Structural and property analysis of different components in coal liquefaction residue raffinate based on density separation

Abstract

Given China's coal-centric energy structure, direct coal liquefaction technology assumes a pivotal role in addressing oil shortages and ensuring stable energy supplies. Efficient handling of copious residues from liquefaction, alongside environmental concerns, poses a major challenge

the technology of direct coal liquefaction is crucial for alleviating oil shortages and ensuring energy security. The effective utilization of the vast amount of residual sludge generated from re-utilization of coke oven residues and the issues of their environmental impact are becoming key challenges.

This study applies float-sink separation to stratify coal liquefaction residue raffinate into six density distributions, employing advanced analytical techniques (SEM-EDS, XRD, Raman, elemental analysis, XRF, XPS, TGA) to probe the structures and properties across these densities. Findings reveal a predominately fine particle size with a median diameter (D50) of 12.1μm, peaking at a density of 1.6–1.8 g/cm³ . Increasing density correlates with heightened ash and sulfur content, diminishing carbon content, which reduces combustibility, decelerates burning velocity, and lowers weight loss. Enhanced crystallinity of SiO₂ and CaCO₃ is noted. Samples below 2.0 g/cm³ exhibit higher carbon content and superior graphitization, contrasting with higher densities revealing greater disorder. Changes in sulfur's chemical bonding states across densities highlight transformations among pyrite, organic sulfur, and sulfates. Rising density corresponds to declining combustibility and degraded combustion performance. These outcomes furnish a foundational theory for the resource recovery and exploitation of coal liquefaction residue raffinate.