Membrane-based air dehumidification:A comparative review on membrane contactors,separative membranes and adsorptive membranes

This review compares the different types of membrane processes for air dehumidification.Three main categories of membrane-based dehumidification are identified–membrane contactors using porous membranes with concentrated liquid desiccants,separative membranes using dense membrane morphology with a pressure gradient to drive the separation of moisture from air,and adsorptive membranes using nanofibrous membranes which adsorb and capture moisture to realise dehumidification.Drawing upon the importance of dehumidification and humidity control for urban sustainability and energy efficacy,this review critically analyses and recognizes the three unique categories of membrane-based air dehumidification technologies.Essentially,the discussion is broken into three sections-one for each category-discriminating in terms of the driving force,membrane structure and properties,and its performance indicators.Readers will notice that despite having the same objective to dehumidify air,the polymers used amongst each category differs to suit the operating requirements and optimize dehumidification performance.At the end of each section,a performance table or summary of dehumidifying membranes in its class is provided.The final section concludes with a comparative review of the three categories on membrane-based air dehumidification technologies and draw inspiration from parallel research to rationalise the potential and innovative use of promising materials in membrane fabrication for air dehumidification.

Mass transfer correlations for membrane gas-solvent contactors undergoing carbon dioxide desorption

Membrane gas-solvent contactors are a hybrid technology combining solvent absorption with membrane gas separation, which demonstrates potential for CO_2 capture through the ability of the membrane to rigidly control the mass transfer area. Membrane contactors have been successfully demonstrated for CO_2 absorption, and there is strong research interest in using membrane contactors for the complimentary CO_2 desorption process to regenerate the solvent. However, understanding and modelling the various stages of mass transfer in the desorption process is less well-known, given the existing mass transfer correlations had been developed from absorption experiments. Hence, mass transfer correlations for membrane contactors are reviewed here, and their appropriateness for desorption analysed. This is achieved through simulating CO_2 desorption through a membrane contactor from loaded 30 wt% monoethanolamine solvent to enable comparison of the correlations. It was found that the most cited correlations by Yang and Cussler were valid for shell side parallel flow, while that of Kreith and Black was viable for shell side cross flow. A limitation of all of these correlations is that they assume single phase flow on both sides of the membrane; however, the high temperature of CO_2 desorption can lead to partial solvent vaporisation and hence two phases present on one side of the membrane contactor during desorption. A mass transfer correlation is established here for two phase parallel flow on the shell side of a membrane contactor, based on experimental results for three composite and one asymmetric hollow fibre membrane contactors stripping CO_2 from loaded MEA at 105–108 °C. This correlation is comparable to that reported in the literature for mass transfer in other two phase systems, but differs from the standard format for membrane contactors in terms of the exponent on the dimensionless Schmidt and Reynolds numbers.

CO_(2) capture using membrane contactors:a systematic literature review

With fossil fuel being the major source of energy,CO_(2) emission levels need to be reduced to a minimal amount namely from anthropogenic sources.Energy consumption is expected to rise by 48%in the next 30 years,and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis.Nonetheless,exploring CO_(2) capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post-and pre-combustion of CO_(2).A systematic review of the literature has been conducted to analyse and assess CO_(2) removal using membrane contactors for capturing techniques in industrial processes.The review began with a total of 2650 papers,which were obtained from three major databases,and then were excluded down to a final number of 525 papers following a defined set of criteria.The results showed that the use of hollow fibre membranes have demonstrated popularity,as well as the use of amine solvents for CO_(2) removal.This current systematic review in CO_(2) removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work.This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO_(2).

