Reliable fabrication of thin and (h0l)-oriented zeolite Al-beta

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Separations

Reliable fabrication of thin and (h0l)-oriented zeolite Al-beta membranes for separation of methanol/methyl tert-butyl ether mixtures Yun Li, Ning Ma, and Baoquan Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b06068 • Publication Date (Web): 24 Apr 2019 Downloaded from http://pubs.acs.org on April 25, 2019

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Industrial & Engineering Chemistry Research

Reliable fabrication of thin and (h0l)-oriented zeolite Al-beta membranes for separation of methanol/methyl tert-butyl ether mixtures

Yun Li, Ning Ma, and Baoquan Zhang*

State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China

ABSTRACT: Dense, ca. 1 μm thick and (h0l)-oriented zeolite Al-beta membranes have been successfully fabricated on randomly oriented seed layers by secondary growth in the fluoride medium. The incorporation of Al species into the zeolite framework is demonstrated by FTIR, EDS, and

29Si

and

27Al

MAS NMR measurements. The Al

incorporation enhances the nucleation rate. The synthesized zeolite Al-beta membranes

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

are applied in methanol/methyl tert-butyl ether (MeOH/MTBE) separation via pervaporation. It exhibits a high flux of 1.83 kg m−2 h−1 with respect to 20 wt% MeOH/MTBE mixture at 50 °C, while the corresponding separation factor is 20.39. Compared with available zeolite membranes reported in the literature, the synthesized Al-beta membrane is more promising for MeOH/MTBE separation due to its high flux with a moderate separation factor.


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1. INTRODUCTION Methyl tert-butyl ether (MTBE) is an octane enhancer and an excellent oxygenated fuel additive being used to reformulate gasoline to mitigate air pollution caused by vehicle emissions.1 MTBE is mainly synthesized by a reaction between methanol (MeOH) and isobutylene, where excess MeOH is added to achieve a higher yield. However, MTBE and excess MeOH could form an azeotrope when the concentration of MeOH is 14.3 wt%.2 The conventional separation process is mainly conducted by various distillation techniques, such as reaction distillation, pressurized distillation, saline distillation and extractive distillation.3,4 Obviously, these techniques are both capital and energy intensive, and have some adverse impacts on the environment. Pervaporation is an attractive separation technique owing to its low energy consumption and no contamination. Therefore, it has been considered as a promising alternative technique for MeOH/MTBE separation. At present, the research has been focused on polymer membranes for MeOH/MTBE mixtures separation by pervaporation, including poly(vinyl alcohol) based membranes5–7, cellulose based membranes8,9 and polyelectrolyte complex based


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membranes10,11. Although these membranes exhibit excellent separation factors of ca. 17~2300, their fluxes (ca. 0.006~0.42 kg m−2 h−1) are not satisfactory at all for actual separation processes. Additionally, they are vulnerable to swell in MeOH/MTBE mixtures, resulting in poor stability in actual applications. Some novel metal-organic frameworks-based materials have also been explored for MeOH/MTBE separation. However, these materials suffer from poor chemical or thermal stabilities under rigorous conditions and their fabrication processes are sufficiently challenging.12 To avoid above defects, zeolite membranes including NaY13, silicalite-114 and Bbeta membranes15 have been regarded as ideal candidates for MeOH/MTBE separation. Well-crystallized zeolite beta grains possess a three-dimensional interconnected channel system with pore diameters of 0.53 × 0.57 nm and 0.71 × 0.73 nm,15 which exhibit excellent thermal, mechanical and chemical stabilities. The incorporation of Al into the framework of all-silica zeolite beta could give zeolite beta catalytic properties and enable its framework to be changed from hydrophobic to hydrophilic. It could be expected that zeolite beta membranes would show a great potential for separation of MeOH/MTBE mixtures. The synthesis of zeolite Al-beta


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membranes is commonly performed in an alkaline medium, which causes poor crystallinity and stability as well as defects after the template removal.16,17 In contrast to the alkaline medium, zeolite Al-beta membranes synthesized in a fluoride medium possess high crystallinity and an enhanced control of the crystal orientation. However, the zeolite beta membranes synthesized in the fluoride medium are generally thick, resulting in low fluxes in separation processes.18,19 In this contribution, thin zeolite Al-beta membranes with (h0l)-orientation are fabricated by secondary growth method in the fluoride medium for the first time. It will be demonstrated that the Al species is introduced into the framework of zeolite beta. The effect of metal incorporation on the crystal growth of zeolite beta membranes is illustrated. The synthesized zeolite Al-beta membranes are further applied in MeOH/MTBE mixtures separation by pervaporation. The effects of operation parameters on the pervaporation performances will be investigated in detail. The availability of high-quality zeolite Al-beta membranes will trigger their actual application in the separation of MTBE/MeOH mixtures.


