Biofuels in Perspective

90 Biofuels
KOH
Methano
Oil/Fat
Acid
Catalyst
Preparation
Oil Pretreatment
Fully automatic
Transesterification
Methylester
Methanol-Recovery
Methylester
Purification –
Distillation
Qlitt Cl
Glycerine phase
After- treatment
Fertilizer
Separation
Free Fatty Acid
Recovery
Crude Glycerine
Methanol-Recovery
Pharmaceutical
Glycerine Production
Figure 5.6 Multifeedstock production scheme according to BioDiesel International. 39
Fertilizer
Crude Glycerine
Pharmaglycerine
BioDiesel
Distillation side-product
technologies is the use of additional reaction steps, like pre-esterification of free fatty acids.
So in a first step free fatty acids are pre-esterified with the use of acidic catalysts, followed
by one or two alkaline catalyzed transesterification steps. The raw fatty acid methyl esters
are purified by water washing steps and additionally can be further refined by vacuum
distillation. The main advantage of this technology is the fact that the yield of conversion
of fatty acid material into fatty acid methyl esters is almost 100 %. The highest yield can
be obtained, when remaining soaps in the glycerol layer are recycled by acidification of
the glycerol and separation of free fatty acids, which can be reintroduced into the preesterification
step or first step of transesterification. 39 Another approach for converting
high acidic oils into fatty acid methyl esters is the conversion of fatty acids into glycerides,
followed by traditional transesterification. 40
5.8.3 Small Scale Production Units
A lot of production plants have a production capacity of up to 5000 t/a, using different
feedstocks and different production technologies. Mostly these plants have not been built by
big biodiesel technology companies, but the technology has been developed by individual
groups and organizations based on own experience and development. The glycerol layer
must be used directly without any purification, e.g. as substrate for biogas plants, or will be
purified to be sold as raw glycerol. The catalyst for transesterifications is mainly potassium
hydroxide, because it gives the highest conversion rates. Several of these production plants
are organized as co-operatives, using vegetable oils produced locally, and also the biodiesel
will be used by the members directly. Most of the very small production units don’t have
their own facilities for quality control, so the quality of the product might vary and is not
guaranteed to meet EN 14214.