The composite material K2CO3/Al2O3 is a promising solid absorbent for direct CO2 capture from ambient air. In the current work the kinetics of CO2 absorption by this composite material was studied in the perfectly mixed reactor. The dependence of CO2 absorption rate on temperature and characteristic grain size of the composite sorbent was investigated. It was revealed that the total CO2 uptake decreases in the temperature range from 50 to 80°C. Comparison of CO2 absorption kinetics of by fractions of the composite with characteristic grain sizes of 0.8-1.0 mm and 1.6-2.0 mm showed that the initial rate of CO2 absorption inversely depends on characteristic grain size of the composite material, which indicates that the absorption process is limited by mass transfer. The results obtained are of interest for the capture of air-borne CO2 with subsequent renewable methane production using H2 from alternative sources of energy.