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Membranes and Membrane Technologies

, Volume 1, Issue 2, pp 99–106 | Cite as

Pervaporation Purification of Oxygenate from an Ethyl tert-Butyl Ether/Ethanol Azeotropic Mixture

  • A. Yu. PulyalinaEmail author
  • M. N. Putintseva
  • G. A. Polotskaya
  • V. A. Rostovtseva
  • A. M. Toikka
Article
  • 114 Downloads

Abstract

Ethyl tert-butyl ether (ETBE) is one of the most promising oxygenates used as high-octane components of fuels. A method to purify ETBE from an ethanol/ETBE azeotropic mixture formed during industrial synthesis is pervaporation. In this study, hybrid membranes containing nanodiamond particles incorporated into the P84 copolyimide matrix have been synthesized for the pervaporation purification of ETBE. The membrane structure has been studied by scanning electron microscopy and via determining the experimental and theoretical density and free volume. The transport properties of the membranes have been determined in sorption and pervaporation experiments. It has been shown that the introduction of up to 1 wt % of nanodiamonds in the P84 matrix leads to an increase in the main mass transfer parameters, namely, the flux and the separation factor of the azeotropic mixture.

Keywords:

P84 nanodiamonds pervaporation ethyl tert-butyl ether–ethanol mixture 

1 INTRODUCTION

The introduction of environmentally friendly and cost-effective technologies is one of the priority areas of industrial development. Membrane technologies are successfully used to solve many problems, in particular, the production of high-purity substances for the chemical, pharmaceutical, petrochemical, gas, and food industries; the technologies provide minimum economic costs owing to the efficient use of energy and resources [1, 2, 3, 4]. Pervaporation is a promising membrane process, which makes it possible to separate liquid mixtures by evaporation through a nonporous membrane [5, 6, 7]. One of the main advantages of pervaporation is the possibility of separating mixtures of azeotropic, thermally unstable, and close-boiling substances. The purification of ethyl tert-butyl ether (ETBE), particularly the separation of an azeotropic mixture of ETBE containing 20 wt % of ethanol at a temperature of 50°C and normal atmospheric pressure, is one of the most complex processes in the chemical industry [8].

Ethyl tert-butyl ether is one of the most effective oxygenate additives to gasoline and diesel fuels, because it has a high octane number (109–113). Since oxygenates (alcohols and ethers, such as methyl tert-butyl ether and ETBE) are characterized by a high weight content of oxygen, they significantly increase the detonation properties of the fuel and decrease the volatility of the gasoline mixture and the carbon monoxide content in the exhaust [9]. Methyl tert-butyl ether has long been the most commonly used additive; however, after the discovery of a negative impact of this material on the environment, the demand for bioether ETBE, which has a higher octane number, more readily undergoes decomposition, and exhibits a lower solubility in water, is increasing in Europe and Japan [10].

The main industrial method of the production of ETBE is the reaction between isobutylene and ethanol taken in a large excess in the presence of an acid catalyst. The target product contains up to 20% of unreacted alcohol, which forms an azeotropic mixture with the ether and requires further purification, which is typically conducted via an energy-intensive triple distillation process. Recently, it has been reported that the use of pervaporation is promising for the purification of ETBE from ethanol. The efficiency of this method is largely determined by the property of the membrane material. Most of the reports are focused on studying polymer membranes and composites based on cellulose acetate [10], which provide the passage mostly of ethanol; however, the flux is extremely low (0.08 kg/(m2 h)) at 40°C. To improve the flux, the authors of [9] synthesized graft copolymers with polylactide; the grafting led to an increase in the flux by 12 times compared with the flux of pure cellulose acetate; however, the selectivity decreased. The use of mixed esters (cellulose acetate butyrate and cellulose acetate propionate) gave a similar effect in [11]. Broad possibilities of polyimide membranes for solving many urgent industrial problems, particularly the separation of an ethanol–ETBE mixture, are shown in review [12].