Effect of polytetrafluoroethylene hollow fiber microstructure on formaldehyde carbonylation performance in membrane contactor

Membrane contactor is regarded as a promising method for reaction and process intensification. The feasibility of formaldehyde carbonylation to synthesize glycolic acid using polytetrafluoroethylene(PTFE)membrane contactor has been proved in our previous study. In this paper, the effect of membrane microstructure on process performance was further investigated. Three porous PTFE hollow fibers with different pore sizes and one polydimethylsiloxane(PDMS)/PTFE composite membrane with dense layer were fabricated for comparison. The physical and chemical properties of four membranes, including chemical composition, morphology, contact angle, liquid entry pressure, thermodynamic analysis and gas permeability, were systemically characterized. Experiments of formaldehyde carbonylation under different reaction conditions were conducted. The results indicated that the yield of glycolic acid increased with decreasing pore size for porous membranes, which was due to the improvement of wetting behavior. The dense layer of PDMS in composite hollow fiber could effectively prevent the solvent from entering membrane pores, thus the membrane exhibited the best performance. At reaction temperature of 120℃ and operation pressure of 3.0 MPa, the yield of glycolic acid was always higher than 90% as the mass ratio of trioxane and phosphotungstic acid increased from 0.2:1 to 0.8:1. The highest turnover frequency was up to 26.37 mol·g^(-1)·h^(-1). This study provided a reference for the understanding and optimization of membrane contactors for the synthesis of glycolic acid using solvent with low surface tension.

Reduction of VOC emissions by a membrane-based gas absorption process

A membrane-based gas absorption （MGA） process was evaluated for the removal of volatile organic compounds （VOCs） based on C6H6/N2 mixture. The absorption of C6H6 from a C6H6/N2 mixture was investigated using a hydrophobic polypropylene hollow fiber membrane contactor and the aqueous solution of N-formyl morpholine （NFM） as absorbent. The effects of various factors on the overall mass transfer coefficient was investigated. The experimental results showed that the removal efficiency of C6H6 could reach 99.5% in present studied system. A mathematical model based on resistance-in-series concept was presented to predict the value of overall mass transfer coefficient. The average error between the predicted and experimental values is 7.9%. In addition, conventional packed columns for VOCs removal was also evaluated for comparison.

Progress involving new techniques for liposome preparation

The article presents a review of new techniques being used for the preparation of liposomes.A total of 28 publications were examined.In addition to the theories,characteristics and problems associated with traditional methods,the advantages and drawbacks of the latest techniques were reviewed.In the light of developments in many relevant areas,a variety of new techniques are being used for liposome preparation and each of these new technique has particular advantages over conventional preparation methods.However,there are still some problems associated with these new techniques that could hinder their applications and further improvements are needed.Generally speaking,due to the introduction of these latest techniques,liposome preparation is now an improved procedure.These applications promote not only advances in liposome research but also the methods for their production on an industrial scale.

Hydrodynamic characteristics of 30%TBP/kerosene-HNO3 solution system in an annular centrifugal contactor

Annular centrifugal contactors (ACCs) have many advantages and are recognized as key solvent-extraction equipment for the future reprocessing of spent nuclear fuel (RSNF). To successfully design and operate ACCs for RSNF, it is necessary to understand the hydrodynamic characteristics of the extraction systems in ACCs. The phase ratio (R = Vaq/Vorg, A/O) and liquid holdup volume (V) of the ACC are important hydrodynamic characteristics. In this study, a liquid-fast-separation method was used to systematically investigate the effects of the operational and structural parameters on the V and R (A/O) of a φ20 ACC by using a 30%TBP/kerosene- HNO3 solution system. The results showed that the operational and structural parameters had different effects on the V and R (A/O) of the mixing and separating zones of the ACC, respectively. For the most frequently used structural parameters of the φ20 ACC, when the rotor speed was 3500 r/min, the total flow rate was 2.0 L/h, and the flow ratio (A/O) was 1, the liquid holdup volumes in the mixing zone and rotor were 8.03 and 14.0 mL, respectively, and the phase ratios (A/O) of the mixing zone and separating zone were 0.96 and 1.43, respectively.

