Pretreatments for the organosolv pulping process in aqueous acetic acid containing a small amount of sulfuric acid at atmospheric pressure were investigated with six species of hardwoods to improve cooking yield and delignification. Birchwood was cooked effectively by refluxing in 90% aqueous acetic acid for 1 h as pretreatment. The pulp yield and delignification of beechwood were improved by removal of pretreatment liquor which contained extracts, since water soluble extracts from beechwood inhibits the delignification significantly. Facilitation of permeation of pretreatment liquor to woods under reduced pressure indicated the acceleration of pulping for alder and eucalyptus, but it did not affect pulping for acacia. Improved balsam poplar (Hokkai poplar) was readily delignified under the same conditions as for beechwood.
These results suggested that this pulping process could be applied for a wide species of hardwoods and is useful for conventional separation of wood components.