Olefin sulphonates

Although used very little in Europe, a-olefin sulphonates are a very important class of surfactants with widespread use in Asia, India and many developing regions. 

The properties of the two species are very different in terms of their solubility, viscosity and detergency. The alkene sulphonate is the better performing surfactant and the manufacturing process is developed to maximise this more desirable product. The sulphonation process is significantly more exothermic than LAB sulphonation, requiring careful control of reactor temperatures and more dilute S03 which often results in lower reactor loadings and hence lower productivity, compared to LAB. Low product colours can be achieved but require very careful control of sulphonation, neutralisation and hydrolysis. Earlier processes relied heavily 

Composition vs. performance. cr-Olefin sulphonates are produced from a number of olefin cuts, with differing performance characteristics. Typical products are Ci4 i6, C16-18 and Ci4 i8. These differing cuts give different performance attributes with the more soluble, lower molecular weight products being better foamers and the higher molecular weight 

Ci2 i4 olefin sulphonates are also used in personal care formulations since they are less aggressive than LAS and will not over-strip (i.e. degrease to leave an excessively dry or squeaky feel) the skin or hair although some care maybe required in formulating to compensate for a dry feel to the foam. AOS-based formulations are also more difficult to thicken than products based on alkyl sulphates or alkyl ether sulphates but use of alkanolamides or sarcosinates as secondary surfactants can overcome both problems and give a product more acceptable to the consumer. 

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Optimal Salinities Phase inversions at optimal salinity were assessed routinely by salt titrations into systems maintained at constant temperature. For the Leonox IOS surfactant system, increasing levels of salinity were necessary to cause the emulsion state to phase invert as the alkane molecular weight increased (Figure 11). Ihe initial conductivity value at the condition where zero salt had been added may in part reflect the salt contamination naturally present within the supplied formulation. Ihe internal olefin sulphonate species again revealed a linear relationship between EACN and optimal salinity as did all ionic formulations under test (see Figures 12 and 13, plus Table III). Ihe estimation of EACN values for both toluene... 

Aromatic - alkylbenzene, alkyltoluene, alkylxylene, alkylnaphthalene Aliphatic - a-olefin sulphonates, alkane sulphonates, sulphosuccinates... 

Chemistry and general properties. The chemistry of the olefin sulphonates is more complex than the sulphonates previously considered. They are manufactured in a three-stage process sulphonation, neutralisation and hydrolysis. Sulphonation is carried out in standard sulphonation reactors and yields a mixture of sulphonates (Figure 4.8). 

Composition vs. performance. Paraffin sulphonates have excellent solubility and surfac-tancy with detergent performance equivalent to LAS and solubility significantly better. As with olefin sulphonates, optimum detergency is found at a chain length of C15. 

As a class of surfactant, sulphonated methyl esters (SMEs) have been known since the 1980s, but have not been widely commercialised. Through the late 1990s into 2000, there were signs of increased use in Asia and the United States across a variety of applications. They share many similarities with olefin sulphonates but, importantly, they are made from renewable oleochemical feedstocks. This is preferred by many formulators, particularly in cosmetic and personal care applications. 

Hu, P.C. (1992). Foaming characteristics of alpha olefin sulphonate and its components. Proceedings 3rd CESIO International Surfactants Congress, vol. D, pp. 334 17. 

Nansa Series Alkyl benzene sulphonic acids and salts Olefin sulphonates... 

Calsoft Series Alkyl benzene and alpha olefin sulphonates... 

Stratification of asymmetric aqueous films from NaDoS, CTAB and a commercial surfactant (alpha-olefin sulphonate) solutions at C > Ccmc on a decane substrate have been studied by Bergeron and Radke [236], They found three transitions by thickness in the metastable multilayer films. They observed also stratified CTAB aqueous films on glass. The n(/i) isotherms of stratified films were analysed considering also the oscillatory structural component of disjoining pressure. 

Another class of sulphonates is the a-olefin sulphonates which are prepared by reacting linear a-olefin with sulphur trioxide, typically yielding a mixture of alkene sulphonates (60-70%), 3- and 4-hydroxyalkane sulphonates ( 30%), and some disulphonates and other species. The two main a-olefin fractions used as starting material are C 2 ie Fatty acid and ester sulphonates are produced... 

Roberts, D. W. Kinetics and mechanism in olefin sulphonation. Riv. Ital. Sostanze Grasse, 74(12), 567-570,1997. 

The neutralised product of alpha-olefin sulphonation requires hydrolysis to remove sultones... 

Only the alpha-olefins are sulphonated commercially to make alpha-olefin sulphonate (AOS). The chemistry of alpha-olefin sulphonation is usually described in terms of 3 stages. 

Thus the basic principles for minimising colour are good control of the reaction temperature and use of the minimum of SO3 necessary for complete conversion. Olefins are colour precursors in any feedstock which is sulphonated under conditions more severe than those appropriate for olefin sulphonation. 

Nagayama M. et al. (1974). Bull. Chem. Soc. Japan 47 p 2158. (Topic Alpha-Olefin Sulphonation). 

Table 34 Specification of alpha-olefin sulphonates based on top quality C,.-C, and Ci -Cu ...

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