Pyrolysis of Dutch mixed plastic waste: Lifecycle GHG emissions and carbon recovery efficiency assessment

Abstract

Plastic production and consumption contribute to climate change and the depletion of non-renewable fossil resources, necessitating a shift towards a circular economy. This study explored the potential of pyrolysis as a novel approach to managing plastic waste and achieving plastic circularity in the Netherlands. Specifically, we focused on the pyrolysis of DKR-350, a low-quality mixed-plastic sorting residue. Using the life cycle assessment framework, we analysed DKR-350 pyrolysis, based on empirical data from pilot-scale trials, from two perspectives depending on the system's primary function: waste management or naphtha production. We also considered the impacts of pyrolysis feedstock pre-treatment, including washing. Our findings demonstrated that pyrolysis of DKR-350, with lifecycle greenhouse gas (GHG) emissions of 876 kg CO₂ eq. per 1000 kg pyrolysed unwashed DKR-350, can offer significant environmental benefits compared to incineration, resulting in a 28%-31% reduction in lifecycle GHG emissions. Sensitivity analysis showed the potential for achieving a 39%-65% reduction in GHG emissions by 2030, with lifecycle GHG emissions representing a mere 470 kg CO₂ eq. per 1000 kg pyrolysed unwashed DKR-350 for the best sensitivity case. Lastly, we analysed the carbon recovery efficiency - a potential circularity indicator based on substance flow - resulting in 38%-55% of recovered carbon in pyrolysis oil, the system's main product from a lifecycle perspective.

Keywords: DKR-350; LCA; chemical recycling; circularity; environmental impacts; plastics recycling.

Figure 1.

Framework for the LCA perspectives defined for the study: waste management perspective (left) and naphtha production perspective (right). LCA: life cycle assessment.

Figure 2.

System boundaries defined for the study: (a) waste management perspective; (b) naphtha production perspective.

Figure 3.

Cradle-to-gate lifecycle GHG emissions for waste management perspective (left) and naphtha production perspective (right). GHG: greenhouse gas.

Figure 4.

Carbon flow of the pyrolysis system, unwashed case. Data are normalised to 100 kg C in the feedstock to the pyrolysis reactor. The green dashed flow represents uncertain pyrolysis oil yield, assuming uncollected mass from the pilot-scale reactor is pyrolysis oil.

Figure 5.

Sensitivity analysis for the 50:50 approach. Results are expressed in cradle-to-gate lifecycle GHG emissions from the waste management perspective (left) and the naphtha production perspective (right). GHG: greenhouse gas.

Figure 6.

Results of the sensitivity analyses for the pyrolysis unwashed case, waste management perspective. Results are expressed in lifecycle cradle-to-gate GHG emissions (kg CO₂ eq.) per 1000 kg DKR-350 waste management. GHG: greenhouse gas.