Vacuum distillation

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Figure 1: At atmospheric pressure, dimethyl sulfoxide boils at 189 degC. In the vacuum apparatus here, it distills off into the connected receiver flask on the left at only 70 degC. Vacuum distillation of DMSO at 70C.jpg
Figure 1: At atmospheric pressure, dimethyl sulfoxide boils at 189 °C. In the vacuum apparatus here, it distills off into the connected receiver flask on the left at only 70 °C.

Vacuum distillation or distillation under reduced pressure is a type of distillation performed under reduced pressure, which allows the purification of compounds not readily distilled at ambient pressures or simply to save time or energy. This technique separates compounds based on differences in their boiling points. This technique is used when the boiling point of the desired compound is difficult to achieve or will cause the compound to decompose. [1] Reduced pressures decrease the boiling point of compounds. The reduction in boiling point can be calculated using a temperature-pressure nomograph using the Clausius–Clapeyron relation. [2]

Contents

Laboratory-scale applications

Compounds with a boiling point lower than 150 °C typically are distilled at ambient pressure. For samples with high boiling points, short-path distillation apparatus is commonly employed. [3] [4] This technique is amply illustrated in Organic Synthesis. [5] [6]

Rotary evaporation

Rotary evaporation [7] 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 amount of solvents in paints, coatings and inks. [8]

Safety considerations

Safety is an important consideration when glassware is under vacuum pressure. Scratches and cracks can 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.[ citation needed ]

Industrial-scale applications

Figure 2: Simplified animation of a typical dry vacuum distillation column as used in oil refineries Vacuum Distillation Column.gif
Figure 2: Simplified animation of a typical dry vacuum distillation column as used in oil refineries
Figure 3: Large-scale vacuum distillation tower at the Fawley oil refinery Vacuum Column.jpg
Figure 3: Large-scale vacuum distillation tower at the Fawley oil refinery

Industrial-scale vacuum distillation [10] 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. [11] Vacuum distillation columns (as depicted in Figures 2 and 3) typically used in oil refineries have diameters ranging up to about 14 meters (46 feet), heights ranging up to about 50 meters (164 feet), and feed rates ranging up to about 25,400 cubic meters per day (160,000 barrels per day).[ citation needed ]

Vacuum distillation can improve a separation by:[ citation needed ]

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.[ citation needed ]

Vacuum distillation in petroleum refining

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. [12] [13] [14] The refining of crude oil begins with distilling the incoming crude oil in a so-called atmospheric distillation column operating at pressures slightly above atmospheric pressure. [10] [12] [13]

Vacuum distillation can also be referred to as "low-temperature distillation".[ citation needed ]

In distilling the crude oil, it is important not to subject the crude oil to temperatures above 370 to 380 °C because high molecular weight components in the crude oil will undergo thermal cracking and form petroleum coke at temperatures above that. 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.[ citation needed ]

The constraint imposed by limiting the column inlet crude oil to a temperature of less than 370 to 380 °C yields a residual oil from the bottom of the atmospheric distillation column consisting entirely of hydrocarbons that boil above 370 to 380 °C.

To further distill the residual oil from the atmospheric distillation column, the distillation must be performed at absolute pressures as low as 10 to 40 mmHg / Torr (About 5% atmospheric pressure) so as to limit the operating temperature to less than 370 to 380 °C.

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. [15]

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 25,400 cubic meters per day (160,000 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 products are withdrawn 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. [16]

Many industries, other than the petroleum refining industry, use vacuum distillation on a much smaller scale. Copenhagen-based Empirical Spirits, [17] a distillery founded by former Noma chefs, [18] uses the process to create uniquely flavoured spirits. Their flagship spirit, Helena, is created using Koji, alongside Pilsner Malt and Belgian Saison Yeast. [19]

Large-scale water purification

Vacuum distillation is often used in large industrial plants as an efficient way to remove salt from ocean water, in order to produce fresh water. This is known as desalination. The ocean water is placed under a vacuum to lower its boiling point and has a heat source applied, allowing the fresh water to boil off and be condensed. The condensing of the water vapor prevents the water vapor from filling the vacuum chamber, and allows the effect to run continuously without a loss of vacuum pressure. The heat from condensation of the water vapor is removed by a heat sink, which uses the incoming ocean water as the coolant and thus preheats the feed of ocean water. Some forms of distillation do not use condensers, but instead compress the vapor mechanically with a pump. This acts as a heat pump, concentrating the heat from the vapor and allowing for the heat to be returned and reused by the incoming untreated water source. There are several forms of vacuum distillation of water, with the most common being multiple-effect distillation, vapor-compression desalination, and multi-stage flash distillation. [20]

Molecular distillation

Molecular distillation is vacuum distillation below the pressure of 0.01 torr [21] (1.3 Pa). 0.01 torr is one order of magnitude above high vacuum, where fluids are in the free molecular flow regime, i.e. the mean free path of molecules is comparable to the size of the equipment. [1] 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.[ citation needed ]

Molecular distillation is used industrially for purification of oils. [20]

See also

Related Research Articles

<span class="mw-page-title-main">Distillation</span> Method of separating mixtures

Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still.

