Parametric study of biodiesel production in supercritical methanol in a tubular reactor

Abstract

Biodiesel production in supercritical methanol (SCM) has several advantages over that employing homogeneous catalysts; i.e. better production efficiency and feedstock flexibility. However, the maximum methyl esters (ME) content, which was found in our continuous SCM reactor, was slightly lower than the batch SCM reactor. The first objective was to investigate effects of co-solvents used for viscosity reduction in scale-up continuous reactor, on ME content. The investigation was successfully done by 2[superscript 3] factorial design and found that the amount of cosolvents had no significant effect on ME content. The second objective was to develop residence time estimation method for continuous production of biodiesel in SCM. A compressible flow model, derived from general mole balance in a tubular reactor, transesterification kinetic of palm oil in SCM, and thermodynamic model (PR-MHV2-UNIQUAC) with adjusted binary interaction parameters was employed. The model was adequate to predict final conversion at below 320℃, when thermal degradation reaction of unsaturated fatty acids (UFA) did not interfere. It was illustrated that development of compressibility factor slowed down the rate of transesterification reaction in SCM in a tubular reactor. Finally, the residence time estimation method based on compressibility changes was successfully attempted and demonstrated that ME content in continuous tubular reactor was only slightly reduced by thermal degradation of UFA at 350℃ and residence time longer than 30 min.