1

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: dprao@iitk.ac.in; Phone: +91-512-2597873; Fax: +91-512-2590104.

2

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

3

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

4

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

5

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

6

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

7

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

8

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

9

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

10

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+ +

11

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

12

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

13

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

14

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.

15

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

Backhaus, A.A. (1921). Continuous process for the manufacture of esters. US Patent 1400849. Backhaus, A.A. (1922). Apparatus for producing high grade esters. US Patent 1403224. Backhaus, A.A. (1923a). Process for producing high grade esters. US Patent 145662. Backhaus, A.A. (1923b). Process for esterification. US Patent 1454463. Chandra, A. (2004). Studies on a Higee with split packing. M.Tech Thesis, Department of Chemical Engineering, IIT Kanpur, INDIA. Chen, F., Huss, R.S., Doherty, M.F., & Malone, M.F. (2002). Multiple steady states in reactive distillation: kinetic effects. Computers and Chemical Engineering, 26, 81-93. Ciric, A.R., & Miao, P. (1994). Steady state multiplicities in an ethylene glycol reactive distillation column. Industrial and Engineering Chemistry Research, 33, 2738-2748. Da Silva, F.A. & Rodrigues, A.E. (2001). Propylene/Propane Separation by Vacuum Swing Adsorption using 13X Zeolite. AIChE Journal, 47 (2), 341-357. van Hasselt, B.W., Lebens, P. J.M., Calis, H.P.A., Kapteijn, F., Sie, S.T., Moulijn, J.A. & van den Bleek, C.M. (2004). A numerical comparison of alternative three-phase reactors with a conventional trickle-bed reactor. The advantages of countercurrent flow for hydrodesulfurization. Chemical Engineering Science, 54, 4791-4799. Jacobs, R., & Krishna, R. (1993). Multiple solutions in reactive distillation for methyl-tert-butyl ether synthesis. Industrial and Engineering Chemistry Research, 32, 1706-1709. Lander, E.P., Hubbard, J.N. & Smith, Jr., L.A. (1983). Revving-up refining profits with catalytic distillation. Chemical Engineering, 90, 36-39.

16

Meili, A. (1997). Practical process intensification shown with the example of a hydrogen peroxide distillation system. In Proceedings of the 2nd International Conference on Process Intensification in Practice; BHR Group Conference Series 28; BHR Group: London, U.K. Murthy, D.S., Sivakumar, S.V., Kant, K. & Rao, D.P. (2004). Process Intensification in a ‘Simulated Moving-Bed’ Heat Exchanger. In ASME Heat Transfer / Fluids Engineering Summer Conference: North Carolina, USA. Nijhuis, S.A., Kerkhof, F.P.J.M., & Mak, A.N.S. (1993). Multiple steady states during reactive distillation of methyl tertiary butyl ether. Industrial and Engineering Chemistry Research, 32, 2767-2774. Oxley, P., Brechtelsbauer, C., Ricard, F., Lewis, N. & Ramshaw, C. (2000). Evaluation of Spinning Disk Reactor Technology for the Manufacture of Pharmaceuticals. Industrial Engineering and Chemistry Research, 39 (7), 2175-2182. Pratheeba, C.N. (2002). Liquid-liquid extraction using immobilized phase in bed of soft and hard particles. M.Tech Thesis, Department of Chemical Engineering, IIT Kanpur, INDIA. Ramachandran, R. & Dao, L.H. (1994). Method of producing unsaturated hydrocarbons and separating the same from saturated hydrocarbons. US Patent 5,365,011. Ramshaw, C. (1983). “Higee” Distillation - An Example of Process Intensification. Chemical Engineering, 389, 13-14. Ramshaw, C. & Mallinson, R. H. (1984). Mass transfer apparatus and its use. European Patent 0,002,568. Rao, D.P., Sivakumar, S.V., Kumar, A.S., Chakravarti, J., & Ramaprasad, B.S.G. (2004). Process intensification in fixed beds using moving-port systems. In AIChE Spring National Meeting: New Orleans, LA, USA. Rao, D.P., Sivakumar, S.V., Mandal, S., Kota, S., & Ramaprasad, B.S.G. (2004). A Novel Simulated Moving-Bed Adsorber for the fractionation of gas mixtures. Journal of Chromatography A (Article in press). Rao, D. P., Bhowal, A., & Goswami, P.S. (2004). Process Intensification in Rotating Packed Beds (HIGEE): An Appraisal. Industrial Engineering and Chemistry Research, 43 (4), 1150-1162. Rege, S.U., Padin, J. & Yang, R.T. (1998). Olefin/Paraffin Separations by Adsorption: π-Complexation vs. Kinetic Separation. AIChE Journal, 44(4), 799-809.

17

Rege, S.U. & Yang, R.T. (2002). Propylene/propane separation by pressure swing adsorption: sorbent comparison and multiplicity of cyclic steady states. Chemical Engineering Science, 57, 1139-1149. Ruthven, D.M. (1984). Principles of Adsorption and Adsorption Processes, John Wiley & Sons, U.S.A. Siirola, J.J. (1995). An industrial perspective on process synthesis. AIChE Symposium Series, 91(304), 222-233. Sikavitsas, V.I., Yang, R.T., Burns, M.A., & Langenmayr, E.J. (1998). Magnetically stabilized Fluidized Bed for Gas separation: Olefin-Paraffin Separations by π-Complexation. Industrial Engineering and Chemistry Research, 34, 2873-2880. Sivalingam, G., Radhika, M., Rao, D. P., & Rao, M. S. (2002). Process Intensification in a Model Trickle-Bed Reactor. Industrial Engineering and Chemistry Research, 41(13), 3139-3144. Sneesby, M.G., Tade, M.O., Datta, R., & Smith, T.N. (1998). Steady state transitions in the reactive distillation of MTBE. Computers and Chemical Engineering, 22, 879-892. Stankiewicz, A. & Moulijn, J.A. (2002). Process Intensification. Industrial Engineering and Chemistry Research, 41(8), 1920-1924. Taber, R. E, & Hawkinson, D. R. (1959). Fluid Mixing Device. U.S. Patent 2,894,732. Towler, G.P., and Frey, S.J. (2002). Reactive Distillation. In Kulprathipanja, S. (Ed) Reactive Separation Process. New York: Taylor and Francis. Trent, D. & Tirtowidjojo, D. (2001). Commercial operation of a rotating packed bed (RPB) and other applications of RPB technology. In Proceedings of the 4th International Conference on Process Intensification for the Chemical Industry; Gough, M., Ed.; BHR Group Ltd.: Cranfield, U.K. Tsouris, C. & Porcelli, J.V. (2003). Process Intensification – Has Its Time Finally Come? Chemical Engineering Progress, 99 (10), 50-55.

18

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.

19

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

20

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