Hyper-Cross-Linked Additives that Impede Aging and Enhance

Subscriber access provided by Uppsala universitetsbibliotek

Article

Hypercrosslinked Additives that Impede Aging and Enhance Permeability in Thin Polyacetylene Films for Organic Solvent Nanofiltration Xi Quan Cheng, Kristina Konstas, Cara M. Doherty, Colin D. Wood, Xavier Mulet, Zongli Xie, Derrick Ng, Matthew R Hill, Lu Shao, and Cher Hon Lau ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b02295 • Publication Date (Web): 04 Apr 2017 Downloaded from http://pubs.acs.org on April 6, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33

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

ACS Applied Materials & Interfaces

Hypercrosslinked

Additives

that

Impede

Aging

and

Enhance

Permeability in Thin Polyacetylene Films for Organic Solvent Nanofiltration Xi Quan Cheng,a,b Kristina Konstas,a Cara M. Doherty,a Colin D. Wood,c Xavier Mulet,a Zongli Xie,a Derrick Ng,a Matthew R. Hill,a,d,* Lu Shao, b,* and Cher Hon Laua,e* a

CSIRO, Private Bag 10, Clayton South VIC 3169, Australia.

b

MIIT Key Laboratory of Critical Materials Technology for New energy Converson and Storage,

State Key Laboratory of Urban Water Resource and Environment, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, China. c

CSIRO, Australian Resources Research Centre, Kensington, WA 6155, Australia.

d

Department of Chemical Engineering, Monash University, Clayton VIC 3800, Australia.

e

Department of Chemical Engineering, University of Edinburgh, EH9 3JL, United Kingdom

ACS Paragon Plus Environment

1


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

Page 2 of 33

KEYWORDS: Organic solvent nanofiltration; Physical aging; Porous aromatic frameworks (PAF1); Hypercrosslinked polymer (HCP); Solvent treatment

ABSTRACT

Membrane materials with high permeability to solvents whilst rejecting dissolved contaminants are crucial to lowering the energy costs associated with liquid separations.

However, the current

lack of stable high permeability materials require innovative engineering solutions to yield high performance, thin membranes using stable polymers with low permeabilities. Poly[1(trimethylsilyl)-1-propyne] (PTMSP) is one of the most permeable polymer but is extremely susceptible to physical aging.

Despite recent developments in anti-aging polymer membranes,

this research breakthrough has yet to be demonstrated on thin PTMSP films supported on porous polymer substrates - a crucial step towards commercializing anti-aging membranes for industrial applications.

Here we report the development of scalable, thin film nanocomposite membranes

supported on polymer substrates that are resistant to physical aging whilst having high permeabilities to alcohols.

The selective layer is made up of PTMSP and nanoporous polymeric

additives. The nanoporous additives provide additional passageways to solvents, enhancing the high permeability of the PTMSP materials further.

Through intercalation of polyacetylene chains

into the sub-nm pores of organic additives, physical aging in the consequent was significantly hindered in continuous long term operation.

Remarkably we also demonstrate that the additives

enhance both membrane permeability and rejection of dissolved contaminants across the membranes, as ethanol permeability at 5.5 × 10-6 L m m-2 h-1 bar-1 with 93 % Rose Bengal (1017.6 g mol-1) rejection; drastically outperforming commercial and state-of-the-art membranes.

These


2

Page 3 of 33

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


membranes can replace energy-intensive separation processes such as distillation, lowering operation costs in well-established pharmaceutical production processes.

Introduction Alcohols are a valuable commodity material and an important chemical building block, and are widely used for purifying valuable chemical and pharmaceutical products in the industry to minimize product waste.

Depending on end application, alcohols purification can also be

designed to maximize product recovery.1,

2

Batch solvent purification techniques, such as

distillation and molecular sieving, are fundamental processes for the production of alcohols despite their high energy and spatial requirements. A green alternative for these energy-intensive purification techniques is membrane separation techniques (including pervaporation, membrane distillation) where energy consumption and investment costs are significantly lower.3

In

applications where alcohols are isolated from solid molecules, organic solvent nanofiltration (OSN) membranes are preferred. 1, 4 Such membranes are characterised by their ability to prevent certain molecular weight compounds from permeating and their solvent-resistance.

OSN membranes are typically fabricated using glassy polymers with low intrinsic permeabilities5 such as polyamide (PA), polyimide (PI) and polyelectrolytes (PEs).

These polymers are chosen

for their high rejection performance and excellent performance stability (permeance or rejection).2, 6-8

Clearly, the choice of glassy polymers for OSN membranes is limited due to the trade-off

between membrane permeance, rejection performance and performance stability.

This hampers

the widespread application of OSN membranes. To enhance the alcohols permeance of OSN


3


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

Page 4 of 33

membranes without compromising rejections, the selective membrane layer should be as thin as possible (reducing thickness) or created with additional solvent passageways (increasing porosity). However performance instability is omnipresent in thin membranes as alcohol permeances decline over time.

This is attributed to physical aging where pore sizes are reduced and pore

concentration is reduced (loss of FFV).9-11

For example, the alcohol permeances of

ultrapermeable 95 nm thin PA OSN membranes were extremely unstable when supported on polymeric substrates12. The ultrathin polyamide selective layers coated on polyimide supported membranes exhibit about 50 % permeance decline after 4 hours continuous operation under 10 bar.12

Physical aging in this ultrathin PA membrane was only overcome by replacing the

polymeric support with inorganic supports. in ultrathin films remain unknown.

The role of substrates in overcoming physical aging

Moreover, the etching of Cd(OH)2 nanostrands sacrificial

layer to create additional porosity for ultrapermeable membranes, generates heavy metal ions (Cd2+) which is carcinogenic and harmful to the environment.

A greener alternative to yield ultrapermeable OSN membranes is to use super glassy polymers such as PIMs and PTMSP.13-16

The key advantage of these polymers is the exceptionally high

FFV content i.e. additional porosity for molecular transport.13-16

The high permeability of these

membrane materials precludes the need to develop ultrathin membranes that are prone to defects using harmful synthesis procedures.

