Synthesis of a Novel K2CO3 /Humic Acid Microspherical Adsorbent for Post-Combustion CO2 Capture

Air pollution resulting from carbon emissions has received a great deal of attention in recent years. It is very vital and urgent to address this global issue by reducing the amount of CO₂ emitted into the atmosphere. Several technologies are under development to help meet the imposed environmental policies. CO₂ capture and storage (CCS) technology has been designated as one of the promising technologies that necessitate intensive direct research for its development. Among the various CCS technologies under development, the use of solid materials for the physical and chemical adsorption of CO₂ from flue gas is considered a very promising low-cost option. The process of adsorption can overcome the drawbacks faced while using liquid sorption by ensuring low regeneration energy and high adsorption capacity. The focus nowadays is to develop solid adsorbents that could be commercialized on large scales. Although current adsorbents such as Metal-Organic Frameworks (MOF) are efficient and attractive carbon capture materials that exhibit a high CO₂ adsorption capacity of 4.6 mmol/g, their high material synthesis cost, sensitivity to impurities present in flue gas, and low cyclic capacity, warrant the need for development of other sorbent materials.

A low-cost material, humic acid (HA), derived from raw coal was used to synthesize a novel porous adsorbent for carbon dioxide capture. The proposed technology involves fabricating the microsphere substrate with a mixture of Humic Acid (HA) and potassium carbonate solution, followed by chemical activation at high temperatures. The key to developing fast and high CO₂ adsorption is to create active sites that contribute to the chemical bonding of CO₂ with the porous material. In this work, potassium carbonate is an active CO₂ chemical adsorbent and HA is the porous substrate. The distribution of potassium carbonate on the surface of HA microspheres was controlled by adjusting the synthesis conditions and the initial concentration of potassium carbonate in the extraction solution. These loaded solid sorbents with potassium carbonate could offer high CO₂ adsorption capacity. Potassium carbonate reacts with water and carbon dioxide at room temperature (30°C) to form potassium hydrocarbonate. Hence, the synthesized material could offer 1) high CO₂ capture and 2) and low desorption energy which are essential benefits to commercializing it. Preliminary results indicate that the CO2 adsorption capacity increased with increasing potassium carbonate loading. At optimal conditions, microspheres with small particle sizes and uniformly distributed shapes were obtained. The recorded CO₂ adsorption capacity exceeds 2 mmol/g.