*3.6. FTIR*

The results obtained from the FTIR study of the spectrum of coconut oil, FAEE and bio-jet fuel are given in Figure 7. The peaks shown in between 3000 to 2800 cm−<sup>1</sup> indicate the stretching vibration of = C-H (alkene) and C-H (alkane) functional groups [50], which contributed by the esters chain of the samples. The characteristics peak at wavenumber of 1743 cm<sup>−</sup>1, 1742 cm−1, and 1740 cm−<sup>1</sup> in the spectrum of coconut oil, FAEE and bio-jet fuel, respectively, show the occurrence of C=O stretching. Although this peak is shorter in the bio-jet fuel as compared to FAEE, however, the presence of this peak showing that there is a need for deoxygenation process to remove the oxygen content in the jet fuel. Besides, blending of the bio-jet fuel with the conventional fossil-based jet fuel is also recommended to balance the bio-jet fuel property deficiency. Furthermore, it is noted that an extra peak at 1437 cm−<sup>1</sup> in the spectrum of FAEE and bio-jet fuel in comparison to the spectrum of coconut oil. This peak can be explained by the bending vibration of C-H groups in the samples. In addition, it confirms the transesterification process was successfully conducted and converted triglycerides in the coconut oil into ethyl esters in biodiesel (FAEE) and bio-jet fuel [44,51,52].

**Figure 7.** FTIR spectrum for coconut oil, FAEE, and bio-jet fuel.
