Page 4 - 81Sulfonation-Sulfation Processing Technology for Anionic Surfactant Manufacture_opt

Sulfonation/Sulfation Processing Technology for Anionic Surfactant Manufacture 271

2.2 Primary alcohol sulfates (PAS)
PAS are categorized in different groups regarding the number carbon that compose them:
The so called lauryl alcohol sulfates C 12-C 14, the “tallow” alcohol sulfates (TAS) C 16-C 18, and
the broader cut C 10-C 18 alcohol sulfate comprising coconut fatty alcohol sulfates. The broad
cut (C 10-C 18) alcohol sulfates presents cost/performance equilibrium in terms of detergency,
solubility and foaming properties. This product can partially or totally substitute other
anionic surfactants either in liquid or powder detergent formulations with adequate
biodegradability and low “defatting action”, which is important for human tissue and
delicate natural or synthetic fibers. The narrow cut (C 12-C 14) alcohol sulfates find their main
application in a wide range of personal care products such as shampoos, bubble bath
products, tooth pastes, dishwashing liquid, delicate products for laundry wash. The C 16-C 18
alcohol sulfates (“tallow”) are used as sodium salts in the formulation of heavy duty
laundry products for hand and machine washing. Their detergency power is up to 10%
higher than LABS in a wide range of detergent formulations (de Groot, 1991). Furthermore,
TAS shows controlled foam, which is important mainly at high temperatures, still keeping
the advantage of softness in the wash of sensitive natural and synthetic fibers (Rosen, 2005).
The physical detergency and biodegradability of primary alcohols can be affected by the
carbon chain length distribution. Therefore, each new supply may require testing to
determine whether the desired properties in the chosen application can be achieved. The
mechanism for alcohol sulfation is thought to be similar to that for linear alkylbenzene
sulfonation with ∆H = —150 kJ/mol (Figure 3).

Fig. 3. Mechanism of alcohol sulfation (adapted from Roberts, 1998)

2.3 Alcohol ether sulfates (AES)
Primary alcohol ethoxylates are made by the addition of ethylene oxide to a primary alcohol
in the presence of an alkaline catalyst (Boskamp & Houghton, 1996). The addition of the
second ethylene oxide molecule to the alcohol is kinetically favored in comparison with the
addition of the first ethylene oxide; hence the product of ethoxylation contains a distribution
of ethylene oxide chain lengths attached to the alcohol along with the starting alcohol itself.
Consequently the physical, detergency and biodegradation characteristics are affected not
only by the carbon chain length distribution as is the case for primary alcohols, but also by
the ethylene oxide distribution which in turn can be supplier depend (de Groot, 1991). The
most common alcohol ethoxylates found as feedstocks for sulfation have an average of 2 to 3
molecules of ethylene oxide (2EO or 3EO).

During the sulfating of alcohol ethoxylates the by-products 1,4-dioxane may be formed
(Figure 4). Although the formation of 1,4-dioxane is governed predominantly by sulfation
and neutralization conditions and by the chemical composition of the feedstock, other
factors such as the quality of the raw material also contribute. These factors must be
considered during the store and handling of the alcohol ethoxylate feedstock.

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