Thesis Proposal Membrane Chuyên đề luận văn màng lọc

Ho Chi Minh University of Technology
Faculty Of Chemical Engineering
Office For International Study Programs

Thesis Proposal
Study on Separation Performance of Polyamide Based
Nanofiltration Membrane for Arsenic Removal

Submitted by
NGUYEN HUU QUANG MINH – ID Number: 1652374
Instructor:
MAI THANH PHONG Assoc. Prof., Ph.D.

Ho Chi Minh city, January 2020


TABLE OF CONTENTS
I.

PURPOSE OF A RESEARCH PROPOSAL..........................................................1

II. OVERVIEW...........................................................................................................1
1.

Arsenic.................................................................................................................1

2.

Arsenic Contamination in Vietnam.....................................................................2

3.

Arsenic Removal Techniques..............................................................................2
3.1. Oxidation Technique....................................................................................2
3.2. Coagulation – Flocculation..........................................................................2
3.3. Adsorption and Ion Exchange......................................................................3
3.4. Membrane technology..................................................................................4

III.

LITERATURE REVIEW....................................................................................5

IV.

METHODOLOGY............................................................................................10

1.

Materials............................................................................................................10

2.

Membrane preparation.......................................................................................10

3.

Membrane characterization...............................................................................10

4.

Measurement of the NF separation performance testing...................................10

5.

Research content................................................................................................11
5.1. Investigation of the effects of diamine monomers on NF membrane
seperation performance.........................................................................................11
5.2. Study on the effects of additives on NF membrane performance..............11

V. PLAN....................................................................................................................12
VI.

STRUCTURE OF THESIS REPORT...............................................................13

REFERENCES.............................................................................................................14
ABBREVIATION........................................................................................................15

LIST OF TABLE
Table 1. Comparison of main arsenic removal technologies.....................................................3
Table 2. Overview of pressure-driven membrane processes.....................................................4
Table 3. Schedule for completion of the research....................................................................12


I.

PURPOSE OF A RESEARCH PROPOSAL

Arsenic in drinking water has been reported as the most widespread geogenic
contaminant in water sources worldwide [1]. The World Health Organization (WHO)
reports [2] long-term exposure to arsenic from drinking-water and food can cause
cancer, skin lesions, cardiovascular disease and diabetes. WHO’s standard content of

arsenic in drinking water is 10 µg/L while in Vietnam, the number is 50 µg/L [3].
Although there is numerous conventional technology available for treating arsenic in
water such as oxidation, coagulation – floculation, adsorption and ion exchange, the
resulting quality of such technologies does not meet the technical committee of Vietnam
(TCVN), and furthermore, the requirement for As concentration tend to reduce to the
lower level (10 µg/L) from the community due to a higher risk of As exposure [3].
Additionally, there are several possible drawbacks such as huge cost, complex
operational condition and handling techniques. Modern technology such as
nanofiltration (NF) polyamide-based membrane is a promising alternative to the
existing removal processes, which show various advantages in terms of operational
costs, efficiency, selectivity and energy consumption. In the NF process, the
separation performance of the membrane in term of permeability and selectivity is
depended on the structure and physicochemical properties of the membrane and thus
controlled by the structure of the monomers, concentration of the monomers and
reaction conditions. For my knowledge, there is few studies in the fabrication of
membrane for As removal. In this work, my purpose is to investigate the separation
performance of polyamide based nanofiltration membrane synthesized in laboratory
for removing As (V) from water.
Following research objectives would facilitate the achievement of this aim:
(i). Sucessfully synthesizing NF thin-film composite (TFC) membrane based
polyamide via interfacial polymerization in which I can evaluate the effect of
monomer structures on the separation performance of the prepared membrane.
(ii). Investigation of the effect influence of the additives on the separation
performance
II.

OVERVIEW

1. Arsenic
Arsenic is a toxic heavy metal which is highly detrimental to ecological systems,

and long-term exposure to it, especially in its inorganic form mainly through drinkingwater, is highly dangerous to life as it can cause serious health effects. Skin lesions
and skin cancer are the most characteristic effects.
Depending on redox conditions, it is stable in the +5, +3, -3, and 0 oxidation states.
As(III) is 60 times more toxic than As(V), the pentavalent (+5) or arsenate species are
AsO4 -3, HAsO4- and H2AsO4- . The trivalent (+3) or the arsenite species include
As(OH)4 - , AsO2OH-2 and AsO3-3. The pentavalent arsenic As(V) species are
predominant and stable in oxygen-rich aerobic environments, whereas the trivalent
arsenite As(III) species are predominant in moderately reducing anaerobic
environments such as groundwater [4-5].
1


