Membrane Pore Size Research Articles

Contributions of Colloidal Forces to the Heterogeneous Separation of Stable Oil-In-Water Emulsions.

We use theory to study the distribution of spherical emulsion oil droplets in water near a lipophilic surface as a guideline for designing membranes for oil/water phase separation. Heterogeneous phase separations are shown in our laboratory using hydrophilic and hydrophobic membrane designs, where the affinity of the membrane surface to one of the phases in the mixture locally increases its concentration. Considering a colloidal emulsion (nano- to microemulsions) of spherical and noncoalescing droplets, we assess the contribution of colloidal forces, i.e., van der Waals, electrical double layer, and hydrophobic interactions and the finite size of the droplets to the accumulation of spherical emulsion droplets near a surface. We use our theory to study an experiment-inspired case study and find that an isolated lipophilic membrane surface in contact with an oil-in-water emulsion supports the oil-enriched emulsion phase in a thin layer near the membrane surface, suggesting that a membrane pore size comparable to this thickness should support oil-enriched emulsion in the membrane pores and hence past the membrane.

Self-assembled nanostructured membranes with tunable pore size and shape from plant-derived materials.

Nanostructured materials derived from sustainable sources are of interest as viable alternatives to traditional petroleum-derived sources in membrane applications due to environmental concerns. Here, we present the development of pore size-tunable nanostructured polymer membranes based on a plant-derived material. The membranes were fabricated using a tri-functional amine as the templating core species and a cross-linkable ligand synthesized from rose oil-derived citronellol. The self-assembly of a supramolecular complex between the template core and the ligand forms a hexagonally packed columnar (Colh) mesophase, the dimensions of which can be precisely controlled by changing the stoichiometric ratio between these constituents. Within the hexagonal mesophase stoichiometric range, the pore size of the nanostructured membranes can be tuned from 1.0 to 1.3 nm, with a step size of approximately 0.1 nm. The membranes exhibited a clear distinction in molecular size selectivity, as demonstrated by dye adsorption experiments. The membrane fabricated with a ligand-to-core ratio of 3 to 1 demonstrated shape-based selectivity, exhibiting a higher permeability for propeller-shaped penetrants and highlighting its potential for shape-selective transport. We anticipate that this straightforward approach, using plant-derived materials, can contribute to important sustainability aspects while enhancing the performance of current state-of-the-art nanostructured membranes by enabling precise control over pore size.

Lesser mealworm (Alphitobius diaperinus) protein concentrate conjugated with tannic acid improves the oxidative stability of W1/O/W2 emulsions loaded with beet by-product extract and linseed oil

For improving the oxidative stability of a polyunsaturated oil, we co-encapsulated polyphenols from a concentrated beet by-product extract (CEB) with linseed oil using W1/O/W2 emulsions produced through emulsification with dynamic membranes of tunable pore size (DMTS), a low-energy high-throughput emulsification technology. Emulsions were stabilized with lesser mealworm protein concentrate (LMPC) and with an LMPC-derived antioxidant emulsifier (LMPC conjugated to tannic acid (LMPC-TA)). Regarding productivity, values of transmembrane flux were high (above 100 m3 m−2 h−1), and of industrial interest. Regardless of the protein used, emulsions showed an encapsulation efficiency higher than 67.5 %, while droplet size (D4,3) was below 8.28 μm. All emulsions were physically stable for 16 days at 4 °C, while at 25 °C, those stabilized with LMPC-TA had a less pronounced increase in D4,3. In all cases, emulsions containing CEB and LMPC-TA inhibited oil oxidation, increasing the shelf life of the emulsions.

