Author: Kwong, Tsz Lung
Title: Green heterogeneous catalysts for biofuel synthesis
Advisors: Yung, Ka-fu Joseph (ABCT)
Wong, Wing-tak (ABCT)
Degree: Ph.D.
Year: 2016
Subject: Hong Kong Polytechnic University -- Dissertations
Biodiesel fuels
Department: Department of Applied Biology and Chemical Technology
Pages: xliv, 392 pages : color illustrations
Language: English
Abstract: Owing to limited reserve of fossil fuel and the associated environmental pollution, searching for a sustainable liquid fuel has become an important research area to support our future needs. This research encompasses the design, synthesis and characterization of green heterogeneous catalysts for biodiesel synthesis through catalytic transesterification of oils with alcohols, which exhibits high catalytic performance, high durability, high robustness, easy recovery and high compatibility with low grade unrefined feedstock. A srebrodolskite typed calcium iron oxide (Ca₂Fe₂O₅) nanoparticle was synthesized via a direct decomposition of calcium iron containing mixed metal complex. Due to its high surface basicity, its catalytic activity towards biodiesel synthesis was investigated. Through Taguchi orthogonal experimental design method, the optimized oil feedstock conversion up to 99.5 % was achieved by transesterification at 120 °C for 1 hour only. With use of ANOVA test, the reaction temperature is identified as the most prominent factor which contributes 82.84 % to the final catalytic activity. The as synthesized catalyst shows a high free fatty acid (FFA) tolerance with high catalytic activity for one-step simultaneous esterification and transesterification for low grade unrefined feedstock. However, its reusability is relatively low as a significant leaching of active metals is observed.
ZnO nanostar was synthesized by microwave assisted surfactant free hydrolysis and its catalytic activity towards transesterification and simultaneous esterification and transesterification reactions were examined. We found that ZnO reacted with the FFA present to yield zinc oleate (ZnOl) as an intermediate and finally became zinc glycerolate (ZnGly) when the FFA and oil was depleted. Our finding suggests that ZnO does not serve only as a catalyst but also an efficient support for the deposition of the in-situ formed ZnOl and ZnGly to enhance catalyst recovery and stability. The rate of transesterification is highly dependent on the amount of FFA available as it promotes the formation of ZnOl which is an efficient homogeneous catalyst for esterification and transesterification. It proves that the contradicting results reported on ZnO biodiesel catalysis is due to the overlook on the presence of FFA that triggers the formation of ZnOl and ZnGly, overwhelming the low catalytic activity from ZnO itself. The present ZnO nanostar is a promising candidate for transesterification for low grade unrefined feedstock with high activity and high FFA tolerance. A new bimetallic transition metal oxide was synthesized by low temperature calcination of its corresponding bimetallic complex with the presence of polymer and was found to be an efficient catalyst for one-step simultaneous esterification and transesterification of oil with high durability and lifetime. By using Taguchi method, the optimized reaction condition was found to be at 140 °C for 9 hours to give over 99 % conversions. Through ANOVA analysis, the reaction temperature is found to give the highest contribution (94.23 %) to the overall activity. The as synthesized oxide exhibited high reusability with no significant activity drop for 20 cycles and high FFA tolerance up to 30 wt.%. It is surprising to find that the reaction rate can be increased by simply increase the FFA content in the oil to reduce the time to 4 hours only. An improvement of water tolerance was also observed when FFA was added. A different type of bimetallic oxide was synthesized by hydrothermal synthesis with the presence of polymer and was found to show high catalytic performance and high reusability for transesterification at 140 °C for 6 hours only as suggested by the Taguchi method analysis. With the presence of polymer on the catalyst surface, the catalyst shows a faster kinetics towards catalytic transesterification reaction.
Rights: All rights reserved
Access: open access

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