Chemistry Reference
In-Depth Information
6.6.4 Biodiesel Glycerine Applications
Biodiesel glycerine, as a catering oil by-product, has found treatment routes as
a landspread agent; although environmentally acceptable, this is a costly
activity. In the UK, the type of glycerine most suitable for this purpose must
contain less than 3 wt% methanol (above that the concentration of methanol
glycerine is considered a toxic and flammable substance)
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and preferably
potassium phosphates as the major inorganic component (formed after the use
of MeOK in the transesterification step and phosphoric acid in the purification
of biodiesel).
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Alternatives to this disposal route are the objective of our
research. Despite the limitations for this type of coproduct, there are a number
of possibilities that have attracted interest recently.
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6.6.4.1 Conversion into Technical-Grade Glycerine
Methanol recovery after the transesterification step is economically attractive
for biodiesel producers. It reutilises one of the reagents to be employed as feed
in the process (methanol costs
d
250-375/tonne),
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whilst increasing the
glycerol content in the glycerine. Methanol recovery should ideally be effective
to the point of leaving less than 3% methanol in crude glycerine. Slightly
acidic/neutral pHs (5-7) are preferred in this material as it increases the
commercial value of glycerine. Distillation under vacuum to recover methanol
and ultrafiltration
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for certain types of applications (cosmetics, humectants,
plasticiser, or chemical conversion amongst others) would both lead to
technical-grade glycerine.
6.6.4.2 Energy Generation
Despite its lower calorific value compared with other fuels and biofuels,
(Table 6.2) glycerine has been employed in energy generation.
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For instance,
Aquafuel Research (a UK-based company) claims to have developed a tech-
nology wherein glycerine from biodiesel production is directly employed in
Table 6.2 Calorific values for some conventional
fuels and biofuels.
Calorific Value
(MJ/ kg)
Fuel type
Petrodiesel
46
Coal
35-42
Natural gas
38.1
Biodiesel (FAME)
37.3
Ethanol
30
Pyrolysis char
27.4
Biodiesel glycerol (37 wt%
glycerol; 21 wt% methanol).
25.30
Pyrolysis oil
16-23
Wood (15 wt% water)
19.0
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