Study On Mass Transfer Characteristic Of CO₂ Capture Process Using Sodium Amino Acid Aqueous Solution In Microreactor

The microreactor has shown great potential in the development and production of chemical products owing to its high efficiency,environmental protection and safety,it consequently received extensive attention in recent years.Sodium amino acid is a new type of absorbent with low volatility,low toxicity and good absorption performance to CO₂.In this paper,the efficiency and mass transfer characteristics of CO₂ absorbed by amino acid sodium aqueous solution in serpentine microchannel and parallel multi-channel microreactor were investigated experimentally by a high-speed camera.The densities and viscosities of aqueous solutions of amino acid sodium were measured.The volumetric and viscometric properties such as the activation energy for viscous flow（Ea）,the viscosity B-coefficient（B）,the limiting partial molar volume（V_φ⁰）and the apparent molar volume（V_φ）were calculated according to the experimental densities and viscosities and analyzed based on the molecular structure and intermolecular interaction.Moreover,the group contribution method was utilized to study the limiting partial molar volume（V_φ⁰）.The flow process and mass transfer characteristics of CO₂ absorbed by amino acid sodium aqueous solutions in serpentine microchannel were studied.Due to the differences in the groups and molecular structure,the CO₂ loadings（L_O）of the five kinds of sodium amino acids decrease in the order:L_O（sodium L-argininate）>L_O（sodium glycinate）>L_O（sodium L-alaninate）>L_O（sodium L-threoninate）>L_O（sodium L-valinate）.The results of CO₂ absorbed into sodium glycinate aqueous solution indicate that the larger gas flow rate,smaller CO₂ concentration,liquid flow rate and concentration of sodium glycinate solution could lead to the higher specific surface area.The overall mass transfer coefficient（k）declines slightly with rising gas flow rate,while k grows with the increase of CO₂ concentration,liquid flow rate or concentration of sodium glycinate solution.The overall volumetric mass transfer coefficient（ka）increases with the gas flow rate,CO₂ concentration,liquid flow rate or concentration of sodium glycinate solution.For CO₂/N₂ gas mixture,the CO₂absorption fraction firstly increases and then decreases with the increase of gas flow rate,and there exist a critical gas flow rate.The critical gas flow rate decreases with the increase of CO₂ concentration in gas mixture.The CO₂ absorption fraction can reach up to 99.59%,indicating a good removal effect.Taking the enhancement of chemical absorption on mass transfer process into account,two modified dimensionless correlations were proposed to predict volumetric mass transfer coefficient,which show high prediction accuracy.The mass transfer and gas-liquid distribution of CO₂ absorbed by sodium glycine in a parallel multi-channel microreactor were studied.The results show that the increase of gas flow rate would aggravate the heterogeneity of gas-liquid distribution,while the rise of liquid flow rate and liquid phase concentration have opposite effects on it.Within the range of experiment,the average heterogeneity of the microreactor is less than 5.57%.Under the same conditions,the parallel multi-channel microreactor has the similar mass transfer performance to the single channel microreactor,and there is no significant difference for CO₂ absorption fraction in each channel of the parallel multi-channel microreactor.The results show that the CO₂ absorption fraction increases with the decrease of gas flow rate,and the increase of liquid flow rate and concentration of sodium glycine aqueous solution.The liquid-side volumetric mass transfer coefficient increases with the increase of gas flow rate,liquid flow rate and concentration of sodium glycine aqueous solution.In addition,a dimensionless correlation was proposed to predict the average liquid-side volumetric mass transfer coefficient,which shows good prediction effect.