Page 7 - 81Sulfonation-Sulfation Processing Technology for Anionic Surfactant Manufacture_opt

274 Advances in Chemical Engineering

i. Adaptability: All types of organic feedstocks, like alkylbenzenes, primary alcohols,
alcohol ethers, alfa-olefins and fatty acid methyl esters, can be successfully transformed
to high-quality sulfonate/sulfate active detergents using SO 3/air as sulfonating reagent.
Sulfonating reagents like sulfuric acid and oleum are less desirable because only
alkylbenzene feedstocks can be converted to high-quality alkylbenzene sulfonic acids.
ii. Security: Concentrated sulfuric acid, liquid SO 3, and oleum (20 or 65%) are hazardous
to be handled, transported, and storage. Sulfur, either in liquid or solid form, although
less dangerous option as initial material for the manufacture of SO 3, is still risky.
iii. Price: SO 3 obtained directly from the sulfur combustion is the most economical option
among all the others options mentioned above regarding transport, handle and storage.
iv. Availability: Liquid SO 3, 65% and 20% oleum and even sulfuric acid are not produced
everywhere. Even close to sulfuric acid plants, it is not guaranteed the availability of all
the gamma of oleum concentrations.
Several studies have been done about absorption along with exothermic reaction in a Falling
Film Reactor - FFR (Mann & Moyes, 1977; Villadsen & Nielsen, 1986), particularly for
dodecylbenzene and tridecylbenzene sulfonation. However, due to de complexity of
processes taking place inside the FFR has not been completely elucidated, being of special
interest today. The SO 3-sulfonation is carried out in tubular reactors where the organic
matter (liquid) wets the wall of the tubes while a gas stream containing the sulfonating
reagent flows in co-current with the organic matter to avoid over-sulfonation (MacArthur et
al., 1999). The simplest FFR configuration can be described as a two concentric tubes
arranged in a vertical way (Figure 6).

Fig. 6. Sketch of falling film reactor
Organic matter forms a thin film covering the inner wall of the inner tube. The film descends
from the top of the reactor in laminar flow forming an annulus for whose interior a gas stream
flows in turbulent regimen. In the first reaction section the concentrated sulfonate reagent get
in touch with fresh organic matter. The reaction rate is high as well as the amount of heat
released (150 – 170 kJ/mole). A coolant stream flows by the external wall of the inner tube in
parallel with the reactant streams. As long as the reaction advances the viscosity of the liquid
phase increases (ca. 100 times the initial value). The depletion of reactants reduces the reaction
rate and the increase of viscosity slow down the mass transfer process in the film. In this point
the co-current coolant, this has already removed a huge amount of heat from the first reactor
zone, works as a heating current that controls the viscosity of the film.

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