Mass Transfer And Pressure Drop Of CO₂ Absorption Into Ionic Liquid-Based Aqueous Solution In Microreactor

Micro-chemical technology has shown great potential in chemical synthesis and process intensification due to its excellent heat/mass transfer efficiency,good controllability and high safety.As a type of common multiphase system,gas-liquid two-phase flow has been widely used in chemical processes such as absorption,reaction and separation,etc.Consequently,it is of significant importance and scientific value to study the gas-liquid two-phase flow and mass transfer in microchannel.Recently,ionic liquids have shown notable advantage and applicability in CO₂ absorption.Therefore,in this study,the reaction mechanism,hydrodynamics and mass transfer of CO₂absorption into ionic liquids and alkanolamine mixing solutions were studied systemically in microreactor.The densities and viscosities of binary and ternary mixtures of various alkanolamines and water systems were measured at atmospheric pressure and T=（293.15-313.15 K）.Subsequently,the volumetric and viscometric properties of solutions were calculated,and the molecular interactions in mixed solution were analyzed,which provided needed thermodynamic properties for subsequent studies of mass transfer in microchannels.The gas-liquid two-phase flow pattern and mass transfer performance of CO₂absorption into alkanolamine aqueous solutions were investigated.It is found that the mass transfer coefficient could be significantly affected by chemical absorption and gas-liquid flow rate,and a new correlation for predicting mass transfer coefficient accompanied by chemical reactions was proposed.The flow characteristics,absorption rates and pressure drop of functionalized ionic liquids/halide-free ionic liquids-CO₂ system in microchannels were investigated and compared,and the absorption mechanisms were analyzed by means of ¹³C NMR spectroscopy.The results showed that chemical absorption could enhance the absorption rate significantly,while physical absorption performance mainly depends on free volume of ionic liquid.Furthermore,the effects of gas-liquid flow rate and ionic liquid properties on the two-phase pressure drop were studied.By analogy to the gas-liquid two-phase flow without mass transfer,the prediction models of pressure drop with physical/chemical absorption under different flow patterns were proposed.Meanwhile,the performance of CO₂ absorption into a novel hybrid absorbent combining ionic liquid with alkanolamine was investigated experimentally in microchannel.The optimal ratio of ionic liquid to alkanolamine was determined by analyzing the variation of CO₂ loading and mass transfer coefficient at different the concentration ratios.The gas-liquid two-phase flow pattern,flow distribution and mass transfer performance in a honeycomb fractal microreactor with equal channel size were investigated.The fluid uniformity was found to closely related to the bubble breakup at each bifurcation,the pressure fluctuation and the downstream feedback.The intrinsic dependence of mass transfer coefficient on fluid uniformity was revealed.Additionally,a honeycomb fractal microreactor with various channel size was designed according to Murray law.The operating range of symmetrical flow pattern for honeycomb fractal microreactor with various channel size was verified to be less than that with equal channel size.At low gas-liquid flow rate ratio,gas-liquid two-phase flow in these two microreactors was the symmetrical flow regime,the mass transfer performance of microreactor with various channel size was better than that with equal channel size,and the energy consumption was also lower.However,at high gas-liquid flow rate ratio,the mass transfer performance of microreactor with various channel size was approximative to or even below that with equal channel size.