- Title
- Study on the heterogeneous catalytic hydroesterification of varying oil types to develop an understanding of FAME Formation
- Creator
- Mowla, Omid
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Biodiesel, comprised of fatty acid alkyl esters, can be produced from renewable and waste feedstocks and can replace or used as a blend with fossil fuel based petroleum products. Hydroesterification is relatively new and evolving technology for biodiesel synthesis, which is not susceptible to many of the disadvantages of the traditional transesterification process used for biodiesel production. Producing biodiesel via hydroesterification is a two-step process which involves the hydrolysis of the oil feedstock and esterification of the free fatty acids thus produced. The elimination of foaming problems and obviating the deleterious effect of moisture and acidity level of the feedstocks are the main (potential) advantages of the hydroesterification over transesterification. In addition to these advantages, the production of a high purity (and thus high value) glycerol as the primary hydrolysis product stream and the recovery of water from esterification step are additional important advantages of the hydroesterification process that can offset the cost of biodiesel production. Heterogeneous catalysts have the important advantages of being readily separated from the feed and products of reaction by filtration and they can be reused. Zeolites, as porous crystalline aluminosilicate structures with pores that are interconnected to smaller internal channels, have significant adsorption capacities and can be used as catalysts for many chemical reactions. Aluminium atoms located in zeolite framework and located in the zeolite pores provide the Brønsted acid sites which are sites deemed responsible for zeolite activity. This thesis investigates the heterogeneously catalysed hydroesterification of various oils to develop an understanding of hydroesterification biodiesel synthesis process. HBEA zeolite displayed high catalytic activity for biodiesel synthesis via hydroesterification. At low temperatures (T< 100 ºC), no conversion was detected via non-catalysed reaction, but using HBEA zeolite (Si/Al=175) enhanced the hydrolysis and esterification conversion level to 71% and 55%, respectively. The hydrolysis conversion was increased to approximately 90% over HBEA over a zeolites containing additional aluminium (Si/Al=12.5) and for esterification a conversion level of to 80% over HY (Si/Al=6) zeolite was observed. NH3-TPD results showed that zeolites with lower Si/Al ratio have larger number of Brønsted acid sites rendering them as highly hydrophilic but reducing the average strength of their acid sites. Although a greater number of Brønsted acid sites improves the conversion level, the catalyst efficiency, describes in terms of a turnover frequency (TOF), is decreased as the lower strength of the acid sites increases the rate of zeolite deactivation with water. A higher Si/Al ratio in the zeolite induces a greater level of hydrophobicity to the zeolite that in turn leads into higher affinity for the oil and fatty acid molecules to be adsorbed onto the zeolite, and lowers the rate of deactivation due to adsorption of water on to the active site. For both hydrolysis and esterification reactions, HBEA (Si/Al=175) with highest Si/Al ratio showed significantly higher specific rate of reaction (TOF) comparing to the lowest Si/Al ratio zeolite used HY (Si/Al=6).The influence of reaction variables show that presence of acid sites and reaction temperature and stirring rate are the primary, dominating factors for preferred catalytic performance. The potential of zeolite regeneration via thermal treatment was also confirmed, as more than 95% of the original zeolite activity was recovered over a zeolite recalcined at 450 ºC in air. Conducting hydroesterification reactions at various stirring rates from 60 to 600 rpm it was concluded that external mass transfer did not have a significant influence on the observed reaction rate. In addition, conducting reactions over various zeolites at carefully controlled particle sizes ranges (bins), from 50 to 600 μm, no substantial change in the conversion level was observed, which is indicative of the absence of any significant internal mass transfer limitation on the observed reaction rate. The values of Thiele modulus, estimated to be less than 0.4, and rather high activation energy values, 25.9 kJ/mol for hydrolysis and 24.8 kJ/mol for esterification, confirms the kinetically controlled reactions occurring in the absence of significant diffusion limitations. The FTIR analysis indicates the hydrogen bonding interaction of hydroxyl groups of zeolite, which acts as a proton donors, with the both surrogate ester (ethyl acetate) and fatty acid (acetic acid) molecules. The protonation of carbonyl group is also evident via hydrogen bonding with bridging O-H in Si-OH-Al groups (Bronsted acid sites) of the zeolite.
- Subject
- FAME Formation; oil types; heterogeneous catalytic hydroesterification
- Identifier
- http://hdl.handle.net/1959.13/1383618
- Identifier
- uon:31970
- Rights
- Copyright 2018 Omid Mowla
- Language
- eng
- Full Text
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