Thermal cracking of Athabasca bitumen at various reaction conditions with and without the presence of steam was investigated to determine if steam has a chemical influence on coking. The reactions were done in 15 mL microautoclave reactors and a 3" diameter fluidized bed coking pilot unit over a range of reaction severity (350-530 °C, 10-60 min reaction time). The differences between reactions with and without steam were investigated by comparing elemental composition of the products and coke yield. The presence of steam decreased coke yield and decreased sulfur removal, and reduced the H/C ratio of the liquid products. Hydrogen exchange from steam to thermally cracked bitumen molecules was tested by doping water with deuterium oxide (D 2 O) and analyzing liquid and coke products by NMR and stable isotope mass spectrometry, respectively. Preferential deuteration of benzylic carbons was observed along with a trend of increasing deuterium transfer to liquids and coke as reaction severity increased. Free-radical, ionic, and physical mechanisms that can account for these experimental results are discussed.

Thermal cracking of +524 °C Athabasca bitumen at temperatures greater than 500 °C with various thicknesses of feed deposited on the reactor walls was investigated to determine if mass-transfer limitations were significant in controlling product yields. A quartz tube microreactor was used for the bitumen cracking reactions. Volatile products were removed as they evolved by constant purging of the reactor with nitrogen. Coke yields decreased from 23 to 18% with decreasing initial film thickness from 150 to 15 μm. A 13C-labeled tracer representative of reaction fragments from bitumen was synthesized and added to the feed in order measure incorporation of products into the coke via retrograde reactions. A 23% decrease in overall incorporation of the tracer was observed when the initial film thickness was reduced from 150 to 15 μm. A mechanism involving competition between mass-transfer of volatile compounds through the reacting liquid and retrograde reaction is proposed.

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