【作者】 王永胜；

【导师】 郝广平；

【作者基本信息】 大连理工大学 ， 化学工艺， 2024， 博士

【摘要】 氢同位素在同位素标记及受控核聚变领域具有重大需求,因此氢同位素分离（D₂/H₂）引起广泛关注。D₂与H₂的沸点等物化性质极为相似,其主要区别仅为中子数不同导致的质量差异,分离难度大且能耗高。分子振动及扩散特性与其质量密切相关。在低温环境中,D₂和H₂存在量子化的振动态差异,这导致它们在窄纳米孔内的扩散速率存在明显差异,表现出动力学量子筛分效应。近年来,在多孔材料的孔结构精准调控方面取得了重要进展,为基于量子筛分效应的吸附分离D₂/H₂提供了有利条件。但在D₂/H₂分离上,多孔材料在吸附量、选择性、扩散动力学等方面仍需进一步提升。此外,对限域孔结构和D₂/H₂分离性能之间的关联规律仍不清晰。本论文以具有可调狭缝孔的炭分子筛为模型,研究了孔径尺寸、孔可及性与D₂/H₂分离性能之间的关联规律。研究内容如下:（1）针对孔径大小对D₂/H₂分离选择性影响认识不清的问题,基于热诱导分子印迹策略,通过改变前驱体中伯胺碳链长度,制备了一系列超微孔尺寸在4.0（?）至4.3（?）区间梯度可控的整体式炭分子筛。揭示了前驱体中不同碳链长度伯胺对衍生的炭分子筛超微孔结构调控的机制。通过使用不同尺寸的分子探针,探究炭分子筛中超微孔尺寸梯度变化差异。关联了孔径梯度差异对氢同位素吸附行为和分离性能的影响。在40 K和100k Pa下,具有4.0（?）超微孔的炭分子筛对D₂的静态吸附容量为10.1 mmol g^-1,D₂和H₂的吸附量比值为1.9。当狭缝型超微孔尺寸从4.3（?）减小至4.0（?）,炭分子筛在40 K时对D₂/H₂的动态选择性从3.0提升至10.1。（2）针对炭分子筛中量子筛分位点密度低且可及性差的问题,基于原位涂敷缩孔层策略,在二维希夫碱表面生长聚苯并噁嗪缩孔层,制备了具有高密度量子筛分位点的二维炭分子筛。通过改变前驱体合成过程中酚、醛、胺的比例可以调控希夫碱表面缩孔层的厚度,实现对二维炭分子筛超微孔尺寸的调控。进一步建立了炭分子筛中可及量子筛分位点密度的计算方法。探究炭分子筛中可及量子筛分位点密度对D₂/H₂分离性能的影响。通过优化合成条件,二维炭分子筛的可及量子筛分位点密度比商业炭分子筛高8.5倍,在77 K时,对D₂/H₂动态选择性达到1.4。基于低温双塔变压吸附耦合梯级提浓度工艺的Aspen模拟,可将1%D₂/99%H₂组成的原料气中的D₂提浓至93%。（3）针对极窄的狭缝孔对具有明显量子效应的氢同位素实际吸附分离效果不佳的问题,通过控制前驱体碳化温度,制备了不同超微孔结构的炭分子筛,探究了超微孔结构差异对D₂/H₂选择性吸附和脱附行为的影响。与极窄孔口的狭缝孔相比,具有分子扩散路径和丰富狭窄节点的狭缝孔在40 K下展现出更高的D₂选择性吸附性能。最优的炭分子筛的超微孔尺寸集中分布在0.6 nm,在40 K的动态条件下对D₂和H₂的吸附量差异为2.9 mmol g^-1,炭分子筛再生过程中D₂/H₂的热脱附选择性为10.0。此外,通过分子堵孔策略可以屏蔽在77 K下无选择性的超微孔,提高炭分子筛对氢同位素的动态选择性。更多还原

