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Innovations for Process Intensification in the Process Industry
S.V. Sivakumar, N. Kaistha, D.P. Rao* Department of Chemical Engineering
Indian Institute of Technology Kanpur, Kanpur 208 016, INDIA.
Abstract
Our recent work on innovations for process intensification for distillation, adsorption,
trickle-bed reactors, absorption, extraction and reactive distillation is presented. The key
to process intensification lies in novel designs that substantially enhance mass transfer
rates for equipment miniaturization and that combine distinct tasks such as reaction and
separation for improved overall performance. A modification to existing rotating packed
bed (HIGEE) is described using which the HETP reduces by an order of magnitude. Thus
the complete column section in a distillation column can be miniaturized to fit inside a
reboiler. The use of the modified rotating packed bed for the hydrogenation of α-methyl
styrene gave an experimentally measured 60 fold increase in the reaction rate over
conventional trickle-bed reactors. A two-bed simulated moving-bed pressure swing
adsorption scheme incorporating reflux to separate a binary gas mixture into pure
products and a moving-port system that realizes countercurrent flow for adsorption is also
described. For extraction and absorption processes, the use of immobilized solvents as a
means for enhancing throughputs is proposed. A brief overview of reactive distillation
technology and its miniaturization using HIGEE is presented. Our recent results are
extremely encouraging and suggest that process equipment / plants miniaturization is
achievable in the near future.
Keywords: Process intensification, HIGEE, Simulated moving beds, Reactive
distillation. * Corresponding author - email: [email protected]; Phone: +91-512-2597873; Fax: +91-512-2590104.
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1. Introduction
‘Process Intensification’ refers to the development of radical technologies for the
miniaturization of process plants while achieving the same production objective as in
bulky conventional processes. The goal is to bring down the plant size by 10-1000 times
(Stankiewicz and Moulijn, 2002) by replacing large, expensive and energy-intensive
equipment or processes with ones that are smaller, less costly and more efficient (Tsouris
and Porcelli, 2003). Hybridization of multiple unit operations and processes into a single
compact device is the rule of thumb for process intensification.
Smaller is safer! Hence, process intensification dramatically increases the intrinsic
safety of chemical processes. The aftermath when something goes wrong in process
vessels of large volume was evident in the tragedies of Flixborough and Bhopal. Though
the philosophy behind process intensification has been in existence for several years, it
had a conservative reception from industries due to their unwillingness in taking the risks
with a new technology. However, companies like ICI (Ramshaw, 1983 and Ramshaw,
1984), Shell (Taber and Hawkinson, 1959), Sulzer (Meili, 1997), SmithKline Beecham
(Oxley, Brechtelsbauer, Ricard, Lewis & Ramshaw, 2000), Eastman Chemical (Siirola,
1995) and Dow (Trent and Tirtowidjojo, 2001) embraced the process intensification
philosophy and adopted it in several of their recent processes with great commercial
success.
One of the reasons why conventional units like distillation / absorption towers and
reactors are so bulky is that the interphase transfer rates are governed by gravity. One
way to enhance throughputs and the interphase transfer rate is to replace the gravitational
field with centrifugal fields which are higher by a few orders of magnitude. Process
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intensification research has therefore naturally focused on the use of rotating packed beds
for the miniaturization of reactors and separators.
Another area receiving much attention in process intensification is the development
of adsorption based gas separation technologies for replacing the large and expensive
cryogenic distillation units. Adsorptive gas separations carried out in fixed beds suffer
from small driving force for mass transfer. It is virtually negligible on either side of the
mass transfer zone, as the flowing fluid is almost in equilibrium with the solid phase.
Therefore, the bed is not completely utilized and hence the productivity is low in fixed
beds. On the other hand, due to countercurrent contact in moving beds there is complete
bed utilization and the productivity is high, but is difficult to realize in practice due to
inherent difficulties in solid handling (Ruthven, 1984). A simulated moving-bed can
accomplish a moving-bed like operation in a fixed bed.
Absorption and extraction columns, the other major unit operations in the chemical
industry, are limited by flooding and hence cannot be operated at high throughputs. By
immobilizing the solvent in a medium having high porosity, one can increase the
throughput of the continuous phase without the problem of flooding.
