Yen Nhi Le recently completed her Master’s thesis for the Life Science Technologies programme, majoring in Biosystems and Biomaterials at Aalto university, making a comparison between carbon, energy and CO2 efficiency of plastic recycling routes. Her research is very much at the core of the SPIRIT programme and in the interest of Borealis, where she will now start work as a Production Engineer. We had a chat with Nhi to learn about the conclusions of her research.
For starters, Nhi Le reminds of the key figures of processing plastic waste: only 9% of the total plastic waste is recycled and nearly half is incinerated. Further, 99% of the recycled plastics is processed through mechanical recycling. These figures form the objective of the thesis: how do five different recycling technology routes compare with each other. In fact, such comparisons between the studied recycling technologies for all three parametres of carbon yield, energy efficiency and CO2 emissions have not been carried out before. As for the carbon yield, it was studied how much of the feed is converted back to polyolefins, and for the energy efficiency, the study focused on the amount of energy needed in total conversion route, and for the CO2 emissions, the direct CO2 emissions of the route were evaluated.
In her study, Nhi compared the above-mentioned parameters using mechanical recycling as her base case of a technology route. She then made the following comparisons:
- plastic waste pyrolysis and pyrolysis oil upgrading to steam cracker feed;
- plastic waste gasification directly to olefins;
- plastic waste incineration followed by CO2 capture, CO2 conversion to methanol and eventually methanol used in methanol-to-olefins (MTO) technology;
- plastic waste incineration followed by CO2 capture, CO2 conversion to syngas and syngas used in Fischer-Tropsch-to-olefins (FTO) technology.
Two to four feedstocks for each technology route were selected: optimal feed (100% polyolefins, PO); typical feed (85% PO and 15% others); dirty typical (80% PO and 20% mixed waste) and mixed waste (100% mixed waste).
For her research, Nhi used several public literature sources and consulted the experts at Borealis and other organisations. The thesis supervisors Ismo Savallampi and Mikko Rönkä from the SPIRIT programme at Borealis proved to be valuable sources of in-depth information, insights as well as inspiration to Nhi Le during her research, complementing her findings and data she collected.
Regarding the results of the study, Nhi learned each route has its strengths and weaknesses. Mechanical recycling provides good carbon yield, good energy efficiency with low CO2 emissions but it requires very high quality of feedstock. CO2 capture routes create surprisingly high direct CO2 emissions and consume significantly energy but provide good carbon yield. Gasification has superior energy efficiency and low emissions as well as feedstock sensitivity, but the carbon yield is low. Finally, both waste incineration technologies with CO2 capture provide superior carbon yield and have low feedstock sensitivity but consume a lot of energy and produce high process emissions.
What also varied among the different technology routes was related to Technology Readiness Levels (TRL) which has an impact on the implementation of the technologies. However, this study did not discuss of the technology readiness levels. The CAPEX and OPEX figures were also outside the scope, and relevant topics for further studies.
According to Nhi, the study certainly increased the awareness and overall understanding of the pros and cons of each technology route. It also provides ideas on how the technologies could be used to complement each other for the best results in the quest to increase the plastic waste recycling rate in Finland and beyond.
Mikko and Ismo share their sentiments regarding the research Nhi has completed: “Nhi’s study covers all aspects of SPIRIT programme. There’s a lot of talk about increasing the recycling rate, but the differences between various technologies and what causes them haven’t been considered before. In this work, the technologies are clearly compared, and strengths and weaknesses are well highlighted. It became clear that no technology is overwhelmingly the strongest overall.”
Nhi concludes: “As a firm believer in circular economy and green transition, I was excited over the chance of doing my Master’s for Borealis. Now my thesis is complete and after having grown my overall understanding on the plastic recycling routes, I am overjoyed at the opportunity to start working at Borealis’ cracker and experience in practice the actual processes related to plastic production and recycling and how the technologies will evolve in the near future.”