Computational Fluid Dynamics Simulation of Mass Transfer in the Separation of Fermentation Products Using Nanoporous Membranes

The simulation of fermentation product separation using nanoporous membranes is presented. The aim of the simulation was to predict the performance of an extraction process to remove compounds from aqueous solutions. The simulation was conducted using computational fluid dynamics techniques for the solution of governing equations. The system studied was a membrane‐based extractor of acetone from aqueous solutions using near‐critical CO₂ as solvent. The predicted extraction percentages obtained by the simulations were compared to experimental values reported in the literature and showed very good agreement. The simulation can predict the concentration profile of acetone in the membrane and also predicts the formation of a concentration boundary layer.     

Development of a mathematical model for studying bioethanol–water separation using hydrophilic polyetherimide membrane

An essentially predictive mathematical model was developed to simulate pervaporation process. The group contribution method UNIFAC was used for calculating the upstream activity coefficients. The diffusion coefficient in the membrane was predicted using free‐volume theory. Free‐volume parameters were determined with viscosity and temperature data, and the binary interaction solvent–polymer parameter was calculated by a group‐contribution lattice‐fluid equation of state (GCLF‐EOS). A simulator named PERVAP was developed applying the mathematical model. Pervaporation process was simulated for separating bioethanol–water through polyetherimide membrane. The simulated results were validated using experimental data of bioethanol/water separation through polyetherimide membrane. The model presented a satisfactory performance compared to experimental data. Related to the simulation of the studied separation, a 99% molar enriched bioethanol stream was obtained with a recovery of 94%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mass Transfer in Molybdenum Extraction from Aqueous Solutions Using Nanoporous Membranes

Modeling of non‐disperse solvent extraction of molybdenum(VI) with PC‐88A as extractant and a nanoporous hollow‐fiber membrane contactor as extractor was performed. Computational fluid dynamics was applied for modeling and simulation of molybdenum extraction. Concentration, pressure, and velocity distributions for molybdenum were determined. The extraction of Mo⁶⁺ was greatly influenced by the flow rate of feed solution. The extraction efficiency was reduced with higher feed flow rate and increased with the molybdenum content in the feed. The pressure drop along the shell side of the membrane extractor was found to be not significant, being one of the advantages of membrane extractors which assist in reducing the operational costs. The proposed simulation method is capable to prognosticate the performance of solvent extraction of molybdenum in membrane extractors.     

Modeling of Thallium Extraction in a Hollow-Fiber Membrane Contactor

A mass transfer model was developed to simulate the solvent extraction of thallium by butyl acetate through a hollow-fiber membrane contactor. The model was based on the solving conservation equations including mass and momentum transfers for thallium in both aqueous and solvent phases as well as membrane. The model equations were solved by a numerical method based on the finite element method. The simulations were conducted using experimental data obtained from literature for two different modules consisting of hydrophobic polypropylene (PP) and polyvinylidene fluoride (PVDF) fibers. The fibers had different effective membrane areas. The model findings were then verified through comparison with experimental data. The comparison showed an average deviation of 9% with the experimental data. The effect of process variables on thallium mass transfer was investigated. The results confirmed that the developed model predicts well the general behavior of thallium extraction versus process variables.     

Pore Network Modeling of Nanoporous Ceramic Membrane for Hydrogen Separation

Pore network modeling of porous media has this advantage that can consider the pore structure incorporating any desired details, but it has not been studied sufficiently. In addition, most studies are limited to mathematical modeling only which need validation. In the present study, this approach was applied to hydrogen separation from syngas by nanoporous ceramic membrane to predict the membrane permeance theoretically based on its pore structure. Gas transport through nanoporous membrane was modeled with the aim of a 2D network model. A dusty gas model was used for gas transport in the individual pores. Model validation showed that the model predictions are in good agreement with the experimental data with the coordination number of 2.5 and the pore length of about 20 nm. A parametric study indicated that hydrogen permeance through the membrane increases with the average and minimum pore size and decreases with temperature and pressure. Also, hydrogen selectivity increases slightly with temperature and decreases with pressure and average pore size.     

