The Study On Mass Transfer Characteristics Of CO₂ Absorption Into Mixed Alkylamine Aqueous Solution In Microchannels And Single-dimensional Scale-up

The microchannel equipments have the characteristics of strong controllability,good safety and high mass transfer efficiency,and have received increasing attention.Mixed amine aqueous solution has many advantages in absorbing CO₂ over the single amine solution.In this paper,MEA+MDEA mixed amine aqueous solution was used to absorb CO₂ in the rectangular cross section microchannels.The gas-liquid mass transfer mechanism and the single-dimensional scale-up of microchannel were studied.A high-speed camera was used to record the gas-liquid two-phase flow in the channel and four flow patterns were observed:bubble flow,slug-bubble flow,slug flow and slug-annular flow.The slug flow was easily appliable for a large range of operating condition.The length of generated gas bubble varies significantly with gas-liquid flow rate and cross section,however,less is affected by MEA concentration.The void fraction and pressure drop increase with gas velocity,but the trend of increase would gradually slow down.The increase of liquid velocity and MEA concentration could reduce the void fraction and increase the pressure drop.In the microchannel with cross section of 400×400μm,the mass transfer coefficient k _L,specific surface area a and volumetric mass transfer coefficient k _La were calculated by image method.The mass transfer coefficient increases significantly with liquid velocity and MEA concentration,however,it is insensitive to gas velocity and MDEA concentration.The specific surface area and volumetric mass transfer coefficient increases significantly first and then tends to a constant with the gas velocity.As the liquid velocity and MEA concentration increase,the specific surface area decrease,but the volumetric mass transfer coefficient increases.Considering the enhancement of chemical reaction on mass transfer,the Hatta number Ha was introduced into the prediction model of volumetric mass transfer coefficient.The predicted values are at good agreement with experimental data.For given superficial gas and liquid velocities,the mass transfer coefficient and volumetric mass transfer coefficient increase first and then decrease,but the specific surface area decreases with the broadening of microchannel.In this experimental range,the mass transfer coefficients and volumetric mass transfer coefficient in 400×1000μm microchannel has the maximum.The results of single-dimensional scale-up for microchannel show that the microchannels could still maintain excellent mass transfer performance when the width of microchannel is enlarged within proper range.