Thermal degradation of various lignins by TG-MS/FTIR and Py-GC-MS

• The thermal behaviour of four lignins differing in raw material origin and processing method was compared.
• The degradation products of the lignins were analysed as a function of temperature by TG-MS/FTIR and Py-GC-MS.
• Processing method affected the degradation products in some cases, e.g. acetic acid was released from the acetylated organosolv lignin, and demethylation took place in the strong acid hydrolysis during the Klason treatment.
• Some sulfur compounds originating from the Kraft pulping were found in pyrolysis oils from Lignoboost lignin.

Thermal degradation was comparatively studied by TG-MS/FTIR and Py-GC-MS for four lignins of different raw materials and manufacturing processes. Acid hydrolysis by the Klason method was applied to wheat straw and oak, organosolv process based on acetic acid/phosphinic acid cooking to white birch and kraft cooking to Scandinavian mixed softwood, followed by the Lignoboost® process to recover lignin from the black liquor. The temperature domains of degradation were determined and indications on the main compounds produced during each stage were obtained. The composition of pyrolysis oils was determined. Similarities and differences in thermal behaviour and composition of degradation products among studied lignins were observed and discussed. Klason wheat straw and Lignoboost® softwood lignins showed a similar thermal behaviour but different composition of pyrolysis oils while the lignin obtained by acid hydrolysis from oak (Klason quercus) and Organosolv birch had similar composition of pyrolysis oils.