Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Patent
1994-05-26
1996-10-08
Lewis, Michael
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
210683, C01D 712
Patent
active
055628907
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the production of alkali metal carbonates, particularly but not exclusively, sodium carbonate.
Sodium carbonate also known as Soda Ash is obtained by `synthetic` routes (i.e. the non-"Natural Ash" routes) and is also obtained from naturally occurring deposits of sodium sesquicarbonate.
Most of the current synthetic routes for obtaining sodium carbonate can be described by the following overall equation:
However the reaction cannot be achieved in a single stage and the most commonly used synthetic route (the Ammonia Soda process) uses the following series of reactions: ##STR1##
The ammonia, and half the carbon dioxide, are recycled within the process, so the overall reaction is as stated above.
The sodium chloride for reaction 3 is generally supplied to the process as a saturated or near saturated brine obtained by dissolving naturally occurring (solid) salt in water. The brine must be purified prior to use in the process to remove magnesium and calcium ions which would otherwise precipitate in the process as carbonate-containing compounds and cause blockage problems. The usual method of brine purification is to add sodium carbonate and sodium hydroxide to the brine so as to form precipitates of calcium carbonate and magnesium hydroxide which may then be removed. Obviously the sodium carbonate used for this process may be a portion of that produced in reaction 4.
The Ammonia Soda process does however suffer from a number of disadvantages. In particular, reactions 4 and 5 require considerable energy inputs (in the form of heat) to achieve the reactions desired, so the overall process is energy intensive in spite of very sophisticated efforts to recover and re-use heat energy within the process. The energy requirements of reactions 4 and 5 are a particular disadvantage when one considers that a portion of the energy is required directly or indirectly to produce that portion of the sodium carbonate which is not saleable, i.e. the portion used for brine purification. Further disadvantages of the Ammonia Soda process are that yield of sodium bicarbonate in reaction 3 does not generally exceed 80% and that the separation of this bicarbonate from the ammonium chloride also produced in reaction 3 is comparatively costly.
Attempts to overcome some or all of the abovementioned disadvantages have been made. For example, amines have been proposed as alternatives to ammonia as the carrier and have been investigated at great length. Soluble amines can give higher yields of insoluble sodium bicarbonate intermediate and lower energies of separation, but amine losses in use tend to be too costly. Long-chain insoluble amines potentially give even cheaper separation costs (e.g. gravity), but in practice the amine losses are still too costly due to emulsification problems and significant (albeit low) solubility of the amine in the effluent. Attempts to alleviate this problem using amine/organic solvent systems are being investigated widely, but again amine and solvent losses, and also solvent processing costs, are rather too high.
A further proposal is described in ZA-A-785962 (Klipfontein) in which a weak base (R--N) is carbonated to give R--NH.sub.2 CO.sub.3 and then contacted with a sodium chloride solution (brine) so that sodium bicarbonate is obtained in accordance with the following equation
The sodium bicarbonate solution produced by this reaction is readily recovered from the resin (which may then be regenerated with milk of lime) so that the costly NaHCO.sub.3 /NH.sub.4 Cl separation associated with reaction 3 of the Ammonia Soda process is avoided.
A similar process is disclosed in an article by Robers Kunin entitled "Ion Exchange in Chemical Synthesis" (Industrial and Engineering Chemistry, Vol.56, No. 1, January 1964, pages 35-39). This article discloses a process which proceeds according to the overall equation
It will be appreciated that, in this process as well as in shat described in ZA-A-785962, the resin is used as a direct replacement for the ammonia in the bicarbonation stag
REFERENCES:
patent: 2989370 (1961-06-01), Lee et al.
Industrial And Engineering Chemistry, vol. 56, No. 1, Jan. 1964, Columbus pp. 35-39, Robert Kunin "Ion Exchange in Chemical Synthesis".
Chemical Abstracts, vol. 113, Nov. 1990, Columbus, OH, US, abstract No. 194332e, Zhenliang Zu et al. "Laboratory Study of the Production of Soda using Amines".
Sanji Nishimura et al. `Proceedings of the International Solvent Extraction Conference,` 1981 see pp. 143-148, Application of the Solvent Extraction to Inorganic Synthesis (no month).
D. F. Othmer et al. `Kirk-Othmer Encyclopedia of Chemical Technology, vol. 1` 1978, Wiley & Sons, New York, USA, see p. 869, paragraph 3 through 877, paragraph 1 (no month).
Brunner Mond and Company Limited
Hendrickson Stuart L.
Lewis Michael
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