Effects of KCl, KOH and K2CO3 on the pyrolysis of Cβ-O type lignin-related polymers

Abstract

An understanding of the catalytic effect of potassium on lignin pyrolysis is crucial for the industrialized application of biomass. In this paper, the catalytic effect of potassium additives (KCl, KOH and K2CO3) on lignin pyrolysis was studied using two Cβ-O type lignin related polymers with a carbonyl group (CO polymer) and a hydroxyl group (OH polymer), respectively, on Cα. With or without potassium additives, the two polymers were injected into a thermogravimetric analyser coupled to a Fourier transform infrared spectrometer (TG-FTIR) and a CDS pyrolyser equipped with a gas chromatography and a mass spectrometer (Py-GC/MS). The results show that the catalytic effect of potassium additives is greatly affected by the associated anion. KOH and K2CO3 strongly reduced the thermal stability of the two polymers and increased the char yield of their pyrolysis, while limited effect of KCl was observed. A promoting effect of KOH and K2CO3 was also observed on the removal of side chains such as methoxy, acetyl and hydroxyethyl groups leading to the formation of CO2 and making phenol the main product. Furthermore, the depolymerization of CO polymers through Cβ-O bond cleavage were promoted by KOH and K2CO3. Finally, the catalytic mechanism of potassium and the overall pathway of pyrolysis of the two polymers were elucidated in this study.