Utilization of 2H and 18O isotope labeling of pyrolysis products during lignin pyrolysis

This is the authors' abstract. We don't add key points for this paper.

Four major pyrolysis products of lignin in supercritical water (H2O, D2O, H218O) were investigated using Py-GC/MS technique and isotope tracing using lignin as the basic pyrolysis feedstock: phenol (PH), 2-methoxy-4-vinyl phenol (MV), 2,6-dimethoxyphenol (DP), 4-allyl-2,6-dimethoxyphenol (ADP). Abundance ratios were used to study the location of chemical bond breakage during pyrolysis of the four target compounds based on the characteristic signals of the four compounds labeled by stable isotopes in the mass spectra. Experimental results show that stable isotopes can be labelled into the pyrolysis products by co-pyrolysis and that SIM mass spectrometry can be used to characterise and quantify the isotopes in the products. The method of isotope exchange illustrates that the fundamental reason for different temperatures, pyrolysis times and tracer doses hindering radical exchange is the change in bond energy due to steric hindrance effects, conjugation effects and induction effects, which affect the rate and extent of exchange. For all four compounds, changes in temperature had a greater effect on the rate and extent of free radical exchange. In addition to this, tracer dose and pyrolysis time both had a greater effect on PH. For ADP only the degree of hydroxyl radical exchange was a little greater at high doses of H218O. This work could provide a viable method for isotopic labelling of lignin pyrolysis products.