ePTFE Membrane for Oil Aerosol

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Materials and Interfaces

Amphiphobic PFTMS@nano-SiO2/ePTFE Membrane for Oil Aerosol Removal Chong Xu, Jian Fang, Ze-xian Low, Shasha Feng, Min Hu, Zhaoxiang Zhong, and Weihong Xing Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02385 • Publication Date (Web): 16 Jul 2018 Downloaded from http://pubs.acs.org on July 22, 2018

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Industrial & Engineering Chemistry Research

Amphiphobic PFTMS@nano-SiO2/ePTFE Membrane for Oil Aerosol Removal Chong Xu,a Jian Fang, a Ze-Xian Low,b Shasha Feng, a Min Hu, a Zhaoxiang Zhong, * a Weihong Xinga a

State Key Laboratory of Materials-Oriented Chemical Engineering, National Engineering

Research Center for Special Separation Membrane, Nanjing Tech University, Nanjing 210009, China b

Department of Chemical Engineering, Monash University, Clayton, Victoria 3800,

Australia. Abstract：：Synthetic expanded polytetrafluoroethylene (ePTFE) membrane has a wide range of applications, including aerosol and dust removal, and exhibits high dust removing efficiency, high air permeability and cost-effectiveness. However, the intrinsic oleophilic surface of ePTFE limits its application in oil bearing gas-solid separation process. Herein, we report a surface modification method to prepare amphiphobic

ePTFE

membranes

via

coating

of

a

layer

of

1H,1H,2H,2H-Perfluorooctyltrimethoxysilane (PFTMS) – modified nano-SiO2 onto the surface of ePTFE fibers. The oil contact angle of the modified ePTFE membranes was increased from 0° to 123°, while retaining the initial water contact angle of 142°. The amphiphobic membrane shows excellent oil aerosol filtration efficiency with a comparative low pressure drop and high oil rejection rate of 99.5%. Remarkably, the membrane can be reused after simple rinsing with water. The oil aerosol filtration efficiency of membrane remained as high as 98.5% after five cycles of filtration and cleaning. Keywords: amphiphobic, expanded polytetrafluoroethylene (ePTFE) membrane, surface modification, oil aerosol removal

Introduction Various industry processes, including those in petroleum refinery, heavy oil incineration, and printing and dyeing industries, produce and release oily fume that contain harmful substances such as aldehydes, ketones, hydrocarbons, aromatic ACS Paragon Plus Environment

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

compounds, and esters.1-6 These pollutants cause various pollution-related diseases such as ischaemic heart disease, stroke, immunodeficiency, and lung cancer.7 The pollutants often undergo a gas purification step before they can be released.8 Electrostatic precipitator, thermal oxidation incineration, adsorption, and filtration technique are among the most common gas purification methods for oil-bearing system. However, there are some disadvantages associated with the cost, footprint, operation, and removal efficiency in the conventional technologies. Recently, membrane separation based on expanded polytetrafluoroethylene (ePTFE) membrane emerges as one of the potential gas purification techniques for oily aerosol treatment. ePTFE membrane has wide range of applications, including aerosol and dust removal, exhibiting high dust removing efficiency, high air permeability and cost-effectiveness.9-14 The high hydrophobicity of ePTFE membrane makes it particularly suitable to be used in high moisture environment.15 The membrane filtration system based on ePTFE membrane can maintain high filtration efficiency over a long period of time even in a high moisture environment. However, ePTFE membrane is not suitable for oil mist separation as the oleophilicity of the ePTFE will cause oily aerosol to easily adhere on the membrane surface and the ePTFE pore channels. Various approaches including plasma treatment,16-22 chemical vapor deposition (CVD)23-25, and fluorosilane coating26-32 were employed to improve hydrophobicity and oleophobicity of membranes. Coulson et al.33 modified the ePTFE membrane through oxygen plasma with a low surface free energy monomer fluorine-containing monomers to form the super-repellent composite fluoropolymer surfaces. Deposition of the fluorine-containing monomers on the surfaces of ePTFE membrane improved its liquid repellence. The modified membrane exhibited amphiphobic surface with the contact angles of water and decane are greater than 133°. Yang et al.34 fabricated robust superoleophobicity surfaces by coating a copper perfluorooctanoate aqueous solution onto surfaces of objects. The rough surfaces with the fairly low surface energy can effectively resist liquid penetrated into substance surface. Most researches targeted the amphiphobic modification for flat sheet, and few of them focused on ACS Paragon Plus Environment

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porous material. The irregular surface morphology of porous material made it challenging to modify its surface property35. Herein we report the preparation of anti-fouling anti-wetting amphiphobic porous ePTFE membranes for organic aerosol filtration. Florinated superamphiphobic nano-SiO2 were used as surface modifier of the ePTFE fibers (Figure 1). Nano-SiO2 were selected for their three-dimensional network structure, large specific surface area and

high

thermal

stability

to

ensure

high

membrane

porosity.

