Brief introduction of testing principles of dynamic chromatography and static volume method

Dynamic chromatography

Static volume method

Test principle

A certain proportion of mixed gas of carrier gas (He) and adsorbate gas (N2) is continuously introduced into the sample tube. At a low temperature (liquid nitrogen bath), the sample is adsorbed and balanced, and the temperature is raised to desorb the N2 molecules adsorbed by the sample. , The concentration of the mixed gas changes and is detected by the detector to obtain the adsorption amount of the sample to be tested;

Adjust the ratio of carrier gas and adsorbent gas to obtain different partial pressure points, and repeat the upward and downward liquid nitrogen cups for adsorption and desorption, and measure the adsorption amount under different partial pressures;

Since a certain flow rate of gas always flows through the sample to be tested during the test, the sample to be tested acts like an adsorbent in a chromatographic column, so it is called dynamic chromatography;

Under low temperature (liquid nitrogen bath) conditions, a certain amount of adsorbate gas (N2) is introduced into the sample tube, and the adsorption partial pressure is directly measured by controlling the equilibrium pressure in the sample tube, and the partial pressure point is obtained by the gas state equation Adsorption capacity;

By gradually increasing the equilibrium pressure of adsorbate gas, the adsorption isotherm is obtained; by gradually extracting the adsorbate gas, the adsorption equilibrium pressure is lowered to obtain the desorption isotherm; the relative dynamic method requires no carrier gas (He) and no need for repeated liquid nitrogen cups Lift

Because the sample to be tested is in a fixed-volume sample tube, the adsorbate does not flow relative to dynamic chromatography, so it is called the static volume method;

Testing process

Test Range

Partial pressure 5% ~ 95%, corresponding to pore size range 1.29-50nm,

Specific surface area above 0.01m2 / g

The partial pressure is 0.0001% ~ 99.6%, corresponding to the pore size range of 0.35-500nm,

Specific surface area above 0.01m2 / g

Time-consuming test

Reference method specific surface area, 15min / 3 samples

Single point BET specific surface area is about 20-30min / 4 samples,

5 points BET specific surface area is about 120min / 4 samples;

A single partial pressure point is about 3-10min,

The 5-point BET specific surface area is about 20-40min,

40 adsorption desorption points about 3-10 hours

Isotherm type

Adsorption isotherm

Adsorption isotherm, desorption isotherm

Do you need to evacuate

no

Yes

Advantages and Disadvantages

It is suitable for specific surface area analysis and testing. It has a faster specific surface analysis speed, better accuracy, and higher resolution. It is especially suitable for small and medium surface area samples, such as battery materials, organic materials, and metal powders. It has a lower specific surface analysis lower limit and high repeatability. Due to the limitations of low partial pressure range and the inability to test true desorption isotherms, it is not suitable for pore size analysis.

It is suitable for the analysis of specific surface area and pore size, especially for the resolution and accuracy of samples with medium and large specific surface and pores. It is suitable for the analysis and test of the specific surface and pore size distribution of porous and large surface samples such as catalysts and molecular sieves;