L-LACTIC ACID FERMENTATION IN A ROTATING-DISC CONTACTOR WITH SIMULTANEOUS PRODUCT SEPARATION BY ION-EXCHANGE

A rotating disk contactor（RDC）was designed to perform L-lactic acid fermentation with afilamentous fungi,Rhizopus oryzae,which was immobilized on the surfaces of the rotating discs.Thebioreactor was operated using repeated-batch method as well as continuous feeding method.Ananionic resin,D354,slightly basic in nature and of high selectivity and capacity was chosen for lacticacid separation.A coupled process of L-lactic acid fermentation and ion-exchange separation wasevaluated experimentally.The results indicated that the pH value of the fermentation broth could bemaintained at about 3-3.5 without any addition of alkali.The conversion ratio of glucose to L-lacticacid was about 0.7 g·g-1 and the fermentation rate reached as high as 62.5 g·h-1·m-2.

Modelling of a tubular membrane contactor for pre-combustion CO_2 capture using ionic liquids:Influence of the membrane configuration, absorbent properties and operation parameters

A membrane contactor using ionic liquids(ILs) as solvent for pre-combustion capture CO_2 at elevated temperature(303-393 K) and pressure(20 bar) has been studied using mathematic model in the present work. A comprehensive two-dimensional(2 D) mass-transfer model was developed based on finite element method. The effects of liquid properties, membrane configurations, as well as operation parameters on the CO_2 removal efficiency were systematically studied. The simulation results show that CO_2 can be effectively removed in this process. In addition, it is found that the liquid phase mass transfer dominated the overall mass transfer. Membranes with high porosity and small thickness could apparently reduce the membrane resistance and thus increase the separation efficiency. On the other hand, the membrane diameter and membrane length have a relatively small influence on separation performance within the operation range.

Discharge instability in a plasma contactor

Like the hollow cathode,discharge instability also occurs during the operation of a plasma contactor.Voltage and current probes were employed to test the change of keeper voltage,keeper current,anode voltage,and anode current parameters with time under different working conditions.The anode current range corresponding to the discharge instability phenomenon is about 0.4 A to 1.2 A,and the emission characteristic curve in this area appears to bulge wherein the four parameters all produce different degrees of oscillation,the anode current oscillation being the greatest.Its waveform is considered to consist of a small-amplitude,high-frequency triangular wave and a large-amplitude,low-frequency sawtooth wave,and we have explained the shape of the wave.Each parameter shows hundreds of Hz in oscillation frequency and the phases of the four parameters appear to be regular.After fast Fourier transform processing,the frequency and amplitude of the main peak of the anode current oscillation tend to change with changes of the anode current,and there are differences in the trends under different keeper currents and xenon flows.

HYDRODYNAMICS AND AXIAL MIXING OF LIQUIDSOLID SYSTEM IN OPEN TURBINE ROTATING DISC CONTACTOR

The open turbine rotating disc contactor (OTRDC) has been installed simply by adding three narrow strips to the lower surface of each rotating disc in the rotating disc contactor (RDC), so it can be used for the system with high solid particle content. Hydrodynamics and axial mixing have been investigated in a 0.152m diameter OTRDC of different compartment height for the system of tap water and quartz particles. A model has been developed to describe the flow of liquid and solid phases. The solid phase holdup can be calculated satisfactorily according to the model equations. Axial mixing data have been treated by the backflow model and the correlations for predicting backflow ratios of liquid and solid phases in OTRDC have been presented.

RESISTANCE OF IMPINGING STREAM CONTACTOR TO SOLID-AIR SUSPENSION FLOW

1 INTRODUCTIONAs mentioned in our previous paper impinging stream contactor(ISC)is aninnovative device for phase contact operations and has proved itself capable to en-hance transfer processes in heterogeneous systems effectively,and thus is of poten-tial application in many chemical engineering processes,such as drying of solidparticles,solid-solid,liquid-liquid and gas-gas mixing,absorption and desorptionof gases into or from liquids with or without chemical reactions,combustion

Petroleum waste biodegradation with porous biomass support system (PBSS) on rotating biological contactor

