Coal-oil mixtures. 3. Stabilization of powders vs. colloids: coal/oil vs. carbon black/oil systems

Abstract

The concept of colloid stability is explored in a practical study of the effectiveness of additives as stabilizers for mixtures of powdered coal (80% -200 mesh) and no. 6 fuel oil. Further insight is added by the results of a parallel study of the stability of colloidal suspensions of carbon black at high concentratln In mineral oil. Sedimentation, subsidence, consistency, and viscosity are measured and interpreted in terms of practical stability arid colloid stability. It is shown that flocculation and network formation are important in powders as well as in colloids. The dependence of the effectiveness of stabilizers on molecular weight of the additive suggests a mechanism of bridging flocculation and network formation. Certain anionic surfactants stabilize carbon black in mineral oil as shown by the slow sedimentation of dilute suspensions and the low viscosity of pastes, but the same surfactants destabilize coal-oil mixtures (COM) since the particles readily settle to a closely packed bed. Surfactants that confer practical stability on COM by promoting rapid flocculation and network formation Increase the viscosity of carbon black pastes.

Surface Potential of Coal Particles in Coal-Oil Mixture and Control of Settling Stability Under Gravity

“…For the COM with industrial application commonly is concentrated, we consider that the average center-center interparticle separation is assumed to be equal to that in a regular 12-coordinated lattice of the same particle at the same particle volume fraction (u). [7,9] That is,…”

“…Most of the experiments used for the assessment of the sedimentation stability of COM. [5][6][7] But these studies investigated the settling phenomenon of coal-oil solids as a function of concentration, initial slurry height, settling volume, temperature, etc.…”