Scale Up Production of Nanoparticles: Continuous Supercritical Water Synthesis of Ce-Zn Oxides

A new continuous supercritical water pilot plant was used for the large-scale production of nanomaterials in the Zn-Ce oxide system. Similar to an existing laboratory continuous process, the pilot plant mixes aqueous solutions of the metal salts at room temperature with a flow of supercritical water (450 degrees C and 24.1 MPa) in a confined jet mixer, resulting in the formation of nanoparticles in a continuous manner. The Zn-Ce oxide system, as synthesized here under identical concentration conditions than those used in our laboratory scale process (but 17.5 times total flow rate), has been used as a model system to identify differences in particle properties due to the physical enlargement of the mixer. The data collected for the nanoparticles from the pilot plant was compared to previous work using a laboratory scale continuous reactor. In the Ce-Zn binary oxide series, it was shown that Zn had an apparent solubility of about 20 mol% in the CeO2 (fluorite) lattice, whereafter a composite of the two phases was obtained, consistent with the high solubility observed in previous studies using a continuous hydrothermal process. Because of the inherent scalability of the continuous process and excellent mixing characteristics of the confined jet mixer, it was found that the pilot plant nanoparticles were almost indistinguishable from those made on the laboratory scale.