All the above methods enhance either the mass transfer coefficient, or the driving
force thereby effecting process intensification. Another approach is the combination of
multiple tasks such as reaction and separation into a single unit. The basic philosophy is
to choose the tasks in a manner such that their combination leads to better overall
performance. Since any chemical process involves unit operations for reaction and
separation, most such task combinations fall under the umbrella of reactive separation
processes. The combination of reaction and separation is effective when either the
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reaction substantially improves separation through enhanced mass transfer rates or the
separation drives the reaction to higher conversions or both. We thus have traditional
examples of reactive absorption, chemical adsorption and reactive extraction processes
where reaction is used as a means for enhancing mass transfer for better separation. A
more recent development is the combination of reaction and distillation in a single
reactive distillation column where the continuous removal of products drives the reaction
to near completion for equilibrium limited reactions.
The ways and means to accomplish process intensification thus boil down to
innovations that result in:
• Increasing the process throughputs
• Increasing the transfer coefficients
• Increasing the interfacial area
• Increasing the driving force for mass transfer
• Hybridization of different unit operations
In this article, we have presented our on-going work in process intensification using
rotating packed beds, rotating trickle-bed reactors, simulated moving beds, and
absorption/extraction with immobilized solvent. We also discuss reactive distillation as it
has been used commercially with phenomenal success.
2. HIGEE
Figure 1 shows the schematic of a horizontally aligned rotating packed bed (RPB) with a
continuous packing. This unit is also called HIGEE. The rotor is driven at 500-2500 rpm
to achieve high centrifugal fields. The vapor is introduced into the casing which flows
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through the packing and comes out from the eye of rotor. Liquid is fed through a
stationary distributor placed at the eye of the rotor.
The liquid flows as a thin film over the packing due to the high centrifugal
acceleration (100-1000 times of g) and therefore raises the upper limit of flooding and
permits using packing of high surface area in the range of 1000-5000 m2/m3 which is 3-
10 times of that used in conventional packed columns. This in itself enhances the liquid-
side mass transfer coefficient, kL, by 5 to 8 times compared to conventional columns
(Rao, Bhowal & Goswami, 2004). However, the gas-side coefficient, kg, is in the range of
that for conventional columns. The gas undergoes a solid-body-like rotation in the rotor.
Therefore process intensification is limited to the extent of the increase in surface area of
packing. If this limitation can be overcome, then Higee can replace the conventional
distillation and absorption columns.
2.1. Modified HIGEE: We have modified the rotor of the HIGEE to enhance kg, when
the transfer rate is limited by the gas-side resistance as in the case of distillation. Figure 2
shows the photograph of the modified HIGEE unit. Instead of a single packing element, it
has been split into annular rings with spacing in between the rings. One set of alternate
rings have been fixed to one of the cover plates of the rotor. The other set of rings have
been fixed on the other plate. Types of packing material that could be used are metal-
foam and wound wire-mesh. The two plates can be made to rotate in the same direction,
or directions opposite to each other. When the packing elements are rotating in counter
direction, the angular velocity of vapor gets reversed as it flows through the successive
packing elements. The slip velocity between the liquid and the gas of 20 m/s or more can
be achieved in the rotor. This may lead to an enhancement in kg by 5-10 times. In
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contrast, the angular slip velocity is only 2-5 cm/s in the conventional RPB. Note that the
centrifugal force is in the outward direction even if the alternate rings are rotated in the
opposite directions. Therefore the liquid flows over the packing as films, but flows out of
the ring as fine spray droplets. This is likely to enhance liquid-side mass transfer
coefficients as well.
2.2. Distillation in modified HIGEE: The significant increase in the liquid side and gas
side mass transfer coefficients result in a reduction in the HETP from 25-50 cm in
conventional packed beds to a about 1-2 cm in RPBs. The volume of the RPB is thus very
small and can be housed either in the reboiler or the condenser. Figure 3 shows the sketch
of a distillation setup with the rotor housed in the reboiler. The split packing permits the
feed to be introduced in between the annular rings. Both the stripping and enriching
sections are integrated within the reboiler. There is no need for columns. This makes the
unit compact.
3. Rotating Trickle-bed Reactor
In a trickle-bed reactor (TBR), the reaction rates are generally limited by the mass tranfer
rates. Sivalingam, Radhika, Rao & Rao (2002) have shown that the rate of hydrogenation
of α- methyl styrene over a rotating string of catalyst particles was 5-7 times compared to
that of the rate that could be achieved with a gravity flow over string catalyst particles. In
order to explore enhancement of reaction rates, we carried out studies on a rotating bed of
metal-foam packing coated with Palladium. The photograph of the rotating TBR used to
study the intensification in reaction rates is given in Figure 4. Figure 5 shows the reaction
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rate vs. liquid superficial velocity. The enhancement in reaction rate was roughly 60
times compared to trickle-bed of alumina beads of 2.5 mm size under gravity conditions.
