Oxalate formation during ClO2 bleaching of bamboo kraft pulp

Abstract

Abstract This study aimed to investigate the oxalate formation mechanism during chlorine dioxide ( ClO 2 {\mathrm{ClO}_{2}} ) bleaching of bamboo kraft pulp, and thus explore favourable ClO 2 {\mathrm{ClO}_{2}} bleaching conditions to better control oxalate formation. The amount of oxalate formed varied linearly with ClO 2 {\mathrm{ClO}_{2}} dosage within the whole research range, while it rose exponentially within the first 90 mins of pulp bleaching. Then the actual bleaching process was simulated by reacting ClO 2 {\mathrm{ClO}_{2}} with three representative lignin model compounds and comparatively studied. The rule of oxalate formation in the simulated reaction system was identical to that in pulp bleaching by ClO 2 {\mathrm{ClO}_{2}} , except for oxalate production by veratraldehyde with prolonged reaction time. Under identical conditions, vanillin formed the highest amount of oxalate, while veratraldehyde formed the least. Furthermore, the amount of oxalate formed increased by 19.59 mg/kg when the kappa number of the delignified pulp was reduced by one unit. Considering the satisfactory pulp brightness and decreased oxalate formation, the recommended conditions for ClO 2 {\mathrm{ClO}_{2}} bleaching of bamboo kraft pulp were a ClO 2 {\mathrm{ClO}_{2}} dosage of 4 %, 60 °C and 70 mins.