Crop description. Hevea brasiliensis—commonly known as Para rubber tree, rubber tree, jebe, cauchotero de para, seringueira, or siringa— belongs to the family Euphorbiaceae (see Fig. 4.12). The rubber tree originates from the Amazon rain forest (Brazil). Today, most rubber tree plantations are located in Southeast Asia and some are also in tropical Africa. The tree can reach up to 30 m high. Oil can be extracted from the seeds. Although there are variations in the oil content of the seed from different countries, the average oil yield has been 40% [118].

Its fatty acid composition includes palmitic acid (10.2%), stearic acid (8.7%), oleic acid (24.6%), linoleic acid (39.6%), and linolenic acid (16.3%) [118].

Main uses. The crop is of major economical importance because it pro­duces latex. The wood from this tree is used in the manufacture of high — end furniture. In Cambodia and other rubber-manufacturing countries, rubber seeds are used to feed livestock. Rubber seed contains cyanogenic glycosides that will release prussic acid in the presence of enzymes or in slightly acidic conditions. Press cake or extracted meal can be cau­tiously used as fertilizer or feed for stock [119].

Several studies to check its feasibility as a source of biodiesel have been undertaken. Ikwuagwu et al. have prepared methyl esters of rubber seed oil using excess of methanol (6 M) containing 1% NaOH as a catalyst. Petroleum ether was added to the reaction to produce two phases. Analysis of the properties have shown a good potential for use as an alternative diesel fuel, with the exception of the oxidative stability [120]. Ramadhas et al. have performed a previously acid — catalyzed esterification to reduce the high FFA content, followed by an alkaline esterification. Sulfuric acid 0.5% by volume and a methanol — oil molar ratio of 6:1 was used in the pretreatment. A molar ratio of 9:1 and 0.5% by weight of sodium hydroxide was used during the second step. The authors found a reduction in exhaust gas emissions. The lower blends of biodiesel increased brake thermal efficiency and reduced fuel consumption [121].