Unit Operations Lecture Nov 2010

Transcription

1 Unit Operations Lecture Nov

2 Liquid-Liquid xtraction (solvent extraction) Overview Pioneered during 1940 s (uranium purification) Alternative to distillation, absorption/stripping nerg savings ometimes easier separation Lower temperatures Usuall two distinct phases formed Usual purpose, to either purif the Raffinate, or olute 2

3 Liquid-Liquid xtraction xtract eed eparation at accomplished b [s + a] (+b) [a+b] chemical differences Usuall in two phase - light phase a=solute - heav phase b = diluent Usuall coupled with another s = solvent separation technique olvent [s] Raffinate [b] (+ a & s) eparator could be: column w/ stages or packing column with moving internals single stage mixer/settler equilibrium stage(s) let: x mass fraction solute in raffinate phase mass fraction solute in extract phase * in equilibrium with associated x 3

4 xample Industrial Processes eader & Henle (2006) 4

5 Tpical LL xtraction Process eader & Henle (2006) 5

6 quipment xamples Trebal (1980) eader & Henle (2006) 6

7 pra Columns: eader & Henle (2006) 7

8 Packed-bed Column eader & Henle (2006) Light liquid - dispersed phase Trebal (1980) 8

9 ieve-tra xtraction Column: light phase dispersed d Trebal (1980) 9

10 Oldshue-Rushton (Mixco Lightnin CMContactor) column cheibel column eader & Henle (2006) 10

11 eader & Henle (2006) 11

12 Podbielniak xtractor Trebal (1980) 12

13 quipment eader & Henle (2006) 13

14 quipment xamples eader & Henle (2006) 14

15 quilateral Triangular Diagrams R [ kg ] raffinate mixture [ kg] extract mixture M [ kg] combined mixture [s] Rearrange: R x M x M x R [b] Overall material balance: R M [kg] Component material balance (on a): x R R x M M Lever arm rule: [s] [b] R e m M MR 15

16 quilateral Triangular Diagrams [s] [b] [s] [b] Tpe I Tpe II xamples: water (b), ethlene glcol (a), furfural (s) water (b), acetone (a), chloroform (s) xample: n-heptane (b), methlcclohexane (a), aniline (s) 16

17 Distribution Curves [s] Tpe I [b] xr [s] [b] Tpe II 17

18 Distribution Curves [s] Tpe I [b] xr [s] Tpe II [b] xr 18

19 Distribution Curves [s] Tpe I [b] xr [s] Tpe II [b] xr 19

20 ffect of Temperature (and Pressure) Trebal (1980) 20

21 ffect of Temperature (and Pressure) Trebal (1980) 21

22 electivit separation factor Choice of olvent a b extract 1; better 1 xa x b raffinate Distribution Coefficient better if 1 Insolubilit of olvent better if less soluble in R phase olvent Recoverabilit should be eas to separate solvent from and R Densit large densit differences between the two phases is desired K Interfacial Tension would like large for easier coalescence of dispersed phase Others: solvent stable, inert, nontoxic, nonflammable, low cost low viscosit low vapor pressure low freezing point 22

23 Mixer ettler (single stage extraction) eed Raffinate solvent recover New olvent mixer settler t xtractt solvent olvent recover Reccled olvent Purified Raffinate Purified xtract Black Box: Material balance: R eed x olvent M 1 stage Raffinate x R xtract R [] [s] [b] 23

24 given: Mixer ettler (single stage extraction) x,,, find: x, M, x,, R M R, Component material balance (on a in feeds): x x M M x M x Component material balance (on a in products): M x M x R x R x R R x M M [] [s] [b] 24

25 Mixer ettler (single stage extraction) Minimum olvent (rate): min D D x x D x D Maximum olvent (rate): max K K x x K x K [s] [b] 25

26 Cross-Current (multi-stage extraction) inal xtract eed x tage 1 R 1 x 1 tage 2 R 2 x 2 tage 3 R 3 x 3 inal Raffinate olvent olvent olvent inal xtract: [s] [b] 26

27 Continuous Multistage Countercurrent xtraction eed x xtract 1 1 R 1 x R x 2 2 R N 2 x N 2 3 N 1 3 N 1 N-1 R N x 1 N 1 N N N R N x N Raffinate olvent Total MB: Total MB on a: 1 x M x R N M If 1 & x N known (specified), then flowrates 1 & R N can be found. [s] [b] 27

28 Continuous Multistage Countercurrent xtraction eed x xtract 1 1 R 1 x R x 2 2 R N 2 x N 2 3 N 1 3 N 1 N-1 R N x 1 N 1 N N N R N x N Raffinate olvent Total MB: MB from feed to N-1 stage: R R N 1 Operating Point: R 1 N 1 N 1 R [s] [b] 28

29 Continuous Multistage Countercurrent xtraction eed x xtract 1 1 R 1 x R x 2 2 R N 2 x N 2 3 N 1 3 N 1 N-1 R N x 1 N 1 N N N R N x N Raffinate olvent Now step off to find number of equilibrium stages: R [s] [b] 29

30 Questions? 30