Fenton/Coughlin/Fall 01
CHEG 237
Bubble-Cap Distillation Column
The objective of this experiment is to gain experience in operation of large
equipment, to practice sampling and analysis techniques, to review the
principles and hardware of distillation, and to compare experimental
results to theoretical predictions.
Information on the theory of distillation is given in References 1-5.
Theoretical prediction of compositions throughout the column can by
obtained by solving simultaneous material and energy balances using
ASPEN or other means. The references provide equations for estimating
limiting conditions in the column such as minimum reflux and minimum
number of stages at total reflux.
The reagents used in this lab may be flammable. Smoking in the
laboratory is reason for immediate ejection and safety glasses must
be worn at all times. Hard hats are required in the bay area.
Make sure the condenser vent is open and that all other valves are
properly positioned before turning on steam. There are many drain
lines, etc., which may be open to the atmosphere.
During shut-down, do not turn the condenser water off until the
reboiler temperature has dropped to 140oF. This is to prevent
escape of uncondensed distillate out the vent. On shut-down, turn
off two valves in series on the reboiler system.
Concentration analysis will be performed using a gas
chromatograph. Make a group inspection of the apparatus.
Preliminary Preparations:
Review the necessary theory.
Examine the spare column sections. Note the details of the sample piping
and the plate construction.
Plan your experiments. Note that steady state operation is required to give
meaningful results and determine an efficient procedure for getting to
steady state. Plan a technique for sampling from the trays to avoid
compositional changes and include a trial to evaluate the reproducibility of
your experimental runs and the precision of your sampling and analytical
techniques. Run at total reflux until the group is familiar with all aspects
of the operation.
Develop a specific plan for converting the gas chromatograph output into
the concentrations you desire. Review the information in the instruction
Review continuous operation of distillation columns before operating the
equipment. The column is to be run continuously using various reflux
ratios (making sure the column is operating above the predicted minimum
reflux). Students should include a run at total reflux. Students may also
choose to investigate the effect of feed plate location at constant reflux on
component distribution or experimentally determine the minimum reflux
ratio. The instructor will specify the mixture to be separated.
Rich Kozel will review start-up and shut-down procedures for the
distillation column with students prior to operation.
Determine the precision of your measurements and the reproducibility of
your runs by making repeat measurements and performing repeat trials.
For all runs check mass and energy balances. Determine the effect that
various controllable variables have on the distribution of components
throughout the column (including the tops and bottoms products). Using
published correlations or ASPEN, estimate the minimum reflux ratio,
minimum number of trays at total reflux, and optimal feed plate location
for this process.
Describe the design of your experiments and the results obtained,
including an error analysis. Provide thoughtful and quantitative discussion
of results, explain trends using physical principles and relate your
experimental observations to predicted results (optimal feed plate location,
minimum number of trays, minimum reflux ratio, etc). Express any
discrepancies between observed and predicted results in terms of
quantified experimental uncertainties or limitations of the correlations or
computational software used.
Bennett, C. O. and Myers, J. E., Momentum, Heat, and Mass Transfer, 3rd
Ed, McGraw-Hill, New York, NY (1982), Chapters 4 and 6.
Geankoplis, C.J., Transprot Processes and Unit Operations, 3rd Ed.,
Prentice Hall, New Jersey, (1993).
Hengsteback, R. J., Distillation Principles and Design Procedures,
Reinhold Publishing Corp., New York, (1961).
McCabe, W. L. and Smith, J. C., and Harriott, P., Unit Operations of
Chemical Engineering, 6th Ed., McGraw-Hill Publishing Co., New York,
NY, (2001).
Perry, J. H, Ed., Chemical Engineer’s Handbook, 7th Ed., McGraw-Hill,
New York, NY (1997).