低(等)压合成氨的最佳H_2/N_2与催化活性的关系

Relationship between Optimum Ratio of Hydrogen to Nitrogen and Catalytic Activity for Low Pressure Ammonia Synthesis

采用高压催化剂性能评价实验装置,在压力分别为7.0,10.0和15.0MPa,温度分别为350, 400和450℃条件下,在H2/N2为1.6~3.0范围内研究了H2/N2对A301,ZA-5和A110-2型催化剂的活性和合成塔出口氨浓度的影响.在压力和空速一定的条件下,最佳H2/N2随反应温度而异.在350,400和450℃下,最佳H2/N2分别为1.8~2.2, 2.2~2.5和2.5~3.0.由此可见,合成氨反应的速率达到最大值时的最佳H2/N2值与反应的进程有关.为此提出了催化剂效率K (Catalysis efficiency) 的概念来表征在催化剂作用下反应器出口氨浓度趋近平衡的程度,即K＝CNH3 / C*NH3.根据实验结果,得到了最佳H2/N2与催化剂效率的定量关系:(H2/N2)m = 1.5(1+ CNH3 / C*NH3) = 1.5(1+K).由此可以根据催化剂在不同反应条件下的催化剂效率来确定最佳H2/N2.凡是会降低催化剂效率的因素,都会使最佳H2/N2降低.各种影响因素对最佳H2/N2的影响中,反应温度的影响最大,其次是空速和催化剂的活性,而压力和惰性气体含量的影响相对较小.在低温(低压)下合成氨,宜采用较低的H2/N2.

The effect of H2/N2 on reaction rate of ammonia synthesis or outlet ammonia concentration by using A301, ZA-5 and A110-2 catalysts was studied. The experimental conditions were that the amount of catalyst used was 5.76 g and size of 1.0-1.4 mm putting in a tube packed bed reactor of 12 mm internal diameter, the range of H2/N2 was 1.6-3.0, the pressure was 7.0, 10.0 and 15.0 MPa and the temperature was 350°, 400° and 450°C respectively. Under certain pressure and space velocity conditions, the optimum H2/N2 was different for different reaction temperature. For example, the optimum H2/N2 are 1.8-2.2, 2.2-2.5 and 2.5-3.0 for temperature of 350, 400 and 450°C respectively. From the results, we believe that the optimum H2/N2 of maximum reaction rate was related to the extent of approaching equilibrium of ammonia synthesis reaction. The extent of reaction may be expressed by the concept of catalyst efficiency K=C(NH3)/C(NH3)* proposed by author, and the optimum (H2/N2)m may quantitatively be related to a function of the catalyst efficiency: (H2/N2)m=1.5(1+K), that is, optimum ratio of hydrogen to nitrogen is directly proportional to catalyst efficiency under concerned operating conditions. Therefore (H2/N2)m at different operating conditions may be determined by the activity of catalyst under the same conditions. Any factor decreasing catalyst efficiency will make (H2/N2)m decrease. In all the influence factors of (H2/N2)m, influence of reaction temperature is the largest, activity of catalyst and space velocity is the next, and the influence of pressure and the content of inert gas is smaller. Using lower H2/N2 is suitable for ammonia synthesis at low temperature and low pressure.