CHEN-2120, Fall 2009 Exam 3 Open Book. Please print your name on this cover page and sign your name on this cover sheet as. Name.

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1 CHEN-2120, Fall 2009 Exam 3 Open Book Please print your name on every page! When you turn the exam in, you will separate it into individual problems and turn them in separately at the front table. You will need to remove the staple and to work the problems on the paper provided. If you need more paper for an individual problem, go ahead and add it, make sure your name is on it, and that it is stapled to the first page which is given. Do not work out more than one problem on an individual sheet! You Must Show All Work in order to receive credit! Correct solutions without shown work will receive no credit! Please print your name on this cover page and sign your name on this cover sheet as indicated below. Thanks. Good Luck!! Name Signature Open Book READ THIS CAREFULLY!! Assume ideal gas law unless otherwise stated. PUT ALL ENTHALPIES IN A TABLE WITH REFERENCES. FAILURE TO DO SO WILL RESULT IN A ZERO FOR THE ENERGY BALANCE!!!

2 1. (30 pts) An equimolar liquid mixture of n-pentane and n-hexane at 80 degrees C and 5.00 atm is fed into an evaporator at mol/s. The temperature in the tank is maintained at 65 degrees C by adding heat. The vapor and liquid phases in equilibrium with each other are separated and discharged as separate streams. The liquid stream contains 41 mole % pentane. Find : a. the system pressure b. the mole fractions in the vapor stream c. the required rate of heat addition to the evaporator NOTE: If you can t solve the material balance, use a vapor stream of 35 moles and a liquid stream of 65 moles with a vapor mole fraction of 0.70 to do the energy balance. This will result in a loss of 14 points. You will not get any credit for the material balance if you choose to use these values.

3 2. (10 pts) A turbine discharges 200 kg/h of saturated steam at 10.0 bar absolute. The discharge is mixed with a second stream of superheated steam at 300 degrees C and 10.0 bar. a X 10 4 kj/hr is required to produce 300 kg/h of product steam at 10 bar. What is the temperature of this product steam? (6 pts) b. If instead the process is carried out adiabatically at the same conditions, how much product steam is generated? (DO NOT ASSUME THAT THE SECOND STREAM HAS THE SAME MASS AS IN PART A). If you could not do the first part, assume a temperature for the product stream of 200 o C. (4 pts) You do not need to put together an enthalpy table for this problem.

4 3. (40 pts) Ethylene oxide is produced by the following reaction: C 2 H 4 (g) + ½ O 2 (g) C 2 H 4 O (g) An undesired competing reaction is the combustion of ethylene to CO 2. The feed to the reactor contains 2 mol C 2 H 4 /mol O 2. The conversion of ethylene in the reactor is 25 %, and there is 0.70 mol C 2 H 4 O produced/mol C 2 H 4 consumed. The reactor stream components are separated the recyle stream contains the unreacted O 2 and C 2 H 4, and the rest of the products are removed. The reactor inlet is at 25 o C and outlet stream is at 450 o C. The fresh feed and all the species leaving the separation process are at 25 o C. Using a basis of 2 mol of ethylene entering the reactor, calculate the heat requirement for: a) the entire process b) the reactor alone Data for C 2 H 4 O (g) : ΔH o f = kj/mol C p (J/(mol-K)) = T X 10-5 T 2 where T is in K. The material balance must be done using atomic species balances. The energy balance must be done using heat of formation method. Failure to use these methods will result in no credit. If you can t do the material balance use the following values for the energy balance: For the C 2 H 4 in the fresh feed, use 0.6 moles. For the O 2 in the fresh feed use 0.7 moles. Use the following for the flow out of the reactor: C 2 H 4 : 1.3; O 2 : 0.3; C 2 H 4 O : 0.5; CO 2 : 0.4; H 2 O : 0.4 (all in moles). This will result in a loss of 9 points. You will not get any credit for the material balance if you choose to use these values.

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