Testing plug flow in a reaction delay coil

The reaction delay coils (also called knitted open tubular ‘KOT’ reactors) from Biotech Fluidics are designed to maintain plug flow in a variety of liquid flow systems. They accomplish this through a winding flow path design that enhance radial mixing, while minimizing axial dispersion. This makes reaction delay coils ideal flow elements to allow time for reactions, or for automatic decision making during a continuous flow. These features make reaction delay coils popular for example, in plug flow chemistry reaction development or in liquid chromatography reaction detection.

To showcase the potential of reaction delay coils, we had an experiment performed to compare the effect on chromatographic peaks when transported through a reaction delay coil, versus when being conveyed through a straight tube of identical material and dimensions. The setup was suppressed ion chromatography, but the outcomes would apply to any flowing liquid of similar linear flow rate and viscosity. The results clearly show that the reaction delay coil prevented most of undesired axial mixing and preserved the peak integrity, only causing a peak broadening of 3-11%. In contrast, the peaks passing through a straight tube of identical dimension and volume, were affected up to ten times more and increased in width by 32-70%. This distinctly displays that the straight tube exposed the peaks to significantly more zone dilution by the transport liquid compared to the reaction delay coils.

The applied linear flow rate in this experiment was 10 cm/s (1.2 mL/min), which corresponds to the lowest recommended flow rate to establish stable radial mixing in a reaction delay coils with the present internal diameter (0.5 mm). At higher flow rates it would thus be expected that the dispersion in the straight tube would be even more problematic relative to the reaction delay coil. All data in this example were generated by an independent laboratory (Diduco AB) according to established scientific principles.

Learn more about the Biotech Fluidics reaction delay coils at the product webpages linked below, or contact Biotech Fluidics to discuss the most appropriate reaction delay coils for your application.

Experimental details: An ion chromatography setup separating chloride and sulphate (10 µM in water) using a Shodex SI-90 4E column (250×4 mm) operated with an eluent of 3.9 mM NaHCO3 and 3.1 M Na2CO3 delivered at 1.2 mL/min. The delay flow element (reaction delay coil or straight tube 0.5 mm ID, 4 m length, 785 µL volume) was inserted between the suppressor (XAMS membrane suppressor automatically regenerated by ASUREX-A200), and the conductivity detector cell. Injection of 50 µL standard solution created original peak volumes (at triangulated base) of 210 µL and 440 µL, respectively. Data was plotted compensated for delay volume to facilitate visual comparison. Experiments performed by Diduco AB.

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