Continuous sonochemical nanotransformation of lignin – Process design and control

•Nanotransformation for valorization of macromolecular lignin.•Design and control of a continuous sonochemical lignin nanotransformation process.•Setting the basis for a large-scale lignin nanotransformation.•DoE, DLS and UV–vis spectroscopy allow a mechanistic interpretation of the process.•UV–vis spectroscopy could be used as an in-line tool to control/customize the process. As the most abundant renewable aromatic polymer on the planet, lignin is gaining growing interest in replacing petroleum-based chemicals and products. However, only