Periodic Reporting for period 1 - CATALEPTIC (A developed thermochemical approach for catalytic depolymerization of plastics)
Okres sprawozdawczy: 2021-08-01 do 2023-07-31
This study aims to tackle one of the most pressing environmental issues, which is the accumulation of plastic waste, through the adoption of innovative and circular technologies aimed at increasing the recycling rate of plastics. Chemical recycling techniques have emerged as an effective method to treat mixed polymer streams by producing virgin monomers from waste plastics while at the same time remaining less sensitive to fluctuations in the global oil market. This feature makes chemical recycling a more environmentally friendly alternative to linear plastic recycling. However, chemical recycling has some limitations, such as the need for mandatory feedstock separation, the difficulty of converting PET, and the energy-intensive processing of recalcitrant polyolefins, which hinder the scaling up and industrial implementation of chemical recycling.
This EU-funded project aimed to assess the potential of the Hot Compressed Water (HCW) technology in handling waste plastics. Hydrothermal Processing (HTP) was utilized to convert challenging plastics into energy-dense oils or original monomeric compounds. The project targeted the efficient decomposition of polyolefin packaging waste and subsequent selectivity improvement towards naphtha/monomeric production using appropriate catalysts. However, real-world plastic waste's complex chemical and physical composition necessitates using various operating conditions and catalytic materials for optimal conversion. Moreover, innovative separation and purification methods are required to meet market quality standards, such as removing heteroatom impurities in the reaction mixture. Ultimately, the proposal aims to reduce dependence on crude oil for plastic production, enhance plastics' recycling rate, and mitigate plastic waste's environmental impact.
This EU-funded project aimed to assess the potential of the Hot Compressed Water (HCW) technology in handling waste plastics. Hydrothermal Processing (HTP) was utilized to convert challenging plastics into energy-dense oils or original monomeric compounds. The project targeted the efficient decomposition of polyolefin packaging waste and subsequent selectivity improvement towards naphtha/monomeric production using appropriate catalysts. However, real-world plastic waste's complex chemical and physical composition necessitates using various operating conditions and catalytic materials for optimal conversion. Moreover, innovative separation and purification methods are required to meet market quality standards, such as removing heteroatom impurities in the reaction mixture. Ultimately, the proposal aims to reduce dependence on crude oil for plastic production, enhance plastics' recycling rate, and mitigate plastic waste's environmental impact.
The project began with a comprehensive study of plastic waste in Denmark, using local and foreign resources to prepare a report. The report is believed to be important for those interested in continuing similar work, especially in Denmark. The document was prepared as an ongoing project, with information being collected and compiled alongside experimental work.
From the experimental perspective, the project focused on performing a feasibility study on polyolefins' hydrothermal processing (HTP). Experimental campaigns were conducted to screen the behavior of Polyethylene (PE), Polypropylene (PP), and Polystyrene (PS) under hot-compressed water conditions. The results showed that the strong C-C bonds with SP3 configuration in the polymer backbone of PE and PP made their hydrothermal decomposition almost invisible below 400 °C. At the same time, even at higher temperatures, the pyrolytic condition would outweigh the outcome significantly. However, PS showed promising results due to the existence of the tertiary bonds that made the structure prone to fracture under HTP conditions. While the decomposition of PS was recorded at a lower temperature than its thermal degradation temperature, the composition of the final product was far from an efficient conversion, especially from a circularity viewpoint. Application of pyrolysis condition at around thermal degradation temperature of PS in the presence of appropriate catalyst resulted in promising reproduction of Styrene.
The second half of the project focused on the treatment of PVC under HTP conditions. Due to Chlorine's inclusion in its chemical structure, PVC caused serious problems upon decomposition by producing highly corrosive HCl and forming a considerable amount of char under pyrolytic conditions. In this phase, a developed catalytic HTP of PVC was successfully implemented to remove around 98% of the Cl from PVC plastic waste, a great step toward the production of Refuse Derived Fuels (RDFs) with maximum of 1% chlorine contamination. The study was expected to be continued by working on different techniques of purification and separation, especially those licensed as PureStep technology. The project's main results were supposed to be disseminated in a summer school on plastic recycling, which AAU ENERGY will run.
From the experimental perspective, the project focused on performing a feasibility study on polyolefins' hydrothermal processing (HTP). Experimental campaigns were conducted to screen the behavior of Polyethylene (PE), Polypropylene (PP), and Polystyrene (PS) under hot-compressed water conditions. The results showed that the strong C-C bonds with SP3 configuration in the polymer backbone of PE and PP made their hydrothermal decomposition almost invisible below 400 °C. At the same time, even at higher temperatures, the pyrolytic condition would outweigh the outcome significantly. However, PS showed promising results due to the existence of the tertiary bonds that made the structure prone to fracture under HTP conditions. While the decomposition of PS was recorded at a lower temperature than its thermal degradation temperature, the composition of the final product was far from an efficient conversion, especially from a circularity viewpoint. Application of pyrolysis condition at around thermal degradation temperature of PS in the presence of appropriate catalyst resulted in promising reproduction of Styrene.
The second half of the project focused on the treatment of PVC under HTP conditions. Due to Chlorine's inclusion in its chemical structure, PVC caused serious problems upon decomposition by producing highly corrosive HCl and forming a considerable amount of char under pyrolytic conditions. In this phase, a developed catalytic HTP of PVC was successfully implemented to remove around 98% of the Cl from PVC plastic waste, a great step toward the production of Refuse Derived Fuels (RDFs) with maximum of 1% chlorine contamination. The study was expected to be continued by working on different techniques of purification and separation, especially those licensed as PureStep technology. The project's main results were supposed to be disseminated in a summer school on plastic recycling, which AAU ENERGY will run.
While the implemented HTP technology would have a small role in the polyolefin decomposition playground, it has shown great potential in the impurity removal sector. Catalytic HTP of PVC at moderate temperature and the pressure showed that the chlorine content of the plastic waste could be removed by more than 98%, which could largely remove our reliance upon a highly expensive hydrotreating post-treatment. Furthermore, such a pre-purification pathway could also increase the overall yield of the process by minimizing char formation. Hydrothermal purification is not restricted to chlorine removal from PVC and could also embrace heteroatoms existing in other layers of a commercial plastic film. If it were just for dechlorination, the future would not be bright for the technology since a limited percentage of the total plastic waste, around 8-12%, is made of PVC waste.
Nevertheless, fortunately for HTP technology, the commercial plastic product has a significant fraction of additive layers, such as flame retardant concentrated in heteroatoms. It needs special attention to lower their concentration below the permitted level. Low temperature, ease of separation, and production of value-added side products such as HCl have provided HTP technology enough space to mature in the plastic chemical upcycling field, where it may not be used as the main actor but could still have a significant impact on the circular economy.
Nevertheless, fortunately for HTP technology, the commercial plastic product has a significant fraction of additive layers, such as flame retardant concentrated in heteroatoms. It needs special attention to lower their concentration below the permitted level. Low temperature, ease of separation, and production of value-added side products such as HCl have provided HTP technology enough space to mature in the plastic chemical upcycling field, where it may not be used as the main actor but could still have a significant impact on the circular economy.