670 kg h–1 of a slurry containing 120 kg solute and 50 kg solvent is to be extra
ID: 2078057 • Letter: 6
Question
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.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.(b) Which of these methods would you recommend for the extraction? Give three reasons for your choice.
by this question b and c part
(c) Suggest two alternative ways of carrying out the extraction and the circumstances under which they might be used.
Explanation / Answer
(c)
Two other alternative ways for extraction of solute from sovent are Adsorption chromatography and distillation. To allow an optimal removal process, it is crucial to ensure a good mixing between the solvent and the feed, to have enough contact time between the two phases and to give enough settling time to distinct the two phases. As these process, a number of requirements for a suitable solvent for extraction can be indicated:
• high capacity for solute
• high selectivity for solute
• low solubility in for solvent in feed
• simple separation between solute and raffinate solvent
• considerable difference in the densities
• low surface tension
• low viscosity
• chemical and thermal stability
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