Q.1. x A =0.8, ε A =δ A *y A = 0.8*5=4 (because feed contains 80 mol% A, y A = 0.8, δ A =((6-1)/1)=5) k= 0.3 hr -1. So, θ = hr Q.

Transcription

1 Q.1 k [ 1 ln(1 x)] x x =.8, ε =δ *y =.8*5=4 (becaue feed contain 8 mol%, y =.8, δ =((6-1)/1)=5) k=. hr -1 So, θ = hr Q.2

2 Q.2 Continue (c) V PFR << V CSTR becaue, in CSTR, the concentration drop to.1 C everywhere. So, the rate of reaction i low. Wherea in PFR, the concentration of gradually drop from C to.1c. Here rate of reaction gradually decreae along the length of the (becaue, n>). So, PFR i more efficient.

3 Q. Etimate the ma of catalyt required in an iothermal fixed-bed for the firt-order, heterogeneou reaction required for 95% converion of. B C r kc, k = Here, rate r i expreed per unit catalyt ma, and ha the unit of [mol/(kg cat.)]. The ga feed conit of, B and an inert (I), with molar flow rate of 1, 1 and 1 mol/, repectively. The total preure at the inlet p = 4. bar and the temperature T = T = 525 K. The catalyt conit of pherical particle with a diameter d p =1.5 cm. The catalyt particle denity i.9 g/cm. The effective diffuivity of i D e =.6 cm 2 / and may be aumed contant. ume the preure drop gradient to be.2 bar per meter of bed length. The bed croectional area =.55 m 2 and the void fraction of the bed ε =.2. You may further aume the fluid and pellet urface concentration to be equal (i.e., there are no external ma tranfer limitation). In addition, the ideal ga law aumption may be made. Solution Finding relation between component flowrate: FB FB FC FC FB 11 mol/ and FC 1 mol/ FI FI 1 mol/ Finding preure: P L dp 5.2 bar/m dp.2 dl P 4.2L1 Pa dl 4 bar Finding concentration: P C yct F F F F RT B C I 4.2L 1 5 F 4.2L 1 5 mol/m F 11 F 1 F F Calculate (for 1 t order reaction) 1/2 2 Rp k Rp k (contant everywhere, ince not 4 De De.61 depending on C ) Notice,, how high diffuion reitance, and hence Component balance of for fixed bed give

4 1 1 df r dv k C dl C dl.5 CdL 14 d dl.5c Subtitute for C in term of F.5 L df 5 = 4.2 L 1 dl.5 F = 4.2 LdL.51 L 2 L L.2 2 Solving we get L = 1.91 m or L = 8.9 (unrealizable, becaue preure become negative: bar!!) V L W 1 V 64 kg. Q m and catalyt The following elementary third order reaction take place in a pherical porou catalyt B -2-1 r kc, k 1 mol/m with both external and internal ma tranfer limitation. The catalyt denity, = 1 kg cat /m. The (actual) external ma tranfer rate i given by the expreion r k C C where, ob ext, bulk -1 kext 2 i the external ma tranfer reitance, C, bulk 6 mol/m i the bulk concentration and C i the catalyt urface concentration. The value of catalyt particle radiu Rp 2k ( R p ) and effective diffuivity ( D e ) are uch that 5 mol/m -1. Find the oberved D rate of diappearance of ( r, ob ) in mol/kg cat. 1 Hint: Strong diffuion limitation aumption (i.e. ) can be made to tart with. fter olving for the urface concentration by equating the rate, r k C C kc, ob ext, bulk you can verify if the aumption i valid (i.e. ). If not, ue the general expreion of effectivene factor ( ) for a pherical catalyt. e Solution:

5 1/2 2 p 4kC R p 2k C 5C De De R uming, 5C,, k C C k C r ext bulk ob 1 26 C 1C 5C Rearranging we have 2 C C 6 C or C 2 Concentration cannot be negative, therefore C 2 mol/m 5 1, hence our aumption i valid!! C r, ob kext C, bulk C r, ob r 8 (mol/m )/.8 mol/kg, ob cat Q.5