The adsorption and desorption isotherms of materials such as metal organic frameworks (MOFs) and carbons can be evaluated with the Particulate Systems HPVA (High-Pressure Volumetric Analyzer) using different gases at pressures up to 200 bar. Carbon dioxide capture measurement on carbons is a key application of the HPVA towards achieving greener industrial and manufacturing processes.
Analysis of Carbon Dioxide Capture on Porous Carbons
Carbon dioxide generated during the burning of fossil fuels in chemical refineries and power plants can be captured using stack scrubbers containing carbons. With its high-pressure system the HPVA is capable of simulating the conditions of sequestration used for subterranean storage of carbon dioxide.
In this experiment, the amount of carbon dioxide adsorbed onto Ultra Microporous Carbon (UMC) and Carbosieve S-III porous carbons was evaluated at pressures up to 40 bar using the HPVA. Carbon was introduced into a sample tube, which was then attached to the degas port of the HPVA for evacuation under vacuum conditions followed by heating to 350°C.
The sample was maintained at 350°C for 20 hours to ensure that all adsorbed gases and water vapor were removed. After this period the sample was allowed to return to ambient temperature before being connected to the analysis port of the HPVA.
The possibility of sample contamination by water vapor or other atmospheric gases after degassing is avoided by using an isolation valve on the sample tube stem. At the analysis port carbon analysis was performed at three temperatures: 30°C, 50°C and 70°C.
A re-circulating temperature control bath was used to maintain sample temperature within ± 0.1°C throughout each analysis. An RTD integrated into the HPVA system measured the exact sample temperature. Each isotherm analysis required about 24 hours for completion.
Figures 1 and 2 show the isotherms. The compressibility factor (z) of carbon dioxide is used as a function of pressure and temperature to correct the volumetric calculations because of the non-ideal nature of carbon dioxide at high pressures. The compressibility factor at each pressure and temperature is obtained using the NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP), Version 8.0, 2007.
Figure 1. The carbon dioxide excess adsorption/desorption isotherms of carbon S-III. For differentiation purposes, the desorption curve is a lighter shade than the adsorption curve.
Figure 2. The carbon dioxide excess adsorption/desorption isotherms of carbon DW509. For differentiation purposes, the desorption curve is a lighter shade than the adsorption curve.
This information has been sourced, reviewed and adapted from materials provided by Micromeritics Instrument Corporation.
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