Biodiesel was found to be the best candidate to replace diesel fuel mainly due to
being renewable, biodegradable, and non-toxic and reduce greenhouse gases, which
cause global warming. Nowadays, biodiesel is blended with diesel fuel in
different concentrations depending on the country of usage and is used in diesel
engines. Concerns about biodiesel were raised after premature fouling of fuel
filters were reported before meeting their mileage requirement. Three filters
from Brazil were analyzed using different techniques (Energy Dispersive X-Ray
[EDX], Fourier Transform Infrared Spectroscopy [FTIR], Thermogravimetric
Analysis [TGA], Time of Flight-Secondary Ion Mass Spectrometry [ToF-SIMS], and
Gas Chromatography/Mass Spectrometry [GC/MS]) to understand the chemical
composition of the filter deposits and highlight the main compounds responsible
for the blockage. EDX showed that the deposits are mainly composed of carbon (C)
and oxygen (O) with traces of sodium (Na), calcium (Ca), iron (Fe), phosphorus
(P), and other elements. FTIR showed that the dominant bands in the filter
deposits spectra are attributed to C-O bonds with a broad OH peak always
present. TGA showed that the deposits vaporize at three different regions with
peak temperatures around 250°C, 350°C, and 480°C, which correspond to the
vaporization of glycerol, sterol glucosides (SGs), and metal carboxylates,
respectively. Combining the data from the previous techniques, it was concluded
that the filter deposits are mainly organic in nature with glycerol and SGs as
the main compounds forming the bulk of the filter deposits with metal
carboxylates present in lower amounts. This conclusion was further confirmed by
ToF-SIMS and GC/MS where all three compounds were detected. In addition, free
sterols and monoglycerides (MGs) were also detected in the deposits with traces
of diglycerides and triglycerides also present.
