1
1. INTRODUCTION[9]
In chemical engineering, a separation process is used to transform mixture of substances into
two or more distinct products. The separated products could be different in the chemical
properties or some physical property such as size, or crystal modification or other separation into
different components.
Barring a few exceptions, almost every compound/element is found naturally in an impure state
such as a mixture of two or more substances. Many times need to separate it into its individual
components arises and separation applications in the field are very important. A good example is
that of crude oil which is a mixture of various hydrocarbons and is valuable in this natural form.
Demand is greater for the purified various hydrocarbons such as natural gases, gasoline, diesel,
jet fuel, lubricating oils, asphalt, etc.
Separation processes can be termed as mass transfer processes. The classification can be based
on means of separation, mechanical or chemical. The choice of separation depends on pros and
cons of each. The mechanical separations are usually favored if possible due to the lower cost of
the operations as compared to chemical separations but for the systems that cannot be separated
by purely mechanical means (e.g. crude oil), only chemical separation is the remaining solution.
The mixture could exist as a combination of any two or more states: solid-solid, solid-liquid,
solid-gas, liquid-liquid, liquid-gas, gas-gas, solid-liquid-gas mixture, etc.
Depending on raw mixture, various processes can be employed to separate mixtures. Many times
two or more of these processes have to be used in combination to obtain the desired separation
and in addition to chemical processes, mechanical processes can also be applied where possible.
In separation of crude oil, one upstream distillation operation will feed its two or more product
streams into multiple downstream distillation operations to further separate the crude, and so on
until the final products are purified.
2
2. LIST OF DIFFERENT SEPARATION PROCESSES[9]
Separation Operation Separating Agent Industrial Application
Distillation Mass transfer Purification of styrene
Absorption Liquid absorbent Separation of CO2 from
combustion products by
ethanolamine
Liquid-liquid extraction Liquid solvent Recovery of aromatics
Evaporation Heat transfer Evaporation of water from a
solution of urea and water
Leaching Liquid solvent Extraction of sucrose from
sugar beets with hot water
Dialysis Porous membrane with
pressure gradient
Recovery of caustic from
hemicelluloses
Reverse osmosis Nonporous membrane with
pressure gradient
Desalination of water
Microfiltration Microporous membrane with
pressure gradient
Removal of bacteria from
drinking water
Ultrafiltration Microporous membrane with
pressure gradient
Separation of whey from
cheese
Pervaporation Nonporous membrane with
pressure gradient
Separation of azeotropic
mixtures
Adsorption Solid adsorbent Purification of water
Chromatography Solid adsorbent or liquid
adsorbent on a solid support
Separation of xylene isomers
and ethyl benzene
Electrolysis Electric force field Concentration of heavy water
Electrodialysis Electric force field and
membrane
Desalination of water
Table 1
3
3. MEMBRANE SEPARATION PROCESSES
The separation of liquids and gases are commonly accomplished using membrane separation
methods. This includes dialysis, reverse osmosis, and ultra filtration. Hybrid and more exotic
membrane methods that have also proven effective are electro dialysis, helium separation
through glass, the hydrogen separation through Palladium and alloy membranes, immobilized
solvent and liquid-surfactant membranes.
The permeation of liquids and gases through polymeric membranes occurs where a constituent
passes through the membrane by diffusion and sorption by fluid on other side of the membrane.
The driving force is achieved either by the pressure or concentration difference across
membrane.
In general, the membrane separation techniques are especially useful in separating:
1. Mixtures of the similar chemical compounds,
2. Mixtures of the thermally unstable components since no heating is needed, and
3. In conjunction with the conventional separation methods such as using membranes to
break the azeotropic mixtures before feeding them to a distillation column.
In membrane separation, spent metal removal fluids are pumped from a process tank at a
moderate pressure and rapid flow permeable membrane to the series of membranes. This flow is
referred to as the feed rate. The large molecules and virtually all petroleum products are blocked
at membrane surface and the compounds that do not pass through the membrane are referred to
as reject.
The water-like solutions that pass through membrane are referred to as the "permeate" and rate at
which permeate flows through the membrane is called the flux rate.
3.1 OSMOSIS[3]
Osmosis is the movement of water molecules through a selectively-permeable membrane down a
water potential gradient. More specifically, it is the movement of water across a selectively
permeable membrane from an area of high water potential (low solute concentration) to an area
of low water potential (high solute concentration). It may also be used to describe a physical
4
process in which any solvent moves, without input of energy, across a semipermeable membrane
(permeable to the solvent, but not the solute) separating two solutions of different concentrations.
Osmosis releases energy, and can be made to do work, but is a passive process, like diffusion.
Net movement of solvent is from the less-concentrated (hypotonic) to the more-concentrated
(hypertonic) solution, which tends to reduce the difference in concentrations. This effect can be
countered by increasing the pressure of the hypertonic solution, with respect to the hypotonic.
The osmotic pressure is defined to be the pressure required to maintain an equilibrium, with no
net movement of solvent. Osmotic pressure is a colligative property, meaning that the osmotic
pressure depends on the molar concentration of the solute but not on its identity.
Osmosis is important in biological systems, as many biological membranes are semipermeable.
In general, these membranes are impermeable to organic solutes with large molecules, such as
polysaccharides, while permeable to water and small, uncharged solutes. Permeability may
depend on solubility properties, charge, or chemistry, as well as solute size. Water molecules
travel through the plasma cell wall, tonoplast (vacuole) or protoplast in two ways, either by
diffusing across the phospholipid bilayer directly, or via aquaporins (small transmembrane
proteins similar to those in facilitated diffusion and in creating ion channels). Osmosis provides
the primary means by which water is transported into and out of cells. The turgor pressure of a
cell is largely maintained by osmosis, across the cell membrane, between the cell interior and its
relatively hypotonic environment.
3.2 VARIATION
3.2.1 Reverse osmosis
Reverse osmosis is a separation process that uses pressure to force a solvent through a
semipermeable membrane that retains the solute on one side and allows the pure solvent to pass
to the other side. More formally, it is the process of forcing a solvent from a region of high solute
concentration through a membrane to a region of low solute concentration by applying a pressure
in excess of the osmotic pressure.
5
3.2.2 Forward osmosis
Osmosis may be used directly to achieve separation of water from a "feed" solution containing
unwanted solutes. A "draw" solution of higher osmotic pressure than the feed solution is used to
induce a net flow of water through a semipermeable membrane, such that the feed solution
becomes concentrated as the draw solution becomes dilute. The diluted draw solution may then
be used directly (as with an ingestible solute like glucose), or sent to a secondary separation
process for the removal of the draw solute. This secondary separation can be more efficient than
a reverse osmosis process would be alone, depending on the draw solute used and the feedwater
treated. Forward osmosis is an area of ongoing research, focusing on applications in desalination,
water purification, water treatment, food processing, etc.
