Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
1999-09-10
2001-11-13
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S558000, C423SDIG001, C423SDIG002, C252S182320
Reexamination Certificate
active
06315975
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for suspending sulfates in acid, and more particularly relates to the use of fumed silica to suspend iron sulfates in concentrated sulfuric acid.
BACKGROUND INFORMATION
Sulfuric acid is conventionally manufactured, transported, and stored in carbon steel vessels. The carbon steel does not corrode in the presence of concentrated sulfuric acid because of the formation of a protective layer of iron sulfate (ferrous sulfate) on the walls and bottom of the vessels. Over time, the iron sulfate layer builds up and in some older vessels can be measured in inches or feet. When vessels are cleaned, the iron sulfate has to be removed. Since it is denser than the acid, it is found in the bottom of the vessel and has to be removed physically, e.g., shoveled out. Alternatively, the iron sulfate may be dissolved with water. However, this method of removal is a problem since dilute sulfuric acid develops with high concentrations of iron sulfate, which is very corrosive.
Development of a suspension system in concentrated sulfuric acid to keep the iron sulfate fluid is a complex problem. Most polymer viscosity enhancers employed in the industry are used in aqueous or organic systems. However, sulfuric acid either reacts with such polymers to form SO
2
and water, or the material is not soluble in it. To date, satisfactory compounds have not been developed for the control of viscosity and suspension of iron sulfate in concentrated sulfuric acid.
SUMMARY OF THE INVENTION
An aspect of the present invention is to provide a composition comprising concentrated sulfuric acid, iron sulfate suspended in the concentrated sulfuric acid, and fumed silica.
Another aspect of the present invention is to provide a steel container comprising concentrated sulfuric acid, iron sulfate, and fumed silica, wherein a substantial portion of the iron sulfate is suspended in the concentrated sulfuric acid.
A further aspect of the present invention is to provide a method of suspending iron sulfate in concentrated sulfuric acid comprising adding fumed silica to the concentrated sulfuric acid.
Another aspect of the present invention is to provide a method of reducing iron sulfate deposits on steel vessels containing concentrated sulfuric acid, the method comprising adding fumed silica to the concentrated sulfuric acid.
REFERENCES:
patent: 1489347 (1924-04-01), Davison
patent: 3097064 (1963-07-01), Caldwell
patent: 3203758 (1965-08-01), Wainer
patent: 3677701 (1972-07-01), Hollingsworth et al.
patent: 3689217 (1972-09-01), Capaul et al.
patent: 4153628 (1979-05-01), Gerken et al.
Cillo Daniel P.
Eckert Seamans Cherin & Mellott , LLC
Griffin Steven P.
Rhodia Inc.
Towner Alan G.
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