Properties of direct coal liquefaction residue water slurry: Effect of treatment by low temperature pyrolysis

• The slurryability is improved from 73.5% of DCLR to 74.6% of P-400.
• The adsorption layer of P-450 is the thinnest among the four samples.
• Pyrolysis deoiling could cause obvious deterioration in the stability of DCLRCHWS.
• DCLRCHWS (P-300 and P-400) exhibit weak pseudoplastic behavior just as DCLRWS.
• 400 °C is the optimum pyrolysis temperature to prepare the gasification feedstock.

Low-temperature pyrolysis could effectively recover heavy oil from direct coal liquefaction residue (DCLR), and the derived DCLR char (DCLRCH) could be gasified to compensate hydrogen consumption during liquefaction. The staged processing of DCLR, pyrolysis and gasification, is thought to be a promising method for its high-efficient usage. In the work, DCLR was pyrolyzed under different pyrolysis temperatures (300, 400 and 450 °C) in a fixed-bed reactor to prepare DCLRCH, designated as P-300, P-400 and P-450, which were then used to prepare DCLRCH water slurries. The results of FTIR and successive sequential extraction show that the oxygen-containing functional groups and aliphatic chains of DCLR are removed during pyrolysis and the aromaticity of DCLRCH increases with pyrolysis temperature increasing. The dispersant adsorption behavior suggests that the adsorption layer of P-450 is the thinnest among the four samples. The slurryability, rheological behavior and static stability of DCLRCH water slurries (DCLRCHWS) were systematically investigated. Compared with direct coal liquefaction residue water slurry (DCLRWS), the slurryability of DCLRCHWS prepared with P-300 and P-400 is enhanced and their static stability deteriorates further. DCLRWS and DCLRCHWS are all weak shear-thinning fluids. However, the mixture of P-450 and water is not a homogeneous and stable suspension. Under the experimental condition, 400 °C is the optimum pyrolysis temperature of DCLR for maximizing production of high-value components and preparing high-quality feedstock for gasification.