Nylon has long been produced from petroleum-based raw materials. However, this is quite detrimental to the environment, as non-renewable fossil resources are used, a large amount 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 for the production of adipic acid (one of the two building blocks of nylon) from phenol by electrochemical synthesis and using microorganisms. The team also claims that phenol can be replaced by waste from the wood industry. These wastes can be used to produce bio-based nylon. The research work was published in the journal “Green Chemistry”.
Polyamides are widely used as synthetic fibers in T-shirts, stockings, shirts and ropes, or as components in parachutes and car tires. In the late 1930s, this synthetic polyamide was given the name “nylon”. Nylon 6 and Nylon 6,6 are two types of polyamides that account for approximately 95% of the global nylon market. Until now, they have all been produced from fossil raw materials. However, this petrochemical process is harmful to the environment, as it emits about 10 percent of climate-damaging nitrous oxide globally and is energy-intensive. Falk, Head of the Electronic Biotechnology Working Group at the Helmholtz Center for Environmental Research (UFZ)
“Our goal is to make the entire nylon production chain environmentally friendly. Our goal is possible if we use bio-based waste as raw material and make the synthesis process sustainable,” says Dr. Harnisch.
by Falk Harnisch and Rohan
In an article published in Green Chemistry, researchers at the University of Leipzig led by Dr. Karande describe how this can be achieved. Nylon, for example, is composed of about 50 percent adipic acid, which until now was extracted industrially from petroleum. In the first step, phenol is converted to cyclohexanol and then to adipic acid. This energy-intensive process requires high temperatures, high pressures and large amounts of organic solvents. It also releases large amounts of nitrous oxide and carbon dioxide. The researchers have now developed a process by which they can convert phenol to cyclohexanol using an electrochemical process. Falk
Dr. Harnisch explains: “The chemical transformation behind it is the same as the existing process. However, the electrochemical synthesis uses electrical energy instead of hydrogen, and it takes place in aqueous solution, requiring only ambient pressure and temperature.”
First author of the study, Mijel Chávez, a chemist at the Helmholtz Center for Environmental Research (UFZ)
“In order for this reaction to proceed as quickly and efficiently as possible, a suitable catalyst is required. This will maximize the number of electrons required for the reaction and increase the efficiency of the conversion of phenol to cyclohexanol,” said Dr. Morejón. In experiments, carbon-based rhodium catalysts showed the best production efficiencies (almost 70% electrons and slightly more than 70% cyclohexanol). Relatively short reaction times, high yields, efficient use of energy, and The synergy of biological systems makes this process attractive for co-production of adipic acid.”
In an earlier study by Dr. Katja Bühler and Bruno
Two other working groups at the Helmholtz Center for Environmental Research (UFZ) led by Dr. Bühler discovered how Pseudomonas syringae converts cyclohexanol into adipate in a second step. Rohan
“Until now, it has not been possible to convert phenol to cyclohexanol by microorganisms. We have filled this gap with an electrochemical reaction,” says Dr. Karande.
Researchers at the University of Leipzig have filled another gap in the environmentally friendly production of nylon by developing an alternative to phenol produced from fossil raw materials. To do this, they used monomers such as eugenol, catechol and guaiacol, which are all produced as degradation products of lignin, a waste product of the wood industry. Falk
“For these model compounds, we have been able to show that they can be synthesized up to adipic acid,” says Harnisch.
However, there is still a long way to go before lignin-based nylons hit the market. For example, the scientists have so far achieved a yield of 57% over the entire 22-hour process (i.e., from monomers of lignin residues to adipic acid via microbial and electrochemical reaction steps). Micjel
Chávez
“It’s a very good yield,” says Morejón. These results are still only based on milliliter level lab tests. In the next two years, the prerequisites will be created for scaling up the process. Such technology transfer requires not only a better understanding of the overall process, but also the use of real lignin mixtures rather than model mixtures, and improvements in electrochemical reactors. Falk
Harnisch and Rohan Karande agree:
“The process of lignin-based nylon embodies the great potential of the electrochemical-microbial process, since an optimal process chain can be established through an intelligent combination of components.”
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