Application Of Membrane Contactors Research Articles

The Application of Membrane Contactors for the Removal of Ammonium from Anaerobic Digester Effluent

The present study investigated the removal of ammonia from anaerobic digester effluent using membrane contactors. For mass transfer, hollow fiber membrane contactors offer a multitude of advantages compared to stripping technologies. In conventional applications of membrane contactors, the ammonia rich solution circulates through the fibers. For this kind of application, the very high content of suspended solids in digester effluents requires an additional removal step in order to guarantee undisturbed operation conditions. In a new approach, the membrane fibers were simply submerged into the anaerobic digestate and the performance was investigated at moderate temperatures ranging from 20 to 40°C and pH values lying in the range of 8.6 to 10.0. It was demonstrated that the new approach can be applied efficiently for the treatment of particle rich solutions with high ammonia concentrations of 3.000–3.500 mg/L, obtaining removal rates from 80 up to 98.5%. The mass transfer coefficients lay in the range of 12.4–37.0 × 10−3 m/h and were absolutely comparable to values reported by other authors.

The Application of Membrane Contactors for Ammonia Recovery from Pig Slurry

The Application of Membrane Contactors for Ammonia Recovery from Pig Slurry

Influence of membrane morphology on characteristics of porous hydrophobic PVDF hollow fiber contactors for CO2 stripping from water

Wetting resistance and gas permeability are the main factors for membrane contactor applications, which can be optimized according to the membrane morphology. In present study, three different types of the membrane morphology were obtained via a dry–wet spinning technique. By measuring cloud point data and viscosity, the polymer dope composition was adjusted to produce the different morphologies. The membranes with large finger-like, small finger-like and almost sponge-like morphology were obtained. The plain PVDF membrane with large finger-likes morphology presented the higher N2 permeance, lower wetting pressure and larger mean pore size (0.08μm). By addition of phosphoric acid into the spinning dope, the prepared sponge-like morphology resulted in the high surface porosity with small pore sizes, which demonstrated good permeability and wetting pressure. It was found that the mean pore size measured by gas permeation method was approximately three times larger than those from FESEM examination. CO2 stripping from water was conducted through the gas–liquid membrane contactors. The membranes with smaller pore sizes and higher wetting pressure presented higher stripping performance. In conclusion, a structurally developed PVDF hollow fiber membrane for gas–liquid contactor applications can be achieved by controlling the membrane morphology.

Novel chemical surface modification to enhance hydrophobicity of polyamide-imide (PAI) hollow fiber membranes

Membrane wetting is a major concern for the application of membrane contactors. In order to develop a novel hydrophobic membrane that can be used in membrane contactors, a hydrophobic surface modification method for Torlon ® polyamide-imide (PAI) membrane was explored, which has not been reported previously. Asymmetric microporous hollow fiber membranes were fabricated using PAI material followed by a simple surface modification using a silane coupling agent, 3-aminopropyltrimethoxysilane (APTMS), and a perfluro-compound (Fluorolink S10) to produce PAI hollow fiber membranes with a hydrophobic surface. The reactions between PAI and the modification reagents have been confirmed by experiments. Optimal modification conditions were investigated by varying the modification parameters, such as APTMS treatment temperature, APTMS concentration, APTMS treatment time, and Fluorolink S10 treatment time. The modified PAI membranes were, subsequently, characterized by a series of standard protocols in terms of membrane morphology, chemical structure, contact angle, porosity and critical water entry pressure. A preliminary study of using the modified membranes in a membrane contactor for CO 2 absorption was also carried out. The newly developed PAI hollow fiber membranes showed much higher hydrophobicity, the contact angle was improved from 76° to 108–117° and the critical water entry pressure was improved from 0.7–0.8 bar to 2.1–4.0 bar. Moreover, the modified PAI hollow fiber membranes showed reasonably high CO 2 flux by using water as a physical absorption liquid. The results indicate that the modified PAI membranes have great potential to be used in membrane contactor applications.

