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C. Li et al.
4.1 Introduction to Biodiesel
Global petroleum resources are facing depletion due to unrestrained exploitation and
utilization. Waste gas pollution caused by petroleum fuel also poses a huge challenge
to the human beings. With the improving living standard and an increasing awareness
of environmental protection, people begin to realize the severe nature of air pollution
caused by petroleum fuel. In particular, frequent occurrence of photochemical smog
and acid rain endangers our survival, while the greenhouse effect brought about by an
excessive amount of CO 2 produced destabilizes the ecological equilibrium of nature.
Therefore, international petroleum organizations believe that it is urgent to develop
a new energy to replace petroleum fuel. Researches have shown that biodiesel is a
promising alternative for diesel fuel.
The National Biodiesel Board defines biodiesel as a clean alternative fuel made
from renewable biological resources, including vegetable and animal oils and fats,
which can be used in compression-ignition engines. Chemically, biodiesel includes
a series of long-chain fatty acids and methyl esters. Most natural oils and fats consist
of a linear fatty acid, fatty acid triglycerides. After transesterification, their molecular
weight is reduced almost to the level of diesel. Meanwhile, they are an environmentfriendly alternative fuel with diesel-like properties.
Biodiesel has significant advantages over petroleum diesel: (1) it is environmental.
Biodiesel, with exceptional biodegradability, has a low sulfur content and does not
contain aromatic hydrocarbons, so that its combustion exhaust causes less harm than
that of diesel. (2) It has great lubricity. Even with only 0.4% biodiesel in petroleum
diesel, biodiesel shows outstanding performance in abrasion resistance. It reduces
abrasion caused by low sulfur content in the emerging clean fuels, and improves
the overall performance of vehicle diesel. (3) It is safe. With a higher flash point
than petroleum diesel, biodiesel is not regarded as a hazardous fuel. It has significant
advantages in terms of transport, storage, and utilization. (4) It has good combustion
performance. With a higher cetane number, it has better combustion performance than
diesel. The combustion residues are slightly acidic, which lengthens the life cycle
of catalyst and engine oil. As a renewable energy, it has an inexhaustible supply. (6)
A biodiesel system requires only small investment. The original engine, refueling
equipment, and maintenance equipment needs little adaptation. (7) Biodiesel can
be mixed with petroleum diesel in a certain ratio, which reduces oil consumption,
improves dynamics, and cuts exhaust pollution.
Biodiesel researches began in the 1970s, first with the aim to address the energy
crisis. Back then, global petroleum price was soaring due to the oil crisis. Some
developed countries initiated the development of biomass energy to solve the energy
crisis of their own. Most researches focused on the direct use of vegetable oils or animal fats as fuel. However, due to their large molecular weight and long carbon chain,
the consequent fuel has a high viscosity and poor low-temperature performance, and
tends to carbonize coke to clog up the nozzle. Moreover, vegetable oils cannot be
sufficiently oxidized, making it an unrealistic alternative to diesel.
C. Li et al.
4.1 Introduction to Biodiesel
Global petroleum resources are facing depletion due to unrestrained exploitation and
utilization. Waste gas pollution caused by petroleum fuel also poses a huge challenge
to the human beings. With the improving living standard and an increasing awareness
of environmental protection, people begin to realize the severe nature of air pollution
caused by petroleum fuel. In particular, frequent occurrence of photochemical smog
and acid rain endangers our survival, while the greenhouse effect brought about by an
excessive amount of CO 2 produced destabilizes the ecological equilibrium of nature.
Therefore, international petroleum organizations believe that it is urgent to develop
a new energy to replace petroleum fuel. Researches have shown that biodiesel is a
promising alternative for diesel fuel.
The National Biodiesel Board defines biodiesel as a clean alternative fuel made
from renewable biological resources, including vegetable and animal oils and fats,
which can be used in compression-ignition engines. Chemically, biodiesel includes
a series of long-chain fatty acids and methyl esters. Most natural oils and fats consist
of a linear fatty acid, fatty acid triglycerides. After transesterification, their molecular
weight is reduced almost to the level of diesel. Meanwhile, they are an environmentfriendly alternative fuel with diesel-like properties.
Biodiesel has significant advantages over petroleum diesel: (1) it is environmental.
Biodiesel, with exceptional biodegradability, has a low sulfur content and does not
contain aromatic hydrocarbons, so that its combustion exhaust causes less harm than
that of diesel. (2) It has great lubricity. Even with only 0.4% biodiesel in petroleum
diesel, biodiesel shows outstanding performance in abrasion resistance. It reduces
abrasion caused by low sulfur content in the emerging clean fuels, and improves
the overall performance of vehicle diesel. (3) It is safe. With a higher flash point
than petroleum diesel, biodiesel is not regarded as a hazardous fuel. It has significant
advantages in terms of transport, storage, and utilization. (4) It has good combustion
performance. With a higher cetane number, it has better combustion performance than
diesel. The combustion residues are slightly acidic, which lengthens the life cycle
of catalyst and engine oil. As a renewable energy, it has an inexhaustible supply. (6)
A biodiesel system requires only small investment. The original engine, refueling
equipment, and maintenance equipment needs little adaptation. (7) Biodiesel can
be mixed with petroleum diesel in a certain ratio, which reduces oil consumption,
improves dynamics, and cuts exhaust pollution.
Biodiesel researches began in the 1970s, first with the aim to address the energy
crisis. Back then, global petroleum price was soaring due to the oil crisis. Some
developed countries initiated the development of biomass energy to solve the energy
crisis of their own. Most researches focused on the direct use of vegetable oils or animal fats as fuel. However, due to their large molecular weight and long carbon chain,
the consequent fuel has a high viscosity and poor low-temperature performance, and
tends to carbonize coke to clog up the nozzle. Moreover, vegetable oils cannot be
sufficiently oxidized, making it an unrealistic alternative to diesel.