基于多级孔道分子筛的新型氨法脱碳富液中低温催化再生特性及其机理研究

This project is proposed according to a major national demand for CO2 emission reduction. It is also an important basic research in the field of engineering thermophysics and energy utilization, and the current research frontier and hot topic in the cross field of energy and environment. Ammonia-based CO2 capture is internationally recognized as one of the most promising CO2 emission reduction technologies for industrial applications in the near term. However, for this technology, the problems of high regeneration energy, low regeneration rate and inadequate basic research have not yet been solved. To solve the problems, a new idea of catalytic regeneration process in mid-low temperature, different from the traditional process, has been proposed in this project. That is, the decarburization product directly decomposes at the active site of the solid acid catalyst, avoiding a large amount of energy consumption in heating and evaporation of the rich solvent. Based on ZSM-5 zeolite and through the method of “modification-characterization-test-analysis-optimization”, the key characteristics that affect the catalytic performance will be revealed. Subsequently, the catalyst formulation will be continuously upgraded. Also, according to the comprehensive results of experiments and quantum chemistry calculation, the catalytic mechanisms will be illustrated. A catalytic regeneration experimental platform will be established to exhibit the characteristics of catalytic regeneration process. The multiphase flow models coupled with heat and mass transfer and reaction will be developed, and numerical experiments will be conducted to optimize the process parameters. Consequently, the two key scientific problems, “efficient and inexpensive ammonia catalytic regeneration catalysts” and “optimization of parameters for catalytic regeneration process”, will be solved, providing a theoretical basis and fundamental data for future large application of CO2 emission reduction.

本项目针对CO2减排的国家重大需求提出，是当前能源与环境交叉领域的前沿热点方向，是工程热物理与能源利用领域的重要基础研究内容。氨法脱碳是国际公认的有望在近期实现工程应用的CO2减排技术之一，但目前还存在再生能耗过高、再生速率缓慢、基础性研究不足等问题。与传统再生工艺不同，本项目提出氨法中低温催化再生的新思路，即脱碳产物在分子筛催化剂的热活性位处直接发生再生反应，避免富液升温与汽化的大量能耗。基于ZSM-5分子筛，通过“改性—表征—试验—分析—优化”的方法揭示影响催化效能的关键特性，优化催化剂配方；结合试验结果与量子化学计算，阐述催化再生反应机理；建立催化再生实验平台，揭示催化再生过程特性；建立流动、传热传质与化学反应耦合的数理模型，并通过数值实验优化催化再生工艺参数；解决“高效廉价再生催化剂研制”与“催化再生工艺参数优化”两个关键性科学问题，为今后大规模CO2减排提供理论依据与基础数据。

针对脱碳富液再生过程能耗高、再生速率缓慢等问题，本项目提出了脱碳富液催化再生的新思路。首先开展了无催化条件下脱碳富液再生的机理研究。拉曼光谱分析表明，当碳负载α<0.35时，氨基甲酸根为液相主要成分。随着碳负载进一步增高，碳酸氢根转变为液相主要成分且脱碳速率大幅升高。拉曼光谱分析表明高碳负载下脱碳速率增高是由于碳酸氢根的大量分解，而氨基甲酸根、碳酸根浓度先增加后下降。脱碳富液在不同温度下再生的结果表明，其峰值脱碳速率符合二级反应速率方程，表观活化能为14.9 kcal/mol，指前因子为856000 m3/(kmol·s)。量子化学计算表明：碳酸氢根分解过程中由OH基团夺取铵根中的H+，同时C－O键协同断裂，一步形成CO2、NH3。而氨基甲酸根分解则分两步进行，首先由氨基甲酸根的NH2基团夺取铵根的H+形成两性中间产物，随后C‒N键断裂，生产NH3、CO2。对于碳酸根直接分解过程，没有计算得到相关反应路径。催化再生试验首先探究了以分子筛为代表的固体酸，包括：HZSM-5、SAPO-34、r-Al2O3等。对比结果表明HZSM-5的催化再生效能最好，使得再生能耗下降23.9%。通过表征发现，催化再生性能随分子筛BET surface area × BAS的数值增加而呈线性增长的趋势。针对以金属氧化物纳米颗粒为代表的固体酸，包括Fe2O3、MnO、La2O3、CeO2、Nb2O3、Sb2O3等。发现Fe2O3催化再生效果最好，La2O3、Sb2O3、MnO效果次之，而其他金属氧化物几乎无效果。本项目还通过浸渍法制备了硫酸化金属氧化物，发现硫酸化进一步提升了Fe2O3的催化再生性能。本项目进一步提出催化再生机理：Brønsted酸位点可为氨基甲酸根、碳酸氢根、碳酸根的分解提供H+，同时失去H+的Brønsted酸位点可作为铵根中H+的接受位点，促进铵根的去质子化。Lewis酸位点则可吸附N原子上的孤电子对，并减弱C－N键，促进C－N键断裂形成CO2与NH3。此外，本研究还基于欧拉-拉格朗日法，建立了耦合气液流动、热质传递及化学反应的三维数值模型，并基于热力一致性原理简化了模型中的热力学表达, 为后续的吸收过程优化及再生过程数值模拟奠定了基础。