Crop description. Ricinus communis L., commonly known as the castor — oil plant, belongs to the family Euphorbiaceae (see Fig. 4.3). This peren­nial tree or shrub can reach up to 12 m high in tropical or subtropical climates, but it remains 3 m tall in temperate places. Native to Central Africa, it is being cultivated in many hot climates. The oil contains up to 90% ricinoleic acid, which is not suitable for nutritional purposes due to its laxative effect [52]. This hydroxycarboxylic acid is responsi­ble for the extremely high viscosity of castor oil, amounting to almost a hundred times the value observed for other fatty materials [53].

Main uses. Castor bean is cultivated for its seeds, which yield a fast­drying oil used mainly in industry and medicine. Coating fabrics, high — grade lubricants, printing inks, and production of a polyamide nylon-type fiber are among its uses. Dehydrated oil is an excellent drying agent and is used in paints and varnishes. Hydrogenated oil is utilized in the man­ufacture of waxes, polishes, carbon paper, candles, and crayons. The pomace or residue after crushing is used as a nitrogen-rich fertilizer. Although it is highly toxic due to the ricin, a method of detoxicating the meal has been developed, so that it can safely be fed to livestock [54]. Several authors have found that castor-oil biodiesel can be considered as a promising alternative to diesel fuel. Transesterification reactions have been carried out mainly by using both ethanol and NaOH, and through enzymatic methanolysis [55-57]. Several authors have studied the influ­ence of the nature of the catalyst on the yields of biodiesel from castor oil. They found that the most efficient transesterification of castor oil could be achieved in the presence of methoxide and acid catalysts [58]. The influence of alcohol has also been studied. Comparing the use of ethanol versus methanol, Meneghetti et al. have found that similar yields of fatty acid esters may be obtained; however, the reaction with methanolysis is much more rapid [59]. Cvengros et al. produced both ethyl and methyl esters, using NaOH in the presence of ethanol and methanol, respectively. Despite the high viscosity and density values, they concluded that both methyl and ethyl esters can be successfully used as fuel. A positive solution to meet the standard values for both viscosity and density parameters can be a dilution with esters based
on oils/fats without an OH group, or a blending with conventional diesel fuel [60].