Ethanol-permselective Membranes Research Articles

Breakthroughs on tailoring membrane materials for ethanol recovery by pervaporation

• Mixed matrix membranes (MMMs) with well-designed membrane structures may provide both high permeability and membrane selectivity to break trade-off effect due to the better control over physi-/chemical micro-environment and cavity/pore size as well as size distribution. • Fillers should be orderly arranged in polymer matrix and form continuous transport channels for ethanol to full play the synergistic effect of polymer and fillers. • Building firm bonding interactions between filler and polymer is one of the most promising methods to strengthen the PV performance of MMMs. • The development of bioinspired materials and structures provides enlightening ideas for the construction of ethanol perm-selective membranes. Bioethanol, as a clean and renewable fuel, has gained increasing attention due to its major environmental benefits. Pervaporation (PV) is a promising and competitive technique for the recovery of ethanol from bioethanol fermentation systems due to the advantages of environmental friendliness, low energy consumption and easy coupling with fermentation process. The main challenge for the industrial application of ethanol perm-selective membranes is to break the trade-off effect between permeability and selectivity. As membrane is the heart of the pervaporation separation process, this article attempts to provide a comprehensive survey on the breakthroughs of ethanol perm-selective PV membranes from the perspectives of tailoring membrane materials to enhance PV separation performance. The research and development of polymeric and organic/inorganic hybrid membranes are reviewed to explore the fundamental structure-property-performance relationships. It is found that mixed matrix membranes with well-designed membrane structures offer the hope of better control overphysi-/chemical micro-environment and cavity/pore size as well as size distribution, which may provide both high permeability and membrane selectivity to break the trade-off effect. The tentative perspective on the possible future directions of ethanol perm-selective membranes is also briefly discussed, which may provide some insights in developing a new generation of high-performance PV membranes for ethanol recovery.

Highly selective carbon nanotube‐coupled graphene oxide‐incorporated polydimethylsiloxane membrane for pervaporative membrane bioreactor ethanol production

AbstractBACKGROUNDIn this work, a pervaporation membrane bioreactor (PVMBR) with the novel ethanol permselective membrane was used to achieve ethanol production with high yield. For this purpose, ethanol produced by Saccharomyces cerevisiae from glucose and pervaporation was performed via dense hydrophobic polydimethylsiloxane (PDMS) having carbon nanotube‐graphene oxide (CNT‐GO) mixed matrix membrane. Different percentages of CNT‐GO (0, 0.25, 0.5, 0.75, and 1) were loaded in polymer matrix. Synthesized membranes were analyzed using FESEM, AFM, FTIR and XRD.RESULTSThe bonding of groups in CNT‐GO, that was synthesized in this work, and membranes was characterized and confirmed using FTIR test. Considering the existence of 0.75 wt% of CNT‐GO in PDMS showed the highest ethanol selectivity of 22.5 in synthetic ethanol‐water solution, this incorporation was selected to use in PVMBR. The high ethanol selectivity was proved using XRD patterns. Also, FESEM indicated the optimum dispersion of nanoparticles at 0.75% of loading and AFM proofed the optimum surface roughness at this percentage.CONCLUSIONSThe results showed that maximum ethanol production in PVMBR was achieved after 44 h with productivity of 0.5g.l−1.h−1 in feed side and 9.89 g.l−1.h−1 in permeate side. In fact, PVMBR enhanced the ethanol concentration up to 26 times. © 2020 Society of Chemical Industry

Molecular simulation of penetration separation for ethanol/water mixtures using two-dimensional nanoweb graphynes

Abstract Graphyne is expected to be a new-class of highly-efficient sieving membranes due to its controllable uniform pore structure and ultrathin single-atom thickness. Herein, we computationally investigate the permeation performance of liquid ethanol–water mixtures across polyporous two-dimensional γ-graphyne sheets. It was found that, in the mixture, ethanol with larger molecular diameter permeates faster through the graphyne pores than water. The simulations demonstrate that pristine graphynes could act as highly-efficient ethanol-permselective membranes for separation of ethanol–water mixtures, with ethanol permeability remarkably higher than conventional membranes. This separation mechanism is distinctly different from the molecular-size dependent sieving process. The stronger hydrophobic interfacial affinity between graphyne and ethanol makes ethanol molecules preferentially adsorb on graphyne surface and selectively penetrate through graphyne pores. This penetration mechanism provides new understanding of molecular transport through atomically thick two-dimensional nanoporous membranes and this work is expected to be valuable in the potential development of highly-efficient membranes for liquid-phase mixture separation.

A Review of Membrane Materials for Ethanol Recovery by Pervaporation

Due to an emerging scarcity of oil resources and an associated increase of oil prices, biofuels (e.g., ethanol) play an important role in the energy crisis. Fermentation is a common process for producing ethanol from renewable biomass. Pervaporation is an attractive technique for the recovery of ethanol from the fermentation systems. Separation membrane is the key element in the pervaporation separation equipments. In this article, the pervaporation performances of ethanol-permselective membranes presented in the recovery of ethanol from dilute ethanol aqueous solution are reviewed. An analytical overview on the challenges and opportunities, and the prospect of ethanol-permselective membranes by pervaporation is also discussed.

