Vargas-Bustamante Jaquebet, Salcedo Roberto, Balmaseda Jorge
Departamento de Polímeros, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, Coyoacán, Ciudad de México 04510, Mexico.
Materials (Basel). 2023 Oct 7;16(19):6587. doi: 10.3390/ma16196587.
Ethylene production has a negative environmental impact, with its separation step being one of the major contributors of pollution. This has encouraged the search for energy-efficient alternatives, among which the adsorptive separation of ethane and ethylene stands out. ZIF-8 is a molecular sieve that is potentially useful for this purpose. It is selective to ethane, an exceptional property that remains unexplained. Furthermore, the adsorption of ethane and ethylene above room temperature, such as at steam cracking process outlet temperatures, has not been addressed either. This work aims to fill this knowledge gap by combining experiments at very low volumetric fillings with density-functional theory modelling methods. Adsorption isotherms of ethane and ethylene on ZIF-8 at pressures below 0.3 bar and 311 K, 333 K, and 363 K were measured using zero-length column chromatography. The low-pressure domain of the isotherms contains information on the interactions between the adsorbate molecules and the adsorbent. This favors the understanding of their macroscopic behavior from simulations at the atomic level. The isosteric enthalpy of adsorption of ethane remained constant at approximately -10 kJ/mol. In contrast, the isosteric enthalpy of adsorption of ethylene decreased from -4 kJ/mol to values akin to those of ethane as temperature increased. ZIF-8 selectivity to ethane, estimated from ideal adsorbed solution theory, decreased from 2.8 to 2.0 with increasing pressure up to 0.19 bar. Quantum mechanical modelling suggested that ethylene had minimal interactions with ZIF-8, while ethane formed hydrogen bonds with nitrogen atoms within its structure. The findings of this research are a platform for designing new systems for the adsorptive separation of ethane and ethylene and thus, reducing the environmental impact of ethylene production.
乙烯生产对环境有负面影响，其分离步骤是污染的主要来源之一。这促使人们寻找节能替代方法，其中乙烷和乙烯的吸附分离备受关注。ZIF-8是一种可能适用于此目的的分子筛。它对乙烷具有选择性，这一特殊性质尚无合理解释。此外，在室温以上，如蒸汽裂解工艺出口温度下，乙烷和乙烯的吸附情况也未得到研究。本研究旨在通过结合极低体积填充率下的实验与密度泛函理论建模方法来填补这一知识空白。采用零长度柱色谱法测量了在压力低于0.3 bar以及温度为311 K、333 K和363 K时乙烷和乙烯在ZIF-8上的吸附等温线。等温线的低压区域包含了吸附质分子与吸附剂之间相互作用的信息。这有助于从原子水平的模拟来理解它们的宏观行为。乙烷的等量吸附焓在约-10 kJ/mol处保持恒定。相比之下，随着温度升高，乙烯的等量吸附焓从-4 kJ/mol降至与乙烷相近的值。根据理想吸附溶液理论估算，ZIF-8对乙烷的选择性在压力升至0.19 bar时从2.8降至2.0。量子力学建模表明，乙烯与ZIF-8的相互作用极小，而乙烷在其结构内与氮原子形成了氢键。本研究结果为设计用于乙烷和乙烯吸附分离的新系统提供了平台，从而减少乙烯生产对环境的影响。