Further, besides co-current and countercurrent flow of gas and liquid, cross current
flow can also be achieved to facilitate removal of a gas product which inhibits the
reaction rate. For instance, the cross sectional-flow in the removal of H2S is
recommended for diesel hydrodesulfurization (Hasselt, Lebens, Calis, Kapteijn, Sie,
Moulijn et al., 2004). This mode of flow can be easily achieved in a rotating trickle-bed
reactor. An industrial trickle-bed reactor of 60 m3 can be replaced with 1 m3 rotating bed
reactor.
4. Simulated moving beds
As in distillation, a high driving force can be maintained across the interphase in the
simulated moving beds (SMB). Application of SMB for solid-gas contact is not reported
in the open literature to our knowledge. We have developed ‘moving-port systems’ to
design simulated moving beds.
Moving-port systems: Figure 6 shows the schematic of a moving-port system. It consists
of two closely fitted circular tubes. The inner tube has a straight slot along its length and
the outer one a helical slot. When the slots cross each other, a rhombus-shaped port is
formed. This port moves from the left to the right or the other way depending on the
direction of rotation of one of the tubes using a stepper motor. The speed of rotation sets
the port velocity. When the port reaches one end of the slot, it abruptly shifts to the other
end and continues to move in the same direction. It is possible to introduce or withdraw a
fluid from a bed of solids if the moving-port system is embedded in the bed. Several
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variants of moving-port systems are possible (A patent pending on the variants and the
applications of the moving-port systems). Simulated moving beds are designed by
embedding the moving-port systems in a fixed bed. The number of moving-ports needed
is equal to the number of streams leaving and entering the bed. These beds can be used
for the exchange heat between gases (Murthy, Sivakumar, Kant, & Rao, 2004) and
separation of gas mixtures (Rao, Sivakumar, Kumar, Chakravarti & Ramaprasad, 2004).
The potential for process intensification for the fractionation of propylene-propane in the
simulated moving-bed has been discussed elsewhere (Rao, Sivakumar, Mandal, Kota &
Ramaprasad, 2004).
Fractionation of a gas mixture: A schematic of the fractionation of a gas mixture in two
SMB adsorbers constructed with three moving-port systems each is shown in Figure 7.
For clarity the moving-ports in the bed 2 undergoing regeneration is not shown and the
ports are shown as thick slanted lines. The ports labeled 1 and 2 are used for injection of
the extract reflux and the feed gas respectively, and the port labeled 3 is for the
withdrawal of light component as one product. Ahead of the port 3, the bed is saturated
with the light component and behind port 1; it is saturated with the heavy component.
Mass transfer occurs in the stripping and the enriching zones. Light component is drawn
until the enriching zone reaches the other end of the bed. The enriching zone is
transferred to the bed 2 before bed 1 is regenerated by pressure swing. Meanwhile, the
heavy component is drawn as the other product by reducing the pressure in bed 2.
Thereafter a part of the light component product stream is used to purge the bed; the same
stream is used to presaturate the bed by pressurization. The effluent from the purge is
recycled with feed. During regeneration the moving-ports are inactive. When the
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enriching zone from bed 1 is transferred to bed 2, it should be presaturated with the light
component by then to draw light component product. When the roles of bed 1 and bed 2
are switched alternatively, the process will attain a cyclic steady state and accomplish gas
fractionation. The switching of the streams can be done using solenoid valves.
The comparison of the performance of the proposed adsorber for the fractionation of
the propylene-propane mixture against those reported in the open literature is presented in
Figure 8. The productivity was a few orders of magnitude higher than those reported in
other studies because of the higher driving force achieved due to the realization of
countercurrent flow.
5. Absorption and extraction with immobilized solvent
When a suitable solvent is immobilized in a porous medium, absorption and extraction
can be carried out like conventional pressure swing adsorption. In conventional extraction
columns, flooding restricts employing high throughputs. If the density difference between
the two phases is low, it further compounds the problem of operating the column.
