High Pressure Laboratory

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Distillation

Excellent Resource books:

The elements of fractional distillation / by Clark Shove Robinson.
by Robinson, Clark Shove, 1888-1947.
Published 1922
http://babel.hathitrust.org/cgi/pt?id=wu.89077806107

Fractional distillation / by Sydney Young.
by Young, Sydney, 1857-
Published 1903
http://babel.hathitrust.org/cgi/pt?id=uc1.b277728

Basic principles

The concept of a theoretical plate

Distillation tube imageThe proportion of components of a simple A-B system in the vapor phase over a liquid phase is a function of the relative proportions and relative volatilities of the two components. A simple distillation involves sipping off the vapor phase in its relative proportions of A and B. A theoretical plate can be thought of as a simple distillation. If one arranges a series of simple distillations, one component will ultimately come out pure in the end. If one were to arrange a verticle column that loses heat to its surroundings, and thus condenses a vapor phase, allowing some liquid to return below, yet uses the heat of the vapors below to drive the lower boiling component higher up the column, the column will constitute a series of simple distillations. If one provides for efficient return of the liquid phase down and increased surface area to heat the lower boiling vapors, one increases the number of simple distillation or plates. (The term “plate” comes from the old petroleum distillation columns which actually incorporated plates in their fractionating towers). The more plates, the better the separation. Since the whole method is based on sipping off an equilibrium mixture, fractional distillation requires the column to be mostly refluxing, and only a little to be removed at the top at a time. Thus a fractionating column is totally negated if the distillate is driven over. Little separation will result. Time is the price of purity.

Distillation apparatus 2Distillation apparatus 3

Fractionating column image


A high efficiency, low holdup, low pressure drop fractionating column, vacuum jacketed with observation stripe. Suitable for samples as small as 2mL. Center tube is removable for cleaning. Double expansion spiral eliminates choking. Joints are 14/20. Approximately 40 theoretical plates at 80 cc/hr. boil-up. Operating pressure drop less than 1mm Hg. Column holdup (approx.): Operating with 9362 head, 0.6mL at 80cc/hr. Static with 9362 head, 0.25mL Xylene. Static: Column alone, 0.1mL Xylene. Replacement inner tube, only, 9333-08.

Your Rotary Evaporator
Care and Use
The vacuum seal
Bump traps and their use

image of Kjeldahl
Kjeldahl-type:practically useless.

classic bump trap image

Classic bump trap. Good for removal of high-boiling solvents. Can't be used for continuous addition, and if the material bumps, you use a lot more solvent than you started with to return the material to the flask.

6703 TRAP, Rotary Evaporator, Self-washing, Boulanger

Self-washing Rotary Evaporator - Boulanger image

Self washing, rotary evaporator trap design by Dr. William Boulanger. Superior design prevents blow-through and enables continuous addition with rotary evaporators. Solvent vapor rapidly flows out while condensed solvent continuously rinses both the trap walls and the evaporator shaft returning any material to the flask. Center hole allows complete drainage of the evaporator shaft.

The Kugelrohr

Need for a vacuum gauge and a bleed
Continuous feed

Principle on which it is based

image of Kugelrohr apparatus Kugelrohr properly done is distinct from classic distillation. Where in classic distillation, enough energy is given the system to drive the liquid into the vapor state and then on to condensation, Kugelrohr is a line-of-site phenomenon where an equilibrium is established between the vapor state and liquid state. However, the vapors being heavy, spill over into a cooler site and are thus condensed. Think of a pan of water on a radiator and a cold window nearby. Eventually the water will slowly evaporate, fill the room, then condense on the window pane. The water is transferred through the vapor phase, but never boils. The advantage of Kugelrohr is that it requires less heat and is more suitable for thermally delicate compounds.

Micro kugelrohr
Medium scale
The large scale alternative: wiped-film still

Simple distillation

Fractional distillation

Fractionating columns and their number of theoretical plates:

Fractionating head distillation apparatus None: One plate
Vigreaux: 2-4 plates
Packed columns: Up to 50 plates, depending upon length and packing
Specialty (spinning band, micro-insert (ACE): Up to 40 plates

"Flooding" is a big problem with packed columns; this destroys their efficiency. This is where the liquid phase cannot easily return down against the vapor pressure. The column fills with liquid. Glass bead packings are worst for this, followed by Rashig rings. The best compromise of surface area/ liquid return is found with Berl saddles and the high-tech folded wire-mesh packings ( #6624 from ACE Glass). These are available as stainless-steel or monel.

Fractionating heads
Vacuum distillation
Spinning band column
Steam distillation

Examples of distillation apparatus (pdf)



University of Illinois at Urbana-Champaign
High Pressure Laboratory
School of Chemical Sciences
Roger Adams Lab Penthouse
600 S. Mathews Avenue
Urbana, IL  61801
Dr. William A. Boulanger
Faculty Advisor
wboulang [at] illinois [dot] edu
217-621-4023 (cell)
217-359-1626
Webmaster
scs-webmaster [at] illinois [dot] edu