Experimental and Modelling Study of CO2 Adsorption for Carbonized Residues Using a Thermo-Gravimetric Fluidized Bed

Higher value products from CO₂ and waste, can play a role in meeting climate goals as an application that contribute to a future net-zero CO₂ emission economy. The objective of the present work is to obtain KOH activated biochar from pyrolysed biogenic residue in a two-stage process and to evaluate its CO₂ adsorption performance in a thermo-gravimetric fluidized bed, operated as bubbling bed.

The fluidized bed TGA reactor consists of a 0.1 l reaction zone and is able to measure gas solid interactions such as drying, oxidation, adsorption and catalytic reactions during fluidization of the particles. It was validated with measurements of the adsorption isotherm of LEWATIT VP OC 1065 and the requested manufacturer data as well as results from literature data at a fluidization number of U/U_mf 2.05. The comparison with literature showed an R² of 0.929-0.0994 with respect to the conformity of the own collected data and the data from literature.

In addition, adsorption isotherms were determined for industrial carbon, non-activated biochar and activated biochar. A Langmuir-Freundlich model was applied to calculate the isometric heat of adsorption.

Improved adsorption of activated biochar compared to inactivated biochar was demonstrated. A maximum CO₂ uptake of 1.84 mmol/g was obtained at 50 °C and 100 % CO₂. A comprehensive comparison of all Langmuir models of all adsorbents show a comparable adsorption performance of the activated biochar with that of commercially produced activated carbon from hard coal.

The new developed fluidized bed reactor can help to develop cost reduced products from CO₂ and biogenic residues through multi stage processes adopted to locally available waste streams.