Lignin Pyrolysis Assisted by Molten Salt Medium: Evolution Behavior of Volatiles and Biochar Structure

This study focuses on the use of a molten salt reaction medium (NaCl-KCl-LiCl) in the lignin pyrolysis process to modify the pyrolysis volatiles and biochar structure. The effect of pyrolysis reaction temperature (400°C, 500°C, and 600°C) and lignin/molten salt mass ratios (3:1, 1:1, and 1:3) on the evolution behavior of volatiles and biochar structure was explored. The pyrolysis products were obtained were determined using gas chromatography/mass spectroscopy, N2 adsorption analyses, scanning electron microscopy, and elemental analysis. Results indicated that the introduction of molten salt can enhance the lignin depolymerization, leading to the production of phenolic precursors. Moreover, the metal cation (Na+, K+ and Li+) of molten salt can in-situ induce the modification of biochar structure with high porosity. The lower sulfur content in biochar was attributed to the immobilize function of molten salt. The evolution behaviour of volatiles and biochar structure during molten salt-assisted lignin pyrolysis was proposed. This study can serve as a benchmark for the high-value recycling of industrial lignin waste.