In this study, the pervaporation separation of an ethanol/ETBE azeotropic mixture is conducted using a membrane based on copolyimide P84; it is a copolyimide of benzophenone-3,3'-4,4'-tetracarboxylic acid dianhydride and two diamines—meta-phenylenediamine (80%) and diaminodiphenylmethane (20%)—(BTDA–TDI/MDI); it is a commercially available aromatic copolyimide exhibiting high mechanical properties, chemical resistance, and low hydrophilicity. The P84 copolyimide was extensively studied as a membrane material for ultrafiltration [13], nanofiltration [14], and gas separation [15]. The authors of [16, 17, 18] found that P84 is a promising material for the pervaporation of water–alcohol mixtures, namely, for the dehydration of ethanol, isopropanol, and tert-butyl alcohol. Modification of polymers with inorganic nanoparticles makes it possible to improve the transport characteristics of the membrane material. At the previous stage of research, a hybrid gas-separation membrane containing 1 wt % of nanodiamonds (NDs) in the P84 copolyimide matrix was developed [19]. The introduction of NDs into the membrane led to an increase in selectivity during the separation of hydrogen from gas mixtures formed during steam methane reforming, namely, H2, CO2, and CH4. The derived data gave an impetus to the development of these studies.

The carbon particles of ultrafine diamonds (1–10 nm) exhibit unique physicochemical properties and surface activity associated with the presence of various functional groups (OH, –COOH, =C=O, etc.) [20]; at present, NDs are effectively used to design nanocomposite materials for various purposes [21, 22, 23, 24, 25].

Diffusion membranes with ND particles incorporated into the matrix of polyphenylene oxide and polyphenylene isophthalamide exhibited improved transport properties in gas separation processes [26, 27] and in the pervaporation of a methanol–methyl acetate mixture [28].

The aim of this study is to determine the transport properties of P84/ND hybrid membranes containing 0, 0.5, 1, and 2 wt % NDs in the separation of ETBE from an azeotropic mixture with ethanol by the pervaporation method and examine the structure, physicochemical parameters, and sorption properties of the membranes.

2 EXPERIMENTAL

2.1 Materials

In this study, a commercial P84 copolyimide was used (HP Polymer GmbH, Austria). Nanodiamonds with a density of 3.0 g/cm3 were prepared by detonation synthesis and supplied by Tekhnolog Special Design and Technology Bureau (Russia). The average size of NDs was 4–5 nm (coherent scattering region); the specific surface area was 330 m2/g. The solvent was N,N-dimethylformamide (DMF) manufactured by Vekton (Russia).

2.2 Synthesis of P84/ND Membranes

To prepare a P84/ND composite containing 0.5, 1, and 2 wt % NDs, P84 and ND powders were thoroughly mixed in an agate mortar for 1 h. After that, the composite powder was dissolved in DMF with a solid phase concentration of 10 wt %. To provide the complete homogenization of the mixture, it was subjected to vigorous stirring with a mechanical stirrer for 1 h and then in an ultrasonic bath at 40°C for 40 min. After that, the composite solution was filtered off to remove dust impurities.

Membranes in the form of dense nonporous films of both P84 and P84/NDs with a thickness of ~25–35 μm were prepared by casting a 10 wt % solution in DMF on a siliconized glass plate. The solvent was removed by evaporation at 40°C; the membrane was separated from the substrate and dried in a vacuum at 60°C to constant weight.

2.3 Membrane Characterization

2.4 Membrane structure

Membrane morphology was studied on a Zeiss SUPRA 55VP scanning electron microscope. Before the experiment, a 20-nm-thick platinum layer was deposited on the surface of the membrane samples by cathode sputtering on a Quorum 150 instrument (United Kingdom).

The experimental density of the membranes ρ was measured by the flotation method [27] in a isopropanol–carbon tetrachloride solution at 25°C (ρ(iPrOH) = 0.786 g/cm3, ρ(СCl4) = 1.594 g/cm3).

