RECENT DEVELOPMENT IN MEMBRANE AND ITS INDUSTRIAL APPLICATIONS
Membrane Technology in Oil and Gas Industry
I G. Wenten
Department of Chemical Engineering, Institut Teknologi Bandung
Jl. Ganesha 10 Bandung - Indonesia
The word membrane comes from Latin word, “membrana” that means a skin . Today’s word
”membrane” has been extended to describe a thin flexible sheet or film, acting as a selective boundary
between two phases because of its semi permeable properties. Physically a membrane could be solid or
liquid. Its function is as a separation agent that very selective based on the difference of difusivity
coefficient, electric current or solubility.
Actually membrane has become an integral part of our daily lives. All cells composing living
things, including ours are surrounded with membrane. Biological membranes (membrane cells) are very
selective that transfer only particular species.
Synthetic membrane history began in 1748 when French Abble Nollet demonstrated
semipermeability for the first time, that animal bladder was more semi-permeable to water than to wine.
One century later, Fick published his phenomenological law of diffusion, which we still use today as a first-
order description of diffusion through membranes. He was also the first man to prepare and study artificial
semi permeable membranes. These membranes were made from an ether-alcohol solution of cellulose
called “collodion”. After that many researches were done and many inventions were found such as dialysis,
different permeability of gases at rubber, osmotic pressure, and Donan’s ion equilibrium phenomena.
Sartorius Werke GmbH, Germany manufactured industrial scale membranes, microfiltration
membranes, for the first time in 1950. Before that, membranes were developed in small scale for laboratory
applications . However, the most fundamental breakthrough in membrane technology came in late 1950s
when Loeb and Sourirajan discovered very thin membrane for reverse osmosis, the asymmetric
Nowadays membrane applications spread over various industries: metal industries (metal
recovery, pollution control, air enriching for combustion), food and biotechnology industries (separation,
purification, sterilization and byproduct recovery), leather and textile industries (sensible heat recovery,
pollution control and chemicals recovery) . Other industries that also use membrane technology are pulp
and paper industries (replacing evaporation process, pollution control, fiber and chemicals recovery), and
chemical process industries (organic material separation, gas separation, recovery and recycle chemicals).
Medical sector including health-pharmaceutical-and medical industries (artificial organs, control release
(pharmaceutical), blood fractionation, sterilization and water purification), and waste treatment (separation
of salt or other minerals and deionization).
Generally, there are several processes to synthesize membrane, some of them are sintering,
stretching, track-etching, phase inversion, and coating. There are several ways to classify membranes.
Based on their materials, membranes are classified as polymeric membrane, liquid membrane, solid
(ceramics) membrane and ion exchange membrane. Based on their configuration, membranes are classified
as flat (sheet) membrane, spiral wound, tubular, and emulsion. Based on what they do and how they
perform, membranes are classified as fine filtration (microfiltration/MF, ultrafiltration/UF,
nanofiltration/NF, and reverse osmosis/RO), dialysis, electrodialysis (ED), gas separation (GS), carried-
mediated transport, control release, membrane electrode, and pervaporation (PV).
II. MEMBRANE PROCESSES
Membrane processes discussed in this paper are classified based on various driving forces, some
use pressure difference (microfiltration, ultrafiltration, reverse osmosis, and piezodialysis), while others use
other driving forces such as concentration difference (gas separation, pervaporation, liquid membrane and
dialysis), thermal (membrane distillation, thermo osmosis) and electric (electrodialysis).
The principal advantages of membrane processes compared to other separation processes are low
energy consumption, simplicity and environmentally friendliness. Membrane-based separation is a result of
different rate of transfer between each substance in membrane and not a result of phase equilibrium or
mechanically based separation. Therefore, there is no need to add additive material such as extractor and
adsorber to proceed the separation. Then we can say that membrane technology is “clean technology”, in
which no additive materials, which may be potential pollutants, are needed.
One of the major advantages of membrane technology is low energy consumption. As discussed
elsewhere in this paper, membrane-based separation is not a result of phase equilibrium that takes a lot of
energy to achieve and maintain. It also means that the process could be done in normal conditions where no
phase change occurs. Phase change may affect the quality of materials and products. Therefore, membrane
technology is suitable for the pharmaceutical, biochemical and food industries.
Designs of membrane module are very simple, compact and easy-to-use. In addition, not much
auxiliary equipment is needed. There is a unique phenomenon in membrane where the scale of process and
operating costs are related proportionally. This phenomenon may be caused by the modular-nature of
membrane. This nature distinguishes membrane processes from other processes such as distillation, in
which an increase in the process scale is followed by a decrease in cost until economical condition is
reached. Not only in cost spent, but also in operating condition. Adding several modules including its
auxiliary to existing system can do scaling up membrane processes.
Besides the advantages described above, membrane processes also posses several disadvantages,
such as flux optimization and selectivity, material sensitivity, fouling and dependability. Until now there
have been several studies conducted to overcome the disadvantages and drawbacks in membrane processes.
Flux and selectivity problems arise as an increase in flux is usually followed by a decrease in
selectivity, while we aim at increasing both. Therefore membrane processes are suitable for very selective
separation in which flux is not concerned such as that carried out in pharmaceutical industries.
The dependability problems arise as the characteristics of membrane differ from each other. It is
due to the different characteristics of each membrane that a direct scale up of membrane processes is
virtually impossible. Before a process is applied in an industrial scale, it is suggested to have a laboratory
assessment of the membrane. In this way we may have better prediction on process performance.
Other major problems are material sensitivity and fouling. Polymeric membranes have limited
stability (chemically, physically, and biologically), which restrict the conditions of membrane processes
applied. Nowadays, there are efforts to invent materials, which may overcome these constraints. Fouling
causes a decline in performance of membrane processes, in which flux (performance) is very high initially
but then decline drastically as materials of foulant accumulate on membrane surface. Solutions to the
problem may lie in the hydrodynamic of the process and pretreatment processes.
III. MEMBRANE INDUSTRY AND MARKET POTENTIAL
Membrane-based market industry covers the membrane itself and its module, including additional
equipment and the systems. Commercial success is one of indicator showing the important role played by
membrane technology in various applications. The benefits in membrane process applications include
reduced operating costs relative to competitive technology, saving of product, recovery of by products,
savings of water, energy, chemical, etc. In effluent reduction applications, savings in transport and disposal
cost become important. Membranes and membrane processes are used in four main areas, which are, in the
separation of molecular and particulate mixtures, in the controlled release of active agents, in membrane
reactors and artificial organs, and in energy storage and conversion systems. Membrane has become a multi
billion-dollar business and still growing fast. The worldwide membrane market in 1998 particularly in sales
of membrane and modules reached more than 4 billion USD. While sales of membrane system reached
more than 15 billion USD . The annual sales of membrane and modules for various membrane processes
were increased over the years and reached a value of approximately 4500 million USD in 1998 [4, 5].
From the applications view, approximately 40% of membrane sales are destined for water and
wastewater applications, while food and beverage processing combined with pharmaceuticals and medical
applications account for another 40% of sales and the use of membranes in chemical and industrial gas
production is growing . The total membrane market is unevenly distributed, 75% of the market share
belongs to USA, Japan and Western Europe . The development of membrane market is determined by
energy costs, required product quality, environmental protection needs, new medical therapies, and the
availability of new and better membranes and membrane processes .