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2. EXPERIMENTAL SECTION 2.1. Materials and Chemicals. The homemade porous -Al2O3 disks (2 mm in thickness, 20 mm in diameter) were used as substrates. Other chemical reagents were described in Supporting Information in detail. 2.2. Synthesis of Zeolite Al-beta Membranes. The zeolite Al-beta membrane was synthesized by secondary growth method. The zeolite beta seed layer was formed as reported elsewhere.20,21 The detailed process was described in Supporting Information. For the synthesis of zeolite Al-beta membranes, the molar composition is tetraethylammonium hydroxide (TEAOH) : SiO2 : hydrofluoric acid (HF) : Al : H2O = 0.6 : 1.0 : 0.6 : 0.04 : 4 with the similar manner as reported previously.21 In brief, fumed silica was added to TEAOH solution to form a clear solution. Al(NO3)3 aqueous solution was mixed with the silica solution. Then HF was added to the resultant solution under hand stirring to form a viscous gel. The seeded substrates were fixed vertically in the dense gel and hydrothermally treated at 140 °C for 7 d. The leaking test was used to check the quality of the as-synthesized membranes. Then the template of samples was removed at 320 °C in hydrogen atmosphere with the heating and cooling rate of 0.5 °C min-1,


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which was determined based on the results of Ref. (22).22 For comparison, the zeolite Sn-beta was synthesized following the same synthesis procedure where Al was substituted by Sn for a prolonged crystallization time of 12 d. The all-silica and Fe-beta membrane were synthesized as reported previously.21 2.4. Characterization. The surface morphology of zeolite Al-beta membranes was estimated using scanning electron microscopy (SEM, XL30ESEM) coupled with energy dispersive spectroscopy (EDS) to analyze the chemical composition. The crystal type and preferential orientation of zeolite Al-beta membranes were determined by X-ray diffraction (XRD, D/MAX-2500) using Cu K radiation. The Al species incorporated into the framework of zeolite beta was demonstrated by Fourier transform infrared spectra (FTIR, Nicolet 6700), 29Si and 27Al MAS NMR spectra (Infinityplus 300). The surface hydrophilicity of zeolite Al-beta membranes was measured by the water contact angle (WCA, DropMeter A–200) with a total drop size of ~3 μL. 2.5. Pervaporation Performance. Pervaporation experiments was carried out for 4 h using a homemade pervaporation apparatus as reported previously (Figure 1).23 The zeolite Al-beta membrane was sealed with Teflon gaskets and tapes in a membrane


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module, which was placed in a designated glass vessel with prefilled MeOH/MTBE mixture. The temperature of the feed solution was controlled at 30, 40 and 50 °C in a water bath. The pressure in permeate side was maintained at 133 Pa. The effective membrane area was ca. 1.1 cm2. Two cold traps with liquid nitrogen was connected in series to collect the permeate vapor. The first cold trap was used to collect the permeate vapor. The second one was employed to collect trace incompletely condensed permeate vapor, and played a protective role to the vacuum pump. The flux (J) was calculated according to J = W/(A×t), where W is the permeate mass (kg), A the membrane area (m2), and t the collecting time (h). Both the feed and the permeate liquid were analyzed in a Varian 3380 gas chromatograph equipped with a thermal conductivity detector. The separation factor (α) was defined according to αA/B = (YA/YB)/(XA/XB), where XA, XB and YA, YB are the mass fractions of MeOH (A) and MTBE (B) in the feed and permeate sides. The permeability (Pi) and selectivity () of the zeolite Al-beta membrane were determined to further demonstrate its intrinsic properties as reported in the literature (see Supporting Information for details).24


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Pi =

ji × l = sat ji × l pio ― pil pio γioχio ― pil Pi

β = Pj

(1) (2)

where ji is the molar flux of component i, l the membrane thickness, pio and pil the partial pressures of component i on either side of the membrane, psat io the saturated vapor pressure of pure component i, io and io the activity coefficient and mole fraction of component i in the feed solution, and Pi and Pj the permeabilities of component i and j.

Figure 1. A batch pervaporation system.

