| 摘要 |
<p>An improved process for the preparation of melamine from a feed of urea, thermal decomposition products of urea, or a mixture thereof, in the presence of a catalyst and an ammonia-containing gas. The reactor is divided into a lower and an upper reaction zone by a permeable grid or other restriction which reduces the catalyst flow between the two zones to 5 to 75% of what it would have been in the absence of such restriction. The feed is introduced into the lower reaction zone, which is maintained at a temperature of between 325 DEG and 425 DEG C., wherein substantially all of the urea is decomposed into thermal decomposition products, and a major portion of the thermal decomposition products are converted into melamine, which together with the remaining unreacted thermal decomposition products, is passed into the upper reaction zone. In the upper reaction zone, which is maintained at a temperature at least as high as the temperature of the lower reaction zone, substantially all of the remaining unconverted thermal decomposition products are converted into melamine.</p> |
