Cross-flow Module Research Articles

High efficient thin-film composite membrane: Ultrathin hydrophilic polyamide film on macroporous superhydrophobic polytetrafluoroethylene substrate

Interfacial polymerized thin-film composite (TFC) membranes have been widely investigated for molecule separation and water purification. While the support is limited to the hydrophilic micro and/or mesoporous support with concentration polarization, which may compromise the separation efficiency. Here, a copper hydroxide nanostrands (CHNs) assisted interfacial polymerization process was developed to form ultrathin hydrophilic polyamide (PA) films on macroporous and hydrophobic polytetrafluoroethylene (PTFE) substrates by confining the m-phenylenediamine (MPD) aqueous solution in the preformed CHNs networks on the PTFE substrate. The porous hydrophilic CHNs serve as the micro-reservoir for amine aqueous solution, smooth and seal the macroporous PTFE substrate, and confine the interfacial polymerization closely on their surface. The thickness of the top PA layer could be easily controlled by the thickness of the CHNs layer. The resulted Janus PA/PTFE TFC membrane with 102nm thick PA selective layer demonstrates 93% rejection for Rhodamine B (molecular weight 479) with a permeance of 420Lm−2h−1bar−1 in industrial preferred cross-flow module. This performance is one order higher than that of the commercial membranes with similar rejections. The newly developed PA/PTFE TFC membrane holds a widely application in separation and purification of small molecules.

CFD Study of Hybrid Membrane Contactors for Absorption and Stripping of Carbon Dioxide

Carbon capture and storage (CCS) has been identified as an essential technology to meet the internationally agreed goal of limiting the temperature increase to 2°C. Compared to traditional gas-liquid contactors, the membrane contactors provide many beneficial features, including the high specific area, independent gas and liquid flows, modular units and easy to include internal heat exchange. The solvent carbon dioxide absorption processes employing membrane contactors is an important technology. Limited by the low partial pressure of carbon dioxide, physical absorption is not a feasible technology for post-combustion flue gas treatment. However, chemical absorption technology is high energy consumption. In this study, an innovative hybrid absorption/stripping membrane contactor (HASMC) for physical solvent carbon capture is proposed. The simultaneous absorption and stripping can enhance the effectiveness of carbon capture. The device can raise the feasibility of applying physical solvent technology to the treatment of gases with low carbon dioxide partial pressure. In this paper, computational fluid dynamics simulation of the concentration profiles and mass fluxes for parallel-flow and cross-flow modules are presented.

Gas-liquid absorption in industrial cross-flow membrane contactors: Experimental and numerical investigation of the influence of transmembrane pressure on partial wetting

Membrane wetting is a limitation to mass transfer in industrial Hollow-Fiber Membrane Modules (HFMM). The influence of transmembrane pressure on wetting is investigated through both experimental and numerical works. On the one hand, experiments for CO2 absorption in softened water are carried out at pilot scale with Liqui-Cel® Extra-Flow modules operating in a cross-flow mode. After several hours of operation (50–300min), the membrane partially wetted mode is established at steady state and decreases the absorbed CO2 flowrates up to 10.5% compared to membrane dry mode. Interestingly, CO2 absorption is found to be independent on different transmembrane pressure (0.5 and 2.5bar), both in the dry and partially wetted mode. On the other hand, a 2D predictive tool is developed to help in the design of HFMM gas absorption systems. The model depicts the complex hydrodynamics in commercial cross-flow modules. The liquid in the shellside is flowing through the fiber bundle considered as a porous medium. The liquid mass-transfer coefficient is non-uniform over the membrane module and is estimated at a local scale. The parameters from the empirical Chilton-Colburn correlation are optimized with experimental results in the dry mode through a Particle Swarm Optimization (PSO) algorithm. The simulation results are in good agreement with the experiments (−13/+17%). In the partially wetted mode at steady state, wetting is then described by considering a log-normal pore size distribution and the Laplace-Young equation. The transmembrane pressure decreases the simulated absorbed CO2 flowrate. By comparing to experimental data, the numerical relative error is increasing with transmembrane pressure. Therefore, a suggestion is made to adapt the description of wetting in HFMM gas-liquid models.