A dense membrane contactor for intensified CO 2 gas/liquid absorption in post-combustion capture

Membrane contactors based on microporous hydrophobic materials already offer remarkable performances for different separation applications at industrial scale, especially for gas–liquid mass transfer operations. Impressive process intensification effects can indeed be achieved in certain cases, due to the large interfacial area provided by hollow fiber membranes. Nevertheless, depending on the membrane and fluid properties, great differences in mass transfer can be obtained; undesirable effects due to liquid contact such as gradual changes in membrane structure and/or partial wetting of the pores can dramatically affect mass transfer performances. Numerous studies have addressed these difficulties for one of the most attracting and challenging application of membrane contactors: the absorption of CO 2 in a chemical solvent in order to achieve post-combustion CO 2 capture from flue gases. For this application, given the fast chemical reaction which takes place in the liquid phase, a highly permeable membrane material is absolutely necessary. Additionally, the membrane material has to withstand long term contact with a chemically reactive solvent (typically an amine such as monoethanolamine: MEA) and has to remain non wetted. A possible solution which prevents wetting problems together with a minimal impact on the membrane mass transfer coefficient is reported in this study; the key idea is to make use of a composite membrane based on a thin dense skin, based on a highly permeable glassy polymer, coated on a microporous support. In a first step, screening tests have been performed in order to identify potential polymer candidates for the thin skin, combining a high CO 2 permeability and solvent (MEA) compatibility on long time scales. In a second step, composite hollow fibers with a thin skin (Teflon AF ®, PTMSP) coated on a porous support (PP) have been prepared and tested. The concept has been finally tested and validated at lab scale for CO 2 capture from a gas mixture into aqueous solutions of MEA with hollow fiber modules. Remarkably, the overall mass transfer performances of the composite fibers compete with the most permeable microporous membranes classically proposed for membrane contactor applications. The possible use of these novel composite fibers for other applications and the extension of the concept to different industrial situations are discussed.

Novel Hollow Fiber Membrane Contactors Used in Waste Treatment

Novel membrane contactors offer a number of important advantages over conventional dispersed phase contactors, including absence of emulsions, no flooding at high flow rates, no unloading at low flow rates, no density difference between fluids required, and surprisingly high interfacial area. Based on the former work of our group, this paper provides a general review of recent progress in the application of hollow fiber membrane contactors in liquid/liquid and gas/liquid separation and in the environmental waste treatment including VOCs and CO2 separation, metal ion recovery, and alcohol purification.

Membrane contactors for the oxygen and pH control in desalination

The use of membrane contactors for the oxygen removal, as well as the pH control, in a reverse osmosis (RO) desalination plant was studied. Experimental tests were carried out in a lab set-up using a flat membrane module with 40 cm 2 of membrane area, by feeding in a counter-current mode the liquid and a gas stream of CO 2 or N 2. Several operating conditions were varied, such as temperature, streams flow rates and liquid composition. The liquid streams sent to the system were distilled water and synthetic solutions (prepared for simulating the reverse osmosis permeate and brine and the nanofiltration permeate). Four different hydrophobic membranes (PVDF, PVDF-treated, acrylic-based, and PTFE membranes) were characterized in terms of water uptake, CAM and SEM analysis, tested in the membrane contactor and, finally, compared. Based on the experimental results, the application of membrane contactors for the pH adjustment in the pre-treatment line of a desalination plant when coagulation is used, was considered as case study.

Application of hollow fiber membrane contactor for the removal of carbon dioxide from water under liquid–liquid extraction mode

In this study, we investigate the application of a hollow fiber membrane contactor operated in the LLE mode for the removal of dissolved CO 2 from water. The membrane contactor consists of hydrophobic polypropylene microporous hollow fibers. Experiments are performed to determine the extent of CO 2 removal from the feed water flowing through the lumens of the hollow fibers. The feed at different concentration levels of dissolved CO 2 was extracted using aqueous diethanolamine solution flowing on the shell side of the contactor. A mathematical model was developed, incorporating radial and axial diffusion of solute CO 2 in the lumen and its permeation through the pores of the membrane. The governing second order partial differential equation of species balance was numerically solved using the alternate direction implicit technique. The developed mathematical model was used to predict the concentration profiles of CO 2 and study its transport through water and membrane pores. The numerical value of the permeation coefficient obtained for CO 2 in the hollow fiber membrane was found to be in good agreement with the data in literature.

