Plastic materials constitute an important environmental problem after disposal. They are often mixed in a very small scale with other materials, because of the use of additives that enhance certain properties of plastics (e. g. flame-retardants, fillers) and because they can be part of composite materials that incorporate different materials such as cardboard and metals (e. g. tetrapack packaging materials). The recovery of these elements and compounds (that can be toxic or critical raw materials) could contribute to the circular economy but is a scientific challenge today. 

The objective of the PhD is to develop methodologies for the recovery of metals, metalloids and hydrocarbon components from challenging recycling waste streams containing plastics like composite materials.

The work is strongly supported in experimentation which will be mainly developed in Geolab and in DynaCat lab.

The work plan encompasses the following main tasks:

T1- Identification of waste streams containing plastics that are environmental problems due to the lack of technical and economical solutions for their recycling. Stream macroscopic characterization and materials analysis, including elemental and thermal analysis. The waste streams may include, for instance, plastic mixtures like plastic/cardboard, plastic composites with aluminium foil, or aluminium-plastic laminates, mono-component plastics with additives.

T2- Pre-processing, including shredding and separation of components that can be separated by physical or physico-chemical processes (e. g. froth flotation).

T3- Thermochemical processing of the remaining fractions, which are the recycling challenging ones, to produce gas, liquid, and solid products. From these, the relevant components will be extracted, not only hydrocarbons but also metal and metalloids. Metals will typically be recovered by processing of solid products but other components, like metalloids may be recovered from solids or from volatile components. This will be carried-out in a multi-scale approach, combining quantum chemical and kinetic modelling techniques, to better understand the processes that occur during the chemical transformation, experimental approaches at different scales and, also process modelling.

T4- Identification of the components present in the solids (slags) and extraction of the relevant components, with emphasizes on restricted access ones. Preliminary economic evaluation of the whole processing diagram.

T5- Proposal of a technical, environmental, and economically viable integrated processing of composite wastes containing plastics and recovery of the most relevant components.

The work is a multidisciplinary approach combining the environmental aspects, scientific studies, technical feasibility end economic interest, involving also industrial partners (waste management and companies that are raw materials producers or consumers).

As the end results, we expect this project to be able to:

i) Identify the most relevant waste streams and the components that can be recovered from them.

ii) Propose an integrated process that can be used to recover hydrocarbon components, metals, and metalloids from the previously identified waste streams, including pre-processing methods and a suitable thermochemical process.

iii) Environmental and pre-feasibility studies.

careers@cerena.tecnico.ulisboa.pt