Numerical Simulation of Multiple Step Transesterification of Waste Oil in Tubular Reactor

Abstract

Biodiesel is considered as a sustainable alternative to diesel fuel, as it can be utilized in current internal combustion (IC) diesel engine without any modification. It is transesterified from the combination of methanol or ethanol and triglycerides to form monoalkyl ester under the presence of catalyst. In this work, a newly designed continuous tubular reactor is modeled using coupled reactive flow. The model is based on Navier-Stokes, three-dimensional (3D), multiple-fluid species, turbulent internal flow for reactive and nonreactive flow. In particular, this work entails a nonreactive flow to estimate the total residence time and pressure drop in a newly developed tubular reactor assembly. The residence time in the new reactor found to be nearly an order of magnitude larger than the length-based transfer time under reasonable pressure drop. With the intent of developing a robust numerical model, a parametric study of the reactive flow was conducted. The simulation accounts to the different reaction temperatures and reactants molar ratios. The results demonstrated that higher conversion and product yield is achieved at higher temperature and prior to reaching boiling of the alcohol; whereas a lower product is achieved at higher alchol:oil ratios. The latter result is due to departing from the stoichiometric state (dilution of the flow) and to the reverse reaction.