Study on liquid–liquid two-phase mass transfer characteristics in the microchannel with deformed insert

In this work, the liquid-liquid two-phase mass transfer characteristics in the microchannel with deformed insert were studied. The experiment used di-(2-ethylhexyl) phosphoric acid/kerosene-Cu^(2+)as the mass transfer evaluation system. The effects of some key factors such as the total flow velocity,channel inner diameter, channel length, insert diameter, extractant concentration on the extraction efficiency and mass transfer coefficient were systematically investigated. Compared with a simple microreactor, the liquid-liquid mass transfer enhancement effect of the insert was quantitatively analyzed. The study found that the regular deformation of the insert could cause fluid interface deformation and promote flow state chaos, effectively increasing the mass transfer rate. And the enhancement effect of the insert was more significant at high flow velocities. The highest mass transfer coefficient in the microchannel with deformed insert was 7.886 s^(-1), the enhancement factor could reach 4.17. And only needed 0.095 s to approach the extraction equilibrium. The deformed center insert exhibited an effective liquid-liquid mass transfer enhancement effect, which can be used as a micro-chemical process enhancement method to be applied in the fields of higher throughput mass transfer and chemical synthesis,and at the same time provide ideas for development and structural optimization of microreactors.

Numerical study on the hydrodynamics behavior of a central insert microchannel

In this work, the computational fluid dynamics method is used to study the liquid hydrodynamics behavior in the microchannel without central insert(MC1) and the central insert microchannel(MC2), respectively. The maximum deviation between simulation and experiment is 24%. The formations of flow patterns are explained based on contours and force analysis where the flow pattern maps are established by two-phase flow rate. The effects of aqueous phase viscosity and two-phase flow rate on the characteristic sizes of each flow pattern are also explored. Specifically, four unconventional flow patterns are found in MC2, namely the unique droplet flow, the unique slug flow, the unique coarse annular flow and the unique film annular flow. Though the insert occupies part of the channel, the pressure difference in the channel is significantly reduced compared with MC1. Moreover, the insert significantly changes the formation velocity range of each flow pattern, greatly broadens the formation range of annular flow and also has an important influence on the characteristic size of the flow pattern. The organic-phase dimensionless axial size(Lo/W) and the dimensionless radial size(Do/W) of the droplet(slug) are negatively related to the aqueous-phase viscosity(μa) and flow rate(ua). The Do/W of the annular is negatively correlated with μaand positively correlated with organic-phase flow rate(uo). This study provides direct numerical evidence that the insert is key to the formation of bicontinuous phase flow pattern, as well as further strengthens our understanding of the flow characteristics and optimization design of insert microchannels.

Specific cross-dimerization of terminal alkynes via Pd/TMEDA catalysis

The cross-dimerization of terminal alkynes is the most straightforward and attractive approach to differently substituted 1,3-enynes,which are vital structural motifs in natural products,biologically active compounds,and organic functional materials,etc.However,due to the inherent issues of the stereo-,regio-,and chemoselectivity,the strategy is less explored and remains problematic in substrate scope,selectivity,and screening of catalytic system,etc.Herein,a specific cross-dimerization of terminal alkynes is developed under Pd/TMEDA catalysis,which produces a series of gem-1,3-enynes(58 examples)in totally moderate to high yields with outstanding functional group tolerance.A cyclopalladium compound might be the key imtermediate,which performs anti-addition-carbometallation,and leads to the exclusive cross-selectivity.The unprecedented features of the reaction,such as anti-addition-carbometallation,easy control of selectivity,wide range of the donor alkynes,and very simple catalytic conditions,allow it not only a facile and functionally diverse synthesis of 1,3-enynes,but also a substantial progress for the textbook reaction.