3.3 REVERSE OSMOSIS
Reverse osmosis (RO) is a filtration method that removes many types of large molecules and
ions from solutions by applying pressure to the solution when it is on one side of a selective
membrane. The result is that the solute is retained on the pressurized side of the membrane and
the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not
allow large molecules or ions through the pores (holes), but should allow smaller components of
the solution (such as the solvent) to pass freely.
In the normal osmosis process the solvent naturally moves from an area of low solute
concentration, through a membrane, to an area of high solute concentration. The movement of a
pure solvent to equalize solute concentrations on each side of a membrane generates a pressure
and this is the "osmotic pressure." Applying an external pressure to reverse the natural flow of
pure solvent, thus, is reverse osmosis. The process is similar to membrane filtration. However,
there are key differences between reverse osmosis and filtration. The predominant removal
mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically
achieve perfect exclusion of particles regardless of operational parameters such as influent
pressure and concentration. Reverse osmosis, however, involves a diffusive mechanism so that
separation efficiency is dependent on solute concentration, pressure, and water flux rate. Reverse
6
osmosis is most commonly known for its use in drinking water purification from seawater,
removing the salt and other substances from the water molecules.
3.3.1 APPLICATIONS
Drinking water purification
Around the world, household drinking water purification systems, including a reverse osmosis
step, are commonly used for improving water for drinking and cooking.
Such systems typically include a number of steps:
a sediment filter to trap particles, including rust and calcium carbonate
optionally, a second sediment filter with smaller pores
an activated carbon filter to trap organic chemicals and chlorine, which will attack and
degrade TFC reverse osmosis membranes
a reverse osmosis (RO) filter, which is a thin film composite membrane (TFM or TFC)
optionally, a second carbon filter to capture those chemicals not removed by the RO
membrane
optionally an ultra-violet lamp for disinfecting any microbes that may escape filtering by
the reverse osmosis membrane
3.4 DESALINATION[1][2]
Areas that have either no or limited surface water or groundwater may choose to desalinate
seawater or brackish water to obtain drinking water. Reverse osmosis is the most common
method of desalination, although 85 percent of desalinated water is produced in multistage flash
plants.
Large reverse osmosis and multistage flash desalination plants are used in the Middle East,
especially Saudi Arabia. The energy requirements of the plants are large, but electricity can be
produced relatively cheaply with the abundant oil reserves in the region. The desalination plants
are often located adjacent to the power plants, which reduces energy losses in transmission and
7
allows waste heat to be used in the desalination process of multistage flash plants, reducing the
amount of energy needed to desalinate the water and providing cooling for the power plant.
Sea Water Reverse Osmosis (SWRO) is a reverse osmosis desalination membrane process that
has been commercially used since the early 1970s. Its first practical use was demonstrated by
Sidney Loeb and Srinivasa Sourirajan from UCLA in Coalinga, California. Because no heating
or phase changes are needed, energy requirements are low in comparison to other processes of
desalination, but are still much higher than those required for other forms of water supply
(including reverse osmosis treatment of wastewater).
The Ashkelon seawater reverse osmosis (SWRO) desalination plant in Israel is the largest in the
world. The project was developed as a BOT (Build-Operate-Transfer) by a consortium of three
international companies: Veolia water, IDE Technologies and Elran.
The typical single-pass SWRO system consists of the following components:
Intake
Pretreatment
High pressure pump
Membrane assembly
Remineralisation and pH adjustment
Disinfection
Alarm/control panel
3.4.1 Pretreatment
Pretreatment is important when working with RO and nanofiltration (NF) membranes due to the
nature of their spiral wound design. The material is engineered in such a fashion as to allow only
one-way flow through the system. As such, the spiral wound design does not allow for
backpulsing with water or air agitation to scour its surface and remove solids. Since accumulated
material cannot be removed from the membrane surface systems, they are highly susceptible to
fouling (loss of production capacity). Therefore, pretreatment is a necessity for any RO or NF
system. Pretreatment in SWRO systems has four major components:
8
Screening of solids: Solids within the water must be removed and the water treated to
prevent fouling of the membranes by fine particle or biological growth, and reduce the
risk of damage to high-pressure pump components.
Cartridge filtration: Generally, string-wound polypropylene filters are used to remove
particles between 1 – 5 micrometres.
Dosing: Oxidizing biocides, such as chlorine, are added to kill bacteria, followed by
bisulfite dosing to deactivate the chlorine, which can destroy a thin-film composite
membrane. There are also biofouling inhibitors, which do not kill bacteria, but simply
prevent them from growing slime on the membrane surface and plant walls.
Prefiltration pH adjustment: If the pH, hardness and the alkalinity in the feedwater result
in a scaling tendency when they are concentrated in the reject stream, acid is dosed to
maintain carbonates in their soluble carbonic acid form.
CO3−2
+ H3O+ = HCO3
- + H2O
HCO3- + H3O
+ = H2CO3 + H2O
Carbonic acid cannot combine with calcium to form calcium carbonate scale. Calcium
carbonate scaling tendency is estimated using the Langelier saturation index. Adding too
much sulfuric acid to control carbonate scales may result in calcium sulfate, barium
sulfate or strontium sulfate scale formation on the RO membrane.
Prefiltration antiscalants: Scale inhibitors (also known as antiscalants) prevent formation
of all scales compared to acid, which can only prevent formation of calcium carbonate
and calcium phosphate scales. In addition to inhibiting carbonate and phosphate scales,
antiscalants inhibit sulfate and fluoride scales, disperse colloids and metal oxides, and
specialty products can be to inhibit silica formation.
High pressure pump
The pump supplies the pressure needed to push water through the membrane, even as the
membrane rejects the passage of salt through it. Typical pressures for brackish water range from
9
225 to 375 psi (15.5 to 26 bar, or 1.6 to 2.6 MPa). In the case of seawater, they range from 800 to
1,180 psi (55 to 81.5 bar or 6 to 8 MPa). This requires a large amount of energy.
3.4.2 Membrane assembly
Fig. 1 The layers of a membrane.
The membrane assembly consists of a pressure vessel with a membrane that allows feedwater to
be pressed against it. The membrane must be strong enough to withstand whatever pressure is
applied against it. RO membranes are made in a variety of configurations, with the two most
common configurations being spiral-wound and hollow-fiber.
3.4.3 Remineralisation and pH adjustment
The desalinated water is very corrosive and is "stabilized" to protect downstream pipelines and
storages, usually by adding lime or caustic to prevent corrosion of concrete lined surfaces.
