Molecular distillation equipment has extremely high requirements for sealing performance and needs to remain stable in high vacuum (usually ≤-10 Pa) and high temperature (up to 300°C) environments. Its sealing forms mainly include the following four categories:
1. Mechanical seal
(1) Structure and principle
Mechanical seals achieve sealing by fitting the end faces of the dynamic ring and the static ring, relying on elastic elements (springs/bellows) and auxiliary sealing rings (such as O-rings) to compensate for wear. Common types include:
Push-type seal: Axial pressure is provided by springs or bellows, suitable for high-pressure conditions (≤20.69 MPa).
Balanced seal: Optimizes the end face pressure distribution, reduces the risk of leakage under high pressure, and is suitable for high vacuum molecular distillation.
(2) Technical advantages
High temperature resistance: Made of silicon carbide or cemented carbide materials, the temperature resistance can reach 400°C.
Low leakage rate: The leakage can be controlled below 10⁻⁶ mbar·L/s, meeting the vacuum requirements of molecular distillation.
(3) Application scenarios
Commonly used in conventional molecular distillation equipment, such as laboratory short-range distillation devices.
2. Magnetic seal
(1) Structure and principle
Non-contact transmission is achieved through permanent magnet coupling, and there is no physical contact between the dynamic ring and the static ring. Silicone sealant is combined to enhance the sealing performance. For example:
Multi-layer sealing design: 350℃ resistant silicone sealant is applied on both sides and chamfers of the O-ring to form a composite sealing layer.
Rotary adjustment mechanism: The fit between the plug and the slot is adjusted by rotating the ring to enhance the sealing stability.
(2) Technical advantages
Zero leakage: No mechanical contact, the theoretical leakage rate is zero, suitable for the separation of toxic and high-purity materials.
High pressure resistance: Can withstand pressures greater than 14 MPa, suitable for heavy oil fractionation in petrochemicals.
Pollution-free: Dry static seal, no lubricating oil is required, and will not contaminate the raw materials.
(3) Application scenarios
High-end molecular distillation equipment (such as industrial-grade continuous production lines) and high vacuum demand scenarios.
3. Packing seal
(1) Structure and principle:
Soft packing (such as graphite, polytetrafluoroethylene) or hard packing (metal ring) is used to fill the gap between the shaft and the sealing cavity, and the seal is achieved by pressing the cover. For example:
Double fluororubber O-ring: diameter > 10 mm, high temperature and corrosion resistant, used for static sealing of connecting rings.
(2) Technical advantages:
Low cost: simple structure, convenient maintenance, suitable for medium and low pressure working conditions.
Quick replacement: packing can be replaced locally to reduce downtime.
(3) Limitations:
Long-term operation is prone to wear and requires frequent maintenance, not suitable for extreme working conditions.
4. Dry gas seal
(1) Structure and principle:
The fluid dynamic pressure groove is used to form an air film (1-308 μm) on the sealing end face to achieve non-contact sealing.For example:
Spiral groove design: The medium pressure is balanced by gas pressure to prevent leakage.
(2) Technical advantages:
Oil-free lubrication: avoids contamination of materials, suitable for the pharmaceutical and food industries.
Low energy consumption: power consumption is only 20%-30% of traditional seals.
(3) Application scenarios:
High-speed centrifugal molecular distillation equipment, such as oil refining equipment.
5. Comparison of sealing types and selection recommendations
Seal type | Applicable pressure | Temperature range | Typical scenarios | Maintenance costs |
Mechanical seals | Medium and high voltage | -20~400℃ | Conventional laboratory/industrial short path distillation | middle |
Magnetic seal | high pressure | -50~400℃ | High vacuum, toxic medium separation | high |
Packing seal | low pressure | -20~200℃ | Pilot equipment, low-cost requirements | low |
Dry gas seal | Medium pressure | -40~200℃ | Food/pharmaceutical grade high purity separation | medium to high |
6. Summary
(1) The sealing type of molecular distillation equipment should be selected based on the vacuum degree, temperature, and medium characteristics:
(2) High vacuum/high temperature scenarios: Magnetic seals or balanced mechanical seals are preferred.
(3) Medium and low pressure/conventional working conditions: Packing seals or dry gas seals are more economical.
(4) Extreme working conditions (such as high pressure toxic media): Composite sealing technology (such as magnetic + mechanical seals) is required.