(370c) New Multi-Sample Volumetric Instrument for High Throughput Adsorption Measurements

High throughput adsorption
measuring methods are a requirement for fast screening or characterization of
new materials (e.g. MOF). Also, routine quality control measurements of fresh
or reactivated adsorbents prior to their application need fast, reliable, and
high throughput methods. Today multi-sample volumetric instruments are state of
the art for BET and porosity measurement in the sub-atmospheric pressure range.
However, no high throughput instrument is available for measuring data at application
relevant higher pressures and temperatures.

Therefore, we designed
a new multi-sample volumetric instrument (MSVI) for measuring the ad- and
desorption of gases in a technically relevant pressure and temperature range. The
development and test of the instrument is carried in a co-operation between
Rubotherm and the Ruhr-University within a national research project for biogas
purification. One task of the project is to screen many different adsorbents
and solvents and identify the most promising substances.

The modular design
of the MSVI allows combining the volumetric gas dosing manifold with different numbers
of sample modules. A sample module consists of two independent sample ports,
each equipped with its own pressure sensor and a valve. The manifold and the sample
modules are designed as thermostated stainless steel blocks in which the valves
and the P-sensors are installed. The blocks are connected by means of metal
gaskets without leakage. The first prototype consists of 6 sample ports; the
flow scheme is shown in figure 1.

Figure
1:   Flow schematics of the multi-sample volumetric instrument for high
pressure adsorption measurements.

The dosing
manifold can be operated in the pressure range up to 100 bar and is equipped
with two different pressure sensors (100 bar and 20 bar full scale) for good
accuracy at all pressure levels. The sample modules are equipped with 50 bar P-sensors.
Thus, in the current instrument measurements can be performed from vacuum up to
50 bar. The dosing manifold and valve blocks of the sample modules are
thermostated to a constant temperature for best accuracy. This part of the
volumetric instrument can be heated up to 70°C, thus allowing performing high
pressure measurements with CO₂ without condensation problems.

The samples are
located in pressure and temperature resistant SS tubes connected to the valve
blocks by means leak free of Swagelok VCR connections. All samples can be
thermostated to the same temperature either by liquid thermostation or
electrical heating. The current design allows cooling / heating the samples in
the temperature range between -30°C?400°C. Other thermostat devices (e. g. cold
gas or LN2 cooling) can easily be adopted thanks to the modular design for
increased sample temperature ranges.

We will briefly
present the design and working principle of the new MSVI. Further the
performance of the instrument will be demonstrated by presenting results of
measurements performed with the prototype. So far adsorption measurements with
N₂ and CH₄ were performed. The instrument was checked
first by performing adsorption measurements with the same sample at all ports and
comparing the results. No unexpected deviations between the different ports
were found. Then adsorption measurements with different activated carbons were
performed and compared to literature data and the results of simultaneously performed
gravimetric measurements. Results for CH₄ adsorption measurement on
activated carbon at 25°C and 50°C are shown in figure 2 and are in good
agreement.

Figure
2:   Comparison of adsorption isotherm data measured with the new MSVI and a
gravimetric instrument on activated carbon at 25°C and 50°C.

These results
prove the high resolution, reproducibility and accuracy of the new MSVI
instrument for high throughput adsorption measurements in application relevant
pressure and temperature ranges.