Studies on Soda Oxygen Pulping of Wood

Abstract

In order to obtain more detailed information concerning the degradation of lignin in the oxygen-alkali cooking, the milled wood lignin from Japanese red pine (Pinns densiflora) was cooked with the alkaline liquor of various pH values containing NaOH and NaHCO3 in the presence of oxygen under the conditions shown in Table 1. The reaction mixtures thus obtained were studied for the fractionation curve of the gel filtration, UV-absorption spectrum, weak-acidic dissociation group, COD, and BOD (cf. Fig. 14 and Table 2). Furthermore, the ether-soluble fraction of the reaction products was studied by means of gas-liquid and thin-layer chromatographies (cf. Table 3 and Fig. 6). Main results are as follows : 1. When cooked the lignin with alkaline liquor adjusted to pH 13.5 in the presence of oxygen, a small amount of lignin fraction having lower molecular weight was formed even in the cooking at 70°C, and the higher the cooking temperature was, the lower molecular weight the lignin degraded into and the larger number of weak-acidic dissociation group the degraded lignin had. 2. In the case of the alkaline liquor of pH 8.5, even in the cooking at a higher temperature viz. 120 to 140°C, some of lignin having high molecular weight remained without degradation. 3. The BOD/COD ratio of the cooking mixture with alkaline liquor of pH 13.5 at a temperature of 120 to 140°C was 0.61 to 0.71, and much higher than that of the cooking mixture with the liquor of lower pH value, suggesting that lignin fraction in the waste liquor of the oxygen-alkali cooking at a high pH probably can be decomposed more easily by micro-biological treatment than can the lignin fraction in waste liquor of the ordinary alkali cooking. 4. The yields of the ether-soluble components were as listed in Table 3. Among the degradation products in the oxygen-alkali cooking with alkaline liquor of pH 13.5, methanol was in the highest yield, and acetic acid and formic acid were in comparatively high yield. It was remarkable that, in the oxydation products of the milled wood lignin, a small amount of acetone was found in addition to the aromatic and aliphatic compounds which have already been reported as the oxydation products of lignin. The above mentioned results indicate that the degradation reaction of lignin during the oxygen-alkali cooking is markedly affected by pH value of the cooking liquor.