Reaction Pathways of Binuclear Aromatics Containing 5-membered Rings

Abstract

There is a growing need to decrease the viscosity of bitumen using minimal diluent addition to reduce the cost of transportation. However, due to the inherently free radical rich nature of bitumen, even on exposure to low autoxidative conditions adverse effects on the viscosity and hardening of bitumen were observed. These effects were postulated to be caused by a compound class containing 5-membered rings attached to an aromatic ring since they have a high propensity to undergo free radical addition reactions. The objective of the work was to develop a better fundamental understanding of addition reactions in binuclear aromatic compounds with one 5-membered ring when exposed to different reaction environments. The compounds selected for this study were: indene, indane, indole, benzofuran and thianaphthene. The reaction environments focused on initiation of addition reactions caused by the addition and removal of hydrogen from the compounds. This was achieved by performing reactions in the presence of acids, bases, thermal conversion conditions and supported metal hydrogenation conditions. The reactions with acids and bases were performed at very low temperatures of 70 and 120 ° C in the presence of nitrogen at atmospheric pressure with a dilution in toluene of 2 wt% acid/base with 10 wt% model compounds. On reactions with acids, the aromatics containing a 5-membered ring polymerized to form much denser and heavier compound chains. The polymers in the cases of indole and benzofuran formed solid particles upon reactions with acids. Bases, however, did not react with indene, indole and benzofuran. Thianaphthene reacted only in the presence of NaH. Thermal cracking conditions of 400 °C and 2 MPa promoted free radical reactions in indene, indole and benzofuran. While indane and thianaphthene did not react, indene, indole and benzofuran underwent addition reactions. The addition reactions led to formation of heavier compounds. Indene also produced asphaltenes in the product. The increase in asphaltene formation was linked to an increase in temperature. Hydrogenation in the presence of a metal supported catalyst was performed in a flow reactor in the presence of H2 gas. The reactions were performed between a temperature range of 150-180 °C at a gauge pressure of 1 MPa, for indene, indole and benzofuran. The compounds hydrogenated in the descending order: indene >> benzofuran ~ indole. Thianaphthene, however, did not undergo hydrogenation at 180 °C, it required a higher temperature of 220 °C.