Liming material is used to adjust pH between 6.8 and 8.1 to meet the potable water
specifications, primarily for effective disinfection and for corrosion control.
3.4.4 Disadvantages
Household reverse osmosis units use a lot of water because they have low back pressure. As a
result, they recover only 5 to 15 percent of the water entering the system. The remainder is
discharged as waste water. Because waste water carries with it the rejected contaminants,
methods to recover this water are not practical for household systems. Wastewater is typically
connected to the house drains and will add to the load on the household septic system. An RO
10
unit delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of wastewater
per day to the septic system.
Large-scale industrial/municipal systems have a production efficiency closer to 48%, because
they can generate the high pressure needed for more efficient RO filtration.
3.5 NANOFILTRATION [9]
Nanofiltration is a relatively recent membrane filtration process used most often with low total
dissolved solids water such as surface water and fresh groundwater, with the purpose of
softening (polyvalent cation removal) and removal of disinfection by-product precursors such as
natural organic matter and synthetic organic matter.
Nanofiltration is also becoming more widely used in food processing applications such as dairy,
for simultaneous concentration and partial (monovalent ion) demineralisation.
Fig. 2 Nanofiltration operation
3.5.1 Principle
Nanofiltration (NF) is a cross-flow filtration technology which ranges somewhere between
ultrafiltration (UF) and reverse osmosis (RO). The nominal pore size of the membrane is
11
typically about 1 nanometer. Nanofilter membranes are typically rated by molecular weight cut-
off (MWCO) rather than nominal pore size. The MWCO is typically less than 1000 atomic mass
units (Daltons). The pressure drop across the membrane required is lower (up to 3 MPa) than the
one used for RO, reducing the operating cost significantly. However, NF membranes are still
subject to scaling and fouling and often modifiers such as anti-scalants are required for use.
3.5.2 Water purification applications
In much of the developing world, clean drinking water is hard to come by, and nanotechnology
provides one solution. While nanofiltration is used for the removal of contaminants from a water
source, it is also commonly used for desalination. As seen in a recent study in South Africa, tests
were run using polymeric nanofiltration in conjunction with a reverse osmosis process to treat
brackish groundwater. These tests produced potable water, but as the researchers expected, the
reverse osmosis removed a large majority of solutes. This left the water void of any essential
nutrients (calcium, magnesium ions, etc.), placing the nutrient levels below that of the required
World Health Organization standards. This process was probably a little too much for the
production of potable water, as researchers had to go back and add nutrients to bring solute
levels to the standard levels for drinking water consumption.
Providing nanofiltration methods to developing countries, to increase their supply of clean
water, is a very inexpensive method compared to conventional treatment systems. However,
there remain issues as to how these developing countries will be able to incorporate this new
technology into their economy without creating a dependency on foreign assistance.
3.5.3 Nanofiltration membranes broaden the use of membrane separation technology
Most reverse osmosis (RO) research has concentrated on the development of single-pass
seawater membranes. The success of these high rejection membranes has created interest in other
applications requiring less demanding salt rejection, or desiring the elimination of salt from a
feed stream (diafiltration), or having severe chemical resistance requirements. All would prefer
to operate at lower net driving pressures than demanded by the high rejection membranes. These
membranes have been designated as ―quo; nanofiltration‖quo; membranes to distinguish them
from the ―quo; hyperfiltration‖quo; seawater membranes. The first is XP45, a polyamide
12
membrane with a low sodium chloride rejection that makes it an excellent candidate for
applications such as the processing of salty cheese wheys and pharmaceutical preparations. The
second is NF70, another polyamide, a low pressure membrane with rejections suited for
converting mildly brackish water and organic-laden raw water to potable water that meets WHO
standards. The third is XP20, a new developmental membrane for the maintenance of electroless
copper plating baths.
13
4. DISTILLATION[9]
Distillation is a method of separating mixtures based on differences in their volatilities in a
boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a
chemical reaction.
Commercially, distillation has a number of applications. It is used to separate crude oil into more
fractions for specific uses such as transport, power generation and heating. Water is distilled to
remove impurities, such as salt from seawater. Air is distilled to separate its components—
notably oxygen, nitrogen, and argon—for industrial use. Distillation of fermented solutions has
been used since ancient times to produce distilled beverages with a higher alcohol content. The
premises where distillation is carried out, especially distillation of alcohol, are known as a
distillery.
4.1 Types of Distillation
1. Laboratory scale distillation
Simple distillation
Fractional distillation
Steam distillation
Vacuum distillation
Air-sensitive vacuum distillation
Other Types
o The process of reactive distillation involves using the reaction vessel as the still.
In this process, the product is usually significantly lower-boiling than its
reactants. As the product is formed from the reactants, it is vaporized and
removed from the reaction mixture. This technique is an example of a continuous
vs. a batch process; advantages include less downtime to charge the reaction
vessel with starting material, and less workup.
o Pervaporation is a method for the separation of mixtures of liquids by partial
vaporization through a non-porous membrane.
14
o Extractive distillation is defined as distillation in the presence of a miscible, high
boiling, relatively non-volatile component, the solvent that forms no azeotrope
with the other components in the mixture.
2. Azeotropic distillation
Breaking an azeotrope with unidirectional pressure manipulation
Pressure-swing distillation
3. Industrial distillation
Multi-effect distillation
4.2 Separation of azeotropic mixtures [15]
A separation through the azeotropic point in one column can not be done. There is a need for
different unit operation for such kind of problems. For a main classification of azeotropic
distillation operation we can distinguish between unit operation with use of an entrainer
(extractive distillation and azeotropic distillation) and without an entrainer (Vacuum distillation
and pressure swing distillation).
There exist three types of azeotropic mixtures, the heterogeneous and the low boiling and the
high boiling homogeneous azeotropic mixtures. Homogeneous azeotrops have one liquid phase,
heterogeneous azeotrops separate into two liquid phases at the azeotropic point. These mixtures
have a miscibility gap. For low-boiling (e.g. acetonitrile/water) azeotrops the azeotropic mixture
is separated from the top of the column and the pure product from the bottom of the column. For
high-boiling azeotrops it is the other way around. The product is at the top, the azeotropic
mixture at the bottom of the column (e.g. water/nitric acid). The ten most produced basic
products in Germany (methanol, benzene, toluene, xylene, acetic acid, ...) generate over 120
homogeneous azeotropic mixtures [VCI 2006, Ponton 2007], so there is a big industrial
relevance for the separation of homogeneous azeotropic mixtures. In this work I will concentrate
on low boiling azeotrops because most azeotrops - especially those encountered in solvent
recycling applications - fall in this category [Frank 1997].
