Bitumen thermal hydrogenation

Bitumen is a hydrogen-deficient oil that is upgraded by carbon removal (coking) or hydrogen addition (hydrocrackiag) (2,4). There are two methods by which bitumen conversion can be achieved by direct heating of mined tar sand and by thermal decomposition of separated bitumen. The latter is the method used commercially, but the former has potential for commercialisation (see Fuels, SYNTHETIC). 

Of the above-mentioned challenges of oil-sands production, the heavy dependence on natural gas is among the most critical. Table 3.5 shows the specific natural gas demand per barrel of bitumen for mining and extraction, (thermal) in-situ recovery and upgrading operations, as well as for the production of hydrogen. Depending on the recovery process, up to 25% of the energy content of the SCO is used in the form of natural gas. 

The pour point is the lowest temperature at which the bitumen will flow. The pour point for tar sand bitumen can exceed the natural temperature of tar sand deposits. It is important to consider because for efficient production a thermal extraction process to increase the reservoir temperature to beyond the pour point temperature must supply supplementary heat energy. Elements related to pour point are depth, bitumen viscosity, original reservoir temperature, and atomic hydrogen/carbon ratio. 

Thermal conductivity, H/C ratio, specific volume and specific heat vary during the chemical evolution of the deposit. Unfortunately, there is very small quantity of data in the literature on thermal conductivity. In fact, what little there is refers to coke or bitumen and provides limited or sometimes contradictory information because of the high dependency on the structure and composition of the solid. More reliable data refer to disordered graphite, similar to an aged deposit, without hydrogen and with a low porosity. The available experimental data on the time evolution of pressure drop and tube metal temperature in pyrolysis coils of ethylene crackers only permit rough estimates of the overall and average thickness and thermal conductivity of the deposit. 

This means that hydrogenation of asphaltenes cannot be responsible for asphaltene cracking during the thermal treatment of bitumen and plastics at temperatures over 400°C. 

The effects of hydrogen on the thermal cracking of bitumen are obvious in the results. Most dramatically, high carbon residue material is converted in virtually 100% yields to liquid and gaseous products. The effect is most pronounced for the... 

The basic difference between the formation of sulfur and the carbon gases and its influence on the isotopic ratios of kerogen, bitumen, oil and gas lies in the chemical activity of the thermally derived fragments. Both elemental sulfur and hydrogen sulfide formed at elevated temperatures could re-react with all fractions (Stoler et al., 2003). Research on changes in both carbon and... 

It is well documented that the conversion of resid to lighter products, whether or not in the presence of hydrogen and/or a catalyst, is largely thermally driven. The h5q)othetical molecular structure of bitumen and... 

Furthermore, the analysis of polyaromatic fractions following the reaction (M3 products) showed that these molecules had relatively lower MW, shorter chains and were more aromatic. The results of this woik confirm that side chain fragmentation and hydrogenation/dehydrogenation reactions are major routes in the thermal cracking of heavy oils and bitumen (see Tables 9-10). 

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