Cork Institute of Technology. Autumn 2005 CE 2.7 Separation Process & Particle Technology (Time: 3 Hours) Section A

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1 Cork Institute of Technology Bachelor of Engineering (Honours) in Chemical and Process Engineering Stage 2 (Bachelor of Engineering in Chemical and Process Engineering Stage 2) (NFQ Level 8) Autumn 2005 CE 2.7 Separation Process & Particle Technology (Time: 3 Hours) Instructions Answer FOUR questions, at least ONE question from Section C and THREE questions from any Section A, B or C Use separate answer books for each section. Section A Examiners: Mr. P. Kennedy Mr. N. B. Duffy Dr. A. O Gorman Mr. D. O Connor Prof. R. Ocone Q1. A stream containing 8 kmol s -1 of a mixture of methanol and isopropanol is fed to a simple distillation column, with a partial reboiler and a total condenser. A distillate containing 0.9 mole fraction methanol is produced. You are provided with a figure showing the equilibrium curve and the operating lines, and a second figure showing the flow profiles (caution: this follows the Chemsep numbering convention for stages). Answer each of the following questions, ensuring you explain your answer. (a) What is the composition of the bottom product? (2 (b) What is the value of the actual reflux ratio? (2 (c) How many equilibrium stages, including the reboiler, are required for this separation? (2 (d) What fraction of the feed is vapour? (2 (e) What is the composition of the reflux liquid? (2 (f) What is the composition of the feed? (3 (g) Derive the expression for the top operating line in this column. (3 (h) What is the minimum number of stages required for this separation, with the same stream specifications? Under what conditions would this apply? (3 (i) Show, with the aid of a sketch of a Txy diagram, how you would determine the temperature of the reboiler. (3

2 (j) Calculate the relative volatility of the components on a stage selected by you. Clearly identify your choice of stage. (3 HINT: if you draw on a figure as part of the answer, ensure you hand it up, having written your name on it! Q2. A vent gas stream contains 15 % w / w of pollutant, the rest is air. You intend to reduce this to 5% w / w by isothermally absorbing the pollutant into water. The equilibrium data may be approximated by y = 0.5 x (where x and y are the weight fractions of pollutant in the liquid and gas, respectively). (a) Determine the minimum water to air ratio (in pollutant-free terms). (10 (b) With an actual water to air ratio of 1.2 times the minimum (in pollutant-free terms), find: (i) the required number of equilibrium stages; and (10 (ii) the outlet liquid concentration, in weight fraction of pollutant. (5 Section B Q3. A process produces 5000 kg hr-1 of a mixture that contains 60 wt % toluene and 40 wt % isopropanol. Cross-current extraction at 25 C is being considered as an option to remove the isopropanol using pure water as a solvent. A mass flow of water equal to 75 % of the feed stream to each stage is to be used. (a) How many stages will be required to reduce the raffinate to 5 wt %? (18 (b) If the solvent streams from each stage are combined, what is the mass fraction of the isopropanol in this combined stream? (7 Equilibrium Data for the system isopropanol-toluene-water at 25 C Water Layer wt % Toluene Layer wt % Isopropanol Water Toluene Isopropanol Water Toluene

3 Q4. The following results were obtained for the adsorption of a solute on an ion exchange resin at 20 C : mg solute / g solution mg solute / g dry resin (a) Can this adsorption be described by a Langmuir isotherm, ac q = 1 + bc (15 (b) What are the values of the Langmuir constants for this system? (10 Section C Q5. What is the main purpose of Size Reduction in industry? Briefly describe three industrial applications where size reduction is an important procedure. (6 List four methods of size reduction, describe the product from each briefly and give an example of a type of industrial machinery which uses each method. (12 Experimental work done with Limestone indicates a Work Index for wet grinding of 14. If a Dry mill is used to crush a limestone feed from 5 cm to 100µm, calculate the energy required. (7 3

4 Q6. (a) Calculate the equivalent volume diameter for the sample having the following size distribution, when all increments have the same density. (18 Cumulative weight of 500 g sample Diameter smaller than d p, µm (b) Outline the coning and quartering procedure used to obtain a representative sample from a particulate bulk. (25 4

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