Instituto de Química Física Rocasolano, CSIC , Serrano 119 , E-28006 Madrid , Spain.
Instituto de Tecnología Química , Universitat Politècnica de València-CSIC , Avenida de los Naranjos, s/n , Valencia 46022 , Spain.
Langmuir. 2018 Oct 30;34(43):12739-12750. doi: 10.1021/acs.langmuir.8b02326. Epub 2018 Oct 19.
In this paper, we present a comparative study of the adsorption behavior of short chain alcohols (pure and in aqueous solution) into silicalite-1 (MFI-type zeolite) and silicalite-2 (MEL-type zeolite). For quite some time, silicalite-1 has been the reference material to address the problem of adsorptive-based separation, mostly for hydrocarbon mixtures. Interestingly, being structurally close to silicalite-1, adsorption studies using silicalite-2 are scarce and to the best of our knowledge, a comparative study of their behavior for alcohol-water mixtures has not been published to date. We have here resorted to molecular simulation techniques to analyze the adsorption and diffusion phenomena in both zeolites at 25 and 50 °C for pure methanol, ethanol, 1-butanol, and water, and for some relevant compositions of alcohol/water mixtures. In addition to the dilute regime in the mixture, our study ranges from intermediate alcohol concentrations to alcohol-rich phases, relevant to alcohol purification processes. Besides, we have performed volumetric and calorimetric measurements of single-component adsorption of alcohols in pure silica MEL zeolite, which were used to validate the model potentials used in the simulations. We observe that the zigzag channels of MFI zeolite are most likely responsible for its somewhat higher affinity for alcohols. This leads to higher adsorption selectivities when compared to those of MEL zeolite. We have also found that the choice of water model strongly conditions water coadsorption into the zeolites and subsequently the predictions of the adsorbent's selectivity in alcohol/water systems. Despite considerable differences for adsorbed pure components, diffusivities of alcohol and water adsorbed from mixtures are relatively similar, as a consequence of the strong hydrogen bonds between hydroxyl groups and water.
本文对短链醇（纯物质和水溶液）在 silicalite-1（MFI 型沸石）和 silicalite-2（MEL 型沸石）中的吸附行为进行了比较研究。在相当长的一段时间里，silicalite-1 一直是解决吸附分离问题的参考材料，主要针对烃类混合物。有趣的是，silicalite-2 在结构上与 silicalite-1 接近，但使用 silicalite-2 进行吸附研究却很少，据我们所知，迄今为止尚未发表过关于其用于醇-水混合物的行为的比较研究。我们在这里采用分子模拟技术，在 25 和 50°C 下分析了两种沸石中纯甲醇、乙醇、1-丁醇和水以及一些相关醇/水混合物组成的吸附和扩散现象。除了混合物中的稀相外，我们的研究范围还包括从中等醇浓度到富醇相，这与醇的纯化过程有关。此外，我们还对纯硅 MEL 沸石中醇的单组分吸附进行了体积和量热测量，这些测量结果用于验证模拟中使用的模型势。我们观察到 MFI 沸石的之字形通道很可能是其对醇具有较高亲和力的原因。这导致其对醇的吸附选择性高于 MEL 沸石。我们还发现，水模型的选择强烈影响水在沸石中的共吸附，进而影响醇/水体系中吸附剂选择性的预测。尽管吸附纯物质的差异很大，但从混合物中吸附的醇和水的扩散系数相对相似，这是由于羟基和水之间的氢键很强。
