CHE-201. I n t r o d u c t i o n t o Chemical E n g i n e e r i n g. C h a p t e r 6. Multiphase Systems

Transcription

1 I n t r o d u c t o n t o Chemcal E n g n e e r n g CHE-201 I N S T R U C T O R : D r. N a b e e l S a l m b o - G h a n d e r C h a t e r 6 Multhase Systems

2 Introductory Statement: Phase s a state of matter. Do you beleve that: ll chemcal rocesses nvolve oeratons n hch materal s transferred from one hase (gas, sold, lqud) to another.

3 reng a cu of Coffee (leachng):

4 Removal of Sulfur doxde from a gas stream (Scrubbng): go g SO g 2SO g H Ol H SO aq SO

5 Searaton:

6 Rate of transortaton: seces transfers from one hase to another untl the second hase s saturated,.e. holdng as much as t can hold at the revalng rocess condton. When the concentraton of all seces n each hase no longer change th tme, the hase are sad to be n hase equlbrum.

7 Phase Dagram: Phase dagram of a ure seces s defned as a lot of one system varable versus another shong the condtons at hch the substances exst as a sold, a lqud and a gas.

8 Phase Dagram: Crossng Phases doesn t occur nstantaneously but gradually n hch the substance asses through three man stages,.e. hase 1, hase 1 & 2, then hase 2.

9 Man onts on the hase dagram: Normal bolng ont temerature s the ont at hch lquds start to bol at one atmosherc ressure. Trle ont s the ont at hch the three hases,.e. sold, lqud and vaor coexst n equlbrum. Crtcal temerature s the temerature at hch a substances can t coexst n to hases hatever ressure s aled. Sublmaton onts are located on sold-vaor equlbrum curve.

10 6.1b Estmaton of Vaor Pressures: Vaor ressure s the equlbrum ressure of the vaor above ts lqud. It ndcates the tendency of a seces to transfer from one hase to another. Volatlty of a seces s the degree to hch the seces tends to transfer from lqud (or sold) to state to the vaor state. Four methods can be used to estmate the comonent vaor ressures: 1. Vaor ressure tables n references 2. Claeyron equaton. 3. Cox chart. 4. ntone equaton.

11 Claeyron equaton: It s an emrcal equaton gven as: d dt T Hˆ v Vˆ Vˆ g l Where: vaorressureof uresubstance T absolutetemerature Vˆ ˆ g, V l secfc molar volumes of vaorand lqud Hˆ v latent heat of vaorzat on

12 Claeyron equaton: Vˆ V ˆ g Vˆ l Vˆ g t lo ressure, and substtutng for from deal gas lo yelds the Clausus-Claeyron equaton: l 0.0 d * Hˆ v * R dt 2 T H v 1 ln * ˆ R T Vˆ g It s a straght lne equatons here a mnmum of one ont s needed to obtan the value of.

13 Claeyron equaton: Examle 6.1-1: Vaor Pressure Usng the Clausus-Claeyron Equaton: The vaor ressure of benzene s measured at to temeratures, th the follong results: o * T C 1 o * T C 2 40mmHg 60mmHg Calculate the latent heat of vaorzaton and the arameter n the Clausus-Claeyron equaton and then estmate * at 42.2 o C usng ths equaton.

14 Cox Plot:

15 ntone Equaton: It s an emrcal equaton exressed as: here: log 10 * T C,, C are constant cked u from references

16 Table of Constant (Table.4):

17 V L V L t the begnnng of contact, dfferent T, P, and comoston t equlbrum, T, P, and no drvng forces for mass or molar beteen hases 6.2 The Gbbs Phase Rule:

18 6.2 The Gbbs Phase Rule: Varables can be dvded nto: 1. Extensve varables: deend on the system sze. Examles, mass and volume. 2. Intensve varables: don t deend on the system sze. Examle, temerature, ressure, densty, secfc volume, and comoston.

19 6.2 The Gbbs Phase Rule (Cont.): To correctly secfy a system, only ntensve varables are consdered, manly temerature, ressure and mole or mass fractons. The number of ntensve varables hch should be secfed for a gven system at equlbrum s calculated for nonreactve system by: DF 2 c here: DF c : Degree of freedom : Number of chemcal seces : Number of hases n a system at equlbrum

20 6.2 The Gbbs Phase Rule (Cont.): Examle 6.2-1: The Gbbs Phase Rule Determne the degree of freedom for each of the follong systems at equlbrum. Secfy a feasble set of ndeendent varables for each system. 1. Pure lqud ater. 2. mxture of lqud, sold, and vaor ater. 3. vaor-lqud mxture of acetone and methyl ethyl ketone.

21 6.3 GS-LIQUID SYSTEMS: ONE CONDENSILE COMPONENT DF Dry r at T=75 o C and 760 mm Hg Dry r at T=75 o C and 760 mm Hg In contact th lqud ater Eventually equlbrum s establshed beteen the to hases. Searaton rocesses nvolvng sngle condensable comonents are: evaoraton, dryng, humdfcaton, condensaton, and dehumdfcaton.