2. Arsenic Contamination in Vietnam
All Vietnam regions are potentially arsenic contaminated. Arsenic has formed in
soil, rock and sediments and dissolved into groundwater for thousands of years.
Arsenic pollution in the Red River Delta is more serious than in the Mekong River
Delta. Particularly in rural areas of Hanoi such as Thuong Tin, Ung Hoa, Dan Phuong,
Thanh Oai and Thanh Tri, the groundwater sources are heavily contaminated with
arsenic [3].
Survey results of arsenic concentration in groundwater in 345 craft villages in
Hanoi city of Hanoi Department of Science and Technology (October 2012) showed
that there were 338/345 water samples (97.97%) had Arsenic content is 2-50 times
higher than the standard. In the Mekong River Delta , 4876 samples of groundwater
surveyed have 56% of samples contaminated with arsenic (over 50 µg/L) [3].
3. Arsenic Removal Techniques
3.1. Oxidation Technique
Oxidation involves the conversion of soluble arsenite to arsenate. This alone does
not remove arsenic from the solution, thus, a removal technique, such as adsorption,
coagulation, or ion exchange, must follow. For anoxic groundwater, oxidation is an
important step since arsenite is the prevalent form of arsenic at near neutral pH. Aside

from atmospheric oxygen, many chemicals, as well as bacteria, have already been
used to directly oxidize arsenite in water [6].
Atmospheric oxygen, hypochlorite, and permanganate are the most commonly
used oxidants. Oxidation of arsenite with oxygen is a very slow process, which can
take hours or weeks to complete. On the other hand, chlorine, ozone, and
permanganate, can rapidly oxidize As(III) to As(V). However, despite this enhanced
oxidation, interfering substances present in water need to be considered in selecting
the proper oxidant as these substances can greatly affect and dictate the kinetics of
As(III) oxidation. For instance, it was shown that competing anions and organic matter
in groundwater greatly affect the use of UV/titanium dioxide (TiO2) in arsenic
oxidation. Furthermore, this involves a complex treatment, which produces an Asbearing residue that is difficult to dispose. Thus, to efficiently remove arsenic from a
solution by oxidation, oxidants should be selected carefully. Moreover, all cited
disadvantages of oxidation alone make it a less competent method for arsenic removal
[6].
3.2.

Coagulation – Flocculation

Coagulation process is traditionally realized by adding ferric or aluminum ions
(e.g., FeCl3 and Al2(SO4)3). Fine particles in water first aggregate into coagulates
because added ferric or aluminum ions strongly reduce the absolute values of zeta
potentials of the particles. Then, arsenic ions (arsenate or arsenite) precipitate with the
ferric or aluminum ions on the coagulates, and thus concentrate in the coagulates.
After that, the coagulates are separated from water through filtration, eliminating
2


arsenic from the water [6-7]. Flocculation, on the other hand, involves the addition of
an anionic flocculant that causes bridging or charge neutralization between the formed
larger particles leading to the formation of flocs. Finally, solids are removed

afterwards through filtration or sedimentation [6].
A review of these ferric or aluminum ions along with their distinct advantages and
disadvantages is shown in Table 1 [7].
Table 1. Comparison of main arsenic removal technologies
Ions

Advantages

- Durable powder chemicals are
available.
Aluminum - Low capital cost and simple in
coagulatio operation.
n
- Effective over a wider range of
pH.
Ferric
coagulatio
n
3.3.

Disadvantages
- Produces toxic sludges.
- Low removal of arsenic.
- Pre-oxidation may be
required.

- Common chemicals are available . - Medium removal of
- More efficient than alum
As(III).
coagulation on weigh basis.

- Sedimentation and
filtration needed.

Removal
(%)

90

94.5

Adsorption and Ion Exchange

Adsorption is a process that uses solids as medium for the removal of substances
from gaseous or liquid solutions. Basically, substances are separated from one phase
followed by their accumulation at the surface of another. This process is driven mainly
by van der Waals forces and electrostatic forces between the adsorbate molecules and
the adsorbent surface atoms. This makes it important to characterize first the
adsorbent surface properties (e.g., surface area, polarity) before being used for
adsorption [6].
Adsorption has been reported as the most widely used technique for arsenic
removal due to its several advantages including relatively high arsenic removal
efficiencies, easy operation, and handling, cost-effectiveness, and no sludge
production. However, adsorption of arsenic strongly depends on the system’s
concentration and pH. Additionally, contaminated water does not only contain arsenic,
it is always accompanied by other ions (E.g., phosphate and silicate), competing for
the adsorption sites. Moreover, The effectiveness of adsorption in arsenic removal can
also be hindered by the type of adsorbent itself. In addtition, Most conventional
adsorbents have irregular pore structures and low specific surface areas, leading to
low adsorption capacities. Lack of selectivity, relatively weak interactions with
metallic ions, and regeneration difficulties can also confine the ability of these

