Green Advancements in Adipic Acid Synthesis: From Petrochemical Routes to Circular Bioeconomy Strategies

Abstract

Adipic acid, an important industrial chemical with an annual production of more than 3 million tons can be produced by the nitric acid oxidation of cyclohexane derivatives (KA-oil) . This conventional method uses corrosive reagents and produces significant emissions of nitrous oxide (N?O). This review looks at innovative, eco-friendly routes for the production of adipic acid. These include advanced catalytic techniques like paired electrolysis and photocatalysis , as well as bio-based pathways using renewable feedstocks including guaiacol, catechol, lignin, and furan derivatives. Under mild conditions, bio-based pathways—especially those using modified Escherichia coli and Pseudomonas putida—show promise for converting aromatics generated from lignin. Moreover, novel photo-electro-catalytic systems and heterogeneous catalytic oxidations with molecular oxygen provide ways to replace nitric acid while preserving or increasing efficiency. This review highlights the transition from petrochemical route to renewable, low-emission pathways and represents important research goals for moving sustainable adipic acid production towards commercial feasibility.

Introduction

Adipic acid (HOOC-(CH?)?-COOH) is an important industrial chemical with a global production capacity exceeding 3 million metric tons annually. Around 90% of adipic acid is used in nylon-6,6 manufacturing, while other applications include plasticizers, food additives, and polyurethanes.

Traditional adipic acid production relies on the KA-oil process, which oxidizes cyclohexane to cyclohexanol and cyclohexanone, followed by nitric acid oxidation. Although widely used, this process generates significant amounts of nitrous oxide (N?O), a greenhouse gas with approximately 300 times the global warming potential of CO?, and produces toxic acidic waste. The use of benzene-derived feedstocks further increases environmental concerns.

To address these issues, research has focused on two major sustainable approaches:

1. Bio-based production routes
   • Use renewable biomass-derived feedstocks such as glucose, guaiacol, catechol, and lignocellulosic waste.
   • Employ engineered microorganisms, particularly Escherichia coli and Pseudomonas putida, through metabolic engineering techniques such as CRISPR/Cas9.
   • Produce adipic acid or intermediates like muconic acid under mild fermentation conditions.
   • Reduce dependence on fossil resources and eliminate direct N?O emissions.
2. Advanced catalytic methods
   • Replace nitric acid with environmentally friendly oxidants such as oxygen (O?) or hydrogen peroxide (H?O?).
   • Utilize novel catalysts including metal-incorporated molecular sieves, metal-based ionic liquids, and doped metal composites.
   • Conduct reactions in batch or continuous-flow reactors with improved selectivity and lower environmental impact.

Recent developments (2020–2026) have introduced electrochemical and photocatalytic technologies:

• Electrochemical methods use electricity and water to drive oxidation and reduction reactions, avoiding hydrogen gas and nitric acid while achieving good yields.
• Photocatalytic methods employ light-activated semiconductor catalysts to promote carbon–carbon bond formation under mild conditions.
• Hybrid photo-electro-catalytic systems further improve energy efficiency and sustainability.

Overall, adipic acid production is shifting from energy-intensive petrochemical processes toward renewable, low-emission, and environmentally friendly technologies, with bio-based, catalytic, electrochemical, and photocatalytic methods offering promising alternatives for sustainable manufacturing.

Conclusion

Adipic acid is an important chemical used in synthesis of many products, but the conventional method of synthesis, which is as the KA-oil process, gives environmental problems of nitrous oxide emission in large amounts,which is an important greenhouse gas & cyclohexane synthesized from carcinogenic benzene having significant impact on human health.Researchers have developed new routes of synthesis between 2020 and 2026 to find green, ecofriendly & more sustainable pathways that avoid this pollution and avoid the use of carcinogenic benzene as a raw material for synthesis of cyclohexane.Researchers are currently working on two innovative pathways . One path involves biological engineering, where scientists use metabolic processes using bacteria like e-coli —specifically the ?-ketopimelate pathway—to teach microorganisms like E coli to produce adipic acid naturally without use of hazardous substances. The other path mainly involves the use of advanced electrical methods such as high-current-density electrocatalysis. This technique uses electricity along with specialized materials, such as CoFe?O?@CuO/CF, to produce the chemical more efficiently.Another important part of this shift is changing the raw materials for manufacturing . An alternative raw material such as non-edible plant waste can be used as renewable feedstock, such as wood-based lignin or general biomass waste. This modification is a way to a circular economy, where we consider waste is reclaimed into valuable resources.While we are much nearer to a green ,non conventional and low-emission value chain than we were a few years ago, there are still hurdles to clear. Scientists are presently working to overcome major challenges related to scaling up these greener synthesis for large-scale industrial application and increasing the quantity of acid the microorganism can produce, which is essential to make these green methods preferred to traditional methods.

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Copyright

Copyright © 2026 Sanjay Patil, R. P. Patil. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.