Principle, type and application of silicone defoamer

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   1. The mechanism of organosilicon defoamer:

   The ability of silicone to defoam or suppress foam is due to its very low surface tension. The organosilicon compound (silicone oil) interferes with the surface tension of the gas/liquid boundary, resulting in a defoaming effect.

   When the silicone defoamer is added to the foam medium, the small particles of silicone oil fall on the surface of the foam, and at the same time it effectively reduces the surface tension of the contact point, causing a weak point in the foam skin, which causes the foam to break. The best defoaming activity standard can be described as follows: The free silicone oil particles must be completely, as quickly and effectively as possible dispersed into the active area. Silicone oil is quickly dispersed with the help of a small proportion of SiO2 fillers with a large surface area added during production and processing, and causes demulsification and foam breaking outside the contact points of SiO2 particles. The squeezed foam is caused by the rupture of the adjacent foam. The unstable state accelerates the effect of causing continuous bubble breaking, and finally reaches a stable state. If it is an emulsion defoamer, the emulsion is too stable and will reduce the defoaming effect. When the stability is poor, there is greater activity. Therefore, it is necessary to balance between stability and activity, and to choose organosilicon compounds that have low solubility in water and oil phases and extremely high activity.

   The function of silicone defoamer is also defined by three mechanisms: foam breaking, defoaming, and foam suppression.

   Bubble break: Compared with the foam, it enters the bubble from the air side and breaks the bubble together.

   Bubble suppression: Enter the bubble from the liquid side, and destroy the bubble together.

   Defoaming: Infiltrate the bubble from the interface of the bubble, so that the bubble unites and rises to the surface.

   defoamers include oil type, solution type, emulsion type, solid powder type and composite type. All should have the following properties:

  1, strong defoaming power, low dosage;

  2, the basic properties of the system will not be affected after joining;

  3, the surface tension is small;

  4. Good balance with the surface;

  5, good diffusion and permeability;

   6. Good heat resistance, acid and alkali resistance;

  7, chemically stable, strong oxidation resistance;

   8. Gas solubility, good permeability;

  9, small solubility in foaming solution;

   10. High physiological safety.

   2. Types of silicone defoamers:

   1. Water emulsion type defoamer:

With polydimethylsiloxane (silicone) as the main body, and white carbon black compound, under the action of surfactant (emulsifier), it is prepared into O/W type water emulsion defoaming of various concentrations (suitable for When using aqueous medium for defoaming) or make high-concentration silicone paste, use the smearing method or temporarily dilute it before use.

  2, oil system defoamer:

   The silicone oil is carried by a solvent and dispersed in the blasting liquid. The solvent diffuses, and the silicone oil or microdroplets play a defoaming effect (generally high and low viscosity silicone oils are blended) or made into a silicone oil/mineral oil dispersion.

   Crude oil demulsification and dehydration:

   When the crude oil occupies a certain proportion, it is obtained in the form of W/O emulsion without removing most of its water. This kind of oil cannot be processed. The petroleum industry needs a large amount of silicone surfactants as demulsifiers. This is a white solid, and the surface tension of a 1% aqueous solution is 20.6 mN/m.

  3, solid powder defoamer:

   Containing 2%~5% organic silicon defoaming ingredients and 98%~50% powder solid carrier.

  4. Defoaming stick:

   Silicone oil, sodium sulfonate and wax preparations.

   5. Self-emulsifying and self-dispersing defoamer:

The silicone surfactant copolymerized with polysiloxane and polyether, and the introduction of hydrophilic groups into the molecular chain of polysiloxane can significantly improve the dispersibility of silicone in water, or become self-emulsifying, becoming a special type The defoaming agent, which defoams above the cloud point, is suitable for defoaming such as high temperature and high pressure jet dyeing.

"Self-emulsifying" defoaming agent has heat resistance, mechanical stability, acid and alkali resistance, defoaming under harsh conditions, such as polyester fiber high temperature dyeing, diethanolamine aqueous solution desulfurization system, various oil cutting fluids, antifreeze systems, etc. Defoaming.

  3. silicone defoamer application:

  1, Textile printing and dyeing:

  (1) Sizing process: water emulsion type silicone defoamer, such as Shinchem AF 50, the addition amount in the sizing tank is 0.2~0.25g/L.

  (2), chemical fiber oil: add 0.02~0.04% water emulsion type defoamer for chemical fiber oil. The chemical fiber oil formulation should contain silicone polyether silicone oil.

  (3) Desizing refining: Use polyether silicone.

   (4), bleaching: strong acidity, silicone defoamer.

   (5), dyeing: silicone emulsion defoamer. It is best to use polyether silicone for jet dyeing, which is defoaming at high temperature and water soluble at low temperature, and does not stain the fabric.

  2, petrochemical industry:

   (1) Drilling: Ethyl silicone oil (or methyl silicone oil layer emulsion) is used as a mud additive.

  (2) Oil production: oil and gas separation, defoaming stick. The melting point is 2.8~13.9℃ higher than the wellhead foam temperature.

   (3) Natural gasoline absorption: Use gasoline to mix simethicone into a 2% solution.