22 Searaton Processes: Evaoraton: Lqud ater Evaorator Lqud ater Water vaor Dryng: Wet solds Dryer Dred solds Water vaor Transfer of Lqud nto Gas hase Humdfcaton: Dry ar Lqud ater Humdfer Humdfed ar

23 Searaton Processes: Condensaton and dehumdfcaton: Wet ar Condenser or Dehumdfer Lqud ater r of less ater Transfer of comonent from Gas to Lqud hase

24 Raoult s La, Sngle Condensable Seces If a gas at temerature T and ressure P contans vaor hose mole fracton s y (mol vaor/ mol total gas), and f ths vaor s the only seces that ould condense f the temerature ere slghtly loered, then the artal ressure of the vaor n the gas equals the ure-comonent vaor ressure at the system temerature: Raoult s La, Sngle Condensable Seces: y P * T

25 6.3 GS-LIQUID SYSTEMS: ONE CONDENSILE COMPONENT Examle Comoston of a saturated Gas-Vaor System r and lqud ater are contaned at equlbrum n a closed chamber at 75 o C and 760 mm Hg, calculate the molar comoston of the gas hase.

26 Table.3 n endx : Vaor Pressure of Water 26

27 Remarks on Equlbrum Concet: gas n equlbrum th a lqud must be saturated th the volatle comonents of that lqud. The artal ressure of a vaor at equlbrum n a gas mxture contanng a sngle comonent can t exceed the vaor ressure of the ure comonent at the system temerature. If, the vaor s saturated; any attemt to ncrease ether by addng more vaor to the gas hase or by ncreasng the total ressure of the system at constant temerature, ll lead to condensaton. vaor resent n a gas n less than ts saturaton amount s referred to as a suerheated vaor. For such a vaor, chevng the condensaton requred changng the system condtons tll equlbrum s mantaned, then ether the ressure s ncreased at constant temerature or the temerature s loered at constant ressure. * T y P * T 27

28 Remarks on Equlbrum Concet: If a gas contanng a sngle suerheated vaor s cooled at constant ressure, the temerature at hch the vaor becomes saturated s referred to as the de ont of the gas: y P * T d Degree of suerheat of a gas s the deference beteen the temerature of the gas and the de ont. 28

29 29 egnnng of contact beteen the Phases r th suerheated vaor r saturated th vaor mmhg O H T P y O H O H O H * T P y O H O H O H * Equlbrum Concet:

30 Examle Materal alances round a Condenser steam of ar at 100 o C and 5260 mm Hg contans 10.0% ater by volume. 1. Calculate the de ont and degrees of suerheat of the ar. 2. Calculate the ercentage of the vaor that condenses and the fnal comoston of the gas hase f the ar s cooled to 80 o C at constant ressure. 3. Calculate the ercentage condensaton and the fnal gas-hase comoston f, Instead of beng cooled, the ar s comressed sothermally to 8500 mm Hg. 4. Suose the rocess of art 2 s run, the roduct gas s analyzed, and the mole fracton of ater dffers consderably from the calculated value. What could be the resonsble for the dsarty beteen calculated and measured values? (Lst several ossbltes). 30

31 Table.3 n endx : Vaor Pressure of Water 31

32 Table.3 n endx : Vaor Pressure of Water 32

33 6.3 GS-LIQUID SYSTEMS: ONE CONDENSILE COMPONENT Relatve Saturaton (Relatve Humdty) Molal Saturaton (Molal Humdty): s r h r * T 100 s m h m P molesof vaor molesof vaor free(dry)gas bsolute Saturaton (bsolute Humdty): s a h a M mass of vaor P M mass of vaor free(dry) gas dry Percentage Saturaton (Percentage Humdty): s s / m 100% P h * * * s / P m 100% 33

34 Examle 6.4-2: Raoult s and Henry's La Examle 6.4-2: Humd ar at 75 o C, 1.1 bar, and 30% relatve humdty s fed nto a rocess untl at a rate of 1000 m 3 /h. Determne: 1. The molar florate of ater, dry ar, and oxygen enterng the rocess unt. 2. The molal humdty, absolute humdty, and ercentage humdty of the ar. 3. The de ont. 34

35 35 C C C C C C C C C C lready dscussed n 6.3 (Pure Lqud) Wll be dscussed n 6.4 (Lqud Mxtures) T P y * T x P y * 6.4 MULTICOMPONENT GS-LIQUID SYSTEMS

36 6.4 MULTICOMPONENT GS-LIQUID SYSTEMS General Raoult s la for multcomonent mxtures s: If the lqud mxture s a dluted one,.e. to: Henry's La: y T H : Henry s constant of n a secfc solvent, Raoult s la can be reduced If the lqud hase s a ure one, Raoult s la can be reduced nto: y P P x x x * H 0.0 T y P * T 36

37 6.4 MULTICOMPONENT GS-LIQUID SYSTEMS Problem 6.46: gas contanng ntrogen, benzene, toluene s n equlbrum th a 40 mole% benzene-60 mole% toluene lqud mxture at 100 o C and 10 atm. Estmate the gashase comoston usng a Raoult s la. 37

38 6.4 MULTICOMPONENT GS-LIQUID SYSTEMS Use ether Raoult s la or Henry s la to solve the follong roblems: 1. gas contanng 1.0 mol% ethane s n contact th ater at 20 o C and 20.0 atm. Estmate the mole fracton of the dssolved ethane. 2. n equmolar lqud mxture of benzene () and toluene (T) s n equlbrum th ts vaor at 30 o C. What s the system ressure and the comoston of the vaor. 38

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