ch01 - Exercise 1.1 (i) Known: Fluorocarbons can be...

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Exercise 1.1 (i) Known : Fluorocarbons can be produced from the reaction of carbon tetrachloride and hydrogen fluoride followed by a number of separation steps. Given: Flow diagram and a brief description of a fluorocarbons production process in "Chemical Process Industries" , 4th edition, by Shreve and Brink and also in "Shreve's Chemical Process Industries", 5th edition, by G. T. Austin, pages 353-355 (Fig. 20.4). Find: Draw a process flow diagram and describe the process. Description of Process: Two main reactions occur: CCl 4 + HF CCl 3 F + HCl CCl 3 F +HF CCl 2 F 2 + HCl Excess carbon tetrachloride is reacted in R1 with HF in the presence of antimony pentoxide catalyst and a small amount of chlorine to maintain catalyst activity. The HF contains a small amount of water as an impurity. The effluent from the R1 is HCl, CCl 3 F, CCl 2 F 2 , unreacted CCl 4 , and small amounts of water and chlorine. The normal boiling points in o C of these components in the order of decreasing volatility are: HCl -84.8 Cl 2 -33.8 CCl 2 F 2 -29.8 CCl 3 F 23.7 CCl 4 76.7 H 2 O 100
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Exercise 1.1 (i) (continued) The reactor effluent is distilled in D1 to remove the CCl 4 as bottoms, which is recycled to R1. The distillate enters absorber A1, where HCl is absorbed by water to produce a byproduct of aqueous HCl. The gas from A1 contains residual HCl, which is neutralized, and chlorine, which is absorbed, by aqueous NaOH, in A2. The effluent liquid from A2 is waste. Moisture is removed from the gas leaving A2 by absorption with H 2 SO 4 in A3. The exit liquid from A3 is also waste. The gas leaving A3 is distilled in D2 to obtain CCl 2 F 2 as a distillate, which is then dried in S1 by adsorption with activated alumina. Bottoms from D2 is distilled in D3 to recover a distillate of CCl 3 F, which is dried with activated alumina in S2. Bottoms from D3, containing residual CCl 4, is recycled to reactor R1.
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Exercise 1.2 Subject : Mixing is spontaneous, but separation is not. Given: Thermodynamic principles. Find: Explanation for why mixing and separation are different. Analysis: Mixing is a natural, spontaneous process. It may take time, but concentrations of components in a single fluid phase will tend to become uniform, with an increase in entropy. By the second law of thermodynamics, a natural process tends to randomness. The separation of a mixture does not occur naturally or spontaneously. Energy is required to separate the different molecular species. Exercise 1.3 Subject : Separation of a mixture requires a transfer of energy to it or the degradation of its energy. Given: The first and second laws of thermodynamics. Find: Explain why the separation of a mixture requires energy. Analysis:
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This note was uploaded on 04/21/2008 for the course CHE 31 taught by Professor Gilchrest during the Fall '08 term at Lehigh University .

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ch01 - Exercise 1.1 (i) Known: Fluorocarbons can be...

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