Biodegradation branched alkylbenzene sulfonates

It is common practice to put the experimentally obtained values for biodegradation and aquatic toxicity into a kind of matrix, as is illustrated by Fig. 2. The shaded areas in the matrix are the approved areas . Out of the six product types discussed above linear alkylbenzene sulfonates, alcohol ethoxylates, and ester quats lie within the shaded areas, while branched alkylbenzene sulfonates, alkylphenol ethoxylates and stable quats do not. 

A major shift in the anionic conqionent of the agrochemical EC emulsifier systems is finally taking place in die U.S. as linear alkylbenzene stdfoiuite is replacing hard, or branched alkylbenzene sulfonate. Ilie linear version is more easily biodegraded, and has replaced the branched version in almost all application areas in the U.S. outside of agrochemicals already. In Asia and Europe, the switch to linear has already taken place even in ag applications. 

The three transitions mentioned above, replacement of branched alkylben-zene sulfonates by linear alkylbenzene sulfonates, replacement of alkylphenol ethoxylates by alcohol ethoxylates and substitution of ester quats for stable quats are all driven by environmental concerns. Rate of biodegradation and aquatic toxicity are the major parameters taken into account, and, in order to pass the regulations that the European Union has adopted, a surfactant must pass the criteria of showing ... 

Alkylbenzene. Alkylbenzene is an intermediate for the production of alkylbenzene sulfonate. Alkylbenzene consists of a mixture of phenyl substituted n-alkanes of 9 to 14 carbon atoms. Prior to 1965, alkylbenzene was synthesized from propylene tetramer, obtained by oligomerization of propylene. The resulting hard alkylate was a highly branched chain compound. However, the slow biodegradability of propylene tetramer-based materials soon became apparent and by 1965, most of the detergent industry had switched over to linear alkylbenzene. Extensive research has demonstrated... 

In the mid- 1960s branched-chain surfactants were replaced by more biodegradable analogs in all laundry products. In heavy-duty liquids sodium alkylbenzene-sulfonate, derived from an alkylbenzene with a tetrapropylene side chain, was replaced by its straight-chain analog, referred to as sodium linear alkylbenzesul-fonate (LAS). 

The separation of linear and branched alkanes is also of importance in the process known as dewaxing, in which the removal of normal alkanes makes the product hydrocarbon less viscous and reduces the so-called pour point temperature. Such processes can be combined with catalytic isomerisations to optimise the value of oil fractions (Chapter 8). Linear paraffins are also separated using a zeolite-based process from kerosene fractions to give reactants for the synthesis of linear alkylbenzene sulfonate anionic surfactants, which are both cost effective and biodegradable. 

Since linear alkylbenzene derivatives are more readily biodegradable than branched ones, the use of branch-chain alkylbenzene sulfonates has sharply declined with the introduction of respective regulations since the mid-1960 s (e.g. the West German Detergents Law of 1962). 

Some recent patents describe the use of modified alkylbenzene sulfonate surfactant mixtures. The modified LAS is synthesized to contain some branching in the alkyl chain, while attempting to maintain the required biodegradability. It is claimed that using mixtures that contain branched... 

Ethanolamine soaps obtained from alkylarylsulfonic acids, preferably alkylbenzene sulfonic acids, or from alcohol sulfates are growing steadily in importance and dominate the market for household cleansers. The use of linear alkyl groups instead of branched chains in these products has resulted in greater biodegradability. 

Description. Today, the linear alkylbenzene sulfonate is the most important surfactant used. Linear chains are preferred over the branched ones due to their improved biodegradability. The reaction of linear olefins or chlorinated straight-chain paraffins with benzene in the presence of Friedel-Crafts-type catalysts (AICI3 or HF) yields linear alkylbenzene (LAB), the precursor of LAS this raw material can be procured under very attractive commercial conditions. The LAB isomer distribution depends on the type of catalyst selected. Isomers with the phenyl in the 2-position are present at about 20% and 30% in the mixture resulting from HF- and AlCls-catalyzed processes, respectively. 

Sulfonation of substituted benzenes is used in the synthesis of detergents. Thus, long-chain branched alkylbenzenes are sulfonated to the corresponding sulfonic acids, then converted into their sodium salts. Because such detergents are not readily biodegradable, they have been replaced by more environmentally acceptable alternatives. We shall examine this class of compounds in Chapter 19. 

Particularly important members of this family are the alkylbenzene sulfonates (ABS) and the linear alkylbenzene sulfonates (LABS). The ABS family, as mentioned earlier, is based on highly branched tetrapropylene alkyl groups that resist biodegradation processes, something that is less of a problem with the linear alkyl analoges. 

In contrast to TPS with its branched alkyl chain, n-dodecylbenzene sulfonate exhibits an extremely fast rate of biodegradability. The change-over from a branched to a straight-chain structure is easily achieved, and thus by the use of Ziegler synthesis and molecular-sieve extraction techniques, industrial processes for the production of linear olefines and -alkanes soon became readily available. These are the basic starting materials for the synthesis of linear alkylbenzene derivatives. 

---