Absorption with immobilized solvent: The schematic of absorptive separation in a solvent
immobilized bed is given in Figure 9. Consider that a solvent S is immobilized in the
particles of the bed, say heavy oil. When a gas mixture of CH4 and H2 is introduced into
the bed, CH4 is absorbed by the solvent immobilized in the bed. Pure H2 can be had as the
product until the mass transfer zone breaks through the bed. After breakthrough, CH4 can
be regenerated as in PSA.
Extraction with immobilized solvent: The schematic of extractive separation in a solvent
immobilized bed is given in Figure 10. Consider a binary liquid mixture of components A
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and B, where component A shows no affinity to the solvent. The solvent S1 is
immobilized. When the mixture of A and B is introduced into the bed, component B is
selectively transferred into the immobilized phase and A is drawn as the raffinate product
until the mass transfer zone breaks through. Since the immobilized phase is a liquid, B
along with the solvent can be drawn by squeezing and flash distilled to separate B from
the solvent S1. Experiments carried on the separation of toluene-hexane mixture with
sulfolane as solvent and toluene-methanol mixture with water as solvent shows the
feasibility of extractive separation by solvent immobilization (Pratheeba, 2002).
Alternatively, another solvent S2 can be used to selectively extract the component B in the
immobilized phase. The solvent S1 is always immobilized. However, a flash distillation is
required to separate B from solvent S2.
6. Reactive Distillation
Reactive distillation (RD) technology, an old concept first considered for esterification by
Backhaus in the 1920s (Backhaus, 1921; Backhaus, 1922; Backhaus, 1923a and
Backhaus, 1923b), has received much attention in both industry and academia in recent
years. In RD, reaction and separation are carried out in the same equipment instead of the
conventional “reaction followed by separation” scheme. The RD technology is very
interesting because of the potential for process intensification with substantial economic
benefits over conventional processes. The first and classic commercial success story of
this technology was that of Eastman Chemical Company for the production of methyl
acetate in the early 1980s. The main reaction is
3 3 3 3 2 CH COOH CH OH CH COOCH H O+ +
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Figure 11 shows a schematic of both the RD process and the conventional process. In
the conventional process there are nine distillation columns to separate methyl acetate
completely. The separation is difficult because of the formation of azeotropes between
methyl acetate and methanol, methyl acetate and water and a near azeotrope between
acetic acid and water. The reactive distillation process consists of a single column with
three sections: rectifying, reactive and stripping sections.
In the RD column, methyl acetate with greater than 95.68% purity is produced from
the top while nearly pure water leaves the bottom. Close to 100% conversion is achieved
in the equilibrium limited reaction due to continuous removal of products by Le
Chatelier’s principle. The need for expensive recycle is thus eliminated. The azeotrope
between methyl acetate and water is “reacted away” as it forms a four component mixture
due to the reverse reaction. Thus, not only does the separation affect the reaction
conversion favorably, the reaction makes the separation easier by effectively eliminating
an azeotrope. The single RD column is thus a complete plant in itself and the consequent
process intensification results in capital and operating costs that are a fifth of the
conventional process (Siirola, 1995).
The realization of the advantages noted above in practice, requires that the relative
volatilities of the components be such that high reactant concentration in the reactive
section is obtained. Also, the reaction rates should be high enough at the bubble point
temperature of the mixture. In cases where the relative volatilities and reaction rates are
favorable, RD has emerged as an alternative with significant economic advantages over
conventional processes. Industrial examples include esterification systems such as methyl
acetate and etherification systems such as methyl tertiary butyl ether (MTBE), ethyl
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tertiary butyl ether (ETBE) and tertiary amyl methyl ether (TAME) (Lander, 1983; and
Hickey and Adams, 1994).
Practical Design Considerations: Implementation of reaction and distillation in a single
column requires addressing practical issues related to the installation and removal of
large amounts of catalyst, proper liquid contact with the catalyst, vigorous vapor-liquid
contact in the reactive section and ensuring large liquid hold-up in the reactive section
(Towler and Frey, 2002). Operability and control issues also need to be considered at the
design stage since the combination of reaction and separation is known to cause high
non-linearity in the system with multiple steady states being routine phenomena (Jacobs
and Krishna, 1993; Nijhuis, Kerkhof & Mak, 1994; Ciric and Miao, 1994; Sneesby, Tade,
Datta & Smith, 1998; and Chen, Huss, Doherty & Malone, 2002).
For internal access to the RD column, the current practice is to provide to manways.
