ORGANOSOLV PULPING-VII - DELIGNIFICATION SELECTIVITY OF FORMIC-ACID PULPING OF EUCALYPTUS-GRANDIS

Eucalyptus grandis wood was ca. 80% delignified in 79-92% (v v-1) form ic acid containing 0.22% (w v-1) HCl as a catalyst under reflux and me chanical stirring for 90 min. Pulps obtained under these conditions pr esented pulp yield, Kappa number and Klason lignin in the ranges of 44 -52%, 30-40 and 8-10%, respectively. The presence of water in the expe riments with the more diluted formic acid concentration (79%) showed a beneficial effect on the pulp fiber length and pulp yield. Formic aci d sawdust treatments were carried out under the best chip pulping cond itions. Plots of yield versus lignin loss show comparable delignificat ion selectivity for sawdust and chips. The most selective pulping expe riments were those with 79% formic acid employing a mechanical stirrer blade of polytetrafluorethylene (PTFE) and those with 99% formic acid using a stainless steel blade.