Catalytic pyrolysis of xylan over alkali metal salts as revealed by synchrotron vacuum ultraviolet photoionization mass spectrometry

Abstract

Xylan is the primary hemicellulose polysaccharide found in biomass. In this study, catalytic pyrolysis of xylan with Na2CO3 and K2CO3 was conducted in a homemade tubular furnace at 300 °C. As a result of on-line sampling and the use of tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), the evolution of unstable products, such as 4-hydroxy-5,6-dihydro-pyran-2-one (m/z 114), could be monitored in real time. The obtained photoionization mass spectra were interpreted by statistical analysis and the mechanisms of xylan pyrolysis with alkali metal salts were further discussed. The differences in thermogravimetry curves, photoionization mass spectra and time-evolved profiles revealed the important effects of alkali metal ions on both the decomposition temperature and reaction rates during xylan pyrolysis. Furthermore, we showed that alkali metal ions can promote the formation of char and lighter compounds. This work can provide guidance on the better utilization of hemicellulose resources with the help of alkali metal salts.