Transport of Components in the Separation of Ethanol from Aqueous

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Transport of Components in the Separation of Ethanol from Aqueous Dilute Solutions by Forward Osmosis Alan Ambrosi,*,† Mustafa Al-Furaiji,‡,∥ Jeffrey R. McCutcheon,§ Nilo Sérgio M. Cardozo,† and Isabel Cristina Tessaro† †

Department of Chemical Engineering, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul 90040-040, Brazil ‡ Faculty of Science and Technology, University of Twente, Meander/ME, 7500 AE Enschede, The Netherlands ∥ Environment and Water Directorate, Ministry of Science and Technology, Baghdad, Iraq § Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269, United States S Supporting Information *

ABSTRACT: Membrane-based technologies have been considered for separation of ethanol/water mixtures as an alternative to thermal based separations. In this work, we consider forward osmosis (FO) for ethanol separation from aqueous solutions using commercial cellulose triacetate (CTA) and thin film composite (TFC) forward osmosis membranes. Aqueous solutions containing ethanol were used as feed solution and sodium chloride was used as osmotic agent for the tests. The total permeate flux and the reverse salt flux are increased with the increase of the osmotic pressure difference, while the ethanol−water separation factor is decreased. CTA and TFC membranes presented similar total permeate fluxes (from 4 to 8 kg m−2 h−1), but CTA presented lower reverse salt flux (below 5 g m−2 h−1) and higher separation factor (αethanol−water between 1 and 2). Additional tests using reverse osmosis (RO) were conducted to compare with the FO results. production.22−25 Dialysis is based on the selective diffusion of the component due to the concentration gradient between a feed solution and a dialysate solution that are in contact with a nanoporous semipermeable membrane.26,27 Beer and wine dealcoholization by dialysis was studied in the 1980s and 1990s,15,28−30 but the very low ethanol transport rates and the loss of beverage compounds limited the industrial use. In hydraulic pressure-driven processes such as reverse osmosis and nanofiltration, water and low-molecular-weight compounds pass through a hydrophilic membrane, while ethanol is partially retained and other larger compounds are totally retained. The reduction of the ethanol content of beer, wine, and cider was studied by several authors in the 2000s.8,17,18,31 Catarino et al. tested several RO and NF membranes for beer dealcoholization and found that cellulose membranes provided higher permeate flux and lower ethanol rejection than polyamide-based membrane.18 In such applications, the diafiltration mode has to be used to dilute feed and reduce ethanol concentration as it permeates the membrane. Such processes are prone to high

1. INTRODUCTION The separation of organic compounds from relatively dilute solutions is a need for several industrial processes, such as treatment of plant effluents and wastewaters,1−3 separation of mixtures with azeotropes,4 and separation of ethanol from fermentation broths or alcoholic beverages.5−9 Membrane separation processes have been investigated as alternatives for ethanol separation from diluted aqueous solutions, showing significant advantages over traditional thermal processes, for instance, the lower thermal impact on product and the lower energy consumption. Membrane techniques being studied for alcohol separation from water include pervaporation (PV),10−13 membrane distillation (MD),5,6,14 dialysis,15,16 reverse osmosis (RO),17,18 nanofiltration (NF),19 and osmotic distillation (OD).20 These various membrane processes have different means of driving separation. Pervaporation, for example, is driven by the vapor pressure differences of solution components, and a dense hydrophobic membrane that preferentially permeates ethanol over water.21 Poly(dimethylsiloxane) membranes have been proved to be attractive for continuous ethanol recovery from small scale fermentation processes, reducing the inhibition of the microorganisms by the ethanol, increasing the sugar consumption and consequently increasing the ethanol © XXXX American Chemical Society

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November 29, 2017 February 6, 2018 February 9, 2018 February 9, 2018 DOI: 10.1021/acs.iecr.7b04944 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

used it as a membrane for FO.47,48 Both membranes were soaked in deionized (DI) water for at least 24 h prior to the experiments. The chemicals used in this work are of analytical grade: ethanol (absolute, anhydrous, Pharmco-Aaper, USA) and sodium chloride (>99.9%, Fisher Scientific, USA). Deionized water from a Milli-Q ultrapure water purification system (Millipore, USA) was used to prepare the solutions at 20 °C and rinse the unit throughout the tests. 2.2. Reverse Osmosis Experiments. 2.2.1. Membrane Characterization. Intrinsic pure water permeance (A), salt permeability (B), and salt rejection (R) are performance parameters determined using standard protocols that make reasonable the comparisons between membranes of different materials or even membranes from different batches.46,47,49 These performance parameters of the commercial FO membranes were evaluated using our benchtop RO unit, the description of which can be found elsewhere.47,50 Pure water flux (Jw) at 20 °C was measured at five hydraulic pressure differences (Δp), decreasing from 450 to 125 psi (from 31 to 8.5 bar). The average of the water flux was calculated from the averages of three membrane coupons to calculate the intrinsic water permeability coefficient as

