Pyrolysis study of moxa floss with different storage years using online photoionization mass spectrometry

Abstract

The pyrolysis behaviors of moxa floss with 5–9 storage years were investigated by thermogravimetry (TG) and online synchrotron radiation photoionization mass spectrometry. The online fragment-free mass spectra of moxa floss pyrolysis products were obtained within 300–800 ℃ and characterized as hydrocarbons, nitrogenous and oxygenated compounds. The results indicate that pyrolysis temperature plays a leading role in the low-molecular-weight product distribution, while the storage year has secondary effects. Controlling the pyrolysis temperature in a lower range (<650 ℃) can effectively reduce the generation of benzene, toluene and other harmful substances. Aromatics could be released from the break of large molecules with aromatic structures and formed from the aromatization of small unstructured compounds at high temperatures. At the temperature lower than 400 ℃, short-year samples exhibit a higher intensity of oxygenated compounds. However, with the increase of storage years, nitrogenous heterocyclics such as pyrrole and pyridine are preferably formed at higher temperatures. In addition, increasing the storage year of moxa floss leads the TG curve to exhibit a lower maximum mass loss rate. These results will enrich the understanding of the storage year effect on the beneficial oxygen-containing components generation and the release of harmful components in the moxa floss pyrolysis.