Final short 2003

Made By: Dev Mehta Guided By: Dr. Bina SenguptaCo-Guide: Mrs. Sumita Panchal

• The simulated counter-current process (Simulated Moving Bed - SMB) was developed in the early 1960's by the Universal Oil Products Company.

• It is an adsorptive separation technology, which keeping a solid bed fixed imitates the same process carried out in imaginary countercurrent moving beds.

• This is carried out by patented adsorbent chambers and rotary valves.

• The presentation is focused on this technology and the following topics will be covered.

Introduction

http://www.arifractal.com/What%20is%20SMB%20chromatography.pdf

•The batch process is one in which the adsorption bed becomes completely saturated and needs to be regenerated after a fixed amount of time.

•The continuous process is one in which a counter current staged contact between the feed (which needs to be purified), adsorbent and the desorbent is either by true or by simulated recirculation of the adsorbent.

The continuous process has various advantages over the batch process:

•Efficiency of adsorption is higher in the continuous mode. •Large portion of adsorbent bed unused in batch.

•Composition at any level is invariant of time in continuous mode. •HETP 3X more for batch processes.

•25X more adsorbent required in batch + 2X times desorbent inventory.

Batch vs. Continuous Operations:

ADSORPTION, LIQUID SEPARATION -Stanley A. Gembicki, James A. Johnson, Anil R. Oroskar and James Rekoske UOP

• Consider a hypothetical moving bed system.

• Solid adsorbent circulated as dense bed in closed loop.

• Liquid streams flow down– counter current to solid.

• 4 Streams- two input and two output.

• The locations of injection points remain fixed.

System has various disadvantages.

• Fluidized beds – Hard to maintain uniform flow & inefficient.

• Conveying solid in screen buckets--bypassing of flow around the individual beds.

• Screw Conveying– Erosion & Attrition, mechanical parts friction.

Desorbent

Extract

Feed

Raffinate

Moving Bed Systems


Simulated Moving bed Sorption SeparationsDesorbent

Extract

Feed

Raffinate

• Bed held stationary, liquid flows down and lines periodically change positions downward.

• A shift flow through the bed, simulates the movement of solid in the opposite direction. Same as a moving bed.

• Not continuous however, approximately the same effect is produced by providing multiple adsorbent beds and liquid lines to the chamber, and sequentially switching each net stream from one bed to the next bed.

• Consider a feed of material A and B, A is more selectively adsorbed on the solid adsorbent and is the desirable product.

• D is the desorbent, which has the ability to displace A from the adsorbent pores.


Liquid Flow

AdsorbentParticles

ZeoliteCrystals

InterstitialVoids Non-Selective

Macro-Pores

Contains Selective Volume

(Micro-Pores)

Mass Transferby Convection

Mass Transferby Diffusion

Mechanisms• Solid zeolites as adsorbent

particles.

• Porous inner structure & interstitial voids.

• Separation only takes place in inner pores and this is called the selective

Vw

Bulk Liquid Phase

Vw

Bulk Liquid Phase

Va

Adsorbed Phase

Va

Adsorbed Phase

FeedT=0

FeedT=T

AW bulk liquid flow

Li’ (downward flow in moving bed)

Li (total flow)

• Shift in position of feed point after T seconds.

• From point of view of feed the bed is at higher location at time T sec and bed is simulated.

• Complication, motion of selective and non-selective volume both simulated.

Simulation Mechanism

Mass Transfer

Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL

Solid adsorbent bed

Bed Line“Ports”

Net Streams“Tracks”

Crossover Lines

Rotor Plate

Track Plate

Drive Shaft

• Key to exact simulation, it sequences and directs the flows of feed, desorbent, and extract in and out of the multiple adsorbent beds.

• Hydraulically driven, does the job of 300 plus individual valves.

• The CMI directs the flows to the correct beds of the adsorbent chamber by aligning the crossover pipes of the rotor plate to the ports of the bottom head of the CMI.