<span class="mw-page-title-main">Oil refinery</span> Facility that processes crude oil

An oil refinery or petroleum refinery is an industrial process plant where petroleum is transformed and refined into products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petroleum gas and petroleum naphtha. Petrochemical feedstock like ethylene and propylene can also be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha. The crude oil feedstock has typically been processed by an oil production plant. There is usually an oil depot at or near an oil refinery for the storage of incoming crude oil feedstock as well as bulk liquid products. In 2020, the total capacity of global refineries for crude oil was about 101.2 million barrels per day.

Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to fractionate. Generally the component parts have boiling points that differ by less than 25 °C (45 °F) from each other under a pressure of one atmosphere. If the difference in boiling points is greater than 25 °C, a simple distillation is typically used.

<span class="mw-page-title-main">Fractionating column</span> Equipment to separate liquids by distillation

A fractionating column or fractional column is equipment used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on their differences in volatility. Fractionating columns are used in small-scale laboratory distillations as well as large-scale industrial distillations.

<span class="mw-page-title-main">Sublimation (phase transition)</span> Transition from solid to gas

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. The verb form of sublimation is sublime, or less preferably, sublimate. Sublimate also refers to the product obtained by sublimation. The point at which sublimation occurs rapidly is called critical sublimation point, or simply sublimation point. Notable examples include sublimation of dry ice at room temperature and atmospheric pressure, and that of solid iodine with heating.

<span class="mw-page-title-main">Rotary evaporator</span> Device used in chemical laboratories

A rotary evaporator (rotavap) is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the use of this technique and equipment may include the phrase "rotary evaporator", though use is often rather signaled by other language.

<span class="mw-page-title-main">Steam distillation</span> Method of separation in organic chemistry

Steam distillation is a separation process that consists of distilling water together with other volatile and non-volatile components. The steam from the boiling water carries the vapor of the volatiles to a condenser; both are cooled and return to the liquid or solid state, while the non-volatile residues remain behind in the boiling container.

<span class="mw-page-title-main">Volatility (chemistry)</span> Tendency of a substance to vaporize

In chemistry, volatility is a material quality which describes how readily a substance vaporizes. At a given temperature and pressure, a substance with high volatility is more likely to exist as a vapour, while a substance with low volatility is more likely to be a liquid or solid. Volatility can also describe the tendency of a vapor to condense into a liquid or solid; less volatile substances will more readily condense from a vapor than highly volatile ones. Differences in volatility can be observed by comparing how fast substances within a group evaporate when exposed to the atmosphere. A highly volatile substance such as rubbing alcohol will quickly evaporate, while a substance with low volatility such as vegetable oil will remain condensed. In general, solids are much less volatile than liquids, but there are some exceptions. Solids that sublimate such as dry ice or iodine can vaporize at a similar rate as some liquids under standard conditions.

<span class="mw-page-title-main">Continuous distillation</span> Form of distillation

Continuous distillation, a form of distillation, is an ongoing separation in which a mixture is continuously fed into the process and separated fractions are removed continuously as output streams. Distillation is the separation or partial separation of a liquid feed mixture into components or fractions by selective boiling and condensation. The process produces at least two output fractions. These fractions include at least one volatile distillate fraction, which has boiled and been separately captured as a vapor condensed to a liquid, and practically always a bottoms fraction, which is the least volatile residue that has not been separately captured as a condensed vapor.

<span class="mw-page-title-main">Vacuum evaporation</span>

Vacuum evaporation is the process of causing the pressure in a liquid-filled container to be reduced below the vapor pressure of the liquid, causing the liquid to evaporate at a lower temperature than normal. Although the process can be applied to any type of liquid at any vapor pressure, it is generally used to describe the boiling of water by lowering the container's internal pressure below standard atmospheric pressure and causing the water to boil at room temperature.

<span class="mw-page-title-main">Fragrance extraction</span> Separation process of aromatic compounds from raw materials

Fragrance extraction refers to the separation process of aromatic compounds from raw materials, using methods such as distillation, solvent extraction, expression, sieving, or enfleurage. The results of the extracts are either essential oils, absolutes, concretes, or butters, depending on the amount of waxes in the extracted product.

<span class="mw-page-title-main">Kugelrohr</span> Vacuum distillation apparatus

A Kugelrohr is a short-path vacuum distillation apparatus typically used to distill relatively small amounts of compounds with high boiling points under greatly reduced pressure.

<span class="mw-page-title-main">Evaporator</span> Machine transforming a liquid into a gas

An evaporator is a type of heat exchanger device that facilitates evaporation by utilizing conductive and convective heat transfer to provide the necessary thermal energy for phase transition from liquid to vapor. Within evaporators, a circulating liquid is exposed to an atmospheric or reduced pressure environment, causing it to boil at a lower temperature compared to normal atmospheric boiling.

<span class="mw-page-title-main">Condenser (laboratory)</span> Laboratory apparatus used to condense vapors

In chemistry, a condenser is laboratory apparatus used to condense vapors – that is, turn them into liquids – by cooling them down.

