A Scalable and Sustainable Adsorbent Composed of Self-Assembled Epoxide-Functionalized Polyethyleneimine/Silica for Capturing Carbon Dioxide from Exhaust Gas

Amine-based solid adsorbents, composed of a mixture of amines and porous solid supports, demonstrate excellent carbon capture performance by combining carbon chemisorption by the amines with carbon physisorption by the solid support. This dual functionality has garnered considerable interest from researchers specializing in post-combustion carbon capture.

In most air-based CO₂ capture systems, amine-based solid adsorbents are used in powder form (< 1 mm). However, in continuous flow conditions like diesel engine exhaust emissions, powder adsorbents can be lost due to the drag force of the exhaust flow, resulting in a gradual decrease in CO₂ capture capacity.

Herein, we propose a simple and scalable method to synthesize the self-assembled-CO₂-adsorbent pellets by extruding functionalized polyethylenimine (PEI)/silica for use in exhaust emission aftertreatment. This self-assembled pellet shaping creates a new hierarchical porosity, including nano-sized pores (micropores (< 2 nm), mesopores (2-50 nm)) than those found in the original materials.

Silica-based substrates were extruded with an inert binder to enhance handling and mechanical strength, then formed into pellets. Post-extrusion, the organic binder was calcined at temperatures between 150-750°C. These calcined pellet substrates were subsequently self-assembled with functionalized PEI. To evaluate the CO₂ adsorption capacity and efficiency of the self-assembled solid adsorbents (functionalized PEI/silica adsorbents) at various calcination temperatures, we measured the CO₂ adsorption capacity and efficiency under 5% CO₂ using thermogravimetric analysis (TGA550, TA Instruments, U.S.A) and breakthrough system.

The results showed that the pellet substrates calcined at 550 °C had the highest total pore volume (0.98 cm^3/g), and the highest average carbon dioxide adsorption efficiency over 5 minutes (22.64%). Subsequently, the porous pellet (calcined at 550 °C) could be effectively self-assembled with the functionalized PEI/silica adsorbents due to its higher proportion of nano-sized mesopores compared to the original material (silica powder). The developed self-assembled-CO₂-adsorbent pellets included approximately 45 wt% of the CO₂ adsorption component.

These findings suggest that this scalable and sustainable method for synthesizing and self-assembling solid-supported amine adsorbents into pellets could be an effective solution for carbon capture systems in areas of energy and environment on post-combustion aftertreatment conditions.

This work was supported by the Korea Institute of Marine Science & Technology Promotion (KIMST), funded by the Ministry of Oceans and Fisheries (20220568).