Ethanol Dehydration Performance Research Articles

Enhanced ethanol dehydration performance of cationic COFs filled anionic alginate hybrid membranes

Adding charged fillers to incorporate long-range electrostatic interactions is an effective way to reduce structure defects and improve separation performance of polyelectrolyte membranes. In this study, three cationic covalent organic frameworks (COFs), TpEB, TpTGCl, and TpPy, were incorporated into anionic alginate to prepare hybrid membranes for pervaporation dehydration of ethanol. With the increase of electrostatic interaction, the decrease in the mobility of polymer chains leads to an increase in the crystallinity and selectivity. Meanwhile, the inherent hydrophilic channels of iCOFs provided additional mass transfer channels, increasing the membrane permeability. When separating a 90 wt% ethanol/water mixture at 76 °C, the hybrid membrane containing 15 wt% TpEB exhibited the highest separation performance with a permeation flux of 2460 g m-2 h-1 and a separation factor of 2110, and it also demonstrated ideal long-term stability. This work provides a new perspective for the selection of fillers in the design process of hybrid membranes in the future.

PDMS-b-PI-b-PDMS triblock copolymer self-supported membranes with microphase separated structures for efficient ethanol dehydration

High concentration ethanol dehydration had attracted great attentions through membrane separation methodology in the past years, of which membrane is the key factor to decide the separation performance. In this paper, a series of novel self-supported membranes were prepared based on PDMS-b-PI-b-PDMS triblock copolymers by solution casting method. The composition and structure of the copolymers were confirmed by FTIR, GPC and 1HNMR. The self-supported dehydrated membranes showed good thermal, chemical, and mechanical stability. Their water contact angle decreased obviously from 96° to 61° with the increasing PI contents from 50% to 100% in the triblock copolymers. The clear microphase separation with continuous PI domains of PDMS-b-PI-b-PDMS based membranes were observed in the TEM image. The microphase domain size increased with the increasing of molecular weight and content of PDMS. The higher domain size resulted in lower flux and higher separation factor of these membranes. The membrane M3, which has 70 wt% of PI content in the triblock copolymer, exhibit excellent ethanol dehydration performance with flux of 3.96 kg·m−2·h−1, separation factor of 255 and maintained 120 h with barely decreasing in separation performance, for 95 wt% ethanol solution at 20 °C. When elevated the feed temperature upto 60 °C, the dehydration flux increased to 16.90 kg·m−2·h−1, and the separation factor decreased to 37. Membranes with microphase separation have great potential application in the ethanol dehydration.

Recent advances in sodium alginate‐based membranes for dehydration of aqueous ethanol through pervaporation

AbstractSodium alginate (SA) is a progressive material for membrane fabrication. The technological development of SA‐based membranes has made a significant contribution to the separation techniques, especially in aqueous organic solutions. The outstanding performance of SA is attributed to its outstanding structural flexibility and hydrophilicity. In view of structural characteristics, SA membranes have immense utilization in the pervaporation separation of organics. Among various organics, dehydration of aqueous ethanol is employed as a standard to check the success of pervaporation (PV) membrane. Because ethanol and water have comparable molecular sizes, thus difficult to extract water from aqueous ethanol mixtures than it is for other organics. A literature survey shows that wide‐ranging data are available on the PV performance of SA and its modified membranes. In this context, the present review addresses the recent advances made in SA membranes for enhanced ethanol dehydration performance during the last decade. Available data since 2010 has been compiled for grafted, crosslinked, blend, mixed matrix, and composite hybrid sodium alginate membranes in terms of separation factor, permeation flux, and pervaporation separation index PSI. The data are assessed with reference to the effect of feed composition, membrane selectivity, flux, and swelling behavior.

Ethanol dehydration performance of three types of commercial-grade zeolite permselective membranes.

