Ch4 Material Balances-part2(1)

Problem442page172 n1 165mol s n1e n1hb n2 c2h4

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Unformatted text preview: l/min nC2H6 = 60 kmol/min nC2H4 = 40 kmol/min Material balance for reactors (including total process): Only balance Independent molecular or atomic species, and Independent reactions If two molecular or atomic species are in the same ratio to each other wherever they appear in a process, balances on those species are not independent equations. Example: dimerization of ethylene in presence of nitrogen (p. 128) C2H4 C4H8 n2 n1 100 mol / s n1C H 60 24 n1N 40 n2C H 24 n2C H 48 n2N 2 2 • 3 independent molecular species (N2, C2H4,C4H8) • 2 independent atomic species N & C or H Nbalance : 2n1N 2n2N 80 2 2 Cbalance :2n2C H 4n2C H 2n1C H 120 24 48 24 Hbalance :4( ) 8( ) 4( ) 240 H balance 2(C balance) not independent Can' t Solve! Problem 4.42 (page 172)… n1 165mol / s n1E n1HB n2 C2H4 HBr C2H5Br E HB EB y 2HB 0.173 y 2EB 0.517 y 2E 1 0.173 0.517 0.310 Flow, mol/s Total ni 1 165 2 n2 Comp, nij ndf= nuk + nindrx ‐ nmol bal ‐nother 2 + 1 ‐ 3 ‐ 0 = 0 niE n1E 0.310n2 niHB 165 n1E 0.173n2 niEB 0 0.517n2 nuk one reaction: molecular balance 1 1 molecular balance input + generation = output + consumption + accumulation (products) (reactants) (none) total: cannot use, moles do not balance ethylene: input = output + consumption n1E 0.310n2 0.517n2 n1E 0.827n2 HBr: input = output + consumption 165 n1E 165 n1E 0.173n2 0.517n2 0.690n2 n1E 0.827n2 165 0.690n2 165 0.690n2 n2 109 mol / s same as the amount of EB formed Flow, mol/s 1 2 165 109 niE 90 33.8 niHB 75 18.9 0 56.4 Total ni Comp, nij niEB Answers to questions: (1) The limiting reactant is HBr 90 ‐ 75 (2) % excess ethylene = x 100 = 20% 75 75 ‐ 18.9 (3) Conversion of HBr, fHBr = = 0.75 (75%) 75 (4) Extent of reaction, ξ = 75 – 18.9 = 56 moles Example 4.7‐3 36 Combustion Produce energy from fuel. Complete combustion = full oxidation to CO2, H2O, SO2, etc Partial/incomplete combustion yields some CO. Air is common source of O2. Typically ~ 50% excess air **Air: 21% oxygen 4.76 mole air / mole O2 “Stack Gas” or...
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