The global plastic crisis has emerged as one of the most urgent environmental challenges of the 21st century, with annual production exceeding 390 million tons and recycling rates falling below 10%. In Saudi Arabia alone, over 3.4 million tons of plastic waste are generated annually, yet less than 15% is recovered. This widening gap between consumption and recycling capacity underscores the need for innovative waste-to-chemicals pathways that reduce environmental burdens while supporting the transition to a circular carbon economy.

This study investigates thermochemical conversion routes for transforming mixed plastic waste into high-value light olefins, specifically ethylene and propylene, which serve as essential building blocks for the petrochemical industry. Two distinct pathways were designed and rigorously modeled using Aspen Plus® process simulation. At a proposed scale of 40,000 kg/hr (equivalent to diverting over 350,000 tons of plastic waste per year), these routes demonstrate both environmental and economic potential, contributing directly to decarbonization strategies in the Gulf region.

The first pathway integrates pyrolysis, hydrotreating, and steam cracking. Mixed plastic waste undergoes pyrolysis to yield pyro-oil, gases, and char. Subsequent hydrotreating upgrades pyro-oil into lighter hydrocarbons, which are then cracked to maximize olefin production. Simulation results indicate overall olefin yields of up to 70 wt.% with approximately 30 wt.% as light olefins, alongside a 40–60% reduction in CO₂ emissions compared to conventional fossil-based naphtha cracking. Process efficiency exceeds 90% with minimal char formation, enabling effective resource recovery.

The second pathway employs steam gasification followed by a methanol-to-olefins (MTO) process. Gasification converts plastic feedstock into high-quality syngas, with sensitivity analyses performed to optimize temperature and steam-to-plastic ratio. The syngas is subsequently synthesized into methanol, which is upgraded to light olefins via MTO. Although more complex, this route offers flexibility for integration with existing petrochemical infrastructure and can diversify product streams while enabling future syngas-based energy systems.

Both pathways demonstrate substantial decarbonization potential, with estimated reductions of 0.6–1.0 million tons of CO₂ annually at the proposed scale. While pyrolysis delivers higher olefin yields and simpler operation, the gasification–MTO route provides strategic advantages for infrastructure integration and syngas valorization. Together, these findings highlight the role of advanced thermochemical technologies in addressing plastic waste, reducing emissions, and reinforcing the circular carbon economy.

By linking waste management with petrochemical innovation, this work presents a viable pathway to produce sustainable olefins at scale. The outcomes align with global energy transition goals and Saudi Arabia’s Vision 2030 strategy, offering practical contributions toward cleaner production, carbon reduction, and sustainable growth in the energy and chemicals sector.

Co-author/s:

Umer Zahid, Associate Professor, King Fahd University of Petroleum & Minerals.