Recausticizing kraft green liquor

Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...

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423183, 423165, 423192, 423432, 423641, D21C 1112, D21C 1114, C01D 1302, C01F 524

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active

046683429

ABSTRACT:
A process of recausticizing kraft green liquor in which the green liquor containing sodium carbonate is passed in a stream in admixture with particles comprising slaked lime, in which stream the liquid phase becomes progressively weaker in sodium carbonate and stronger in sodium hydroxide. Lime is added in order to provide a continuous supply of slaked lime for reaction with the sodium carbonate, and the stream is passed to a solids/liquid separator which recovers liquid phase from said stream, strong in NaOH, continuously and separately from the solid phase of the stream, as white liquor. The rate of the recausticizing reaction is limited by the rate of diffusion of carbonate ion into the solid particles, and of hydroxyl ion out of the solid particles. Typically, these rates limit the amount of causticizing achieved to less than the equilibrium value. In order to overcome this diffusion limitation, more reaction time for partially reacted lime particles is provided by increasing the time for which solids are detained in the system, e.g. by recycling solids. The recycling can be conducted in a system employing co-current flow of the solids and liquids, or, advantageously, counter-current flow.

REFERENCES:
patent: 1754208 (1930-04-01), Bradley
patent: 2211908 (1940-08-01), O'Connor
patent: 2539732 (1951-06-01), Donohue
patent: 2552183 (1951-01-01), Knight
patent: 3194638 (1965-07-01), Neuville
patent: 3268388 (1966-08-01), Bauman et al.
patent: 3366535 (1968-01-01), Cann
patent: 3414468 (1968-12-01), Copeland
patent: 4302281 (1981-11-01), Ryham
patent: 4329199 (1982-05-01), Andersson et al.
Glasson, Reactivity of Lime and Related Oxides, IV, Carbonation of Lime, J. Appl. Chem., 10, Jan. 1960, pp. 42-48.
Gillespie, D. C., "Some Notes on Current Recausticizing Practice", IAPPI (Apr. 1953) vol. 36, No. 4, pp. 147-151.

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