Fluorine-free biomimetic membranes with leaf vein-like and lotus leaf dual structure for high-performance waterproof and breathable textiles

Intelligent microporous membranes with excellent water resistance and moisture permeability have a huge market demand owing to their wide applications in personal protection, outdoor equipment and wearable electronics. However, the construction of such high-performance waterproof and moisture-permeable membranes (WBMs) based on a simple preparation process without post-coating treatment presents significant challenges. Herein, we present a simple strategy for constructing a fluorine-free polyethylene terephthalate (PET)-based WBM with a novel composite structure by combining a leaf vein-like nanofibrous substrate membrane and lotus leaf-inspired biomimetic nanofibrous skin using multi-needle electrospinning and heat treatment techniques. Surface hydrophobicity, along with the stable crosslinked structure of PET-based membranes, was achieved by in-suit doping of fluorine-free two-component reactive silicone rubber (PDMS). In addition, the small pore size and high porosity of the composite membranes were regulated by co-assembling PET/PDMS fibers and microspheres with different morphologies and structures. The resulting composite membranes based on substrate membrane-1:3 (BNFM-1:3) achieved excellent waterproof performance of 90.3 kPa, good moisture permeability of 5116 g m−2 d−1, and air permeability of 1.82 mm s−1. The WBMs based on novel composite structures are expected to be applied in various fields because of their ideal comprehensive performance.

Effect of pore size and temperature on the behaviour of alpha-lactalbumin and the A and B genetic variants of beta-lactoglobulin during protein fractionation microfiltration

The aim of this study was to investigate the influence of membrane pore size and filtration temperature on six individual milk protein fractions (αS-CN, β- CN, κ-CN, α-LA, β-LG A, β-LG A) during the protein fractionation microfiltration process. Pasteurised skimmed milk was microfiltrated using two different pore sizes of spiral-wound membranes, with pore sizes of 0.2 μm and 0.5 μm, at temperatures of 15 °C and 45 °C respectively. The microfiltration process was carried out with a final volume reduction of 66% and a diafiltration volume of 120% (300 L) of the original feed (250 L). It was observed that neither the pore size nor the filtration temperature significantly (p<0.05) affected the permeation of the α-LA fraction. However, the permeation of the β-LG A and β-LG B fractions can be influenced by membrane pore size and filtration temperature, and the behaviour of the three whey protein fractions, A and B genetic variants of the β-LG and α-LA fractions differs significantly during the microfiltration process. The results of this study could form the basis for the development of new, unique tailor-made milk protein ingredients.

Effect of silicon powder dosage on the microstructure and performance of SiC/Si3N4 composite ceramic microfiltration membranes

The SiC/Si3N4 composite ceramic microfiltration membranes were fabricated using the in-situ nitridation process of silicon powder at 1350 °C, utilizing SiC powder and silicon powder as the raw materials. The effects of silicon powder dosage on the phase composition, basic physical properties, pure water flux, pore size distribution, and microstructure of membrane materials were investigated. With an increase in the silicon powder quantity from 5 wt% to 20 wt%, the flexural strength of the membrane materials increased from 6.6 MPa to 42.4 MPa, while the apparent porosity remained stable at 37.0%–39.0 %. The experimental results indicated a substantial correlation between the pore size distribution and the pure water flux. As the average pore size of the ceramic membranes decreased from 463.87 nm to 132.68 nm, the pure water flux gradually decreased from 265.99 L/(m2⋅h⋅bar) to 50.34 L/(m2⋅h⋅bar). The systematic investigation reveals that the Si3N4 binding phase, generated from the in-situ nitriding reaction of silicon powder, is the primary factor responsible for enhancing the mechanical properties of the membrane material. The process of in-situ nitriding silicon powder is accompanied by an increase in volume, which is beneficial in filling and refining the pores. Moreover, the formation of silicon nitride whiskers during the nitriding process can enhance the material's mechanical properties and further divide and refine the pores.

Sorption of PFOS onto polystyrene microplastics potentiates synergistic toxic effects during zebrafish embryogenesis and neurodevelopment

