Comprehensive Adsorption–Desorption Kinetics of Shaped UTSA-16(Co)/Polyacrylate Composites for Fixed-Bed CO2 Capture

Pristine metal–organic frameworks (MOFs) generally suffer from low mechanical strength and poor processability, hindering their direct application in fixed-bed adsorption systems. In this work, we propose a stepwise impregnation strategy that enables uniform in-situ crystallization of UTSA-16(Co) within amino-functionalized polyacrylate (PAA-NH2) matrices via pre-anchored cobalt ion sites, designed to overcome the low loading and inhomogeneous distribution issues of conventional one-step impregnation methods. Three synthesis protocols (one-step impregnation, stepwise impregnation, and secondary growth) were systematically compared, and the stepwise approach achieved the highest MOF loading of 53 wt%. The optimal composite exhibited a thermogravimetric (TGA) pure-CO2 uptake of 95.0 mg/g at 25 °C and 1 bar and retained 98.6% of its initial capacity after 10 consecutive adsorption–desorption cycles, indicating good short-term cyclic stability. Systematic fixed-bed tests revealed that the empirical Avrami fractional-order model (R2 ≥ 0.994) accurately described the heterogeneous adsorption kinetics of the composite, and the dynamic breakthrough behavior was jointly regulated by gas flow rate, bed temperature, inlet CO2 concentration, and relative humidity. The composite was found to be moisture-sensitive: at 60% RH, the capacity fell by 52.6%. A desorption efficiency above 99% was achieved within 20 min under optimal conditions (90 °C, 0.6 L/min purge gas). Overall, this work provides systematic kinetic data and operational guidelines for the optimization of MOF–polymer composite adsorbents in laboratory-scale fixed-bed applications.