Oxidation of organosolv lignins in acetic acid - Influence of oxygen pressure

The oxidation of four lignins obtained by organosolv pulping of eucalyptus wood (Acetosolv-eucalyptus Acetosolv lignin [EAL]), sugarcane bagasse (Acet osolv-bagasse Acetosolv lignin [BAL] and in;acetone/water/FeCl3-bagasse ace tone/water lignin [BAWL]), and a softwood mixture (Organocell, Munich, Germ any) was performed to obtain vanillin, vanillic acid, and oxidized lignin. Experiments were carried out in acetic acid under oxygen flow using HBr, co balt(II), and manganese(II) acetates as catalysts. After 10 h the total van illin and vanillic acid yields were BAL 0.05 mmol, EAL 0.38 mmol, BAWL 0.45 mmol, and Organocell 0.84 mmol. Acetosolv lignins are crosslinked, which e xplains the lower yields in mononuclear products. The reaction volume (Delt a V) of this reaction is -817 cm(3)/mol, obtained in experiments performed under oxygen pressure, showing the high influence of pressure on the oxidat ion. The major part of the lignin stays in solution (oxidized Lignin), whic h was analyzed by infrared spectroscopy, showing an increase in carbonyl an d hydroxyl groups in comparison with the original lignin. The oxidized lign in can be used as chelating agent in the treatment of effluents containing heavy metals.