energy consumption and fouling rates due to the high pressures applied.8,17,32 Recent studies have applied osmotic distillation for wine and beer dealcoholization; the difference in ethanol vapor pressure at the two sides of a porous hydrophobic membrane is the driving force that promotes the preferential diffusion of ethanol as vapor phase.20,33 Forward osmosis (FO) has gained attention as a technology that can be used to handle “difficult” solutions containing biological, inorganic, and organic substances.34−37 FO is driven by the chemical potential gradient (expressed in terms of osmotic pressure difference) existent between two solutions separated by a semipermeable FO membrane: the feed solution (FS), of low osmotic pressure, and the draw solution (DS), of very high osmotic pressure. The resultant osmotic gradient drives water from the feed into the draw solution.38 Typical membranes used in forward osmosis are based on integrated cellulose acetate structures or thin film composite aromatic polyamides. The latter are similar in chemistry and morphology to those used in reverse osmosis and nanofiltration applications. However, when compared to pressure-driven membrane processes, FO presents a series of advantages, including low operating pressures, lower membrane fouling tendency, and potentially lower cost. Moreover, the much higher osmotic pressure that can be generated using specific draw solutes in comparison to the hydraulic pressure applied in RO may contribute to a faster water permeation. The applications of FO are far-reaching, though many studies have focused on using FO for desalination, wastewater reclamation, and food concentration processes.34−36,39 Ethanol concentration and dehydration has been investigated,40,41 but the observed low ethanol rejection was deemed problematic. The low rejection of ethanol observed in these previous works may indicate that FO could be used to extract low molar mass compounds such as ethanol from aqueous solutions. If ethanol and water could be removed from a complex solution, dilution of the concentrated product through diafiltration could be used to create an alcohol-free solution, or even recover ethanol from a more specific solution (the draw solution with known composition). In this work, we explore the transport of components in the separation of ethanol from aqueous dilute solutions by forward osmosis aiming the decrease of the ethanol concentration in the feed. For the first time we evaluated the effects of the osmotic pressure difference on the total permeate flux, on the reverse solute flux, and on the ethanol−water separation factor, and compared to reverse osmosis experiments in order to provide a better understanding.

A = Jw /Δp

(1)

Salt rejection (R) was measured at 125 psi (8.6 bar) using a feed solution with 2000 mg L−1 sodium chloride. Observed salt rejection (R) was determined from the values of bulk feed concentration (Cb,RO) and permeate concentration (Cp,RO), according to R = 1 − (Cp,RO/C b,RO)

(2)

Feed and permeate concentrations were determined using a conductivity meter. Salt permeability coefficient (B) was determined by47,49 ⎛ Jw ⎞ ⎛1 − R ⎞ ⎟ exp⎜ − B = Jw ⎜ ⎟ ⎝ R ⎠ ⎝ k⎠

(3)

where k is the cross-flow cell mass transfer coefficient calculated from correlations for the RO cell geometry.26,51 2.2.2. Ethanol Removal. Total permeate flux, ethanol flux, and membrane rejection for ethanol were evaluated at different hydraulic pressure differences using aqueous solutions containing 3.0, 4.5, and 6.0 vol % ethanol. Initially, deionized water was used to equalize the system temperature to 15 °C and compact the membranes with gradual increase of the hydraulic pressure up to 450 psi (31 bar), with a cross-flow velocity of 0.22 m s−1. Pure water flux was evaluated at three hydraulic pressures. Thereafter, anhydrous ethanol (99.5%) was added to the feed tank to reach the desired concentration and, after an equalization time, the total permeate flux was determined as the mass of permeate collected in a fixed time divided by the membrane area. Three membrane coupons were used to obtain the average total permeate flux. Permeate and concentrate streams returned to the feed tank, and samples were collected to analyze the ethanol concentration. The ethanol concentration in the permeate was used to calculate the ethanol flux and the ethanol rejection that was calculated similarly to the salt rejection. 2.3. Forward Osmosis Experiments. The forward osmosis system used in this study is described in detail in our previous works.35,47 In our tests, the temperature was held

2. EXPERIMENTAL SECTION 2.1. Membranes and Chemicals. Two different commercial forward osmosis membranes were kindly provided by Hydration Technologies Innovations (HTI, USA). One was a cellulose triacetate (CTA) membrane, which is asymmetric with an embedded mesh in the supporting layer. This membrane is the first commercial membrane developed exclusively for forward osmosis, so it has been the most commonly studied membrane in a variety of applications.35,42−47 The other membrane contained a thin film composite membrane with a polyamide based selective layer supported by a series of support materials. Its structure and chemistry are similar to those of an RO membrane, though it has been tailored for FO, is thinner, and has a more hydrophilic support layer. It was released only recently, so few studies have B

DOI: 10.1021/acs.iecr.7b04944 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research Table 1. Experimental Conditions Used in the Forward Osmosis Tests feed side experiment CTA 3.0 and TFC 3.0

CTA 4.5 and TFC 4.5

step

composition

1

pure water flux and reverse salt flux

28

pure DI water

2

total permeate flux, ethanol flux and reverse salt flux

15

ethanol/water mixture 3.0 vol % (2.4 wt %)

3 4 5 1 2

CTA 6.0 and TFC 6.0

calculated fluxes

Δπ (bar)

3 4 5 1 2

pure water flux and reverse salt flux total permeate flux, ethanol flux, and reverse salt flux

pure water flux and reverse salt flux total permeate flux, ethanol flux, and reverse salt flux

3 4 5

25 35 45 34 15 25 35 45 40 15

pure DI water ethanol/water mixture 4.5 vol % (3.5 wt %)

pure DI water ethanol/water mixture 6.0 vol % (4.8 wt %)

25 35 45

at 15 °C by a chiller and the cross-flow velocity was fixed at 0.22 m s−1. Tests were performed in a cocurrent mode, with the membrane selective layer facing the feed solution (FO mode). No spacers were used in the feed and draw channels. Three experiments were performed for each membrane (CTA and TFC), using three different ethanol concentrations in the feed solution (3.0, 4.5, and 6.0 vol %). Each experiment was divided into five sequential steps, as detailed in Table 1. In the first step, pure water flux and reverse salt flux were evaluated using pure deionized water as feed and sodium chloride as a draw. Then, total permeate flux, ethanol flux, and reverse salt flux were evaluated by adding pure ethanol to the feed tank to reach the desired concentration (3.0, 4.5, or 6.0 vol %) while 5 M stock solution of sodium chloride was added to the draw tank to maintain the draw solution concentration. The concentration of DS was adjusted in each step considering a fixed bulk osmotic pressure difference (Δπ = 15, 25, 35, and 45 bar), assuming Δπ = πDS − πFS = (iDSC DS − iFSC FS)RT

draw side ethanol concn (g L−1)

πFS (bar)

NaCl concn (g L−1)

πDS (bar)