1H,1H,2H,2H-Perfluorooctyltrichlorosilane (FOTS), 1H,1H,2H,2H-perfluorodecyl acrylate (PFDAE) and 1H,1H,2H,2H-Perfluorooctylrimethoxysilane (PFTMS) were used as the fluorinating agents for their lower surface free energy. The surface properties and the oil aerosol removal performance of the new amphiphobic membrane were evaluated.

Figure 1. Illustration for amphiphobic ePTFE membrane preparation.

Experimental Material. 1H,1H,2H,2H-Perfluorooctyltrichlorosilane (FOTS) [C8H4Cl3F13Si, 97%] was purchased from Shangfluoro Co. Ltd. 1H,1H,2H,2H-perfluorodecyl acrylate

(PFDAE)

[C13H7F17O3,

97%]

and

1H,1H,2H,2H-Perfluorooctyltrimethoxysilane (PFTMS) [C11H13F13O3Si, 96%] were obtained from Bailingwei Co. Ltd. Nano-SiO2 (~30 nm) was purchased from Aladdin Co. Ltd. The Polyethylene terephthalate (PET) was purchased from Foshan Qianyou

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Chemical Co. Ltd. Polytetrafluoroethylene membrane (pore diameter: 5 µm) was obtained from Sartorius Co. Ltd. with a diameter of 47 mm in a round shape.

Preparation of fluorinated silica. The nano-SiO2 were hydrophilic and oleophilic. To improve the hydrophobic and oleophobic performance of silica, fluorinating agent was used. A typical fluorination of silica is as follows: First, 0.5 g nano-SiO2 was added to 40 ml cyclohexane and homogeneously dispersed using an ultrasonic homogenizer (Scientz-2400F, Ningbo Scientz Biotechnology Co. Ltd, China) for 15 min. 0.5 ml fluorinating agent was added to the solution followed by stirred at ambient temperature for 10 h. Then the resultant suspension was separated at 10000 rpm for 8 min under centrifugation (3K15, Sigma, China). The final fluorinated nano-SiO2 were dried at ~60 ºC for 5 h. Three different fluorinating agents FOTS, PFDAE and PFTMS monomers were used. The resulting fluorinated nano-SiO2 samples

were

named

as

FOTS@nano-SiO2,

PFDAE@nano-SiO2

and

PFTMS@nano-SiO2, respectively.

Preparation of ePTFE membrane with fluorinated silica. Taking the preparation of the PFTMS@nano-SiO2/ePTFE membrane by dip-coating as an example, 0.3 g of fluorinated nano-SiO2 was dispersed in 20 ml of ethanol for 90 min under stirring, and subsequently 0.5 ml of PFTMS and 0.5 ml of PET were added dropwise. After 4 hours, a homogeneous solution was obtained. The porous ePTFE membrane was placed in the suspension for 10 h, before removed and dried in the oven of 85 °C. The membrane was described as PFTMS@nano-SiO2/ePTFE-1. The

same

fluorinated

nano-SiO2

were

also

used

to

prepare

the

PFTMS@nano-SiO2/ePTFE membrane by pressure filtration. Nano-SiO2 were adsorbed on the surface of ePTFE fibers by filtrating the suspension of fluorinated nano-SiO2 at a pressure of 0.1 MPa. The resulting membrane was washed with deionized water. Finally, the membrane was dried in the oven of 85 °C. The derived membrane was described as PFTMS@nano-SiO2/ePTFE-2. In order to distinguish the effect of fluorinating agent and fluorinated nano-SiO2 on the amphiphobicity of ePTFE membrane, a series of experiments were designed to


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examine the effect of the monomer on the membrane without the use of nano-SiO2. A typical example of coating of ePTFE membrane using PFTMS is as follows: 0.5 ml of PFTMS monomers was added to 40 ml of ethanol under stirring to produce a homogeneous solution. A pristine ePTFE membrane was soaked in the mixed solution for 12 h, before removed and dried in the oven of 85 °C. after which the membrane was removed. and dried in the oven of 85 °C. The derived membrane was described as PFTMS/ePTFE.

