Mass transfer simulation on pervaporation dehydration of ethanol through hollow fiber NaA zeolite membranes

A multi‐layer series‐resistance mass transfer model was developed to simulate mass transfer behaviors of water/ethanol mixture through hollow fiber NaA zeolite membranes. The mass transfer through zeolite layer was described by Maxwell‐Stefan mechanism based on adsorption and diffusion parameters obtained from molecular simulation. The mass transfer through asymmetric hollow fiber support was described by dusty gas model involving Knudsen diffusion and viscous flow. It was found that the sponge‐like layer of support besides of zeolite layer made an important contribution to overall membrane transfer resistance while the finger‐like layer had less effect. When permeate pressure shifted from 0.2 to 7.5 kPa, the mass transfer resistance contribution of sponge‐like layer varied from 27.1 to 17.8%. Effects of microstructure parameters of support on mass transfer through membrane were investigated extensively. Large pore size and thin thickness for sponge‐like layer of support were beneficial to improve water permeation flux. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2468–2478, 2016     

Validation of mass‐transfer model for VIPS process using in situ measurements performed by near‐infrared spectroscopy

Combined experimental and modeling approaches were performed in order to investigate the influence of formulation and process parameters on mass transfers during VIPS process, using the water/N‐methyl‐pyrrolidone (NMP)/poly(ether imide) (PEI) system. The experiments were conducted using a thick polymer solution at increasing polymer concentrations for various operating conditions. The global water intake rate in the bulk solution was determined by gravimetric measurements (global), and insitu measurements were conducted by near‐infrared spectroscopy at three points in the solution. In parallel, a fully predictive model was developed for predicting mass‐transfer phenomena involved during the VIPS process. The comparison between experimental data and numerical predictions exhibited a good agreement for moderate polymer concentration, but for higher polymer concentrations, the model overestimated the nonsolvent‐transfer rate. This result was explained by the aggregation process of the polymer chains due to water intake. The numerical predictions were improved by modifying the average hole‐free volume expression. © 2012 American Institute of Chemical Engineers AIChE J, 59: 671–686, 2013     

Modelling of transient mass transfer in liquid and liquid‐solid pulsating systems: Applications and extension to heat transfer

The dynamic surface renewal model of Maucci et al. (2001) is applied to transient mass transfer problems and extended to transient heat transfer measurements in pulsating, two‐phase flows. The model is also used to simulate mass transfer for square‐wave liquid velocity pulses in a liquid‐solid column. Experiments and simulation show that, when flow reversal occurs, the average mass transfer for a pulsating flow can be significantly higher than for steady state flow at the same bulk flow rate. This increase depends mainly on the relative pulse magnitude. The influence of pulse frequency and symmetry is second‐order. Apparent differences between various published studies are resolved.     

Modeling of coupled mass and heat transfer through venting membranes for automotive applications

Experimental and theoretical approaches based on a mathematical model, have been developed to study the evolution of environmental parameters (temperature, total pressure, relative humidity, and water vapor partial pressure) inside a housing of an electronic device with a window containing a macroporous membrane. The model was based on the coupling of mass and heat transfer taking into account the effects of polarization of concentration in boundary layers. Membranes have been characterized by mercury porosimetry, liquid entry pressure measurements, scanning electron microscopy, and gas permeation. Once the model was experimentally validated, it was applied to investigate the influence of membranes on heat and mass transfer and to study the impact of the boundary layers on the global mass transport. The results demonstrated the importance of the membrane choice and dimensions to get the best temperature regulation and avoid water condensation inside an automotive electronic control unit (ECU). © 2008 American Institute of Chemical Engineers AIChE J, 2009     

New development in flow‐through pressure‐swing frequency response method for mass‐transfer study: Ethane in ZIF‐8

A new pressure‐swing frequency response (PSFR) method has been developed to study mass transfer in adsorption systems as a function of temperature and pressure, from ?70 to 180°C, and up to 7 bar. New in‐phase and out‐of‐phase functions have been derived for the PSFR in a general way to allow information extracted from it independent of whether the system is operated in a batch volume swing or a flow‐through pressure swing mode. A new mathematical model that considers distribution of diffusion rates has been introduced to account for diffusive transport in heterogeneous samples. Numerical simulation results have shown that a single rate diffusion model works well when heterogeneity can be described by a normal distribution, but not for asymmetrically bimodal distributions. As a test reference system, the transport of ethane in ZIF‐8 was investigated at different pressures and temperatures using the new PSFR method. The mass transfer was found to be dominated by micropore diffusion. Diffusivity was found to be weakly dependent on pressure or loading, but quite strongly dependent on temperature. The results agree very well with our independent batch volume frequency response technique experiments. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1077–1090, 2017     

A dimensionless model for predicting the mass‐transfer area of structured packing

