Abstract
Triethanolamine was applied as an efficient ?green? cosolvent for biodiesel production by CaO-catalyzed ethanolysis of sunflower oil. The reaction was conducted in a batch stirred reactor and optimized with respect to the reaction temperature (61.6-78.4?C), the ethanol-to-oil molar ratio (7:1-17:1) and the cosolvent loading (3-36 % of the oil weight) by using a rotatable central composite design (RCCD) combined with the response surface methodology (RSM). The optimal reaction conditions were found to be: the ethanol-to-oil molar ratio of 9:1, the reaction temperature of 75?C and the cosolvent loading of 30 % to oil weight, which resulted in the predicted and actual fatty acid ethyl ester (FAEE) contents of 98.8 % and 97.9?1.3 %, respectively, achieved within only 20 min of the reaction. Also, high FAEE contents were obtained with expired sunflower oil, hempseed oil and waste lard. X-ray diffraction analysis (XRD) was used to understand the changes in the CaO phase. The CaO catalyst can be used without any treatment in two consecutive cycles. Due to the calcium leaching into the product, an additional purification stage must be included in the overall process.
Highlights
Biodiesel represents an alternative to petroleum diesel due to its favorable properties
The presence of TEOA in the present work resulted in a continual fatty acid ethyl ester (FAEE) content increase since the start of the reaction
Even after only 20 min, the FAEE content was 79.3±6.5 %, which was much higher than that achieved in the absence of TEOA (2.3±1.6 %)
Summary
Biodiesel represents an alternative to petroleum diesel due to its favorable properties (biodegradability, low toxicity, reduced CO2 and sulfur emissions, etc.). Methanol is the most commonly used alcohol in biodiesel production, its replacement with ethanol is becoming more popular [1]. Ethanol can be produced from bio-wastes and is less toxic and more soluble in oils than methanol. Fatty acid ethyl esters (FAEEs) possess higher heat capacity and cetane number, as well as better cold-flow and lubrication properties than the respective fatty acid methyl esters (FAMEs) [2]. FAEEs cause lower exhaust gas emissions and have higher biodegradability in water than FAMEs, while higher ester yields are obtained with ethanol than with methanol [3]. Ethanol is more expensive and less reactive in transesterification than methanol and forms an azeotrope with water, making its separation more problematic. Ethanolysis requires more energy, it is more sensitive to the presence of water and results in the formation of more stable emulsions, while FAEEs are more viscous and have higher acid value than FAMEs
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