Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
1999-09-09
2001-08-07
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C023S30200R, C423S421000, C423S206200
Reexamination Certificate
active
06270740
ABSTRACT:
This invention relates to an improved process for producing an amended sodium carbonate product. More particularly, this invention relates to producing a sodium carbonate product that has an enhanced reactivity with carbon dioxide to produce sodium bicarbonate.
BACKGROUND OF THE INVENTION
Trona ore is mined and calcined for use in the manufacture of sodium carbonate, which in turn can be used to make sodium bicarbonate (NaHCO
3
), a valuable product. The naturally occurring trona ore material generally has the formula Na
3
H(CO
3
)
2.
2H
2
O, and is characterized as a hydroxyacid sodium carbonate. Trona is found in, or contiguous to, oil shale, and thus contains large amounts of organics, which it is desirable to remove from the sodium carbonate product. Unfortunately, insoluble organic and inorganic materials are contiguous in the trona ore, and are not easily separated. These impurities impact the characteristics of the final soda ash produced.
The processes used to produce soda ash from crude trona ore include various steps of calcination, dissolution of the converted soda ash to concentrated liquor, solids/liquids separation steps, filtration and/or purification, evaporation/crystallization, and drying the monohydrate formed to anhydrous soda ash for industrial use.
In accordance with the present commercial process, the crushed and calcined trona ore is treated with water to dissolve the soluble sodium carbonate product. The resultant liquid solution, or liquor, is clarified, decanted and then filtered to remove the solids. Treatment of the solution with activated carbon may follow to remove some portion of the organic materials. However, treatment with activated carbon is expensive. In addition to the high costs of the activated carbon itself, there are several auxiliary processing costs; the carbon must be filtered out after the carbon is sufficiently inactivated, requiring additional manpower, testing and filtering equipment, and the spent carbon must be disposed of, which is also expensive.
After the carbon treatment step, when used, the liquor is evaporated to obtain a crystallized sodium carbonate product. Antifoam agents are often added during this step to prevent foaming that would foul condensing liquids. These liquids are re-used as pure water when clean enough.
When the sodium carbonate product is to be used to make sodium bicarbonate, the anhydrous soda ash is dissolved in water and the resultant sodium carbonate solution is then reacted with carbon dioxide to form sodium bicarbonate in accordance with the following reaction:
Na
2
CO
3
+CO
2
+H
2
O→2NaHCO
3
However, even if treated with activated carbon, objectionably some organic materials from the anhydrous soda ash are passed on to the sodium bicarbonate process. This residual organic material interferes with the ability of the soda ash to react with carbon dioxide.
Thus considerable engineering skill is needed to maximize the carbon dioxide adsorption efficiency of sodium carbonate and the rate of sodium bicarbonate crystal formation from sodium carbonate. An improved method for modifying the sodium carbonate source that enhances the carbonation reaction would be highly advantageous.
SUMMARY OF THE INVENTION
We have found that the carbonation reaction to form sodium bicarbonate from sodium carbonate is enhanced when the sodium carbonate is produced using the process of the invention. In accordance with the present process, the addition of particular amounts of a cationic compound, e.g., a quaternary amine, to treat the 25-30% by weight sodium carbonate liquor prior to filtration, results in a modified sodium carbonate liquor product that, when crystallized and converted to an anhydrous product, is more readily carbonated with carbon dioxide in the production of sodium bicarbonate. The cationic additive reacts with organic materials in the sodium carbonate liquor to form solid polymeric by-products. Thus the treatment with a cationic compound is made prior to filtering the liquor. After filtering to remove the polymeric by-products and other solid materials, the liquor is evaporated to produce a purified and modified sodium carbonate. During the evaporation step, an antifoaming agent can be added to control foaming and ensure the ability to re-use the generated condensate.
REFERENCES:
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patent: 3981686 (1976-09-01), Lobunex et al.
patent: 4374102 (1983-02-01), Connelly et al.
patent: 4472280 (1984-09-01), Keeney
Boyle Kenneth Douglas
Braman Victor Eugene
Moore Carter Jay
Shepard James Milo
General Chemical Corporation
Nguyen Ngoc-Yen
Plantamura Arthur J.
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