During the project, extensive lab-scale research on the synthesis and physicochemical characterization of Fischer-Tropsch catalysts based on cobalt as the major active metal has been done. More than 30 catalyst samples have been produced to enable testing their catalytic performance - at the lab scale and under conditions relevant for industrial application. The lab-scale studies revealed a trade-off between the overall conversion rate and the selectivity to olefins in the C5-C10 hydrocarbon product fraction. Catalysts more selective to said fraction showed to be less active per unit mass/volume than catalysts less selective to that product slate.
Overall, the performance of four catalyst samples was assessed prior to selection for upscaling activities. The catalyst finally chosen for demonstrator purpose enabled high olefin shares of >40%, what results in an alcohol content of up to 30% in the final fuel. Still, the overall activity of the catalyst has to be improved to enable an economic utilization of the process.
For the development of a catalytic system for an efficient hydroformylation/hydrogenation process, two possible catalytic systems have been developed which are able to transform the olefin feedstock in high selectivity to the desired alcohols. Within a catalytic system a rhodium catalyst in combination with water soluble phosphine ligands is used. The water soluble phosphine ligand allows for a recycling of the catalyst by immobilization in a water phase. An experimental setup to test this recycling strategy revealed very low leeching of the rhodium catalyst.
Due to volume limitation of the real REDIFUEL product, fuel analysis and engine tests have been conducted with commercially available surrogate fuels that match the composition of the real product from lab experiments very well. REDIFUEL’s composition has been proposed based on the properties optimization and process products, which consists of Gas-to-Liquid (GtL) and linear alcohols in a ratio of 70:30 vol %. Tailoring a fuel is always a conflict of interests, i.e. emission behavior, ignitability and density. A blend of REDIFUEL/UCOME was found to be most promising with a density of 798 kg/m3, which is very close to the minimum arctic grade EN590 density limit of 800 kg/m3. Due to the hydrophilicity of the alcohols, special attention must be paid on storage and transport of REDIFUEL to keep the overall water content of the fuel within the EN590 limits.
Engine tests with a single cylinder research engine, derived from a state-of-the-art heavy-duty engine, have shown that REDIFUEL significantly reduces pollutant without the need of any engine hardware or software changes. Generally, the particulate matter (- 20%), carbon monoxide (- 20%), and hydrocarbon emissions (- 30%) are reduced with increasing share of REDIFUEL thanks to its oxygen and paraffinic content. Moreover, all the blends of REDIFUEL with Diesel exhibited a rise in efficiency up to +0.5%-points.
The REDIFUEL was also investigated at a series production demonstrator truck. By means of a portable emission monitoring systems (PEMS), real-driving emissions could be investigated. According to the initial single cylinder engine test, also the truck tests revealed the superior emission formation compared to fossil fuel under latest EU VI legislation.
In order to fully exploit the potential of such a renewable fuel, CFD simulations are performed to design an optimal shape of piston bowl and injector nozzle. For validation of this model, optical investigations by means of High Pressure Chamber (HPC) experiments have been undertaken. The results have proven that REDIFUEL blends feature similar mixture formation as Diesel, but a faster self-ignition.
