What is the optimal pressure for the melamine process?
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The melamine production process is divided into high-pressure, low-pressure, and atmospheric-pressure methods. The operating pressure in the high-pressure method is generally 8.0–15.0 MPa, and no catalyst is required for the reaction. The operating pressure in the low-pressure method is generally from atmospheric pressure to 1.0 MPa, and a catalyst is required for the reaction. It is said that normal pressure is not as good as 0.6 MPa; industry professionals, please share your views on this.
Melamine is classified according to operating pressure into high-pressure methods (5–15 MPa); representative processes include the new Nissan method, the Montedison method, the American ACC method, and the Italian ETCE process； Representative processes for the medium-pressure method (0.5~1MPA) include DSM’s process in the Netherlands and the OSW process in Austria ； The atmospheric pressure process (below 0.3 MPA) includes processes such as BASF’s method in Germany and the improved low-pressure process developed in China. The atmospheric pressure and medium pressure methods each have their own characteristics: The production of melamine using low-pressure methods involves a liquid-phase reaction that takes place in the presence of a catalyst. This approach offers good selectivity, high product quality, and few by-products. It was developed early on and is therefore quite mature. However, the process is complex, with a long sequence of steps; the capture equipment suffers significant corrosion. Higher-grade materials are required, there are many pieces of equipment, the space needed is large, the initial investment is high, operation is difficult, clogging can occur easily, it is challenging to make use of the exhaust gases, energy consumption is high, and it takes a long time to obtain qualified products after the process starts up. The production of melamine under normal pressure involves a gas-phase reaction with dry capture; it causes less corrosion, requires equipment made of lower-grade materials, has low initial investment, a simple process, few pieces of equipment, a short workflow, and easy control. However, the equipment is large, occupying much space, the operation is complicated, and it requires significant labor effort. The pressure of the by-product gases is low, making recovery difficult, and energy consumption is high. Over time, the catalyst used in the reaction sees a decline in its capacity, the system tends to get clogged, requiring frequent shutdowns for maintenance, which makes long-term operation very challenging.
The characteristics of the high-pressure process are also listed below. The production of melamine using this high-pressure method involves a liquid-phase reaction, which makes clogging less likely. However, under high temperature and pressure, the reaction medium is highly corrosive, requiring higher-grade materials for the equipment. The control system is complex, and the initial investment is high. No catalyst is needed for this reaction, so there are no concerns regarding catalyst poisoning or contamination of the product. The operation is stable, the product quality is good, and the plant has great operational flexibility. It takes less time to produce qualified products after startup. This method allows for larger scale operations, results in low energy consumption and operating costs. The by-product gases, due to their high pressure, are easy to utilize, enabling the simultaneous production of urea and thus reducing the cost of the final product.