Kunchana Bunyakiat

Biofuel production from palm oil with supercritical alcohols: Effects of the alcohol to oil molar ratios on the biofuel chemical composition and properties

Biofuel production from palm oil with supercritical methanol (SCM) and supercritical ethanol (SCE) at 400 °C and 15 MPa were evaluated. At the optimal alcohol to oil molar ratios of 12:1 and 18:1 for the SCM and SCE processes, respectively, the biofuel samples were synthesized in a 1.2-L reactor and the resulting biofuel was analyzed for the key properties including those for the diesel and biodiesel standard specifications. Biofuel samples derived from both the SCM and SCE processes could be used as an alternative fuel after slight improvement in their acid value and free glycerol content. The remarkable advantages of this novel process were: the additional fuel yield of approximately of 5% and 10% for SCM and SCE, respectively; the lower energy consumption for alcohol preheating, pumping and recovering than the biodiesel production with supercritical alcohols that use a high alcohol to oil molar ratio of 42:1.

Effect of co-solvents on production of biodiesel via transesterification in supercritical methanol

Previous studies on the transesterification of vegetable oil in supercritical methanol in a batch reactor resulted in a non-saponified product with high methyl esters content and high glycerol purity. For the continuous reactor, the high viscosity of vegetable oil might result in problems in the flow system. This study selected THF and hexane as co-solvents to reduce the viscosity of the vegetable oil. The effect of co-solvents was investigated in both 250 mL and 5.5 mL batch reactors by 2-replicate 23 factorial design at temperatures from 290–350 °C, a molar ratio of methanol to vegetable oil from 12–42 and a molar ratio of co-solvent to vegetable oil from 0–5. The reaction time was fixed at 10 min. The products from the employed and unemployed co-solvent process were analyzed by GC-MS to confirm that the reaction among the vegetable oil, methanol and co-solvent was non-existent. However, some thermal cracking was observed in a 250 mL reactor at 350 °C and 30 min reaction time. The amount of co-solvents had no significant effect on methyl esters content and also did not allow the reaction to be completed under milder conditions. Thus, it was concluded that both THF and hexane were appropriate co-solvents to reduce the viscosity of vegetable oil for the continuous production of biodiesel in supercritical methanol.

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 knowledgebase to further develop a better model for continuous production of biodiesel with SCM in a tubular reactor.