Some applications of membrane processes, such as water desalination or wastewater treatment,
have high industrial relevance. However, in these applications the membrane processes compete with
conventional water desalination or water treatment techniques, such as multistage flash evaporation or
biological sewage treatment plants. In other applications of high commercial relevance, such as in
hemodialysis or in fuel cells, membranes are key components, and no economic alternative technique that
could compete with membrane is currently available. There are other applications, such as the production
of ultrapure water, where membrane processes compete with conventional techniques, but have a clear
advantage. There are also a large number of membrane applications of lower industrial relevance, such as
the dehydration of organic solvents by pervaporation or the recovery of organic vapors from waste air
streams by gas and vapor permeation membranes. In certain biosensors and diagnostic devices, membranes
are key components, but in terms of the total costs of the final device, the cost of the membranes in these
devices is negligibly low. Therefore, this application is often of lesser interest to the membrane producing
industry . As the membrane market has grown, the scale of membrane facilities has become more
ambitious. The first UF facility for potable water treatment, inaugurated in 1988 at Aubergenville, France,
had a design capacity of 160 m3/day. Today, facilities’ exceeding 100,000 m3/day is being planned .
In spite of impressive sales and growth rate of the industry, the use of membranes in industrial-
scale separation process is not without technical and economic problems. Technical problems are related to
insufficient membrane selectivities, relatively poor transmembrane fluxes, general process operating
problems, and lack application know-how. Economic problem originate from the multitude of different
membrane products and processes with very different price structure in a wide range of applications, which
are distributed by a great number of sales companies, very often as individual products .
In future, the largest market for membrane will continue to be water treatment, with sales to
manufactures of consumer water purification equipment becoming more important. The primary group of
customers (electric utilities, industrial water users and municipal water works) will continue to dominate
demand in this sector, but this segment is rapidly maturing and sales are increasingly dependent upon
replacements for existing systems. In addition, as both the physical and chemical means of cleaning
membranes continue to improve, the average life span of the membranes is lengthening, thus reducing
replacement sales .
IV. MODULE AND SYSTEM DESIGN
Membranes can be fabricated essentially in one of two forms: tubular or flat sheet. Membranes of
these designs are normally produced on a porous substrate material. The single operational unit into which
membranes are engineered for use is referred to as a module. This operational unit consists of the
membranes, pressure support structures, feed inlet, concentrate outlet ports, and permeate draw-off points.
Two major types of membranes modules can be found in the market, i.e., hollow fibers (capillary), and
spiral wound (Fig. 1). Other modules are plate and frame, tubular, rotary modules, vibrating modules, and
Fig. 1. Major types of membrane modules: (a) spiral wound and (b) hollow fiber
Each type of modules have its particular characteristics based on its packing density, ease of
cleaning, cost of module, pressure drop, hold up volume and quality of pre-treatment required. Hollow fiber
module has the highest packing density compare with other types of modules, including the easiest to clean
and relatively cost competitive as well as spiral wound module. Based on pressure drop, the tubular module
and rotating disc/cylinder have the lowest pressure drop compare with others. Hold up volume of hollow
fiber module is the highest, followed by plate and frame, spiral wound, tubular, and rotating disc/cylinder
module. Requirement of pre-treatment is lowest in tubular and rotating disc/cylinder modules .
Ultrafiltration membranes can be made from both organic (polymer) and inorganic materials.
There are several polymers and other materials used for the manufacture of UF membrane. The choice of a
given polymer as a membrane material is based on very specific properties such as molecular weight, chain
flexibility, chain interaction, etc. Some of these materials are polysulfone, polyethersulfone, sulfonated
polysulfone, polyvinylidene fluoride, polyacrylonitrile, cellulosics, polyimide, polyetherimide, aliphatic
polyamides, and polyetherketone. Inorganic materials have also been used such as alumina and zirconia
. The structure of UF membrane can be symmetric or asymmetric. The thickness of symmetric
membran (porous or nonporous) is range from 10 to 200 m. The resistance to mass transfer is determined
by the total membrane thickness. A decrease in membrane thickness results in an increased permeation rate.
Ultrafiltration membranes have an asymmetric structure, which consist of very dense toplayer or skin with
thickness of 0.1 to 0.5 m supported by a porous sublayer with a thickness of about 50 to 150 m. These
membranes combine the high selectivity of a dense membrane with the high permeation rate of a very thin
membrane. The resistance to mass transfer is determined largely or completely by thin toplayer.
In porous membranes, the dimension of the pore mainly determines the separation characteristics.
The type of membrane material is important for chemical, thermal, and mechanical stability but not for flux
and rejection. Therefore, the aim of membrane preparation is to modify the material by means of an
appropriate technique to obtain a membrane structure with morphology suitable for a specific separation.
The most important techniques are sintering, stretching, track-etching, phase-inversion, sol-gel process,
vapour deposition, and solution coating. Characterisation method of porous membranes can be performed
based on structure-related parameters (determination of pore size, pore size distribution, top layer
thickness, surface porosity) and permeation-related parameters (cut-off measurements) . The molecular
weight cut-off (MWCO) is a specification used by membrane suppliers to describe the retention capabilities
of UF membrane, and it refers to the molecular mass of a macrosolute (typically polyethylene glycol,
dextran, protein) for which the membrane has a retention capability greater than 90%. The MWCO can
therefore be regarded as a measure of membrane pore dimensions .
Current membrane systems are typically modular with high packing density. Most are suitable for
scale-up to larger dimensions. A broad range of membrane devices, useful for small-scale separation in the
laboratory or large industrial-scale operation, is available . Full-scale membrane facilities comprise
series/parallel modules and operate according to various modes, range from intermittent single-stage
system to the continuous multistage system .
Operation of membrane can be performed in two different service modes, i.e., dead-end flow and
cross-flow. The dead-end flow mode of operation is similar to that of a cartridge filter where there is only a
feed flow and filtrate flow. The dead-end flow approach typically allows optimal recovery of feed water on
the 95 to 98% range, but is typically limited to feed streams of low suspended solids (<1 NTU). The cross-
flow mode different with dead-end mode in which there is an additional flow aside from feed flow and
filtrate flow (permeate), i.e., the concentrate. The cross-flow mode of operation typically results in lower
recovery of feed water, i.e., 90 to 95% range .
Nowadays, full-scale membrane elements are designed in a number of ways to optimise membrane
area to element size. The design of facilities has also been optimised with the increasing plant capacities.
Individual units (skids mounted units) are usually used for small plant capacities whereas for larger plant
capacities (10,000 m3/d and above) racks with ancillary equipment designed. Today, racks comprised of up
to 48 membrane modules are being constructed and additional scale-up savings are therefore observed .
Example of typical large scale UF plant is shown in Fig. 2.
Flux decline has a negative influence on the economics of a given membrane operation. Flux
decline usually attributed to fouling phenomenon. Consequently, the modules must be cleaned periodically.
Membrane cleaning is the removal of foreign material from the surface and body of the membrane and
associated equipment to reduce fouling to some extent. The frequency of cleaning is a critical economic
factor, since it has a profound effect on the operating life of a membrane. Cleaning and sanitizing
membranes is desirable for several reasons, that is, laws and regulations may demand it in certain
applications (e.g., the food and biotechnological industries), reduction of microorganisms to prevent
contamination of the product stream, and process optimisation. A clean membrane can be defined in three
terms according to Cheryan , i.e., physically clean membrane, chemically clean membrane, and
biologically clean membrane. Flux recovery to initial flux of a new membrane after cleaning can be used as
indication of clean membrane.