Characterizations. DropMeterA-100P apparatus was used to measure the contact angle between solid and liquid of the ePTFE membrane surfaces. Water and hexadecane droplets (5 µL) were dropped on different areas of the horizontal substrate surfaces and the measurement was triplicated for averaging. The droplet was left on the sample for 30 s before the measurement. The contact angle of nano-SiO2 was measured by compressing the powder to form a disc. Fourier Transform Infrared (FT-IR) spectroscopy was chose to study the changes of the samples’ functional groups. The spectra of nano-SiO2 and ePTFE membrane were measured by KBr pellet method and ATR-FTIR measurements, respectively. The FT-IR spectra of samples were recorded by scanning using a Nicolet 8700 spectrometer (USA) at 400–4000 cm-1. The microstructures of the modified ePTFE membranes were characterized using a

HitachiS-4800

scanning

electron

microscopy

(FESEM)

instrument.

Thermogravimetric analysis of the modified membranes were carried out between 20−800 °C using a thermogravimetric analyzer (STA 449F3). The structure of the membrane was further characterized using X-ray diffractometer (MiniFlex 600), with measurements recorded on a XRD with Cu-Ka radiation generated at 15 mA and 40 mV. The step length and scanning speed were 0.02 °/min and 5 °/min, respectively. Gas permeability test was performed for the ePTFE membranes by the PSDA-20 pore-size distribution analyzer (Gaoqian function Co. Ltd., China) with Nitrogen. The effective test area of the membrane is 0.79 cm-2.



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Filtration performances assessment. The air filtration performance of modified ePTFE membranes were tested using a self-made filtration experimental device (Figure 2). The oily aerosol with corn oil was generated by Laskin Nozzle Generators 4B and 4Blite (TDA-4B). The concentrations of the sub-micro oily aerosol were from 10 to 100 µg/L and the average size of the corn oily aerosol was 0.26 µm. The pressure of the oily generator was kept at 0.1 MPa. The test area of filtration was 7.07 cm2 and the filtration processed at ordinary temperatures. The oil was put into the aerosol generator, and the intake air flow was controlled by adjusting the pressure of the generator. The gas permeation rates was held at 0.4 m3/h by controlling the pressure of the generator. The concentration of sub-micro oil aerosol was tested by the CEL-712 aerosol detector. CEL-712 Microdust Pro is a real-time dust monitor, especially for the measurement of dust, smoke, pollen and other suspended solids in combustion, material processing, manufacturing, energy production, vehicle exhaust and construction industry.

Figure 2. Aerosol filtration test rig.

Results and discussion Characterisation of fluorinated nano-SiO2. The hydrophobicity and oleophobicity

of

nano-SiO2,

FOTS@nano-SiO2,

PFDAE@nano-SiO2,

and

PFTMS@nano-SiO2 were determined by contact angle goniometry. Nano-SiO2 were superhydrophilic and superoleophilic (WCA and OCA of 0°) due to the hydroxyl group on the surface (Figure 3(a)). After fluorination with three different types of fluorinating agents, the WCAs of FOTS@nano-SiO2, PFDAE@nano-SiO2, and


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PFTMS@nano-SiO2 were 120°, 154°, and 152°, respectively while their OCAs were 130°, 143°, and 171°, respectively (Figure 3(b-d)). The amphiphobication occurred during the dip-coating of the nano-SiO2 in the PFTMS monomer solution, in which the fluorine-containing monomers react with the –OH group on the surface of nano-SiO2. The monomers with low surface free energy grafted onto the silica surface changed its surface to amphiphobic. The nano-SiO2 based on PFTMS fluorination exhibited the highest amphiphobicity. This may be because the –O-Si group in PFTMS is more reactive than the other monomers36. The chemical structures of the utilized fluoro-compounds was shown in Figure 4.

Figure 3. Water and hexadecane contact angle; (a) nano-SiO2; (b) FOTS@nano-SiO2, (c) PFDAE@nano-SiO2 and (d) PFTMS@nano-SiO2.



Figure 4. chemical structures of the fluorinating agents used in this study.

