Feed Mixture Composition Research Articles

Maximizing Adsorption Involving Three Solutes on Enhanced Adsorbents Using the Mixture-Process Variable Design.

Unmodified (UN), acid-treated (AT) and microwave-acid-treated (MAT) activated carbons were optimized for their solute removal efficacies by adjusting feed mixture compositions and process conditions. Acetaminophen, benzotriazole, and caffeine were used either individually or as binary/ternary mixtures in this study. The process conditions considered were the pH, adsorbent dosage, and type of adsorbent. Experimental responses such as total adsorbent loading (qtotal) and total percentage removal (PRtotal) were fitted with empirical models that had high adjusted R2 (>0.95), insignificant lack of fit (p-value > 0.22), and high model predictive R2 (>0.93). Mixture compositions of the feed were found to interact significantly not only among themselves but with process variables as well. Hence, adsorption optimization must simultaneously consider mixture as well as process variables. The conventional response surface methodology for mixtures, termed as ridge analysis, optimizes mixture compositions at specified values of process variables. An improved steepest ascent method which considers mixture and process variables simultaneously was developed in this work. This could track the path of steepest ascent toward globally optimal settings, from any arbitrary starting point within the design space. For the chosen adsorbent, optimal settings for feed mixture compositions and pH were found to change along this steepest ascent path. The feed compositions, pH, and adsorbent dosage identified for maximum adsorbent utilization were usually quite different from those identified for maximum total percentage removal. When both these objectives were optimized together, the most favorable compromise solutions for qtotal and PRtotal were, respectively, 264.1 mg/g and 43.4% for UN, 294.9 mg/g and 52.5% for AT, and 336.6 mg/g and 55.9% for MAT.

Characterisation of Romakon™-PM pervaporation membranes for the separation of dilute aqueous alcohol mixtures

Thin-film composite pervaporation membranes with selective layer from pyromellitic dianhydride -4,4′ oxydianiline polyimide on porous poly(amide-imide) support (Romakon™-PM) for treatment of water/ethanol mixtures with exceeding water content (>50 wt% water) are characterised by the use of scanning electron microscopy, atomic force microscopy and X-ray diffraction. Membranes showed high values of flux, separation factor and PSI (up to 774) in the selected feed mixture composition range. The influence of the support and structural features of the polyimide in the coating layer on the transport properties is discussed. The membranes are successfully tested in terms of pervaporation dehydration of beer. The influence of the permeate temperature on the separation process performance is discussed.

Anaerobic co-digestion of the process water from waste activated sludge hydrothermally treated with primary sewage sludge. A new approach for sewage sludge management

Hydrothermal carbonization (HTC) is a suitable technology for managing wastes with a high moisture content, providing a carbon-rich and high energy density material called hydrochar and a process water (PW) with significant organic matter content. The aim of this work was to develop a new approach to sewage sludge management involving anaerobic digestion (AD) of the PW of dewatered waste activated sludge (DWAS) with primary sewage sludge (PSS). The process was optimized by performing semi-continuous experiments with different feed mixture compositions (10% PW/90% PSS and 5% PW/95% PSS, on a COD basis), organic loading rates (OLR; 1.5 and 2.5 g COD L−1 d−1), and temperature regimes (mesophilic and thermophilic). The combination of mesophilic conditions, a 10% PW/90% PSS feed mixture and OLR of 1.5 g COD L−1 d−1 provided concentrations of volatile fatty acids <400 mg COD L−1 in addition to a methane yield (172 ± 11 mL CH4 g−1 CODadded), 1.15 times the value for the control test (100% PSS). Therefore, the energy content of hydrochar from HTC of DWAS followed by AD of the process water with primary sewage sludge enhances the valorization of this renewable residue.

Ionic liquid modified multiwalled carbon nanotube embedded styrene butadiene rubber membranes for the selective removal of toluene from toluene/methanol mixture via pervaporation

