Surface modification of pervaporation Surface modification of pervaporation membrane by UV-radiation and membrane by UV-radiation and

application of shear stressapplication of shear stress

P. IzákP. Izák,, M. H. Godinho, P. Brogueira, J.L. FigueirinhasM. H. Godinho, P. Brogueira, J.L. Figueirinhas, , J. G. CrespoJ. G. Crespo

Institute of Chemical Process Fundamentals, Czech Republic

Universidade Nova de Lisboa, Portugal

Outline

SSurface modified PU/PBDO urface modified PU/PBDO membranemembrane

Characterization of a modified PU/PBDO-UVCharacterization of a modified PU/PBDO-UV

Swelling of polymeric membranesSwelling of polymeric membranes

Pervaporation experimentPervaporation experiment

Impact of results and conclusionsImpact of results and conclusions

The aim We looked for ways to promote a microtur-

bulence to minimize the concentration polarization at the membrane surface during pervaporation separation process

The aim

fine-tuned surface of the dense membrane UV fine-tuned surface of the dense membrane UV radiation and application of shear radiation and application of shear

stress stress

different feed flow rate in the pervaporation different feed flow rate in the pervaporation module module (0.340.34 ml/min; e.g. Reynoldsml/min; e.g. Reynolds number, number, Re Re = = 2.06×102.06×10−4−4 and 2.49 ml/min; e.g. and 2.49 ml/min; e.g. Re Re = 1.51×10= 1.51×10−3−3)); ; long channel module 0.25m laminar flowlong channel module 0.25m laminar flow

IntroductionIntroduction

the major problem associated with the solute recovery by pervaporation a restrictive compromise between selectivity and flux

the urethane–urea elastomers - unique elastic properties of the microphase separation of hard (isocyanate) and soft (polyol) segments into domain structures during material preparation and processing

IntroductionIntroduction

the fine-tuned surface of the membranethe fine-tuned surface of the membrane,, prepared prepared from liquid crystalline polyurethanefrom liquid crystalline polyurethane primary primary (stripes) and secondary (bands) set of periodic (stripes) and secondary (bands) set of periodic structures, which are perpendicular to each otherstructures, which are perpendicular to each other

the the solute recovery fromsolute recovery from ionic liquids by ionic liquids by pervaporation pervaporation the solutes permeate the the solutes permeate the membrane and aremembrane and are recovered in the permeate, while recovered in the permeate, while the solvent the solvent ((RTIL) does notRTIL) does not permeate due to its permeate due to its extremely low vapour pressureextremely low vapour pressure

Room Temperature Ionic LiquidsRoom Temperature Ionic Liquids

(R= methyl group, R= butyl group, R= decyl group), X _ = PF6_, X _ = BF4 _ )

N N R Cl+ Reflux 80ºC24 h

HX(X

_ = PF6

_, BF4

_ )

RT – 24hN+ N R +Cl - N+ N R X -

Non-measurable vapour pressure Non-measurable vapour pressure Green solventGreen solvent

High ionic conductivity and thermal stabilityHigh ionic conductivity and thermal stability

Ability to solubilize a large range of organic Ability to solubilize a large range of organic molecules and transition metal complexesmolecules and transition metal complexes

Room Temperature Ionic LiquidsRoom Temperature Ionic Liquids

Do not permeate through either organophilic or Do not permeate through either organophilic or hydrophilic dense membranes hydrophilic dense membranes

Possibly an environmentally benign alternative to Possibly an environmentally benign alternative to classical organic solventsclassical organic solvents

High viscosity and low heat transferHigh viscosity and low heat transfer ( (CC = 0.12 = 0.12 Pa.s)Pa.s)

Purification of ionic liquidsPurification of ionic liquids

Structure of surface modified PU/PBDO blend

PBDO: HO CH2 CH CH CH2 OHy

( ≈ 263 Å)

( ≈ 47 Å)

+

(PU)(PBDO)

Solvent

PU:

CH2 CH O CNH CH3O

NCOOCH3

CH2

H3C

OCN

NHC O

O

CH

CH3

CH2 O CH

CH2 CH2 CH O CNH CH3

NCOCH3

O

Ox

x

x

(Toluene)

≡

ShearY

where

≡

X

Transverse direction

Casting direction

Controlled shear rate (F = 85 N m-2) was then periodically (at least 30 stretching cycles) applied reaching maximum elongation of 1.2

UV radiated (λ = 254 nm) for 24 hours

POM images of a surface modified PU/PBDO-UV dry membrane (a) and of PU/PBDO-UV membranes after 7 days of immersion in binary mixtures of 1% w/w hexyl acetate and

[C4mim] [BF4] at T=25ºC (b), T=35ºC (c) and T=45ºC (d).