Functional groups of the fabricated fluorinated nano-SiO2 were investigated by using infrared absorption spectra (Figure 5). In the spectra of the nano-SiO2, the –OH stretching vibration shows the presence of the bands at 3443 cm-1. After fluorination, the band is no longer detected, confirming the chemical reaction between the fluorinating agent and the –OH group.37 The nano-SiO2 powder, modified with PFTMS, FOTS and PFDAE using the dip-coating method, showed the characteristic peaks of C-F symmetric and asymmetric stretching at approximately 1211 cm-1 and 1245 cm-1, respectively.38 The result confirms the successful grafting of the C-F group onto the nano-SiO2.

Figure 5. Infrared absorption spectra of (a) pure nano-SiO2, (b) PFTMS@nano-SiO2, (c) FOTS@nano-SiO2, (d) PFDAE@nano-SiO2.

The thermal stability of the fluorinated nano-SiO2 with different grafting monomers were evaluated through the thermogravimetric experiment. As shown in Figure 6, two weight loss phases were observed. The first weight loss from 28 ºC to 200 ºC was mainly owing to the elimination of the water molecule adsorbed on the silica surface. The second weight loss from 300 to 550 ºC was due to the decomposition of the monomer. Nano-SiO2 shows a linear mass loss with increasing temperature, which is similar to the uniform mass loss of the surface hydroxyl group


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and absorbed water. The grafted nano-SiO2 displays two weight loss with decomposition of absorbed water and fluorinating agent, respectively. There are three different monomers that were used for the fluorination of the nano-SiO2.

Thermogravimetry

and

IR

characterization

showed

that

the

fluorine-containing monomer had successfully weaved on the surface of nano-SiO2. PFTMS monomer was chosen as the fluorination agent based on the contact angle test, where the hydrophobicity and oleophobicity of nano-SiO2 after treated with PFTMS monomer were the highest.

Figure 6. TGA spectra of nano-SiO2, PFTMS@nano-SiO2, FOTS@nano-SiO2 and PFDAE@nano-SiO2.

Surface morphology of membranes. The basic PTFE membrane property data is shown in Table 1. Figure S1 shows the morphology of nano-SiO2 after fluorination. It can be seen from the electron micrograph that the particle size of the nano-SiO2 is between 20 and 40 nm. Figure 7(a) shows the morphology of a typical ePTFE membrane manufactured by a stretching process. It exhibits a net-like structure, which consists of parallel and smooth fibers.39 The morphology of the ePTFE fibers remained the same after the PFTMS treatment (Figure 7(b)). The morphology of the modified ePTFE fibers produced by dip-coating and pressure filtration are shown in Figure 7(c) and Figure 7(d), respectively (SEM images at



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different magnifications in Figure S2 and Figure S3, respectively). Nano-SiO2 were clearly observed on the surface of the ePTFE membrane modified via dip-coating (Figure 7(c)). On the other hand, the ePTFE membrane prepared by pressure filtration (PFTMS@nano-SiO2/ePTFE-2) showed rough nanofibrils due to the penetration and coating of the nano-SiO2 into the pores and onto the surface of the ePTFE fibers due to pressure filtration. These nano-SiO2 with micro-structure and fluorosilane endow PFTMS@nano-SiO2 modified membranes amphiphobic property with a high WCA and OCA. Elemental mapping of PFTMS@nano-SiO2/ePTFE-2 membrane (Figure 7(e)) shows the relatively uniform distribution of nano-SiO2 throughout the ePTFE fibers. EDS characterization (Figure S4) analysis further reveals the nano-SiO2 were adsorbed on the ePTFE fiber. Table 1 The property data of pristine ePTFE membrane. Membrane size Membrane

Pore size

Thickness

WCA

OCA

122°

0°

(diameter) ePTFE

5 µm

50 µm

47 mm


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Figure 7. SEM graphics of (a) ePTFE membranes; (b) PFTMS/ePTFE membrane; (c) PFTMS@nano-SiO2/ePTFE-1 membrane; and (d) PFTMS@nano-SiO2/ePTFE-2 membrane; (e) Region of the EDS mapping; (f) EDS spectrum of the region highlighted in (e) EDS map of element (g) carbon, (h) fluorine, (i) silicon, (j) oxygen.

Crystal structure and optical properties of the membrane. The presence of nano-SiO2 deposition on the ePTFE fibers was also confirmed by the XRD measurements. The ePTFE XRD patterns (Figure 8(a)) represent the prominent Bragg peaks at 2θ values of 17.8°, 36.85° and 31.05°, assigned to the crystalline ePTFE.40 According to Bragg equation, the interchain d-spacings of ePTFE were 4.9,



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2.4 and 2.8 Å, respectively.41 This indicates that ePTFE is a semicrystalline material and interact with the metal oxide precursor effectively. Figure 8(a, b) shows the similar peaks for ePTFE and PFTMS/ePTFE membranes due to the non-crystallinity nature

of

PFTMS.

