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For those who like the taste of coffee but do not want the caffeine, decaffeinated coffee is available. Decaffeinated coffee was first made from roasted green coffee beans with the solvent chloroform. Later, safer organic solvent methylene chloride was used. Today, most of the Decaffeinated coffee is extracted by supercritical carbon dioxide. Now answer the questions. (i) What is supercritical carbon dioxide and how is it produced? (ii) Why supercritical fluids have recently gained importance as extracting solvents? (iii) What are the solvents which are presently used for dry cleaning clothes? Can supercritical carbon dioxide be used as a solvent for dry cleaning clothes? (iv) Would this excessive use of carbon dioxide not contribute to global warming? Explain. |
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Answer» (i) The critical temperature CO2 is 304 K and its critical pressure is 73 atm. Therefore, in a tank of CO2 above its critical temperature and pressure, the liquid & gas phases of CO2 are replaced by a single phase called the supercritical carbon dioxide. Although supercritical CO2 is a gas, it being very dense can be used as a solvent. (ii) Supercritical carbon dioxide and other supercritical fluids have gained importance in recent times because of the possibility of replacing toxic and environmentally unfriendly solvents for extraction of organic compounds from natural sources. (iii) These days the most common solvent used for dry cleaning clothes is perchloroethylene, Cl2C = CCl2 but is an air pollutant. Therefore, clothes can be dry cleaned with supercritical carbon dioxide if we use a special detergent. (iv) Although carbon dioxide is a greenhouse gas, but the gas once used can be recirculated and not allowed to escape into the atmosphere. Consequently, its impact on global warming will be negligible. |
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