Molecular structure and size of asphaltene and preasphaltene from direct coal liquefaction

• Fluorophors distributions of AS and PA mainly depend on original coal.
• PA has significantly larger average size and stronger aggregation than AS.
• Archipelago structure is valid molecular architecture of PA derived from coal.

The heavy organic components in the direct coal liquefaction residue (DCLR), such as asphaltene (AS) and preasphaltene (PA) have significant influence on the direct coal liquefaction (DCL) technology. In this paper, the molecular structure and size of two types of AS and PA from the DCLR of 6 t/d Shenhua process developing unit and a batch hydro-liquefaction in laboratory were characterized. Results indicated that two types of AS and PA from different liquefaction technologies respectively display similar distribution of fluorophors. 3 ~ 4 rings fused aromatic nucleus (ANs) and/or more rings peri-condensed ANs are the predominating structures in the AS and PA. The scale of PA molecule is significantly larger than that of AS molecule. The molecular model, in which several ANs linked by bridge bonds or hydrogenated aromatic rings, is valid at least for the PA. Both AS and PA from direct coal liquefaction can form aggregates while the PA exhibits stronger aggregation than the AS.