13th International Colloquium Fuels - September 2021 45 Latest developments in modular Power-to-X technologies in INERATEC´s micro-structured reactor technology Dr. Tim Böltken INERATEC 1. Introduction The European Union has not only been striving to reduce their carbon footprint since the Paris Agreement in 2015, but ever since the efforts have been intensified significantly. Amongst others, this led to the European Green Deal, which had been announced in 2019 by the European Commission and is currently being implemented 1 . Strong efforts have been taken, especially in the last years, to overcome the dependency from fossil resources in all sectors. While the energy sector has made significant advances in the installation of renewable sources and minimizing the CO 2 emission, the transportation sector still has a long way to go. Currently, there is an intense and in parts very lobby-driven political discussion on the right direction for the transport sector to turn to in order to minimize CO 2 emissions in the upcoming years and to reach the climate goals set on an international and also a national level in various countries. At a first glance, battery-driven cars might seem to be the preferred solution for urban traffic due to their superior efficiency in utilization of the renewable electricity. On the other hand, there are still unanswered questions like the availability of suitable charging infrastructure or the environmental footprint of the battery production. One aspect further ignored in this discussion is also that renewable energy sources, such as wind or solar, are highly volatile not only on minute or hour scale but also on a daily and seasonal scale. Downturns of wind on weekly basis can occur several times throughout a year. Renewable carbon-based fuels produced from renewable energy, so called e-Fuels, on the other hand could be utilized instantly in the available infrastructure for distribution and also in the current car fleets. They could help to overcome these power fluctuations while being produced only in times of energy availability. Despite lower wellto-wheel efficiency, e-Fuels have significant advantages when it comes to accessing renewable energy in remote locations, so called Power-to-X sweet spots 2 . Even if the above-described challenges of electric mobility can 1 Communication from the Commission to the European Parliament, the European Council, the Council, the European Economic and Social Committee and the Committee of the Regions — The European Green Deal (COM(2019) 640 final, 11.12.2019) 2 THE CONCEPT OF EFFICIENCY IN THE GERMAN CLIMATE POLICY DEBATE ON ROAD TRANSPORT, Frontier Economics, November 2020 be solved, there are still important sectors that will most presumably rely on carbon-based fuels also on the midand long-term. These sectors are aviation, long distance heavy-duty and maritime transport. Carbon based fuels, like Diesel or kerosene outmatch solid-state batteries or hydrogen fuel cell technology in terms of available energy density of the fuel by orders of magnitude 3 . That is why carbon-based fuels will play an important role also in the long-term future in the named sectors. There are various candidates for the described e-Fuels, like Methanol (MeOH), Dimethylether (DME), Oxymethylene ethers (OME), Synthetic natural gas (SNG) or Fischer-Tropsch-based (FT) hydrocarbons 4 . Of course, in the production of all of these e-Fuels, one needs to make sure that the carbon feed is originating from an unavoidable CO 2 or renewable source (originating from biomass or air). Power to produce these e-Fuels via power-to-x technologies (PtX) should as well come from renewable sources to generate the hydrogen via electrolysis. Therefore, the costs for these e-Fuels currently cannot be considered equal or even lower than their fossil-based counterparts. Probably the most interesting e-Fuels, especially in short-term, are FT-based fuels. Those are chemically similar to current fuels like Diesel or kerosene but contain no hetero-atoms which generate poisonous emission and can additionally be tuned to combust even cleaner than fossil fuels. Therefore, these e-fuels could directly be handled in the existing infrastructure and used in the available engines and turbines. Of course, this might require adaptions in the legal framework but in contrary to other e-Fuels it does not require to install a completely new infrastructure-network. INERATEC GmbH, a spin-off from the Karlsruhe Institute for Technology, has developed an innovative Power-to-X (PtX) technology that can produce FT-based fuels and MeOH efficiently and load-flexible. The modular approach renders INERATEC´s application an ideal fit for the upcoming challenges of future energy systems, like volatile energy availability or decentralized production of electricity. 