3. RESULTS AND DISCUSSION 3.1. (h0l)-Oriented Zeolite Al-beta Membranes. The zeolite beta seeds possess sphere morphology with the average particle size of ca. 200 nm (Figure S1). The uniform seed layer is fabricated on the substrate with the thickness of ca. 1.4 μm (Figure S2). SEM images of the zeolite Al-beta membrane are shown in Figure 2a,b.


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The well-intergrown zeolite Al-beta grains constitute a continuous and smooth zeolite Al-beta membrane. The truncated bipyramidal crystals with their (h0l)-orientation are perpendicular to the substrate surface, resulting in the formation of the (h0l)-oriented zeolite Al-beta membrane (Figure 2a). The corresponding cross-sectional view displays that an intergrown and dense crystal layer around 1 μm in thickness is tightly adhered to the substrate surface (Figure 2b). The all-silica zeolite beta membrane with the thickness of 8.5 μm has been reported in our previous work.21 By comparison, the Al incorporation into the zeolite framework leads to a significant reduction in the membrane thickness.

Figure 2. SEM images of top view (a) and cross-sectional view (b) of the zeolite Al-beta membrane.


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The XRD patterns of the synthesized zeolite Al-beta membrane are consistent with the above SEM observations (Figure 3). All samples only display the Bragg peaks corresponding to the BEA polymorph A topology. The randomly oriented seed layer is fabricated on the substrate (Figure 3, trace C). After secondary growth, the diffraction peaks in the XRD pattern appears at 2 = 7.74°, 21.37° and 22.11°, corresponding to the reflections of (101), (106) and (302) planes (Figure 3, trace D). The features of the peak at the low angle suggest that the synthesized sample has a stacking probability and may be nearer polymorph A.25 This result further demonstrates that the zeolite Al-beta membrane is preferentially (h0l)-oriented.


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Figure 3. XRD patterns of the standard BEA polymorph A topology (trace A), -Al2O3 substrate (trace B), the seed layer (trace C) and the as-synthesized zeolite Al-beta membrane (trace D). The peak marked by a star is attributed to the -Al2O3 substrate. 3.2. Incorporation of Al Species into the Zeolite Framework. Figure 4 gives the FTIR spectra of all-silica and Al-beta powdery samples. All samples have similar FTIR spectra with seven framework adsorption bands at around 424, 465, 523, 569, 781, 1072 and 1219 cm−1. The bands at 424 and 465 cm−1 are attributed to the TO (T = Si, Al) bending vibrations. The bands at 523 and 569 cm−1 correspond to the double-ring stretching modes. The peak at approximately 781 cm−1 is ascribed to the OTO symmetric stretch. The bands at 1072 and 1219 cm−1 are attributed to the internal and external TO asymmetric stretching vibrations, respectively. Notably, compared with allsilica zeolite beta samples, most bands of zeolite Al-beta crystals either as-synthesized or calcined shift to lower frequency due to the decrease of force constant of TO after isomorphous substitution of Si by Al atoms, which could be taken as an indication of Al incorporation into the zeolite framework.26 In addition, it can be seen that the frequencies of framework adsorption bands shift toward higher frequency after the


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template removal, which may be attributed to the dealumination from framework during decomposition of the template.27

Figure 4. FTIR spectra of as-synthesized all-silica (trace A) and Al-beta (trace C), as well as calcined all-silica (trace B) and Al-beta (trace D) samples. In addition to FTIR spectra, the solid state 29Si and 27Al MAS NMR spectra could give a strong evidence on the introduction of Al into the zeolite beta framework (Figure 5). Only Si(4 Si) resonances signals at ca. −111, −113 and −116 ppm are observed in the 29Si MAS NMR spectra of the all-silica zeolite beta (Figure 5a, trace A). There is no signal assigned to connectivity defects in all-silica zeolite beta crystals. Compared with


