A catalyst made from discarded fish bones could turn one of agriculture’s most persistent waste streams into a concentrated source of valuable hydrocarbons, according to a new study. Researchers report that fishbone-derived char, modified with phosphoric acid and iron, converted low-density polyethylene (LDPE) agricultural film into an olefin-rich pyrolysis oil with a yield of 89.32 wt.% and an olefin selectivity of 84.03%. The work brings together two difficult waste problems—used plastic mulch and fish-processing residues—in a single chemical-recycling strategy.
Agricultural plastic films are widely used to conserve soil moisture, suppress weeds, regulate temperature, and improve crop yields. After several months in the field, however, the thin LDPE sheets can become contaminated with soil, plant residues, pesticides, and fertilizers. Their low weight and large surface area make collection expensive, while conventional recycling is often impractical when the material is heavily soiled. As a result, used films may be buried, burned, or abandoned, wasting a carbon-rich resource and creating additional environmental risks.
The researchers investigated microwave-assisted catalytic pyrolysis as an alternative. In pyrolysis, plastic is heated in the absence of oxygen, causing its long polymer chains to break into shorter hydrocarbon molecules. LDPE is composed primarily of repeating carbon and hydrogen units, but uncontrolled thermal cracking can produce a broad mixture of gases, waxes, aromatic compounds, and liquid hydrocarbons. The central challenge is therefore not simply to decompose the plastic, but to steer the reaction toward a narrow range of molecules that can be used as chemical feedstocks or fuels.
To achieve that control, the team first converted fish bones into a carbon-based material and then treated the char with phosphoric acid and iron. Fish bones naturally contain hydroxyapatite, a calcium phosphate mineral that can provide a stable inorganic framework. Phosphoric acid altered this mineral-rich structure and introduced phosphate-containing acidic groups. Iron was subsequently incorporated into the material, generating strongly interacting iron–oxygen–phosphorus structures known as Fe–O–P linkages. Together, these features created a catalyst with both acidic and metal-associated reaction sites.
The best-performing material was designated 20Fe-30P@FC. It was produced using a 30 wt.% phosphoric acid treatment and a nominal iron loading of 20 wt.%. Under optimized conditions, the plastic was pyrolyzed at 550 °C, while the catalyst operated at 350 °C, with a catalyst-to-feedstock mass ratio of 1:2. Microwave heating supplied energy directly to the reaction system rather than relying solely on heat transfer from the outside of a conventional reactor. This approach can promote rapid and more uniform heating, although the efficiency of microwave processing depends strongly on the material’s ability to absorb electromagnetic energy.
The catalyst produced a substantial improvement over uncatalyzed pyrolysis. Without the modified fishbone char, LDPE generated a liquid product yield of 72.3 wt.% and an olefin selectivity of 43.78%. With 20Fe-30P@FC, the liquid yield increased to 89.32 wt.%, while olefin selectivity nearly doubled to 84.03%. The researchers also found that compounds containing six to twelve carbon atoms represented 99.78% of the targeted hydrocarbon fraction under the optimized conditions. Molecules in this range are important because they overlap with valuable chemical and fuel intermediates.
The catalyst’s performance appears to arise from a division of chemical labor between its active sites. Acidic phosphate groups can promote the cleavage of carbon–carbon bonds in the polyethylene chain, lowering the energy required to fragment the polymer. Iron-associated sites may then influence dehydrogenation and hydrogen-transfer reactions, helping stabilize and redirect the newly formed hydrocarbon fragments. Rather than allowing the intermediates to undergo extensive uncontrolled rearrangement or condensation, the catalyst appears to favor the formation and preservation of olefins, which contain carbon–carbon double bonds and are widely used in the manufacture of polymers, solvents, and other chemicals.
The findings are particularly notable because the catalyst is produced from a waste material that would otherwise have limited value. Fish bones are commonly discarded or processed into low-value products, despite their mineral-rich composition. Converting them into a functional catalytic support could reduce the need for more expensive or resource-intensive catalyst materials. At the same time, using agricultural film as a feedstock could recover carbon that would otherwise be lost through landfilling or open burning. The combined approach does not eliminate the need for collection, cleaning, reactor operation, or emissions control, but it offers a route for transforming two difficult waste streams into higher-value products.
Repeated-use experiments suggested that the catalyst could retain much of its activity after regeneration. Following five cycles, the bio-oil yield declined only from 89.32 wt.% to 86.52%, while olefin selectivity remained at 82.32%. The C6–C12 fraction also remained high, at 99.11%. These results indicate that the catalyst’s active structure was reasonably stable during repeated processing, although longer-term testing will be needed to determine how it performs in the presence of real agricultural contaminants. Industrial systems would also need to address catalyst deactivation caused by carbon deposits, mineral impurities, and compounds originating from pesticides or soil.
The study, published in Sustainable Carbon Materials, presents the modified fishbone char as a promising platform for selective plastic conversion rather than a finished industrial solution. Questions remain about the energy balance of microwave-assisted operation, the economics of catalyst preparation, the treatment of contaminated films, and the quality of the resulting oil after repeated processing. Scale-up could also reveal challenges associated with microwave penetration, continuous feeding, heat management, and product separation. Even so, the sharp increase in olefin selectivity and the catalyst’s ability to use fish-processing waste point toward a compelling circular-economy model: discarded biological minerals helping convert discarded agricultural plastics into concentrated chemical building blocks.
Subject of Research: Selective catalytic conversion of waste low-density polyethylene agricultural films into olefin-rich pyrolysis oil using microwave-assisted pyrolysis and fishbone-derived catalyst.
Article Title: Iron and phosphoric acid co-modified fishbone char for olefin-rich bio-oil production from waste agricultural films via microwave-assisted pyrolysis
News Publication Date: 30-Jun-2026
Web References: https://doi.org/10.48130/scm-0026-0021
References: Yang J, Zhang Y, Duan D, Chen X, Lan X, et al. 2026. “Iron and phosphoric acid co-modified fishbone char for olefin-rich bio-oil production from waste agricultural films via microwave-assisted pyrolysis.” Sustainable Carbon Materials 2: e026. DOI: 10.48130/scm-0026-0021
Image Credits: Jie Yang, Yue Zhang, Dengle Duan, Xun Chen, Xiaoyan Lan, Lu Gan, Leilei Dai, Yunpu Wang, Roger Ruan, Erguang Huo, Rongge Zou, Lianfu Zhang, Jian Zhang, and Yunfeng Zhao
Keywords
Waste agricultural plastic, low-density polyethylene, fishbone char, catalytic pyrolysis, microwave-assisted pyrolysis, olefins, bio-oil, hydroxyapatite, iron–phosphorus catalyst, chemical recycling, sustainable carbon materials, plastic waste conversion
