 emissions into an environmentally harmless solid, namely carbon under release of oxygen. Such carbon remains present as elemental carbon (C), which can be safely stored for long term period in Switzerland. In particular, the focus is on storing the captured carbon at the extraction sites of the cement industry in opencast mines, because no additional transport costs and transport–related CO2 emissions are caused.Carbon can be used as activated carbon in water treatment and purification or as fertiliser in agriculture. Moreover, carbon could even be used as filler in concrete in cement industry and thus represent an interesting. The integration of the elemental carbon obtained through this process represents an attractive additional CO2 sink. Such a concrete is called "climate concrete" (KLARK 2022a and b) or "carbon storage concrete". (CarStorCon 2021). Resulting CO2 emissions - even geogenic ones - would thus no longer be emitted into the environment and thus make an enormous contribution to the CO2 reduction for an industrial partner and Switzerland.A few scientific papers have shown that carbon compounds principally can be decomposed using liquid metals. Methane (CH4) decomposes into its components of elemental carbon and H2 when in contact with liquid zinc (Zn) at 1200°C (methane pyrolysis 2022). CO2 could be decomposed by adding electricity (electrolysis) in a mixture of a solvent in which CO2 is dissolved (e.g. water or dimethylfuran) and a liquid metal (Tang et al. 2022, Esrafilzadeh et al. 2019). However, these methods are not suitable for the cementitious waste gases that are produced in quantities of about 100000 m3/h. The challenge and innovative aspect of the LMC process presented here is: it is an energetically attractive process is applied, since it does not use electricity it is applied to liquid metal at room temperature it does not require a solvents, such as amines or dimethylfuran for CO2 separation as it is used in CCS plants it produces CO2 in the form of elemental carbon (C) (transportable & permanently storable, e.g. quarries, open-cast mining)it could be reused in innovative concrete systems as a C sink.Work Packages In the strategy of CO2 decomposition by means of a liquid metal based process, series of experiments needed to obtain optimal processing conditions relations between process parameters and resulting CO2 decomposition efficiency. From this a higher TRL level must be reached in order to make the process accessible to a cement industry. The following work packages (WP) are defined to make progress:WP1: Construction and commissioning of a continuous bubble column reactor for temperatures from RT to ~500°CWP2: Synthesis of eutectic liquid metal compounds from Gax and In(1-x) Metal (GaIn) with x = 0…100% together with possibly other catalytic promoters (e.g. Sn, Ce)WP 3.1: Determination of the CO2 conversion efficiency to carbon as a function of GaxIn1-x, temperature (20°C - 500°C), space velocity (GHSV), gas compositions (xCO2), and determination of the carbon quality (dp, BET, impurities)WP3.2: Identification of limitations with regard to technology transfer and development needs for a scale-up and industrialisation.WP4: Dissemination of the results, Contact with other Research Groups (Life Cycle Assessment), Publication in social mediaWhat has been done already:Set up a small experiment in a glas tube (Figure 2 in the attachment) at room temperature (Figures in the attachment)We are in contact with Jura Cement (a letter of intent is in the attachment), Holcim (CH) and Heidelberg Cement (D).Innovation (novelty, originality)The innovation content is briefly summarised: A process via liquid metals with high implementation potential because CO2 has only to be conducted through a liquid bubble column.CO2 could be stored as solid carbon. Transport infrastructure and storage capacities exist in Switzerland through limestone quarries via local raw material extraction of the past decades.The liquid metal based process does not require expensive catalytic noble metals or electricity and can be tempered by existing waste heat from a cement plantThe concept causes significantly lower investment costs (CAPEX) compared to electrolysis of H2 for PtG A liquid metal technology does not require any major plant adaptations or conversions, it can be carried out as retrofiitingThe resulting O2 can be used as an oxidising agent in the combustion process itself, thus eliminating the need to add oxygen via air, in which 79% nitrogen is uselessly coheatedReferencesMethanpyrolyse 2022: https://www.ites.kit.edu/738.php.Tang et al, 2022. Liquid-Metal-Enabled Mechanical-Energy-Induced CO2 Conversion. Adv. Mat. 2022, 34, 2105789, https://doi.org/10.1002/adma.202105789Esrafilzadeh et al. 2019. Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces. Nature Communications volume 10, Article number: 865 (2019). https://doi.org/10.1038/s41467-019-08824-8.Klark Logbau 2022a: https://www.klark.ch https://www.srf.ch/sendungen/10vor10/die-idee/die-idee-die-idee-co2-neutraler-beton-beigemischter-pflanzenkohleKlark Logbau 2022b: https://www.srf.ch/sendungen/10vor10/die-idee/die-idee-die-idee-co2-neutraler-beton-beigemischter-pflanzenkohleCarStorCon 2021: https://www.report.at/energie/19729-kohlenstoff-aus-der-atmosphaere-in-den-beton-gebracht

