What is it about?
Ethanolysis of four different vegetable oils (sunflower, soybean, cotton seed, and used frying oil) was studied using sodium ethoxide as a catalyst. The ester preparation involved a two-step transesterification reaction, followed by purification. The effects of the mass ratio of catalyst to oil, the molar ratio of ethanol to oil, and the reaction temperature were studied on conversion of sunflower oil to optimize the reaction conditions in both stages. The rest of the vegetable oils were converted to ethyl esters under optimum reaction parameters. Ethyl esters of four different types of vegetable oils were blended with the diesel fuel at 2 %, 5 %, 10 %, and 20 %, on a volume basis. The experimental results showed that the densities and viscosities of the blends increased with the increase of biodiesel concentration in the fuel blend. Cold flow properties were negatively affected as ethyl ester content was increasing. Distillation characteristics and cetane indexes were not significantly altered. These results are promising, and ethyl esters can be seen as a viable fully renewable alternative to petroleum diesel.
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Why is it important?
The second and most important reason why this study was undertaken came about as a result of the M/393 Mandate of the European commission to CEN for the development of a European Standard for Fatty Acid Ethyl Ester (FAEE) to be used as a fuel for diesel engines. To briefly outline what the mandate entails it should be noted that the European market is characterized by a significant and continuously growing demand for diesel fuel. Therefore the demand for diesel fuel type replacements is significant greater than that for gasoline. Bioethanol has been used in the European market mainly as ETBE (ethyl tert butyl ether) on the basis of the specifications of the Fuel Quality Directive 98/70/EC and its amendments. Although used in low blends (5 %), as ETBE and E85, bioethanol still faces problems to penetrate the European market further.
Perspectives
The following conclusions can be drawn from this study: • The sodium ethoxide is an active and promising homogeneous catalyst for the production of ethyl esters. • The optimized reaction conditions for one stage transesterification of vegetable oils were a 12:1 molar ratio of ethanol to oil, the addition of 1 % NaOCH2CH3 catalyst, a 80C reaction temperature, and about 2.5 h of reaction time. • The two-stage transesterification improved the results obtained in the single-stage transesterification. An improvement of about 16 % in relation with the one-stage transesterification, was obtained under the following optimal conditions: Catalyst concentration 0.75 %, ethanol/oil molar ratio 6:1 and 30 min of reaction time. • The values of density, viscosity, and higher heating value of ethyl esters were similar to those of automotive diesel. However, the CFPP values were higher, which may conduce to potential difficulties in cold starts. On the other hand, the flash points, which were higher than those of diesel fuel constituted a safety guarantee from the point of view of handling and storage. • The density and viscosities of the blends increased with the increase of biodiesel concentration in the fuel blend. Cold flow properties were negatively affected as ethyl ester content was increasing. Distillation characteristics were affected mainly at the higher ethyl esters concentrations. Cetane indexes were in all cases improved, and especially at the higher ethyl esters contents.
Associate Professor Stamatios S. Kalligeros
Hellenic Naval Academy
Read the Original
This page is a summary of: Fuel Quality Assessment of Ethyl Esters Produced from Vegetable Oils and Their Blends With Petroleum Diesel, Journal of ASTM International, May 2012, ASTM International,
DOI: 10.1520/jai104528.
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