Metal oxide solubility behavior in high temperature aqueous solutions

The solubility behavior of metal oxides in sub- and super-critical aqueous solutions is quantified using thermodynamic concepts. Three physicochemical phenomena are discussed: (1) metal oxide solid phase stability; (2) metal oxide dissolution reaction equilibria; and (3) metal ion hydroxocomplex formation. Thermochemical properties of metal oxides/ions representative of the most common constituents of construction metal alloys, i.e., elements having atomic numbers between 22 (Ti) and 30 (Zn), are summarized on the basis of metal oxide solubility studies conducted at General Electric and elsewhere.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Resistance in series model for micellar enhanced ultrafiltration of eosin dye

A study has been performed to quantify the extent of flux decline during micellar enhanced ultrafiltration (MEUF) of an acid dye (eosin red) using hexadecyl (cetyl) pyridinium chloride as the cationic surfactant. Effects of the operating conditions, e.g., transmembrane pressure drop and feed-surfactant-to-dye ratio, on the permeate flux profile and observed retention have been investigated in an unstirred batch ultrafiltration (UF) cell. A simple resistance-in-series model has been used to quantify the flux decline. From the flux decline history, it has been found that the membrane permeability decreases rapidly due to reversible pore blocking and further flux decline is caused by the growth of a gel-type layer over the membrane surface. The different resistances and growth kinetics of the gel layer have been investigated as functions of the operating conditions.     

Quantitative measurements of the concentration polarisation layer thickness in membrane filtration of oil-water emulsions using NMR micro-imaging

In this paper we report measurements of the thickness of the concentration polarisation layers formed during crossflow membrane filtration of an oil-water emulsion. The formation and development of the oil polarisation layers was visualised non-invasively using NMR chemical shift selective micro-imaging. A series of images was acquired during the transient state of the filtration, (i.e. while the polarisation layer was forming and the flux of filtrate was changing), prior to the establishment of steady state conditions. An estimate of the specific resistance of the concentration polarisation layers was then obtained by determining the average oil layer thicknesses and concentration at a given time from the resulting images and measuring the corresponding (length averaged) flux of filtrate gravimetrically. After the establishment of steady state conditions, the dependence of the steady state filtrate flux on crossflow Reynolds number was found to be consistent with Brownian diffusion being the main mechanism controlling the build-up of the oil polarisation layers, at least under our range of operating conditions.     

Reduction and Elimination of Humic Acid Fouling in Air Sparged Membrane Distillation Using Nanocarbon Immobilized Membrane

In this paper, we present the treatment of humic acid solution via carbon nanotube immobilized membrane (CNIM) distillation assisted by air sparging (AS). Carbon nanotubes offer excellent hydrophobicity to the modified membrane surface and actively transport water vapor molecules through the membrane to generate higher vapor flux and better rejection of humic acid. The introduction of air sparging in the membrane distillation (MD) system has changed the humic substance fouling by changing the colloidal behavior of the deposits. This modified MD system can sustain a higher run time of separation and has enhanced the evaporation efficiency by 20% more than the regular membrane distillation. The air sparging has reduced the deposition by 30% in weight and offered lesser fouling of membrane surface even after a longer operating cycle. The water vapor flux increased with temperature and decreased as the volumetric concentrating factor (VCF) increased. The mass transfer coefficient was found to be the highest for the air sparged—carbon nanotube immobilized membrane (AS-CNIM) integrated membrane distillation. While the highest change in mass transfer coefficient (MTC) was found for polytetrafluoroethylene (PTFE) membrane with air sparging at 70 °C.     

