Adsorption kinetics of difluoromethane on biomass-derived activated carbon through experimental and modeling approaches

This study investigated the adsorption kinetics of difluoromethane (R32) on mangrove-derived activated carbon (MAC) over 30–90°C and 0–3000 kPa using a thermogravimetric (TGA) setup. To capture the transient uptake and investigate the equilibrium pressure effects on adsorption kinetics, a dual pseudo-first-order (dual-PFO) model was adopted, in which total uptake is expressed as the sum of two branches with distinct rate constants ( k 1 , k 2 ); their contributions to total uptake are characterized by the fractional capacity α . The model fitted all the experiments with high accuracy (average R 2 = 0.9976). Parameter analysis showed that α and k 1 decrease as the equilibrium pressure increases, whereas k 2 is nearly pressure-invariant. Applying the dual-PFO model to literature datasets (Maxsorb III/R32 and MAC/CO 2 ), α , k 1 and k 2 exhibited the same pressure dependence trend as MAC/R32. Comparison of fitted parameters across three working pairs together with pore-structure differences between MAC and Maxsorb III indicates a mesopore-associated fast branch and a micropore-controlled slow branch. Parameters ( α , k 1 , k 2 ) were regressed as functions of pressure and temperature, yielding a global correlation formula that reproduces representative curves with high accuracy. Embedding the correlation in a dynamic two-bed R32/MAC adsorption cooling model yielded a coefficient of performance (COP) of 0.173 and a cooling power (CP) of 1.47 kW under representative conditions ( T evap = 10°C, T cond = 30°C, T des = 75°C), suggesting that MAC/R32 is a promising working pair and that the dual-PFO kinetics can facilitate system-level performance evaluation under the examined conditions.