*2.4. Analytical Method*

Reaction products were monitored by capillary column gas chromatography, using a 5890 series II instrument (Hewlett-Packard, Palo Alto, California, USA) equipped with a flame ionization detector (FID) and an HT5 capillary column (25 m × 0.32 mm × 0.10 μm), using *n*-hexadecane (cetane) as internal standard. The heating ramp was: 50 to 200 ◦C at a rate of 7 ◦C/min, followed by another ramp from 200 to 360 ◦C at a rate of 15 ◦C/min, maintaining the oven temperature at 360 ◦C for 10 min [29]. The quantification of the ethyl esters (FAEE), monoglycerides (MG), diglycerides (DG) and triglycerides (TG) allow to determine the Conversion, i.e., Conv = FAEE + MG + DG, whereas the Selectivity is calculated as the sum of FAEE + MG. The differentiation between both parameters is determined by the similarity of the FAEE and MG with the standard n-hexadecane. Therefore, it represents the proportion of biofuel directly comparable with fossil fuels.

#### *2.5. Determination of Kinematic Viscosity*

The kinematic viscosity has been measured in an Ostwald-Cannon-Fenske capillary viscometer (Proton Routine Viscometer 33200, size 150, Proton Technology AB, Sjöåkravägen 28, SE-564 31 Bankeryd, Sweden), determining the time required for a certain volume of liquid to pass between two marked points on the instrument, placed in an upright position. From the flow time (t), expressed in seconds, we obtain the kinematic viscosity expressed in centistokes, υ = C·t, where C is the calibration constant of the measurement system in mm2/s2, which is specified by the manufacturer (0.040350 mm2/s2 at 40 ◦C, in this case). All measures have been carried out in duplicate and are presented as the average of both, proving that the variation is below 0.35% between measures, as required by the standard American Society for Testing and Materials ASTM D2270-79 method for the calculating viscosity index from kinematic viscosity at 40 and 100 ◦C.