15
Fig. 3 Y vs X Diagram
4.2.1 Extractive distillation
For the separation of homogeneous close boiling or azeotropic mixtures, extractive
distillationcould be used. A low volatile liquid is added to the mixture as an entrainer to increase
the volatility over the whole concentration region by decreasing the partial pressure or the
volatility of one component. The main problem of the process is the choice of the right entrainer.
The entrainer has to fulfil many different properties. The boiling point of the entrainer must be
much higher than the boiling points of the other components, it has to be thermal stable, cheap
and non toxic, to mention only the main characteristics [Düssel & Warter 1998]. In general, it is
difficult and expensive to use an entrainer because of the additional recycling process. This
means additional investment and operation costs and a more complex automation.
The newest type of extractive distillation uses ionic liquids as an entrainer. The main advantage
of ionic liquids is the absence of its own vapor pressure, so it is easy to separate them from
vaporizable liquids. Because of their saline character, they have a big influence on the phase
equilibrium. It is much easier to shift azeotropic points or create miscibility gaps [Beste et al.
2005, Jork et al. 2004, Seiler et al. 2004].
16
4.2.2 Azeotropic distillation
In contrast to the extractive distillation the azeotropic distillation uses an entrainer to create a
heterogeneous low boiling azeotrope with one of the original components [Knapp & Doherty
1992, Lei et al. 2005]. In this case the phase separation of the condensed vapor is used. For this a
decanter on top of the column is necessary. Both liquid phases have different concentrations of
entrainer. For example the light phase has more entrainer with more low boiling liquid and in the
other phase has more high boiling liquid inside. Each phase is separated in a different column to
get pure products and recycle of the entrainer at the same time. So in this constellation the
process structure sketched in Fig.3 will be used.
The main disadvantage of the azeotropic distillation against the extractive distillation is the
higher energy demand because of the vaporization of the entrainer [Hoffmann 1964, Onken
1975, Doherty & Caldarola 1985, Lei et al. 2005].
4.2.3 Vacuum distillation
If it is possible to shift the azeotropic point with temperature change induced from a pressure
change, a pressure reduction in the column can be used. The azeotropic point shifts to higher
concentrations of the low boiling component and it is also possible to erase the azeotrope. The
disadvantages of the vacuum distillation are mainly the costs of the process and the complexity
of the process because of the vacuum, so it is not often used [Grassmann et al. 1997].
17
4.2.4 PRESSURE SWING DISTILLATION
The pressure swing distillation (PSD) is a process for the separation of homogeneous azeotropic
mixtures.
The PSD process uses the pressure sensitivity of the binary azeotropic point [Sattler & Feindt
1995, Lei et al. 2005]. If the pressure is increased, the azeotropic point shifts to lower
concentrations of the low boiling component. So a separation of the azeotropic mixture at
different pressures is possible (Fig. 4). In this work the mixture acetonitrile/water is used as an
example for low-boiling homogeneous azeotropic mixtures.
Depending on the feed composition based on the component acetonitrile, the feed concentration
could be lower or higher than the azeotropic point. The effect is that it is possible to get two
different high-boiling products. If the feed concentration is lower than the azeotropic point, the
bottom product is water and above the bottom product is acetonitrile.
For the process structure this means that in the continuous case two columns operating at two
different pressures are needed or in the discontinuous case one column operating at two different
pressures in at least two loops.
XAcetonit
ririle
Fig. 4 Y vs X diagram of the mixture acetonitrile –
water at different pressure
18
The main advantage of the PSD process is the process intensification which means an abdication
of an entrainer and therefore a reduction of columns and stages for the recycling of the entrainer.
Furthermore there is a possibility of heat integration for the continuous process. In this case the
heat of the condenser of the high pressure column (HP) is used for heating up the low pressure
column (LP). The disadvantages of the process are a higher complexity of the process and a
more complex automation, therefore the development of applicable process control strategies are
much more difficult. There is also a gap of experimental data in the literature and industrial
applications are seldom published. An overview about industrial applications and PSD-suitable
azeotropic mixtures is given in table 1. There is a big relevance for industry using this process.
One possible reason why process designers do not consider PSD is that azeotropic data
frequently are not available at non-atmospheric pressures and the generating of such data is
expensive [Frank 1997]. To solve the problem of missing azeotropic data see the work of
[Wasylkiewicz et al. 2003]. Wasylkiewicz and his co-author developed an algorithm that applies
bifurcation theory together with an arc length continuation and a rigorous stability analysis. This
method is a robust scheme for finding all homogeneous as well as heterogeneous azeotrops
predicted by a thermodynamic model at a specified pressure. Also a lot of research is done to
expand the thermodynamical properties data bases for pure components and mixtures [Gmehling
et al. 1981, Ponton 2007, Gmehling 2004].
4.2.4.1 Continuous pressure swing distillation
Two columns are in operation for the continuous pressure swing distillation system at two
different pressures (Fig. 4, Fig. 5-A). Feed streams with different concentrations have to be put
into the suitable column, depending on the concentration under or above the azeotropic point.
For concentrations under the azeotropic point, the feed is put into the low pressure column. For
concentrations above the azeotropic point the feed has to be put into the high pressure column. In
both columns pure product is withdrawn from the bottom, acetonitrile from the bottom of the
high pressure column and pure water from the bottom of the low pressure column. At the top of
the columns there are azeotropic mixtures with concentrations depending on the pressure in the
column. Each distillate stream is recycled into the other column, so there is a mass integration
between the columns. The respective distillation region of low and high pressure operation are
overlapping.
19
4.2.4.2 Batch pressure swing distillation
The batch process is one of the best known distillation processes. It is mostly used in fine
chemistry, for seasonal products, in the pharmaceutical, and in food industry, despite the
competition of the continuous process [S0rensen 1994, S0rensen & Skogestad 1996, Mutjaba
2004]. Mainly the energy demand is much higher than for the continuous processes [Hasebe et
al. 1999]. But if the whole producing costs are considered there could be an advantage of the
discontinuous process compared to the continuous process [Oppenheimer & S0rensen 1997]. But
one main advantage is that the process structure (one column) is much simpler than for a
continuous operation and or flexible in the scope of product changes and also product amount
changes.
The discontinuous process uses one column which is operated in two loops at different operation
pressures (Fig. 5-C1/C2). In the first loop (e.g. atmospheric pressure) the mixture is added to the
column and the high boiling component (component 1, high boiling) is drained at the bottom and
the azeotropic mixture at the top. The process ends if the bottom purity runs out of specification
and then the process stops. After that the pressure will be changed (e.g. high pressure). The
pressure change leads to a shift of the azeotropic point and therefore of the azeotropic
concentration at the top of the column. Now the other component (component 2, high boiling)
will be drained from the bottom because the column operate in the other distillation region (Fig.