Wear Characterization of High Temperature Oxidized Ni Based Superalloys

Objectives: This work presents a study of the effect of membrane surface with dimples on the heat transfer in vacuum membrane distillation (VMD). Methods/Statistical Analysis: Polyvinylidene fluoride (PVDF) membrane and distilled water as feed solutions are tested in a laboratory-scale cross-flow flat-sheet membrane module with membrane area of 72.4 cm2. A perforated aluminum support embedded in the permeate compartment is used to support the membrane during the VMD process. Findings: The results show that the dimples stamped on the membrane surface by the perforated support having the diameter and depth approximately 5 and 1 mm, respectively. The permeability of the membrane with dimples increases by 3 - 20% at the corresponding feed temperature of 75 - 95°C. The deviations between the heat transfer coefficients predicted by a Nusselt correlation with dimpled effect and the experimental values are less than 10%. Application/Improvements: These findings are significant to reveal the influence of membrane deformation effect on the heat transfer correlation which is used to predict the VMD flux.

Atmospheric CO2 capture for the artificial photosynthetic system

The scope of these studies is to evaluate the ambient CO 2 capture abilities of the membrane contactor system in the same conditions as leaves works during photosynthesis, such as ambient temperature, pressure and low CO 2 concentration, where the only driving force is the concentration gradient. The polysulfone membrane was made by phase inversion process and characterized by ESEM micrographs which were used to determine the thickness, asymmetry and pore size. Besides, the porosity of the membrane was measured from the membrane and polysulfone density correlation and hydrophobicity was analyzed by contact angle measurements. Moreover, the compatibility of the membrane and absorbent solution was evaluated, in order to exclude wetting issues. The prepared membranes were introduced in a cross flow module and used as contactor between the CO 2 and the potassium hydroxide solution, as absorbing media. The influence of the membrane thickness, absorbent stirring rate and absorption time, on CO 2 capture were evaluated. The results show that the efficiency of our CO 2 capture system is similar to stomatal carbon dioxide assimilation rate.

A scale-down cross-flow filtration technology for biopharmaceuticals and the associated theory

Use of microfiltration (MF) and ultrafiltration (UF) in cross-flow mode has been intensifying in downstream processing for expensive biopharmaceuticals. A scale-down cross-flow module with ring channel was constructed for reducing costs and increasing throughput. Commensurate with its validation, a new scale down (or scale up) theoretical framework has been further developed to 3 operational parities: (1) ratio of initial sample volume to membrane area, (2) shear force adjacent to membrane surface, and (3) initial permeate flux. By keeping identical initial physicochemical properties, we show that these 3 operational parities are equivalent to 2 further time-dependent theoretical parities for flux and transmission respectively. Importantly, transmission sensitively reflects membrane conditions for partially transmissible molecules or particles. Computational fluid dynamics simulation was conducted to confirm nearly identical shear forces for the mini and its reference filters. Permeate fluxes in suspension containing Escherichia coli phage T7, a monoclonal antibody (MAb) or other proteins, and transmission (with phage T7) were measured. For application demonstration, diafiltration and concentration modes were applied to the MAb, and separation mode to a mixture of bovine serum albumin and lysozyme. In conclusion, the developed scale-down filter has been shown to behave identically or similarly to its reference filter.

