Development of technologies for CO2 capture and conversion

Gabriele Mulas (UNISS)

The acronymous CCUS is used in the scientific literature to refer to a set of technologies which are expected to play a crucial role, in the upcoming years, to meet global energy demand, CO2 emissions control and climate goals. As a matter of the fact, CCUS deals with the development of different steps in CO2 managing, its transforming or storing. It involves the capture of CO2 directly from the atmosphere, or from different point sources, including power generation or industrial facilities etc. If not being used on-site, the captured CO2 may also be compressed and transported by pipeline, ship, rail or truck and subjected to different chemical transformation or be used in a range of applications, or also injected into deep geological formations trapping the CO2 for permanent storage.

In the chapters of the Module I, different issues of the CCUS are presented, with specific reference to the activities implemented within the CO2MPRISE project, an MSCA, Marie Curie Rise Action, aimed at developing new technologies in CO2 capture and conversion.

Gabriele Mulas (UNISS)

Carbon Capture, Utilization and Storage technologies are recognized to play an important role in supporting the transition to CO2 net-zero emissions, according to the plans defined in all the recent climate-change mitigation agreements.

Main strategies rely on the deepening and optimization of CO2 storage in geological formations and on the use of captured carbon dioxide as a feedstock for different chemical syntheses or further industrial processes. Regarding the latter point, CO2 can be seen as a commodity that can be traded and generate a revenue stream through the deployment of CO2-conversion or -non-conversion-based processes. Then, CCUS can be retrofitted to existing power and industrial plants, can tackle emissions in sectors where other technology options are limited, and is of relevance in the least-cost low-carbon hydrogen production.

At present, main open issues, and related scientific efforts, are addressed to research and innovation projects for basic and applied science deepening, as well as to technology development. Momentum is also for the set up of pilot and demonstration plants, up industrial application, focusing also to the creation of a proper regulatory framework.

Gabriele Mulas (UNISS)

CCUS programs are addressed not only to basic and applied research: different technologies already reached industrial application level and, today, CCUS facilities around the world have the capacity to capture more than 40 MtCO2 each year. Some of these facilities have been operating since the 1970s and 1980s, when natural gas processing plants in the Val Verde area of Texas began supplying CO2 to local oil producers for enhanced oil recovery operations. Since then, several projects started and are now operating, and large investments are continuously announced, and new facilities planned.

The potential applications for CO2 use include direct use, where the CO2 is not chemically altered (non-conversion), and the transformation of CO2 to a useful product (conversion). Today it includes the production of fertilizers, green fuels, food, and beverage. But new CO2 use pathways, involving chemical and biological technologies, offer further opportunities for future CO2 use. Many of these pathways are still in a stage of development, but early opportunities are being realized.

Gabriele Mulas (UNISS)

The focus of the Chapter 1.3 is to present the main policy actions which are being pursued in different countries and world regions, with the aim to parallel and favor CCUS-related technological development.

As a matter of the fact the possibility to develop and implement on a large scale the CCUS supply chain, is surely related to the set-up of a regulatory and legal regime, which may offer a proper framework for supporting technology investments and manage potential risks occurring at various parts of the value chain.

The two main CO2 emission costs mechanisms for main emitters, the so-called “Carbon-tax mechanism” and the “EU-ETS, Emissions Trading Scheme” are presented and discussed.

Then, a summary of the key regulatory issues and challenges which are being adopted in large areas, including EU, China, Middle-East, US, are listed and shortly discussed.

Sebastiano Garroni (UNISS)

Considering the current fervent research addressed to explore new and feasible ways for converting efficiently carbon dioxide by using abundant and cheap raw materials, we deliver this module with the aim to account how carbon dioxide can be efficiently converted to light hydrocarbons and carbonates, by mechanochemical activations of olivine (a natural and abundant mineral) in presence of water. Concepts concerning the importance of milling and its benefits respect to the thermal process will be provided, together with the description of the mechanism behind the weathering process. The final objective is to offer a general overview of the potential applications of this technology and the emerging materials which will be the object of intensive investigation in the near future.

