| abstract |
The present invention facilitates the recovery of desirable chemicals from a raw material that is formed in substantial amounts during the production of cellulose pulp from renewable lignocellulose material. Recovery of the chemicals comprises two steps. The method starts with acidification of the raw material, that is, an ammonia/ammonium-containing methanol/water mixture (4) with an acid (5) that has the ability to form ammonium salt with the ammonium, and the mixture is allowed to circulate (1, 8, 9, 2) and thereby pass through an apparatus comprising an indirect heat exchanger (2), combined with an storage volume (1) fitted with a gas collection device (3), wherein heating in the range of 70-105°C results in that methanol and volatile sulphur-containing substances are expelled in gas form (6) and transferred to a condenser (18) where the methanol condenses while the volatile sulphur-containing substances remain in gas form, whereafter the liquid phase (19) and the gas phase (16) are separately removed from the condenser (18), at the same time that a part of the said circulating ammonium salt containing mixture is removed from a position (10) where the water content in the mixture has been increased by at least 2-5 fold. The liquid form methanol (19) withdrawn is further purified in a second step (20). |