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Downstream processing of ABE fermentation broth is challenging issue. In this work, results of the application of both hydrophobic and hydrophilic commercial membranes during the pervaporation of ABE aqueous mixtures were investigated and presented. Hydrophobic pervaporation experiments were performed using ABE-water mixtures containing 0-5 wt% of organics in feed, using commercial membranes: POMS, PEBAX, and PervapTM4060. Separation factor and Pervaporation Separation Index were employed to discuss hydrophobic pervaporation results. PervapTM4060 membrane revealed the best separation performance in the removal of ABE components from diluted aqueous mixtures mimicking the fermentation broth, resulting in two-phase permeate containing ca. 34 wt% of organics. The subsequent liquid-liquid phase separation resulted in the organic phase containing 62 wt% of ABE. Hydrophilic pervaporation experiments were performed in contact with ABE-water system initially comprising 38 wt% of water applying both the PervapTM4100 PVA based polymeric membrane and modified silica ceramic one. Application of hydrophilic membranes allowed for the complete dewatering of ABE-water mixtures. Eventually, the combination of membrane separation processes (microfiltration, hydrophobic pervaporation, hydrophobic thermopervaporation, membrane distillation, and hydrophilic pervaporation) enhanced by the liquid-liquid phase separation was suggested for the recovery and dehydration of ABE aqueous mixture.

A novel and efficient method is proposed to evaluate the concentration polarization (CP) effect in pervaporation process. The novelty of the method results from the approach towards the CP phenomenon, that proposes the calculation algorithm on the basis of permeate fluxes and feed/permeate compositions as a function of the feed flow velocity only. The main advantage of the method over the approaches available in the literature is that the intrinsic enrichment factor is calculated directly from the experimental data instead of being found as one of the regression parameters. To prove this approach, pervaporation experiments were carried out using commercial hydrophobic composite PDMS based membrane Pervatech for the recovery of methyl acetate (MeAc) from diluted aqueous solutions (0–1.5 wt% MeAc in feed mixture). Pervaporation performance of PDMS membrane was investigated at various feed flow rates in the range 4.8–70 dm3 h−1 and at three different temperatures of feed mixture (i.e. 30 °C, 40 °C, and 50 °C). It was shown that the intrinsic enrichment factor changes noticeably when the process parameters are altered and this change is one of the key factors affecting the concentration polarization modulus value during pervaporative removal of organic compounds from diluted aqueous solutions. With increasing temperature and feed flow rate, the concentration polarization modulus increases, reaching the value close to 1 at temperature of 50 °C and at the average feed flow rate equal to 1.34 cm s−1. Moreover, under these conditions, the thickness of the boundary layer tends to zero.

In this study the efficiency of three various commercial membranes based on poly(octylmethyl siloxane), poly(ether-block-amide), and poly(dimethylsiloxane) polymers were investigated in pervaporative separation of acetone, butanol, and ethanol from aqueous binary solutions (0–5 wt% of organics) at 60 °C. The influence of fermentation broth microfiltration on membrane performances in pervaporative removal of ethanol was also investigated. The use of microfiltration improved the effectiveness of the removal of ethanol from the broth comparing with the unfiltered one. Molar ratios of organics to water fluxes and Pervaporative Separation Index (PSI) values were employed to discuss membranes' performance in removal of organic solvents from binary aqueous mixture. It was found that PDMS based (Pervap4060) membrane shows the best separation efficiency in all tested binary aqueous mixtures. Modelling of the process proved the feasibility of pervaporation process for the removal of acetone, butanol and ethanol from binary and quaternary aqueous mixtures.

Pervap™ 2200, 2201, 2216, 2255, and 2510 hydrophilic, PVA membranes were investigated in pervaporation of water-tetrafluoropropanol mixtures. Physicochemical properties of membranes were characterized by determining the contact angle (CA) of water and glycerol and the surface free energy (SFE). The separation and transport properties of membranes were determined during vacuum pervaporation in contact with water-TFP mixtures containing up to 22 wt.% water. It was found that all membranes were hydrophilic (CA < 90°) and the polar component of SFE was much higher than the dispersive one. The apparent activation energy for water transport was very high (Eapp = 81.3 kJ/mol), indicated that water transport is activated thermally. Pervap™ membranes were very selective during the dehydration process of TFP. In contact with the Pervap™ 2200, 2201, and 2216 permeate contained practically pure water, regardless the feed composition. The process separation index (PSI) for Pervap™ 2200 and 2216 was close to 5000 kg m−2 h−1, suggesting that both membranes can be efficiently applied in the batch pervaporation process for TFP dehydration.