The mass‐transfer area of nine structured packings was measured in a 0.427 m ID column via absorption of CO₂ from air into 0.1 kmol/m³ NaOH. The mass‐transfer area was most strongly related to the specific area (125–500 m²/m³), and liquid load (2.5–75 m³/m²·h). Surface tension (30–72 mN/m) had a weaker but significant effect. Gas velocity (0.6–2.3 m/s), liquid viscosity (1–15 mPa·s), and flow channel configuration had essentially no impact on the mass‐transfer area. Surface texture (embossing) increased the effective area by 10% at most. The ratio of mass‐transfer area to specific area (a_e/a_p) was correlated within the limits of ±13% for the entire experimental database ${{a_{\rm{e}} } \over {a_{\rm{p}} }}= 1.34 \left[ {\left( {{{\rho _{\rm{L}} } \over \sigma }} \right)g^{1/3} \left( {{Q \over {L_{\rm{p}} }}} \right)^{4/3}} \right]^{\,0.116}$ . © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Mass transfer model,preparation and applications of zeolite membranes for pervaporation dehydration:A review

Pervaporation (including vapor permeation) is a kind of new membrane separation technology, possessing the advantages of high efficiency, energy saving and convenient operation. It has promising application in the separation and purification of organic solvents. Dehydration is an important step in the production and recovery of organic solvents. Zeolite membranes have attracted wide attention for pervaporation dehydration due to their high separation performance and good thermal/chemical stability. So far, zeolite membranes have been preliminarily industrialized for dehydration of organic solvents. This paper reviews the recent development of zeolitemembranes for pervaporation dehydration, includingmass transfermodels, preparation and applications of zeolite membranes. The review also discusses the current industrial applications of zeolite membranes and their future development in pervaporation.     

A pseudo‐transient optimization framework for periodic processes: Pressure swing adsorption and simulated moving bed chromatography

Periodic systems are widely used in separation processes and in reaction engineering. They are designed for and operated at a cyclic steady state (CSS). Identifying and optimizing the CSS has proven to be computationally challenging. A novel framework for equation‐oriented simulation and optimization of cyclic processes is introduced. A two‐step reformulation of the process model is proposed, comprising, (1) a full discretization of the time and spatial domains and (2) recasting the discretized model as a differential‐algebraic equation system, for which theoretical stability guarantees are provided. Additionally, a mathematical, structural connection between the CSS constraints and material recycling is established, which allows us to deal with these conditions via a “tearing” procedure. These developments are integrated in a pseudo‐transient design optimization framework and two extensive case studies are presented: a simulated moving bed chromatography system and a pressure swing adsorption process. © 2017 American Institute of Chemical Engineers AIChE J, 64: 2982–2996, 2018     

Development of a hybrid neural network model to predict feeding method in fed‐batch cultivation for enhanced recombinant streptokinase productivity in Escherichia coli

BACKGROUND: A simple and efficient model for enhancing production of recombinant proteins is essential for cost effective development of processes at industrial scale. A hybrid neural network (HNN) model is proposed combining an unstructured model and neural network to predict the feeding method for the post‐induction phase of fed‐batch cultivation for increased recombinant streptokinase activity in Escherichia coli. RESULTS: The parameters of the unstructured model were estimated from experiments conducted with various feeding methods. The simulated model described the dynamics of the process satisfactorily, however, its predictive capability of the process for different feeding methods is limited due to wide disparity in process parameters. In contrast, a neural network model trained to map the variations in process parameters to state variables complements the ‘first principle’ model in predicting the state variables effectively. CONCLUSIONS: The HNN model is able to predict the product profile for different substrate feed rates. Further, the average volumetric streptokinase activity predicted by the HNN model matches closely the experimental values for fed‐batches having high as well as low streptokinase activity. The HNN model developed in this study could facilitate development of a process for recombinant protein production with minimum number of experiments. Copyright © 2011 Society of Chemical Industry     

Flow through diffusion cell method: A novel approach to study in vitro enzymatic degradation of a starch‐based ternary semi‐interpenetrating network for gastrointestinal drug delivery

A ter‐polymeric semi‐IPN has been synthesized by aqueous polymerization of methacrylamide in the presence of polyethylene glycol (PEG) and natural polysaccharides starch, and its enzymatic degradation has been studied in the phosphate buffer medium of pH 6.8 at the physiological temperature 37°C. With the increase in content of enzyme in the external solution and starch in the hydrogel, the degradation is enhanced while the extent of degradation is lowered with the increase in the amount of PEG in the hydrogel. The initial water content also affects the degradability of the polymer matrix. The degradation follows Michaelis–Menten kinetics and K_M was found to be 3.92 × 10^?5 mol dm^?3. The hydrogel exhibits different degradation behavior when studied by “traditional degradation method” (TDM) and “flow through diffusion cell” (FTDC) method. The degradability is suppressed in FTDC method because of the absorption of amylase molecules onto filler particles. Finally the nature and size of the filler particles also affects the degradation behavior of hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2975–2984, 2006