Low-temperature solidification problem of vehicle urea

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Our company’s vehicle urea is a urea solution with a concentration of 32.5% and a solvent of ultra-pure water; the raw materials used in its production are urea crystals and ultra-pure water, and the key factor lies in the purity of these raw materials. From the perspective of production processes, although automotive urea requires a higher level of purity in its raw materials compared to general industrial applications, domestic manufacturing processes are already capable of meeting the needs of practical use. The production process for vehicle urea does not provide sufficient barriers to entry; domestically, vehicle urea is primarily obtained by purifying industrial urea. The main principle behind this process is as follows: 1) At a temperature of 70–75°C, urea undergoes hydrolysis in an aqueous solution. 2) At temperatures below 30°C, urea crystallizes out of the aqueous solution again. 3) With each hydrolysis and crystallization process, the purity increases significantly; generally, one hydrolysis and crystallization cycle using industrial-grade urea is sufficient to meet the standards for urea used in vehicles, with a yield ratio of 1.5:1. 　　Electronic-grade ultra-pure water must be used for vehicle urea. In vehicle urea systems, the SCR catalyst carrier is highly susceptible to metal ion poisoning, which leads to a loss of its catalytic efficiency; therefore, vehicle urea solutions must use ultra-pure water of grade 1 suitable for the electronics industry (resistivity ≥ 18 MΩ·cm). Automotive urea solution begins to freeze at -11°C, and in actual use it freezes completely at -20°C. Current techniques involve reducing the freezing point of the solution by adding modifiers, as well as using external heating devices to prevent the solution from freezing. The modifier mainly explains the active components and their mechanism; the actual effects achieved and the relevant data are still unclear?