sorbents in lowering arsenic concentrations to levels below maximum concentration
level [6].
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3.4. Membrane technology
3.4.1. General review of membrane technology
A membrane is an interphase between two adjacent phases acting as a selective
barrier, regulating the transport of substances between the two compartments. In
membrane processes, a membrane separates two phases. The membrane allows
transport of one or few components more readily than that of other components. The
driving force for transport can be either a pressure gradient, a temperature gradient, a
concentration gradient or an electrical potential gradient [6].
Typically, membranes are synthetic materials with billions of pores acting as
selective barriers, which do not allow some constituents of the water to pass through.
Generally, there are two categories of pressure-driven membrane filtrations (as shown
in Table 2): (i) low-pressure membrane processes, such as microfiltration (MF) and
ultrafiltration (UF); and (ii) high-pressure membrane processes, such as reverse
osmosis (RO) and nanofiltration (NF) [6].
Table 2. Overview of pressure-driven membrane processes
Parameter
Permeability
(1/h·m2 ·bar)
Pressure (bar)
Pore size (nm)

MF

UF

RO

NF

>1000

10 – 1000

1.5 – 30

0.05 – 1.5

0.1 – 2
100 – 10,000

0.1 – 5
2 – 100

3 – 20
0.5 – 2

5 – 120
< 0.5

MF alone cannot be used to remove dissolved arsenic species from arseniccontaminated water. Thus, the particle size of arsenic-bearing species must be
increased prior to MF; the most popular processes for this being coagulation and
flocculation. However, the pH of the water and the presence of other ions are major
factors affecting the efficiency of this arsenic immobilization. This can be a
disadvantage of this technique especially since arsenate is negatively charged in this
pH range, it can bind by surface complexation resulting in efficient arsenate removal.

Therefore, complete oxidation of arsenite to arsenate is needed for this technique to be
effective [6].
As MF, UF alone is not an effective technique for the treatment of arseniccontaminated water due to large membrane pores. Arsenic removal was reported to
decrease with decreasing pH. Moreover, despite the effective removal of arsenic, the
concentration of the surfactant in the effluent is so high that it needs to be further
treated with powdered activated carbon before being discharged to the environment
[6].
Both NF and RO are suitable for the removal from water of dissolved compounds
with a molecular weight above 300 g/mol. These techniques can significantly reduce
4


the dissolved arsenic level in water given that the feed is free from suspended solids
and that arsenic is preferably present as arsenate [6].
3.4.2 NF versus RO
NF membranes have low molecular weight cut-offs (200 - 1000 Da) and smaller pore size
(∼1 nm). They also have a surface electrostatic charge which gives them great selectivity
towards ions or charged molecules. More specifically, NF membrane can be used to remove
small neutral organic molecules while surface electrostatic properties allowed monovalent
ions to be reasonably well transmitted with multivalent ions mostly retained. NF membrane's
operating pressure ranged from 3 to 20 bars, which was much lower than RO membranes
[8]. Indeed, RO cannot be used for partial and or selective demineralization. NF is more
suitable for directly producing drinking water and the post treatment can be simplified. The
argument, that NF membranes are more selective was also presented. It was clearly shown
that NF selectivity for monovalent ions is higher than RO [9]. Moreover, NF offers several
advantages, such as low operation pressure, high flux, high retention of multivalent anion
salt and organic molecular above 300, relatively low investment, low operation and
maintenance cost. Furthermore, NF membranes available in the market show a wide range
of properties and thus this variation affects the membrane performances. Additionally, NF
membranes properties can be characterized in terms of the hydrophobicity, membrane

roughness, membrane charge, membrane molar weight cut-off, retention properties and
permeability. Modeling can also be used to analyze and to predict the membranes
performances [10-11].
To sum up, it can be confidently stated that a competing membrane process for

arsenic removal in the near future is NF. Therefore, an adequate understanding of the
arsenic treatment using NF is necessary.
III.

LITERATURE REVIEW.

The separation performance of polyamide membrane is influence by many factors
such as: monomers structure, monomers concentration, reaction time, pre-treatment,
additives. Therefore, the control of the preparation condition is the key to produce the
polyamide-based NF membrane which is suitable for individual purpose.
Mai Thanh Phong et al. [12] has synthesized NF thin-film composite (TFC) via
polymerization between piperazine (PIP) in water and trimesoyl chloride (TMC) in
hexane onto polyacrylonitrile (PAN) supporting substrate. The effect of PIP and TMC
concentration on separation process has been studied. The characteristic peaks are
assigned to the amide II band (C – N – H) and and amide I band (N – C = O) of the
PA thin film, and also the carboxylic groups, which is the result of the hydrolysis of
unreacted acyl chloride. The results showed that the cross-linking degree enhanced as
increasing TMC concentration in the range from 0.05 wt.% to 0.15 wt.%. With the
TMC concentration higher than 0.15 wt.%, the ratio of I(COOH ) /I (CONH )
exhibited an opposite trend. It indicated that the IP reaction was improved with the
increase in TMC concentration.
The interfacial polymerization occurred at the organic side of the interface of water
and organic solvents which can be controlled by the diffusion of m-phenylenediamine
(MPD) and TMC. Therefore, an increase in either MPD or TMC concentrations might
5