Effect of polyethylene glycol (PEG) as an additive on the fabrication of polyvinylidene fluoride- co-hexafluropropylene (PVDF-HFP) asymmetric microporous hollow fiber membranes

Polyvinylidene fluoride- co-hexafluropropylene (PVDF-HFP) has received much attention recently as a promising membrane material for membrane contactor application. A systematic study has been carried out to investigate the effects of polyethylene glycol (PEG) with different molecular weights and different loadings as an additive on the fabrication of PVDF-HFP asymmetric microporous hollow fiber membranes. Moreover, the synergetic effects of coagulation temperature and the second additive (lithium chloride: LiCl) with PEG are also evaluated. Experiments revealed that the addition of PEG into the PVDF-HFP/NMP solution resulted in the system thermodynamically less stable in reaction with water, promoting rapid phase demixing in the phase inversion process. When the same 3 wt% PEG was added into the dope solution, the dimension of finger-like macrovoids of the resultant membrane increased in parallel with the increase of PEG molecular weight from 200 to 600 and 6000 kDa, and pure water permeability (PWP) also increased accordingly. An increase in PWP was also observed when PEG-200 loading in the dope solution was increased from 3 to 5 and 10 wt%, corresponding to the morphology change of resultant membranes. As a synergetic effect of coagulation temperature with PEG, the finger-like pores occurred in the membrane at room temperature expanded to much larger macrovoids using 10 °C water as the coagulant, and the big finger-like pores almost disappeared when the coagulation bath temperature was increased to 40 °C because of delayed phase demixing. The big macrovoid size can also be suppressed by adding the second small molecule additive, LiCl, due to its strong interactions with NMP and PVDF-HFP to delay the dope precipitation. The irregular inner contour of the membrane can be eliminated by the increase of coagulation bath temperature to 40 °C. The hollow fiber membrane made by a dope of PVDF-HFP/PEG-6000/LiCl/NMP (15/3/3/79 in weight) using 40 °C water as the coagulant exhibited a high PWP of 117 L/m 2 h atm and reasonably good MWCO of 150 kDa. An improvement has been made in the current work as compared to previous PVDF-HFP hollow fiber membranes reported in literatures.

High-performance catalytic wet air oxidation (CWAO) of organic acids and phenol in interfacial catalytic membrane contactors under optimized wetting conditions

This paper is intended to evaluate the effect of membrane wetting on the performance of interfacial catalytic membrane contactors applied to the wet air oxidation of organic pollutants. To this aim, two wetting methods (i.e. by capillarity at ambient pressure and under dynamic vacuum) have been used prior to the oxidation tests. A series of monometallic and bi/trimetallic catalytic membranes have been prepared and tested using both wetting methods for the oxidation of formic, acetic and oxalic acids as model pollutants. In these experiments, the solution with the target pollutant was pumped along the contactor on the catalytic layer side, while air or pure oxygen was pumped along the other side. The gas/liquid interface was located within the membrane wall by means of a transmembrane pressure compensating capillary forces. In all cases, higher catalytic activites have been obtained after wetting the membranes under dynamic vacuum. On the basis of the coarse-grained nature of the membranes, wetting under vacuum might help removing air blocked in larger sized pores and cavities, allowing therefore a more accurate control of the position of the confined gas–liquid interface by the transmembrane pressure. Using optimized wetting conditions, we show promising results on the application of interfacial catalytic membrane contactors to the oxidation of phenol at room temperature and air overpressures in the range 1–4 bar.

Highly porous and macrovoid-free PVDF hollow fiber membranes for membrane distillation by a solvent-dope solution co-extrusion approach

Highly porous and macrovoid-free PVDF hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux and long term stability of the process. For the first time in this paper, porous PVDF hollow fiber membranes with high outer surface porosity were fabricated by applying a two-phase flow consisting of a solvent and a dope solution in the air-gap region of spinning through a non-solvent induced phase separation process (NIPS). In this approach, the dope solution and the N-methylpyrrolidone (NMP) solvent were co-discharged from the middle and outer channels of a triple orifice spinneret, respectively. Then, the two-phase flow went through an air-gap region and finally entered the coagulation bath. It was observed that the introduction of the two-phase flow greatly increased the outer surface porosity of the PVDF fibers and eliminated the formation of macrovoids in the cross-section of the fibers as well. It was also found that the energy efficiency and the flux of the fibers spun through the solvent-dope solution co-exterusion were two to three times higher than the standard dry jet wet-spun fibers. A water vapor flux as high as 67 kg/(m 2 h) at 80 °C was obtained through the newly spun fibers.