Studies On hydrolysis of skimmed milk using immobilized β-galactosidase in a membrane reactor

In the present investigation, an attempt has been made to investigate the hydrolysis of skimmed milk in a batch membrane bioreactor using β-galactosidase immobilized on a 30 kDa PES membrane. The skimmed milk solutions of different concentrations(30 kg m-3 – 80 kg m-3)were deproteinated through 30 kDa and 5 kDa cross-flow ultrafiltration membrane modules successively and about 95%-97% lactose present in the feed was recovered in the permeate stream. The deproteinated milk permeates thus obtained were subjected to hydrolysis in a batch membrane bioreactor fitted with the enzyme-immobilized PES membrane. Immobilization of enzyme on the ultrafiltration membrane was performed by cross-linking using two different concentrations of glutaraldehyde (3%v/v and 4%v/v). It was observed that high percent retention ofenzyme activity(94.2%) and percent enzyme loading(98%) were attained when the immobilization was performed using 4%v/v glutaraldehyde. For an initial feed concentration of 70 kg m-3,the percentage lactose conversion achieved were 45.2% and 21.4% using β-galactosidase immobilized with 4%v/v and 3%v/v glutaraldehyde respectively. However, a significant percentage reduction in pure water fluxwas observed in case of enzyme-immobilized membranes (27.5% and 67.5% for immobilization carried out using 3% and 4%v/v glutaraldehyde respectively)from that obtained using the fresh membrane. The enzyme-immobilized membrane(cross-linked with 4%v/v glutaraldehyde) could be used for six successive runs with more than 90% retention in activity and less than 5% loss due to leaching. The unsteady state mass balance equation was developed in order to predict the concentration profile above the membrane surface.The model equation could also predict the permeate concentration well within 95% confidence interval

A comparative study between stirred dead end and circular flow in microfiltration of China clay suspensions

A well-defined comparative study between stirred dead end and circular crossflow for microfiltration of china clay suspensions has been undertaken. The comparisons have been made with respect to convective mass transfer coefficients, permeation and rejection rates, and energy consumption. Similar operating and hydrodynamic conditions were implemented for the comparison. According to our experimental data the circular crossflow module was proven to perform better as compared with the stirred dead end system due to the higher mass transfer coefficients, higher permeation rates and lower energy consumption. The mass transfer coefficients observed are comparable to those previously found in vortex flow filtration and dead end flow filtration. The presence of Dean vortices in the circular crossflow module promotes flow instabilities in the curved channel flow path which reduce the concentration polarization effect during the filtration process. The concentration polarization effect however deteriorated due to solute build up (high solute concentration at the membrane surface) and decrease of the shear stress, i.e., the particle lift forces on the membrane surface. This resulted in deposition of particles on the membrane surface. In terms of energy consumption, for the same energy cost the limiting flux reached in circular crossflow was found to be higher than in the stirred dead end unit.

Forward Osmosis: Temperature Effects By Using Pome as Feed Solution

Forward osmosis (FO) has recently been considered as one of the promising technologies for low energy applications. Factors that influence FO performance are draw solution, types of membrane, membrane orientation, cross flow velocity, module configuration and temperature effect. In this study, the influence of temperature on the performance of FO process has been studied in terms of water flux by using raw POME as feed solution. A higher temperature creates a higher water fluxes at various draw solution concentrations. Percentages of water flux increments for raw POME are between 7% to 9% from 25ºC to 35ºC and 32% to 75% from 25ºC to 45ºC.

A novel forward osmosis-nano filtration integrated system for coke-oven wastewater reclamation

A forward osmosis–nanofiltration (FO–NF) integrated new system in flat-sheet cross-flow module was designed to separate reusable water from coke-oven wastewater with reduced concentration polarization and high flux using low energy. Investigations were carried out under different sets of operating conditions of pressure, cross-flow rate, pH of the feed solution and run time for better understanding of the phenomena of concentration polarization and reverse salt diffusion in the new system. A set of polyamide composite membranes were investigated to screen out the best performing ones (NF-2 for forward osmosis and NF-1 for draw solute recovery) for the final experiments. While investigating effects of different draw solutions (DS) on the water flux and rejection of target contaminants, 1.5M NaCl was found to be the best for forward osmosis. Removal of about 96–98% of cyanide, phenols, NH4+ -N and chemical oxygen demand from real coke-oven could be achieved along with pure water flux of 46L/(m2h) in FO system under optimized conditions. Downstream nanofiltration module ensured continuous recovery and recycle of 99% of the draw solute while ensuring recovery of reusable water at the rate of 45L/(m2h).

