(380n) Novel Closed Spiral Reactor for Supercritical Hydrothermal Synthesis of Nanoparticles

A novel spiral device that combines the mixing and phase separation for liquid-liquid applications is presented conceived [1]. Its application to the supercritical hydrothermal synthesis of nanoparticles involving mixing of supercritical water and metal salt solution producing nano-particles is studied. There is a growing interest for scale-up of the hydrothermal synthesis of nanoparticles. It is a challenging problem in this field. Therefore, there is a need for novel reactors for hydrothermal synthesis of nanoparticles. The mixing of reactants plays a crucial role in controlling the hydrothermal reactions and particle growth rates.. The novel reactor is explored computationally for the synthesis of nanoparticles.

A multiphase coupled Computational Fluid Dynamics(CFD)-Population Balance Model(PBM) model based on the Eulerian-Eulerian approach is employed to simulate the flow, heat transport, reactions and particle population inside the novel reactor. The model is built using, ANSYS Fluent 16.0 and tested with published experimental data of ceria nanoparticle synthesis.

The reactor configuration, wherein metallic precursor solution is introduced through the inner tube of the mixer whereas supercritical fluid is introduced through the outer tube is studied for nanoparticle synthesis. The mixing inside the reactor is driven by centrifugal force due to the curvature of a spiral turn, which makes the heavier fluid (metal salt solution) penetrating into the lighter fluid phase (supercritical water) resulting in the efficient mixing followed by chemical reaction. The subsequent counter spiral causes the mixing to repeat enabling greater mixing of the phases.

Based on our simulation studies, we observed that flow ratio, ratio of metallic precursor flow rate to supercritical fluid flow rate (FR) provides better insights into the mixing and chemical reactions inside the reactor. Figure 1 shows the exit concentration of ceria at different FR. It can be observed that ceria concentration is unaffected for different flow rates for FR<1. However, it is more sensitive to flow rates when FR>1. The maximum ceria concentration is obtained at FR=1 for different flow rates of the reactants. Hence, the production rate of the ceria nanoparticles is independent of flow rates (up to 3400 ml/min) for FR=1, which facilitates the design and scale-up of the reactor for nanoparticle production. Then we have evaluated the product PSD at the exit of the reactor for the best operating conditions (FR=1) to control and optimize the properties of ceria nanoparticles. Thus, the current study is helpful in the design and scale-up of a novel reactor for scaling-up the production of nanoparticles using the hydrothermal method.

References:

1. “INTEGRATED APPARATUS FOR MIXING AND SEPARATING FLUID PHASES AND METHOD THEREFOR” A Patent Application Filed at Indian Patent Office on 14^th March 2018. Application Number 201822007888 Inventors: Arjun Kumar Pukkella, Sivakumar Subramanian and Raviraju Vysyaraju