(566d) Improving Global Nitrogen Cycle Management Via Mechanochemical High Efficiency Urea Cocrystal Fertilizer Material Synthesis and Utilization

The world is experiencing unprecedented economic growth and increase in human population, thereby requiring more sustainable utilization of natural resources. Fertilizer production and usage is strongly correlated with food output and food security. While more than 200 million fewer people are undernourished than in 1990, 795 million people still remained undernourished in 2015. With the world population expected to grow by 35% to 9 billion by 2050, providing people around the world with nutritious supply of food at reasonable cost, is one of the greatest challenges. Fertilizer demand hence is expected to grow to about 200.5 million metric tons of (N+P₂O₅+K₂O) in 2018. Urea, CO(NH₂)₂, has been the most prominent N fertilizer making up ~60% of global nitrogen fertilizer use. Since the process to synthesize ammonia (NH₃), a reactant used to make urea, remains energy intensive and uses up to 1 % of the global energy and ~4 % of natural gas, it is critical that the urea nitrogen applied to soils is fixated in plants and not released in the form of gaseous NH₃ or otherwise lost to the environment. Unfortunately, only about 50% of the nitrogen fertilizer applied is absorbed by the crops and conceptually new chemical engineering processes are needed to avoid large exergy loss in the overall N-fertilizer production process as well as the emissions of reactive nitrogen into the environment.

The presented work will describe an approach to pre-emptively mitigate N-losses to the environment by describing mechanochemical synthesis of urea ionic cocrystals in combination with natural minerals. This will be done by converting urea powder and Ca- and Mg-containing natural minerals into value-added high volume sustainable fertilizers. In particular, mechanochemical methods applied to urea-CaSO4*2H2O and urea-Ca(H2PO4)2 were utilized and the corresponding reaction kinetics as well as the resulting product crystal structure and properties were monitored using in situ methods including XRD, TGA-DSC and Raman spectroscopy. Further, phase diagrams of the resulting cocrystals were described in silico by accounting for the environmental conditions of relative humidity and temperature. Resulting cocrystals possessed remarkable stability under moist conditions with decreased N-emissions. Finally, sustainable synthesis of CaSO4:4urea cocrystal was performed using widely available industrial gypsum drywall waste and the resulting enhanced efficiency fertilizer materials were tested in the laboratory as well as field experiments.