Many organic solvents form difficult-to-separate mixtures with water and have an affinity for water, making drying a potential reuse prerequisite. Pervaporation (PV) and vapor permeation (VP) membrane technologies hold promise for energy-efficient solvent drying. Several water-selective membrane materials are commercially available, but performance data is limited, particularly for two recently commercialized membrane materials: chabazite (CHA) and T-type zeolites. In this work, commercial-grade samples of CHA and T-type membranes, along with a NaA zeolite membrane, were evaluated for the removal of water from ethanol. The CHA sample had the highest initial PV water permeance (6820 GPU) and water permselectivity (3430) with 5 wt% water in ethanol at 50 °C. Initial NaA membrane performance was slightly lower (6060 GPU and 3260), while the T-type membrane had the lowest initial permeance and selectivity (4260 GPU and 1090). Performance declined over time, most notably for the NaA membrane, for which water permeance fell over 50% through 39 days of testing. The T-type membrane exhibited the steadiest PV water permeance, but the most variable ethanol permeance. The PV performance of the three membranes largely overlapped the predicted range for T-type membranes. That performance generally exceeds the anticipated ethanol drying performance of non-zeolitic PV membranes but is less than that predicted for NaA and CHA membranes. The present CHA membrane results, along with other recent reports, refine earlier predictions of the ethanol dehydration performance of that type of zeolite. The changing performance with time should be understood to properly design a solvent dehydration system.

Preparation and pervaporation performance of PVA membrane with biomimetic modified silica nanoparticles as coating

Polyvinyl alcohol (PVA) has been widely used in pervaporation dehydration due to its low price and good stability. However, the inherent “trade-off” effect of polymer membrane makes the pervaporation performance relatively limited. In this work, the rough and super-hydrophilic surface were constructed by biomimetic modification of silica (SiO2) coating on the PVA membrane, which achieved simultaneous growth of total flux and separation factor compared with the control, and overcame the “trade-off” effect. The morphology, structure and hydrophilicity of membranes were characterized. Results demonstrated that PVA/polydopamine (PDA)/SiO2 composite membranes had strong hydrophilicity and high surface roughness. In addition, the effects of SiO2 loading amount, operating temperature, feed ethanol concentration and long-term stability on the ethanol dehydration performance were investigated. For the PVA/PDA/SiO2-6 composite membrane, total flux was 1388 g m−2 h−1, and the separation factor was 150(69 °C,90 wt% ethanol concentration), which was 1.8 times and 1.4 times that of the pristine PVA membrane, respectively.

Semi-pilot Tests of Ethanol Dehydration using Commercial Ceramic Pervaporation Membranes

Most research efforts about pervaporation in the literature have focused on membrane synthesis, trying to improve the membrane properties (flux and selectivity). However, industrial applications of the pervaporation technology could become attractive if the current available membranes proved to have sufficient and stable performance in order to be integrated in the toolbox of process engineers, as a complementary separation process. In this study, the ethanol dehydration performance of commercial hybrid silica membranes (HybSi®) was assessed in a semi-pilot pervaporation unit from a process-based perspective. The aim of the study is to reveal the high potential of the process and to create a benchmark for future studies in the field. The experimental results revealed that the proposed pervaporation process can efficiently break the ethanol/water azeotrope, allowing the production of high purity ethanol. The overall assessment of the obtained pilot results showed that the proposed process is quite efficient for attracting the industrial interest.

Ternary cross-linked PVA-APTES-ZIF-90 membrane for enhanced ethanol dehydration performance

Ternary cross-linked PVA-APTES-ZIF-90 membrane for enhanced ethanol dehydration performance

Vertically oriented Fe3O4 nanoflakes within hybrid membranes for efficient water/ethanol separation

Two-dimensional (2D) materials have exhibited tremendous potential as functional fillers of hybrid membranes. Manipulating the orientation of 2D fillers in hybrid membranes, a decisive factor in determining the separation performance, proves a critical challenge. In this study, hybrid membranes with vertical superparamagnetic Fe3O4 nanoflakes and sodium alginate (SA) matrix were prepared via the external magnetic field. The vertically aligned Fe3O4 nanoflakes constructed highly efficient interfacial regions for penetrants transport in hybrid membranes, which shortened the molecular diffusion pathways. In addition, the orientated fillers increased surface hydrophilicity of the hybrid membranes by enhancing the surface roughness. The effect of Fe3O4 nanoflakes orientation and content in hybrid membranes on the separation performance was systematically investigated. When the filler content is 0.4 wt%, the hybrid membrane with vertically aligned Fe3O4 nanoflakes achieved superior ethanol dehydration performance with an optimized selectivity of 3248 ± 233 and a decent water permeability of 1436 ± 169 Barrer, which increased by 68% and 133% compared to the hybrid membranes with horizontally aligned Fe3O4 nanoflakes, respectively. This strategy of manipulating 2D filler orientation may render hybrid membranes with more possibilities for enhanced separation performances.

