CaO固硫过程中Ca^(2+)在CaSO_4产物层内扩散的研究

Ca^(2+) Cation Diffusion through CaSO_4 Product Layer during Sulfur Retained Reaction with CaO

应用标记实验技术 ,研究CaO固硫反应过程中产物层扩散控制阶段的反应机理 .利用扫描电镜和反射式光学显微镜 ,对压制烧结并带有Pt标记的CaO样品在固硫反应前后的形貌变化观察 ,结果表明 :经过较长时间的固硫反应后 ,在Pt标记层外表面形成一层覆盖物 ,XRD分析结果证明该覆盖物是CaSO4.利用电化学综合测试仪测量了CaO及CaSO4在高温下的电导率 ,结果表明在 10 0 0℃时CaSO4的电导率达到了 10 -3 数量级 ,说明在高温下CaSO4内Ca2 + 有较高的离子迁移特性 .根据标记实验、电导率测试的结果和CaO掺杂体系的固硫动力学数据的分析认为 :CaO固硫反应在后期的扩散层控制阶段的主要反应是Ca2 + 通过CaSO4产物层扩散至CaSO4外表面与SO2 和O2 进行反应 ,生成CaSO4,而不是SO2 和O2 气体通过CaSO4产物层向内扩散 ,在颗粒内部与CaO发生固硫反应 .

Sintered CaO tablets covered with platinum marker on the surface were exposed to simulated coal gas containing SO2 at 1200 degreesC in a tube reactor. The SEM micrograph and reflex optical micrograph were used to observe morphology changes of the tablets. After the CaO tablet covered with platinum marker being reacted for 120 h, a thick layer of product CaSO4 formed on the surface of the platinum marker. The layer of product CaSO4 is compact. At high temperature, the conductivity of CaSO4 reached 3.5 x 10(-3) S (.) cm(-1). This means that Ca2+ ions in CaSO4 have higher mobility. A new reaction mechanism of sulfur retained by CaO is suggested as follows: In the diffusion stages of CaO desulphurization, Ca2+ ion in CaO diffuses outward through the sulfate product layer to the interface of CaSO4 and gas to form CaSO4 with O2-, O-2 and SO2, rather than that SO2, O-2 diffuse through the sulfate product layer into the interface of CaSO4 and CaO to react with CaO.