Catalytic Cracking of Polystyrene and Low-Density Polyethylene over Synthesized Zeolite Na-A with Optimized Crystallinity

Nowadays, waste plastics made a significant environmental problems. Chemical converting of the polymers to valuable liquids is a promising method to solve the problem and make excellent benefit. This study investigates the utilization of kaolin, a natural resource, for synthesizing zeolite Na-A and significance of the catalyst crystallinity on the catalytic cracking of a 50:50 mixture of polystyrene (PS) and low-density polyethylene (LDPE). This research aims to identify the optimal hydrothermal conditions for producing crystalline zeolite Na-A and evaluate the effect of crystallinity of synthesized zeolite Na-A on production of liquids. A central composite design (CCD) model is employed to achieve this, selecting three independent variables: hydrothermal temperature (80, 85, 90, 95 and 100 degrees C), the molarity of the alkaline solution (NaOH concentration = 1,2,3,4 and 5 molar), and hydrothermal time (8, 10.43, 14, 17.56 and 20 h). Fourier transform infrared spectroscopy (FTIR) determines the functional groups which proves the presence of sodium aluminosilicate in the synthesized zeolite. The crystallinity of the produced zeolite Na-A is evaluated through X-ray diffraction (XRD) analysis, optimizing the results using the CCD model. Scanning electron microscopy (SEM) reveals well-formed cubic crystalline structures of zeolite Na-A. The optimum conditions for polymer cracking are determined as hydrothermal temperature of 89 degrees C, a hydrothermal time of 13 h, and a NaOH molarity of 2.8, while predicted liquid production was obtained 81%. The analysis of ANOVA indicates that the designed model based on CCD calculations is valid for prediction of the process. Finally, gas chromatography with flame ionization detection (GC-FID) is employed to characterize the main resulting value-added components (styrene, toluene, and ethylbenzene) under optimum conditions.