Graduation Semester and Year

2011

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Brian Dennis

Abstract

Biodiesel, Fatty Acid Methyl Ester (FAME), is a renewable fuel that is a promising alternative to fossil fuels in the future. Biodiesel not only has similar properties to diesel derived from fossil fuel, but it also provides more environmentally friendly due to lower carbon monoxide and sulfur emissions. Biodiesel is composed of methyl esters which can be synthesized from various fatty acid sources with a present of catalyst. Typical feed-stocks include vegetable oils, such as waste cooking oil, animal fats, and even oil from algae. Four primary ways to use vegetable oil as a fuel are direct use, blending with diesel via a co-solvent, using oil produced by thermo cracking (pyrolysis), and using methyl esters made by transesterification/esterification. The transesterification process is the most frequently used methods for making biodiesel because it gives the fuel that has similar or better properties as diesel fuel. However, most biodiesel is still produced using batch reactor technology that is decades old. Improvements in biodiesel quality and economics can be achieved by employing alternate reactor technology for biodiesel synthesis that can reduce reactor size and energy consumption. Recently, microreactor technology, an important method of process intensification, was widely used to apply in biodiesel to reduce the residence time. In addition, the biodiesel producers typically employs as catalyst to speed the transesterification reaction. The catalysts are usually homogeneous bases but strong acids can work as well. In this work, the use of capillary reactor technology for the intensification of transesterification was studied. Both homogeneous alkaline and heterogeneous acid catalysis were investigated. Reactions were conducted experimentally in stirred batch and continuous flow capillary reactors. To confirm the intensification process, the titanium micro-reactor was also presented to verify the rapid mass transfer in microscale. Moreover, the batch reactor and capillary reactor are compared to show the effectiveness of biodiesel production in capillary reactor. The results show that, from the homogeneous alkali-catalyst, conversion of vegetable oil greater than 98% could be achieved for significantly lower residence times and energy input compared to the stirred batch reactor case. This enhanced performance was due to the intensification of mass and heat transfer enabled by the use of the capillary reactor. In order to reduce the purifying process, the experiment is investigated the use of a heterogeneous acid catalyst for the transesterification reaction in a capillary reactor. The catalyst will be immobilized in the reactor as a packed bed of micro-particles. The results indicated that high surface area of packed bed reactor gave the 84% oil conversion with a significant reducing in residence time for 1 h. Because of the micro-particles, there was to high pressure drop in the reactor during the experiment. A mathematical model for the multiphase flow in a capillary including transesterification reaction kinetics was developed. The model was solved approximately using a time accurate finite element-based computer code. The predictions made by the model follow the same trends observed in the experiments.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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