The theoretical density of the P84/ND membranes was calculated taking into account the properties of the membrane components assuming volume additivity [29]:

$${{\rho }_{{{\text{theor}}}}} = \frac{{\text{1}}}{{\frac{{{\text{1}} - {{w}_{{{\text{ND}}}}}}}{{{{\rho }_{{{\text{P84}}}}}}}{\text{ + }}\frac{{{{w}_{{{\text{ND}}}}}}}{{{{\rho }_{{{\text{ND}}}}}}}{\text{ }}}},$$
(1)

where ρP84 and ρND are the density of Р84 and NDs, respectively, and wND is the weight fraction of the modifier in the polymer membrane.

Fractional free volume FFV for the P84 membrane was calculated by the Bondi method [30]:

$${\text{FFV = }}{{{\text{ (}}{{V}_{{\text{0}}}} - {\text{1}}{\text{.3}}{{V}_{{\text{w}}}}{\text{)}}} \mathord{\left/ {\vphantom {{{\text{ (}}{{V}_{{\text{0}}}} - {\text{1}}{\text{.3}}{{V}_{{\text{w}}}}{\text{)}}} {{{V}_{{\text{0}}}}}}} \right. \kern-0em} {{{V}_{{\text{0}}}}}},$$
(2)

where V0 = 1/ρР84 is the specific volume of the sample and Vw is the van der Waals volume of P84 calculated according to a scheme using the group contributions tabulated by Askadskii [31].

Fractional free volume for the P84/ND composite was calculated by the following equation [32]:

where ρР84, ρND, and ρC are the density of the polymer, the NDs, and the composite, respectively; wND is the weight fraction of the modifier in the polymer membrane.

2.5 Contact angles and surface tension

The contact angles of the surface of the studied membranes were measured by the sessile drop method on a Drop Shape Analyzer DSA 10 system (Krüss, Germany) at a temperature of 25°C and atmospheric pressure.

The test liquids were water and ethanol with a surface tension of 72.4 and 21.4 mN/m, respectively.

The measured contact angle values were used to calculate the surface tension of the membranes by the Owens–Wendt method [33]; according to this method, the interfacial surface tension (σs) is the sum of the polar \(\left( {\sigma _{{\text{s}}}^{{\text{p}}}} \right)\) and dispersive components \(\left( {\sigma _{{\text{s}}}^{{\text{d}}}} \right)\):

$${{\sigma }_{{\text{s}}}} = \sigma _{{\text{s}}}^{{\text{d}}} + \sigma _{{\text{s}}}^{{\text{p}}}.$$
(4)
Using the data on the measured contact angles for two liquids, it is possible to construct the following relationship:
$$\frac{{(\cos \theta + 1){{\sigma }_{1}}}}{{\sqrt[2]{{\sigma _{1}^{{\text{d}}}}}}} = \sqrt {\sigma _{{\text{s}}}^{{\text{p}}}} \sqrt {\frac{{\sigma _{{\text{1}}}^{{\text{p}}}}}{{\sigma _{{\text{1}}}^{{\text{d}}}}}} \sqrt {\sigma _{{\text{s}}}^{{\text{d}}}} ,$$
(5)
where \(\sqrt {\sigma _{{\text{s}}}^{{\text{p}}}} \) and \(\sqrt {\sigma _{{\text{s}}}^{{\text{d}}}} \) are determined by the slope and the y-intercept, respectively.

2.6 Sorption

The sorption experiment was conducted by the immersion method via immersing the membrane samples in individual liquids at 20°C. At certain intervals, the samples were withdrawn and weighed on an analytical balance with an accuracy of ±10–4 g. The experiment was continued for 1 month to a constant weight of the samples, i.e., until the establishment of sorption equilibrium. The amount of the sorbed substance was calculated by the following formula:
$$S = \frac{{m - {{m}_{0}}}}{{{{m}_{0}}}} \times 100\% ,$$
(6)
where m is the weight of the membrane after the establishment of sorption equilibrium and m0 is the initial weight of the sample.