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the all-silica zeolite beta, the zeolite Al-beta exhibits a broadening band, which is attributed to the reduced local order resulting from the incorporation of Al.28 Extra three bands at around −108, −104 and −99 ppm appear (Figure 5a, trace B). The bands at −108 and −99 ppm correspond to Si(3Si, 1Al) and Si(2Si, 2Al). The signal at −104 ppm could be ascribed to the superposition of Si(3Si, 1Al) and Si(3Si, 1OH). The appearance of connectivity defects in the zeolite Al-beta framework is generated by dealumination during the calcination.28 Figure 5b shows the 27Al MAS NMR spectra of the assynthesized and calcined zeolite Al-beta (Figure 5b). The appearance of a unique resonance at 56.1–52.7 ppm of the as-synthesized zeolite beta is ascribed to Al in tetrahedral coordination (Figure 5b, trace A), indicating that the Al species is introduced into the framework of the zeolite beta. For calcined zeolite Al-beta, an additional signal around 0 ppm attributed to the formation of octahedral Al species is observed (Figure 5b, trace B), suggesting the presence of exframework Al species generated during the calcination.28 This result is consistent with results of the 29Si MAS NMR and FTIR measurements. Furthermore, the Si/Al ratio of zeolite Al-beta membranes is 12.3 by using the EDS measurement, which also indicates the presence of Al.


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Figure 5. 29Si MAS NMR spectra (a) of calcined all-silica (trace A) and Al-beta (trace B) powders, and 27Al MAS NMR spectra (b) of as-synthesized (trace A) and calcined (trace B) zeolite Al-beta powders. To further illustrate the effect of metal incorporation on the crystal growth of zeolite beta membranes, Al-beta, Fe-beta, Sn-beta and all-silica beta powdery samples are collected from the autoclave bottom. SEM images of these particles are shown in Figure 6. All samples possess the same truncated bipyramidal shape. It should be noted that the size of zeolite Al-beta crystals is smaller than those of Fe-beta, Sn-beta and all-silica beta. Al species incorporated into the framework enhances the ratio of the nucleation rate to the crystal growth rate of zeolite beta.28 However, Fe-beta and Sn-beta crystals


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possess almost the same size as that of the all-silica zeolite beta, which is attributed that the incorporation of Fe and Sn atoms other than Al species retards the crystal nucleation.29 In addition, the crystal lengths along (l00) and (00l) directions of all-silica, Al-beta, Fe-beta and Sn-beta crystals are summarized in Table 1. The ratio of the length along (l00)-direction to that of (00l)-direction increases after isomorphous substitution of Si by Al, Fe or Sn atoms, indicating that metal atoms other than Al species introduced into the framework of zeolite beta crystals could slow down the growth rate of crystals along the (00l)-direction. Therefore, compared with the all-silica zeolite beta, smaller crystal size of zeolite Al-beta grains leads to the formation of thin zeolite Al-beta membranes.


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Figure 6. SEM images of all-silica (a), Al-beta (b), Fe-beta (c) and Sn-beta (d) crystals. Table 1. Comparison of the crystal lengths along (l00) and (00l) directions for allsilica, Al-beta, Fe-beta and Sn-beta crystals. Samples

(l00)-direction (μm)

(00l)-direction (μm)

(l00)/(00l)

all-silica beta

13.1

12.4

1.06

Al-beta

2.8

3.6

0.78

Fe-beta

13.3

9.2

1.45

Sn-beta

14

6.5

2.15

3.3. Pervaporation Performances of Zeolite Al-beta Membranes. Based on the leaking test, the as-synthesized zeolite Al-beta membranes are dense and continuous because the measured N2 permeance is less than 10−11 mol m−2 s−1 Pa−1. After the template removal, the synthesized zeolite Al-beta membranes are utilized in MeOH/MTBE mixtures separation via pervaporation. Due to the incorporation of Al into its framework, the zeolite Al-beta membrane exhibits hydrophilic characteristics with WCA of 45° (Figure 7), which results in a preferential adsorption for MeOH.30 Additionally, the pore size of zeolite Al-beta crystals is larger than the kinetic diameter of


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MeOH (3.8 Å), but close to that of MTBE (6.3 Å). Thus, it can be expected that zeolite Al-beta membranes would exhibit preferential selectivity to MeOH over MTBE owing to their surface hydrophilicity and pore sieving effect.

Figure 7. WCA on the synthesized zeolite Al-beta membrane. Dependence of MeOH mole fraction in the permeate side on its feed solution is plotted in Figure 8. As expected, the preferential transfer of MeOH to the permeate side and the MTBE enrichment in the feed solution are observed in the pervaporation process through the zeolite Al-beta membrane. Moreover, it should be noted that the azeotropic separation limitation is easily surmounted via the pervaporation through the zeolite Al-beta membrane. Therefore, the pervaporation technique possesses a great potential in MeOH/MTBE separation.


