Breakthrough curves: dynamic sorption of gas- and vapor mixtures

Investigation experiments of practically relevant separation processes by standard gas sorption instruments for pore size analysis are limited.

Regarding the assignment of tasks such as

• investigation of the adsorption of CO₂ from dry and wet air
• adsorption of methane of biogas
• differentiation of practically relevant sorption behaviour of adsorbents like gas or vapor mixtures.

BET- or pore size distribution cannot predict or model separation processes.

The dynamic flow method is applied for practical investigation such as

• dynamic gas flow adsorption and desorption
• determination and evaluation of breakthrough curves
• investigation of sorption kinetics
• investigation of co-adsorption and replacement effects
• determination of sorption selectivities
• determination of sorption equilibria of gas mixtures
• transfer of technical sorption processes to lab-scale
• investigation of thermal balance of dynamic adsorption processes

Analyzers

mixSorb S series:

Measurement of breakthrough curves; vapor option; designed for very small sample amounts

mixSorb L series:

Measurement of breakthrough curves; vapor option; safe and easy-to-use bench-top instrument

Measuring method

The figure above shows a breakthrough curve of CO₂ at activated carbon measured with the mixSorb L. The vertical, red line marks the start of the breakthrough measurement. From this point a gas mixture of 5 Vol.-% CO₂ in Helium flows through the adsorbent at a pressure of 5 bar at 40 °C with a flow of 1 L min^-1. The black line represents the concentration of CO₂ at the end of the adsorber column. One can observe that after 15 minutes traces of CO₂ are detected. Before that time CO₂ is completely withheld by adsorption on the activated carbon followed by a steep increase of the CO₂ concentration, which is called mass transfer zone. From the shape of the breakthrough curve in this zone different parameters concerning sorption kinetics or concentration distribution can easily be determined. After approximately 30 minutes the activated carbon reaches the maximum sorption capacity under this experimental conditions. Consequently the CO₂ concentration at the end of the column approaches the initial CO₂ concentration

The releasing heat of sorption results in a temperature increase of the adsorber bed. To follow this process the mixSorb L is equipped with four temperature sensors along the adsorber. Their position is sketched at the right side of the figure. The four sensors respond in accordance to the direction of the gas flow starting with T1 and ends with T4. The measured temperature curves (orange, grey, yellow and blue) are also depicted. They give information of the released heat, the speed of energy exchange processes and the dispersion of the concentration profile in the adsorber column.

The following figure illustrates how to determine the technical usable sorption capacity from a breakthrough curve under certain experimental conditions. The BET surface area or the micropore volume, which are exactly known by standard gas sorption methods, are not accessible completely in technical flow processes for certain kind of purification or separation processes. As an example: The separation of CO₂ from N₂ (40 °C, 2 L min^-1, 5 bar, initial gas composition: 5% CO₂ in N₂) occurs with the breakthrough of CO₂ when the sorption capacity reaches 75% of the maximum sorption capacity. The dynamic sorption analyzer mixSorb L can help to predict technical relevant sorption processes in an easy a quick way.

Literature and Norms

• Webinar mixed gas/vapor adsorption: Working with Vapors and Low Concentrations in Breakthrough Experiments (Video on Demand)
• PARTICLE WORLD 19; p. 20 – 25, “From the idea to the technology behind the separation process:
  mixSorb L is gearing up!”
  
• Dynamic and equilibrium-based investigations of CO₂-removalfrom CH₄-rich gas mixtures on microporous adsorbents; A. Möller, R. Eschrich, C. Reichenbach, J. Guderian, M. Lange, J. Möllmer: Adsorption (2017) 23: 197-209; external Link to pdf-view
• conference poster 2017 – Deutsche Zeolithtagung, “Porous solids for heat storage applications: In-depth material testing by vapor breakthrough measurements”, pdf-Download
• conference poster 2016 – Fundamentals of Adsorption – “Dynamic and equilibrium-based investigations of CO₂ removal from CH₄-rich gas mixtures on zeolites”, pdf-Download
• conference poster 2016 – Reaktionstechniktagung – “Dynamische Untersuchungen zur Adsorption an Aktivkohlen”, pdf-Download
• conference poster 2016 – Fachgruppe Adsorption und Gasreinigung – “dynaSim – A Modeling and Evaluation Tool for Dynamic Sorption Data” pdf-Download
• conference poster 2015 – Carbon – “Breakthrough Curves of CO₂ and CH₄ on Carbon Molecular Sieves”, pdf-Download