Nitrogen In the Circular Economy (NICE): The valorisation of nitrogenous waste

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Project background (identification of the problem and its importance and relevance to sustainability) Nitrogen containing molecules are ubiquitous and form the basis of many essential agrochemicals, pharmaceuticals, additives, textiles, and performance materials. The synthesis of nearly all nitrogen containing molecules requires ammonia, which is derived from the Haber-Bosch (HB) process. The HB process has a large detrimental environmental impact: it uses around 2% of global energy and contributes an estimated 2% to global carbon dioxide emissions. Consequently, the production of nitrogen containing compounds comes at a high environmental cost. Additionally, these resources are overconsumed and then discarded as waste once their initial purpose has been fulfilled. This is a symptom of our linear economy; fortunately, the circular economy provides a solution. To transition from a linear to a circular economy, processes need to be developed that enable waste to be transformed into useful, high value products and materials. Protein-rich biomass waste streams are abundant, yet the nitrogenous fraction remains undervalued and underused. The valorisation of such protein-rich waste streams into useful, high value, nitrogenous chemicals is one approach to improve the sustainability of their synthesis. The development of chemoselective disconnections for unactivated C-N bonds, particularly in underexplored transformations will enable the synthesis of small nitrogen containing compounds from nitrogenous waste, reducing both our dependence on the HB process and the environmental cost of producing such chemicals. Proposed solution and methodology This research project strives to develop methods to valorise nitrogenous waste streams that are abundant, currently underused, and for which valorisation into fine chemicals will not disrupt the food chain or require the growth of more crops. Through research into selective C-N sigma bond cleavage of various nitrogenous substrates, this project is envisioned to develop methods to valorise these waste streams to improve the flow of nitrogen containing compounds through the nitrogen cycle and to enable the transition towards a more circular economy. The current state of the art for selective C-N sigma bond cleavage requires incredibly forcing conditions and/ or activated substrates which limit the current applications of these methods. There is also a lack of mechanistic understanding in the literature, which can impede the development of novel approaches. This project seeks to address these issues by developing novel catalytic systems for selective C-N bond cleavage. Catalyst screening will be performed to find catalysts which can facilitate C-N sigma bond activation and cleavage using model N-compounds to explore and compare catalyst reactivities and selectivities, selected according to their activity towards C-N bond cleavage, commercial availability, ease of synthesis, and their scale-up potential. In particular, complexes of first row transition metals will be prioritised due to their sustainable credentials, low cost, and research group expertise. Upon the identification of a suitable catalyst system, optimisation will be carried out focusing on delivering high product yield and selectivity, whilst considering reaction sustainability in accordance with the 12 Principles of Green Chemistry. Substrate scope will be expanded by testing a large range of substrates with a variety of properties to gain insight into the limitations of the catalyst system. Data collected throughout this project will be continually analysed to gain insight into the catalyst mechanism of action, including isolation of potential reaction intermediates, along with detailed kinetic investigations; together this insight will enable a plausible catalytic cycle to be proposed.