Patent ID: 6955743

Claim:
A process for recovering formic acid, acetic acid and furfural and simultaneously forming same in a pulp production process where an acid mixture containing mainly formic acid and acetic acid is used as a cooking liquor, the cooking liquor is separated from the pulp, the pulp is washed, and the cooking liquor is subjected to a recovery phase, wherein the recovery phase comprises a) evaporating the used cooking liquor obtained from the separation of cooking liquor and pulp and including an organic substance and/or a chemically bound organic acids, wherein the evaporation yields as condensate a concentrated acid mixture which contains formic acid and acetic acid and is at least partly returned to the cooking, and as a first evaporation residue an evaporation concentrate, where acetic acid, formic acid and furfural have formed in the evaporation from the organic substance included in the used cooking liquor and/or from the chemically bound acids included therein, b) separating the evaporation concentrate into a volatile part and a second evaporation residue, c) separating the volatile part of the evaporation concentrate obtained in step (b) and/or part of the condensate obtained in step (a) into four fractions comprising a mixture of acetic acid and formic acid, water, furfural and acetic acid by distillation, which comprises an azeotropic-extractive distillation phase by utilizing the furfural formed and recovered in the process as a distillation aid, wherein the azeotropic-extractive distillation phase comprises introducing the volatile part of the evaporation concentrate obtained in step (b) and/or the condensate obtained in step (a) and including acetic acid, formic acid, furfural and water feedstream into a first distillation column and recovering a mixture of furfural and water as the top product of the distillation and a concentrated mixture of acetic acid and formic acid containing also water and furfural as the bottom product of the distillation, followed by separating the top product of the distillation to recover water and furfural and distilling the bottom product of the distillation to recover a mixture of acetic acid and formic acid, water, furfural and acetic acid, and, d) returning the mixture of formic acid and acetic acid obtained from the distillation to cooking, returning at least part of furfural to the distillation of step (c), recovering the rest of furfural and acetic acid and returning water to pulp washing.