Abstract Present work reports the fabrication of elastomeric membrane based on ionic liquid functionalized multiwalled carbon nanotubes (f-MWCNT) incorporated Styrene butadiene rubber (SBR) for the separation of azeotropic composition of toluene and methanol. The fabricated membranes were characterized by morphological analysis using transmission electron microscopy and glass transition temperature and heat capacity measurements by differential scanning calorimetry. Composite membranes demonstrate impressive separation performance with preferential selectivity towards toluene and 5 phr f-MWCNT loaded membranes was found to show the best result with respect to toluene flux and selectivity. Optimal separation performance with the permeation flux 225% of SBR control membrane and separation factor of 128 (1.6 times of SBR control membrane) is obtained for this membrane. The concurrent optimization of the physical and chemical structures of toluene permeation path on f-MWCNT surface provides the membrane with high-efficiency toluene permeation. Ionic liquid on MWCNT surface confer aromatic pi-pi interaction with toluene molecules leading to greater toluene affinity and higher repellency against methanol. Pervaporation characteristics of the membranes were also strongly influenced by the feed mixture composition. The study confirmed that increasing toluene concentration improved the toluene flux but reduced the separation factor. The experimental pervaporation fluxes were compared with the calculations based on modified Maxwell–Stefan equation. The model allows a good quantitative prediction of experimental flux values.

Development and characterisation of carotenoid-rich microencapsulates from tropical fruit by-products and yellow tamarillo (Solanum betaceum Cav.)

Mango (Mangifera indica) peel powder (MP), banana (Musa paradisiaca) peel powder (BP), and yellow tamarillo freeze-dried pulp (Solanum betaceum Cav.) (YT), were selected as raw materials to obtain eight microencapsulates (M1-M8) by spray-drying with maltodextrin (MD) at two air inlet temperatures (130 °C and 180 °C) and with four feed mixture compositions. Their physicochemical characterisation was performed by measuring: pH, soluble solids (°Brix), Aw, and colour CIELAB (L*, a* and b*) parameters. The morphology analysis performed by SEM, determined that the powders showed a regular and spherical microstructure. The qualitative and quantitative carotenoid analyses carried out by HPLC-PDA-APCI/MS methodology, both in the raw materials and microencapsulates, showed that the drying temperature significantly affected the carotenoid content. The major carotenoids in the samples were β-cryptoxanthin C14:0, β-cryptoxanthin C16:0, β-carotene, β-cryptoxanthin C12:0, β-cryptoxanthin, zeaxanthin, and lutein. Among the microencapsulates, M2 and M4 samples (dried at 130 °C) exhibited the highest values of carotenoid content with 1.025 and 1.296 mg β-carotene/100 g sample, respectively. Thermal analyses showed that the powders were stable up to 100 °C. During the storage stability test at 18 °C, the carotenoid content diminished following a first order kinetic, showing the RH strongly influences the stability of microencapsulates.

The effect of dha omega-3 feeding in the high yielding holstein herd

The aim of this study was to analyse the effect of supplementary feeding of DHA (Docosahexaenoic Acid) rich algae product (Algae STM Alltech Inc.) on production of milk, fat and protein as well as on reproduction of high yielding Holstein dairy herd. Field trial was set up on Top 10 dairy farm in western part of Slovakia, under commercial conditions. The data of high yielding dairy cows, separated in two groups of 30 (control) and 29 (trial) animals, were recorded for period of 3 subsequent months from October to December 2015. Animals were fed once a day Total Mixed Ration based diet with different feed mixture composition in trial group (+100 g Algae STM Alltech Inc. per cow and day). Performance data were collected in accordance with official milk recording system of Breeding Services of Slovak Republic s. e. and milk samples were collected once per month according to the A4 standard methodology. The control group showed higher level of milk production compared to trial. Our study indicated that the feeding of algae caused milk fat depression and generally lower protein content in milk. Significant impact of algae feeding was found also for the level of urea in milk. In addition, the supplementary feeding of DHA may represent effective strategy to increase the percentage of pregnancies per inseminations in lactating dairy cows.

Separation of methanol-dimethyl carbonate vapour mixtures with PDMS and PTMSP membranes

Abstract In this work, we report on the permeation of methanol and dimethyl carbonate (DMC) vapour mixtures through dense membranes made from cross-linked polydimethylsiloxane (PDMS) and from poly[(trimethylsilyl)propyne] (PTMSP). Since methanol forms a methanol-rich pressure-maximum azeotrope with dimethyl carbonate, vapour permeation through hydrophobic (DMC selective) membranes is presumably a favourable method of azeotrope breaking. Permeation of vapours of pure compounds and of binary vapour mixtures was measured at 40 °C for a series of feed mixture compositions. Both membranes showed practically constant permeabilities of both studied compounds, thus indicating that no significant coupling of fluxes occurred. The membrane prepared from PTMSP was ca. 2–5 times more permeable and showed higher separation factors (αDMC ⩽ 4.2) than the one prepared from PDMS (αDMC ⩽ 2.8). In the case of the PDMS, the separation factors decreased with the increasing dilution of the feed mixtures with inert gas (hydrogen). Conversely, the separation factors increased with increasing feed mixture dilution in the case of PTMSP. The highest separation factors were observed near the azeotrope composition for both polymers (ca. 82 mol.% of methanol), thus enabling the development of effective hybrid processes combining rectification columns and vapour permeation units.

