Toluene diisocyanate (TDI) is an important organic chemical raw material widely used in polyurethane foam, coatings, elastomers, adhesives and other fields. The manufacturing method of toluene diisocyanate will be introduced below.
I. Raw material preparation
The main raw materials for manufacturing toluene diisocyanate are toluene, nitric acid and urea. Among them, toluene requires high purity, generally need to use industrial grade toluene, nitric acid using dilute nitric acid, urea using industrial grade urea.
II, toluene nitrification
will be toluene and dilute nitric acid at a certain temperature and pressure for nitrification reaction to generate methyl nitrobenzene (MNB). The nitrification reaction is generally carried out in kettle reactor or tube reactor, with the reaction temperature controlled at 350-400°C and the pressure controlled at 0.3-0.5 MPa. In order to ensure the smooth progress of the nitrification reaction, it is necessary to control the proper acidity, temperature and residence time.
Three, methyl nitrobenzene hydrogenation reduction
Methyl nitrobenzene and hydrogen at a certain temperature and pressure for hydrogenation reduction reaction to produce methyl aniline (MA). The hydrogenation reduction reaction is generally carried out in a fixed-bed reactor or slurry-bed reactor, with the reaction temperature controlled at 180-220°C and the pressure controlled at 2.0-3.0 MPa. The catalyst is generally a copper-chromium or nickel catalyst. In this process, it is necessary to control the appropriate hydrogen flow, reaction temperature and residence time to ensure the complete reduction reaction.
Four, methyl aniline photogasification
will methyl aniline and phosgene gas under certain conditions for photogasification reaction to generate toluene diisocyanate. The photogasification reaction generally adopts the phosgene method or gas phase method, with the reaction temperature controlled at 80-120°C and the pressure controlled at 0.1-0.3 MPa. During the process, attention needs to be paid to controlling the flow rate of the phosgene and the reaction temperature to avoid the occurrence of side reactions. At the same time, the generated exhaust gas needs to be effectively treated to avoid pollution of the environment.
V. Post-treatment
After the photogasification reaction, the crude toluene diisocyanate obtained needs to be post-treated, including distillation, crystallization, centrifugation and other steps, in order to obtain the toluene diisocyanate product with higher purity. In the post-treatment process, appropriate operating conditions need to be controlled to ensure the quality and yield of the product.
In conclusion, the method for manufacturing toluene diisocyanate involves a number of reaction steps and post-treatment processes, and the operating conditions of each step need to be strictly controlled to ensure the quality and yield of the product. At the same time, attention needs to be paid to safe production and environmental protection requirements to ensure the smooth progress of the production process.