聚偏氟乙烯微孔膜处理含铬(Ⅲ)水溶液的研究

采用自制聚偏氟乙烯（ＰＶＤＦ）微膜和商品ＰＶＤＦ膜对含铬（Ⅱ）水溶液进行了减压膜蒸馏分离实验研究。结果表明,两种膜的膜通量相接近,商品对铬的截留率达９０％以上,了膜性能参数和实验条件对膜通量和截留率的影响。     

Chemical cleaning of oil contaminated polyethylene hollow fiber microfiltration membranes

The primary aim of this paper was to develop a more effective and economical procedure for cleaning polyethylene hollow fiber microfiltration membranes that have been used for removing oil from contaminated seawater. Alkaline cleaning showed higher recovery of operating cycle time but lower permeate flux recovery than acid cleaning. The combination of both alkaline and acid cleaning agents gave the best operating cycle time and flux recoveries (e.g. 96% and 94%, respectively). As the cleaning agent soaking time was reduced, the actual operating cycle time was reduced. However, the ratio of operating time/chemical cleaning time increased as the soaking time was reduced. The soaking time was recommended to be as short as possible (8–10 h) in the design of small capacity plants and 30 h or higher in case of large capacity plants. SEM analysis showed that in case of alkaline cleaning, most of the pores remained covered with a foulant layer, resulting in low flux recovery. The SEM results of acid cleaned membranes showed more complete removal of the foulant layer from the pores resulting in better flux recovery. Surface analysis of membranes cleaned with combined acid/base agents showed the best results. A membrane surface similar to the original one was obtained. The long-term objective is to increase the understanding of membrane fouling phenomena, preventive means and membrane cleaning processes as it applies to the clean-up and desalination of oil contaminated seawater.     

Radial Basis Function Neural Networks-Based Modeling of the Membrane Separation Process： Hydrogen Recovery from Refinery Gases

Membrane technology has found wide applications in the petrochemical industry, mainly in the purification and recovery of the hydrogen resources. Accurate prediction of the membrane separation performance plays an important role in carrying out advanced process control (APC). For the first time, a soft-sensor model for the membrane separation process has been established based on the radial basis function (RBF) neural networks. The main performance parameters, i.e, permeate hydrogen concentration, permeate gas flux, and residue hydrogen concentration, are estimated quantitatively by measuring the operating temperature, feed-side pressure, permeate-side pressure, residue-side pressure, feed-gas flux, and feed-hydrogen concentration excluding flow structure, membrane parameters, and other compositions. The predicted results can gain the desired effects. The effectiveness of this novel approach lays a foundation for integrating control technology and optimizing the operation of the gas membrane separation process.     

Change in molecular weight retention curves of ultrafiltration membranes with respect to lignosulfonates under gel formation conditions

The paper considers ultrafiltration of lignosulfonates (LS) under predominantly the gel formation conditions. An effort is to determine the molecular weight retention (MWR) curves of a series of ultrafiltration membranes differing in their pore size under in turn different operating pressures (1–32 bar). The initial separative properties (both retentivity and volume flux) of all membranes are shown to change because of gel formation occurring actually instantly as a cake layer placed mostly onto the membrane surface. The transmembrane pressure-drop sets up primarily these properties but the initial hydrodynamic permeability coefficient of a membrane (i.e. its mean pore size) is also of concern. As a result, an increase in that pressure results in a shift of the molecular weight retention curves of all membranes under study towards lower molecular weights: the more, the higher their mean pore size. Further, these curves become more abrupt in their form, and such a change depends on the mean pore size of a membrane as well.     

Influence of operating conditions on performance of ceramic membrane used for water treatment

The removal of natural organic matter (NOM) is a critical aspect of potable water treatment because NOM compounds are precursors of harmful disinfection by-products, hence should be removed from water intended for human consumption. Ultrafiltration using ceramic membranes can be a suitable process for removal of natural substances. Previously reported experiments were dedicated to evaluating the suitability of ultrafiltration through ceramic membrane for water treatment with a focus on the separation of natural organic matter. The effects of the membrane operating time and linear flow velocity on transport and separation properties were also examined. The experiments, using a 7-channel 300 kDa MWCO ceramic membrane, were carried out with model solutions and surface water at trans-membrane pressure of 0.2–0.5 MPa. The results revealed that a loose UF ceramic membrane can successfully eliminate natural organic matter from water. The permeability of the membrane was strongly affected by the composition of the feed stream, i.e. the permeate flux decreased with an increase in the NOM concentration. The permeate flux also decreased over the period of the operation, while this parameter did not influence the effectiveness of separation, i.e. the removal of NOM. It was observed that the increased cross-flow velocity resulted in the decrease in the membrane-fouling intensity and slightly improved the retention of contaminants.     