Project Idea Metadata

• Project Idea Name: ChemCarb
• Date: 5/31/2022 2:05:44 PM
• Administrators:

Project Idea Description

Background

The worldwide increase in population in combination with a steady growth in prosperity leads to a high level of construction activity around the globe as well as in Switzerland, for which large quantities of cement are needed. The cement industry meets this demand and is thus one of the largest CO2 emitters (in Switzerland: 2.5 Mt/yr CO₂), whereby the emissions can be divided into 40% from fossil fuels for the thermal calcination process (e.g. CH4 - Eq. 1) and 60% from unavoidable geogenic sources by means of raw materials (CaCO3 - Eq. 2).

1. CH4 + O2 <---> CO2 + 2 H2O
2. CaCO3 <---> CaO + CO2

While the use of fossil, carbon-based fuels and their CO₂ emissions could already be reduced, the geogenic CO2 emissions from the calcination process of CaCO3 cannot be reduced any further. However, in order to counteract and even further reduce CO2 emissions - while always meeting environmental, energy and economic interests - novel and above all, innovative approaches are required.

Issues with "conventional" solution

Currently, approaches such as Power-to-X concepts (PtX) and synthetic fuels are discussed and developed in which methane, methanol, diesel or kerosine can be synthesised from CO2 emissions in order to prevent direct emission. These processes can be summarised under the term Carbon Capture Utilisation (CCU). In this process, CO2 emissions are catalytically converted by means of electrolyser-based renewable hydrogen, according to Eq. 3:

3. CO₂ + 4 H₂ <---> CH₄ + 2 H₂O

With respect to the price level of the aimed "clinker" product in cement industry, this is an economically and energetically highly unattractive path. On the one hand, the investment costs (CAPEX) and on the other hand operation costs (OPEX) of electrolysers are expensive. While their energetic efficiency is about 60%, another additional 50% of the expensive H2 produced, is converted into "useless" water according to Eq. 3. On the other hand, only 25% of a cement waste gas consists of CO2 and - even when purified with common exhaust gas treatment technologies - it still contains particles that can quickly degrade catalytic converters. Both measures together are therefore very costly and make the price of CO2 methanation or the production of synfuels from such CO2 emission even more expensive.

In contrast to that, an economically more attractive alternative is provided by so-called "carbon capture storage" technology (CCS), in which the CO2 is only removed from the stream. However, afterwards the CO2 is not put to any use, but it is "stored" underground or maritime as liquid CO2. This process may be feasible for some industries and regions, but it is not a long-term solution to the CO2 problem and may be critically questioned, because of the long transport routes from Switzerland to e.g. Norway. For captured CO2, whether liquid or gaseous, Switzerland cannot offer storage capacities and a CO2 pipeline through neighbouring countries is highly unlikely, so the dilemma is clear. In this sense, new and innovative approaches are needed for the challenging problem at hand.

New Innovative Approaches from UMTEC at OST

The project team consisting of Samuel Hecht (Process Engineer) and Dr Stefanie Mizuno (Chemical Engineer) under supervision of Prof. Dr Andre Heel (head of the R&D group Advanced Materials & Processes) at UMTEC (Institute of Environmental and Process Engineering). The R&D group “Advanced Materials & Processes” (AMP) has extensive expertise in the CO₂ processing (PtG, PtX, synfuels, catalysis and innovative material conversion processes) and developed several innovative high-efficiency processes. Two of these - a high-efficiency CO2 methanation and a plasma process for alternative fuels from CO2 - have already been awarded with the FUTUR Foundation's Innovation Prize for Technology Transfer. In the last two years over 12 students completed their bachelor's theses on these two projects and thus contributed to their success.

