AN634 – Adsorption and desorption of CO2 on active coal

INTRODUCTION

Capture of carbon dioxide from fossil fuel power plants via adsorption and sequestration of carbon dioxide in unmineable coal seams are achievable near-term methods of the reducing atmospheric emissions of this greenhouse gas. The evaluation of CO2 adsorption and desorption characteristics on finely crushed and uncrushed samples is critical for CO2 sequestration in coal beds.

The TG-DSC technique is the ideal tool for such investigations:
– the thermogravimetric signal provides the amount of CO2 adsorbed or desorbed on the coal sample
– the DSC signal measures the corresponding enthalpy: exothermic during adsorption (that means an increase of the temperature during the sequestration process) or endothermic during the desorption (that means cooling of the coal material)

AN-634

EXPERIMENTAL

Sample: active coal
Mass: 29.1 mg
Temperature range: -50 °C to 50 °C
Atmosphere: CO2

RESULTS AND CONCLUSIONS

The sample of active coal is cooled down from 50 °C to -50 °C, then maintained at -50 °C during more than one hour before reheated at 50 °C under pure CO2.
The TG curve shows the mass increase of the sample corresponding to the CO2 adsorption. The saturation of the sample is obtained during the isothermal step at -50 °C. When heating the mass loss on the TG curve indicates the CO2 desorption. It is noticed that the desorption is not complete.
The DTG curves give an information on the rate of CO2 adsorption and desorption.On the DSC curve, the CO2 adsorption corresponds to an exothermic effect and the desorption to an endothermic effect.
With such a TG-DSC experiment, it is possible to determine the corresponding enthalpies of adsorption or desorption versus the amount of CO2 adsorbed or desorbed on the sample.