Development of mangosteen peel ash as a heterogeneous catalyst for palm oil-derived fatty acid methyl ester production

Importance of the work: A solid carbon catalyst was derived from mangosteen peel ash (MA) activated by potassium hydroxide and used as a support for potassium carbonate (K₂CO₃). It was prepared as a heterogeneous catalyst for the transesterification of palm oil to fatty acid methyl esters. Objectives: A central composite response surface methodology was used to optimize the biodiesel yield. The effects were investigated of different K₂CO₃impregnation levels on MA (0 by weight percentage (wt.%), 25 wt.%, 30 wt.% and 35 wt.%) and then on the catalyst loading (2.32-5.68 wt.%), the methanol-to-oil molar ratio (3.95:1-14.05:1), and the reaction time (39.55- 140.45 min) of the transesterification reaction at 65 °C. Materials & Methods: The mangosteen peel was procured from Songkhla province, Thailand and the palm oil was purchased from a local supermarket in Songkhla province. The catalysts were prepared using the incipient wetness impregnation method and applied for transesterification of palm oil with methanol to produce biodiesel. The reaction process was optimized in terms of the biodiesel yield using response surface methodology based on a central composite design. Results: The results demonstrated that the catalyst consisting of 30 wt.% K₂CO₃loaded MA (30K-MA) had the highest catalytic activity. Using the 30K-MA catalyst at 65 °C, the maximum biodiesel yield of 97.9% was prodcued at a catalyst loading of 4.5 wt.%, a methanol-to-oil molar ratio of 10.8:1 and a reaction time of 98.7 min. Main finding: The 30K-MA catalyst maintained sufficient catalytic activity (above 65% biodiesel yield) until the fourth reaction cycle, demonstrating the possibility of developing heterogeneous alkali catalysts from MA for biodiesel production.