具有形貌可控微纳结构催化层的微反应器光催化转化CO2制甲醇的多相传递及转化研究

In order to improve the performance of photocatalytic reactors for conversion CO2 into the fuel and promote the development of reducing emissions of CO2 and solar energy utilization technology, the micro-nano structure photocatalytic layer of controllable morphology will be grown in the microchannel reator in this program which is put forward for converting CO2 of gas phase into methanol efficiently by using the photocatalytic method. For the problems of mass transfer, flow and photocatalytic conversion in the microchannel reactor with micro-nano structure photocatalytic layer of controllable morphology, the research of physical adsorption process and conversion characteristics of reactants in the micro-nano structure catalytic layer will be carried out, and the mass transfer process, flow and conversion characteristics of single-phase and two-phase flow with photocatalytic reaction boundary in the microchannel reactor will also be studied. The inner relationship between different morphology of catalytic layer and photocatalytic activity of CO2 will be confirmed in this program based on the study of physical adsorption, transfer and conversion process of reactants in the catalytic layer. And the theory model between different morphology of catalytic layer and photocatalytic conversion rate will be established. On this basis, the systematic experimental and theoretical research aimed at the mass transfer behavior, flow and conversion mechanism with the photocatalytic boundary in the microchannel reactor will be carried out. The single-phase reactants mass transfer rule and two-phase flow mechanism with the photocatalytic boundary of microchannel reactor will be studied. The coupling relationship between mass transfer, two-phase flow and photocatalysis will be revealed. The theory model of two-phase flow and mass transfer with the photocatalytic boundary of microchannel reactor will be established. All above work will lay a good theoretical basis for the future industrial application of photocatalytic technology to convert CO2.

为了提高光催化转化CO2制取燃料的反应器性能，促进CO2减排和太阳能利用技术的发展，本项目提出具有形貌可控的微纳结构光催化层的微通道反应器结构形式，以实现高效的光催化转化气相CO2生成可燃性物质-甲醇。针对具有形貌可控微纳结构光催化层的微通道反应器内物质传递、流动及转化问题，分别开展：微纳结构催化层内反应物质的扩散吸附和转化特性的研究，以及具有光催化反应边界微通道内单相和两相流体的物质传递、流动及转化特性的研究。从而确定不同形貌微纳结构催化层与光催化CO2活性之间的内在关系，建立催化层形貌结构与催化转化速率之间的理论模型；揭示具有光催化反应边界微通道内单相反应物质的传递机理和流动特性以及气液两相流的流动机理；确定气液两相流物质传递、两相流动与光催化反应之间的耦合关系；建立具有光催化反应边界微通道内两相流流动与物质传递转化的理论模型。最终为微通道光催化CO2技术的工业化应用奠定理论基础。

本项目提出在微通道反应器壁面构筑形貌可控的微纳结构光催化层，以针对光催化转化CO2为可燃性物质的过程进行深入研究，期望能够实现CO2的高效减排以及碳元素的循环利用。首先，针对平板微反应器内不同形貌结构催化层（主要是Cu2+掺杂和CdS-Cu2+敏化处理的一维TiO2纳米棒阵列薄膜以及进行石墨烯掺杂和CdS/ZnS复合量子点敏化处理的一维TiO2纳米管阵列薄膜）的光催化转化气相CO2特性进行实验研究。发现在紫外光和可见光下纳米管阵列催化层的产物产量均高于纳米棒阵列。在紫外光下，当氧化石墨烯的掺杂浓度为0.2mg/mL时，制备出的RGO-TNTA性能最佳。而在可见光下，经过10次SILAR循环得到的CdS/ZnS-TNTA催化剂的光催化转化CO2性能最好。并且对于任一种催化剂条件下的反应，均存在一个最佳反应物质流量。其次，采用数值模拟的方法，通过对比经典L-H平衡吸附模型和自定义动力学传质模型，发现在平板微反应器内光催化还原气相CO2的过程中，反应物质的传质过程是影响反应速率的主导因素，并建立了相应的传质特性关联式。而当在平板微反应器的顶部加入倒置凸台后，反应物质的传递过程得到强化，其不同入口流量下的产物产量相对于平板微反应器都有所提高，并且合理的凸台结构参数能进一步促进光催化转化CO2反应的进行。最后，通过对底面负载微纳结构催化层的T型微通道反应器内气液两相流光催化还原CO2过程的研究，确定了气液两相流物质传递、两相流动与光催化反应之间的耦合关系。发现相比于单相流态，当反应物为气液两相状态时，光催化反应速率更快。当控制反应物质两相流动状态为弹状流时，产物产量随着气相入口流量的增加相应提高；而随着液相入口流量的增大，产物产量先增大后减小。此外，对于T型微通道反应器，较小的入口截面尺寸更有利于反应的进行。综合上述结果，本研究有效提升了光催化CO2的转化效率，并为微通道光催化CO2技术的工业化应用奠定了一定理论基础。