Concentration of Natural Vitamin E Using a Continuous Countercurrent Supercritical CO2 Extraction‐Distillation Dual Column

A continuous countercurrent supercritical CO₂ extraction‐distillation dual‐column process was developed to extract and concentrate natural vitamin E (VE) from soybean oil deodorizer distillate (SODD). The experimental results demonstrated that process parameters such as extraction pressure, temperature, and solvent‐to‐feed ratio significantly impacted on the extraction efficiency of natural VE. A new five‐parameter mass transfer model for the continuous countercurrent supercritical CO₂ extraction‐distillation dual‐column process was presented based on the Penetration and Double‐Film theories. The calculated values of the mathematical model agreed well with the experimental data, with absolute average relative deviation values of less than 25 %.     

Process design and economic analysis of methacrylic acid extraction for three organic solvents

In this work, a techno-economic study for the solvent based extraction of methacrylic acid from an aqueous solution is presented. The involved phase equilibrium calculations in process design are verified by measured experimental data. First, experiments are conducted with different solvent candidates to measure LLE (liquid–liquid equilibrium) data and to establish the effects of extraction temperature and dosage of solvent. Next, the binary interaction parameters for the UNIQUAC model to be used for equilibrium calculations are fine-tuned with measured data. Then, a process for the solvent based extraction of methacrylic acid recovery is designed and verified through simulation with the regressed UNIQUAC model parameters. The optimal configuration of the process flowsheet is determined by minimizing the total annualized cost. Among the three solvent candidates considered-cyclohexane, hexane and toluene-the highest efficiency and the lowest total annualized cost is found with toluene as the solvent.     

Transient computational fluid dynamics modeling of pervaporation separation of aromatic/aliphatic hydrocarbon mixtures using polymer composite membrane

Pervaporation (PV) separation of toluene/n‐heptane mixtures was studied experimentally and theoretically by means of a molecular surface engineering (MSE) polymer composite membrane. A comprehensive mathematical model was developed to predict unsteady state transport of toluene and n‐heptane (nC₇) through the membrane. Conservation equations including continuity, and heat transfer equations were solved using finite element method (FEM). Computational fluid dynamics (CFD) technique was applied to solve the model equations. The model was then verified with PV experimental data. The simulation results were in good agreement with the experimental data. The simulation results revealed that the proposed model could provide a general simulation of transport in the PV process. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Modeling of water transport through nanopores of membranes in direct‐contact membrane distillation process

In this research, computational fluid dynamic simulation of direct‐contact membrane distillation process is carried out. The process consists of a nanoporous flat‐sheet membrane as contactor, a saline liquid feed, and permeate phase. The flow pattern is considered to be counter‐current. The aim of the process is to produce pure water from saline water. Heat and mass transfer equations are derived and solved for water by finite element analysis. The simulations are then validated by comparing simulation predictions with the experimental data reported in literature. Good agreement was obtained which confirmed the validity of simulation procedure in simulation of water desalination using membrane distillation. Diffusion of water vapor through pores of membrane is simulated by combination of the Knudsen and Poiseuille flow. POLYM. ENG. SCI., 54:660–666, 2014. © 2013 Society of Plastics Engineers     

Separation of Diacteone Alcohol‐Water Mixtures by Membrane Pervaporation

Abstract

A study was conducted to evaluate membrane pervaporation for the separation of diacetone alcohol‐water mixtures using commercially available membranes for organic enrichment and dehydration. Empirical correlations for the effect of the process parameters of feed concentration, feed temperature, permeate‐side pressure, and scale‐up were developed. The solvent‐water mixture was successfully separated with a poly(vinyl alcohol) based Sulzer PERVAP 2210 dehydration membrane. Various dehydration membranes were evaluated and a comparison of the flux and separation factor was made. The membrane performance in separating acetone‐water mixtures was also studied. An overall model to predict the membrane area needed for a scale‐up was developed based on the results.     

