Calhoun S G K, Chandran Suja V, Fowler R, Agiral A, Salem K, Fuller G G
Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.
Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA; School of Engineering and Applied Sciences, Harvard University, MA - 02134, USA.
J Colloid Interface Sci. 2024 Dec;675:1059-1068. doi: 10.1016/j.jcis.2024.07.013. Epub 2024 Jul 5.
HypothesisFoaming in diesel fuels is not well understood and leads to operational challenges. To combat deleterious effects of foaming, diesel formulations can include additives called antifoams. Existing antifoams, unfortunately, are inherently ash-generating when combusted, with unknown environmental impacts. They are prohibited in certain countries, so identifying effective alternative ash-free antifoam chemistries is needed. ExperimentsWe conduct systematic characterization of foam stabilization and antifoaming mechanisms in diesel for two different antifoams (silicone-containing & ashless chemistries). Employing a custom technique combining single-bubble/single-antifoam-droplet manipulation with white light interferometry, we also obtain mechanistic insights into foam stability and antifoam dynamics. ResultsCoalescence times from both bulk foam and single bubble experiments confirm ashless antifoams are effective at reducing foaming, demonstrating the potential of ashless antifoams. Further, we perform single-antifoam-droplet experiments and obtain direct experimental evidence revealing the elusive antifoaming mechanisms. Interestingly, the silicone-containing and ashless antifoams seemingly function via two different mechanisms: spreading and dewetting respectively. This surprising finding refutes conventional wisdom that spreading is likely the only antifoam mechanism in diesels. These results and the reported experimental framework significantly enhance the scientific understanding of non-aqueous foams and will accelerate the engineering of alternative antifoam chemistries for non-aqueous systems.
假设
柴油中的泡沫现象尚未得到充分理解，并且会导致操作上的挑战。为了对抗泡沫的有害影响，柴油配方中可以包含一种叫做消泡剂的添加剂。不幸的是，现有的消泡剂在燃烧时会产生灰烬，其对环境的影响未知。在某些国家，它们是被禁止使用的，因此需要确定有效的无灰替代消泡剂化学物质。
实验
我们对两种不同的消泡剂（含硅酮和无灰化学物质）在柴油中的泡沫稳定和消泡机制进行了系统表征。通过将单气泡/单消泡剂液滴操作与白光干涉测量相结合的定制技术，我们还获得了关于泡沫稳定性和消泡剂动力学的机理见解。
结果
大量泡沫和单气泡实验的聚并时间证实了无灰消泡剂在减少泡沫方面是有效的，证明了无灰消泡剂的潜力。此外，我们进行了单消泡剂液滴实验，并获得了直接的实验证据，揭示了难以捉摸的消泡机制。有趣的是，含硅酮和无灰消泡剂似乎通过两种不同的机制起作用：分别是铺展和去湿。这一惊人发现驳斥了传统观点，即铺展可能是柴油中唯一的消泡机制。这些结果和所报道的实验框架显著增强了对非水泡沫的科学理解，并将加速非水系统替代消泡剂化学物质的工程设计。
