Second step transterification

The production methodology followed in this study was according to Tomosevic and Si — ler-Marinkovic [2003] with some modification, where the alkali-catalyzed transesterifica­tion was applied. Basically, methanol was the alcohol of choice and KOH was used as the catalyst. Potassium methoxide solution (PMS) was prepared freshly by mixing a pre­determined amount of methanol (« 12 wt % of oil) with KOH (« 1.0 wt % of oil) in a container until all the catalyst dissolved. The PMS was then added to 200 g of oil and

stirred vigorously for 30 min at 30oC. Then after, the mixture was carefully transferred to a separating funnel and allowed to stand for 4 h. the lower layer (glycerol, methanol and most of the catalysts) was drained out. The upper layer (methyl esters MEs, some methanol and traces of the catalyst) was transferred into another flask containing fresh­ly prepared PMS mixed at 60 rpm under reflux at 60oC for 30 min. afterwards; the mix­ture was carefully transferred to a separating funnel and allowed to stand there over night. The glycerol was removed by gravity settling, whereas the obtained crude esters layer was transferred into water bath to remove excess methanol at 65oC and 20 kPa. The obtained crude methyl esters were then cleaned thoroughly by washing with warm (50oC) deionized water, dried over anhydrous Na2SO4, weighted and applied for further analy­sis (Shalaby and Nour, 2012; Shalaby, 2011).

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