enhance the driving force for diffusion of monomers to the reaction region to form
rapidly a dense thin-film and thereby limited the growth of thickness of the
membrane. However, increasing TMC concentration may induce a deficiency in the
available MPD at the organic side of the interface. It would lead to an increase of a
linear structural fraction with carboxylic acid functional groups, associated with a
more hydrophilic surface in the organic [12].
By increasing PIP concentration, the diffusion of PIP to the reaction side of the
interface was accelerated. Consequently, the reaction rate is faster and a dense PA
film with high extent of cross-linking was formed. The dense film also plays as a role
of a barrier, which prevents and blocks the diffusion of PIP to the organic side of the
interface for reacting with TMC. Therefore, the obtained membrane became thinner,
denser, and more hydrophobic. It can be seen from the results that the PA membrane
produced with the TMC concentration of 0.15 wt.% and the PIP concentration of 2.0
wt.% exhibited a good separation performance with permeation flux of 64 Lm-2h-1 and
As(V) rejection of 95%, respectively [12].
S. Veríssimo et al. [13] investigated the influence on membrane performance of
the use of different piperazine derivatives. Composite membranes were prepared by
interfacial polymerization of PIP, N,N′-diaminopiperazine (DAP), 1,4-bis(3aminopropyl)-piperazine (DAPP) and N-(2-aminoethyl)-piperazine (EAP) with TMC
separately. Their nanofiltration performance was evaluated with solutions of NaCl,
MgSO4 and Na2SO4 (3g/l and pH 6) at 10×105 Pa. The surface charge was
investigated by zeta-potential measurements and the morphological studies by atomic
force microscopy (AFM) and scanning electron microscopy (SEM) [13].
The PIP–TMC membranes presented an average water permeability of 6.6 × 10-5 l
(m-2h-1Pa-1) and the average rejection to the divalent salts MgSO4 (93%) and Na2SO4
(95%) was higher than to the monovalent salt NaCl (40%). The membranes have
slight acidic property and have a negatively charged surface at the pH 6. The
morphological studies revealed a somewhat rough surface [13].
The DAP–TMC membranes gave the highest average water permeability, around

8.8 × 10-5 l (m-2h-1Pa-1) The average salt rejections for NaCl, MgSO4 and Na2SO4
were 21, 72 and 89%, respectively. The membranes also showed some acidic property
and were negatively charged at pH 6. The membranes surface was very flat and had a
very thin film [13].
The DAPP–TMC membranes have an average water permeability of 3.2 × 10-5 l
(m-2h-1Pa-1) and different average salt rejections to NaCl (57%), MgSO4 (75%) and
Na2SO4 (35%). The membranes surface is amphoteric and at pH 6 is positively
charged. A smooth surface characterizes the membranes [13].
The EAP–TMC membranes presented an average water permeability of 3.1 × 10-5 l
(m-2h-1Pa-1) and the average rejection to the divalent salts MgSO4 (90%) and Na2SO4
(92%) was higher than to the monovalent salt NaCl (31%). The membranes have
amphoteric surface and are negatively charged at pH 6. The membranes surface was
flat and had a very thin film [13].

6


Overall, DAP – TMC has the highest average water permeability. The average salt
rejection of divalent salts is higher than the monovalent one except DAPP – TMC. PIP
– TMC showed the rough surface while the surface of the rest ones are flat.
Asim K. Ghosh et al. [14] reported on the attempt to correlate MPD–TMC reaction
and curing conditions to RO membrane separation performance (water flux, salt
rejection), film structure and interfacial characteristics (hydrophilicity, roughness).
Polyamide composite membranes are formed by immersing the polysulfone support
membrane in an aqueous solution of MPD for 15s. The gas is applied to the wetted
membrane surface until the surface appears dull and dry. The MPD saturated support
membrane is then immersed into the organic solution of TMC for 15 s, which results
in formation of an ultra-thin polyamide film over the polysulfone support. The
resulting composite membranes are heat cured at 50oC for 10 min (unless otherwise
specified), washed thoroughly with deionized (DI) water, and stored in DI water filled

