尿素催化水解特性实验研究

Experimental Investigation on the Properties of Urea Thermohydrolysis With Catalysts

在一石英管式炉上进行了尿素掺杂不同金属氧化物热解制取氨气的实验研究,比较了不同氧化物作为床料催化尿素水解制取氨气的性能。实验结果表明:纯尿素的分解不受水汽的影响,产氨率在50%左右,氨气主要生成在133～230℃区间;在水汽存在的情况下,金属氧化物的添加能大大促进尿素的分解和产氨率,氨气主要生成在133～300℃区间,产氨率可达100%。在150～400℃下对不同金属氧化物对HNCO水解的催化活性进行了实验,催化活性如下:TiO2>γ-Al2O3>沸石分子筛>SiO2。催化条件下HNCO水解反应的活化能很低,水解反应主要受传质作用的影响。流化态金属氧化物催化水解实验结果表明,γ-Al2O3具有较高的催化活性和优良的稳定性、耐磨性,更适合当作床料进行流化态催化尿素水解。

The thermohydrolysis and pyrolysis of urea with and without the catalytic function of ten kind of metal oxides for ammonia were studied under quartz tube reactor and the properties of different oxides as a catalytic bed material for urea hydrolysis were compared. The results show that the water vapor has no effect on the urea decomposition and ammonia （NH3） productive rate keeps about 50%. Most of the ammonia is produced at 133-230 ℃. The added metal oxides significantly improve the urea thermohydrolysis in the presence of water vapor. NH3 is produced at 133-300 ℃ and the productive rate reaches 100%. The hydrolysis of isocyanic acid （HNCO） over different metal oxides was investigated experimentally at 150- 400 ℃ and it is found that the catalytic effect decreases in the order TiO2, γ-Al2O3, zeolites, SiO2. On the catalytic condition, the apparent activation energy of the HNCO hydrolysis reaction is low, which suggests the reaction is mainly controlled by gas-phase mass transfer. Ammonia production from urea solution over metal oxides was investigated in a fluidized bed reactor, which shows that γ-Al2O3 is most suitable as a fluidized bed material due to its high catalytic activity, as well as good abrasion resistance and stability.