Catalytic degradation of polyethylene over SAPO-37 molecular sieve

The degradation of high-density polyethylene (HDPE) was studied alone and in presence of silicoaluminophosphate type silicoaluminophosphate (SAPO-37) as catalyst. This material was synthesized by the hydrothermal method using tetrapropylammonium hydroxide and tetramethylammonium chloride as organic templates. The characterization by X-ray diffraction, infrared spectroscopy, thermogravimetry and scanning electron microscopy showed that typical faujasite structure for the SAPO-37 was obtained. The total acidity, determined by n-butylamine adsorption, it was equivalent to 0.558 mmol g(-1), corresponding to moderate acid strength. For catalytic reaction, a physical mixture of 25%SAPO-37/HDPE was decomposed in a thermobalance at heating rates of 5, 10 and 20 degreesC min(-1), from 380 to 520 degreesC. At the maximum degradation rate, the products were collected in a cold trap and analyzed by a coupled gas chromatograph/mass spectrometer. The degradation of HDPE without catalyst was carried out at the same conditions for comparison with the obtained data with SAPO-37. The HIVE alone suffers decomposition to a wide range of hydrocarbons (C-5-C-25) while in the presence of catalyst, light hydrocarbons (C-2-C-12) were obtained. By the application of the Vyazovkin model-free kinetic method, it was observed that the activation energy decreased from 290 kJ mol(-1) for HDPE alone, to 220 kJ mol(-1) for 25%SAPO-37/HDPE, evidencing that SAPO-37 is an effective catalyst for polyethylene degradation. (C) 2002 Published by Elsevier Science B.V.