Besides nonedible oils, there are some edible oils from plants that yield a relatively lower-cost source to produce biodiesel compared to biodiesel from rapeseed oil or soybean oil.

4.3.1 Cardoon oil

Crop description. Cynara cardunculus L.—commonly known as car­doon, Spanish artichoke, artichoke thistle, cardone, dardoni, or cardo— belongs to the family Asteracea (see Fig. 4.14). Artichokes originated in the Mediterranean region and climates, becoming an important weed of the Pampas in Argentina, and in Australia, and California because of its adaptation to dry climate. Its fatty acid composition mainly includes palmitic acid (19.3%), stearic acid (6.1%), oleic acid (39%), and linoleic acid (30%) [123].

Main uses. The leaf stalks are eaten as a vegetable. The leaves contain cynarin, which improves gall bladder and liver functions, increases bile flow, and lowers cholesterol. The down from the seed heads is used as rennet.

Encinar et al. transesterified C. cardunculus oil using methanol and several catalysts (sodium hydroxide, potassium hydroxide, and sodium methoxide) to produce biodiesel. Best properties were achieved by using 15% methanol and 1% sodium methoxide as catalyst, at 60°C temperature [124].

The reaction can also be accomplished by using an ethanol-oil molar ratio of 12:1 and 1% sodium hydroxide, at 75°C [125]. C. cardunculus methyl esters also provide a significant reduction in particulate emis­sions, mainly due to reduced soot and sulfate formation [126].