Oleochemical surfactants

A reexamination of so-called renewabdity has shown that advantages for oleochemicals are not sufftcientiy clear (115), especially because manufacture of surfactants ia the United States accounts for only 0.03% of aimual cmde oil consumption (62). On these bases, the primary determinants of surfactant choice will continue to be cost effectiveness and availability. The 1993 U.S. market has been estimated to be worth 3.7 x 10 (110). Approximately one-half was anionic surfactant ( 1.8 x 10 ) and one-third nonionic surfactant ( 1.2 x 10 ). The balance was made up by cationics ( 1.2 X 10 ) and amphoterics ( 600 x 10 ). The U.S. International Trade Commission (116) provides a minutely detailed breakdown of surfactant production. 

Compared with the fatty alcohol sulfates, which are also oleochemically produced anionic surfactants, the ester sulfonates have the advantage that their raw materials are on a low and therefore cost-effective level of fat refinement. The ester sulfonates are produced directly from the fatty acid esters by sulfona-tion, whereas the fatty alcohols, which are the source materials of the fatty alcohol sulfates, have to be formed by the catalytic high-pressure hydrogenation of fatty acids esters [9]. The fatty acid esters are obtained directly from the fats and oils by transesterification of the triglycerides with alcohols [10]. 

Surfactant alcohols are linear, primary alcohols with carbon chain lengths in the C12-C14 and the C16-C18 range. Surfactant alcohols can be derived from either petrochemical or oleochemical feedstocks, and thus are referred to either as synthetic alcohols or as natural (oleochemical) alcohols. Petrochemical feedstocks used for surfactant alcohol production are ethylene and, to a lesser degree, paraffins. 

For at least the next 25 years enough lauril (natural C12-C14) oil will not be available to replace petrochemical-based surfactants even if this were desired. However, the oleochemical share of the surfactant intermediate market will grow because a large portion of excess lauric oil (coconut and palm kernel) will be designated for the surfactant market and used to supply the fatty alcohol capacity that has been announced for startup in the coming years. 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

Surfactants can be produced from both petrochemical resources and/or renewable, mostly oleochemical, feedstocks. Crude oil and natural gas make up the first class while palm oil (+kernel oil), tallow and coconut oil are the most relevant representatives of the group of renewable resources. Though the worldwide supplies of crude oil and natural gas are limited—estimated in 1996 at 131 X 1091 and 77 X 109 m3, respectively [28]—it is not expected that this will cause concern in the coming decades or even until the next century. In this respect it should be stressed that surfactant products only represent 1.5% of all petrochemical uses. Regarding the petrochemically derived raw materials, the main starting products comprise ethylene, n-paraffins and benzene obtained from crude oil by industrial processes such as distillation, cracking and adsorption/desorption. The primary products are subsequently converted to a series of intermediates like a-olefins, oxo-alcohols, primary alcohols, ethylene oxide and alkyl benzenes, which are then further modified to yield the desired surfactants. 

A certain shift from petrochemically-based to oleochemically-based surfactants, namely on the alcohol derivatives field, has occurred in recent years in industrialised countries. Figure 1.2 represents the key derivatives and major intermediates used in the production of surfactants. 

Alcohols in the range C12—Ci8 are important raw materials for the production of a key group of surfactants ethoxylates, sulfates and ethoxysulfates among others. Alcohols used in the surfactant industry are primary, linear, or with different degrees of branching, and they can be produced from either petrochemical sources (ethylene or linear paraffins) or from oleochemical products (animal fats and vegetable oils). 

In polymer applications derivatives of oils and fats, such as epoxides, polyols and dimerizations products based on unsaturated fatty acids, are used as plastic additives or components for composites or polymers like polyamides and polyurethanes. In the lubricant sector oleochemically-based fatty acid esters have proved to be powerful alternatives to conventional mineral oil products. For home and personal care applications a wide range of products, such as surfactants, emulsifiers, emollients and waxes, based on vegetable oil derivatives has provided extraordinary performance benefits to the end-customer. Selected products, such as the anionic surfactant fatty alcohol sulfate have been investigated thoroughly with regard to their environmental impact compared with petrochemical based products by life-cycle analysis. Other product examples include carbohydrate-based surfactants as well as oleochemical based emulsifiers, waxes and emollients. 

The shift to oleochemicals has been supported by increasing environmental concerns and a preference by some consumers, especially in Europe, for materials based on natural or renewable resources. Although linear alkylbenzenesulfonates (LASs) are petrochemically based, alcohol ethoxylates, alcohol ethoxysulfates, and primary alcohol sulfates are derived from long-chain alcohols that can be either petrochemically or oleochemically sourced. There has been debate over the relative advantages of natural (oleochemical) vs synthetic (petrochemical) based surfactants. However, detailed analyses have shown there is litde objective benefit for one over the other. 