Unfortunately, membranes fabricated with high FFV

materials suffer from serious physical aging.

During physical aging, polymer chains that are

propped further apart by kinks or bulky functional groups converge towards a thermodynamic equilibrium, collapsing the free space i.e. FFV between polymer chains.

This is more prevalent

in ultrathin-membranes.16, 17 For example, 140 nm thin PIM-1 membranes demonstrated heptane


4

Page 5 of 33

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


permeances as high as 18 L m-2 h-1 bar-1(permeability as 2.8×10$% L m m-2 h-1 bar-1), which is about two magnitudes higher than that of commercial polyimide membranes, Starmem240 with similar rejection.16 Interestingly, the permeance of 35 nm-thick of PIM-1 is much lower than that of the 140 nm of PIM-1, implying that the loss of FFV content in thinner membranes is more significant.16

Crucially, physical aging in super glassy polymers must be overcome to exploit

their high intrinsic permeances to develop ultrapermeable OSN membranes in a sustainable, green manner.

A simple approach that simultaneously overcomes both physical aging and low alcohol permeance is to deploy mixed matrix membranes that do not age.

Super glassy polymers and nanoporous

additives such as porous aromatic frameworks, PAF-1,18 or a hypercrosslinked polymer such as polydichloroxylene (p-DCX)19 can provide longevity whilst enhancing gas transport in PTMSP. The key to anti-aging PTMSP membranes is the immobilization of polymer chains through their compatibility with similar functional groups on specific porous frameworks (non-bonding interactions).

The anti-aging capabilities of these mixed matrix membranes were demonstrated

using 100 µm thick films.

The physical aging rates of polymer films with various thicknesses

are different as thin films age faster than thick films.20

More importantly, these anti-aging

mechanisms were observed in batch experiments where low pressure gases were only exposed to these thick films periodically.

Although these experiments demonstrated the world’s first anti-

aging membranes, the performance of these membranes in continuous operating conditions remain unknown.


5


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

Page 6 of 33

Alternative to using these anti-aging membranes for batch gas separation processes, we deployed 1 µm thick PTMSP composite membranes for continuous organic solvent nanofiltration (OSN). It is important to note that the separation mechanism of gas separation and nanofiltration are usually different so it is not intuitive that this approach would work.

The gas separation

mechanism in our anti-aging, dense film membranes can be described with the solution-diffusion model,21 while the separation mechanism for most OSN membranes is based on the pressure-driven model.1,6 Due to their intrinsic porosity, PAF-1 and p-DCX will further enhance the solvent permeabilities and possibly, dye rejections and minimize physical aging in 1 µm thin PTMSP membranes supported on porous polymeric (polycarbonate) substrates for OSN. Our approach removed the need to sacrifice initial membrane performances for stability or complex engineering means to achieve fast alcohol permeance (Figure 1).

In order to mimic industrial pharmaceutical

recovery from alcohols, a continuous long term membrane operation in OSN conditions (5 bar, 25 °C, stirring speed of 700 rpm) was carried out and revealed that these porous additives drastically enhanced alcohol permeances of PTMSP membranes, increased stability, improved dye rejections and provided resistance against compaction.

Overall the membrane separation performances are

‘locked’ in their initial state which justifies revisiting super glassy polymers for high speed alcohol purification at low operating pressures as our anti-aging, thin PTMSP composite membranes demonstrate higher separation efficiency than most state-of-the-art OSN membranes.

Experimental Chemicals and Materials Analytical grade methanol, ethanol, isopropanol, Rose Bengal (RB), Crystal Violet (CV), and Thiazole Yellow (TY) (Sigma-Aldrich) (Figure 2) were purchased and used without further


6

Page 7 of 33

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


purification.

PTMSP was purchased from Gelest Inc (SSP070-10GM, Lot 4I-23599, Mw

210kDa, 95 % purity) and used without purification.

Chloroform, dichloromethane (DCM), and

hydrochloric acid (HCl) were used as received. 1,4, dichloroxylene (DCX) 98 %, Iron (III) chloride, reagent grade, anhydrous 97 %, Tetraphenylmethane, bis(1,5-cyclooctadiene) nickel, and 2,2’-bipyridyl were purchased from Sigma Aldrich, and used without further purification. 1,2 Dichloroethane (DCE) was supplied by Chem-Supply. The polycarbonate porous substrate was commercial microfiltration membranes (Nuclepore) with mean effective pore size of 0.2 μm and ethanol permeances above 500 L m-2 h-1 bar-1 provided by Whatman, GE company.

Synthetic procedures PAF-1 synthesis PAF-1 was synthesised according to Zhu and co-workers22 to yield an off-white powder with a BET surface area of 3760 m2/g). 1,5-cyclooctadiene (dried over CaH2) was added into a solution of bis(1,5-cyclooctadiene) nickel and 2,2’-bipyridyl in dehydrated DMF, and heated at 80 °C to form a purple solution. Tetrakis(4-bromophenyl)methane was added to the mixture and stirred overnight at 80 °C. The mixture was allowed to cool to room temperature and concentrated HCl was added. The solids were collected and washed with chloroform, THF, and deionized water. The particle size was typically in the range of 100-200 nm characterized by a nanoparticle size analyser.19

p-DCX synthesis To a solution of DCX monomer (0.171 mol, 30 g) in anhydrous DCE (388 mL), a DCE solution (388 mL) of FeCl3 (0.173 mol, 28 g) was added. The resulting mixture was stirred in an open vessel


7


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

Page 8 of 33

at room temperature. The precipitated p-DCX was washed once with water, three times with methanol (until the filtrate was clear), and with diethyl ether followed by drying for 24 h at 60 °C. The BET surface area of the p-DCX nanoparticles is 1330 m2/g; the diameter of p-DCX nanoparticles is between 20-50 nm.19

Membrane preparation The polymer solution was prepared by dissolving 2 wt. % of PTMSP (Gelest Inc.) in cyclohexane. 10 wt. % (with respect to PTMSP concentration) of porous additives, PAF-1 or p-DCX, were added to the polymer solution and stirred for 24 hours. plate.