Membrane contactor applications

In a membrane contactor the membrane separation is completely integrated with an extraction or absorption operation in order to exploit the benefits of both technologies fully. Membrane contactor applications that have been developed can be found in both water and gas treatment. Several recently developed applications that have been introduced in industry — selective removal of heavy metals from a galvanic process bath, organic component recovery from a process water in chemical industry and ammonia recovery from an off gas stream — will be discussed technically and economically to show the wide scope of the technology.

Hollow fiber membrane contactor for air humidity control: Modules and membranes

The application of membrane contactors in air humidity control offers advantages over the conventional treatment methods, e.g. dew pointing by cooling (high energy consumption) and direct absorption (risk of air contamination by the absorbent). In gas/liquid membrane contactors the applied absorption liquid is separated from the feed air by a liquid tight but water vapor permeable membrane. Air and absorption liquid can be operated independently of each other and large and well-defined contact areas are provided. In the present work the properties of transversal flow modules were investigated with respect to the air side pressure drop and the water vapor transport. In order to realize a reliable prevention of leakage in long-term operation composite membranes with a thin but dense layer of PDMS were applied. Main subject of this work was the investigation of coated polyetherimide hollow fiber membranes with respect to the water vapor permeance. The measurements were carried out under actual contactor conditions using prototype modules and LiCl as liquid absorbent. The influence of both the support membranes and the coating layer as well were determined. It was shown that the negative effect of the coating on the permeance could be restricted to a permeance loss of about 20% by applying a very thin coating layer. With composite membranes based on highly asymmetric support membranes water vapor permeances up to 0.64 g m −2 h −1 Pa −1 could be realized.

Modelling of cross-flow membrane contactors: Mass transfer with chemical reactions

Conventionally, carbon dioxide and hydrogen sulphide are absorbed using aqueous alkanolamines or carbonate solution in column type of equipment. However, in view of the unparallel advantages offered, the use of microporous hollow fiber membrane modules is an attractive alternative. In the present study application of cross-flow membrane contactors for absorption of these gases using aqueous potassium carbonate as a solvent is explored. The carbon dioxide and hydrogen sulphide absorption into aqueous solutions carbonate involves complex chemical reactions. The effect of these chemical reactions on the absorption into a liquid flowing though a hollow fiber membrane may not be described using conventional mass transfer models like e.g. the penetration or surface renewal model due to the lack of a well defined liquid phase bulk and the presence of a laminar velocity profile in the mass transfer zone. Moreover, in the case of cross-flow membrane contactors, the concentrations of both fluids, inside and outside the fibers, vary in both directions i.e. in the direction of flow and in the direction normal to the flow. Hence the theoretical analysis of the cross-flow membrane contactor is more complicated. To describe the effect of the chemical reaction on the absorption rate in the cross-flow hollow fiber contactor, a detailed mathematical model was developed using first principles. A complete scheme of the reversible ionic reactions and equilibria involved was implemented in the model to describe the solute uptake. The experiments were carried out study the effects various parameters such as gas and liquid velocities, bulk concentrations of solute gas and liquid phase reactant. The theoretical predictions were compared with experimental results. An excellent match between experimental results and model predictions was obtained.

Membrane Contactors in Industrial Applications

In a membrane contactor the membrane separation is completely integrated with a conventional phase contacting operation like extraction or absorption. In this way the benefits of both technologies can be fully exploited. The membrane contactor technology is a new technology. The first full scale membrane contactor installations that have been installed in industry are running successfully for some years now. Industrial applications of membrane contactors, including aromatics recovery from a process water, selective removal of heavy metals from a galvanic process bath and ammonia product recovery from an off gas stream, are discussed. Membrane contactors are of interest for the chemical, petrochemical, pharmaceutical and galvanic industry for both water and gas treatment as end of pipe technology but also for product recovery and as integrated process solution. New applications under development—CO2 membrane gas absorption and pertraction for produced water treatment—are discussed technically and economically to show the wide scope of the technology.

Application of hollow fiber membrane contactors for catalyst recovery in the WPO process.

