Continuous Production of Biodiesel with Supercritical Methanol: a Simple Compressible Flow Model for Tubular Reactors

From an industrial point of view, the continuous process for biodiesel production with supercritical methanol (SCM) is more appropriate than the batch process. However, lab-scale studies on the continuous process have shown that the maximum conversion always remains slightly lower than that obtained in the batch process. This work proposes a simple compressible flow model to predict the conversion of methanol and oils into methyl esters (ME) along the length of a tubular reactor and further demonstrates the effect of the development of the compressibility factor of the reaction mixture upon the conversion efficiency to ME. The governing equation was derived from a general molar balance in the tubular reactor using transesterification kinetics of refined-bleached-deodorized (RBD) palm oil in SCM coupled with a suitable thermodynamic model with adjusted binary interaction parameters. Vapor-liquid equilibrium data for triolein + methanol, methyl oleate + methanol and glycerol + methanol mixtures were obtained from the literature and then refitted with the thermodynamic model consisting of the Peng-Robinson equation of state and MHV2 mixing rules to find the set of adequate interaction parameters. In order to check the validity of the proposed model, the predicted ME contents were compared with observed values in a lab-scale continuous reactor at various operating temperatures, pressures and methanol to oil molar ratios. The proposed model proved to be adequate for predicting the final conversion to ME for operating temperatures below 320°C, when the thermal degradation reactions of unsaturated fatty acids did not interfere. Our results also illustrate the importance of taking into account the development of the compressibility factor with time and reactor length, since this was shown to be the cause of the lower transesterification reaction rate in the tubular SCM process. The findings in this work could be employed as a knowledge base to further develop a better model for continuous production of biodiesel with SCM in a tubular reactor

In-situ Transesterification of Jatropha curcas L. Seeds for Biodiesel Production using Supercritical Methanol

In-situ supercritical methanol transesterification for production of biodiesel from Jatropha curcas L. (JCL) seeds was successfully being carried out via batch-wise reactor system, under varying temperatures of 180 - 300 °C, pressures of 6 - 18 MPa, reaction time of 5 - 35 min and seeds-to-methanol ratio of 1:15 - 1:45 (w/v). In this study, the extracted oil obtained showed the presence of FAME referring as biodiesel, indicating that transesterification reaction had occurred during the extraction process. The results showed that the biodiesel yield was obtained at optimum conditions of 280 °C, 12 MPa, 30 min and 1:40 (w/v) were 97.9%