Kinetics of hydrogen peroxide bleaching of ALCELL® derived pulp

Abstract

In this study, a kinetic model of the final bleaching stage with hydrogen peroxide in a totally chlorine free (TCF) bleaching sequence for ALCELL@ processed pulp was developed. The model was based on the rate of chromophore destruction characterized by the decrease in the light absorption coefficient of bleached pulp at 457 tun, C,. Based on the fact that the chromophore destruction proceeds rapidly in an initial phase followed by a much slower reaction during which a "floor-level" chromophore concentration is approached asymptotically, we propose that the hydrogen peroxide stage of the ALCELL@ derived pulp in the studied TCF sequence consists of two distinct phases, The initial phase is a very fast reaction. The rate equation of the second phase was determined as:which is valid in a pH range of 10.5 to 11.5 and a temperature range of 60 to 92.5"C.Dans cette etude, on a mis au point un modele cinetique de la phase finale de blanchiment avec du peroxyde d'hydrogene dans une sequence de blanchiment sans chlore (TCF) pour la mise en plte par le procede ALCELL@. Le modele est base sur la vitesse de destruction de chromophore caracterisee par la diminution du coefficient d'absorption de la lumiere de la plte blanchie a 457 nm, C , . En tenant compte du fait que la destruction de chromophore s'effectue rapidement dans une phase initiale suivie d'une reaction beaucoup plus lente au cours de laquelle une concentration "plancher" en chromophore est atteinte asymptotiquement, nous proponsons que la phase du peroxyde d'hydrogbne de la plte ALCELL@ dans la sequence TCF Btudiee comprenne deux phases distinctes: une phase initiale correspondant a une reaction tres rapide et une seconde phase dont I'equation cinktique est determinee cornme etant: -5 = 1.41 x 10" e~p(-69610/RT)[HOO-]~.'[C~ -CKS]* dt et qui est valide dans une gamme de pH de 10,s a 11,5 et une gamme de temperatures de 60 a 92,S"C.

Clean Bleaching Engineering Practice for Bagasse Pulp: Totally Chlorine-Free and Elemental Chlorine-Free Bleaching Realized with the Same Production Line

“…Increasing the pressure and temperature enables reaching higher brightness in a much shorter time, and higher pressure makes it possible to run the process at high temperature and avoid boiling (Stromberg et al 1994;. By the kinetics of peroxide bleaching, the reaction rate of chromophore destruction proceeds via a very fast phase initially, followed by a second phase, which is much slower and approaches asymptotically a "floor level" of chromophore concentration (Ni et al 1997;Wang et al 2008). In addition, to prevent undesired peroxide decomposition in the initial reaction, static pressurization is needed to mitigate peroxide decomposition reactions (Chen 2007).…”

Ethanol‐water pulping: Cooking variables optimization

“…From results in Table 3 it can be established that autocatalyzed pulping at 180°C provides pulp with acceptable viscosity. Although kappa number is relatively high compared to those of kraft hardwood, it can be fiuther reduced to values below kraft pulp in bleaching stage (Cronlund and Power, 1992;Ni et al, 1997). Therefore, among the cooking systems studied, the autocatalyzed process is the most suitable for Eucalyptus globulus wood pulping.…”

“…Acceptable viscosity values can only be obtained when the temperature is around 185°C and the cooking time is long. The viscosity is low when compared to usual kraft pulp viscosity, but the viscosity of ALCELL@ pulps remains high after bleaching stage (Cronlund and Power, 1992;Ni et al, 1997).…”

“…E-mail address: teresap@eucmax.sim.ucm.es liquors, which can be accomplished by simple flashing and distillation. The ALCELL@ process is an example of ethanolbased autocalalyzed process that is being developed in New Brunswick, Canada (Harrison, 1991, Ni et al, 1997. Kraft equivalent pulp, valuable byproducts and viability at very small capacities are its most noticeable advantages.…”