Chemical and biological oxidation of Pinus pinaster lignin of the production of vanillin

Oxidation of kraft black liquor with 14·39% solids content, obtained by cooking of Pinus pinaster wood, was studied by three different process; chemical oxidation with molecular oxygen at 120–138°C (oxygen partial pressure ≈ 0·15 MPa); biological (enzymatic) oxidation; and combined oxidation (in the sequence: chemical + enzymatic). Lignin degradation was followed by high pressure liquid chromatography (HPLC). Production of low molecular weight compounds, e.g. vanillin, was monitored by gas chromatography (GC). Chemical oxidation produced about 1.5 g of vanillin per dm 3 of liquor (0·904 g per 100 g of solids). Biodegradation products had molecular weights near to that of vanillin and mainly around 100 daltons, but vanillin was not detected. In the combined oxidation process, vanillin was consumed with a concomitant reduction of the HPLC peak.