(a) Dry membrane before use

10 m

10 m (b) 25°C

(d) 45°C (c) 35°C 10 m 10 m

Characterization of a modified PU/PBDO-UV membrane by AFM before (a) and after (b) a pervaporation experiment.

The cross-section = 9 – 10 mThe peak-to-valley height h = 350 - 500 nmThe mean roughness Ra = 118.85 nmThe roughness root mean square (rms) Rq = 170.59 nm.

(a) (b)

Characterization of a modified PU/PBDO-UV membrane by POM before (a) and after (b) a pervaporation experiment. Characterization of a modified PU/PBDO-UV membrane by SEM after a

pervaporation experiment (c).

(a) 10 m 20 m

(b) (c)

Small Angle Light Scattering patterns (SALS) obtained before the pervaporation experiments.

qsx/qi

-0.06 -0.03 0.00 0.03 0.06

qsy

/qi

-0.06

-0.03

0.00

0.03

0.06

0 80 160 240 320 400 480

SALS technique = detection of periodic patterns in the membrane interior that cannot be accessed by AFM.

Swelling of polymeric membranesSwelling of polymeric membranes TTransport into the membraneransport into the membrane two ways two ways

of mutual affecting of components may be of mutual affecting of components may be considered:considered:

TThe free volume effecthe free volume effect generally generally increasing the diffusivity of components (i.e. increasing the diffusivity of components (i.e. plasticizing effect).plasticizing effect).

TThe coupling effecthe coupling effect due to due to remaining remaining interaction among molecules in the polymerinteraction among molecules in the polymer increaseincreasedd or decrease or decreasedd diffusivity of diffusivity of molecules in the membrane (i.e. the molecules in the membrane (i.e. the interaction effect).interaction effect).

Apparatus for swelling kinetics of membranes

C

MG

SH

TV

TCS

RCT

digital camera

magnifying glass

circle teflon cell

thermostated vessel infra-red remote control and timer

stand with holders

The accuracy of this optical method The accuracy of this optical method better better than that of usually used gravimetric methods than that of usually used gravimetric methods

To exclude the influence of the liquid meniscus To exclude the influence of the liquid meniscus destorsion in Teflon cell, blank experiments with destorsion in Teflon cell, blank experiments with Teflon square (which does not swell) were done Teflon square (which does not swell) were done for each mixture and pure liquids. for each mixture and pure liquids.

Optical correction was then subtracted from the Optical correction was then subtracted from the length and the width of the wet membrane length and the width of the wet membrane (typically 2 pixels, where 1 pixel is 13 μm). (typically 2 pixels, where 1 pixel is 13 μm).

The evaluation of the measurement The evaluation of the measurement commercial software Zoner Media Explorer 6 commercial software Zoner Media Explorer 6 from Olympus, Czech republic. from Olympus, Czech republic.

Dimensions of the membrane in dry and wet Dimensions of the membrane in dry and wet state state in pixelsin pixels,, the extension was evaluated as the extension was evaluated as a relative change a relative change

The absolute error in determining the membrane The absolute error in determining the membrane extension extension 1 pixel i.e. ± 0.3 % or ± 13 1 pixel i.e. ± 0.3 % or ± 13 m for m for used membrane dimensionused membrane dimension

Membrane swelling equilibrium in hexyl acetate at 25°C

0

5

10

15

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (s)

Rel

ativ

e S

wel

lin

g [

rel.