Four cleaning methods can be distinguished, i.e., hydraulic cleaning, mechanical cleaning,
chemical cleaning, and electrical cleaning. The choice of cleaning method mainly depends on the module
configuration, the type of membranes, the chemical resistance of the membrane and the type of foulant
Hydraulic cleaning methods include back flushing, alternate pressurising and depressurising and
by changing the flow direction at a given frequency. In bacfkflush technique, the direction of the permeate
flow through the membrane is periodically reversed. However, backflushing also reduces the effective
operation time, and gives a loss of permeate to the feed solution. The impact of backflushing in industrial
application is very limited, because of its fundamental limitation, i.e. loss of permeate and operation time,
therefore the backflush process needs adequate optimisation. The backflush process is optimized both for
the duration of the backflush and for the backflush interval. The improvement of the product rate upon
backflushing is mainly a function of the backflush pressure and the interval between two backflushes.
Recently, the time interval of back flushing has been reduced to seconds which implies that the cake
resistance remains low since it has no time to built up a layer. A novel backflush technique with a high
frequency and extremely short duration times has been introduced. It was found that extremely good results
could be obtained using very short backflush time (typically 0.06 second) with an interval time of
maximum 5 seconds, preferably 1 to 3 seconds. Since the effective backflush time is very short and the
backflush pressure is relatively high (typically 1 bar over the feed pressure) the name “backshock” is
introduced. The loss of permeate during backshocking is very low and hardly affects the net permeate flow.
The backshock technique in combination with the use of reversed asymmetric membrane structures allows
filtration at extremely low crossflow velocities with very stable permeate fluxes. Very frequent backshock
prevents the membrane from definitive clogging, and enables a filtration process with an extremely stable
flux level .
Mechanical cleaning using oversized sponge balls can only be applied in tubular systems. Several
researchers are developing other mechanical cleaning using ultrasonic wave. Chemical cleaning is the most
important method for reducing fouling, with a number of chemicals being used separately or in
combination. The concentration of the chemical and the cleaning time are also very important relative to
the chemical resistance of the membrane. Electrical cleaning is a very special method of cleaning. By
applying an electric field across a membrane, charged particles or molecules will migrate in the direction of
the electric field. Electrical cleaning can be applied without interrupting the process and the electric field is
applied at certain time intervals .
Fig. 2. Example of typical large scale UF plant
V. EMERGING PROCESSES (Strathmann 2001, )
Development of improved membranes and membrane materials Significant progress has been
made during recent years in the development of new membranes and their applications. New inorganic and
organic materials, super molecular structures with specific binding properties, are used as membrane
materials. For the separation of gases, especially oxygen/nitrogen and methane/carbon dioxide, new glassy
polymers and inorganic materials such as zeolites are used to produce membranes with better selectivity
and higher fluxes. For the separation of enantiomers, carrier-facilitated transport membranes are produced
using molecular imprint techniques. In reverse osmosis, membranes with better chemical stability and
higher fluxes are now available. Surface-modified membranes with better compatibility and affinity
membranes for the removal of endotoxins or other toxic components from blood may soon be available.
The recent development in membrane technology have been assisted by new research tools, such as atomic
force microscopy, acoustic time-domain reflectometry, molecular dynamic simulations, and computer-
aided process design.
High-Performance Reverse-Osmosis Membranes The Nitto Denko Corporation developed the
progress that has been made in improving reverse-osmosis seawater desalination membranes during the last
20 years, which shows the salt rejection in excess of 99.5% and the water flux of various membranes by a
factor of 3. The reason for this significant progress is based on the preparation technique of the barrier layer
of the composite membrane, which has many folds, with the result, that the surface of the actual barrier
layer is about three times larger than the area of the support structure.
Stabilization of Supported Liquid Membranes One of the shortcomings of today’s supported
liquid membranes is their short useful life. In thin membranes the solvent or carrier can be lost within
several hours, which makes the membrane useless. The stability of liquid membranes can be increased
drastically up to 1000 hours by placing a thin polymer layer on top of the liquid membrane.
Preparation of Composite Hollow Fiber by the Triple-Nozzle Spinneret Asymmetric hollow fiber
or capillary membranes with a denser skin on the in- or outside of the fibers are generally made by a phase-
inversion process. Dip-coating process is mostly used to produce composite hollow fiber membrane
although it require additional production step. A triple-nozzle spinneret was developed for the preparation
of composite hollow-fiber membranes. The main advantage of composite hollow fibers made in one step
with the triple-nozzle spinneret compared to those made by dip-coating is a simplified production process
because it can be done in a single production step. Generally, higher fluxes are also obtained in the single-
step production, since pore penetration, which is often a problem with dip-coating, is avoided.
Inorganic Membranes for Gas and Vapor Separation with High Selectivity Historically,
inorganic membranes are produced by a slip-coating and sintering procedure based on metal oxides such as
-Al2O3. These membranes can be considered as state-of-the-art structures and are used today in micro-and
ultrafiltration. An interesting recent development is the preparation of zeolite membranes. Because of the
unique properties of zeolite crystals such as molecular sieving, ion exchange, selective adsorption, and
catalysis, these membranes have a large number of potential applications in gas and vapor separation and in
membrane reactors and chemical sensors. Dense inorganic membranes based on palladium and palladium
alloys have been used for many years for the selective transport of hydrogen. However, their large-scale
industrial applications are limited due to high price of the metal. Dense ceramic membranes based on
perovskites exhibit high mixed electronic and oxygen ion conductivity, and are widely studied for
applications in solid oxide fuel cells, oxygen sensors, and membrane reactors. An increasingly important
research area is related to nanoporous ceramic membranes with well-defined pore structures prepared by
template-assisted, self-assembling methods. Furthermore, an increasing amount of research effort is
concentrated on the development of proton-conducting membranes for high-temperature applications in
fuel cells and membrane reactors.
Development of improved membrane modules The overall performance of the state-of-the art
membrane modules, such as the plate-and-frame, the spiral-wound, and the hollow-fiber and capillary
membrane modules has been improved gradually over recent years, and production costs have been
reduced significantly. However only very few completely new module concepts have been developed. Two
exceptions are the so-called transversal flow capillary membrane module and the spiral-type tubular
module. The transversal flow module is used mainly in dialysis. The characteristics of these modules are
straight membrane capillaries and axial flow through the fiber lumen and the shell. In spite of the poor flow
distribution, and thus mass transfer, at the shell-side membrane surface, this type of module is preferred
because of its high packing density and low production costs. Spiral-type tubular membrane module
involves flow around a curved tube at a sufficiently high velocity so as to produce centrifugal instabilities
and secondary flow from the membrane surface to the center of the tube, and results in a substantial
increase in flux. However, higher production costs and poor performance of the spiral-type membrane
modules have so far limited any large-scale industrial applications.