An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases.

<span class="mw-page-title-main">Reflux</span> Condensation of vapors and their return to where they originated

Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions over a long period of time.

<span class="mw-page-title-main">Petroleum refining processes</span> Methods of transforming crude oil

Petroleum refining processes are the chemical engineering processes and other facilities used in petroleum refineries to transform crude oil into useful products such as liquefied petroleum gas (LPG), gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils.

Refining of crude oils essentially consists of primary separation processes and secondary conversion processes. The petroleum refining process is the separation of the different hydrocarbons present in crude oil into useful fractions and the conversion of some of the hydrocarbons into products having higher quality performance.

The low-temperature distillation (LTD) technology is the first implementation of the direct spray distillation (DSD) process. The first large-scale units are now in operation for desalination. The process was first developed by scientists at the University of Applied Sciences in Switzerland, focusing on low-temperature distillation in vacuum conditions, from 2000 to 2005.

Crude oil stabilisation is a partial distillation process that renders crude oil suitable for storage in atmospheric tanks, or of a quality suitable for sales or pipeline transportation. Stabilization is achieved by subjecting ‘live’ crude to temperature and pressure conditions in a fractionation vessel, which drives off light hydrocarbon components to form a ‘dead’ or stabilized crude oil with a lower vapor pressure.

References

  1. 1 2 3 Hickman, K. C. D. (1945), "Adventures in vacuum chemistry", American Scientist, 33 (4), Scientific american: xxx–231, JSTOR   27826079 , retrieved 2021-09-01
  2. ↑ "Pressure-Temperature Nomograph Interactive Tool". Sigma-Aldrich. Retrieved 2018-03-23.
  3. ↑ Introduction to Organic Laboratory Techniques: A Small Scale Approach By Donald L. Pavia, Gary M. Lampman, George S. Kriz, Randall G. Engel. Chapter 16.
  4. ↑ Leonard, J.; Lygo, B.; Procter, Garry (8 January 2013). Advanced practical organic chemistry (3rd ed.). Boca Raton. ISBN   9781439860977. OCLC   883131986.{{cite book}}: CS1 maint: location missing publisher (link)
  5. ↑ Fastuca, Nicholas J.; Wong, Alice R.; Mak, Victor W.; Reisman, Sarah E. (2020). "Asymmetric Michael Addition of Dimethyl Malonate to 2 Cyclopenten-1-one Catalyzed by a Heterobimetallic Complex". Organic Syntheses. 97: 327–338. doi: 10.15227/orgsyn.097.0327 . PMC   9128456 . PMID   35614904.
  6. ↑ Bartko, Samuel G.; Deng, James; Danheiser, Rick L. (2016). "Synthesis of 1-Iodopropyne". Organic Syntheses. 93: 245–262. doi: 10.15227/orgsyn.093.0245 .
  7. ↑ Operation of a Rotary Evaporator (Rotovap) (from the website of the University of British Columbia)
  8. ↑ SCAQMD Test method 302-91
  9. ↑ Energy Institute website page
  10. 1 2 Kister, Henry Z. (1992). Distillation Design (1st ed.). McGraw-Hill. ISBN   0-07-034909-6.
  11. ↑ Karl Kolmetz, Andrew W. Sloley et al. (2004), Designing Distillation Columns for Vacuum Service, 11th India Oil and Gas Symposium and International Exhibition, September 2004, Mumbai, India (also published in Hydrocarbon Processing, May 2005)
  12. 1 2 Gary, J.H. & Handwerk, G.E. (1984). Petroleum Refining Technology and Economics (2nd ed.). Marcel Dekker, Inc. ISBN   0-8247-7150-8.
  13. 1 2 Leffler, W.L. (1985). Petroleum refining for the nontechnical person (2nd ed.). PennWell Books. ISBN   0-87814-280-0.
  14. ↑ James G, Speight (2006). The Chemistry and Technology of Petroleum (4th ed.). CRC Press. 0-8493-9067-2.
  15. ↑ Karl Kolmetz, Andrew W. Sloley et al (2004), Designing Distillation Columns for Vacuum Service, 11th India Oil and Gas Symposium and International Exhibition, September 2004, Mumbai, India (also published in Hydrocarbon Processing, May 2005)
  16. ↑ Photo gallery Archived 2009-02-07 at the Wayback Machine (from website of Graham Manufacturing Company)
  17. ↑ "Empirical Spirits". empiricalspirits.co. Retrieved 2018-10-15.
  18. ↑ Kahn, Howie (2018-04-25). "A Fresh Take on Liquor From Two Noma Alums". Wall Street Journal. ISSN   0099-9660 . Retrieved 2018-10-15.
  19. ↑ "Empirical Spirits". Empirical Spirits. Retrieved 2018-10-15.
  20. 1 2 Desalination and Water Treatment, Murat Eyvaz, Ebubekir Yüksel 1988/2018. Chapter 5.
  21. ↑ Vogel's 5th ed.
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