Multi-stage coking for more tar and formed coke of higher strength. 4. Formed coking of residues extracted from heat-treated single coals with a mixed solvent of N-methylpyrrolidinone and carbon disulphide

A mixed solvent of N-methylpyrrolidinone and carbon disulphide (MP-CS₂) was found to extract very large amounts of tarry substance from bituminous coals of C% above 80% and the residue provided a high mechanical strength of its formed coke. However, coals of C% below 80% exhibited rather low solubility and the formed cokes from their residues were not strong enough. The preheat-treatment at 450 °C under 1 MPa nitrogen pressure increased significantly the extract yield and tensile strength of the formed cokes from the residues especially with coals of C% below 80%. The origins of coking properties of the coal are briefly discussed based on the present particular results obtained by MP-CS₂ extraction.