A laboratory scale study was conducted to assess the feasibility of the new coupling of rotating biological contactor (RBC) plus porous biomass support system (PBSS) using polyurethane foam as porous support media to biodegrade petroleum refinery wastewater. Polyurethane foam was attached on disks of two four-stage laboratory scale cascade connected RBC units.The two RBC units were operated simultaneously at different but constant, flowrates giving hydraulic loading rates of 0.01, 0.02, 0.03, 0.04 m3/m2/d in two runs keeping the same rotational speed 10 r/min throughout. Organic loading was a less controllable factor in this study.For all of the hydraulic loadings, it was found that the removal efficiency of total chemical oxygen demand (TCOD) and oil were above 80 percent. Ammonia nitrogen and phenol removal were above 90 and 80 percent respectively. The maximum biomass concentration within polyurethane foam was about 30 g/m2 in the first stage for 0.03 m3/m2/d hydraulic loading.The results show that this new technology can be applied effectively for practical purposes with moderate hydraulic loading rates.

Design and Application of a MCU-based Smart Contactor System

This paper aims to design a MCU-based smart contactor system, which will realize functions of real time surveillance of contactors’ work status and data exchange with host computer, thus instantly reflect different status of the system. In case of abnormal status such as over-current or under-voltage, the contactor will be able to automatically cut off power supply to protect electrical load and the circuit. Through ARINC485 bus, system computer will collect and record contactor parameters, including contact voltage, contact current, supply frequency, contact temperature and contact status to provide critical data to the examination and repair of contactors.

Pilot plants of membrane technology in industry:Challenges and key learnings

Membrane technology holds great potential in gas separation applications,especially carbon dioxide capture from industrial processes.To achieve this potential,the outputs from global research endeavours into membrane technologies must be trialled in industrial processes,which requires membrane-based pilot plants.These pilot plants are critical to the commercialization of membrane technology,be it as gas separation membranes or membrane gas-solvent contactors,as failure at the pilot plant level may delay the development of the technology for decades.Here,the author reports on his experience of operating membrane-based pilot plants for gas separation and contactor configurations as part of three industrial carbon capture initiatives:the Mulgrave project,H3 project and Vales Point project.Specifically,the challenges of developing and operating membrane pilot plants are presented,as well as the key learnings on how to successfully manage membrane pilot plants to achieve desired performance outcomes.The purpose is to assist membrane technologists in the carbon capture field to achieve successful outcomes for their technology innovations.

Fabrication and characterization of affordable hydrophobic ceramic hollow fibre membrane for contacting processes

Affordable hydrophobic hollow fibre membranes were prepared using kaolin and alumina based ceramic powders via a combined phase inversion and sintering technique,followed by a grafting with fluoroalkylsilane(FAS).The crux of the matter in this paper is to study the changes in the properties of the hollow fibre membranes(gas permeation,mechanical strength,pore size,porosity,tortuosity,morphology,and contact angle)by the addition of alumina(Al2O3)to the pure kaolin with mono or multiparticle sizes.By varying the overall loading and particle size of alumina addition,different morphologies of the membranes were obtained due to the differences in the path lengths during phase inversion process for each solvent and nonsolvent exchange.The successful grafting with FAS was evidenced by the increase in contact angle from nearly equal to zero degree before grafting to 140°after grafting.Kaolin-alumina-4,one of the hollow fibres fabricated in this work,achieved a mean pore size of 0.25μm with the bending strength of 96.4 MPa and high nitrogen permeance of 2.3×10^(-5) mol·m^(-2)·Pa^(-1)·s^(-1),which makes the hollow fibre most suitable for the membrane contactor application.

