Semibatch Reactors Consider the following elementary reaction: A+B C+D -rA=kCACB The combined Mole Balance, Rate Law, and Stoichiometry may be written in terms of number of moles, conv[r]
(1)Lecture 5d Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place (2) Lecture 10 – Tuesday 2/12/2013 Block 1: Block 2: Block 3: Block 4: Mole Balances Rate Laws Stoichiometry Combine (3) Selectivity in Multiple Reactions Selectivity Yield Instantaneous SD/U = rD/rU YD = rD / − rA Overall ŜD/U = FD/FU YˆD = FD /( FA0 − FA ) Keep CA high and CB low (4) Semibatch Reactors Semibatch reactors can be very effective in maximizing selectivity in liquid phase reactions The reactant that starts in the reactor is always the limiting reactant (5) Semibatch Reactors Semibatch reactors A+B→C+D Liquid level and volume increase (6) Semibatch Reactors 1) Mass Balance: dm = m dt m = 0 dV = 0 dt t = V = V0 and m = V (7) Semibatch Reactors 1) Mole Balance on Species A: [in] – [out] + [gen] = [acc] dN − + r AV = dt dV = 0 dt A (8) Semibatch Reactors 1) Mole Balance on Species B: dN B FB − + rBV = dt FB = C B 0 dV = 0 dt ( C B − C B ) dC B = rB + dt V (9) Semibatch Reactors 1) Mass and Mole Balance Summary (1) (2) (3) (4) (5) 0C A dC A = rA − dt V 0 (C B − C B ) dC B = rB + dt V dCC 0CC = rC − dt V 0C D dC D = rD − dt V V = V0 + 0t (10) Semibatch Reactors 2) Rate Laws 3) Stoichiometry 10 4) Parameters − rA − rB rC rD = = = 1 1 (8) rC = −rA (9) rD = −rA (10) N A0 − N A X= N A0 (12) N A = C AV C A0 , V0 , 0 , k , C B (11) Semibatch Reactors 11 (12) Semibatch Reactors 12 (13) Equilibrium Conversion in Semibatch Reactors with Reversible Reactions Consider the following reaction: Everything is the same as for the irreversible case, except for the rate law: 13 (14) Equilibrium Conversion in Semibatch Reactors with Reversible Reactions Where: N A0 (1 − X ) V ( FB 0t − N A0 X ) C B= V C A= At equilibrium, − rA = then Xe changes with time 14 (15) P6-6B - Semibatch Reactors Sodium Bicarbonate + Ethylene Chlorohydrin → Ethylene Glycol + NaCl + CO2↑ 15 (16) P6-6B - Semibatch Reactors Semibatch Reactors in terms of Moles Mole Balances A B C D CO2 dN a (1) = rAV dt dN b (2) = FB + rBV dt dN c (3) = rCV dt (4) N D = N C = − FCO2 + rCO2V (5) 16 Stoichiometry FCO2 = rCO2V − rA = −rB = rC =r D = rCO2 (17) (6) (7 ) (8) (9) Rate Laws 17 dV = 0 − CO2 dt FCO2 MWCO2 CO2 = RHO MW = 44 RHO = 1000 (10) Ca = N A V (11) C B = N B V (12) rA = −kC AC B N a0 − N a (13) X = N a0 (14) N a = V0Ca (18) P6-6 Semibatch: Moles, Na, Nb, etc (19) 19 (20) 20 (21) 21 (22) P6-6 Semibatch: Concentrations CA, CB, CC (23) 23 (24) 24 (25) Semibatch Reactors Three Forms of the Mole Balances applied to Semibatch Reactors: Molar Basis Conversion 25 dN A = rAV dt dN B = FB + rBV dt dX − rAV = dt N A0 (26) Semibatch Reactors Consider the following elementary reaction: A+B C+D -rA=kCACB The combined Mole Balance, Rate Law, and Stoichiometry may be written in terms of number of moles, conversion, and/or concentration: Conversion This image cannot currently be displayed 26 Concentration No of Moles dN A = rAV dt dN B = FA0 + rBV dt (27) Polymath Equations 27 (28) End of Lecture 5d 28 (29)