The role of inorganic sulfur compounds in the pyrolysis of Kraft lignin

• Kraft lignin produces one order of magnitude more CO2 than the amount of carboxyls.
• The oxidative role of inorganic sulfates on lignin pyrolysis was proposed.
• As a proof, the removal of sulfates reduced the amount of carbon dioxide formed.

In this study we have evaluated the production of gas during lignin pyrolysis under static vacuum conditions, the quantity of the most important gases produced, and the role of sulfur compounds. In fact, sulfates can act as oxidizers at the high temperature of pyrolysis (>200 °C) increasing the amount of carbon dioxide formed. This is related to the detection of reduced volatile sulfur compounds by GC–MS. We have evaluated the decrease in the production of CO2 and of reduced sulfur species after a simple acid treatment for the removal of inorganic sulfates from the pristine lignin. The thermovolumetric analysis (TVA) was found as effective as thermogravimetric (TGA) one for the investigation of lignin pyrolysis.