14 Feb Innovative project on Modified Roll-Type Electrostatic Separator & BFRs is unveiled through interview with Professor Emeritus Lucian Dascalescu

Following the publication of the scientific article “Modified Roll-Type Electrostatic Separator for the Processing of Polymer Mixtures Containing Brominated Flame Retardants” on the Institute of Electronics and Electrical Engineers (IEEE) Transactions on Industry Applications Journal in May 2023, we took this opportunity to contact Professor Emeritus Lucian Dascalescu to discover more about his and his colleagues’ innovative BFR-related project. We hope you enjoy reading this interview.

Could you please introduce yourself and the project? 

As Emeritus Distinguished University Professor, I co-share with Prof. Thami Zeghloul the responsibility of the “Tribo-electrostatics” Research Group on the Angoulême Campus of the PPRIME Institute [1]. For more than 40 years, my research activity has been focused on the development of novel electrostatic separation technologies, with applications in the recycling industry, minerals beneficiation or seed purification. During recent years, our research team patented several tribo-electrostatic separation methods and devices for the separation of plastics from industrial wastes. The extraction of brominated plastics from Waste Electrical and Electronic Equipment (WEEE) is one of the major research projects that we have been carrying out since 2021, in response to the demand of Environment Recycling Company, Domerat, France (R&D Manager, Farida Tomasella) and with the scientific assistance of Lavoisier Company.

Could you tell us more about electrostatic separators (later called ES) and how does it work?

Electrostatic separation is the generic term of a large group of physical processes that make use of the forces exerted on charged or polarized bodies when immersed in an electric field, generated between two electrodes connected to a high-voltage power supply of several tens on kilovolts. In the case of granular plastics mixtures, the constituents are charged by triboelectric effect (i.e. contact and friction between dissimilar bodies); the positively and negatively-charged granules are attracted to the electrodes of opposite polarities and recovered in different compartments of a collector system.

Can this deal with all sorts of polymers or only a limited few of these? Would this technology also be able to deal with other polymers, and if so which ones?

Any sorts of polymers can be sorted using appropriate electrostatic separation techniques. Of major interest are ABS, PS, PE, et PP.

What is the robustness for practical WEEE plastics with varying particle size and sometimes wet plastics, a pre drying step needed?

The efficiency of the electrostatic separation (i.e., the purity and the recovery rate of the products) depends on the characteristics of the granular mixtures that are processed. In the standard electrostatic processes, the granule size should not be smaller than 0.25 mm or larger than 5 mm. Narrow granulometric distributions (e.g., 0.25 mm to 1 mm; 1 mm to 3 mm; 3 mm to 5 mm) guarantee better electrostatic separation performances. The pre-drying of the mixtures originating from a humid technological process is a pre-requisite for a good electrostatic separation.

Can ES deal with polymer mixtures containing Brominated Flame Retardants? And if so, can something be said about the yield and bromine sorting efficiency using ES?

Recent studies carried out by our research group have demonstrated the feasibility of separating granular brominated plastics from bromine-free ones. The experiments were carried out with “model” granules of ABS, PS, PE, et PP waste.

The main use of BFRs is especially for ABS and Styrenes. How much of such plastics are processed and would it be possible to recover Bromine with this technique as well?

We have not conducted any market studies to have the answer to the first part of your questions. Nevertheless, in France, eco-organizations speak of about 10,000 tons/year of brominated plastics that are currently incinerated at very high costs. Regarding the possibility of recover Bromine with this technique, the answer is no. The electrostatic separation enables only the extraction of bromine-bearing granules from those that are Bromine-free, but this is a key operation for the treatment of these wastes, as envisioned by the DEVIPEEE project [2].

What roadblocks have you faced and how have you overcome them?

The triboelectric properties of brominated and non-brominated plastics are quite similar, and this has been a major roadblock for the development of an efficient electrostatic separation method. The exposure of the granular plastics to the action of non-thermal plasma was found to modify the triboelectric charging behavior of the various plastics and facilitate their sorting.

Given your work and looking forward would you consider Bromine to be an issue for achieving a circular economy?

Yes. In plastics derived from WEEE, more than 35% are considered non-recyclable because they contain a high level of BFR (within the meaning of the Stokholm Convention). Incineration, in addition to its significant cost, brings only a low energy recovery. By combining several technologies, in addition to the tribo-electrostatic separation operation, DEVIPEE project is expected to transfer to the industry a viable solution for the decontamination of plastic waste and the recovery of critical materials. In this way, it will contribute not only to the development of a circular economy, but also to increase our sovereignty in terms of access to raw materials.

We understand this is work at lab-scale – are there plans for further development?

Our research team is already working with a local manufacturer of special machinery to carry out pilot-plant level tests and design of an industrial tribo-electrostatic separator.

What is the current technical readiness level and what will be the time for a demo-plant and direction of a full-scale plant (>10000 ton/y)?

A demo-plant will be built by the end of 2024. The tests that will be done at that time will show us if the treatment of more than 10000 t/y can be achieved with only one separator or a second unit is needed to attain this processing capacity.

As you may know, there are ongoing discussion with regards to UTC thresholds. Options include PBDE for products for the general public to 10 PPM, and for other products declining up to a 200 PPM value by the end of 2027, or UTC of 100 PPM by the end of 2027 for mixtures with PBDE-containing recyclates, and 10 PPM for mixtures and articles. This would be a considerable lowering of thresholds compared to those that are valid today. Do you believe that this would negatively impact innovations and projects such as yours?

Electrostatic separation techniques developed up to now are not capable of detecting such low levels of PBDE, which may be present in plastic products due to the regulations that impose the use of certain percentages of recycled materials. Nevertheless: (1) research is in progress to lower the detection level, by using non-thermal plasma treatment as a tool for modifying the triboelectric charging of PBDE-containing recyclates; (2) electrostatic separation is only one operation in complex physico-chemical processes that are developed for the treatment of PBDE-bearing wastes.

We note that Most of WEEE plastics are black. This is achieved by adding carbon black to the plastic. Carbon black has certain electric conductivity. Will it affect separation?

None of the studies carried out to this day has pointed out a detrimental effect of carbon black. We have been able to tribocharge and electrostatically separate mixtures containing plastics of all colours, including black. Indeed, high levels of carbon black might significantly modify the conductivity of the plastic granules, which will restrict the use of certain electrostatic separation techniques for the recycling of such wastes.

BSEF would like to express their gratitude to Professor Lucian Dascalescu and his colleagues for the time which was dedicated to this interview, and for the opportunity to learn more about their innovative research in the field of extraction of brominated plastics from WEEE.

Should you wish to have further details on this project, please don’t hesitate to contact us at info@bsef.org

Footnotes:

[1] Pprime Institute (P’) is a research laboratory specialized in the fields of Physics and Engineering Sciences. It is a UPR CNRS linked with the University of Poitiers (The Faculty of Fundamental and Applied Sciences, the Faculty of Sport Sciences and the National Higher School of Engineers of Poitiers -ENSIP) and the ISAE-ENSMA (National Higher School of Mechanics and Aeroengineering). More info here: https://pprime.fr/en/institute/

[2] Literally: Décontamination et Valorisation Innovante des Plastiques bromés issus des DEEE (eng: Decontamination and Innovative Valorization of Brominated Plastics from WEEE). More info here: https://www.environnement-recycling.com/projet-devipeee/