Microplastics (MPs) have become an emerging anthropogenic pollutant, and their ability to sorb contaminants potentially enhances the threats to the ecosystem. Only a few studies are available to understand the combined effects of microplastics and other pollutants. The present study investigated the sorption of perfluorooctane sulfonic acid (PFOS) onto polystyrene microplastics (PS-MPs) at varying concentrations, using molecular dynamics simulation (MDS) to preliminarily explore the adsorption behavior. The MDS results revealed negative interaction energies between PFOS and PS-MPs, underscoring PS-MPs' role as a potential adsorbent for PFOS in an aqueous solution. Thereafter, zebrafish embryos were employed to explore the toxic effects of combined exposure to PS-MPs and PFOS. Fluorescence and Scanning Electron Microscopy (SEM) suggested PS-MP accumulation individually and in combination with PFOS on the embryonic chorion membrane. As a result, the exposed group showed increased inner pore size of the chorionic membrane and accelerated heartbeat, indicating hypoxic conditions and hindered gaseous exchange. PS-MPs aggravated the toxicity of PFOS during larval development manifested by delayed hatching rate, increased mortality, and malformation rate. Additionally, increased ROS accumulation and altered antioxidant enzymatic status were observed in all the exposed groups suggesting perturbation of the redox state. Additionally, co-exposure of zebrafish larvae to PS-MPs and PFOS resulted in an abrupt behavioral response, which decreased AChE activity and altered neurotransmitter levels. Taken together, our results emphasize that PS-MPs can act as a potential vector for PFOS, exerting synergistic toxic effects in the aquatic environment, and hence their health risks cannot be ignored.

Method evaluation for viruses in activated sludge: Concentration, sequencing, and identification

Activated sludge (AS) in wastewater treatment plants is one of the largest artificial microbial ecosystems on earth and it makes enormous contributions to human societies. Viruses are an important component in AS with a high abundance. However, their communities and functionalities have not been as widely explored as those of other microorganisms, such as bacteria. This gap is mainly due to technical challenges in effective viral concentration, extraction, and sequencing. In this study, we compared four kinds of concentration methods, two sequencing approaches, and four identification bioinformatic tools to evaluate the whole analysis workflow for viruses in AS. Results showed flocculation, filtration, and resuspension (FFR) could get the longest DNA lengths and ultracentrifugation obtained the highest DNA yields for viruses in AS. Based on the results of present study, FFR and tangential flow filtration with the membrane pore size of 100 kDa were most recommended to concentrate viruses in AS samples with huge volumes. Besides, different concentration methods could get different viral catalogs and thus multiple methods should be combined to get the whole picture of viruses in the system. In addition, geNomad was the most recommended identification tool for viruses in the present study and the long-read sequencing could improve the assembly statistics of viruses when compared with the short-read sequencing. For the 8192 viral operational taxonomic units in this study, 95.1 % of them were phages and belonged to the same lineage at the order level of Caudovirales. Virulent phages dominated the AS system and Pseudomonadota were the main host. Taken together, this study provides new insights into methods selection for virus research of AS.

Optimized ceramic membrane-based method for efficient and acid-free rice protein preparation from alkaline extracts

Rice protein, stands out as a high-quality plant-based protein, suitable for dietary supplementation and food processing. Traditional methods, involving alkaline extraction and acid precipitation, are challenged by the extensive use of chemicals and the difficulty in desalination. This study proposed a novel separation method that utilizes ceramic membranes for direct alkali filtration, eliminating the formation of salts by acid neutralization. The membrane pore size and the operating parameters such as transmembrane pressure, cross-flow velocity, and pH were optimized to enable a high flux (>80 L m−2·h−1) and favorable protein rejection (>95 %) while permitting the removal of excess alkali. Additionally, the effects of non-protein substances, e.g., starch, present in the alkaline extract on the separation performance were explored. Subsequently, an optimized strategy for starch removal was proposed, involving the concentration of the alkali extract using an ultrafiltration membrane, followed by enzymatic hydrolysis of starch and diafiltration to eliminate the residuals of starch hydrolysates and alkali. Under stabilization of protein particles by carboxymethyl cellulose, rice protein with a uniform particle size of 25 nm and a purity of over 80 % was produced. The direct removal of alkali from alkali extracts of rice by ceramic membranes presents a promising strategy for producing rice protein with high purity and reduced aggregation degree, enabling better functionalities such as solubility than the conventional alkali-extraction and acid-precipitation method.

Performance Investigation of PSF-nAC Composite Ultrafiltration Membrane for Protein Separation.