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Figure 8. Selectivity comparison between pervaporation through the zeolite Al-beta membrane and vapor-liquid equilibrium for MeOH/MTBE mixtures. Pervaporation experiments are carried at 30 °C. The operating conditions of pervaporation processes have great influences on the separation performances. Figure 9a gives the effect of the operating temperature on separation performances of zeolite Al-beta membranes with respect to 20 wt% MeOH/MTBE mixture. It can be seen that a higher pervaporation temperature is beneficial not only for the permeation flux but also for the separation factor, which is attributed to the enhanced vapor pressure driving force for mass transfer. Such


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temperature dependency of the separation factor could be described by the Arrhenius equation:

Ji = J0 e

― E RT a

(1) where Ji is the permeation flux of component i (kg m−2 h−1), J0 the pre-exponential factor (kg m−2 h−1), Ea the activation energy (kJ mol−1), R the gas constant (kJ mol−1 K−1), and

T the temperature (K). The plots of MeOH and MTBE fluxes as a function of temperature for zeolite Albeta membranes are shown in Figure 9b. The activation energies for MeOH and MTBE permeation through zeolite Al-beta membranes are 22.92 kJ mol−1 and −25.55 kJ mol−1, respectively. The positive value of activation energy indicates that the permeation flux increases with temperature or vice versa. The flux of MeOH increase with temperature while MTBE flux decreases, which results in an increase in the separation factor at elevated operating temperature. Furthermore, the permeabilities of components and membrane selectivity are calculated to illustrate the temperature effect. As shown in Figure 9c, the permeabilities


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of MeOH and MTBE decrease while the membrane selectivity increases with temperature. The relationship between the permeability and temperature is also described by an Arrhenius equation:

Pi = P0 e

― E RT P

(2) where Pi is the permeability of component i (Barrer), P0 the pre-exponential factor (Barrer), EP the apparent activation energy (kJ mol−1), R the gas constant (kJ mol−1 K−1), and T the temperature (K). The transport mechanism of permeating molecules through zeolite membranes is mainly described with the adsorption–diffusion model.31 The EP value is a combination of the enthalpy of sorption and the activation energy of diffusion. A positive value of EP indicates that the transport is governed by diffusion, while a negative EP suggests that the sorption is dominant in the transport process.32 As shown in Figure 9d, the negative

EP values for MeOH (−14.42 kJ mol−1) and MTBE (−54.18 kJ mol−1) indicates that the decreased permeabilities may be attributed to a reduction in sorption of MeOH and MTBE on membrane surface. In addition, the absolute value of EP, MTBE is larger than


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that of MeOH, suggesting that the MTBE permeability is more sensitive to temperature, that is to say, the sorption of both MeOH and MTBE decreases but more for MTBE molecules. Thus, the selectivity increases at higher temperature.

Figure 9. Effect of the operating temperature on pervaporation performances of zeolite Al-beta membranes with respect to the total flux and separation factor (a), and MeOH and MTBE permeabilities and selectivity (c). Arrhenius plots of MeOH and MTBE fluxes (b) and permeabilities (d). Pervaporation performances for different feed compositions is investigated for zeolite Al-beta membranes at 30 °C. The total flux elevates while the separation factor


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declines with MeOH content in feed (Figure 10a). A higher MeOH content in feed facilities MeOH adsorption on the zeolite Al-beta membrane, which increases the driving force for MeOH transport. In addition, the diffusion rate of MeOH molecules in zeolitic channels is larger than that of MTBE owing to the smaller molecular diameter of MeOH. The above factors contribute to the increase in the total flux. The decreased separation factor may be attributed to the fact that the adsorption coverage of MeOH on the membrane surface did not increase proportionally with the MeOH concentration in feed. Thus, the MeOH fluxes did not increase as much as the feed concentration33, leading to a decrease in the separation factor. Figure 10b shows the permeability and selectivity for MeOH and MTBE through zeolite Al-beta membranes at different feed composition. It is evident that the permeability of MeOH and the membrane selectivity decrease as MeOH content in feed increases, while the permeability of MTBE changes slightly. This may be related to a crowding effect of MeOH diffusion through zeolitic pores.24


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Figure 10. Effect of MeOH concentration in the feed solution on separation performances of zeolite Al-beta membranes: (a) total flux and separation factor, and (b) MeOH and MTBE permeabilities and selectivity. The pervaporation performances of synthesized zeolite Al-beta membranes and reported zeolite membranes for MeOH/MTBE separation are given in Table 2. The synthesized zeolite Al-beta membrane exhibits a high flux of 1.83 kg m−2 h−1 with respect to 20 wt% MeOH/MTBE mixture at 50 °C, while the corresponding separation factor is 20.39. Compared with other zeolite membranes, the zeolite Al-beta membrane has a much higher flux with a moderate separation factor, which is more desirable for actual MeOH/MTBE separation.


