Abstract: A process for isolating lignin from an alkaline process stream of thickened black liquor which is introduced continuously into a lower region of at least one circulation reactor having two reactor zones in concentric arrangement, liquid level of the alkaline process stream in the interior of the reactor is at a level with an upper end of an inner tubular reactor zone, a CO2-containing gas is blown continuously from the bottom into the inner tubular reactor zone of the reactor, wherein the CO2-containing gas is absorbed by the alkaline process stream in the inner circulation reactor zone and offgas is drawn off with residual amounts of the CO2 at the top of the reactor, the process is run at 1 atm, and thickened black liquor with a reduced lignin content together with precipitated lignin present are drawn off optionally after settling at the base of the reactor.

Abstract: A process for separating lignin and volatile reaction products from a black liquor derived from pulp production, lignin is demethylated in a heat treatment reactor and CH3+ ions separated out are reacted with reduced sulphur-containing components from cooking chemicals in the black liquor to form DMS a rise in pressure in the heat treatment reactor is controlled and DMS is withdrawn when a pressure of ?15 bar to ?40 bar, is reached in the heat treatment reactor the black liquor which is depleted in DMS is transferred to a first precipitation stage and CO2 and/or sulphur-containing reaction products are added to precipitate out a slurry containing demethylated lignin which is transferred into a second precipitation stage with at least one sulphur-containing acidifying agent, and the precipitated unrefined slurry containing demethylated lignin is discharged from the second precipitation stage; and supplied to a demethylated lignin separation step.

Abstract: A process for isolating lignin from an alkaline process stream of thickened black liquor which is introduced continuously into a lower region of at least one circulation reactor having two reactor zones in concentric arrangement, liquid level of the alkaline process stream in the interior of the reactor is at a level with an upper end of an inner tubular reactor zone, a CO2-containing gas is blown continuously from the bottom into the inner tubular reactor zone of the reactor, wherein the CO2-containing gas is absorbed by the alkaline process stream in the inner circulation reactor zone and offgas is drawn off with residual amounts of the CO2 at the top of the reactor, the process is run at 1 atm, and thickened black liquor with a reduced lignin content together with precipitated lignin present are drawn off optionally after settling at the base of the reactor.