Frothers and gas dispersion: A review of the structure-property-function relationship

Over the past 20 years quantitative measures of frother functions have been developed to try to replace such qualitative descriptors as “weak” and “strong”. One of these metrics is the critical coalescence concentration (CCC) that quantifies a frother’s ability to reduce bubble size; another is the concentration at minimum velocity (CMV) that quantifies a frother’s ability to reduce bubble rise velocity. The experimental procedure for the two measures is briefly outlined and the measures are shown to be related. Using CMV, based on more than 50 surfactants from the two main frother families, alcohols and polyglycols, the frother structure-property-function link is investigated. The structure variables were: in alcohols, alkyl chain length, and position of the methyl branch and hydroxyl group(s); and in polyglycols, alkyl chain length, and number of propylene oxide (PO) or ethylene oxide (EO) groups. On the argument that low CMV represents the desired outcome, the main findings are: the dominant effect of alkyl chain length in both alcohols and polyglycols; that for alcohols branched-chain isomers are superior to straight chain, with the best combination being OH at the terminus and the methyl branch as far away as possible; and for polyglycols, PO-based are superior to EO-based. Interpretation of these observations included the effect of structure on the following properties: surface activity, mass transfer rate, H-bonding, and molecule packing