Volumetric device
Brand/Model: HPA-100 from VTI Corporation
Description/use:
The volumetric device is used to measure equilibrium sorption isotherms of different gases by using the static volumetric method. A known amount of gas is introduced into the sample holder containing ± 0.5 grams of material. After that, a certain time is needed to reach the equilibrium. The time needed for reaching equilibrium varies from a couple of minutes to a couple of hours, depending on the gas and material that is used. The amount of adsorbed gas is calculated from initial and final equilibrium pressures. For this the ideal gas law or van der Waals gas law is used. The procedure is repeated for different pressures until maximum pressure is reached. Each of the resulting equilibrium points (amount adsorbed and corresponding equilibrium pressure) is then plotted to form the isotherm. The sample can be activated separately by heat and by vacuum.
Technical specifications:
Temperature range (isotherm): 253K to 343K
Temperature range (activation): 293K to 673K
Pressure range: vacuum to 30 bar
Experiment examples:
Via this device isotherms of CO2, CH4, N2, H2, C2H6 and C3H8 were measured on the MOF amino-MIL-53. This was done for a range of temperatures in order to see how the material behaves at different temperatures and gases.
Gravimetric device
Brand/Model: VTI Corporation (USA)
Description/use:
This set-up enables one to measure pure water and organic vapour phase adsorption isotherms using the gravimetric technique. A reservoir, filled with the liquid organic adsorbate, is held at constant temperature through Peltier elements. Helium (He) bubbling through the container entrains the organic vapour. This He-organic vapour stream continuously flows over the sample positioned in a sample holder connected to the microbalance. The adsorbate partial pressure is altered by changing the temperature of the reservoir and/or by diluting the saturated flow.
Technical specifications:
Temperature range oven: 298 – 773K
Dew point range: 258 – 323K
He flow rate range: 0 – 325 ml/min
Evaporator capacity: 130 ml
Required adsorbent mass: approx. 10 mg
Experiment examples:
Adsorption of water, n-alcohols, n-alkanes and xylenes on zeolites and MOFs
Binary gas phase adsorption
Brand/Model: Magnetic suspension balance from Rubotherm.
Description/use:
This gravimetric device can measure static and dynamic single component as well as multi-component isotherms (static) from gases. For single component isotherms, measurements are quite straight forward. A certain pressure is introduced to the sample holder containing ± 0.2 gram. The balance records the weight as it changes by increasing or decreasing pressure. From this recorded weight, the amount adsorbed is calculated. This can be done in either static or dynamic conditions. As for multi-component isotherms, an accompanying GC is necessary. 2 inlets can be used for the multi-component measurement. A known amount of a mixture, determined by the GC, is introduced to the sample holder. Weight is recorded as the material adsorbs certain gases from the mixture. After equilibrium is reached, the remaining gas phase is analyzed by the GC in order to determine what component was adsorbed. After measurement the sample can be regenerated by heat, vacuum or under inert gas flow.
Technical specifications:
Temperature range (isotherm): 293K to 423K
Temperature range (activation): 293K to 673K
Pressure range: 0 to 40 bar.
Flow range: 0 to 500 ml/min (depending on the gas)
Experiment examples:
As this device is brand new, only single-component isotherms of CO2 en CH4 were measured on the MOF Amino-MIL-53.