Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using HFC-32 and sodium dodecyl sulfate
Surfactant effects on hydrate formation in an unstirred gas/liquid system: An experimental study using HFC-32 and sodium dodecyl sulfate
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DOI：
10.1016/j.ces.2005.03.043
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发表时间：
2005-09
影响因子：
4.7
通讯作者：
Kazuyoshi Watanabe;S. Imai;Y. Mori
中科院分区：
文献类型：
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作者：
Kazuyoshi Watanabe;S. Imai;Y. Mori
本文研究了在静止的客气/液体-水体系中，表面活性剂添加剂对笼状水合物形成的影响。本文首先对液水相表面活性剂-胶束形成促进水合物形成的现有假设提出了强烈的怀疑。指出十二烷基硫酸钠(十二烷基硫酸钠)是以前水合物形成实验中常用的一种阴离子表面活性剂，其克拉夫特点可能高于这些实验中设定的体系温度，因此在这些实验中可能没有形成胶束。然后描述了我们对氢氟烃气体HFC-32(CH2F2)形成水合物的实验观察，以显示当与HFC-32接触时，向水中添加十二烷基硫酸钠对水合物形成行为的影响。在每个实验中，HFC-32气体被连续供应到部分装满静止水池(纯水或十二烷基硫酸钠水溶液)的长方形腔室，以补偿因水合物形成而产生的气体消耗，从而保持腔室内的恒定压力。本实验具有以下特点：(A)通过测试室中的大侧窗沿水平轴进行详细的目测，以及(B)借助插入同一测试室的悬挂式滴定装置测量十二烷基硫酸钠水溶液的表面张力，以确定十二烷基硫酸钠在水中的溶解度，在以前的一些研究中，它似乎被误解为水合物形成条件下的临界胶束浓度(CMC)。前者表明，在成藏水中加入十二烷基硫酸钠，不仅在液池表面，而且在液池表面以上的腔壁上都形成了厚厚的、高孔隙率的水合物层，使液池的大部分没有水合物晶体。后者导致了一个重要的发现，水合物形成速率峰值的十二烷基硫酸钠浓度略低于溶解度(假CMC)。加入过量的十二烷基硫酸钠会降低水合物的生成速度，但会增加水合物的最终转化率。
This paper deals with the effects of a surfactant additive on the formation of a clathrate hydrate in a quiescent guest-gas/liquid–water system. The paper first presents our strong suspicion against the existing hypothesis that the surfactant-micelle formation in the liquid–water phase promotes the hydrate formation. It is pointed out that the Krafft point for sodium dodecyl sulfate (SDS), a popular anionic surfactant often used in previous hydrate-forming experiments, is presumably higher than the system temperatures set in these experiments and hence that no micelles may have formed in these experiments. The paper then describes our experimental observations of the hydrate formation from a hydrofluorocarbon gas, HFC-32 (CH2F2), to show how the hydrate formation behavior is affected by the addition of SDS to the water when brought into contact with HFC-32. In each experiment, HFC-32 gas was continuously supplied to a rectangular chamber partially filled with a quiescent pool of water (pure water or an aqueous SDS solution) to compensate for the gas consumption due to the hydrate formation, thereby maintaining a constant pressure inside the chamber. The present experiments featured the following characteristics: (a) detailed visual observations along horizontal axes through large side windows in the test chamber, and (b) surface tension measurements of the aqueous SDS solutions with the aid of a pendant-drop device inserted in the same chamber to determine the SDS-in-water solubility, which seems to have been misunderstood as the critical micelle concentration (CMC) in some previous studies, under the hydrate-forming conditions. The former revealed that the addition of SDS to the pool-forming water results in the formation of thick, highly porous hydrate layers not only on the liquid-pool surface but also on the chamber walls above the level of the pool surface, leaving the bulk of the liquid pool free from hydrate crystals. The latter led to an important finding that the SDS concentration at which the rate of the hydrate formation peaks is slightly lower than the solubility (the false CMC). An excessive addition of SDS beyond the solubility was found to cause a decrease in the rate of hydrate formation but an increase in the final level of the water-to-hydrate conversion.