Peroxyformic acid pulping of Eucalyptus grandis wood chips and sugar cane bagasse in one stage and characterization of the isolated lignins

An improvement in the peroxyformic acid process for the production of chemical pulps from Eucalyptus grandis wood chips and sugar cane bagasse is described. The pulping of these lignocellulosics was carried out in a single stage at 75 degrees C (3 h) in order to benefit from the action of the peroxyformic acid and a subsequent formic acid reflux (110 degrees C, 2 h), using the same liquor. Efficient distillation of the spent liquor allowed recovery of a large quantity of formic acid and phenolic lignin, the latter obtained after mild saponification, followed by precipitation in acidic media. The pulping process was completed with a 0.25M NaOH extraction of the pulp at 60 degrees C to dissolve more lignin. Good quality unbleached pulps were obtained. Kappa numbers (KN) of 14 and 13, and intrinsic viscosities [eta] of 1130 and 980 dm(3) kg(-1) were obtained, respectively, for E. grandis and sugar cane bagasse. The structures of the lignin fractions were studied by size exclusion chromatography; methoxyl content analysis; elemental analysis; UV; IR; and H-1, C-13, and P-31 NMR. The lignins were found to undergo demethylation, condensation, ring opening, formylation of hydroxyl groups, and aryl-alkyl ether cleavage during pulping.