A single model-free rate expression describing both non-isothermal and isothermal pyrolysis of Norway Spruce

•A strictly model-free reaction rate expression for Norway Spruce has been derived.•The rate expression derived from heating rate data can model isothermal pyrolysis.•This rate expression might be used to model industrial pyrolysis.

A strictly isoconversional rate expression has been derived for pyrolysis of biomass. This rate expression, derived from non-isothermal thermogravimetric experiments using heating rates 2–10 K/min, can successfully predict the conversion rates of experimental data at heating rates 1–100 K/min and quasi-isothermal experiments at 539–650 K. The methodology used is based on an extension of the incremental integral method by Vyazovkin (2001). Being able to derive an intrinsic reaction rate expression from non-isothermal data, without any assumption regarding the chemical processes present, opens up for the possibility to model industrial pyrolysis reactors, with a variety of temperature profiles.