Search

The conversion of equilibrium-limited reactions can be efficiently improved by selective removal of product using a Pervaporation Membrane Reactor (PVMR), which attracts substantial attentions due to its excellent performance. For modeling the PVMR process, a pseudo-binary system was often assumed, nevertheless, it is inadequate to predict the performance when both the reactant and product have the similar properties and can simultaneous permeate through the membrane. A detailed model was established by coupling multi-component pervaporation and reaction kinetics with the butanoxime hydrolysis reaction employed as the experiment system. A modified Flory–Huggins (FH) approach and the Maxwell–Stefan (MS) formulation were used to describe the pervaporation model. The mass transfer fluxes and the concentration profiles of permeants within the membrane were modeled by a finite difference approach. Two coexisted behaviors, i.e. competitive adsorption and plasticizing effects were considered to influence mass transfer. The PVMR performance was predicted and a good agreement between experiment and calculation was obtained. The mechanism that how the simultaneous permeation of reactant and product influence the PVMR performance were further clarified in different operating conditions, including initial reactant concentration, downstream pressure, membrane thickness, ratio of membrane area to reaction volume, and temperature. [ABSTRACT FROM AUTHOR]

A mathematical model was proposed to elucidate the mass transfer of a hollow fiber membrane absorption process taking the effect of membrane porosity into account. This model was derived based on the mass transfer differential equation and discretized considering the micropores on the membrane wall. The model was numerically solved by using upwind difference technique, and the solute concentration profiles were obtained. Effects of porosity under various conditions, including membrane pore size, fiber length, pH of absorbent and liquid velocity on the mass transfer process, were quantitatively investigated. The results indicated that the porosity plays an important role in forming the solute concentration profile, and thus influenced the mass transfer performance. Low porosity (or high pH and liquid velocity, or low fiber length) corresponded to the heterogeneous profiles, while opposite conditions led to the homogeneous profiles. The model gave calculation results in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Abstract: A catalytically active pervaporation membrane with a novel composite structure has been prepared by using the immersion phase inversion method. SEM images show its structure containing three layers: the top layer is a porous catalytic layer, the middle layer is the dense PVA selective layer and the bottom layer is the commercially available PES support layer. Esterification reaction of acetic acid and n-butanol is used as a model reaction to test its performance. Batch reaction results show that its catalytic activity is comparable to that of catalyst beads. The result of esterification reactions in pervaporation membrane reactors (PVMRs) shows that the acetic acid conversion reaches 91.4% in 20h at 85°C by using the catalytically active membrane, while the equilibrium conversion is around 71.9% under the same condition. The increase of temperature also facilitates the enhancement of acetic acid conversion. The catalytic activity and structure stability of the catalytically active membrane are further confirmed by consecutive experiments and SEM analyses. [Copyright &y& Elsevier]

Abstract: Extraction separation of Cu(II) and Co(II) from sulfuric wastewater is studied with hollow fiber renewal liquid membrane (HFRLM) technique. The organic solution of LIX 984N in kerosene is used as the liquid membrane phase to selectively separate and concentrate Cu(II) from aqueous solution; and the extractant of CYANEX 272 is used as carrier to remove and concentrate Co(II) from aqueous solution. In the selective separation process, LIX 984N has good selectivity on Cu(II); the interactions among metal ions can be negligible; the pH in the feed aqueous solution has significant influence, while the influence of hydrogen ion concentration in the stripping phase is slight. The removal efficiency of Cu(II) increases with the increasing flow rate on lumen side, while decreases with the increasing flow rate on shell side. The results of lab-scale cascade experiments show that the HFRLM technique is a promising treatment method for simulated sulfuric wastewater containing copper and cobalt with separation factor higher than 100. The Cu(II) and Co(II) concentrations in the raffinate are lower than 0.50mgL−1 and 1.0mgL−1, respectively, which are both below the standard of wastewater discharge in China. Based on the surface renewal theory, resistance-in-series model and mass balance law, a corresponding mass transfer mathematical model is developed; and the calculated results are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Membrane gas absorption technique is one of the most attractive alternatives for CO2 capture. In this paper, a mathematical model for membrane gas absorption process has been developed to describe the solute concentration profile and the mass transfer behavior near the membrane surface, which are important factors for the process. The finite volume method is used to solve the model. The modeling results show that the different solute diffusing distances in the vertical and parallel directions near the membrane surface result in varied concentration profiles. For the membrane with small pore size, the solute concentration profile near the membrane surface can reach uniform distribution instantly, and the membrane porosity has little effect on mass transfer. Contrarily, for the membrane with large pore size, especially at higher absorbent pH value or liquid velocity, the solute concentration distribution is comparatively non-uniform. The mass transfer is significantly affected by membrane porosity. That is the mass transfer coefficients are varied at different membrane porosities. Experiments are conducted to verify the model for CO2 removal using flat sheet membrane contactor with de-ionized water or NaOH solution as absorbents. The comparison between the experimental results and the prediction results shows that the model is validated. [Copyright &y& Elsevier]

