Abstract: Processes for the preparation of prehydrolyzed pulp from lignin-containing cellulosic material are described including prehydrolyzing the cellulosic material with steam at a first pressure, terminating the prehydrolyzing by at least one addition of an alkaline liquid at the first pressure followed by at least one pressure reduction and delignifying the prehydrolyzed cellulosic material in a cooking stage. The pressure reduction can be a single pressure reduction or a gradual pressure reduction carried out in incremental stages.

Abstract: This invention refers to a method for producing pulp in an alkaline digesting process comprising the following steps: charging lignocellulosic material to a digester system; pre-treating said lignocellulosic material with an impregnation liquor and subsequently with a hotter liquor containing black liquor, simultaneously displacing spent liquor; heating and cooking said lignocellulosic material to produce cooked lignocellulosic material and cooking liquor; displacing a portion of said cooking liquor at cooking temperature from said digester to a first section by supplying a washing liquid; further displacing a second portion of displaced liquor from said digester system to at least a second section by supplying further washing liquid until the temperature of said second portion of displaced liquor drops to a temperature of at least about the boiling point of said cooking liquor at atmospheric pressure, said second portion of displaced liquor having a dry solids content substantially lower than the initial dry