水对<i>原位</i>ATR-FTIR光谱研究Na-ZSM-5沸石中甲烷和二氧化碳吸附的影响,The Journal of Physical Chemistry C

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水对原位ATR-FTIR光谱研究Na-ZSM-5沸石中甲烷和二氧化碳吸附的影响
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-12-15 00:00:00 , DOI: 10.1021/acs.jpcc.6b09224
Lindsay Ohlin ₁ , Vladimir Berezovsky ₁ , Sven Öberg ₁ , Amirfarrokh Farzaneh ₁ , Allan Holmgren ₁ , Mattias Grahn ₁

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甲烷与水和二氧化碳等污染物一起是沼气和天然气中的主要成分。因此，将甲烷与这些污染物分离是升级过程中的重要一步。沸石吸附剂和沸石膜具有成为提高沼气和天然气成本效益的候选材料的巨大潜力，在这两种应用中，了解竞争性吸附的性质对于进一步开发沸石材料的性能至关重要。在某种程度上已经研究了甲烷和二氧化碳在沸石中的二元吸附，但是对水的影响的研究却少得多。在目前的工作中，就地使用ATR（衰减全反射）-FTIR（傅立叶变换红外）光谱研究了在各种气体成分和温度下高硅Na-ZSM-5沸石膜中二元混合物中水/甲烷和水/二氧化碳的吸附。从记录的红外光谱确定所有物种的吸附浓度，并将实验值与使用理想吸附溶液理论（IAST）预测的值进行比较。在较低的温度（35、50和85°C）下，IAST能够预测水和甲烷的二元吸附，而IAST预测的值与最高温度（120°C）下的实验数据有所不同。对于水和二氧化碳的二元吸附，IAST无法准确预测吸附值。这种差异归因于亲水位点上高硅MFI形成簇中水的特殊吸附行为。但是，预测值确实遵循与实验值相同的趋势。确定了吸附选择性，发现H在低温下，₂ O / CH _4的吸附选择性随气相中水含量的增加而降低，而在较高温度下，选择性则随其含量的增加而增加。在所有温度下，H ₂ O / CO _2的吸附选择性都随着水含量的增加而增加。

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Effect of Water on the Adsorption of Methane and Carbon Dioxide in Zeolite Na-ZSM-5 Studied Using in Situ ATR-FTIR Spectroscopy

Methane is the main component in biogas and natural gas along with contaminants such as water and carbon dioxide. Separation of methane from these contaminants is therefore an important step in the upgrading process. Zeolite adsorbents and zeolite membranes have great potential to be cost-efficient candidates for upgrading biogas and natural gas, and in both of these applications, knowing the nature of the competitive adsorption is of great importance to further develop the properties of the zeolite materials. The binary adsorption of methane and carbon dioxide in zeolites has been studied to some extent, but the influence of water has been much less studied. In the present work, in situ ATR (attenuated total reflection)–FTIR (Fourier transform infrared) spectroscopy was used to study the adsorption of water/methane and water/carbon dioxide from binary mixtures in a high-silica Na-ZSM-5 zeolite film at various gas compositions and temperatures. Adsorbed concentrations for all species were determined from the recorded IR spectra, and the experimental values were compared to values predicted using the ideal adsorbed solution theory (IAST). At lower temperatures (35, 50, and 85 °C), the IAST was able to predict the binary adsorption of water and methane, whereas the values predicted by the IAST deviated from the experimental data at the highest temperature (120 °C). For the binary adsorption of water and carbon dioxide, the IAST could not predict the adsorption values accurately. This discrepancy was assigned to the particular adsorption behavior of water in high-silica MFI forming clusters at hydrophilic sites. However, the predicted values did follow the same trend as the experimental values. The adsorption selectivity was determined, and it was found that the H₂O/CH₄ adsorption selectivity was decreasing with increasing water content in the gas phase at low temperatures whereas the selectivity was increasing at higher temperatures. The H₂O/CO₂ adsorption selectivity was increasing with increasing water content at all temperatures.

更新日期：2016-12-15

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