ENIN 350 - 001 Chemical Manufaturing Process Spring/Summer 2012 H. Ibrahim
Faculty of Engineering & Applied Science University of Regina Sample Review Questions June 22, 2012
Problem 1 A common method method used in manufacturing manufacturing sodium sodium hypochlorite hypochlorite bleach is by the reaction Cl2 + 2NaOH → NaCl + NaOCl + H 2O Chlorine gas is bubbled through an aqueous solution of sodium hydroxide, after which the desired product is separated from the sodium chloride (a by-product of the reaction). A water-NaOH solution that contains 1145 lb of pure NaOH is reacted with 851 lb of gaseous chlorine. The NaOCl formed weighs 618 lb. (a) What was the limiting reactant? (b) What was the percentage excess of the excess reactant used? (c) What is the degree of completion of the reaction, expressed as the moles of NaOCl formed to the moles of NaOCl that would have formed if the reaction had gone to completion? (d) What is the yield of NaOCl per amount of chlorine used (on a weight basis)? (e) What was the extent of reaction?. Answers: (a) Cl2 , (b) 19.4% excess NaOH, (c) 0.69, (d) 0.726 lb/lb, (e) 8.3 reacting moles Problem 2 The gas-phase reaction between methanol and acetic acid to form methyl acetate and water CH3OH + CH3COOH = CH3COOCH3 + H2O (A) (B) (C) (D) takes place in a batch reactor and proceeds to equilibrium. When the reaction mixture comes to equilibrium, the mole fractions of the four reactive species satisfy the relation yc yD = 4.87 y A yB
(a) Suppose the feed to the reactor consists of n A0, n B0, n C0, n D0, and nI0- gram-moles of A, B, C, D and an inert gas, I, respectively. Let ξ (mol) be the extent of reaction. Write expressions for the gram-moles of each reactive species in the final product, n A (ξ), nB (ξ), nC (ξ), and nD (ξ). Then use these expressions and the given equilibrium relation to derive an equation for ξC, the equilibrium extent of reaction, in terms of n A0, …, nI0. (b) If the feed to the reactor contains equimolar quantities of methanol and acetic acid and no other species, calculate the equilibrium fractional conversion. (c) It is desired to produce 70 mol of methyl acetate starting with 80 mol of acetic acid. If the reaction proceeds to equilibrium, how much methanol must be fed? What is the composition of the final product? (d) If you wanted to carry out the process of part (b) or (c) commercially, what would you need to know besides the equilibrium composition to determine whether the process would be profitable? Answers: (a) see Example Example 4.6-2 in textbook, textbook, (b) (b) 0.67, (c) y A=0.40, y B = 0.04, y C = 0.279, y D = 0.279, (d) cost of reactants, product selling price, rate of reaction, heating/cooling requirements, etc. Problem 3 An orifice is used to measure the flow rate of a gas through a pipe as shown in the figure below. The pressure drop across the orifice is measured with a mercury manometer, both legs of which are constructed of 1/4 - in. inner diameter (ID) glass tubing. If the pressure drop across the orifice is equivalent to 4.65 in. Hg, calculate h 2 and h3 (both in inches) if h1 is equal to 13.50 in.
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ENIN 350 - 001 Chemical Manufaturing Process Spring/Summer 2012 H. Ibrahim
Faculty of Engineering & Applied Science University of Regina Sample Review Questions June 22, 2012
. Answers: h3 = 7.15 in Problem 4 Ethane is burned with 50% excess air. The percentage conversion of the ethane is 90%; of the ethane burned. 25% reacts to form CO and the balance reacts to form CO 2. Calculate (a) the molar composition of the stack gas on a dry basis and (b) the mole ratio of water to dry stack gas. C2H6 + 7/2 O2 → 2CO2 + 3H2O C2H6 + 7/2 O2 → 2CO + 3H2O
Answers: (a) y1 = 0.4%, y 2 = 9.7% mol, y 3 = 82.4%, y 4 = 1.9%, y 5 = 5.6% mol, (b) 0.113 Problem 5 Find the equilibrium composition ( yi) for the WGS reaction (CO + H 2O ↔ CO2 + H2) if the reaction mixture comes to equilibrium at 1105 K and the feed consisted of 1.0 mol CO and 2.0 mol H 2O. K = 1.0 at 1105 K. Calculate (a) the amount of limiting reactant at equilibrium and (b) its fractional conversion? Answers: (a) 0.33 mol CO, (b) 0.67
Problem 6 TiCl4 can be formed by reacting titanium dioxide (TiO 2) with hydrochloric acid. TiO 2 is available as an ore containing 78 % TiO 2 and 22 % inerts. The HCl is available as 45 wt% solution (the balance is water). The per pass conversion of TiO 2 is 75 %. The HCl is fed into the reactor in 20 % excess based on the reaction. Pure unreacted TiO 2 is recycled back to mix with the TiO 2 feed. TiO2 + 4 HCl → TiCl4 + 2H2O For 1 kg of TiCl 4 produced, determine: (a) the kg of TiO2 ore fed in (kg F/kg P). (b) the kg of 45 wt % HCl solution fed in (kg F1/kg P). (c) the ratio of recycle stream to fresh TiO 2 ore (in kg R/kg F). (MW : TiO2 79.9; HCl 36.47; TiCl4 189.7)
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ENIN 350 - 001 Chemical Manufaturing Process Spring/Summer 2012 H. Ibrahim
Faculty of Engineering & Applied Science University of Regina Sample Review Questions June 22, 2012
Answers: (a) 0.54, (b) 2.05, (c) 0.26
Problem 7 A distillation column separates 10,000 kg/h of a 50 % Benzene – 50 % Toluene mixture. The product D contains 95 % Benzene and the Bottom is W and contains 96 % Toluene. The vapor stream is 8000 kg/h. A portion of the product is recycled. The composition of V, D and the reflux are identical (totally condensed). Find the ratio R/D. Answers: 0.58 Problem 8 The Colburn equation for heat transfer is
where C = heat capacity, Btu/(lb of fluid)(°F); μ = viscosity, lb/(hr)(ft); k = thermal conductivity, Btu/(hr)(ft2)(°F)/ft; D = pipe diameter, ft; and G = mass velocity, lb/(hr)(ft 2) of cross section. What are the units of the heat transfer coefficient h? Answers: Btu/(hr)(ft2 )( oF)
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