As a promising wastewater treatment technology, ultrafiltration membranes face challenges related to fouling and flux reduction. To enhance these membranes, various strategies have been explored. Among them, the incorporation of nano-activated carbon (nAC) powder has emerged as an effective method. In this study, composite polysulfone (PSF) ultrafiltration membranes were fabricated using nAC powder at concentrations ranging from 0 to 8 wt.%. These membranes underwent comprehensive investigation, including assessments of membrane morphology, hydrophilicity, pure water flux, equilibrium water content, porosity, average pore size, and protein separation. The addition of activated carbon improved several desirable properties. Specifically, the hydrophilicity of the PSF membranes was enhanced, with the contact angle reduced from 69° to 58° for 8 wt.% of nAC composite membranes compared to the pristine PSF membrane. Furthermore, the water flux test revealed that 6 wt.% activated carbon-based membranes exhibited the highest flux, with a nearly 3 times improvement at 2 bar. Importantly, this enhancement did not compromise the protein rejection. Additionally, the introduction of nAC had a significant effect on the membrane's pore size by improving lysozyme rejection up to 40%. Overall, these findings will guide the selection of the optimal concentration of nAC for PSF ultrafiltration membranes.

Monolithic Polyepoxide Membranes for Nanofiltration Applications and Sustainable Membrane Manufacture.

The present work details the development of carbon fiber-reinforced epoxy membranes with excellent rejection of small-molecule dyes. It is a proof-of-concept for a more sustainable membrane design incorporating carbon fibers, and their recycling and reuse. 4,4'-methylenebis(cyclohexylamine) (MBCHA) polymerized with either bisphenol-A-diglycidyl ether (BADGE) or tetraphenolethane tetraglycidylether (EPON Resin 1031) in polyethylene glycol (PEG) were used to make monolithic membranes reinforced by nonwoven carbon fibers. Membrane pore sizes were tuned by adjusting the molecular weight of the PEG used in the initial polymerization. Membranes made of BADGE-MBCHA showed rejection of Rose Bengal approaching 100%, while tuning the pore sizes substantially increased the rejection of Methylene Blue from ~65% to nearly 100%. The membrane with the best permselectivity was made of EPON-MBCHA polymerized in PEG 300. It has an average DI flux of 4.48 LMH/bar and an average rejection of 99.6% and 99.8% for Rose Bengal and Methylene Blue dyes, respectively. Degradation in 1.1 M sodium hypochlorite enabled the retrieval of the carbon fiber from the epoxy matrix, suggesting that the monolithic membranes could be recycled to retrieve high-value products rather than downcycled for incineration or used as a lower selectivity membrane. The mechanism for epoxy degradation is hypothesized to be part chemical and part physical due to intense swelling stress leading to erosion that leaves behind undamaged carbon fibers. The retrieved fibers were successfully used to make another membrane exhibiting similar performance to those made with pristine fibers.

Boosted Intracavity Aperture in Macrocyclic Amines Enabling Finely Regulated Microporous Membranes.

Finely tuning the pore structure of traditional nanofiltration (NF) membranes is challenging but highly effective for achieving efficient separations. Herein, we propose a concept of using macrocyclic amines (1,4,7-triazacyclononane, 3A; 1,4,7,10-tetraazacyclododecane, 4A1; and 1,4,8,11-tetraazacyclotetradecane, 4A2) with different intra-annular apertures to finely modulate the pore structure of microporous membranes via interfacial polymerization (IP). The boost in the intracavity size of the building blocks results in heightened steric hindrance of these amine monomers, leading to a controlled increase in membrane pore size, as demonstrated by both film characterizations and multiscale simulations. In conjunction with the increased intracavity size, the water permeability follows an augmented trend of 3A-TMC, 4A1-TMC, and 4A2-TMC (TMC: trimesoyl chloride) while exhibiting increased molecular weight cut-offs due to larger free-volume elements and stronger pore interconnectivity. Our proposed macrocyclic amine design strategy provides a guideline for finely regulated microporous membranes with high potential in NF-related applications.

