In T-shirts, socks, shirts, and ropes—or as components of parachutes and car tires—polyamides are used everywhere as synthetic fibers. At the end of the 1930s, the name Nylon was coined for such synthetic polyamides. Nylon-6 and Nylon-6.6 are two polyamides that account for nearly 95% of the global nylon market.
Until now, it was made from fossil-based raw materials. However, this petrochemical process is harmful to the environment because it releases about 10% of the climate-damaging nitrous oxide (laughing gas) worldwide and requires a lot of energy. “Our goal is to make the entire nylon production chain environmentally friendly. This is possible if we access bio-based waste as feedstock and make the synthesis process sustainable,” said Dr. Falk Harnisch, head of the Electrobiotechnology working group at the Helmholtz Center for Environmental Research (UFZ).
Leipzig researchers led by Falk Harnisch and Dr. Rohan Karande (University of Leipzig/Research and Transfer Center for bioactive Matter b-ACTTHINGS) describes how this can be achieved in an article published in Green Chemistry. For example, nylon contains about 50% adipic acid, which until now has been obtained by industry from petroleum.
First, phenol is converted to cyclohexanol, which is then converted to adipic acid. This energy-intensive process requires high temperatures, high gas pressure, and large amounts of organic solvents. It also emits large amounts of nitrous oxide and carbon dioxide. Researchers have now developed a process where they can convert phenol into cyclohexanol using an electrochemical process.
“The chemical transformation behind it is the same as the established processes. However, electrochemical synthesis replaces hydrogen gas with electrical energy that occurs in an aqueous solution and requires only ambient pressure and temperature,” Harnisch explained.
In order for this reaction to run as quickly and efficiently as possible, a suitable catalyst is needed. This increases the yield of electrons required for the reaction and the efficiency of the conversion of phenol to cyclohexanol. In laboratory experiments, the best yield (almost 70% electrons and more than 70% cyclohexanol) was shown with a carbon-based rhodium catalyst.
“The relatively short reaction time, the efficient yield, and the effective use of energy as well as the synergies of the biological system make this process attractive for an integrated production of adipic acid,” said dr. Micjel Chávez Morejón, UFZ-chemist and first author of the study.
In the first research, two other groups working at UFZ led by Dr. Katja Bühler and Dr. Bruno Bühler discovered how the bacterium Pseudomonas taiwanensis is able to convert cyclohexanol into adipic acid in a second step. “Until now, it was not possible to microbially convert phenol into cyclohexanol. We closed this gap with the electrochemical reaction,” said Dr. Rohan Karande, who is currently continuing this work in cooperation with the UFZ at the University of Leipzig.
Researchers in Leipzig have managed to close another gap in making nylon environmentally friendly by creating an alternative to phenol made from fossil-based raw materials. To do this, they used monomers such as syringol, catechol, and guaiacol, all of which are produced as degradation products of lignin—a byproduct of the wood industry.
“For these model substances, we were able to show that together we can go as far as adipic acid.”, says Harnisch. Rohan Karande added, “About 4.5 million tons of adipic acid are produced worldwide. If we use waste products from the wood industry for this, it will have a big impact on the world market.”
However, there is still a long way to go before nylon-based lignin is ready for the market. For example, scientists have so far achieved a yield of 57% for a 22-hour total process (ie from monomers from lignin residues through microbial and electrochemical reaction steps to adipic acid). “This is a very good harvest,” said Micjel Chávez Morejón.
The results are still based on laboratory tests on a milliliter scale. Requirements for scaling up the process will be developed over the next two years. This technological transition requires not only a better understanding of the whole process but also, among other things, the use of real lignin mixtures instead of model mixtures (as has been the case so far) and the improvement of electrochemical reactors. Harnisch and Karande say, “The process for lignin-based nylon shows great potential in electrochemical-microbial processes because an optimal process chain can be set up through an intelligent way where various ingredients combined.”
Micjel Chávez Morejón et al, Integrated electrosynthesis and biosynthesis for the production of adipic acid from lignin-derived phenols, Green Chemistry (2023). DOI: 10.1039/D3GC01105D
Provided by the Helmholtz Association of German Research Centers
Citation: Research team develops process for bio-based nylon (2023, July 6) retrieved 6 July 2023 from https://phys.org/news/2023-07-team-bio-based-nylon.html
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