PFTMS@nano-SiO2/ePTFE-1

membrane

and

PFTMS@nano-SiO2/ePTFE-2 membrane have the same peak at 2θ values of 16.47°, which are also found in the pure nano-SiO2 spectrum (Figure 8(c, d, e)).

Figure 8. XRD pattern of different samples (a) ePTFE; (b) PFTMS/ePTFE; (c) nano-SiO2; (d) PFTMS@nano-SiO2/ePTFE-1 membrane; and (e) PFTMS@nano-SiO2/ePTFE-2 membrane.

Figure 9 shows the FT-IR spectra of the (a) pristine and (b-d) the modified ePTFE membranes. Compared to pristine ePTFE, the existence of –CF2– and –CF3 groups (1210 cm-1 and 1248 cm-1) from PFTMS reduces the surface free energy and resulting in the formation of anti-wetting surface. From Figure 9(c, d), it is obvious that the Si–O–Si bonds (1069 cm-1) become wider and stronger, indicating an effective PFTMS@nano-SiO2 deposited in the surface of ePTFE membrane.


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Figure 9. FT-IR spectra of (a) pristine ePTFE, (b) PFTMS/ePTFE, (c) PFTMS@nano-SiO2/ePTFE-1, (d) PFTMS@nano-SiO2/ePTFE-2.

Wettability and gas permeation of membranes. Figure 10 shows the WCA and OCA of the ePTFE, PFTMS/ePTFE, PFTMS@nano-SiO2/ePTFE-1 and PFTMS@nano-SiO2/ePTFE-2, respectively. The WCA and OCA for the pristine ePTFE membrane are 122° and 0°, respectively. Hexadecane easily penetrated into the ePTFE pore channels owing to the low surface free energy (Figure S5). The WCA and OCA of PFTMS/ePTFE membrane with wet-chemical modification was slightly improved than that of the ePTFE membrane, but the approach was not effective. This is because C-F has very high bond energy and the surface of ePTFE membrane does not contain active groups. It was difficult to graft fluorine-containing monomers through simple wet-chemical modification.42 The WCA and OCA of the PFTMS@nano-SiO2/ePTFE-1 and PFTMS@nano-SiO2/ePTFE-2 membranes were greatly increased (to more than 110°) relative to the pristine membrane.



Figure 10. WCA and OCA of (a) ePTFE; (b) PFTMS/ePTFE; (c) PFTMS@nano-SiO2/ePTFE-1; (d) PFTMS@nano-SiO2/ePTFE-2.

Figure 11 indicates that the N2 permeability for the ePTFE membrane was 690 m3 m−2 h−1 kPa−1. After the dipping treatment of PFTMS monomer, the N2 permeability of the PFTMS/ePTFE membrane (673 m3 m−2 h−1 kPa−1) did not vary by much. PFTMS@nano-SiO2/ePTFE-1 membrane indicated a decrease in N2 permeability of 13.8% to 595 m3 m−2 h−1 kPa−1 due to the agglomeration of nano-SiO2 on the surface of the membrane. Nevertheless, the N2 permeability of the PFTMS@nano-SiO2/ePTFE-2 membrane (679 m3 m−2 h−1 kPa−1) was comparable to the ePTFE membrane and the PFTMS/ePTFE membrane. This is because the nano-SiO2 were uniformly distributed on the surface of fibers, as shown in Figure 7(d). In addition, the filtration method, unlike the dip-coating method did not clog the pore of the ePTFE membrane and therefore did not affect its gas flux.


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Figure 11. Gas permeation of (a) ePTFE; (b) PFTMS/ePTFE; (c) PFTMS@nano-SiO2/ePTFE-1; and (d) PFTMS@nano-SiO2/ePTFE-2.

The adhesion between fluorinated nano-SiO2 and membrane. Even though both PFTMS@nano-SiO2/ePTFE-1 and PFTMS@nano-SiO2/ePTFE-2 membrane showed remarkable hydrophobicity and oleophobicity, the durability of the coating

may

differ

as

different

coating

methods

were

used.43

Both

PFTMS@nano-SiO2 modified membranes were placed in hot water at 85 °C for 10 h under ultrasonication. Figure 12 shows the WCA and OCA of the modified membranes

before

and

after

ultrasonication.