Performance regulation of the TFC NF membrane via the introduction of oleic acid into different organic solvents

AbstractBACKGROUNDTailored design of high‐performance nanofiltration membranes is desirable. The physicochemical properties of the organic phaseare essential for the preparation of nanofiltration membranes. Therefore, byfine‐tuning the organic phase, it is possible to achieve nanofiltrationmembranes with enhanced performance.RESULTSIn this work, oleic acid, a naturally extracted fatty acid, wasintroduced into three different organic solvents (n‐heptane, n‐octane andisopar G) to construct special oil phases for interfacial polymerization. Testingresults showed that proper dosage of oleic acid addition can effectivelydecrease the nanofiltration membrane pore size and enhance the salt rejectionregardless of the solvent type. Taking n‐octane as example, 5% oleic acidaddition in it can decrease the mean pore size from 0.500 nm to 0.341 nm and improve the MgSO4 rejection from 52.4% to 95.5%. Further characterizationindicated that the introduction of oleic acid into organic solvent cansignificantly reduce the interfacial tension and promote the diffusion of piperazinefrom aqueous phase to the oil phase. In addition, oleic acid could react with piperazineand produce some white particles that could be embed into the polyamide layer, thus altering the surface morphology.CONCLUSIONIn this work, a novel modified thin film composite nanofiltration membrane was prepared by a simple and controllable oleic acid assisted interfacial polymerization strategy, which exhibits good water permeability, solute selectivity and antifouling property. Without changing the existing process, our strategy opens up a simple, environmentally friendly and operable route for the synthesis of thin film composite nanofiltration membranes. © 2024 Society of Chemical Industry (SCI).

Partitioning of proteins and small molecular weight compounds from alfalfa juice during ultrafiltration

Ribulose-1,5-biphosphate-carboxylase/oxygenase (RuBisCO) from alfalfa is a promising source of alternative food protein, but it is challenging to purify. Ultrafiltration shows potential for concentrating and fractionating RuBisCO from low molecular weight compounds present in the extracted juice, but there is limited information on their partitioning depending on the membrane pore size. Therefore, the objective of this study was to evaluate the partitioning of various compounds from the juice depending on membrane pore size. It was hypothesized that both membrane pore sizes will retain RuBisCO but might partition low molecular weight compounds within the matrix differently. RuBisCO was fully retained by both the 300 and 100 kDa polyethersulfone (PES) membranes, while ash (29.7%–35.4% dry matter (DM)), non-protein nitrogen (2.38%–2.53% DM), and free N-terminals (10.13–10.34 mg glutamic equivalent/100 mg DM) were transmitted through both membranes. The retentates showed a distinct yellow color when filtering with 100 kDa membranes, but not when using 300 kDa membranes. Although no significant differences in total polyphenol permeation were observed through a spectrophotometric assay, a metabolomics screening analysis showed that the 100 kDa membranes had less transmission of the flavonoids apigenin, chrysoeriol, tricin, and tricin glycosides, which might contribute to the yellow color. These results reiterate the importance of measuring individual polyphenols using hyphenated techniques as opposed to spectrophotometric total reducing capacity. Sixteen saponins were identified and their permeation was lower in the 100 than the 300 kDa membranes, indicating a better potential for higher degree of protein refinement for the latter. This study demonstrates for the first time the difference in partitioning of the small molecular weight components, using PES membranes of similar chemistry but different size, during ultrafiltration of alfalfa juice.

Uncovering the membrane and pore formation mechanisms of the lysozyme membrane made via the amyloid-like assembly

Biomimetic protein membranes have attracted increasing interests because of their distinctive separation properties in the membrane field. Low-cost and stable protein lysozyme has been intensively invetigated to fabricate high-performance sepration membranes via a facile and scalable method of amyloid-like assembly. However, the pore formation mechnism of the lysozyme membrane remains unclear. Herein, the lysozyme membranes were fabricated and the membrane formation mechnism and separation properties were investigated experimentally. Molecular dynamics simulation (MDS) was also employed to reveal the pore formation mechanism of the lysozyme membrane. The fabricated lysozyme membrane achieved a stable high water permeance of 10.2 L m−2 h−1 bar−1, as well as a relatively high separation factor (9.5) towards antibiotic and sodium chloride. MDS results found that the membrane pore size is governed by the amino acid compositions and is negatively dependent on the intermolecular forces among amino acids around the pores. Selective pores with 0.54 nm in diameter are primarily formed by these amino acids including alanine (35 %), aspartic acid (25 %), arginine (15 %), phenylalanine (11 %), and lysine (7 %), in which half of them have hydrophobic side chains with no charge, and another half have hydrophilic side chains with balanced charges. This work may stimulate the development of highly permeable and selective protein membranes by carefully engineering their amino acid compositions with optimal charges and hydrophobicity for generation of numerous selective pores.

