Study on Modification of

Nanofiltration Membrane

Hai Yuyan

2012.10.9

JOURNAL CLUB

Designing the Next Generation of Chemical

Separation Membranes

Douglas L. Gin and Richard D. Noble

Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309–0424, USA

Science, 2011, 332:674-676

Membrane-based chemical separations can have advantages

over other methods—they can take less energy than distillation

or liquefaction, use less space than absorbent materials, and

operate in a continuous mode.

We discuss how membranes work, and some notable new

approaches for improving their performance.

Background

Membranes are either dense or porous, depending on how the molecules

move across the barrier. In dense membranes, molecules dissolve into the

material and diffuse through it.

Dense Membranes

orange and green molecules move through the membranes at different rates because they

have different permeabilities P. The Robeson plot shows that conventional dense membranes

separate mainly via differences in diffusivity, and performance is limited by an “upper

bound.”

Nanoporous membranes separate via molecular size differences. With

uniform pore sizes, it is possible to get complete separation (smaller molecules

pass through—they have a higher molecular flux; larger ones are completely

blocked). With nonuniform pores, the largest pore sizes (i.e., a distribution)

dictate the selectivity, and both molecules can pass through.

Porous Membranes

A new approach in the design of dense membranes is to use room-temperature

ionic liquids (RTILs) in various morphologies. RTILs are liquid-phase organic

salts (i.e., ionic compounds) with negligible vapor pressure (avoiding evaporation

losses), high thermal stability, and intrinsic solubility for certain gases. Unlike

conventional polymers, RTILs perform gas separations via solubility differences.

For nanoporous membranes, several methods have recently been developed that

afford materials with uniform molecular-size pores. For example, deposition

techniques have been successfully used to reduce the pore size of commercial

nanoporous polymer and ceramic membranes down to molecular dimensions.

Recent advances in blending organic polymers with inorganic zeolites have

afforded viable composite membranes with uniform pore sizes in the 0.3- to 0.7-

nm range for light gas separations, such as CO2 , N2 , and CH4.

New Approaches

pH-responsive nanofiltration membranes

by surface modification

Heath H. Himstedt, Kathryn M. Marshall,S. Ranil Wickramasinghe∗

Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, CO 80523-1370, USA

Journal of Membrane Science, 366 (2011) 373–381

Fouling of nanofiltration membranes remains a major

concern that often limits process viability. One method to

minimize fouling is to modify the filtration surface and perhaps

the pores of the membrane in order to minimize adsorption of

dissolved solutes.

A commercially available nanofiltration membrane (NF 270)

has been surface modified using UV initiated polymerization to

grow polyacrylic acid( 聚丙烯酸 ) nanobrushes from the

surface of the membrane.

Background

The modified membranes

contain a new peak at

approximately 1720 cm−1

corresponding to vibration of

the carboxylic groups(C=O),

indicating the attachment of

polyacrylic acid nanobrush.

The intensity of the peak

increases with increasing

monomer concentration used

during polymerization and UV

reaction time.

ATR-FTIR

XPS

Modified membranes show

a clear carboxylic carbon peak

at approximately 288 eV.

The intensity of the peak

increases with increasing

monomer concentration used

during polymerization and UV

reaction time in agreement with

the ATR-FTIR data.

DI water/HCl/NaOH fluxes

Electrostatic interactions are also important. Studies indicate that

the zeta potential of NF 270 is around 0 at pH 3.5 but about −20 mV

at pH 7.0.

The higher concentration of charged solutes present (e.g. Na+ and

Cl−) will lead to a higher osmotic pressure compared to DI water

resulting in a reduced filtrate flux.

If the pH of the feed is above the pKa=4.25 of acrylic acid, the

carboxylic groups will be deprotonated and swell.

Filtrate Flux

Rejection of glucose

The change in glucose rejection in the presence of other ionic

species is due to interactions between the ionic species and the

membrane. However in their expanded, charged conformation, the

grafted layer affects membrane performance.

