Physicochemical properties and slurry ability changes of lignite after microwave upgrade with the assist of lignite semi-coke

Abstract

Microwave pyrolysis is a promising technique for the clean and effective utilization of low-rank coal, which has aroused widespread concern during the past decades. This paper applied microwave energy with the assist of 10 wt% lignite semi-coke (LSC) to upgrade lignite and prepared the solid residue into lignite water slurry (LWS). The physicochemical property and slurry ability changes of upgraded lignite were analyzed. The micro-mechanisms on interactions between dispersant molecules and upgraded lignite particles were investigated through Molecular Dynamics (MD) simulations. It turns out that LSC could effectively prompt the rapid heating of lignite in the microwave field. And after microwave upgrade the coal quality of lignite was improved, the oxygen-containing functional groups was removed remarkably. The adsorption conformation of dispersant on the lignite-water interface exhibited a double adsorption, while that on upgraded lignite-water interface gradually showed single-layer and multi-point adsorptions. Besides, the physicochemical property changes varied most when lignite was upgraded under 800 W, which leads to the maximum solid concentration of LWS improved most, from 51.84 wt% to 61.45 wt%. It further increased to 62.43 wt% as the LWS was directly prepared from the solid residues after microwave irradiation. Morever, the pseudoplasticity of LWS became weaker, but the static stability became better. Therefore, LSC, a self-product of lignite, exerted an enormous function on improving the slurry ability of lignite.