Pyrolysis of an Indonesian oil sand in a thermogravimetric analyser and a fixed-bed reactor

• The inherent mineral matter acted as an inert material during the bitumen pyrolysis.
• A maximum of 76.4 wt% of the bitumen was converted to pyrolysis liquid at 773 K.
• The pyrolysis liquids contained less than 3.4 wt% asphaltenes.
• The pyrolysis liquids became lighter as pyrolysis temperature increased.
• The pyrolysis gas contains more than 50 vol% H2 at pyrolysis temperatures above 773 K.

Pyrolysis experiments of Buton oil sand were first carried out in a thermogravimetric analyser (TGA) at different heating rates from 5 K min−1 to 80 K min−1 to study the thermal decomposition characteristics and then in a fixed bed reactor (FBR) operating at temperatures varied from 673 to 873 K, to study the effect of temperature on the yields, compositions and properties of pyrolysis liquid, gas and coke. The TGA results suggest that the pyrolysis process of Buton oil sand could be divided into two distinct stages, namely, pyrolysis of bitumen at temperatures below 873 K and decomposition of the residual sand above 873 K. The residual sand was mainly composed of CaCO3 and acted as inert during the bitumen pyrolysis stage. The FBR results show that as temperature increased, the pyrolysis gas yield increased and the coke yield decreased while the pyrolysis liquid yield increased initially and then decreased slightly at above 773 K. More than 60% of bitumen contained in the oil sand was converted into pyrolysis liquid at the temperatures tested, reaching a maximum value of 76.4 wt% at 773 K. The pyrolysis liquid obtained was mainly consisted of maltenes, with the asphaltenes content being less than 3.4 wt%. As the temperature increased from 673 to 873 K, the pyrolysis liquids became lighter with average molecular weight decreasing from 500 Da to 434 Da and the amounts of light oil fractions (with boiling points lower than 811 K) increasing from 70 wt% to 75 wt%. The pyrolysis gas mainly consisted of H2, CH4, C2H6, C3H8, and C2H4, with H2 accounting for ca. 50 vol% in the gas when the pyrolysis temperatures were above 773 K.