Mata2010 Chap11 RPChE (1)

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/280728855
Biodiesel Production Processes
Chapter · January 2010
CITATIONS
14
READS
62,944
2 authors:
Some of the authors of this publication are also working on these related projects:
Special Issue "Energy Storage: from Chemicals to Materials and More" View project
LCA studies View project
Teresa M. Mata
University of Porto
151 PUBLICATIONS8,354 CITATIONS
SEE PROFILE
António Martins
University of Porto
129 PUBLICATIONS7,582 CITATIONS
SEE PROFILE
All content following this page was uploaded by António Martins on 06 August 2015.
The user has requested enhancement of the downloaded file.

11
Biodiesel Production Processes
T.M. MATA* AND A.A. MARTINS
ABSTRACT
This work presents the current state of development concerning different
routes for biodiesel production, focusing on their chemical and technological
aspects. Their relative advantages and disadvantages are presented and
discussed in detail, with a focus on their industrial implementation and
exploration. The full biodiesel production chain is taken into account, with
a brief description of the potential feedstocks that can be used. Not only is
the conventional production process analysed, but also new developments
that can improve significantly the performance of current commercial
production units. In the final sections expected future development for the
production processes are presented and discussed.
1. INTRODUCTION
Biofuels for transportation are not new. The first automobiles used it. For
example, Rudolph Diesel used peanut oil to power up its groundbreaking
combustion engine presented in the World Exhibition in Paris in 1900,
though it can have used a wide range of fuels. However in that time the
vegetable oil fuels were more expensive than petroleum fuels and in the
first decades of the twentieth century there was a significant development
of the petrochemical industry. Besides the widespread availability of cheap
and easy to explore sources of oil, fuels produced were clearly superior in
terms of performance and power output to other fuels. On the other hand,
oil processing allowed the production of many other chemical compounds,
as for example aromatics, that were increasingly used in the production of
other chemical compounds and products used in many human activities,
such as plastics, detergents, paints, among many others. Therefore, fossil
fuels became one of the foundations or modern societies.
Since 1990’s and mainly today due to recent increases in petroleum
prices and uncertainties about petroleum availability, there is a growing
*Faculty of Engineering, University of Porto, Portugal, Rua Dr. Roberto Frias, 4200
465 Porto, Portugal.
*Corresponding authors : E-mail : [email protected]

314 Recent Progress in Chemical Engineering
interest and awareness about the importance of alternative energy from
renewable sources, in particular for transportation fuels, and even an
increasing investment in research and development in this area. Examples
include bio-ethanol from the fermentation of starch or sugar rich
agricultural crops, vegetable oils from plants or microalgae and animal
fats, gasification of biomass, wind, hydroelectric power, solar power,
including photovoltaic energy, among many others (Dewulf and Van
Langenhove, 2006; Gilbert and Perl, 2008).
Nowadays biodiesel is the most important alternative diesel fuel in the
EU representing 82% of the total biofuel production (Bozbas, 2008) and
has been reported to emit substantially lower quantities of most of the
regulated pollutants compared to mineral diesel. When compared to fossil
fuels, their relative degree of development varies widely, and its potential
strongly depends on local conditions and sectors of activity where the energy
is used, making it difficult to select the best option and the design and
operation of renewable production systems. These questions are particular
acute in the transportation sector, a cornerstone of modern society and
one of the drivers of economic development, currently almost dependent
on fossil fuels and one of the main contributor to air pollution, in particular
to greenhouse gas (GHG) emissions (Akoh et al., 2007).
In fact fossil fuels are still the dominant source of energy used either
for domestic or industrial consumption and in the medium to long term
this situation will pose a growing threat, economic, societal, or
environmentally, to the ongoing development of human activities. There is
still no consensus among specialists, but it is common belief that the oil
peak is close and the existing reserves will be increasingly harder and more
expensive to explore in future (Laherrere, 2005). For example, tar sands
and coal are seen as valuable resources that may substitute oil, but they
will create far-reaching environmental problems, such as the destruction
of ecosystems and a significant increase in the carbon dioxide and sulphur
oxides emissions (Toman et al., 2008).
The soaring oil prices and growing concerns for the environment leaded
to an increased interest in other fuel sources. Among them, special attention
is given to energy sources such as biodiesel, hydrogen, and bio-ethanol, in
particular when produced from renewable raw materials (Girard and Fallot,
2006). However biofuel’s industry, too, have their critics, notably among
those concerned about the impact on food prices (when farm commodities
like maize, wheat, and sugarcane are diverted to energy), the conversion
of forests and other critical habitats for biofuel’s feedstocks cultivation with
the associated damage on biodiversity (depending on local biodiversity),
loss of soil quality or land fertility (depending on initial soil conditions),
emissions from carbon stock change (including both soil and vegetation),
and land competition (depending on local availability of land).
The increasing demand for biofuels and the fast-rising of energy costs
will require new and independent energy sources to be developed. This