Countercurrent transport of organic and water molecules through thin film composite membranes in aqueous-aqueous extractive membrane processes. Part II: theoretical analysis

The aqueous-aqueous extraction of organic compounds through thin film composite (TFC) membranes is investigated using a mathematical model describing the mass transfer across the membrane and hydrodynamic boundary layers at both membranes sides. The model accounts for organic diffusion and convection due to water flux, and enables the characterisation of water and organic counter transport encountered in saline-TFC membrane-aqueous extractive processes. The reliability of the model is tested using experimental data on rate of extraction of toluene from aqueous solutions of NaCl into water. The model is then used to predict the effect of ionic strength, thermodynamic properties (e.g. organic salting-out coefficient) and membrane morphology on the rate of organic extraction. The analysis shows that the retarding effect of countercurrent water transport on organic extraction can be severe for organic compounds with low salting-out coefficients (e.g. phenolic compounds) or for salts with strong influence on water activity (e.g. AlCl₃). The model predictions provide the guidelines for choosing the membrane geometry and morphology which minimise this effect and maximise the rate of extraction of a given organic from a given saline solution.     

3D Modeling and Simulation of Mass Transfer in Vapor Transport through Porous Membranes

A 3D mathematical model is developed to predict the transport of water vapor through porous membranes. The model is based on solving the continuity, momentum as well as energy equations for water in the membrane contactor. The model's equations are numerically solved using the finite element method to obtain the concentration and temperature distributions of water in the membrane contactor. The model findings were in good agreement with experimental data. The proposed 3D model proved to be appropriate for predicting the performance of a membrane evaporator. Simulations were carried out in order to study the influence of different operating parameters and membrane structure on the membrane evaporation effectiveness. The results of simulation indicate that the gas velocity is a favorable parameter in the membrane evaporation process due to its tendency to keep the process far from the thermodynamic equilibrium.     

Efficient removal of organic dye pollutants using covalent organic frameworks

A rational design and synthesis of covalent organic frameworks (COFs) displaying efficient adsorption of surrogates for common organic pollutants is demonstrated herein. Significantly, the top performing mesoporous triazine‐functionalized polyimide COF exhibits superior adsorption of the small dye molecule methylene blue, achieving a maximum adsorption capacity of ～1691 mg g^?1 (～169 wt %), surpassing the performance of all previously reported nanoporous adsorbents. The experimental results and accompanying in silico simulations suggest that both the size of the organic dye molecules and the intrinsic pore‐size effect of the COF material should be taken into account simultaneously for the construction of COF‐based adsorbents with efficient dyes adsorption capacities. The structural diversity of COF materials along with the understanding of the encapsulation of organic dyes on COFs holds great promise for developing novel COF adsorbents for the efficient removal of organic pollutants from wastewater. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3470–3478, 2017     

Ethanol purification using polyamide‐carbon nanotube composite membranes

This work presents synthesis and characterization of polyamide‐carbon nanotube (CNT) composite membranes for purification of ethanol. The solution‐casting method was applied for preparation of nanocomposite membranes. The nanocomposite membranes were characterized using scanning electron microscopy to ensure the fine dispersion of nanoparticles in polymer matrix. The effect of CNT loading on membrane performance was investigated. The separation performance of synthesized membranes was evaluated in separation of ethanol from ethanol/water mixture using pervaporation. Effect of feed temperature and feed concentration on separation of ethanol was investigated. The results showed that increasing temperature increases flux of ethanol through the membrane, but decreases separation factor. The results also confirmed that the best separation performance can be obtained at CNT loading of 0.5 wt%. Furthermore, a mathematical model was developed to simulate the separation process. The model was based on solving the continuity equation for ethanol in the feed side and membrane. The simulation results were compared with the experimental data and were in good agreement. POLYM. ENG. SCI., 54:961–968, 2014. © 2013 Society of Plastics Engineers     

