Continuous production of biodiesel with supercritical methanol: Optimization of a scale-up plug flow reactor by response surface methodology

A scale-up plug flow reactor was evaluated for the continuous production of biodiesel from refined palm kernel oil (PKO) with supercritical methanol and optimized by response surface methodology. The effects of the operating temperature (270–350 °C), pressure (15.0–20.0 MPa) and methanol:PKO molar ratio (20:1–42:1) were evaluated at a constant residence time of 20 ± 2 min by using a central composite design. Analysis of variance demonstrated that a modified quadratic regression model gave the best coefficient of determination (R2 = 0.9615) and adjusted coefficient of determination (Adj. R2 = 0.9273). The interaction terms in the regression model illustrated small synergistic effects of both temperature–pressure and temperature–methanol:PKO molar ratio. The optimal conditions were 325 ± 5 °C, 18.0 ± 0.5 MPa and a methanol:PKO molar ratio of 42 ± 2:1, attaining a maximum production rate of 18.0 ± 1.5 g biodiesel/min with a fatty acid methyl ester content of 93.7 ± 2.1%. The product obtained from the optimal conditions had high cetane number, and could be considered as a fuel additive for cetane number enhancement.

Graphical abstractThe biodiesel production from palm kernel oil (PKO) with supercritical methanol in a scale-up tubular reactor was evaluated and optimized by response surface methodology. The effects of temperature, pressure and methanol: PKO molar ratio was investigated by central composite design. The response surface of the % FAME content versus the operational temperature and pressure at a methanol: PKO molar ratio of 42:1 was shown. A FAME content of over 96.5% is shown by the grey shading, and it could not found a FAME content of over 96.5% at a methanol: PKO molar ratio below 40:1. Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Biodiesel production with SC methanol in a scale-up flow reactor was investigated. ► Max. production rate is 18.0 ± 1.5 g biodiesel/min with FAME content of 93.7 ± 2.1%. ► FAME content of 96.5% could not found at methanol to oil molar ratio below 40:1.