Alkali catalyzed transesterification of kenaf (Hibiscus Cannabinus L.) seed oil by microwave irradiation

• Main Author: Rathana, Yuong
• Format: text
• Language: English
• Published: Animo Repository 2009
• Subjects: Kenaf (Hibiscus Cannabinus L.); Transesterification; Triglycerides; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/3820; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/10658/viewcontent/CDTG004671_P.pdf
• Institution: De La Salle University

Currently, most of the biodiesel is produced from the refined or edible type of oils and fats through transesterification of triglycerides (TG) in the presence of methanol and an alkaline catalyst. However, large amount of non-edible type oils and fats are available such as Kenaf (Hibiscus cannabinus L.) seed oil. The Kenaf seed oil contains large amounts of free fatty acids (FFA) which caused a problem while it is subjected to proceed with alkaline-esterification. These FFAs quickly react with the alkaline catalyst to produce soaps that inhibit the separation of the biodiesel produced and by product, glycerin. A two-step transesterification process by microwave irradiation was applied to convert the high free fatty acid (FFA) oils to its methyl esters. First step, acid catalyzed esterification were done twice under microwave irradiation using 2.25 g of methanol and 0.05 g of sulfuric acid for each gram of FFA content, 5 minutes reaction time, at 65oC. The lowest FFA achieved with this process was 0.31 % (AV = 0.625mgKOH/g). The second step, alkali catalyzed transesterification process, was also done under microwave irradiation using potassium hydroxide as the catalyst and methanol as the alcohol. The four major parameters considered in the second step were catalyst concentration (0.1%, 1%), methanol-oil molar ratio (3:1, 6:1), reaction temperature (50oC, 65oC) and reaction time (5min, 8min). The 24 full factorial designs with center points were applied to this study. Software (MINITAB 14) was used to analyze statistically the effect of those variable parameters on the yield and on the purity of biodiesel produced. The catalyst concentration and temperature were found to have a strong significance on the production yield. The calculated optimum yield* was obtained at 96.31 % and purity at 99.35% using 0.55% KOH catalyst, 4.5:1 methanol-oil molar ratio, 57.5 0C and 6.5 min reaction time. The analyses on the biodiesel produced yielded acceptable result that is in compliance with ASTM standard. This study proved that Kenaf (Hibiscus cannabinus L.) is a promising oil feedstock's and suitable for biodiesel production.