Title
Calcium hydroxide as an alternative alkali for the oxygen bleaching stage of kraft pulp
Authors
K. DÖLLE and B. BAJRAMI

Received March 26, 2015
Published Volume 50 Issue 9-10 October-December
Keywords biomass, biogas, pre-preparation, chemical oxygen demand, hydrothermal treatment, grinding

Abstract
In this study, replacement of sodium hydroxide with calcium hydroxide in the oxygen bleaching stage of commercial Kraft pulping was studied using yellow pine Kraft pulp obtained from a company in the US. The impact of sodium hydroxide, calcium hydroxide, reaction time and temperature on Kraft pulp was evaluated. The sodium hydroxide and calcium hydroxide dosage was varied between 0% and 15% based on oven dry fiber content. The bleaching reaction time was varied between 0 and 360 min, whereas the bleaching temperature ranged between 70 °C and 110 °C. The ability to bleach pulp was measured by determining the Kappa number. Optimum bleaching results were obtained at 2% and 3% calcium hydroxide content. Beyond this, the ability to bleach pulp decreased. The optimum bleaching time for using calcium hydroxide was determined at 40 min, with no significant change in the Kappa number up to 60 min of bleaching time.