3 STATUS UND PERSPEKTIVENFLÜSSIGER ENERGIETRÄ- GER INDER ENERGIEWENDE, Prognos, May 2018 4 P. D. Lund et al., Review of energy system flexibility measures to enable high levels of variable renewable electricity, Renewable and Sustainable Energy Reviews 45 (2015), 785-807 46 13th International Colloquium Fuels - September 2021 Latest developments in modular Power-to-X technologies in INERATEC´s micro-structured reactor technology 2. Innovative chemical Reactor technology and scale-up The above-mentioned Fischer-Tropsch synthesis is the conversion of syngas, a mixture of CO and H 2 , into longchain hydrocarbons, usually facilitated by a heterogeneous catalyst. The technology has been available since the first half of the 20 th century and is widely applied in large scale production plants all over the world. Up to date, the technology is mainly used to produce liquid hydrocarbons from coal or methane via the so-called Gasto-liquid process and is conducted in large scale fixed bed or bubble column reactors. These reactors follow the classical economy of scale, with improved efficiencies at very large scales. However, these reactor concepts are dependent on a continuous and large stream of gas supply and therefore hardly fit the above-described volatility of a renewable energy system. One possible solution for the integration of the FT-process into a renewable energy system is the application of novel reactor concepts 5 . Based on research work at the Institute for Micro Process Engineering (IMVT) at KIT, INERATEC has developed a reactor technology that is easily scalable and suitable for the described flexible applications. The technology is based on microstructured reactors. The reactors are equipped with an innovative evaporation cooling in intermediate inside layers, which enables the plants to operate exothermic reactions under stable conditions 6,7 . The current commercially available generation of such reactors can be seen in Figure 1. Figure 1: Rendering of INERATEC´s current commercially available reactor generation 5 Leviness, Steve & Tonkovich, A & Jarosch, Kai & Fitzgerald, Sean & Yang, Bin & Mcdaniel, Jeff. (2011). Improved Fischer-Tropsch Economics Enabled by Microchannel Technology. 6 M. Belimov, D. Metzger, P. Pfeifer, On the temperature control in a microstructured packed bed reactor for methanation of CO/ CO2 mixtures, AIChE J. 63(2017) 120-129 7 P. Piermartini, T. Boeltken, M. Selinsek, P. Pfeifer, Influence of channel geometry on Fischer-Tropsch synthesis in microstructured reactors, Chemical Engineering Journal 313 (2017) 328-335 Over the last decade, the reactor technology has been scaled up from laboratory scale to a size of 6 barrels per day per reactors of production capacity by KIT and INERATEC. This equals a scaling factor of more than 30.000, as can be seen from Figure 2. Figure 2: Reactor upscaling timeline Together with the available advances in automation, which the whole process industry has made over the last couple of years, this opens the possibility to modularize the FT-process. This means that a number of individual FT-modules, that contain all necessary process units, like gas conditioning, one or multiple serial or parallel reactors and product handling, can be produced and combined again on next higher level of modularization in serial or parallel. This allows to establish FT processes that are customized towards the individual customer´s requirements. For example, in biomass-derived syngas (from gasification processes), inert gases like nitrogen might be contained in the feed-gas stream. In such a case it might be of interest to implement a 2-stage process rather than a 1-stage process to obtain near full conversion without inert accumulation while recycling unconverted feed. Both stages could be set up from a multitude of FT-modules with numerous FT-reactors each. Several reactors in each stage or multiple modules offer another dimension of load flexibility as it is possible to operate the synthesis in only a reduced number of reactors or modules and leave the others in standby. Beyond load flexibility the modularization on reactor or module scale might be very useful for maintenance or other services, for which in other cases a complete plant would need to be shut down. On the contrast, the modular plant could then be operated at least in parts while other sections are in refurbishment. Furthermore, it is possible to foster ramp up of production capacity on availability of the renewable source, installing one plant unit at a time and therefore increasing production capacity. Schematically, one can see such the different operational modes in Figure 3. 13th International Colloquium Fuels - September 2021 47 Latest developments in modular Power-to-X technologies in INERATEC´s micro-structured reactor technology Figure 3: Operational modes of the modular concept Going from bottom to top, the production capacity starts off very low at approx. 