Modeling mass transfer and reaction of dilute solutes in a ternary phase system by the lattice Boltzmann method

In this work, we propose a general approach for modeling mass transfer and reaction of dilute solute(s) in incompressible three-phase flows by introducing a collision operator in lattice Boltzmann (LB) method. An LB equation was used to simulate the solute dynamics among three different fluids, in which the newly expanded collision operator was used to depict the interface behavior of dilute solute(s). The multiscale analysis showed that the presented model can recover the macroscopic transport equations derived from the Maxwell-Stefan equation for dilute solutes in three-phase systems. Compared with the analytical equation of state of solute and dynamic behavior, these results are proven to constitute a generalized framework to simulate solute distributions in three-phase flows, including compound soluble in one phase, compound adsorbed on single-interface, compound in two phases, and solute soluble in three phases. Moreover, numerical simulations of benchmark cases, such as phase decomposition, multilayered planar interfaces, and liquid lens, were performed to test the stability and efficiency of the model. Finally, the multiphase mass transfer and reaction in Janus droplet transport in a straight microchannel were well reproduced.

A microdevice assisted approach for the preparation, characterization and selection of continuous aqueous two-phase systems: from micro to bench-scale

Aqueous two-phase systems (ATPS) have emerged as an alternative strategy for the recovery and purification of a wide variety of biological products. Typical process development requires a large screening of experimental conditions towards industrial adoption where continuous processes are preferred. In this work, it was proved that under certain flow conditions, ATPS could be formed continuously inside a microchannel, starting from stocks of phase components. Staggered herringbone chaotic micromixers included within the device sequentially and rapidly prepare two-phase systems across an entire range of useful phase compositions. Two-phase diagrams (binodal curves) were easily plotted using the cloud-point method for systems of different components and compared with previously reported curves for each system, proving that phase formation inside the device correlated with the previously reported diagrams. A proof of concept for sample partitioning in such a microdevice was performed with two different experimental models: BSA and red blood cells. Finally, the microdevice was employed to obtain information about the recovery and partition coefficient of invertase from a real complex mixture of proteins (yeast extract) to design a process for the recovery of the enzyme selecting a suitable system and composition to perform the process at bench-scale.

Continuous synthesis of hedgehog-like Ag–ZnO nanoparticles in a two-stage microfluidic system

Hedgehog-like Ag–ZnO nanoparticles were successfully prepared in a continuous microfluidic system and showed a superior photocatalytic activity in the degradation of methyl orange.

Liquid phase oxidation chemistry in continuous-flow microreactors

This review gives an exhaustive overview of the engineering principles, safety aspects and chemistry associated with liquid phase oxidation in continuous-flow microreactors.

An experimental study on the numbering-up of microchannels for liquid mixing

The numbering-up of zigzag-form microchannels for liquid mixing was experimentally investigated in a multichannel micromixer including 8 parallel channels, based on the Villermaux-Dushman reaction system, with an appropriate sulphuric acid concentration. The results showed that the micromixing performance in such micromixers could reach the same quality as in a single microchannel, when flat constructal distributors with bifurcation configurations were used. The mixing performance did not depend on whether a vertical or horizontal micromixer position was selected. Surprisingly, the channel blockage somewhat increased the micromixing performance in the multichannel micromixer due to the fluid redistribution effect of the constructal distributors. This effect could also be confirmed by CFD simulations. However, the channel blockage resulted in a higher pressure drop and thus higher specific energy dissipation in the multichannel micromixer. The local pressure drop caused by fluid splitting and re-combination in the numbering-up technique could be neglected at low Reynolds numbers, but it became larger with increasing flow rates. The operational zone for the mixing process in multichannel micromixers was sub-divided into two parts according to the specific energy dissipation and the mixing mechanisms.

Ultra-thin liquid film extraction based on a gas–liquid–liquid double emulsion in a microchannel device

A gas–liquid–liquid double emulsion with ultra-thin liquid film is proposed for the mass transfer enhancement of an extreme phase ratio system.

Hydration of acrylonitrile to produce acrylamide using biocatalyst in a membrane dispersion microreactor

In this work, a membrane dispersion microreactor was utilized for the hydration of acrylonitrile to produce acrylamide. Through observation using a microscopy, it was found that the acrylonitrile was dispersed into the continuous phase (the aqueous phase contains nitrile hydratase (NHase)) as droplets with a diameter ranged from 25 to 35 μm, hence the mass transfer specific surface area was significantly increased, and the concentration of acrylamide reached 52.5 wt% within 50 min. By contrast, in stirred tanks, the concentration of acrylamide only got 39.5 wt% within 245 min. Moreover, only a few amounts of acrylonitrile were accumulated in this microreactor system. Through optimizing the flow rate, the concentration of acrylamide reached 45.8 wt% within 35 min, the short reaction time greatly weakened the inhibition of acrylonitrile and acrylamide on the enzyme activity, which is suitable for prolonging the life of free cell.

Photochemical transformations accelerated in continuous-flow reactors: basic concepts and applications

Continuous-flow photochemistry is used increasingly by researchers in academia and industry to facilitate photochemical processes and their subsequent scale-up. However, without detailed knowledge concerning the engineering aspects of photochemistry, it can be quite challenging to develop a suitable photochemical microreactor for a given reaction. In this review, we provide an up-to-date overview of both technological and chemical aspects associated with photochemical processes in microreactors. Important design considerations, such as light sources, material selection, and solvent constraints are discussed. In addition, a detailed description of photon and mass-transfer phenomena in microreactors is made and fundamental principles are deduced for making a judicious choice for a suitable photomicroreactor. The advantages of microreactor technology for photochemistry are described for UV and visible-light driven photochemical processes and are compared with their batch counterparts. In addition, different scale-up strategies and limitations of continuous-flow microreactors are discussed.

Lattice-Boltzmann method for the simulation of multiphase mass transfer and reaction of dilute species

Despite the popularity of the lattice-Boltzmann method (LBM) in simulating multiphase flows, a general approach for modeling dilute species in multiphase systems is still missing. In this report we propose to modify the collision operator of the solute by introducing a modified redistribution scheme. This operator is based on local fluid variables and keeps the parallelism inherent to LBM. After deriving macroscopic transport equations, an analytical equation of state of the solute is exhibited and the method is proven constituting a unified framework to simulate arbitrary solute distribution between phases, including single-phase soluble compounds, amphiphilic species with a partition coefficient, and surface-adsorbed compounds.

Thermal mixing of two miscible fluids in a T-shaped microchannel

In this paper, thermal mixing characteristics of two miscible fluids in a T-shaped microchannel are investigated theoretically, experimentally, and numerically. Thermal mixing processes in a T-shaped microchannel are divided into two zones, consisting of a T-junction and a mixing channel. An analytical two-dimensional model was first built to describe the heat transfer processes in the mixing channel. In the experiments, de-ionized water was employed as the working fluid. Laser induced fluorescence method was used to measure the fluid temperature field in the microchannel. Different combinations of flow rate ratios were studied to investigate the thermal mixing characteristics in the microchannel. At the T-junction, thermal diffusion is found to be dominant in this area due to the striation in the temperature contours. In the mixing channel, heat transfer processes are found to be controlled by thermal diffusion and convection. Measured temperature profiles at the T-junction and mixing channel are compared with analytical model and numerical simulation, respectively.