Autohydrolysis of softwood prior to alkaline pulping

Abstract

This work focused on auto hydrolysis followed by alkaline pulping of softwood. As raw material pine (pinus sylvestris) and spruce (picea abies) were used. The influence of different hydrolysis and cooking conditions was investigated.

The objectives of the thesis were:.

1. To find the optimal hydrolysis conditions in order to extract as much hemicelluloses as possible, while avoiding unfavourable side reactions (for instance lignin condensation reactions).

2. To find the optimal cooking conditions for the pre-hydrolysed wood chips in order to maintain good pulp yield and properties.

3. To investigate the influence of anthraquinone on the pulping of pre-hydrolysed wood chips.

4. Lower the sulphidity level in the cooking process.

The results showed that pre-hydrolysed pulps reached lower kappa numbers at the same H-factor compared to the reference pulps (kraft). Pre-hydrolysed pulps also responded better to oxygen delignification. Due to this, the cooking process could be interrupted at higher kappa numbers compared to the reference pulps. The zero span tensile strength was slightly lower for the pre-hydrolysed pulps compared to the reference. When using anthraquinone (0.1 %) and a sulphidity level of 20%, the screened yield at a certain kappa number was slightly higher than those of normal kraft pulp (sulphidity 40 %).