*2.1. Materials and Equipment*

Coconut oil was purchased from the local market in Selangor, Malaysia. The coconut oil was then analyzed using gas chromatography, GC (Agilent, 7890A, Wilmington, DE, USA) to obtain its fatty acid profile, as reported in Table 1. Ethanol (C2H5OH) and potassium hydroxide (KOH) were purchased from Sigma–Aldrich (St. Louis, MO, USA).


**Table 1.** Fatty acid composition of coconut oil.

#### *2.2. Microwave-Assisted Catalytic Transesterification*

The experiments of this work involve the catalytic transesterification of coconut oil under microwave irradiation. Firstly, coconut oil and ethanol at a specific molar ratio with 0.5 wt% of potassium hydroxide (KOH) catalyst concentration was prepared. Then, the mixture (reactant) was poured into a 250 mL round bottom flask with a magnetic stirrer bar and put into the microwave reactor. Next, the reflux system was attached, and the reactant was then subjected to microwave irradiation with different power settings under different reaction times at a stirring speed of 200 rpm. At the same time, the temperature of the reflux system was maintained at −4 ◦C by using a chiller to condense back the vaporized reactant. After completion, the product of this transesterification process was cooled to room temperature. The equipment used in producing bio-jet fuel via transesterification was a modified microwave oven equipped with a reflux system, as shown in Figure 1.

**Figure 1.** Experimental setup for microwave-assisted catalytic transesterification.

Then, the product was left in a separating funnel to split the liquid phases. The upper layer, which is the fatty acid ethyl ester (FAEE), was washed using warm water three times and dried at 100 ◦C for 1 h in the conventional oven to remove the moisture.
