|Mini and Micro T-jets reactors with high throughput|
CESAM Responsible researcher - Maria Isabel Nunes
Programme - PTDC/EQU-EQU/098617/2008
Execution dates - 2010-05-01 - 2013-10-31 (42 Months)
Funding Entity - FCT
Funding for CESAM - 49988 €
Proponent Institution - Faculdade de Engenharia da Universidade do Porto
Universidade de Aveiro
Over the last decade the chemical engineering community endeavored a quest for reactor miniaturization, due to the breakthrough advantages of microreactors (Jensen, 2001). These advantages are based on the decrease of the reactors' linear dimensions allowing faster heat and mass transfer, which is particularly relevant for the synthesis of products involving fast reactions, particularly fast competitive or consecutive reactions. Examples of such products produced using microreactors are: Polyacrilates at Siemens Axviva (Hessel and Löwe, 2003a) and nanoparticles (Chang et al. 2008).
On the other hand, the microreactors industrial use is being slower than one could foreseen from its advantages. The miniaturization brought new challenges that are preventing the industrial uptake on applications other than lab on a chip. One of the major issues is the low throughput of microreactors. The advantages are based on the small linear dimensions and so the reactors scales most be kept when going to the industrial phase. The way to increase the throughput without compromising the products is to replace the scale-up for a new concept - the number-up of units using arrays of several microreactors (Hessel and Löwe, 2003a).
The main innovation of the present proposal is the introduction of T-jets geometries, capable of high throughputs on a single unit. The T-jets reactors here introduced are aimed to be scalable up to high throughputs without reduction in the critical characteristics of their products, such as size in nanoparticles synthesis. This innovation relies on the yet unpublished discovery of the present research team; that keeping the planar dimensions of the T-jets (width of the chamber and the jets) the depth of the mixing chamber can be increased without compromise mixing. The depth increase on this project is going to reach values 1000 times those used in state-of-the-art microreactors, and thus a single has the same throughput of arrays with 1000 microreactors. The large depths introduce new construction challenges, and so new microfabrication technique for the T-jets reactors is here introduced and is going to be patented.
Another approach to overcome the limits set from the reactors' miniaturization is the design rule that one should only use "as much miniaturization as necessary, not as possible" (Hessel and Löwe, 2003b). The scale of the T-jets is going to be studied to answer the question of how small do we need to get? The mixing scales can be decreased from reactor size but also from convective flow patterns. Chaotic mixing mechanisms of stretching and folding can decrease the scales, avoiding the need for miniaturization of the reactor. Recent studies from this research team proved that mixing scales of the order of those obtained in microreactors at steady flow regimes can be attained in mini reactors of around 1 to 2mm when operating at chaotic flow regimes. Mini reactors also solve major problems related to microreactors other than the throughput, such as reactor fouling, pressure drop and construction techniques complexity.
The mixing scales reduction can also be attained using active mixing, i.e. from an external stimulus to the flow. Recent CFD results of Ashar et al. (2008) proved that the modulation of the jets' flow rate controls the size and shape of vortices formed in T-jets reactors, i.e. the mixing scales. A pulsation device proposed from this research team (Santos et al., 2008b - WO2008/126027 A2) allows to easily modulated a flow stream setting its amplitude, frequency and phase delay to another oscillating flow stream. In this project these parameters are going to be studied.
The tools to study mixing for the several geometries, flow regimes and active mixing parameters, are laser methods for the visualization of mass transfer - Planar Laser Induced Fluorescence (PLIF), experimental visualization of velocity vector maps - Particle Image Velocimetry (PIV) and also Computational Fluid Dynamics (CFD). The CFD simulations are going to be coupled with mass transfer and test chemical reactions, particularly the test reaction system proposed by Bourne et al. (1985).
Experiments are going to be made with the test reaction to determine the reactor mixing times at different conditions.
Reactions with two steps, one almost instantaneous and a slower but fast step, only yield the "slow product" when the mixing time is close to the reaction time of the second step.
The synthesis of BaSO4 nanoparticles is going to be made to study mixing (Gradl et al. 2006). This is a well known system that will be simulated using Population Balance Modelling (PBM) coupled to CFD simulations. Nanoparticles of commercial value - zinc oxide - are going to be made in the T-jets reactor to demonstrate its industrial relevance. The nanoparticles are going to be extensively characterized to ascertain the influence of mixing in the T-jets on its properties.