Early Environmental Issues
concerning Detergent Chemistry
Propylene tetramer benzene sulphonate held almost undisputed sway as the major
ingredient used in washing operations till the early 1960s. Around this time it was noted,
however, that sewage treatment problems were arising. The amount of foam on rivers was
increasing and where water was being drawn from wells located close to household discharge
points, the water tended to foam when coming out of the tap. This was attributed to the
fact that propylene-based alkyl benzene sulphonates are not completely degraded by the
bacteria naturally present in effluents, and was further narrowed down to the fact that it
is the branched-chain formation of the alkyl benzene which hinders the attack by the
bacteria. However, fatty acid sulphates were found to degrade very easily, and since all
naturally occurring fatty acids from which fatty alcohols are produced are of the
straight-chain variety (as also are the Ziegier alcohols which started appearing in
commercial quantities at about this time), it seemed possible that a straight-chain alkyl
benzene might be degradable.
Methods of test were developed and it was, in fact, proved that linear alkyl
benzene is biodegradable. Germany introduced legislation prohibiting the discharge of
non-biologically degradable material into sewer systems. In the USA detergent
manufacturers agreed voluntarily to switch over from PT benzene to linear alkyl benzene by
June 1965. In the United Kingdom a similar type of 'gentleman's agreement' was entered
into.
The change to linear alkyl benzene (which can be considered as a return to a
purified form of the keryl benzene in use twenty years previously) gave some rather
surprising results. It was found that the detergency in a heavy-duty formulation using
linear alkyl benzene sulphonate was approximately 10 per cent better than when using PT
benzene sulphonate, solutions of the neutralized sulphonic acid had a lower cloud point,
and pastes and slurries had a lower viscosity. The first two results were obviously
advantageous and a lower viscosity in slurries had an advantage when the product was
spray-dried to a powder, but when the LAS was sold as a liquid or paste detergent, this
lower viscosity had to be overcome as sales appeal was lost. The manufacture of powders
based on LAS posed some problems, however. Powders became sticky and lost their
free-flowing characteristics, whether made by spray-drying or one of the other methods.
Mausner and Rainer' have indicated that the actual isomer distribution of the
linear alkylate has an effect on the stickiness of the powder, with the 2-phenyl isomer
giving the greatest tendency to stickiness and the 5- or 6-phenyl isomer the least.
Additives to overcome this tendency have therefore been developed.
The switch to linear alkyl benzene is not, however, complete. In many parts of
the world where the problem of sewage treatment is not serious, the PT benzene is still
being used in ever-growing quantities. Also the Ziegler alcohols are now competitively
priced with the linear alkyl benzenes, and alkane sulphonates are reappearing. Having
successfully coped with the problem of biodegradation the industry faced a new attack. It
appeared that in certain lakes and ponds algae started reproducing at an unprecedented
rate. This was blamed on the extensive use of phosphates which are a food for these
organisms, and again the detergent industry became the whipping boy, because tremendous
amounts of sodium tripolyphosphate are used and then discharged down the sewer. (The term
eutrophication, meaning nutrition by chemical means, has been applied to this phenomenon.)
It is not clear whether the blame should be taken solely by the detergent industry, as
concurrently with the increase in the use of detergent phosphates there was an increase in
the use of phosphate fertilizers, which also find their way into natural water systems.
However, with the big international preoccupation with ecology the detergent industry is
searching for an efficient substitute for sodium tripolyphosphate.
To date a complete replacement has not been found but in the Scandinavian
countries particularly, formulations of household powders are beginning to appear with
appreciable portions of the phosphate replaced by NTA (nitrilo triacetic acid) which is a
better sequestering agent than tripolyphosphate but has none of the other properties
exhibited by the phosphate. There are fears that in time the extended use of NTA might
bring new problems of this sort, as it contains nitrogen which is again a good fertilizer
and nutrient for algae.
The search is still going on for a phosphate substitute. NTA on its own will
only partially replace phosphates. A mixture of NTA and borax has been suggested as a
complete replacement but here again the borax might produce more problems than the
phosphate is alleged to produce. Some of the hydroxy-polycarboxylic acids not containing
nitrogen are also being considered.
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