0

0

33.6

28

23.7

12

33.6

27

23.7 23.7 23.7 0

12 12 12 0

45.9 58.3 70.6 41.1

37 47 57 34

35.5

18

41.1

33

35.5 35.5 35.5 0

18 18 18 0

53.4 65.9 78.1 48.6

43 53 63 40

47.3

24

48.6

39

47.3 47.3 47.3

24 24 24

60.9 73.3 85.6

49 59 69

end of each step to determine the ethanol concentration. Each experiment was performed in triplicate. 2.4. Ethanol Concentration Measurement. Ethanol concentration was assessed by UV−vis spectrophotometry (Genesis 10S, Fisher Scientific, USA). The method was adapted from the literature52,53 and is based on the formation of green chromate ions resulting from oxidation of the ethanol with dichromate in the presence of sulfuric acid. The resulting color has a characteristic absorbance of light at a wavelength of 600 nm. Potassium dichromate (>99.0%, Alfa-Aesar, USA) and sulfuric acid (95−98%, Sigma-Aldrich, USA) were used to prepare 0.1 and 4 M solutions, respectively. The reaction between the sulfuric acid solution, the potassium dichromate solution, and the sample was conducted inside glass centrifuge tubes, which were sealed with Parafilm (Pechiney Plastic Packaging Co., USA), stirred, and placed in an oven at 50 ± 2 °C. After 30 min of reaction, the tubes were rapidly cooled in tap water and the absorbance was recorded. Samples from RO experiments (feed and permeate) and FO experiments (feed and draw) were analyzed in duplicate, and the absorbance was related to the ethanol concentration using standard curves. The standard curves obtained are supplied as Supporting Information.

(4)

where π is the osmotic pressure, i is the ionic dissociation constant (considered equal to 2 for the sodium chloride and 1 for the ethanol), R is the gas constant, T is the temperature, C is the molar concentration of solute (ethanol and sodium chloride), and the subscripts “DS” and “FS” stand for draw solution and feed solution, respectively. Concentrations of draw and feed solutions, and consequently the bulk osmotic pressure differences, were considered constant during the experiment once the volumes used were high and the volumetric fluxes obtained were low. Moreover, the running time for each step was fixed to 50 min, in which it was possible to achieve steady state conditions without significant increase of ethanol and salt concentrations in the feed solution or substantial draw solution dilution. Gain of mass of the draw side and electrical conductivity of the feed side were recorded to calculate total permeate flux and reverse salt flux, respectively. Samples of both solutions were collected at the

3. RESULTS AND DISCUSSION 3.1. Intrinsic Separation Properties. The intrinsic separation properties of the commercial CTA and TFC forward osmosis membranes used in this work are presented in Figure 1. In terms of water permeance and salt permeability coefficients, it is possible to observe that the CTA membrane demonstrated much lower values than the TFC membrane. The CTA presented a water permeance (0.49 ± 0.04 L m−2 h−1 bar−1) 4 times lower than the TFC membrane (1.98 ± 0.12 L m2 h−1 bar−1), and a salt permeability (0.18 ± 0.05 L m−2 h−1) 9 times lower than the TFC membrane (1.69 ± 0.64 L m−2 h−1). Results of the CTA membrane are comparable to those obtained by Yip et al., who compared the performance of C


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reported in section 3.1, is apparent here and is illustrated by the difference in the slope of the data. For the CTA membrane, the addition of ethanol to the feed solution resulted in a decrease of about 15% in permeate flux compared to pure water. However, no difference in permeate flux is observed for different ethanol concentrations. The TFC had a decrease of 40% of permeate flux when ethanol was added to the feed solution and the increase of ethanol concentration resulted in even lower fluxes. Similar behavior was observed by Labanda et al., who studied the permeation of organic solutes in water−ethanol mixtures with nanofiltration membranes.57 This decrease of the total permeate flux is attributed to the reduction of the effective driving force of the process, once the presence of ethanol increases the osmotic pressure (decreasing the water chemical potential) of the feed solution.58 However, if ethanol can permeate the membrane to some extent, the osmotic pressure caused by the ethanol will have less of an impact. These results are related to the membrane rejection and/or the separation factor, as explained in the following. 3.2.2. Effect of Hydraulic Pressure Difference on Membrane Ethanol Rejection and on Separation Factor. Figure 3 shows the observed ethanol rejection and the separation factor over a range of hydraulic pressure difference for both membranes. The ethanol separation factor (αethanol/water) is given as the composition ratio of components in the permeate relative to the composition ratio in the feed. It represents the efficiency of the membrane to separate a component from the other, and it is frequently used when separating organic solutes from water by pervaporation, for example.59 For both membranes, there appears to be only a slight increase in ethanol rejection with the increase of hydraulic pressure (Figure 3) over the range tested, though this difference is very small and not necessarily statistically significant. Figure 2 shows that water flux increases with increasing pressure, and due to the hydrophilic character of these membranes, it probably largely offsets the ethanol flux that varied from 0.1 to 0.5 kg m−2 h−1, keeping the rejection fairly constant. The CTA membrane presented much lower ethanol rejection (around 15%) than the TFC (around 45%). This

Figure 1. Water permeance and salt permeability coefficients, and salt rejection of the commercial CTA and TFC FO membranes. Tests were performed at 20 °C and 0.22 m s−1, feed pressure 125−450 psi for the water permeance, and 125 psi and 2000 mg L−1 NaCl for salt permeability and salt rejection.

commercial CTA-FO membranes with hand-cast TFC-FO and commercial TFC-RO.49 The high salt permeability of the TFC membrane is a direct consequence of its low salt rejection (88.9%), much lower than that of the CTA membrane (95.7%). TFC membranes generally present higher salt rejection than CTA membranes, but it is possible that this TFC-FO membrane has nanofiltration characteristics or was slightly damaged during the testing. Several authors have reported that FO membranes may be damaged when tested in RO since they are not intended to be used under high pressure.42,54−56 Similar results were found by Ren and McCutcheon.47 3.2. Ethanol Removal Using Reverse Osmosis. 3.2.1. Effect of Hydraulic Pressure Difference on the Total Permeate Flux. The increase of hydraulic pressure difference promoted a substantial effect on the total permeate flux as observed in Figure 2. The increase of the driving force increases the flux of both membranes. This was not unanticipated, and the difference between CTA and TFC water permeance,