The deformation of dextran molecules. Causes and consequences in ultrafiltration

The transfer of dextran T70 solutions through a skinned polysulfone hollow fiber membrane was studied with and without applied pressure. The molecular weight distributions of dextran in the feed and in the permeate were obtained by high pressure liquid chromatography. Two different phenomena appear to play important roles with regard to solute transfer. One is related to the shear stress imposed by the flow at the pore entrances, i.e. to permeate flux, and the other is related to the influence of solute concentration on the expansion of the macromolecular chains. These phenomena explain the observed variations with operating conditions of the overall rejection coefficient.     

Micellar enhanced ultrafiltration of phenolic derivatives from their mixtures

Micellar enhanced ultrafiltration (MEUF) of different phenolic derivatives including meta-nitrophenol (MNP), catechol (CC), para-nitrophenol (PNP), and beta-napthol (BN) in their binary mixture has been studied. A 1:1 ratio of the mixture of (i) MNP with CC and (ii) PNP with BN is taken for the MEUF experiments using a cationic surfactant, namely, cetyl(hexadecyl)pyridinium chloride (CPC). An organic polyamide membrane with molecular weight cutoff of 1000 is used. Experiments are conducted using an unstirred batch cell and a continuous cross-flow cell. The effects of various operating conditions, e.g., concentrations of surfactant and solute in the feed, transmembrane pressure drop, and cross-flow rate (for cross-flow experiments) on the permeate flux and the observed retention of each solute have been studied in detail. The retention of solutes without using the surfactant varies from 3 to 15% only at a typical feed solute concentration of 0.09 kg/m3, whereas, under the same operating pressure (345 kPa), retention at the end of the experiment increases to about 66 to 99.8% depending on the nature of solute in the batch cell using surfactant micelles (10 kg/m3). Retention of solutes is less in the case of the two-component feed solution compared to the single-component feed solution. An increase in flux to the range of 9 to 16% is realized in cross-flow experiments compared to batch cell flux after one hour of operation.     

Protein type effects on steady-state crossflow membrane ultrafiltration fluxes and protein transmission

The permeate fluxes and percent protein transmission were evaluated for steady-state crossflow ultrafiltration of two proteins of different composition: bovine serum albumin (BSA), containing fatty acid, and “fatty-acid-poor” BSA, from which most of the fatty acids had been removed (BSA/FAP). The influences of protein concentration up to 6.5 percent w/v, transmembrane pressure, ionic environment and membrane type (i.e. nominal molecular weight cut-off) were investigated. For both BSA and BSA/FAP, the fluxes and the protein transmission were dependent on the amount of salt present. The higher fatty acid content in the BSA apparently enhanced protein-protein interaction, resulting in a more cohesive and resistant fouling layer; permeate fluxes were lower with BSA/FAP than with BSA at otherwise corresponding operating conditions. A hysteresis behaviour of the flux (J)-transmembrane pressure (TMP) relationship was observed whenever the ultrafiltration unit was operated at a TMP less than some higher value to which the membrane previously had been exposed.     

Recovery of Anthocyanins and Monosaccharides from Grape Marc Extract by Nanofiltration Membranes

