Page 42 - Plant design and economics for chemical engineers

PROCESS DESIGN DEVELOPMENT 25

ride, sodium sulfate, carbovethyl cellulose, etc., are added to enhance the
detersive, wetting, or other desired properties in the finished product. A flaked,
dried product is obtained by drum drying or a bead product is obtained by spray
drying.
The basic reactions which occur in the process are the following.
Alkylation:

AU,
W% + C,,H, - C&b * W-b,
Sulfonation:

C,H, *C,,HZ + H,SO, + C,,H, *C,H, . SO,H + Hz0

Neutralization:
w%5 - C,H, *SO,H + NaOH + C,,H, . C,H, *SO,Na + H,O

A literature search indicates that yields of 85 to 95 percent have been
obtained in the alkylation step, while yields for the sulfonation process are
substantially 100 percent, and yields for the neutralization step are always 95
percent or greater. All three steps are exothermic and require some form of
jacketed cooling around the stirred reactor to maintain isothermal reaction
temperatures.
Laboratory data for the sulfonation of dodecylbenzene, described in the
literature, provide additional information useful for a rapid material balance.
This is summarized as follows:

1. Sulfonation is essentially complete if the ratio of 20 percent oleum to
dodecylbenzene is maintained at 1.25.
2. Spent sulfuric acid removal is optimized with the addition of 0.244 lb of
water to the settler for each 1.25 lb of 20 percent oleum added in the
sulfonation step.
3. A 25 percent excess of 20 percent NaOH is suggested for the neutralization
step.

Operating conditions for this process, as reported in the literature, vary
somewhat depending upon the particular processing procedure chosen.

Material and Energy Balance

The process selected for the manufacture of the nonbiodegradable detergent is
essentially continuous even though the alkylation, sulfonation, and neutraliza-
tion steps are semicontinuous steps. Provisions for possible shutdowns for
repairs and maintenance are incorporated into the design of the process by I