Date of Award

5-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical and Chemical Engineering

Advisor(s)

Lawrence L. Tavlarides

Second Advisor

Benjamin Akih-Kumgeh

Keywords

transesterification reaction, biofuels

Subject Categories

Chemical Engineering

Abstract

The transesterification reaction in supercritical methanol between various oil feed stocks and alcohols is proposed as an alternative cost effective method to produce biofuels. Two studies were conducted related to this process in order to (a) supplement a previous kinetics study to better understand the reaction mechanism and (b) assess basic reaction conditions for effective conversion of microalgae oil to biofuels in supercritical methanol.

A one-step transesterification reaction has been used in some supercritical batch experiments to explain the kinetic results (He, Sun, Wang, & Zhu, 2007; Kusdiana & Saka, 2001). However, one-step kinetic models ignore the detailed multi-step reaction mechanism and cannot be used to predict the concentration of the intermediates. In this study, reactions were conducted in a continuous flow reactor of supercritical methanol with a model triglyceride compound, triolein (C57H104O6), under various reaction conditions to study the consecutive reactions of this compound and to better understand the reaction kinetics of this transesterification reaction. Triolein is a major triglyceride component in many types of feedstock, such as 40 wt. % in palm oil, 40 wt. % in olive oil, 64 wt. % in rapeseed oil, and 41 wt. % in chicken fat. The effects of process variables (residence time and temperature) on triglycerides conversion and formation of intermediates were assessed. A three-step kinetic model for biodiesel production in supercritical methanol is proposed based on experimental data obtained earlier (Cong & Tavlarides, 2010) and augmented with the experiments and analysis conducted during this work.

The second objective of this study was to determine suitable conditions for the transesterification of microalgae oil with supercritical methanol. Experiments were conducted using microalgae oil at different methanol-to-oil molar ratios (6:1 to 12:1), temperatures (350 to 400 oC), pressures (150 to 300 bar), and residence times (3 to 12 min) in order to find an appropriate reaction condition. The effects of temperature, pressure, molar ratio of the reactants, and residence time on conversion and free glycerol content were assessed. In particular, the kinetic model proposed above for triolein was applied to this system to predict reaction conversion at 385 oC, 200 bar, molar ratio of 9:1, and residence time from 4 to 10 min. These results demonstrate the potential for use of transesterification reactions in supercritical methanol to produce biodiesel fuels from microalgae oils.

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