Nanomaterials could be manufactured through different ways, and there are two different production routes: dry and wet methods. Within wet nanomanufacturing methods, two technologies are employed: sol-gel and hydrothermal synthesis. The latter one offers unique opportunities for the synthesis of high quality nanoparticles and their formulation, but one of the main disadvantages is the scale-up away from batch systems.
Continuous hydrothermal processes would offer a satisfactory option for producing high quality nanoparticles by mixing superheated or supercritical water with a metal-salt solution, but the step from batch to continuous hydrothermal synthesis has prevented the progress of the mentioned mixing.
The SHYMAN (Sustainable Hydrothermal Manufacturing of Nanomaterials) project address this scale-up, together with formulation, weight loading, cost and sustainability of nanomaterials hydrothermal synthesis processes.
One of the key factors that determines the success of such a reactor is how well it can mix the mentioned SCW with the solution of metal salt. An optimal reactor configuration which allows this mixing in a controlled and efficient way (reducing blockages, roping and back mixing – responsible of uncontrolled particle growth) is the Nozzle Reactor, patented by the University of Nottingham.
The reactor has been patented by the University of Nottingham, Prof. Edward Lester:
To improve the performance of this reactor and assess the limits of available design, the University of Valladolid has been performed CFD simulations on bench and pilot scale reactors and has proposed a model to describe and study the formation of nanoparticles during hydrothermal synthesis.
A mesh of a variable number of cells (depending on the case and the zone – i.e. mixing area) and ANSYS FLUENT software were used to solve the 3D system of equations based on the RANS (Reynolds Averaged Navier Stokes) approach and realizable k-epsilon model to describe turbulence. The transport properties were taken from the NIST database.
Temperature and density and particle size distribution
As the pressure is constant the density variations are ruled by changes in temperature throughout the fluid path in the geometry.
The smaller particle sizes are found in the mixing zone. The nanoparticle size increases with the path of the fluid along the reactor, especially in dead volume regions, such as the superior part of the mixing chamber (in red) due to the increase in the residence time. For this reason, it is important to take into account the connection between particle size and the residence time during the scale up.
For more information: SHYMAN Project