Development of novel membrane processes and applications New membrane processes that give
a large breakthrough in its applications are demineralization by electrodeionization technique, new
application in biomedical, and application in fuel cell. Actually, a significant development has been made
in another process, for example, in controlling waste gas emission by membrane contactor and membrane
reactor, for both chemical as well as biological conversion. Development in membrane reactor for
dehydrogenating reaction, esterification, and enzymatic reaction, seem very prospective that has been
developed for a long time, however, until today its industrial application has not been seen yet. It is the
same as membrane contactor for emission control. Typical study and empirical data show a large potential
of this process; however, its application has not also been seen yet.
Electrodeionization and the Use of Bipolar Membranes Electrodeionization are used for the
production of deionized water of high quality by combining conventional ion-exchange techniques with
electrodialysis. The process can be operated continuously without chemical regeneration of the ion-
exchange resin. The only disadvantage of the process is the relatively poor current utilization. Bipolar
membranes are used today in combination with regular ion-exchange membranes for the production of acid
and bases from the corresponding salts in a process referred to as electrodialytic water dissociation. A
bipolar membrane consisting of a cation- and an anion-exchange layer arranged in parallel between two
electrodes. As in electrodialysis, up to 100 cell units can be stacked between two electrodes. Electrodialytic
water dissociation is a very energy efficient way. However, there are still severe problems, such as salt
leakage into the products and low current utilization at high concentrations of the acid and bases.
Membrane contactors In membrane contactors the membrane functions as a barrier between two
phases that avoids mixing but does not control the transport rate of different components between the
phases. The membrane pores are sufficiently small so that capillary forces prevent direct mixing of the two
phases. A key advantage of membrane contactors is a large mass-transfer area in a relatively small device.
A typical large-scale application of a liquid/gas contactor is the removal or delivery of dissolved gases from
or to a liquid, for example, the blood oxygenation during open-heat surgery, the removal of oxygen during
the production of ultrapure water, and the separation of olefin/paraffin gas mixtures.
Membrane reactors A membrane reactor is a device that utilizes the properties of a membrane to
improve the efficiency of chemical or biochemical reactions. Various forms of membrane reactors are
applied mainly in catalytic and enzymatic reactions. In the simplest form of a membrane reactor the
membrane is used as a contactor that separates the catalyst from the reaction medium. The membrane
merely provides a large exchange area between the catalyst and the reaction medium, but performs no
separation function. It is often used in cell culture and fermentation processes such as enzymatic hydrolysis
[17-19] the enzymatic degradation of pectin in fruit juice. In the second type of membrane reactor the
membrane shows the selective mass-transport properties, and is used to shift the equilibrium of a chemical
reaction by selectivity removing the reaction products, for example, in dehydrogenation or oxygenation
reactions such as the dehydrogenation of n-butane. The third type of membrane reactor combines the
membrane contactor and separation function, such as in enzyme catalyzed deesterification reactions.
Membranes for Fuel Cells / Electrolysis  One breakthrough in the application of ionic
conducting polymer membranes is the proton exchange membrane fuel cell, a device that converts chemical
energy directly into electrical energy without burning. As the electrochemical combination of hydrogen
(the fuel) and oxygen produce water, the fuel cell is environmentally clean and is expected to replace the
gasoline engine or rechargeable battery in the automobiles.
Synthetic Membranes in Medical Applications Biomedical applications are by far the most
relevant use of synthetic membranes. Membranes are used in medical devices such as hemodialysers, blood
oxygenators, and controlled drug- delivery system. There is, however, a substantial effort focused on the
development of the membrane for the next generation of artificial organs, such as the artificial liver or
artificial pancreas. In this device, as in other novel vehicles for the delivery of cell and gene therapy,
synthetic membranes are combined with living cells to form so-called biohybrid organs.
VI. BREAKTHROUGH IN INDUSTRIAL APPLICATION
Membrane processes cover a wide-range of application from (waste) water treatment to medical
application. For some application, membranes play an important role in which other technologies are not
capable such as in medical sector (hemodialysis) and energy sector (fuel cell). Table 1 showed a list of
selected industrial applications of membrane processes.
Table 1. Selected Industrial Applications of Membrane Processes [11, 20, 21]
NF, UF, RO
RO, ED, EDI
MF, NF, RO, ED
UF, RO, ED
Fruit and vegetables
UF, RO, ED, MF, NF
MF, UF, RO
Wine and brewery
MF, UF, RO, PV
MF, UF, NF
Concentration of fermentation broth
Proton exchange membrane
From Table 1, it can be seen that pressure-driven membrane processes dominate the application
rather than other driving-force membrane processes. Yet, it doesn’t mean that other driving-force
membrane processes are not having part in industrial sectors. GS (gas separation) and PV (pervaporation),
which are concentration-driven membrane process, are used in chemical industry sector for gas separation
and vapor-liquid separation. In USA and EU, the most important sector that using membrane technology is
food industry especially dairy sector. Membranes are used for desalting and concentration of whey, and
also for conversion of milk into cheese and preparation of egg white and egg yolk. Fruit and vegetable
processing also utilized membrane technology resulted in high energy saving. Beverage industry also an
important sectors to apply membrane process particularly for separation of alcohol from beer. In sugar
sector, membranes are used in almost 20% of the potential application in Netherlands . In chemical
industry, beside listed in table above, electro-coat paint recovery still the biggest industry sector that
utilizes membrane-based processes particularly UF. Other sector that predominant for UF application is
pure water supply for semiconductor industry. High-demand for ultra-high purity chemicals in same
industry also fulfilled by the availability of chemical-resistant membrane. In biotechnology, purification of
enzyme can be accomplished using UF. In medical sector, membranes play a key role particularly in
hemodialysis and control release process. Water-oil separation now also become a potential application for
UF especially in metal cleaning and wool scouring processes .
Membrane technology also makes a breakthrough in water treatment. A revolutionary water
treatment process was accomplished by corporate membrane into the treatment process resulting in high
effluent quality. Water treatment has become an important issue regarding to the fact of the scarcity of
clean water sources. A huge supply of water that covers the earth in form of ocean can not fulfilled the
needs of water readily considering conventional desalination process that must be done before it can be
used as potable water. Desalination with distillation process popular in 1970's is not attractive anymore
because of its high capital cost and wide space demand. In area with high minerals content, distillation
process are also susceptible to corrosion.
Conventional water treatments are not capable in producing potable water that fulfilled the
requirement of water quality standard that becoming more stringent nowadays. An advanced water
treatment like ozonation and activated carbon can improve water quality but in other hand add in a
difficulty in operation and cost. Membrane technology offering one or two simple steps to overcome it.
Membrane as highly selective layer is capable to separate microorganisms' pathogen completely.
Membranes are also capable of reducing hardness, controlling color, and removing inorganic and organic
compounds. Four membrane processes have direct application for potable water treatments are RO, NF,
UF, and MF. These pressure-driven processes differ in the size of the membrane pores, types of
constituents removed, and the way removal is achieved . Water with low quality is acceptable to be
processed by membrane. In space demand, membrane processes require a smaller space compared with
conventional technology. A number of examples from well-known and emerging application of membrane
processes in the drinking water industry are desalination using RO, softening using NF, and production of
drinking water from surface water, backwash water and nitrate removal using ED .
The development of membrane science and technology offers various membrane materials.
