Science, Tech, Math › Science How Does Steam Distillation Work? Share Flipboard Email Print Lazar.zenit/Wikimedia Commons/CC BY 4.0 Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 25, 2019 Steam distillation is a separation process used to purify or isolate temperature-sensitive materials, such as natural aromatic compounds. Steam or water is added to the distillation apparatus, lowering the boiling points of the compounds. The goal is to heat and separate the components at temperatures below their decomposition point. What Is the Objective of Steam Distillation? The advantage of steam distillation over simple distillation is that the lower boiling point reduces decomposition of temperature-sensitive compounds. Steam distillation is useful for the purification of organic compounds, although vacuum distillation is more common. When organics are distilled, the vapor is condensed. Because water and organics tend to be immiscible, the resulting liquid generally consists of two phases: water and the organic distillate. Decantation or partitioning may be used to separate the two layers to obtain the purified organic material. Principle Behind Steam Distillation When a mixture of two immiscible liquids (e.g., water and organics) is heated and agitated, the surface of each liquid exerts its own vapor pressure as though the other component of the mixture was absent. Thus, the vapor pressure of the system increases as a function of temperature beyond what it would be if only one of the components was present. When the sum of the vapor pressures exceeds atmospheric pressure, boiling begins. Because the temperature of boiling is reduced, damage to heat-sensitive components is minimized. Uses of Steam Distillation Steam distillation is the preferred method used to isolate essential oils. It is also used for "steam stripping" in petroleum refineries and to separate commercially important organic compounds, such as fatty acids.