The mechanical design must allow for installation / removal of the catalyst and related
mechanical equipment through these manways. Typically the reaction occurs in a liquid
film surrounding the catalyst so that even liquid distribution across the column cross-
section is crucial. Liquid distributors and redistributors are used for this purpose.
Additional means for wetting the catalyst include partially flooded beds, tray designs that
give a horizontal velocity component to the vapor for better radial mixing and arranging
the catalyst containing device in a manner that enhances mixing.
In addition to proper catalyst wetting, vigorous vapor-liquid contact in the reactive
section is desirable as in equilibrium-limited reactions; the reaction extent is mainly
dependent on the separation achieved. This requires minimization of vertical backmixing
and maximization of radial mixing. For good catalyst wetting and vigorous vapor liquid
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contact the use of structured catalyst packing is recommended. Figure 12 shows the
KATAMAX structured packing patented by Koch-Glitsch. These structured packings
result in efficient vapor-liquid contact, low pressure drops and high hydraulic capacity
leading to higher through puts and mass transfer rates. Note that the liquid flowing
through the reactive section requires some reasonable residence time so that its free fall
must be prevented by providing mechanical features that force the liquid to flow in an
inclined path.
Successful implementation of RD technology also requires addressing operability and
control issues at the design stage. It is essential that the column be operated in a manner
such that the conversion and product purities are maintained near their design values for
primary disturbances such as feed composition and production rate changes. This requires
that the fresh feeds into the column be balanced as per the stoichiometry of the reaction
as an imbalance would lead to the excess reactant exiting with one of the product streams
and reducing the corresponding product purity. Systematic studies on devising the best
control strategy must be conducted at the design stage so that any design modifications to
address operability and control issues can be accommodated whenever possible.
The Miniaturization of Reactive Distillation: The concept of a HIGEE distillation can be
extended to reactive distillation systems. The high centrifugal force fields in the reactive
packing section would lead to excellent catalyst wetting with enhanced liquid mass
transfer coefficients and wetted surface area per kg catalyst. Additionally, the counter
rotation of adjacent beds would significantly enhance the vapor side mass transfer
coefficient as discussed earlier. The HETP thus reduces substantially. The better
separation would assist in driving the equilibrium reaction to complete conversion. The
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scope for process intensification is thus tremendous and it should be possible to fit the
entire column section of an RD column inside a large reboiler (See Figure 3). The single
reboiler is then effectively equivalent to a complete plant producing saleable product!
Conclusions
We have presented our recent work on process intensification and provided suggestions
for miniaturization of traditional unit operations in the process industry. Of all the
innovations studied, in our opinion, modified HIGEE with counter rotation of adjacent
beds shows tremendous potential for the miniaturization of distillation columns, ordinary
or reactive, and trickle-bed reactors. The counter rotation provides high slip to the gas
phase so that significant enhancement in the gas phase mass transfer coefficient occurs in
addition to the usual increase in liquid phase coefficient as in existing HIGEE. With this
modification, the HETP in a distillation column reduces by an order of magnitude so that
the entire column section can be fitted inside a large reboiler. The use of the modified
HIGEE for reactions on a catalyst bed can lead to upto 50-100 fold increase in the
observed reaction rate in mass transfer limited reactions causing a drastic reduction in the
reactor size. The work on SMB adsorption shows that the incorporation of reflux
provides clean gas separation. For intensification of adsorption like processes, we have
illustrated moving-ports as a means for realizing actual counter current flow for increased
mass transfer driving force. In conclusion, our recent results on process intensification are
extremely encouraging and show that the miniaturization of process equipment / plants is
not merely a dream, but a definite reality waiting to happen.
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Acknowledgements
We gratefully acknowledge the financial support provided by the Department of Science
and Technology (D.S.T), India and Praxair, Tonawanda, U.S. towards our work on Higee
and TBR. We also thank RECEMAT® International, Open Cell Material Engineering
(www.recemat.com) for sponsoring their metal foam packing for our research.
References
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Vitae S.V. Sivakumar
Mr Sivakumar got his Bachelor’s in Chemical Engineering from SASTRA University,
Tanjore, India in May 2000. He proceeded to A.C. TECH Anna University, Chennai,
India to obtain his Master’s in Petroleum Refining and Petrochemical Engineering in
December 2001. He is currently pursuing his doctorate in Chemical Engineering from the
Indian Institute of Technology, Kanpur, India. His research interests include mass
transfer and separation processes.