Pervaporation of ethanol—water mixtures through poly(1-trimethylsilyl-1-propyne) (PTMSP) membranes

The separation of alcohol—water mixtures by pervaporation has been preferentially carried out through hydrophobic membranes because it is more practical to permeate alcohol through the membrane. Nevertheless, most polymeric membranes are water permselective as the molecular size of water is smaller than that of ethanol. Ethanol-permselective membranes have been limited to silicon- and fluorine-containing polymers, for example, polydimethylsiloxane (PDMS), poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(tetrafluoroethylene) derivatives. PTMSP is known to show preferential permeation of ethanol in the pervaporation of ethanol—water mixtures. The permselectivity of this material is related to the existence of free volume and to the hydrophobicity of the membrane surface. The separation factor (α H 2O EtOH) reached a value of 10.7 at 10 wt% of ethanol in the feed, and after 450 h it decreased to an average value of 8. The initial value is similar to that of PDMS, a well-known etanol-permselective membrane. Although PTMSP presented good characteristics for the separation of ethanol—water mixtures, the separation factor and the specific permeation rate ( R) decrease with operation time due to a swelling process; however, the latter reached a value similar to the initial one after this period.

Synthesis and stable high oxygen permeability of poly(diphenylacetylene)s with two or three trimethylsilyl groups

We synthesized two new poly(diphenylacetylene)s having two or three trimethylsilyl groups and found these membranes having extremely high oxygen permeabilities of more than 1000 barrers which are of the same order as that for poly[1-(trimethylsilyl)-1-propyne]. Whereas oxygen permeability of poly[1-(trimethylsilyl)-1-propyne] was reported to decrease largely with time, these high oxygen permeabilities were stable for several months. These membranes also showed ethanol permselectivities because of their hydrophobicity. It was found that the introduction of two or three trimethylsilyl groups to poly(diphenylacetylene) was very effective for obtaining stable high oxygen permeable and ethanol permselective membranes.

Poly(p-substituted phenylacetylene) with perfluoroalkyloxydimethylsilyl side groups for oxygen and ethanol permselective membrane

p-(1H,1H,2H,2H-perfluorodecyloxydimethylsilyl)phenylacetylene(ACf8) and p-(1H,1H,2H,2H-Perfluorohexyloxydimethylsilyl)phenylacetylene(ACf4) were synthesized and copolymerized with p-trimethylsilylphenylacetylene(ASi). The resulting copolymers, copoly(ACf8/ASi) and copoly(ACf4/ASi), were fabricated to tough membranes showing high oxygen permeabilities(Po2) of 10-8 cc(STP)·cm/cm2·s·cmHg and high oxygen permselectivities(α=Po2/Pn2) of more than 2.7. In particular, a copoly(ACf4/ASi) containing 15.1 mol% of ACf4 unit showed the best result: Po2=3.51x10-8 cc(STP)·cm/cm2·s·cmHg and α=3.04. The values were in a top level and very close to those of ‘upper bound’ line in an α-Po2 plot of data in the literature. In addition, copoly(ACfn/ASi) membranes were ethanol permselective owing to water repellency of the perfluoroalkyl groups. Copoly(ACf4/ASi) membranes showed better oxygen and ethanol permselectivity than copoly(ACf8/ASi) membranes.

Trimethylsilyl‐group containing polyphenylacetylenes for oxygen and ethanol permselective membranes

AbstractPhenylacetylenes having one or two trimethylsilyl groups at their benzene ring were synthesized, and polymerized by [Rh(cyclooctadiene) (PPh3)2]PF6, [Rh(norbornadiene)Cl]2, or WCl6 to afford high molecular‐weight polymers in high yields. These poly(phenylacetylene)s were soluble in many kinds of solvents and were fabricated to tough membranes by the solvent casting method. The oxygen permselectivities of these membranes were very good. The oxygen permeability coefficients (Po2) and oxygen separation factors (α = Po2/PN2) of poly[2,4‐(o,p)‐bis(trimethylsilyl)phenylacetylene] [poly (o‐1‐p‐1)] and poly[(4(p)‐trimethylsilyl)phenylacetylene] [poly(p‐1)] membranes were 4.73 × 10−8 cc(STP) cm/cm2 s cmHg and 2.65, and 1.52 × 10−8 cc(STP) cm/cm2 s cmHg and 3.39, respectively. In the case of poly(o‐1‐p‐1), Po2 was comparable to that of polydimethylsiloxane (PDMS) and α was higher than that of PDMS. However, the Po2 value reduced to 48% of its initial value in about 1 year. In the case of poly(p‐1), the Po2 value did not change in about 1 year. Ethanol permeated preferentially through these membranes (αEtOH > 1) in pervaporation of aqueous ethanol solution, whereas poly(phenylacetylene) [poly(PhA)] showed water permselectivity (αEtOH < 1). These favorable effects of trimethylsilyl groups on the oxygen and ethanol permselectivities were discussed on the basis of comparison with those of poly(PhA), other poly(substituted phenyl‐acetylene)s, and trimethylsilyl‐group containing polystyrenes. © 1994 John Wiley & Sons, Inc.

