As there are increasing demands to replace plastics especially as packaging material with renewable, easy to recycle and compostable materials as those produced by paper industry, there is an increasing demand also to improve the fundamental scientific understanding of pulp and paper manufacturing systems. High yield pulping (HYP) processes, such as CTMP, are increasingly interesting for packaging material as well as manufacturing of hygiene paper. The yield from wood chips to final fiber is about 90%-98% and due to that, the lignin (28% of coniferous wood) plays a key role when designing properties of packing materials. A key unit operation when producing CTMP is the pre-treatment of wood chips before defibration. In order to separate the wood to individual fibers with a minimum amount of electricity it is necessary to soften the lignin. The lignin is softened by means of a combination of sulphonation at high pH and elevated temperatures in the preheater and in the refiner, where the fiber separation occurs. As the size of wood chips is normally about 20 mm in length, 3-4 mm in thickness at the same time the fiber size is 20-40 μm in width with 1.5-5 mm in length, it is challenging to create a process technology that gives an even distribution across the wood chips of the sodium sulphite (Na2SO3) containing liquid used for impregnation. In order to improve the impregnation technology, it is valuable to measure the sulphonation degree on a detailed level. Our XRF imaging system using a collimated X-Ray source and an energy-dispersive X-Ray spectroscopy can make an image of sulphur (S) and sodium (Na) across wood chips or in individual fibers.