Lecture 10 : SYNTHESIS OF SEPARATION SYSTEM – HOMOGENOUS MIXTURE SEPARATION<br />After separating the heterogenous mixture...
To illustrate the guidelines ….<br />First choice !<br />What circumstances ?  Discuss !<br />ABSORBER<br />ADSORBER<br />...
1<br />Circumstances not favouringdistillation<br />1. Separation of low molecular wt. materials<br />2. Separation of hig...
2<br />Sequencing using minimum vapour flow<br />Use short cut method to determine minimum reflux ratio for specified sepa...
Short Cut Design Method for Distillation Column<br />Stages of Calculation for the Short Cut Method.<br />i. Calculation o...
Stages of Calculation for the Short Cut Method.<br />ii. Calculation of Minimum Number of Stages using Fenske Equation.<br...
Stages of Calculation for the Short Cut Method.<br />iii. Calculation of Minimum Reflux Ratio using Underwood Equation.<br...
Stages of Calculation for the Short Cut Method.<br />iv. Determination of Feed Location<br />Kirkbride Equation<br />ZH an...
Stages of Calculation for the Short Cut Method.<br />v. Determination of Actual No of Stages based on Set Reflux Ratio (Gi...
Stages of Calculation for the Short Cut Method.<br />The correlation allows for the determination of corresponding No. of ...
Example for Short Cut method calculation<br />Given the separation specified below;<br />The separation cut is between n-b...
Solution<br />Calculate the minimum no of stages using Fenske eqn.<br />
Solution<br />Calculate the minimum Reflux Ratio using Underwood Eqn. (Assume sat. liq and therefore q = 1)<br />i. Determ...
Solution<br />ii. Using the calculated root of the Underwood equation q , determine Rmin.<br />a i . xDi<br />Component<br...
Example on Distillation Sequencing<br />Given the mixture to be separated;<br />Each component is to be separated with a s...
Example on Distillation Sequencing<br />The possible sequences are :<br />D/E<br />C/DE<br />C/D<br />CD/E<br />B/CDE<br /...
Example on Distillation Sequencing<br />For each of the column, we need to calculate the minimum vapour flow using Underwo...
Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />ABC/DE<br />AB/C<br />A/B<br />D/...
Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />A/BCDE<br />BC/DE<br />B/C<br />D...
Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />ABCD/E<br />AB/CD<br />A/B<br />C...
Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />ABCD/E<br />ABC/D<br />AB/C<br />...
In Summary…..<br />For homogenous mixture separation, distillation has always been preferred by industry due to their esta...
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10 synthesis of reaction separation system lec 10 homogenous separation

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10 synthesis of reaction separation system lec 10 homogenous separation

  1. 1. Lecture 10 : SYNTHESIS OF SEPARATION SYSTEM – HOMOGENOUS MIXTURE SEPARATION<br />After separating the heterogenous mixture, attempt can then be made to separate the homogenous mixture produced from the reaction. <br />This is a harder separation !<br />Remember from your earlier courses in separation !<br />We need to create or add an extra phase in order to perform the separation. <br />Most common example : Distillation, Liquid Extraction, <br /> Super Critical Fluid Extraction etc...<br />Some guidelines to consider !<br />There used to be a preferred rule long practised by industry whereby<br />distillation was given the first priority as chosen method for separating <br />homogenous mixture. Now, it is used as a benchmark against other methods.<br />1<br />In sequencing the separator for homogenous mixture, a guide which<br />can be used is to develop/design the sequence which consumes the least<br />energy for the required separation.<br />2<br />
  2. 2. To illustrate the guidelines ….<br />First choice !<br />What circumstances ? Discuss !<br />ABSORBER<br />ADSORBER<br />if cannot perform<br />separation or<br />economically <br />unattractive<br />Extraction<br />1<br />1<br />Liquid-Liquid<br />Solid-Liquid<br />DISTILLATION<br />MEMBRANE<br />2<br />Sequence preferred should be<br />the sequence that has highest<br />energy efficiency.<br />2<br />HOW ?<br />Eg. For distillation, assess the <br /> minimum vapour ffow <br /> required for the entire separation<br />
