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two hours the time required to achieve stable conversion of SO to SO so that
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sulfonation can begin. These features significantly reduce the time required for gas plant
start-up and eliminate the use of sulfur as a fuel to heat the gas plant during start-ups.
Production of SO , which must be scrubbed from the exhaust gas prior to discharge to the
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atmosphere, is minimized, therefore reducing plant operating costs.
The SO absorber unit, shown in Figure 23, is capable of treating the total output from
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the SO generation system to form 98% sulfuric acid. It is a convenience in plant start-
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up, shutdown and product changeover. It is also recommended in situations where
frequent power failures can interrupt production. With this equipment, the plant can be
restarted without forming off-specification product. If this unit is not used, the
sulfonation reactor itself must be used to scrub SO from the process gas during gas plant
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start-ups. This is an undesirable procedure, however, as the gas plant has not stabilized
during the start-up process and the mole ratio of SO to feedstock is unknown. The
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practical solution to this problem is to purposely under-sulfonate alkylbenzene during the
start-up. The off-specification material made in this start-up procedure can be stored and
later blended back into the product. The SO absorber system is almost a necessity if
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only alcohol feedstocks are run in the plant, because alcohol sulfuric acids cannot be
stored and reused.
SO mixed in air enters the absorber column where it contacts 98% sulfuric acid. The
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SO is absorbed into the acid, which separates from the remaining air in the scrubber
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body. A mesh pad mist eliminator removes entrained acid mist from the air as it exits the
vessel. Water is added to control the concentration of the sulfuric acid as it flows
through the acid circulation system. An instrument system with dual conductivity
sensors holds the acid concentration at 98% by controlling water addition. A heat
exchanger in the absorber circulation loop removes heat of dilution.
The sulfonator is the heart of a sulfonation plant. Sulfonic acid forms in the sulfonator
when an SO -in-air mixture is injected into the reactor simultaneously with the desired
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organic feed under carefully controlled conditions of mole ratio, SO gas concentration
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and temperature. Potential organic feedstocks include alkylates, alcohols, ethoxylated
alcohols, methyl esters and alpha olefins.
Page 23 of 36 © 1997 The Chemithon Corporation