Surface roughness enhancement by fabricating multi-scale nano/microstructure is an effective strategy to prepare superhydrophobic membranes. Here we report a novel solvent-thermal induced roughening (STIR) method. The method involves the swelling of a polymer surface to create a soft shell/hard core structure under the combined action of solvent and heating, followed by a controllable surface roughening as a result of mismatched thermal expansion between the shell and the core. We show a significant increase of surface roughness for a STIR-treated polyvinylidene fluoride nanofibrous membrane, whose nanofibers were covered with densely-packed nanofins. The treated membrane had greatly enhanced hydrophobicity, resulting in improved anti-wetting performance to low-surface-tension feed water in a membrane distillation process. The STIR method was capable of treating membranes with various pore structures. The novel surface roughening strategy opens up new directions to fabricate superhydrophobic surfaces and membranes, which can greatly benefit a wide range of applications such as membrane distillation, oil/water separation. [ABSTRACT FROM AUTHOR]

Constructing mechanical interlocking structure by allowing casting solution infiltrating into substrate pores is an effective approach to overcome the incompatibility between hydrophilic layers and hydrophobic layers. While the permeance of composite membranes still suffers from pore blockage due to the mechanical interlocking structure. In this work, a spontaneous slender plumes phenomenon was regulated by adjusting the concentration of NaOH aqueous solution. The regulating method was applied to fabricate root-like structure in the pores of the substrate, providing a feasible scheme to overcome the problem of pore blockage. High adhesive strength between chitosan (CS) and polylactic acid (PLA) layers suggested that a robust mechanical interlocking structure was achieved. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) spectra indicated that root-like structure was formed in the substrate without pore blockage. The prepared composite membrane exhibited promising permeance and excellent stability in 72 h experiment further confirmed the conclusion. It is expected that this study will provide an inspiration for mitigating pore blockage in composite membranes. [Display omitted] • A spontaneous plume phenomenon was observed and the regulating method was applied to overcome the problem of pore blockage in the construction of mechanical interlocking structure. • The formation of plume phenomenon was regulated by adjusting the concentration of NaOH aqueous solution. • The stable CS/PLA composite membrane showed promising pure water permeability. [ABSTRACT FROM AUTHOR]

Abstract: The effect of hollow fiber module scale on the mass transfer performance of hollow fiber renewal liquid membrane technique is studied experimentally and theoretically. Five scales of polypropylene hollow fiber membrane modules with same packing density and effective length are used for experiments. CuSO4 aqueous solution is used as feed phase, the organic solution of LIX984N in kerosene is used as liquid membrane phase, and H2SO4 is used as the stripping phase. The non-ideal flow status on the shell-side of the hollow fiber module is described by residence time distribution curves and quantitatively characterized by the Peclet number. Peclet number increases with the increase of L/d in hollow fiber module, and reaches its maximum value when L/d is 20, then decreases. The overall mass transfer coefficient is directly proportional to the Peclet number on the shell side in single-pass, recycling and cascade operation modes in the hollow fiber renewal liquid membrane process. A new mass transfer correlation is proposed to quantitatively describe the non-ideal flow on the shell-side of the hollow fiber module with Peclet number. Then, the corresponding mathematical model for hollow fiber renewal liquid membrane process is developed and the calculated results show good agreement with the experimental data. [Copyright &y& Elsevier]

