1996 Volume 75 Issue 4 Pages 257-264
A solvent de-ashing under high temperature and high pressure has been adopted by Nippon Brown Coal Liquefaction Co., This is applied in the two-stage brown coal liquefaction (BCL) process to remove ash from the heavy product (coal liquid bottom, CLB, b. p.>420°C) in primary hydrogenation (liquefaction).
Naphthas obtained from the primary and secondary hydrogenations, primary naphtha and secondary naphtha, were analysed, and their extraction ability of CLB were measured under high temperature and pressure conditions. These results make clear that the secondary naphtha, which contains cycloparaffins of ca. 60%, is unsuitable for the de-ashing solvent because it provides lower extract yield and sticky residue from CLB at above 170°C. The primary naphtha provides higher extract yield and the residue which is handled as a slurry. The primary naphtha corresponding to toluene is easily prepared by distillation. The extraction ability of the primary naphtha is represented by its density at ambient temperature (20°C). The equation which estimates extract yield from CLBs is introduced by using the density of naphtha and the contents of asphaltene (HI-BS), preasphaltene (BI-PS) and pyridine-insoluble (ash) as parameters.
It is also confirmed that the ash in the CLBs is removed by settling in the primary naphtha at 250°C. The naphtha is better as a de-ashing solvent than toluene because it copes with change in CLB properties by controlling its density by distillation.
