Urea (CO(NH₂)₂) plays a central role in our synthetic methanotrophic system, in which two catalysts—Fe-ZSM-5 and alcohol oxidase—convert methane into formaldehyde, which subsequently reacts with urea to form urea-formaldehyde polymers. The addition of urea not only facilitates polymer formation but also prevents the over-oxidation of carbon intermediates. In terms of mass balance, urea accounts for approximately two-thirds of the final polymer’s mass. Industrially, urea is synthesized by reacting ammonia with carbon dioxide under high-temperature, high-pressure conditions. The primary source of ammonia is the energy-intensive Haber–Bosch process, which contributes over 2% of global energy consumption and greenhouse gas emissions, with 42% of produced ammonia used for urea synthesis. These limitations underscore the need for more sustainable methods of urea production under ambient conditions. While urea can be synthesized via catalytic co-reduction of nitrogen and carbon dioxide, it is also abundantly available as a waste product—particularly in human urine, which contains approximately 200–300 mM urea. Although technologies such as adsorption, membrane separation, and hydrolysis have been proposed for urea removal, there is currently no widely adopted method for recovering urea as a chemical feedstock. In this study, we demonstrate that urea derived from human urine can be directly utilized in our tandem catalytic system—comprising alcohol oxidase and Fe-ZSM-5—to produce methylene diurea (MDU), a key monomer in urea-formaldehyde polymerization. Urine was diluted in phosphate buffer to adjust urea concentrations and minimize interference from biomolecules, enabling efficient polymer formation with higher selectivity and productivity than systems using synthetic urea. These findings present a promising strategy for the chemical upcycling of urea from waste streams into value-added polymeric materials, offering dual benefits of nitrogen waste remediation and sustainable material production.
Keywords: urea, upcycling, methane partial oxidation, polymer, urea removal, green chemistry
