Experimental and theoretical study of the catalytic effects of potassium and calcium additives on the pyrolysis of β-O-4 type lignin model compounds. (15th January 2023)

• Record Type: Journal Article
• Authors: Guo, Yilin; Fang, Yang; Gong, Xun; Liu, Shuai; Tian, Hong; Chen, Jingwei; E, Jiaqiang; Leng, Erwei
• Is Part Of: Fuel. Volume 332(2023)Part 1
• Publication Date: 2023-01-15
• Subjects: Pyrolysis -- Potassium -- Calcium -- Lignin model compound -- β-O-4 linkage; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.125976
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Catalytic effects of K and Ca on lignin pyrolysis were explored. Cβ -O homolytic reaction dominates the initial depolymerization of dimers. Potassium and calcium additives are beneficial to the formation of phenol. The Cβ -O homolytic reaction is further enhanced by both potassium and calcium. Ca 2+ is more conducive to the concerted decomposition of side chains than K + . Abstract: In this work, to investigate the catalytic effects of potassium and calcium additives on lignin pyrolysis, two β-O-4 type model compounds for lignin containing different oxygen-containing functional groups (a carbonyl group or a hydroxyl group) on Cα were prepared, and their catalytic fast pyrolysis experiments were carried out on Py-GC/MS. Furthermore, the possible catalytic mechanism of potassium and calcium additives is further investigated using density functional theory (DFT) calculations. The experimental results show that the addition of potassium acetate and calcium acetate is beneficial to the formation of phenol, while the promotion effect of potassium addition is stronger than that of calcium addition. Moreover, considering the contributions of temperature and activation entropy ΔS ‡, the activation Gibbs free energy ΔG ‡ is required as the basis to explain the pyrolysis mechanism of lignin. It is determined that the Cβ -O homolytic reaction performs the most favorable in the initial depolymerization of both dimers. By comparing the ΔG ‡, it is confirmed that the addition of K + and Ca 2+ are beneficial to the Cβ -O homolytic reaction and further promote the conversion of the intermediate to phenol. Furthermore, the different effects of K + and Ca 2+ additives are compared on the side chains cleavage through homolytic reaction and concerted decomposition. The calculation results show that K + is more conducive to the simple homolytic reaction, while Ca 2+ is more conducive to the concerted decomposition.