After the reaction experiments, three sections of the polymer tubes upstream of the catalyst bed, at the height of the catalyst bed and downstream of the catalyst bed are cut out and studied in a light microscope (OZP558, Kern Optics) to visually assess deposition of material on the polymers as well as abrasion and deformation of the tube. The microscope is equipped with SWH10X objectives and the images are recorded by an ODC825 camera. Pictures are taken in light and dark conditions to distinguish changes at the surface level and inside the polymer.