氨在超临界水中氧化的平衡热力学研究

Equilibrium thermodynamics of ammonia oxidation in supercritical water

城市污泥中含有大量的蛋白质等含氮有机物,而氨是含氮有机物超临界水氧化的中间产物。文章使用热力学方法研究了氨在超临界水中氧化构成的平衡体系。采用Peng-Rob inson状态方程和最小自由能法计算了反应体系中各组分的平衡组成。结果表明,当反应体系达到平衡时,氨在超临界水中可以被完全氧化;其中大部分的氨转化成了氮气,只产生少量的NO和NO2,没有N2O的生成。提高温度和过氧量可以增加NOx的平衡产量,但NOx的选择性最高不超过2%。比较热力学平衡计算结果和前人实验结果发现,N2O只是氨在超临界水中氧化的中间产物。氨在超临界水中的降解效果主要受动力学因素影响。

The sewage sludge contains a lot of nitrogen-containing organics whose intermediate product during the supereritical water oxidation （SCW） process is ammonia. A thermodynamic model was developed to predict the performance of ammonia oxidation in supercritical water. Based on Peng-Robinson EOS formulations and direct Gibbs free energy minimization, the equilibrium composition of the reaction system for different conditions was calculated. The result shows that as the reaction system reaches equilibrium, ammonia can be completely oxidized in the supercritical water, and most of which converts to N2 ; NO2 and NO are the minor by-products and N2O is hardly produced in the system. Increasing temperature and excess oxygen can increase the equilibrium composition of NOx. But the highest selectivity of NOx is less than 2%. Comparing the calculated results with experimental results from other papers, it shows that the N2O is only an intermediate product in the supereritical water oxidation of ammonia, and the degradation of ammonia is mostly affected by dynamic factors.