Temperature lowering of liquid nitrogen via injection of helium gas bubbles improves the generation of parahydrogen-enriched gas

IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Magnetic Resonance in Chemistry Pub Date : 2024-01-03 DOI:10.1002/mrc.5423
James Daley, Joseph Siciliano, Vincent Ferraro, Elodie Sutter, Adam Lounsbery, Nicholas Whiting
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Abstract

The para spin isomer of hydrogen gas possesses high nuclear spin order that can enhance the NMR signals of a variety of molecular species. Hydrogen is routinely enriched in the para spin state by lowering the gas temperature while flowing through a catalyst. Although parahydrogen enrichments approaching 100% are achievable near the H2 liquefaction temperature of 20 K, many experimentalists operate at liquid nitrogen temperatures (77 K) due to the lower associated costs and overall simplicity of the parahydrogen generator. Parahydrogen that is generated at 77 K provides an enrichment value of ~51% of the para spin isomer; while useful, there are many applications that can benefit from low-cost access to higher parahydrogen enrichments. Here, we introduce a method of improving parahydrogen enrichment values using a liquid nitrogen-cooled generator that operates at temperatures less than 77 K. The boiling temperature of liquid nitrogen is lowered through internal evaporation into helium gas bubbles that are injected into the liquid. Changes to liquid nitrogen temperatures and parahydrogen enrichment values were monitored as a function of helium gas flow rate. The injected helium bubbles lowered the liquid nitrogen temperature to ~65.5 K, and parahydrogen enrichments of up to ~59% were achieved; this represents an ~16% improvement compared with the expected parahydrogen fraction at 77 K. This technique is simple to implement in standard liquid nitrogen-cooled parahydrogen generators and may be of interest to a wide range of scientists that require a cost-effective approach to improving parahydrogen enrichment values.

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通过注入氦气泡降低液氮温度,可改善富含对氢的气体的生成。
氢气的对位自旋异构体具有很高的核自旋阶次,可以增强各种分子物种的核磁共振信号。在氢气流经催化剂时,通过降低气体温度,可使氢气常规富集为对位自旋态。虽然在 20 K 的氢气液化温度附近可以实现接近 100% 的对位氢富集,但由于相关成本较低且对位氢发生器总体简单,许多实验人员在液氮温度(77 K)下进行操作。在 77 K 温度下生成的对氢提供了约 51% 的对位自旋异构体富集值;虽然有用,但许多应用可以从低成本获取更高的对氢富集值中获益。在此,我们介绍一种利用温度低于 77 K 的液氮冷却发生器提高对氢富集值的方法。液氮的沸腾温度通过内部蒸发进入注入液体的氦气泡而降低。液氮温度和对氢富集值的变化随氦气流速的变化而受到监测。注入的氦气泡将液氮温度降到了约 65.5 K,副氢富集度高达约 59%;与 77 K 时的预期副氢分数相比,提高了约 16%。这种技术在标准液氮冷却副氢发生器中实施起来非常简单,可能会引起需要以经济有效的方法提高副氢富集值的广大科学家的兴趣。
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来源期刊
CiteScore
4.70
自引率
10.00%
发文量
99
审稿时长
1 months
期刊介绍: MRC is devoted to the rapid publication of papers which are concerned with the development of magnetic resonance techniques, or in which the application of such techniques plays a pivotal part. Contributions from scientists working in all areas of NMR, ESR and NQR are invited, and papers describing applications in all branches of chemistry, structural biology and materials chemistry are published. The journal is of particular interest not only to scientists working in academic research, but also those working in commercial organisations who need to keep up-to-date with the latest practical applications of magnetic resonance techniques.
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