lightproof containers at 5oC. When additives triethylamine (TEA) and
Camphorsulfonic acid (CSA) are employed, 2 g of TEA and 4 g of CSA are added to
75–80 mL of DI water under vigorous stirring. After complete dissolution of the
TEA–CSA mixture, DI water is added to provide a total solution volume of 100 mL.
Finally, 2 g of MPD is added to the 100 mL TEA–CSA aqueous solution.
The use of additives in monomer solutions can influence the rate and extent of
interfacial polymerization as well as the extent of crosslinking. Properties of
polyamide films formed with TEA–CSA added to the aqueous-MPD reaction solution.
The results represent average changes in pure water permeability, salt permeability,
contact angle, and surface roughness relative to the membrane formed without TEA–
CSA in the same solvent. In all the cases, pure water permeability dramatically
increases, salt rejection is practically unchanged, contact angle is slightly reduced, and
roughness is significantly reduced by TEA–CSA addition. Membrane surface features
appear more nodular when TEA–CSA is present compared to the ridge-and-valley
morphology of membranes formed without TEA–CSA. On SEM and transmission
electron microscopy (TEM) images, the nodular morphology is measurably smoother
than the ridge-and-valley morphology according to AFM surface roughness analyses.
Cross-section TEM images of hexane and isopar based membranes prepared with
TEA–CSA looked thinner and smoother than without TEA–CSA membranes.
Three novel polyacyl chloride monomers: 2,4,4′,6-biphenyl tetraacyl chloride
(BTAC), 2,3′,4,5′,6-biphenyl pentaacyl chloride (BPAC) and 2,2′,4,4′,6,6′-biphenyl
hexaacyl chloride (BHAC) were successfully synthesized by Tunyu Wang et al. [15].
TFC RO membranes were prepared by using TMC, BTAC, BPAC as well as BHAC
to interfacial react with m-phenylenediamine (MPDA) on the polysulfone support
through interfacial polymerization respectively, for the purpose of investigating the
effects of the polyacyl chloride functionality on the RO membrane properties. TFC
RO membranes were prepared through interfacial polymerization of trimesoyl
chloride (TMC), BTAC, BPAC, and BHAC with MPDA respectively. The results
reveal that the functionality of the acid chloride monomer strongly influences the
properties of the RO membrane. As the functionality of the acid chloride monomer

increased, the resulting membrane skin layer became more negatively charged, thinner
7


and smoother. In addition, all the four membranes exhibited close salt rejection rates
according to the RO separation performance tests. However, with the increase of acid
chloride functionality the permeate flux of the resulting RO membrane became lower,
due to a combination of the increase in the carboxylic acid groups on the membrane
surface, lower mobility of the crosslinked polyamide chains and lower surface
roughness.
In-Chul Kim et al. [16] perform the experiment on the effect of alkyl phosphate
additives during interfacial polymerization. Polyamide membranes were prepared by
interfacial polymerization on a polysulfone (PSF) UF membrane. The PSF membrane
was dipped into an aqueous solution containing MPD, TEA (2–3 wt.%), dimethyl
sulfoxide (1 wt.%), 2-ethyl-1,3-hexane diol (0.2–0.3 wt.%), and CSA (1–2 wt.%) in
DI water, after which the excess solution was removed by squeezing with a soft
rubbery roller after 1 min. The PSF membrane was then immersed in a solution of 0.1
wt.% TMC and different concentrations of tributyl phosphate (TBP) or triphenyl
phosphate (TPP) in isoparaffin. After 1 min of reaction, the membrane was dried in air
for 5 min. The membrane was rinsed with a 0.2 wt.% Na2CO3 solution.
In order to demonstrate the effect of the additives in an organic solution on the
membrane performance, the concentrations of TBP and TPP were varied under the
same condition to that of the aqueous solution. The water flux and NaCl rejection of
the membranes with additives of TBP and TPP in the TMC organic solution at
different concentrations. For the membranes using TBP as an additive in the organic
solution, an increase in the water flux was observed with no significant loss of salt
rejection when the amount of TBP in the organic solution was increased up to 0.9 wt.
%. However, it was found that with the increase in TPP concentration in the TMC
organic solution, the water flux was slightly decreased without loss of salt rejection.
TBP as an additive has much better performance than TPP due to the complex

formation between TBP and TMC in an organic solution [16].
Both membranes show a unique ridge-and-valley structure. With the addition of
TBP into the TMC organic solution, the surface morphology of the membrane
prepared without TBP addition was changed. The addition of TBP in the TMC organic
solution during interfacial polymerization tends to increase the ridge portion of the
polyamide TFC membrane. Most of the ridge film covers the valley film. The AFM
image of the membrane with no TBP addition shows a ridge-and-valley structure. The
membrane with the addition of 0.6 wt.% TBP in the TMC organic solution indicates
that the surface of the TFC polyamide film has a broad ridge and a loose structure
compared to the membrane without TBP addition [16].
ShanShan Guan et al. [17] investigated the effect of additives on the performance
and morphology of sulfonated copoly (phthalazinone biphenyl ether sulfone)
(SPPBES) composite nanofiltration membranes. SPPBES composite membranes were
prepared from SPPBES coating solutions containing different additives. The effect of
the additives including glycol, glycerol and hydroquinone in the SPPBES solutions on
membrane performance and morphology were studied. For all of SPPBES composite
membranes, the salt rejection increased in the order: R(MgCl2) < R(NaCl) ≤
R(MgSO4 ) < R(Na2 SO4 ). The rejection of SPPBES membranes prepared from
these additives decreased as follows: glycol > glycerol > hydroquinone. The SPPBES
8