  3. 3. 1<br />Circumstances not favouringdistillation<br />1. Separation of low molecular wt. materials<br />2. Separation of high molecular wt. heat sensitive material.<br />3. Separation of components with low concentration.<br />4. Separation of classes of components<br />
  4. 4. 2<br />Sequencing using minimum vapour flow<br />Use short cut method to determine minimum reflux ratio for specified separation<br />UNDERWOOD EQUATION<br />Comparison is based on a consistent basis : infinite no. of stages<br />Calculate minimum vapour flow for each required separation (as specified) in every alternative sequence. Go for the sequence with the least total minimum vapour flow.<br />DISTILLATION<br />DISTILLATION<br />DISTILLATION<br />DISTILLATION<br />DISTILLATION<br />DISTILLATION<br />calculate minimum vapour flow<br />for each column !<br />Use theUnderwood Equation<br />We will look at this in more detail later …<br />
  5. 5. Short Cut Design Method for Distillation Column<br />Stages of Calculation for the Short Cut Method.<br />i. Calculation of component distribution using Hengstebeck Method.<br />Log (di/bi)<br />Log (di/bi) for LK<br />di<br />Log (di/bi) for HK<br />bi<br />aLLK<br />aLK<br />aHK<br />aHHK<br />Log (aij)<br />
  6. 6. Stages of Calculation for the Short Cut Method.<br />ii. Calculation of Minimum Number of Stages using Fenske Equation.<br />Minimum No of Stages (Total Reflux)<br />Geometric average of the relative volatility between LK to HK at the top and bottom of column.<br />Another form of Fenske Equation<br />
  7. 7. Stages of Calculation for the Short Cut Method.<br />iii. Calculation of Minimum Reflux Ratio using Underwood Equation.<br />The equation is used to determine the root q which is then used to solve the minimum reflux ratio equation. <br />q – feed quality<br />ai,j – relative volatility with reference to the heavy key j<br />xi,F – feed composition , x i,D– Distillate composition <br />
  8. 8. Stages of Calculation for the Short Cut Method.<br />iv. Determination of Feed Location<br />Kirkbride Equation<br />ZH and ZL – mole fraction of heavy and light key respectively in feed.<br />Ratio of the no. of stages in rectifying to stripping section.<br />XB,L and XD,H – mole fraction of light key in bottom product and heavy key in top product respectively.<br />B and D – molar flow of bottom product and distillate.<br />
  9. 9. Stages of Calculation for the Short Cut Method.<br />v. Determination of Actual No of Stages based on Set Reflux Ratio (Gilliland Correlation)<br />The correlation was originally represented in graphical form before an empirical was developed.<br />Based on the calculated Rmin from Underwood equation, the X value is determined based on a set Reflux Ratio R.<br />𝑋= 𝑅 −𝑅𝑚𝑖𝑛𝑅+1<br /> <br />Rmin is determined from Underwood Eqn.<br />Then a Y value is determined from the X value using the correlation below;<br />𝑌=0.2788−  1.3154 𝑋+0.4114 𝑋0.2910+0.8628ln𝑋 +  0.9020ln𝑋+ 1𝑋<br /> <br />The Y value obtained is then used to determined the number of stages N corresponding to the Reflux Ratio R using the equation below based on the Nmin determined from Fenske Eqn.<br />𝑌= 𝑁 −𝑁𝑚𝑖𝑛𝑁+1<br /> <br />
  10. 10. Stages of Calculation for the Short Cut Method.<br />The correlation allows for the determination of corresponding No. of Stages N required as the Reflux Ratio R is varied from the minimum reflux ratio.<br />No. of Stages<br />x<br />x<br />x<br />x<br />x<br />x<br />x<br />x<br />x<br />x<br />x<br />Reflux Ratio<br />This will allow for the capital energy trade off to be investigated. (Discuss how it is being done?)<br />
  11. 11. Example for Short Cut method calculation<br />Given the separation specified below;<br />The separation cut is between n-butane and i-pentane<br />Determine the minimum number of stages and minimum reflux ratio.<br />
  12. 12. Solution<br />Calculate the minimum no of stages using Fenske eqn.<br />
