Energy & Fuels, Vol.31, No.12, 13655-13665, 2017
Effectivity of Phenol during Solvent Extraction of a South African Bituminous Coal under Mild Conditions
Solvent extraction of a South African bituminous coal was carried out under mild conditions (<400 degrees C) with a holding time of 20 min and an initial nitrogen (N-2) pressure of 6 MPa. Thermal degradation of coal with phenol results in the depolymerization of the coal, yielding coal-derived liquids and insoluble residues. The effectiveness of phenol for solvent extraction of coal within the temperature range of 300-360 degrees C was investigated, with a focus on the quality of the coal-derived liquids. It was found that an increase in temperature from 300 C to 360 degrees C resulted in an increase in the conversion and yields of both oil and gas, and a reduction in the intermediate components (preasphaltenes + asphaltenes, PAAs). The conversion and extraction yields of hexane-soluble (HS) oils were 49.5% (daf) and 26.3% (daf), respectively (daf = dry ash-free), for thermal depolymerization reactions at 360 degrees C. It seems that the extraction process dissolves molecular fragments of the coal, because the infrared spectra of the coal and the extraction products are similar. The SimDis results of the coal-derived liquids (300-360 degrees C) indicated that the samples consisted of light vacuum gas oil (23-31 wt %), distillate fuel oil (16-30 wt %), heavy vacuum gas oil (18-34 wt %), and residual oil (3-16 wt %). These results show the potential of phenol as a solvent to extract South African bituminous coal at mild temperatures for value-added liquid fuels and add to the general knowledge of the potential utilization of the Permian-aged South African bituminous coals.