composite membrane prepared from glycerol as the additive had the highest flux,
while composite membrane prepared from hydroquinone as the additive showed the
lowest flux. Smooth composite membrane surfaces were obtained when glycol and
glycerol were used as additives, and they were no significant difference.

The most important properties of the TFC membranes are permeability and
selectivity, which are basically determined by the physicochemical properties of the
upper polyamide layer such as surface roughness, hydrophilicity, charge performance

as well as skin layer thickness. Factors affecting these physicochemical properties
include: support membrane structure and chemistry, monomer structures and
concentration, catalysts and other additives in the aqueous solution and/or in the
organic solution during the interfacial polymerization, reaction and curing conditions,
and other post-treatments. Among all these factors, the inherent chemistry of the
monomers employed in the polymerization has been proven to play a major role as
confirmed from various studies over the past decades. In addition, it is common in
practice to use combinations of additives to influence monomer solubility, diffusivity,
hydrolysis, or protonation or to scavenge inhibitory reaction byproducts.
NF is a pressure-driven membrane process that lies between UF and RO, it were
consider “low-pressure RO membrane” thus, some of the study on RO could also be
considered for better understanding about NF membrane [8]. For instance, the work of
Tunyu Wang et al. [15] on the effect of monomers on RO membrane for salt rejection
or the experiment of Asim K. Ghosh et al. [14] on evaluating the addition TEA – CSA
to the aqueous MPD solution using RO membrane.
The studies demonstrate that the physicochemical properties such as flux and
rejection of the membrane are mainly affected during the interfacial polymerization.
Among all the factors, monomers play a central role involving monomers’ structure,
monomers’ concentration, concentration ratio between monomers, reaction time and
reaction temperature, type of solvent, post-heat treatment. Additives, on the other
hand, are able to influence monomer solubility, diffusivity, hydrolysis, or protonation
or to scavenge inhibitory reaction byproducts. Most nanofiltration membranes are
composite and have a polyamide thin film prepared by interfacial polymerization.
Their characteristics and performance are mainly determined by the thin film and
consequently by the monomers used for its preparation.
For example, In S. Veríssimo et al. [14] work, different thin films were prepared
with small structural differences to help understanding how the amines structure
influences the membranes nanofiltration performance, surface charge and
morphology. The results show different average water permeability of the samples
which was correlated with hydrophobic/hydrophilic character of the monomers by use

of the octanol–water partition coefficient. The research on MPD/TMC concentration
of Mai Thanh Phong et al. [12] also show that an increase in either MPD or TMC
concentrations increase the driving force for diffusion of monomers quickly.
However, increasing TMC concentration would lead to an increase of a linear
structural fraction with carboxylic acid functional groups, associated with a more
9


hydrophilic surface due to the deficiency in the available MPD at the organic side.
The study on addtives such as TPP and TBP has been performed by In-Chul Kim et
al. [16], it was found different additives lead to different performance due to the
complex formation between additives and TMC in an organic solution.
In conclusion, the need of studying on NF membrane performance in order to
apply NF membrane process on arsenic treatment process in water is necessarry since
most of the researchs contribute towards the performance of monomers structure and
additives on RO membrane polymerization and a large number of research on NF
membrane is for desalination process purpose only.
IV. METHODOLOGY.
1. Materials
Polyacrylonitrile (PAN) porous support substrate was provided by DowFilmtec (USA). PIP, ethylenediamine (EDA), MPD, triethylenetetramine
(TETA) and TMC with the purity of 99% was received from Sigma-Aldrich
(USA). Deionized (DI) water and hexane (99%) were used as solvents for the
synthesis of polyamide membrane. Arsenate
(Na2AsHSO4) was purchased from Merck (Germany). Additives such as
sodium dodecyl sulfate (SDS), triethylamine (TEA) and triphenyl stannyl
acetate (TPTA) received from Merck (Germany). Other chemicals are reagents
with high purity (98%) using during synthesis and membrane testy process.
2. Membrane preparation
PA thin film was hand-cast on the PAN substrate through interfacial
polymerization. PA based TFC membrane was formed by immersing the PAN