%]

Series5

Series2

Series1

Series3

xyx

mod

ymod

Hexyl Acetate 0 % w/w 0.5 % w/w 1 % w/w 1.5 % w/w 7 % w/w 100 % w/w

Membrane X (%)

Y (%)

X (%)

Y (%)

X (%)

Y (%)

X (%)

Y (%)

X (%)

Y (%)

X (%)

Y (%)

PU/PBDO 0.14 0.25 0.35 0.43 1.01 1.18 1.06 1.53 2.79 2.81 42.0 44.1

PU/PBDO-UV 0.66 0.40 0.68 0.79 1.47 1.54 1.61 1.80 2.89 2.95 44.6 45.5

Pervaporation experiments - different feed flow rate in Pervaporation experiments - different feed flow rate in the pervaporation module (0.34 and 2.49 ml/min) and the pervaporation module (0.34 and 2.49 ml/min) and both flat and fine-tuned surfaces of the dense membraneboth flat and fine-tuned surfaces of the dense membrane

The whole separation process - monitored by gas The whole separation process - monitored by gas chromatography in a classical pervaporation chromatography in a classical pervaporation arrangementarrangement ( (FFAP polar capillary columnFFAP polar capillary column))

Extraction - tridecan was added as an internal calibration standard

Pervaporation experiment

Pervaporation set-up

Pervaporation Pervaporation experimentexperiment – – standard laboratory standard laboratory pervaporation set-up pervaporation set-up with effective with effective membrane area of membrane area of 5 cm5 cm2 2 ; downstream ; downstream pressurepressure pp = 60 Pa = 60 Pa

Permeate samples were analysed by 1H NMR - only hexyl acetate passed through the membrane

Reaction vessel

Cold trap

Retentate

Permeate

Permeate

Vacuumpump

Feed

Thermostat

3D topography image (50 × 50 μm2 scan with an image surface area of 2598 μm2) of the PU/PBDO-UV dense membrane after pervaporation experiment.

0

50

100

150

200

250

300

0 0.002 0.004 0.006 0.008 0.01

Weight Fraction of Hexyl Acetate in the Feed

Flu

x o

f Hexy

l Ace

tate

(g/m2

/h)

0.34 ml/min

UV-0.34 ml/min

2.49 ml/min

UV-2.49 ml/min

Effect of surface modification and feed flow rate on the flux of hexyl acetate versus weight fraction of hexyl acetate in the feed

0

100

200

300

400

500

0 50 100 150 200 250 300

Time (h)

Enr

ichm

ent F

acto

r of

Hex

yl A

ceta

te

0.34 ml/min

UV-0.34 ml/min

2.49 ml/min

UV-2.49 ml/min

Effect of surface modification and feed flow rate on the enrichment factor of hexyl acetate versus time

feedh

pervh

h ww .

Conclusions The increase of the feed flow rate in pervaporation

module from 0.35 to 2.50 ml/min improved the enrichment factor of hexyl acetate by 15%.

The surface modification of the PU/PBDO dense membrane obtained by UV radiation and application of shear stress increased the enrichment factor by 14%.

Conclusions, cont. The active membrane area increased due to the

modification by 4% only we can state that the surface modification of PU/PBDO-UV helps to promote micro-turbulence in the feed boundary layer at the membrane surface this effect also contributes to increase the enrichment factor.

This work demonstrates the potential of using surface modified dense membranes to enhance the pervaporation separation process.

Conclusions, cont. The approach presented may be used in other

membrane processes mass transport represents a significant limitation.

These nano-structured surfaces use in nanobio-applications, such as tissue culture and biosensors, where orientation at a molecular/nano-dimension becomes relevant.

Conclusions, cont. Applications for improved external mass transfer

extremely interesting both at a nano- and at a micrometer scale mini- misation of concentration polarisation effects – better fluxes and improved selectivity

The use of room temperature ionic liquids is particularly interesting in combination with pervaporation in this case the solvent does not permeate through the dense membrane and therefore it is not lost to the environment high enrichment factors are attained.

Acknowledgement P. Izák would like to acknowledge P. Izák would like to acknowledge the post-doc the post-doc

grant (SFRH/BPD/9470/2002) from grant (SFRH/BPD/9470/2002) from Fundação Fundação para a Ciência e a Tecnologia, Portugalpara a Ciência e a Tecnologia, Portugal..

This research was supported This research was supported by by the Czech the Czech Science Foundation grant No. 104/08/0600. Science Foundation grant No. 104/08/0600.

Thank you for your attentionThank you for your attention