Carbon Dioxide Capture by Adsorption of Carbonaceous Materials with Direct-Electrothermal Desorption

 

Abstract:

Some recent studies have highlighted the potential of adsorption technology for greenhouse gas CO₂ capture from the flue gases. The pressure/vacuum swing adsorption (PSA/VPSA), temperature swing adsorption (TSA) and electrical swing adsorption (ESA) have attracted much research effort with the development of the novel CO₂ adsorbents materials. Carbonaceous materials are the promising candidate adsorbents, since they have high BET surface area, better CO₂ adsorption capacity and novel morphologies (monolith, bead, fiber). Moreover, these adsorbents materials are also unique to undergo direct-electrothermal regeneration.

In this paper, carbonaceous materials with four morphologies (granular, monolith, fiber and bead) are used to capture CO₂ from the flue gas. Activated carbon beads were made in our laboratory with 2000-3000 m²/g BET surface area and better electrical conductivity. The research contents include the adsorption equilibrium isotherms, breakthrough curves, electrical energy consumption at direct-electrothermal desortpion, and the optimization of the cycle adsorption/ desorption processes.  

The experimental apparatus for the optimization of the cycle adsorption/ Direct-electrothermal desorption process comprise  an adsorber with 40-100mm height  and 25-50mm diameter, an electricity heating unit, a cooling unit, a vacuum unit, a gas detection unit, a data acquisition and control system. The heating step by electricity is very fast, about 2-5 minutes to raise the temperature of adsorbents from 30^oC to 150^oC when using 50 V voltages. But the cooling step is very slow due to the poor heat conductivity of porous adsorbents, so the alternative cooling units are designed, one using the direct cooling unit with air or nitrogen passing through the column, the other one as the indirect cooling unit by the medium of water or heat transfer oil indirect cooling adsorbents.  

Three processes of the cycle adsorption/desorption to capture CO₂ from the flue gases using carbonaceous materials are investigated, which included the conventional vacuum swing adsorption process, the electrical swing adsorption process, and the combined process of vacuum swing adsorption and direct-electrothermal regeneration. The mathematical models are proposed for different capture processes using activated carbons with four morphologies (granular, monolith, fiber, beads). Based on the experimental and theoretical investigations, the product recovery, purity, and the energy consumption of the adsorption processes for CO₂ capture from the flue gas are compared, and the feasibilities of the capture processes using carbonaceous materials are evaluated comprehensively.

Keywords: CO₂ capture, adsorption, VPSA, ESA, Combined VPESA process, CO₂ mitigation, carbonaceous materials, direct-electrothermal desorption, modeling.