不锈钢阳极表面氧化膜对厌氧消化过程原位电催化脱硫的作用机理研究

Hydrogen sulfide removal or desulfurization process in biogas produced from the anaerobic digestion of livestock operation wastes is a key step to prepare a value-added product of biomethane, i.e., renewable natural gas as a feedstock for compressed natural gas and liquefied natural gas. This project is based on an in-situ desulfurization technology to electrically oxidize and remove hydrogen sulfide during anaerobic digestion by a novel anode material, a surface-oxidized stainless steel (SOSS) as an electrocatalyst. The study aims to elucidate the mechanisms of SOSS surface film in sulfide electrocatalysis conversion and the effects of operating conditions on the efficiency and stability of the electrocatalyst. The surface characterization by morphology analysis and composition analysis will reveal the active sites on the outer layer of the surface film before and after the operation of electrolysis cells where surface sulfidization occurs, and reveal the relationship between the reaction kinetics of aqueous sulfide removal and the surface composition. The study will then quantify the catalytic activity and electrochemical impedance of the inner layer of the surface film by surface interrogation electrochemical scanning microscopic analysis of surface film of different thicknesses and by determining the elemental composition of the inner layer after long-term operation through X-ray photoelectron spectroscopy analysis. The study will further establish quantitative relationship between the anodic overpotential, the physiochemical properties (pH and conductivity) of medium and the reaction kinetics of desulfurization and the stability of the anode materials through surface analysis and kinetics study. The project will provide a fundamental theory and process design principle for the electrochemical in-situ desulfurization based on surface oxidized stainless steel in anaerobic digestion, which will be critical in the sustainable treatment and utilization of livestock waste.

硫化氢脱除是沼气高值化利用的关键步骤之一，电化学脱硫技术可实现原位脱硫且无二次污染问题，有望取代吸收法和吸附法等常规脱硫技术。以钛基贵金属氧化物为代表的传统阳极，因制备工艺复杂、原料成本高而难以推广应用。申请人前期研究发现不锈钢阳极表面氧化膜具有良好的脱硫性能。本项目针对该新型阳极材料，研究其表面氧化膜在厌氧消化过程中的电催化脱硫作用机理。本研究拟通过表面成分与形貌分析及电化学极谱分析，探明不锈钢氧化膜表层的脱硫活性位点成分构成及主要脱硫产物；分析氧化膜内层厚度对脱硫活性位点丰度、分布梯度及电化学阻抗特性的影响，阐明其对脱硫动力学特性的影响机理；测定不同外加电压、沼液pH值和电导率下的产物动力学，在此基础上构建厌氧消化过程原位电催化脱硫作用的综合数学模型，并在反应器中进一步验证该模型。项目研究将为基于不锈钢阳极的原位脱硫设备研制提供理论基础和优化调控策略，促进畜禽粪污能源化利用。

沼气脱硫是生产生物天然气的重要步骤之一。商业化脱硫方法如吸收法和吸附法等常规技术手段需要搭建反应塔、频繁更换或再生吸收液及吸附剂，设备投资成本和运行维护成本较高且易造成二次污染。电催化氧化方法可控性强、无二次污染，易集成到厌氧消化系统实现原位脱硫，具有很强的应用前景。本项目针对表面氧化不锈钢高效电化学脱硫阳极材料，研究了其表面氧化膜电催化脱硫作用机理。针对不锈钢氧化膜对硫离子的电催化氧化作用机理与外加电压对脱硫动力学特性的影响规律两大关键科学问题，按照研究方案部署，取得了如下主要进展：（1）探明了电化学腐蚀时长对表面氧化不锈钢氧化膜三维结构与组分等界面特性及伏安响应与阻抗等电化学特性的影响规律；（2）构建了电化学腐蚀时长与表面氧化不锈钢阳极脱硫动力学模型参数间关系，揭示了外加电压对反应动力学及产物分布的影响规律，优化了表面氧化不锈钢阳极再生性能与运行稳定性；（3）试制优化了基于单原子镍负载氮掺杂石墨烯催化剂及磷化镍催化剂的不锈钢阳极；（4）验证了不锈钢阳极在典型场景中的应用效果。在节能减排及“碳达峰-碳中和”背景下，生产生物天然气的重要性更加突出。以畜禽粪污为原料制取的沼气中硫化氢浓度可达数千ppm，极易腐蚀破坏压缩机、储气罐、管道、发电机、内燃机等设备。硫化氢污染毒害问题广泛存在于养殖与粪污管理、市政污水管网、污水处理厂、食品加工厂等环境中，相应行业也有高效脱硫的技术需求。此外，在硫化氢传感检测、智慧养殖环境感知等领域也有潜在的应用前景。该研究为进一步开发优化高效电化学脱硫技术提供了理论与技术基础。