预氧化耦合高温闪速活化对生物质焦的改性机理研究

In order to improve the tar conversion efficiency in biomass syngas with the catalysis of biochar, we put forward the method of pre-oxidation coupling high- temperature-flash activation for biochar modification. Pre-oxidation pyrolysis will inhibit the pyrolysis tar blocking at the surface of char pore and promote the formation of active surface oxygenic functional groups. Further, through transient high temperature activation at oxidative atmosphere, the surface oxygenic functional groups created at pre-oxidation process will dissociate from the char pore surface, giving rise to the opening of closed pore and the increasing of surface area. What's more, transient activation will not lead to the consumption of carbon skeleton by oxidation. Aiming at revealing the key scientific question 'the reconstruction and dissociation mechanism of surface oxygenic functional groups' for biochar modification, we intend to combine the in situ FTIR surface characterization techniques and quantum chemistry theory to establish the detail molecule reaction mechanism of biochar activation. At the same time, wire-mesh reactor, with the characteristics of high heating rate and small thermal inertia, will be used to investigate the coupling mechanism of pre-oxidation and high temperature activation in biochar modification mechanism. A micro reactor will be set up to investigate the catalytic mechanism of activated biochar on the conversion of PAHs. This project proposes biochar modification method, which is expected to achieve the conversion and reduction of tar with high efficiency at a low cost. This work will provide theoretical support for the breaking through of key problem and the development of biomass gasification commercial application.

以生物质焦高效脱除气化焦油为目标，提出预氧化耦合高温闪速活化的生物质焦改性方法。通过预氧化热解抑制焦油对孔隙的堵塞，在焦表面生成高活性的含氧官能团；再通过有氧气氛下的高温闪速活化，使焦预氧化时生成的含氧官能团迅速脱落打开闭孔增大比表面积，同时又不至于长时间地停留在高温环境下消耗碳骨架结构。针对该改性方法中"含氧官能团的重构与脱落机制"这一关键科学问题，采用原位红外表征技术与量子化学计算模拟相结合，构建详细的分子反应机理；利用热网反应器升温速率快，热惯性小的特点，分析预氧化与高温闪速活化作用的耦合机制对焦物理化学性质的改性机理；搭建微反应器，研究并揭示活化生物质焦对多环芳烃催化转化的作用机理。本项目提出的生物质焦改性方法可望实现焦油的高效低成本脱除及转化，将为突破生物质气化的商业化应用技术瓶颈奠定坚实的理论基础。

针对生物质气化过程中焦油脱除这一瓶颈问题，本项目提出“预氧化耦合高温闪速活化”的生物质焦改性方法，以期实现高效的焦油异相脱除。预氧化条件下生物质焦具有更发达的孔隙结构，且焦表面生成高活性的含氧官能团；闪速高温活化过程使焦预氧化时生成的含氧官能团迅速脱落形成活性位，为焦油异相脱除提供反应位点。针对焦表面含氧官能团的重构与脱落、焦孔隙结构的改良与芳烃类焦油的异相脱除三个层面，本项目采用理论计算与实验表征相结合的方法逐步展开研究，揭示了预氧化耦合高温闪速活化方法改性生物质焦的机理。首先，本项目使用原位漫反射红外（DRIFTS）表征技术，对不同氧浓度和温度条件下生物质三组分和稻秆预氧化成焦过程进行了动态分析，着重考察了其表面含氧官能团的演变规律，并结合量子化学计算，分析了含氧官能团在焦炭分子骨架上重构与脱落的反应路径；其次，在热重实验台上，通过改变气氛、温度和升温速率等主要影响因素，并采用各类表征手段（SEM、FTIR、BET）分析了各个反应条件对产物析出特性、焦表观形貌结构、焦微观孔隙结构、焦表面官能团分布等理化性质的影响，较为全面地总结了预氧化和闪速活化过程的反应规律；再次，在搭建的微反应实验台上，选择了具有代表性的实验条件下制备的生物质焦样品，对其在不同温度和气氛下脱除甲苯和萘两种焦油模型化合物的效果进行了定性与定量分析，总结了生物质焦脱除芳香烃类焦油的一般规律与转化机理，验证了预氧化耦合高温闪速活化对异相焦油脱除效果的显著改良。本项目提出的生物质焦改性方法有望推进生物质气化焦油的高效低成本脱除及转化，可以为突破生物质气化的商业化应用技术瓶颈奠定坚实的理论基础。