Ethanol-kraft pulping and papermaking properties of aspen and spruce

A study was undertaken to investigate the effect of ethanol addition to the kraft cooking liquor on the delignification of aspen (Populus tremuloides) and spruce (Picea excelsa) wood chips and papermaking properties of the resulting pulps. Ethanol addition to the kraft pulping process had a significant impact on delignification and the resultant carbohydrate yields for both wood species. Maximum delignification selectivity was observed at the 0.1 and 0.3 ethanol mole fraction level for aspen and spruce, respectively. Remarkably faster delignification and about 30-50% lower residual lignin content of pulps was found in the solvent-kraft pulping process compared to the kraft process. A 4% gain in pulp yield and a 30% reduction in pulping time were achieved using the solvent-kraft pulping process. An increase in fiber shortening occurred during beating in solvent-kraft pulps, whereas no significant differences in beatability and water retention values were observed between the kraft and solvent-kraft pulps for both species. Solvent-kraft pulp handsheets exhibited higher bulk and comparable strength properties compared to the kraft samples, with the possible exception of tear. Application : these results showed that marked improvements in the pulp yields can be achieved with ethanol additions to the kraft cooking liquor. Additional studies are needed to determine the effects of solvent additives to chemical recovery, black liquor heat value, and solvent recovery before commercial application can be considered.