Studies On Mass Transfer And Crotonic Acid Preparation In Gas-Liquid-Solid Mini-Fluidized Beds

The mass transfer and chemical reaction performances of gas-liquid-solid mini-fluidized bed reactor with inner diameter of 3 mm was studied experimentally in this thesis.The mass transfer performance of gas-liquid-solid mini-fluidized bed was investigated with the model reaction of absorption of CO₂ by NaOH.The liquid side volumetric mass transfer coefficient and interfacial area of the gas-liquid-solid mini-fluidized bed increase with the superficial gas velocity under the same superficial liquid velocity.The increment in superficial gas velocity increases the gas holdup and the interfacial area of the system,meanwhile increasing the gas phase mass transfer flux to promote the liquid side volumetric mass transfer coefficient.In addition,liquid side volumetric mass transfer coefficient of the gas-liquid-solid mini-fluidized bed increases with the superficial liquid velocity at the same ratio of superficial gas velocity to superficial liquid velocity.The increase in superficial liquid velocity enhances the turbulence in the bed and promotes the interphase mass transfer.The liquid side volumetric mass transfer coefficient of gas-liquid-solid mini-fluidized bed reactor is increased by about 13.16%compared with that of the gas-liquid mini-bubble column due to the presence of fluidized particles.The fluidization of solid particles in the three-phase mini-fluidized bed greatly enhances the disturbance and increases the liquid phase mass transfer coefficient of the mini-fluidized bed reactor,thereby increasing the liquid side volumetric mass transfer coefficient.The selective catalytic oxidation of crotonaldehyde with Ag/Al₂O₃ supported catalysts was used as a model reaction to evaluate the performance of the three-phase mini-fluidized bed.40°C is the optimized reaction temperature.In addition,the higher conversion rate in higher bed expansion ratio and greater catalyst size is mainly attributed to the increase in the average residence time of liquid.The selectivity of crotonic acid is only susceptive to the temperature change.The average residence time required for the batch stirred tank reactor is 45.5 times that for the three-phase mini-fluidized bed to reach the same conversion ratio;and the reaction efficiency R of the three-phase mini-fluidized bed reactor is about 2.4 times that of the batch stirred tank reactor.For three-phase mini-fluidized beds,the decrease in the characteristic size would effectively reduce the distance of molecular diffusion.Besides,the presence of fluidized particles and multi mini-bubbles provide the higher specific interface area and enhance the interphase disturbance,which are the reasons for the improved chemical reaction performance of three-phase mini-fluidized bed reactor.