4). The azeotropic mixture (at a different pressure, means a different composition) will drained
from the top of the column. The process ends, if the specification runs out of the set points.
Examples of PSD binary azeotropes
Tetrahydofuran (THF) Water
Acetonitrile Water
Methanol Methyl Ethyl Ketone
Acetone Methanol
Ethanol Ethyl Acetate
Benzene Isopropanol
Phenol Butyl Acetate
Propanol Toluene
Acetic Acid Toluene
Table 2
20
Feed Feed
End of process: ErxJ of process;
Fig.5
Pressure swing distillation;
A: continuous,
B: semi continuous,
C1: discontinuous (inverted),
C2: discontinuous (regular).
21
5. PERVAPORATION
Pervaporation is a method for the separation of mixtures of liquids by partial vaporization
through a non-porous or porous membrane.
5.1 Applications
Pervaporation is effective for diluting solutions containing trace or minor amounts of the
component to be removed. Based on this, hydrophilic membranes are used for dehydration of
alcohols containing small amounts of water and hydrophobic membranes are used for
removal/recovery of trace amounts of organics from aqueous solutions.
Pervaporation is a very mild process and hence very effective for separation of those mixtures
which cannot survive the harsh conditions of distillation.
Solvent Dehydration: dehydrating the ethanol/water and isopropanol/water azeotropes
Continuous water removal from condensation reactions such as esterifications to
enhance conversion and rate of the reaction.
Removing organic solvents from industrial waste waters.
Combination of distillation and pervaporation/vapour permeation
Concentration of hydrophobic flavour compounds in aqueous solutions (using
hydrophobic membranes)
Recently, a number of organophilic Pervaporation membranes have been introduced to the
market. Organophilic Pervaporation membranes can be used for the separation of organic-
organic mixtures, e.g.:
Reduction of the aromatics content in refinery streams
Breaking of azeotropes
Purification of product stream after extraction
Purification of organic solvents
22
5.2 Recent advances in sulfur removal from gasoline by Pervaporation
Pervaporation (PV) is today considered as a promising unit operation for separation of
organic–organic liquid mixtures and is being investigated extensively in chemical and
petrochemical industries. Recently, PV applications in environment cleanup operations,
especially in the removal of sulfur compounds from gasoline have attracted increasing attention
worldwide. Gasoline desulphurization by PV is a newly emerged technology in which sulfur
components can be preferentially removed from the gasoline feed due to its higher affinity
with, and/or quicker diffusivity in the membrane. A considerable amount of background
information, current state and trends of the new PV application in gasoline desulphurization are
dealt with. The article focuses on the PV membranes development, interactions between
gasoline components and membranes, the improvement in process engineering,
techoeconomical analysis and the technology scale up. Finally, some suggestions for further
research were presented with the aim of reducing the cost in introducing the PV process into
refineries for desulphurization.
5.3 Recent advances in cellulosic membranes for gas separation and Pervaporation
Cellulose acetate membranes have been used commercially for many gas separation
applications in recent years. Advances have been made in understanding their behavior in the
presence of various vapors and under severe operating conditions, for example at very high
carbon dioxide and hydrogen sulphide partial pressures. In addition, a new membrane module
design has been developed for use in high recovery systems and at high gas flow rates.
Extension of cellulose acetate gas separation membrane technology into the Pervaporation field
has resulted in a new application related to the production of methyl t-butyl ether (MtBE). In
this case the membrane is used to remove methanol from MtBE and hydrocarbons to increase
the reaction yield.
23
5.4 Novel hybrid separation processes based on Pervaporation for THF recovery
Design of novel hybrid processes is performed for the industrial recovery of tetrahydrofuran
(THF) from two different highly non-ideal mixtures. The novel hybrid processes combine the
advantages of batch and/or continuous distillations, extractive distillation, and pervaporation
for efficient separation of highly non-ideal mixtures. Pervaporation, used for the final
dewatering of the THF, is the last step in the separation technologies and carried out with
available industrial technology (Sulzer Chemtech GmbH, Batch pervaporation BP models,
PERVAP® 2210 membrane type). It is necessary, however, to design a proper pre-separation
process of the mixture to be pervaporated and coordinate its operation with the pervaporation
unit. Since methanol is also present in one of the mixtures, its behavior during pervaporation is
also investigated. It shows that since the methanol is able to permeate the membrane, it should
be separated in the pre-separation process. The vapor–liquid equilibrium data indicate that with
extractive distillation it becomes possible to break the THF—methanol azeotrope and the
appropriate application of pervaporation makes the further reduction of the recovery costs
possible. The total annual costs of the novel hybrid separation processes range between 10.3
and 54% of that of the old technology based on chemical dewatering. The THF loss decreases
to the 7.5 and 17% of that of the old technology and shows that pervaporation is also a
powerful tool for the application of the principles of the sustainable development and
consumption.
24
6. Reactive Distillation [11]
Reactive distillation is an advanced technique of reaction process operation.
The (energetic) advantages of reactive distillation over a process comprising a reactor and a
distillation unit including a recycle stream for unconverted reactant. The reactor + distillation
column was optimized with respect to reboiler energy consumption via the recycle and reflux
ratio.
Reactive distillation is a process where the chemical reactor is also the still. Separation of the
product from the reaction mixture does not need a separate distillation step, which saves energy
(for heating) and materials.
This technique is especially useful for equilibrium-limited reactions such as esterification and
ester hydrolysis reactions. Conversion can be increased far beyond what is expected by the
equilibrium due to the continuous removal of reaction products from the reactive zone. This
helps reduce capital and investment costs and may be important for sustainable development
due to a lower consumption of resources.
Being a relatively new field, research on various aspects such as modeling and simulation,
process synthesis, column hardware design, non-linear dynamics and control is in progress.
The suitability of RD for a particular reaction depends on various factors such as volatilities of
reactants and products along with the feasible reaction and distillation temperature. Hence, the
use of RD for every reaction may not be feasible. Exploring the candidate reactions for RD,
itself is an area that needs considerable attention to expand the domain of RD processes.
WHY REACTIVE DISTILLATION (RD)?
