Page 7 - Microsoft Word - Sulfo and Sulfa 1.doc

waste acid must be separated from the reaction mixture and subsequently disposed. In
North America, the expense of disposing the "spent" sulfuric acid has become so high
that the process economics are now questionable.

Sulfonation with sulfuric acid is a special case of oleum sulfonation. Because the
sulfonation reaction stops when the acid concentration in the reaction mixture drops to
less than approximately 90%, sulfonation of detergent feedstocks with sulfuric acid is not
normally practiced. Today sulfuric acid sulfonation is principally used for production of
hydrotropes by azeotropic reaction with benzene, toluene or xylene. In this special
process, the water formed during the reaction is removed by azeotropic distillation of the
water and unreacted feedstock. The water is then separated from the immiscible organic
feedstock which is returned to the reaction vessel. Because water is removed, the
reaction may continue to completion.

The air/SO sulfonation process is a direct process in which SO gas is diluted with very
3
3
dry air and reacted directly with the organic feedstock. The source of the SO gas may be
3
either liquid SO or SO produced by burning sulfur. As shown in Figure 8, the reaction
3
3
of gaseous SO with organic is rapid and stoichiometric. It is complicated by the
3
possibility of side reactions and therefore tight process control is essential. The cost for
liquid SO is US$0.09 per pound of reactive SO ; while SO from sulfur burning is
3
3
3
US$0.02 per pound of reactive SO . The air/SO sulfonation process is the lowest SO
3
3
3
cost of any sulfonation process and is extremely versatile, producing very high quality
products. However, it is a continuous process best suited to large production volumes.
In addition, it requires expensive precision equipment and highly trained operating
personnel.
Figure 8. Air / SO 3
SO + CH - (CH ) - CH - (O - CH - CH ) - OH
2 10
2
3
3
2
2 3
Sulfur Ethoxylated lauryl alcohol
trioxide
O
–
CH - (CH ) - CH - (O - CH - CH ) - O - S - O H +
2 10
2
2
2 3
3
O
Ethoxylated lauryl alcohol sulfuric acid

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