A Study on Physical Chemistry of Solid Ammonium Materials
Cheon Yoon, Hannam University
A Study on Physical Chemistry of Solid Ammonium Materials for NOx Reduction of Diesel Engine Emissions
Liquid urea based SCR has been used in the market to reduce NOx in the exhaust emission of the diesel engine vehicle. However, this system has several problems at low temperature, which is freezing below â€“12 â„ƒ, solid deposit formation in the exhaust, and difficulties in dosing system at exhaust temperature below 200 â„ƒ. Also, it is required complicated exhaust packaging equipment and mixer due to supply uniform ammonia concentration. In order to solve these issues, ammonia-transporting materials for solid SCR were studied in sequence.
First, basic research on reaction rate of solid urea, ammonium carbonate, and ammonium carbamate as ammonia sources for the application of solid SCR was performed. TGA(Thermogravimetric Analysis) and DTA(Differential Thermal Analysis) tests for these materials were carried out for various heating conditions. From the results, chemical kinetic parameters such as activation energy and frequency factor are obtained from the Arrhenius plot. Additionally, from test results of DSC(Differential Scanning Calorimeter) for these materials, chemical kinetic parameters using the Kissinger method are calculated. Activation energies of solid ammonium from this experiment were compared with proper data of literature study, and then obtained data of this experiment were used for the design of reactor and dosing system for candidate vehicle.
Second, analytical study of re-solidification materials from ammonium carbonate intermediate was carried out. Since the decomposition temperature of ammonium carbonate is around 60 â„ƒ, ammonium carbonate produce ammonia gas through sublimation process by proper heating. After simple reactor which has heater control and temperature control of cooling water with visible window was designed and fabricated, pressures and temperatures are measured. From these data, saturation pressure curve as a function of temperature was obtained and governed the design of dosing system. To simulate real operation conditions under automobile environment, several cycles of heating and cooling condition were settled, two different re-solidification materials were extracted from the reactor and visible window. Analytical study is performed to characterize these unknown materials by XRD(X-Ray Diffraction), FT-IR(Fourier Transform Infrared Spectroscopy), and EA(Elemental Analyzer). From analytical results, byproducts and re-solidification materials from heating and cooling cycles are very similar to original material of ammonium carbonate.