Resin Profile in a Bleached Kraft Pulp Process
The aim with this project was to investigate how the amount and composition of resins varied during the process producing bleached birch pulp at the mill SCA Packaging Munksund. A literature study about how the resin removal can be improved has also been included.
Problems with resins in the process are common at pulp and paper mills, especially when birch is used as a raw material. The resin can cause deposits on the equipment leading to process stops, but also lowered mechanical properties and spots on the paper products.
The addition of tall oil to the digester is one way of improving the removal of resins, seasoning of wood, and a good debarking are other ones. Also the different washing and bleaching steps can affect the amount of resin remaining in the pulp.
In this study pulp samples from eight different positions in the process were analyzed. To extract the samples a Soxtec device was used. Results showed that the most effective resin removal happened during the washing in their first washing step after the digester, a DD-washer. Here 77 % of the resin was removed, of totally 88 % during the whole process. Another step which was effective was the final washing step, the PO-press. About 36 % of the remaining resins in the pulp which entered the PO-press were washed out here.
The extracts were analyzed with GC-FID and GC-MS to identify and quantify the substances, and determine how the composition varied over the manufacturing process. Twelve different compounds were identified, and the birch bark resin, betulinol, turned out to be the hardest component to remove. Over all, the sterols and triterpenols were hard to deresinate, while the removal of resin acids, fatty acids, and fatty alcohols was more effective. The PO-reactors showed a positive effect on the fragmentation of components consisting of long carbon chains and double bonds, like squalene and betulaprenols.
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