Intensification of water/ethanol separation by PVA hybrid membrane with different functional ligand UiO-66-X nanochannels in pervaporation process

In order to investigate the effects of MOFs by altering ligands with various functional groups on separation selection in pervaporation dehydration, three hydrophilic UiO-66-X nanoparticles were respectively synthesized and blended into poly (vinyl alcohol) matrix to fabricate water-selective membrane for ethanol dehydration via PV technology. Both the experimental and molecular simulation results confirmed the UiO-66-X counterbalancing factors of enhanced polarity and suitable pore size gave rise to the optimal performance in ethanol dehydration. The PV performances could be tuned by the type and quantity of functional groups carried by UiO-66-X nanoparticles. As a result, the pore aperture of UiO-66-(COOH)2 nanoparticles provided continuous channel for water diffusion, and water molecules could also be activated attributed to the strong interaction between the UiO-66-(COOH)2 nanoparticles and water molecules which enhanced the penetration and diffusion of water molecular in hybrid membrane to increase the water flux. The optimized hybrid membranes with UiO-66-(COOH)2 loading of 8 wt% exhibited the total flux of 979 ± 7 g/(m2·h) and a separation factor of 2084 ± 21.

Mildly acidic aluminosilicate catalysts for stable performance in ethanol dehydration

Ethanol dehydration is effectively catalyzed by strongly acidic zeolites which, however, exhibit poor time-on-stream stability. For example, HZSM-5 features strong acid sites, catalyzes ethylene oligomerization, and is prone to coking. Alumina and silica-alumina on the other hand have lower acidity, are relatively stable, but reach only low activity. Here, a series of mesoporous aluminosilicate catalysts was prepared by non-hydrolytic sol-gel (NHSG) and are shown to feature an intermediate level of acidity (both in strength and nature), resulting in intermediate catalytic performance. Importantly, the best NHSG-made samples were very stable with time on stream, did not produce any traces of ethylene oligomers, did not show any trace of coke formation, and their texture was unaffected. Characterization (ICP-OES, N2-physisorption, TEM, XPS, IR-pyridine, Raman and solid state NMR spectroscopies) revealed that this behavior must be correlated with the remarkable degree of homogeneity in the NHSG-made aluminosilicate (only tetrahedrally coordinated Al species).

Poly(vinyl alcohol)-Modified Membranes by Ti3C2T x for Ethanol Dehydration via Pervaporation.

In this paper, PVA/Ti3C2Tx mixed matrix membranes (MMMs) were prepared by mixing the synthesized Ti3C2Tx with the PVA matrix, and the pervaporation (PV) performance of the ethanol–water binary system was tested. The morphology, structural properties, and surface characteristics of the membranes were investigated by scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, degree of swelling, and water contact angle. The PVA/Ti3C2Tx MMMs exhibit excellent compatibility and swelling resistance. Moreover the effects of the Ti3C2Tx filling level, feed concentration, and operating temperature on the ethanol dehydration performance were systematically studied. The results demonstrated that the separation factor of PVA/Ti3C2Tx MMMs was significantly increased because of Ti3C2Tx promoting the cross-linking density of the membrane. Specifically, the membrane showed the best PV performance when Ti3C2Tx loading was 3.0 wt %, achieving a separation factor of 2585 and a suitable total flux of 0.074 kg/m2 h for separating 93 wt % ethanol solution at 37 °C.

Ultraviolet-initiated graft polymerization of acrylic acid onto thin-film polyamide surface for improved ethanol dehydration performance of pervaporation membranes

In this study, polyacrylic acid (PAA) was grafted onto a polyamide (PA) surface through ultraviolet-initiated graft polymerization to improve the pervaporative dehydration of aqueous alcohol solutions. The PA layer was formed on the surface of a polyacrylonitrile support by the interfacial polymerization of 1,4-bis(3-aminopropyl)piperazine and trimesoyl chloride. Afterward, the PAA was deposited under varying grafting conditions—different acrylic acid concentrations, periods of irradiation time, and irradiation distances. Attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectra indicated the presence of more carboxyl groups on the membrane surface after grafting PAA. Images from field emission scanning electron microscopy and atomic force microscopy illustrated that the membrane became rougher. PAA also improved the membrane hydrophilicity. The dehydration of 90 wt% aqueous ethanol solutions by pervaporation demonstrated that the flux and water concentration in permeate were enhanced from 803 ± 55 to 830 ± 59 g m−2 h−1 and 84.9 ± 2.5 to 99.5 ± 0.3 wt%, respectively. Furthermore, the PAA-PA membranes showed stable performance at wide operating conditions.