Biodiesel Production Processes 315
means for biofuels that in addition to the feedstocks presently used, new
raw materials will have to be applied to cover the growing demand. For
example, one can expect that next-generation lignocellulosic bio-ethanol
and algal biodiesel technologies will become commercially significant in
the longer term. Together with the search for new feedstocks, measuring
technology and applications need to be developed with a focus on the
continuous process adaptation to future requirements in order to guarantee
a steady quality of biofuels (Geissler, 2008; Eijsink et al., 2008).
Due to the wide variety of biofuel alternatives and different stages of
development, this article focus its attention to biodiesel, a fuel that is already
being produced at industrial scale and can have a significant impact in the
near future. This will allow that other transportation fuels complement
and prevent some of the problems associated with the widespread
production and consumption of biofuels.
Due to its umbilical relationship with the petrochemical industry,
responsible for almost of the fuels produced and consumed for
transportation in a world basis, chemical engineering has a key role tom
play in the developing biodiesel production sector. There is already extensive
knowledge about various industrial processes that can be applied
successfully in the development, design, and effective operation of biodiesel
production facilities. Therefore, as the field is evolving fast, it is expected
that chemical engineering as a discipline will have a profound impact.
This article starts by a brief description of what it is biodiesel,
advantages and disadvantages of its utilization in the transportation sector,
and a brief description of its production chain. Then, attention will be placed
in the production of biodiesel itself, as it is in fact the key part and where
chemical engineering can have the most profound impact. The questions
linked with the type of alcohol used and how it impacts the process, and
the potential destination of glycerol will be considered. To conclude, the
future evolution and interactions with the growing field of biofuels and bio
based economy is discussed, as well its potential contribution to sustainable
development.
2. BIODIESEL-WHAT IT IS?
Biodiesel is a mixture of fatty acid alkyl esters obtained from transesteri-
fication (ester exchange) of vegetable oils and animal fats. These lipid
feedstocks are composed by 90–98% (weight) of triglycerides and small
amounts of mono and diglycerides, free fatty acids (generally 1–5%), and
residual amounts of phospholipids, phosphatides, carotenes, tocopherols,
sulphur compounds, and traces of water. In the transesterification reaction,
a homogeneous or heterogeneous, acid or basic catalyst is normally used to
enhance the reaction rate, although for some processes it may be not
necessary to use a catalyst.
The quality of fatty acid alkyl esters are characterized by their physical
and fuel properties (standardized by the EN 14214 (2003) in EU and the

316 Recent Progress in Chemical Engineering
ASTM D 6751 in USA) such as density, viscosity, composition of fatty acid
esters, iodine value, acid value, cloud and pour points, flash point, gross
heating value, volatility, cetane number, copper corrosion, water content,
carbon residue, ash, and sulphur.
Biodiesel has comparable energy density, cetane number, heat of
vaporization, and stoichiometric air/fuel ratio with mineral diesel (Agarwal,
2007). However, biodiesel has a higher proportion of multi-bonded carbon
compounds that pyrolyse more readily and engines can suffer coking of the
combustion chamber and injector nozzles, gumming and sticking of
the piston rings. The flash point is normally above 170oC and the heating
values of biodiesel (39–40 MJ/kg) are about 10% lower than diesel fuels
(42–46 MJ/kg). The cetane numbers of biodiesel normally range from 40 to
70 while of diesel range from 47 to 55. The iodine value ranges from 0 to
200 depending upon unsaturation (Mondal et al., 2008). The cloud and pour
points of biodiesel are higher than those of diesel fuels. Also, the viscosity
of biodiesel is slightly greater than that of petroleum diesel but
approximately an order of magnitude less than that of the parent vegetable
oil. For example, at 40oC the viscosity values of methyl esters range from
2.8 to 3.7 mm2/s, the viscosity of vegetable oils between 25 and 45 mm2/s,
and viscosity of diesel fuel is about 2.7 mm2/s (Balat, 2008).
Among the many important advantages of biodiesel fuel some can be
pointed when comparing it with petroleum diesel for transportation
(Agarwal, 2007; Bozbas, 2008; Delucchi, 2003; Canakci and Sanli, 2008).
They are listed below:
• Biodiesel is non-aromatic, almost sulfurless, produced from renewable
sources, presently vegetable oils or animal fats. In another hand the
lubricity property of biodiesel is much better than that of low-sulfur
diesel fuel. Little biodiesel additive (about 1%) is enough to
significantly improve the conventional diesel fuel’s lubricity.
• Full life cycle analysis indicates that, on average, biodiesel emit less
CO2 than conventional fossil fuels. The use of biomass energy has the
potential to greatly reduce GHG emissions and thus biodiesel have a
significant smaller contribution to global warming when compared to
fossil fuels. Although fossil fuels release carbon dioxide captured by
photosynthesis millions of years ago, biomass releases carbon dioxide
that is largely balanced by the carbon dioxide captured in its own
growth, depending on how much energy was used to grow, harvest,
and process the fuel.
• Biodiesel tailpipe CO2 emissions per mass unit of biodiesel burnt are
lower than for petroleum diesel. It has reduced visible smoke, noxious
fumes and odours, and emits 40–50% less particulate matter (PM),
30–70% less HC, 20–50% less CO, and less 50% in soot emissions,
although the NOx may be about 10–15% higher this problem can be
overcome by retarding the injection timing.