See Table 1 for abbreviations.
a Calculated from Eq. 6. Numbers in parentheses are standard errors.
b Calculated from Eq. 21.
c Model: f(α) = (1 − α); g(α) = −ln(1 − α) = 0.693 at α* = 0.5 at induction period (IP).
d Model: f(α) = α(1 − α); g(α) = −ln[(1 − α)/α] + C = 4.30 at α* = 0.5 at IP. C = integration constant [g(α) estimated by numerical integration].
The Ea data in Table 8 for PME, SME and MeC18:2 were comparable to Ea data obtained from analysis of P-DSC results in an earlier study (Dunn, 2020). On the other hand, results varied significantly for CaME and MeC18:1, with respect to the earlier study. For these two FAME, the values in Table 8 were −23 kJ mol−1 (lower) and +26 kJ mol−1 for the present work. One study (Litwinienko and Kasprzycka-Guttman, 2000) reported Ea = 95 kJ mol−1 for ethyl oleate and 76.0 kJ mol−1 for ethyl linoleate. A literature review in that study suggested Ea values for oxidation were in the ranges 93-100 kJ mol−1 for MeC18:1 and 69-76 kJ mol−1 for MeC18:2.
Results in Table 8 for the Z0 factors calculated for the first order kinetic model showed that results for CaME, PME and SME were in a relatively narrow range, between 1.33 × 1010 and 6.12 × 1011, compared to results for MeC18:1 and MeC18:2. The same general trend was observed in the Z0 values calculated from the autocatalytic model (range = 8.26 × 1010 to 3.79 × 1012). For both models, the Z0 factors for CaME, PME and SME had values that were between Z0factors for MeC18:1 and MeC18:2. Studies with ethyl esters reported Z0 = 5.66 × 1012 for ethyl oleate and 1.45 × 1011 for ethyl linoleate (Litwinienko and Kasprzycka-Guttman, 2000).
In general, there is a paucity of Ea and Z0 data in the scientific literature for pure FAME and their mixtures (biodiesel). The comparison data described above were obtained from analysis of P-DSC data using model-free kinetic methods. As of this writing, no reliable data from analysis of isothermal induction period (IPR, etc.) could be identified. Future studies on this topic would justify taking these concerns under consideration.