Decomposition of Urea into NH3 for the SCR Process
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- 作者：Sung Dae Yim ; Soo Jean Kim ; Joon Hyun Baik ; In-Sik Nam ; Young Sun Mok ; Jong-Hwan Lee ; Byong K. Cho ; and Se H. Oh
- 刊名：Industrial & Engineering Chemistry Research
- 出版年：2004
- 出版时间：August 4, 2004
- 年：2004
- 卷：43
- 期：16
- 页码：4856 - 4863
- 全文大小：139K
- 年卷期：v.43,no.16(August 4, 2004)
- ISSN：1520-5045
文摘
The thermal and catalytic decomposition of urea over a fixed-bed flow reactor system has beenexamined for the selective catalytic reduction (SCR) of NOx from mobile sources. The conversionof urea into NH3 and HNCO, the two major products from the thermal decomposition of urea,increased with the reaction temperature and the reactor space time. Urea was completely decomposed into NH3 and HNCO at 350 
C when the residence time was longer than 0.1 s. As thereaction temperature increased to 400 C or higher, complete decomposition of urea was possibleat a much shorter residence time of the feed gas stream. The simultaneous thermal and catalyticdecomposition of urea was also examined in a dual-reactor system in which the first reactorwas for thermal decomposition and the second was for catalytic decomposition, specifically overcopper exchanged ZSM5 catalyst. The role of the catalyst in the decomposition of urea into NH3and HNCO was negligible; urea decomposition occurs mainly by the thermal reaction. However,the catalyst was able to rapidly hydrolyze HNCO to NH3 even at a temperature as low as 150C. The catalyst also oxidizes NH3 to N2 in the presence of oxygen at reaction temperaturesabove 250 C. A kinetic model describing all of the major reactions involved in urea decompositionover an SCR reactor has been developed. The model adequately predicts the general trend ofvariations of the urea, NH3, and HNCO concentrations with the reaction conditions.
C when the residence time was longer than 0.1 s. As thereaction temperature increased to 400 C or higher, complete decomposition of urea was possibleat a much shorter residence time of the feed gas stream. The simultaneous thermal and catalyticdecomposition of urea was also examined in a dual-reactor system in which the first reactorwas for thermal decomposition and the second was for catalytic decomposition, specifically overcopper exchanged ZSM5 catalyst. The role of the catalyst in the decomposition of urea into NH3and HNCO was negligible; urea decomposition occurs mainly by the thermal reaction. However,the catalyst was able to rapidly hydrolyze HNCO to NH3 even at a temperature as low as 150C. The catalyst also oxidizes NH3 to N2 in the presence of oxygen at reaction temperaturesabove 250 C. A kinetic model describing all of the major reactions involved in urea decompositionover an SCR reactor has been developed. The model adequately predicts the general trend ofvariations of the urea, NH3, and HNCO concentrations with the reaction conditions.