Solvent Freezing
Solvent Freezing - Related Videos
09:41
Schlenk Lines Transfer of Solvents
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2023
Source: Hsin-Chun Chiu and Tyler J. Morin, laboratory of Dr. Ian Tonks—University of Minnesota Twin Cities Schlenk lines and high vacuum lines are both used to exclude moisture and oxygen from reactions by running reactions under a slight overpressure of inert gas (usually N2 or Ar) or under vacuum. Vacuum transfer has been developed as a method separate solvents (other volatile reagents) from drying agents (or other nonvolatile agents) and dispense them to reaction or storage vessels while...
01:12
Solvents
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2019
A solvent is a substance, most often a liquid, that can dissolve other substances. Here, the substance being dissolved is called a solute. When a solvent and a solute combine, they form a solution - a homogenous mixture of both the solvent and the solute. Water is a universal biological solvent. Its polar structure allows it to dissolve many other polar compounds. The ability of water to dissolve is governed by a balance between water molecules binding to each other and binding to the solute. A...
03:12
Freezing Point Depression and Boiling Point Elevation
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2020
Boiling Point Elevation The boiling point of a liquid is the temperature at which its vapor pressure is equal to ambient atmospheric pressure. Since the vapor pressure of a solution is lowered due to the presence of nonvolatile solutes, it stands to reason that the solution’s boiling point will subsequently be increased. Vapor pressure increases with temperature, and so a solution will require a higher temperature than will pure solvent to achieve any given vapor pressure, including one...
06:43
Rotary Evaporation to Remove Solvent
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2023
Source: Dr. Melanie Pribisko Yen and Grace Tang — California Institute of Technology Rotary evaporation is a technique most commonly used in organic chemistry to remove a solvent from a higher-boiling point compound of interest. The rotary evaporator, or "rotovap", was invented in 1950 by the chemist Lyman C. Craig. The primary use of a rotovap is to dry and purify samples for downstream applications. Its speed and ability to handle large volumes of solvent make rotary evaporation a preferred...
08:53
Freezing-Point Depression to Determine an Unknown Compound
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2023
Source: Laboratory of Lynne O' Connell — Boston College When a solid compound is dissolved in a solvent, the freezing point of the resulting solution is lower than that of the pure solvent. This phenomenon is known as freezing-point depression, and the change in temperature is directly related to the molecular weight of the solute. This experiment is designed to find the identity of an unknown compound by using the phenomenon of freezing-point depression to determine its molecular weight. The...
FAQs
During Solvent Freezing, solvent crystallization changes the composition of the remaining liquid. Because dissolved substances stay preferentially in the unfrozen phase, their concentration increases as more solvent becomes solid. That changing composition affects phase equilibria and the solution’s subsequent freezing behavior, so process design must consider more than the initial freezing point when targeting concentration or solvent recovery.
Nucleation creates the first solid solvent crystals, while crystal growth enlarges them as heat continues to leave the liquid. These stages determine how readily crystals can be separated from the concentrated phase. Cooling rate and mixing influence crystal formation and solute entrapment; controlling both helps favor distinct crystals rather than solids that retain excessive solution.
Unlike evaporation, which removes solvent as vapor, Solvent Freezing separates solvent by forming a solid phase. This distinction is important when a compound could be affected by evaporation conditions or when reducing evaporation-based processing is desirable. The method can therefore support concentration and solvent recovery while limiting reliance on heat removal through vaporization.
A basic workflow begins by cooling the solution below the solvent’s freezing point, then maintaining conditions that allow nucleation and crystal growth. Once sufficient solid has formed, the crystals are separated from the concentrated liquid. The recovered solid and remaining liquid can then be directed toward solvent recovery or solution concentration, depending on the process objective.
Temperature, cooling rate, and mixing must be coordinated because each affects crystal formation and the amount of solute carried into the solid phase. Excessive solute entrapment reduces separation quality, whereas appropriate control helps produce crystals that can be separated more cleanly. Phase-equilibrium information provides the basis for selecting operating conditions and anticipating concentration changes.
In chemistry, the approach is relevant to solutions containing heat-sensitive compounds, where concentration by evaporation may be undesirable. It can also serve energy-conscious processing goals by recovering solvent and concentrating the solution through a solid-liquid separation. The resulting design depends on the solvent’s freezing behavior and on how effectively crystals can be isolated from the concentrated phase.