Basic Principles

The distillation process of a short-path molecular distillation unit takes place under high vacuum conditions (<10 Pa), where molecules evaporated on the heating surface reach the condensation surface in the shortest possible distance for condensation, thus achieving liquid-liquid separation. This process is also known as molecular distillation when the distance between the heating surface and the condensation surface is less than or equal to the average free path of the evaporated molecules at the operating vacuum and temperature. It boasts advantages such as low distillation temperature, high distillation vacuum, short heating time, and high separation degree.

Material enters the short-path molecular distillation unit through the top flange cover, and is continuously and uniformly distributed over the vertical cylinder heating surface by the distribution disc on the rotor. As the material descends under gravity, it is forced into a thin turbulent liquid film on the heating surface by the rotating scraper device.

Molecules evaporated are transported a short distance to the internal condenser where they condense, then discharged through the outlet at the bottom of the evaporator. The reconstituted components are collected in the residue collection tank of the short-path molecular distillation unit and discharged through the side outlet.

The distillation process is divided into the following steps:

Material forms a liquid film on the heating surface – molecules evaporate on the surface of the film – evaporated molecules move from the heating surface to the condensation surface – the evaporated molecules condense on the condensation surface – collection and discharge of the distillate and residue.

Performance Features

High vacuum, low distillation temperature: Operating vacuum: 0.1 Pa ~ 10 Pa.

High thermal conductivity, high evaporation efficiency: The rotating scraping device forms a uniform film of material on the inner surface of the evaporator, effectively reducing thermal resistance. Under high vacuum, it allows easily evaporated substances to be distilled and separated from the material. Due to the intense turbulent state of the liquid film between the inner surface of the tube and the scraper, the transfer of different components within the material and the heat transfer with the heating medium inside the jacket are excellent. Additionally, the high smoothness of the inner surface of the tube and the continuous movement of the scraper prevent the heating surface from scaling and coking, which also helps to increase the overall thermal conductivity and improve evaporation efficiency.

Short heating time: Materials entering the short-path molecular distillation unit are evenly distributed over the vertical heating surface by the distribution disk. Under the combined action of gravity and the scraper, they spiral down along the limited heating surface, with a short residence time inside the evaporator, typically a few to several seconds (the average residence time is related to the length of the heating surface, the type of scraper, the characteristics of the material, and the film thickness, etc.). Additionally, the "no dead corner" design of the DZ series short-path molecular distillation equipment prevents material accumulation in the distribution disk, heating surface, and scraper system, reducing thermal polymerization and thermal decomposition of heat-sensitive substances.

Structural Features

High-precision transmission and mechanical sealing design ensure long-term stable operation of the equipment.

The drive unit and mechanical seal of the DZ series short-range molecular distillation equipment are specially designed and manufactured to ensure high-precision operation for long-term stability. The transmission ratio of the drive unit, lubrication method of the mechanical seal (forced circulation lubrication, static lubrication), and cooling method of the mechanical seal are determined based on the operating conditions and material characteristics of the short-range molecular distillation equipment.

The evaporator body is fully machined and formed as a single unit, without any intermediate flange connections.

The evaporator body of the short-path molecular distillation unit consists of an inner cylinder and a heating jacket, which is a critical component of the short-path molecular distillation unit. The cylinders of the DZ series short-path molecular distillation units are all formed as a single piece, with no intermediate flange connections. The monolithic construction of the cylinder not only eliminates leaks and material accumulation caused by flange connections but also prevents the formation of low-temperature zones on either side of the flange, ensuring that the evaporation surface is effectively utilized. Additionally, the monolithic cylinder design effectively guarantees the precision of the equipment and a superior film-forming effect.

◆ The inner surface of the cylinder has a high degree of smoothness, which is not prone to material adhesion.

The inner surface of the tube serves as the heating and evaporation surface for short-path molecular distillation equipment, and it has strict requirements for surface smoothness. After the rough machining of the inner surface of the tube in the DZ series short-path molecular distillation equipment meets the assembly size requirements, it is finely ground to achieve a surface smoothness of Ra0.8μm, ensuring that the inner surface is not prone to material adhesion and scaling, reducing material retention, and enhancing heat and mass transfer efficiency. In accordance with the special requirements of industries such as food, special polishing techniques can also be employed to achieve a surface smoothness of Ra0.2μm.

◆ Design of liquid distributor and splash-proof devices ensures product quality effectively.

To enhance evaporation efficiency, the material in the short-path molecular distillation equipment is continuously and evenly distributed over the vertical cylinder heating surface. The liquid distributor of the DZ series short-path molecular distillation equipment not only evenly distributes the material over the heating surface but also effectively prevents any material from lingering on the distributor for an extended period, even for high-viscosity materials.

The high-precision design and manufacturing of the DZ series short-range molecular distillation equipment ensure long-term stable operation of the scraping device. Its excellent film-forming performance makes the evaporation process of the material gentle, with minimal splashing and carryover. In most cases, even without splash prevention devices, it can meet product requirements. When handling certain special materials and when there are special requirements for the product, the splash prevention device of the DZ series short-range molecular distillation equipment can more reliably guarantee product quality.

Film Removal Method

◆ A variety of film removers are available, with wide application range.

Tapered groove scraper, drum-type; made with special PTFE material, operating temperature up to 280°C, metal hinge design, fixed scraper.

Application Scope

Can replace conventional film evaporators for distillation, purification, concentration, and decolorization of petrochemical and chemical products; particularly suitable for the distillation refinement of thermally sensitive and easily oxidizable industrial chemicals; also applicable for the distillation separation of high-boiling point products.

Typical Applications

Distillation and refining of polyunsaturated fatty acids (oleic acid, linolenic acid, fish oil fatty acid esters) and their derivatives; refining of monoglycerides; refining of dicarboxylic acids; refining of vitamin E, plant sterols; distillation of liquid crystals; removal of monomers from high molecular polymer; refining of other thermosensitive products.

Product Selection

Based on theoretical calculations and years of experience in the promotion and application of short-path distillation, the processing capacity of short-path distillation is directly related to the molecular weight of the raw material (product), material viscosity, operating conditions, and the effective heat exchange area of the evaporator.

Standard Feed Rate: 100 kg / (m² h)

       Max：80 - 150 kg /（m² h）

Min Spec: DZ-5 Effective Evaporation Area 0.05 sq. ft.

Max Specification: DZ-3600 Effective Evaporation Area: 36 Sq. M

Material: SUS304, SUS316L, SAF2205, and Hastelloy

Operating Temperature: 350℃