Recover of different waste vegetable oils for biodiesel production: a pilot experience in Bahia State, Brazil

In Brazil, and mainly in the Northern State of Bahia (Capital city: Salvador), straight vegetable oils are widely used in the food preparation, both at shop and industrial level. Street shops, restaurants, collective messes make a great use of palm oil, but other types may be used, as soybean oil or dendé (local palm) oil. Concerning not edible, locally produced oil, Castor oil must be cited: castor is widely cultivated in the Sertão Region (inner of the Bahia State) and its oil has countless applications in industry. This massive use in food preparation leads to a huge amount of waste oil of different types to be properly disposed or recovered. At the Laboratorio Energia e Gas (Energy & Gas lab.) of the Universidade Federal da Bahia a cycle of experiences was carried out in order to evaluate the recovery of waste oils for biodiesel production. The waste oils were collected in the Capital city itself. The experiences were conducted at lab scale and, moreover, with a semi-industrial pilot plant able to produce 5,000 m3 y-1 of biodiesel. The biodiesel, produced from different waste oils and from “out-of-spec” oils, was tested in vehicles and stationery engines for energy production. At the same time, laboratory tests were performed to check out the final product quality. The biodiesel production was based on a trans-esterification process of the vegetable oil with methanol and a basic catalyst as NaOH or KOH. The conversion rate (in weight) settled between 81-85%. Altogether the final product showed a good quality, suitable for industrial use and has been tested in generators in great public shows. The greatest problem arose during the production process concerned the acidity of waste vegetable oils. The high acidity level drove to a lower rate of biodiesel production (rate production 11.61% lower using oils with an acidity index going from 2.32 to 7.5) although an acidity neutralization step (with KOH) was introduced in the production process. The best process rate was obtained with ratio (as mole) oil/mentanhol = 1/6 and using KOH as catalyst, in the measure of 1% (in weight) of processed oil