Wastewaters and by-products generated in the winemaking process are important and inexpensive sources of value-added compounds that can be potentially reused for the development of new products of commercial interest (i.e., functional foods). This research was undertaken in order to evaluate the potential of nanofiltration (NF) membranes in the recovery of anthocyanins and monosaccharides from a clarified Carménère grape marc obtained through a combination of ultrasound-assisted extraction and microfiltration. Three different flat-sheet nanofiltration (NF) membranes, covering the range of molecular weight cut-off (MWCO) from 150 to 800 Da, were evaluated for their productivity as well as for their rejection towards anthocyanins (malvidin-3-O-glucoside, malvidin 3-(acetyl)-glucoside, and malvidin 3-(coumaroyl)-glucoside) and sugars (glucose and fructose) in selected operating conditions. The selected membranes showed differences in their performance in terms of permeate flux and rejection of target compounds. The NFX membrane, with the lowest MWCO (150–300 Da), showed a lower flux decay in comparison to the other investigated membranes. All the membranes showed rejection higher than 99.42% for the quantified anthocyanins. Regarding sugars rejection, the NFX membrane showed the highest rejection for glucose and fructose (100 and 92.60%, respectively), whereas the NFW membrane (MWCO 300–500 Da) was the one with the lowest rejection for these compounds (80.57 and 71.62%, respectively). As a general trend, the tested membranes did not show a preferential rejection of anthocyanins over sugars. Therefore, all tested membranes were suitable for concentration purposes.     

How slug flow can enhance the ultrafiltration flux in mineral tubular membranes

The study deals with the use of a gas-liquid two-phase flow to reduce tubular mineral membrane fouling by injecting air directly into the feed stream. The injected air is supposed to create complex hydrodynamic conditions inside the ultrafiltration module which destabilize the concentration layer over the membrane surface. The experimental study was carried out by filtering suspensions (bentonite and yeast) through an ultrafiltration tubular mineral membrane. A range of transmembrane pressures and various liquid and gas flow-rates were tested. Results related to the permeate flux showed an enhancement by a factor of 3, with a slug flow-structure for the two kinds of suspension (200% of flux increase). Furthermore, the applicability of such an unsteady technique was examined with a view to reduce energy consumption.     

Impact of ultrafiltration operating conditions on membrane irreversible fouling

The main limitation of the ultrafiltration (UF) process identified in drinking water treatment is membrane fouling. Although adsorption of natural organic matter (NOM) is known to cause irreversible fouling, operating conditions also impact the degree of irreversible fouling. This study examined the impact of several operating parameters on fouling including flux, concentrate velocity in hollow fibers, backwash frequency, and transmembrane pressure. A hydrophilic cellulose derivative membrane and a hydrophobic acrylic polymer membrane were used to conduct these tests. Pilot testing showed that when short-term reversible fouling was limited during a filtration cycle by increasing the concentrate velocity, reducing the flux, and increasing the backwash frequency, the evolution of the membrane toward irreversible fouling could be controlled. It appeared that operating parameters should be adjusted to maintain the increase of transmembrane pressure below a certain limit, determined to be approximately 0.85 to 1.0 bar for the tested UF membrane, in order to minimize the rate of irreversible fouling. This threshold for transmembrane pressure was confirmed empirically by compiling data from over 36 pilot studies. Other testing results demonstrated that hydraulic backwash effectiveness decreased as the transmembrane pressure applied in the previous filtration cycle increased. Backwash efficiency in terms of membrane flux recovery after hydraulic backwash was reduced by 50% when the transmembrane pressure was increased from 0.4 bar to 1.4 bar.     

Fouling of reverse osmosis membranes by biopolymers in wastewater secondary effluent: Role of membrane surface properties and initial permeate flux

Reverse osmosis (RO) is being increasingly used in treatment of domestic wastewater secondary effluent for potable and non-potable reuse. Among other solutes, dissolved biopolymers, i.e., proteins and polysaccharides, can lead to severe fouling of RO membranes. In this study, the roles of RO membrane surface properties in membrane fouling by two model biopolymers, bovine serum albumin (BSA) and sodium alginate, were investigated. Three commercial RO membranes with different surface properties were tested in a laboratory-scale cross-flow RO system. Membrane surface properties considered include surface roughness, zeta potential, and hydrophobicity. Experimental results revealed that membrane surface roughness had the greatest effect on fouling by the biopolymers tested. Accordingly, modified membranes with smoother surfaces showed significantly lower fouling rates. When Ca²⁺ was present, alginate fouled RO membranes much faster than BSA. Considerable synergistic effect was observed when both BSA and alginate were present. The larger foulant particle sizes measured in the co-existence of BSA and alginate indicate formation of BSA-alginate aggregates, which resulted in greater fouling rates. Faster initial flux decline was observed at higher initial permeate flux even when the flux was measured against accumulative permeate volume, indicating a negative impact of higher operating pressure.     

