EFFECTS OF PRETREATMENT BY VARIOUS GASES ON HYDROPYROLYSIS OF A BELGIAN COAL

The effects of pretreatment of a Belgium Beringen bituminous coal under H2, He, CO2 and H2O on Hy.Py, are studied in a 100 g fixed-bed, semibatch unit. The hydrogen pretreatment is carried out at temperature ranging from 573 to 723 K under 0 to 3 MPa and gas residence time of 2 min for 30 min. Hy.Py is run at 973 K, 3 MPa and gas residence time of 1 min for 30 min. Hydrogen pretreatment of coal under 2 to 3 MPa at 623 to 693 K as the first stage and Hy.Py. of the pretreated coal as the second stage, H2P-Hy.Py. process, is effective for an increase of yields of oil, BTX and PCX. Hy.Py. process, due to the slow rate of hydrogen diffusion and without solvent, seems to be more subject to mass transfer limitation. It is suggested that during hydrogen pretreatment more hydrogen penetrates the coal to stabilize the free radicals formed by pyrolytically, being favourable of the formation of light hydroaromatics and phenols in subsequent Hy.Py. It is found that Hy.Py is unfavourably affected by the pretreatment under He, CO2 and H2O at 648 K, 3 MPa and gas residence time of 2 min for 30 min. Pretreatment under He seems to have no significant influence on Hy.Py. while pretreatment under CO2 and H2O increases the oil yield. However, because of the strong penetration abilities of CO2 and H2O it is very difficult for H2 to replace them in Hy.Py. stage, resulting in hydrogen deficient condition and thus the decrease in the BTX yield. In addition, in H2P-Hy.Py. process, cooling and depressurizing of pretreated coal lead to even a decrease of the yields of BTX and PCX compared with in the absence of pretreatment.