Methods of Crystallization

Do you know about Methods of Crystallization? Crystallization is when a liquid substance becomes a solid with highly organized, tightly bonded structures. These are called crystals, and a crystal’s lattice pattern depends on the material’s characteristics.

Methods of Crystallization

Crystallization can occur under many conditions, resulting in different crystals with varied properties. Managing polymorphism, which occurs when the same compound forms polish crystal multiple crystals, is essential to controlling product purity and optimizing crystallization processes.

Sublimation

Sublimation is a method of crystallization for some substances, for example carbon dioxide (dry ice). It is a form of phase transition that occurs at temperatures and pressures below the compound’s triple point.

Some solids can sublimate at normal temperatures and pressures – such as water, iodine, and arsenic. Others can sublimate at very low pressures.

One of the best examples of this phenomenon is solid carbon dioxide, or dry ice. It can sublimate at room temperature and at one atmosphere of pressure.

Other common substances that sublimate at normal pressures include naphthalene and arsenic. Snow and other water ices also sublimate at below-freezing temperatures, and this phenomenon is used in freeze drying to remove water from fabrics.

Sublimation is a purification technique that can be used to produce high-purity materials as analytical standards. It is also used in a process called lyophilization to make freeze-dried substances. The resulting material is usually much easier to dissolve and resuspend than a liquid produced from a different system, and it is less likely to damage sensitive or reactive substances.

Evaporation

Evaporation is a process by which a liquid changes into a gaseous phase at a certain temperature. This process can be used to convert a soluble substance into solid crystals.

Evaporative crystallization is one of the most commonly used methods for forming crystals of inorganic salts, sucrose, and other substances. It involves heating a solution that contains both the solvent and the soluble compound, which causes the molecules to separate from the liquid.

Cooling crystallization is another common method, involving cooling of the solution until its solubility exceeds that of the chemical compound involved. The solution then begins to form crystals, which can be separated by filtration.

During crystallization, the first atom that forms a crystal structure becomes a nucleus, and more unit cells assemble around it. As the nucleus grows, the entire crystal starts to change its shape and size.

Solvent Diffusion

One of the most effective methods to grow crystals is by liquid diffusion. This method occurs as either a self-diffusion process or when a reaction takes place in the solvent, such as an acid-base pair.

Basically, it involves putting your compound in a solution in one of two liquids that mix well and slowly mixing it with the precipitant. You can use liquid-liquid diffusion, gas-phase diffusion or even a membrane (dialysis).

For this technique to be successful, it is important that the solvents are in close proximity. This means that the sample should be placed in a tube or flask and a second less dense solvent, such as dichloromethane/ethanol, dripped carefully down the side of the tube using a pipette or a syringe so that the two solutions form discreet layers (Fig. 4).

This technique is suitable for samples with milligram quantities that are air- and/or solvent-sensitive. Ideally, the NMR tube/vial/flask should have a perforated cap that allows some of the solution to drip out onto a surface of the vessel.

Sonocrystallization

Sonocrystallization is a method that is based on the application of power ultrasound to solidify liquids. In this process, the crystallization of organic molecules is influenced by the frequency and intensity of the ultrasonic irradiation, causing a wide variety of effects on the physical properties of the products that are obtained.

The underlying mechanisms for these effects have been well established. These include: reduction of induction time and metastable zone width (MZW), sonofragmentation, and bubble interface nucleation.

While reducing induction time and increasing the nucleation rate of crystalline solutions, soon crystallization generally yields smaller crystals with narrower size distributions than conventional crystallization methods.

This may also result in a distorted shape of the resulting crystals and an increase in their agglomeration, but it is largely dependent on the specific system used to carry out the sonocrystallization.

Sonocrystallization has been applied to a broad range of substances, including adsorbents, polymers, and biomolecules. It has been found to be particularly effective for the sonocrystallization of triglyceride oils that are either vegetable or animal origin.