Your SlideShare is downloading. ×
 cre ppt
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

cre ppt

703
views

Published on

Published in: Education

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
703
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
31
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Design for Mutiple Reactions PRESENTED BY: Prakash ch.sahoo Sanjeet kumar Sugyani gouda BRANCH: Chemical engineering
  • 2. Types of reactors 1.Batch- uniform composition everywhere in reactor but changes with time 2. Semi batch- in semi-batch one reactant will be added when reaction will proceed 3. Continuous reactor a. Mixed flow- this is uniformly mixed , same composition everywhere, within the reactor and at exit b. Plug flow- flow of fluid through reactor with order so that only lateral mixing is possible
  • 3. Reactor design parameter Reactor design basically means which type and size of reactor and method of operation we should employ for a given conversation Parameters • Volume of reactor • Flow rate • Concentration of feed • Reaction kinetic • Temperature • pressure
  • 4. Plug flow and mixed flow reactor design Mixed flow reactor design Applying mass balance performance equation for mixed flow reactor Plug flow reactor design Performance equation for plug flow reactor
  • 5. Plug flow vs CSTR • For any particular duty and for all positive reaction order the volume of mixed flow reactor will always be grater then plug flow • Area under curve in figure is very small for plug flow as compared to mixed flow so volume is small for plug flow. • When conversion is small, the reactor performance is only slightly affected by flow type. the perforation ratio very rapidly at high conversion. • Density variation during reaction affects design, however it is normally of secondary importance compared to the difference in flow type.
  • 6. Multiple reactor system • Number of plug flow reactor in series are theoretically same as equivalent volume of a single plug flow reactor. • Number of mixed flow reactor of equal size in series may be used when we need high conversion and can’t perform in a single reactor. • From the given graph, for first order reaction, conversion for series of equal size reactor can be find
  • 7. Mixed flow reactor of different size in series • From the fig it is clear that for plug flow reactor volume can be find by dashed area and for mixed flow whole area. • When we are have to use mixed flow reactor, then we can use different size mixed flow reactor so, that over all volume would be small • To optimized or to find how different size of mixed flow reactor should used we have to maximized lower dashed rectangle. • This optimization gives the slope of diagonal of the rectangle should be equal to slope of curve at intersection of these two reactor. • Levenspiel , has proved that after overall economic consideration equal size reactors in series are economical.
  • 8. Design for parallel reaction • When a reactant gives two product (desired, and undesired)simultaneously with different rate constant then this is called a parallel reaction. • To keep maximum amount of desired product we can take following steps. • Ifa1>a2 or the desired reaction is of higher order then keep reactant concentration high for high product concentration. • If a1<a2 than for desired reaction keep reactant concentration low. • For a1=a2 change in reactant concentration will not affect the product then, because rate constant k1 and k2 are different at different temperature so, we can keep our temperature such that desired product will be high or use of catalyst would be a option which are
  • 9. Reactor design for multiple reaction • In multiple reaction reactor design contacting pattern is most important factor to get a particular product. • In irreversible reaction in series like the mixing of fluid of different composition is the key to formation of intermediate. The maximum possible amount of intermediate is obtained if fluid of different composition and different stage of conversation are not allowed to mixed. • In series of reaction if intermediate reactant is our desired product than semi batch reactor will be used.
  • 10. Irreversible series-parallel reaction • Multiple reaction that consist of steps in series and steps in parallel reaction. • In these reaction proper contacting pattern is very important. • The general representation of these reaction are • Here the reaction is parallel with respect to reactant B and in series with A. Halogenations of alkane is a example of this kind of reaction where reaction is parallel with respect to halogen
  • 11. Reaction type • Chemical kinetics of reaction can be known by knowing the type of reaction • For reactor selection reaction type will tell us about heat of reaction either reaction is endothermic or exothermic. • Selectivity is defined as reaction rate ratio for two parallel reaction. • Catalyst are used to increase reaction rate and selectivity for a specific reaction. • We can determine what type of catalyst will be used. • Reaction temperature range will be determined.
  • 12. Reactor type • Reactor may be a plug flow or mixed flow or batch flow reactor or other. • Contacting pattern of reaction will be known. • In case of expensive catalyst and high heat transfer rate required, mixed flow(fludized bed) reactor are used. • For high mass transfer plug flow (packed bed) reactor will be used.