Membrane for potable water production commonly made from organic polymer  but ceramic materials
also can be used . PVDF (polyvinylidenefluoride) as one of fluorocarbon material is suitable to use as
membrane-produce potable water because of its resistance against various oxidants [24, 27, 28]. PVDF
membrane is a hydrophobic membrane and can easily integrate with other technology i.e. pulsed UV light,
chlorine dioxide, etc. These integrated systems economically fulfilled the SWTR (Surface Water Treatment
Rule) and DBP (Disinfection By Product) regulations .
Modules configuration mostly used are spiral wound and hollow fiber. HFMF (hollow fiber
microfiltration) can be used to produce potable water for small community (300,000-gph equivalent to
3000 peoples). Nowadays, HFMF become Best Available Technology (BAT) to supply small community
by treated surface water / ground water resulted in accomplishment of requirement stated by SWDA (Safe
Water Drinking Act). HFMF can operate with dead-end mode or some degree circulation. For surface water
treatment, it can achieve a flux range 35-50 gallon per feet quadrate per day . In various treated water,
MF PVDF 0,1 micron with outside-in configuration can achieved flux of 75 gph  with 0.3 bar pressure
operation for clean membrane and 2 bar for fouled-membrane. High quality, less than 0.05 NTU drinking
water can be assured by intact MF membranes, which essentially remove 100% of Cryptosporidium and
Giardia and exceed SWTR log removal requirements .
MF and UF started to be used for water treatment since 1980s. Applications of MF and UF as
low-pressure membrane process begin to increase rapidly in 1994. This is caused by the lowering cost of
processes and also a decrease in energy consumption, which can be attained to less than 1 kwh/m3 for 1-10
bar operation pressure . Before the year 1994, the capacities of all MF and UF factories are less than 3
million gallon per day. Nowadays with the growing of understanding and the availability of the technology,
a new facility of membrane with capacity 2 – 10 million gallon per day is being built in US . RO and
ED now become the chosen methods for desalting seawater to produce potable water. RO particularly have
emerged as an effective solution to transform saline, brackish, and contaminated water into usable and/or
potable product . In 1988, 49,4% of total desalination factories worldwide is using RO . Seawater
desalination processes for drinking water purposes is widely practiced in Middle East and claimed to be 2/3
of desalting capacity in the world. However, the largest plant of RO is located in Yuma, Arizona with the
capacity of 660 million gpd followed by a plant in Saudi Arabian . RO plants installed in Bahrain
desalinates highly brackish water, although the cost is relatively high compared with the cost of treating
fresh water by conventional means, it is certainly an economically feasible alternative to transporting water
over long distance .
Technology for wastewater treatment that might provide several advantages compared with
conventional biological process alone is membrane bioreactor. Membrane bioreactor (MBR) can be defined
as the combination of two basic processes, biological degradation and membrane separation. Biological
process commonly used for wastewater treatment combined with membrane process is activated sludge
process. Currently, the majority of installed MBR system are being used for the treatment of wastewater
from the automotive, cosmetic, metal fabrication, food and beverage processing, landfill leachate, and other
industries . MBR can be categorized into three types that are MBR for biomass separation, MBR for
aeration, and MBR for pollutants extraction. Submerged membrane bioreactor for biomass separation is a
breakthrough in membrane bioreactor field for industrial wastewater treatment that for the first time was
introduced by Yamamoto (1989). The submerged MBR system should be distinguished from other MBR
system, in this system membrane is installed inside biological reactor. The driving force for submerged
MBR is the pressure gradient that limits the pressure until 1 atm. This pressure gradient can be applied only
by a suction pump. Energy consumption is low because there is no re-circulation pump. Study which was
done by Yamamoto have succeed to treat waste water with an aerobic system and stable flux of about 0.1
kg COD/kg MLSS.day F/M ratio, critical organic loading from 3 to 4 kg COD/m3.day and a very low
power consumption of about 0.007 kWh/m3.day. In the same manner as the other membrane bioreactor
processes is compared to conventional biological process, this technology have a main advantage in high-
quality effluents (BOD/TSS< 5 ppm), disinfected, a very low excess sludge production, high
biodegradation efficiency and a relatively small place necessity. Therefore, in the future, this technology
has a large potential to be applied in several water and waste water treatment. The key of this technology is
to overcome washout biomass (that to be a problem in conventional process), because in MBR, hydraulic
retention time (HRT) and sludge retention time (SRT) are independent.
In the way of using MBR for water reuse, the application can be seen in several developed
countries such as in Japan and USA. The factor that makes MBR become an attractive alternative is the
superiority of this technology in producing a very low excess sludge or even zero sludge production and it
has been properly proven. The membrane bioreactor process is probably the best technology for water
recycling inside buildings requiring compact system and excellent water quality. Two different systems are
experiencing large commercial success: UBIS in Japan  and Cycle-let in the United States (Irwin,
1989,1990). The Ultra Biological System (UBIS) is a membrane bioreactor system where aerobic-activated
sludge reactor combined with membrane unit. This UBIS system is installed in more than 40 buildings and
produces more than 5000 m3/day . The Cycle-let is also a membrane bioreactor system, which is based
on the combination of a two-phase biological treatment system (anoxic and oxic) with tubular organic
membranes. Activated carbon for color removal and ozone for disinfection are used to finish and improve
the water quality. Today, the Cycle-let is installed in more than 30 installations in USA. Wastewater
treatment and recycling in apartment buildings is also performed in Europe, where the Lyonnaise des Eaux
group developed an MBR process using a ceramic tubular-type membrane. In Japan, the population relies
on three domestic wastewater treatment categories: public sewage, on-site treatment tanks, and collected
human excreta treatment system, which is also called the “night-soil” treatment system (Magara and Itoh,
1991). Magara et al. (1994) reported that there are about 1200 night-soil treatment system across Japan that
treat more than 42 million population equivalents of night soil and 30 million population equivalent of on-
site treatment tank sludge. The technology of membrane bioreactor can treat this high concentration
effluent. Several pilot studies have been reported and at least six full-scale plants are under operation with
the Activated Sludge and Membrane CompleX System (AMEX) technology [5, 32].
EDI (electrodeionization) is a continuous chemical-free deionization process that relies on the
same fundamental principle as for mixed-bed ion exchange . An EDI stack consists of diluted
compartments concentrated compartments and electrode compartments. The diluted compartments are
filled with mixed-bed ion-exchange resins, which enhance the transport toward the ion-exchange
membranes under the force of a direct current. The later configuration, both diluted compartments and
concentrated compartments are filled with mixed-bed ion-exchange resins. Since the concentration of ions
is reduced in the diluted compartment and is increased in the concentrated compartment, the process can be
used for either purification or concentration.
The concept of EDI process has been extensively recognized since the mid-1950s. Walters et al
(1955) investigated a batch EDI process for concentrating radioactive aqueous wastes, based on electrolytic
regeneration of ion-exchange resins, and proposed an ionic conduction mechanism through mixed-bed ion-
exchange resins in contact with dilute solution. In the late 1950s and early 1960s, Glueckauf (1959)
investigated theory, design, and operating parameters of the EDI process. The proposed theoretical model
involved the diffusive transfer from the flowing solution to the ion-exchange resin beads combined with the
electrolytic transfer of ions along the chain of ion-exchange beads. Sammons and Watts (1960) evaluated
multi-cell EDI module and quantified the relationships among solution concentration, flow rate and applied
An extended investigation of operating conditions and performance of the EDI process has been
conducted by Matejka (1971) for high-purity water production from brackish or tap water. Several
researchers were also actively studying EDI process [34-38]. During this time, numerous patents were
granted for various types of EDI device and its applications [39-44].