Comparison of Chemical Cross-Linkers with Branched and Linear Molecular Structures for Stabilization of Graphene Oxide Membranes and Their Performance in Ethanol Dehydration

We report the fabrication of cross-linked graphene oxide (GO) membranes and their use for dehydration of ethanol by vapor permeation. Two compounds with branched structures, namely, a humic acid-li...

Preparation and characterization of chitosan-boehmite nanocomposite membranes for pervaporative ethanol dehydration

Pervaporative ethanol dehydration was studied using some chitosan-boehmite nanocomposite membranes. Nanocomposite membranes were prepared by incorporation of 1 and 2 Wt. % loading of the boehmite nanoparticles synthesized by the low temperature sol-gel process. The prepared samples were characterized by FTIR, FESEM and XRD analysis. The results showed the filler particles uniform distribution within the chitosan matrix. Pervaporation performance of the prepared pristine and the nanocomposite membranes were evaluated for ethanol dehydration. The 2 Wt. % loaded boehmite nanocomposite membrane exhibited highest ethanol dehydration performance for 20 Wt. % water content feed at 50 °C as 0.513 kg/m2 h and 676 as permeation flux and separation factor revealed ∼50% and 2 times increments, respectively.

Two-dimensional MXene membrane for ethanol dehydration

Two-dimensional MXene membranes have been successfully used in separation technology. With controllable interlayer nanochannels, abundant surface-terminating groups and hydrophilicity, MXene membranes also exhibit the potential in alcohol dehydration. Here, 2-μm-thick MXene membranes stacked by Ti3C2Tx nanosheets were fabricated and applied in ethanol dehydration for the first time. Effects of the feed ethanol concentration and operating temperature on the ethanol dehydration performance of the MXene membrane were investigated through a pervaporation process. The water/ethanol separation factor of the MXene membrane increased with increasing feed ethanol concentration. Additionally, the MXene membrane exhibited better ethanol dehydration performance at room temperature compared with that at elevated temperature. It gave a water/ethanol separation factor of 135.2 with a total flux of 263.4 g m−2 h−1 at room temperature for the azeotrope dehydration (95% ethanol mixed with 5% water). MXene membranes are promising in applications of pervaporation dehydration and solvent separation.

Process analysis of extractive distillation for the separation of ethanol–water using deep eutectic solvent as entrainer

Deep eutectic solvents (DESs) as novel entrainers can be used for the separation of azeotropic mixture, and have received much attention in recent years. However, the researches about DESs mainly focus on vapor–liquid equilibrium (VLE) and extractive distillation experiment. In this work, an overall extractive distillation process for ethanol dehydration using ChCl/Urea (1:2) as entrainer is investigated. The physical properties of the DES are defined by correlating the experimental data. Three thermodynamic methods are employed to describe the phase behavior of ethanol–water–ChCl/Urea (1:2) system. COSMO-based theory is adopted to explain the differences in separation performance among ChCl/Urea (1:2), glycerol and [EMIM][BF4]. The design parameters of extractive distillation process are optimized by multi-objective generic algorithm (MOGA) with minimum total annual cost (TAC), minimum CO2 emissions ECO2 and maximum efficiency indicator of extractive section (EExt) as objective functions. In addition, the control structure of extractive process is studied by Aspen Dynamics, and the proposed control structure could resist fresh feed flow rate and composition disturbances. The results show that ChCl/Urea (1:2) exhibits better separation performance in ethanol dehydration compared with glycerol and [EMIM][BF4]. Both COSMOSAC model relying on molecular information and NRTL model based on experimental data can well describe the vapor–liquid behavior containing ChCl/Urea (1:2). Entrainer purity plays an important role in extractive distillation process, and a proper concentration rather than nearly pure entrainer should arouse our attention in extractive distillation process. DESs as promising novel entrainers can be used in extractive distillation industrial for separating azeotrope.

