化学链合成氨技术研究进展及展望

Research progress and prospect of chemical looping ammonia synthesis technology

氨气不仅是重要的化工原料和良好的氢载体,其可以作为无碳燃料的属性也引起了广泛关注。低能耗高效率的合成氨工艺是实现氨作为燃料应用的关键。阐述了合成氨工艺的发展历程,概述了以Haber-Bosch工艺为基础的多相催化和光、电等外场力驱动的合成氨工艺的新发展,重点介绍了化学链合成氨的最新研究成果,并对其研究方向进行展望。传统Haber-Bosch工艺苛刻的反应条件以及热力学和动力学之间的矛盾,促使科研工作者一直努力探索可持续的环境友好型合成氨技术。随着催化科学和表面科学的进步,人们对合成氨的反应机理和催化剂的物化性质有了更深入的认识,这为开发“绿色”合成氨工艺提供了有价值的参考信息,如要提高过渡金属催化合成氨性能,须尽量规避表面物种吸附能间的线性关系。另外,以可再生能源为能量来源的光、电催化合成氨,借助外场作用可以有效影响反应速率和机理。化学链技术的发展为合成氨工艺提供了新思路,将合成氨过程解耦为吸氮和释氮产氨2个或多个分步反应,可较好地缓解合成氨热力学和动力学矛盾,规避反应物竞争吸附。同时,各分步反应可分别优化,使整个化学链合成氨工艺达到最佳反应效果。未来采用太阳能聚热供能以及以生物质炭为碳源,并对化学链合成氨工艺进行经济性分析反馈指导工艺流程的优化,可降低碳基化学链制氨工艺的成本和能耗。

Ammonia is not only an important chemical raw material and a good hydrogen carrier,but also its properties as a carbon-free fu⁃el has attracted widespread attention.A synthetic ammonia process with low energy consumption and high efficiency is the key to realize the application of ammonia as fuel.In this paper,the development of ammonia synthesis process was described,and the new development of ammonia synthesis process driven by heterogeneous catalysis and external field forces such as light and electricity based on Haber Bosch process was summarized.The latest research results of chemical looping ammonia synthesis were mainly introduced,and the research direc⁃tion was prospected.Due to the harsh reaction conditions of the traditional Haber-Bosch process and the contradiction between thermody⁃namics and kinetics,researchers have been trying to explore sustainable and environmental-friendly ammonia synthesis technology.With the progress of catalytic science and surface science,people have a deeper understanding of the reaction mechanism of ammonia synthesis and the physicochemical properties of catalyst,which provides valuable reference information for the development of"green"ammonia syn⁃thesis process.For example,in order to improve the performance of transition metal catalytic ammonia synthesis,it is necessary to avoid the linear rela-tionship between surface species adsorption energy.In addition,the reaction rate and mechanism of light and electro-catalytic synthesis of ammonia using renewable energy as an energy source can be effectively affected by the help of external field effects.The devel⁃opment of chemical looping technology provides a new idea for ammonia synthesis process.The process of ammonia synthesis can be decou⁃pled into two or more step-by-step reactions of nitrogen absorption and nitrogen desorption,which can better alleviate the contradiction be⁃tween thermodynamics and kinetics of ammonia synthesis and avoid competitive adsorption of reactants.At the same time,each step-bystep reaction can be optimized respectively to achieve the best reaction effect of the whole chemical looping ammonia synthesis process.In the future,the cost and energy consumption of carbon-based chemical looping ammonia synthesis process can be reduced by using solar energy for energy gathering,biomass carbon as carbon source,and analyzing the economic feedback of the chemical looping ammonia process to guide the optimization of the process flow.