Ethyl ester production from palm fatty acid distillate (PFAD) with ethanol in the presence of sulfuric acid and potassium hydroxide was performed in a continuous three-step process using the ultrasound clamps and an ultrasonic probe. The ultimate goal was to produce biodiesel from the PFAD. In the first and second esterification steps, 16 units of a 400 W ultrasound clamp (20 kHz) were attached 100-m apart along each tubular reactor. In the third transesterification step, a 1000-W ultrasonic homogenizer (18 kHz) was used in a 100-mL continuous reactor. A composite central design of experiments and the response surface methodology (RSM) were used to develop predictive models and identify the optimal conditions of each step based on the purities of ethyl ester. The optimal conditions in the first step were 46.1 vol.% ethanol, 1.4 vol.% sulfuric acid, and purity 66.68 wt.% ethyl ester. In the second step, the optimized conditions were 57 vol.% ethanol, and 2.1 vol.% sulfuric acid, purity 95.32 wt.% ethyl ester. The final transesterification step was carried out with 14.6 vol.% ethanol and 3.9 gKOH L⁻¹. As a result, a final ethyl ester purity of 98.15 wt.% was achieved in the biodiesel using the three-step process.

This research focuses on the acid value reduction in crude palm oil (CPO) achieved through an esterification process with different types of ethanol in batch and circulation processes. The esterification process was optimized by varying three independent variables, the ethanol content, sulfuric acid (H₂SO₄) concentration, and reaction time, using a response surface methodology to determine the optimal conditions for the acid value reduction in the esterified oil. Three grades of ethanol—95% hydrous ethanol, 99% anhydrous ethanol, and 99% analytical reagent (AR) ethanol—were used to study the batch esterification process. The optimal conditions for hydrous ethanol were 82.7 vol.% ethanol content, 10.6 vol.% H₂SO₄ concentration, and 25.4 min reaction time; for anhydrous ethanol, the optimal conditions were 78.1 vol.% ethanol content, 10.2 vol.% H₂SO₄ concentration, and 26.3 min reaction time; for AR-grade ethanol, the conditions were 77.7 vol.% ethanol content, 10.5 vol.% H₂SO₄ concentration, and 28.6 min reaction time. The experimental results indicate that the acid value of esterified oil could be reduced under optimal conditions using hydrous ethanol, anhydrous ethanol, and AR-grade ethanol at concentrations of 1.85 mg KOH/g, 0.97 mg KOH/g, and 0.95 mg KOH/g, respectively. Anhydrous ethanol had the most cost-effective production. Therefore, anhydrous ethanol was selected to study acid value reduction in esterified oil in a circulation esterification process to increase process efficiency. The results showed an acid value of 1.42 mg KOH/g under optimal conditions of 66.9 vol.% anhydrous ethanol content, 7.3 vol.% H₂SO₄ concentration, and 27.7 min circulation time, with a production cost of 0.460 USD/batch. The circulation esterification process can reduce ethanol content, H₂SO₄ concentration, and production costs by 14.34%, 28.43%, and 16.21%, respectively, compared to the batch esterification process, resulting in significant reductions in chemical and production costs.

This study focuses on the fabrication and application of heterogeneous acid catalytic filaments for free fatty acid (FFA) reduction in crude palm oil (CPO) via esterification. Amberlyst-15 catalyst was blended with acrylonitrile butadiene styrene (ABS) using a single-screw filament extruder to produce Amberlyst-15/ABS catalytic filaments. A 5 wt.% concentration of fine Amberlyst-15 particles was considered optimal for blending with ABS, making them a suitable acid catalyst for FFA reduction. The mechanical properties, thermal behavior, and morphology of the Amberlyst-15/ABS catalytic filaments were assessed. The esterification process was optimized by varying three independent variables: the methanol-to-oil molar ratio, catalytic filament loading, and reaction time. The results revealed that under the recommended conditions—26.7:1 methanol-to-oil molar ratio, 78.5 wt.% catalytic filament loading, and a reaction time of 20.2 h at 500 rpm and 60 °C—the FFA content in CPO was reduced from 10.05 to 0.83 wt.%. Additionally, the reusability of the catalytic filaments was evaluated under the recommended conditions of the esterification process. The results demonstrated that the filaments remained effective for at least two cycles, achieving FFA levels below 2 wt.%, thereby confirming their stability and catalytic efficiency. The methodology employed in this study for the preparation and characterization of Amberlyst-15/ABS catalytic filaments offers a promising approach for fabricating acid catalytic materials via 3D printing, especially for heterogeneous catalysis in esterification reactions.