Until now, the production of nylon has been based on petroleum-based raw materials. This is harmful to the environment because fossil resources are used, a lot of energy is required and climate-damaging nitrous oxide is emitted during production. A research team from the Helmholtz Center for Environmental Research (UFZ) and the University of Leipzig has now developed a process in the laboratory with which adipic acid, one of two basic materials of nylon, can be produced from phenol through electrochemical synthesis and the use of microorganisms. In addition, it was possible to show that phenol can be replaced by waste materials from the wood industry. This could be used to produce bio-based nylon. The research work was published in the specialist journal Green Chemistry.
In T-shirts, stockings, shirts, ropes or even as a component of parachutes and car tires - polyamides are used everywhere as synthetic synthetic fibers, for which the name nylon was created at the end of the 1930s. Nylon-6 and nylon-6,6 are two polyamides that make up around 95 percent of the global nylon market and are produced from fossil-based raw materials. But this petrochemical process is harmful to the environment – on the one hand, because around ten percent of the climate-damaging nitrous oxide (laughing gas) is emitted worldwide, and on the other hand, because it requires a lot of energy. “Our goal is to make the entire nylon production chain green. This is possible if we use bio-based waste as starting materials and make the synthesis process sustainable,” says Prof. Dr. Falk Harnisch, head of the Electrobiotechnology working group at the Helmholtz Center for Environmental Research (UFZ).
The Leipzig researchers led by Falk Harnisch and Dr. Rohan Karande (University of Leipzig/ Research and Transfer Center for Bioactive Matter b-ACTMatter) in an article for the journal Green chemistry described. Nylon consists of around 50 percent adipic acid, which has so far been industrially extracted from crude oil. In a first step, phenol is converted into cyclohexanol, which is then converted into adipic acid. This energy-intensive process requires high temperatures, high gas pressure and organic solvents, and a lot of nitrous oxide and carbon dioxide are released. The researchers have now developed a process in which they can convert phenol into cyclohexanol using an electrochemical process. "The underlying chemical conversion is the same as in the established processes: The electrochemical synthesis, however, replaces the hydrogen gas with electrical energy, takes place in an aqueous solution and only needs ambient pressure and room temperature for this," explains electrobiotechnologist Falk Harnisch. In order for this reaction to run as quickly and efficiently as possible, a suitable catalyst is required. This is designed to maximize the yield of electrons needed for the reaction and the efficiency of how much cyclohexanol is ultimately formed from phenol. In laboratory experiments, the best yields were found with a carbon-based rhodium catalyst with almost 70 percent electrons and just over 70 percent cyclohexanol. "The relatively short reaction time, the efficient yield and the effective use of energy as well as synergies with the biological system make this process attractive for a combined production of adipic acid," says Dr. Micjel Chávez Morejón, UFZ chemist and first author of the study. As in a second step, the bacterium Pseudomonas taiwanensis Converting cyclohexanol into adipic acid had already been done in an earlier research project by two other UFZ working groups led by Prof. Dr. Katja Bühler and Prof. Dr. Bruno Buehler found out. "Until now, it had not been possible to allow the reaction of phenol to form cyclohexanol to take place microbially. We closed this gap with the electrochemical reaction," sums up Dr. Rohan Karande, who is now continuing this work in cooperation with the UFZ at the University of Leipzig.
And the Leipzig researchers were able to close another gap in green nylon production by developing an environmentally friendly alternative to the phenol produced from fossil raw materials. To do this, they used monomers such as syringol, catechol or guaiacol, all of which occur as a breakdown product of lignin – a waste product from the timber industry. "We have been able to show for these model substances that together we can take the path to adipic acid," says Falk Harnisch. And Rohan Karande adds: “Around 4,5 million tons of adipic acid are produced worldwide. If we develop wood residues for this, it would have a decisive impact on the world market.”
However, there is still a long way to go before the lignin-based nylon is ready for the market. The scientists have so far achieved a yield of 22 percent for the 57-hour overall process, i.e. from the monomers from lignin residues using electrochemical and microbial reaction steps to adipic acid. "That's a very good yield," says Micjel Chávez Morejón. The results are still based on laboratory tests on a milliliter scale. For this reason, the conditions are to be created in the next two years to bring the process to the liter scale. This technology transfer not only requires a better understanding of the entire process, but also the use of real lignin mixtures instead of the previous model ones and the improvement of the electrochemical reactors. Falk Harnisch and Rohan Karande agree: "The process for the lignin-containing nylon is an example of the great potential of electrochemical-microbial processes, since an optimal process chain can be set up through the intelligent way in which different components are combined."
The process for developing bio-based nylon is funded by the UFZ program for innovations "trans “, which supports the implementation of ideas in the application at the UFZ. The project funds provided amounting to 250.000 euros are supplemented by the University of Leipzig's own contributions.
Micjel Chávez Morejón, Alexander Franz, Rohan Karande, and Falk Harnisch: Integrated electrosynthesis and biosynthesis for the production of adipic acid from lignin-derived phenols. green chemistry, https://doi.org/10.1039/D3GC01105D
Source: Press release b-ACT matter from 11.07.2023/XNUMX/XNUMX