Microreactors for biodiesel synthesis: design, fabrication, and characterization

Abstract

The present work describes microreactors for biodiesel continuous synthesis that have been designed, fabricated, characterized, and aimed at achieving a reproducible microfluidic device to compose a modular portable biodiesel production demonstration unit. A straightforward method is presented for the microfabrication and sealing of the microfluidic device that performs the role of a microreactor for biodiesel synthesis, built on a brass metal base and sealed with either a metal cover or a glass cover for easy microscopic observation of two-phase flow patterns. The microfluidic device contains a Υ-junction squared microchannel architecture with width and depth of 400 µm. Microchannels were engraved using a micromilling technique and sealed either by welding, with tin as an additional material, in the case of the all metal device, or by using an epoxy glue, which served as an adhesive to seal a metal−glass device. The quality of the metal-on-metal seal was examined using microscopic analysis of multiple cross sections of the device, whereas the quality of the metal-on-glass seal was analyzed via direct visual inspection of flows within the device using an optical microscope to verify the existence or absence of leaks. An experimental setup was then built to carry out biodiesel synthesis in the metal−metal microreactor, using soybean oil of food grade, absolute ethanol, and sodium hydroxide, NaOH, as a catalyst for the reaction. For a molar ratio ethanol/oil 20:1, a quantity of NaOH catalyst of 1.0 wt.% at a controlled temperature of 47.5°C, it was possible to achieve a yield of fatty acids ethyl esters of 87.2% with 98% of triglyceride converted, for a residence time of 10 min. The experimental analysis confirms the applicability potential of the designed microreactor in the synthesis proposed.