低阶煤加压催化气化制甲烷的化学过程研究

The development of methane production from low-rank coal is not only important for meeting the increasingly growing demand of natural gas in China, but also a promising way to high-efficiency and environmentally friendly utilization of low-rank coal resources. Much attention has been paid worldwide to the technology of coal pressurized catalytic gasification for production of methane due to its advantages of low gasification temperature, and high methane yield and high conversion efficiency, but its technical developments are still not commercially mature and full of challenges. This project features in undertaking a research by dividing the complex processes of coal methanation by catalytic gasification to two processes, volatile methanation and char methanation. It mainly includes the following research contents. First, these two processes are studied, respectively, using a fixed-bed two-step hydrogasification reactor and a fixed-bed pressurized char gasification reactor with H2/steam as a gasifying agent to optimize the technological parameters. Second, based on K2CO3, investigations are conducted into bimetallic catalysts of CaO/K2CO3 type and some multi-metallic catalysts to reveal their synergistic effects and multiple catalytic performances and eventually to improve the catalyst. Third, investigations are focused on the transformations and catalytic effects of the alkali and alkali earth metals inherent in low-rank coal as well as their synergies with the external catalyst during pressurized coal gasification. This project is purposed to get the deep understanding of the basic chemical processes of coal pressurized catalytic gasification, and attempts are made to master the approaches for enhancing both the volatile catalytic methanation and char catalytic methanation. Overall, this research will provide the theoretical fundamentals which are useful for developing new coal-to-methane technologies.

发展低阶煤制甲烷生产对于满足我国日益增长的天然气需求，高效和洁净利用低阶煤资源具有重要意义。煤加压催化气化制甲烷工艺具有气化温度低、甲烷产率和转化效率高等优点，备受国内外广泛关注，但技术仍处于开发阶段，富于挑战性。本项目将煤催化气化制甲烷的复杂过程分为挥发分甲烷化和煤焦甲烷化两个过程进行研究。利用固定床两段式加氢反应器和煤焦加压气化反应器分别研究挥发分催化加氢甲烷化和以氢气/水蒸汽为气化剂的煤焦催化甲烷化两个过程，以优化工艺参数；以碳酸钾为基本催化剂，研究氧化钙/碳酸钾类双金属催化剂和多金属催化剂在煤加压催化气化过程中协合作用及多功能性，以改善催化剂性能；研究低阶煤中碱金属和碱土金属在煤加压气化过程中的演变和催化作用及其与外加催化剂的协合作用。本项目旨在深入了解煤加压催化气化的基本化学过程，掌握既促进挥发分催化甲烷化又促进煤焦催化甲烷化的规律与方法，为开发煤制甲烷新工艺提供有益的基础理论。

开发劣质低阶煤制甲烷技术对于满足我国日益增长的天然气需求、解决“气荒”问题具有重要意义。针对低阶煤催化加压气化生成甲烷工艺，本项目着重研究了该工艺涉及的挥发分加氢裂解和煤焦加压催化气化的两个重要化学过程，获得了以下主要研究成果：（1）利用两段式固定床反应器研究了煤加氢生成气态烃的过程，发现通过强化挥发分的二次加氢裂解（温度750°C,压力5MPa），玉溪褐煤的气态烃（主要为甲烷和乙烷）产率达23.1%（无灰煤基），并同时生成轻质液态芳香烃的作用，其中高附加值的BTX（苯、甲苯和二甲苯）产率达7.2% （无灰煤基）；（2）研究了煤结构与加氢裂解产物以的关系，表明褐煤含有较多的烷基侧链，有利于生成气态烃，而褐煤中含氧官能团（羧基等）与氢发生反应，可抑制二氧化碳析出，提高有效碳转化率；（3）研究了氢氧化钙与不同碱金属（Li, Na和K）在煤焦水蒸汽气化过程中的协同催化，揭示了钙与钾配对所具有特殊的协同催化作用；（4）利用自制的独特竖式反应器，研究了以碳酸钾为催化剂的煤焦水蒸汽加压气化过程，发现在消除外扩散和加压（水蒸汽分压0.15Mpa、）条件下，煤焦可在750°C下、5分中内气化完毕，远快于文献中通常观察到的煤焦催化气化速率，在此实验基础上，建立了煤焦水蒸汽加压气化的本征动力学方程；（5）研究了煤焦催化加压气化产生的气体组成，表明加压有利于产生甲烷气体，但在纯水蒸汽条件下，甲烷产率很低，以H2O/H2混合气作为气化剂，可大幅提高甲烷产率，但氢气的气化活性较低，控制混合气比例对于协调气化速率和甲烷生成之间的平衡很关键。上述研究推进了对煤加压催化气化的化学过程及调控因素的认识、积累了开发煤制甲烷新工艺的研究基础。