Extraction of lignite with water in sub- and supercritical states

On a semi-continuous apparatus, Dayan lignite was extracted with water in sub- and supercritical states. The experiments were carried out to investigate the effect of temperature on extract formation rate, extract yields and product components at different pressures and end temperatures. The results indicated that the extract formation rate has a maximum with the variation of temperature, The temperature corresponding to the maximum extract formation rate, changing with the pressure, is between 400 and 450 degrees C. The extraction yields vary with the conditions. With the increase of pressure, the conversion and extract yield increase. With the increase of end temperature, the conversion also increases, but the increment is mainly gas and light oil. The main fraction in extract is preasphaltene and the main gas component is CO2. (C) 1998 Elsevier Science B.V.