Abstract
High-temperature H2O and CO2 can improve the pyrolysis behavior of oil shale. Therefore, in this paper, Jimusar oil shale was selected as the research object and the effect of the reaction atmosphere (H2O, CO2, and N2) on its pyrolysis behavior, pyrolysate distribution, and pyrolysis oil quality was fully compared and studied. The results showed that compared with the N2 atmosphere, the presence of H2O and CO2 both increased the weight loss and weight loss rate during pyrolysis of oil shale and the existence of H2O advanced the initial precipitation temperature of volatiles by 17°C. The comprehensive release characteristic indices of volatiles during pyrolysis of oil shale in the CO2 and H2O atmospheres increased by 49.34% and 114.35%, respectively, which significantly improved its pyrolysis reactivity. Both H2O and CO2 atmospheres improved the pyrolysis oil yield of oil shale, and the pyrolysis oil yield in the H2O atmosphere performed better than that in the CO2 atmosphere. Especially, the H2O atmosphere could increase the pyrolysis oil yield by 41.42%. The existence of CO2 prevented methyl radicals from accepting hydrogen radicals during pyrolysis and reduced the alkane yield, while CO2 participated in the addition reaction of alkane, which increased the alkene yield. High-temperature H2O provided more hydrogen source, which increased the alkane yield and inhibited the alkene formation. Both H2O and CO2 atmospheres promoted the cracking of polycyclic aromatics and increased the yield of small-molecular aromatics in the pyrolysis oil. During the pyrolysis process of oil shale, CO2 and H2O underwent reforming reaction with the heavy oil, which increased the light component fraction, thereby increasing the H/C ratio of pyrolysis oil. Thus, the existence of H2O and CO2 atmospheres improved the quality of pyrolysis oil and the effect of H2O was better than CO2. The H2O and CO2 atmosphere promoted the formation of a well-developed pore structure, which was conducive to mass and heat transfer during pyrolysis of oil shale.
Highlights
Kerogen is a kind of macromolecule polymer with a three-dimensional network structure. It is mainly composed of aliphatic hydrocarbons and contains a small amount of aromatic hydrocarbons and oxygen-containing groups, which is the main source of pyrolysis oil and gas products [7–9]
Tv × Tmax × ΔT1/2 where ðdw/dtÞmax is the maximum weight loss rate during oil shale pyrolysis, %/min, ðdw/dtÞmean is the average weight loss rate during oil shale pyrolysis, %/min, Tv is the initial precipitation temperature of volatiles during oil shale pyrolysis, °C, Tmax is the temperature corresponding to the maximum weight loss rate, °C, and ΔT1/2 is the half-peak width, °C
The weight losses of oil shale during pyrolysis in CO2 and H2O atmospheres were higher than that in the N2 atmosphere, which indicated that the existence of CO2 and H2O promoted the cracking of kerogen and the release of volatiles in oil shale
Summary
With the gradual consumption of traditional energy, exploring a clean and efficient alternative nontraditional energy has become a hot topic [1, 2]. Kerogen is a kind of macromolecule polymer with a three-dimensional network structure It is mainly composed of aliphatic hydrocarbons and contains a small amount of aromatic hydrocarbons and oxygen-containing groups, which is the main source of pyrolysis oil and gas products [7–9]. Ma et al proposed that the water medium reduced the energy required for kerogen cracking because of swelling effect and promoted the generation and release of hydrocarbons. It could reduce the temperature of hydrocarbon generation by about 120°C during pyrolysis of oil shale, compared with anhydrous pyrolysis [17]. These would provide theoretical references and technical guidance for the clean and efficient utilization of oil shale
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