Dehydration of Bioethanol to Ethylene over H-ZSM-5 Catalysts: A Scale-Up Study

Bioethanol dehydration was carried out in a bench scale reactor-loaded H-ZSM-5 molded catalyst, which increased by tens of times more than at lab scale (up to 60 and 24 times based on the amount of catalyst and ethanol flow rate, respectively). From the results of the lab scale reaction, we confirmed the optimum Si/Al ratio (14) of H-ZSM-5, reaction temperature (~250 °C), and weight hourly space velocity (WHSV) (<5 h−1) indicating high ethanol conversion and ethylene selectivity. Five types of cylindrical shaped molded catalysts were prepared by changing the type and/or amount of organic solid binder, inorganic solid binder, inorganic liquid binder, and H-ZSM-5 basis catalyst. Among them, the catalyst exhibiting the highest compression strength and good ethanol dehydration performance was selected. The bench scale reaction with varying reaction temperature of 245–260 °C and 1.2– 2.0 h−1 WHSV according to reaction time showed that the conversion and ethylene selectivity were more than 90% after 400 h on stream. It was also confirmed that even after the successive catalyst regeneration and the reaction for another 400 h, both the ethanol conversion and ethylene selectivity were still maintained at about 90%.

Synthesis of sphere-like polyelectrolyte complexes and their homogeneous membranes for enhanced pervaporation performances in ethanol dehydration

A series of sphere-like polyelectrolyte complexes (PECs) and their homogeneous polyelectrolyte complex membranes (HPECMs) were synthesized by using sodium carboxymethyl cellulose (CMCNa) and poly(diallyldimethylammonium chloride) (PDDA). Different compositions or ionic complexation degrees (ICD) of PECs could be characterized by FT-IR spectra. The circular dichroism spectrum (CD) and field emission scanning electron microscopy (FESEM) were employed to examine the conformation and morphology of PECs, respectively. Zeta (ζ) potential was utilized to investigate the charge density of PEC particles while the surface hydrophilicity of HPECMs was studied by using contact angle (CA) meter. When subjected to ethanol dehydration, HPECMs revealed a satisfactory pervaporation performance and desired anti-trade-off phenomenon. For HPECM 0.31 and HPECM 0.57, the permeation fluxes were 2.25 kg m−2 h−1 and 2.93 kg m−2 h−1, and the water content in permeate reached up to 99.35 wt% and 99.38 wt%, with respect to 10 wt% water in feed under 70 °C. All the results indicated that small-sized and sphere-like PECs were truly in favor of enhancing the pervaporation performance in ethanol dehydration.

Influence of double-network interpenetration on ethanol dehydration performance of PVA-based pervaporation membranes

Thermal crosslinked double-network poly (vinyl alcohol) (PVA) is prepared by applying the sequential method. The obtained membrane is characterized by thermogravimetric analysis (TGA), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy and contact angle analyses. It is concluded from FTIR analysis, contact angle measurements and measuring of swelling degree at different feed concentrations that the interpenetrating of the second network, that is the double network (DN), decreases the hydrophilicity of the membrane, while improving the thermal behavior and stability under high temperature. For the sake of the comparison of PVA and DN-PVAs selectivity, total permeation flux, individual fluxes and pervaporation separation index are evaluated for the dehydration of ethanol solution with a feed composition of 85/15 wt% ethanol/water solution at 40–60 °C. Furthermore, the effect of feed temperature on the permeation flux is expressed by the Arrhenius relationship. The performance of DN-PVAs membrane is appraised according to the change in feed concentration and operating temperature. The ethanol concentration in the feed is 75–95 wt% the DN-PVAs has flux values in the range of 41–414 g/m2 h and separation factor of 105–376 at the operating temperature 40–60 °C.

Graphene oxide quantum dots incorporated nanocomposite membranes with high water flux for pervaporative dehydration

Graphene oxide quantum dots (GOQDs), which inherit the monolayer of sp2 carbon atoms structure and hydrophilic groups as graphene oxide (GO) sheets, but with a quantum lateral size less than 100 nm, may hold great promise in membrane preparation. In this study, a novel nanocomposite membrane by mixing GOQDs with sodium alginate (SA) matrix was prepared for ethanol dehydration. GOQDs with an average lateral dimension around 3.9 nm provided additional shorter and less tortuous transport pathways for water molecules to penetrate the membrane compared to microsized GO sheets. Benefiting from the nanosize and high hydrophilicity of GOQDs, the nanocomposite membrane exhibited favorable ethanol dehydration performance with a total permeation flux of 2432 ± 58 g m−2 h−1, which was 60% higher than that of pristine alginate membrane, and a separation factor of 1152 ± 48. Incorporating GOQDs into the membranes can be an effective approach to improving the water permeation for water-permselective pervaporation membranes.