Benefits
Increased speed
Lower costs – reduced equipment use, energy use and handling
Less waste and fewer byproducts
25
Improved product quality– reducing opportunity for degradation because of less heat
Consider a reversible reaction scheme: A + B ⇌ C + D where the boiling points of the
components follow the sequence A, C, D and B. The traditional flow-sheet for this process
consists of a reactor followed by a sequence of distillation columns; see Fig.6. The mixture of
A and B is fed to the reactor, where the reaction takes place in the presence of a catalyst and
reaches equilibrium. A distillation train is required to produce pure products C and D. The
unreacted components, A and B, are recycled back to the reactor. In practice the distillation
train could be much more complex than the one portrayed in Fig. 6(a) if one or more
azeotropes are formed in the mixture. The alternative RD configuration is shown in Fig. 6(b).
The RD column consists of a reactive section in the middle with non-reactive rectifying and
stripping sections at the top and bottom. The task of the rectifying section is to recover reactant
B from the product stream C. In the stripping section, the reactant A is stripped from the
product stream D. In the reactive section the products are separated in situ, driving the
equilibrium to the right and preventing any undesired side reactions between the reactants A
(or B) with the product C (or D). For a properly designed RD column, virtually 100%
conversion can be achieved.
Fig.6
The most spectacular example of the beneits of RD is in the production of methyl acetate.
26
Fig. 7
(a) Reactive distillation concept for synthesis of MTBE from the acid-catalysed
reaction between MeOH and isobutene. The butane feed is a mixture of reactive
iso-butene and non-reactive n-butene. (b) Reactive distillation concept for the
hydration of ethylene oxide to ethylene glycol (c) Reactive distillation concept for
reaction between benzene and propene to form cumene. (d) Reactive distillation
concept for reaction production of propylene oxide from propylene chlorohydrins and
lime. The reactive sections are indicated by grid lines.
For the acid catalysed reaction between iso-butene and methanol to form methyl tert-butyl
ether: iso-butene + MeOH ⇌ MTBE, the traditional reactor-fol-lowed-by-distillation concept is
particularly complex for this case because the reaction mixture leaving the reactor forms three
minimum boiling azeotropes. The RD implementation requires only one column to which the
butenes feed (consisting of a mixture of n-butene, which is non-reactive, and iso-butene which
is reactive) and meth-anol are fed near the bottom of the reactive section. The RD concept
shown in Fig. 7(a) is capable of achieving close to 100% conversion of iso-butene and
methanol, along with suppression of the formation of the unwanted dimethyl ether
(Sundmacher, 1995). Also, some of the azeotropes in the mixture are "reacted away" (Doherty
& Buzad, 1992).
27
For the hydration of ethylene oxide to mono-ethylene glycol: EO + H2O⟶ EG, the RD
concept, shown in Fig. 7(b) is advantageous for two reasons (Ciric & Gu, 1994). Firstly, the
side reaction EO + EG → DEG is suppressed because the concentration of EO in the liquid-
phase is kept low because of its high volatility. Secondly, the high heat of reaction is utilised to
vaporise the liquid-phase mixtures on the trays. To achieve the same selectivity to EG in a
conventional liquid-phase plug-low reactor would require the use of 60% excess water (Ciric &
Gu, 1994). Similar beneits are also realised for the hydration of iso-butene to tert-butanol
(Velo, Puig-janer & Recasens, 1988) and hydration of 2-methyl-2-butene to tert-amyl alcohol
(Gonzalez & Fair, 1997).
Several alkylation reactions, aromatic + olefin ⇌ al-kyl aromatic, are best carried out using the
RD concept not only because of the shift in the reaction equilibrium due to in situ separation
but also due to the fact that the undesirable side reaction, alkyl aromatic + olefin ⇌ di-alkyl
aromatic, is suppressed. The reaction of propene with benzene to form cumene, benzene +
propene ⇌ Cumene (Shoemaker & Jones, 1987; see Fig. 7(c)), is advantageously carried out in
a RD column because not only is the formation of the undesirable di-isopropylben-zene
suppressed, but also the problems posed by high exothermicity of the reaction for operation in
a conventional packed-bed reactor are avoided. Hot spots and runaway problems are alleviated
in the RD concept where liquid vaporisation acts as a thermal lywheel. The alkylation of iso-
butane to iso-octane, iso-butane + n-butene ⇌ iso-octane, is another reaction that benefits from
a RD implementation because in situ separation of the product prevents further alkylation: iso-
octane + n-butene ⇌ C12 H24 (Doherty & Buzad, 1992).
The reaction between propylene chlorohydrin (PCH) and Ca(OH)2 to produce propylene oxide
(PO) is best implemented in an RD column, see Fig. 7(d). Here the desired product PO is
stripped from the liquid-phase by use of live steam, suppressing hydrolysis to propylene glycol
(Bezzo, Bertucco, Forlin & Barolo, 1999).
28
7. Advanced purification of petroleum refinery wastewater by catalytic vacuum
distillation.
In our work, a new process, catalytic vacuum distillation (CVD) was utilized for purification of
petroleum refinery wastewater that was characteristic of high chemical oxygen demand (COD)
and salinity. Moreover, various common promoters, like FeCl(3), kaolin, H(2)SO(4) and
NaOH were investigated to improve the purification efficiency of CVD. Here, the purification
efficiency was estimated by COD testing, electrolytic conductivity, UV-vis spectrum, gas
chromatography-mass spectrometry (GC-MS) and pH value. The results showed that NaOH
promoted CVD displayed higher efficiency in purification of refinery wastewater than other
systems, where the pellucid effluents with low salinity and high COD removal efficiency
(99%) were obtained after treatment, and the corresponding pH values of effluents varied from
7 to 9. Furthermore, environment estimation was also tested and the results showed that the
effluent had no influence on plant growth. Thus, based on satisfied removal efficiency of COD
and salinity achieved simultaneously, NaOH promoted CVD process is an effective approach
to purify petroleum refinery wastewater.
29
8. Recent Advances in Catalytic Distillation
Catalytic distillation (CD) is a novel green reactor technology that combines a heterogeneous
catalytic reaction and separation via distillation in a single distillation column. It is an excellent
example of process intensification. There are many possible advantages in carrying out a
chemical process using CD. They include enhanced product yield and selectivity, reduction of
capital and operating costs, enhanced catalyst lifetime, reduction of waste treatment streams,
and higher energy efficiency. Owing to the current concern of the impact of greenhouse gases
such as carbon dioxide on the environment, a major benefit of CD is related to the utilization of
the reaction heat for distillation, which reduces the energy consumption and hence reduces the
production of greenhouse gases.
