Mild steam explosion followed by kraft cooking and oxygen delignification of spruce (Picea abies)

The paper considers mild steam explosion as an initial biorefinery process step to make wood more accessible for chemicals and enzymes in subsequent extraction and isolation procedures. Wood chips were exploded at four and seven bars and the effects of the treatments were followed during both kraft cooking and oxygen delignification. The properties of the unbleached and bleached pulps, including kappa number, pulp yield, fibre length, intrinsic viscosity, chemical composition and ISO brightness, were analysed using standard methods. The findings showed a difference between treatment at four and seven bars, as the higher pressure leads to more significant visual changes as well as somewhat increased degradation of hemicelluloses. These changes however, have no apparent significant negative effect on the final pulp properties. To the contrary, a benefit of steam treatment seems that the time to reach a certain kappa number was slightly reduced with steam-exploded wood chips