(604g) Transesterification of Sunflower Oil Produced By Solvent Extraction

Transesterification of Sunflower Oil Produced by Solvent Extraction

The diesel fuel consumption is very important, responding for nearly 60% of market share in fuels. Derived from fossil sources, the availability of diesel depends on the exploration of new petroleum reservoirs and on better use of the known ones. Although there is not a definite answer, it is likely that petroleum production rises to a maximum in a few years and then a decline period will take place. In this scenario, the development of alternative fuels and other sources of energy are very interesting. Biodiesel, derived from renewable sources, is an option in this situation. It is a mono- alkyl ester from fatty acids, like vegetable oils and animal fatties. It is produced by the transesterification of a triglyceride with a short chain alcohol, like methanol and ethanol, resulting in glycerol and esters.
Raw material characteristics are relevant factors in biodiesel production, when compared to process capital costs and energy consumption. At present, the most important raw material for biodiesel production is refined or semi-refined vegetable oil. Therefore, high production costs are expected most of the time, since the starting raw materials have a higher price than the produced biodiesel. When using refined oil, the raw material represents 70 to 80% of total cost process. Due to these disadvantages, several studies have been made to reduce costs on biodiesel production processes, such as the use cheaper raw material, the increase of reaction yield and process intensification.
In this work, the leaching of oil from sunflower seeds using hexane was studied. The solution of oil / hexane was thereafter transesterified, with methanol and potassium hydroxide (KOH) as the catalyst, in a batch reactor, for 1 hour and with a constant temperature of 45 ºC. It is important to point out that the extracted oil was not refined and was directly used on transesterification reactions. The hexane in the oil / hexane solution acted as a cosolvent and made the oil / methanol mixture forms a single-phase.
The influence of methanol / oil mole ratio and of catalyst concentration on reaction yield was analyzed, by using gas chromatography and determining methylic esters produced in the transesterification process. The chromatography was carried out in a model Varian Star 3600, with a FID detector and a DBWAX column with 0,25 mm diameter and length of 60 m. The column initial set point was at 90 ºC and the temperature was risen at a rate of 2 ºC/min, until 240 ºC. The detection and injection temperatures were respectively equal to 225 ºC and 250 ºC.
A factorial planning analyzing two factors (mole ratio of methanol to oil and catalyst concentration) in two levels (5:1 / 7:1 and 0.75% / 1.25%) with a central point (6:1 and 1.00%) was used. The central point experiments were conducted in triplicate and the non-central points were carried out in duplicate.
Sunflower seeds were previously characterized and results showed 8.45% of moisture content. The leaching process indicated that 3.5 hours were required to achieve optimal extraction, with nearly 26% of oil.
Experimental results obtained in the transesterification reactions showed that the increase of methanol / oil mole ratio on reaction yield is negative, whereas the increase of catalyst concentration on reaction yield is positive. Reaction yields decreased 18.00% on average when the mole ratio methanol / oil was increased. When catalyst concentration was augmented, reaction yields increased 15.19%, on average. These results are statistically meaningful, since the standard deviation was equal to 0.48%. Moreover, an interaction between methanol / oil mole ratio and catalyst concentration on reaction yield was observed.
An empirical linear mathematical model relating reaction yield to mole ratio of methanol to oil and catalyst concentration was proposed and it represented well experimental data. In the best operating condition, a 34.13% reaction yield was achieved, which is low. This result is related to the high volume ratio of cosolvent to methanol on the transesterification reaction, inhibiting methanol / oil contact.
Key-words: transesterification, biodiesel, sunflower