Sebastiano Garroni (UNISS)

This chapter will be dedicated to the preparation and reactivity of the olivine powders under mechanical processing. Implementation of the process will be also discussed.

Sebastiano Garroni (UNISS)

This chapter will focus on the potential applications of the process and the products, both solids and gases, obtained.

Sebastiano Garroni (UNISS)

The final objective is to offer a general overview of the potential applications of this technology and the emerging materials which will be the object of intensive investigation in the near future.

Vasiliki Alexiou (Monolithos Ltd)

This module will focus on the development of innovative processes and materials for CO2 storage and conversion applications in the transportation sector since CO2 emissions from road transport account for 46.5% of global CO2 emissions.

We will present an innovative integrated system consisting of a CO2 capture membrane system combined with a novel low-cost catalyst, PROMETHEUS catalyst, for reducing diesel engines’ CO2 emissions enabling the transformation of CO2 to fuels.

At first place, we will talk about the design and development of the CO2 capture/separation systems, the fabrication methods and the removal/separation mechanisms of both O2 and CO2 from the gas stream of flue gases.

Then we will have a look at the potential applications of the developed systems for the conversion of CO2 to value-added products, taking into account the very promising PROMETHEUS catalyst for both the thermal as well as the mechanochemical activation of CO2 and its transformation to fuels.

Finally, we will talk about future perspectives of the systems which rely on the novelty of the developed processes and materials, regarding operative conditions, sustainable costs, and environmental impact.

At the end of the module, there will be a quiz to test your knowledge and further reading for further insight.

Marios Kourtelesis (Monolithos Ltd)

Here we present the CO2 capture/separation device. The system is based on fabrication of carbonate ion conductive electrochemical membranes that utilize the large concentration gradient between the flue gases and the atmosphere. This results in a gradient in the electrochemical potential of the carbonate ions, in diffusion of the latter from the flue gases to the atmosphere, thus enabling the removal/separation of both O2¬ and CO2 from the gas stream of flue gases. Each membrane consists of a mixture of carbonate salts, impregnated into a stainless-steel filter that serves as both mechanical support and electronic contactor.

Membranes are prepared by a direct impregnation method. Carbonate mixture is melted at T > 400oC, to assure that the whole synthesis layout temperature is above the mixture’s eutectic point. The SS tubes are impregnated to create the dual phase membrane. In order to achieve effective membrane impregnation, thermal pretreatment of the SS tubes at 500oC is performed to avoid oxidization due to the temperature difference between molten carbonate mixture and SS filter, thus achieving higher infiltration of carbonates at SS tube porous. The impregnated membrane is left to dry for 24 hours and then calcinated at T>400oC for 1 hour so as for the excess carbonates to be removed.

In order to study the efficiency of the membranes in terms of CO2 and O2 reduction, a customized Synthetic Gas bench has been designed and manufactured at MONOLITHOS premises, which allows us to simulate the emission composition of a diesel-engined HDV.

Concerning the catalyst for the conversion of CO2 to value-added products, PROMETHEUS catalyst, incorporating Cu, Pd and Rh nanoparticles supported on CeO2-ZrO2 mixed oxide can be regarded as a promising catalyst for both the thermal as well as the mechanochemical activation of CO2 and its transformation to fuels such as CH4 or oxygenates (for example C1-C4 alcohols).

The heterogeneous Prometheus catalyst is synthesized by a wet impregnation method following the steps illustrated in the Figure.

Briefly, for the production of the catalyst powder, the metal precursors and the carrier are added successively in the solution under stirring at Room temperature, while the pH value is constantly monitored and stabilized at a desired value. Then the solution is heated for the liquids to be evaporated and the slurry is dried overnight, followed by a calcination step. The production scale can reach 100 kg of catalyst nanopowder, using the tank reactor of 150 L volume present in the picture.

It should be noted that the metal type and loading can be adjusted based on the specific application.

