Thermal oxidation behaviour of softwood kraft lignin

Abstract

Lignin-derived carbon materials has been a keen topic of research in recent years. Lignin is thermally degraded in pyrolysis, a process called carbonization, into a variety of liquid and gaseous compounds and solid residue. The solid residue, called carbon or biochar, is used for carbon products. Lignin, however, has a complex structure and chemical composition making processing challenging, and lignin has a tendency to melt in high temperatures of pyrolysis.

This thesis examines the physico-chemical changes in softwood kraft lignin using thermal oxidation (TO) process. During TO treatment, thermoplastic lignin is treated at relatively low temperatures in the presence of air, which modifies the physical properties of the lignin to thermoset material, making it infusible and easier to process in pyrolysis temperatures.

A full-factorial design of experiment (DOE) was performed for three factors (temperature, time and heating rate) to see main effects on the material properties and to find optimal process conditions in TO treatment for softwood kraft lignin. Analytical methods include organic elemental analysis, thermogravimetric analysis and modulated differential scanning calorimetry. Regression models were made for the results, main effects for each response identified and response optimization including significant analyses was created to identify optimal process conditions.