Extraction of Weakly Reductive and Reductive Coals with Sub- and Supercritical Water

Abstract

On a semi-continuous apparatus, a weakly reductive Shenfu-Dongsheng (SD) coal and a reductive Pingshuo (PS) coal were non-isothermally extracted with sub- and supercritical water to explore the differences between the two coals. The effect of the temperature on the extract formation rate, conversion, and product composition under different pressures was investigated. The extraction results of two coal samples indicate that the extract formation rate has a maximum in the studied temperature range between room temperature and 500 °C. The temperature corresponding to the maximum extract formation rate, changing with the pressure, is between 390 and 410 °C. The gas yield, extract yield, and conversion of two coals increase with the increasing pressure. In comparison to PS coal, SD coal has a low temperature corresponding to the maximum extract formation rate under the same pressure. Both coals have a main fraction of asphaltene, but SD coal has a higher fraction of oil than PS coal. The main gas components are CO2, CH4, and H2. The gas from PS coal has a higher CH4 content and lower CO2 content than that from SD coal. The analysis results of the extraction residue indicated that SD coal has a low residue yield and the residue shows a large surface area and small average pore diameter compared to PS coal.

Some Advances in Supercritical Fluid Extraction for Fuels, Bio-Materials and Purification

“…Increasing pressure and temperatures in the range 673 to 723 K were effective for increasing the yield of liquid fuels, but higher temperatures enhanced mainly gas and light oil production. Supercritical water was also applied to some Chinese coals, the maximal extraction rate occurred near 670 K and the gas (CO, H 2 , CH 4 ) and extract yields increased with pressure [27]. Higher temperatures of 673 to 1033 K and pressures of 30 MPa were used for the supercritical extraction of brown coal from Russia, with a conversion of 48% to 63% to liquid and gaseous products [28].…”

Extraction by Subcritical and Supercritical Water, Methanol, Ethanol and Their Mixtures

“…Sub-and supercritical water were also applied to some Chinese coals, the maximal extraction rate occurred near 670 K and the gas (CO, H 2 , CH 4 ) and extract yields increased with the pressure [37]. Higher temperatures 673 to 1033 K, and pressures, 30 MPa, were used for the supercritical extraction of brown coal from Russia, with conversion of 48% to 63% to liquid and gaseous products [38]. Russian brown coal was treated with supercritical water at 673 to 873 K for the production of combustible volatile products in a continuously supplied reactor [39,40].…”

Conversion of brown coal continuously supplied into the reactor as coal–water slurry in a supercritical water and water–oxygen mixture

“…Moreover, brown coals, due to their appreciably high H/C atomic ratio (0.8-1.1), are considered as the starting material to obtain liquid and gaseous fuels [6,9,10]. By now, SCW conversion of brown coals has been studied in autoclave [11,12] and flow [13][14][15] modes, at continuous supply of coal-water slurry (CWS) [16][17][18][19][20], and in a cyclic pressurization-depressurization mode [21]. Besides, the problems dealing with coal combustion directly in SCW to obtain a working substance of electro-generating devices have been actively discussed [22][23][24].…”