30
9. Hybrid separation processes—Combination of reactive distillation
with membrane separation [14]
Over the years, the focus of the chemical and process industry has shifted towards the
development and application of integrated processes combining the mechanism of reaction and
separation in one single unit. This trend is motivated by benefits such as a reduction in
equipment and plant size and improvement of process efficiency and safety, and hence a better
process economy. Reactive distillation is an important example of a reactive separation
process. Especially for equilibrium reactions like esterifications, ester hydrolysis and
etherifications, the combination of reaction and separation within one zone of a reactive
distillation column is a well-known alternative to conventional processes with sequential
reaction and separation steps (Hiwale et al., 2004; Kaibel et al., 2005). In several cases, non-
ideal aqueous-organic mixtures are formed which tend to form azeotropes. They can be
overcome using membrane separations like pervaporation and vapour permeation since they
are very selective and not limited by vapour-liquid equilibrium (Rautenbach, 1997).
Consequently, a hybrid process consisting of membrane-assisted reactive distillation
contributes to sustainable process improvement due to arising synergy effects and allows for
reduction of investment and operational costs.
A review of hybrid processes combining pervaporation with one or more other separation
technologies can be found in (Lipnitzki et al., 1999). The analysis of hybrid separation
processes combining membrane separation with conventional distillation is described in (Kreis
and Gorak, 2006). An example for the investigation of a reactive hybrid process concept is the
transesterification of methyl acetate and butanol to butyl acetate and methanol by the
combination of reactive distillation and pervaporation, as examined by (Steinigeweg and
Gmehling, 2004). The industrially operated hybrid process for the continuous production of
fatty acid esters by reactive distillation and pervaporation is presented by (von Scala et al.,
2005). In this work, the heterogeneously catalysed esterification of propionic acid (ProAc) with
1-propanol (POH) to n-propyl propionate (ProPro) and water (H2O) is investigated:
C3H8O + C3H6O2 ⇌ C6Hl2O2 + H2O (1)
The esterification reaction is reversible; the equilibrium constant is a weak function of
temperature. As catalyst, the strongly acidic ion exchange resin Amberlyst 46TM
from Rohm &
31
Haas is used. Amberlyst 46TM
has acidic active sites (sulfonic-acid groups) only at the surface
of the styrene-co-divinylbenzene matrix (Lundquist, 1995). This catalyst shows thermal
stability up to 120°C and is tailor-made for esterifications because the competing side product
formations, e.g. etherification and dehydration of the alcohol, are suppressed (Blagov et al.,
2006).
9.1 Process description
One possible process alternative for n-propyl propionate synthesis in one apparatus is the
removal of the desired product (ProPro) at the bottom of the reactive distillation column while
at the top, an almost azeotropic aqueous-organic mixture (POH/H2O) is obtained. A
hydrophilic membrane unit is located in the distillate stream to remove water out of the
process. The water depleted retentate is recycled back to the column. The coupling of the
reactive distillation column with a membrane module results in a hybrid process (Figure 8).
Fig. 8 Reactive distillation column with a membrane separation located in the distillate stream
32
10. Production of Pure Ethanol from Azeotropic Solution by Pressure Swing
Adsorption [12]
Ethanol and water mixture forms an azeotrope at a temperature of 351K and a mixture
concentration of 95% (w/w) ethanol. With the rising demand of pure ethanol for various
applications, there is a need of getting nearly pure ethanol considering the energy and
efficiency aspects.
Conventionally, azeotropic distillation has been employed in production of fuel-ethanol. In
Azeotropic distillation, dehydration is carried out in presence of entrainer like benzene or
cyclohexane. Although benzene has been banned in several countries for its carcinogenic
effect, cyclohexane is still being employed. Moreover, this distillation method is very energy
intensive.
To bring down energy consumption and to ensure high level of dryness in final ethanol
product, Zeolite has proved to be ideal. There have been several researches on adsorption of
water from ethanol/water mixture and it is suggested that dehydration by adsorption on 3A
zeolite has the advantage that the micropores are too small to be penetrated by alcohol
molecules so that water is adsorbed without competition in the liquid phase.
It requires little energy input and operates on cycles of short duration. Therefore, it has high
adsorbent productivity and is often capable of producing very pure product. Despite many
literatures which studied on adsorption of water on 3A zeolite through simulations and
experimental works, there has been no real effort on the investigation of its productivity and
performance on actual PSA system. This research aims to study the actual effects of different
operating parameters on the efficiency of PSA system mainly in terms of product recovery and
enrichment.
33
The process flow diagram for Pressure swing adsorption is shown in the Fig.9.The parameters
which affect the adsorption rate, recovery and enrichment of ethanol are feed rate, feed
concentration, adsorption pressure and cycle time.
Fig. 9 Process flow diagram of the PSA pilot plant
34
Table 3
It can be seen in from the experimental results that increasing flow rate and cycle time could
significantly increase the percentage of ethanol recovery. After every given cycle time the
adsorber needs to be regenerated. Certain amount of ethanol that is left in the voidage and dried
ethanol that is used as purge stream are taken out during regeneration. As a result, the higher
the amount of ethanol being fed during adsorption process, the higher the percentage of the
ethanol recovery of the PSA system. Likewise, the shorter the cycle time, the more amount of
dried ethanol as purge stream is needed during regeneration. However, the effect of the cycle
time on the product concentration cannot be clearly seen since the amount of zeolite packed in
the adsorber was in abundant and the breakthrough had not yet occurred.
It can be suggested that increasing adsorption pressure to increase the water partial pressure
and hence increasing the adsorption capacity can improve the quality of the product or the
ethanol concentration. Furthermore, it was shown that as the flow rate is increased, the ethanol
product concentration was also higher.
35
11. Hybrid PSA-Membrane Gas Separation Process [13]
Advances in non-cryogenic gas separation process applications over the past 20 years have
been driven by the need to improve efficiency and reduce cost, via alternatives to several
traditional, energy-intensive gas separation processes (distillation, chemical absorption). High-
purity hydrogen, which is foreseen as the fuel for the future, is commercially produced by
pressure swing adsorption (PSA), a typically low product recovery process. Previous studies
(Sircar et al., 1999; Sircar & Golden, 2000) identified that integrating a membrane module into
PSA can improve the overall recovery of the separation process. Membrane gas separation
processes are also shown to be cost-effective in separating greenhouse gases from gaseous
mixtures at high purity (CO2 capture and sequestration). Numerous studies (Bhide et al., 1998;
Naheiri et al., 1997, Zolandz & Fleming, 1992) show that combinations of a membrane module
and another separation process offer lower cost and better separation performance than an all-
membrane separation system. The first combination of a membrane and an adsorption
separation process is attributed to Mercea and Hwang (1994); a PSA unit was used to improve
the O2 enrichment performance of a Continuous Membrane Column (CMC), and the
combination featured superior economics and separation performance over both PSA and CMC
processes. Feng et al. (1998) proposed an integrated process in which gas permeation is
included in the sequential steps of PSA, hence considering permeation occurring in a cyclic
fashion. Hydrogen purification from a gaseous mixture has also been studied: results show that
a hybrid PSA-membrane achieves higher purity compared with a standalone PSA process.
