Lecture11 - ChE 210: Meeting 11 February 7, 2011 Outline...

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Unformatted text preview: ChE 210: Meeting 11 February 7, 2011 Outline (F&R Sections 4.5-4.6) Homework Due Friday 02/04/2011 - Recycle 4.32, 4.33, 4.353-0, 4.37 - Process Flow Diagram - Degrees of Freedom - Reaction Terminology Recycle , ’ K .11.; ,17 ' . ‘_ J 'U I" I i mSout = XAISM: 0.02 XB,Sout = mA,Rin = mA; =110k /h 'n m g Separator Complete System: I i, .1. N unknowns - material balances - process specifications - physical properties and laws I ‘ ‘ ~ v . . ~ a ’ ‘, :12: ' _'|Ohysica| constraints i ‘ a. - degrees of freedom 1/8 ChE 210: Meeting 11 February 7, 2011 Reactor: unknowns V v - material balances « ” J i . — process specifications - physical properties and laws - physical constraints 1 degrees of freedom Separator: :» w unknowns fjme n .2 z u m” 3: - :3 material balances v? ' , x/ iridmtirlw‘xl 57H I " ‘ ’ " - i process specifications inn a, ms. - physical properties and laws - "2 physical constraints r-i; degrees of freedom 2/8 ChE 210: Meeting 11 Mix Point: I i l' \ H }. unknowns {, i km:ny H , .36; ‘2,“ - g; material balances u r 7* {’9' Miami“ :' w. . 4 L - J process specifications — physical properties and laws — physical constraints “‘~ degrees of freedom ‘1‘ 3\ t id l 1‘51 E31 / n £Lik£Li§k ) i ‘ i “ LU {EH-"ii 3/8 February 7, 2011 ChE 210: Meeting 11 February 7, 2011 Reaction Terminology Irreversible reaction — reaction can only proceed in one direction; reactants form products * ‘ ‘ 2802+0292803 Reversible reaction — reaction can proceed in forward and reverse direction; reactants form products and those products can react to form the original reactants C2H4 + H20 69 CszOH Side reaction — undesired reaction that either consumes the desired product or uses the reactants to form something other than the desired product ‘ P '1 Desired Reaction: CZHG + H20 H2 Undesired Side Reactions: 02H6 + H2 9 2 :CH41 “:3 iii‘fi; ‘ “ Aux; ‘1‘}! 3“” 13‘ ‘1 Stoichiometric ratio —— ratio of stoichiometric coefficients in a“ balanced reaction equation Example: 2SOz+Oz—>2803 2 mol 803 generated 2 mol 802 consumed 1mol 02 consumed 2 mol 803 generated it», a “1 vi. [ 1'“ "*‘1‘1 Wuy‘i-r N 4/8 icszm CZH6 9”C;’H6+CH'4' ~‘ ChE 210: Meeting 11 February 7, 2011 Stoichiometric proportion — two reactants are in stoichiometric proportion if the ratio of the reactants present equals the stoichiometric ratio Example: 2802+029ZSO3 A feed containing 20 moles of 802 and 10 moles of Oz is in stoichiometric proportion. A feed containing 30 moles of 802 and 10 moles of 02 is not. ,_ . a, it t Limiting reactant — a reactant that is present in an amount less than the stoichiometric ratio relative to the other reactants Example: 2802+0292803 In a feed containing 30 moles of 802 and 10 moles of 02, 02 is the limiting reactant because the stoichiometric ratio of Oz to 802 is 1/2 and the feed ratio is only 1/3 Excess reactant — all reactants that are not the limiting reactant Stoichiometric requirement — the amount of excess reactants necessary to react completely with the limiting reactant Example: 2802+0292803 In a feed containing 30 moles of SOZ and 10 moles of 02, the stoichiometric requirement of 802 is 20 moles 5/8 ChE 210: Meeting 11 February 7, 2011 Fractional excess — ratio of the excess amount of a reactant relative to the stoichiometric requirement moles fed - stoichiometric requirement fractional excess = _ _ , , storchlometnc requirement Example: 2802+02-)2803 In a feed containing 30 moles of 802 and 10 moles of 02, the stoichiometric requirement of 802 is 20 moles and the fractional excess of 802 is 30 moles 802 - 20 moles 802 _ 1 fractional excess = _ _ 20 moles 802 2 Fractional conversion (f) — ratio of moles reacted to moles fed Example: 2802+0292803 If a feed containing 30 moles of 802 is reacted with 02 until only 5 moles of $02 remains, the fractional conversion is fractional conversion (f) = W =3 30 moles 802 6/8 ChE 210: Meeting 11 February 7, 2011 Extent of reaction (E) — moles converted from reactant to product, defined in terms of a single component of a reaction (typically a component with a stoichiometric coefficient of 1) Example: 2802+0292803 If a feed containing 50 moles of 802 and 20 moles of 02, is reacted until only 5 moles of Oz remains, the extent of reaction is 15 moles (defined in terms of Oz) U \lfllkmi :f x: it ‘ i'ifi :‘zlffkiwi 9 “I t\‘ x if: s e v T"f . '1 (no: 2i Equilibrium constant — the ratio of the concentration of products to reactants when a reaction has reached thermodynamic equilibrium Example: CzHe, + H20 9 C2H4 + H2 [c2H5OH] equilibrium constant (K) = W 2 4 2 Yield — amount of product formed relative to the amount of product that would have formed if no undesired side reactions occurred Example: C2H6 + H20 9 CzH4 + H2 [02W] yieid = either [C2H6]O or [H20]0 (whichever is limiting) 7/8 ChE 210: Meeting 11 February 7, 2011 Selectivity — amount of desired product formed relative to undesired products Example: CzHe + H20 9 C2H4 + H2 C2H6 + H2 '9 2 CH4 C2H4 + CzHa 9 C3H6 + CH4 [C2H4] [CH4] [C2H4] selectivity: [C H ] 3 6 or selectivity = 8/8 ...
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This note was uploaded on 07/31/2011 for the course CHEM E 210 taught by Professor Shanks during the Spring '02 term at Iowa State.

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Lecture11 - ChE 210: Meeting 11 February 7, 2011 Outline...

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