Abstract
In this study, low quality oils (waste cooking oils) with high acid value (4.81 mg KOH/g) were utilized as the feedstocks for a transesterification reaction enhanced by additional microwave power and the use of an NaOH catalyst. The kinetics of the transesterification reaction under different reaction times and temperatures was studied. It was found that in the microwave-assisted transesterification reaction, the optimum conditions under a microwave power of 600 W were as follows: an NaOH catalyst of 0.8 wt %, a 12:1 molar ratio of methanol to oil, a reaction time of 2 min, and a reaction temperature of 65 °C. The conversion of waste cooking oil into biodiesel reached 98.2% after this short reaction time. This result conformed to 96.5% of the standard value of Taiwan CNS 15072. In addition, with increases in the reaction temperature from 55 to 65 °C, the reaction rate constant increased from 0.635 to 2.396 min−1, and the activation energy required for the transesterification reaction was 123.14 kJ/mole.
Highlights
In the present world, a shortage of energy resources has been foreseen
The use of homogeneous catalysts to produce biodiesel has a high conversion rate and a fast reaction, but due to the following reasons, it has some disadvantages in the production of biodiesel: (1) the catalyst has to be neutralized when the reaction is completed and cannot be reused; (2) continuous processing methods are limited; (3) it is technically difficult to remove the catalyst; (4) cleaning and separating products and catalysts will produce a lot of wastewater; and (5) reactant purity and free fatty acids (FFA) content affect the process quite sensitively
The results showed that, with an NaOH catalyst of 1.0 wt %, due to the saponification problem occurring at the lowest molar ratio of 3:1, there was a rather low conversion rate of about 71%
Summary
A shortage of energy resources has been foreseen. Fossil fuels are gradually being replaced by sustainable fuels, one of which is biodiesel. One of the most promising methods for sustainable fuels is to convert vegetable oils and other raw materials that mainly contain triglycerides (TGs) and free fatty acids (FFA) into biodiesel [1]. The use of homogeneous catalysts to produce biodiesel has a high conversion rate and a fast reaction, but due to the following reasons, it has some disadvantages in the production of biodiesel: (1) the catalyst has to be neutralized when the reaction is completed and cannot be reused; (2) continuous processing methods are limited; (3) it is technically difficult to remove the catalyst; (4) cleaning and separating products and catalysts will produce a lot of wastewater; and (5) reactant purity and free fatty acids (FFA) content affect the process quite sensitively.
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