Kinetic Measurements on CO2 Hydrate Formation in the Presence of Tetra-n-butyl Ammonium Bromide

Kinetic Measurements on CO2 Hydrate Formation in the Presence of Tetra-n-butyl Ammonium Bromide

Hydrate-based ionic clathrate hydrates are promising materials for hydrate-based CO, capture due to their mild forming conditions. In this work, hydrate crystallizations from different TBAB solutions were measured. The effect of TBAB concentration on hydrate nucleation time, hydrate growth, and gas storage capacity were evaluated. The TBAB concentration ranging from 0.3 to 7.5 mass % was found to be ideal for efficient hydrate formation. The TBAB hydrates were assumed to form first in the liquid bulk which induced the growth of simple CO, hydrate. In dilute TBAB solutions, guest ions in TBAB tended to inhibit hydrate nucleation and increase induction time, while concentrated TBAB solutions were found to reduce gas storage capacities. PXRD measurements revealed that the orthorhombic TBAB hydrate preferred to form where TBAB concentration was below 35 mass %. When the concentration was above 40 mass %, tetragonal and trigonal TBAB hydrate dominated the solid hydrate phase. In Raman measurements, C H stretching modes of the TBA+ cation in different hydrate structures were characterized. CO, was proved to be captured by tetragonal and orthorhombic TBAB hydrates, which was suggested to be beneficial for hydrate stabilization.

基于水合物的离子笼形水合物由于其温和的形成条件，是用于基于水合物的二氧化碳捕获的有前景的材料。在这项工作中，对不同四丁基溴化铵（TBAB）溶液的水合物结晶情况进行了测量。评估了TBAB浓度对水合物成核时间、水合物生长以及气体储存能力的影响。发现TBAB浓度在0.3 - 7.5质量%范围内对高效水合物形成较为理想。据推测，TBAB水合物首先在液相主体中形成，这促进了简单二氧化碳水合物的生长。在稀TBAB溶液中，TBAB中的客体离子往往会抑制水合物成核并增加诱导时间，而浓TBAB溶液则会降低气体储存能力。粉末X射线衍射（PXRD）测量表明，当TBAB浓度低于35质量%时，正交晶系的TBAB水合物更易形成。当浓度高于40质量%时，四方晶系和三方晶系的TBAB水合物在固态水合物相中占主导。在拉曼测量中，对不同水合物结构中四丁基铵（TBA⁺）阳离子的C - H伸缩振动模式进行了表征。证明了二氧化碳可被四方晶系和正交晶系的TBAB水合物捕获，这被认为有利于水合物的稳定。