Synthetic fuels and hydrogen carrier materials

Ammonia and methanol are important basic chemicals that are essential to our economy both now and in the future. The same applies to fuels with a high energy density, which are still required for certain applications such as shipping and aviation.

However, the emissions caused by the traditional production of ammonia or methanol, and the combustion of fuels from fossil resources, contribute significantly to climate change. By using green hydrogen to manufacture these products, and, for example, recovering and utilizing the CO2, it is possible to significantly reduce CO2 emissions while simultaneously generating important precursor materials, for example for industry and agriculture.

In addition, solid and liquid hydrogen compounds enable the long-term storage and transportation of hydrogen in material form. Central elements of this hydrogen infrastructure are efficient production and reconversion processes and the development of technologies for the energetic and material use of these derivatives.

Methanol synthesis and reforming

Global production of methanol is currently around 90 million tonnes per year. This production relies chiefly on natural gas. The joint project »Carbon2Chem«, which was coordinated by Fraunhofer UMSICHT, thyssenkrupp and the Max Planck Institute for Chemical Energy Conversion, has shown that production is also possible with CO2/H2 or CO/CO2/H2 mixtures. Fraunhofer UMSICHT and Fraunhofer ISE, together with the project partners, demonstrated that gas purification and catalytic methanol production can be performed successfully even under volatile operating conditions. Through several thousand hours of testing in their laboratory and pilot plants over the course of the project,

Fraunhofer UMSICHT and ISE investigated the scaling and long-term stability of methanol synthesis, especially under volatile operating conditions, and also with real smelting gases in purified form. The capacities of the systems are between 50 ml/h and 50 l/d. The results were used in process simulations to determine the kinetics for methanol synthesis from such unconventional gases, thus enabling a detailed process design. The experimental investigations and simulations also allow the process to be transferred to other gas sources. It is also possible to simulate the synthesis process in other environments and thus to interconnect the production, chemistry and energy sectors. The co-simulation platform SimuNet, which was further developed in the project, provides support in scale-up and process optimization. The provision of suitable synthesis gases (from CO/ CO2/ H2) for methanol synthesis can also be achieved by the electrolysis of CO2, for example from contaminated process gases. To this end, Fraunhofer UMSICHT is developing processes for the direct co-electrolysis of CO2 and H2O at low process temperatures, for coupling with volatile energy sources such as wind or photovoltaics. Research and development tasks include scaling up the technology to the kW scale and integrating it initially into upstream processes such as amine scrubbing to provide CO2 within the Power-to-X platform project. The CO2-Syn project is furthermore developing novel electrode and catalyst materials for the direct use of cement plant process gases, and for coupling low-temperature co-electrolysis in a laboratory plant with a downstream alcohol synthesis process.

Within several projects, Fraunhofer IMM is developing methanol reformers for mobile and decentralized stationary applications. These produce hydrogen from methanol via steam reforming with a high level of efficiency, and can be used, for example, to supply hydrogen to fuel cells with a power range of up to several 100 kW. With the appropriate purification steps, both low-temperature and high-temperature PEM fuel cells can be supplied. In the scope of the European project »Gamma«, Fraunhofer IMM is developing a 600 kW methanol reformer and a 400 kilowatt ammonia cracker which will supply fuel cells with hydrogen as a power supply for a large maritime cargo vessel

Ammonia – synthesis, cracking and utilization

With an annual production of 180 million tonnes, ammonia is one of the most important non-fossil raw materials. Even though there is no carbon in the molecule itself, the hydrogen it contains is mostly generated from natural gas, which is why ammonia synthesis is responsible for around 2 to 3 % of global CO2 emissions. However, as it is also the most important component in fertilizers, it is essential to meet the needs of the growing global population. To render its production more sustainable, the hydrogen used can be replaced by green hydrogen. The nitrogen required for its production can be obtained from the air. Research is also being carried out into new processes that could replace the established Haber-Bosch synthesis, particularly at decentralized locations. In the project »PICASO« (Process Intensification & Advanced Catalysis for an Ammonia- Sustainable Optimized Process), Fraunhofer ISE is working with partners on a novel power-to-ammonia (PtA) process for sustainable ammonia synthesis. The process could reduce CO2 emissions by 95% compared to the conventional Haber-Bosch process. The main objective of PICASO is to develop an integrated reactor technology and dynamic operating strategies for a flexible ammonia synthesis process based on renewable, green hydrogen, that is also suitable for implementation in remote regions. In a follow-up project, the integrated reactor will be scaled up to demonstration level and tested in a pilot plant.