The metathesis of oleochemicals in the presence of ethylene, also called ethenolysis, provides an efficient way to a-oleftns and 0)-unsaturated esters, which are useful intermediates for the synthesis of polymers, fragrances, surfactants, lubricants, and others [51, 52], The ethenolysis of methyl oleate was demonstrated in 1994 by Grubbs et al. using C3 [32], They could reach productive turnovers of 130-140. In 2001, Warwel et al. carried out the ethenolysis of the methyl esters of oleic, erucic, 5-eicosenoic, and petroselinic acids also in the presence of C3 [53]. The reactions were performed at 50°C and 10 bar using 0.025 mol% of catalyst and gave conversions from 58% to 74%. 

The oldest surfactant is soap, which may be traced back to the ancient Egyptians and beyond. Synthetic surfactants had been produced in the first half of the 20th century but it was only after World War II, with the development of the modern petrochemical industry, that alternative feedstocks to oleochemicals became readily available. Hence chloroparaf-fins and/or alphaolefins and benzene were used to produce alkylbenzene (or alkylate ), processes were developed to produce a range of synthetic fatty alcohols and alkylene oxide chemistry resulted in ethylene oxide and propylene oxide building blocks becoming readily available. 

Figure 1.3 illustrates the use of fatty alcohols as a surfactant feedstock. Derived from either oleochemical or petrochemical sources, they may be needed to produce several families of both non-ionic and anionic surfactants. 

On a global basis, the 11 million tonnes or so of surfactants produced each year (excluding soap) utilises approximately equal volumes of oleochemical and petrochemical feedstocks. However, it is interesting to note that, in the case of fatty alcohols, the balance has changed over the last 20 years (Table 1.4). 

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. 

Raw materials. The hydrophobe for SME is currently derived exclusively from oleochemical sources, rather than from petrochemicals, as in the case of LAS and AOS. While these two sources can often provide surfactants of equivalent performance, oleochemcials are frequently preferred (especially in personal care applications) because they are derived from natural ingredients. The use of renewable resources is also cited as an additional benefit of oleochemical-based surfactants and this is discussed more fully in Section 4.2.1. 

Sulphosuccinates are prepared using a wide variety of alcohols and the choice of alcohol is a major determinant of the properties of the surfactant. In some instances, the consumers view of what materials are acceptable limits the choice of alcohol source with one example of this being the preference for oleochemical alcohols for personal care applications. 

Fatty alcohols, by which the author means those in the range C and above, are split into two classes, petrochemical and oleochemical, or, as they are more usually referred to, synthetic and natural. The discussion of the relative merits of synthetic vs natural products has been at the forefront of surfactant technology for many years and has produced a wealth of literature. It is beyond the scope of this work to discuss whether oleochemicals have an inherent environmental benefit over petrochemicals. A good deal of scientific study on life cycle analysis and macro environmental impact is available but social and ethical arguments, as well as the perceptions of the end consumer, also play a part. On a strictly scientific basis, the author sees no inherent advantage in either source. The performance of a surfactant based on synthetic materials may differ from a naturally derived one but neither is intrinsically better than the other. In terms of impact on humans and the environment, there is also no clear evidence to suggest a difference between the two sources of hydrophobe. 

Fatty acid salts and many polar derivatives of fatty acids are amphiphilic, possessing both hydrophobic and hydrophilic areas within the one molecule. These are surface-active compounds that form monolayers at water/air and water/surface interfaces and micelles in solution. Their surface-active properties are highly dependent on the nature of the polar head group and, to a lesser extent, on the length of the alkyl chain. Most oleochemical processes are modihcations of the carboxyl group to produce specihc surfactants. 

Thus, over the last half-century, petrochemically derived surfactants, led by LAS, have largely replaced soap, which has been the norm for almost five mUlenia. Nevertheless, oleochemically based surfactants continue to play a vital role in detergent formulations. Soap itself is generally present as a minor component to control suds profile, reduce dye transfer, control powder properties, and act as a cosurfactant or cobuilder. 

Thus, in the end, it will be seen there is no real difference between petrochemical- and oleochemical-based (alcohol) feedstocks for surfactants (9). On this basis, the primary determinants of hydrophobe choice for alcohol-based feedstocks have been price and availability. 

Another consideration is the source of the hydrophobic end of the surfactant. It is well known that oleochemical fatty alcohols have even numbers of carbons and petrochemicals fatty alcohols have odd and even numbers. As discussed earlier, carbon chain length has an effect on dishwashing performance. However, when... 

These anionic surfactants (Figure 8.5) are used primarily in Europe as a substitute for LAS [45], Environmental considerations have prompted manufacturers to use surfactants of this type, which can be derived from oleochemical sources. The carbon chain length can range from CIO to Cl8. Tallow alcohol sulfate is the... 

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