For the CO2 hydrogenation experiments, preliminary tests have been performed in a custom-made apparatus equipped with a gas chromatograph, while a new Synthetic gas Bench has been designed and is currently under preparation, for performing experiments at elevated pressures, up to 50 bar. To that end, a stainless-steel reactor has been manufactured recently as presented in the picture. The analysis of the reaction products will be performed using a gas chromatograph equipped with TCD and FID detectors.

Marios Kourtelesis (Monolithos Ltd)

The transportation sector is one of the largest contributors to anthropogenic global greenhouse gas (GHG) and CO2 emissions. In specific, it accounts for more than one fifth of global carbon dioxide emissions. Moreover, although Heavy Duty Vehicles (HDVs) such as buses, trucks etc., only represent a small part of the overall vehicle population, their CO2 emissions account for almost half of global CO2 emissions from road transport. Diesel exhaust gas contains carbon monoxide (CO), unburned hydrocarbons (HCs), nitrogen oxides (NOx), soot, as well as increased concentrations of water vapor (H2O) and carbon dioxide (CO2), which consist the main combustion products.

To that end, the development of an innovative integrated system consisted of a CO2 capture membrane system combined with a novel low-cost catalyst for transforming diesel engines CO2 emissions to fuels is the objective of the present module.

The module should comprise i) a membrane-based system to capture/separate CO2 from the exhaust flue gases, ii) a water electrolysis part to provide H2 and iii) a catalyst for converting CO2 to chemical compounds and fuels.

The system will be used in a multi-tubular module formation, where the exhaust gas is fed through the lumen side and CO2 and O2 permeate across the membrane to the shell side, while total surface area is adjusted to obtain adequate permeation rate.

In the produced shell side mixture, CO2 and O2 will be present in a molar ratio of 2:1, thus generating a stream rich in CO2 (around 67%) that can be then separated or directly utilized for the production of value-added products through hydrogenation.

Vasiliki Alexiou (Monolithos Ltd)

The module can be also applied in other applications, both mobile and stationary. One potential application is related to the maritime sector, for converting the harmful CO2 emissions of ships to C1-C4 alcohols. The aim is to produce e-fuels for ships and loop the specific sector in a sustainable way.

CO2 emissions in the shipping sector are expected to boom in the coming decades, with scenarios approaching the 3000 million tons annually by 2050 if no measures for their reduction are put into place. By adopting such a technology for the treatment of exhaust flue gases from vessels, commercial level e-fuels can be effectively produced, boosting the specific market.

Furthermore, by applying this technology, ships will partially substitute the diesel fuel by making a methanol-diesel mixture. As a result, ships will be able to meet the emissions requirements requested by the regulative authorities.

Finally, the module could also be used for the treatment of exhaust flue gases in stationary applications, for example in cement industries, to provide those industries a complete validated process flowsheet and business plan for valorising their CO2 emissions towards the production of fuels that can be subsequently used to cover their needs.

In this way, human health will be improved with the reduction of CO2 and other gases from the industrial flue gas streams. In addition, circular economy will be promoted by the utilization of an unwanted waste source and the usage of the generated e-fuels back in the industrial site for internal use for example as a resource for heating could result in a near-zero waste sustainable loop, aligning with EC regulations.

Fabiana Gennar (CNEA)

Metal hydrides are formed by the reaction between a metal or an alloy, and H2. By controlling temperature and pressure the reaction is reversible. That is a hydride stores H2 in certain conditions and releases H2 under other conditions of pressure and temperature.

Hydrides can be synthesized by ball milling in an inert atmosphere. In this case, two or more metals are alloyed at room temperature, with simultaneous reduction of grain size and introduction of defects/stresses. After that, these powders react with H2 inside a reactor, under selected pressure and temperature forming a hydride. Another synthesis procedure involves the ball milling of metals under H2, where both the reduction of grain size and the formation of the hydride occurs by the action of mechanical energy.

These hydrides are used as dual materials for CO2 conversion. Dual, because the metal hydride is the source of H2 to favor the transformation of CO2 to CH4 or CH4-H2 blends; and also the hydride provides the necessary catalyst for the reaction.