Millipore introduced the first commercially available module and component systems in 1987
under the trade name Ionpure CDI . There are presently two sizes of EDI modules available from U.S.
Filter. So-called "industrial" module can have 30-240 diluting compartments and are capable of flow rates
of 2.0-64.0 gpm (0.45-14.5 m3/h). The smaller versions, "compact" EDI modules, typically have 10-40
diluted compartments and are capable of flow rates of 0.5-4.0 gpm (0.1-0.9 m3/h). U.S. Filter is dominant
manufacturer of industrial size EDI. Millipore Corporation fabricates low-flow EDI device (under trade
name Elix) for laboratory water purification applications. Recently, other companies (Christ Ltd.,
Electropure Inc., Elga Ltd., Glegg Water Conditioning, Ionics Inc., and Osmonic Inc.) have begun to offer
EDI units. Because of inherent process limitations, the EDI process may be not competitive with
conventional technologies. These limitations include: (1) A mixed-bed ion-exchange resins in stack
compartments is a good filter media; (2) Anion-exchange resin tends to adsorb negative charged-colloids;
(3) Precipitation of inorganic components occur at high pH regions; (4) Quaternary amine is converted into
tertiary amine or unionized group; (5) Channeling due to the stack design is not proper. In addition, the
technology is labor intensive to assemble and requires a multitude of thin compartments. The inability to
produce excellent ion-exchange membranes results in the loss of electrical efficiency.
The limited success in overcoming the challenges mentioned above has been reported. New
membranes have been developed but are not cost effective. Hence, carefully pressure control is much more
effective to minimize electrical efficiency loss due to convective transport across ion-exchange membranes.
In order to reduce scale formation, Tessier et al  proposed the addition of scaling agent into concentrate
and electrode rinse in the concentration range of 1 to 40 ppm. Special techniques for introducing and
removing ion-exchange resins and other particulates from an assembled EDI stack to reduce labor cost also
have been patented by Parsi et al., 1993 .
Since the initial commercialization in 1987, EDI systems have been applied worldwide to meet the
need of high purity water, such as in pharmaceuticals, semiconductors, power, and high quality optics
industries. Limited ability of existing technology to reduce especially the need of high water production
cost effectively and environment friendly offers a significant market opportunity for the commercialization
of EDI systems.
Although EDI is mainly applied to ultrapure water production, it is increasingly used in a wide
variety of applications. Some systems have been installed for wastewater treatment [47, 48]. There may
also be EDI applications for starch processing , recovery of citric acid from fermentation broth [50, 51].
Millipore Corporation has continued to apply EDI to specialty separations in the pharmaceutical industry.
VII. THE BACKSHOCK PROCESS
The performance of membrane in crossflow membrane filtration is strongly influenced by the
build up of a fouling layer that finally may completely plug the porous membrane surface. Jonsson and
Wenten  showed that for MF membranes, the pore blocking type of membrane fouling is by far the
most predominant. Two approaches have mainly used to increase the fluxes in MF: applying high
crossflow velocities (2-6 m/s) and, the use of backflush technique. In bacfkflush technique, the direction of
the permeate flow through the membrane is periodically reversed. However, high velocities are energy
demanding, and give problems with too high-pressure losses in the membrane modules; backflushing also
reduces the effective operation time, and gives a loss of permeate to the feed solution.
Very short backflush intervals were reported by APV passilac where the backflush duration is 1-5
seconds, and they are performed 1-10 times per minute at a pressure difference of 1-10 bar. This generally
means that backflushing accounts for about 10-20% of the total operation time, by which the product flux
may improve up to 100%; however, the negative flux during backflushing has to be taken into account.
Since the impact of backflushing in industrial application is very limited, because of its fundamental
limitation, i.e. loss of permeate and operation time, the backflush process needs adequate optimisation.
The backflush process is optimized both for the duration of the backflush and for the backflush
interval. The improvement of the product rate upon backflushing is mainly a function of the backflush
pressure and the interval between two backflushes. A novel backflush technique with a high frequency and
extremely short duration times has been introduced [16, 53-57]. It was found that extremely good results
could be obtained using very short backflush time (typically 0.06 second) with an interval time of
maximum 5 seconds, preferably 1 to 3 seconds. Since the effective backflush time is very short and the
backflush pressure is relatively high (typically 1 bar over the feed pressure) the name “backshock” is
introduced. The loss of permeate during backshocking is very low and hardly affects the net permeate flow.
The novel backflush technique known as backshock technique in combination with the use of reversed
asymmetric membrane structures allows filtration at extremely low crossflow velocities with very stable
permeate fluxes. A hollow fiber membrane made of a very pressure-stable polymer, with a rather thick skin
layer on the outside of the fiber (pore sizes around 0.6 m) and a very open structure (pore sizes up to 20
m) at the inner surface, is used for clarification of fermentation broth (brewing process). Since the largest
pores are in contact with the feed (beer), the yeast cell can partially penetrate into the porous structure.
Without any backshock at all, this would lead to very low fluxes but the very frequent backshock prevents
the membrane from definitive clogging, and enables a filtration process with an extremely stable flux level
Fig. 3. Comparison between normal and reverse asymmetric membranes in combination with
backshock (backshock duration is 0.1 s, interval is 5 s, crossflow velocity is o.5 m/s; TMP = 0.2 bar
(normal) and 0.05 bar (reverse asymmetric); the backshock was stopped after 72 hours) 
The fouling layer as such is very likely present inside the porous structure of the membrane and
controlled by the backshock technology. Since the fouling layer is deposited during the first few seconds,
and the shear stresses both in the flow channel and at the pore entrance have a significant effect on how
proteins are denaturated and adsorbed at the membrane surface, a hydraulic cleaning of the membrane
surface is performed every few (1-5) seconds using a pressure of less than 0.1 seconds. As a result of the
extremely short durations, the loss of permeate during backshocking is negligible. In addition, it is found
that very good transmissions of high MW components could be obtained in combination with a very low
turbidity of the feed.
VIII. MEMBRANE TECHNOLOGY IN OIL AND GAS INDUSTRY
Large-scale use of membranes has grown tremendously over the last 20 years. Commercial
membrane application today ranged from small-scale analytical and biological application to large-scale
fluid and gas processing in the dairy to petrochemical industry. Paul & Yampolskii (1994)  stated that
techniques and methodologies developed for other industries and other applications of membranes already
exist to permit hollow fiber modules to be produced at much lower cost than is common. Therefore, it
should open up new market and applications, which was considered marginal because of the cost and
availability of membranes and modules.
Oil and gas industry is also having some potential opportunity for applying membrane technology.
Oil and gas industries are important sector in Indonesia. The importance of oil industry can be seen from
one of its product, i.e., petroleum, which is critical to the economy and quality of life as it providing fuels
for transportation, heating, and industrial uses, as well as product of natural gas industry. However, with
increasing concern of environmental protection and conservation, it is a must for oil and gas industry to use
cost-effective technology with lower energy consumption. This can be fulfilled by the use of membrane
technology. Potential applications of membrane technology in oil and gas industry are the gas separation
for removal of CO2 from natural gas, membrane contactor for gas separation, pervaporation for
hydrocarbon mixture separation, separation of water/oil emulsion, and reuse of lubricating oil which will be
explained briefly in the next section below.