CO2 Capture from a Binary CO2/N2 and a Ternary CO2/N2/H2 Mixture by PSA: Experiments and Predictions

The results of pressure-swing adsorption experiments performed in a two-column setup are presented, as a way of validating a model developed to design and optimize cyclic adsorption processes. The experiments were conducted using a commercial activated carbon as the sorbent and an adsorption pressure of 20 bar. Two feed mixture compositions were studied: a binary CO2/N2 mixture representative of a flue gas and a ternary CO2/N2/H2 mixture representative of the product stream of air-blown autothermal reformers. During the experiments, the temperature was measured at five locations along the center of each column, along with the pressure, feed flow rate, product composition, and high-pressure product flow rate. A one-dimensional, nonisothermal, nonequilibrium model was used to simulate the experiments in a fully predictive manner. This model was previously validated in breakthrough experiments as well as PSA experiments using a binary CO2/H2 mixture. A thorough analysis of the experimental results and comparison with the simulation results showed that the model is fully capable of handling rather different feed compositions while still predicting satisfactorily the temperatures within the column, the product composition, and the overall process performance for a variety of process configurations and operating conditions.

Nonlinear model predictive control of biodiesel production via transesterification of used vegetable oils

The economic performance of an industrial scale semi-batch reactor for biodiesel production via transesterification of used vegetable oils is investigated by simulation using nonlinear model predictive control (NMPC) technology. The objective is to produce biodiesel compliant to the biodiesel standards at the minimum costs. A first-principle model is formulated to describe the dynamics of the reactor mixture temperature and composition. The feed oil and mixture composition are characterized using a pseudo-component approach, and the thermodynamic properties are estimated from group contribution methods. The dynamic model is used by the NMPC framework to predict the optimal control profiles, where a multiple shooting based dynamic optimization problem is solved at every sampling time. Simulation results with the economic performance of an industrial scale semi-batch reactor are presented for control configurations manipulating the methanol feed flow rate and the heat duty.

Mixed matrix membranes of H‐ZSM5‐loaded poly(vinyl alcohol) used in pervaporation dehydration of alcohols: Influence of silica/alumina ratio

Mixed matrix membranes of poly(vinyl alcohol) loaded with zeolite particles having different silica alumina ratio were prepared and used in the pervaporation dehydration of ethanol and isopropanol (IPA) from their aqueous mixtures. The membranes were characterized by physicochemical techniques that revealed higher interaction between polymer and zeolite particles having higher alumina than those with lower alumina in the zeolite framework. Both, membrane selectivity to water and flux were increased as the alumina content in the zeolite increases. Separation factors of zeolite with lower alumina incorporated membranes were, respectively, 236 and 334 for the feed mixture compositions of 4 wt% water in ethanol and 10 wt% water in IPA at 30°C. On the other hand, membranes containing zeolites with higher alumina content showed slightly higher separation factors of 349 and 568, respectively, for the same feed mixtures at 30°C. Such an incremental improvement in membrane performance with increase in alumina content in the zeolite framework is attributed to favorable interaction between zeolite particles and the polymer matrix. POLYM. ENG. SCI., 54:1774–1782, 2014. © 2013 Society of Plastics Engineers

Separation of n-hexane/acetone mixtures by pervaporation using high density polyethylene/ethylene propylene diene terpolymer rubber blend membranes

Polymer membranes were prepared by blending high density polyethylene (HDPE) with ethylene propylene diene terpolymer rubber (EPDM). These blend membranes were evaluated for the selective separation of n-hexane from acetone. The flux and selectivity of the membranes were determined both as a function of the blend composition and feed mixture composition. Results showed that polymer blending method could be very useful to develop new membranes with improved selectivity. Pervaporation properties could be optimized by adjusting the blend composition. The effects of blend ratio, feed composition, and penetrant size on the pervaporation process were analyzed. The permeation properties have been explained on the basis of interaction between the membrane and solvents and blend morphology. Flux increases with increasing alkane content in the feed composition.

