Environmental Engineering Reference
In-Depth Information
to remove the traces of glycerol to meet the EEC regulations are often a problem
associated to the chemical production of biodiesel.
Biodiesel Produced by Biochemical Catalytic Methods
The increasing environmental concerns have led to a growing interest in the use of
enzyme catalysis as it usually produces a cleaner biodiesel under milder conditions.
It also generates less waste than the conventional chemical process. Many authors
have reported a wide range of efficient and low energy intentive protocols obtaining
very promising results with lipases (in both free and immobilised form) [38-43] and
combining lipases with alkali catalysts [44].
The limitations of the industrial use of enzymatic methodology is mainly due to
their high production costs, which may be overcome by molecular technologies to
enable the production of the enzymes in higher quantities as well as in a virtually
purified form [45, 46].
Biodiesel Produced by Non-catalysed Processes
The most common and simple non-catalysed biodiesel production process has
been performed using supercritical methanol via simultaneous transesterification of
triglycerides and esterification of fatty acids [47, 48]. The supercritical alcohol con-
ditions are essential because a very low reaction rate is obtained under subcritical
conditions.
The procedure has been claimed to be very effective yielding high FAME con-
tents in a very short time of reaction (typically less than 30 min). The presence of
water also facilitated the formation of the methyl esters. Nevertheless, the super-
critical methodology is still very expensive and the implementation of such costly
technology in industry is currently a challenge.
8.2.1.2 Biofuels Produced by Biological Conversion
Bioalcohols
Bioethanol
Bioethanol is the other common first generation biofuel that is generally used as a
blend that can go up to 85% content (E85) [49]. It is the most employed biofuel on
a world level with the US currently being the world's largest producer and Brazil
the largest exporter, accounting together for 70% of the world's production and 90%
of ethanol used for fuel [49]. In Sweden and the US, a high-proportion bioethanol
blend E85 (85% ethanol and 15% petrol) is being used in Flexible Fuel Vehicles
(FFVs) with modified engines that are able to run on either E85 or petrol, or any
mixture of the two.The E85 can nowadays be also purchased in several petrol sta-
tions in the UK (Fig. 8.5). Neat ethanol (E100) has also been employed in large
scale in Brazil in specially modified engines.
