CPC C07G 1/00 (2013.01) [B01J 19/244 (2013.01); D21C 11/0007 (2013.01)] | 9 Claims |
1. A process for isolating lignin from an alkaline process stream of thickened black liquor, comprising introducing the alkaline process stream continuously into a lower region of at least one circulation reactor having an interior with an inner tubular reactor zone and an outer tubular reactor zone in a concentric arrangement so that a liquid level of the alkaline process stream in the interior of the at least one circulation reactor is chosen at a level with an upper end of the inner tubular reactor zone which level is higher than the liquid level of the outer tubular reactor zone and therefore prevents foaming; continuously blowing a CO2-containing gas from the lower region into the inner tubular reactor zone of the at least one circulation reactor, so that the CO2-containing gas is absorbed by the alkaline process stream in the at least one inner circulation reactor zone and offgas is drawn off together with residual amounts of the CO2-containing gas at the top of the at least one circulation reactor; running the process at ambient pressure of 1 atm, and drawing off a thickened black liquor with a reduced lignin content together with precipitated lignin present therein after settling at a base of the at least one circulation reactor.
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