Thermochemical recycling of mixed plastic wastes through pyrolysis and steam cracking – Assessment of centralized vs. Decentralized approaches

Artikel i vetenskaplig tidskrift, 2025

Thermochemical recycling of medical plastic waste (MPW) was evaluated experimentally and through development of mass & energy balances. Fluidized bed (FB) steam cracking of MPW at a centralized petrochemical site was compared to thermal and catalytic pyrolysis of MPW to intermediate WAX (thermal) and POil (catalytic) feedstocks at a decentralized site, followed by FB steam cracking of WAX and POil at a centralized petrochemical site. Pyrolysis and FB steam cracking experiments were performed in lab-scale reactors. Steam cracking yields of primary products (light olefins, C2-3 alkynes, BTXs) were highest for MPW, followed by WAX, and POil feedstocks. Higher steam cracking temperature increased the primary product yields for the MPW feedstock but showed a less significant effect in WAX and POil cases. For all cases, higher cracking temperature increased chain scission and hydrogen abstraction, resulting in rising yields of ethylene, methane, and hydrogen, and lower yields of longer chain aliphatic hydrocarbons. Material, carbon, and energy balances, developed from experimental results, showed that excess heat from incineration of pyrolysis and steam cracking byproducts can meet the energy demands of the pyrolysis and steam cracking processes. The balances also showed that direct FB steam cracking of MPW can achieve high product yields and high rates of fossil carbon recycling. However, steam cracking of WAX feedstock, the product of pyrolysis pre-treatment, can achieve moderate product yields and fossil carbon recycling while realizing several practical advantages: easier transport, reduced need for feedstock preparation, and removal of ash and heteroatoms for improved steam cracker operability.