Final short 2003
Transcript of 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
ADSORPTION, LIQUID SEPARATION -Stanley A. Gembicki, James A. Johnson, Anil R. Oroskar and James Rekoske UOP
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.
ADSORPTION, LIQUID SEPARATION -Stanley A. Gembicki, James A. Johnson, Anil R. Oroskar and James Rekoske UOP
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
Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL
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.
Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL
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
Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL
• 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
Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL
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.
Molex Section , Operating Manual , LAB Unit , Vinu K Chandran, AK Roy IOCL
•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