【Abstract】 The separation of hydrogen isotopes（D₂/H₂）attracts wide interest due to its significant demand such as isotope labeling and controlled nuclear fusion.However,the boiling point and other physicochemical properties of D₂ and H₂ are very similar.Their main difference lies solely in the mass difference resulting from the difference in neutron number,making their separation difficult and energy-intensive.Consequently,the separation of D₂/H₂ is difficult and energy-intensive.The molecular vibration and diffusion properties are closely related to their masses.Under low-temperature conditions and confined nanopore space,D₂/H₂ exhibits different quantized vibrational energy levels,leading to markedly different diffusion rates within the pores.The confined nanopore structure,such as the size and configuration,will affect the strength of the quantum effect for the isotope.In recent years,important progress has been made in the precise regulation of the pore structure of porous materials,which provides favorable conditions for the low-temperature adsorption separation of D₂/H₂ based on quantum effect.However,the adsorption capacity,selectivity,and diffusion kinetics still need to be further improved for D₂/H₂ separation.Meanwhile,the correlation between confined nanopore structures and D₂/H₂ selective separation performance remains unclear.Herein,we have designed and synthesized a series of porous carbon with tailored pore structures.Furthermore,the correlation between the structural parameters of the porous carbon and the D₂/H₂ separation performance was investigated.Specifically,the work includes the following parts:（1）To address the unclear understanding of the impact of pore size on D₂/H₂ separation selectivity,a series of monolithic carbon molecular sieves with gradient-controllable ultramicropores ranging from 4.0（?）to 4.3（?）were prepared by varying the length of the primary amine carbon chain in the precursor based on a thermally induced molecular imprinting strategy.The mechanism of regulating the ultramicroporous structure of carbon molecular sieves by different primary amine carbon chain lengths in the precursor was revealed.By using molecular probes of different sizes,the gradient variations in ultramicropore size within the carbon molecular sieves were explored.The correlation between pore size gradient differences and hydrogen isotope adsorption behavior and separation performance was established.At 40 K and 100 k Pa,the carbon molecular sieve with 4.0（?）ultramicropores exhibited a static adsorption capacity for D₂ of 10.1 mmol g^-1,with a ratio of D₂ to H₂ adsorption capacity as high as 1.9.When the slit-type ultramicropore size decreased from 4.3（?）to 4.0（?）,the dynamic selectivity of the carbon molecular sieve for D₂/H₂ at 40 K increased from 3.0 to 10.1.（2）To address the issues of low density and poor accessibility of quantum sieving sites in carbon molecular sieves,two-dimensional（2D）carbon molecular sieves with high-density quantum sieving sites were prepared by growing a polybenzoxazine pore-narrowing layer on the surface of 2D Schiff-base materials based on an in-situ coating pore-narrowing layer strategy.The thickness of the surface pore-narrowing layer could be regulated by changing the ratio of phenol,aldehyde,and amine during precursor synthesis process,thereby controlling the ultramicropore size of the 2D carbon molecular sieves.A calculation method for the density of accessible quantum sieving sites in carbon molecular sieves was established.The influence of carbon molecular sieves with different densities of accessible quantum sieving sites on D₂/H₂separation performance was explored.By optimizing the synthesis conditions,the accessible quantum sieving site density of the 2D carbon molecular sieve was 8.5 times higher than that of commercial carbon molecular sieves,achieving a dynamic selectivity of 1.4 for D₂/H₂ at 77K.Aspen simulations based on a low-temperature two tower pressure swing adsorption process coupled with a concentration-gradient enhancement step allowed the enrichment of D₂ from a feed gas composed of 1%D₂ and 99%H₂ to 93.1%.（3）To address the problems of poor practical separation of hydrogen isotopes with strong quantum effects by narrow micropores,carbon molecular sieves with different microporous structures were prepared by controlling the pyrolysis temperature of the precursors.The effects of different microporous structures on the selective adsorption and desorption behavior of D₂/H₂ at different temperatures were explored.Compared to slit pores with narrow orifices,slit pores with molecular diffusion paths and abundant narrow nodes exhibited more excellent D₂selective adsorption performance at 40 K.The optimal carbon molecular sieve had a concentrated distribution of microporous size of 0.6 nm,and its difference in adsorption of D₂and H₂ was 2.85 mmol g^-1 under dynamic breakthrough experimental at 40 K as well as its thermal desorption selectivity for D₂/H₂ during regeneration of the adsorbent was 10.In addition,a molecular plugging strategy allows for the shielding of ultramicropores that are non-selective at 77 K and improves the dynamic selectivity of carbon molecular sieves for hydrogen isotopes.更多还原