Composition and Fuel Properties
The fatty acid concentration profiles and fuel properties of CaME, PME
and SME are summarized in Tables S1 and S2 in the
supporting information. These results were discussed in full in an
earlier study (Dunn, 2020) and a summary of those findings are presented
herein.
Analysis of the FAME concentration profiles (Table S1 ) showed
that the SME had a higher total PUFAME concentration (62.09 mass%) and
a lower total MUFAME concentration (21.67 %) than either CaME (26.8 and
65.74 %) or PME (9.7 and 40.49 %). CaME had the lowest total SFAME
concentration (7.40 %) followed by SME (16.21 %) and PME (49.82 %).
SME had the highest calculated iodine value (IV) = 132.76 g
I2100−1g−1, followed by CaME (109.6) and PME (51.8).
Selected fuel properties of the three biodiesel fuels were summarized inTable S2 . In descending order, IPR at 110 °C
was 9.34 h, 7.71 h and 2.745 h for CaME, PME and SME. The low value for
SME was expected given its high total PUFAME content and comparable with
data reported in other studies (Moser, 2008a, 2014, 2016; Yang et al.,
2013). The experimental IPR value for CaME was also
comparable with data reported in the literature (Joshi et al., 2009;
Moser, 2008b; Yang et al., 2013). However, the IPR of
PME was lower than that of CaME, despite PME having a lower total PUFAME
concentration. Generally higher IPR values (9.2-15.2 h)
were reported for PME in the literature (Moser, 2008b, 2016; Sarin et
al., 2010; Shahabuddin et al., 2012). In the earlier study (Dunn, 2020),
it was postulated that PME had undergone partial degradation before its
use in the study. PME had AV = 0.72 mg KOH g−1(Table S2 ), a value that exceeded the maximum limit (0.50 mg
KOH g−1) in the ASTM biodiesel fuel standard
specification D6751 (ASTM, 2021). This higher value may have indicated
that PME had undergone hydrolytic degradation. PME also exhibited a PV =
11.3 meq kg−1 (Table S2 ), a value that was
nearly twice the PV measured for CaME. Trace concentrations of
hydroperoxides are known to act as autoxidation initiators (Frankel,
2005a; Kamal-Eldin and Yanishlieva, 2005). The effects of high AV and PV
suggested that PME may have experienced autoxidation before being used
in the study.
The pure MeC18:1 and MeC18:2 samples were also analyzed for
IPR. At 110 °C, IPR = 2.12 ± 0.05 h for
MeC18:1, a value that was comparable with data reported in other studies
(Knothe, 2008; Moser, 2009). Those studies also reported
IPR = 0.94 h and 1.0 h for MeC18:2. Nevertheless, no
reliable IPR data were obtained for MeC18:2 at 110°C in
the present study.