Interfacial defect caused by the poor dispersibility of filler particles has been a major obstacle in the application of mixed matrix membranes (MMMs). Improving the fillers dispersibility is an effective approach to improve the separation performance. In this work, for the purpose of preparing defect-free MMMs, a pre-crosslinking strategy was proposed to covalently connect the fillers to the polymer. Such covalently connection realized by the reaction between the additional carboxyl group of the MOF-801 and the hydroxyl group of Polyvinyl alcohol (PVA). The newly reacted ester group, confirmed by Fourier Transform Infrared (FTIR), was identified as a bridge between MOF-801 and PVA. This bridge provides a strong bond between the two and avoids agglomeration between the MOF particles. The uniform distribution of Zr elements observed in the Energy Dispersive Spectrometer (EDS) mapping further confirms that the MOF-801 particles are well dispersed in the MMMs. The prepared membranes exhibited a superior water flux of 3354 g m−2 h−1 for 90 wt % ethanol/water separation at 343 K and excellent stability in 92 h experiment. This study provides an inspiration for mitigating excessive particle agglomeration in MMMs. [Display omitted] • A pre-crosslinking strategy is proposed to enhance the compatibility between MOF particles and polymeric matrix. • A high water flux of 3354 g m−2 h−1 is achieved for 90 wt % ethanol/water separation. • Mixed matrix membrane with thicknesses as low as 0.6 μm are prepared by spray coating. [ABSTRACT FROM AUTHOR]

Catalytically active membranes can realize chemical reaction and membrane separation simultaneously and have been recognized as an effective strategy for process intensification to offer smaller footprint, lower energy consumption, and enhanced process efficiency. Reaction-separation coupling involving high temperature reactions has traditionally evolved around inorganic membranes. However, great advancements have also been achieved on development of more versatile and abundant polymeric catalytically active membranes (pCAM) for a range of niche applications. This review is the first attempt to provide an overview of reaction-separation coupling by pCAM. Liquid phase reactions often occur at mild temperatures and the majority of studies dealing with pCAM are focused on these reactions. Research progress of reaction-separation coupling using pCAM for liquid phase reactions including fine chemical synthetic, photocatalytic and biocatalytic reactions is first examined. The limited studies on the use of pCAM for gas phase reactions are also summarized. Perspectives on the future development of pCAM and their potential applications are also highlighted. Image 1 • Polymeric catalytic membranes for reaction-separation coupling were reviewed. • Principles of different reaction-separation coupling processes were discussed. • Catalytic membranes for liquid phase reactions were critically examined. • Catalytic membranes for gas phase reactions were also summarized. • Perspectives on future development of catalytic membrane were highlighted. [ABSTRACT FROM AUTHOR]

A robust polytetrafluoroethylene (PTFE) nanofibrous membrane was prepared by a simple electrospinning-sintering strategy for efficient oil/water separation. Specifically, a PTFE@PVA hybrid nanofibrous membrane in which PTFE particles were uniformly distributed in PVA nanofiber was first prepared by electrospinning, then a sintering treatment was applied to obtain the PTFE nanofibrous membrane. Electron microscopic characterization revealed that the membrane was formed by a sintering mechanism of a fast decomposition of PVA followed by a slower fusion of PTFE particles. Spectroscopic characterization confirmed that the PVA polymer was completely decomposed after 8 h of sintering. The resulting membrane had a ratio of fluorine to carbon atomic ratio of 2.0, indicating that a pure PTFE nanofibrous membrane was obtained. The as-prepared PTFE membrane exhibited superhydrophobic property with a water contact angle of 155.0° and a sliding angle of 5.1°. Its tensile strength was as high as 19.7 MPa, indicating excellent mechanical strength. The membrane was successfully applied for gravity-driven oil/water separation with a permeate flux of 1215 L m −2 h −1 . Moreover, its excellent corrosion resistance and mechanical stability suggest that the PTFE nanofibrous membrane could stand harsh environment existing in industrial oil/water separation processes. [ABSTRACT FROM AUTHOR]

A composite catalytically active membrane was prepared focusing on the reduction of membrane mass transfer resistance to achieve a better esterification-pervaporation coupling performance. The effect of membrane preparation conditions on the membrane morphology was first evaluated. Under an optimized membrane preparation conditions, a “sandwich-like” composite membrane with a highly inter-connected sponge-like catalytic layer on a polyvinyl alcohol / polyethersulfone bilayer was obtained. The porosity of the membrane was found to be as high as 81.6%. A simple resistance-in-series model was developed to analyze the mass transfer resistance distribution in a traditional inert membrane reactor (IMR), a catalytically active membrane reactor (CAMR) with dense catalytic layer and a catalytically active membrane reactor with porous catalytic layer, respectively. Results showed that the preparation of a highly porous catalytic layer decreased the resistance of catalytic layer from 48.5% to 20.6% of overall resistances, leading to an enhanced water removal ability for the composite membrane. Finally, reaction-separation coupling experiments in IMR, CAMR with porous catalytic layer and CAMR with dense catalytic layer showed that, with a faster reaction kinetics and water removal rate, CAMR with porous catalytic layer exhibited a best coupling performance. [ABSTRACT FROM AUTHOR]