2.7 Pervaporation

Pervaporation experiments were conducted on a laboratory setup with an effective membrane area of 14.8 cm2 at a temperature of 50°C in a vacuum mode (residual downstream pressure of 0.2 bar). The obtained data were used to calculate the transport parameters of the membrane.

Flux J (g/(m2 h)) was determined from the amount of the permeate passing across the membrane per unit area per unit time. Since the thickness of the resulting membranes varied in the range of 25–35 μm, the samples were compared using the flux normalized to 30 μm:

$${{J}_{n}} = \frac{{Jl}}{{30}}.$$
(7)

The composition of the feed mixture and the permeate was determined on a Kristall 5000.2 chromatograph (Chromatec, Russia) equipped with a thermal conductivity detector and a Porapak Q 80/100 mesh column. Helium (99.9%) was used as a carrier gas. The column temperature was set at 200°C, while the temperature of the evaporator and the detector was 240°C. The volume of the liquid sample was 0.1 μL. Separation factor was calculated by the formula

$${{\beta }_{{{{{\text{ethanol}}} \mathord{\left/ {\vphantom {{{\text{ethanol}}} {{\text{ETBE}}}}} \right. \kern-0em} {{\text{ETBE}}}}}}} = \frac{{{{{{X}_{{{\text{ethanol}}}}}} \mathord{\left/ {\vphantom {{{{X}_{{{\text{ethanol}}}}}} {{{X}_{{{\text{ETBE}}}}}}}} \right. \kern-0em} {{{X}_{{{\text{ETBE}}}}}}}}}{{{{{{Y}_{{{\text{ethanol}}}}}} \mathord{\left/ {\vphantom {{{{Y}_{{{\text{ethanol}}}}}} {{{Y}_{{{\text{ETBE}}}}}}}} \right. \kern-0em} {{{Y}_{{{\text{ETBE}}}}}}}}},$$
(8)

where Хethanol, ХETBE and Yethanol, YETBE are the weight fractions of ethanol and ETBE in the permeate and in the feed mixture, respectively.

Fig. 1.

Structure of a P84 copolyimide macromolecule and a ND particle (scheme by O. Shenderova, International Technology Center, United States).

To determine the characteristic properties of the penetrant–membrane system, the permeability of ethanol and ETBE and the membrane selectivity were calculated by the method of Baker et al. [34]. The permeability coefficients of the individual components Pi were determined by the following equation in terms of Barrers (1 Barrer = 1 × 10–10 cm3(STP) cm cm–2 s–1 cmHg–1):

$${{P}_{i}} = {{j}_{i}}\frac{l}{{{{p}_{{i0}}} - {{p}_{{i1}}}}},$$
(9)

where j is the molar flux of the ith component, cm3(STP)/(cm2 s); pi0 and pil are the partial pressures of the ith component on the different sides of the membrane (subscripts 0 and l indicate that the quantity characterizes the surface on the feed and the permeate side, respectively). Membrane selectivity αethanol/ETBE was determined through the ratio of permeability coefficients according to the equation

$${{\alpha }_{{{{{\text{ethanol}}} \mathord{\left/ {\vphantom {{{\text{ethanol}}} {{\text{ETBE}}}}} \right. \kern-0em} {{\text{ETBE}}}}}}} = \frac{{{{P}_{{{\text{ethanol}}}}}}}{{{{P}_{{{\text{ETBE}}}}}}}.$$
(10)

3 RESULTS AND DISCUSSION

3.1 Membrane Structure and Physicochemical Properties

The P84/ND composites prepared by the solid-phase dispersion of 0.5, 1, and 2 wt % NDs in the P84 matrix and subsequent dissolution in DMF were used to synthesize hybrid membranes by casting the resulting solution onto a glass plate and subsequent evaporation of the solvent.