Figure 2. Effect of hydraulic pressure difference on permeate flux of commercial CTA and TFC FO membranes. Tests were performed at 15 °C and 0.22 m s−1 using DI water and aqueous solutions containing 3.0, 4.5, and 6.0 vol % ethanol. Squares represent the pure water flux and circles represent the total permeate flux observed with different feed compositions. Lines were added as a guide, and error bars correspond to the standard deviation of three membrane coupons. D


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Figure 3. Effect of hydraulic pressure difference on ethanol rejection and on separation factor of commercial CTA and TFC FO membranes. Tests were performed at 15 °C and 0.22 m s−1 using aqueous solutions containing 3.0, 4.5, and 6.0 vol % ethanol. Lines were added as a guide, and error bars correspond to the standard deviation of three membrane coupons used in the same experiment.

Figure 4. Effect of bulk osmotic pressure difference on permeate flux of CTA and TFC FO membranes. Tests were performed at 15 °C and 0.22 m s−1. Squares represent the water flux observed in the first step of the three experiments, in which DI water was used as FS; circles represent the total permeate flux observed in the following four steps using 3.0, 4.5, and 6.0 vol % ethanol as FS. Lines were added as a guide, and error bars correspond to the standard deviation of at least three independent replicates for each experiment.

explains why the flux changes more for the TFC membrane in Figure 2. The higher ethanol rejection results in more osmotic pressure effects and thus larger changes in permeate flux over the same range of hydraulic pressure. Other authors also observed lower ethanol rejection for cellulose acetate membranes in comparison to polyamide membranes.18,31 Wang et al. demonstrated that cellulose triacetate membranes suffer degradation by classical Claisen condensation and water condensation reactions when exposed to ethanol, which directly affects the performance and long-term stability in ethanol− water mixtures.60 The polyamide layer of the TFC membranes is highly cross-linked and thus generally has higher selectivity than nonsolvent phase inversion cast cellulose acetate membranes. The more hydrophobic character of the CTA membrane (observed by Ren and McCutcheon47) also suggests that ethanol may be more permeable. Swelling and plasticization effects caused by the organic permeant may also be responsible for low ethanol rejection,41,60 but to a minor extent due to the low ethanol concentration used here. Once both membranes are partially rejecting ethanol, depending on

the volumetric concentration factor obtained, we can anticipate that a concentration of ethanol in the feed solution throughout the ethanol removal process is expected. In order to decrease the total ethanol content of the feed solution, a dilution step (diafiltration) is necessary, and depending on the final ethanol concentration required, the concentration/dilution steps and the volume of solvent added back to the feed solution can be optimized.61,62 By contrast, the separation factor is slightly decreased with the hydraulic pressure difference increase. A separation factor higher than 1 (αethanol/water > 1) indicates that there is separation between ethanol and water, and the former is enriched in the permeate side. When αethanol/water = 1, there is no real separation between the species considered. The separation factors observed here were lower than 1, clearly indicating the preferential transport of water, mainly for the TFC membrane, which presented the higher ethanol rejection. 3.3. Ethanol Removal Using Forward Osmosis. 3.3.1. Effect of Bulk Osmotic Pressure Difference on Total Permeate Flux. To evaluate the effects of osmotic pressure E


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Figure 5. Effect of bulk osmotic pressure difference on reverse salt flux of commercial CTA and TFC FO membranes. Tests were performed at 15 °C and 0.22 m s−1. Squares represent the reverse salt flux observed in the first steps of the three experiments, in which DI water was used as FS; circles represent the reverse salt flux observed in the following four steps, using 3.0, 4.5, and 6.0 vol % ethanol as FS. Lines were added as a guide, and error bars correspond to the standard deviation of at least three independent replicates for each experiment.

Figure 6. Effect of bulk osmotic pressure difference on separation factor of commercial CTA and TFC FO membranes. Tests were performed at 15 °C and 0.22 m s−1. Circles represent ethanol fraction in the permeate of steps two to five, using 3.0, 4.5, and 6.0 vol % ethanol as FS. Lines were added as a guide, and error bars correspond to the standard deviation of at least three independent replicates for each experiment.

difference on total permeate flux, the concentration of sodium chloride in the draw solution was adjusted according to the concentration of ethanol in the feed solution in order to generate 15, 25, 35, and 45 bar of bulk osmotic pressure difference for all tests. Figure 4 illustrates the effect of bulk osmotic pressure difference on the permeate flux for both membranes and the three feed concentrations evaluated. When a range of draw solute concentrations is used in forward osmosis experiments for extracting water from the feed solution, researchers have observed a logarithmic relationship between water flux and concentration difference across the membrane. This behavior is attributed to concentration polarization effects.42,63−65 This nonlinear relationship was not observed in data presented in Figure 4, possibly due to the narrow range of concentrations studied. The TFC membrane presented only a modest higher total permeate flux (average of 12%) compared to the CTA in spite of its much higher water permeance and higher pure water fluxes. The higher ethanol rejection presented by the TFC may be the reason for this behavior, because more ethanol would be hindered by the

membrane, increasing the effective osmotic pressure on the feed side of the membrane. This is supported by the fact that, as seen in Figure 2 with the RO tests, higher ethanol concentrations resulted in lower permeate fluxes. The differences are less pronounced than those depicted in Figure 2, though, because they are only the result of greater external polarization with higher ethanol concentrations since the Δπ (the only driving force in these tests) is kept constant. External polarization is more severe with the TFC membrane because of its higher rejection. 3.3.2. Effect of Bulk Osmotic Pressure Difference on Reverse Salt Flux. For beverage applications, the reverse salt flux has to be carefully considered as it might impair the final product.39,66 The effect of osmotic pressure difference on the reverse salt flux of both membranes is presented in Figure 5. A slight upward trend can be observed in reverse salt flux as the draw solution concentration is increased. Overall, the TFC exhibited an approximately 3.5 times higher reverse salt flux than CTA, in accordance to its higher salt permeability F


