. The first step consists in an acid-catalyzed pretreatment
that converts the FFA content into methyl esters, reducing
acid value below 2 mg KOH/g oil. In summary, 200 g of oil, methanol
(molar ratio methanol to oil of 6:1) and 1 wt.% sulfuric acid as catalyst
were placed into a flat-bottomed flask. The samples were stirred at
300 rpm and kept at 60 °C for 60 min, using a hot plate controlled by
a thermo regulator. After the reaction ending, the reactor content was
transferred to a separating funnel to settle for 1 h. The bottom phase
containing mainly unconverted oil and methyl esters was collected to
carry out the next step