Engineering 435 Lab Report Distillation Column Team Members Brian Vandagriff Marc Moss James Linder Corita Suber November 30, 1998 Introduction The function of distillation is to separate, by vaporization, a liquid mixture of miscible and volatile substances into individual components or, in some cases, into groups of components. The separation of a mixture of alcohol and water into its components; of liquid air into nitrogen, oxygen, argon; and of crude petroleum into gasoline, kerosene, fuel oil, and lubricating stock are examples of distillation. Suppose there are two components, A and B. Both of these components are found in both phases. There are four variables: pressure, temperature, and concentrations of component A in the liquid and vapor phases (the concentrations of component B are unity less those concentrations of A). If the pressure is fixed, only one variable, e.g., liquid-phase concentration, can be changed independently and temperature and vapor-phase concentration follow. In practice, distillation may be carried out either of two principal methods. The first method is based on the production of a vapor by boiling the liquid mixture to be separated and condensing the vapors without allowing any liquid to return to the still. There is then no reflux, which is called batch distillation. The second method is based on the return of part of the condensate to the still under such conditions that this returning liquid is brought into intimate contact with the vapors on their way to the condenser. Either of these methods may be conducted as a continuous steady-state distillation process, including single-stage partial vaporization without reflux (flash distillation) and continuous distillation with reflux (rectification), for systems containing only two components. Background The distillation column experiment is a purification experiment to separate a binary mixture of methanol and water. After becoming familiar with the column and its setup, several experiments were conducted to observe the operation and performance of the column. The holding reservoir, which contained the methanol-water mixture, was analyzed to determine the composition of the liquid. We performed a boiling point test on the mixture to determine the unknown composition of the liquid. The data obtained from the boiling point test allowed us to determine the composition using an x, y, T data plot for methanol-water. Two experiments were performed during the four-week period. A batch distillation was performed first. The distillation column was monitored until the reboiler started to boil. The time was recorded and the volume change was monitored in the reboiler. The second experiment involved a continuous distillation experiment. The column was allowed to reach steady state. Once steady state was obtained the time was recorded and the compositions of each tray were determined during a specific time interval. The collection of this data would allow us to determine the tray efficiency and plot the separation line on the equilibrium diagram. The diagram of our system is given on the following page as Figure 1. Figure 1. Distillation Column Procedure Batch Distillation: 1. Determine the composition of the liquid that is in the holding reservoir containing the mixture by using the boiling point test and an x, y, T plot for methanol-water. 2. Use the LabView program to initiate startup of the heating process to the reboiler. 3. Allow distillation column to reach steady-state. 4. Do composition analysis on the distillate (boiling point test). 5. Record time and volume readings in the rebolier from the time the reboiler begins to boil. Continuous Distillation: 1. Repeat steps 1-3 from above procedure. 2. Record the temperatures of each tray while at steady-state. 3. Perform calculations with the data obtained to determine tray efficiency. Results The batch distillation data results are given in Table 1 below. Table 1. Batch Distillation Data E 435 Distillation Column Analysis Actual Theoretical o Time (min) Volume (L) Temperature ( C) 0 15 77.509 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 14.994 14.988 14.983 14.976 14.968 14.961 14.953 14.946 14.939 14.932 14.925 14.918 14.91 14.903 14.896 77.648 77.57 77.646 77.635 77.649 77.649 77.649 77.65 77.691 77.794 77.651 77.75 77.794 77.791 77.792 Time (min) Volume (L) Temperature (o C) 0 15 77.874 1.772 3.511 5.216 6.889 8.531 10.142 11.724 13.278 14.804 15 14.74 14.486 14.237 13.993 13.754 13.52 13.291 13.066 12.845 12.817 78.064 78.256 78.451 78.65 78.852 79.057 79.265 79.477 79.693 79.722 The continuous distillation data is given in Table 2, which is provided below. Table 2. Continuous Distillation Data Tray 7 8 9 10 11 12 Reboiler Temperature (o C) 64.83 65.8 66.18 68.59 69.53 74.63 79.45 Xm 0.992 0.932 0.89 0.75 0.69 0.42 0.265 Efficiency (%) 125 54.5 42.9 110 34 89.3 41.2 Discussion of Results The data provided in Table 1 for the batch distillation experiment illustrates that we may have a problem with the column or the batch distillation spreadsheet. The spreadsheet shows that the volume in the reboiler should be changing at a much higher rate than the column actually performed. Since the spreadsheet had been successfully used on previous occasions, it is likely that the error is in the column. Attached on the following pages are the results of the batch distillation experiment (spreadsheet solution and graphical solutions). The data provided in Table 2 for the continuous distillation experiment illustrates that trays 1 through 6 had temperature readings slightly below the boiling point of methanol. This is likely due to the RTD's not being calibrated correctly. This sheds some doubt on the accuracy of the results for the remaining trays, which are given in Table 2 provided above. The liquid compositions shown in Table 2 were obtained by using a methanol-water x, y, T diagram. The useable data was plotted on a x, y diagram to determine the individual tray efficiencies. The plot illustrating the individual tray efficiencies is attached on the following page. Conclusions/Recommendations During experimentation of the distillation column the group noticed distillate being formed even during total reflux. This could indicate a problem with the reflux valve. This could also explain the problem with the reboiler volume during batch distillation experiments. The behavior of the reflux valve should be monitored to determine whether it is functioning correctly. Being able to perform experiments on the distillation column was very useful task as it provides practical experience in using the theoretical knowledge acquired in the Unit Operations class throughout the semester. Table of Contents I. Introduction II. Background III. Results IV. Discussion of Results V. Conclusions/Recommendations VI. Appendix APPENDIX