Contribution to the technology of birch wood pulping with acetic acid solutions

The influence of water prehydrolysis, hydrogen peroxide addition to the coo king liquor and some other process parameters on birch wood delignification with acetic acid solutions were determined in laboratory experiments. It was found that the degree of delignification and yield of the screened p ulp depended on the conditions of prehydrolysis, causing dissolution of con siderable amounts of lignin from wood, but made residual lignin resistant t o solvolysis. Water prehydrolysis of birch wood at suitable temperature and time increased acetic acid delignification. The optimum concentration of acetic acid was 80%, and the liquor-to-wood ra tio 4:1. An addition of 1-4% hydrogen peroxide to acetic acid-based cooking liquor extends delignification, but, at the same time, decreases the polym erization degree of the pulp. An improvement in the delignification results is achieved when the one-stage cooking process is split into two stages wi th exchanging a portion of the cooking liquor and with lowering the tempera ture in the second stage. The degree of delignification obtained with the u se of acetic acid is affected to a great extent by the conditions of pulp w ashing. Increasing the amount of acetic acid used for pulp washing extends delignification.