Thermal and Catalytic Pyrolysis of High Density Polyethylene: Lessons Learned on Solid Organic Waste Treatment
Organic waste is characterized by high volume to weight ratio and may pose a hazard due to radiolysis and generation of combustible and explosive gases. Thus, minimizing waste volume and immobilization are of high importance in the treatment of contaminated polymers. In the present study, polymer decomposition of the commonly used thermoplastic polyolefin high density polyethylene (HDPE) was optimized. HDPE was pyrolysed in a batch reactor at 450°C and atmospheric pressure with a range of aluminosilicate catalysts, including Zeolite Y and ZSM-5. The impact of catalysts, their acid strength and catalyst to polymer ratio on decomposition efficiency were evaluated. Product conversion into coke, liquid and gaseous products were measured based on product yields, and gaseous product composition was measured by gas chromatography. Higher conversions to gas were obtained for HDPE in the presence of ZSM-5 zeolites (~90%) than Zeolite Y (~52%) or no catalyst (~20%). The highest impact of ZSM-5 was reached at a catalyst to polymer ratio of 1:10, independent of the Si/Al ratio of the catalysts. Moreover, high fraction of gaseous light hydrocarbons (C1-C4) was observed (~80%) and only minimal oil fractions were obtained (2-7%). Altogether, our data demonstrate that catalytic pyrolysis of HDPE over the ZSM-5 zeolite results in high decomposition efficiency and supports its use for organic solid waste treatment. These results are especially encouraging due to the clear benefits of pyrolysis over incineration techniques, including it being an environmentally friendly, easy to control process.
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