Ammonia is not only an important raw material, but is also potentially one of the most important carrier molecules for hydrogen. Particularly where large quantities are involved, and where long distances must be traveled by sea, the transportation of hydrogen in the form of ammonia is currently the most economical option. Ammonia offers the promising possibility of transporting energy from regions of the world where it is more cheaply available than in Germany, for example. It therefore plays a central role in the future supply of affordable energy. A crucial step toward successful implementation is the development of processes to efficiently produce hydrogen from ammonia. Fraunhofer is working on the development of efficient processes and catalysts for ammonia reformation. For example, within the DYNAFLEX® performance center, Fraunhofer UMSICHT has developed a process for the direct electrical heating of the carrier material, which means that the process can be operated without CO2 emissions and without the combustion of ammonia itself, significantly increasing the efficiency of the entire process chain from hydrogen production through to transportation and use. With the ELIAS (Electrically Heated Catalysts Carriers) platform for endothermic reactions, Fraunhofer ISE has developed a valuable tool for implementing these reactions in very compact reactors. At the same time, Fraunhofer ISE and Fraunhofer UMSICHT are developing new catalyst and carrier materials to reduce the process temperature. The production of pure hydrogen is only one alternative. It can also make sense to crack at least part of the ammonia and then burn it for energy or convert it into CO2-free electricity and heat within a fuel cell.

In the scope of several projects, Fraunhofer IMM is working on the utilization of ammonia for mobile and stationary applications, on the development of catalysts and reactors for ammonia cracking and its homogeneous combustion as well as on downstream hydrogen purification technologies (projects »Ammonpaktor«, »ShipFC«, »Spaltgas« and others). A plate heat exchanger with coated catalysts is applied for cracking, which allows to achieve a high system efficiency of up to 90 % and a reduction in plant size of 90 %.

Synthetic fuels

While the use of ammonia and methanol as fuels will play an important role in the future, for example in the shipping sector, methanol in particular offers a variety of possibilities for synthesizing other fuels. For example, DME (dimethyl ether) or OME (polyoxymethylene dimethyl ether) can be synthesized from methanol for use in diesel engines. OME can be used within the existing infrastructure, especially as an alternative or additive to diesel fuel, leading to a significant reduction in local emissions (e.g. soot and NOx). In the »NAMOSYN« project, Fraunhofer ISE worked on the development of OME production processes up to a scale of one million tonnes per year. In parallel, the use and compatibility of these OMEs with combustion engines was investigated under laboratory conditions and in practice. This study has been completed and published. The methanol-to-gasoline process can significantly increase energy density and produce a fully compatible gasoline. The so-called methanol-to-jet route also offers promising application possibilities. Methanol forms the basis for kerosene production, which is carried out by synthesizing olefins that are then oligomerized and hydrogenated. In the research project »Sustainable Aviation Fuels based on Advanced Reaction and Process Intensification« (SAFari), a consortium of research institutes and industrial partners, under the project management of Fraunhofer ISE, will work on the sustainable production of kerosene from methanol in a pilot plant, and its testing. The project aims to contribute to the full market approval of this methanol-based process route by the American Society for Testing and Materials (ASTM). While CO2 emissions can be largely avoided in crude steel production through the use of green hydrogen, unavoidable process- related emissions, primarily in lime and cement production, can be captured using ceramic membranes and used to produce high-quality products. In the WaTTh project, Fraunhofer IKTS is constructing a fully automated demonstration plant based on its own high-temperature co-electrolysis process, in which liquid hydrocarbons and waxes are produced from CO2 and water using Fischer-Tropsch synthesis. These materials can be used in the chemical industry and for the production of synthetic fuels such as e-kerosene. The plant capacity is 8 liters of liquid products and waxes per day. Using tools developed for process simulation, the researchers are currently working on scaling up the processes to industrial scale.

