Regarding acrylates, where are polymerization inhibitors mainly added? What is the polymerization inhibition mechanism?

The question is too vague! No specificity! There are many ways to add polymerization inhibitors, such as spraying, or adding them in a mist form using a principle similar to that of a jet pump – there are many methods! The equipment and processes used determine the method for adding the polymerization inhibitor! Acrylic acid is a substance that tends to polymerize easily. I have encountered this issue in production as well; I have been involved in the selection of distillation columns and am well aware of how strong its tendency to polymerize is! Currently, no authority can truly resolve it!

Phenolic polymerization inhibitors are generally used; I’ve never heard of a location for adding them. Introduction to polymerization inhibitors: Polymerization inhibitors react with chain radicals to form non-radical species or low-activity radicals that cannot initiate further reactions, thereby terminating polymerization. 　　To prevent the polymerization of olefin monomers during storage, transportation, and other processes, a small amount of inhibitor is often added to the monomers, which is then removed before use. Generally, the polymerization inhibitor is a solid substance with low volatility, and it can be removed during the distillation of the monomer. Hydroquinone, a commonly used polymerization inhibitor, can react with sodium hydroxide to form water-soluble sodium salts; therefore, it can be removed by washing with a 5%–10% sodium hydroxide solution. Inorganic polymerization inhibitors such as cuprous chloride and ferric trichloride can also be removed by acid washing. Function: Inhibitors can prevent the progression of polymerization, resulting in an induction period during the polymerization process (a time interval during which the polymerization rate is zero). The length of this induction period is proportional to the amount of inhibitor present. Once the inhibitor is exhausted, the induction period ends, and polymerization proceeds at the normal rate as if no inhibitor were present. Category: (1) Classified by their activity under different temperature conditions: ① Antioxidants with fixed activity that always react rapidly with free radicals within the normal storage and curing temperature ranges; they are consumed in these reactions, thereby creating an induction period. The antioxidants that are consumed lose their activity, examples include hydroquinone. ②Thermosensitive polymerization inhibitors are inhibitors at normal storage temperatures; they decompose when heated and become ineffective, such as tert-butylhydroquinone. ③Dual-action inhibitors exert an inhibitory effect at lower temperatures and a catalytic effect at higher temperatures; examples include oxygen, organic copper salts, quaternary ammonium salts, sulfur, etc. 　　(2) Classification according to their polymerization inhibition mechanism: ① In the absence of oxygen, in the presence of benzoin without oxygen, it reacts directly with free radicals to form a semiquinone intermediate, which then reacts with another free radical to form a stable compound. ②In the presence of oxygen, hydroquinone and its derivatives react with oxygen to form peroxyl radicals; these peroxyl radicals then react with hydroquinone to form radical complexes, which in turn react with another peroxyl radical to form stable compounds. 　　(3) According to the composition of the inhibitor: ① Single-type: Only one type of inhibitor is required to achieve an inhibitory effect. Such as hydroquinone, paraquinone, etc. ②The composite type refers to the combined use of two or more polymerization inhibitors. To ensure the storage stability of resins and prepregs at room temperature, and to enable adjustment of their shelf life without affecting the final curing rate of the finished products, a composite inhibitor is used in the manufacturing process. The above effect can be achieved by using hydroquinone and tert-butylhydroquinone along with trace amounts of copper salts. Comparison of several polymerization inhibitors: Hydroquinone HQ, also known as hydrogen quinone: it is the most commonly used and inexpensive. It performs well at room temperature, but its curing effect is poor when heated. Para-benzoquinone PBQ: It can still function under oxygen-deficient conditions and is suitable for etherification processes carried out under the protection of nitrogen or other inert gases; it has a yellow color that affects the color of the resin. Methylhydroquinone THQ: It offers good performance and is used in the production of highly reactive unsaturated polyester resins, often in topcoat resins and SMC resins. This product has good solubility and effective heat-resistant polymerization inhibition. p-Hydroxybenzyl ether HQMME: it confers good storage stability to the resin, without delaying or affecting its gelation time during use. This product has the best solubility in organic solvents and the lightest color. 　　2-tert-Butylhydroquinone MTBHQ: It is an effective storage stabilizer for unsaturated polyester resins, as well as a stabilizer for highly active resins. It has the most comprehensive functions and can perform well over a wide temperature range. Moreover, upon heating, it only causes a slight delay in the curing of the resin. This product is often used in combination with other polymerization inhibitors. 　　2,5-Di-tert-butylhydroquinone 2,5-DTBHQ: It can slowly react with free radicals over an extended period of time, thereby eliminating the free radicals that form during resin storage. It improves the storage stability of the resin while having the least impact on the gelation time.

2# over_tim As far as I know, it should be added at locations where phase changes are likely to occur! Esters such as methyl acrylate and butyl acrylate tend to undergo self-polymerization more easily during phase transition! Therefore, a polymerization inhibitor must be added to the vapor outlet at the top of the tower! Polymerization inhibitors generally include hydrogen trapping agents and hydrogen-trapping monomethyl ethers, as well as copper salts, ZJ-701, and so on! Both the polymerization inhibitor and the oxygen inhibitor must be used simultaneously to exert a polymerization-inhibiting effect.

This post was last edited by mss374014210 on 2009-9-4 at 12:48. Using only a polymerization inhibitor is not sufficient; air also needs to be introduced. Without air, the polymerization inhibitor will not be effective, especially in the case of methyl acrylate

May I ask, what is used as a solvent to add the polymerization inhibitor to the AA distillation tower?

Polymerization inhibitors must be added at all locations where phase changes may occur, such as the top of the dehydration tower, the top of the alcohol stripping tower, and the top of the refining tower. Additionally, polymerization-inhibiting air should be introduced, heat tracing should be provided in the gas-phase retention areas, and spraying systems should be installed in other dead zones

How can the amount of air introduced be determined based on the amount of inhibitor added?

Not all polymerization inhibitors require oxygen; it depends on the type of inhibitor