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observed by Leskosek71 and Petkovska16 when studying beer dealcoholization. The ethanol fluxes are quite similar to those observed in our RO experiments and literature data for pervaporation, which present fluxes varying from 0.1 to 0.5 kg m−2 h−1 at similar feed concentration.21,72 The separation factors obtained in pervaporation experiments are usually higher than 3 due to the hydrophobic character of the membranes, but the phase change involved in this process usually leads to high energy consumption.21,24,73 Although low separation factors were obtained, the ethanol removal process can still be benefited with the high water flux obtained, because higher volumetric concentration factors can be obtained in less operating time. For a dealcoholization process, for example, concentration/dilution steps will be required to decrease the ethanol concentration of the feed solution, and as higher concentration factor is obtained, the number of steps required to achieve a desired ethanol concentration in the feed solution is lower.61,74 Furthermore, as the ethanol is being concentrated, it is expected that its flux can be kept constant or even raised during the concentration step time, which is an advance compared to the pure dialysis process, in which the ethanol flux is constantly decreased.

coefficient and lower salt rejection, as measured in the RO experiments. The different ethanol concentrations appeared to have no impact on reverse salt flux for the CTA membrane. However, higher ethanol concentrations yielded significantly higher salt fluxes for the TFC membrane. This is most likely due to the lower salt rejection of TFC membrane in comparison to the CTA. In order to keep the osmotic pressure difference the same for the different ethanol tests, we used a higher draw solution concentration that gives rise to the higher solute flux. Ren and McCutcheon47 observed that the reverse salt flux of TFC membranes previously wetted in a 50 wt % solution of isopropyl alcohol for 5 min increased 55% in comparison to virgin TFC membranes, while the water flux was practically unchanged. They attributed this result to the swelling of the polyamide layer and/or extraction of unreacted amine and condensation reaction products from the polyamide layer by the alcohol, which affected the membrane selectivity and decreased the osmotic pressure difference across the membrane, leading to an unchanged water flux. Although these changes in the membrane properties can be caused by the presence of alcohols, they are not expected in our results due to the low ethanol concentrations used and relatively low experiment time. 3.3.3. Effect of Bulk Osmotic Pressure Difference on Separation Factor. The effect of bulk osmotic pressure difference on the separation factor of the FO membranes and the three feed concentrations evaluated using FO operation mode is illustrated in Figure 6. Similarly to the RO tests, CTA presented higher selectivity than the TFC membrane due to its lower ethanol rejection and higher affinity to this compound. On the other side, in comparison to the separation factors observed in RO tests, it is possible to note that the values were slightly higher than 1 for the CTA membrane, indicating that the ethanol was being concentrated at the permeate side. This result is quite interesting, and it is directly related to the driving force applied, once the hydraulic pressure in the RO promotes higher water transport, while the concentration of the components in FO allows an increased ethanol transport in comparison to the water. Near the membrane surface, the compound velocities are determined by several factors such as the movement of the mixture as a whole, the chemical potential gradient of the compounds, and the friction of these compounds with its surroundings. A slight downward tendency can be observed for the separation factor with the osmotic pressure difference increase, mainly for the TFC membrane. This effect in the FO experiments seems to be greater than that observed in the RO experiments. This occurs because increased osmotic driving force impacts primarily the water transport (water chemical potential), while the ethanol driving force is fixed as the concentration difference between the feed and draw solutions. The increased water flux diluted the permeating ethanol by up to 34% for the TFC and 27% for the CTA, a result similar to that observed in works related to pervaporation experiments to dehydrate ethanol using hydrophilic crystalline polymers, such as poly(vinyl alcohol),67,68 cellulose acetate,69 and polyamide.70 The ethanol fluxes varied between 0.1 and 0.2 kg m−2 h−1 for the TFC membrane and between 0.1 and 0.3 kg m−2 h−1 for the CTA during the FO experiments, without noticeable effect among different osmotic pressures. The diffusive transport of ethanol (by dialysis) through cellulose dialysis membranes was

4. CONCLUSION This study evaluated the opportunity to use forward osmosis as a means of removing ethanol from dilute solutions. In comparison to the reverse osmosis, slightly higher separation factors are obtained by forward osmosis. We found that membrane chemistry (CTA vs polyamide TFC) yielded different performances and thus potentials for ethanol removal. The CTA membrane exhibited very low ethanol rejections (15%) relative to the TFC membrane (40%). For dealcoholization, low rejection is preferred as it leads to higher ethanol removal and less concern for osmotic pressure limitations caused by the ethanol. An added benefit of the CTA membrane was its lower NaCl permeability that resulted in a much lower reverse solute flux (also preferred for dealcoholization processes, especially those involving beverages). The TFC also demonstrated higher reverse solute flux at higher ethanol concentrations. The results presented in this study suggest that there is an opportunity to use FO to remove ethanol from solutions as opposed to more costly thermal processes, but studies regarding specific processes and the economic viability should be conducted in order to expand the use of this technology.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b04944. Standard curves obtained in the methodology adopted to analyze the ethanol concentration of samples collected in the RO and FO experiments (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +55 51 3308 3666. E-mail: [email protected]. ORCID

Alan Ambrosi: 0000-0002-2635-5980 Jeffrey R. McCutcheon: 0000-0002-5638-4926 G


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Industrial & Engineering Chemistry Research Notes

