Separation of acetonitrile/methanol/benzene ternary azeotrope via triple column pressure-swing distillation

The multiphase micro-structured devices such as microchannels have been recently taken into consideration to replace the conventional equipment in different applications. The mass transfer coefficients and the interfacial area in the multiphase microchannels are much larger than those in the conventional equipment. This paper reviews the experimental studies on mass transfer in gas-liquid and liquid-liquid microchannels. Proposed flow pattern maps are compared. The featured researches corresponding to the effects of the operating conditions and the geometry of the microchannels on mass transfer are discussed. Literature review shows that influences of geometrical parameters are not investigated as extensively as those of operating conditions and thus, vague aspects of geometrical parameters effects exist. There are inconsistencies between results of some researchers and most of these are due to using dissimilar microchannel materials, unalike dominant mechanisms at different investigated operating conditions, different approaches to change the independent variable, etc.

Mass transfer between phases in microchannels : A review

This paper deals with design and control of an extractive dividing-wall distillation column (EDWC) for ethanol dehydration using ethylene glycol as entrainer. An initial design, based on a section analogy procedure for a conventional extractive distillation sequence, was obtained and then used in an optimization process to minimize the total annual cost. It was shown that the EDWC can result in significant savings over the conventional process. As these savings sometimes go along with a decrease in the control properties, an investigation of two control structures for the EDWC and one for the conventional column configuration was performed next. It was observed in closed-loop simulations that the EDWC with an appropriate structure exhibited good control properties and that its closed-loop responses were similar to those obtained for the operation of a conventional extractive distillation system.

Control analysis of an extractive dividing-wall column used for ethanol dehydration

Continuous-flow microreactor technology has been embraced by researchers in academia and industry due to its excellent transport properties and the increased safety and control over challenging chemical transformations. Despite its popularity, scaling the benefits associated with the microenvironment has proven to be a daunting challenge. This review provides an up-to-date overview concerning the different scale-up approaches of micro/milli-reactors, including numbering up (both internal and external), sizing up (increasing length, geometry similarity and constant pressure drop strategies) and a combination of numbering up and sizing up. The strategies, design principles and applications of each approach have been discussed in detail. Each scale-up approach has its merits and limitations. However, scale-up factors, that are required in the fine chemical and pharmaceutical industry, are within reach when different scale-up approaches are combined.

Scale-up of micro- and milli-reactors : An overview of strategies, design principles and applications

The hydrodynamic properties of plug flow were investigated in small channels with 0.5-, 1-, and 2-mm internal diameter, for an ionic liquid/aqueous two-phase system with the aqueous phase forming the dispersed plugs. Bright field Particle Image Velocimetry combined with high-speed imaging were used to obtain plug length, velocity, and film thickness, and to acquire velocity profiles within the plugs. Plug length decreased with mixture velocity, while for constant mixture velocity it increased with channel size. Plug velocity increased with increasing mixture velocity and channel size. The film thickness was predicted reasonably well for Ca > 0.08 by Taylor's (Taylor, J Fluid Mech. 1961;10(2):161–165) model. A fully developed laminar profile was established in the central region of the plugs. Circulation times in the plugs decreased with increasing channel size. Pressure drop was predicted reasonably well by a modified literature model, using a new correlation for the film thickness derived from experimental values.

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Effect of channel size on liquid-liquid plug flow in small channels

An alkaline hydrolysis reaction was used as the model reaction to investigate the performance of liquid–liquid slug flow microchannel. The specific interfacial area was determined through the photographic snapshot method physically by means of measuring the lengths of relevant slugs. The overall volumetric mass transfer coefficients were calculated through the Danckwerts’ model chemically. The influences of various operating conditions on the slug length, the overall volumetric extraction rate and the mass transfer coefficient were investigated quantitatively. A decreasing trend of volumetric mass transfer coefficients along the channel length was found. The linear dependence of the volumetric extraction rate on the volumetric mass transfer coefficient indicates that the overall rate of the process is determined by the mass transfer process. In addition, the volumetric mass transfer coefficients were correlated for different channel lengths.

Mass transfer behavior of liquid–liquid slug flow in circular cross-section microchannel

Design and control of an extractive distillation system for tetrahydrofuran (THF) dehydration with ethylene glycol as entrainer is investigated. The main module is a two-column system containing an extractive distillation column, whose top stream is the desired product THF, and an entrainer recovery column. Economic analysis with total annual cost as the objective function is developed. Two kinds of control strategies are explored for THF dehydration. The responses reveal that the control structure with fixed reflux ratio cannot maintain the bottom liquid level of the entrainer recovery column, while the control scheme with fixed reboiler heat duty/feed flow ratio exhibits good control performance in spite of large deviations in feed flow rate and feed composition.

Design and Control of Extraction Distillation for Dehydration of Tetrahydrofuran

Ceramic matrix composite of carbon fiber framework reinforced by silicon carbide (Cf/SiC) is a new material with excellent properties. In order to improve its preparation process, the flow of polycarbosilane solution in carbon fiber is studied based on the computational fluid dynamics method. CT images of carbon fiber porous media are obtained by Micro-CT imaging technology and optimized by means of ImageJ software. The 3D solid matrix and pore space models of carbon fiber porous media are established by using Mimics software, and the pore space model is meshed. Using the computational fluid dynamics software Fluent, the VOF multiphase flow model is adopted, the surface tension model and contact angle model are introduced considering the micro-pore effect of porous media, and a suitable mathematical model for the transport of gas–liquid two-phase flow in carbon fiber porous media is established. The validity of CFD mathematical model is verified by comparing experimental data with simulation results. Based on the CFD simulation results, the effects of feed pressure, surface tension coefficient and contact angle on fluid flow are studied. It is found that the larger the feed pressure and contact angle, the more uniform the distribution of liquid phase, pressure and velocity in the medium, which is conducive to the flow of liquid phase in porous media. The larger the surface tension coefficient, the longer the breakthrough time of liquid, and the more uneven the liquid distribution. This study is helpful to understand the law of fluid transport in porous media and provides theoretical basis for the preparation of Cf/SiC composites.

Simulation of non-Newtonian fluid seepage into porous media stacked by carbon fibers using micro-scale reconstruction model

A new non-invasive visualization technology was successfully developed to determine the hydrodynamics parameters of Taylor flow in monolith channels. With the developed method, the gas and liquid slug lengths as well as the gas holdup in channels of different radial positions were measured. Accordingly, the average gas holdup in different radial zones and the mean slug lengths over the monolith cross-section were calculated with varying superficial gas and liquid velocities. By defining the maldistribution factor, the degree of non-uniform distributions of these parameters over the monolith cross-section was investigated quantitatively. The results showed that a moderate gas-to-liquid velocity ratio can result in uniform distribution for both gas holdup and slug lengths. In addition, the obtained mean slug lengths were well correlated with simplified Qian and Lawal correlations.

Wangfeng Cai

Papers

Mass transfer behavior of liquid–liquid slug flow in circular cross-section microchannel

Design and Control of Extraction Distillation for Dehydration of Tetrahydrofuran

Simulation of non-Newtonian fluid seepage into porous media stacked by carbon fibers using micro-scale reconstruction model

Experimental Investigation of Gas Holdup and Slug Lengths in an Upflow Monolith Reactor