In this work the use of a membrane based liquid extraction process for recovery of the homogeneous catalyst employed in the wet peroxide oxidation process (WPO) is studied. In the WPO process the oxidation agent is the hydroxyl radical that is obtained by using a combination of hydrogen peroxide and a mixture of Fe(II), Cu(II), and Mn(II) in aqueous solution. The mixture of metallic cations permits the almost total degradation of the refractory organic compounds, but the use of metallic salts as catalysts induces additional pollution. To recover the homogeneous catalyst of the WPO process by means of non-dispersive solvent extraction (NDSX) two hollow fiber membrane contactors are employed, one for the extraction step and the second for the back-extraction step. From the initial assays, the extractant LIX 622N was selected for Cu(II) recovery and Cyanex 272 for Fe(II) and Mn(II) recovery. Selective separation of Fe(II) and Mn(II) can be obtained by adjusting the pH of the feed aqueous phase. The three metals are stripped using sulfuric acid to give concentrated solutions of CuSO(4), FeSO(4), and MnSO(4) that can be recycled to the formulation of the catalyst solution of the WPO process. A mathematical model has been proposed to describe the recovery of Cu. Two design parameters are required: the membrane mass transport coefficient of the extraction and stripping modules (k(m) = 3.07 x 10(-7) m/sec) and the equilibrium parameter of the extraction reaction (K(Ex) = 0.0832).

Application of large-scale hollow fiber membrane contactors for simultaneous extractive removal and stripping of penicillin G

Experimental and theoretical studies on simultaneous extractive removal and stripping of penicillin G using two large-scale hollow fiber membrane contactors are performed. The influence of main concentration parameters (penicillin in the aqueous phase and amine-extractant in the organic phase) on the kinetics of the complex mass-transfer process (extraction/stripping) is examined. A mass-transfer model is developed in which both diffusional processes and chemical reactions in the extraction and stripping modules are taking into consideration. The individual and overall mass-transfer coefficients in both modules are determined and compared. The overall mass-transfer coefficient K F in the extraction module is found to be an order of magnitude higher than the corresponding value K R in the stripping module. The rate-controlling step(s) in each module separately and in combination are identified. It is shown that the simultaneous extraction/stripping is limited by the rate of the reverse chemical reaction (at higher penicillin concentration and lower amine concentration) or by the diffusion of the complex through the membrane in the second module (at higher carrier concentration), or combination of both rates of chemical reaction and membrane diffusion. The fractional diffusional resistances of the penicillin/extractant complex in the bulk organic solution are relatively small at all the conditions examined and in both modules. Conclusions are drawn how this process could be optimized.

The membrane contactor: Environmental applications and possibilities

AbstractIn a membrane contactor, separation is fully integrated with another separation technology, such as extraction or absorption, in order to fully exploit the benefits of both technologies. Membrane contactor applications can be found in both water and gas treatment. Several recently developed industrial applications—aromatics recovery from a process water, selective removal of heavy metals from a galvanic process bath, and ammonia recovery from an off gas stream—will be discussed from both technical and economic perspectives to show the wide scope of the technology.

Large-scale application of membrane contactors for gas transfer from or to ultrapure water

Removal or addition of dissolved gases from or to water or aqueous solutions can be accomplished very effectively using hollow fiber membrane contactors. Well-designed contactors, where water flow outside of the hollow fibers is directed transversely across banks of hollow fibers, exhibit significantly enhanced mass transfer coefficients and low pressure drop. The principle of operation, the features of the `transverse-flow' design, and the mass transfer issues in such devices are discussed. The performance of membrane contactors and systems in degassing applications is presented. The predictability and the relative ease of scale-up of such membrane products are highlighted.

Novel application of membrane contactors: solubility measurements of 1-hexene in solvents containing silver ions for liquid olefin/paraffin separations

A new method for measuring the solubility of liquid olefins in solvents containing silver ions has been proposed and tested. The method includes the use of a stationary membrane contactor containing PDMS-based polymeric membranes. Silver-ion-free solvents that have been selected for experiments (e.g., ethylene glycol and 1,3-propanediol) and which are essentially immiscible with olefins are able to dissolve silver nitrate, making it possible for them to absorb olefins due to reversible complexation of silver ions with unsaturated olefinic double bonds. The use of polymeric membranes between the two liquid phases (e.g., olefins and solvents) simplifies the solubility measurement procedure since membranes act as a semipermeable barrier between olefins and solvents. In this study the enthalpy (ΔH 0) for the complex formation reaction between 1-hexene and silver nitrate in ethylene glycol and 1,3-propanediol was estimated. It was shown that 1,3-propanediol containing silver nitrate has greater sorption capacity for 1-hexene than ethylene glycol.