214
R. Tesser et al.
Different studies on the behaviour of these compounds have been performed. In
particular, the behaviour of other surfactants strengthens as the fatty acids become
ionized and turn to soaps with an increasing pH. This transition, and its effect on
surface-active properties, has consequently been subject to several studies. At low
pH values, the predominant molecule is the undissociated fatty acid. At intermediate
values (pH 4–8), undissociated acid, anionic carboxylates as well as so-called acid
soaps, (RCOO) 2 H
− , coexist in the system. At alkaline pH, carboxylate anions and
acid–soap salts, (RCOO) 2 HNa, dominate the solution and the surface layer [207].
Polyethylene glycol fatty acid esters
In industry, polyethoxylation and polypropoxylation reactions are usually performed
to prepare non-ionic surfactants and polymers [55, 57, 189]. Direct ethoxylation of
fatty acids and fats with conventional catalysts yields a complex mixture of monoand diesters, as well as various polyethylene glycols as by-products, with a wide
range in the number of polyethylene glycol units. Usually, the polyethoxylation and
polypropoxylation reactions are usually performed using as catalyst an alkaline compound as sodium hydroxide, sodium methylate, sodium acetate, potassium hydroxide
or related alkoxides [133]. In the past years, based on experiences of narrow-range
ethoxylation catalysis, new catalysts have been developed that enable a direct ethoxylation of short-chain alkyl esters of fatty acids [207]. Products obtained are used as
emulsifiers in food and technical applications. In general, polyoxyethylene esters
of fatty acid methyl esters have been found to have good emulsifying, lubricating,
dispersing and suspending power and these properties, combined with detergent and
antistatic characteristics, provide a potential use in a variety of textile processing
applications. Good wetting, penetrating and dispersing properties have made them
useful as adjuvants in agricultural products. A comparison between fatty acid methyl
ester ethoxylates and the corresponding range of alcohol ethoxylates shows that the
critical micelle concentration value is somewhat higher and surface tension at this
value lower for the methyl ester ethoxylates [207]. For what concern the other differences between ethoxylates methyl esters and the corresponding alcohol ethoxylates
are: detergency is similar, foam is lower due to methyl group terminating the alcohol
chain, cloud point is approximately 10 °C lower.
Methyl ester sulfonates
The reaction between fatty acid methyl esters and an excess of sulphur trioxide (15–
30%) produce methyl ester sulfonates [68]. The reaction is carried out in a falling
film reactor at about 90 °C and it is followed by neutralization with alkali, such as
KOH [68].
Methyl ester sulfonates are an important class of anionic biosurfactants. Methyl
ester sulfonates’ biosurfactants market size may generate over USD 900 million by
2024. These products offer superior properties such as good detergency, excellent
biodegradability and improved calcium hardness tolerance. Methyl ester sulfonates
are environment friendly as it is low toxicity and high biodegradability characteristics. These products are cost-effective and have excellent detergent properties which
R. Tesser et al.
Different studies on the behaviour of these compounds have been performed. In
particular, the behaviour of other surfactants strengthens as the fatty acids become
ionized and turn to soaps with an increasing pH. This transition, and its effect on
surface-active properties, has consequently been subject to several studies. At low
pH values, the predominant molecule is the undissociated fatty acid. At intermediate
values (pH 4–8), undissociated acid, anionic carboxylates as well as so-called acid
soaps, (RCOO) 2 H
− , coexist in the system. At alkaline pH, carboxylate anions and
acid–soap salts, (RCOO) 2 HNa, dominate the solution and the surface layer [207].
Polyethylene glycol fatty acid esters
In industry, polyethoxylation and polypropoxylation reactions are usually performed
to prepare non-ionic surfactants and polymers [55, 57, 189]. Direct ethoxylation of
fatty acids and fats with conventional catalysts yields a complex mixture of monoand diesters, as well as various polyethylene glycols as by-products, with a wide
range in the number of polyethylene glycol units. Usually, the polyethoxylation and
polypropoxylation reactions are usually performed using as catalyst an alkaline compound as sodium hydroxide, sodium methylate, sodium acetate, potassium hydroxide
or related alkoxides [133]. In the past years, based on experiences of narrow-range
ethoxylation catalysis, new catalysts have been developed that enable a direct ethoxylation of short-chain alkyl esters of fatty acids [207]. Products obtained are used as
emulsifiers in food and technical applications. In general, polyoxyethylene esters
of fatty acid methyl esters have been found to have good emulsifying, lubricating,
dispersing and suspending power and these properties, combined with detergent and
antistatic characteristics, provide a potential use in a variety of textile processing
applications. Good wetting, penetrating and dispersing properties have made them
useful as adjuvants in agricultural products. A comparison between fatty acid methyl
ester ethoxylates and the corresponding range of alcohol ethoxylates shows that the
critical micelle concentration value is somewhat higher and surface tension at this
value lower for the methyl ester ethoxylates [207]. For what concern the other differences between ethoxylates methyl esters and the corresponding alcohol ethoxylates
are: detergency is similar, foam is lower due to methyl group terminating the alcohol
chain, cloud point is approximately 10 °C lower.
Methyl ester sulfonates
The reaction between fatty acid methyl esters and an excess of sulphur trioxide (15–
30%) produce methyl ester sulfonates [68]. The reaction is carried out in a falling
film reactor at about 90 °C and it is followed by neutralization with alkali, such as
KOH [68].
Methyl ester sulfonates are an important class of anionic biosurfactants. Methyl
ester sulfonates’ biosurfactants market size may generate over USD 900 million by
2024. These products offer superior properties such as good detergency, excellent
biodegradability and improved calcium hardness tolerance. Methyl ester sulfonates
are environment friendly as it is low toxicity and high biodegradability characteristics. These products are cost-effective and have excellent detergent properties which