A flexible strategy to fabricate trumpet-shaped porous PDMS membranes for organ-on-chip application.

Porous polydimethylsiloxane (PDMS) membrane is a crucial element in organs-on-chips fabrication, supplying a unique substrate that can be used for the generation of tissue-tissue interfaces, separate co-culture, biomimetic stretch application, etc. However, the existing methods of through-hole PDMS membrane production are largely limited by labor-consuming processes and/or expensive equipment. Here, we propose an accessible and low-cost strategy to fabricate through-hole PDMS membranes with good controllability, which is performed via combining wet-etching and spin-coating processes. The porous membrane is obtained by spin-coating OS-20 diluted PDMS on an etched glass template with a columnar array structure. The pore size and thickness of the PDMS membrane can be adjusted flexibly via optimizing the template structure and spinning speed. In particular, compared to the traditional vertical through-hole structure of porous membranes, the membranes prepared by this method feature a trumpet-shaped structure, which allows for the generation of some unique bionic structures on organs-on-chips. When the trumpet-shape faces upward, the endothelium spreads at the bottom of the porous membrane, and intestinal cells form a villous structure, achieving the same effect as traditional methods. Conversely, when the trumpet-shape faces downward, intestinal cells spontaneously form a crypt-like structure, which is challenging to achieve with other methods. The proposed approach is simple, flexible with good reproducibility, and low-cost, which provides a new way to facilitate the building of multifunctional organ-on-chip systems and accelerate their translational applications.

Insights into the pore size distribution of amorphous silica membranes using gas permeation activation energies

Silica-based membranes exhibit significant promise for the separation of hydrogen from other larger gas molecules based on size sieving mechanism, particularly when employed in membrane reactors. Nevertheless, the migration of silanol bonds (Si–OH) formed under hydrothermal conditions leads to alterations in pore size, ultimately compromising the performance of the membrane. Therefore, this study focuses on determining the pore size of cobalt-doped silica membranes before and after hydrothermal treatment by the apparent activation energy of gas permeation. The Oscillator model and the effective medium theory are employed to estimate the potential pore size distribution, as well as to calculate the apparent activation energy and permeability. The calculated apparent activation energy is compared with experimental data to identify the most probable pore size distribution, which showed the minimum activation energy error to the experimental value. The calculated permeability based on the identified pore size distribution is in line with experimental permeability, which validated the identified pore size distribution. Since silica-based membrane is generally applied in hydrothermal conditions, our model successfully identifies the changes in pore size of silica-based membranes after hydrothermal treatment. The results demonstrated that hydrothermal treatment significantly impacts the pore size of silica-based membranes. Specifically, 5-membered rings are prevalent in the intact membrane, but after hydrothermal treatment, there is a gradual shift of the pore size distribution towards larger pores, potentially leading to a decrease in sieving performance. This methodology presents a promising approach for determining intriguing pore size information of porous materials.

