This report is the scientific result of a research project undertaken by the FVV eV and performed by the Institute of Environmental and Sustainable Chemistry (IÖNC) at Technische Universität Braunschweig under the direction of apl. Prof. Dr. agr. Robert Kreuzig and by the Institute of Internal Combustion Engines (ivb) at Technische Universität Braunschweig under the direction of Prof. Dr.-Ing. Peter Eilts. We gratefully acknowledge the support received from the project coordination and from all members of the project user committee. The research project was self-financed (FVV funding no. 601341) by the FVV eV. The project ended this year and the results were presented on the 19th FAD Conference in Dresden on 3th of November 2022.
Since Ultra Low Sulfur Fuel Oils (ULSFOs) are used in response to 0.1 % sulfur limits in maritime Emission Control Areas (ECA), there have been some returns of SCR catalysts of large marine engines showing a thin SiO2-layer on the catalyst surface. The catalyst activity was decreased drastically after only 8000 h of engine operation. In this context, the presence of various silicon compounds in marine fuels and their effects on SCR catalysts were investigated.
For the analysis of marine fuels, a dilution method for the determination of total Si content using ICP-OES with a limit of quantification of 2 mg/L and for the determination of organic silicon compounds (OSC), a Heartcutting-GC-FID/MSD method including a clean-up with solid phase extraction in order to separate siloxanes from the complex hydrocarbon matrices were developed. The quantification limits for the siloxanes were in the range of 50 to 100 µg/L. When these methods were applied to 64 marine fuel samples, siloxanes were detected in 30% of the samples in a concentration range between 0.052 mg/L and 40 mg/L. No correlation was found between total silicon contents or other determined fuel parameters and siloxane contents.
Experiments with silicon-doped fuels on a fuel burner test bench revealed a fast catalyst deactivation due to organic silicon compounds in the fuels. Even low silicon fuel concentrations caused a significant loss of SCR activity. In this context, different organic silicon compounds had a similar influence on catalyst deactivation. Differences appeared under fuel variation. Organic silicon precursors in distillates induced stronger deactivation than in residual-containing fuels. The formation of SiO2 deposits from OSCs was shown by ATR-FTIR measurements. SEM-EDX analyses showed increasing Si concentrations with layers of up to 5 µm on the catalyst surfaces with increasing operating hours and increasing OSC concentrations in the fuels. From the catalyst inlet to the outlet, the Si concentrations on the surfaces decreased. Organic silicon compounds in light and middle distillate marine fuels tend to deactivate SCR catalysts more strongly than those in residual-containing marine fuels.