Diagnostic and modelling investigation on the ion acceleration and plasma throttling effects in a dualemitter hollow cathode micro-thruster

Hollow cathode discharges are widely used as neutralizers for the electric propulsion systems and recently developed into micro-thrusters for the small satellites.In this work,a dualemitter hollow cathode thruster is developed,which can be operated in two different modes—the neutralizer mode and the micro-thruster mode.For characterizing this kind of new device,the Langmuir probe,Faraday probe,and retarding potential analyzer are used to determine the electron temperature,electron density,ion flux,and ion energy distribution function.The operating parameters,including the thrust,and specific impulse,are also measured.A two-dimensional self-consistent extended fluid model is employed to calculate the spatial distribution of plasma parameters and the fluid field of electrons in the region around the emitters.By comparing the diagnostic and modelling results,it is found that the change in the electric field and ionization zone is the essential reason for the different performances of the device in the neutralizer and micro-thruster modes.Variation in the electric field leads to an ion acceleration effect in the micro-thruster mode;moving of the ionization zone raises the plasma pressure in the orifice region of the hollow cathode,and thus leads to enhanced plasma throttling and gas expanding effects.By analyzing the above mechanisms,the possible methods for improving this kind of hollow cathode micro-thruster are discussed.

Solvent-resistant porous membranes using poly(ether−ether ketone): preparation and application

Poly(ether−ether ketone)(PEEK)is a linear aromatic macromolecule,which can form semi-crystalline aggregative status,allowing PEEK materials to have strong environment tolerance and excellent physicochemical properties.PEEK materials have become a promising alternative to fabricate particular membranes used in extreme conditions.In the past few decades,many researches and evolutions have emerged in membrane fabrication with PEEK materials and its applications for treating organic solvents and their mixtures;however,there are little systematic and comprehensive literature to summarize fabrication approaches,compile applications,and elaborate PEEK property-structure relationship.In this review,the main approaches to fabricate PEEK-based membranes are illustrated concretely,including conventional thermal-induced and non-solvent-induced phase separation,and novel chemical-induced crystallization;the representative applications in ultrafiltration,nanofiltration and membrane contactor containing organic solvents are demonstrated systematically.Meanwhile,the mechanism to tune PEEK solubility in solvents,which can be achieved by altering monomers in synthesis processes or changing membrane preparation routes,is deeply analyzed.Moreover,the existing problems and the future prospects are also discussed.This review provides positive guidance for designing and fabricating membranes using PEEK and its derivative materials for task-specific applications in harsh conditions.

Catalytic bubble-free hydrogenation reduction of azo dye by porous membranes loaded with palladium nanoparticles

Catalytic bubble-free hydrogenation reduction of azo dye by porous membranes loaded with palladium （Pd） nanoparticles was studied for the first time. The effects of Pd loading, dye concentration and reuse repetitions of membranes were investigated. In reduction, the dye concentration decreased whereas the pH rose gradually. An optimal Pd loading was found. The catalytic membranes were able to be reused more than 3 times.

Electrospinning in membrane contactor:manufacturing Elec-PVDF/SiO2 superhydrophobic surface for efficient flue gas desulphurization applications

In membrane contactors,maintaining a high SO_(2)absorption flux and an excellent wetting resistance are crucial for hazardous gas removal.In this study,we adopted an electrospinning strategy to fabricate highly robust superhydrophobic dual-layer Elec-PVDF/SiO_(2)composite membrane contactors used for flue gas desulfurization.The composite membrane contactor consisted of a durable and ultrathin three-dimensional(3D)superhydrophobic surface and a porous supporting layer,where the formulation was optimized by regulating the PVDF concentration,solvent ratio and SiO_(2)particles content in electrospinning solution.The scanning electronic microscopy(SEM),EDS-mapping,water contact angle(WCA)and surface roughness of as-prepared Elec-PVDF/SiO_(2)composite membrane contactors were conducted to explore the physical and chemical structure.The SiO_(2)nanoparticles were uniformly loaded in ElecPVDF/SiO_(2)composite membrane contactor,and constructed micro-nano dual-coarse lotus-leaf-like morphology,which noticeably elevated surface roughness(Ra).The SiO_(2)nanoparticles also functioned as hydrophobic modifiers,which boosted the WAC up to 155.The SO_(2)absorption fluxes and SO_(2)removal efficiencies were investigated.In particular,the membrane contactor doped with 20 wt%SiO_(2)nanoparticles significantly elevated the stability of desulfurization performance.Besides,the membrane mass transfer coefficient(Km)and corresponding membrane mass transfer resistance(H/Km)were explored.