Flash pyrolysis of coal modified through liquid phase oxidation and solvent swelling

A new flash pyrolysis method of coal is presented for increasing the total volatiles and the tar yield through suppression of the cross-linking reactions during the pyrolysis. Coal was oxidized in liquid phase at 25-60 degrees C for several hours using H2O2, NaOH, or Na2Cr2O7; then the coal was swollen by tetralin at 100-220 degrees C under 1 MPa of nitrogen. The oxidation pretreatment significantly enhanced the solvent swellability of the coal. Pyrolysis of the coal samples was performed using a Curie-point pyrolyzer at 590-920 degrees C in atmospheric pressure of helium. When the oxidized coal alone was pyrolyzed, the tar yield decreased as compared with the raw coal. When the coal oxidized and swollen by tetralin was pyrolyzed, on the other hand, the tar yield successfully increased as compared with that of the raw coal swollen by tetralin. The net increase in the tar yield by the tetralin swelling reached up to 19.9 kg/100 kg of coal for a Morwell brown coal oxidized with hydrogen peroxide at 25 degrees C, and 16.9 kg/100 kg of coal for a Taiheiyo subbituminous coal oxidized with hydrogen peroxide at 25 degrees C. These values were respectively 1.7 times and 2.3 times larger than the tar yields of the raw coals. The tar yield increased further when a solvent mixture of tetralin and tetrahydrofuran was used as a swelling solvent. Evaluating the amounts of hydrogen transferred during the pyrolysis, it was found that these increases in the tar yield were brought about through the suppression of cross-linking reaction forming H2O as well as the effective hydrogen transfer from tetralin to coal.