Influence of the operating variables used in the O step of the XOP bleaching sequence of soda pulp from wheat straw on the quality of black liquor

Black liquor obtained in the bleaching with the cartazyme anzime - oxygen - hydrogen peroxide (XOP) sequence of soda pulp from wheat straw was charact erized. A central composite design was used to examine the influence of ope rating variables of the O bleaching-step (temperature, time and soda concen tration) on various properties of the black Liquor (pH, chemical oxygen dem and, total carbon, total organic carbon, total inorganic carbon, total soli ds, total volatile solids, total mineral solids and colour). Equations that relate the dependent variables to the independent ones were derived that p redict the former with errors less than 25%. The least polluting black liqu or was obtained by using a medium temperature (100 degrees C), a medium sod a concentration (1.65%) and a short time (15 min) in the O step of the XOP bleaching sequence. Under these conditions, the properties of pulp bleached with the XOP sequence (yield, brightness and viscosity), and those of the paper sheets obtained from them (breaking length, stretch, burst index, tea r index and double fold number), were found to be only 6% smaller than the optimum values in most instances.