Slug Flow And Hydrogenation Reaction Characteristics In Serpentine Microchannel With Catalytic Walls

With the rapid development of micro-fabrication and ultra-precision, micro-devices attract many researchers to study it from various fields. As one of micro-devices,microreactor are widely used in chemical, chemcial industry, energy, biology, materials and many other fields because of its large surface area, high transmission efficiency, short contact time, less by-products, high security, good operation, easy amplification design, short development cycle and other prominent advantages.Microreactor has become a new focus for experts.This paper aims at the gas-liquid-solid microreactor with catalytic walls.Seting in the hydrogenation of nitrobenzene, visualization experiments were carried out to investigate two-phase flow and reaction characteristics in a serpentine microchannel under slug flow condition. Highly-dispersed Pd/γ-AL2O3 catalyst was prepared by chemical reduction method and the rectangular serpentine microchannel was coated the Pd-loaded γ-AL2O3 catalyst on the walls.The dimension of microchannel is 400μm(wide) ×220μm(depth)×846mm(length); Slug flow characteristics and bubble length, liquid slug length, void fraction in different gas and liquid flow rate in microchannel were discussed, the coupling relationship between two phase flow characteristics, catalytic reaction and conversion were also discussed; better catalyst was prepared for increasing the hydrogenation of nitrobenzene conversion, studied two-phase flow characteristics in serpentine microchannel which have obstacles, analysed bubble length and bubble velocity change caused by obstacles, in different structure microchannels, aniline yield was compared; The liquid velocity distribution in different structure microchannels was tested and analysed by micro-PIV system. Here is the main conclusion of this paper.1) The Pd/γ-AL2O3 catalyst prepared by chemical reduction method can be used to hydrogenation of nitrobenzene reaction with high reaction rate under the atmospheric pressure and room temperature because of its high active caused by small size and high dispersion of catalyst.2) The variation in gas and liquid flow rates led to differences in the initial gas bubble length and liquid slug length as well as the initial velocity. Because of hydrogenation reaction, occurred from slug flow to bubble flow flow pattern transition under low gas and liquid flow rate; The void fraction and bubble velocity increased with increasing the gas flow rate and decreased with increasing the liquid flow rate.Moreover, with increasing the gas flow rate, the produced aniline and nitrobenzene conversion efficiency firstly increased and then decreased, when the gas flow rate is 40 μl·min-1, highest conversion occurred; with increasing the liquid flow rate the produced aniline and nitrobenzene conversion efficiency decreased; In a certain range of residence time longer bubble and shorter liquid slug caused higher conversion efficiency.3) The bubble length and bubble velocity inceased when they flow though obstacles region in different gas and liquid flow rate, bubble length and velocity occurred fluctuation in the obstacles region and high obstacles lead to larger fluctuation; The increase and fluctuation becomed more evident under high gas flow rate and low liquid flow rate; The yield of aniline in the microchannel which have obstacles is higher than microchannel which have not obstacels.