This mixture was then poured onto a glass

Doctor blades with thickness 30, 50, 80, 100, 150 um were used cast membranes.

Upon

solvent evaporation, the glass plate with a thin layer of membrane was lowered into a water bath. This enabled the flotation of the thin polymer membrane film onto the surface of the water.

A

polycarbonate porous substrate was lowered into the water bath, and came into contact with the PTMSP-based membrane.

Water was then drained out, and a free-standing PTMSP-based

membrane supported on a polycarbonate substrate was obtained (Figure 3).

Due to similarities

in chemical structure, PAF-1 and p-DCX are well-dispersed in the PTMSP matrix. 19

Methods Organic Solvent Nanofiltration The permeances or fluxes of OSN membranes were measured using a self-made, stainless steel dead-end pressure cell with a membrane area of 21.2 cm2.

The feed solution was pressurised

with nitrogen to 5 bar at room temperature. During filtration, the feed solution was stirred at 11.66 Hz (700 rpm) to avoid concentration polarization.

Permeate samples were collected in cooled


8

Page 9 of 33

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


flasks as a function of time, weighed and analysed.

The solvent flux and solvent permeance were

calculated using the following equations:

𝐹 = 𝑉 𝐴 ×𝑡

(1)

𝑃𝑒𝑟𝑚𝑒𝑎𝑛𝑐𝑒 = 𝐹 ∆𝑃

(2)

𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = 𝑃𝑒𝑟𝑚𝑒𝑎𝑛𝑐𝑒/𝑛

(3)

where F represents the solvent flux (L m-2 h-1), V (L) is the volume of the solvent (or solution) passing through the membrane, A is the effective membrane area (m2), t is the operation time (h); and ∆P is trans-membrane pressure (bar), n presents the thickness of the membranes (m). Solvent permeances were tested in the order of MeOH > EtOH > i-PrOH.

The solute rejections of NF membranes were calculated using Eq.4 𝑅 = 1 −

;< ;=

∙ 100%

(4)

where Cp and Cf are the solute concentrations in the permeate and the feed solution, respectively. Dye concentrations in IPA were measured with a UV–VIS CINTRA20-GBC apparatus (λmax of RB = 548 nm).

Each data point is an average of three repetitions of each test, with ± 5 % standard

deviation.

Scanning Electron Microscopy (SEM) All membrane films were cryo-fractured, to achieve a clean break, and then mounted on crosssection SEM sample stubs. The average thickness for the selective layer is ~1 µm.

Nitrogen Adsorption Isotherms


9


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

Page 10 of 33

Gas adsorption isotherms between the range of 0 – 700 mmHg were measured by a volumetric approach using a Micrometrics ASAP 2420 instrument. All the samples were transferred to predried analysis tubes, sealed with Transeal stoppers, evacuated and activated at 120 °C under a 106

dynamic vacuum for 24 hours. Ultra-high purity N2 gases were used for these experiments.

adsorption measurements were conducted at 77 K.

N2

The pore size distributions of PAF-1 and p-

DCX polymers are shown in Figure 4.

Positron Annihilation Lifetime Spectroscopy (PALS) Bulk PALS experiments that were used to characterize the changing of pores and the FFV in the material bulk were performed at CSIRO using an EG&G Ortec fast-fast coincidence system with fast plastic scintillators and a resolution function of 260 ps FWHM (60Co source with the energy windows set to 22Na events).

Due to the long lifetimes, and the low counting rate, the coincidence

unit was removed and the range of the TAC extended to 200 ns.

The film samples were stacked

to a thickness of 2 mm, and powdered samples were packed (>1.5 mm depth), on either side of a 30 µCi 22NaCl source sealed in a 2.54 µm thick Mylar envelope (source correction 1.605 ns and 2.969%) and measured at ~ 5 Í 10 -7 Torr.

At least five spectra of 4.5 million integrated counts

were collected with each spectrum taking about 4.6 h to collect.

Data analysis was performed

using LT9. The spectra were best fitted with five components with the shortest lifetime fixed to 125 ps, characteristic of p-Ps annihilation. 23, 24

For the long lifetimes obtained, the Tao-Eldrup model

traditionally used for calculating mean pore sizes from mean o-Ps lifetimes is not valid;

therefore, the mean free path (nm) of the pores was calculated using the Rectangular Tao Eldrup (RTE) model.25 The FFV content of free-standing 1 µm thin membranes are shown in Table 1.


10

Page 11 of 33

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


Contact Angle Measurements A contact angle measuring system (G10 Kruss, Germany) was used to measure the static water contact angle of membranes.

A deionized water droplet was placed on a dry flat membrane

surface and the contact angle was obtained.

The reported contact angle value was calculated by

averaging over more than five contact angle values at different sites.

The contact angles of

PTMSP and PTMSP/PAF-1 membranes are summarized in Table 2.

Results and discussion Ethanol (EtOH)

is commonly used to isolate water-soluble pharmaceuticals;1 and is an ideal

solvent choice for OSN experiments with different dyes, and physical aging tests.13

Since the

osmotic pressure is low for purification or ethanol recovery, 5.0 bar of operation pressure is chosen here to minimize energy consumption; precluding the need of a high driving force to achieve high separation efficiencies of our ultrapermeable membranes.

The incorporation of PAF-1 and p-

DCX into PTMSP drastically enhanced ethanol permeation by 42 % and 90 %, respectively (Figure 5A); whilst improving dye rejection.

The increase in EtOH permeance was attributed to

the intrinsic pores of PAF-1 and p-DCX nanoparticles that provided additional molecular transportation pathways,18,19 the hydrophobicity of additives,26,27 and increase in pore size for PTMSP membranes .