Gas separation for CO2 removal from natural gas
Natural gas is very important as fuel and as a basic industrial raw material. The composition of
raw natural gas varies widely from field to field. Natural gas contains impurities such as carbon dioxide,
hydrogen sulfide, and moisture that must be removed prior to delivery to a pipeline. Carbon dioxide and
hydrogen sulfide (acid gases) are both corrosive to the pipeline, and hydrogen sulfide is very toxic.
Moisture must also be removed to prevent corrosion and line pluggage due to its freezing. The removal of
these impurities must also be accompanied with minimal loss of methane.
Membrane technology has been developed in various industries for gas selective separations. The
purification of natural gas is an industrial process that can be economically accomplished with membrane
system. The application of membrane technology for acid gas generally falls within the following
categories, i.e., bulk removal of acid gases, production of pipeline quality natural gas, upgrading the
heating value of low Btu-fuel, and recovering carbon dioxide for reinjection from gas produced in
enhanced recovery [58, 59]. The advantages of membrane are low capital investment, the ability to treat gas
at the wellhead, and wellhead treatment to eliminate corrosion and safety problems with “feeder” lines to a
central location .
The membrane gas separation process is based on selective permeation, by which a specific gas
can be separated from a mixture containing the gas. Membrane used for gas separation is asymmetric or
composite membrane with an elastomeric (polydimethysiloxane, polymethylpentene) or glassy polymeric
(polyimide, polysulfone) top layer . Type of module used is either flat or tubular. The application of
membrane process for CO2 removal is reasonable in which both carbon dioxide and hydrogen sulfide are
much more permeable than methane, enabling concentrated methane to be recovered as high-pressure
stream . Dehydration of natural gas also occurs simultaneously with CO2 removal since water is
typically highly permeable. Several studies concerning the removal of CO2 via membrane process has been
done by Bhide & Stern (1993), Kumazawa, et al. (1994), and White, et al. (1995). Membranes can treat
natural gas to less than 2% carbon dioxide, 4 ppm hydrogen sulfide and 7 lb/MMSCF of water .
Single-stage membrane systems are suitable for low flow rate applications, while higher flow rate
often require the use of membrane recycle designs to minimize the loss of hydrocarbons which occur
through incomplete separation. Membrane process can also be applied for treatment of a gas containing
carbon dioxide produced from a fracture well. High-pressure carbon dioxide and water are injected into the
well to fracture the tight formation trapping the natural gas. For this kind of application, 500 to 1200 tons of
carbon dioxide are used which can increase natural gas production 10-20 times. When the well is first
fractured, the produced gas is highly enriched in carbon dioxide. A membrane system can be either
temporarily or permanently used to render this gas suitable for pipeline specifications .
Carbon dioxide flooding is often needed to effectively enhance oil production from depleted oil
fields and to extend the life of these oil fields. Carbon dioxide is pumped into the ground on the periphery
of the field at high pressures. Carbon dioxide then diffused through the formation to drive the residual oil
toward existing oil wells. Large quantities of carbon dioxide are required in the initial stages of the
injection program. When the oil is produced, the casing head gas, which is produced simultaneously with
the oil, becomes contaminated by the carbon dioxide. The objective of these gas separations is to separate
both natural gas and carbon dioxide. Natural gas can be sold and carbon dioxide recompressed for
reinjection into the field. Membranes have been utilized for this application because both the volume and
composition of the gas change with time and because of their effectiveness at high carbon dioxide removal.
Carbon dioxide permeate stream, which is recompressed prior to reinjection places special design
considerations on the membrane process. Increasing the permeate pressure reduces the recompression
requirements. However, a higher permeate pressure reduces the membrane efficiency. A staged approach
needs to be optimized to balance membrane efficiency and minimize recompression cost. Figure 4 shows a
schematic of laboratory membrane unit for CO2 removal.
Fig. 4. Gas separation membrane unit for CO2 removal
Membrane contactor for gas separation
Membrane contactor is an emerging technology for replacing conventional scrubber for gas/liquid
contacting. Conventional scrubbers are characterized by having huge space requirements and related high
capital costs. In addition, conventional scrubbers suffer from several operational limitations such as
entrainment and loading limitations . The membrane contactor can potentially overcome these
operational limitations due to the physical separation of liquid and gas.
Various kinds of membrane contactors are gas-liquid contactor, liquid-gas contactor, and liquid-
liquid contactor. In the gas-liquid or liquid-gas contactor, one phase is a gas or a vapour and the other phase
is a liquid whereas in the liquid-liquid contactor both phases are liquid. The separation performance in
membrane contactor is determined by the distribution coefficient of a component in two phases and the
membrane acts only as an interface . Owing to their high specific surface area as can be found in
hollow fiber and capillary modules, membrane contactors promise higher volumetric mass transfer rates
than conventional scrubbers. The specific surface area is typically 500-5000 m2/m3 in membrane contactors
compared to 20-500 m2/m3 in conventional scrubbers. The membrane contactor also holds a potential of
improving the mass transfer in the boundary layers due to the small dimensions present in the contactor
. Hence, the major advantages of membrane contactor lie in the drastic reduction of the contactor
volume and related possible reductions in the investment and operating costs. Furthermore, due to the
principle of contacting, many disadvantages present in conventional contacting equipment such as flooding,
loading, and entrainment can be overcome. Thus, the operation of the membrane contactor can easily be
adjusted to meet changes in plant load. Finally, the compactness and modular shape of membrane contactor
make it well suited for retrofit applications.
Membrane contactors are a promising alternative to packed towers for gas treating. As mentioned
by Zhang & Cussler (1985), acid gas treatment with hollow fiber contactor can take place over ten times
faster than that in packed tower. Other examples of membrane contactor application are separation of
saturated/unsaturated hydrocarbons (paraffin/olefin) and removal of acid gas from flue gas. In the
separation of saturated/unsaturated hydrocarbons, two systems may be applied, an absorption stage and a
desorption stage . Iversen, et al. (1997) studied the methods of selecting applicable membranes for use
in membrane contactors for flue gas desulfurization. Modelings of membrane contactor have also been
studied . An example of membrane contactor for gas separation process can be seen in Fig. 5 below.
Fig. 5. Membrane contactor for gas separation
Pervaporation for hydrocarbon separation
Pervaporation is a membrane process in which a pure liquid or liquid mixture is in contact with the
membrane on the feed or upstream side at atmospheric pressure and where the permeate is removed as a
vapour . The permeate phase coming from pervaporation process is changed from liquid to vapour.
Hence, it offers a mean of separating miscible liquid of similar molar mass as an alternative method to
distillation . The driving force in the membrane is achieved by lowering the activity of the permeating
components at the permeate side. Components in the mixture permeate through the membrane and
evaporate as a result of the partial pressure on the permeate side being lower than saturation vapour
pressure . Essentially, the pervaporation process involves a sequence of three steps, i.e., selective
sorption into the membrane on the feed side, selective diffusion through the membrane, and desorption into
vapour phase on the permeate side. Because of the existence of a liquid and a vapour, pervaporation is
often considered as a kind of extractive distillation process with the membrane acting as a third component.
