Polytetrafluoroethylene Packing In A Rotating Packed Bed:Mass-transfer And Micromixing Studies

Rotating packed bed(RPB),a typical reactor based on the Higee process intensification technology,has outstanding mass transfer and micromixing efficiency in liquid-liquid,gas-liquid,or gas-liquid-solid systems.As a core part of RPB,the packing plays an important role in the mixing and transfer performance between the different phases.However,the corrosive environment always seriously damages the traditional packing,and then impacts on the normal running of the RPB.As an anti-corrosive packing,polytetrafluoroethylene(PTFE)was researched by the effects of rotational speed,liquid flow rate,and gas flow rate on the mass transfer in a RPB.To study the gas-liquid mass transfer,the effective interfacial area(ae)and the volumetric liquid-side mass-transfer coefficient(kLae)was measured via the experiments of NaOH-CO2 system and oxygen-water,and then the experimental correlations of ae and kLae were proposed.Using the parallel competing reaction of the iodate-iodide system,the effects of rotational speed,liquid flow rate,and liquid viscosity on the segregation index Xs was specified to measure the micromixing efficiency of the RPB.Based on the experimental results,the micromixing characteristic time was calculated through the incorporation model.To explore whether the PTFE packings can be used to produce the nanoparticles or not,a certain kind of PTFE packing was chosen to prepare the Mg(OH)2 nanoparticle in the RPB.Some conclusions are listed as below:(1)Both ae and kLae increased with rotational speed of the RPB and liquid flow rate.Gas flow rate had little influence on the mass transfer performance.The PTFE wire mesh equipped with a smaller fiber diameter and pore size had higher ae and kLae.The mass transfer property of the stainless steel wire mesh packing was higher than PTFE packing.(2)On the base of experimental data,the experimental correlations of ae and kLae were proposed,respectively.The calculated data by the correlations were within ±20%of the experimental data.(3)The micromixing performance of PTFE packing in the RPB increased significantly with the increase of rotational speed and liquid flow rate,and decreased as the liquid viscosity increased.Smaller hole size and thinner fiber diameter of wire mesh lead to lower Xs,and PTFE wire mesh packing had better micromixing efficiency than stainless steel material.The calculated results of the micromixing characteristic time indicated that the smallest tm of PTFE packing was only 2.762 × 10-5s.(4)Preparation of Mg(OH)2 nanoparticles by the liquid phase precipitation approach had characteristics of strong corrosion and fast reaction,therefore,the KWP-1 packing was chosen to prepare the Mg(OH)2 nanoparticles.The product crystals had the shape of regular hexagonal plates with the size from 38nm to 74nm.The Mg(OH)2 nanoparticles had the advantages like high purity,small particle size,and uniform distribution.,indicating that PTFE wire mesh packing had an excellent effect on nanometer particles preparation.