Highly hydrophobic 5 Å pores in PAF-1 nanoparticles optimize alcohol

absorption and alcohol diffusion.27

There are two pore size distributions centered at 5.9 Å and

13.5 Å in p-DCX nanoparticles, while there are three overlapping pore size distributions in PAF1 in the region between 11.8 to 17.2 Å (Figure 4). As the side-chain of the PTMSP can thread the larger pores, larger pores of the PAF-1 and p-DCX were partly blocked, leaving the smaller pores intact.18,19 Alcohol molecules can pass through these unblocked 5.9 Å pores27 in p-DCX, hence


11


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

contributing to the 90 % enhancement in EtOH permeance.

Page 12 of 33

The smaller pores of p-DCX

nanoparticles also accounted for the 15 % improvement in rejecting Safranine O, the smallest dye studied here (Mw 350.13 g mol-1).

PAF-1 and p-DCX nanoparticles slightly improved the 90 %

rejection rate of PTMSP membranes for both the larger Rose Bengal (Mw 1017.64 g mol-1) and Thiazol Yellow (Mw 695.74 g mol-1) dyes.

Unlike other mixed matrix membranes, the

incorporation of porous additives did not reduce dye rejection rates; indicating an absence of large nanogaps between the porous additives and polymer chains.28 The dye rejection rates of present PTMSP/additive membranes are comparable to commercial membranes.29 Remarkably, the permeability of the PTMSP/p-DCX nanocomposite reaches 5.5 ×10$% L m m-2 h-1 bar-1, which is higher than that of PIM-1 based membranes16 and ultrathin PA membranes12.

Physical aging was investigated using OSN membranes operated continuously for 500 hours at 5 bar (Figure 5B).

The EtOH permeance in PTMSP control membranes was reduced by 45 %, and

stabilized within the first 100 hours of aging.

Physical aging reduced the pore sizes and

concentration in PTMSP, hence impeding ethanol transport in aged PTMSP membranes.

PAF-1

and p-DCX inhibited or abated the shrinkage and loss of such pores in anti-aging,18 and selectiveaging gas separation PTMSP membranes.19 Here we report that this was also valid for alcohol transport across 1 µm thin PTMSP membranes.

The enhanced EtOH permeances of PTMSP

membranes loaded with PAF-1 and p-DCX were only reduced by 20 and 12 %, respectively, and stabilized within 13 hours of testing.

Subsequently, the permeances of membranes loaded with

p-DCX and PAF-1 remained stable during 487 hours of continuous operation. effect is more pronounced with p-DCX nanoparticles.

The anti-aging

Different from gas separation membranes

where only the permeation of large molecules like nitrogen (kinetic diameter 3.64 Å) were affected


12

Page 13 of 33

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


by physical aging,

18,19

we observed that the permeation of even larger molecules like ethanol

(kinetic diameter 4.5 Å 30), and i-PrOH (kinetic diameter 4.7 Å) 30 (Figure 6) were not affected in our PTMSP/additive OSN membranes.

Clearly, there is a different anti-aging mechanism for

OSN.

Positron annihilation lifetime spectroscopy (PALS) was used to track changes in pore size and concentration, and FFV content within 1 µm thin free-standing PTMSP-based films in wet (presoaked in EtOH) and dry states (Figure 7).

There is a bimodal pore size distribution centred at

5.5 Å (d3) and 14 Å (d4) in PTMSP (Figure 7A). in PTMSP by ~ 0.5 and 2 Å, respectively.

Physical aging reduced the d3 and d4 pore sizes

The incorporation of PAF-1 and p-DCX nanoparticles

did not alter the pore sizes and concentration in as-cast PTMSP, indicating the good compatibility between PTMSP and the porous additives.

With PAF-1 and p-DCX, the d4 pores in aged PTMSP

films were only reduced by 1 Å, while the d3 pore size and the d3 and d4 pore concentrations remain unchanged.

Aged 1 µm thin PTMSP, PTMSP/PAF-1, PTMSP/p-DCX membranes lost 48, 40,

and 20 % of FFV content (Figure 7B).

Higher FFV content i.e. porosity in aged PTMSP/additive

membranes lowered transmembrane resistance and enhanced total flux.31

The relative losses in

FFV content were smaller than relative losses in EtOH permeances in aged PTMSP/additive membranes. The impact of lost FFV content on EtOH transport could be mitigated by alcohol adsorption.

This view is reinforced by the fact that PTMSP/PAF-1 membranes with higher FFV

content had lower EtOH permeances when compared to PTMSP/p-DCX membranes with lower FFV content.


13


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

Page 14 of 33

We also observed changes in pore sizes and concentrations in aged dry and wet (soaked in EtOH) PTMSP-based films (Figure 7C).

Polymer films were soaked in EtOH for 24 hours, dried with

tissue paper, prior to characterization.

In the presence of EtOH, the pore sizes in and the

concentration of d3 and d4 pores decreased. molecules.

This indicated that d4 pores were filled up with EtOH

The filling of pores with EtOH molecules was also observed across both d3 and d4

pores in both aged PTMSP/PAF-1 and PTMSP/p-DCX membranes.

The filling of d3 pores in

PTMSP/additive films could be attributed to film hydrophobicity.

PAF-1 and p-DCX

nanoparticles increased the hydrophobicity of PTMSP films (Table 2), that improved alcohol adsorption.27

This accounted for the highest EtOH adsorption of 6.4 cm3/g in PTMSP/p-DCX

membranes, 17 % higher than PAF-1 loaded membranes (Figure 7D).

Higher EtOH adsorption

did not swell PTMSP/additive membranes, but filled up the pores present in these membranes. The lack of swelling due to EtOH adsorption in our PTMSP/additive membranes indicated that the rigidification of PTMSP polymer chains by porous nanoparticles; stabilizing membrane permeances during long term operation.