  • 13.  Parallel rxns (competing rxns)Parallel rxns (competing rxns) B A C  Series rxns (consecutive rxns)Series rxns (consecutive rxns) A B C  Complex rxns (Parallel + Series rxns)Complex rxns (Parallel + Series rxns) A + B C + D A + C E  Independent rxnsIndependent rxns A B + C D E + F k1 k2 k1 k2 k1 k2 k1 k2 Definition of Multiple Reaction
  • 14. Different reactors and schemes for maximizing the desired productDifferent reactors and schemes for maximizing the desired product A B A B A B B A A B (a) CSTR (b) tubular reactor (c ) batch (d) semi-batch 1 (e) semi-batch 2 A B A B (f) Tubular reactor with side streams (g) Tubular reactor with side streams A B (i) Tubular reactor with recycle (h) Series of small CSTRs B A Figure 6-3Figure 6-3
  • 15. Figure 6-3Figure 6-3 Different reactors and schemes for maximizing the desired productDifferent reactors and schemes for maximizing the desired product
  • 16. Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants for the parallel reaction D (Desired Product) A + B U (Undesired Product) Case I : α1 > α2, β1 > β2, a = α1-α2 > 0, b = β1-β2 > 0 the rate selectivity parameter k1 k2 b B a A U D DU CC k k r r S 2 1 == To maximize the SDU, maintain the concentration of both A and B as high as possible  a tubular reactor (Figure 6.3 (b))a tubular reactor (Figure 6.3 (b))  a batch reactor (Figure 6.3 (c))a batch reactor (Figure 6.3 (c))  high pressures (if gas phase), reduce inerthigh pressures (if gas phase), reduce inert
  • 17. Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants for the parallel reaction D (Desired Product) A + B U (Undesired Product) Case II : α1 > α2, β1 < β2, a = α1-α2 > 0, b = β2-β1 > 0 the rate selectivity parameter k1 k2 b B a A U D DU Ck Ck r r S 2 1 == To maximize the SDU, maintain CA high and CB low.  a semibatch reactor in which B is fed slowly into A.a semibatch reactor in which B is fed slowly into A.  a tubular reactor with side stream of B continuallya tubular reactor with side stream of B continually  a series of small CSTRs with A fed only to the first reactora series of small CSTRs with A fed only to the first reactor
  • 18. Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants for the parallel reaction D (Desired Product) A + B U (Undesired Product) Case III : α1 < α2, β1 < β2, a = α2-α1 > 0, b = β2-β1 > 0 the rate selectivity parameter k1 k2 b B a AU D DU CCk k r r S 2 1 == To maximize the SDU, maintain the concentration of both A and B as low as possible  a CSTRa CSTR  a tubular reactor in which there is a large recycle ratioa tubular reactor in which there is a large recycle ratio  a feed diluted with inert materiala feed diluted with inert material  low pressures (if gas phase)low pressures (if gas phase)
  • 19. Example 6-3: Minimizing unwanted products for two reactantsExample 6-3: Minimizing unwanted products for two reactants for the parallel reaction D (Desired Product) A + B U (Undesired Product) Case IV : α1 < α2, β1 > β2, a = α2-α1 > 0, b = β1-β2 > 0 the rate selectivity parameter k1 k2 a A b B U D DU Ck Ck r r S 2 1 == To maximize the SDU, maintain the concentration of both A and B as high as possible
  • 20.  In parallel rxns, maximize the desired product  by adjusting the reaction conditions  by choosing the proper reactor  In series rxns, maximize the desired product  by adjusting the space-time for a flow reactor  by choosing real-time for a batch reactor Maximizing the desired product in series reaction k1 k2 A B C
  • 21.  If the first reaction is slow and second reaction is fast, it will be extremely difficult to produce species B.  If the first reaction (formation of B) is fast and the reaction to form C is slow, a large yield of B can be achieved.  However, if the reaction is allowed to proceed for a long time in a batch reactor or if the tubular flow reactor is too long, the desired product B will be converted to C.  In no other type reaction is exactness in the calculation of the time needed to carry out the reaction more important than in series reactions. Maximizing the desired product in series reaction k1 k2 A B C Desired Product
  • 22. Reaction paths for different ks in series reactionReaction paths for different ks in series reaction A B C k1 k2 1 1~ 1 2 1 2 1 2 1 < > k k k k k k A C B ' 1τ ' 2τ For k1/k2>1, a Large quantity of B Can be obtained For k1/k2<1, a Little quantity of B Can be obtained 1st rxn is slow 2nd rxn is fast ' 3τ Long rxn time in batch or long tubular reactor -> B will be converted to C
  • 23. Multiple reactions in a CSTRMultiple reactions in a CSTR For a CSTR, a coupled set of algebraic eqns analogous to PFR differential eqns must be solved. Rearranging yields where After writing a mole balance on each species in the reaction set, we substitute for concentrations in the respective rate laws. If there is no volume change with reaction, we use concentrations, Cj, as variables. If the reactions are gas-phase and there is volume change, we use molar flow rates, Fj as variables. q reactions in gas-phase with N different species to be solved j jj r FF V − − = 0 VrFF jjj −=−0 ),...,,( 2 1 1 N q i jijj CCCfrr ∑= ==−       ⋅⋅⋅⋅=−=−       ⋅⋅⋅⋅=−=−       ⋅⋅⋅⋅=−=−=− ∑= 00 1 0 00 1 0 1 00 1 111110 ,, ,, ,, T T N T T NNNN T T N T T jjjj q i T T N T T i C F F C F F fVVrFF C F F C F F fVVrFF C F F C F F fVrVVrFF
  • 24. THANK YOU