Biodiesel Production in a Two-Step Non-Catalytic Process

Biodiesel is an environmentally friendly fuel, which can be used in an unmodified diesel engine. The current commercial process for biodiesel production usually proceeds via the base catalyzed transesterification of triglycerides with methanol. However, Biodiesel from this production path is more expensive than petroleum diesel due to the need in acquiring the purified feedstock. There is interest in developing new processes thatwould produce biodiesel at a lower cost. Non-catalytic processes, typically at supercritical conditions, are among those being investigated. In one such process for catalyst-free biodiesel production, triglyceride is first hydrolyzed to free fatty acids. These are then esterified to make biodiesel in the second step. The schematic of the reaction is shown below.

Hydrolysis of Triglyceride

Esterification of Fatty Acid

We chose this path of biodiesel production and explore wide range of condition beyond the one that already been studied in non catalytic biodiesel process. The kinetics of both hydrolysis and esterification are the aim of our study. We have investigated the second step by studying the esterification of oleic acid with ethanol. The experiments were conducted in quartz tube batch reactors to ensure the absence of unintentional metal catalysis, which has occurred in other studies. The samples were analyzed by high pressure liquid chromatography (HPLC). We explored the effects of temperature, phase behavior, molar ratio of ethanol to oleic acid, and water content in the feed mixture and used these results to determine the kinetics of the reaction. The preliminary results show the possibility of esterification at subcritical condition with less molar ratio of alcohol to oil required and more tolerance to water content in feed than traditional transesterification reaction. The simple kinetic model of single phase and first order respect to each reactant was used. The model shows a good agreement with experimental data in single phase system as shown in figure 1.

Figure 1: Comparison of conversion from experimental data and kinetic model at 200oC, Ethanol: Oleic acid 10:1 and f =0.80

Further complex kinetics model, which includes the phase behavior of the system, will be studied to get more accurate prediction in the two phases systems. The kinetics of triglyceide hydrolysis will also be investigated.