Claudio Pistidda (Hereon)

Metal hydrides and complex metal hydrides are potential catalytic species for the methanation process. It has recently been demonstrated that these compounds containing transition metal (TM) elements and chemically bonded hydrogen are capable of catalyzing the CO2 conversion process, achieving high reaction yields and high conversion selectivity (i.e., favored formation of CH4). Selvam and co-workers were the first to discuss the potential for using alloys and a few chemicals, typically used for hydrogen storage puroses (FeTi, LaNi5, CaNi5, Mg2Cu, Mg2Ni, and Mg2NiH4), in CO2 harvesting and conversion processes. It has been shown that the ability of these materials to generate carbonates, hydroxides, and oxides on their surfaces enhances their efficiency in the CO2 conversion process. Interestingly, it has been noticed that the nature of the utilized hydrides significantly affects the CO2 hydrogenation mechanisms. As an example, differently from complex hydrides, where the MH bond is mostly covalent, ionic hydrides such as LiH and NaH interacting with CO2 lead to the formation of C which in turn, by reacting with the H contained in the hydride leads to the formation of CH4 and oxide species. Interstitial metal hydrides, where the MH bond is of the metallic type, appear to be highly interesting materials for the development of membranes for the fabrication of reactors capable of efficiently converting CO2/H2 streams into CH4 (and H2O).

Recommended literature:

• P. Selvam, B. Viswanathan, V. Srinivasan. The influence of atmospheric CO2 on the surface properties of Mg2NiH4 and a comparison with some hydrogen storage alloys. J Less Common Met., 1990,158, L1-L7.

• P. Selvam, B. Viswanathan, V. Srinivasan. Evidence for the formation of surface carbonates on some hydrogen storage intermetallic compounds: an XPS study. Int J Hydrogen Energy,1990, 15 (2), 133-137.

• M. L. Grasso, J. Puszkiel, F.C. Gennari, A. Santoru, M. Dornheim, C. Pistidda. CO2 reactivity with Mg2NiH4 synthesized by in situ monitoring mechanical milling. Phys. Chem. Chem. Phys. 22 (2020) 1944-1952.

• B. X. Dong, L.-Z. Wang, L. Song, J. Zhao, Y.-L. TengThermochemical Reduction of Carbon Dioxide with Alkali Metal Hydrides, Producing Methane and Hydrogen Fuels at Moderate Temperatures. Energy and Fuels 2016, 30 (8) 6620–6625.

Francisco Gracia (University of Chile)

Due to its high thermodynamic stability and low kinetics, CO2 activation and conversion requires the use of a solid catalyst to increase the reaction rates and the selectively to specific products. Catalytic hydrogenation of carbon dioxide has been recognized a promising approach since it can generate synthetic fuels and other important chemicals, like methanol. This module analyses Ni containing solid oxides and graphene oxide catalysts during the CO2 thermal activation to produce methane.

Chapter 5.1. focuses on the synthesis protocols and different characterizations of solid oxides- and graphene oxide- based Ni catalysts.

Chapter 5.2. reports on the catalytic performance of these materials during thermal CO2 activation evaluating activity for CO2 conversion, the product distribution or selectivity towards methane or carbon monoxide, and thermal stability over time.

Finally, Chapter 5.3. presents a discussion about novel approaches regarding new catalytic materials and photo-thermal activation of CO2.

Francisco Gracia (University of Chile)

Sabatier and Sanderens reported the catalytic CO2 hydrogenation to CH4 for the first time in 1902. Since then, numerous studies have tried to develop stable catalysts with high activity and selectivity for methanation at low temperatures. Among these, nickel catalysts supported on different solid oxides are considered suitable options for catalytic activity and economic efficiency. However, most of these catalysts face problems like metal nanoparticles sintering or deactivation by carbon deposits limiting their development and technological applications. Therefore, synthesis strategies are a key parameter to improve the stability and activity of Ni catalysts. This chapter analyses the preparation of perovskite (CTO) and carbon-based supported catalytic systems.