Characterization of membrane pore size using statistical model by facile method of air bubbling in liquid media

Research has shown the correlation between porous membrane pore size and bubble formation including bubble size, frequency, and operating parameters. However, attempts to create a governing equation to establish this correlation have often suffered from low accuracy due to variable interactions. Therefore, it is necessary to identify the significant effects of membrane pore size on bubble formation to establish effective correlations. This study aimed to identify the significant effect of porous membrane pore size on bubble formation using analysis of variance (ANOVA) to establish a mathematical model that predicts porous membrane pore size using bubble formation. To achieve this, various porous membranes were fabricated by varying hydrophilic silica loadings. The resulting membranes were characterized regarding pore size and employed in an aeration device under variable air flow rates and inlet pressures to obtain bubble size and frequency data. JMP software developed a statistical model to characterize membrane pore sizes. The results show a significant effect of bubble formation information on pore size, with a p-value of 0.0089, R2 of 0.96, and root mean squared error (RMSE) value of 0.02. Validation of the model using three membranes demonstrated minor deviations of 0–6.5 %, emphasizing the model's effectiveness in predicting membrane pore size.

Onset, rate, and depth of wetting front progression in membrane distillation

In this study, electrochemical impedance spectroscopy (EIS) is used to characterize the onset, rate, and depth of wetting front progression in real time through commercial polytetrafluoroethylene (PTFE) membrane distillation (MD) membranes. Results showed that higher salinities, elevated transmembrane hydraulic pressures, and larger membrane pore sizes are associated with earlier onset, higher rates, and/or greater depths of wetting front progression – but, notably, in the absence of pore breakthrough. It was also shown that wetting is not an on/off switch; instead, membrane wetting resistance acts as a frictional force that can slow down or stop wetting front progression at different depths in the membrane. PTFE MD membranes were observed to often operate in a deeply wetted, but stable, transition state with normalized impedance values of ∼0.6 to ∼0.1, indicating mid-depth wetting, where the wetting front progresses into the bulk of the membrane and holds its position, or deep wetting, where the wetting front holds its position near the distillate-side surface of the membrane without pore breakthrough. Normalized impedance values as low as 0.04 held constant throughout a 14-day experiment in which pore breakthrough did not occur. These new impedance results strongly support the hypothesis that during MD, for saline feed solutions and under elevated transmembrane pressures – and especially for larger membrane pore sizes – the distillate-side surface can act as a final barrier to pore breakthrough.

Modeling &amp; experimental studies on enhancement of H2S conversion using catalytic membrane reactor for hydrogen production

Abstract Acidic gases such as H2S and CO2 are generated in the refineries during coal gasification. These pollutant gases need to be treated before releasing to the atmosphere. Conventionally, H2S gas is treated by Claus process in which H2S is converted to elemental S and H2O, in presence of O2 at ∼1,200 K. In the present energy scenarios, hydrogen has got importance as a source of clean fuel for industrial application. The H2S generated in the refineries can be a potential precursor of hydrogen. If this hydrogen can be obtained by thermal decomposition of H2S, that can increase the overall economic value of the H2S containing streams and the produced hydrogen can be used for hydrocracking and hydro-treating in refineries, as well as to synthesize value-added products for chemical industries. However, H2S thermal decomposition is an endothermic and equilibrium limited reaction (equilibrium conversion is only ∼15 % at 1,000 K), requiring a very high temperature (∼1,500 K) to achieve even a conversion of greater than 40 %. Packed Bed Catalytic Membrane Reactor (PBCMR) for thermal decomposition of H2S can be a potential technology augmentation and process intensification to increase this equilibrium conversion. In this work, modeling and experimental studies of H2S thermal decomposition using in-house designed &amp; developed PBCMR have been carried out. The modeling studies were validated with experimental data. Clay-alumina ceramic tubular membrane (L: 250 mm; OD: 12 mm; thickness: 2 mm) was fabricated using extrusion process having an average membrane pore size of ∼1 μm and with a porosity of ∼20 %. Pt (2 %) coated alumina extrudes were used as catalyst to accelerate the reaction kinetics. Experimental studies showed that H2S to hydrogen conversion of ∼90 % is achieved using PBCMR at ∼1,523 K, compared to only ∼40 % conversion in a conventional packed bed tubular reactor (without membrane). Modelling studies were carried out to study the influence of operating parameters such as, reactor wall temperature, feed temperature, pressure and feed velocity. Studies showed that reactor wall temperature is having the most dominant effect on H2S conversion, which is confirmed by experimental findings. The studies offer useful insights into the application of PBCMR technology for management of waste gas stream containing H2S and recovery of hydrogen.