Several deep eutectic solvents (DESs) have been recently developed for extraction of hydrogen sulfide from natural gas. Among these newly designed DESs, a combination of caprolactam and tetrabutylammonium halides at a molar ratio of 1:1, as the DESs, has the highest desulfurization efficiencies. In this work, we explored the formation of caprolactam-based DESs using molecular dynamics (MD) simulations and ab initio computations. The results, based on the time average of the equilibrated production run of MD simulations, revealed ∼15% decrease in the ionic interactions of tetrabutylammonium halides and, more interestingly, ∼92% decrease in the hydrogen bonds between caprolactam, thereby explaining the strong depression in the melting point observed in experiments during the formation of the DES. Next, simulations of the DES with mixtures of methane and hydrogen sulfide were performed to mimic the natural gas desulfurization process. Efficient absorption of hydrogen sulfide from natural gas under different operating conditions (5000 and 10,000 ppm H₂S, at 25 and 60 °C, and at 1 and 10 bar) can be observed from the simulations. The results further unveiled strong interactions between the anions of the DESs and hydrogen sulfide, with interaction energies 10-fold higher than those of methane/hydrogen sulfide, explaining the mechanism of desulfurization by these DESs. Additionally, two different DESs composed of monoethanolamines/methyltriphenylphosphonium bromide and urea/choline chloride were used to evaluate and compare their capacity to absorb hydrogen sulfide; however, we observed that the caprolactam-based DESs are highly efficient, particularly at low temperatures, low pressures, and low fuel/DES mole ratios. As the existing literature covers only experiments on the removal of hydrogen sulfide via the DESs, the simulations presented herein provide insights into the mechanism of absorption, thereby paving a way forward for better design of the DESs.

中文翻译：

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探索基于己内酰胺的深共熔溶剂的形成及其在天然气脱硫中的应用的综合计算分析

最近已经开发了几种深共熔溶剂（DES），用于从天然气中提取硫化氢。在这些新设计的DES中，己内酰胺和卤化四丁基铵的摩尔比为1：1的DES，具有最高的脱硫效率。在这项工作中，我们使用分子动力学（MD）模拟和从头算来探索基于己内酰胺的DES的形成。根据MD模拟平衡生产运行的时间平均值得出的结果表明，卤化四丁基铵的离子相互作用降低约15％，更有趣的是，己内酰胺之间的氢键降低约92％，从而解释了强烈的抑郁在DES形成过程中在实验中观察到的熔点。下一个，用甲烷和硫化氢的混合物对DES进行了模拟，以模拟天然气的脱硫过程。在不同的运行条件下（5000和10,000 ppm H，从天然气中有效吸收硫化氢₂可以从模拟中观察到25°C和60°C以及1和10bar的S. 结果进一步揭示了DES的阴离子与硫化氢之间的强相互作用，其相互作用能比甲烷/硫化氢高10倍，说明了这些DES脱硫的机理。另外，使用两种不同的由单乙醇胺/甲基三苯基溴化and和尿素/氯化胆碱组成的DES来评估和比较它们吸收硫化氢的能力。但是，我们观察到己内酰胺基DES是高效的，特别是在低温，低压和低燃料/ DES摩尔比的情况下。由于现有文献仅涵盖有关通过DES去除硫化氢的实验，因此本文提供的模拟可提供有关吸收机理的见解，