Synthesis of pure CTO and Ni-doped CTO catalysts was carried out by a sol–gel method, while impregnated Ni catalysts were prepared following the a impregnation method using an aqueous solution of nickel precursor. Multiwalled carbon nanotubes (CNTs) supported Ni catalysts were obtained using commercial CNTs as starting material. Preparation of different Ni containing samples proceed sequential impregnation (SEQ) and co-impregnation (COI) method of Ni and Zr precursors. Finally reduced graphene oxide (rGO) based catalysts were synthetized with rGO as starting material obtained through a modified Hummers method, followed by functionalization through NaOH treatment, nitrogen doping and nickel nanoparticles decoration, to provide active sites for CO2 methanation.

Francisco Gracia (University of Chile)

Carbon dioxide activation and conversion over the different synthesized materials were analysed through catalytic experiments in lab-scale flow-through packed bed quartz reactors at atmospheric pressure and temperature range between 200ºC and 500ºC. Once the reactor was loaded with the catalyst, the sample was pre-treated by reduction at 500 ◦C for 1 h in flowing pure hydrogen. After the catalyst reduction, the reactor was flushed with pure He, and the temperature decreased to room temperature in order to stablish same starting conditions for all studied samples. A typical gas-phase reactants mixture composition is CO2:H2 = 1:4 regulated by mass flow controllers, including He as inert carrier, and Ar as internal reference gas concentration measurements in an on-line mass spectrometer (MS). The experimental conditions used in these experiments have been proved in our group to prevent any mass transfer limitation. In addition to the MS quatification, the online gas concentration measurement system included a gas chromatograph with a thermal conductivity detector and a packed column.

Francisco Gracia (University of Chile)

Lately, there has been a strong interest on new materials and synthesis methods to obtain high surface area catalysts with strong metal-support interactions that would facilitate high metal dispersion with enhanced sintering resistance. A particular group of materials (2D materials) are of great interest due to their high surface area and the possibility to control their properties by chemically modifying the surface, which makes up most of the material. 2D materials have a nanometric thickness (the magnitude order of an atom size, for which their properties are largely determined by their dimensionality) that differs from higher dimensions’ structures due to quantum size effects and the electrons’ confinement degree.

The first graphene sheet obtained by mechanical exfoliation of pyrolytic graphite (HOPG) was reported in 2004 by Novoselov. Its exceptional electrical, mechanical, and optical properties made it attractive for a wide variety of applications, and lately has gathered the attention of researchers due to its use in heterogeneous catalysis. Similarly, a different class of 2D materials are artificially synthesized using laminar materials such as graphene or graphene oxides as templates to form thin sheets of solid oxides whose behavior resembles a 2D material. This chapter discusses the opportunities of such materials for catalytic and thermal activation of CO2.

Stefano Enzo (UNISS)

Diffraction techniques are a powerful tool for obtaining a good characterisation of different classes of materials, i.e. to analyse structural features and microstructural parameters of solid state and undercooled liquid phases. Then, a pre-requisite is the knowledge of some elementary concepts of crystallography, which are briefly presented, followed by the discussion of some key rules and strategies to perform diffraction analyses.

Stefano Enzo (UNISS)

Attention is here addressed to the implementation of a diffraction experiment: data collection of X-ray patterns involves determination of a strategy in terms of instrument resolution and performance.

In a powder instrument aligned with Bragg-Brentano geometry there are at least three different meaning for "resolution":

i) lowest 2-theta resolution;

ii) highest 2-theta resolution;

iii) best peak width resolution.

Moreover, suitable counting times have to be selected on account of the time machine allocated for the "experiment" in order to maximize the signal-to-noise and signal-to-background ratios.

Fabiana Gennari (CNEA)

The reactions of CO2 capture and CO2 conversion into fuels generally occur between a gas, CO2, and a solid (or a liquid).

