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    Home > Chemicals Industry > Chemical Technology > Product performance and technical formula of salicylic acid

    Product performance and technical formula of salicylic acid

    • Last Update: 2021-08-15
    • Source: Internet
    • Author: User
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    Salicylic acid (salicylic acid), also known as 2-hydroxybenzoic acid (2-hydroxyl benzoic acid), salicylic acid , salicylic acid , Shali Xi acid, sprinkle acid, of the formula C .
    H .
    O .
    , a molecular weight of 138.
    1 , The structural formula is

    Product performance

    White needle-like crystal or crystalline powder, with a spicy taste; melting point 158~161℃, boiling point 211℃ (2.
    6664kPa), sublimation at 76℃; relative density (d
    4 20 ) 1.
    443; flammable; low toxicity; in air It is stable in medium, but gradually changes color when exposed to light; slightly soluble in water, soluble in acetone, turpentine,
    ethanol , ether , benzene and chloroform, its aqueous solution is acidic; it produces a special purple color with aqueous ferric chloride solution

    Production principle

    After phenol and caustic soda form a salt, it undergoes carboxylation reaction with carbon dioxide , and then acidifies to obtain salicylic acid

    Process flow

    Technical formula (kg/t)

    Main equipment

    Salt carboxylated gold, water separator, acid precipitation pot, sublimation kettle, condenser, cooling tower, centrifuge, refining kettle (stainless steel)

    Production process

    (1) Salt formation and carboxylation
    Put 100kg of phenol (98%) into the cast iron reactor and stir, add 86kg of 50% sodium hydroxide solution, and take samples after 0.
    5h reaction

    The measured free base should be 1% (if the free base exceeds 1%, it needs to be supplemented to balance)

    Distill water at atmospheric pressure for 2h, stir, and then dehydrate under reduced pressure at 170℃/(20~160)×133.
    3Pa for 1~1.
    5h, and then add 100kg of phenol as a solvent for azeotropic dehydration

    When the internal temperature rises to 128°C/160×133.
    3Pa, the reduced pressure azeotropic dehydration is completed

    Sodium phenate was carboxylated in 100 kg of solvent phenol, and CO
    2 was introduced for 3 hours, and the internal temperature was raised from 128°C to 200°C
    When the temperature drops, start to recover phenol under reduced pressure, pass CO
    2 for the second time after 2 to 3 hours , carboxylate for 2 hours, then recover phenol under reduced pressure for 1 to 2 hours, and the carboxylation is completed
    Add water to dissolve, get 50% sodium salicylate solution


    (2) Acid precipitation
    Under stirring, add about 1000 kg of 7% to 8% sulfuric acid solution to the 50% sodium salicylate solution generated above to make the pH 1-2

    After cooling to below 30°C, centrifugal filtration and vacuum drying, 63kg of crude salicylic acid was obtained


    (3) Sublimation
    The crude salicylic acid is added to the sublimation tank, and the sublimation is carried out at 150~170℃/20×133.
    3Pa under reduced pressure

    The sublimation tower is cooled by atmospheric pressure water, and the salicylic acid vapor enters the tower for cooling, and 60kg of sublimation salicylic acid is obtained


    (4) Refined
    Put 60kg of sublimated salicylic acid, 360L of water, and 0.
    36kg of phosphoric acid into a stainless steel refining tank in turn, stir and raise the temperature to 90°C, keep it for 1h, lower the temperature to 35°C, filter, and vacuum dry to obtain 58kg of salicylic acid


    Laboratory preparation method

    Dissolve 47 g of phenol in 20.
    5 g of NaOH and 30 mL of water in a nickel evaporating dish, and heat on an asbestos net to prepare powdered sodium phenate

    Add the powdered sodium phenate to a 250mL three-necked bottle, heat the oil bath to 110°C, and start to pass in the CO
    2 after being washed by the sulfuric acid bottle and the silica gel column .
    The CO
    2 tube should be directly connected to the surface of the sodium phenate
    After ventilation for 1 hour, the temperature was gradually increased, and the temperature rose to 190°C within 4 hours

    Heat at 200°C for another 2h

    After the reaction product is cooled, it is dissolved by adding water, and then 1 g of activated carbon is added

    Heat at 60°C for 15 min and then hot filter

    Concentrated hydrochloric acid was added to the filtrate to precipitate salicylic acid

    Crystallize in an ice-salt bath and filter with suction to obtain a crude product

    Then recrystallize with water

    The pure product has a melting point of 156°C




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