On-line photoionization mass spectrometric study of the catalytic pyrolysis of acrylonitrile-butadiene-styrene copolymer over HZSM-5, HUSY and Al-MCM-41

Three molecular sieve-based catalysts, HZSM-5, HUSY, and Al-MCM-41, were employed in the catalytic pyrolysis of acrylonitrile-butadiene-styrene (ABS) copolymer. The on-line synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) together with pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used to evaluate the performances of these catalysts in the catalytic pyrolysis processes, especially their denitrogenation ability on the pyrolysis oil. Based on the Py-GC/MS results, the formation of N-containing oligomers can be significantly suppressed with the presence of HZSM-5 and HUSY, over which a high content of Bronsted acid sites were detected. In contrast, although large amounts of polycyclic aromatic hydrocarbons can be formed over Al-MCM-41, little effect was exhibited on the yields of major products owing to its inferior acidity. Given the relative production of light nitrogenous compounds, it can be concluded that HUSY is more applicable to the denitrogenation than HZSM-5. On account of the temperature-evolved profiles of the aromatic products acquired with SVUV-PIMS in real time, two different reaction paths were proposed for the catalytic pyrolysis over zeolite catalysts, by which the formation of valuable compounds can be clearly demonstrated, including benzene, toluene, ethylbenzene, and styrene. Moreover, it has been directly evidenced that the framework structure of HUSY can facilitate intermolecular hydrogen transfer to a great extent. This work highlights the superiority of SVUV-PIMS in the study of catalytic decomposition mechanisms of complex copolymers.