Other PSA-membrane combinations are shown to improve the performance of either of the two
units (Sircar et al., 1999; Esteves & Mota, 2002), yet none presents a detailed mathematical
model and numerical solution procedure for simulation and optimisation. The main goal of this
paper is thus to study the potential of a PSA-membrane HSS by developing a rigorous
mathematical model for its dynamic simulation and optimisation, and by using it to obtain
relevant results and design conclusions. Air separation is the exemplary case study for the
hybrid gas separation process.
36
11.1 Process Description: Hybrid Separation Systems (HSS)
All hybrid PSA-membrane processes are classified into two categories in the literature: (a)
Membrane followed by PSA (Class I), (b) PSA followed by membrane (Class II). Rigorous
mathematical models combine all equations describing the dynamic behaviour of the
membrane separation module into the cyclic operating steps of the PSA process; such models
are sets of Integral Partial Differential and Algebraic equations (IPDAEs) and their
implementation for dynamic simulation and optimization is often challenging and
cumbersome.
HSS I: In a Class-I HSS flowsheet, the membrane comes before the PSA (Figure 10a). The
first processing step is feeding fresh compressed gas into a hollow fibre module: the permeate
is obtained at the shell side (atmospheric pressure), while the residue stream (assumed to be at
feed pressure) is obtained at the tube side of the fibre module. Depending on PSA selectivity,
the membrane residue or permeate is used as PSA feed: in N2 production (HSS with same
selectivity) the N2-rich (residue) stream is fed to PSA; in O2 production (HSS with opposite
selectivity) the O2-rich (permeate) stream is used. Either the residue or the recompressed
permeate is fed in the first step (pressurisation), yet the high-pressure residue stream is the only
fed in the second step (adsorption).
HSS II: In a Class-II HSS flowsheet, the membrane comes after the PSA (Figure 10b); Sircar
et al. (1999) considered such a HSS to improve the recovery of a H2 PSA process. The cyclic
steps of this HSS start with fresh feed introduction into the PSA unit; then, the purge gas from
each PSA bed passes through the membrane to increase recovery. The membrane residue
stream obtained can be recycled as fresh feed to the PSA bed or (in the case of multiple beds),
the permeate stream can be used for purging other beds. Generally, feed conditions for the PSA
unit depend on the membrane module (HSS I); feed conditions for the membrane unit depend
on the PSA beds effluent (HSS II).
The present study is based on separation selectivity towards the target species. A binary gas
mixture Hybrid Separation System (HSS) in which the gas more adsorbed in the PSA is more
permeable through the membrane is a HSS with same selectivity; when the same gas is the
least permeable, then we have a HSS with opposite selectivity. Polymeric membranes are
usually only selective to O2 (O2 being obtained as permeate), but for PSA, either O2 or N2 can
be more adsorbed (depending on the adsorbent used). The combined HSS mathematical model
37
of this paper thus considers (Akinlabi, 2006): (a) A dual-bed PSA unit (producing N2 on
carbon molecular sieve and O2 on zeolite 5A), and (b) A steady-state, isothermal, cross-flow
permeation hollow fibre membrane module.
Fig. 10 The two Hybrid Separation System (HSS) flow sheets considered:
(a) HSS I,
(b) HSS II.
38
REFERENCES
1. http://en.wikipedia.org/wiki/Desalination_membrane,24/01/11, 12:32
2. www.dae.gov.in/ni/nimay05/PDF/Desalination%20Of%20Water.pdf, 26/01/11, 8:45
3. http://en.wikipedia.org/wiki/Osmosis, 02/02/11, 9:30
4. http://en.wikipedia.org/wiki/Separation_process, 10/02/11, 7:50
5. http://en.wikipedia.org/wiki/Azeotropic_distillation, 15/02/11, 9:15
6. www.epa.gov/opptintr/greenengineering/pubs/malone.pdf, 14/03/11, 10:25
7. en.wikipedia.org/wiki/Reactive_distillation, 25/03/11, 8:50
8. www.che.iitb.ac.in/courses/uglab/cl431/ms402-crd, 15/04/11, 10:10
9. J.D.SEADER AND ERNEST J. HENLEY,‖SEPARATION PROCESS PRINCIPLES‖,
Wiley Publication,2ND
EDITION, CH 1 Separation Processes(Page No.8-17)
10. R. TAYLOR, R. KRISHNA ―MODELLING REACTIVE DISTILLATION‖
DEPARTMENT OF CHEMICAL ENGINEERING, CLARKSON UNIVERSITY,
POTSDAM, NY 13699-5705, USA. (Page No. 2-7)
11. A. V. SOLOKHIN AND S. A. BLAGOV ―REACTIVE-DISTILLATION IS AN
ADVANCED TECHNIQUE OF REACTION PROCESS OPERATION ― , Lomonosov State
Academy of Fine Chemical Technology, prospekt Vernadskogo 86, 117571, Moscow, Russia.
12. P. PRUKSATHORN AND T. VITIDSANT‖ PRODUCTION OF PURE ETHANOL
FROM AZEOTROPIC SOLUTION BY PRESSURE SWING ADSORPTION‖, AMERICAN
J. OF ENGINEERING AND APPLIED SCIENCES 2 (1): 1-7, 2009 ,ISSN 1941-7020
13. CHARLES O. AKINLABI, DIMITRIOS I. GEROGIORGIS, MICHAEL C.
GEORGIADIS AND EFSTRATIOS N. PISTIKOPOULOS ―MODELLING, DESIGN AND
OPTIMISATION OF A HYBRID PSA-MEMBRANE GAS SEPARATION PROCESS‖, 17th
European Symposium on Computer-Aided Process Engineering (ESCAPE17) , (V. Plesu and
P.S. Agachi, Editors)
14. CARSTEN BUCHALY, PETER KREIS, ANDRZEJ GÓRAK ―HYBRID SEPARATION
PROCESSES – COMBINATION OF REACTIVE DISTILLATION WITH MEMBRANE
SEPARATION‖, Proceedings of European Congress of Chemical Engineering (ECCE-6),
Copenhagen, 16-20 September 2007
15. S. ENDERS, G. WOZNY, E. SORENSEN ” AZEOTROPIC PRESSURE SWING
DISTILLATION‖ , Tag der wissenschaftlichen Aussprache:14.April 2008, Berlin 2008 D83
39