Static Melting Crystallizer：A new idea of energy-saving, efficient and economic lactide purification

Static melting crystallizer is a proprietary platecoil plate static melt crystallizer. It uses the process of precipitation of a crystalline layer of stationary molten lactide on the surface of a cooling plate of a crystallization plate to carry out step-by-step crystallization and get the purification of lactide ultimately. Since no solvent is used in the process of crystallization and separation, it is called a solvent-free crystallizer.

Static melting crystallizer innovatively uses platecoil crystallization plate as the heat transfer element, which has the advantages that traditional separation technology does not have.

Working Principle

Static melting crystallizer is a kind of process equipment for purification and separation by using the difference in melting point (crystallization point) of lactide and other component impurities, which achieves crystallization and separation by cooling down to reach the melting point of lactide, and the whole process is divided into three major steps: crystallization, sweating and melting.

* Crystallization: Molten lactide is slowly cooled below its melting point by a heat-conducting medium and precipitates crystals on the surface of the crystallization plate, forming a crystalline layer. Impurities are mainly present in the lactide mother liquor and are discharged from the crystallizer.

* Sweating：The crystalline layer of lactide can be purified by sweating (partial melting), i.e. It is slowly heated to the melting point and the impurities encapsulated and attached to the crystalline layer are expelled in the sweated melt. Sweating is a key step in the further purification of the product. 

* Melting：After sweating, the temperature of the heating medium in the crystallization plate is further increased, and all of the crystalline layer of lactide is melted and flowed out, obtaining high purity liquid lactide, which is discharged from the crystallizer.

Technical Advantages

Comparison with distillation

* Low energy consumption, the heat of fusion is much lower than its latent heat of vaporization, and its energy consumption is only 1/7 to 1/3 of distillation.

* Low working temperature, suitable for heat-sensitive substances

* Suitable for special systems (e.g. isomers) with small differences in boiling points, but the melting points of these mixtures can often differ by several tens of degrees, which can be well separated by solvent-free crystallization.

* No gas phase, low requirements for equipment sealing, can be carried out at atmospheric pressure,safe operating environment, and easy pollution control.

* Industrial and pilot scale crystallizers are composed of the same Platecoil plates for easy industrial scale-up.

Comparison with solution crystallization

* The crystallization process of the static melting crystallizer doesn't‌ require solvents, which means that there is no contamination of the product by solvents and the loss of solvents in the solvent recovery process is avoided.

* No handling and filtration of the crystallization slurry, thus simplifying the operating process.

Comparison with tube crystallizer

* More uniform temperature field distribution.

* Higher heat transfer efficiency, shorter crystallization cycle for the same volume.

* High heat transfer density, equal volume heat transfer area is more than 2 times that of the traditional tube technology.

* High separation efficiency, obtaining a product with a purity of 99.99 %or more

* Because of anti-collapse design, the crystal layer is not easy to collapse during the sweating process.