Purifying fluoride-contaminated water by a novel forward osmosis design with enhanced flux under reduced concentration polarization

For purifying fluoride-contaminated water, a new forward osmosis scheme in horizontal flat-sheet cross flow module was designed and investigated. Effects of pressure, cross flow rate, draw solution and alignment of membrane module on separation and flux were studied. Concentration polarization and reverse salt diffusion got significantly reduced in the new hydrodynamic regime. This resulted in less membrane fouling, better solute separation and higher pure water flux than in a conventional module. The entire scheme was completed in two stages-an upstream forward osmosis for separating pure water from contaminated water and a downstream nanofiltration operation for continuous recovery and recycle of draw solute. Synchronization of these two stages of operation resulted in a continuous, steady-state process. From a set of commercial membranes, two polyamide composite membranes were screened out for the upstream and downstream filtrations. A 0.3-M NaCl solution was found to be the best one for forward osmosis draw solution. Potable water with less than 1% residual fluoride could be produced at a high flux of 60-62 L m(-2) h(-1) whereas more than 99% draw solute could be recovered and recycled in the downstream nanofiltration stage from where flux was 62-65 L m(-2) h(-1).

Comparative study of red grape must nanofiltration: Laboratory and pilot plant scales

A consequence of global warming is the early ripening of grapes which promotes, among others, a higher fermentable sugar (glucose and fructose) content. This leads to wines with an alcoholic degree higher than desired.In this work, the main differences between red grape must nanofiltration at laboratory and pilot plant scale were studied in order to perform the scale-up of a nanofiltration process to reduce the sugar content. For this, previous results of the nanofiltration of commercial red must using the SR3 membrane in a flat sheet crossflow module were compared with those obtained for the filtration of natural red must using the same membrane in a spiral wound module at two different applied pressures.The aim of this publication is to analyze the main differences between red grape must nanofiltration at laboratory and at pilot plant scale. Resultsshowed that the flow destabilization and eddy promotion caused by spacers in the spiral wound module mitigate the rate at which the cake thickens and compacts on the membrane surface. This causes a less sharp flux decrease, less variable sugars rejection and osmotic pressure difference. Moreover, higher applied pressure promotes a higher membrane fouling and osmotic pressure that worsen the flux decay.

Production of liposomes using microengineered membrane and co-flow microfluidic device

Two modified ethanol injection methods have been used to produce Lipoid® E80 and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) liposomes: (i) injection of the organic phase through a microengineered nickel membrane kept under controlled shear conditions and (ii) injection of the organic phase through a tapered-end glass capillary into co-flowing aqueous stream using coaxial assemblies of glass capillaries. The organic phase was composed of 20mgml−1 of phospholipids and 5mgml−1 of cholesterol dissolved in ethanol and the aqueous phase was ultra-pure water. Self-assembly of phospholipid molecules into multiple concentric bilayers via phospolipid bilayered fragments was initiated by interpenetration of the two miscible solvents. The mean vesicle size in the membrane method was 80±3nm and consistent across all of the devices (stirred cell, cross-flow module and oscillating membrane system), indicating that local or temporal variations of the shear stress on the membrane surface had no effect on the vesicle size, on the condition that a maximum shear stress was kept constant. The mean vesicle size in co-flow microfludic device decreased from 131 to 73nm when the orifice diameter in the injection capillary was reduced from 209 to 42μm at the aqueous and organic phase flow rate of 25 and 5.55mlh−1, respectively. The vesicle size was significantly affected by the mixing efficiency, which was controlled by the orifice size and liquid flow rates. The smallest vesicle size was obtained under conditions that promote the highest mixing rate. Computational Fluid Dynamics (CFD) simulations were performed to study the mixing process in the vicinity of the orifice.

