Vacuum distillation#Industrial-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.Introduction to Organic Laboratory Techniques: A Small Scale Approach By Donald L. Pavia, Gary M. Lampman, George S. Kriz, Randall G. Engel. Chapter 16.{{Cite book |title=Advanced practical organic chemistry |last1=Leonard |first1=J. |last2=Lygo |first2=B. |last3=Procter |first3=Garry |date=8 January 2013 |isbn=9781439860977 |edition=3rd |location=Boca Raton |oclc=883131986}} This technique is amply illustrated in Organic Synthesis.{{cite journal |doi=10.15227/orgsyn.097.0327|title=Asymmetric Michael Addition of Dimethyl Malonate to 2 Cyclopenten-1-one Catalyzed by a Heterobimetallic Complex|year=2020|journal=Organic Syntheses|volume=97|pages=327–338|first1=Nicholas J.|last1=Fastuca|first2=Alice R.|last2=Wong|first3=Victor W.|last3=Mak|first4=Sarah E.|last4=Reisman|pmid=35614904 |pmc=9128456 |doi-access=free}}

{{cite journal |first1=Samuel G.|last1=Bartko |first2=James |last2=Deng|first3=Rick L. |last3=Danheiser|doi=10.15227/orgsyn.093.0245|title=Synthesis of 1-Iodopropyne|year=2016|journal=Organic Syntheses|volume=93|pages=245–262|doi-access=free}}

{{Main|Rotary evaporation}}

Rotary evaporation[http://www.chem.ubc.ca/courseware/235/danalabsess/rotovap.html Operation of a Rotary Evaporator (Rotovap)] {{Webarchive|url=https://web.archive.org/web/20100902033710/http://www.chem.ubc.ca/courseware/235/danalabsess/rotovap.html |date=2010-09-02 }} (from the website of the University of British Columbia) 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.[http://aqmd.gov/tao/methods/lab/303-91.pdf] {{Webarchive|url=https://web.archive.org/web/20101108134427/http://aqmd.gov/tao/methods/lab/303-91.pdf |date=2010-11-08 }} SCAQMD Test method 302-91

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.{{cn|date=July 2023}}

Image:Vacuum Distillation Column.gif

Image:Vacuum Column.jpg[http://resources.schoolscience.co.uk/SPE/knowl/4/2index.htm?vacuum.html Energy Institute website page]]]

Industrial-scale vacuum distillation{{cite book |author=Kister, Henry Z.|title= Distillation Design|edition=1st|publisher=McGraw-Hill|year=1992|isbn=0-07-034909-6}} 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.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) 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).{{cn|date=July 2023}}

Vacuum distillation can improve a separation by:{{cn|date=July 2023}}

• Prevention of product degradation or polymer formation because of reduced pressure leading to lower tower bottoms temperatures,
• Reduction of product degradation or polymer formation because of reduced mean residence time especially in columns using packing rather than trays.
• Increasing yield, and purity.

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.{{cite book|author1=Gary, J.H. |author2=Handwerk, G.E. |name-list-style=amp |title=Petroleum Refining Technology and Economics|edition=2nd |publisher=Marcel Dekker, Inc|year=1984|isbn=0-8247-7150-8}}{{cite book|author=Leffler, W.L. |title=Petroleum refining for the nontechnical person|edition=2nd |publisher=PennWell Books|year=1985|isbn=0-87814-280-0}}{{cite book|author=James G, Speight |title=The Chemistry and Technology of Petroleum|edition=4th |publisher=CRC Press|year=2006|id=0-8493-9067-2}} 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.

Vacuum distillation can also be referred to as "low-temperature distillation".{{cn|date=July 2023}}

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.{{cn|date=July 2023}}

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.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)

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.[http://www.graham-mfg.com/ejphotos.html Photo gallery] {{Webarchive|url=https://web.archive.org/web/20090207173354/http://graham-mfg.com/ejphotos.html |date=2009-02-07}} (from website of Graham Manufacturing Company)

Many industries, other than the petroleum refining industry, use vacuum distillation on a much smaller scale. Copenhagen-based Empirical Spirits,{{Cite web|url=https://empiricalspirits.co/|archive-url=https://web.archive.org/web/20180225153559/https://empiricalspirits.co/|url-status=usurped|archive-date=February 25, 2018|title=Empirical Spirits|website=empiricalspirits.co|language=en|access-date=2018-10-15}} a distillery founded by former Noma chefs,{{Cite news|url=https://www.wsj.com/articles/a-fresh-take-on-liquor-from-two-noma-alums-1524666332|title=A Fresh Take on Liquor From Two Noma Alums|last=Kahn|first=Howie|date=2018-04-25|work=Wall Street Journal|access-date=2018-10-15|language=en-US|issn=0099-9660}} uses the process to create uniquely flavoured spirits. Their flagship spirit, Helena, is created using Koji, alongside Pilsner Malt and Belgian Saison Yeast.{{Cite web|url=https://shop.empiricalspirits.co/|archive-url=https://web.archive.org/web/20171220105129/https://shop.empiricalspirits.co/|url-status=usurped|archive-date=December 20, 2017|title=Empirical Spirits|website=Empirical Spirits|language=en|access-date=2018-10-15}}

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.Desalination and Water Treatment, Murat Eyvaz, Ebubekir Yüksel 1988/2018. Chapter 5.

Molecular distillation is vacuum distillation below the pressure of 0.01 torrVogel's 5th ed. (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. 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.{{cn|date=July 2023}}

Molecular distillation is used industrially for purification of oils.

Image:Short path distillation apparatus.svg| A simple short path vacuum distillation apparatus

Image:Kugelrohr_-_numbered.jpg| Kugelrohr – a short path vacuum distillation apparatus

Image:Perkin triangle distillation apparatus.svg| Perkin triangle – for air-sensitive vacuum distillation

Image:Vaccum_distillation.jpg|Vacuum distillation apparatus

• Continuous distillation
• Fractionating column
• Fractional distillation
• Kugelrohr

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• [https://web.archive.org/web/20080901002137/http://www.fractional-distillation.com/automatic_astm_d_1160.html D1160 Vacuum Distillation]
• [http://www.nhe.uk.com/process-water-recycling/water-treatment/vacudest-vacuum-distillation-system/vacuum-distillation-work/ How vacuum distillation works]
• [https://www.sigmaaldrich.com/chemistry/solvents/learning-center/nomograph.html Pressure-temperature nomograph]
• [http://www.chemtechservicesinc.com/en/shortpath.html Short path distillation] {{Webarchive|url=https://web.archive.org/web/20180919171358/http://www.chemtechservicesinc.com/en/shortpath.html |date=2018-09-19 }}, includes a table comparing methods

{{Distillation}}

Category:Distillation

Category:Industrial processes

Category:Vacuum