Influence of Thermal Treatment of HUSY on Catalytic Pyrolysis of Polypropylene: An Online Photoionization Mass Spectrometric Study

Refuse-derived fuels or chemicals have attracted much attention because of their ecological and economical utilization of municipal solid waste. However, the related conversions involve complex chemical reactions that prevent the use of conventional analytical methods for characterization of the detailed profiles. In this study, the influence of the thermal pretreatment of HUSY on the catalytic pyrolysis of polypropylene (PP) was investigated using online pyrolysis photoionization time-of-flight mass spectrometry (Py-PI-TOFMS). The experiments were carried out in two modes: (1) In temperature-fixed mode, the mass spectra of the pyrolyzates of PP and PP/HUSY at different temperatures were obtained in real time. Moreover, the selectivity of the pyrolyzates and conversion of PP over HUSY zeolites calcined at different temperatures were studied. (2) In temperature-programmed mode, the formation temperatures of the PP pyrolysis products in the presence of HUSY were determined. HUSY zeolites that are pretreated at different temperatures in the range from 200 to 800 degrees C exhibit distinct catalytic properties. The results of catalytic pyrolysis with a pretreatment temperature of 200 or 800 degrees C differed compared with those obtained using a pretreatment temperature of 350, 500, or 650 degrees C. However, the performances of catalysts prepared using these three pretreatment temperatures were similar, consistent with the changes in the HUSY structures observed from the XRD results and the acidities measured by NH3-TPD. The different acidities of the HUSYs resulted in different catalytic activities and pyrolysis product distributions. The results of this study indicate that Py-PI-TOFMS is a powerful technique for the comprehensive study of pyrolysis products and their pyrolysis behaviors, as well as catalysts prepared using different pretreatment conditions.