The structure of the P84/ND membranes containing 0, 0.5, 1, and 2 wt % NDs was studied by scanning electron microscopy. Figure 2 shows micrographs of transverse cleavages of the P84 and hybrid membranes. The cross-sectional morphology of the unmodified P84 membrane is fairly uniform (Fig. 2a). All the images of the hybrid membranes, after the incorporation of NDs into the P84 matrix, show the presence of fractal lines, which typically indicates a decrease in the elasticity of the material; this fact can apparently be attributed to the aggregation of macromolecules, which is facilitated by functional groups on the ND surface. The absence of visible defects in the cross section of the membranes containing 0.5 and 1 wt % NDs indicates a high compatibility of the nanoparticles with P84 and the stability of the hybrid membrane [35]. An increase in the ND content in the P84 matrix to 2 wt % leads to a nonuniform distribution of NDs and the formation of defective membranes.

Fig. 2.

Scanning electron microscopy images of a transverse cleavage of the membranes: (a) P84, (b) P84/ND(0.5%), (c) P84/ND(1%), and (d) P84/ND(2%).

To identify the specific features of the hybrid membranes that affect the separation of liquid mixtures, the contact angles, surface tension, density, free volume, sorption, and pervaporation characteristics of the P84/ND membranes containing 0, 0.5, and 1 wt % NDs were studied.

Surface tension is one of the most important characteristics of solids. The contact angles of the membrane surface with respect to water and ethanol were measured and used to calculate the critical surface tension. Table 1 shows that, after the introduction of NDs into the P84 matrix, the contact angles with respect to water and ethanol decrease; this finding indicates the surface hydrophilization of the membranes. At the same time, the critical surface tension of the studied membranes increases with an increase in the modifier content in the membrane owing to an increase in the polar component, which is apparently attributed to the effect of polar functional groups on the ND surface.

Table 1.

Contact angles and critical surface tension of the membranes

Membrane

Contact angle Θ, °

Surface tension σs, mN/m

\(\sigma _{{\text{s}}}^{{\text{d}}},\) mN/m

\(\sigma _{{\text{s}}}^{{\text{p}}},\) mN/m

water

ethanol

P84

71.2

21.5

31.7

8.9

22.8

P84/ND(0.5%)

70.4

21.0

32.4

8.8

23.6

P84/ND(1%)

70.0

19.7

32.5

8.7

23.8

Analysis of the structure of the P84/ND membranes was conducted using the experimentally determined density values, the calculated theoretical density, and the FFV, which are listed in Table 2. With an increase in the ND content, the theoretical density increases; this finding can be associated with the fact that the density of NDs (3.0 g/cm3) is significantly higher than the density of the P84 polymer (1.323 g/cm3). With an increase in the ND content in the hybrid membrane, the experimental density values also increase; however, they are higher than the theoretical density values. This fact indicates an increased compaction of the structure of the hybrid membranes, which is apparently attributed to additional interactions between the P84 macromolecules and the ND modifier containing surface functional groups. Calculations of the FFV in the membrane structure showed that the introduction of NDs into P84 leads to a decrease in the FFV, which is also a consequence of the densification and compaction of the membrane structure.

Table 2.  

Density and FFV

Membrane

ptheor, g/cm3

pexp, g/cm3

FFV

P84

1.323

1.323

0.082

P84/ND(0.5%)

1.327

1.330

0.079

P84/ND(1%)

1.331

1.343

0.073

3.2 Transport Properties

The mass transfer of ethanol and ETBE across the P84/ND membranes containing 0, 0.5, and 1 wt % NDs was studied in sorption and pervaporation experiments. Table 3 shows the physical properties of the studied liquids. Ethanol and ETBE have similar densities and boiling points; however, the molar weight and molar volume of ETBE significantly exceed the respective parameters of ethanol. Solubility parameters δ listed in Table 3 were used to characterize the polymer–solvent interaction. According to the theory of solubility [36, 37], the smaller the difference in the solubility parameters of the polymer and the liquid organic substance |Δδ|, the higher the solubility of this substance in the polymer. The solubility parameter δ of pure P84 is 22.3 (J/cm3)1/2 [38]. Thus, for P84, the interaction with ethanol (|Δδ| = 3.6) will be preferable to the interaction with ETBE (|Δδ| = 7.2).

