Abstract:

With kaolin-SiO₂ as silicon source, lithium orthosilicate sorbents were prepared by impregnation- precipitation method. The crystal structures and morphologies were characterized by XRD and SEM, respectively. The CO₂ absorption performance was studied by a thermogravimetric analyzer. The results indicated that the adsorbing capacity of kaolin-Li₄SiO₄ was higher than SiO₂-Li₄SiO₄ at 350-700℃ in comparison with Li₄SiO₄ prepared with commercial SiO₂. The high purity Li₄SiO₄ can be prepared by the impregnation-precipitation method successfully. The maximum adsorption of Li₄SiO₄ made by impregnation-precipitation method got up to 35.7% (mass) (704℃), which was 5.9% (mass) higher than Li₄SiO₄ made by solid method. The CO₂ chemisorption produced directly over the Li₄SiO₄ particles was the limiting step of the whole reaction process when the temperature was lower than 600℃. The CO₂ chemisorption process controlled by diffusion process was the limiting step of the whole reaction process when the temperature was higher than 650℃. The lithium diffusion rate of samples made by impregnation-precipitation method was nearly double for samples made by solid method. The rate of CO₂ chemisorption produced directly over the Li₄SiO₄ particles made by impregnation-precipitation method was higher.

Key words: kaolin, lithium orthosilicate, impregnation-precipitation method, carbon dioxide, kinetic

摘要：

以煤系高岭土为硅源,采用浸渍沉淀法制备硅酸锂吸附剂。采用X射线衍射仪、扫描电子显微镜分别表征和分析了样品的结构特征和形貌特征,并使用差热-热重联用分析仪研究了硅酸锂吸附CO₂的性能。实验结果表明,与以市售-SiO₂为硅源制备的硅酸锂相比,高岭土-硅酸锂在较低温度下有明显的吸附CO₂优势;采用浸渍沉淀法可成功制备出纯度较高的硅酸锂,最大吸附量为35.7%(704℃)(文中吸附量均为质量分数),高出固相法5.9%;采用双指数模型对硅酸锂吸附CO₂进行动力学分析,温度低于600℃时,表面化学反应过程是整个反应过程的控制步骤。高于650℃,锂迁移成为控制步骤。在吸附CO₂的过程中,浸渍沉淀法制备的样品锂迁移速率是固相法的1.5～2.2倍,低于650℃时的吸附,浸渍沉淀法的样品表面化学反应速率皆高于固相法。

关键词: 高岭土, 正硅酸锂, 浸渍沉淀法, 二氧化碳, 动力学