Energy: ENEA devises new process to turn plastic marine litter into oil

An ENEA research team has devised a process to turn over 90% of plastic waste from the sea into new "oil"^[1] to be used as fuel or to produce new plastics, paints, solvents and countless organic compounds^[2]. This activity was conducted as part of the European interregional Italy-Croatia project "NETWAP"^[3] on the reduction and innovative management of waste, whose outcomes were published in the ACS Sustainable Chemistry & Engineering, the online scientific journal of the American Chemical Society.

"We treated samples of plastic collected at sea with a particular thermo-chemical technique called pyrolysis, which causes plastic material to convert - at a temperature above 400°C and in the absence of oxygen - into oil and gas rich in hydrocarbons, which can potentially be used to produce new fuels and chemical products", explained Riccardo Tuffi, researcher at the ENEA Laboratory of Technologies for the Reuse, Recycling, Recovery and Valorisation of Waste and Materials, who conducte the study with Lorenzo Cafiero and Doina De Angelis.

"To further improve yield and quality - said Tuffi - we used a catalyst^[4], obtained in turn from the processing of a waste material, i.e. the ash produced by gasification and coal combustion plants, an industrial waste whose annual global production amounts to approximately 1 billion tons, Considered a potential cause of environmental pollution, its use for the synthesis of catalysts could represent a step forward to make production processes more sustainable".

The waste plastic sample examined was converted into high-value hydrocarbons (about 87% in light oil and 8% in gas) and the gases produced during the thermo-chemical treatment proved to be more than sufficient to meet the process energy requirement (450 °C).

Collection and mechanical recycling of plastic collected at sea is much more complicated than urban waste treatment, because it involves heterogeneous materials composed of many polymers of different shapes and sizes, which are difficult to identify and collect. In addition, they may contain a considerable quantity of sand, salt, shells and algae and generally also undergo different degradation processes, like photooxidation, caused by solar radiation.

"All these factors make mechanical recycling a challenging task while catalytic pyrolysis can be regarded as one of the best options for the treatment of marine plastic, because it can process large quantities of highly heterogeneous and non-pretreated waste", pointed out the ENEA researcher.

A recent survey revealed that none of the more than 100 small and medium-sized companies processing marine plastic waste worldwide used pyrolysis. "In the near future, however, small pyrolysis plants installed in ports could even produce fuel for boats from the plastic recovered at sea," said Tuffi.

The European Packaging and Packaging Waste Directive[5] has set plastic recycling targets of 50% by 2025 and 55% by 2030. Furthermore, the Circular Economy Action Plan has been issued to encourage recycling, with a strong focus on plastic waste, and to prevent and reduce the impact of single-use plastic products on the environment^[6].

However, according to the 2022 report by Plastics Europe, the European association which comprises over 100 polymer producers, covering 90% of the market, global plastic production was constantly growing until 2019 with 368 million tons. Most of this plastic, used for single-use packaging, consequently quickly becomes waste.

Unfortunately, plastic waste is often disposed of inadequately, causing serious environmental problems: according to UNESCO^[7] 8 to 10 million tonnes of plastic materials end up in the ocean, making up up to 80% of marine litter, mostly accumulating on the ocean floor (70%), while the rest remains on the coasts (15%) and on the water surface (15%)

Diagram of the transformation process of marine plastic into hydrocarbons