  13. 13. Solution<br />Calculate the minimum Reflux Ratio using Underwood Eqn. (Assume sat. liq and therefore q = 1)<br />i. Determine the root of Underwood equation q value.<br />a i . zi<br />Component<br />a i . zi<br />a i - q<br />q = 1.5<br />q = 1.3<br />q = 1.35<br />0.071<br />0.355<br />1.0<br />-0.4<br />-0.462<br />0.564<br />0.068<br />0.312<br />0.769<br />-0.571<br />-0.600<br />-0.022<br />0.068<br />0.30<br />0.714<br />-0.667<br />-0.667<br />-0.252<br />Propane<br />i-butane<br />n-butane<br />i-pentane<br />n-pentane<br />0.25<br />0.39<br />0.50<br />0.20<br />0.30<br />Close enough, take q value = 1.35<br />Sum<br />
  14. 14. Solution<br />ii. Using the calculated root of the Underwood equation q , determine Rmin.<br />a i . xDi<br />Component<br />xDi<br />a i - q<br />q = 1.35<br />0.15<br />0.69<br />1.66<br />-0.06<br />-0.02<br />2.42<br />Propane<br />i-butane<br />n-butane<br />i-pentane<br />n-pentane<br />0.11<br />0.33<br />0.53<br />0.02<br />0.01<br /> = Rmin + 1<br />Sum<br />Therefore Rmin = 1.42<br />
  15. 15. Example on Distillation Sequencing<br />Given the mixture to be separated;<br />Each component is to be separated with a specification of 99 %. Assume that the non key component will not distribute but end up either at the top or bottom depending on their relative volatility compared to the key component.<br />Determine the best sequence(s).<br />
  16. 16. Example on Distillation Sequencing<br />The possible sequences are :<br />D/E<br />C/DE<br />C/D<br />CD/E<br />B/CDE<br />D/E<br />B/C<br />BC/DE<br />A/BCDE<br />B/C<br />BC/D<br />BCD/E<br />B/CD<br />C/D<br />C/DE<br />D/E<br />A/B<br />AB/CDE<br />CD/E<br />C/D<br />ABCDE<br />AB/C<br />A/B<br />ABC/DE<br />D/E<br />A/BC<br />B/C<br />D/E<br />ABCD/E<br />AB/CD<br />C/D<br />A/B<br />A/BCD<br />C/D<br />B/CD<br />B/C<br />BC/D<br />A/BC<br />B/C<br />ABC/D<br />AB/C<br />A/B<br />
  17. 17. Example on Distillation Sequencing<br />For each of the column, we need to calculate the minimum vapour flow using Underwood Eqn….<br />D/E<br />C/DE<br />C/D<br />CD/E<br />B/CDE<br />D/E<br />B/C<br />BC/DE<br />A/BCDE<br />B/C<br />BC/D<br />BCD/E<br />B/CD<br />C/D<br />C/DE<br />D/E<br />A/B<br />AB/CDE<br />CD/E<br />C/D<br />ABCDE<br />AB/C<br />A/B<br />ABC/DE<br />D/E<br />A/BC<br />B/C<br />D/E<br />ABCD/E<br />AB/CD<br />C/D<br />A/B<br />A/BCD<br />C/D<br />B/CD<br />B/C<br />The minimum vapour flow for each column in the sequence is added up to give the total minimum vapour flow for the sequence.<br />BC/D<br />A/BC<br />B/C<br />ABC/D<br />AB/C<br />A/B<br />
  18. 18. Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />ABC/DE<br />AB/C<br />A/B<br />D/E<br />A<br />ABC<br />B<br />ABCDE<br />BC<br />Mixed Sequence<br />D<br />C<br />DE<br />S Vmin = 5584 kmol/hr<br />E<br />
  19. 19. Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />A/BCDE<br />BC/DE<br />B/C<br />D/E<br />A<br />B<br />ABCDE<br />BC<br />C<br />Mixed Sequence<br />D<br />DE<br />S Vmin = 5670 kmol/hr<br />E<br />
  20. 20. Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />ABCD/E<br />AB/CD<br />A/B<br />C/D<br />AB<br />ABCD<br />Mixed Sequence<br />A<br />C<br />ABCDE<br />CD<br />S Vmin = 5106 kmol/hr<br />B<br />E<br />D<br />
  21. 21. Example on Distillation Sequencing<br />Calculation done for some of the sequences…<br />ABCD/E<br />ABC/D<br />AB/C<br />A/B<br />CD<br />ABC<br />A<br />Indirect Sequence<br />ABCD<br />C<br />S Vmin = 5188 kmol/hr<br />ABCDE<br />D<br />B<br />E<br />
  22. 22. In Summary…..<br />For homogenous mixture separation, distillation has always been preferred by industry due to their established position over other methods and their versatility /flexibility in addressing range of feed mixture.<br />As most reactor effluent mixture consist of many components, the separation for the individual components has to be done is a sequence. The sequence of these separators can be determined using established methods such as the short cut method (Fenske-Underwood Equation) for distillation column<br />

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