Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkaline earth metal
Patent
1983-11-01
1984-12-04
Doll, John
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkaline earth metal
162 29, 162 301, 162 3011, 162 32, 162 36, 423183, 423207, 423637, 423641, C01D 104
Patent
active
044863942
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved method of preparing alkali metal hydroxides from alkali metal carbonates or from the spent liquor generated by the alkaline pulping and/or bleaching of cellulosic materials. The method is particularly relevant to the regeneration of sodium hydroxide from the spent liquor generated by the pulping and/or bleaching of cellulosic materials with sodium hydroxide, with or without various pulping aids, and especially when the system is substantially sulphur-free.
A method of recovery of alkali metal hydroxides by reaction with transition metal oxides (particularly ferric oxide) in a fluidized bed and subsequent submergence of the solid product in water is already described in Australian Pat. No. 519,156 (U.S. Pat. No. 4,224,289). This Patent discloses a method of recovering an alkaline or alkaline earth metal oxide or hydroxide from a solution containing organic chemicals and other impurities which compriss burning said solution with an oxide of a suitable transition metal selected from the group consisting of Ti, Fe, Co, Ni, and Mn, to form a product containing a mixed oxide compound of said alkaline or alkaline earth metal and said transistion metal, subsequently washing said mixed oxide in cold water and then submerging the washed solid in water of a higher temperature than said washing step to form a solution of an oxide or hydroxide of an alkaline or alkaline earth metal and a precipitate of said transition metal oxide and subsequently separating said precipitate for recycling to said first addition steps and recovering a solution of said alkaline or alkaline earth metal oxide or hydroxide. This method enables large particles of transition metal oxide to be used, thus permitting the use of high gas velocities in the fluidized bed.
When a method as described in Patent 519 156 is employed there is inevitably some degradation of particle size at various points in the system. For simplicity, the small particles so produced will hereafter be referred to generally as "fine material" irrespective of where in the system they are generated or of their chemical form (be it transition metal oxide, double-oxide of transition metal and alkaline metal). It is comparatively difficult to separate that fine material which is present after the submergence in water from the regenerated alkali metal hydroxide solution or from the water (if any) used to wash the transition metal oxide. This results in losses of alkali metal hydroxide if the fine material is subsequently discarded, or reduction in the thermal efficiency of the process if the fine material is returned to the fluidized bed reaction stage (because of the heat required to evaporate water associated with the fine material). For the same reason it is undesirable to contact fine material from other parts of the system, particularly dust collected from the flue gas, directly with hot water to recover alkali metal hydroxide. Further, in the case of recycled transition metal oxide because of the relatively high gas velocities employed in the fluidized bed, the fine material may be entrained before it has reacted with the compounds of the alkaline metal and so its efficiency of utilization will be reduced. Also, if the fine material is recycled and the losses from the system are small, then the mean size of the transition metal oxide will be progressively reduced and the performance of the system will deteriorate.
It is an object of this invention to reduce the problems presented by the presence or generation of fine material in the regeneration process.
To this end the present invention provides a method of recovering an alkaline or alkaline earth metal oxide or hydroxide from a solution containing an alkaline or alkaline earth metal carbonate, organic chemicals and impurities which comprises burning said solution in a fluidized bed of particles of an oxide of a transition metal selected from Ti, Fe, Co, Ni, and Mn, and maintaining said fluidized bed at or above a temperature of which said alkaline or alkaline earth metal carbonate bec
REFERENCES:
patent: 3796791 (1974-03-01), Nielsen et al.
patent: 3878288 (1975-04-01), Commins
patent: 4224289 (1980-09-01), Covey et al.
Covey Geoffrey H.
Keogh Andrew J.
Nguyen Kien L.
Australian Paper Manufacturers Limited
Doll John
Langel Wayne A.
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