Green Self-Activating Synthesis System for Porous Carbons; Celery Biomass Wastes as a Typical Case for CO2 Uptake with Kinetic, Equilibrium and Thermodynamic Studies

A green self-activating synthesis system (SASS) has been introduced for porous carbons. In the presented system, there is no external support for the activation process, and the activating agents are the circulating gases released during the pyrolysis treatment. As a typical case, this system was used for the synthesis of hierarchical porous carbons from celery wastes in hydroponic greenhouses. Based on the adsorption-desorption results, the optimal porous carbons were synthesized at 700°C, providing a surface area as high as 1126 m2g−1 and micropore volume of approximately 0.7 cm3g−1. X-ray photoelectron spectroscopy indicated the presence of graphitic nitrogen in the synthesized porous carbon structure. The synthesized porous carbons were applied as an adsorbent for CO2 capture. CO2 adsorption was performed at low and high pressures at various temperatures. Under low pressures (0-1 bar), the synthesized carbons adsorbed 5 mmolg−1 at 0°C and 2.03 mmolg−1 at 25°C. The adsorption capacity of the synthesized carbon at 25°C and a relatively high pressure of 9.5 bar was 9.57 mmolg−1. Based on the thermodynamic and kinetic models, it was clarified that the adsorption process can be regarded as physisorption with an adsorption enthalpy of 23.2 kJ.mol−1. Additionally, the fractional-order kinetic model was found to be the best match in the kinetic curves. The synthesis system described herein represents a promising strategy for producing green porous carbon from various waste organic precursors.