Table 3.  

Physical properties of ethanol and ETBE

Liquid

Molar weight, g/mol

Density, g/cm3

Molar volume, L/mol

Тboil, °С

Viscosity, mPa s

Solubility parameter δ, (J/cm3)1/2

Ethanol

46.07

0.789

0.058

78.4

0.983

25.9

ETBE

102.18

0.745

0.137

72.8

0.400

15.1

3.3 Sorption

To study the sorption, the membrane samples were immersed in individual ethanol and ETTE liquids at atmospheric pressure and a temperature of 20°C; the experiment was continued until a constant weight of the samples. All the studied membranes were inert to ETBE; however, their sorption capacity with respect to ethanol was fairly high. Figure 3 shows the dependence of the ethanol sorption on the ND content in the polymer matrix. An increase in the ND content in the membrane contributed to surface hydrophilization and an increase in the polar component of the surface tension, which led to an increase in the ethanol sorption compared with that for the matrix polymer.

Fig. 3.

Dependence of the degree of sorption of ethanol on the ND content in the membrane.

3.4 Pervaporation experiment

The transport properties of the P84-based membranes containing 0, 0.5, and 1 wt % NDs were studied in the separation of an ethanol–ETBE mixture of an azeotropic composition (20/80 wt %) by the pervaporation method. All the studied membranes were predominantly permeable to ethanol. Figure 4 shows the experimental results in the form of a dependence of separation factor αethanol/ETBE and flux on the ND content in the membrane. With an increase in the ND content in the membrane, the separation factor increases, while the flux decreases; this finding is associated with compaction of the structure and a decrease in the free volume in the membrane (Table 2). It is evident from the results that the P84/ND(1%) membrane is most effective for the separation of the azeotropic mixture.

Fig. 4.

Dependence of (1) separation factor βethanol/ETBE and (2) flux on the ND content in the P84/ND membrane during the pervaporation of an ethanol/ETBE azeotropic mixture (20/80 wt %).

To determine the effect of the nature of the material on the separation properties of the membranes, the permeability coefficients of the individual components of the separated system and the selectivity of separation on this membrane were calculated as described in [34]. Figure 5a shows the dependence of the permeability coefficients of the individual components (ethanol and ETBE) on the ND content in the P84/ND membrane during the pervaporation of an ethanol/ETBE azeotropic mixture (20/80 wt %). If the effect of driving forces is eliminated, it is evident that the ethanol permeability for the test membranes significantly exceeds the ETBE permeability. An increase in the ND content in the membrane leads to a decrease in the permeability of both ethanol and ETBE.

Fig. 5.

Dependence of (a) the permeability coefficient of ethanol and ETBE and (b) selectivity αethanol/ETBE on the ND content in the P84/ND membrane during the pervaporation of an ethanol/ETBE azeotropic mixture (20/80 wt %).

Figure 5b shows the dependence of selectivity βethanol/ETBE on the ND content in the P84/ND membrane during the pervaporation of an ethanol/ETBE azeotropic mixture (20/80 wt %). It is evident from Fig. 5b that, if the effect of driving forces is eliminated, the ethanol selectivity βethanol/ETBE is even quantitatively higher than αethanol/ETBE. This finding is attributed to the fact that ethanol molecules are significantly smaller than ETBE molecules; this feature facilitates their diffusion across the membrane matrix. In addition, the lower value of separation factor compared with the selectivity value is determined by the effect of the driving force, namely, the higher volatile ability of ETBE than that of ethanol.