Treatment of phenol-containing aqueous solutions by membrane-based solvent extraction in coupled ultrafiltration modules

Extractive treatment of phenol-containing aqueous streams by two coupled hollow fiber modules (for simultaneous extraction and stripping) is experimentally and theoretically studied. The effects of hydrodynamic conditions (linear velocities of all three liquids) and concentrations (initial phenol concentrations) are explored and an optimal combination of these process parameters is found for maximisation of the phenol fluxes in both modules. The extraction/stripping performance of the coupled HF modules was compared when using different organic solvent (alcohols and alkanes). Analysis of the mass-transfer resistances of the different liquid layers in both modules is presented based on mathematical model and experimental data from equilibrium measurements and kinetic experiments. It is found that an important part of the overall resistance is located in the aqueous phase’s boundary layers. A substantial improvement of the stripping yield is reached by using a series of stripping modules.     

三辛胺萃取草酸的第3相特性

以三辛胺（TOA）萃取草酸时出现第3相的基本规律为研究对象,实验测定了无水溶剂及液液萃取平衡有机相中草酸的溶解度及其随TOA和正辛醇浓度的变化规律.结果显示,正辛醇对草酸及其与TOA形成的缔合物在溶剂中的溶解度影响显著;随正辛醇含量的增加,草酸及其缔合物在溶剂中的溶解度提高,因而溶剂对草酸的萃取能力随之增大;在TOA与草酸以1∶1的化学计量比饱和后,草酸溶解度出现阶跃现象,这与形成草酸二聚体的缔合物有关;相比之下,液液萃取平衡实验中有机相对草酸的溶解度大于无水溶剂的结果,溶剂中水的存在有助于缔合物溶解.同时建立了描述液液萃取平衡有机相中草酸及其缔合物溶解度的数学模型,并通过参数寻优求得了相应的模型参数.     

Numerical simulation studies on heat and mass transfer using vacuum membrane distillation

A general 2D mathematical model was developed to simulate the purification of water from volatile organic compounds (VOCs) via vacuum membrane distillation (VMD) process in hollow fiber membrane contactors. The model was developed for hydrophobic membrane material conditions, taking into consideration axial and radial diffusion in the tube, membrane and compartments of the contactor and was simplified to the two‐dimensional structure with a single porous membrane wall. The simulation has studied the mass and heat transfer of VMD system in the porous media, in which aqueous volatile organic solution was considered as an incompressible and steady fluid. Effect of the downstream pressure on the removal of 1, 1, 1‐trichloroethane (TCA) was studied to validation of simulation results with experimental data that it was obtained from literature. The temperature, Reynolds number, and total mass flux (convective and diffusive) distribution of TCA are determined in the membrane module. POLYM. ENG. SCI., 54:2553–2559, 2014. © 2013 Society of Plastics Engineers     

From laboratory to scale-up by modelling in two cases of β-carotene extraction from vegetable products

The laboratory investigation of β-carotene separation from rose hip fruits (RHFs) powder and carrot noodles (CNs) was analyzed by means of mathematical modelling, in order to develop models for process scale-up. The developed models contain parameters characterizing species transport inside and outside of vegetal material particle as well as species interphase equilibrium distribution. The model parameters were estimated by experimental data capitalization. The solvent type, liquid–solid ratio and extraction temperature were selected as process factors in β-carotene extraction. Having a significant influence on the process yield, these factors determined the values of model parameters. A model based on process control by external diffusion of extracted species and particle swelling was adopted for β-carotene extraction from RHFs, whereas an internal diffusion one was chosen to describe the process in the case of β-carotene extraction from CNs. The model parameters were identified by least squares method using theoretical and experimental data characterizing the dynamics of species extraction yield. The scale-up of counter current multistage extraction was performed through analysis of the processes studied at laboratory level.