Solid hydrogen carriers and POWERPASTE

In contrast to compressed gas or liquid hydrogen storage systems, the use of metal hydrides as solid hydrogen carriers (SHCs) is an economically promising option for safe storage of hydrogen with a very high purity (7.0) at low operating pressures (2 to 40 bar), in a confined space (up to 0.15 kg H2/dm³) and without evaporation losses. In SHCs, hydrogen is chemically bound to a solid carrier material, so that if the storage tank leaks, the bound hydrogen does not escape abruptly, but rather is released very slowly. SHC storage systems are therefore considered extremely safe. Hydrides have the potential for further application fields in hydrogen technology, such as the thermo-chemical compression of hydrogen and the purification of hydrogen-containing gas mixtures. In addition to reversible thermolysis, a hydrolysis reaction, i.e. decomposition of the hydride through a reaction with water, can be carried out with metal hydrides. »POWERPASTE« is a suspension consisting of magnesium hydride, a metal salt as a catalyst and an ester for fluidization. Magnesium hydride reacts exothermically with water, releasing hydrogen. The by-product is non-toxic magnesium hydroxide (see equation 1). A notable advantage of the technical application is the co-utilization of water for hydrogen production, and consequently the doubling of the amount of hydrogen produced per equivalent of metal hydride.

Equation 1: MgH2 + 2 H2O → 2 H2 + Mg (OH)2
 

POWERPASTE can be stored unpressurized and at room temperature under exclusion of moisture. To release the hydrogen, hydrogen generators are required to combine the paste with the water. Together with partners from industry and research, Fraunhofer IFAM is developing several demonstrators and prototypes for hydrogen production for various applications (stationary, portable, mobile) in the power classes of 500 to 1,000 W. The hydrogen generators are coupled with PEM fuel cells of the corresponding power class. Current developments concern weight-related optimizations for mobile applications in order to achieve the highest possible specific energy at system level. Several technological milestones were achieved in 2022. For example, a self-sufficient, POWERPASTE-based emergency power system was presented at the Hannover Messe together with Grünland Innovations GmbH. In addition to stationary applications, mobile applications are also being developed and demonstrated in publicly funded projects (»POWERPASTE – Mobile hydrogen supply in the next generation« (funded by the German Federal Ministry for Economic Affairs and Climate Action, BMWK). Increasing the hydrolysis performance is another important focus of current projects, in order to open up new application fields. The upscaling of POWERPASTE production is ongoing at the Fraunhofer Project Center for Energy Storage and Systems ZESS in Braunschweig. The aim was to produce up to 5 tonnes of POWERPASTE at ZESS in 2023, for use in pilot applications.

Power-to-X Potential Evaluation

Power-to-X (PtX) refers to processes where electricity is converted into storable energy carriers. Synthetic fuels and energy carriers produced with green hydrogen hold great promise: they aim to replace fossil fuels in industries, transportation, and other sectors. Like many other countries, Germany places a high value on these PtX energy carriers within its climate policy framework. Many regions worldwide offer favorable conditions for producing green hydrogen and renewable synthetic fuels and energy carriers. The specific potentials of these regions can be technically and economically calculated and evaluated.

Researcher from the Fraunhofer Institutes can analyze and quantify which regions are potential suitable for hydrogen and Power-to-X production, along with the transportation of these energy carriers to Germany. The Fraunhofer Institute for Energy Economics and Energy System Technology (IEE) developed the Global PtX Potential Atlas. This user-friendly tool provides insights into the Power-to-X potentials of coastal and inland locations globally. The analyses utilize high-resolution spatial data, long-term weather data, and time-series-based, cost-optimized plant and expansion plans for PtX technologies.

The assessment of technical and economic PtX potentials is based on extensive analyses, including land availability and weather conditions. Parameters such as peripheral, storage, and transport costs were also considered, along with variations in system design. Another crucial factor is the socio-economic conditions of the individual regions, evaluated using seventy indicators, such as those from the World Bank. With the Atlas, interested parties can access information on the suitable areas for PtX, the achievable full-load hours and possible production quantities, the specific production costs for various PtX energy carriers, and the costs for their transport to Europe.