Subcritical Water Extraction of Huadian Oil Shale at 300 °C

Abstract

In this work, Huadian oil shale was extracted by subcritical water at 300 °C over different time periods to better characterize the underground mining of oil shale in situ. The results revealed that the kerogen in the oil shale mostly transformed into bitumen through extraction over a long time period by subcritical water at 300 °C; however, a portion of the bitumen remained in the shale matrix. The yields of both bitumen 1 (the bitumen extracted by subcritical water) and bitumen 2 (the bitumen remaining in the shale matrix) reached maximums at approximately 250 h. It should take a long time for bitumen 2 to be released because the ability of the transporting substrates of subcritical water was insufficient, the solubility of bitumen 2 was poor, and tiny fractures were generated in the oil shale matrix at such a low temperature. The gas chromatography–mass spectrometry analysis showed that the major components of bitumen 1 and bitumen 2 were similar and consisted of n-alkanes, n-alkanoic acids, n-alk-2-ones, and isoprenoid alkane. Initially, kerogen decomposition produced a large number of n-alkanes with low molecular weights; however, as the reaction continued, comparatively higher-molecular-weight n-alkanes were obtained more. In addition, the bitumen underwent a secondary cracking in the subcritical water, resulting in its decreased yield over time, whereas the contents of gaseous C2–C6 hydrocarbons increased. The organic matter dissolved in the spent aqueous solution consisted of mainly paraffins, isoparaffins, cyclohexanone derivatives, and phenolic derivatives. The analysis of the oil shale residue showed that minerals were less reactive in the subcritical water except for feldspar and calcite and that mesopores developed in the oil shale with prolongated extraction time, as more bitumen diffused out and into the subcritical water at 300 °C.

Constrain on Oil Recovery Stage during Oil Shale Subcritical Water Extraction Process Based on Carbon Isotope Fractionation Character

“…The oil shale used in this study was sampled from the fourth layer of the Dachengzi mine area, Huadian, Jilin Province, China, with 0.35% R o . Before being separated into 100 g samples for later experiments, the oil shale samples were crushed and sieved into a diameter around 0.60−0.90 mm, and to reduce the experimental errors caused by sample heterogeneity, the samples were uniformly mixed [4]. To know the basic properties of HD oil shale, the proximate analysis, ultimate analysis, and Fischer assay analysis were conducted according to [6] (Table 1).…”

“…Oil shale has become an important backup energy of conventional fossil energy in the world, and its pyrolysis exploitation mode has changed from aboveground (ex situ) to underground (in situ) [1][2][3][4][5][6][7][8], as the former technology encounters significant challenges, such as environmental pollution and inefficiencies [2]. The in situ technology underground could be further divided into [3] (a) in situ artificial crushing and retorting and (b) real underground in situ retorting.…”

“…The in situ technology underground could be further divided into [3] (a) in situ artificial crushing and retorting and (b) real underground in situ retorting. Subcritical water extraction of oil shale is one of the in situ retorting technologies, and the oil generation process can be optimized through altering the heating time, type, and amount of catalyst and maximum temperature [4][5][6][7][8][9]. The quality of oil shale pyrolysis products mainly relates to the heating temperature and time [4], overheating or insufficient heating temperature will lead to a high mining cost with a low resource utilization rate; thus, precise heat transfer and adequate heating conditions are important to maximize oil yield [10].…”

“…Subcritical water extraction of oil shale is one of the in situ retorting technologies, and the oil generation process can be optimized through altering the heating time, type, and amount of catalyst and maximum temperature [4][5][6][7][8][9]. The quality of oil shale pyrolysis products mainly relates to the heating temperature and time [4], overheating or insufficient heating temperature will lead to a high mining cost with a low resource utilization rate; thus, precise heat transfer and adequate heating conditions are important to maximize oil yield [10]. In this sense, the early detection of Energies 2021, 14, 7839 2 of 12 the oil recovery stage during oil shale pyrolysis can lead to a quick corrective heating process being implemented, lowering the production costs.…”

Study on pore and fracture evolution characteristics of oil shale pyrolysed by high-temperature water vapour

“…According to heat source, they can be divided into conduction, convection and radiation heating [13]. Among these heating methods, convective heating outstands for high heat conduction, fast heating and high recovery rates [14,15]. During an in situ heat injection exploitation of oil shale, with the pyrolysis of organic matter and the thermal fracture of the inorganic mineral skeleton, there takes place a constant evolution of the pore structure of oil shale.…”