Exploring the influence of initial liquor pH in the pre-hydrolysis stage on alpha-cellulose production from poplar

The effect of using auto pre-hydrolysis liquor, acidic pre-hydrolysis liquor, and alkaline pre-hydrolysis liquor on the production of alpha cellulose from poplar was investigated across this research work. Poplar chips were pulped with soda-AQ pulping process at a kappa number of 15 after being pre-hydrolyzed with different pre-hydrolysis liquors at 170 °C. The residual lignin of chips were more delignified by about 40% using a single stage oxygen delignification and totally bleached with a D₀ED₁ bleaching sequence. The results indicated that the yield and kappa number of the pulps can be affected by the kind of pre-hydrolysis liquor. In general, using acidic and alkaline catalysts in pre-hydrolysis liquor led to an acceleration in the rate of hemicellulose separation and kappa number reduction. The alkaline pre-hydrolysis and auto pre-hydrolysis had the highest and the least efficiency to remove hemicelluloses from the wood and purify the produced alpha cellulose, respectively. The alkaline pre-hydrolyzed dissolving pulp of poplar due to existing alkali catalyst in the pre-hydrolysis liquor and occurring alkaline darkening had the least brightness, while the acidic pre-hydrolyzed dissolving pulp, because of the effect of acidic catalyst on the reduction of chromophore compounds, had the highest brightness among the pulps. The results illustrated that a dissolving pulp with more purity and alpha-cellulose content is achievable from Poplar through employing an alkaline pre-hydrolysis stage, soda-AQ pulping, and OD₀ED₁ bleaching sequence.