this is a repeat for previously issues paper that has been answered incorrectly - please take care to read question - please do not copy from other websites such as Chegg - they also have the wrong answer -
Question 1
a. A coal gas is to be 'freed' of 95% of its benzene content (a contaminant) by counter current washing with an oil in a plate column. The original amount of benzene vapour is 1%. The equilibrium data at the conditions of the absorption process is:
NOTE: X and Y are mole ratios
If the liquid to gas ratio used is to be 1.5 times the minimum, find the number of theoretical stages required for the system to perform the required duty.
b. Within the lessons of this module, a method of calculating the height of packing for a given separation was given. This cannot be used with the information available in (a).
(i) What other information would be required for the height of packing to be calculated?
(ii) Describe a simpler way of estimating the height of packing required for a given duty, stating the additional information required in this case.
(iii) What is the main problem that occurs in packed columns which will affect the performance of a column of this estimated height?
Question 2:
a. 670 kg h–1 of a slurry containing 120 kg solute and 50 kg solvent is to be extracted. The maximum permitted amount of solute in the final raffinate is 5 kg h–1. When a simple mixer-settling unit is used to separate extract and raffinate, the amount of solvent retained by the solid is 50 kg. Assuming perfect mixing and a constant ratio of solvent in extract and raffinate, determine the number of stages and the strength of the total extract for each of the following conditions:
(i) Simple multiple contact is used for the extraction with a solvent addition of 100 kg h–1 per stage
(ii) The same total amount of solvent as in (i) is provided in countercurrent operation.
(iii) Half the total amount of solvent in (i) is used in countercurrent operation.
b. Which of these methods would you recommend for the extraction? Give three reasons for your choice.
c. Suggest two alternative ways of carrying out the extraction and the circumstances under which they might be used
Question 3:
40 kg s–1 of heptane is to be used to extract sunflower oil from sunflower seeds in a counter-current process which uses a centrifuge to separate extract and raffinate. 100 kg s–1 of sunflower seeds which contain 40% oil are to be extracted until the final raffinate contains less than 2% by mass of oil. The ratio of solution to insoluble solids in the raffinate is 1:4 by mass and no insoluble solids are present in the extract. There is sufficient solvent to ensure all the oil is dissolved.
Determine:
a. the composition and amount of the final extract and raffinate
b. the number of stages required. A blank triangular diagram is provided in Figure 1.
Question 4:
The table 1 shows experimentally determined extract and raffinate concentrations of ethanoic acid (Solute A) in water (original solvent S) and an extracting solvent, L, called methyl isobutylketone at 20°C. (Results are rounded off to whole percentages.) Note: methyl isobutylketone is abbreviated to MIBK and ethanoic acid to HAc Table
a. Plot the ternary equilibrium diagram for this system on Figure 2 at the end of this TMA – you should take several photocopies of this for use in this question.
b. 50 kg of feed solution of 50% A in S is to be extracted such that the raffinate is less than 5% A. The extraction can be performed in one of two ways:
(i) 50 kg of L (MIBK solvent) added at each stage of simple multiple contact.
OR (ii) 65 kg of L (MIBK solvent) in counter current multiple contact. Use your equilibrium diagram to obtain and specify the number of stages in each case
