Production of Synthetic Fuels and Chemicals from Biomass - Biomass Gasification, Pyrolysis and Torrefaction - page 400

Being oxygenated, biodiesel is a better lubricant than petrodiesel, and
therefore gives longer engine life.
Its higher oxygen content allows biodiesel to burn more completely.

11.5.3.1 Biodiesel Production
Biodiesel is generally produced from vegetable oil and/or from animal fats
with major constituents that are triglycerides. It is produced by transesterifi-
cation of vegetable oil or fat in the presence of a catalyst. Biodiesel carries
the name fatty acid methyl (or ethyl) ester, commonly abbreviated as
“FAME.” A popular production method involves mixing waste vegetable oil
or fat with the catalyst and methanol (or ethanol) in appropriate proportion.
A typical proportion is 87% oil, 1% NaOH catalyst, and 12% alcohol. Both
acid and base catalysts can be used, but the base catalyst NaOH is most com-
monly used. Because NaOH is not recyclable, a “nongreen” feed is required
to produce “green” biodiesel. Efforts are being made to produce recyclable
catalysts and thereby make the product pure “green.”
Figure 11.8 shows the reaction for the conversion of triglyceride into bio-
diesel FAME and its by-product, glycerol. Glycerol cannot be used as a
transport fuel, and its disposal is a major issue.
An alternative noncatalytic conversion route for biodiesel is under devel-
opment in which transesterification of triglycerides is by supercritical metha-
nol (above 293 C, 8.1 MPa) without a catalyst (Kusdiana et al., 2006). The
methanol can be recycled and reused, but the process for this must be carried
out at high temperatures and pressures. Efforts are also being made to use
woody biomass (lignocellulose) instead of fats or oil to produce biodiesel
using the supercritical method (Minami and Saka, 2006). The reaction is car-
ried out in a fixed or fluidized bed. The fluidized bed has the advantage of
continuous catalyst regeneration and efficient removal of the heat of reaction.

11.5.4 Transport Fuel Production from Nonfood Biomass
Use of food cereals, such as wheat and corn for the production of biodiesel
or ethanol, has been commercially successful; however, it has had a major
impact on the world's food market, driving up prices and creating shortages.

O

R 2

+3CH 3 O H

O OH

R 1,2,3

O

R 1 R 3 + HO OH

O O

O

O

O

Triglyceride Fatty acid methyl ester Glycerol

FIGURE 11.8 Diesel (FAME) production from triglyceride.