Fluidised bed pyrolysis of polypropylene over cracking catalysts for producing hydrocarbons

Polypropylene (PP) was pyrolysed over various catalysts using a laboratory fluidised-bed reactor operating isothermally at ambient pressure. The yield of volatile hydrocarbons for zeolite catalysts (HZSM-5 > HUSY ≈ HMOR) was higher than that for non-zeolite catalysts (SAHA ≈ MCM-41). Product distributions with HZSM-5 contained more olefinic materials with about 60 wt% in the range of C3-C5. However, both HMOR and HUSY produced more paraffin streams with large amounts of isobutane (i-C4) and both catalysts were deactivated during the course of the degradation. SAHA and MCM-41 showed the lowest conversion and generated an olefin-rich product with a rise to the broadest carbon range of C3-C7. Experiments carried out with various catalysts gave good yields of volatile hydrocarbons with differing selectivity in the final products dependent on reaction conditions. The selectivity could be further influenced by changes in reactor conditions; in particular, olefins and iso-olefins were produced by low temperatures and short contact times. It is demonstrated that under appropriate reaction conditions suitable catalysts can have the ability to control both the product yield and product distribution from polymer degradation, potentially leading to a cheaper process with more valuable products.