5 % of the maximum capacity. This can be realized by only one reactor module, which not even needs to be operated at full load. Increasing the production capacity to 50% would then require 2 modules fully operated. Increasing capacity 100% would in this case require two more modules to be operated at full load. The above-described reactor and core process development has been achieved in the two EU-funded research project COMSYN 8 and FLEXCHX 9 . Both projects focused on the utilization of biomass for sector coupling and the flexible (day-wise and seasonal) application of FT synthesis for the chemical storage of energy. 3. Plant scale-up and numbering-up This modular approach will be basis for the plant scale-up of the company in the nearand mid-term future following a 3-dimensional numbering-up strategy. In the first dimension, the number of reaction plates per reactors are multiplied by increasing the reactor volume. Secondly, the number of reactors per module will be increased, which leads to an increase of the overall production capacity per module. And thirdly the number of modules can be multiplied to match the requirements of the customer site and the available feed streams, without significant re-engineering to be necessary. This way, plant volumes between 50 t/ a and 35.000 t/ a will be reachable by 2025 (see Figure 4) 8https: / / www.comsynproject.eu/ 9 http: / / www.flexchx.eu/ Figure 4: Plant Scale-Up concept 4. Feedstocks and FT-Products One feature that makes the FT synthesis so extraordinarily interesting, especially for sector coupling, is the large adaptability towards feedstock. As an example, the syngas used in FT can be biomass-derived, in which case one would speak of biomass-to-liquid (BtL) process. Another possibility is to employ hydrogen, which has been generated via electrolysis together with CO 2 . In addition, the source for CO 2 is neither pre-defined. This means it could be provided from a biogas-source or from an industrial exhaust but also from ambient air. Together with partners in various research project, national and international, INERATEC has developed and applied various BtL and PtL value chains. In the REDIFUEL project, just like in the forementioned projects COMSYN and FLEXCHX, biomass is used as feedstock but this time the process is designed to produce high-performance fuels 10 . For this purpose, INERA- TEC´s FT-reactor is equipped with a specially designed catalyst and produces crude which can be converted to the desired fuels via hydroformylation. Another example for BtL is currently under investigation in the EU-funded project GLAMOUR. Here glycerol, which currently is a mostly unused by-product from the biodiesel production, is used as very cheap feedstock for the production of renewable maritime and aviation fuels. INERATEC is evaluating novel 3D-printed reactor designs against their established technology and will elaborate in the course of the project a possible upscaling route for the process 11 . A completely different use case is the integration of the FT synthesis into industrial waste gas streams, and the direct utilization of CO 2 to produce chemicals. This process has been investigated and technically proven in the ICO2CHEM project, together with international partners 12 . During the project, a demonstration plant has been engineered and implemented at the industrial site of the partner InfraServ Höchst. It was shown that it is possible to produce high quality waxes from the utilized exhaust gases. Consequently, this project laid the basis for the upcoming integration of PtL-technologies at various industrial sites. This includes chemical plants but also production sites for cement or steel. The latter two in- 10 https: / / redifuel.eu/ 11 https: / / www.glamour-project.eu/ 12 https: / / www.spire2030.eu/ ICO2CHEM 48 13th International Colloquium Fuels - September 2021 Latest developments in modular Power-to-X technologies in INERATEC´s micro-structured reactor technology dustries intrinsically produce CO 2 as part of their process and have an accordingly high urge to find solutions for the utilization of their waste streams. As shown, modular PtL-technologies can provide such solutions. In a future energy system, point sources of CO 2 , like the beforementioned steel and cement plants, will be very scarce and therefore not sufficient to satisfy the demand for carbon sources. Hence, the capture of CO 2 from ambient air will become more and more important for future applications. The integration of such a direct air capture together with an innovative co-electrolysis has already been shown in a world-first demonstration plant back in 2019 in the German Kopernikus project P2X. A picture of the plant can be found in Figure 5. Figure 5: World-first demonstration plant for the integration of direct air capture, co-electrolysis and Fischer- Tropsch-synthesis All these