Scheme 1 | Scientific Reports

Scheme 1

From: Nano-synthesis of solid acid catalysts from waste-iron-filling for biodiesel production using high free fatty acid waste cooking oil

Scheme 1

Proposed mechanism for the trans-esterification reactions on AlFe2O3/SO4. From Scheme 1, item (a) is the RBCs active chemical compound that was developed from calcination and sulphonation of α-\({\text{ Fe}}_{2} {\text{O}}_{3}\) synthesized from WIF. Generally, a reaction catalyzed by mineral acid and metal ions such as Al–O=Fe–O–Fe=O/SO4 generates hydrogen ion (H+) in the initiation step through the protolysis of the \({\text{CH}}_{3} {\text{OH}}\) as shown in item (b). The next stage of the reaction is the protonation of the carbonyl group in the triglyceride by the metal ions in the solid acid catalyst as shown in item (c) to form methyl ester and a diglyceride anion as shown in item (d). This cycle is repeated from item (e) to (f), forming another methyl ester and a monoglyceride anion as shown in item (g). It is repeated the third time as shown in items (h) and (i) to form another methyl ester and glycerol as shown in item (j). From each cycle, Al–O=Fe–O–Fe=O/SO4 component of the RBCs is recovered, which is a good characteristic of solid catalysts.

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