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    Home > Chemicals Industry > Chemical Technology > Reaction feeding sequence for exothermic or gas production (2)

    Reaction feeding sequence for exothermic or gas production (2)

    • Last Update: 2022-01-28
    • Source: Internet
    • Author: User
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    (2) The quenching substance cannot be added to the liquid with high reactivity

    When preparing a dilute sulfuric acid solution, it is necessary to slowly add concentrated sulfuric acid with high reaction activity to the continuously stirred water.


    Case 1

    A researcher poured water into about 600 mL of recovered phosphorus oxychloride , held the bottle and shook it for several times before exploding, as shown in Figure 24-36


    The face, hands, and legs were severely injured.


    Water and phosphorus oxychloride reaction, unlike water and concentrated sulfuric acid immediately upon mixing as heat, which is made of a potential reservoir, depending on temperature, short as a few seconds may be needed at several low temperatures Minutes or longer


    Reason analysis: the feeding sequence is incorrect, and water should not be added to the phosphorus oxychloride


    Lessons: phosphorus oxychloride security quenching process is Phosphorus oxychloride constant stirring slowly into hot water, depending on the elevated temperature and cooled with ice


    Case 2

    A researcher quenched the leftover sodium azide waste liquid.


    Reason analysis: First, the concentration of azide and sodium hypochlorite is high, the reaction is violent, a large amount of gas is generated and heat is released; the second is that the quenching liquid is added to the high-concentration sodium azide waste liquid, and the order of addition is reversed


    Lesson: The process of quenching the excess azide waste liquid should be carried out in a plastic beaker or waste liquid bucket.


    A similar explosion accident:


    At -20°C, sodium azide (14.


    Pour the sodium hypochlorite aqueous solution into the mixed wastewater solution containing excess sodium azide and needle ammonium nitrate, shake the reaction bottle, the lip of the bottle flashed red and exploded


    Lesson: Same as Case 2


    Case 3

    A R&D staff made the following response:


    Feeding materials: 120gA (0.


    The accident occurred during the post-processing stage of the reaction



    Figure 24-38 Photos of the scene after the accident

    Reason analysis: the order of addition of quenching reaction is reversed
    .
    The molar ratio of triethylboron to the substrate, which will react violently with water, is 4:1, and the molar ratio is too large: the total amount of feed for the entire reaction is large, and the remaining amount of triethylboron is greater
    .
    In this case, the order of addition of the quenching reaction should be considered
    .

    Lesson: The molar ratio of triethylboron to the substrate should not be too large; the quenching temperature of 40~50℃ is too high, and at the same time, the temperature is too low and it is easy to cause the accumulation of latent heat of the reaction, leading to the explosion of the late reaction and the occurrence of flushing and accidents
    .
    If there are indeed many high-energy reagents in the reaction solution, the reaction solution needs to be slowly poured (or dropped) into the quenching solution under stirring
    .

    Only when the reaction solution is very dilute, the quenching solution can be directly added to the reaction solution
    .
    For example, reactions involving butyllithium are mostly carried out at low temperatures, and the molar ratio of butyllithium is often not too much.
    Therefore, it is possible to directly add saturated ammonium chloride aqueous solution to the reaction solution.
    This operation method is similar to that of pouring the reaction solution.
    Compared to entering the quenching liquid, it is much more convenient
    .
    If the reaction solution does not contain high-energy hazardous materials, the order of addition can be ignored and it can be done as convenient as possible
    .

    (3) Dilution safely and avoid intensive intervention

    When two compounds with strong chemical activity meet directly, they will react violently.
    Appropriate dilution and other methods must be taken in advance, and they must be protected with inert gas to avoid accidents
    .

    A researcher uses boron tribromide to perform the demethylation reaction on methyl ether.
    After measuring the boron tribromide in a graduated cylinder and adding it with a constant pressure dropping funnel, add methanol to the graduated cylinder to quench the residue in the graduated cylinder.
    The trace amount of boron tribromide in the medium suddenly caught fire at this time and caused the entire operating table to catch fire
    .
    When a researcher from a research institute removed the dropping funnel after adding boron tribromide, the remaining drop of boron tribromide at the end of the dropping funnel accidentally fell on the experimental table, because there was ethanol and other liquids on the table.
    It caused the entire countertop to catch fire
    .

    Reason analysis: Boron tribromide is a highly active Lewis acid.
    Any reaction involving boron tribromide can only be diluted with inert non-flammable solvents such as dichloromethane.
    If it directly encounters polar reagents such as alcohols, it will It reacted violently and caught fire
    .

    Lesson: Without control (dilution, low temperature, slow addition, etc.
    ), if the active reagent is directly added to another active reagent (system) that will produce a violent reaction, accidents are inevitable
    .
    When disposing of the residual boron tribromide, first dilute it with an inert solvent such as dichloromethane to increase the heat capacity and reduce the risk, and then slowly add polar reagents such as alcohols for quenching, and keep stirring to avoid accidents
    .
    There are many fire accidents of boron tribromide, and most of them are caused by ignorance of its nature, wrong feeding order, or awkwardness
    .

     

     

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