This was further demonstrated through alcohol

regeneration and membrane compaction tests.

Alcohol regeneration is used to rejuvenate the collapsed FFV content between mobile polymer chains.32

Here we used this technique to reveal the rigidification of PTMSP chains by PAF-1 and

p-DCX nanoparticles.

Membranes were first exposed to 5 bar EtOH for 100 hours, and

regenerated by a 100 hour EtOH soak.

EtOH permeance in PTMSP, PTMSP/PAF-1 and

PTMSP/p-DCX membranes was reduced by 45 %, 20% and 12 %, respectively, after 100 hours continuous operation (Figure 8).

After depressurize of 5 hours, the alcohol permeance of aged

PTMSP membranes recovered 12 %. After 100 hours continuous soaking in ethanol, the


14

Page 15 of 33

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


permeances of the aged PTMSP were further recovered by 33 %. Without PAF-1 or p-DCX nanoparticles, PTMSP chains possessed more freedom and mobility.18,

19

Through alcohol

regeneration, alcohol molecules occupied and recovered the free spaces between these mobile polymers chains.32 Mobile PTMSP chains relaxed upon depressurization and regained some free volume content that contributed to the recovery of molecular transportation rates;33 hence accounting for the significant recovery of EtOH permeance in pure PTMSP membranes. As PTMSP chains were immobilized by PAF-1 or p-DCX nanoparticles, the rigidification of PTMSP chains membranes was enhanced, thereby inhibiting physical aging and subduing alcohol regeneration. Interestingly, even without alcohol regeneration, the EtOH permeances of PTMSP/PAF-1 and PTMSP/p-DCX membranes remained stable, and significantly higher than regenerated PTMSP.

Conclusions In the preceding, the unique interactions between porous additives such as PAF-1, p-DCX, and the super glassy polymer PTMSP have been utilized to enhance membrane permeabities and dye rejections and reduce physical aging of the membranes.

This also ensures that the initial

tantalising separation properties of the membranes are stable in continuous separation process. Addition of p-DCX reduced physical aging rates by 12%, whilst also doubling the permeance rates of EtOH through the fresh membrane. Careful experiments simulating applied settings delivered over 500 hours of continuous operation with stabilized performance, with as much as 90 % higher permeance than aged controls.

Detailed studies of various alcohols demonstrated the potential

use of this system across a platform of low-energy liquid purification applications. The permeabilites of our PTMSP/porous additive membranes stabilized to values that were higher than


15


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

Page 16 of 33

the initial permeances of as-cast PTMSP membranes, outperforming current state-of-the-art membranes.1,12-13,34-38 (Figure 9).

Unique threading of the polymer side chains into the additive

pores was found to underpin this remarkable performance.

Taken together, these findings enable

further use of our compaction-free OSN membranes that retain most of their initial permeances as low energy separation alternatives, and further empower the highest performing polymers to be included in these membranes by imbuing them with stable solvent permeabilities.

Conflict of Interest: For conflict of Interest, please exclude Prof. Bart Van der Bruggen and Prof. Ivo F.J. Vankelecom from Katholieke Universiteit Leuven as reviewers

AUTHOR INFORMATION Corresponding Author * Dr Cher Hon Lau, Email: [email protected] Associate. Prof. Matthew R. Hill, Email: [email protected] and Prof. L. Shao

E-mail: [email protected]

Acknowledgements XQC and CHL have contributed equally for this work. MRH, KK and CHL acknowledge the Science and Industry Endowment Fund (SIEF).

MRH, and AJH acknowledge the generous

support of the CSIRO Office of the Chief Executive Science team.

MRH acknowledges FT


16

Page 17 of 33

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


130100345. CMD is funded through an Australian Research Centre DECRA project (DE140101359). This work was supported by National Natural Science Foundation of China (21676063, U1462103), the Open Research Fund Program of Collaborative Innovation Center of Membrane Separation and Water Treatment of Zhejiang Province, State Key Laboratory of Urban Water Resource and Environment (Harbin Institute Technology) (No. 2017DX05), and HIT Environment and Ecology Innovation Special Funds (HSCJ201619)..

References (1) Marchetti, P.; Jimenez Solomon, M. F.; Szekely, G.; Livingston, A. G. Molecular separation with organic solvent nanofiltration: a critical review. Chem. Rev. 2014, 114, 10735-10806. (2) Szekely, G.; Jimenez-Solomon, M. F.; Marchetti, P.; Kim, J. F.; Livingston, A.G. Sustainability assessment of organic solvent nanofiltration: from fabrication to application. Green Chem. 2014, 16, 4440-4473. (3) Schneiderman, S. J.; Gurram, R. N.; Menkhaus T. J.; Gilcrease, P. C. Comparative technoeconomic analysis of a softwood ethanol process featuring posthydrolysis sugars concentration operations and continuous fermentation with cell recycle, Bioethanol. Prog. 2015, 31, 946-956. (4) Székely, G.; Marchetti, P.;

Jimenez-Solomon, M. F.; Livingston, A. G.; Hoek E. M. V.;

Tarabara, V. V., in Encyclopedia of Membrane Science and Technology, John Wiley & Sons, Inc., 2013. (5) Campbell, J.; Davies, R. P.; Braddock D. C.; Livingston, A. G. Improving the permeance of hybrid polymer/metal–organic framework (MOF) membranes for organic solvent nanofiltration (OSN)– development of MOF thin films via interfacial synthesis, J. Mater. Chem. A 2015, 3, 9668-9674.


17


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

(6) Vandezande, P.; Gevers, L. E. M.; Vankelecom, I. F. J.