Styrene–butadiene rubber membranes for the pervaporative separation of benzene/cyclohexane mixtures

AbstractStyrene–butadiene rubber membranes with methylene bridges, stemming from the concomitant in situ Friedel–Crafts alkylation during a chloromethylation reaction, were prepared and used in the pervaporative separation of benzene/cyclohexane mixtures. A set of four membranes with different crosslinking extents was achieved by the variation of the [Trimethylchlorosilane (TMCS)]/[Paraformaldehyde (PF)] molar ratios with respect to the styrene (St) unit. Study of the swelling of membranes by the mixture components individually and by their feed mixture compositions, 1 : 1 and 1 : 9, was conducted. The total flux (J) and the separation factor (α) were assessed as a function of the feed composition, temperature, and [St unit]/[TMCS]/[PF] molar ratios. The highest J and α measured in this study were 1401 g m−2 h−1 and 28.50, respectively. The diffusion selectivity was found to depend on the crosslinking extent of the membrane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Selective polydimethylsiloxane/polyimide blended IPN pervaporation membrane for methanol/toluene azeotrope separation

The paper describes the preparation and investigation of membranes based on new interpenetrating polymer network (IPN) of vinyl terminated poly(dimethyl siloxane) (PDMS) and aromatic polyimide (PI) with respect to their thermal and pervaporation properties. The modified membranes were prepared using simultaneous IPN (SIPN) technique by variation of polyimide loading of 5, 10 and 15wt% respectively. These membranes were characterized by different thermal, mechanical, morphological, spectroscopic and pervaporative techniques and compared with those of neat PDMS membranes. The IPN membranes exhibited synergistic improvement in the thermal stability in the range of 445–490°C in air and 410–520°C in inert atmosphere for 10% loss. Activation energies for the decomposition of polymers and their IPN's were calculated using Coats and Redfern equation. Permeation properties of PDMS and IPN blends were evaluated by water diffusion, measured by Fourier transform-attenuated total reflectance (FT-ATR) method and moisture vapour transmission rate (MVTR) as per ASTM E 96. 15wt% polyimide content in PDMS membrane slows down the water diffusion and MVTR significantly. All the IPN's form mechanically strong membrane with tensile strength up to 15.5MPa and elongation at break up to 20%. IPN membranes prepared in this work were employed in pervaporation separation of azeotrope forming toluene/methanol mixtures. The pervaporation properties could be tuned by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing polyimide content for methanol/toluene liquid mixtures. Toluene permeated preferentially through all tested blend membranes, and the selectivity increased with increasing polyimide content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The flux increased exponentially with increasing toluene concentration in the feed mixtures, whereas the selectivities decreased for liquid mixtures. This study demonstrates that polymer IPN blends is a simple way to modulate membrane's transport properties and can achieve higher performance than the pristine polymer materials.

Bioethanol recovery using the pervaporation separation technique

PurposeThe purpose of this paper is to demonstrate applicability of the pervaporation technique for separation ethanol/water mixtures.Design/methodology/approachFor the purposes of membrane material development for pervaporation zeolite filled and unfilled cellulose acetate membranes were prepared. Zeolite types were 4A, 13X. The effect of incorporation of nano‐sized zeolites prepared in a colloidal form in membranes was also investigated. Equilibrium sorption experiments were carried out. Degrees of swelling were calculated at different liquid feed mixture compositions for separating an azeotrope forming mixture, ethanol/water by pervaporation.FindingsZeolite 13X filled CA membrane may have the better pervaporation performance than zeolite 4A filled CA membrane. From the sorption tests it is concluded that ethanol/water azeotropy can be achieved by pervaporation.Practical implicationsApplication of CA membranes in industrial scale pervaporation units may be feasible for separation of ethanol/water mixtures. Specially ethanol/water azeotropy will be achieved by pervaporation. Using distillation and pervaporation hybrid systems, bioethanol can be produced economically.Orginality/valueThe paper illustrates the success of pervaporation techniques in separating ethanol/water mixtures.

