Effect of High Pressure on Nonisothermal Pyrolysis Kinetics of Oil Shale and Product Yield

Abstract

The current work presents a comprehensive study on nonisothermal high-pressure pyrolysis kinetics of oil shale and the influence of pressure on product yield. High-pressure thermogravimetric analyses of the oil shale samples were carried out from 30 to 900 °C, at heating rates of 5, 10, 15, and 20 °C min −1 , under isobaric pressure values of 5, 10, 20, and 30 bar using a wellcontrolled high-pressure thermogravimetric analyzer (HP-TGA). The organic matter decomposition zone was identified from HP-TGA data and the activation energy values were determined using isoconversional methods. Under the pressurized condition, oil shale exhibited mean apparent activation energy values ranging from 341 to 451 kJ mol −1 . The possible decomposition mechanisms were identified as D3 diffusion model, followed by second-order reaction model, and A3 Avrami−Erofeev nucleation model as the decomposition progressed and products formed. Further, the lab-scale pyrolysis experimental matrix was designed based on HP-TGA data, and the products obtained were characterized for compositional analysis. The percentage of permanent gases viz. hydrogen (H 2 ), carbon dioxide (CO 2 ), and carbon monoxide (CO) decreased dramatically with the increase of pyrolysis pressure. The derived pyrolytic oils showed a decrease in specific density (879−831 g cm −3 ) and carbon number (C 38 to C 22 ) with an increase in pressure. Nuclear magnetic resonance ( 1 H NMR) analysis of the pyrolytic oil indicated a reduction in the total aromatic content (from 22 to 9 wt %) due to coking of aromatics, and a subsequent increase in the percentage of aliphatics and alkanes due to cracking of straight-chain moieties. The octane number of obtained pyrolytic oils ranged from 83 to 88. The results obtained suggest that the choice of the pressurized pyrolysis (temperature−pressure combination) system may help in controlling the product distribution and compositions.

Compositional and kinetic study of thermal degradation of kerogen using TG‐FTIR, NMR, and microscopic study

“…The reliability and accuracy of different isoconversional methods have been discussed previously. 7 In this study, the apparent activation energy values have been calculated using advanced isoconversional (AIC), 35,36 Starink, 37 and Friedman method. 38 The error values of each method have been discussed.…”

“…30 The occurrence of the D3 Diffusion model may indicate the release of hydrocarbons from the pores on the surface of oil shale. 7 In addition, the occurrence of the A2 Avrami Eroffev reaction model may describe the catalytic effect of inherent minerals on the coking reaction of produced hydrocarbon vapors. 24,56 Therefore, the kinetic study of kerogen can be summarized as the breakdown of heterogeneous macromolecules to release low-molecular-weight volatiles in the form of gaseous matter and the formation of char intermediates due to secondary cracking.…”

“…5,6 Oil shale can be converted to valuable oil and gas by pyrolysis. 4,7 During pyrolysis, kerogen decomposes simultaneously with the mineral matter present in oil shale, leading to a complex kinetic mechanism. The mechanism of kerogen and oil shale degradation can be better understood by investigation of the pyrolysis kinetics.…”

Progress in Catalytic Pyrolysis of Oil Shale

“…The high-pressure thermogravimetric analysis of oil shale pyrolysis shows that the volatilization temperature of hydrocarbon increases with the increase of pyrolysis pressure. With the increase of pyrolysis pressure, oil production rate decreases, and gas production rate increases [ 14 , 15 ].…”

Release performance and kinetic behavior of volatile products from controlled pressure pyrolysis of oil shale in nitrogen atmosphere

“…Baruah et al studied the kinetics and the effect of pressure on product yield of oil shale pyrolysis under non-isothermal and high-pressure conditions. They believe that with the increase of pyrolysis pressure, the secondary reaction of oil vapor will occur, affecting the oil composition and reducing the oil yield 17 . Zhang et al tested the permeability change characteristics of oil shale pyrolysis in nitrogen atmosphere with axial pressure of 3.75 MPa and confining pressure of 4.5 MPa.…”