Positron Imaging of Segregation, Mixing and Transport of Plastics in Fluidised Beds: Toward a Circular Economy for Plastics

Plastic waste represents one of the foremost global challenges of our
age. A promising technique for the creation of a true circular economy in
plastics is the use of heated fluidised beds to pyrolise waste plastics,
cracking long-chain molecules into shorter-chain hydrocarbons which are then
fractionated and condensed into valuable `virgin' petrochemical feedstocks.
While this methodology has been proven to be viable, and the fractionation
processes are well-understood and refined, knowledge of the internal dynamics
of the fluidised bed systems remains heavily limited. As such, current attempts
at optimisation remain purely empirical, and reliant on measurements of basic,
bulk properties.

In order
to address this issue, we must gain an improved understanding of the
fundamental mixing and transport behaviours of mixed sand-plastic systems, and
how these behaviours may be optimised. To this end, we have performed detailed
imaging of such systems using Positron Emission Particle Tracking, gaining
novel insight into their internal dynamics and their variation with key system
parameters. We demonstrate that the large disparities in both particle size and
density in the systems of interest lead to behaviours significantly divergent
from those of binary systems more commonly studied in academic research.