Root causes for low-temperature filter blocking at petrol stations – A field study

[Display omitted] •Filter samples from unexplainable non-mibrobial filterblocking events were collected.•Applying extraction methods and various analyticals did not explain the root cause.•Mass spectrometry was successfully used to distinguish reference and blocked filters.•All blocked filters showed distinct amounts of saturated monoglycerides.•Findings lead to improved guidelines for fuel quality control and fuelling techniques. Non-microbial filter blocking can be observed in filters of fuel dispensers that dispense biodiesel B7 (diesel with 7 % bio content). Initially, to identify the cause(s), an extensive matrix of affected sample filters (blocked) and reference filters in used and unused conditions were screened over 1.5 years. Information about possible influencing factors such as changes in temperature, weather, duration of use and location was gathered wherever possible. Furthermore, a gentle extraction method was set up to remove large amounts of fuel from selected filters and retrieve those blocking substances. For essential characterisation, the filter surfaces were assessed by light microscopy and gravimetry, and the deposits were analysed by ATR-FTIR and ICP-OES. However, a differentiation between blocked and reference filters was not possible. A qualitative assessment of fuel samples and filter deposits was carried out by direct infusion electrospray ionisation high-resolution mass spectrometry (ESI-HR-MS), which showed an apparent accumulation of saturated monoglycerides (SMGs) within the range of C16:0 to C22:0 in blocked filters. However, only unsaturated monoglycerides (from C16 to C18) were predominantly found in reference filters. Furthermore, a gas chromatography (GC)-flame ionisation detection (FID)-MS method was applied to evaluate the difference in SMG content in good and blocked filter samples.