Short-path molecular distillation equipment

Basic Principle

The distillation process of short-path molecular distillation equipment occurs under high vacuum conditions (less than 10 Pa), where molecules evaporated on the heating surface reach the condensing surface over the shortest possible distance for condensation, thereby achieving liquid-liquid separation. When the distance between the heating and condensing surfaces is less than or equal to the average free path of the evaporated molecules at the operating vacuum and temperature, this distillation process is also known as molecular distillation. It boasts advantages such as low distillation temperature, high distillation vacuum, short heating time, and high degree of separation.

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

Molecules evaporated are condensed in the built-in condenser over a short distance and 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 from the surface of the film—evaporated molecules move from the heating surface to the condensation surface—evaporated molecules condense on the condensation surface—collection and discharge of 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 scraper device forms a uniform film of material on the inner surface of the evaporator drum, 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 drum and the scraper, the transfer of different components in the material and the heat transfer with the heating medium in the jacket are excellent. Additionally, the high smoothness of the inner surface of the drum and the continuous movement of the scraper make it difficult for the heating surface to clog or scale, which also contributes to increasing the overall thermal conductivity and improving the evaporation efficiency.

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

Structural Features

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

The transmission unit and mechanical seals of the DZ series short-range molecular distillation equipment are specially designed and manufactured to ensure the high-precision equipment operates stably over the long term. 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 drum is fully machined and formed as a single piece, 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 crucial component of the short-path molecular distillation equipment. The cylinders of the DZ series short-path molecular distillation units are all formed in one piece, without any intermediate flanges. The one-piece construction of the cylinder not only prevents leaks and material accumulation associated with flange connections but also avoids the formation of low-temperature zones on either side of the flanges, ensuring that the evaporation surface is effectively utilized. Furthermore, the one-piece cylinder construction effectively guarantees the equipment's precision and excellent film-forming performance.

◆ The inner surface of the cylinder has a high degree of smoothness, making it less likely to adhere materials.

The inner surface of the cylinder 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 cylinder inner surface of the DZ series short-path molecular distillation equipment meets the dimensional requirements, it is finely ground to achieve a surface smoothness of Ra0.8μm, which ensures that the inner surface is not prone to material adhesion and scaling, reducing material retention, and improving heat and mass transfer efficiency. In accordance with the special requirements of industries such as food, special polishing techniques can be employed to achieve a surface smoothness of Ra0.2μm.

◆ Liquid distributor and splash prevention device design ensure effective product quality.

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-path molecular distillation equipment ensure the 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 a splash prevention device, it can meet the product requirements. When handling certain special materials or when the product has special requirements, the splash prevention device of the DZ series short-path molecular distillation equipment can provide a more reliable guarantee for product quality.

Film Peeling Method

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

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

Application Scope

Suitable as a substitute for conventional film evaporators, used for distillation, purification, concentration, and decolorization of petrochemical and chemical products; particularly suitable for the distillation refining of thermosensitive, 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, linoleic acid, fish oil fatty acids (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 application and promotion of short-path distillation, the treatment 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 square

Equipment Material: SUS304, SUS316L, SAF2205, and Hastelloy

Operating Temperature: 350℃