Page 18 of 33

Solvent resistant nanofiltration:

separating on a molecular level. Chem. Soc. Rev. 2008, 37, 365-405. (7) Ahmadiannamini, P.; Li, X. F.; Goyens, W.; Meesschaert, B.; Vanderlinden, W.; De Feyter,

S.;

Vankelecom, I.F.J. Influence of polyanion type and cationic counter ion on the SRNF performance of polyelectrolyte membranes, J. Membr. Sci. 2012, 403, 216-226. (8) Li, X. F.; De Feyter, S.; Chen, D. J.; Aldea, S.; Vandezande, P.; Du Prez, F.; Vankelecom, I.F.J. Solvent-resistant nanofiltration membranes based on multilayered polyelectrolyte complexes, Chem. Mater. 2008, 20, 3876-3883. (9) Goulas, A. K.; Kapasakalidis, P. G.; Sinclair, H. R.; Rastall, R. A.; Grandison, A. S. Purification of oligosaccharides by nanofiltration, J. Membr. Sci. 2002, 209, 321–335. (10) Schmidt, P.; Kose, Y.; Lutze, P. Characterisation of organic solvent nanofiltration membranes in multi-component mixtures: Membrane rejection maps and membrane selectivity maps for conceptual process design, J. Membr. Sci. 2013, 409, 103-120. (11) Rezzadori, K.; Penha, F. M.; Proner, M. C.; Zin, G.; Petrus, J. C. C.; Prádanos, P.; Palacio, L.; Hernández, A.; Luccio, M. D. Evaluation of reverse osmosis and nanofiltration membranes performance in the permeation of organic solvents, J. Membr. Sci. 2015, 492, 487-489. (12) Karan, S.; Jiang, Z.; Livingston, A. G. Sub–10 nm polyamide nanofilms with ultrafast solvent transport for molecular separation. Science, 2015, 348, 1347-1351. (13) Volkov, A.V.; Parashchuk, V.V.; Stamatialis, D. F.; Khotimsky, V. S.; Volkov, V. V.; Wessling, M. High permeable PTMSP/PAN composite membranes for solvent nanofiltration, J. Membr. Sci. 2009, 333, 88-93.


18

Page 19 of 33

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


(14) Volkov, A.V.; Tsarkov, S. E.; Gokzhaev, M. B.; Bondarenko, G. N.; Legkov, S. A.; Kukushkina, Y. A.; Volkov, V. V. Nanofiltration and sorption of organic solvents in poly(1-trimethylsilyl-1propyne) samples of different microstructures, Petrol. Chem. 2013, 52, 598-608. (15) Fritsch, D.; Merten, P.; Heinrich, K.; Lazar, M.; Priske, M. High performance organic solvent nanofiltration membranes: Development and thorough testing of thin film composite membranes made of polymers of intrinsic microporosity (PIMs), J. Membr. Sci. 2012, 401, 222-231. (16) Gorgojo P.; Karan S.; Wong H. C., Jimenez-Solomon M. F., Cabral J. T., Livingston A. G. Ultrathin polymer films with intrinsic microporosity: anomalous solvent permeation and high flux membranes. Adv. Funct. Mater. 2014, 24, 4729-4737. (17) Ong, Y. H., Shi, G. M.; Le, N. L.; Tang, Y. P.; Zuo, J.;

Nunes, S.; Chung, T. S. Recent

membrane development for pervaporation processes, Prog. Polym. Sci. 2016, 57, 1–31 (18) Lau, C. H.; Nguyen, P. T.; Hill, M. R.; Thornton, A. W.; Konstas, K.; Doherty, C. M.; Mulder, R. J.; Bourgeois, L.; Liu, A. C. Y.; Sprouster, D. J.; Sullivan, J. P.; Bastow, T. J.; Hill, A. J.; Gin D. L.; Noble, R. D. Ending aging in super glassy polymer membranes, Angew. Chem. Int. Ed. 2014, 53, 5322-5326. (19) Lau, C. H.; Mulet, X.; Konstas, K.; Doherty, C. M.; Sani, M.-A.; Separovic, F.; Hill M. R.; Wood, C. D. Hypercrosslinked additives for ageless gas- separation membranes, Angew. Chem. Int. Ed. 2016, 55, 1998-2001 (20) Horn, N. R.; Paul, D. R. Carbon dioxide plasticization and conditioning effects in thick vs. thin glassy polymer films, Polymer 2011, 52, 1619-1627. (21) Lau, C. H.; Konstas, K.; Doherty, C. M.; Kanehashi, S.; Ozcelik, B.; Kentish, S. E.; Hill, A. J.; Hill, M. R. Gas- separation membranes loaded with porous aromatic frameworks that improve with age, Chem. Mater. 2015, 54, 2669-2673.


19


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

Page 20 of 33

(22) Ben, T.; Ren, H.; Ma, S.; Cao, D.; Lan, J.; Jing, X.; Wang, W.; Xu, J.; Deng, F.; Simmons, J. M.; Qiu S.; Zhu, G. Targeted synthesis of a porous aromatic framework with high stability and exceptionally high surface area, Angew. Chem. 2009, 121, 9621-9624. (23) Tao, S. J. Positronium annihilation in molecular substances, J. Chem. Phys. 1972, 56, 54995510. (24) Eldrup, M.; Lightbody D.; Sherwood, J. N. The temperature dependence of positron lifetimes in solid pivalic acid, Chem. Phys. 1981, 63, 51-58. (25) Dull, T. L.; Frieze, W. E.; Gidley, D. W.; Sun J. N.; Yee, A. F. Determination of pore size in mesoporous thin films from the annihilation lifetime of positronium, J. Phys. Chem. B 2001, 105, 4657-4662. (26) Zheng, J.; Lennon, E. M.; Tsao, H.-K.; Sheng Y.-J.; Jiang, S. Transport of a liquid water and methanol mixture through carbon nanotubes under a chemical potential gradient, J. Chem. Phys. 2005, 122, 214702. (27) Ahmed, A.; Xie, Z.; Konstas, K.; Babarao, R.; Todd, B. D.; Hill M. R.; Thornton, A. W.

