Page 14 - Microsoft Word - Sulfo and Sulfa 1.doc

through an external heat exchanger. Because it is an equilibrium reaction, except for the
special case of azeotropic sulfonation of hydrotropes with sulfuric acid, a large surplus of
sulfuric acid forms. When the sulfonation reaction is complete, the sulfuric acid may be
separated from the sulfonated detergent alkylate by adding water. The water addition
(typically about 10% by weight of the reaction mixture) causes a phase separation to
occur between the sulfonic acid and the diluted sulfuric acid. The separation usually
takes place in a separate, glass lined vessel and occurs over a period of about

Figure 14. Batch Oleum Sulfonation of Detergent Alkylate

Optional Sodium
Alkyl Benzene
Sulfonate
Alkylate

Oleum 20%
CW CW
Spent
Sulfuric Acid
Weigh Tanks Sulfonator Gravity Acid Separator Neutralizer

10 hours. Materials of construction are crucial because the dilution process makes
sulfuric acid which is in a very corrosive temperature and concentration range. After
separation, the sulfonic acid may be neutralized with aqueous sodium hydroxide, usually
in a separate neutralization vessel. Including neutralization, total batch time is 15 to 20
hours. The product contains about 15% sodium sulfate after neutralization if the acid is
separated, and about 60% sodium sulfate if not. Without separation, the product's
application is limited to low active, traditional detergent powders where the large content
of sodium sulfate is used as a filler.

In the special case of azeotropic sulfonation of toluene, cumene or xylene with 98%
sulfuric acid to form hydrotropes, a reflux condenser is added at the top of the reactor.
The condenser separates the unreacted feed from the water produced in the reaction. The
water is removed from the condenser, and the feed is refluxed back to the reactor.
Because the water is removed, the reaction proceeds to completion and a large excess of
sulfuric acid is not required. Typical equipment for hydrotrope sulfonation is shown in
Figure 15.

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