## Oil Shale Chemical Characteristic
### Oil Shale Pyrolysis
#### 4.2.2 Pyrolysis Products  
The extraction of oil from oil shale can be performed using two major methods, in situ conversion and surface mining followed by retorting. In situ conversion is a method where the oil shale is heated underground to extract the oil. In this process, heating elements are placed deep into the oil shale formation, and heat is applied over an extended period, usually a couple of years. The heat prompts a chemical process that converts kerogen, the organic material in the shale, into oil and gas. The oil and gas are then pumped to the surface. On the other hand, surface mining followed by retorting, involves digging the oil shale from the ground, bringing it to the surface, and then heating it in a process called retorting. The retorting process involves heating the shale in a vessel or retort to a high temperature, typically around 500 \({}^{\circ}\)C, causing the kerogen to decompose. The process of pyrolysis conducted on oil shale sourced from the Green River Formation, as documented by [PERSON] et al., resulted in the extraction of highly valuable hydrocarbons, colloquially termed shale oil, from the kerogen contained within. In the course of oil shale pyrolysis, the primary yield comprises light gases, char, and a tar-like substance. The light gas fraction primarily consists of butane, propane, ethane, and methane. The tar-like substance is a complex hydrocarbon amalgamation, which has the potential for further refinement and subsequent application in diverse sectors, notably as fuels for transportation. The char, which is the solid remnant post-pyrolysis, is chiefly constituted of residual carbon and mineral matter. An in-depth analysis of the kerogen under study revealed that the carbon content was predominantly aromatic and aliphatic, accounting for approximately 79.8% of the total. Smaller proportions were found to be carbonyl, carbides, and carboxyl groups. This insight is crucial since the carbon type present within kerogen directly influences the nature of the hydrocarbons that can be generated during the pyrolysis process. Additionally, the study determined that the release of hydrogen and carbon during pyrolysis outpaced that of sulfur and nitrogen. This may indicate that sulfur and nitrogen are likely situated within the kerogen's more thermally stable aromatic clusters. Through gas chromatography/mass spectrometry (GC/MS) analysis, an abundance of 1-alkenes and alkanes was detected, signifying that linear hydrocarbons form a substantial product of the pyrolysis operation. This substantiates the proposition that in the kerogen's chemical structure model, sulfur and nitrogen heteroatoms should be located in the aromatic region, representing the kerogen's portions that exhibit stability at moderate temperatures. This kind of investigation underscores that oil shale pyrolysis is a multifaceted process yielding diverse products, predominantly light gases, tar (or shale oil), and char. The product composition hinges on multiple factors, most notably the kerogen composition within the oil shale and the pyrolysis conditions employed [55]. The primary environmental factor that affects pyrolysis products is temperature; other factors also play important roles. Based on the study by [PERSON] et al., on Jimsar oil shale, varying the thermal input from 400 to 520 \({}^{\circ}\)C substantially influences the product stream from oil shale pyrolysis, including the increase in yields of shale oil, non-condensable gases, and aqueous products. Moreover, the constituent distribution within shale oil experiences changes, with n-paraffins diminishing and aromatic hydrocarbons augmenting as the retort temperature escalates from 400 to 550 \({}^{\circ}\)C. Additionally, a rise in retort temperature enhances the yield of C6-C19 hydrocarbons while reducing the output of C20+ hydrocarbons. [PERSON] et al. (2022) conducted a temperature-dependent oil shale pyrolysis study of Fushun oil shale.