Biodiesel is a green, low-carbon, and renewable fuel with the potential to substitute fossil fuels. The effects of reaction temperature (175–290 °C), residence time (5–75 min), and molar ratio of methanol to palmitic acid (6:1–35:1) on the non-catalytic esterification of palmitic acid with methanol to produce biodiesel were investigated by using a batch reactor. Moreover, the reaction parameters were optimized by using the response surface methodology (RSM), and the reaction kinetics were analyzed. The results showed that the conversion rate of palmitic acid to methyl palmitate increased to 100% as the reaction temperature rose from 175 °C to 225 °C, slightly changed until 275 °C, and then decreased to 94.81% at 290 °C. The conversion rate increased with residence time and reached the maximum value of 94.93% at 60 min. With increasing the molar ratio, the conversion rate rose to a maximum value of 85.46% at 15:1 and subsequently decreased. RSM results indicated the relative influence of factors on the conversion rate as reaction temperature > residence time > molar ratio. The optimal reaction parameters were 224 °C, 26 min, and a molar ratio of 16:1, affording a palmitic acid conversion rate of 99.30%. The esterification reaction between methanol and palmitic acid follows the first-order kinetics model.

Biodiesel is a promising green and renewable fuel that can replace fossil fuels and reduce greenhouse gas emissions. The effects of reaction temperature (200–290 °C), residence time (0–75 min), and methanol-to-oleic acid molar ratio (6:1–35:1) on the esterification of oleic acid with supercritical methanol were investigated in a batch reactor. Furthermore, orthogonal experiments were designed to explore the optimal reaction conditions. and the influences of H₂O (0–33.3 wt%) and Fe (0–20.0 wt%) contents were examined. Results showed that the conversion of oleic acid to methyl oleate exhibited a volcano-type dependence on both temperature and molar ratio, peaking at 250 °C and a ratio of 15:1, respectively. Conversion initially increased with residence time, then plateaued around 30 min. Under the optimal conditions of 250 °C, 30 min, and a 15:1 molar ratio, the conversion reached 76.8%. Both additives enhanced conversion at low loadings (≤5.0 wt%). However, higher water content inhibited conversion, whereas the promotional effect of Fe saturated beyond 5.0 wt%. The co-addition of 5.0 wt% water and 5.0 wt% Fe yielded a positive but sub-additive effects: conversion exceeded that with water alone but remained lower than with Fe alone. These findings contribute to advancing the high-efficiency and low-cost production of biodiesel.