3.9.1 Glycerol-based Fuel Oxygenates for Biodiesel and Diesel Fuel Blends

Glycerol (1,2,3-propanetriol or glycerine) is a trihydric alcohol. It is a colorless, odorless, sweet-tasting, syrupy liquid. It melts at 291 K, boils with decomposition at 563 K, and is miscible with water and ethanol (Perry and Green 1997). The chem­ical formula for glycerol is OH-CH2-CH(OH)-CH2-OH. Glycerol is present in the form of its esters (triglycerides) in vegetable oils and animal fats.

Glycerol is a byproduct obtained during the production of biodiesel. As biodiesel production is increasing exponentially, the crude glycerol generated from the trans­esterification of vegetables oils has also been generated in large quantities (Pachauri and He 2006). With the increasing production of biodiesel a glut of glycerol has been created, causing market prices to plummet. This situation warrants finding al­ternative uses for glycerol. Glycerol is directly produced with high purity levels (at least 98%) by biodiesel plants (Ma and Hanna 1999; Bournay et al. 2005). Re­search efforts to find new applications of glycerol as a low-cost feedstock for func­tional derivatives have led to the introduction of a number of selective processes for converting glycerol into commercially valued products (Pagliaro et al. 2007). The principal byproduct of biodiesel production is crude glycerol, which is about 10 wt% of vegetable oil. For every 9 kg of biodiesel produced, about 1 kg of a crude glycerol byproduct is formed (Dasari et al. 2005).

Oxygenated compounds such as methyl tertiary butyl ether (MTBE) are used as valuable additives as a result of their antidetonant and octane-improving properties. In this respect, glycerol tertiary butyl ether is an excellent additive with a large potential for diesel and biodiesel reformulation.

Glycerol can be converted into higher-value products. The products are 1,3- propanediol, 1,2-propanediol, dihydroxyacetones, hydrogen, polyglycerols, suc­cinic acid, and polyesters. The main glycerol-based oxygenates are 1,3-propanediol, 1,2-propanediol, propanol, glycerol tert-butyl ethers, ethylene glycol, and propylene glycol.