Discussion on VCM inhibitor types
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Regarding VCM polymerization inhibitors, there are those used in the production process to prevent self-polymerization and blockages in pipes or equipment. There are also cases, such as those involving shipment for sale, where a certain amount of inhibitor must be added to prevent VCM from polymerizing on its own. Question: 1. Is the type of inhibitor added in the latter the same as that in the former? 2. What type of inhibitor is generally used for the latter, and what is the typical addition level in ppm? Are there any industry standards in this area? 3. To elaborate, what are the main polymerization inhibitors used in PVC production? What are the characteristics of its incorporation?
This post was last edited by wang*neng on 2021-2-7 at 10:16. There are many reports on the use of antipolymerization agents to prevent self-polymerization in pipeline equipment; I have also been paying attention to this issue lately and came across this post, so I’m replying to discuss it. Before distillation, a polymerization inhibitor is added to vinyl chloride to prevent the self-polymerization and clogging of the distillation column trays. Generally, nonylphenol is used for this purpose; when it comes into contact with active free radicals, a transfer of active centers occurs – the original active free radicals lose their activity by acquiring hydrogen atoms, thereby generating new free radicals (nonylphenol free radicals). Nonylphenol radicals are inert and cannot initiate the polymerization of vinyl chloride; they can only couple with other active radicals to terminate them, thereby exerting a chain-inhibition effect. The typical addition level results in a concentration of 10×10-6 to 50×10-6 in vinyl chloride. This addition amount is difficult to control; generally, drip addition is used. Some manufacturers have achieved good results by washing the VCM monomer using a polymerization inhibition tower. Since nonylphenol is relatively viscous and difficult to add, it can be reacted with caustic soda to be converted into sodium nonylphenolate (which also has antipolymerization properties) for addition drop by drop. As for the treatment of recycled monomers, the approach is basically the same; a few years ago, discussions were held with some manufacturers, and adding hydroquinone at the water ring compressor to prevent polymerization also yielded good results. The autopolymerization of VCM monomer is influenced by oxygen, moisture, residual initiator radicals (from recycled monomer), and storage temperature. Reducing the oxygen and moisture levels as much as possible, destroying residual initiator radicals through alkaline washing, and keeping the storage tank temperature below 15°C can all effectively prevent the autopolymerization of the monomer.