Analysis on Selecting Production Process & Technical Route of TDI.MUCHID B2B Leader.
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Analysis on Selecting Production Process & Technical Route of TDI
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Source:www.muchid.com               Date:2021.11.18


There are mainly two methods for producing TDI: phosgene method and non-phosgene method.



The phosgene method includes the gas phase phosgene method and the liquid phase phosgene method.

The phosgene reaction is roughly composed of 5 processes: carbon monoxide and chlorine react to form phosgene; toluene reacts with nitric acid to form dinitrotoluene (DNT); DNT reacts with hydrogen to form toluene diamine (TDA); treated dry TDA It reacts with phosgene to generate toluene diisocyanate (TDI); purification of TDI.

TDI is the starting material for the production of flexible polyurethane foam, mainly prepared by the phosgenation method of toluene diamine (TDA). In the traditional process, TDA and phosgene react in the form of a highly diluted solution in the liquid phase, and a large amount of solvent is removed by distillation to purify the TDI product, which consumes a lot of energy.



At present, there are three processes for producing isocyanates instead of phosgene, namely: (1) primary amines and carbon dioxide or dimethyl carbonate to produce isocyanates; (2) primary amines and carbon monoxide for oxidative carbonylation to produce isocyanates and nitrobenzene; (3) Carbon monoxide reduction carbonylation produces isocyanate. More promising and promising is that primary amines and dimethyl carbonate will generate carbamate under the action of a catalyst, and the carbamate will be thermally decomposed to generate TDI. Its by-product methanol can be reused to produce dimethyl carbonate. Methyl ester is a non-toxic and low-pollution basic chemical. It replaces phosgene, which is beneficial to environmental protection and safety. Also, because it does not contain chlorine during the reaction process, it is less corrosive and has low requirements for equipment materials. A green and clean production process. But at present, these three processes have high cost, low yield, and are in the process of research and development, and cannot realize industrialized production.



From the perspective of the future development direction of the chemical industry, non-phosgene synthesis of TDI will replace the phosgene method. At present, there are three processes for producing isocyanates instead of phosgene. They are isocyanates produced from primary amines and CO2 or DMC, primary amines and CO are oxidatively carbonylated to produce isocyanates, nitrobenzene and CO are reductively carbonylated to produce isocyanates, but these three are The process is in the process of research and development, and industrial production has not yet been realized. More promising is that primary amine and DMC will generate carbamate under the action of catalyst, carbamate will be thermally decomposed to generate TDI, and its by-product methanol can be reused to produce DMC. Because DMC is a non-toxic and low-pollution basic chemical, replacing phosgene with it is beneficial to environmental protection and safety; and because it does not contain chloride during the reaction process, it is less corrosive, and has low requirements for equipment materials. A green and clean production process.


 
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