Nov-2023

Transforming a refinery unit into a key component of end-of-life plastic circularity (ERTC 2023)

Every year, in Europe alone, roughly 30 million tonnes of plastic waste is collected. However, more than 80% of that resource is not recycled into new products because the majority of it is still incinerated, exported, or dumped in landfills.

Nicolas MENET, Ana-Isabel PACO and Thomas MALLET
AXENS

Article Summary

This is a waste of precious resources that could be used as secondary raw materials in place of fossil feedstock in addition to being a source of CO₂ emissions. A rapid scale-up of mechanical and chemical recycling capability is required to further increase plastic recycling and support Europe in meeting its recycled content targets.

Plastic production pathways
Generally, today, the economics of a circular, sustainable plastics economy remain challenging in terms of profitability. Strengthening the links in the plastics value chain and implementing a solid policy framework will be key. However, efficient, innovative solutions will need to be implemented to improve the economics of the different recycling pathways (see Figure 1).

The pyrolysis pathway will play an important role in addressing the difficult-to-recycle end-of-life plastic while meeting the production objectives of virgin-quality food-grade plastics. When considering it, we see that an economically viable and efficient way of scaling up that route is to integrate it into existing refineries or petrochemical sites. The efficiency will not only come from utilities sharing, process synergies, and overall yield optimisation but also from opportunities to reduce projects’ Capex, repurposing existing hydroprocessing units for the purification and upgrading of the recycled oil prior to processing in the steam cracker.

REWIND® MIX: A UNIQUE SOLUTION TO PURIFY PYROLYSIS OILS AND MEET STRINGENT STEAM CRACKER SPECIFICATIONS
Pyrolysis of mix plastic waste is today considered the unique industrially available route to permit a true closed-loop recycling of polyolefin, meeting quality requirements and regulatory objectives. That route, however, relies on the ability to properly purify the pyrolysis oil (pyoil) for reprocessing in an existing petrochemical plant.

That purification step is not a trivial refining kind of processing as pyrolysis oil usually combines multiple contaminants and unstable molecules that, if not removed and stabilised, would jeopardise the safe operation and performance of the petrochemical plant steam cracker.

Repsol, Axens, and IFP Energies nouvelles (IFPEN), fully committed to playing a major role in the chemical recycling industry, have joined their efforts to unlock the recovery of plastic waste that would otherwise remain in the landfills or be incinerated so that it could be turned into high-quality, virgin-like circular polyolefins and other chemical products through pyrolysis. How? By solving the issue of purification/decontamination of those pyrolysis oils. Those efforts resulted in the development and commercialisation of the Rewind Mix technology.

The Rewind Mix process removes impurities such as silicon, chlorine, di-olefins, and other metals from the plastics pyrolysis oils produced, allowing direct and undiluted feed to the steam cracker. Proper purification is key, as contaminants could jeopardise the operation of the petrochemical steam cracker. Besides, contaminants can also flow on downstream units and ultimately end up in final polymers products.

The successful commercialisation of that purification technology would not have been possible without the expertise IFPEN, Axens, and Repsol have built throughout the last decades on the hydroprocessing of various polluted petrochemicals streams.

Moreover, the development of new analysis methods by IFPEN to properly assess the different qualities of pyoil has been a key factor in success. Indeed, pyoil products concentrate a large proportion of multiple contaminants, making it difficult to analyse them through conventional analysis methods.

As pyrolysis oil qualities also vary substantially, depending on the nature of the feedstock to the pyrolysis plant, the Rewind Mix process has a unique flexibility to cope with those quality changes. It is able to continually guarantee the production of on-specification products suitable for direct undiluted processing on a naphtha steam cracker.

In addition to its capacity to process a full range of pyrolysis oil to maximise closed-loop production of polyolefin circular polymer, Rewind Mix can also embed a hydrocracking function that will turn heavier products back into virgin equivalent recycled naphtha.

AXENS: A CASE-BY-CASE PRAGMATIC APPROACH TO ENHANCE REVAMP CAPABILITIES
Axens, through its Process Licensing Department, is able to conduct feasibility studies for identifying all technical solutions to overcome pyrolysis oil processing impacts on existing hydrotreatment units: catalyst poisoning, reactor pressure drop, exotherm, corrosion, hydrogen partial pressure, hydrogen consumption, unit turndown, unbalanced stripping, and fractionation.

Axens proposes a case-by-case pragmatic approach to select the best revamp solution. This approach consists of successive phases performed before the beginning of the detailed engineering design to optimise available resources: a scoping study, a process study, and then a process design package could be proposed (see Figure 2).

To better optimise the existing process and to check the possible bottlenecks on the existing unit, a site check-run survey of the unit is highly recommended as a first stage. The check-run is carried out by Axens technical experts who are specialised in units’ start-up, follow-up, troubleshooting, and operating excellence.

CASE STUDY: REVAMPING AN EXISTING EUROPEAN DHT UNIT INTO REWIND MIX
Rewind Mix process scheme has been developed relying on Axens’ proven experience in hydrotreatment and, therefore, uses similar codes as conventional hydrotreatment units typically found in refinery and petrochemical complexes. Retrofitting existing or idle units into Rewind Mix is therefore feasible, and hydrocracking and hydrotreatment units are great candidates.

Axens has already performed several studies of retrofitting hydrotreatment units  into Rewind Mix, demonstrating that the conversion of idle units allow significant investment cost reduction compared to a grassroots unit.

As an example, Axens has been working on the possibility of revamping an existing European DHT unit into Rewind Mix. After a preliminary assessment of the existing unit, consisting of gathering all relevant information (equipment as-built documentation, operation history) to identify the main bottlenecks, Axens has elaborated several revamping options focusing on different drivers the client was interested in:
υ    Identify the maximum pyrolysis oil treatment capacity while reusing most of the existing equipment.
ϖ    Maximise the pyrolysis oil throughput while minimising the capital investment; for example, reusing main equipment such as reactors, heaters, and compressors.

After agreeing with the client on the most profitable scenario, Axens developed a detailed study of the selected option with the objective to provide more accurate economics and LCA information. The results of the study revealed that the DHT unit is a good candidate for being retrofitted into Rewind Mix. Indeed, the unit retrofit cost has been estimated to be up to 65% lower than a grassroots Rewind Mix with the same capacity and performance.

This short article originally appeared in the 2023 ERTC Newspaper, which you can VIEW HERE