176
Y. Cao et al.
lubricants are inevitably discharged into the environment due to transportation, leakage, and natural replacement. Mineral oil-based lubricants which have high ecological toxicity and poor biodegradability may result in pollution to the environment.
Such problems have aroused the increasing concern of the government and public.
Therefore, the development and utilization of environmentally friendly lubricants
is an important issue in the current development of lubricants. In this regard, biolubricants may play an important role as substitutes of mineral oil-based lubricants,
resulting in significant economic and social sustainable benefits.
7.2 Development of Bio-Lubricants
The present consumption of fossil fuels has led to significant levels of environmental
pollution and is rapidly diminishing petrochemical and energy reserves. Biomass
could be regarded as a promising carbon-based alternative energy source and a
sustainable chemical feedstock.
In this context, vegetable oil, which is extracted from the seeds or fruits of plants,
is the most commonly used feedstock for developing lubricants. The base oils of
bio-lubricants are mainly highly unsaturated or High Oleic Vegetable Oils (HOVOs),
including soybean oil, rapeseed oil, olive oil, peanut oil, castor oil, palm oil, etc. Compared with mineral oil-based lubricants, bio-lubricants are environmentally friendly
alternatives. Bio-lubricants have a number of advantages over mineral lubricants,
such as
1. Renewable ability: very low or almost negligible aquatic toxicity; good lubricating properties.
2. Excellent biodegradability: in general, the biodegradation rate of vegetable oils
is between 90 and 98%, whereas in the case of mineral oils this value is around
20% [4].
3. High Viscosity Index (VI): because of the strong intermolecular interactions of
the double bonds and the molecule linearity.
4. Low evaporation rates: they have an approximately 20% lower evaporation rate
than mineral oil-based fluids [28].
Molecularly, vegetable oil is an unsaturated fatty acid glyceride with an average
relative molecular weight of 800–1000. The chain length of the fatty acids is usually
in the range of C 12 –C 24 . The saturated fatty acids in vegetable oils mainly contain
soft fatty acids (such as palmitic acid), stearic acid, etc. The unsaturated fatty acids
mainly include oleic acid, erucic acid, linoleic acid, linolenic acid, and ricinoleic
acid. Accordingly, the composition of fatty acids varies between feedstocks, thus
determining the properties of vegetable oil.
A low melting point and good oxidative stability are essential to high-performance
lubricants. The number of the carbon–carbon double bond and the chain length of
fatty acids are two main factors to affect the oil properties. In general, increasing
the number of double bonds, i.e., increasing the degree of unsaturation of the oil
Y. Cao et al.
lubricants are inevitably discharged into the environment due to transportation, leakage, and natural replacement. Mineral oil-based lubricants which have high ecological toxicity and poor biodegradability may result in pollution to the environment.
Such problems have aroused the increasing concern of the government and public.
Therefore, the development and utilization of environmentally friendly lubricants
is an important issue in the current development of lubricants. In this regard, biolubricants may play an important role as substitutes of mineral oil-based lubricants,
resulting in significant economic and social sustainable benefits.
7.2 Development of Bio-Lubricants
The present consumption of fossil fuels has led to significant levels of environmental
pollution and is rapidly diminishing petrochemical and energy reserves. Biomass
could be regarded as a promising carbon-based alternative energy source and a
sustainable chemical feedstock.
In this context, vegetable oil, which is extracted from the seeds or fruits of plants,
is the most commonly used feedstock for developing lubricants. The base oils of
bio-lubricants are mainly highly unsaturated or High Oleic Vegetable Oils (HOVOs),
including soybean oil, rapeseed oil, olive oil, peanut oil, castor oil, palm oil, etc. Compared with mineral oil-based lubricants, bio-lubricants are environmentally friendly
alternatives. Bio-lubricants have a number of advantages over mineral lubricants,
such as
1. Renewable ability: very low or almost negligible aquatic toxicity; good lubricating properties.
2. Excellent biodegradability: in general, the biodegradation rate of vegetable oils
is between 90 and 98%, whereas in the case of mineral oils this value is around
20% [4].
3. High Viscosity Index (VI): because of the strong intermolecular interactions of
the double bonds and the molecule linearity.
4. Low evaporation rates: they have an approximately 20% lower evaporation rate
than mineral oil-based fluids [28].
Molecularly, vegetable oil is an unsaturated fatty acid glyceride with an average
relative molecular weight of 800–1000. The chain length of the fatty acids is usually
in the range of C 12 –C 24 . The saturated fatty acids in vegetable oils mainly contain
soft fatty acids (such as palmitic acid), stearic acid, etc. The unsaturated fatty acids
mainly include oleic acid, erucic acid, linoleic acid, linolenic acid, and ricinoleic
acid. Accordingly, the composition of fatty acids varies between feedstocks, thus
determining the properties of vegetable oil.
A low melting point and good oxidative stability are essential to high-performance
lubricants. The number of the carbon–carbon double bond and the chain length of
fatty acids are two main factors to affect the oil properties. In general, increasing
the number of double bonds, i.e., increasing the degree of unsaturation of the oil