(589b) Effects of Isotherm Nonlinearity on Zero Length Column Equilibration Time and Partial Loading Experiment

In the zero-length column (ZLC) technique, the partial loading experiment has been introduced as an additional useful experiment to identify rate-controlling mechanisms [1,2]. This experiment verifies unambiguously the measured time constant and determines whether a surface barrier is the dominant mass transfer mechanism. In ZLC experiments, at least one partial loading experiment is recommended along with full loading runs at different flow rates (at least two) [3].

For a partial loading experiment, the average concentration in the adsorbent is lower than that for full equilibration. This implies that for a nonlinear isotherm, the partial loading desorption response is closer to linearity [3,4]. Due to the difference in the degree of nonlinearity, simultaneous fitting of full loading and partial loading experiments with a linear model could give inaccurate results, since the ZLC response shift due to nonlinearity would be different for the two experiments.

In this work, the effect of nonlinear equilibrium on the ZLC equilibration time and partial loading experiments is investigated for different mechanisms: micropore diffusion, macropore diffusion, equilibrium control and surface barrier. As in [5] a single-site Langmuir isotherm is used as the nonlinear model as this results in only one additional model parameter that is directly related to nonlinearity. The model response is studied as nonlinearity is increased, particularly, the equilibration behaviour of the adsorbent and the partial loading response. The key features predicted in the analysis are validated with full-loading and partial-loading experiments conducted on the nonlinear system CO₂ on zeolite 5A pellets.

Acknowledgements

This work was supported by UK Research and Innovation GCRF South Asian Nitrogen Hub- Grant NE/S009019/1

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