Biofuels in Perspective

Heavy layer
from alkaline
neutralisation
Acid
Figure 9.2 Alcohol refining (Westfalia).
9.3.2.5 Removal of Contaminants
Crude oil
Alcohol neutralisation
Transesterification
Heavy layer
Soap splitting
Glycerol layer
Production of Biodiesel from Waste Lipids 161
FAME
The majority of the contaminants are mainly removed by either bleaching on adsorbens
(clay, silicates, active carbon) and/or by deodorization.
Bleaching is carried out by treatment of the oil with 0.5–2 % bleaching earth at 90 ◦ C
for 30 minutes. During this process traces of soaps and phospholipids are removed next
to residues of pesticides and artifacts, colored material and metals (O’Brien et al., 2000).
Bleaching is an expensive process due to the high costs of the adsorbens, the disposal of
the waste adsorbens (solid waste) and the loss of oil (oil can constitute 20–40 % of the
weight of the disposed adsorbens).
Stripping of contaminants together with FFA is an alternative when the artefacts have a
relatively low vapour pressure.
9.3.2.6 Production of Biodiesel from Crude and Waste Oil with Low Free Fatty Acid
Content by Alkali-Transesterification
Alkali catalysts such as NaOH, KOH, NaOMe and KOMe are the most common catalysts
for the transesterification of crude and waste lipids with a FFA content of less than 3 %.
There is a direct link between lipid quality, expressed as the inverse of the FFA content,
and the costs. For lipids with levels lower than 4 % FFA, the loss of the catalyst due to soap
formation must be compensated by adding additional catalyst. For higher concentrations
of FFA this will be impractical and uneconomical. An acid catalyst can also be used but
acid transesterification is much slower (Canacki and Van Gerpen, 1999).
The choice of the catalyst is dependent upon the price, the work-up conditions and
country. In the US normally NaOH is used while in the EU KOH is preferred due to a
faster transesterification and the fact that the waste stream has a higher economical value
FFA