Sorption, diffusion, and pervaporation characteristics of dimethylformamide/water mixtures using sodium alginate/polyvinyl pyrrolidone blend membranes

Separation of aqueous dimethylformamide (DMF) solutions in the concentration range of 0–100 wt% were studied using sodium alginate (NaAlg)/polyvinyl pyrrolidone (PVP) blend membranes. The NaAlg was blended in different ratios with PVP. Prepared membranes were crosslinked with CaCl 2 for testing in pervaporation (PV) separation of DMF/water mixtures. Effects of feed composition (0–100 wt%), operating temperature (30–50 °C), and membrane thickness were investigated. Best results were obtained at the conditions of 75/25 NaAlg/PVP blend ratio (w/w), 40 °C temperature, 20 wt% DMF concentration, and 70 μm membrane thickness. Blending of PVP with NaAlg increased permeation flux whereas it decreased the separation factor. NaAlg/PVP membranes gave separation factors of 5.5–27 for permeation flux of 0.96–1.81 kg/m 2h depending on the operating temperature and the feed mixture composition. Arrhenius plot of permeation flux data versus reciprocal of temperature exhibited linear trends. Permeation activation energy of DMF and water in the PV was calculated as 6.76 and 1.88 kcal/mol, respectively, using an Arrhenius type relationship. Sorption–diffusion properties of the NaAlg/PVP membranes were also investigated at the operating temperature and the feed composition.

Recovery of hydrocarbons from mixtures containing C 3H 6, C 3H 8 and N 2 using NaX membranes

The separation of light hydrocarbon (C 3H 6 and C 3H 8)/N 2 mixtures was investigated using faujasite membranes synthesized on α-Al 2O 3 disks. The motivation for studying this separation stems from the existence of vent streams in polyolefin production plants that contain these gases. These streams are usually flared and, as result, their valuable hydrocarbon content is lost. Permeation measurements of equimolar binary mixtures (C 3H 6/N 2 and C 3H 8/N 2) were carried out as a function of permeation temperature, feed mixture composition and total feed pressure. The maximum separation factors for C 3H 6/N 2 and C 3H 8/N 2 equimolar mixtures were ∼28.4 (with C 3H 6 flux 1.93 mmol m −2 s −1) and ∼8.1 (with C 3H 8 flux 1.34 mmol m −2 s −1), respectively and have been observed at 90 °C. As the total feed pressure was increased from 1 to 3.5 atm the permeation fluxes of all gases increased and the separation factor decreased. In particular, the separation factor of C 3H 6/N 2 dropped from ∼28 to ∼13 and of C 3H 8/N 2 from ∼8 to ∼5. Permeation experiments were carried out using a ternary mixture having a simulated composition of a typical polypropylene vent stream (12.5% C 3H 6/12.5% C 3H 8/75% N 2). The permeation results indicate that only C 3H 6 can be recovered from such a mixture. This result is very important because C 3H 6 is the valuable monomer and if recovered with suitable purity it can be recycled back to the polymerization reactor.

Separation characteristics of dimethylformamide/water mixtures using sodium alginate-g- N-vinyl-2-pyrrolidone membranes by pervaporation method

In this study, sodium alginate (NaAlg) was grafted with N-vinyl-2-pyrrolidone (NVP) under atmosphere of N 2 with benzophenone. The graft polymerization was carried out by irridiating with UV light. The copolymer was synthesized with the % grafting of 33, by using this copolymer (NaAlg-g-NVP), membranes were prepared and used in the separation of dimethylformamide (DMF) and water mixtures by the pervaporation (PV) method. The effects of the feed composition (0–100 wt%) and operating temperature (30–50 °C) on the permeation rate and the separation factor were investigated. Grafting of NVP onto alginate increased the permeation rate whereas decreased the separation factor. NaAlg-g-NVP membranes gave separation factors of 5.6–15.4 permeation rates of 0.96–2.05 kg m −2 h −1 depending on the operating temperature and the feed mixture composition. Permeation activation energy of dimethylformamide and water in the pervaporation were calculated as 3.50 kcal/mol and 2.38 kcal/mol, respectively, using an Arrhenius type relationship. In addition sorption-diffusion properties of the NaAlg-g-NVP membranes were investigated at the operating temperature and the feed composition. It was found that the sorption selectivity was dominant factor for the separation of DMF/water mixtures.