Separation of three divalent cations (Cu2 +, Co2 + and Ni2 +) by NF membranes from pHs 3 to 5

Separation mechanisms for the three model divalent cations with very similar atomic weights (Cu, 63.5Da; Co, 58.9Da and Ni, 58.7Da) by two nanofiltration (NF) membranes (Nitto Denko ESNA and GE Osmonics DK) were studied in a cross flow module from pHs3 to 5. The results show that the rejection order for the two selected membranes was Ni2+>Cu2+>Co2+ from the conducted experiments, and the removal efficiency was increased as pH was decreased for all three metals. It was found that enthalpy of hydration and concentration polarization exerted the controlling effect on the membrane selective transport rather than atomic weight, Stokes radius and hydrated radius. Besides, the counterion of sulfate enhanced the removal efficiencies, but an increase of sulfate more than 0.01M reduced the removal efficiencies. Moreover, the removal efficiency of DK membrane was better than that of the ESNA membrane due to the positive charge of DK membrane at low pH.

Recovery of Whey Proteins and Enzymatic Hydrolysis of Lactose Derived from Casein Whey Using a Tangential Flow Ultrafiltration Module

In this study, ultrafiltration (UF) of pretreated casein whey was carried out in a cross-flow module fitted with 5 kDa molecular weight cut-off polyethersulfone membrane to recover whey proteins in the retentate and lactose in the permeate. Effects of processing conditions, like transmembrane pressure and pH on permeate flux and rejection were investigated and reported. The polarised layer resistance was found to increase with time during UF even in this high shear device. The lactose concentration in the permeate was measured using dinitro salicylic acid method. Enzymatic kinetic study for lactose hydrolysis was carried out at three different temperatures ranging from 30 to 50 °C using β-galactosidase enzyme. The glucose formed during lactose hydrolysis was analyzed using glucose oxidase–peroxidase method. Kinetics of enzymatic hydrolysis of lactose solution was found to follow Michaelis–Menten model and the model parameters were estimated by Lineweaver–Burk plot. The hydrolysis rate was found to be maximum (with Vmax = 5.5091 mmol/L/min) at 30 °C.

In situ characterization of fouling in reverse osmosis membranes using electrical impedance spectroscopy

Analytical solutions of the Nernst-Planck, Poisson and continuity equations for a membrane undergoing reverse osmosis in a cross-flow system reveal that the flow of alternating ionic charge induced in the membrane during impedance measurements is actively assisted by the flow of water. The actively driven current manifested "inductive" responses in impedance measurements of a Filmtec BW30 reverse osmosis membrane mounted in an Inphaze flat-bed cross-flow module after 16 hours of filtering a mineral salt solution seeded with CaCl2 and NaHCO3 at pressure of 900 kPa. Fitted transfer functions resolved conduction and capacitive properties of four membrane layers, diffusion/concentration phenomenon and a pseudo "inductor" shunted by a conductor. A 10-fold decrease in the shunt conductance correlated with smaller increases in the conductance values for the filtrate and membranous layers, and the onset of fouling diagnosed by a rapid increase in flux decline.

Particle migration leads to deposition-free fractionation

In membrane filtration, the pore size of the membrane determines the size of ‘particles’ that should be rejected, leading to accumulation of particles on the membrane surface and changed particle retention in time. A process without accumulation and thereby constant retention as function of time would be well suited for fractionation of components close in size.In this research, emulsions consisting of small droplets (∼2.0µm) and large droplets (∼5.5µm), with total concentrations between 10% and 47%, were fractionated. The cross-flow module consisted of a closed channel to allow particles to migrate, followed by a membrane area with 20µm pores where emulsion fractions could be removed. Under appropriate process conditions, the permeate consisted of only small droplets, at concentrations higher than in the original emulsion, leading to very high selectivities. Especially at high concentrations, known to cause severe fouling in regular membrane filtration, these effects were occurring as a result of shear-induced diffusion of the droplets. If only small particles are targeted, the module can be operated at fluxes of 40L/(m²/h); if fractionation is targeted the fluxes can be considerably higher. These fluxes are comparable to current operational fluxes, but here cross-flow velocity and trans-membrane pressure are much lower (corresponding to fluxes of 1–4m3/(m²/h/bar)) with stable retention and flux as function of time.

