engleski

Scale-up of agrochemical urea-gypsum cocrystal synthesis using thermally-controlled mechanochemistry

Nitrogen fertilizers have been an important part of supporting the growing human population by enabling increased food production. However there are ongoing challenges in their sustainability, both during their production, and during their use. For instance, urea, one of the most common nitrogen fertilizers, decomposes under ambient conditions, releasing ammonia and causing losses in the nitrogen cycle, as well as lower fertilizer efficiency. Increasing urea retention time can be achieved by incorporating it into adducts that stabilize it, and preferably also provide additional nutrients. We here explore the atom- and energy-efficient synthesis of crystalline calcium urea sulfate ([Ca(urea)_4]SO_4, CSD code: URCASU3), a combined calcium, nitrogen, and sulfur fertilizer. We study its mechanochemical formation from urea and three different calcium sulfate sources (CaSO_4⋅xH_2O, x=0, 0.5, 2), one of which – gypsum – is a common waste product of the construction industry. We monitor the kinetics of URCASU formation on a small scale (0.5 g) in a mixer mill (MM) by in situ Powder Xray Diffraction (PXRD) and Raman spectroscopy, to establish the catalytic effects of water contained in the starting materials, at both room temperature and elevated temperatures. We then use the obtained results to inform scale-up procedures, using planetary milling (PM – 50 g and 100 g scale) and twin screw extrusion (TSE – 300 g/h scale). We compare the time-space yield and energy consumption of both methods, as well as the conversion efficiency, to ascertain the most efficient and sustainable scale-up procedure. Dissolution and stability studies of the prepared URCASU adducts show significantly higher urea retention in both laboratory and real-world conditions, compared to pure urea.

urea ; mechanochemistry ; cocrystal ; gypsum

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