Development of crosslinked poly(ether-block-amide) membrane for CO 2/CH 4 separation

Thin film composite membranes of poly(ether-block-amide) (PEBAX-1657) were prepared on PVDF ultra-porous substrate by solution casting and solvent evaporation method. The membrane was crosslinked by a novel method using 2% (v/v) 2,4-toluylene diisocyanate (TDI) in hexane medium. Sorption studies were carried out in pure water to confirm crosslinking. Both the unmodified and modified membranes were characterized by scanning electron microscopy (SEM) to study the morphologies of the surface and cross-section. X-ray diffraction (XRD) experiments were carried out to understand the intermolecular interactions and separation mechanisms. Thermal stability of the membrane was assessed by differential scanning calorimetry (DSC). Single gas permeabilities of CO 2 and CH 4 and the resultant ideal selectivities were determined for unmodified PEBAX-1657 membrane using an indigenously built high-pressure gas separation manifold. A comparison was made with PEBAX-2533 membrane, also prepared in this study, to evaluate the effect of rigid block content in the polymers. As the pressure was varied from 10 to 40 kg/cm 2, the permeance and ideal selectivity for the unmodified PEBAX-1657 were found to range from 3.0 to 4.8 GPU and 18 to 25, respectively. On the other hand PEBAX-1657 membrane crosslinked for 5 min exhibited only one-fifth the permeance (0.6–0.9 GPU) but almost twice the selectivity (38–47). The effect of crosslinking time (0–60 min) and binary feed mixture composition (5–20% CO 2) on performance of membrane was studied at a constant pressure. PEBAX-1657 was found to be promising for the separation of CO 2 from CH 4.

Highly water selective silicotungstic acid (H 4SiW 12O 40) incorporated novel sodium alginate hybrid composite membranes for pervaporation dehydration of acetic acid

Silicotungstic acid incorporated sodium alginate (STA-NaAlg) hybrid composite membranes were prepared by incorporating 1, 2, 3 and 5 wt.% of silicotungstic acid (STA) into sodium alginate (NaAlg) and crosslinked with glutaraldehyde. Scanning electron microscopy and universal testing machine were used to investigate the morphology and the mechanical strength properties of the membranes. These membranes were tested for pervaporation (PV) dehydration of acetic acid at lower water concentrations of 10–25 wt.% in the feed. Addition of STA into NaAlg could result in a dramatic increase of water selectivity over that of plain NaAlg membrane dehydrating acetic acid for lowest STA containing NaAlg membrane. Thus, infinite selectivity was observed for STA-NaAlg membrane containing 1 wt.% of STA for all feed mixture compositions ranging from 10 to 25 wt.% water. With increasing STA content from 2, 3 and 5 wt.% in NaAlg membranes, selectivities ranged from 22,491 to 288, 12,848 to 192 and 6914 to 108, respectively for the studied composition range of the feed mixtures. PV performances of STA-NaAlg hybrid composite membranes were also tested at 40, 50, 60 and 70 °C typically in case of 10 wt.% water-containing feed mixture, which indicated a decrease in selectivity and increase in flux for all hybrid composite membranes. Arrhenius plots of flux data versus reciprocal of temperature exhibited linear trends. The hydrophilic STA is responsible to offer increased selectivity and flux to water as compared to plain NaAlg membrane for the feed mixtures studied. Of all the membranes tested, the 1 wt.% STA containing NaAlg membrane exhibited the best PV performance characteristics. Temperature did not influence much the selectivity data of STA-NaAlg membrane containing 1 wt.% of STA up to 50 °C, but flux increased with increasing temperature for all membranes. The results of this study are far superior to the previously reported data on acetic acid dehydration by the PV technique.

Effect of the hard segment domains on the permeation and separation ability of the polyurethane-based membranes in benzene/cyclohexane separation by pervaporation

A series of membrane materials made of the poly(oxytetramethylene) (PTMO)-based polyurethanes was studied in pervaporation separation of benzene/cyclohexane mixtures. Polyurethanes with a domain morphology synthesised by using different aromatic diols as chain extenders were investigated and their transport properties were compared to those of pure copolymers of 2,4-tolylene diisocyanate (TDI) and PTMO. The chain extended polyurethanes (PUs) showed generally better permselectivity towards benzene and lower pervaporation flux than the respective TDI-based ones. They also exhibited different transport behaviour with respect to the variations in the feed mixture composition that was attributed to the hard segments capability to control membrane swelling. The general trend of increasing permselectivity accompanied by decreasing permeability was observed for both PUs with increasing hard segment length and PUs with decreasing soft segment length. However, the effect of the hard segment aromatic content was found to be more complex and to depend on the length of hard segments. These results were discussed with respect to the microphase-separated structure of segmented PUs and the differences in its nature being a consequence of the PU molecular structure. It was also postulated that the microphase-separated structure may undergo transformation in contact with a feed mixture, the evidence of which was an abrupt change in the transport parameters of the membranes applied in pervaporation of the mixtures with a higher benzene concentration. For those systems, the role of the diffusion step in determining the separation efficiency was strongly diminished.