Separation and concentration of a low-penetrating impurity by membrane gas separation

The process of concentrating low-penetrating impurities in membrane modules was studied theoretically and experimentally. An expression was derived for the degree of separation in a radial cross-flow module; the degree of separation substantially depends on the gas-phase diffusion coefficient of the impurity. The experimental results obtained for a mixture of carbon dioxide with an impurity of Freon 14 and a mixture of Freon 12 with an impurity of Freon 218 agree with calculated data.

Comparison of nanofiltration membranes’ performance in flat sheet and spiral wound configurations: a scale-up study

ABSTRACT Nanofiltration (NF) membranes have been largely developed and commercialised over the past decade and are currently one of the most promising technologies for the separation of neutral and charged solutes in aqueous solutions. Sometimes NF is defined as a process between ultrafiltration and reverse osmosis; however, the separation mechanisms of this kind of membranes are not clear enough, and even today there are some questions remaining about how NF membranes work. Nowadays, there are many different types of NF membranes commercially available, so the first step before developing a new NF treatment plant is to know which one is going to be the most suitable membrane. There are two main configurations in which NF can be used: flat sheet and spiral wound module. The cross-flow module using flat sheet membranes is the simplest option to test an NF membrane but at the industrial scale, NF is basically used in the spiral wound configuration. Currently, there are no studies available regarding the difference of using both configurations. The objective of this work is to do an experimental study regarding the performance of two different NF membranes, NF270 (Dow Chemical) and ESNA 1-LF2 (Hydranautics), in two different scales, laboratory and pilot plant, using the most typical configurations in each case: flat sheet and spiral wound respectively. Using the same feed water, the operating conditions and the rejections of the membranes in both configurations will be studied in order to check if both operating scales can be comparable.

A New Short–Cut Design Method for Ultrafiltration and Hyperfiltration Cross–Flow Hollow Fiber Membrane Modules

Although ultrafiltration and hyperfiltration have replaced many liquid phase separation equipment, both are still considered as “non–unit operation” processes because the sizing of both equipments could not be calculated using either the equilibrium stage, or the rate–based methods. Previous design methods using the dead–end and complete–mixing models are unsatisfactory because the dead–end model tends to underestimate the membrane area, due to the use of the feed concentration in the driving force, while the complete–mixing model tends to overestimate the membrane area, due to the use of a more concentrated rejection concentration in the driving force. In this paper, cross–flow models for both ultrafiltration and hyperfiltration are developed by considering mass balance at a differential element of the cross–flow module, and then integrating the expression over the whole module to get the module length. Since the modeling is rated–based, the length of both modules could be expressed as the product of the height of a transfer unit (HTU), and the number of transfer unit (NTU). The solution of the integral representing the NTU of ultrafiltration is found to be the difference between two exponential integrals (Ei(x)) while that representing the NTU of hyperfiltration is found to be the difference between two hypergeometric functions. The poles of both solutions represent the flux extinction curves of ultrafiltration and hyperfiltration. The NTU for ultrafiltration is found to depend on three parameters: the rejection R, the recovery S, and the dimensionless gel concentration Cg. For any given Cg and R, the recovery, S, is limited by the corresponding flux extinction curve. The NTU for hyperfiltration is found to depend on four parameters: the rejection R, the recovery S, the polarization β, and the dimensionless applied pressure difference ψ. For any given ψ and R, the recovery, S, is limited by the corresponding flux extinction curve. The NTU for both ultrafiltration and hyperfiltration is found to be generally small and less than unity but increases rapidly to infinity near the poles due to flux extinction. Polarization is found to increase the NTU and hence the length and membrane area of the hollow fiber module for hyperfiltration. Key words: Ultrafiltration; hyperfiltration; reverse osmosis; hollow fiber module design; crossflow model; number of transfer unit; height of a transfer unit