Concentrated coal-water suspensions containing nonionic surfactants and polyelectrolytes 2. Adsorption of nonyl phenyl propylene oxide-ethylene oxide on coal and the rheology of the resulting suspension

Abstract

Adsorption isotherms of a series of nonionic surfactants (Synperonic NPE) on coal showed a systematic decrease in the amount of adsorbed surfactant (Γ in μmol g −1) with increase in polyethylene oxide (PEO) chain length. A plot of Γ vs. n 1 2 (where n is the number of EO units) was linear indicating that the adsorbed amount is determined by the size of the PEO chain. Viscoelastic measurements on coal dispersions stabilized by these nonionic surfactants showed a rapid increase in the complex and storage moduli ( G ∗ and G′ respectively) at a critical volume fraction of coal, Φ cr. The latter was highest for the surfactant containing 48 EO units. The lower Φ cr obtained with the surfactant containing the shorter PEO chain (27 units) was due to the weak flocculation obtained with these dispersions. At longer PEO chains (79 and 174) desorption of the chains may occur and this results in greater flocculation. It was concluded that an optimum PEO chain length was required for maximum stability.