Reaction Kinetics of Biodiesel Production by Using Low Quality Feedstock

Date
2013-10
Authors
Zhou, Ling
Journal Title
Journal ISSN
Volume Title
Publisher
Faculty of Graduate Studies and Research, University of Regina
Abstract

Biodiesel is considered to be one of the potential renewable alternatives to petroleum since it is biodegradable, non-toxic, and has low emission profiles. The main challenge of its commercialization is the associated high production cost due to the high quality feedstock used. Low quality feedstocks such as waste cooking oils are much cheaper and more widely available. However, low quality feedstocks normally contain a large amount of free fatty acids (FFAs), which consume the alkaline catalyst in the biodiesel production, thereby decreasing the biodiesel production rate. An acid-catalyzed esterification process can effectively pretreat the FFAs prior to or during the biodiesel production. Previous studies on biodiesel production processes including esterification and transesterification were conducted in a well-mixed system, in which the hydrodynamic effect on the reaction could not be completely defined. Therefore, the objective of this research is to provide a better understanding of the reaction kinetics of acid-catalyzed esterification and alkali-catalyzed transesterification for optimizing the biodiesel production process when using low quality feedstocks. This study developed a new reaction system of esterification reaction in an immiscible two-phase system, which eliminates the hydrodynamic effect on the reaction. Based on the new reaction system, a series of experiments were conducted by using oleic acid/linoleic acid as FFA to mix with the virgin canola oil as a low quality feedstock. The reaction rate constant and activation energy of esterification were determined at different temperatures. The impact of different reaction variables was evaluated in terms of FFA conversion or acid value, including: temperature, catalyst concentration, initial FFA content, and type of FFA. Results showed that reaction temperature, catalyst concentration, and initial FFA content had great impacts on the esterification. The effect of the catalyst concentration also depends on the reaction temperature. It had a significant impact on esterification at high temperatures of 50°C and 62°C, but little impact at the low temperature of 35°C. Additionally, an increase in initial FFA content increased the reaction rate instead of the reaction rate constant. The reaction performance of oleic acid and linoleic acid were also compared in terms of reaction rate constant and activation energy. Oleic acid and linoleic acid were found to have the same reaction behaviour under the same reaction conditions. The parametric effect on the alkali-catalyzed transesterification reaction was also evaluated in terms of FAME (fatty acid methyl esters, biodiesel) content (wt.%) of the reaction product as a function of reaction time. The experiments were carried out in a different experimental setup by using virgin canola oil as feedstock to react with methanol catalyzed by sodium hydroxide (NaOH). The tested reaction parameters include reaction temperature, catalyst concentration, and initial FFA content. The biodiesel production rate was found to increase as the reaction temperature increased regardless of the catalyst concentration. The achieved maximum biodiesel content ranged from 86 to 90% (w/w). An increase in catalyst concentration led to a higher biodiesel production rate, and as expected, high contents of FFA decreased the biodiesel production rate and made the subsequent separation process difficulty due to the undesirable soap formation. Based on the kinetics study on transesterification, the reaction kinetics were found to be different for low temperatures (25oC and 35oC) and high temperatures (50°C and 65°C), which resulted in different designs for reactor volume for a given duty based on different temperatures.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Applied Science in Environmental Systems Engineering, University of Regina.xiv, 125 p.
Keywords
Citation
Collections