Nitin Kaistha
Dr Kaistha obtained his Bachelor’s in Chemical Engineering from the Indian Institute of
Technology, Kanpur, India in May 1996. He received his doctorate in Chemical
Engineering form the University of Tennessee, Knoxville, USA in December 1999. He is
currently an Assistant Professor at the Indian Institute of Technology, Kanpur. His
research interests include process development, simulation, design and control.
D.P. Rao
Dr. Rao obtained his Bachelor’s in Chemical Engineering from Andhra University,
Vishakhapatnam, India in 1965. He received a doctorate in Chemical Engineering from
Birla Institute of Technology and Science, Pilani, India in 1974. He joined the Indian
Institute of Technology, Kanpur in 1976 and has since, pursued a productive research and
teaching career there. His research interests include process intensification and separation
processes.
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Figure Captions Figure 1: Schematic of a HIGEE unit Figure 2: Schematic of the modified HIGEE Figure 3: Schematic of a HIGEE unit integrated with RPB to stage distillation Figure 4: Schematic of a rotating TBR with metal-foam packing
Figure 5: Reaction rate vs. liquid superficial velocity. Figure 6: Schematic of the moving-port system
Figure 7: Two bed SMB adsorber configuration for gas fractionation Figure 8: Histogram comparing the proposed adsorber performance against similar work in literature Figure 9: Absorptive separation with immobilized solvent Figure 10: Extractive separation with immobilized solvent Figure 11: A pictorial comparison between conventional scheme and RD for methyl
acetate production (Siirola, 1995)
Figure 12: Koch-Glitsch, Inc. KATAMAX packing installation
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Gas Inlet Gas Outlet
Liquid Outlet
Liquid Inlet
Continuous Packing
Rotating Shaft
Figure 1: Schematic of a HIGEE unit
21
Figure 2: Schematic of the modified HIGEE
22
DISTILLATE REFLUX
BOTTOM PRODUCTS DISTILLATE
Reboiler integrated with Stripping and Enriching Sections
Condenser Novel RPB
FEED
Figure 3: Schematic of a HIGEE unit integrated with RPB to stage distillation
23
Basket holding the metal-foam packing coated with Palladium
Figure 4: Schematic of a rotating TBR with metal-foam packing
24
Figure 5: Reaction rate vs. liquid superficial velocity.
0
20
40
60
80
100
120
140
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
reac
tion
rate
x107 , m
ol/(c
c of
bed
. s)
Liquid Superficial velocity, cm/s
RECEMAT Rings, 360 g, ap 2500 m2
/m3
2.2 mm Alumina Beads, 1 g, ap 1336.7 m2
/m3
25
Inner tube
Figure 6: Schematic of the moving-port system
Outer tube Port
Figure 7: Two bed SMB adsorber configuration for gas fractionation
Raffinate
Raffinate reflux
Extract reflux
Vacuum pump
Extract
REGENERATION SECTION (Moving Ports Inactive)
SEPARATION SECTION (With three ports)
Stripping Zone Enriching Zone
Feed
Purge
Bed 1
Bed 2
26
99 99.5
99.9
99.3
98.5
90.0
45.0
71.7
27.3
87.699
12.5
0
20
40
60
80
100
120
140
1 2 3 4 5 6
Ram
acha
ndra
n et
al.,
199
4
Reg
e et
al.,
199
8
DaS
ilva
& R
odrig
uez,
200
1
Reg
e &
Yan
g, 2
002
(%)P
urity
, (%
) Rec
over
y, P
rodu
ctiv
ity (m
ol/k
g h)
0.01
4
Sika
vitsa
s et a
l., 1
995
2.7
Prop
osed
SM
B290
0.01
5
0.8
% Product Purity % Product Recovery Product Productivity
Figure 8: Histogram comparing the proposed adsorber performance against similar work in literature
27
Figure 9: Absorptive separation with immobilized solvent
Pressure Swing Regeneration
Feed (CH4 + H2)
Solvent immobilized bed
H2 CH4
Figure 10: Extractive separation with immobilized solvent
A
Reg
ener
atio
n by
m
echa
nica
l squ
eezi
ng
Feed (A + B)
S1 +B
Reg
ener
atio
n by
usi
ng a
ne
w so
lven
t
S2
S2 + B
or
28
Figure 11: A pictorial comparison between conventional scheme and RD for methyl acetate
production (Siirola, 1995)
29
Figure 12: Koch-Glitsch, Inc. KATAMAX packing installation