According to the researchers, the method could help reduce dependence on fossil resources as well as decrease waste. The study, which provides new insights for the development of chemical recycling processes for waste plastics and the utilization of carbon dioxide, was published in the scientific journal Fuel.
The idea of a three-step process consisting of pyrolysis, catalytic upgrading of pyrolysis vapors, and subsequent dry reforming of the pyrolysis gas was proposed about a year ago by one of the article’s authors, Amer Inayat. He presented it as a “proof of concept” at the international catalysis conference EuropaCat 2023 in Prague. In the following months, he and his colleagues fine-tuned the experimental setup, process conditions, and catalysts in the laboratory. For the experiments, the scientists used polypropylene, a common packaging material, especially in the food industry. In the future, other types of plastics will also be tested.
“We developed a three-step system in which the first stage involves the thermochemical decomposition of waste plastics to form organic vapors and gases with a low hydrogen content. These then pass over the first catalyst, where catalytic cracking and aromatization of hydrocarbons take place. To obtain a higher amount of hydrogen, we decided to further transform the resulting gas and, in the third stage, carry out a dry reforming reaction. After the second stage, the gaseous products were separated, mixed with carbon dioxide, and passed over a second catalyst to produce synthesis gas. This resulted in an upgrade of the pyrolysis gas while simultaneously utilizing carbon dioxide,” explained one of the members of the author team, Pavel Leštinský from IET, which is part of the Centre for Energy and Environmental Technologies at VŠB–TUO.
According to him, the key to success was precisely the integration of the three processes, which have been studied for more than five years in the Industrial Chemistry laboratory at IET. Thanks to this integration, the reaction proceeds smoothly and catalyst deactivation, common in other approaches, does not occur. At the end of the three-step process, the researchers obtain a clean synthesis gas containing only hydrogen and carbon monoxide, which can be further utilized in the chemical industry. “We introduced an additional step into commonly used procedures, in which we first produce aromatic hydrocarbons and then separate them. The clean pyrolysis gas, free of liquid substances that would cause catalyst coking, is then fed into the reforming step. As a result, the reaction proceeds smoothly and we avoid problems with catalyst deactivation and reduced conversion,” Leštinský added. According to him, the results were also achieved thanks to the use of the Large research infrastructure ENREGAT and the support of the REFRESH project.
The article builds on previous work by IET focused on the chemical recycling of waste plastics and the catalytic transformation of pyrolysis vapors. The long-term goal of the researchers is to use plastic waste to obtain chemical substances that can serve either for the production of other types of plastics or as feedstocks for the chemical industry. Increasingly strict environmental regulations related to carbon dioxide emissions also represent a major challenge, which is why the scientists are seeking new options and approaches.
Text: Martina Šaradínová
Photo source: IET