Highly selective conversion of mixed polyolefins to valuable base chemicals using phosphorus-modified and steam-treated mesoporous HZSM-5 zeolite with minimal carbon footprint

Catalytic fast pyrolysis of polyolefinic waste streams was investigated to recover valuable base chemicals at high selectivity. HZSM-5 zeolite with different properties, affected by Si/Al, mesoporosity, phosphorus stabilization, and steaming, were tested and thoroughly characterized. Different feeds, catalyst/feed ratios and reaction temperatures were evaluated in a micropyrolysis reactor coupled to two-dimensional gas chromatography. While unmodified HZSM-5 rapidly deactivated, phosphorus-modified and steamtreated HZSM-5 showed almost no deactivation due to its lower coking propensity during 130 runs with stable conversion towards C₅₊ aliphatics and high C₂-C₄ olefins selectivity (~75%) using post-consumer mixed polyolefins. The performance of this direct olefins production route with unprecedented high olefin selectivity was further evaluated in a plantwide context. It was found that it requires ~37% lower energy input than the plastics pyrolysis followed by pyrolytic oil steam cracking, while it results to at least a one order of magnitude lower environmental burden as compared to waste incineration.