  (4) Oil and gas separation and demulsification:

  A, oil and gas separation, adding 0.025~0.0065 mg/Kg to crude oil can increase production capacity;

  B. Demulsification: Oil-gas separated crude oil is generally micro-W/O emulsion, adding about 0.2mg/Kg of suitable defoaming agent can achieve the effect of demulsification and defoaming.

  (5) Refining: Add defoamer to vacuum distillation, improve the color of the distillate, and relax the range of the distillate. The diesel solution with silicone oil is commonly used.

  (6) High-energy fuel (internal combustion, jet, aviation fuel) is dispersed in high flash point kerosene with cyanoalkyl polysiloxane, and then added to high-energy fuel as a high-efficiency defoamer.

  (7) Asphalt, residual oil: the amount of silicone oil added is 0.2×10-6~2.0×10-6

  (8) Delayed coking, decoking, descaling: defoamer addition reference amount: 0.05~100×10-6

(9) Defoaming drilling fluid: high-viscosity sulfonate metal salt (calcium petroleum sulfonate: sodium sulfonated asphalt = 1:1), the addition amount of siloxane is about 100~400×10-6 or 5~15mg/Kg, Sulfonate: The siloxane is preferably close to 1:1.

   (10) Lubricants: such as internal combustion engines, automotive lubricants, metalworking fluids, compressor oils, etc. When silicone oil is used for defoaming, it is because of the following advantages:

  A, hardly soluble in lubricating oil, in a dispersed state, which is good for adsorbing on the bubble film to break bubbles;

   B, there are alkyl groups similar to mineral oil, which can squeeze into the bubble film and weaken the molecular attraction;

  C, low surface tension, good penetration, the local surface tension is reduced when adsorbed on the bubble film surface, and the bubble is broken due to uneven surface tension of the bubble film.

  Heavy oil selects low-viscosity silicone oil, and the addition amount is 1-10×10-6. In addition, alkyl polyacrylates are also better and have better gas release properties.

   Branched chain amine is added to naphtha, naphtha, and then added to lubricating oil. It can also be used as a defoamer. The addition amount is 0.05 to 1%. This defoamer can be added to metal cutting fluid.

  3, paper industry

   (1) Pulping: Silicone emulsion defoamer (90g/T paper).

  (2) Coated paper: Coated paper, paper used for printing posters after calendering, and non-silicon defoamer is generally used for coating bubbles.

  (3) Sewage treatment: water emulsion type silicone defoamer.

   4. Application in coatings and inks

   I. Requirements for defoamers in paint production:

   (1) It has a certain affinity with the active material on the foam surface, but it should be insoluble and insoluble in the bubble liquid;

   (2) The surface tension is lower than the surface tension of the bubble liquid, and has a lower HLB value;

  (3) The emulsion (latex) should be stabilized;

  (4) After the coating is formed into a film, it cannot cause the undesirable consequences of fish eyes and shrinkage;

   (5) Antifoaming agent for water-based coatings: use more water-soluble substances, such as mineral oil, higher alcohols, and silicone resins. Silicone is the best defoaming agent for water-based coatings.

Antifoaming agent for non-aqueous coatings: commonly used substances that are difficult to dissolve in organic solvents, such as lower alcohols and silicone resins (the amount of silicone resin should be appropriate, if excessive, it is easy to shrink and cavities, and modified silicone resins are now used. Or emulsified silicone resin).

  II. Silicone defoamers recommended for water-based coatings:

  (1) Silicone oil, hydrophobic SiO2 mixture is applicable:

   epoxy resin, poured, the amount is 0.3%;

   Thermoplastic acrylic resin, spraying, dosage 0.3%

  (2) The mixture of polyether polysiloxane and hydrophobic SiO2 is applicable:

   thermosetting alkyd resin, 0.3% dip coating, 0.1% scratch coating

  (3) Mixture of hydrophobic SiO2, hydrocarbons and silicone oil is applicable:

   Thermoplastic acrylic resin, printing, ink, dosage 0.1%;

   Air-drying acrylic resin, pouring, 0.5%.

  (4) Silicone oil and hydrophobic SiO2 mixture emulsion is applicable:

  Alkyd modified styrene-acrylic resin, poured, the dosage is 0.5%

  5. Silicone defoamer for detergent industry

Polysiloxane and modified sodium tripolyphosphate are used as powder detergent additives. Dimethicone (1500c.s) emulsion containing SiO2 of 2 to 6% is mixed with anhydrous sodium tripolyphosphate. The amount of emulsion is 10-40 %, forming a hydrate as an additive.

  Metal cleaning fluid requires alkali resistance. It is best to add liquid products to be transparent and have defoaming activity.

  6. Silicone defoamer for food industry:

Food-specific polysiloxane resin: dimethyl polysiloxane as the main body, when food containing less than 15% SiO2 is an aqueous solution, the emulsified product can be directly used for other oil-based products, and the dosage is controlled at 0.05g/ Below Kg, such defoaming occasions include fermentation and sugar production. Silicon-glycol copolymer is suitable for foam suppression during fermentation.