基于煤矸石制备沸石/炭分子筛及其在CH4/N2吸附分离中的应用

Development and integrative utilization of coal bed gas is important for reducing green house gas emission, minimizing environmental pollution, relieving energy shortage and decreasing coal mine accidents. But it is a crucial problem how to concentrate and purify methane from CH4/N2 by pressure swing adsorption. The new zeolite/carbon molecular sieve composite with double micropore structures and surface properties is prepared from elutrilithe as main raw material and pitch as binder, which show high N2 kinetic adsorption selectivity and N2 equilibrium adsorption selectivity. The adsorption kinetics of gas molecules depends on the size, shape and electrical properties of the adsorbate, leading to specific interactions with the adsorbent. By controlling the ratio of raw material, synthesis parameters, ion-exchange and surface modification, the micropore structure and surface properties of the composite materials are adjusted finely to enhance separation ability for CH4/N2. The data obtain from CH4 and N2 isothermal adsorption on the composite materials is simulated with Langmuir, Freundlich, Langmuir-Freundlich adsorption models. Based on the analysis of fitting parameters and adsorption heat calculated, the relevant thermodynamic parameters are obtained. The Fick model is adopted to simulate the adsorption kinetics data from the composite materials, the diffusion coefficients of CH4 and N2 are obtained, while the optimum separation conditions are obtained, and the separation mechanism of the composite materials is clarify. In addition, the breakthrough curves of the pure CH4 and N2 and their mixture are determined on the fixed adsorption bed. Base on the data of breakthough curves, the CH4 yield is be calculated. Study the effects of synthesis parameters, micropore structure and surface properties, adsorption/desorption and diffusion behavior on the separation ability for CH4/N2 and the CH4 yield, the high efficiency adsorbent for PSA are obtained, and the basis data is provided for the practical application of the zeolite/ carbon molecular sieve composite material.

本项目旨在研究变压吸附技术提浓煤层气中甲烷的核心难题-CH4/N2的分离。为解决炭分子筛存在N2动力学选择性与CH4优先吸附的矛盾；沸石具有N2平衡选择性但吸附容量低等问题，本项目采用煤矸石和沥青粉为原料设计合成具有N2动力学选择性和N2平衡选择性的新型沸石/炭分子筛复合材料。通过碳沉积对炭分子筛微孔孔口进行精细调控，使CH4扩散活化能增加，扩散速率降低，提高CH4/N2动力学分离效应；通过离子交换调变沸石孔口尺寸和静电作用，提高N2吸附选择性；通过表面改性，降低表面亲烃性，降低CH4吸附能力，实现CH4/N2的高效分离。研究CH4和N2的吸附/脱附动力学、热力学和穿透曲线，利用吸附模型拟合计算吸附热、活化能等参数；建立复合材料的制备条件-孔结构和表面性质-气体吸附/脱附和扩散行为-CH4/N2分离效果-甲烷回收率间的内在联系；阐明复合材料的分离机理；为变压吸附提浓甲烷的工业应用奠定基础。

随着环境保护、能源结构改善及煤矿安全意识的提高，煤层气中甲烷的浓缩对于发展和提高其有效利用率和经济价值具有重要意义。煤层气的主要成分为CH4和N2，还含有少量CO2，CO2和N2的存在影响了甲烷的利用率。本项目采用由煤矸石和沥青粉为原料制备具有双重孔结构和表面性质的新型沸石/炭分子筛复合材料作为CH4/N2分离吸附剂，通过对复合材料的孔结构和表面性质的精细调节，优化复合材料对CH4/N2的吸附分离能力，建立复合材料的孔结构和表面性质与CH4/N2吸附分离性能之间的影响规律。.1.研究了活化时间对复合材料吸附性能的影响。结果表明，当活化时间达到24h时，复合材料BET比表面积、微孔比表面积和孔体积最大达到1018m2/g、868m2/g和0.765cm3/g，并且所含微孔（<2nm）量最多，有利于复合材料对CH4、N2平衡吸附量的增加，但CH4/N2的平衡吸附分离比未见显著提高。.2. 以酚醛树脂和葡萄糖作为沉积剂，研究碳沉积对复合材料的孔结构及吸附分离性能的影响。结果表明，随着碳沉积次数增加，酚醛树脂沉积后样品在0.45-0.55 nm的微孔相对含量增加，微孔分布更加均一，CH4/N2分离比提高至2.7。而葡萄糖沉积后则是在表面形成碳膜，CH4/N2分离比提高至3.0。.3. 以KCl、CaCl2和MgCl2溶液对复合材料进行离子交换后发现，经K+交换之后复合材料的微孔孔径分布集中在0.45-0.55nm范围内, CH4的吸附量达到14.6cm3/g，同时对CH4/N2的平衡分离比达到3.1。.4. 以不同铵盐溶液对复合材料进行表面改性，处理之后的复合材料晶体结构坍塌，微孔损失严重，表面碱性官能团减少，酸性官能团增加。经NH4Cl处理之后的复合材料其平衡选择性达到3.1且动力学选择性达到9.7。.5. 研究了碳含量及晶化时间对复合材料吸附性能的影响。结果发现，CH4吸附能力主要由活性炭的含量和微孔孔容决定，而N2吸附能力取决于X沸石的含量和表面性质。当碳含量为38.2%时，NH4Cl处理之后或晶化12h的复合材料CH4/N2分离比均达到3.4，且吸附容量较高分别为13.4mL/g和13.7mL/g，使得该样品有望应用于变压吸附分离CH4/N2.