Vapor permeation (VP) is applied to be integrated with ethanol fermentation as an in situ product recovery technique which could avoid the ethanol inhibition in this study. The polydimethylsiloxane o(PDMS) membrane is used in separating ethanol from model ethanol/water mixture and fermentation integrated processes. And the performance of VP-fermentation process is investigated and compared to that of Pervaporation (PV)-Fermentation and batch fermentation processes. Experimental results show that the ethanol removal is successfully achieved, while it still suffers low flux. Then, in order to reduce the mass transfer resistance in gas boundary layer and thus improving the ethanol removal rate, gas stripping is coupled with VP process to form a new configuration of VP process, i.e. external mode. Benefited from its high ethanol removal rate, the ethanol productivity of External VP-Fermentation process reaches 3.33 g/(L·h), much higher than 2.13 g/(L·h) in batch fermentation and 2.90 g/(L·h) in PV-Fermentation under its optimal condition, i.e. vapor cyclic flow of 1.3 L/min and module temperature of 35 ℃. In VP-fermentation process, membrane deterioration is also efficiently alleviated, which commonly occurs in PV-fermentation process. It makes the membrane process more feasible for industrial fermentation process. [ABSTRACT FROM AUTHOR]

Enantioselective separation of salbutamol enantiomers was carried out through the simultaneously synergistic extraction and stripping method with Ο,Ο-dibenzoyl-(2S,3S)-tartaric acid (+)-DBTA and di (2-ethylhexyl) phosphoric acid (D2EHPA) as chiral and non-chiral extractants, respectively. Chiral recognition mechanism of salbutamol enantiomers with (+)-DBTA was investigated using the Density Functional Theory (DFT) methods. The results showed that the chiral recognition in separation process was realized by the hydrogen-bond interaction. The binding energy of the complex resulting from (+)-DBTA and R -salbutamol was −86.14 kJ/mol, which was higher than that of the complex resulting from (+)-DBTA and S -salbutamol. The synergistic extraction experiment was preliminarily performed and the maximum separation factor was up to 1.65. Enantioseparation of salbutamol was conducted in the hollow fiber supported liquid membrane process. Various operating conditions, including the feed phase concentration, the component of membrane phase, the flow rate, and the pH of stripping side, were investigated. The results showed that the mass transfer resistance mainly focused on the membrane phase. The synergistic effect in liquid membrane system was also discussed. When the ratio of chiral to achiral extractant was 1.0:0.6, the separation factor was up to 2.0 in the stripping phase. [ABSTRACT FROM AUTHOR]

Bioethanol is a promising substitute for fossil fuels and is mainly produced through yeast fermentation. However, in conventional batch fermentation process extracellular ethanol accumulation restricts yeast excretion of intracellular ethanol, and results in suppressed yeast viability and ethanol productivity. The present study reports a yeast-immobilized catalytically active membrane for efficient extracellular ethanol removal towards enhanced bioethanol productivity in pervaporation membrane reactor. The membrane was fabricated by immersion phase inversion through coating a porous yeast/polyethersulfone catalytic layer on a polydimethylsiloxane (PDMS) pervaporation membrane. Benefited from the high porosity of biocatalytic layer, the immobilized yeast exhibited superior fermentation capacity in high substrate concentration when compared with free yeasts. Most importantly, by comparing the fermentation performances in catalytically active membrane reactor (CAMR), inert membrane reactor and batch reactor, CAMR exhibited the highest ethanol productivity (3.05 g L−1 h−1) and yeast mass concentration (26.41 g L−1), indicating a superior yeast growth rate and viability in CAMR. We attribute this to a "genuine" in situ removal ability of the bio-catalytically active membrane: the extracellular ethanol was promptly removed from the vicinity of the yeast, promoting a more rapid excretion of the inhibitor (intracellular ethanol) and thus maximally eliminated undesirable inhibition of the intracellular ethanol. • A yeast-immobilized catalytic membrane was fabricated by immersion phase inversion. • Superior fermentation capacity was obtained in high substrate concentration. • The catalytic membrane enhanced ethanol productivity in PVMR. • An increase of 35% in ethanol productivity was achieved. • The membrane exhibited a robust durability during long-time coupling process. [ABSTRACT FROM AUTHOR]