Molecular Sieve Drying in the Plastics Industry

In the plastics industry, molecular sieves are primarily used for the deep dehumidification and drying of hygroscopic engineering plastics (such as PET, PA, PC, and ABS), a critical pre-treatment process to ensure the quality of the final product. The core principle is to utilize the micropores of the molecular sieve adsorbent to adsorb moisture impurities from the plastic raw materials, thereby reducing the water content of the plastic to PPM levels. This prevents defects such as hydrolytic degradation, silver streaks, and bubbles during subsequent high-temperature processing.

Molecular Sieve Working Principle

Hot and humid raw material air passes through the molecular sieve adsorption bed, where moisture is captured, and the air is deeply dried. Subsequently, the saturated molecular sieve bed is switched to regeneration mode, introducing high-temperature air at 200-350°C to desorb and remove the moisture. The regenerated high-temperature molecular sieve needs to be cooled to the operating temperature to restore its optimal adsorption capacity. Dual-tower or multi-tower systems alternate between adsorption and regeneration to achieve continuous and stable deep dehumidification.

Molecular Sieve Desiccant Selection

3A molecular sieves are the preferred choice. With a pore size of only 3 angstroms, they effectively remove moisture while hardly adsorbing larger organic molecules that may volatilize from the plastic, such as monomers and plasticizers, ensuring a long service life.

In addition to static water adsorption capacity, compressive strength and abrasion rate are also crucial, as they directly determine whether the molecular sieve is easily pulverized under continuous airflow, thus affecting system life and plastic cleanliness.

Application Scenarios

1. Polyethylene Terephthalate (PET) Industry:

Bottle flake recycling and granulation, as well as fiber production, are the largest application areas. Deep drying is vital to prevent hydrolytic degradation and ensure product viscosity and strength.

2. Polyamide (Nylon, PA) Processes:

Whether for automotive parts or electronic components, thorough drying is key to achieving high strength and toughness.

3. Optical Grade and Specialty Plastics:

When polycarbonate (PC) and acrylic (PMMA) are used for lenses and light guides, even trace amounts of moisture can lead to optical distortion and appearance defects.

High-temperature engineering plastics, such as PEEK and PEI, require higher processing temperatures and have stricter requirements for water content.