The influence of surfactants on coalescence filtration

Abstract

Coalescence filters are used to separate dispersions. We have studied how the efficiency of filters are affected by diferent filter structure, surface coatings, and additions of surfactants. Filters with parallel fibers bunched like spaghetti showed the same efficiency as fibermats, for the same average pore size. A naked glass surface (negatively charged) showed best performance, an amin-coated was second best, and a non polar was worst, although the difference was not very significant. — An anion tenside with HLB value 9 was compared with a nonion with HLB 9 and a nonion with HLB 14 in fiber filters, but also in thin precoat filters. The nonion tenside with HLB 14 showed the poorest filter efficiency, followed by the nonion with HLB 9, and the anion showing the best result for tenside conc 2.5–100 ppm in water. A correlation between surface tension and filter efficiency can be seen, while interfacial tension shows a correlation only at very high concentrations. Several authors have shown correlations between emulsion stability and surface-film viscosity and elasticity. From our results we conclude that also considering complete filter performance film elasticity and viscosity are of major importance, compared to other properties.