FAQ

Activated Molecular Sieve Powder

• 1. What is Activated Molecular Sieve Powder? How does it differ from conventional molecular sieve?

  Activated Molecular Sieve Powder is a highly fluid powder produced by high-temperature calcination of molecular sieve raw powder to remove water within the pores, followed by special processing.

  The term "activated" refers to its highly desiccated state, which grants it immediate moisture adsorption capability. In contrast, conventional molecular sieve particles may contain a certain amount of moisture if not pretreated, thus not achieving optimal adsorption capacity.

• 2. Why is Activated Molecular Sieve Powder added to two-component polyurethane systems?

  Although two-component polyurethane adhesive systems do not cure via moisture like single-component adhesives, their primary raw material—polyester polyol—is highly hygroscopic and readily absorbs water.

  This water can undergo a side reaction with the -NCO groups in the isocyanate component, generating CO₂ gas and urea linkages. This leads to a series of issues such as bubble formation in the adhesive layer, increased viscosity, elevated internal stress after curing, and reduced bonding strength.

  The function of Activated Molecular Sieve Powder is to preemptively scavenge this internal moisture.

• 3. Into which component is Activated Molecular Sieve Powder primarily added, and why?

  It is added to the polyol component (Component A). This is because moisture primarily originates from the hygroscopic polyester polyol, fillers, and additives.

  By incorporating the molecular sieve directly into Component A, moisture can be adsorbed at the source. This protects the purity of the subsequent reaction when Component A is mixed with the isocyanate component (Component B), preventing adverse side reactions.

• 4. What are the advantages of using Activated Molecular Sieve Powder compared to using chemical water scavengers?

  The core advantage is the absence of byproducts. Chemical water scavengers react with water to form new compounds (such as alcohols, amines, etc.). These byproducts can:

  Generate unpleasant odors.

  Cause discoloration (yellowing) of the system.

  Potentially continue to react with -NCO groups, interfering with the formation of the proper curing network structure.

  In contrast, molecular sieve physically adsorbs moisture without introducing any new chemical substances, thereby ensuring the purity of the system.

Molecular Sieve

• 1. Does Activated Molecular Sieve Powder require special storage conditions?

  Imperative! It must be stored in a strictly sealed container, in a cool and dry place. After opening, any unused portion must be immediately resealed in its original packaging and used as soon as possible. Exposure to ambient air will cause it to rapidly absorb moisture and lose its effectiveness.

• 2. What is a Molecular Sieve?

  A molecular sieve is a type of porous material characterized by uniformly sized micropores, with pore diameters comparable to the size of common molecules.

  It is primarily composed of elements such as silicon, aluminum, and oxygen. Its fundamental framework is built from silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra.

  Due to its properties, it can perform selective adsorption based on the size and polarity of molecules, thereby "sieving" or separating molecules of different sizes, which is the origin of its name "molecular sieve."

• 3. How does a Molecular Sieve work?

  A molecular sieve operates based on two primary mechanisms:

  Size-Selective Sieving (Based on Molecular Size):

  The pore size of a molecular sieve is uniform and fixed. Only molecules with a diameter smaller than this pore size can enter and be adsorbed within the channels. Molecules larger than the pore diameter are excluded at the entrance, achieving the "sieving" effect.

  Selective Adsorption (Based on Molecular Polarity and Unsaturation):

  For molecules of similar size, the molecular sieve exhibits a preferential adsorption affinity for molecules with higher polarity and unsaturation. For example, it will preferentially adsorb water (H₂O) over other non-polar or weakly polar molecules.

• 4. What are the main application fields of Molecular Sieves?

  The primary application fields of molecular sieves include:

  Drying and Purification: Used for deep drying of various gases and liquids, such as petroleum cracking gas, natural gas, air, refrigerants, and organic solvents.

  Separation and Purification: Employed in processes like separating normal/isomeric alkanes, oxygen generation (PSA), nitrogen generation, and separating carbon dioxide from air.

  Catalysis: Serving as catalysts or catalyst supports, widely used in petrochemical reactions such as catalytic cracking and hydrocracking.

  Ion Exchange: Commonly used as builders in detergents to soften water by exchanging calcium and magnesium ions in water.

• 5. What precautions should be taken when using Molecular Sieves?

  The following key points should be noted when using molecular sieves:

  Avoid Oil Mist and Dust: Oil contaminants can block the pores, leading to permanent deactivation.

  Pre-drying: If the gas to be treated has excessively high moisture content, preliminary drying should be conducted first. This reduces the load on the molecular sieve and extends its service life.

  Regeneration Temperature: During regeneration, the temperature should not be excessively high to avoid damaging the crystalline structure of the molecular sieve, which would cause permanent damage.

  Prevent Breakage: Avoid severe impact and friction during loading and unloading, as the resulting fines can increase gas flow resistance.

Activated Alumina

• 1. What is Activated Alumina?

  Activated alumina is a porous, highly dispersed solid material produced by the dehydration and activation of aluminum hydroxides (such as gibbsite) at elevated temperatures.

  It possesses a high specific surface area and a rich pore structure, making it a commonly used adsorbent, desiccant, and catalyst support. Its primary chemical composition is γ-Al₂O₃.

• 2. What are the main applications of Activated Alumina?

  The primary applications of activated alumina include:

  Desiccant: Primarily used for drying compressed air. Due to its high mechanical strength and excellent resistance to liquid water, it is the desiccant of choice for compressed air drying towers.

  Adsorbent: Employed in drinking water and industrial wastewater treatment for the efficient removal of harmful substances such as fluoride and arsenic.

  Catalyst Support: Owing to its high specific surface area and inert nature, it is widely used as a catalyst support (e.g., for carrying active components like palladium and platinum) in fields such as petrochemicals and automotive exhaust gas purification.

• 3. Why does Activated Alumina become deactivated, and how can it be regenerated?

  Deactivation Cause:
  The primary reason for deactivation is the saturation of its surface adsorption sites by water molecules or other impurities (such as fluoride ions), rendering it unable to continue adsorption.

  Regeneration Methods:

  Thermal Regeneration (Most Common):
  Similar to molecular sieves, the adsorbed moisture is removed by heating. Typically, heating it at around 350°C for a specified duration (e.g., 3-5 hours) can restore most of its activity. The temperature should not exceed 600°C to avoid damaging its pore structure.

  Chemical Regeneration:
  Used after adsorption of substances like fluoride or arsenic in water treatment. This requires soaking with specific chemical agents (such as aluminum sulfate solution or sodium hydroxide solution) for regeneration, a process that is relatively more complex.