The usage of capillary tubes for CO

2

absorption suffers from small residence time

which leads to reduced performance for large throughput. This work presents a method of connecting expansion units to capillary tubes to serve as a residence time delayer. The effect of the expansion unit on gas-liquid hydrodynamics

pressure drop and mass transfer coefficient (

k

L

a

) are investigated under various operating pressures up to 4.0 MPa

for both physical and chemical absorption. A novel periodic jetting flow is found in the expansion unit

which can intensify the CO

2

absorption. Experimental results show that the strategy can significantly decrease the pressure drop while maintaining the absorption performance to a large extent. The overall

k

L

a

for physical and chemical absorption are correlated to pressure drop

respectively. Besides

CO

2

loading in rich absorbents increases dramatically compared to literature studies with only micromixers or capillary tubes

which is beneficial to regenerate solvent. The study verifies the concept that pre-treatment with water can largely

reduce the usage of amines

and can also provide a guide for process design in natural gas purification such as biogas recovery.