Effects of Modified Poly (vinyl alcohol)s as a Dispersant for Coal-water Slurry

Abstract

Ability of ionically modified poly (vinyl alcohol) (PVA) with a dodecylthio end group as a dispersant for coal-water slurry (CWM) was investigated. The ability was lower in the case of PVA with no ionic groups compared with sodium salt of naphthalenesulfonic acid-formaline condensate (NSF). By introducing sodium sulfonate groups to the PVA with copolymerization, the viscosity of the CWM was lowered markedly and a dilatent fluidity occurred at lower shear rate region below 100 s-1. In the case of sodium carboxylate groups instead of sodium sulfonate groups, the phenomenon was similar. In the case of quaternary ammonium salt groups, the fluidity of the CWM immediately after preparation was poor and the viscosity was high. Precipitation took place in the CWM using the PVA containing 3 mol% sodiurn sulfonate after 3 days storage. With increase in the amount of sodium sulfonate groups, the storagestability of CWM was improved. Shear viscosity of CWM was studied with changing the shear rate up to 400 s-1. While CWM using NSF showed large thixotropy in the first-run, that using PVA containing 3 mol% sodium sulfonate groups revealed dilatency at lower shear rate range and weak thixotropy at higher shear rate over 120 s -1. Poor storage-stability of the CWM using the PVA seemed to coincide with the absence of increase in viscosity at lower shear rate.