Abstract:

In this work, porous carbon materials were prepared by using starch as carbon source. The starch first went through polymerization under hydrothermal condition and followed by a KOH activation. Their structures and adsorption performances for CO₂ and CH₄ were characterized and tested. The isosteric heat of adsorption and the selectivity toward CO₂/CH₄ were estimated based on the adsorption isotherms, and the effect of carbon material structure on its adsorption properties was also discussed. The results showed that the specific surface area and pore volume of the prepared materials increased as more KOH was used, and the pore size distribution also became wider. The derived carbon material had a high specific surface area of 2972 m²·g^-1, the H₂O adsorption isotherms of the materials showed an IV-typed isotherm. It was found that the CO₂ adsorption capacity of the materials mainly depended on the cumulative pore volume with pore size less than 0.8 nm. That is, the larger the ultramicro pore volume(Vd < 0.8 nm) of the material, the greater the CO₂ adsorption capacity at 298 K and 101325 Pa. The CO₂ adsorption amount on the C-KOH-1 was 4.2 mmol·g^-1 in our work, and the isosteric heat of CO₂ adsorption was higher than that of CH₄, the selectivity toward CO₂/CH₄ is in the range of 3.7-4.26. At the same time, the water adsorption isotherms of the materials were also examined and the results showed that the materials were mainly hydrophobic, which can be a potential adsorbent being used in the reality.

Key words: starch, porous carbon materials, carbon dioxide, isosteric heat of adsorption, selectivity, separation

摘要：

以淀粉为原料，使用水热法将其碳化后用活化剂KOH对其活化，制备了淀粉基多孔碳材料，并对其进行结构表征和CO₂/CH₄的吸附性能测试，计算吸附热以及材料对CO₂/CH₄的吸附选择性，讨论了碳材料结构对其吸附性能的影响。结果表明：在制备过程中，随着活化剂KOH用量比例的增大，所制得的材料其比表面积和孔容增大，其孔径分布也就越宽。所制得的碳材料其比表面积可达2972 m²·g^-1。这些淀粉基多孔碳材料对水蒸气的吸附等温线呈现出Ⅳ类等温线。所制备材料对CO₂吸附容量主要取决于其孔径小于0.8 nm的累积孔容（Vd < 0.8 nm）。材料的超微孔的孔容越大，其对CO₂吸附容量也越大。所制备的C-KOH-1材料在101325 Pa和298 K条件下，对CO₂的吸附量达到4.2 mmol·g^-1，其对CO₂的吸附热明显高于其对CH₄吸附热，其对CO₂/CH₄吸附选择性为3.7～4.26，同时本文通过对材料的水蒸气吸附等温线进行测试，结果表明所得材料主要表现为中等憎水性，这对材料在实际工况的应用奠定了基础。

关键词: 淀粉, 多孔碳材料, 二氧化碳, 吸附热, 选择性, 分离