support membrane in a PIP aqueous solution for 2 min. Excess PIP solution
was removed from the support membrane surface using a tissue. The PIP
saturated support membrane was then immersed into the TMC-hexane solution
for 1 min, which resulted in the formation of an ultra-thin polyamide film over
the PSF support. The derived membrane was vertically held for 2 min before it
was immersed in a 200 ppm NaClO for 2 min and then dipped in 1,000 ppm
Na2S2O5 solution for 30 s. The membrane was finally dipped in DI water for 2
min. Before the obtained membrane can be used for the experiments, it was
immersed in a DI water container with the water replaced regularly.
3. Membrane characterization
Attenuated total reflectance Fourier transform infrared (ATR- FTIR)
spectroscopy was employed to analysis the functional groups of the
membranes.
The water contact angle will be used to represent the hydrophilicity of the
TFC membrane surface.
Membrane samples were prepared for scanning electron microscope (SEM)
for characterizing the surface morphology and cross section.
10


The roughness of the membrane surface will be analysed by atomic force
microscopy (AFM).
4. Measurement of the NF separation performance testing.
The NF membrane was evaluated by filtering a solution at 150 ppb using a
cross-flow system. Firstly, the NF membrane was used for deionized water in 3
hours at P = 250 psi. After the flux of the membrane reaches a stable value,
replace deionized water with a solution of 150 ppb As (V) and operate at P =
150 psi. After 30 minutes, the water flux is measured and the permeate water
flow rate is sampled to be measured by internal concentration polarization
(ICP) to determine As concentration in the product flow. The measurement

result is the result of 3 replicate experiments.
Water flux J ( L m−2 h−1 ) can be determined from permeate water flow rate as
equation (1):
J=

QP
Am ×t

(1)

Where QP is the permeate water flow rate, Am is the effective membrane
area (0.0024 m2) and t is the filtration time. The As(V) concentrations in the
feed and permeate solutions were used to calculate the observed arsenic
rejection Xs (%) as shown in equation (2):

(

X s= 1−

)

C P , As
×100 %
C F , As

(2)

Where CP,As and CF,As are the arsenic concentration in feed and permeate
sides, respectively.
5. Research content

5.1. Investigation of the effects of diamine monomers on NF membrane
seperation performance
Composite membranes were prepared by interfacial polymerization of
PIP, MPD and EDA with TMC separately. Polyamide composite membranes
are formed by immersing for 2 minutes. The concentration of each monomer
and TMC is fixed at 2 wt.% and 0.15 wt.%, respectively. The membrane
characterization is described in study 3. at section IV and the separation
performance testing is demonstrated in study 4. At section IV.
5.2.

11

Study on the effects of additives on NF membrane performance


The diamine-based NF membrane has the most suitable water flux (J) and
arsenic rejection (Xs) that achieved in study 5.1. at section IV will be prepared
with varied concentration from 0.02 wt.% To 0.30 wt.%.

V.

PLAN

This section presents my schedule and qualifications for completing the
proposed research. This research culminates in a formal report, which will be
completed by May 25th, 2020. To reach this goal, I will follow the schedule presented
in Table 3. Most of my time will be spent performing the process to find key results,
and presenting those results to the thesis report.
Table 3. Schedule for completion of the research.
Month (2020)

February

March

April

May

Week
Activities
Material preparation
Membrane
preparation
Analyze different
type of monomers
Performe
experiment on
impact of additives
Analyze membrane
morphology
12

1 2 3 4 5 6 7 8 9 10 11 12 13 14

1
5

16 17 18

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Review Statistical
analysis of data
Report writing

13

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


VI.

STRUCTURE OF THESIS REPORT

This section presents my expected structure of my thesis report for obtaining the
objectives discussed in the previous section.

ACKNOWLEDGEMENT
TABLE OF CONTENT
LIST OF FIGURES
LIST OF TABLES
ABBREVIATION
ABSTRACT
Chapter I. INTRODUCTION
Chapter II. OVERVIEW
II.1 Arsenic
II.2 Arsenic Contamination in Vietnam
II.3 Arsenic removal techniques
II.3.1 Oxidation Techniques

II.3.2 Coagulation – Flocculation
II.3.3 Adsorption and Ion Exchange
II.3.4 Membrane technology (MF,UF,RO and NF)
II.4 NF membrane
Chapter III. SYNTHETIC LITERATURE REVIEW
Chapter IV. MATERIAL AND METHODS
IV.1 Membrane material
IV.2 Membrane preparation
IV.3 Monomer and solvent characterization
IV.4 Membrane characterization
IV.5 Method
Chapter V. RESULTS
VI.1 Properties of membranes formed in different organic solvents
VI.2 Properties of membranes formed with additives PIP,MPD and EDA
VI.3 Properties and morphology of NF membranes formed at different
temperatures
Chapter VI. DISCUSSTION AND CONCLUSION
REFERENCES

14


REFERENCES
[1] Nordstrom, D.K. Worldwide occurrences of arsenic in groundwater. Science
2002, 296, 2143-2145.
[2] World Health Organization 2018, Arsenic, United Nations, accessed 15th
December 2019, < />[3] Vinit Institute of Technology 2019, Arsenic Pollution in Vietnam, accessed 15th
december 2019. <>.
[4] Lenntech n.d., Chemical properties of arsenic - Health effect of arsetic Environmental effects of arsenic, accessed 15th december 2019,
<>.

