Look up distillation in Wiktionary, the free dictionary. In batch distillation, the batch vaporizes, which changes its composition; in fractionation, liquid higher in the fractionation column contains more lights and boils at lower temperatures. Problems of Atomic Science and Technology in Russian. Therefore, starting from a given mixture, it appears to have a boiling range instead of a boiling point, although this is because its composition changes:
Once the apparatus is assembled, and the liquid to be distilled is in the still pot, the desired vacuum is established in the system by using the vacuum connection on the short-path distillation head. Care is taken to prevent potential "bumping" as the liquid in the still pot degases. While establishing the vacuum, the flow of coolant is started through the short-path distillation head. Once the desired vacuum is established, heat is applied to the still pot.
If needed, the first portion of distillate can be discarded by purging with inert gas and changing out the distillate receiver. When the distillation is complete: While under the inert gas purge, remove the distillate receiver and cap it with an air-tight cap.
The distillate receiver can be stored under vacuum or under inert gas by using the side-arm on the distillation flask. Rotary evaporation  is a common technique used in laboratories to concentrate or isolate a compound from solution.
Many solvents are volatile and can easily be evaporated using rotary evaporation. Even less volatile solvents can be removed by rotary evaporation under high vacuum and with heating. It is also used by environmental regulatory agencies for determining the number of solvents in paints, coatings and inks.
Safety is an important consideration when using glassware as part of the set-up. All of the glass components should be carefully examined for scratches and cracks which could result in implosions when the vacuum is applied.
Wrapping as much of the glassware with tape as is practical helps to prevent dangerous scattering of glass shards in the event of an implosion. Industrial-scale vacuum distillation  has several advantages. Close boiling mixtures may require many equilibrium stages to separate the key components.
One tool to reduce the number of stages needed is to utilize vacuum distillation. Vacuum distillation increases the relative volatility of the key components in many applications. The higher the relative volatility, the more separable are the two components; this connotes fewer stages in a distillation column in order to effect the same separation between the overhead and bottoms products.
Lower pressures increase relative volatilities in most systems. The second advantage of vacuum distillation is the reduced temperature requirement at lower pressures. For many systems, the products degrade or polymerize at elevated temperatures. Another advantage of vacuum distillation is the reduced capital cost, at the expense of slightly more operating cost. Utilizing vacuum distillation can reduce the height and diameter, and thus the capital cost of a distillation column. Petroleum crude oil is a complex mixture of hundreds of different hydrocarbon compounds generally having from 3 to 60 carbon atoms per molecule , although there may be small amounts of hydrocarbons outside that range.
Formation of coke would result in plugging the tubes in the furnace that heats the feed stream to the crude oil distillation column. Plugging would also occur in the piping from the furnace to the distillation column as well as in the column itself. Figure 2 is a simplified process diagram of a petroleum refinery vacuum distillation column that depicts the internals of the column and Figure 3 is a photograph of a large vacuum distillation column in a petroleum refinery.
The 10 to 40 mmHg absolute pressure in a vacuum distillation column increases the volume of vapor formed per volume of liquid distilled. The result is that such columns have very large diameters. Distillation columns such those in Images 1 and 2, may have diameters of 15 meters or more, heights ranging up to about 50 meters, and feed rates ranging up to about 25, cubic meters per day , barrels per day. The vacuum distillation column internals must provide good vapor-liquid contacting while, at the same time, maintaining a very low-pressure increase from the top of the column top to the bottom.
Therefore, the vacuum column uses distillation trays only where withdrawing products from the side of the column referred to as side draws.
Most of the column uses packing material for the vapor-liquid contacting because such packing has a lower pressure drop than distillation trays. This packing material can be either structured sheet metal or randomly dumped packing such as Raschig rings.
The absolute pressure of 10 to 40 mmHg in the vacuum column is most often achieved by using multiple stages of steam jet ejectors. Many industries, other than the petroleum refining industry, use vacuum distillation on a much a smaller scale. Copenhagen-based Empirical Spirits,  a distillery founded by former Noma chefs,  uses the process to create uniquely flavoured spirits. Molecular distillation is vacuum distillation below the pressure of 0. The gaseous phase no longer exerts significant pressure on the substance to be evaporated, and consequently, the rate of evaporation no longer depends on pressure.
That is, because the continuum assumptions of fluid dynamics no longer apply, mass transport is governed by molecular dynamics rather than fluid dynamics. Thus, a short path between the hot surface and the cold surface is necessary, typically by suspending a hot plate covered with a film of feed next to a cold plate with a line of sight in between. Molecular distillation is used industrially for purification of oils. A simple short path vacuum distillation apparatus.
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