(726c) Fuel Me up!

An engineer should have the capability of combining various disciplines for solving complex problems in challenging environments. This work presents a case study for bachelor students in chemical engineering combining experimental and modeling work. A wide variety of (chemical) engineering topics is covered, among others chemical reactors, unit operations, analysis techniques, kinetic modeling and transport phenomena. The starting point for this was a radio controlled (RC) model car equipped with a glow engine, which is of the internal combustion type. Typical fuels for such a 2 stroke engine consist of a mixture of 10 – 40 % nitromethane mixed with methanol and additives for lubrication. In the framework of evolving towards a more sustainable society, the students’ assignment was to produce a bio based fuel and have the car running.

Because of the open-ended character of the assignment, an overview of possible renewable alternatives was composed and resulted in the selection of bioethanol and biodiesel for an in-depth study. A multi scale approach was used for a critical evaluation of the two biofuel candidates: experimental study, kinetic modeling and industrial plant simulation.

For the bioethanol production, a lab scale fermentation was performed starting from sugar and baker’s yeast. Special attention was given to the necessity for nutrient addition  and the effect of ethanol on the performance of the yeast. For fuel application purposes, the ethanol mixture obtained after fermentation needs to be more concentrated via distillation. Due to the presence of an azeotrope between 95-96% ethanol in water, not all water could be removed. The ultimately obtained ethanol concentration was determined using a density measurement and amounted to ± 93%. The biodiesel production occurred through the transesterification of a triglyceride, e.g., sunflower oil, with an alcohol, i.e., methanol, using a homogenous catalyst, i.e.,  NaOH. A hands-on approach was required to acquire reliable lab scale information on the reaction kinetics: ensuring that all reagents are dry prior to reaction, phase mixing during reaction and purification of the product by catalyst removal and separation of the organic biodiesel phase from the polar glycerol-methanol phase.

The product analysis for both the bioethanol and biodiesel experiments were performed  via spectroscopic techniques. UV/VIS was used to study the progress of fermentation while FTIR-ATR was used to follow the yield of biodiesel as function of time. For the latter, a simple kinetic model was used to describe the experimental obtained data. Several preliminary industrial plant configurations for biodiesel production were designed using this kinetic model and were evaluated via ASPEN.

Finally, a fuel was composed using the produced ethanol and biodiesel to substitute resp. the methanol and lubrication components in the original RC car fuel.  Nitromethane still needed to be added to this mixture to ensure the proper ignition of the fuel. The fuel was successfully tested in a RC car by the students. Overall, the project resulted in a critical evaluation of biofuels indicating both the opportunities and challenges of a bio-based society.