(18) Catarino, M.; Mendes, A.; Madeira, L. M.; Ferreira, A. Alcohol Removal From Beer by Reverse Osmosis. Sep. Sci. Technol. 2007, 42 (13), 3011. (19) Labanda, J.; Vichi, S.; Llorens, J.; López-Tamames, E. Membrane Separation Technology for the Reduction of Alcoholic Degree of a White Model Wine. LWT - Food Sci. Technol. 2009, 42 (8), 1390. (20) Varavuth, S.; Jiraratananon, R.; Atchariyawut, S. Experimental Study on Dealcoholization of Wine by Osmotic Distillation Process. Sep. Purif. Technol. 2009, 66 (2), 313. (21) Verhoef, A.; Figoli, A.; Leen, B.; Bettens, B.; Drioli, E.; Van der Bruggen, B. Performance of a Nanofiltration Membrane for Removal of Ethanol from Aqueous Solutions by Pervaporation. Sep. Purif. Technol. 2008, 60 (1), 54. (22) Vane, L. M. A Review of Pervaporation for Product Recovery from Biomass Fermentation Processes. J. Chem. Technol. Biotechnol. 2005, 80 (6), 603. (23) Ding, W. W.; Wu, Y. T.; Tang, X. Y.; Yuan, L.; Xiao, Z. Y. Continuous Ethanol Fermentation in a Closed-Circulating System Using an Immobilized Cell Coupled with PDMS Membrane Pervaporation. J. Chem. Technol. Biotechnol. 2011, 86 (1), 82. (24) Jain, A.; Dalai, A. K.; Chaurasia, S. P. Estimation of Permeance and Activation Energy for Separation of Ethanol from Ethanol/Water Binary Mixture by Pervaporation with PDMS Membrane. Int. J. Res. Sci. Innovation 2017, IV (VII), 113. (25) Lee, K. P.; Arnot, T. C.; Mattia, D. A Review of Reverse Osmosis Membrane Materials for Desalination - Development to Date and Future Potential. J. Membr. Sci. 2011, 370 (1−2), 1. (26) Mulder, M. Basic Principles of Membrane Technology; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1996. (27) de Castro, M. D. L.; Capote, F. P.; Á vila, N. S. Is Dialysis Alive as a Membrane-Based Separation Technique? TrAC, Trends Anal. Chem. 2008, 27 (4), 315. (28) Sablani, S. S. Food Preservation and Processing Using Membranes. In Handbook of Food Preservation; Rahman, M. S., Ed.; CRC Press Inc.: Boca Raton, FL, 2007; pp 365−385. (29) Leskošek, I.; Mitrović, M.; Nedović, V. Factors Influencing Alcohol and Extract Separation in Beer Dialysis. World J. Microbiol. Biotechnol. 1995, 11, 512. (30) Leskosek, I. J.; Mitrovic, M. Optimization of Beer Dialysis with Cuprophane Membranes. J. Inst. Brew. 1994, 100 (4), 287. (31) Lopez, M.; Alvarez, S.; Riera, F. a.; Alvarez, R. Production of Low Alcohol Content Apple Cider by Reverse Osmosis. Ind. Eng. Chem. Res. 2002, 41 (25), 6600. (32) Catarino, M.; Mendes, A.; Madeira, L.; Ferreira, A. Beer Dealcoholization by Reverse Osmosis. Desalination 2006, 200, 397. (33) Diban, N.; Arruti, A.; Barceló, A.; Puxeu, M.; Urtiaga, A.; Ortiz, I. Membrane Dealcoholization of Different Wine Varieties Reducing Aroma Losses. Modeling and Experimental Validation. Innovative Food Sci. Emerging Technol. 2013, 20, 259. (34) Cath, T. Y.; Childress, A. E.; Elimelech, M. Forward Osmosis: Principles, Applications, and Recent Developments. J. Membr. Sci. 2006, 281, 70. (35) Anastasio, D.; McCutcheon, J. R. Using Forward Osmosis to Teach Mass Transfer Fundamentals to Undergraduate Chemical Engineering Students. Desalination 2013, 312, 10. (36) Sant’Anna, V.; Marczak, L. D. F.; Tessaro, I. C. Membrane Concentration of Liquid Foods by Forward Osmosis: Process and Quality View. J. Food Eng. 2012, 111 (3), 483. (37) Benavides, S.; Oloriz, A. S.; Phillip, W. A. Forward Osmosis Processes in the Limit of Osmotic Equilibrium. Ind. Eng. Chem. Res. 2015, 54 (1), 480. (38) McCutcheon, J. R.; McGinnis, R. L.; Elimelech, M. A Novel Ammoniacarbon Dioxide Forward (Direct) Osmosis Desalination Process. Desalination 2005, 174 (1), 1. (39) Zhao, S.; Zou, L.; Tang, C. Y.; Mulcahy, D. Recent Developments in Forward Osmosis: Opportunities and Challenges. J. Membr. Sci. 2012, 396, 1.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Conselho Nacional de Desenvolvimento ́ Cientifico e Tecnológico (CNPq, Process No. 311854/2015-0 and Process No. 454552/2014-9), the Coordenaçaõ de ́ Superior (CAPES), and Aperfeiçoamento de Pessoal de Nivel the Fundaçaõ de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS) of Brazil. Some funding for supplies and equipment was provided by the National Science Foundation (CBET No. 1160098). We also acknowledge Hydration Technology Innovations for kindly providing membranes.