[5] Viraraghavan, T., Subramanian, B. S., Aruldoss, J. A., Arsenic in Drinking Water
– Problems and Solutions, Wat. Sci. Tech., 40, 69-76, 1999.
[6] Nina Ricci Nicomel , Karen Leus , Karel Folens , Pascal Van Der Voort and Gijs
Du Laing. (2015). Technologies for Arsenic Removal from Water: Current Status and
Future Perspectives. International Journal of Environmental Research and Public
Health (MDPI), 4-24.
[7] Dejan V. Dimitrovski, Zoran Lj. Bozinovski Kiril T. Lisichkov Stefan V.
Kuvendziev. (2011). Arsenic removal through coagulation and flocculation from
contaminated water in Macedonia. Scientific paper, 58.
[8] Bowen, W. R. and Welfoot, J. S., (2002), Modelling the performance of membrane
nanofiltration—critical assessment and model development, Chemical Engineering
Science, 57, 1121-1137.
[9] Hanane Dach. Comparison of nanofiltration and reverse osmosis processes for a
selective desalination of brackish water feeds. Engineering Sciences [physics].
Université d’Angers, 2008, 26-28, 37-38.
[10] Eriksson, P., (1988), Nanofiltration extends the range of membrane filtration,
Environmental Progress, 7, 58-62.
[11] Conlon, W. J. and McClellan, S.A., (1989), Membrane softening: treatment
process comes of age, Journal. AWWA, 81, 47–51.
[12] Tran Le Hai, Nguyen Thi Nguyen, Mai Thanh Phong. 2019. Synthesis of
polyamide thin film composite nanofiltration membrane for Arsenic removal. science
& Technology Development Journal – Engineering and Technology, 60-66.
[13] S. Veríssimo, K.-V. Peinemann, J. Bordado, (2006), Influence of the diamine
structure on the nanofiltration performance, surface morphology and surface charge of
the composite polyamide membranes, Journal of Membrane Science, 266-274
[14] Asim K. Ghosh, Byeong-Heon Jeong, Xiaofei Huang, Eric M.V. Hoek., (2008),
Impacts of reaction and curing conditions on polyamide composite reverse osmosis
membrane properties, Journal of Membrane Science, 35 – 44.
[15] Duan,M. Wang, Z, Xu, J.,Wang,J.,Wang, S.2010. Influence of hexamethyl
phosphoraminde on polyamide composite reverse osmosis membrane performance.

Separation and Purification Technology. 75, 145-155.
[16] In-Chul Kim, Bo-Reum Jeong, Seong-Joong Kim, Kew-Ho Lee, 2013., Journal
of Membrane Science, 266-274,
15


[17] Shanshan Guan, Shouhai Zhang, Peng Liu, Guozhen Zhang, Xigao Jian, 2014.
Effect of additives on the performance and morphology of sulfonated copoly
(phthalazinone biphenyl ether sulfone) composite nanofiltration membranes, Journal
of Membrane Science, 131-135.

ABBREVIATION
WHO
AFM
ATR-FTIR
BHAC
BPAC
BTAC
CSA
DAP
DAPP
DI
EAP
EDA
MF
MPD
MPDA
NF
PAN
PIP

PSF
RO
SEM
SPPBES
TBP
TEA
TEM
TFC
TMC
TPP
UF

16

World Health Organization
Atomic force microscopy
Attenuated total reflection - fourier-transform infrared
2,2′,4,4′,6,6′-biphenyl hexaacyl chloride
2,3′,4,5′,6-biphenyl pentaacyl chloride
2,4,4′,6-biphenyl tetraacyl chloride
Camphorsulfonic acid
N,N’’ – Diaminopiperazine
1,4-Bis(3-aminopropyl)-piperazine
Deionized
N-(2-Aminoethyl)-piperazine
Ethylenediamine
Microfiltration
m-phenylenediamine
m-phenylenediamine
Nanofiltration

Polyacrylonitrile
Piperazine
Polysulfone
Reverse osmosis
Scanning electron microscopy
Sulfonated copoly (phthalazinone biphenyl ether sulfone)
Tributyl phosphate
Triethylamine
Transmission electron microscopy
Thin-film composite
Trimesoylchloride (TMC)
Triphenyl phosphate
Ultrafiltration


17