The separation principle in distillation is based on the vapour-liquid equilibrium whereas separation in
pervaporation is based on differences in solubility and diffusivity . Pervaporation proves itself as an
useful method in the separation, or removal, of small amounts of one liquid from a liquid mixture.
Pervaporation is also then becomes attractive for separation azeotrope mixtures.
Pervaporation can also be applied for separation of hydrocarbon mixtures such as isomer mixtures,
aromatics-alcohols, aromatic-alkanes, aromatic-naphtene, and alkanes . The conventional methods of
separating various hydrocarbons involve technology such as extraction, absorption, distillation etc., which
in present time is relatively expensive. Scott (1995) also stated that the dominant separation method for
organic mixtures in the petroleum and chemical process industry is distillation. It is energy intensive
process, estimated that around 40% of the total energy consumed by the chemical processing industries is
in distillation. When the organic components have similar boiling point and relative volatilities, the
separation is difficult and energy cost is particularly high. As mentioned before, one of the advantages of
membrane process is low energy consumption. Therefore, the capability of membrane process, i.e.,
pervaporation, to separate hydrocarbon mixture is a potential opportunity to employ in the processing of
products in the oil industry.
For good overall separation factor for pervaporation, ideally both the membrane separation factor
and the evaporation separation factor (relative volatility) should be large. With mixture of low volatility,
good separation is reliant upon a reasonable separation factor for the pervaporation membrane. For
example, with benzene/cyclohexane mixture that has an azeotrope composition of approximately 50%
benzene, pervaporation with a 20 m thick cross linked membrane will produce permeate with more than
90% benzene. The production of methyl tertiary butyl ether from methanol and isobutene is also an
interesting example of pervaporation applied for organic/organic separations. This process produces a
reactor product mixture of all three component of which both the methanol-ether and methanol-C4 form
azeotrope. A process has been developed in which pervaporation is integrated in the system to separate out
the methanol and recycle it back to the reactor. The membrane used is made from cellulose acetate.
Cellulose acetate membrane has separation factor for methanol from MTBE of over 1000, because the
material is hydrophilic and methanol is more polar than MTBE or the isobutene . Figure 6 shows a
laboratory pervaporation unit.
Fig. 6. Pervaporation unit
Oil emulsion separation
The separation of oil emulsion in oil-polluted effluent can also be achieved using membrane
process. In general, oily wastes can be grouped into three broad categories, i.e., free-floating oil, unstable
oil/water emulsions, and highly stable oil/water emulsions. Free oil can be readily removed by mechanical
separation. Unstable oil/water emulsions can be mechanically or chemically broken, then separated by
gravity. Meanwhile, stable emulsion requires more sophisticated treatment to meet today’s effluent
standards . The conventional chemical treatment resulted in oil phase and water phase which both of
them needed additional treatment to meet environmental standards for discharge into sewer.
Ultrafiltration membrane with pore dimension 2-10 nm, enable efficient separation of oil/water
emulsion. Ultrafiltration of highly stable oil/water emulsion produces a water phase that can be discharged
to a sewer with no post-treatment, and an oil phase that can be incinerated. Even if it cannot be burned,
only 3-5% of the original volume of oily wastewater will have to be hauled away . In this application,
ultrafiltration is used for concentrate oil/water emulsions rather than splitting the emulsion. In commercial
scale, ultrafiltration is already used to concentrate stable oil/water emulsions containing up to about 40%
oil. The concentrate is considerably reduced in volume since 90-99% of water is removed . Oily
wastewaters suitable for treatment by UF contain 0.1 to 10% oil in a stable emulsion. A limited amount of
free oil can be processed but usually quantities above 1 to 5% are removed with a centrifuge prior to UF.
The secret of successful UF is to maintain discrete and stable emulsoid particles of oil (generally over 0,1
m in size) that are larger than the membrane pore size (0,01 m or below). When this is the case, oil in the
permeate will generally be less than 10 to 50 ppm .
As mentioned by Cheryan (1998), an example of membrane application for oily feed is observed
in an automobile transmission plant in Sweden, which generated more than 1 million liters of spent
coolants per year in its machining operation. The oily wastewater was first entering the prefilter to remove
particles larger than 400 m. The pretreated oily wastewater was then pumped to ten ultrafiltration
modules. The total surface area was 25 m2 for a design feed capacity of 1500 m3/year. Another example is
the application of Membrex ESP spiral module system in processing 40,000 gal per month of spent coolant
containing 5-6% of oil by volume. The volume is reduced to 4000-6000 gal of concentrate, containing 30-
50% oil. Several study have also been done to investigate the application of membrane for the treatment of
various oily wastewater such as metal working fluid , spent copper wire drawing , and spent cutting
Reuse of waste lubricating oil
The reuse of waste lubricating oil can also be accomplished by employing membrane process. The
idea of recycling lubricants has flourished when oil is scarce. In US, the motorists discard about 1.25
billion gallons of oil every year by changing the oil in their automobile crankcase . Only about 100
million gallons reach recyclers to be re-refined into clean lubricants. The rest burned as fuel or disposed of
as waste. The conventional re-refining process uses sulfuric acid to dissolve sludge. The oil phase is further
cleaned by clay filtration. The process is so inefficient that one-third of the oil is lost and disposal of the
acid solution is increasingly difficult. The “water-alcohol” methods utilized isopropyl alcohol to
decompose metallic soap. The mixture is then centrifuged to yield clean oil and a watery metallic sludge.
Alcohol is recovered for reuse. Ultrafiltration membrane has the potential of removing all contaminants
without the needs of chemicals. Inorganic UF membranes operating at 300oC and a pressure of 7 bar are
capable of processing the oil economically. In one plant in Europe, where the spent lubricating oil is
pretreated with thermal shock and centrifugation at 180oC, the UF flux is reported stable between 1000-
2000 LSMD (25-50 GSFL) over six months without cleaning .
IX. FUTURE INDUSTRIAL PROSPECT
Intensive researches and development in membrane area is related closely to the rapid growth of
membrane technology. It is certainly not easy to predict the future of this technology. However, below is
presented some facts that can roughly describe the future trend of this technology. Firstly, current rapid
development in alternatives of membrane materials, membrane production processes and the increase of
membrane production, and followed by the membrane quality enhancement. Consequently, membrane
price tends to decrease and the process is more economical. This is causing wider membrane technology
implementation especially in application that requires high productivity and low cost like in water and
wastewater treatment. Secondly, for high-pressure and large capacity membrane process like high-pressure
reverse osmosis, energy recovery units have already been developed. This allows 70% energy recovery, so
that the process becomes less expensive. Thirdly, ultra low-pressure membrane with high productivity has
also been developed; hence reverse osmosis process that used to operate on high pressure (60-80 bars)
could operate on lower pressure ( 20 bars). This condition obviously lowers the energy consumption.
Moreover, process system and equipment specification become simpler. Next, fourth factor deals with the
environmental conservation fee. With refers to environmental regulation, industry that produce waste has to
pay an environmental fee, amount to the production capacity or waste volume produced. Since membrane
technology is a clean technology, it produces minimum waste or even none. In addition, membrane
technology is one of the waste treatment technologies that improve waste quality or even better than that
conditioned in the Industrial Waste Water Standard. It is a technology that can reuse water. In some
application, zero waste effluent is also possible. Therefore, although the applications of this technology are
still very limited, large market potential is awaiting.
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