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REFERENCES

(1) de Oliveira Sampa, M. H.; Rela, P. R.; Las Casas, A.; Mori, M. N.; Duarte, C. L. Treatment of Industrial Effluents Using Electron Beam Accelerator and Adsorption with Activated Carbon: A Comparative Study. Radiat. Phys. Chem. 2004, 71 (1−2), 459. (2) Busetti, F.; Heitz, A.; Cuomo, M.; Badoer, S.; Traverso, P. Determination of Sixteen Polycyclic Aromatic Hydrocarbons in Aqueous and Solid Samples from an Italian Wastewater Treatment Plant. J. Chromatogr. A 2006, 1102 (1−2), 104. (3) Arenson, D. R.; Kertes, A. S.; King, C. J. Extraction of Ethanol from Aqueous Solution with Phenolic Extractants. Ind. Eng. Chem. Res. 1990, 29 (4), 607. (4) Lei, Z.; Wang, H.; Zhou, R.; Duan, Z. Influence of Salt Added to Solvent on Extractive Distillation. Chem. Eng. J. 2002, 87 (2), 149. (5) Lewandowicz, G. G.; Białas, W.; Marczewski, B. B.; Szymanowska, D. Application of Membrane Distillation for Ethanol Recovery during Fuel Ethanol Production. J. Membr. Sci. 2011, 375 (1−2), 212. (6) Gryta, M. The Fermentation Process Integrated with Membrane Distillation. Sep. Purif. Technol. 2001, 24 (1−2), 283. (7) Nguyen, V. D.; Auresenia, J.; Kosuge, H.; Tan, R. R.; Brondial, Y. Vacuum Fermentation Integrated with Separation Process for Ethanol Production. Biochem. Eng. J. 2011, 55 (3), 208. (8) Catarino, M.; Mendes, A. Dealcoholizing Wine by Membrane Separation Processes. Innovative Food Sci. Emerging Technol. 2011, 12 (3), 330. (9) Fornari, T.; Hernández, E. J.; Ruiz-Rodriguez, A.; Javier Señorans, F.; Reglero, G. Phase Equilibria for the Removal of Ethanol from Alcoholic Beverages Using Supercritical Carbon Dioxide. J. Supercrit. Fluids 2009, 50 (2), 91. (10) Cho, C.-W. W.; Hwang, S.-T. T. Continuous Membrane Fermentor Separator for Ethanol Fermentation. J. Membr. Sci. 1991, 57 (1), 21. (11) Hickey, P. J.; Juricic, F. P.; Slater, C. S. The Effect of Process Parameters on the Pervaporation of Alcohols through Organophilic Membranes. Sep. Sci. Technol. 1992, 27 (7), 843. (12) Le, N. L.; Wang, Y.; Chung, T.-S. Pebax/POSS Mixed Matrix Membranes for Ethanol Recovery from Aqueous Solutions via Pervaporation. J. Membr. Sci. 2011, 379 (1−2), 174. (13) Brüschke, H. E. A. Removal of Ethanol from Aqueous Streams by Pervaporation. Desalination 1990, 77, 323. (14) Gryta, M.; Morawski, A. W.; Tomaszewska, M. Ethanol Production in Membrane Distillation Bioreactor. Catal. Today 2000, 56 (1−3), 159. (15) Moonen, H.; Niefind, H. J. Alcohol Reduction in Beer by Means of Dialysis. Desalination 1982, 41 (3), 327. (16) Petkovska, M.; Leskosek, I.; Nedovic, V. Analysis of Mass Transfer in Beer Diafiltration with Cellulose-Based and Polysulfone Membranes. Food Bioprod. Process. 1997, 75 (4), 247. (17) Pilipovik, M. V.; Riverol, C. Assessing Dealcoholization Systems Based on Reverse Osmosis. J. Food Eng. 2005, 69 (4), 437. H


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Industrial & Engineering Chemistry Research (40) Schrier, J. Ethanol Concentration by Forward Osmosis with Solar-Regenerated Draw Solution. Sol. Energy 2012, 86 (5), 1351. (41) Zhang, X.; Ning, Z.; Wang, D. K.; Diniz da Costa, J. C. A Novel Ethanol Dehydration Process by Forward Osmosis. Chem. Eng. J. 2013, 232, 397. (42) Tiraferri, A.; Yip, N. Y.; Straub, A. P.; Romero-Vargas Castrillon, S.; Elimelech, M. A Method for the Simultaneous Determination of Transport and Structural Parameters of Forward Osmosis Membranes. J. Membr. Sci. 2013, 444, 523. (43) Zou, S.; Wang, Y.-N.; Wicaksana, F.; Aung, T.; Wong, P. C. Y.; Fane, A. G.; Tang, C. Y. Direct Microscopic Observation of Forward Osmosis Membrane Fouling by Microalgae: Critical Flux and the Role of Operational Conditions. J. Membr. Sci. 2013, 436 (0), 174. (44) Parida, V.; Ng, H. Y. Forward Osmosis Organic Fouling: Effects of Organic Loading, Calcium and Membrane Orientation. Desalination 2013, 312, 88. (45) Alsvik, I.; Hägg, M.-B. Pressure Retarded Osmosis and Forward Osmosis Membranes: Materials and Methods. Polymers (Basel, Switz.) 2013, 5 (1), 303. (46) Cath, T. Y.; Elimelech, M.; McCutcheon, J. R.; McGinnis, R. L.; Achilli, A.; Anastasio, D.; Brady, A. R.; Childress, A. E.; Farr, I. V.; Hancock, N. T.; et al. Standard Methodology for Evaluating Membrane Performance in Osmotically Driven Membrane Processes. Desalination 2013, 312 (0), 31. (47) Ren, J.; McCutcheon, J. R. A New Commercial Thin Film Composite Membrane for Forward Osmosis. Desalination 2014, 343, 187. (48) HTI. HTI Starts Producing Thin-Film Composite FO Membrane. Membr. Technol. 2012, 2012 (7), 5−6. (49) Yip, N. Y.; Tiraferri, A.; Phillip, W. A.; Schiffman, J. D.; Elimelech, M. High Performance Thin-Film Composite Forward Osmosis Membrane. Environ. Sci. Technol. 2010, 44 (10), 3812. (50) Bui, N. N.; McCutcheon, J. R. Hydrophilic Nanofibers as New Supports for Thin Film Composite Membranes for Engineered Osmosis. Environ. Sci. Technol. 2013, 47 (3), 1761. (51) McCutcheon, J. R.; Elimelech, M. Influence of Concentrative and Dilutive Internal Concentration Polarization on Flux Behavior in Forward Osmosis. J. Membr. Sci. 2006, 284, 237. (52) Gibson, J. G.; Blotner, H. The Determination of Ethyl Alcohol in Blood and Urine with the Photoelectric Colorimeter. J. Biol. Chem. 1938, 126, 551. (53) Sumbhate, S.; Nayak, S.; Goupale, D.; Tiwari, A.; Jadon, R. S. Colorimetric Method for the Estimation of Ethanol in AlcoholicDrinks. J. Anal. Technol. 1 2012, 1, 1. (54) Li, X.; Zhang, S.; Fu, F.; Chung, T.-S. Deformation and Reinforcement of Thin-Film Composite (TFC) Polyamide-Imide (PAI) Membranes for Osmotic Power Generation. J. Membr. Sci. 2013, 434 (0), 204. (55) Kim, Y. C.; Elimelech, M. Adverse Impact of Feed Channel Spacers on the Performance of Pressure Retarded Osmosis. Environ. Sci. Technol. 2012, 46 (8), 4673. (56) Coday, B. D.; Heil, D. M.; Xu, P.; Cath, T. Y. Effects of Transmembrane Hydraulic Pressure on Performance of Forward Osmosis Membranes. Environ. Sci. Technol. 2013, 47, 2386. (57) Labanda, J.; Sabaté, J.; Llorens, J. Permeation of Organic Solutes in Water−ethanol Mixtures with Nanofiltration Membranes. Desalination 2013, 315 (0), 83. (58) Choudhury, J. P.; Ghosh, P.; Guha, B. K. Separation of Ethanol from Ethanol-Water Mixture by Reverse Osmosis. Biotechnol. Bioeng. 1985, 27, 1081. (59) Smitha, B.; Suhanya, D.; Sridhar, S.; Ramakrishna, M. Separation of Organic-Organic Mixtures by Pervaporation - a Review. J. Membr. Sci. 2004, 241 (1), 1. (60) Wang, D. K.; Zhang, X.; Diniz da Costa, J. C. Claisen-Type Degradation Mechanism of Cellulose Triacetate Membranes in Ethanol-Water Mixtures. J. Membr. Sci. 2014, 454, 119. (61) Paulen, R.; Fikar, M.; Kovács, Z.; Czermak, P. Process Optimization of Diafiltration with Time-Dependent Water Adding for Albumin Production. Chem. Eng. Process. 2011, 50 (8), 815.

