Warm-Up Problems

Leader: German Parada Midterm Exam Review Course: ChE 210 Supplemental Instruction Instructor: Lamm/Scheider Iowa State University Date: 10/09/12

Warm-up problems: a. Two identical containers with pressure-reading devices at the bottom are placed side by side. One of them is filled with milk (SG=1.03) and the other is filled with honey (SG=1.36). Which container will have a higher gauge pressure? Why? b. A furnace burns 15kg/min of propane. Calculate the theoretical amount of oxygen required by this furnace. c. Calculate the volumetric flow rate of dry air that needs to be provided to the furnace in the example above, if the air is fed at atmospheric pressure and temperature (5 C). How would the flow rate be affected if the air is preheated to 65 C? d. On the furnace example below, an analysis of the exhaust gases found 680 mol CO2/min and some unreacted propane. What is the percent conversion of fuel in the furnace?

Exam-style problems:

1) Material Balance on an Intravenous (IV) injection bag: A nurse sets up an IV drip for a patient with an infection consisting of a standard saline solution (and aqueous solution containing 0.95 wt. % salt) mixed with with an antibiotic solution (15 mg/mL antibiotic and 0.85 wt. % salt). All solutions are aqueous, and have the same physical properties as water. The standard saline solution drips through the line at a rate of 0.75 mL/min. The patient should receive 150 mg of antibiotic per hour, as prescribed by the doctor. Indicate how you would determine the flow rate of each stream in units of mL/min.

2) The Haber-Bosch process is one of the greatest achievements of chemical engineering. Through this process, ammonia (important fertilizer and chemical precursor) is synthesized from atmospheric nitrogen and hydrogen on an industrial scale. In a test reactor, gaseous nitrogen and hydrogen are fed at a 1:3 molar ratio. This reactor generates 1400 L/h of ammonia and achieves a conversion of 45%. At the outlet conditions, the specific gravity of ammonia is 0.0091. Determine the volumetric feed rates of nitrogen and hydrogen at STP.

3) A methanol and water liquid mixture enters a solvent recovery flash separation unit. This feed stream is 60% methanol on a mol basis, and enters the unit at 80C and 3atm. At the flash unit, the pressure on the incoming stream is abruptly reduced, vaporizing some liquid and forming two distinct liquid and gas phases, which exit the unit at equilibrium. The leaving streams have a pressure of 760 mmHg and a temperature of 73C.

Vapor pressures: Water – 355.0 mmHg at 80C, 265.6 mmHg at 73C. Methanol – 1360.3 mmHg at 80C, 1053.9 mmHg at 73C.

Supplemental Instruction 1060 Hixson-Lied Student Success Center v 294-6624 v www.si.iastate.edu a- What do you expect the vapor and liquid compositions to be? Are they going to be richer, poorer or the same in methanol? b- A basis of 10 mol/s of the feed stream is used. Assume Raoult’s law applies for the entire range of methanol compositions. What is the expected flow rate of methanol in the vapor and the liquid streams? c- At a pilot plant, the mol fractions of methanol in the exit streams were measured for the same flash evaporation process, and were found to be y=0.793 and x=0.519. What can explain the difference observed?

4) Sorbitol is an ingredient in “sugar-free” candy. It is sweet it is considered diet food because humans do not metabolize it well. Sorbitol (C6H14O6) is made from glucose (C6H12O6) and hydrogen. 100 kg/day of a 45 wt% glucose solution in water is fed to a reactor with a stoichiometric flow rate of hydrogen; 80% of the glucose is converted to sorbitol. The hydrogen is then separated from the sugar solution as a gas stream. How much sorbitol is created in this process? A partially labeled flowchart is given below.

a – Complete labeling the flowchart b – What is the basis of calculation? c – Perform a degree of freedom analysis. Is this system solvable? d – Write a list of the equations you would use to solve the problem. Indicate the order in which you would solve the equations.