The

OCA

of

PFTMS@nano-SiO2/ePTFE-1 was decreased from 121° to 0°. On the contrary, the PFTMS@nano-SiO2/ePTFE-2 membrane showed negligible changes on WCA (146° to 143°) and OCA (123° to 119°). This is because the PFTMS@nano-SiO2 infiltrate deep into the pores of the PFTMS@nano-SiO2/ePTFE-2 membrane and were highly integrated

to

the

surface

of

the

fibers.44

It

is

clear

that

the

PFTMS@nano-SiO2/ePTFE-1 membrane loses its oleophobic properties after ultrasonic cleaning. Owing to the poor adhesion of PFTMS@nano-SiO2, the amphiphobic surface with the method of dip-coating is less stable.



Figure 12. WCA and OCA values of PFTMS@nano-SiO2/ePTFE membranes before and after ultrasonication.

Organic aerosol laden air filtration. Based on the stability of the modified ePTFE membranes, PFTMS@nano-SiO2/ePTFE-2 membrane was selected for the performance test. The air filtration performance of ePTFE and PFTMS@nano-SiO2/ePTFE-2 membrane were tested using an self-made filtration experimental device. The gas flow rate was fixed at at 6.67 L/min, which realized by controlling the pressure of the generator. Figure 13(a) shows that the inlet oil concentration is always kept at 1320 mg/m3 throughout the whole process of 60 min. The initial concentration has fallen from 1320 mg/m3 to 6 mg/m3 after filtration. The PFTMS@nano-SiO2/ePTFE-2 membrane exhibits a rejection of the organic aerosol of 99.5% throughout the whole filtration process. The pressure drop over the filtration time of pristine ePTFE and PFTMS@nano-SiO2/ePTFE-2 membrane is presented in Figure 13(b). As shown, the filtration pressure drop of ePTFE membrane increased sharply from 3 kPa to 37 kPa in 6 min. Instead, the PFTMS@nano-SiO2/ePTFE-2 membrane increased slightly in filter pressure, from 2 kPa initial to 8.25 kPa at the end. The modified membrane not only showed low pressure drop but also excellent filtering performance in the oil-solid smoke system.


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Figure 13. (a) concentration of the feed and product stream and the rejection of the oil fume of PFTMS@nano-SiO2/ePTFE-2 membrane (b) The pressure drop over the filtration time of pristine ePTFE and PFTMS@nano-SiO2/ePTFE-2 membrane.

In a real-world application, the concentration of oil in the flue gas typically ranged between 150 mg/m3 and 250 mg/m3. The concentration of oil in a real flue gas was used in the following filtration experiment. The concentration of oil fumes was controlled at 200 mg/m3 and the gas flux was maintained at 0.46 L/min. The whole filter experiment lasted for 60 min, and the rejection rate and the pressure drop were collected after 1 hour. The membrane was cleaned by rinsing in water and dried before the next performance test. 5 cycles of the filtration and cleaning steps were ACS Paragon Plus Environment


performed. As shown in Figure 14, there is a slight change in the rejection rate and the pressure drop with the increasing number of cleaning cycle. After the fourth cycle, the pressure drop and the rejection rate become stable, at 3.1 kPa and 97.7%, respectively. The PFTMS@nano-SiO2/ePTFE-2 membrane exhibits excellent removal efficiencies and stability in conditions resembling that of the real world oil-bearing system filtration process.

Figure 14. Long term stability of PFTMS@nano-SiO2/ePTFE-2 membrane.

Conclusions Anti-wetting anti-fouling PFTMS@nano-SiO2/ePTFE membrane has been successfully fabricated by coating of fluorinated nano-SiO2 via pressure filtration. The modified membrane exhibited large contact angles of water and oil at 146° and 123°, respectively. The PFTMS@nano-SiO2/ePTFE membrane exhibited high filtration performance stability and low filtration pressure drop for organic aerosol filtration. More importantly, the membrane maintains its very high removal efficiency after simple rinsing with water. The novel amphiphobic ePTFE membrane has promising applications in air purification.

Acknowledgments Financial support was provided by the National Key R&D Program (2016YFC0204000), the National Natural Science Foundation of China (U1510202),


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and the Jiangsu Province Scientific Supporting Project (BK20170046, BE2015023 and BE2015695).

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ePTFE Membrane for Oil Aerosol

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