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Methodologies providing new insights into the fundamentals of the pulping process

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Today’s knowledge of what happens concerning the kinetics and other phenomena in the digester during the pulping process is mainly the result of the use of inductive methods. Based on these methods, generalised models have been formulated that are applied for process development as well as for industrial process optimisation. Recent studies (e.g., Mattsson et al. 2017) have shown that the kinetics of delignification is predominantly controlled mass transport processes (mainly ion transport in the wood chips and lignin in the cell wall). To pursue this further, detailed knowledge is needed on processes and mechanisms occurring in the cell wall, including how they can be influenced during processing. Through the development of modern large-scale neutron and synchrotron light plants, there are possibilities of studying dynamic chemical processes and material structure changes at high spatial and temporal resolution (100 nm-10 um @ 1 kHz). The analytical methods available include SAXS – Small-Angle X-ray Scattering, EXAFS – Extended X-Ray Absorption Fine Structure and XANES – X-ray Absorption Near Edge Structure. With these, it should be possible to study how structural changes occur in a sample (from Å to um at the same time) as well as composition and state of chemical substances (even at low concentrations). The project proposal is to perform a methodology development work aimed at developing opportunities to study what is happening in the pulping process under relevant cooking conditions (temperature, pressure and relevant chemical environment). The starting point of this project is the “reactor” developed within the framework of the pre-project conducted by KTH, Chalmers coupled to the development of the beamline ForMAX at MAX IV. This digester/reactor is designed to expose a test piece to the relevant environment and at the same time study changes in structure and chemical composition. Examples of characterisation needs that this methodology development project addresses are: • Swelling of wood fibres, including porosity and internal structure (bulk) • Ion transport in the sample (scanning SAXS / EXAFS) • Local variations of lignin chemical structure (in fibres and wood)

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