Influence of Temperature on the Product Distribution during the Fast Pyrolysis of Indonesian Oil Sands and the Relationships of the Products to the Oil Sand Organic Structure

The influence of temperature on the product distributions of oil sand fast pyrolysis was studied by a combined pyrolyzer-gas chromatography/mass spectrometry (Py-GC/MS) technique. Characteristics of the organic structure in bitumen deduced from the pyrolytic products and given by ¹H/¹³C nuclear magnetic resonance (NMR) spectrometry were compared as well. The oil sand sample was pyrolyzed at temperatures from 300 to 650 °C in intervals of 50 °C in an inert atmosphere (helium gas), and more than 200 types of compounds were detected, including carbon dioxide, aliphatics (alkanes, cycloalkanes, olefins, dialkenes, cycloolefins), aromatics (alkyl benzenes, alkyl naphthalenes, alkyl indenes), oxygen-containing compounds, and sulfur-containing compounds. From the evolution of the product yields, it was clearly observed that temperature affected both the primary and secondary reactions during fast pyrolysis. Major thermal cracking took place until about 400 °C, as evidenced by a dramatic increase in product species and yields. However, temperatures higher than 600 °C were beneficial for generating smaller molecules as products. Among the pyrolytic products, alkanes and olefins were predominant and were mainly derived from the thermal cracking of abundant polymethylene substituents linking to the aromatic cores. It was found that the yields of alkanes and olefins decreased with increasing carbon number, and more olefins were generated at higher temperatures. Monoaromatics with more alkyl or alkenyl multisubstituent groups appeared above 400 °C, but the substituent groups were no longer than isopropyl. In the range of 300–650 °C, few polycyclic aromatic hydrocarbons were observed. Higher temperatures also obviously enriched the species of naphthalene, indene, and compounds with heteroatoms. In addition, the raw aliphatic sulfur in the sample tended to be converted into sulfur-containing heterocycles during fast pyrolysis in an inert atmosphere. The results of this study show that both the NMR and Py-GC/MS methods can provide information on the organic structures in oil sand. However, NMR spectrometry is able to present an overview of the structure of hydrocarbons, whereas Py-GC/MS can help to deduce some characteristics of the macromolecules in oil sand organics.