Generation and evaluation of different pyrolysis oil upgrading configurations

Plastics are a constant presence in human life. They have improved our quality of life, and many of their features are hard to find somewhere else. Unfortunately, as a society, we have failed to find a sustainable way to dispose plastic waste, as a result, we are now facing a plastic waste crisis. Due to the magnitude of the problem several companies have started to explore alternatives to tackle the mentioned situation. Shell, one of the main ethylene and propylene (Precursor of polyethylene and polypropylene) producers worldwide, is committed to recycling 1 million tonnes of waste plastic per year by 2025. The technology chosen for this task is the thermal conversion of plastic waste, known as pyrolysis. After the conversion, the resulting pyrolysis oil (PO) would, in principle, make a suitable feedstock for steam cracker furnaces, the unit where the thermal cracking of paraffins into olefines takes place. Nevertheless, the presence of different contaminants makes the processing of untreated PO undesirable, and different upgrading (cleaning) steps are required prior to cracking. The goal of the present project is to explore, select and finally design an alternative line-up to the actual upgrader unit that Shell has designed and is currently operating at a pilot-scale.
In order to fulfill the company requirements, the project was divided into two main phases. First, A screening phase whereby implementing a process synthesis methodology, a set of feasible alternatives were generated and evaluated. Finally, a design phase where the two most promising alternatives were designed at a basic engineering level was implemented.
The two most promising alternatives compress simple unit operations that either split PO or create small “pure” PO fractions able to fulfill steam cracker specifications, bypassing the upgrading step and reducing energy consumption. Aspen simulations, lab experiments and sensitivity analysis have been performed in order to understand the effect of the previously mentioned separation possibilities on utilities consumption, CO2, and byproduct generation.
With the selected configuration, the utilities consumption can be reduced up to 20%, the CAPEX up to 10%, the CO2 generation is reduced by 22%, and the byproducts diminish by 3% with respect to the initial Shell design. The selected technology is being tested at a bench scale by a third party to assess its suitability and applicability within the plastic to chemicals Shell initiative.