Agricultural plastic mulch films are widely used around the world to increase crop yields, conserve soil moisture, and suppress weeds. However, once these films are discarded, they can persist in the environment for decades, contributing to soil contamination and plastic pollution. A new study shows that these difficult to recycle plastics could instead be transformed into valuable chemical products using a biochar based catalytic process.
Researchers investigated a method for converting waste plastic mulch film into useful chemicals through catalytic pyrolysis. In this process, plastic is heated in the absence of oxygen, causing the long polymer chains to break down into smaller molecules that can be used as fuels or chemical feedstocks. The team used a catalyst made from walnut shell biochar activated with phosphoric acid, demonstrating a promising way to recycle both agricultural plastic waste and biomass residues at the same time.
Plastic mulch films are commonly made from low density polyethylene and are widely used in agriculture in countries such as China, the United States, and across Europe. Because these materials degrade extremely slowly and are often contaminated with soil after use, recycling them is challenging. Chemical conversion technologies such as pyrolysis offer an alternative approach by breaking plastics down into smaller molecules that can be reused.
In the study, scientists focused on a critical but often overlooked factor in catalytic pyrolysis: the temperature of the catalytic bed. The team tested how three different temperatures affected the conversion of waste plastic mulch film and the behavior of the catalyst. They found that temperature strongly influenced both the types of products produced and how quickly the catalyst became deactivated by carbon deposits known as tar.
At a catalytic temperature of 350 degrees Celsius, the process produced the highest yield of valuable olefins, which made up about 69 percent of the liquid products. Olefins are important chemical building blocks used in the production of plastics, fuels, and many industrial materials. Under these conditions, the total yield of pyrolysis oil reached about 72 percent, indicating highly efficient conversion of the plastic waste.
However, the study also revealed a trade off. Although 350 degrees Celsius maximized olefin production, it also promoted chemical reactions that generated oxygen containing tar on the catalyst surface. This tar gradually blocked the catalyst pores and reduced its activity.
At a higher catalytic temperature of 400 degrees Celsius, the reaction pathway shifted. Aromatic compounds became more abundant in the liquid products and the overall amount of tar decreased. More importantly, the carbon deposits formed under these conditions were easier to remove because they had lower thermal stability. Kinetic analysis showed that the activation energy required to decompose the deposited tar decreased to around 40 to 50 kilojoules per mole at this temperature, indicating that the catalyst could be regenerated more easily.
According to the researchers, these findings highlight a fundamental balance in catalytic plastic recycling systems.
“Our results show that catalytic temperature controls not only the product distribution but also the long term stability of the catalyst,” said the study’s authors. “While 350 degrees Celsius is ideal for maximizing olefin production, a higher temperature of 400 degrees Celsius produces carbon deposits that are easier to regenerate. Understanding this trade off is essential for designing practical plastic upcycling technologies.”
The researchers also demonstrated that walnut shells, an abundant agricultural by product, can be converted into effective catalysts for plastic recycling. Using biomass derived catalysts could help reduce costs and improve sustainability compared with conventional catalyst materials.
By linking product chemistry, tar composition, and kinetic analysis, the study provides new insights into how catalysts behave during plastic pyrolysis. The findings offer guidance for developing more efficient and durable catalytic systems that can convert agricultural plastic waste into valuable chemical resources.
As plastic waste continues to accumulate globally, technologies that combine waste recycling with renewable materials could play an important role in building a more circular and sustainable chemical industry.
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Journal reference: Tan C, Lan X, Chen X, Wang Y, Dai L, et al. 2026. Controlling catalyst deactivation: temperature regulation for the directed synthesis of easily regenerable and refractory tar in the pyrolysis of waste films. Sustainable Carbon Materials 2: e008 doi: 10.48130/scm-0026-0004
https://www.maxapress.com/article/doi/10.48130/scm-0026-0004
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Controlling catalyst deactivation: temperature regulation for the directed synthesis of easily regenerable and refractory tar in the pyrolysis of waste films
5-Mar-2026