Xiaoyang Yu,Fan Li,Xuyang Miao,Ning Jiang,Ruowen Zong,Shouxiang Lu,Changhai Li
The presence of ethanol has an adverse effect on foam spreading, and ethanol fire is difficult to extinguish with aqueous fire-fighting foams. Thus, it is necessary to explore the foam formulation suitable for ethanol fuels and study the spreading behavior of foam over ethanol surface. In the current work, stable foams based on hydrocarbon surfactant (SDS), fluorocarbon surfactant (FC1157), and polymers (XG) were prepared by using the compressed-air foam system. The spreading behaviors of foam on polar ethanol and non-polar heptane surface were observed and compared. Furthermore, the effects of stabilizer concentrations, foam flow rates and expansion ratios on foam spreading performance were investigated, respectively. The results indicate that aqueous SDS foam can spread on the heptane layer continuously, but it is difficult to cover the ethanol surface. The addition of XG and FC1157 can synergistically improve the spreading performance of aqueous foam over ethanol. Depending on stabilizer concentrations, there are remarkable differences in foam spreading behaviors. Besides, different foam application parameters including expansion ratios and foam flow rates significantly affect the foam spreading rate, despite the same foam formulation. The research methods and results guide the optimal design of foam formulations as well as the practical application of aqueous foam for ethanol fire extinguishment.
Li Zhang,Kun Yan,Qianqian Hou,Bin Zheng,Jinlei Wang,Lianli Wang,Lei Wang
Aqueous foams are widely used in many fields and ionic surfactants are commonly used foaming agent. However, potential trouble may arise when they are used in hard water or at low temperatures. The anionic surfactants like sodium dodecyl sulfate (SDS) may precipitate to form crystals when the concentration of counterions such as K + and Ca 2+ exceeds a certain limit. In this paper, an attempt has been made to study the effect of surfactant crystals on the properties of aqueous foams by adding the inorganic salts KCl and CaCl 2 to SDS. The results showed that the stability of the CaCl 2 -SDS system was better than that of the KCl-SDS in the range of surfactant concentrations that produced crystalline precipitates. The straight line separated the stable and unstable foam regions with an equation of [KCl] = 0.6 [SDS] + 25 mM and [CaCl 2 ] = 0.5 [SDS] − 30 mM, suggesting that smaller concentrations of CaCl 2 are needed to prepare stable foams compared to KCl. The effect of crystal size on the properties of foams was investigated by ultrasonication, and it was found that changing the crystal size only changed the foaming properties of foams, and had almost no effect on the stability. A two-phase molecular dynamics model at the foam interface was constructed to study the effects of different metal ion valences on the stability of surfactant foam. The results showed that the metal ion Ca 2+ inhibited the diffusion of water in the foam wall more than K + and the binding ability between Ca 2+ - DS - head-groups are stronger than that of K + − DS - , thus the stability of the foam liquid film obtained in CaCl 2 -containing solution is better.
Volatile organic compounds (VOCs) are prevalent soil contaminants. During the ex situ soil remediation process, VOCs may overflow from the soil and cause gas to diffuse into the atmosphere. Moreover, some VOCs, such as trichloromethane, are categorized by the EPA as emerging contaminants, imparting toxicity to organs, and the endocrine and immune systems, and posing a huge threat to human health and the environment. To reduce VOCs’ emissions from contaminated soil, aqueous foam suppression is a prospective method that provides a durable mass transfer barrier for VOCs, and it has been widely used in odor control. Based on an aqueous foam substrate, in order to enhance the foam’s stability and efficiency of suppression, SiO2–TiO2-modified nanoparticles have been used as stabilizing agents to improve the mechanical strength of liquid film. The nanoparticles are endowed with the ability to photocatalyze after the introduction of titanium dioxide. From SEM imaging, IR, and a series of morphological characterization experiments, the dispersibility of the SiO2–TiO2-modified nanoparticles was significantly improved under the polar solvent, which, in turn, increased the foam duration. The foam dynamic analysis experiments showed that the foam liquid half-life was increased by 4.08 h, and the volume half-life was increased by 4.44 h after adding the novel synthesized nanoparticles to the bulk foam substrate. From the foam VOC suppression test, foam with modified nanoparticles was more efficient in terms of VOCs’ suppression, in contrast with its nanoparticle-free counterparts, due to the longer retention time. Moreover, in a bench-scale experiment, the SiO2–TiO2nanoparticles foam worked against dichloroethane, n–hexane, and toluene for almost 12 h, with a 90% suppression rate, under UV irradiation, which was 2~6 h longer than that of UV-free SiO2–TiO2nanoparticles, the KH–570-modified nanosilica foam, and the nanoparticle-free bulk foam. XPS and XRD results indicate that in SiO2–TiO2nanoparticles, the proportion of titanium valence was changed, providing more oxygen vacancies compared to raw titanium dioxides.Keywords:volatile organic compounds;emerging pollutants;aqueous foam suppression;nanoparticle silica;TiO2photocatalysis
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