Porous

aromatic frameworks impregnated with fullerenes for enhanced methanol/water separation, Langmuir 2014, 30, 14621-14630 (28) Hill, R. J. Reverse-selective diffusion in nanocomposite membranes, Phys. Rev. Lett. 2006, 96, 216001. (29) Vandezande, P.; Gevers, L. E. M.; Paul, J. S.; Vankelecom I. F. J.; Jacobs, P. A. High throughput screening for rapid development of membranes and membrane processes, J. Membr. Sci. 2005, 250, 305-310. (30) Kuiper, S.; van Rijn, C. J. M.; Nijdam W.; Elwenspoek, M. C. Development and applications of very high flux microfiltration membranes, J. Membr. Sci. 1998, 150, 1-8.


20

Page 21 of 33

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


(31) Wu, H.; Gong, Q.; Olson D. H.; Li, J. Commensurate adsorption of hydrocarbons and alcohols in microporous metal organic frameworks, Chem. Rev. 2012, 112, 836–868 (32) Hill, A. J.; Pas, S. J.; Bastow, T. J.; Burgar, M. I.; Nagai, K.; Toy L. G.; Freeman, B. D. Influence of methanol conditioning and physical aging on carbon spin-lattice relaxation times of poly (1trimethylsilyl-1-propyne), J. Membr. Sci. 2004, 243, 37-44. (33) Pope, D. S.; Koros W. J.; Hopfenberg, H. B. Sorption and dilation of poly (1-(trimethylsilyl)-1propyne) by carbon dioxide and methane, Macromolecules 1994, 27, 5839-5844. (34) Li, Y., Wee, L. H.; Volodin, A.; Martens J. A.; Vankelecom, I. F. J. Polymer supported ZIF-8 membranes prepared via an interfacial synthesis method, Chem. Commun. 2015, 51, 918-920. (35) Shao, L.; Cheng, X. Q.; Wang, Z. X.; Ma J.; Guo, Z. Tuning the performance of polypyrrolebased solvent-resistant composite nanofiltration membranes by optimizing polymerization conditions and incorporating graphene oxide, J. Membr. Sci. 2014, 452, 82-89. (36) Tsarkov, S.; Khotimskiy, V.; Budd, P. M.; Volkov, V.; Kukushkina J.; Volkov, A. Solvent nanofiltration through high permeability glassy polymers, Effect of polymer and solute nature, J. Membr. Sci. 2012, 423–424, 65-72. (37) Geens, J.; Peeters, K.; Van der Bruggen B.; Vandecasteele, C. Polymeric nanofiltration of binary water–alcohol mixtures: influence of feed composition and membrane properties on permeability and rejection, J. Membr. Sci. 2005, 255, 255-264. (38) Florian, E.; Modesti M.; Ulbricht, M. Preparation and characterization of novel solvent-resistant nanofiltration composite membranes based on crosslinked polyurethanes, Ind. Eng. Chem. Res. 2007, 46, 4891-4899.


21


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

Page 22 of 33

List of Figures

Figure 1. (A) Chemical structures of PTMSP, p-DCX, and PAF-1. (B) As-cast PTMSP membranes cast on porous polycarbonate substrates are selective towards alcohols over molecular dyes. After continuous operation for 500 hours, PTMSP membranes are no longer selective. (C) The incorporation of porous additives such as PAF-1 or p-DCX into PTMSP enhanced the permeance of alcohols, and remained permeable and selective towards alcohols. (D)

The average

thicknesses of membranes studied here is ~1 µm, the standard deviation of membrane thickness is ±10 % measured using SEM.

Figure 2.

Chemical structures of molecular dyes used in this work.

Figure 3 Fabrication of thin film PTMSP, PTMSP/PAF-1, and PTMSP/p-DCX membranes

Figure 4 The pore size distribution of PAF-1 (blue) and p-DCX (red) nanoparticles obtained from nitrogen adsorption isotherms performed at 77 K.

Figure 5. (A) The effects of physical aging (after 500 hours of continuous operation at 5 bar of solvent pressure and 25 °C) on ethanol transport in PTMSP (black), PTMSP/PAF-1 (blue), and


22

Page 23 of 33

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


PTMSP/p-DCX (red). Membranes were cast using 0.5 wt. % of doping concentration. (B) Dye rejection rates of as-cast (solid) and aged (empty) membranes studied here. The molecular weights of Rose Bengal, Thiazol Yellow, and Safranine O are 1017.64 g mol-1, 695.74 g mol-1, and 350.13 g mol-1, respectively. Each separation performance data point is obtained from an average of three repeated experiments, with ± 6 % standard deviation.

Figure 6

The methanol (black), ethanol (red) and isopropanol (blue) permeances of as-cast

(solid) and aged (empty) 1 um thin (A) PTMSP, (B) PTMSP/PAF-1 and (C) PTMSP/p-DCX membranes supported on polycarbonate substrates. The Rose Bengal (orange), Thiazole Yellow (green), and Safranine O (purple) dyes rejection rates from ethanol of (D) PTMSP, (E) PTMSP/PAF-1 and (F) PTMSP/p-DCX membranes. Each separation performance data point is obtained from an average of three repeated experiments, with ± 5 % standard deviation.

Figure 7. (A) The bimodal pore size distribution of as-cast vs aged PTMSP (black), PTMSP/PAF1 (blue), and PTMSP/p-DCX (red) membranes determined using PALS. (B) The relationship between relative EtOH permeances of PTMSP, PTMSP/PAF-1 and PTMSP/p-DCX membranes and FFV content losses due to physical aging.

(C) Pore size distribution of as-cast wet (dotted

lines) vs dry (solid lines) PTMSP composite membranes studied here. (D) The influence of additives on the EtOH adsorption in PTMSP membranes studied here.


