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New catalytic bleaching sequences for kraft pulp
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Kemian tekniikan korkeakoulu |
Master's thesis
Ask about the availability of the thesis by sending email to the Aalto University Learning Centre oppimiskeskus@aalto.fi
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Mcode
CHEM3021
Language
en
Pages
50
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Abstract
The modern pulp industry has endeavoured to maximize its efficiency and minimize its environmental impact for decades. The bleaching process has a major impact on the heat, power and chemical consumption of the pulp mill, and hence bleaching constitutes an at-tractive process to be optimized in order to increase the performance of the mill further. Catalytic bleaching is a novel discovery which could decrease the duration of the bleaching processes. So far the catalytic bleaching has been demonstrated to work successfully only in the HcatZP sequence. For this reason, the goal of this thesis was to clarify if new kraft pulp bleaching sequences with initial chlorine dioxide (D) stage and an intermediate Hcat stage could provide fully bleached pulps.
In order to design the new catalytic sequences, a literature review was elaborated on diffrerences between softwood and hardwood kraft pulps, the basics of pulp bleaching, the reactions of lignin and carbohydrates during bleaching processes and the ideal operational parameters in these processes.
The eucalyptus pulp bleaching sequences studied included D0EHcatP which achieved a final brightness of 88.0% ISO and HcatZ/DP which attained a brightness of 89.2% ISO. Addi-tionally, a reference trial AEOPDP was performed to check the bleachability of the pulp. This sequence achieved a brightness of 88.0% ISO, which suggested that the pulp used was quite hard to bleach. In conclusion, HcatZ/DP was the best sequence for catalytic bleaching of eucalyptus kraft pulp. The softwood bleaching sequence OEOPHcatDP reached a final brightness of 75.2% ISO.
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Supervisor
Vuorinen, TapaniThesis advisor
Afsahi, GhazalehVehmaa, Janne