This study focuses on synthesizing and applying a heterogeneous acidic Zirconium metal-organic framework (Zr-MOF) catalyst, UiO-66/SO₃H, for the highly efficient esterification of palm fatty acid distillate (PFAD) with methanol to produce fatty acid methyl ester (FAME). The catalyst was synthesized via the post-synthetic modification of the UiO-66 precursor, specifically aimed at significantly enhancing acid site concentration and catalytic activity.

Comprehensive characterization was performed using techniques including infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. Crucially, ammonia-temperature programmed desorption (NH₃-TPD) quantified the acidic sites, showing a significant increase in acidity from 3.14 mmol/g in the UiO-66 precursor to a high 7.98 mmol/g in the functionalized UiO-66/SO₃H catalyst. Surface textural analysis confirmed that the MOF structure retained stability post-functionalization, with a surface area of 503.02 m²/g, down from 714.77 m²/g for UiO-66.

Initial catalytic screening tests under fixed parameters confirmed the superior performance of the new catalyst. UiO-66/SO₃H achieved an excellent FAME yield of 72.3%, dramatically outperforming the pristine UiO-66, which yielded only 45.9%. Optimization was then rigorously conducted using Response Surface Methodology coupled with Central Composite Design (RSM-CCD). Following 31 experimental runs, the optimal conditions were determined to be a moderate temperature of 75°C, a short reaction time of 1.3 hours, 4.2 wt% catalyst loading, and a methanol to PFAD molar ratio of 21:1. These optimized parameters resulted in a maximum FAME yield of 98.6%.

Reusability tests demonstrated robust stability, as the catalyst maintained high activity for seven consecutive cycles, averaging 72.4% yield. However, a noticeable decline in activity was recorded after the eighth cycle, dropping to 53.8%. Finally, the environmental viability was assessed using Life-Cycle Assessment (LCA) across seven impact categories, including global warming potential (GWP) and acidification potential. The LCA revealed that the PFAD process had a substantial GWP but exhibited lower acidification potential than processes using soybean or lignocellulosic biomass. This advanced method, characterized by minimal methanol and low electricity usage, offers an environmentally friendly and high-efficiency pathway for sustainable biodiesel production.

Figure 1: Graphical abstract

Figure 2: Contour plots for the effect of various binary reaction parameters on biodiesel yield: (a) catalyst loading and reaction time, (b) catalyst loading and methanol to PFAD molar ratio, (c) catalyst loading and reaction temperature, (d) time and temperature, (e) time and methanol to PFAD molar ratio, and (f) temperature and methanol to PFAD molar ratio.

Source:

Chai Balkis Hazmi, Umer Rashid, Bryan R. Moser, Mohd Hafizuddin Ab Ghani, Fahad A. Alharthi, Jeehoon Han, Jiyun Yoo

(https://www.sciencedirect.com/science/article/pii/S2666952824000864)

Date of Input: 31/10/2025 | Updated: 31/10/2025 | roslina_ar