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Table 2. Comparison of pervaporation performances of synthesized zeolite Al-beta membrane with available zeolite membranes in the literature for MeOH/MTBE separation. T

MeOH in feed

Flux

Separation

(°C)

(wt%)

(kg m−2 h−1)

factor ()

NaY

50

10

0.32

7600

13

Silicalite-1

30

20

0.08~0.12

2.67

14

B-beta

30

20

–

6.81

15

Al-beta

50

20

1.83

20.39

This work

Membranes

Ref

4. CONCLUSIONS Thin and (h0l)-oriented zeolite Al-beta membranes have been fabricated on randomly oriented seed layers using secondary growth method in the fluoride medium. An intergrown and dense crystal layer around 1 μm in thickness is tightly adhered to the substrate surface. The FTIR, EDS and 29Si and 27Al MAS NMR measurements demonstrate that Al species have been incorporated into the zeolite beta framework. Metal incorporation has great effects on the crystal growth of zeolite beta membranes. Al species could enhance the nucleation rate, while Fe and Sn retard the crystal


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formation and slow down the growth rate of crystals along the (00l)-direction. The synthesized zeolite Al-beta membranes are applied in MeOH/MTBE mixtures separation via pervaporation, where the azeotropic separation limitation is surmounted. With the increase of operating temperature, the permeabilities of MeOH and MTBE decrease while the membrane selectivity increases due to the dominance of MeOH adsorption in the pervaporation process. Increasing MeOH content in feed, the permeability of MeOH and membrane selectivity decrease while the permeability of MTBE changes slightly. The zeolite Al-beta membrane exhibits a high flux of 1.83 kg m−2 h−1 with respect to 20 wt% MeOH/MTBE mixture at 50 °C, while the corresponding separation factor is 20.39. Compared with reported Y- and MFI-type zeolite membranes in the literature, the synthesized Al-beta membrane is more promising for separation of MeOH/MTBE mixtures due to its high flux with a moderate separation factor. The synthesized zeolite beta membranes show great potentials in high-efficient purification of MTBE from its MeOH mixtures.

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ASSOCIATED CONTENT


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Supporting Information Materials and chemicals; Preparation of zeolite beta seed layers; The calculation process of the permeability; The morphology of zeolite beta seeds; The morphology of the zeolite beta seed layer. This material is available free of charge via the Internet at http://pubs.acs.org.



AUTHOR INFORMATION

Corresponding Author *Tel./Fax: +86 2285356517. E-mail: [email protected].

ORCID Baoquan Zhang: 0000-0001-7571-8103

Notes The authors declare no competing financial interest.



ACKNOWLEDGMENT


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We are grateful for the financial support from the National Natural Science Foundation of China (Grant Nos. 21136008 and 21476171)

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REFERENCES

(1) González, B. G.; Uribe, I. O. Mathematical modeling of the pervaporative separation of methanol−methylterbutyl ether mixtures. Ind. Eng. Chem. Res. 2001, 40, 1720–1731. (2) Sridhar, S.; Smitha, B.; Shaik, A. Pervaporation-based separation of methanol/MTBE mixtures—A review. Sep. Purif. Rev. 2005, 34, 1–33. (3) Isla, M. A.; Irazoqui, H. A. Modeling, analysis, and simulation of a methyl tert-butyl ether reactive distillation column. Ind. Eng. Chem. Res. 1996, 35, 2696–2708. (4) Loras, S.; Aucejo, A.; Muñoz, R.; Wisniak, J. Azeotropic behavior in the system methanol plus methyl 1,1-dimethylethyl ether. J. Chem. Eng. Data 1999, 44, 203–208. (5) Zhou, K.; Zhang, Q. G.; Han, G. L.; Zhu, A. M.; Liu, Q. L. Pervaporation of water– ethanol and methanol–MTBE mixtures using poly (vinyl alcohol)/cellulose acetate blended membranes. J. Membr. Sci. 2013, 448, 93–101.


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GRAPHICAL ABSTRACT

KEYWORDS: zeolite Al-beta membrane; (h0l)-orientation; thin membrane; MeOH/MTBE separation


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Reliable fabrication of thin and (h0l)-oriented zeolite Al-beta

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