Polydimethylsiloxane (PDMS) membranes were synthesised by varying the degree of crosslinking and were characterised in a pervaporation system coupled to a mass spectrometry (MS) for on-line monitoring and collecting data points with an interval of 2 s. This monitoring approach allows obtaining very precise information about the impact of solutes’ solubilisation within the membrane and their influence on solvent permeation. Using dilute aqueous solutions of ethyl acetate and hexyl acetate, it is shown how solutes with diverse nature and diverse partitioning into the membrane, determine the transport of solvent and solute by progressively modifying the membrane transport properties. From the evolvement of the time-dependent diffusion coefficients of the selected solutes during transient transport, it is possible to infer about solute-membrane molecular interactions and their impact in terms of membrane rearrangement and fluidification.

Air gap membrane distillation technique (AGMD) was applied for removal of ethanol, butanol and acetone–butanol–ethanol mixture from water. The influence of various parameters (feed temperature, cooling wall temperature) on pure water transport in AGMD was determined and the efficiency of organic solvents removal from water through two porous membranes (PTFE and PP) was investigated in the detail. Selectivity of organic components recovery did not change significantly with an increase of feed temperature from 41 °C to 63 °C in case of AGMD applied for ethanol and butanol recovery, however significantly higher fluxes were obtained at higher feed temperature. Slightly higher fluxes were obtained during experiments performed with PTFE membrane comparing with PP one. It was found that both PTFE and PP membranes are wetted during AGMD process of water–butanol feed mixture if organic concentration exceeds 2.5 wt% (PTFE) and 1 wt% (PP) at 63 °C feed temperature. This fact limits the possibility of wider AGMD application in organic solvent recovery. The comparison of the efficiency of AGMD with the efficiency of thermopervaporation (TPV) was also performed. In case of 1 wt% ethanol feed mixture it was found that AGMD seems to be more suitable due to higher process separation index value (PSI in the range of 6 kg m −2 h −1 ) than in the case of TPV (PSI in the range of 3 kg m −2 h −1 ). On the contrary, in the case of water–butanol or water–ABE systems TPV is much more efficient method for organics recovery from aqueous mixtures than AGMD. In contact with 3 wt% ABE mixture PSI is equal to 28 and 9 kg m −2 h −1 for TPV and AGMD processes, respectively.

PDMS based membranes were prepared using various modification approaches. Structural and surface properties of prepared membranes were investigated applying a number of instrumental techniques (AFM, FT-IR, DSC, SEM, CA). Finally, transport and separation properties of the developed membranes were determined during pervaporation (PV) experiments in contact with water and water-ethanol mixture. The results were compared with efficiency of the native and commercial PDMS based membrane. Applied preparation procedures resulted in creation of membranes possessing different morphology and pervaporative performance, e.g. modification of membrane matrix with salt method resulted in smaller crosslinking ratio of poly(dimethyl siloxane) sample comparing with pristine PDMS membrane. Whereas, plasma treatment of PDMS sample caused reduction of hydrophobic properties of PDMS membrane resulting in much lower separation factor (β = 6.0). PV results showed that PDMS_NaCl (β = 10.5) and PDMS_Al2O3_mod._C8 (β = 10.8) possessed the most selective properties towards organics among all PDMS based membranes tested in this study, showing that salt method and filling of poly(dimethylsiloxane) matrix with triethoxy(octyl)silane (C8) modified Al2O3 allowed to obtain improved membranes performance in hydrophobic pervaporation.

Temperature driven membrane thermopervaporation was studied in this work. Impact of various experimental conditions (feed temperature – T f , type of membrane, type of organic solvent in binary aqueous mixture, feed composition) on transport and selectivity in TPV was investigated experimentally. Two commercially available dense PDMS based membranes (Pervatech and Pervap 4060) were utilized during TPV experiments in contact with pure water and binary aqueous mixtures of acetone, butanol and ethanol. Intrinsic properties (permeance and selectivity coefficient) of membranes were determined and discussed. Transport in thermopervaporation increases with an increase of feed temperature (at constant temperature of permeate). During TPV experiments performed with Pervatech in contact with acetone–water system, permeance of acetone increased from 0.12 mol m −2 h −1 kPa −1 at T f = 30 °C to 0.24 mol m −2 h −1 kPa −1 at T f = 42 °C, whereas permeance of butanol increased from 0.45 mol m −2 h −1 kPa −1 at T f = 30 °C to 0.64 mol m −2 h −1 kPa −1 at T f = 41 °C. Pervap 4060 membrane showed better properties in thermopervaporative recovery of butanol and ethanol from water than Pervatech membrane. It was also found that the application of stainless steel porous support reduces ethanol and water fluxes, but it does not affect the selectivity up to 3 wt.% of ethanol in feed.

The monitoring of concentration of methane dissolved in water is important for the security of underwater pipelines, delineation of oil and gas fields, and optimization of proper location of oil and gas wells. The reported system consists of metal oxide gas sensor separated from water by hydrophobic pervaporation membrane. Methane MEMS sensor was based on multilayer SiO 2 /Si 3 N 4 film equipped with platinum heater and coated with sensing layer made of nanoparticle SnO 2 /Pd (3 wt. %). Methane saturation of water leads to a decrease in sensor resistance by a factor of 6 – 7, the response time of the system is of 200–300 s.