The CO2 conversion can be followed by analyzing the gas composition using gas chromatography or mass spectroscopy. In this way, the changes in the gas composition or the fuel formation are determined. In the case of materials that capture CO2, the reaction can be followed by thermogravimetry, i.e. measuring the changes in weight with time. Another possibility is to study the structural and/or microstructural changes of solids or liquids using Raman spectroscopy or infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. These techniques are useful to determine the phases present at different reaction stages, the changes in the surface composition and the variation in the crystallite sizes/agglomerates with the reaction progress, among some characteristics.

Recommended lliterature:

• N. Gamba, V. Farina, S. Garroni, G. Mulas y F. C. Gennari. CO2 storage and conversion to CH4 by wet mechanochemical activation of olivine at room temperature. Powder Technology 377 (2021) 857-867.

• M. L. Grasso, J. Puszkiel, L. Fernández Albanesi, M. Dorheim, C. Pistidda, F. C. Gennari. CO2 utilization for methane production via a catalytic process promoted by hydrides. Phys. Chem. Chem. Phys. 21(6) (2019) 19825-19834.

• M. L. Grasso, M. V. Blanco, F. Cova, J. Gonzalez, P. Arneodo Larochette y F. C. Gennari. Evaluation of the formation and carbon dioxide capture of Li4SiO4 using in situ synchrotron powder X-ray diffraction studies. Physical Chemistry Chemical Physics 20 (2018) 26570-79, doi: 10.1039/C8CP03611J

• M. L. Grasso, P. A. Larochette, F.C. Gennari. CO2 capture properties of Li4SiO4 after aging in air at room temperature. J. CO2 Utilization 38 (2020) 232-240.

• V. Farina, N. S. Gamba, F. C. Gennari, S. Garroni, F. Torre, A. Taras, S. Enzo, Gabriele Mulas. CO2 hydrogenation induced by mechanochemical activation of olivine with water under CO2 atmosphere. Front. Energy Res., vol. 7, October 2019.

Santiago Aparicio (ICCRAM-Universidad de Burgos)

The objective of this chapter is show the applications of the in-silico methods -the use of computational techniques for designing materials-. The reason: advanced materials are assential to economic security and human well being, with applications in industries aimed at addressing challenges in clean energy and environment (CO2 problem). Also it can take 20 or more years to move a material after initial discovery to the market and accelerating the pace of discovery and deployment of advanced material systems will therefore be crucial to achiving global competitiveness in the 21st century. Finally, to discover and deploy adavanced materials twice as fast, at a fraction of the cost.

Carlos Rumbo (ICCRAM- University of Burgos)

Toxicological studies are essential to determine the safety of new materials before they can be applied and their use become more widespread. This presentation gives a brief introduction of the different techniques and model organisms applied in this kind of experiments, focusing particularly on the importance of in vitro methodologies.

References:

• Toxicological assessment of nanocrystalline metal alloys with potential applications in the aeronautical field C. Rumbo, A. Bianchin, A. M. Locci, R. Barros, S. Martel Martín, Juan Antonio Tamayo-Ramos. 2022. Scientific Reports 12 (1), 1523

• In vitro safety evaluation of rare earth-lean alloys for permanent magnets manufacturing C. Rumbo, C. C. Espina, J. Gassmann, O. Tosoni, R. Barros García, S. Martel Martín, J. A. Tamayo-Ramos. 2021. Scientific Reports 11 (1), 1-12.

• Toxicological evaluation of MnAl based permanent magnets using different in vitro models C. Rumbo, C. C. Espina, V. V. Popov, K. Skokov, JA Tamayo-Ramos. 2021 Chemosphere 263, 128343

• Toxicological assessment of commercial monolayer tungsten disulfide nanomaterials aqueous suspensions using human A549 cells and the model fungus Saccharomyces cerevisiae. B. Domi, K. Bhorkar, C. Rumbo, L. Sygellou, S. M. Martin, R. Quesada, S. N. Yannopoulos, J. A. Tamayo-Ramos. 2021. Chemosphere 272, 129603

Gabriele Mulas (UNISS)