Batch Rectification

Safety Procedures

Please be aware of any potential hazards prior to operating any experiment. During the experiment, a denatured ethanol vapors will be produced within the boiler and rectification column. All samples will be collected once they are cooled and are to be returned to the experiment when done. There are several hot surfaces on the experiment and are marked with yellow warning labels. If in contact with these surfaces or exposed to the boiling solution, run cool water over the affected area, shut down experiment, contact lab personal, and use the emergency protocols at the exits to contact Health and Safety if additional medical attention is required. 

Other Safety Concerns:

• Wear a lab coat and safety glasses at all times

• Boiler and Rectification Column will be hot (~75 C to 100 C)

• The ethanol in the tank is not safe to drink, meaning that however desperate you are to get through the lab, drinking your distilled product will not get you done any faster. You will likely go to the hospital, it'll cause a big ruckus, and I will have to do a lot of paperwork. Not fun for anyone.

Programs, Equipment, and Instruments

• Laptop with CE600 Software

• Water chiller with pump

• Thermocouple and flow meter

• Balance

Objectives

1. Estimate the initial moles of ethanol in the reboiler.

2. Achieve steady state under infinite reflux conditions. The column pressure drop should be roughly constant and less than 45 mbar. Generally this can be accomplished by heating at full power until the first few drops of distillate appear, then reducing power to about 350-650 W and adjusting as needed until the pressure drop stabilizes aboves 7.5 mbar.

3. Measure the pot composition (by flash calculation) and average cumulative distillate product composition (by sampling) as a function of time for any reflux above Rmin.

4. Compare your data to the predictions made by the Smoker-Rose method (see Perry’s Handbook, 8th ed, pg 13-112). This consists of roughly two steps:

   1. Given the initial total moles in the system, the initial mole fraction of ethanol in the system, and the mole fraction of ethanol in the pot at any time, use Eq. 13-134 to calculate the estimate total moles in the pot at any time. The means of evaluating the integral in Eq. 13-134 was described in the pre-lab questions.

   2. Use the values found in the previous step and Eq. 13-135 to estimate the average (cumulative) distillate composition.

Tips

1. Make sure you operate above Rmin, which can be determined for a batch distillation unit by the method given in Fig. 13-122 and/or Fig. 13-123. Failure to do so will make it impossible to use the Smoker-Rose (or any other) method.

2. To determine the pot composition during operation, use the VLE data generated as part of the pre-lab questions.

3. To determine the average cumulative distillate product composition, drain Tank V into a beaker, stir to mix, measure the density using a volumetric flask, then look up the composition using the tables attached to this page.

4. Stop the experiment if/when the reboiler temperature exceeds 99 C.

5. Your theory section should include a derivation of Eq. 13-134 and 13-135 (an excellent start is provided just above Eq. 13-126).

6. Density tables have been included as an attachment at the bottom of this page, which you can use to determine ethanol concentration of the distillate product. 

References

1. Van Ness, H., Abbott, M. In: Perry's Chemical Engineers Handbook, Green, D., Perry, R., Eds., 8th ed.; McGraw Hill: New York, 2008, Ch. 4

2. Doherty, M. et al. In: Perry's Chemical Engineers Handbook, Green, D., Perry, R., Eds., 8th ed.; McGraw Hill: New York, 2008, Ch. 13.

3. McCabe, W.L.; Smith, J.C.; Harriott, P. Unit Operations of Chemical Engineering, 7th ed. McGraw-Hill: New York, 2005. pp. 712-722.

4. Smoker, E.; Rose, A. Trans. AIChE, 1940, 36, 285-293.

5. Seader, J.; Henley, E.; Roper, D. Separation Process Principles, 3rd Ed., John Wiley & Sons: Hoboken, NJ, 2011; Ch. 13.

6. Seriously, have you seen the paperwork from hospitals? Even the CEO of United Healthcare couldn't understand the bill his own company gave a patient. And now you want to put me through that? I shouldn't have told you it was denatured in the first place with an attitude like that. Jerk.

Ethanol-Water Density Tables