Advantages:Better Process PerformanceHigher ReliabilityLower Operating Costs

Rotary Valve

Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL Web:http://www.uop.com/products/equipment/aromatics-separation/

DesorbentExtractFeed Raffinate

Simulated Moving bed Sorption Separations

D

E

F

R

desorbent

extractraffinate A (desired product)

Circulating pump

RV

B (Undesirable Product)A+B Feed


Zone 1 Adsorption Zone

Solid Adsorbent

Solid Adsorbent

A

BD

B

B

A

A

A

A

D

B

B

B

pores

Feed

Raffinate

B

• It is defined as the section between the feed and raffinate points.

• The primary function of Zone 1 is to adsorb A from the liquid feed.

• The solid adsorbent initially in this zone only contains B & D in its pores.

• As the liquid stream flows downward, A is transferred from the liquid to the pores, also B&D are desorbed at the same time due to concentration driving forces and selectivity difference.

• This means B&D is transferred from the pores to the liquid making room for A.

• A is adsorbed and hence is called adsorption zone.


Solid Adsorbent

Solid Adsorbent

D

BAA

A

B

D

D

DD

AA

• When zone two reaches the solid adsorbent the solid contains still some B because the separation is not complete.

• It is the section between extract and feed points.

• The primary function of zone two is to remove the remaining B from the pores of the solid.

• The liquid entering the top of Zone 2 contains no B, and B is gradually displaced from the pores by A & D.

• B can be desorbed almost completely this can be done without simultaneously desorbing A because A is more strongly adsorbed.

Zone 2 Purification Zone

Extract

FeedMolex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL

Solid Adsorbent

Solid Adsorbent

A

D

AA

D

D

D

D

D

DD

D

• Zone 4 is defined as the section between the desorbent and extract points.

• The main function of this zone is to desorb A from the pores.

• The solid entering the bottom of this zone carries only A & D in its pores.

• As liquid flows down A in the pores is displaced by D.

• Zone 3 is the zone in which A is desorbed and thus its is referred to as the desorption zone.

Zone 3 Desorption Zone

Desorbent

Extract


• Zone 4 is defined as the section between the Raffinate and desorbent points.

• The purpose of Zone 4 is to keep B, which is at the bottom of Zone 1, from entering Zone 4 and flowing through Zone 4 to Zone 3 where it can contaminate the extract material.

• If the flow rate is set so that desorbent flows up in Zone 4, raffinate material would be prevented from gaining access to Zone 3 where it would contaminate the purified extract stream.

• This means that the main function of Zone 4 is to separate Zone 3 from Zone 1 and as a result it is referred to as the buffer zone.

Desorbent,D

Feed,A + B

Raffinate,B + D

Extract,A + D

IV

IV

III

II

I

Zone 4 Buffer Zone


Zone IV Flow

1

D2

E

F

R

7

16

t = 0

IV

III

II

I

IV

23

Zone I Flow

1

D4

E

F

9

18

t = 90 s.

IV

III

II

I

R

Zone II Flow

1

D11

E16

t = 360 s.

I

IV

III

II

F

R8

• Minor complication arises, because lines are successively employed in carrying feed or extract from it.

• Goal to remove feed from lines through which extract will flow & remove extract from lines through which desorbent will flow.

• High recovery and Purity.

• Desorbent displaces extract from its bedline. Extract displaced displaces feed left in the bedline.

III

II

III

II

RVRV

D

Ho

Hi

F

E

Z

Flushes

Line Flush

Zone Flush

• The zone flush non selective material from the non-adsorbed volume of the adsorbent before desorbent is sent to the zone.


•First commercial application of SMB- UOP Molex in 1960 used to manufacture detergents.

•Since then UOP alone has about 134 units put on stream in a variety of applications that produce in access of 20 million t/year of products, worth more than 10 billion USD/yr. The extent of Sorbex technology commercialization as of 2001, is shown below.

ADSORPTION, LIQUID SEPARATION Stanley A. Gembicki, James A. Johnson, Anil R. Oroskar and James Rekoske UOP

Commercial Applications

Documents

Final short 2003