(83aa) On-Chip Parallelization of Microreactors: Up-Scaling Synthesis Microreactor Technology

Several microreactors exist, mainly single ones, though the first steps for up-scaling by parallelization have been taken [1, 2]. This presentation describes the design models one has to obey when up-scaling a common on-chip fluidic synthesis microreactor consisting of several inlets and one outlet, without loss of yield and conversion.

Up-scaling a fluidic synthesis microreactor, with remaining volume-to-surface ratio at the reaction area, can only be achieved by parallelization of the microreactors. An on-chip system has preferably a minimum number of inlets, one for each reactant and/or fluid catalyst, and one outlet. To achieve this, flow splitters are required, to split the inlet flows into n flows, where n is the number of parallel reactors, see Figure 1. The schematic in this figure shows necessity for crossing fluidic channels, acquiring a stacked wafer chip of at least three layers. At the start of the mixing area, or reaction area for instantaneous reactions, the different flow splitters are connected. Just connecting flow splitters to form a parallel microreactor chip without a well considered design easily lead to large errors in mixing ratio per micromixer, or in bubble encapsulation in one of the parallel channels. Both scenarios will lead to decrease of yield.

In microchannels small deflections and imperfections always exist, easily varying the hydraulic resistance over parallel channels in the range of a few percent, resulting in flow variations. We will present that flow variations can lead to mixing ratio errors in unbalanced flow splitters, and how balanced flow splitters can be achieved. In highly exothermic reactions flow splitter balancing becomes very important, due to the relation between temperature, viscosity and flow resistance. We will present a model to calculate the yield drop based on the deflections in channel cross-sectional area and shape.

The second objective in designing parallel microreactors is avoiding bubbles blocking channels. At encapsulated bubbles two forces are applied: capillary forces that tend to keep the bubble in position and pressure drops across the bubbles that try to push the bubble out of position. We will present the mechanism behind these forces, based on conventional microfluidics theory, and we will give a calculation model for minimizing the risk for bubble blocking to a well defined level.

Currently, flow splitter reactor chips with 8 parallel reactors are being fabricated by

, Enschede, the
Netherlands. At the conference, the fabricated chip and experimental results will be shown.

[1]          W.P. Bula, D.N. Reinhoudt, W. Verboom and J.G.E. Gardeniers, Microreactors for reaction kinetics monitoring on a chip ? from single line to multichannel quench-flow device, proceedings of µTAS2007 conference, 2007

[2]          M.B. Fox, D.C. Esveld, R.M. Boom, Conceptual design of a mass parallelized PEF microreactor, Trends in Food Science and Technology, 18, p. 484-491, 2007