The separation of an ethanol–ETBE mixture was the aim of other studies [10, 11, 39, 40, 41]. Table 4 shows comparison of the transport properties of the new membranes with the literature data on the pervaporation of an ethanol–ETBE mixture of an azeotropic composition (20/80 wt %). Table 4 lists the flux, the ethanol concentration in the permeate, the separation factor, and the experimental conditions for pervaporation in a number of reports [39, 40, 41] and in this study. It should be noted that the P84/ND(1%) hybrid membrane is highly efficient in the purification of ETBE from ethanol impurities at a moderate flux and exhibits chemical resistance and transport properties that do not change for a long time of operation compared with the properties of other membrane materials, such as cellulose acetate. The flux of the developed hybrid materials can be improved by designing asymmetric or composite membranes with a thin selective layer of P84/ND(1%).

Table 4.  

Comparison of the transport properties of the P84/ND(1%) membrane and various reported membranes in the pervaporation of an ethanol/ETBE mixture

Membrane

T, °C

Flux,

g/(m2 h)

Ethanol in permeate, wt %

Separation factor

Reference

Cellulose Acetate (CA)

50

4.6

99.0

329

[39]

GL37 Cellulose acetate-graft-poly(methyldiethylene glycol methacrylate)(37%)

50

190

92.5

49

[39]

Poly(urea imide) (PUI)

50

2

97.0

129

[40]

PUI-g-50PMDEGMA graft copolymer with polymethacrylate

25

105

93.0

53

[40]

Polylactide + 2.5% polyvinylpyrrolidone

30

75

81.0

17

[41]

P84/ND(1%)

50

4.9

96.3

104

This study

4 CONCLUSIONS

It has been first shown that the use of P84/ND hybrid membranes for the pervaporation of an ethanol/ETBE azeotropic mixture leads to an effective purification of the oxygenate additive. The structure of the P84/ND membranes has been studied by scanning electron microscopy; it has been shown that the incorporation of up to 1 wt % NDs provides a high compatibility of the copolyimide with the nanoparticles and the stability of the hybrid membrane. The introduction of NDs into the polymer matrix leads to an increase in density and a decrease in free volume in the membrane structure. Data on the contact angle of the membrane surface with respect to water and ethanol suggest that the membrane undergoes surface hydrophilization with an increase in the modifier content in the membrane, while the critical surface tension of the studied membranes increases.

The mass transfer of ethanol and ETBE across the P84/ND membranes containing 0, 0.5, and 1 wt % NDs has been studied in sorption and pervaporation experiments. After the introduction of ND additives into the polymer matrix, the transport properties of the membranes are improved owing to an increase in the main parameters of mass transfer, i.e., flux and separation factor. The best separation properties in the pervaporation separation of an ethanol/ETBE azeotropic mixture (20/80 wt %) exhibits the membrane containing 1 wt % NDs. Comparison with the literature data has shown that the P84/ND(1%) hybrid membrane is highly efficient in the purification of ETBE from ethanol impurities at a moderate flux.

Notes

ACKNOWLEDGMENTS

This work was supported by the Russian Science Foundation, project no. 16-13-10164; the project executors were A.Yu. Pulyalina, G.A. Polotskaya, V.A. Rostovtseva, and A.M. Toikka, who studied the physicochemical and transport properties, discussed the results, and prepared the text of the manuscript; M.N. Putintseva participated in the sorption and pervaporation experiments, the discussion of the results, and the preparation of the text of the manuscript. The authors thank V.Yu. Dolmatov (Tekhnolog Special Design and Technology Bureau) for supplying the NDs. This work was performed using the equipment of the Interdisciplinary Resource Center for Nanotechnology of St. Petersburg State University.

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Copyright information

© Pleiades Publishing, Ltd. 2019

Authors and Affiliations

  • A. Yu. Pulyalina
    • 1
    Email author
  • M. N. Putintseva
    • 1
    • 2
  • G. A. Polotskaya
    • 1
    • 3
  • V. A. Rostovtseva
    • 1
  • A. M. Toikka
    • 1
  1. 1.Institute of Chemistry, St. Petersburg State UniversitySt. PetersburgRussia
  2. 2.Topchiev Institute of Petrochemical Synthesis, Russian Academy of SciencesMoscowRussia
  3. 3.Institute of Macromolecular Compounds, Russian Academy of SciencesSt. PetersburgRussia

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