末端にアルコキシシリルスチレンを持つパーフルオロアルカンの合成，重合と得られたポリマーの酸素及びエタノール選択透過膜への利用

末端にアルコキシシリルスチレンを持つ2種のパーフルオロアルカンを合成, 重合し, 酸素及びエタノール選択透過膜への利用を検討した. p- (1H, 1H, 2H, 2H-パーフルオロアルキルオキシジメチルシリル) スチレンをバルク共重合することにより丈夫な膜を得ることができ, この膜は優れた酸素選択透過性を有していた (α=3.36, PO2=6.99×10-9cc (STP) ・cm/cm2・s・cmHg). このポリマーを少量架橋ポリジメチルシロキサン (PDMS) に添加した膜は高いエタノール選択透過性を示した (αEtOH=22.3, P=2.06×10-2g・m/m2・h). いずれもパーフルオロアルキル基の性質が透過に効果的に生かされた結果であると考えられた. またp- (1H, 1H, 2H, 2H-パーフルオロアルキルジアルコキシシリル) スチレンのパーフルオロアルキル基の性質とアルコキシキ基の反応を生かしてPDMS膜の酸素選択透過性を改善することができた.

Relationship between permselectivity and permeability in pervaporation of water/alcohol mixture

The evaporation mechanism of a water/alcohol mixture with a polymeric membrane was investigated. Flory-Huggins thermodynamics was adopted to introduce the selective dissolution factor, R. It was shown that the value of R of a water permselective membrane increases as permeability decreases, and that it has no upper limit. For an ethanol permselective membrane, R has a maximum value at a certain value of the swelling ratio. Making some assumptions for R, a semi-quantitative relationship between permselectivity and permeability, J, was derived for a water permselective membrane and examined experimentally. When the swelling ratio is changed, it can be said that selectivity is proportional to J 1−( 1 s ) depending on s, the molecular volume ratio of water to alcohol.

Poly[ p-1H,1H,2H,2H-perfluoroalkyloxydimethylsilyl)styrenes] as materials for ethanol-permselective membranes

Several p-(1H,1H,2H,2H-perfluoroalkyloxydimethylsilyl)styrenes having perfluoroalkyl groups with different chain lengths were synthesized and polymerized. The polydimethylsiloxane-based blend membranes which contained a very small amount (1.0 wt%) of poly[ p-(1H,1H,2H,2H-perfluoroalkyloxydimethylsilyl)styrene] had good ethanol permselectivity. All of their separation factors ( α EtOH) and permeation rates ( P) were higher than those of polydimethylsiloxane. In particular, poly[ p-(1H,1H,2H,2H-perfluorohexyloxydimethylsilyl)styrene] showed the best performance ( α EtOH = 22.3, P = 2.06 × 10 −2 g m m −2 h −1). This was attributed to the characteristics of the fluorine-containing polymers which were accumulated at the membrane surface.

Pervaporation of organic liquid-water mixtures through substituted polyacetylene membranes

A poly [1-(trimethylsilyl)-1-propyne][poly(TMSP)] membrane proved highly permselective for ethanol in EtOH-H 2O pervaporation, where the separation factor, α H 2O EtOH, reached 17 at 10 wt.% of ethanol in the feed. This value is similar to that for poly (dimethylsiloxane), a well-known ethanol-permselective membrane. Because of membrane swelling, α H 2O EtOH value decreased and the total specific permeation rate increased with increasing ethanol content in the feed. In the pervaporation of combinations of water and various organic liquids through poly (TMSP), the α H 2O org.liq. values for acetonitrile and acetone exceeded 70 at ≈10% of organic liquid in the feed. In the EtOH-H 2O pervaporation through various substituted polyacetylene membranes, aliphatic polymers {e.g., poly [1-(n-hexyldimethylsilyl)-1-propyne] and poly (1-chloro-1-octyne)} showed more or less ethanol permselectivity, while aromatic polymers [e.g., poly (1-chloro-2-phenylacetylene) and poly (1-phenyl-1-propyne)] were rather water-permselective.

Separation of ethanol from ethanol/water mixtures by plasma-polymerized membranes from silicone compounds

The separation by pervaporation of ethanol/water mixtures was investigated. Plasma polymerization was used to produce membranes. Ethanol-permselective membranes can be prepared from various silicone and silane monomers under extremely mild polymerization conditions. These membranes have polydimethylsiloxane-like structures and selectivity factors of 1.5~5.2. Further investigations were carried out on the mechanism of permeation through plasma-treated silicone rubber membranes and silicone oil membranes. Highly permselective membranes can be prepared by surface treatment of thin polydimethylsiloxane membranes with silane compounds containing octadecyl groups. An ethanol permselectivity, α EtOH, of 18.0 and a flux of 0.015 kg/cm 2-hr were obtained with these membranes. This report gives a novel method for producing ethanol-permselective membranes.