HNCO hydrolysis performance in urea-water solution thermohydrolysis process with and without catalysts  

作　　者：Zhen-chao CHEN Wei-juan YANG Jun-hu ZHOU Hong-kun LV Jian-zhong LIU Ke-fa CEN 

机构地区：[1]State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China

出　　处：《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》2010年第11期849-856,共8页浙江大学学报（英文版）A辑（应用物理与工程）

基　　金：Project supported by the National High-Tech Research and Development Program (863) of China (No. 2009AA05Z301);the National Basic Research Program (973) of China (No. 2006CB-200303)

摘　　要：The thermolysis of urea-water solution and its product, HNCO hydrolysis is investigated in a dual-reactor system. For the thermal decomposition below about 1073 K, the main products are ammonia (NH3) and isocyanic acid (HNCO) whereas at higher temperatures the oxidation processes take effect and the products include a low concentration of nitric oxide (NO) and nitrous oxide (N2O). The gas HNCO is quite stable and a high yield of HNCO is observed. The ratio of NH3 to HNCO increases from approximately 1.2 to 1.7 with the temperature. The chemical analysis shows that H radical is in favor of HNCO hydrolysis by instigating the reaction HNCO+H·→·NH2+CO and high temperature has positive effect on H radical. The hydrolysis of HNCO over an alumina catalyst made using a sol-gel process (designated as γ-Al2O3) is investigated. The conversion of HNCO is high even at the high space velocities (6×105 h-1) and low temperatures (393–673 K) in the tests with catalysts, which enhances HNCO hydrolysis and raises the ratio of NH3 to HNCO to approximately 100. The pure γ-Al2O3 shows a better catalytic performance than CuO/γ-Al2O3. The addition of CuO not only reduces the surface area but also decreases the Lewis acid sites which are recognized to have a positive effect on the catalytic activity. The apparent activation energy of the hydrolysis reaction amounts to about 25 kJ/mol in 393–473 K while 13 kJ/mol over 473 K. The overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.The thermolysis of urea-water solution and its product, HNCO hydrolysis is investigated in a dual-reactor system. For the thermal decomposition below about 1073 K, the main products are ammonia （NH3） and isocyanic acid （HNCO） whereas at higher temperatures the oxidation processes take effect and the products include a low concentration of nitric oxide （NO） and nitrous oxide （N2O）. The gas HNCO is quite stable and a high yield of HNCO is observed. The ratio of NH3 to HNCO increases from approximately 1.2 to 1.7 with the temperature. The chemical analysis shows that H radical is in favor of HNCO hydrolysis by instigating the reaction HNCO＋H-→NH2＋CO and high temperature has positive effect on H radical. The hydrolysis of HNCO over an alumina catalyst made using a sol-gel process （designated as γ-Al2O3） is investigated. The conversion of HNCO is high even at the high space velocities （6×105 h-1） and low temperatures （393-673 K） in the tests with catalysts, which enhances HNCO hydrolysis and raises the ratio of NH3 to HNCO to approximately 100. The pure γ-Al2O3 shows a better catalytic performance than CuO/γ-Al2O3. The addition of CuO not only reduces the surface area but also decreases the Lewis acid sites which are recognized to have a positive effect on the catalytic activity. The apparent activation energy of the hydrolysis reaction amounts to about 25 kJ/mol in 393-473 K while 13 kJ/mol over 473 K. The overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.

关 键 词：Urea-water solution Sol-gel method Γ-AL2O3 HNCO hydrolysis 

分 类 号：X5[环境科学与工程—环境工程]