Page 15 - 81Sulfonation-Sulfation Processing Technology for Anionic Surfactant Manufacture_opt

282 Advances in Chemical Engineering

higher sulfonation degrees. Although the coloration is identified mostly as an esthetic factor
for the commercialization of sulfonates, higher colorations can also be a qualitative indicator
of over-sulfonation. Anionic surfactants in aqueous solution have colors ranging from
yellow to reddish orange (Inagaki, 2001).

6. Film SO 3-sulfonation applied
6.1 Sulfonation of methyl ester with SO 3

Use of methyl esters (ME) in the industry detergent, although under investigation and
development since more than 25 years, has not yet expanded to high levels, mainly because
the following reason:

i. Controversial forecasts about availability of petrochemical feedstocks with related cost
comparison via vs. natural sources;
ii. Viability of sufficient quality of sulfonation grade methyl esters;
iii. The process to produce high quality -sulfonated methyl ester (SME) is generally more
complex than that for alkyl benzene sulfonates;
iv. Application know-how is not yet completely availed and low FAMES solubility
involves some restrictions in application, notably concerning the use in liquid detergent
products and low temperature washing cycles.

Complex chemistry is not yet fully elucidated, but may be summarized as is shown in
Figure 15 (Morales & Martínez, 2009).

Fig. 15. Mechanism of methyl ester sulfonation in sulfonator (Torres et al., 2009b)

The methyl ester molecule is initially di-sulfonated in a relatively fast reaction accompanied
with a high amount of heat released (Roberts, 2003). There is a third reaction stage
considerably slower than the previous ones, where an SO 3 group is liberated (on aging). For
some researchers, this SO 3 group just released would be especially active and therefore
capable of directly sulfonating another methyl ester molecule in an alfa position. The

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