A comparison of heterogeneous and homogeneous catalysts for the transesterification of refined, bleached and deodorized coconut oil

• Main Authors: Diamante, Joseph Angelo R., Tan, Millicent C., Yan, Lee Rainier C.
• Format: text
• Language: English
• Published: Animo Repository 2008
• Subjects: Catalysts; Methanol; Coconut oil; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/5765
• Institution: De La Salle University

This study had the primary objective of evaluating a strong base anion exchange resin (PA306s provided by Mitsubishi Chemicals) as a substitute for the homogenous catalyst sodium methoxide in the transesterification of coconut oil using anhydrous methanol. The free fatty acid content of the oil was first determined through titration with 1 M NaOH. The performance of the PA306s as a transesterification catalyst was then compared to that of sodium methoxide, in terms of glycerol byproduct quality. The effects on conversion of specific parameters, namely, varying temperature from 40ËšC to 60Ëš, varying agitation time from 1 to 2 hours, varying catalyst-liquid ratio from 1:200 (w/w) to 1:150 (w/w), and varying methanol : oil weight ratio from 1:6 (w/w) to 1:4 (w/w) were also determined. Finally, the stability of the anion exchange resin was assessed by regeneration. The newly-developed method of preparing PA306s involves washing the resin in 7% anhydrous sodium methoxide overnight, and then washing the treated resin with anhydrous methanol. The coconut oil used in both homogeneous and heterogeneous-catalyzed transesterification had a free fatty acid value of 0.0198%. The glycerol byproduct produced using the PA306s resin as catalyst was colorless, as compared to the amber-colored glycerol byproduct produced using sodium methoxide as catalyst. The biodiesel phase from the heterogeneous-catalyzed transesterification had an average acid value of 0.16 mg KOH/g, average water content of 0.323%, average methanol content of 1.45%, average methyl laurate content of 47%, average specific gravity of 0.892 and average total glycerol of 7.26%. The minimum percent conversion for batch transesterification using pretreated PA306s resin as heterogeneous catalyst reached 83.43% for one set of input parameters, as compared to 96.83% for the homogeneous catalyzed reaction. When a line fit analysis was used to correlate conversion to the input parameters, the line fit analysis showed that conversion in the resin-catalyzed transesterification was barely dependent on varying temperature, catalyst-feed ratio and methanol-oil ratio. In contrast, transesterification using homogeneous catalyst appeared to be influenced by methanol-oil ratio and by temperature. The rate-controlling step in heterogeneous-catalyzed transesterification is mass transfer, specifically external diffusion, as suggested by the results of experiments using intense manual agitation and by the relatively low sensitivity of percent conversion with temperature. The resins were proven to be stable for up to three uses. When the catalyst was regenerated, the volume of the glycerol phase formed after the second run was only 9.52% less than that formed after the first run, as compared to 36.36% when the catalyst was not regenerated.