(62) Allegrezza, A.; Ireland, T.; Kools, W.; Phillips, M.; Raghunath, B.; Wilkins, R.; Xenopolous, A. Membranes in the Biopharmaceutical Industry. In Membranes for the Life Sciences; Peinemann, K.-V., PereiraNunes, S., Eds.; Wiley-VCH: Weinheim, Germany, 2008; Vol. 1, p 91. DOI: 10.1002/9783527631360.ch4. (63) Tang, C. Y.; She, Q.; Lay, W. C. L.; Wang, R.; Fane, A. G. Coupled Effects of Internal Concentration Polarization and Fouling on Flux Behavior of Forward Osmosis Membranes during Humic Acid Filtration. J. Membr. Sci. 2010, 354 (1−2), 123. (64) Seppälä, A.; Lampinen, M. J. On the Non-Linearity of Osmotic Flow. Exp. Therm. Fluid Sci. 2004, 28 (4), 283. (65) McCutcheon, J. R.; Elimelech, M. Modeling Water Flux in Forward Osmosis: Implications for Improved Membrane Design. AIChE J. 2007, 53 (7), 1736. (66) Hancock, N. T.; Cath, T. Y. Solute Coupled Diffusion in Osmotically Driven Membrane Processes. Environ. Sci. Technol. 2009, 43 (17), 6769. (67) Svang-Ariyaskul, A.; Huang, R. Y. M.; Douglas, P. L.; Pal, R.; Feng, X.; Chen, P.; Liu, L. Blended Chitosan and Polyvinyl Alcohol Membranes for the Pervaporation Dehydration of Isopropanol. J. Membr. Sci. 2006, 280 (1−2), 815. (68) Yong, S. K.; Sang, W. L.; Un, Y. K.; Jyong, S. S. Pervaporation of Water-Ethanol Mixtures through Crosslinked and Surface-Modified Poly(vinyl Alcohol) Membrane. J. Membr. Sci. 1990, 51, 215. (69) Kaewkannetra, P.; Chutinate, N.; Moonamart, S.; Kamsan, T.; Chiu, T. Y. Separation of Ethanol from Ethanol-Water Mixture and Fermented Sweet Sorghum Juice Using Pervaporation Membrane Reactor. Desalination 2011, 271 (1−3), 88. (70) Lee, K.-R.; Wang, Y.-H.; Teng, M.-Y.; Liaw, D.-J.; Lai, J.-Y. Preparation of Aromatic Polyamide Membrane for Alcohol Dehydration by Pervaporation. Eur. Polym. J. 1999, 35, 861. (71) Leskoŝek, I.; Nedović, V.; Petkovska, M. Effect of Convecitve Mass Transfer on Beer Diafiltration. J. Inst. Brew. 1997, 103 (5), 279. (72) Fu, C.; Cai, D.; Hu, S.; Miao, Q.; Wang, Y.; Qin, P.; Wang, Z.; Tan, T. Ethanol Fermentation Integrated with PDMS Composite Membrane: An Effective Process. Bioresour. Technol. 2016, 200, 648. (73) González-Marcos, J. A.; López-Dehesa, C.; González-Velasco, J. R. Effect of Operation Conditions in the Pervaporation of EthanolWater Mixtures with Poly(l-Trimethylsilyl-1-Propyne) Membranes. J. Appl. Polym. Sci. 2004, 94 (4), 1395. (74) Cheryan, M. Ultrafiltration and Microfiltration Handbook, 2nd ed.; CRC Press: Boca Raton, FL, 1998.

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Transport of Components in the Separation of Ethanol from Aqueous

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