23


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

Page 24 of 33

Figure 8. The incorporation of PAF-1 and p-DCX voids the need to regenerate PTMSP membranes to recover initial EtOH permeances: aged membranes (100 hours continuous separation); depressurized membranes means the aged membranes was soaked in ethanol under atmosphere for 5.0 hours to recover the deformation of polymer chain under pressure; regenerated membranes means the aged membranes soaked in ethanol for 100 hours

Figure 9 Membranes reported in literature are of different thicknesses. compared the EtOH permeabilities and Thiazol Yellow (Mw 695.74

1, 12-13, 34-38

Hence we

g mol-1) dye rejection rates

of our aged, thin film, composite membranes with other membranes. The molecular weight of most dyes reported in these literature ranged between 422 to 626 g mol-1. The dotted line represented Karan, Jiang and Livingston’s state-of-the-art polyamide membrane with a sub-10 nm ultrathin selective layer.12

In their work, dye (Mw 246.2 to 585.5 g mol-1) rejection experiments were only

conducted using methanol. List of Tables Table 1

FFV content of free-standing as-cast, aged and wet (EtOH soaked) PTMSP,

PTMSP/PAF-1, and PTMSP/p-DCX membranes.

Table 2. Contact angles of PTMSP and PTMSP/PAF-1 membranes studied here in this work


24

Page 25 of 33

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


Figure 1. (A) Chemical structures of PTMSP, p-DCX, and PAF-1. (B) As-cast PTMSP membranes cast on porous polycarbonate substrates are selective towards alcohols over molecular dyes. After continuous operation for 500 hours, PTMSP membranes are no longer selective. (C) The incorporation of porous additives such as PAF-1 or p-DCX into PTMSP enhanced the permeance of alcohols, and remained permeable and selective towards alcohols. (D)

The average

thicknesses of membranes studied here is ~1 µm; the standard deviation of membrane thickness is ±10 % (measured using SEM).

Figure 2. Chemical structures of molecular dyes used in this work.


25


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

Page 26 of 33

Figure 3 Fabrication of thin film PTMSP, PTMSP/PAF-1, and PTMSP/p-DCX membranes

Figure 4 The pore size distribution of PAF-1 (blue) and p-DCX (red) nanoparticles obtained from nitrogen adsorption isotherms performed at 77 K.


26

Page 27 of 33

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


Figure 5. (A) The effects of physical aging (after 500 hours of continuous operation at 5 bar of solvent pressure and 25 °C) on ethanol transport in PTMSP (black), PTMSP/PAF-1 (blue), and PTMSP/p-DCX (red). Membranes were cast using 0.5 wt. % of doping concentration. (B) Dye rejection rates of as-cast (solid) and aged (empty) membranes studied here. The molecular weights of Rose Bengal, Thiazol Yellow, and Safranine O are 1017.64 g mol-1, 695.74 g mol-1, and 350.13 g mol-1, respectively. Each separation performance data point is obtained from an average of three repeated experiments, with ± 6 % standard deviation.


27


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

Figure 6

Page 28 of 33

The methanol (black), ethanol (red) and isopropanol (blue) permeances of as-cast

(solid) and aged (empty) 1 um thin (A) PTMSP, (B) PTMSP/PAF-1 and (C) PTMSP/p-DCX membranes supported on polycarbonate substrates. The Rose Bengal (orange), Thiazole Yellow (green), and Safranine O (purple) dyes rejection rates from ethanol of (D) PTMSP, (E) PTMSP/PAF-1 and (F) PTMSP/p-DCX membranes. Each separation performance data point is obtained from an average of three repeated experiments, with ± 5 % standard deviation.


28

Page 29 of 33

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


Figure 7. (A) The bimodal pore size distribution of as-cast vs aged PTMSP (black), PTMSP/PAF1 (blue), and PTMSP/p-DCX (red) membranes determined using PALS. (B) The relationship between relative EtOH permeances of PTMSP, PTMSP/PAF-1 and PTMSP/p-DCX membranes and FFV content losses due to physical aging.

(C) Pore size distribution of as-cast wet (dotted

lines) vs dry (solid lines) PTMSP composite membranes studied here. (D) The influence of additives on the EtOH adsorption in PTMSP membranes studied here.


29


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

Page 30 of 33

Figure 8. The incorporation of PAF-1 and p-DCX voids the need to regenerate PTMSP membranes to recover initial EtOH permeances: aged membranes (100 hours continuous separation); depressurized membranes means the aged membranes was soaked in ethanol under atmosphere for 5.0 hours to recover the deformation of polymer chain under pressure; regenerated membranes means the aged membranes soaked in ethanol for 100 hours.


30

Page 31 of 33

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


Figure 9 Membranes reported in literature are of different thicknesses. compared the EtOH permeabilities and Thiazol Yellow (Mw 695.74

1, 12-13, 34-38

Hence we

g mol-1) dye rejection rates

of our aged, thin film, composite membranes with other membranes. The molecular weight of most dyes reported in these literature ranged between 422 to 626 g mol-1. The dotted line represented Karan, Jiang and Livingston’s state-of-the-art polyamide membrane with a sub-10 nm ultrathin selective layer.12

In their work, dye (Mw 246.2 to 585.5 g mol-1) rejection experiments were only

conducted using methanol.


31


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

Table 1

Page 32 of 33

FFV content of free-standing dry and wet (EtOH soaked) PTMSP, PTMSP/PAF-1, and

PTMSP/p-DCX membranes.

Sample Name

FFV in dry-state (%)

FFV wet-state (%)

PTMSP

20

11

PTMSP/PAF-1

21

14

PTMSP/p-DCX

30

12

Table 2. Contact angles of PTMSP and PTMSP/PAF-1 membranes studied here in this work.

Sample Name

Water Contact Angle (°)

PTMSP

117

PTMSP/PAF-1

127

PTMSP/p-DCX

122


32

Page 33 of 33

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


Table of Contents

The incorporation of porous nanoparticles including PAF-1 and p-DCX into PTMSP based OSN membranes provide more solvent passageways and immobilized the polymer chains, greatly enhancing both the permeability and the performance stability of the nanocomposite membranes.


33

Hyper-Cross-Linked Additives that Impede Aging and Enhance

Recommend Documents