Project description and solution

Climate-effective CO2 is a chemically very stable molecule that can conventionally only be split using very high thermal energies or catalytically converted using expensive hydrogen. In order to clearly emphasise the innovative content and originality of the project, the very harsh or expensive conditions under which CO2 can be converted have to be mentioned. In principle, the following processes and conditions are conceivable:

1. Thermal (>3000 K) CO₂ <---> CO + ½ O₂

2. Kinetic (3 times supersonic) CO₂ <---> C + O₂

3. Electrolysis + Catalysis CO₂ + 4 H₂ <---> CH₄ + 2 H₂O

Processes 1 (thermal) and 2 (kinetic) are practically mutually exclusive because either high temperatures of >3000 K are required, or typical cement exhaust gas flows of some 100000 m3/h would have to be accelerated to supersonic speed. Process 3 (electrolysis/catalysis) involves, as discussed above, an expensive, complex plant for hydrogen production and additionally catalysis at 300 - 700°C. However, the CO2 would at least be assigned to a use. Overall, this corresponds to a Power-to-Gas (PtG) technology and - at current CO2 prices and as long as no surplus electricity is available - is not economically viable.

The aim of this study is therefore to evaluate a new and highly innovative strategy for its applicability to combustion intensive industry, such as the cement and incineration plants. In an almost revolutionary new approach, a direct CO2 decomposition to carbon (C) and oxygen (O2) is to be investigated by means of a liquid metal based carbonisation process (LMC):

4. CO₂ <---> C (solid) + O₂

For this purpose, the CO2-rich exhaust gas is simply passed through a thermally activated bubble reactor with a so-called monophasic liquid metal. A liquid metall is typically a monophasic metal alloy of post transition elements such as Ga, In, Tl, Sn, Al or Bi. While the CO2-rich gas flows through the liquid metal from the bottom to the top, the CO₂ stays in close contact with the metal alloy surface, causing it’s “catalytic” decomposition to carbon and O₂. Since carbon is practically insoluble in most liquid metals, carbon is accumulated on the bubble surfaces or floats due to its lower density (r_C,hex= 2.25 g/cm³ vs. r_Ga-In= 6.44 g/cm³) and the resulting buoyancy effect to the surface (Fig. 1, Attachment Files).

In comparison to a conventional heterogenous catalytic process with a solid catalyst, the carbon would be deposited as solid on the surface of the catalytic element and it would be deactivate within a very short time. This is one of the reasons why CO₂ splitting by hetrogeneous catalysis is not pursued.

This process is intended to convert gaseous climate-impacting CO2 emissions into an environmentally harmless solid, namely carbon under release of oxygen. Such carbon remains present as elemental carbon (C), which can be safely stored for long term period in Switzerland. In particular, the focus is on storing the captured carbon at the extraction sites of the cement industry in opencast mines, because no additional transport costs and transport–related CO2 emissions are caused.

Carbon can be used as activated carbon in water treatment and purification or as fertiliser in agriculture. Moreover, carbon could even be used as filler in concrete in cement industry and thus represent an interesting. The integration of the elemental carbon obtained through this process represents an attractive additional CO₂ sink. Such a concrete is called "climate concrete" (KLARK 2022a and b) or "carbon storage concrete". (CarStorCon 2021). Resulting CO2 emissions - even geogenic ones - would thus no longer be emitted into the environment and thus make an enormous contribution to the CO2 reduction for an industrial partner and Switzerland.

A few scientific papers have shown that carbon compounds principally can be decomposed using liquid metals. Methane (CH4) decomposes into its components of elemental carbon and H2 when in contact with liquid zinc (Zn) at 1200°C (methane pyrolysis 2022). CO2 could be decomposed by adding electricity (electrolysis) in a mixture of a solvent in which CO2 is dissolved (e.g. water or dimethylfuran) and a liquid metal (Tang et al. 2022, Esrafilzadeh et al. 2019). However, these methods are not suitable for the cementitious waste gases that are produced in quantities of about 100000 m³/h.

