Page 8 - Microsoft Word - Sulfo and Sulfa 1.doc

As previously mentioned, a commercially successful sulfonation process requires
reaction of SO with the organic feedstock under tightly controlled conditions. Figure 9
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[3]
illustrates the level of control demanded by the air/SO sulfonation process . This
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illustration shows the production of 1,4-dioxane, an undesirable by-product formed
during the sulfation of ethoxylated alcohols. The 1,4-dioxane formed is a function of
mole ratio (kg moles per unit time of SO fed to the reactor divided by kg moles per unit
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time of feedstock fed to the reactor). As the mole ratio of SO to organic feedstock
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increases, the level of dioxane in the product remains relatively low at 20 to 30 ppm. A
critical point of over-sulfation occurs at a mole ratio of approximately 1.03. Once over-
sulfation occurs and the mole ratio exceeds 1.04, dioxane production increases rapidly to
values measured in hundreds of parts per million. Similar adverse responses are
observed with product color or levels of unsulfonated or unsulfated (free oil) materials in
the product. Clearly, the sulfonation process must be controlled to within 1% of the
desire mole ratio in order to achieve excellent product quality. Other important process
variables are reaction temperature, SO gas concentration, time to neutralization,
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neutralization pH and neutralization temperature. These variables also influence product
quality although the effect is not as dramatic as the effect of mole ratio.

Figure 9. 1,4-Dioxane vs. Mole Ratio

Five minutes acid recycle residence time at
30°C and 2.5% SO inlet gas concentration
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1,4-Dioxane, AM Basis (ppm) 600
800
700

500

400
300
200
100
0
0.97 0.98 0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 1.07
Mole Ratio (SO /A3EO)
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Page 7 of 36 © 1997 The Chemithon Corporation