IMPROVEMENTS IN PULP PROPERTIES BY ALKALI PRE-EXTRACTION AND SUBSEQUENT KRAFT PULPING WITH CONTROLLING H-FACTOR AND ALKALI CHARGE

The objective of this study was to determine the processing conditions for obtaining improved pulp properties from the kraft pulping process with an alkali pre-extraction stage.Before the kraft pulping, a pre-extraction of hemicelluloses from mixed hardwood chips was performed with two different alkali concentrations (3% and 12% as Na 2 O) at 150 °C for 90 minutes.The kraft pulping of the pre-extracted chips was then conducted in two ways: with either the H-factor alone controlled or with both the Hfactor and the alkali charge controlled.When the chips were preextracted with the 3% alkali charge and with the kraft pulping controlled to an H-factor of 500, the yield and properties of the pulp were higher than those of the reference kraft pulp.The 12% alkali pre-extraction and kraft pulping resulted in a low yield of screened pulp.However, when the alkali charge and the H-factor were adjusted together, the pulp yield remained constant and the pulp properties improved in comparison to the reference pulp for both the 3 and 12% cases.