Thermodynamics of adsorption
Pulse Gas Chromatography
A HP4890 system with a thermal conductivity detector (katharometer) of which the mass flow of the helium carrier gas is externally controlled by mass flow controllers (Bronkhorst, 50 ml/min, 1-3 barg). Sampling is done by a PAL (0.005-0.1 µl) or ALS (0.005-0.1 µl) injection system. Pulses can be studied by Chemstation software (or EZChrom if necessary). Traces of selected compounds are injected and vaporized in an inert carrier gas and travel through a homemade column of a material under investigation (an adsorbent). From the response curve, Henry constants, adsorption enthalpy, adsorption entropy and the pre-exponential factors of the van ’t Hoff plot can be calculated at low coverage. This method is useful for studying the fundamental adsorbent-adsorbate interactions at low coverage.
- Flow rate range: 0-100 ml/min (limited by pressure drop considerations)
- Temperature range: RT-400°C (no cooling on these devices)
- Pressure range: 1-2.5 bar (at higher pressures the equations for calculating the adsorption properties will have to be adjusted)
- amount of components needed: a 2 ml vial of liquid
- precision: up to 4% of relative standard deviation on Henry constants
Studying low coverage adsorbent-adsorbate interactions on MOF, Mesoporous silica and zeolites. Adsorbents often used are linear/branched alkanes, aromatic components (BTX), thiophene,… Also separation behavior at low coverage can be studied.