project results show how flexible INERATEC´s FT reactors are in the various PtL and BtL processes and that many feedstocks can be used for the process. Interestingly, the FT synthesis in microstructured reactors is at least as flexible with respect to the downstream side. With the process being an a-priori undirected chain growth mechanism, which is dependent on the process conditions, it is relatively simple to adapt the product spectrum to the customers´ requirements. Very short chain products, like gasoline or even gaseous hydrocarbons can, in principle, be as well produced as long chain waxes for fine chemical applications. The product distribution usually follows the Anderson-Schulz-Flory (ASF) distribution, given by the equation ,where w n is the mass content of the product, α is the chain growth probability and n is the specific chain length. With α being a constant that is (given a fixed catalyst) directly dependent on the process conditions - mainly space velocity, temperature and pressure - the ASF distribution is easily adaptable by these parameters. It needs to be pointed out here, while there are limits to the product distribution selection and side products cannot be excluded completely, it is still possible to adapt the process in a wide range. This has been proven for INERATECs microstructured FT-reactor technology in a number of projects. As mentioned before, in the ICO2CHEM project, long chain waxes, that could be introduced into chemical production lines, were produced. Simultaneously, INERATEC is working together with partners in the EU-funded project KEROGREEN 13 and the project by the German Federal Ministry of Economic Affairs and Energy PowerFuel 14 on the development of drop-in renewable jet-fuel alternatives. Results indicated that the FT-products can come close to the relevant ASTM-norms and suitable refining procedures can be implemented also on a modular level. Depending on the future regulatory framework, product upgrading might even be possible without the need for a complex infrastructure of a large-scale refinery. Another product, INERATEC has successfully developed is drop-in ready Diesel. Alongside gasoline pre-cursors this is under investigation in the reFuels project together with a number of car manufacturers. Finally, it needs to be stated that the microstructured reactor technology of course can also be used for other exothermic reactions, like MeOH-synthesis - which is, as stated above, another path for PtX. This reaction pathway is investigated in the German national research project E 4 MeWi 15 . 5. Summary and Outlook Modular FT-technology has made significant advances over the last couple of years. The technology is ready to be spread out on an industrial level and INERATEC is taking steps towards this roll-out. An important step on this path will be the realization of the newly acquired EIC Accelerator project IMPOWER2X. INERATEC will use this project to prepare a serial production for the reactor modules and chemical plant units. Such a serial production can reduce the CAPEX for new plants significantly, as it reduces the individualizing efforts for the PtX-plants. The individual process units of the plant will be re-engineered and standardized to suit the modular concept and to be producible in a serial production line. Furthermore, the complete company will undergo a re-structurization procedure with the overarching goal to effectively implement the serial production on al organizational levels. Finally, INERATEC will be able to “produce chemical plants like cars”: modular products manufactured on a serial production line with the possibility to individualise them with very little effort towards the needs of the customers. This enables INERATEC not only to be supplier of plants for customers but will render the company towards a provider of fuel. For this case INERATEC implements an offtake business model in which the company identifies 13 https: / / www.kerogreen.eu/ 14 https: / / www.elab2.kit.edu/ powerfuel.php 15 https: / / www.e4mewi.de/ 13th International Colloquium Fuels - September 2021 49 Latest developments in modular Power-to-X technologies in INERATEC´s micro-structured reactor technology interesting locations for PtX plants and sells the produced fuels to customers directly, opening novel customer groups who would not consider operating chemical plants themselves. Acknowledgements [1] This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 884197 (GLAMOUR), 817612 (COMSYN), 768543 (ICO2CHEM), 763909 (KEROGREEN), 763919 (FLEXCHX), 817612 (REDIFUEL) and 970564 (IMPOWER2X). Further funding from the Federal Ministry of Economic Affairs and Energy (BMWi) and the Federal Ministry of Education and Research is highly acknowledged in the framework of the projects PowerFuel (03EIV071A), E4Me- Wi (03EI3035C), and Kopernikus P2X Phase I (03SFK2D1) and II (03SFK2D1-2).