Rejection of glucose

UV-Photo Graft Functionalization of Polyethersulfone

Membrane with Strong Polyelectrolyte Hydrogel and

Its Application for Nanofiltration

Roy Bernstein, Enrique Anton, and Mathias UlbrichtLehrstuhl fu I r Technische Chemie II, Universita I t Duisburg-Essen, 45117 Essen,

GermanyDepartment of Chemical and Environmental Engineering, University of Oviedo,

33006 Oviedo, Spain

ACS Applied Materials & Interfaces, 2012, 4: 3438 – 3446

The feasibility of charged nanofiltration (NF) membranes fabrication using polyelectrolytes as the active layer is being explored in the past few years. This is primarily done through two methods.

The first one is synthesis of a polyelectrolyte, either inside the pores of an ultrafiltration (UF) base membrane, thus obtaining a pore-filling composite membrane, or on the outer surface of an UF membrane, resulting in a thin-film composite membrane.

The second method is through the deposition of polyelectrolyte, the “layer by layer” (LBL) technique, on or within a porous polymeric support, or inorganic support.

Yet, these membranes still have some drawbacks compared with the commercially available NF membranes that withhold their further expansion. The photoirradiation-induced radical graft copolymerization technique was recently successfully applied for surface modification of hydrogels on UF membranes. This technique has several advantages: it generates a rapid reaction and is performed under mild conditions with various monomers using simple equipment at a relatively low cost.

Background

A strong polyelectrolyte hydrogel was graft copolymerized on a

polyethersulfone (PES 聚醚砜 ) ultrafiltration (UF) membrane using

vinyl sulfonic acid (VSA 乙烯磺酸 )as the functional monomer, and

N,N'-methylenbisacrylamide (MBAA) as the cross-linker monomer. This

was carried out in one simple step using the UV photoirradiation method.

VSA MBAA

Degree of grafting

The degrees of modification

measured by the two techniques

have a similar trend: a linear

increase in the DG with cross-

linker concentration.

The DG without cross-linker

was very low. This is probably a

consequence of wetting or

di usion limitation due to ff

incompatibility between the

charged monomer and the

hydrophobic surface.

Degree of grafting The increase of the DGs with

modification time is monotonic.

However, the DGg rises fast in the

early stages and then the increase

moderates.

Therefore, it can be assumed that

in the early stages it is mainly the

cross-linker monomer that is grafted

to the surface, and then, either

because of the cross-linker ’ s two

double bonds or a change in the

surface properties, the functional

monomer (VSA) grafting is

enhanced.

Degree of grafting It was found that when the

modification was carried out using low

UV intensity the modification degree

and the membrane performance were

better than for modification at high UV

intensity.

Polymerization at too high

intensities can be monomer di usion ff

limited immediately in the early stages,

due to the high initiator radicals

concentration, whereas for

polymerization at low UV intensities,

the di usion limitation occurs at later ff

stage.

salt rejection

The salt rejection was in the

order Na2SO4 > MgSO4 ≈ NaCl >

CaCl2 , as expected for rejection

based on Donnan exclusion for

negatively charged NF membranes.

Because rejection of uncharged

solutes with charged NF membranes

derives mainly from steric

exclusion.

Conclusion

It is well known that the hydrophilic surface has lower tendency to fouling[1].

对自制的聚酰亚胺纳滤膜 (BTDA-ODA 型，其自身含有光敏性基团 )，进行紫外辐照接枝改性。随着光照时间的增长，改性膜的接枝率逐渐增加，意味着膜表面微孔孔径随光照时间的增长而减小 [2].

研究了不同操作条件对自制的氟酐型聚酰亚胺纳滤膜分离螺旋霉素 - 乙酸丁酯萃取液性能的影响 [3]。

在紫外光照射条件下把丙烯酸或甲基丙烯酸甲酯接枝到自制的氟酐型聚酰亚胺纳滤膜上 [4].

[1] Ahmad Rahimpour Korean J. Chem. Eng., 2011, 28: 261-266.[2] 陈洪杰（孔瑛） . 聚酰亚胺纳滤膜改性的研究 [D]. 东营 : 中国石油大学 (华东 ), 2010. [3] 宋力航 , 孔瑛 , 杨金荣 , 史德青 , 李阳初 . 化学工业与工程 , 2009, 26(1): 50-53.[4] 李林英 , 丛晓英 . 内蒙古石油化工 , 2009, 1: 8-9.

Using the UV photoirradiation method for membrane surface modification.

Thank you !