6
the emissions of carbon compared to fossil fuels. Moreover, their sustainability and
renewability should also be highlighted. Biodegradable biofuels prevent underground water and soil pollution and therefore provide a lower level of environmental risk compared to non-renewable fuels [11].
Biofuels can be applied in different types of vehicles from trucks to airplanes
with the requirements in engine modifications or the infrastructure of fuel distribution. The application of biofuels can lead to a considerable reduction in CO 2 emissions of 50–80% in comparison with fossil fuels [12]. Biofuels have three forms:
solid, gas and liquid. The liquid biofuel can be a replacement for the present fossil
diesel or petrol.
3 Biofuel Classes
Biofuels are characterized into two main classes. The first is “primary biofuels”, and
the second is “secondary biofuels”. The traditional form of producing biofuels for
generating heat and electricity is from “primary biofuels”, which is utilized through
direct combustion of natural materials. This kind of biofuel is not an appropriate
energy source for large-scale industrial processes due to its environmental risks, low
efficiency and toxicity [13].
“Secondary biofuels” are the other class of biofuels, which are obtained through
biomass processing and produced in the form of gas (biogas or synthesis gas),
liquid (bio- liquid) and solid charcoal (biochar) which are used as transport fuels or
for other industrial applications. The second class of biofuel itself is also categorized into three groups according to their processing technology and their feedstock,
known as the first, second and third generations of biofuels [14]. In the next section,
first, second and third generations of biofuels will be explained.
3.1 First Generation
First-generation biofuels are mostly obtained from sugars, oil-rich food crops or
starch which includes oils (biodiesel) and alcohols (bioethanol) [13, 15, 16]. The
required technology for the production of first-generation biofuels is known and has
been subjected to considerable process development. Furthermore, the production
of these types of biofuels is simple on a commercial scale. One of the most crucial
challenges in this generation of biofuels is the research on the cost optimization for
processes where their products are intended to compete with their non-renewable
competitors [15].
Another critical problem associated with this type of biofuel is the rivalry
between fuel and food production from edible crops [17, 18]. This is the most
important criticism for the use of first-generation biofuels and has caused considerable increases in the prices of food in many countries that produce biofuels [19, 20].
H. Jahangiri et al.
the emissions of carbon compared to fossil fuels. Moreover, their sustainability and
renewability should also be highlighted. Biodegradable biofuels prevent underground water and soil pollution and therefore provide a lower level of environmental risk compared to non-renewable fuels [11].
Biofuels can be applied in different types of vehicles from trucks to airplanes
with the requirements in engine modifications or the infrastructure of fuel distribution. The application of biofuels can lead to a considerable reduction in CO 2 emissions of 50–80% in comparison with fossil fuels [12]. Biofuels have three forms:
solid, gas and liquid. The liquid biofuel can be a replacement for the present fossil
diesel or petrol.
3 Biofuel Classes
Biofuels are characterized into two main classes. The first is “primary biofuels”, and
the second is “secondary biofuels”. The traditional form of producing biofuels for
generating heat and electricity is from “primary biofuels”, which is utilized through
direct combustion of natural materials. This kind of biofuel is not an appropriate
energy source for large-scale industrial processes due to its environmental risks, low
efficiency and toxicity [13].
“Secondary biofuels” are the other class of biofuels, which are obtained through
biomass processing and produced in the form of gas (biogas or synthesis gas),
liquid (bio- liquid) and solid charcoal (biochar) which are used as transport fuels or
for other industrial applications. The second class of biofuel itself is also categorized into three groups according to their processing technology and their feedstock,
known as the first, second and third generations of biofuels [14]. In the next section,
first, second and third generations of biofuels will be explained.
3.1 First Generation
First-generation biofuels are mostly obtained from sugars, oil-rich food crops or
starch which includes oils (biodiesel) and alcohols (bioethanol) [13, 15, 16]. The
required technology for the production of first-generation biofuels is known and has
been subjected to considerable process development. Furthermore, the production
of these types of biofuels is simple on a commercial scale. One of the most crucial
challenges in this generation of biofuels is the research on the cost optimization for
processes where their products are intended to compete with their non-renewable
competitors [15].
Another critical problem associated with this type of biofuel is the rivalry
between fuel and food production from edible crops [17, 18]. This is the most
important criticism for the use of first-generation biofuels and has caused considerable increases in the prices of food in many countries that produce biofuels [19, 20].
H. Jahangiri et al.