SULFUR-PROMOTED DEGRADATION OF POLYETHYLENE POLYPROPYLENE DETECTED BYELECTRON-SPIN-RESONANCE SPECTROSCOPY/

In situ electron spin resonance (ESR) spectroscopy is employed to inve stigate the thermal and catalytic degradation of a sample of commingle d plastics (CP) containing about 95% polyethylene and 5% polypropylene . The materials tested include elemental sulfur (S), NiMo/Al2O3, and z eolite MZSM-5 for temperatures between ambient and 450 degrees C and p ressures up to 500 psig of H-2. The depolymerization temperature T-d o f CP, where an ESR signal is first observed, is about 360 degrees C th ermally. With 1 wt % loading of CP with S, T-d is reduced to about 250 degrees C. With 10 wt % S plus 10 wt % NiMo/Al2O3, T-d is further red uced to about 230 degrees C and the free radical intensity N is reduce d considerably compared to the CP + S case. HZSM-5 does not affect the T-d of CP, but N is reduced considerably and with. increase in temper ature, N decreases, similar to the NiMo/Al2O3 case. These results, alo ng with the observed increase in the ESR, line width for the HZSM-5 an d NiMo/Al2O3 cases, suggest capping of the free radicals by hydrogenat ion. For sulfur loading of CP, the significant increase in N and lower ing of % (also observed by thermogravimetry) suggest enhanced depolyme rization of CP. This sulfur-promoted depolymerization of polyethylene/ polypropylene is supported by the liquefaction experiments of Sivakum ar et al, (Fuel Process. Technol, 1996, 49, 219) where sulfur loadings of polyethylene and polypropylene produced a nearly 2-fold increase i n the gasoline-range oil yield.