138
C. Li et al.
KOH do not require strict reaction conditions. They are widely used in industrial
production because of their affordable price.
5.2.1 Acid-Catalyzed Transesterification
Acid catalysts for transesterification include sulfuric, phosphoric, hydrochloric, and
sulfonic acids [20, 21]. Acid-catalyzed transesterification is much slower than basecatalyzed transesterification, but in cases when glycerides have a high level of free
fatty acid and water, acid-catalyzed transesterification is the better option. The transesterification process can be sufficiently completed in an acidic condition of the given
vegetable oil is low-grade oil (such as sulfatized olive oil). On-site transesterification
is different from traditional reaction methods with which vegetable oils are extracted
from the mixture. Instead, the raw material containing vegetable oils is in direct
contact with acidified alcohols. That is, extraction and transesterification take place
simultaneously. Alcohols serve as both extractant and reactant of esterification. By
on-site transesterification, sunflower oil reacts with acidified methanol to form fatty
acids methyl ester. Its reaction yield is larger than the traditional method with which
vegetable oils are extracted in advance.
5.2.2 Base-Catalyzed Transesterification
Base catalysts for transesterification include strong bases (for example NaOH and
KOH for unrefined oils and fats), carbonate, and alkyl oxides [22–25] (for example
sodium methoxide, sodium ethoxide, sodium isopropoxide, and sodium n-butoxide
for refined oils and fats). Generally, NaOMe has a higher catalytic efficiency than
NaOH because the mixture of NaOH and MeOH will produce a small amount of
H 2 O, which can lead to saponification. However, Ma et al. came up with an opposite
conclusion that transesterification of cattle tallow requires 0.3% and 0.5% (W/W)
of NaOH and MeOH, respectively, as catalysts to maximize the level of activity.
Freeman et al. found that if the molar ratio of alcohol/oil is 6:1, the reactions catalyzed
by 1% NaOH or 0.5% MeOH will produce almost identical resultants after onehour reaction time. In particular, NaOH has become the first-choice catalyst for
transesterification because of its low price, making it widely applicable in large-scale
industrial production.
5.2.3 Enzyme-Catalyzed Transesterification
Despite that base-catalyzed transesterification is capable of producing a high yield
in a short period of time, it has the following shortcomings: the reaction consumes
C. Li et al.
KOH do not require strict reaction conditions. They are widely used in industrial
production because of their affordable price.
5.2.1 Acid-Catalyzed Transesterification
Acid catalysts for transesterification include sulfuric, phosphoric, hydrochloric, and
sulfonic acids [20, 21]. Acid-catalyzed transesterification is much slower than basecatalyzed transesterification, but in cases when glycerides have a high level of free
fatty acid and water, acid-catalyzed transesterification is the better option. The transesterification process can be sufficiently completed in an acidic condition of the given
vegetable oil is low-grade oil (such as sulfatized olive oil). On-site transesterification
is different from traditional reaction methods with which vegetable oils are extracted
from the mixture. Instead, the raw material containing vegetable oils is in direct
contact with acidified alcohols. That is, extraction and transesterification take place
simultaneously. Alcohols serve as both extractant and reactant of esterification. By
on-site transesterification, sunflower oil reacts with acidified methanol to form fatty
acids methyl ester. Its reaction yield is larger than the traditional method with which
vegetable oils are extracted in advance.
5.2.2 Base-Catalyzed Transesterification
Base catalysts for transesterification include strong bases (for example NaOH and
KOH for unrefined oils and fats), carbonate, and alkyl oxides [22–25] (for example
sodium methoxide, sodium ethoxide, sodium isopropoxide, and sodium n-butoxide
for refined oils and fats). Generally, NaOMe has a higher catalytic efficiency than
NaOH because the mixture of NaOH and MeOH will produce a small amount of
H 2 O, which can lead to saponification. However, Ma et al. came up with an opposite
conclusion that transesterification of cattle tallow requires 0.3% and 0.5% (W/W)
of NaOH and MeOH, respectively, as catalysts to maximize the level of activity.
Freeman et al. found that if the molar ratio of alcohol/oil is 6:1, the reactions catalyzed
by 1% NaOH or 0.5% MeOH will produce almost identical resultants after onehour reaction time. In particular, NaOH has become the first-choice catalyst for
transesterification because of its low price, making it widely applicable in large-scale
industrial production.
5.2.3 Enzyme-Catalyzed Transesterification
Despite that base-catalyzed transesterification is capable of producing a high yield
in a short period of time, it has the following shortcomings: the reaction consumes