Impact of Membrane Types and Catalyst Layers Composition on Performance of Polymer Electrolyte Membrane Fuel Cells

Performance of a low temperature polymer electrolyte membrane fuel cell (PEMFC) is highly dependent on the kind of catalysts, catalyst supports, ionomer amount on the catalyst layers (CL), membrane types and operating conditions. In this work, we investigated the influence of membrane types and CL compositions on MEA performance. MEA performance increases under all practically relevant load conditions with reduction of the membrane thickness from 50 to 15 μm, however further decrease in membrane thickness from 15 to 10 μm leads to reduction in cell voltage at high current loads. A thick anode CL is found to be beneficial under wet operating conditions assuming more pore space is provided to accommodate liquid water, whereas under dry operating conditions, an intermediate thickness of the anode CL is beneficial. When studying the impact of catalyst layer thickness, too thin a catalyst layer again shows reduced performance due to increased ohmic resistance ruled out the performance of the MEAs which have identical Pt crystallite sizes on the cathode CLs i. e. the thinnest the cathode CL, the highest the voltage were achieved at a defined current load. Adaptation of the operating conditions is highly anticipated to achieve the highest MEA performance.     

Mitigated membrane fouling in a vertical submerged membrane bioreactor (VSMBR)

In a laboratory-scale study, characteristics of membrane fouling in an A/O (anoxic/oxic) series membrane bioreactor (MBR) and in a vertical submerged membrane bioreactor (VSMBR) treating synthetic wastewater were compared under the same operating conditions. Accordingly, fouling characteristics of a pilot-scale VSMBR treating municipal wastewater were studied under various operating conditions. Various physical, chemical, and biological factors were used to describe membrane resistances. As a result, it was concluded that high concentrations of extracellular polymeric substances (EPS), high viscosity and a high sludge volume index (SVI) corresponded to high membrane resistance indicating severe membrane fouling in both the laboratory-scale MBRs and the pilot-scale VSMBR. In addition, high fouling potential was observed in the pilot-scale VSMBR at 60-day sludge retention time (SRT). In this case, as hydraulic retention time (HRT) decreased from 10 to 4 h, EPS concentrations increased and the average particle size increased, leading to reduced settling of the sludge and increased membrane fouling. To mitigate fouling, two different methods using air bubble jets were adopted in the pilot-scale VSMBR. As a result, it was found that air backwashing was more efficient for fouling mitigation than was air scouring.     

Coupled pervaporation/mass spectrometry for investigating membrane mass transport phenomena

The integration of organophilic pervaporation into processes of varying feed concentration, such as bioconversions, chemical reactions, or analytical sample preparation, requires not only the understanding of mass transport phenomena across the membrane under steady-state conditions, but also the insight into the transient response of the pervaporation membrane to changes as they occur in practice. For this purpose, a laboratory-scale pervaporation unit was coupled to a mass spectrometer for on-line permeate analysis, maintaining the overall pervaporation operating conditions controllable independently, and without introducing any inert gases for sample transfer.The experimental set-up was employed for investigating the transport of aroma compounds across a POMS–PEI composite membrane, focusing in particular on the so-called “membrane conditioning”; the possible synergetic effect of ethanol on the flux of one model aroma compound, ethyl hexanoate; the application of the system proposed to the rapid screening of the effect of the hydrodynamic upstream conditions on the degree of concentration polarisation.The method proposed proved to be robust and flexible, not only allowing insights into transient mass transport phenomena otherwise not attainable, but also reducing experimental workload significantly when characterising the effect of varying operating conditions on the pervaporation performance.