Mechanism study on the pyrolysis of lignin in cotton stalks catalyzed by K2CO3 to produce guaiacol: Experiment and DFT simulations

Abstract

In this study, the regulation mechanism of K₂CO₃ catalytic pyrolysis of lignin in cotton stalk for producing guaiacol was explored, and its effects on tar components were studied through the combination of experiments and density functional theory. The results showed that the addition of 7.5 % K₂CO₃ to cotton stalk significantly altered the composition of tar, and guaiacol content in phenols increased from 2.47 % to 33.11 %. At the same time, the contents of alkanes and esters decreased by 29.21 % and 28.43 %, respectively. The simulation results revealed that K⁺ changed from a three-dimensional structure to a planar structure by coordinating with the oxygen atoms in the model compound. The structural change significantly weakened the stability of the bond, thereby decreasing the bond dissociation energy of the C_β-O bond, which preferentially promoted the homolytic cleavage of the C_β-O bond of the model compound to generate free radical intermediates. These intermediates accelerated the reaction process in the early stage of pyrolysis. In addition, K⁺ regulated the subsequent free radical reaction pathway by adjusting the energy barrier, mainly inhibiting the homolytic side reaction. The reaction energy barrier increased by approximately 32.19 % and promoted the co-decomposition path. The energy barrier decreased by approximately 11.14 %, thus significantly improving the selective generation of guaiacol.