**Acknowledgements**

This work has been carried out at the Laboratory of Molecular Science and Engineering, Åbo Akademi University, as part of the activities at the Johan Gadolin Process Chemistry Centre (PCC). The authors are grateful to Svenska Kulturfonden and PoDoCo (Post Docs in Companies) for the grant for Dr. Meheretu Jaleta Dirbeba under the project "Role of feedstock impurities in novel pyrolysis based technologies for low-grade biomass and waste feedstocks" (PoDoCo application no. 173788). Support from Valmet Technologies Oy is also gratefully acknowledged.
