Limitations of Breakthrough Curve Analysis in Fixed-Bed Adsorption

Area of Science:

• Chemical Engineering
• Adsorption Science
• Transport Phenomena

Background:

• Predicting axial dispersion coefficients using correlations can be inaccurate.
• Experimental breakthrough data offers an alternative for determining dispersion and mass transfer coefficients.
• Non-plug flow conditions can lead to erroneous extraction of parameters from experimental data.

Purpose of the Study:

• To evaluate the accuracy of obtaining axial dispersion and mass transfer coefficients from experimental breakthrough data.
• To investigate the consequences of using a 1-D axially dispersed plug flow model with Danckwerts boundary conditions.
• To assess parameter extraction under non-plug flow conditions and concentration front sharpening.

Main Methods:

• Utilized a 1-D axially dispersed plug flow model with Danckwerts outlet boundary condition.
• Analyzed experimental breakthrough curves for CO2 and H2O vapor in zeolite 5A.
• Compared a priori correlation predictions with experimentally derived parameters.
• Validated model-derived parameters by plotting breakthrough curves inside and outside the adsorbent bed.

Main Results:

• Demonstrated that accurate mass transfer and dispersion information can be extracted from experimental breakthrough curves.
• Identified potential for erroneous coefficient extraction under non-plug flow conditions.
• Observed significant non-plug flow behavior in both CO2-zeolite 5A and H2O-zeolite 5A systems.
• H2O-zeolite 5A exhibited concentration front sharpening, deviating from constant pattern behavior.

Conclusions:

• A 1-D axially dispersed plug flow model can accurately yield mass transfer and dispersion data from experimental breakthrough curves.
• Plotting internal and external breakthrough curves and their derivatives is crucial for validating model accuracy.
• The developed methodology allows for accurate parameter extraction even with concentration front sharpening and non-ideal flow behavior.