Polystyrene transformation by thermal and catalytic pyrolysis

LILIANA B. PIERELLA; MARÍA S. RENZINI; DANIEL S. CAYUELA

Taiwan

Conferencia; Southeast Asia Environmental Forensics Conference; 2005

Plastic is a very useful commodity consumed in many aspects of human life in large volumes. It has become apparent that waste produced from this very useful material was becoming environmentally problematic.  Catalytic transformation of waste polymers into hydrocarbons with higher commercial value shows a great interest. Polystyrene (PS) was transformed mainly to liquid hydrocarbons (LHC = >94.96 wt %), by thermal degradation and catalytic cracking over MEL modified zeolites, H-ZSM-11 and Zn-ZSM-11. The conversion levels were nearly complete between 400-500oC. The main LHC products of PS catalytic degradation were 1,5-hexadiene and styrene, and in minor proportion indanes and α-methyl styrene, being these compounds  very important in the polymers technology and chemical fine field. Styrene was the most important product in the thermal cracking. A single-pass reactor and atmospheric pressure was employed. The crystallinity, the nature of the structure and the stability of the synthesized and modified catalysts after cation incorporation were confirmed by XRD, FTIR and surface area by BET.  The nature of acidic sites was determined by FTIR of pyridine adsorbed. According to FTIR experimental data of pyridine adsorbed (at room temperature and 3 Torr) and desorbed at different temperatures, we found the Brönsted (1550 cm-1) and Lewis (1450 cm-1) acidic sites in both samples. Zn-ZSM-11 material shows the formation of new and strong Electron-Donor-Acceptor Adduct (EDA) of pyridine to Lewis sites, compared with the H-ZSM-11, since they retain more pyridine than the parent H-ZSM-11 material after outgassing at 400°C under vacuum. The reactant (atactic PS) was characterized by TG-DSC. The glass transition temperature and thermal degradation temperatures can be observed.  Reaction products were analyzed by gas chromatography and mass spectrometry.  By means of the development of a competitive catalytic system, we determine the feasibility of the process of degradation of PS  towards the synthesis of LHC products.