Experiments with plug flow in a KOT tubular coil reactor

The knitted open tubular (KOT) coil 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 KOT reactors ideal flow elements to allow time for reactions, or for automatic decision making during a continuous flow. These features make KOT reactors popular for example, in plug flow chemistry reaction development or in liquid chromatography reaction detection.

To showcase the potential of KOT reactors, we had an experiment performed to compare the effect on chromatographic peaks when transported through a KOT reactor, 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 KOT reactor 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 KOT reactor.

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 KOT reactor 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 KOT reactor. All data in this example were generated by an independent laboratory (Diduco AB) according to established scientific principles.

Learn more about the Biotech Fluidics KOT reactors at the product webpages linked below, or contact Biotech Fluidics to discuss the most appropriate KOT reactor 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 (KOT 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 (www.diduco.com).