The challenge and innovative aspect of the LMC process presented here is:

• it is an energetically attractive process is applied, since it does not use electricity
• it is applied to liquid metal at room temperature
• it does not require a solvents, such as amines or dimethylfuran for CO2 separation as it is used in CCS plants
• it produces CO2 in the form of elemental carbon (C) (transportable & permanently storable, e.g. quarries, open-cast mining)
• it could be reused in innovative concrete systems as a C sink.

Work Packages

In the strategy of CO2 decomposition by means of a liquid metal based process, series of experiments needed to obtain optimal processing conditions relations between process parameters and resulting CO2 decomposition efficiency. From this a higher TRL level must be reached in order to make the process accessible to a cement industry. The following work packages (WP) are defined to make progress:

• WP1: Construction and commissioning of a continuous bubble column reactor for temperatures from RT to ~500°C
• WP2: Synthesis of eutectic liquid metal compounds from Ga_x and In_(1-x) Metal (GaIn) with x = 0…100% together with possibly other catalytic promoters (e.g. Sn, Ce)
• WP 3.1: Determination of the CO2 conversion efficiency to carbon as a function of Ga_xIn_1-x, temperature (20°C - 500°C), space velocity (GHSV), gas compositions (x_CO2), and determination of the carbon quality (dp, BET, impurities)
• WP3.2: Identification of limitations with regard to technology transfer and development needs for a scale-up and industrialisation.
• WP4: Dissemination of the results, Contact with other Research Groups (Life Cycle Assessment), Publication in social media

What has been done already:

• Set up a small experiment in a glas tube (Figure 2 in the attachment) at room temperature (Figures in the attachment)
• We are in contact with Jura Cement (a letter of intent is in the attachment), Holcim (CH) and Heidelberg Cement (D).

Innovation (novelty, originality)

The innovation content is briefly summarised:

• A process via liquid metals with high implementation potential because CO2 has only to be conducted through a liquid bubble column.
• CO2 could be stored as solid carbon. Transport infrastructure and storage capacities exist in Switzerland through limestone quarries via local raw material extraction of the past decades.
• The liquid metal based process does not require expensive catalytic noble metals or electricity and can be tempered by existing waste heat from a cement plant
• The concept causes significantly lower investment costs (CAPEX) compared to electrolysis of H2 for PtG
• A liquid metal technology does not require any major plant adaptations or conversions, it can be carried out as retrofiiting
• The resulting O2 can be used as an oxidising agent in the combustion process itself, thus eliminating the need to add oxygen via air, in which 79% nitrogen is uselessly coheated

References

• Methanpyrolyse 2022: https://www.ites.kit.edu/738.php.
• Tang et al, 2022. Liquid-Metal-Enabled Mechanical-Energy-Induced CO2 Conversion. Adv. Mat. 2022, 34, 2105789, https://doi.org/10.1002/adma.202105789
• Esrafilzadeh et al. 2019. Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces. Nature Communications volume 10, Article number: 865 (2019). https://doi.org/10.1038/s41467-019-08824-8.
• Klark Logbau 2022a: https://www.klark.ch https://www.srf.ch/sendungen/10vor10/die-idee/die-idee-die-idee-co2-neutraler-beton-beigemischter-pflanzenkohle
• Klark Logbau 2022b: https://www.srf.ch/sendungen/10vor10/die-idee/die-idee-die-idee-co2-neutraler-beton-beigemischter-pflanzenkohle
• CarStorCon 2021: https://www.report.at/energie/19729-kohlenstoff-aus-der-atmosphaere-in-den-beton-gebracht

The cement industry is one of the largest CO2 emitters and a new and highly innovative strategy would be a direct CO2 decomposition to carbon and oxygen by means of a liquid metal process. In this process, the CO2-rich exhaust gas is fed into a reactor containing a liquid metal alloy. Due to the close contact with the metal alloy, the CO2 is decomposed in carbon and O2. The solid carbon collects on the surface and can be separated and deposited or alternatively used as activated carbon in water treatment.