| Fluorocarbon surfactants are widely used in foam fire extinguishing agents due to their strong oil and water repellent interface characteristics.However,it is a refractory organic matter that has been restricted in use by a number of international conventions,seeking to reduce or replace fluorocarbon surfactants has become an industry hotspot in the research and development of new environmentally friendly fire extinguishing agents.Gleditsia saponin(GS)is a class of natural non-ionic surfactant extracted from Gleditsia sinensis Lam,which has good foaming and foam stabilizing effect.In this paper,the saponins are extracted and purified from Gleditsia sinensis Lam.A three-factor(GS,Fluorad FC-170C,CAB)three-level optimization experimental design was carried out using the central composite response surface analysis method,the surface tension,foaming ability,foam stability and average bubble size are used as indicators.The physical and chemical characterization of the fire extinguishing foam and the synergistic effect of the compound were discussed.The main research results are as follows:(1)Vanillin-perchloric acid colorimetric method were used to quantify the Gleditsia saponin which is refined by solvent extraction and column chromatography,the total saponins content of the saponins was 7.1%.the Gleditsia saponin analyzed by gel permeation chromatography yielded a single chromatographic peak with the molecular weight of 4366.the Gleditsia saponin were hydrolyzed by hydrochloric acid to obtain aglycone,which were qualitatively identified by HPLC.Aglycones include oleanolic acid(63.9%)and echinocystic acid(36.1%);The initial thermal decomposition temperature of the Gleditsia saponin in thermogravimetric analysis is 244.3℃.(2)To explore the synergistic effect of the surface tension reduction of the mixed system,Intermolecular interaction parameters of surfactants in the FC-170C+CAB,FC-170C+GS,CAB+GS binary mixed system and FC-170C+CAB+GS ternary mixed system in the gas-liquid interface and mixed micelles were measured.βα-βM<0 with |βα-βM>|ln(C10,CMC C2M/C20,CMC C1M)| under a certain molar ratio,which means there is a synergistic effect to reduce the surface tension.Mixed CMC is less than CMC under ideal status,and average minimum area occupied on the interface is less than average minimum area under ideal status,which proved the intermolecular attraction between surfactant molecules.The aggregation behavior of surfactant micelles observed by Cryo-TEM showed that the shape changed from sphere to strip of the micelles makes the arrangement of the molecules at the liquid-gas interface become tighter,which makes the mixed system have a synergistic effect on the surface properties.(3)The response surface analysis results of the concentration of Fluorad FC-170C、CAB and GS aqueous solution to be 0.000678%and 0.18%and 0.07%,the surface tension of the mixed fire extinguishing agent can reach 17.30mN/m,The initial foam height under the Ross-miles method is 116.95mm.the foam stability R5min can reach 97.98%,and the average bubble size is 116.38 μm under the model predicts.The experimental datas are 17.25 mN/m,117.33mm,98.12%,115.21 μm.The relative errors were 0.29%,0.32%,0.14%,and 1.01%,respectively.International conventions restrict the use of fluorocarbons not to exceed 50mg/kg,and the use of fluorocarbon surfactants in the mixed fire extinguishing foam is reduced to 6.78mg/kg. |
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