Synergistic effect and hydrogen migration during co-pyrolysis of oil shale and cherry pit

Abstract

The pyrolysis oil of oil shale is characterized as being of better quality and having a lower yield, whereas the bio-oil from cherry pit has a higher yield but a higher oxygen content, which limits their efficient and clean application. Thus, the pyrolysates characteristics of oil shale and cherry pit have been investigated using a fixed bed reactor to fully utilize their inherent properties in this paper. In addition, the interaction mechanism during co-pyrolysis is explored by analyzing the hydrogen migration pathways. The results reveal that a remarkable synergistic effect on the oil and gas occurs during co-pyrolysis, and the co-oil yield of OS30CP70 improves by 14.63 % compared with the weighted value. During co-pyrolysis, the concentrations of hydrogen- and oxygen-containing gases are higher than expected, and the hydrogen and oxygen contents of char are lower than expected, which is related to that more hydrogen and oxygen of oil shale and cherry pit migrate into gas instead of char. Additionally, more hydrogen and less oxygen migrate into the co-oil during pyrolysis, causing an increase in aliphatics and a reduction in aromatics and oxygenated compounds, and enhancing the quality of the co-oil. 1H NMR shows that the H· free radical is most likely to attack the Hα and Har sites of cracking fragments rather than Hβ and Hγ sites, resulting in the co-oil containing more short-chain aliphatics and aromatics with fewer rings. Besides, the alkali and alkaline earth metals in cherry pit improve the cracking of hydroxyl and carboxyl groups and inhabit the migration of oxygen into co-oil, leading to a decrease in Ho content. The energy efficiency of co-pyrolysis is higher than that of individual pyrolysis, which all exceed 90 %.