(112c) Plastic Pyoil Learnings for Ethylene Producers

Chemical plastic recycling is an emergent technology for plastics circularity in Europe, where many pyoil production plants are starting operations.

Pyoil from chemical plastic recycling is a very complex and challenging mixture to process in ethylene plants compared to the historic feedstocks used. Traditional light feedstocks like ethane, propane and C4s have simple composition and specifications. Traditional liquid feedstocks like naphtha or gasoils have a more complex composition with a wide range of hydrocarbons, yet impurities are minimum and specifications simple. Waste plastic does not only have polyolefins (PE and PP) but also have small amounts of other plastic materials like PET, Nylon and PVC. In the conditions of the pyrolysis reactors (cooler than cracking furnaces) a significant heavy fraction of aliphatic compounds with waxy nature remains. Pyoil formed is also highly olefinic as one can expect from polyolefins chains being broken. Olefinic compounds and waxy streams are somehow not new for the ethylene industry. The most relevant chemistry challenge that pyoil from chemical plastic recycling brings to the ethylene industry is the presence in significant amounts of heteroatom-containing (O, N, Cl and others) compounds like caprolactam (and derivatives), bezoic acids, ammonium chloride and others. These compounds pose challenges not only in the cracked gas processing equipment after furnaces, but also in furnaces and upstream in the pyoil production process, transportation and handling.

While there are research groups which have studied and simulated pyoil cracking, the impact in downstream cracked gas processing units is based on a theoretical analysis since the % of pyoil in the total feedstock used by ethylene plants is still very low as to see any major difference / impact. By the time the % of pyoil in the feedstock reaches figures like >30% pre-treatment units to remove contaminants and reduce olefinic content will be a must. The investment in such pre-treatment units will request the right business case (government policies, customers paying premium for circular plastic, etc...). The question remains how can ethylene producers deal with pyoil composition challenges as they ramp in % of pyoil in the feedstock until the business case is clear enough to invest in pre-treatments.

Nalco Water started almost 10 years ago to explore chemical treatment solutions to overcome pyoil production, storage, transportation and handling challenges and is right now working side-by-side with many of the pyoil producers starting operations in Europe to solve problems like the cold-flow stability, oxidation, corrosion and demulsification of pyoil. But most novel developments are regarding fouling mechanisms in the pyoil production process and its mitigation.

Sabic Technology group is heavily investing also in the development of technology for the processing of pyoil from a “consumers” perspective and is collaborating with Nalco Water in the development of antifoulant solutions for Pyoil.

In this paper we will review the learnings from the early experiences solving pyoil production, transportation, storage and handling issues at industrial scale, as well as the latest developments in fouling control for pyoil from the point of view of the ethylene producers and how they translate in valuable knowledge for their operations processing pyoil. This is particularly relevant during the early stages where the pre-treatment of pyoil will be little or inexistent.