Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkali metal
Patent
1995-05-03
1996-08-13
Bos, Steven
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkali metal
423198, 423207, 423DIG3, C22B 2610, C01D 132
Patent
active
055453856
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the recovery of sodium hydroxide from organic liquors such as black liquor.
BACKGROUND OF THE INVENTION
Wood may be mechanically or chemically pulped. The chemical pulping processes normally employed are the sulphate, sulphite and soda pulping processes. The economics of these processes rely heavily on the recovery of chemicals employed in them.
In the sulphate process wood chips are digested in a solution of sodium hydroxide, sodium sulphide and possibly some sodium carbonate. In the sulphite process wood chips are cooked in the presence of sulphur dioxide and a bisulphite or a sulphite. In the soda process the wood chips are cooked in the presence of a solution of sodium hydroxide and possibly some sodium carbonate. The wood pulp is separated from the liquor. The liquor from the sulphate process and the soda process is normally referred to as black liquor. The present invention is concerned with the recovery of sodium hydroxide from black liquors derived from the soda process.
The specification of Australian Patent No. 486132 describes a method of recovering sodium hydroxide from black liquor which involves the following process steps: a precipitate of ferric oxide; and repeating steps 3 and 4.
The specification of Australian Patent No. 519156 describes a process for recovering sodium hydroxide from black liquor which differs from the process described in Patent No. 486132 by the inclusion of a cold washing step. Sodium ferrite is washed in cold water to remove sodium chloride, sodium sulphate and other soluble impurities. The specification of Australian Patent No. 519156 also describes the use of a fluidised bed in the burning step.
The specification of Australian Patent No. 552973 describes a process similar to the process described in Australian Patent No. 519156 with the exception that it includes the step of agglomerating fines of ferric oxide and fines of sodium ferrite with black liquor before or during burning in a fluidised bed. The fines of ferric oxide are derived from the ferric oxide precipitated when sodium ferrite is added to warm water.
There are also a considerable number of Japanese patent applications that describe similar processes for recovering sodium hydroxide from black liquor. Some involve mixing the ferric oxide with the black liquor prior to combustion in a fluidised bed. Some involve combustion of the black liquor in a fluidised bed comprised of particles of ferric oxide or other transition metal oxide such as titanium dioxide. Some also involve combustion of black liquor in a fluidised bed comprised of another metallic oxide as well as ferric oxide. Sodium ferrite forms on the substrate oxide and the substrate oxide and ferric oxide are recovered when the agglomerate from the fluidised bed is added to hot water. The substrate oxides may be magnesia or alumina. However, only one patent specification describes the step of dissolving the sodium ferrite in an aqueous solution of sodium hydroxide. This is the specification of Australian Patent No. 599933. In a preferred form of this process the aqueous solution of sodium hydroxide has a concentration in the range from 10 to 150 gms per litre and more preferably 50 to 150 gms per litre. However, again the iron oxide recovered by the hydrolysis of the sodium ferrite is stated to be a mixture of hydrated iron oxide and unreacted iron oxide.
SUMMARY OF THE INVENTION
The present applicants discovered that when sodium ferrite is added to water the temperature of the water needs to be about 80.degree. C. before the hydrolysis of the sodium ferrite commences at an economically satisfactory rate. However, at this temperature the rate of hydrolysis is so rapid that the temperature of the solution becomes uncontrollable and commences to boil. Consequently, an object of the present invention is to overcome this and other problems associated with practicing the inventions of the prior art. Accordingly, the present invention provides a method for recovering alkali metal hydroxide fr
REFERENCES:
patent: 4000264 (1976-12-01), Nagano et al.
patent: 4224289 (1980-09-01), Covey et al.
patent: 4486394 (1984-12-01), Nguyen et al.
patent: 4522685 (1985-06-01), Feldmann
Patent Abstract of Japan, C-301, p. 63, JP,A, 60-81015 (Babcock Hitachi K. K.) 9 May 1985 (Aug. 5, 1985).
Corrigan Mark C.
Maddern Kenneth N.
Scott-Young Robert E.
Wunder Heiko
Amcor Limited
Bos Steven
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