Determination of mass transfer coefficients in high-pressure CO2-H2O flows in microcapillaries using a colorimetric method

•Mass transfer of CO2 into a H2O-rich phase at high pressure in a microreactor is studied.•Volumetric kLaL and local kL mass transfer coefficients are determined.•The influence of CO2 and H2O flow rates on the volumetric mass transfer coefficient is studied.•kLaL and kL vary along the length of the microcapillary.